Naloxone-induced changes in tachykinin NK3 receptor modulation of experimental anxiety in mice

This study investigates the influence of naloxone, an opioid antagonist, up on the effects of drugs acting on tachykinin NK3 receptor in the elevated p lus-maze test. Mice were intracerebroventricularly (i.c.v.) injected either with vehicle, 10 pmol of senktide, an NK3 agonist, or 100 pmol of [Trp(7)b eta-Ala(8)]NKA((4-10)) or SR142801, NK3 antagonists. Senktide alone signifi cantly increased the frequency of entries and the time spent in open arms, an anxiolytic-like effect, whereas the NK, antagonists alone showed no effe ct at the dose used. Naloxone alone did not alter the behavior of the anima ls on the plus-maze apparatus. Nevertheless, animals pretreated with naloxo ne (2 mg/kg, i.p.) showed an increase in senktide's anxiolytic-like effect and a similar profile of action for [Trp(7)beta-Ala(8)]NKA((4-10)), but not for SR142801, which presented an anxiogenic-like effect. Altogether, these findings indicate a putative neurokinin-opioid relationship in the modulat ion of experimental anxiety in mice. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.