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Figure 13.21 C. elegans touch receptor neurons. There are two fields of touch sensitivity in the nematode's body an anterior and a posterior field. The position of these fields is determined by the positions of the touch detector neurons. ALML anterior lateral microtubule cell left ALMR anterior lateral microtubule cell right PLML posterior lateral microtubule cell left PLMR posterior lateral microtubule cell right AVM anterior ventral microtubule cell. From Tavernarakis and Driscoll (1997),...

The Muscarinic Acetylcholine Receptor mAChR

Acetylcholine (ACh) (Figure 8.18) was the first neurotransmitter to be discovered - by Loewi in 1922 (see Box 16.2). ACh, or cholinergic, synapses exist in both the peripheral and central nervous systems. In the peripheral nervous system of vertebrates the neuromuscular junction is always cholinergic and it was here that the pharmacology of ACh was first investigated. We shall look further at this pharmacology in Chapter 16. Before going any further it is important to make a distinction between...

Kir62 An ATPsensitive Potassium Channel KATP

ATP-sensitive K+ channels have a weak voltage sensitivity and are controlled by the concentration of an internal agent, in this case ATP. They are closed by high concentrations of ATP. In this way cell metabolism can be linked to the electrical excitability of the membrane. The KATP channel consists of Kir6.2 and an unrelated modulator subunit (Figure 11.5). The latter subunit is a large (17TM) sulphonylurea receptor (SUR). There are two variants of SUR and these mix and match with the two...

Diversity

As shown in Table 11.7, the a-subunits of the Na+ channels are encoded by a gene family consisting of Figure 11.21 Schematic to show current flow through patch of excitable membrane when clamped 10 mV positive to resting potential. (A) The membrane patch is clamped 10 mV positive to resting potential. (B) The current through the membrane measured in picoamps. (C) The current in B is due to the random opening and closing of ten individual sodium channels in the membrane. Figure 11.21 Schematic...

V

-PNa Na+ p + Pa Cl- j PNa Na+ i + PCl Cl- o where P is the permeability constant of the ion concerned, square brackets indicate concentration of the ion either inside (subscript 'i') or outside (subscript 'o') the cell, and R, T and F have their usual connotations. Note that whereas the external concentrations of the cations, K+ and Na+, appear in the numerator of the equation, the internal concentration of the anion, Cl, is placed alongside them in this position. Let us try some test runs on...

Mag

Figure 19.21 N-CAM triskelions Electron micrographs of N-CAM triskelions from embryonic chicken. The triskelions were rotary-shadowed and viewed at a magnification of x200000. Each arm measures about 40 nm. Reproduced with permission, from Edelman (1984), Annual Review of Neuroscience, 7, 339-377, 1984 by Annual Reviews www.AnnualReviews.org. Figure 19.21 N-CAM triskelions Electron micrographs of N-CAM triskelions from embryonic chicken. The triskelions were rotary-shadowed and viewed at a...

Delayedresponse Potassium Channels Hodgkin Huxley Channels Kvdr

The pioneering work of Hodgkin and Huxley in the 1950s showed that the recovery phase of an action potential, the phase in which the axonal membrane Figure 11.11 Disposition of a- and p-subunits in shaker-type channels. N N-terminal inactivation ball. Figure 11.11 Disposition of a- and p-subunits in shaker-type channels. N N-terminal inactivation ball. reverts to its normal polarity (see Chapter 14), is due to the efflux of potassium ions. This efflux is through potassium channels in which...

Gaba

Somatostatin Substance P Enkephalin Neuropeptide Y Thalamus (cat) Medulla (rat) Medulla (rat) Basal ganglia (rat) Adapted from Lundberg and Hokfelt, 1983, Trends in Neurosciences, 6, 325-332. Adapted from Lundberg and Hokfelt, 1983, Trends in Neurosciences, 6, 325-332. with a non-peptide transmitter. Table 16.11 shows that practically all combinations of peptide and non-peptide transmitters have been found. As these cohabitations have been largely established by immunohistochemical techniques...

Molecular Evolution

Evolutionary depth of the molecular realm new molecular classifications - new insights into neuropathologies - new possibilities for therapy - new recognitions of the relatedness of molecular processes. Point mutations mutability of DNA - synonymous and non-synonymous mutations - conservative and radical substitutions - chemical mutagens - transitions - transversions - frameshift - triplet expansion diseases (TREDs). Proof-reading and repair DNA polymerases - exonuclease and endonuclease...

Potassium Channels

Episodic ataxia (EA1) is caused by point mutations of the potassium channel gene KCNA1. This disorder, which generally lasts only minutes, is provoked by abrupt postural change and vestibular stimulation. Benign familial neonatal convulsions, beginning within days of birth but clearing away in weeks to months, are due to mutations in the KCNQ3 potassium channel gene. Andersen's syndrome, characterised by periodic muscle paralysis, cardiac arrhythmia and abnormal growth, a very rare condition,...

Sensory Transduction

Classification entero- and exteroreceptors - chemo-, mechano-, photoreceptors. General features stimulus detection and transduction - specific nerve energies - unifying role of molecular biology - sensory and neurosensory cells - receptor and generator potentials. Chemoreceptors prokaryocytes bacterial chemotaxes - flagellar motion - genetic and molecular analysis - binding proteins - R-T proteins - signal transduction - sensory adaptation - prospects for complete molecular understanding of a...

Mmm

Figure 11.18 Subunit structure of brain Na+ channel. (A) Schematic cross-section of channel inserted in membrane. The channel complex consists of the 260 kDa a-subunit and the two smaller br and b2-subunits. All three subunits are heavily glycosylated on their extracellular surfaces and the a-subunit has binding sites for a-scorpion toxins (ScTX) and tetrodo-toxin (TTX). The intracellular surface of the a-subunit has numerous phosphorylation sites. The b1-subunit is associated non-covalently...

Chemosensitivity in Vertebrates

Let us now turn from chemosensitivity in one of the simplest of living forms to chemoreception in some of the most advanced. In this section we shall look briefly at mammalian olfactory and gustatory reception. Olfactory reception is carried out by the olfactory epithelium in the nasal cavity and vomero-nasal organ. The area that this epithelium covers in the nasal cavity ranges from a few square centimetres (human) to well over a hundred square centimetres (dog). It consists of three types of...

Ionotropic Glutamate Receptors iGluRs

Mammalian brains possess two important excitatory amino acids (EAAs) glutamate and aspartate. They are widely distributed throughout the brain and spinal cord. Glutamate and its receptors (GluRs) are the best known. Stimulation leads to three major types of response. In the first case glutamate induces rapid (c. 1 ms) membrane depo-larisations. In this respect glutamate resembles the action of acetylcholine on the nicotinic acetylcho-line receptor. In the second, and perhaps more interesting,...

E

Figure 7.14 Formation of myelin around a peripheral axon. The process starts at A and proceeds through to E and beyond so that ultimately a tight spiral of perhaps fifty layers of myelin results. Note how the growing myelin whorl tucks under earlier whorls. This process is assisted by Po and MAG, which both project into the extracellular space and have similar structures to the cell adhesion molecules (CAMs). It can be seen from Table 7.1 that the lipid composition of myelin differs markedly...

Ho

Figure 16.16 Deamination of serotonin by MAO. decreased adenylyl cyclase activity. Activation of the system by 5-HT leads to presynaptic inhibition. As in the GABA system described above, there is evidently a negative feedback loop controlling the release of serotonin from serotoninergic terminals. In contrast 5-HT2 receptors are located postsynap-tically and, although they are similarly coupled to a G-protein mechanism, activation by 5-HT leads to depolarisation and thus excitation of the...

Lipids

It has been computed that a small patch of membrane with an area of 1 mm2 is built of some 5 x 106 lipid molecules. It can be shown that different membranes consist of slightly different Figure 7.1 Phosphoglycerides (A) schematic diagram (B) phosphatidylcholine (lecithin) (C) phosphatidylethan-olamine (cephalin) (D) phosphatidylserine (E) phosphatidylinositol. Note the fatty acid chains are very variable in both length and saturation. Figure 7.1 Phosphoglycerides (A) schematic diagram (B)...

Fishing For Genes In A cDna Library

There are several procedures for finding the gene of interest in a cDNA library. One much used technique (as we shall see in subsequent chapters) is analogous to that described in Section 5.8. It depends on the amino acid sequence of at least a small section of the gene product being known. If this is the case, then an oligonucleotide probe can be prepared - as described in Section 5.8. The cDNA corresponding to the protein can then be 'fished' out by the hybridisation technique described in...

Conclusion And Forward Look

This chapter has covered a very wide and rapidly advancing topic. Biomembranes are at the heart of brain physiology. The next four chapters build on the fundamental concepts of membrane structure and function developed here, applying them to the specific characteristics of nerve cell membranes. Thus in Chapter 8 we look at a superfamily of important membrane receptors and note how their action depends on the ability of proteins (so-called G- or N-proteins) to shuttle to and fro in the lipid...

Mechanosensitivity in Caenorhabditis elegans

Like all animals C. elegans is sensitive to touch. Two touch stimuli have been investigated. A gentle touch on the body with an eyelash glued to a cocktail stick and a more vigorous prod with a thin wire. The most interesting results have come from investigations of the response to the gentle stimulation. When C. elegans is placed in a Petri dish it moves forward with a sinusoidal motion until it encounters a tactile stimulus. If it is given a gentle touch on the anterior part of its body the...

The Postsynaptic Density

If synaptosomes are exposed to strong detergents such as Triton X the pre- and postsynaptic membranes are released from the rest of the complex (Figure 17.2). This, the so-called synaptic plasma membrane (SPM), may then be isolated from the other elements of the synaptosome by density gradient centrifugation. The fact that the pre- and postsynaptic membranes stay together when the rest of the synaptosome has been liquidated suggests that they are held together by some electron-translucent...

Print

Sakmann, 1992, 'The patch clamp technique', Scientific American, 266(3), 28-35 Persigian, V.A., ed., 1984, 'Biophysical discussions ionic channels and membranes', Biophysical Journal, 45, 1-359 Rose, M.R., 2001, Channelopathies of the Nervous System, Oxford Butterworth-Heinemann Sakmann, B. and E. Neher, eds, 1983, Single-Channel Recording, New York Plenum Press Sakmann, B. and E. Neher, 1984, 'Patch clamp techniques for studying ionic channels in excitable membranes', Annual...

Multiplicity of Shaker Channels

The Drosophila shaker (sh) gene is a highly complex unit. It contains at least 23 exons and it has multiple promoter sites so that the initiation of transcription may occur at different places in different tissues. Furthermore, the primary mRNA once transcribed may be spliced at different points, combining different exons, and thus giving rise to different mature mRNA strands. These would then be translated into subtly different channel proteins. These proteins could then assemble to give...

Conclusion

We observed at the outset of this chapter that the brain is perhaps the ultimate challenge for the developmental biologist. It is clear from the remainder of the chapter that we still have far to go. Yet the molecular approach here, as elsewhere, is beginning to yield dividends. It begins to seem feasible that increasing knowledge of the selective stickinesses of membranes, of the subtleties of a cell's control of N-CAMs, of the distribution, uptake and effect of tropic and trophic factors and...

H N

Point mutations may be caused by a large number of agents some chemical (e.g. nitrous acid, 5-bromouracil), some physical (UV irradiation, X-rays, radioactive emissions). Furthermore, the DNA molecule itself has an inherent tendency to mutate. This is yet another feature which makes it a good genetic molecule. Without mutation living forms could not be selected to fit their environments evolution could not have occurred. Indeed DNA's mutability is perhaps too great for its own good. It has to...

Signal Transduction

Chemotactic signalling is initiated by the binding of the attractant molecule or of the attractant-binding molecule complex to the periplasmic domain of the R-T molecule. There is evidence that this causes a conformational change which is transmitted through the membrane to alter the configuration of the cytoplasmic domain. This altered cytoplasmic domain then initiates a biochemical signalling cascade which ultimately affects the activity of the flagellum. Genetic analysis has allowed the...

Genes

(Mentioned in text alternative names in square brackets) Many of these genes have close homologues in several organisms. When an organism is specified in the following list it usually only means that the gene was first detected there, or that it is best known in that organism. Hyphenated suffix 'n' indicates a number thus unc-n might be unc-86 brn-n might be brn-1, brn-2, etc. Where appropriate the letters giving rise to the abbreviation have been highlighted. abd-A B (abdominal) member of...

Acetylcholine

Acetylcholine is synthesised in synaptic terminals from choline and acetate. The latter is derived from acetyl coenzyme A. Choline, on the other hand, is partly obtained by reuptake from the synaptic gap Phosphatidylcholine or free choline in circulation Figure 16.1 Synthesis of acetylcholine. Explanation in text. and partly from the blood where some of it is transported partly as free choline and partly as the phospholipid phosphatidylcholine. Acetyl coen-zyme A is derived from glucose through...

AMPA Receptors

The first four GluRs to be characterised (GluR1-GluR4) were members of the Q or AMPA group. They are all of a similar size (about 900 amino acids) and their sequences are about 70 identical. Hydropathy analysis implies three transmembrane segments. In place of the second transmembrane helix (M2) of the AChR family there is a hairpinlike loop (Figure 10.17). This, as we shall see in Chapter 11, has some similarity to the voltage-gated cation channels although their hairpins are made from the...

Initial Subdivision Of The Drosophila Embryo

The first genes to express themselves in the zygote nucleus after fertilisation are members of the gap class. Mutations of these genes lead to flies lacking a particular region along the pre-established A-P axis. The most intensively studied members of this class are named hunchback (hb), Krupple (Kr) and Knirps (kni). These genes delimit the domains of expression of the homeotic genes which we shall discuss below. They also define the position at which the so-called pair rule genes are...

Transport Along The Axon

The secretory vesicles budding off the trans face of the Golgi body have far to go. The recurrent laryngeal nerve fibres of a giraffe stretching all the way down the neck, under the aortic arch, and back up again to the larynx may be several metres in length. Whilst this is exceptional, axons of over a metre in length are quite common in large animals. The topic of axoplasmic transport has thus been one of considerable interest. Conventional microscopical techniques have revealed, as we shall...

1

Immediate early genes (IEGs) 66, 69, 70F control by second messengers 414F, 415-16 Immortalisation 121 Immunoglobulins 155, 457-9, 459F Inducer 68 Inferior mesenteric ganglion 395 Informational macromolecules 22, 46 defined 22 Inhibitory post synaptic potential (IPSP) 409-10, 410F see also synapses Inhibitory transmitters see neurotransmitters Initiation factors see translation Inositol triphosphate see messengers Inositol triphosphate receptor see ligand gated channels Insertion sequence see...

Web sites

The Chemoreception Web www.csa.com crw websites.html Olfaction in mammals www.leffingwell.com olfaction.htm The human olfactory repertoire (July 2001) Retinitis pigmentosa - a valuable guide to RP organisations and web sites is at The British RP Society is at http www.brps.demon.co.uk

Other Members of the Family

Once the sequence of the Drosophila shaker gene had been determined it became possible to search cDNA libraries for other K+ channel genes. Drosophila quickly yielded three other genes, Shab, Shal and Shaw, which coded for three similar K+ channels. Homologues of all four Drosophila K+ channels have been found throughout the animal kingdom, all of which show the same 6TM 'core' structure. In mammals the homologous channels are called Kv1.x, Kv2.x, Kv3.x and Kv4.x, respectively. The Kv1 channel...

L

Lambert-Eaton myasthenia (LEM) 221-2 and PD 337, 524 Leak channels 245 Lecithin see phosphatidyl choline Leech see Hirudo Lesch-Nyan syndrome 125-6 Lewy bodies 525, 526 Ligand-gated channels (LGICs) 207-36 evolutionary relationships 235-6 GABAa-R (g-amino-butyric acid receptor) 92, 224-6 and epilepsy 225 expressed in Xenopus oocyte 118 pharmacology 224 structure 224-5, 225F, 226F CNG (cyclic nucleotide gated) 246, 246F, 294F in olfactory cilia 294, 294F in rod outer segments 294, 301-3...

Genomes Web sites

Http www.ornl.gov hgmis http www.nature.com (b) Caenorhabditis elegans http www.wormbase.org (c) Danio rerio (zebra fish) (d) Drosophila http fly.ebi.ac.uk (e) Mus musculus (mouse) (f) Xenopus (clawed frog) http vize222.zo.utexas edu (g) Saccharomyces cerevisiae (yeast) (h) Oryza (rice) http nucleus.cshl.org riceweb http www.ncbi.nlm.nih.gov omim Social, legal and ethical issues http www.nhgri.nih.gov ELSI

Biophysics

The physiology of sodium channels has been studied by several of the methods by which the nAChR was studied (see Section 10.1.2). In particular the patch-clamp and bilayer techniques have proved important. If a small patch of neural or muscle fibre membrane is clamped some 10 mV positive to its resting potential, sodium channels open and current can be recorded as shown in Figure 11.21. Figure 11.21 shows that the channels open for about 1 ms and allow about 2 pA of current to pass. A single...

Intermediate Filaments IFs

Unlike either microfilaments or microtubules, intermediate filaments are biochemically extremely heterogeneous. Five major classes are recognised. Each class is found in a specific cell type. In the nervous system glial cells contain glial filaments (a single protein of 51 kDa) whilst in neurons three different types of IF protein are recognised NF-L (63 kDa), NF-M (160 kDa) and NF-H (200 kDa) (i.e. low, middle and high molecular weight). Although IFs are extremely various they all seem to...

Sitedirected Mutagenesis

Recombinant DNA technology also enables us to carry out another instance of 'reverse genetics'. Instead of finding a phenotypic change and then looking to see which genes have caused the change Insert plasmid into E. coli and allow Insert plasmid into E. coli and allow Figure 5.21 Expression of a eukaryotic gene by an E. coli plasmid. The promoter and operator sequences of E. coli's lac operon (see Figure 3.17) have been inserted into a plasmid. The plasmid is cut with a restriction enzyme and...

The Origin Of The Resting Potential

The giant axon preparation and subsequently other preparations have allowed investigators to determine the ionic concentrations on either side of a neuronal membrane. We have already seen in Chapter 9 how it is possible to calculate the difference in 'free energy' (AG) represented by the distribution of a substance on two sides of a membrane. But in that chapter we explicitly put on one side consideration of any electrical forces that might be acting on charged particles such as ions. In this...

Synaptosomes

Synaptosomes can be obtained from the central nervous system by homogenisation in buffered sucrose solutions and subsequent density gradient centrifugation. One of the fractions in the centrifuge tube contains broken-off nerve endings or Figure 17.1 Synaptosome. Synaptosome from rat cerebral cortex after incubation in physiological saline for 10 minutes. cv coated vesicle m mitochondria post post (i.e. sub-) synaptic density pre presynaptic grid element ps postsynaptic 'bag'. From Csillag and...

Ebe

Habituation see memory Haeckel, E. 5, 419, 426 Haemoglobin 37-8, 38F compared with nAChR 90 development 89-90 structure 38F see also globins Haemophilus haemolyticus 98 Haemophilus parainfluenzae 98 Hair cells 312-18, 314F, 315F Halobacterium halobium 190 Halothane 165, 422 Hameroff, S. 542 HD see Huntington's disease Heat shock proteins (hsp) see chaperonins Helmholtz, H. von 318, 326 Hermissenda crassicornis 485, 491 Heterochrony, defined 420 Heterosynaptic facilitation, defined 496 Hha1 see...

Macromolecules

Definition of informational macromolecules. Proteins levels of structure. Primary structure -amino acids and their properties - polypeptides - neuroactive peptides - glycosylation. Secondary structure - b-pleated sheets, hairpins and barrels - collagen three-stranded ropes -AchE - the a-helix - amphipathic helices. Tertiary structure - modularisation, domain structures and motifs - allosteric flexures. Quaternary structures - haemoglobin - fragility -necessity for synthesis to be chaperoned -...

Preface To The First Edition

This book is intentionally entitled 'elements'. It is intended as an introductory account of what is now a vast and rapidly expanding subject. Indeed so rapid is the advance that any writer finds difficulty in steering between the Scylla of up-to-dateness (with its danger of rebuttal) and the Charybdis of received understanding (with its danger of obsolescence). I hardly expect to have safely navigated between these twin sirens at first attempt. But I hope to have avoided shipwreck to the...

Restriction Maps

By subjecting DNA to different restriction endo-nucleases, or the same endonuclease for different durations, assortments of fragments of different lengths are obtained. By carefully examining the fragments it is possible to find overlapping sequences and hence determine the order in which Figure 5.2 Construction of a restriction map. The DNA molecule in the figure contains 12 000 nucleotide base pairs (i.e. (2.4+2.6+3.2+0.9+1.2+1.7) kbp). It contains three recognition sites for endonuclease A...

Homeobox Genes And The Early Development Of The Brain

The segmentation of the vertebrate skull was something of a cause celebre in the early and mid-nineteenth century. Anatomists from Goethe through Richard Owen to Thomas Henry Huxley made significant contributions. In general it was believed that the skull developed by modification of a number of vertebrae at the anterior end of the animal. It was Huxley in his 1858 Croonian Lecture 'On the Theory of the Vertebrate Skull' who first showed the superiority of the embryological method over the...

Mobility Of Membrane Proteins

We have already referred to membrane proteins as floating in a lipid sea. It is not surprising, therefore, to find that they have considerable lateral mobility. We shall see in Chapter 8 that this lateral mobility has been pressed into service, with great effect, in the development of signalling systems based on protein shuttling in the plane of the membrane. Protein diffusion coefficients range from about 10 9cm2 s for rhodopsin in retinal rod outer segments (i.e. about 0.1 mm2 s) to about...

THE KcsA Channel

As we shall see in Section 11.2.3, the first K+ channel to be sequenced was the Drosophila 'shaker' channel. In the early 1990s the amino acid sequence of the extracellular pore region (P) of this channel was established. With the rapid growth in knowledge of genomes it became possible to search the gene libraries of other organisms for similar sequences. One such organism was the Gram-positive soil bacterium, Streptomyces lividans. A 1080 nucleotide sequence between start and stop signals with...

C U M Smith

Department of Vision Sciences Aston University Birmingham, UK Copyright 2002 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England Email (for orders and customer service enquiries) cs-books wiley.co.uk Visit our Home Page on www.wileyeurope.com or www.wiley.com All Rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording,...

The Nicotinic Acetylcholine Receptor

As mentioned above, the type example of a ligand-controlled gate is the nicotinic acetylcholine receptor (nAChR). We have already met this entity several times in previous chapters. Its structure is nowadays very well known. We noted in Chapter 8 that cholinergic receptors can be divided into two major classes nicotinic and muscarinic. In that chapter we looked at the muscarinic receptor in some depth. We saw that it was coupled to a complex membrane molecular biology involving G-proteins and...

Measurement Of The Resting Potential

We noted above that resting potentials are believed to be developed across all cell membranes - whatever the type of cell. Most mammalian neurons, however, have extremely small diameters - seldom more than about 20 mm. The recognition that certain large tubular structures (diameter 500-600 mm) in the squid, Loligo, were in fact single giant axons was thus of enormous value to electrophysiologists. They were at last able to place fine glass micropipettes filled with an electrolyte inside an axon...

Ion Selectivity And Voltage Sensitivity

We have noted, as we reviewed the K+, Ca2+ and Na+ voltage-dependent channels, that the core region of each was remarkably similar. In particular we saw that the polypeptide chain between S5 and S6 was believed to take the form of a hairpin inserted into the membrane. In the K+ channels this region is believed to resemble the structure elucidated in the KcsA bacterial channel, while in the Ca2+ and Na+ channels, although its exact structure remains unknown, it is unlikely to differ from the...

Index Of Neurological Diseases

Alpha-synuclein diseases 526 Alzheimer's disease 147, 346, 353, 371, 478, 482, 526-40 Amino acid metabolism diseases 512 Amytrophic lateral sclerosis (ALS) 137, 514 Anosomia 296 Andersen's disease 137, 271 Angelman syndrome 137, 553 Aniridia 435 Ataxia telangiectasia (ATM) 137 Audiogenic epilepsy 205 Autosomal nocturnal frontal lobe epilepsy (ADNFLE) 224 Bipolar affective disorder see depression Bovine spongiform encephalopathy (BSE) 508, 511 Cataract 137, 164, 435 Channelopathies 135, 271-2...

Xql

BAC see bacterial artificial chromosome Bacterial artificial chromosome see cloning vectors Basal ganglia, pathology 326, 345, 452, 462 Basal lamina 455 Basement membrane at motor end plate 192, 307, 308F see also basal lamina, laminin Basic protein see myelin Bateson, W. 37, 425 Benzodiazepines 224, 375 Beta-adrenergic receptor (b-AR) see G-coupled receptor proteins Beta-adrenergic receptor kinase (b-ARK) 183 Beta-arrrestin 183, 193 Beta-blockers 180 Beta-endorphin see neuroactive proteins...

Aplysia and the Molecular Biology of Memory

Figure 20.10 shows a dorsal view of Aplysia. It is a large marine mollusc measuring several hundred millimetres from head to tail. The figure shows the position of the siphon and gill which play so large a role in the behaviour we are about to examine. When a weak mechanical stimulus is applied to the siphon both siphon and gill tend to withdraw beneath the mantle shelf. This is a protective reflex. Habituation, sensitisation and also classical conditioning can be demonstrated (Figure 20.11).

Synthesis Of Biomembranes

We have noted throughout this chapter that membranes are extremely fragile, tenuous structures. It is thus not surprising to find that they are continuously synthesised and broken down throughout the life of the cell. The rate at which this is done is often extraordinarily high. It has been calculated, for instance, that the membrane of Xenopus retinal rod discs is synthesised at a rate of 3.2 mm2 min. This, no doubt, is an extreme case, but it seems that in many cells an area of membrane equal...

Voltageclamp Analyses

The modern phase of our understanding of the action potential began with the experiments of Hodgkin and Huxley in the early 1950s. Working with the squid giant axon preparation they were able to model closely the shape of the action potential and determine the nature of the ion flows responsible for that shape. Figure 14.1 shows a classical recording from this preparation. Figure 14.1 shows that when a microelectrode is placed within a squid axon a resting potential (Vm) of about 60 mV can be...

Ca

This expression gives the 'free energy' (symbolised as AG) which is available to do work when the chemical substance passes from its high potential to its low potential state. Let us now simplify the symbolism a little. Let us remove the signs indicating the two phases, a and p, in which our solute is supposed to be present, and merely refer to the concentration of the solute on either side of the partition as C1 and C2. We can then write If we now insert the usual values for R and T, i.e. R...

Microfilaments

Microfilaments are mostly composed of actin. We met this cytoskeletal component in Chapter 7 when we were considering the nature of the sub-membranous cytoskeleton. There it was believed to play a role in maintaining the shape of the cell. Actin is also, of course, well known in muscle, where it is crucially involved in the contractile mechanism. It is likely that it plays a part in cytoplasmic movements of all types. It is thus not surprising to find microfilaments well represented in axons....

A

Many other chemical and voltage-activated channels have subsequently been expressed in Xenopus oocyte. These include GABA-activated channels from the chick brain ACh-activated channels from cat muscle serotonin-, neurotensin-and substance-P-activated channels from rat brain kainate and glycine receptors from bovine retina glycine-, GABA- and serotonin-activated channels from human fetal cerebrum, and voltage-activated Na+ and K+ channels from rat and human fetal brain and cat muscle. It is...

Kir31 GIRK1 Gproteinlinked Muscarinic Potassium Channel KACh

We noted in Section 8.9 that the M2 muscarinic AChR controlled a K+ channel through a G-protein system. This G-protein-linked channel, when open, allows a 7-50 pS K+ current to flow inwards. It may be blocked by Cs2+ and Ba2+ ions and by tetra-ethyl ammonium chloride (TEA Cl). Its biophysics were first analysed in cardiac muscle. The molecular structure of this channel has now been elucidated. It was determined by screening a rat heart cDNA library and isolating a 4.2 kbp clone. cRNA from this...

Xenopus Oocyte As An Expression Vector For Membrane Proteins

One of the best expression vehicles for eukaryotic genes is the large oocyte of Xenopus, the clawed frog. This cell may be up to 1 mm in diameter. It is primed, ready to develop into a frog after maturation and fertilisation. It possesses all the appropriate transcriptional and translational machinery in large amounts and 'well-oiled' condition. mRNA from other cells can be injected into it through a glass micropipette. These mRNAs succeed where endogenous mRNAs - probably due to inhibition by...

Establishing An Anteroposterior Ap Axis In Drosophila

Embryology has a long and fascinating history dating back at least to the times of Aristotle. One thing became clear as experimental studies of development began in the nineteenth and twentieth centuries position was all-important. Grafting experiments in the early embryo showed that grafted organs or tissue were strongly influenced by just where in the body it was placed. Gradients seemed to be everywhere and nowhere more significant than along the anteroposterior axis. A great deal of...

Short And Longterm Memory

One of the ground rules of scientific theorising was summed up by William of Occam in the thirteenth century 'Entia non sunt mutiplicanda praeter necessitated - 'entities are not to be multiplied beyond necessity' - an aphorism that has come to be known as Occam's razor. This principle holds as strongly in the study of memory as elsewhere in science. Neurobiologists hope to find a single mechanism at work underlying the phenomenon. Yet the facts may be otherwise. It may be that memory is a...

Histology

Although neuroscientists (like all scientists) search always for unifying principles underlying diversity, the fate of predecessor theories and hypotheses must make them cautious. Although the CREB protein theory makes a very satisfying story we should always bear in mind the morphology of mammalian neurons. In Section 1.3.1 we noted how very large neurons are compared with most of the body's cells. In Box 20.1 the nature of dendritic spines, upon which most of the hippocampal synapses are...

Ncam

Figure 19.19 Homotypic binding between N-CAMs. The schematic shows the principle of homotypic binding between N-CAMs of two neighbouring neurons. stage and only appear after mitosis has ceased. The great importance of neuron-glia interactions was emphasised in Section 19.1 above. The two types of neural adhesion molecule also have somewhat different binding properties. N-CAMs show 'homotypic' binding, i.e. N-CAMs in one neural membrane bind to N-CAMs in a neighbouring neural membrane (Figure...

M2

SstS'SAWPLI GKYMLFTMVFVl AS I I 1 TV 1 V I NTHH RSPSTHVMPfflWV RK VF I DT i PN MFF STMK RP SREKQDKK FTED 10 I SD I SGKPGPPPMGr HS Pi jsTSSAVPLIGKYMLFTMVFVIASl I I TV IV1 NTHH RS PSTH VHPtEiwV RKy 1 DT I PHI MFF STMKRP SREKQPJCK IF TED IDI SD 1SGKPG PPPMGF HSPI IsTSSflVPLl GKYMLFTIIITiFV1 sis I I trvivlv t WTHH BSPSTHfTlHPOIHVRK JF I T f PWVIHFFSTMKRj isiKtEKQlE> iiK i F AP d I D SD t SGKIqYiTSejV Id& iH ILIKHPEVKSAIEG1KY1 AET'IKSDQESNN AAUiE WK Y V AMVflQH I LUGiVFMLVC 11 GTLAVFAGRL...

Gap Junctions And Neuropathology

At least 15 connexin genes have been identified in the mammals. These genes are spread over five or six chromosomes human 1, 6, 13, 15 and X mouse 3, 4, 10, 11, 14 and X. Although they are so widespread, the genes (with the exception of that for Cx36) have a common structure a single intron separating a small non-coding exon from a much larger exon which encodes the whole connexin sequence. Mutations of these genes have been implicated in a number of neuropathologies. Although over a hundred...

Voltage Sensitivity

First of all we have to distinguish 'gating' from channel 'opening'. The first thing necessary when the voltage across a membrane changes is that the change should be somehow 'sensed'. This 'sensing' has been found to be accompanied by a small but detectable current, the gating current. This current can be detected at the beginning and end of any small depolarisation. The gating 'activates' the channel, which may then open. We have already noted that S4 is suspected to be the sensor responsible...

And Gating

The schematic diagrams of ion channels in Chapter 11 are at best idealised cartoons of the molecular reality. They are inevitably drawn as if they were devices in the macroscopic everyday world of billiard balls, tubes, barrels, balls and chains, etc. Hopefully, they give a good first approximation and are certainly invaluable in fixing ideas. However, we do not have to go all the way into the counter-intuitive mysteries of quantum physics to recognise that the world of the very small (like the...

Xum

Szczeg Konstrukcji Dachu

Figure 19.10 Formation of spine-varicosity synapses. (A) The dendrite is continuously forming searching filopodia. When an axon crosses its path the closest filopodium is stimulated. (B) The filopodium grows toward the axon and transforms into a proto-spine. At the same time its influence causes a varicosity to start forming on the passing axon. This collects synaptic elements (synaptophysin, presynap-sin, etc.) and transmitter vesicles. (C) The release of neurotransmitter attracts PSD-95 and...

Amino Acids

A number of amino acids found in the central nervous system satisfy at least a majority of the criteria for synaptic activity listed in Box 16.1. In most cases their actions are ionotropic rather than metabotropic. Although some fifteen amino acids have been proposed as neurotransmitters only four have so far met with general acceptance. There are two acknowledged excitatory amino acids (EAAs) glutamic acid and aspartic acid. Both have two carboxylic acid groups (Figure 16.5). There are two...

Abc

Figure 11.24 S4 'sliding helix' voltage sensor. (A) 'Ball and stick' representation of the S4 helix of domain 4 of the sodium channel. Dark circles represent the a-carbon atoms of each amino acid residue open circles are labelled with the amino acid single-letter code and show the direction in which the side chain projects. (B) and (C) Movement of the helix in response to voltage change (A V) across the membrane. At resting potential (B) all positively charged side chains are paired with fixed...

The 7tm Serpentine Receptors

Neuronal membranes have many different receptors designed to detect many different primary messengers. In this chapter we shall consider six of these receptors the p2-adrenergic receptor (p2-AR), the muscarinic acetylcholine receptor (mAChR), the metabotropic glutamate receptor (mGluR), the neurokinin receptor (NKR), the cannabinoid receptor (CBR) and the visual pigment proteins (opsins) of photoreceptor cells. The molecular structure of these receptors is well understood. With the exception of...

Dhc

Figure 15.15 Structure of kinesin and cytoplasmic dynein. (A) Kinesin. There are several forms of kinesin which vary in the structure of their 'cargo attachment' domains. (B) Cytoplasmic dynein. These are much larger molecules than kinesins with a more complex structure. DHC dynein heavy chain DIC dynein intermediate chain DLC dynein light chain. After Almenar-Queralt and Goldstein (2001), Current Opinion in Neurobiology, 11, 550-557. Figure 15.15 Structure of kinesin and cytoplasmic dynein....

Homeosis And Homeotic Mutations

The stage is now set for the switching on of genes that control segmental morphology. These, as we shall see, show fascinating homologies across the whole metazoan subkingdom. The term 'homeosis' was introduced by William Bateson a century ago in his 1894 Materials for the Study of Variation 'something has been changed into the likeness of something else'. The first case of a homeotic mutation was observed by Bridges in 1915 when he observed that in some rather rare cases the third thoracic...

APOE and its Alleles

The APOE gene, located on the long arm of chromosome 19, has three alleles APOE-e2, APOE-e3 and APOE-e4. The protein, apolipopro-tein E (ApoE), encoded by APOE has an Mr of 37 and consists of 299 amino acid residues. Corresponding to the three APOE alleles there are three major isoforms e2, e3 and e4. They differ only in amino acids at positions 112 and 158 (e2 Cysn2, Cys158 e3 Cysm, Arg158 e4 Argm, Cys158). In spite of this seemingly insignificant difference the presence of the e4 isoform...

Other Units

A (Angstrom) 10-1 m a (annum) year bp (base pair) nucleotide base pair (measure of the length of a nucleic acid or polynucleotide) cal (calorie) the quantity of heat required to raise 1 g of water from 14.5 C to 15.5 C Ci (curie) unit of radioactivity 1 Ci 3.7x1010 nuclear transformations per second Mr relative molecular mass mass of a molecule expressed as a multiple of the mass of a hydrogen atom S (svedberg) sedimentation coefficient in a centrifugal field of force

Homeobox Genes

Further analysis showed that both bx and antp were in fact members of complexes consisting of several genes these complexes have been labelled BX-C and ANT-C. In the late 1980s and early 1990s both complexes were cloned and their DNA sequenced. When the DNA sequences of the two complexes were compared it was found that they both contain a very similar 180 bp sequence. This region was consequently named the homeobox. BX-C and ANT-C were thus seen to constitute a so-called homeobox cluster, HOM-C...

Npy

H Hypothalamus B-H brain minus hypothalamus SC spinal cord N peripheral nerve GI gastrointestinal tract Pa pancreas Sk skin Pi pituitary. H Hypothalamus B-H brain minus hypothalamus SC spinal cord N peripheral nerve GI gastrointestinal tract Pa pancreas Sk skin Pi pituitary. Figure 16.27 SP-induced 'slow' EPSP. (A) Response of a neuron in the inferior mesenteric ganglion to stimulation in the presence of cholinergic blockers hexamethonium (400 mM) and atropine (4 mM). The response was induced...

Sensory Adaptation

Sensory adaptation occurs when the bacterium finds itself in an unvarying concentration of attractant. This is due to methylation of the R-T protein. For this reason these proteins are sometimes referred to as methyl-adapting chemotaxis proteins (MCPs). That adaptation is due to methy-lation was shown by the isolation of mutants in which methylation domains of the R-T proteins (Figure 13.5) were inactivated. Such mutants did not adapt in the presence of an attractant they would cease tumbling...

Introductory Orientation

Origins of molecular neurobiology - outline of nervous systems - significance of invertebrates -developmental introduction to vertebrate nervous systems - cellular structure of brains -neurons - glia - nature and organisation of synapses - organisation of neurons in the mammalian brain - complexity of the cortex - modular structure - columns - integrality The nervous system and, in particular, the brain is commonly regarded as the most complex and highly organised form of matter known to man....

Tm

Zagotta, 1993, 'Recent advances in the understanding of potassium channel function', Current Opinion in Neurobiology, 3, 283-290 Jan, L.Y. et al., 1985, 'Application of Drosophila molecular genetics in the study of neural function - studies of the Shaker locus for a potassium channel', Trends in Neurosciences, 8, 234-238 McLarnon, J.G., 1995, 'Potassium currents in motoneurones', Progress in Neurobiology, 47, 513-531 Monor, D.L., 2001, 'Potassium channels life in the...

Structure

A purified DHP receptor preparation was used to synthesise an oligonucleotide probe and this in turn for extracting and cloning the receptor cDNA. It was found that the protein thus obtained consists of 1873 amino acids with a molecular weight of approximately 170 kDa. It must be borne in mind when considering this Ca2+ channel that it has been obtained from skeletal muscle, and neuronal channels may differ in detail. Examination of this polypeptide shows it to have four homologous domains of...

Time s

The reduction in the dark current is dependent on the intensity of the flash stimulus. The bottom line of the graph results from a stimulus 94 x the intensity of flash responsible for the top line. From Baylor, Lamb and Yau (1979), Journal of Physiology, 288, 589-611 reproduced by permission of the Physiological Society. transmitter on to the dendritic ending of the underlying bipolar cell. Illumination inhibits this release. The transmitter is, in most cases, glutamate. This, as we...

Nf023

Supplement, Trends in Cambridge, Elsevier. et al., 2001, Nomenclature Pharmacological Sciences, that they reduce release of ACh and noradrenaline from cholinergic and adrenergic terminals. They have similar effects on many other transmitter systems. Because of this, considerable interest has focused on a possible use in the treatment of stroke. In stroke a reduction of blood flow to the affected region leads to the release of excitatory amino acids and a consequent fatal...

Positional Cloning

This technique is primarily used in the discovery of disease-causing genes. In a sense, it can be seen as a type of 'reverse genetics'. Clinicians describe a disease condition in the human population and positional cloning can be used to run down the gene, clone it, and detect the mutation leading to the disease. The first requirement is accurate epidemiology. The disease is traced through pedigrees in the population. This, of course, is usually the human population but similar analyses are...

Voltagegated Ion Channels

Central role of voltage-gated channels in neurophysiology. Classification. The KcsA bacterial K+ channel - structure - biophysics. Neuronal K+ channels - nomenclature and overview. Kir channels (2TM (1P)) - inward rectification - genetics, distribution and role. K+ 'leak' channels (4TM (2P)) - structure - genetics - role. Kv channels (6TM (1P)) - shaker channels -structure - biophysics - heterogeneity - genetics - accessory subunits - Kvdr (delayed-response K+ channels) - KCNQ channels - MinK -...

Protein Evolution

We are now in a position to consider the evolution of proteins. There are several different aspects to this study. First, we can look at orthologous proteins. These are proteins appearing in different species but which can be traced back to a common ancestor. In other words we can examine the amino acid sequences of orthologous proteins in a variety of organisms and by noting degrees of similarity 4.2.1 Evolutionary Development of Protein Molecules and Phylogenetic Relationships We shall see in...

Other Genes Involved In Neuronal Differentiation

The genetics of the nervous system is a 'hot' area at the time of writing and there is little doubt that many other genes coding for transcription and other factors will be detected in the next few years. Already a class of genes encoding proteins showing about 80 amino acid homology with Drosophila achaete-scute proteins has been detected early in the embryogenesis of mammalian brains. The Drosophila achaete-scute gene complex (AS-C) is well known to encode transcription factors which play an...

Phenylketonuria

A large number of congenital defects in amino acid metabolism are now known to affect the brain. The most important of these are shown in Table 21.2. These metabolic defects are expressed in many of the body's organs but the major symptoms are neurological mental retardation, convulsions, ataxia. The infant brain is particularly sensitive to any abnormal biochemistry. We noted the significance of sensitive periods in Chapter 19 when we discussed the brain's development. In children this period...

TM1P Channels Kv Channels

The first 6TM K+ channels were cloned and analysed in 1988 some five years before the 2TM Kir channels and some seven years before the 4TM leak channels were discovered. Since 1988 a great variety of 6TM K+ channels have been found and analysed (see Table 11.2). They all share a common architecture of 6TM segments numbered S1 to S6 with a 'hairpin' between S5 and S6 known either as H5 or P which, as we have seen, selects with exquisite sensitivity K+ from all other ions. It is probable that the...

Single Nucleotide Polymorphisms Snps

As we noted in Section 6.2, no two of us have exactly the same sequence of base pairs in our genomes. Similarly, none of us (except the volunteers for the sequencing projects) have exactly the same sequence as that published (or to be published in 2003) as the human reference sequence. We differ from each other and from the reference sequence by about 0.1 which, as there are 3.2 Gbp, works out as about one base pair in every 3000, or, to use round numbers (after all, these are all...

Hoog Cooh

Aminoacyl Trna Synthetase Mechanism

Figure 3.7 Major structural features of 'special' transcription factors (TFs). (A) Helix-turn-helix. This family includes the homeodomain proteins which play important roles in cell differentiation (Chapter 18). (B) Zinc finger. Characterised by a zinc-coordinated binding motif. They, too, develop a helical segment which interacts with specific base sequences in the DNA major groove. (C) Leucine zipper. Like most of the special transcription factors this family interacts with DNA as dimers. In...

NMDA Receptors

Although NMDA receptors have a rather low amino acid homology with non-NMDA GluRs (25-29 ) they once again share the 3TM architecture and pentameric quaternary structure of Figure 10.17. The hydrophobic (presumably transmembrane segments) are, as before, arranged in the 1+2 pattern allowing a lengthy intracellular domain between M2 and M3. The NMDA receptor differs, however, from the non-NMDA GluRs in possessing a rather more extensive N-terminal, extracellular sequence. It is believed that...

Ton

Ear 312-18 cochlea 312, 313F, 318 membranous labyrinth 312 'place' theory 318 see also deafness, mechanoreceptors E. coli 49, 66, 97 chemosensitivity 287-92 lac operon 68, 68F mechanosensitivity 239, 269 Economo, C. von 17 EcoR1 see restriction enzymes EKO neurons 330 Electric organs see electroplax Electrical synapse see synapse see gap junction Electrochemical potentials 278-81 defined 278 Electrocytes 404, 405F Electrophorus 208 Electroplax 209, 210F, 259 Electrotonic conduction 10, 281-5,...

The Memory Trace In Mammals

Let us, in conclusion, return from the simple systems of invertebrates to our 'proper study' mammals and humankind. Does the elucidation of invertebrate memory systems help us to understand what is happening in mammals We started this chapter by alluding to Occam's razor. Let us use it again here. Let us suppose that the molecular mechanisms underlying memory are much the same Figure 20.19 Putative mechanisms underlying long-term sensitisation. The same triadic system of facilitatory...

Proteins

So far we have been discussing the universal scaffolding of biomembranes. Although the Figure 7.11 Freeze-fractured membrane showing positions of E-, EF-, PF- and P-faces. Reproduced with permission from B. Satir (1975), Scientific American, 233(4), 29-37. Copyright 1975 by Scientific American Inc. All rights reserved. Figure 7.11 Freeze-fractured membrane showing positions of E-, EF-, PF- and P-faces. Reproduced with permission from B. Satir (1975), Scientific American, 233(4), 29-37....

Gcgccgcg

Elementary statistics tell us that groups of four nucleotides are much more likely to turn up by chance than groups of six. They should indeed appear every 44, i.e. 256, nucleotides. Hence the application of these restriction enzymes results in much shorter fragments than those obtained with endonucleases recognising sextuplets. The length of time the restriction endonuclease is allowed to act on the DNA double helix materially affects the number of fragments obtained. Only by allowing an...

KCNQ Channels

These channels first came to light because of mutations leading to long QT cardiac syndrome. Three genes have so far been identified KCNQ1-3 (Table 11.3). They encode a typical 6TM K+ channel with a P hairpin between S5 and S6. Figure 11.12 The 'classical' delayed potassium current. (A) The membrane is depolarised at time zero. The outward potassium current, K, commences about 2 ms after time zero. It rises to its full height in about 100 ms. If the membrane is held in a depolarised condition...