Plants Affecting The Dopaminergic Neurotransmission

Dopamine is a catecholamine neurotransmitter in the CNS and at some ganglia in the autonomic nervous system. To date, three main types of receptors have been found: Dj, D2, and D 3. The main dopaminergic systems in the brain are the nigro-neostriatal

Fig. 64. Hunteria zeylanica (Retz.) Gardn. & Thw. From KLU 1658. Field collector: 4/17/1970, E. Soepadmo. Geographical localization: Sempam River, Raub, Pahang, altitude: 2000 feet, Malaysia. Botanical identification: Margraf, 1973.

system, which is concerned with the control of locomotor activity; the midbrain mesolimbic forebrain system, which is involved with behavior; and the tubero-infundibular system of the hypothalamus, which releases dopamine into the portal vessels and thereby inhibits pituitary prolactine disease (Fig. 65).

Dopamine

Fig. 65. (a) Dopaminergic system: the three important brain dopaminergic systems. (b) Dopaminergic system: the dopaminergic neurons. NS, nigrostriatal dopaminergic neurone; PP, prolactin pituitary, PV, portal vein; MG, mammary gland; MDS, mesolimbic dopaminergic system; B, behaviour; LA, locomotor activity; TIDS, tuboinfundibular dopaminergic system; DA, dopamine; DO, DOPA; DC, DOPA decarboxylase; T, tyramine; TH, tyrosine hydroxylase; D1/D2, dopaminergic receptor D-, or D2; D2/D3, dopaminergic receptor D2 or D3; AC, adeny-late cyclase.

Fig. 65. (a) Dopaminergic system: the three important brain dopaminergic systems. (b) Dopaminergic system: the dopaminergic neurons. NS, nigrostriatal dopaminergic neurone; PP, prolactin pituitary, PV, portal vein; MG, mammary gland; MDS, mesolimbic dopaminergic system; B, behaviour; LA, locomotor activity; TIDS, tuboinfundibular dopaminergic system; DA, dopamine; DO, DOPA; DC, DOPA decarboxylase; T, tyramine; TH, tyrosine hydroxylase; D1/D2, dopaminergic receptor D-, or D2; D2/D3, dopaminergic receptor D2 or D3; AC, adeny-late cyclase.

In normal physiological conditions, the dopaminergic neurons of the substancia nigra control the cholinergic output but if they do not, as is the case in Parkinsonism, the skeletal muscles experience tremors, rigidity, and akynesia. L-DOPA given by mouth is effective in restoring the ability to initiate movements and is the most effective treatment for this condition; however, high doses are needed that produce nausea, vomiting, and hypotension. Because of the side effects associated with L-DOPA treatment, a number of dopamine receptor agonists have been tried including apomor-phine, and ergolines such as bromocriptine. Another alternative to treat Parkinsonism is the use of anticholinergic agents, such as crude extract of Atropa belladona L. (Solanaceae) and, more recently, anticholinergic alkaloids and their derivatives, which attenuate the tremor and relieve the muscular rigidity but are better to be used sparingly in elderly, as these these induce heavy nervous side effects. In summary, the drugs developed for the last 30 years have led to a significant reduction in the mortality of patients with Parkinsonism, but fail to prevent the progression of the disease.

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