A tonic inhibitory control of rat pepsin secretion is mediated by central GABA-A receptors

Abstract

Polidori, C., I. Panocka, R. Ciccocioppo, M. Broccardo, G. Improta, D. Regoli and M. Massi. Further evidence that the tachykinin Pg-Kii is a potent agonist at central Nk-3, but not Nk-1, receptors. Peptides 18(6) 825–833, 1997.—Intracerebroventricular (ICV) injection of tachykinins (TKs) inhibits ethanol intake and angiotensin II-induced water intake; the effects are apparently mediated by NK-3 and NK-1 receptors, respectively. The present study evaluated the effect of the TK PG-KII, a novel kassinin-like peptide isolated from the skin of the Australian frog Pseudophryne güntheri, in these in vivo tests for central activity. PG-KII, given by ICV injection, potently inhibited alcohol intake in genetically selected alcohol-preferring rats, being about 3 times more potent than the selective NK-3 receptor agonist NH2-SENK. The dose of 100 ng/rat, that markedly inhibited ethanol intake, did not inhibit food intake and prandial drinking in food deprived rats, providing evidence that the effect of PG-KII on ethanol intake is behaviorally selective. The effect on ethanol intake was inhibited by ICV injection of the NK-3 receptor antagonist R820, but was not modified by the NK-1 receptor antagonist SR 140333. PG-KII inhibited drinking induced by angiotensin II only at doses of 300 or 1000 ng/rat, being about 5 times less potent than the selective NK-1 receptor agonist [Sar9,Met(O2)11]substance P. These doses of PG-KII produced also marked increase in competing behaviors, such as grooming and locomotion. The dose of 1000 ng/rat evoked a general inhibition of the ingestive behavior, reducing also food intake. The ICV injection of the NK-1 receptor antagonist SR 140333 only slightly inhibited the effect of PG-KII on angiotensin II-induced drinking, while it markedly reduced that of [Sar9,Met(O2)11]substance P. These findings, in accordance with those of previous studies, indicate that PG-KII is endowed with marked activity at central NK-3 receptors, and low activity at NK-1 receptors.