INVOLVEMENT OF THE MIDBRAIN PERIAQUEDUCTAL GRAY 5-HT1A RECEPTORS IN SOCIAL-CONFLICT INDUCED ANALGESIA IN MICE

Recent results from our laboratory have shown that 30-bites social con flict in mice produces a high-intensity, short-term analgesia which is attenuated by systemically injected 5-HT1A receptor agonists, such as BAY R 1531 i-n-propylamino)-1,3,4,5-tetrahydrobenz(c,d)indole hydroch loride) and gepirone. The present study investigated the effects of th ese drugs, as well as the 5-HT1A receptor antagonist WAY 100135 ethoxy phenyl)piperazine-1-yl)-2-phenylpropanamide) injected into the midbrai n periaqueductal gray matter of mice on 30-bites analgesia. Four to fi ve days after guide-cannula implantation, each mouse received microinj ection of gepirone (30 nmol/0.2 mu l), BAY R 1531 (10 nmol/0.2 mu l), WAY 100135 (10 nmol/0.2 mu l), saline (0.9% NaCl) or vehicle (saline 4% Tween 80) 5 min before either an aggressive (30 bites) or a non-ag gressive interaction. Nociception was assessed by the tail-flick test made before as well as 1, 5, 10 and 20 min after social interaction. T he full 5-HT1A receptor agonist BAY R 1531 blocked, whereas, WAY 10013 5 and gepirone intensified 30-bites analgesia, Neither non-aggressive interaction, per se, nor the three compounds given after this type of social interaction significantly changed nociception. These results in dicate that 5-HT1A receptors in the periaqueductal gray inhibit analge sia induced by social conflict in mice. (C) 1998 Elsevier Science B.V.