Neurotransmitters physiological aspects

The diverse physiological actions of capsaicin described in the previous sections have motivated numerous, equally diverse, in vivo and in vitro studies in search of biochemical correlates. The most attention, however, has been focused on the sensory system since a direct effect of capsaicin on sensory nerves has been suspected for a long time. More recent observations of capsaicin-induced sensory neuron degeneration in neonatal animals have added further impetus to determine the resultant neurochemical deficits of this lesion. It is perhaps fortunate that the small type B neurons of dorsal root ganglia which appear anatomically to succumb to capsaicin after both neonatal and adult treatment are also among the neurons for which putative neurotransmitter markers have been identified. Accordingly, these markers, two of which are the peptides somatostatin and substance P, have provided both a means to assess the neurotoxic potential of capsaicin, and to some extent relate anatomical with neurochemical investigations. For the sake of coherence the biochemical aspects of some reports cited in the previous sections are discussed here. The major conclusions in these reports will be summarized in Section 13. 

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