The aim of this application is to examine the participation of myenteric neuropeptides in the regulation of an integrated neuromuscular function: the intestinal peristaltic reflex. Initial work focused on the identification of vasoactive intestinal peptide (VIP) and its cosynthesized, coreleased homolog, peptide histidine isoleucine (PHI) as the neurotransmitters responsible for neurally- induced relaxation. The stoichiometry of VIP release and muscle relaxation was established and the existence of presynaptic inhibitory autoreceptors regulating release of VIP/PHI was demonstrated. VIP/PHI neurons were shown to be tonically active and to mediate the dominant inhibitory neural tone that normally masks myogenic phasic activity. A preparation was devised that enabled separate measurement of the components of the peristaltic reflex (ascending contraction and descending relaxation) and identification of peptide and non-peptide neurotransmitters released with each component. The identification was made possible by the use of specific antisera and is being confirmed by use of selective peptide antagonists of VIP, tachykinin, GRP/bombesin, CCK and opioid peptide receptors. The modulatory influence of somatostatin and opioid neurons on VIP/PHI neurons- the mediators of descending relaxation- is being investigated. Somatostatin neurons act as facilitatory interneurons in descending pathways whereas opioid neurons appear to act as restrictive neurons: the two types of neurons modulate release of VIP/PHI in opposite directions. These studies are being extended to other myenteric neuropeptides (CCK, GRP/bombesin, substance P and galanin) to determine the mechanism of release and the reciprocal influence each has on its own release (autoregulation) and the release of other peptides. The approach will be facilitated by the use of dispersed myenteric ganglia immobilized in Biogel and perfused in minichambers. An important advance is the development of a flat sheet muscle preparation which enables measurement of the components of the peristaltic reflex in human intestinal muscle tissue obtained at surgery. Preliminary studies have demonstrated the versatility of this preparation and its usefulness in identifying the neurotransmitters involved in the regulation of the peristaltic reflex in humans. The identification of neurotransmitters is made increasingly possible by the availability of specific antisera for immunoneutralization and immunoassay and of selective peptide antagonists, including antagonists presently available for VIP, CCK, tachykinins/bombesin and opioid peptides.
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