THE PRESENCE AND THE EFFECTS OF NEUROPEPTIDE-Y IN RAT ANOCOCCYGEUS MUSCLE

Isolated anococcygeus muscle from male rats was examined for the prese nce of neuropeptide Y-immunoreactive nerves and for the effects of neu ropeptide Y on its tone and its contractile/relaxant responses to elec trical field stimulation, acetylcholine, guanethidine and noradrenalin e. Using peroxidase anti-peroxidase immunohistochemistry in stretch pr eparation of the anococcygeus, neuropeptide Y-immunoreactive nerve fib res were observed, in abundance, running along both vascular as well a s non-vascular smooth muscle cells. Neuropeptide Y (> 250 nM) evoked p hentolamine and tetrodotoxin-resistant contractile response. Neuropept ide Y, even in subspasmogenic concentrations, potentiated contractions evoked by acetylcholine, guanethidine and noradrenaline. Electrical f ield stimulation (trains of 3-4 pulses, 0.1 ms, 10 Hz) of the isolated anococcygeus preparation produced robust, phentolamine and tetrodotox in sensitive contractions. Neuropeptide Y (< 10 nM) exerted a biphasic effect on the electrical field stimulation-evoked contractions; an ea rly potentiation was followed by a delayed and progressive inhibition. Neuropeptide Y (> 10 nM) caused a concentration-dependent potentiatio n of electrical field stimulation-evoked contraction alone, matching i ts potentiation of noradrenaline-evoked contraction. Electrical field stimulation (5 pulses, 0.1 ms, 10 Hz) of guanethidine (50 mu M)-contra cted anococcygeus induced a relaxant response and neuropeptide Y (1-10 0 nM) exerted a concentration-related slight and variable effect on th e electrical field stimulation-evoked relaxant response (1 nM, augment ation; 10 nM, no effect; 100 nM, reduction). It is concluded that rat anococcygeus muscle has a rich neuropeptide Y-containing innervation a nd neuropeptide Y is mostly stored within adrenergic nerves. The main functional roles of neuropeptide Y in the anococcygeus muscle are like ly to be post-junctionally mediated facilitation and prejunctionally m ediated inhibition of adrenergic motor transmission. (C) 1997 Elsevier Science B.V.