Substance P- and Somatostatin-Like Immunoreactivity in Avian Encapsulated Mechanoreceptors
The identity of neurotransmitters utilized by primary sensory neurons has not been firmly established, although several candidates for neurotransmitters or modulators have been suggested (Salt and Hill, 1983). In particular, many attempts to prove histochemically any of the well-known neurotransmitters or modulators in sensory receptors have been unsuccessful. Moreover, the well documented distribution of neuropeptides in some somata of primary sensory ganglia (substance P (SP) — Katz and Karten, 1980; somatostatin (Som) — Kummer and Heym, 1986; vasoactive intestinal polypeptide (VIP) — Skofitsch et al., 1985; cholecystokinin (CCK) — Kuwayama and Stone, 1986; opioid peptides — Weihe et al., 1985) has not been generally confirmed in corresponding sensory nerve fibers of encapsulated or non-capsulated receptors. Some efforts have been made to localize in the light microscope SP-LI (like-immunoreactive) nerve fibers in human digital skin including the sensory nerves entering Meissner corpuscles (Dalsgaard et al., 1983). On the other hand, Hartschuh et al. (1979) visualized immunohistochemically a met-enkephalin-LI in Merkel cells. Recently, Björklund et al. (1986) found SP- and neurokinin A-LI only in sensory nerve fibers, whereas VIP-LI has been observed predominantly in autonomic nerves but also in some sensory nerve fibers. All known available immunohistochemical investigations examine the above mentioned neuropeptides at the light microscopical level. The aim of the present communication is to extend the knowledge concerning the existence of new peptides in bird mechanoreceptors and to define their precise cytological localization at the electron microscopical level.
KeywordsNerve Fiber Vasoactive Intestinal Polypeptide Sensory Receptor Primary Antiserum Trigeminal Neuron
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