In conclusion, a massive body of evidence has been presented to show that the medicinal plants of the Pacific Rim hold serious potential as source of drugs for the treatment of CNS-related disorders. In summary, the most remarkable feature is the taxonomical and chemical diversity of these drugs. Given the number of medicinal plants in the Pacific Rim, the number of molecules with effects on the CNS is likely to expand in the future, and it is vital to establish a systematic neuropharmacological investigation of these plants in vitro and in vivo. It is likely that in the near future methods will be developed to assess more efficiently the CNS properties of plant secondary metabolites, including in vitro cultures of neurones or neuronal systems and even brains. The availability of original natural products together with the techniques for studying the affinity of plant products to receptors, will contribute significantly to the discovery of centrally active agents. In addition to the knowledge pertinent to the major neuronal systems, one may eventually begin to conceive of strategies for the control of diseases in which serotonin, GABA, glycine, and dopamine, and as of yet unveiled neurotransmittors. In regard to the taxonomic distribution, it appears that alkaloid-producing families are the predominant source of CNS-acting agents, especially in the Magnoliidae and Asteridae (134). One wonders if other sorts of plant metabolites have been skipped.
Note that the families Rubiaceae, Solanaceae, and Convolvulaceae are known to elaborate a series of neuroactive alkaloids, some of clinical value, and represent an interesting pool of potentially centrally active agents. The Rubiaceae in particular has attracted a great deal of interest on account of Mitragyna speciosa, from which mitragy-nine has been characterized , an indole alkaloid of possible value for the treatment of opioid dependence. Gorniak et al. studied the effects of Palicourea marcgravii (Rubi-aceae) leaf on dopamine related behaviors in rats and made the interesting observation that the extract given had a blocking action on a mesostriatal dopamine receptor (135). In the Convolvulaceae-Solanaceae group, some evidence currently available suggests the presence of GABAergic principles. The methanolic extract of stem of Cuscuta reflexa (Convolvulaceae) protected rodents against convulsion induced by chemoconvulsive agents in mice, and increased the levels of dopamine and, surprisingly, of GABA in mice brain after a few weeks (136).
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