抄録
Pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) have the same sequence of amino acid residue in 68%. PACAP is known to regulate gastrointestinal secretion and motility. Indeed, electrophysiological studies of the myenteric plexus neurons of the guinea-pig ileum have shown that PACAP depolarized AH neurons (96%) and S neurons (36%). In the present study, we investigated actions of PACAP on the postsynaptic membrane and on evoked synaptic potentials of cecum submucosal neurons. Intracellular recordings were made from submucosal neurons in vitro with glass microelectrodes. PACAP applied by superfusion (3-300 nM) caused membrane depolarizations in the submucosal neurons (92%) in a dose-dependent manner (EC50 = 6.3 nM), often accompanied by repetitive firings (45%). PACAP reduced the amplitude of fast EPSPs by ACh and slow IPSPs by noradrenalin. Since PACAP did not affect the postsynaptic sensitivity to ACh, it was suggested that PACAP inhibited the presynaptic release of ACh; effect of PACAP on the neuronal sensitivity to noradrenalin has to be tested. It was concluded that PACAP excited postsynaptically ganglion neurons and modulated presynaptically ganglionic transmission in the submucosal plexus of the guinea-pig cecum. [J Physiol Sci. 2007;57 Suppl:S240]
