SEROTONIN MAY PLAY A ROLE IN THE ANOREXIA INDUCED BY AMPHETAMINE INJECTIONS INTO THE LATERAL HYPOTHALAMUS

Amphetamine (AMPH) injections into the lateral hypothalamus (LH) are known to inhibit feeding and this effect has been shown to be mediated by the release and the reuptake blockade of catecholamines. LH serotonin (5-HT) has been suggested to be involved in feeding inhibition and a recent study showed that LH amphetamine infusion increases extracellular dopamine (DA), norepinephrine (NE) and 5-HT, which suggests that 5-HT might also be involved in amphetamine anorexia. The present study investigated this possibility. A correlational study was performed between the anorectic effect of LH unilateral microinjections of each monoamine and the anorectic effect of AMPH. Six groups of male rats were used. The rats in each group were submitted to 2 series of 6 experimental sessions. Each session consisted of one microinjection in 24 h food-deprived rats, followed by the measurement of food intake 30 min later. The first series was similar for all groups and explored the AMPH effect (difference between the mean food intake after 3 AMPH injections (40-mu-g/0.5-mu-l) and the mean food intake after 3 saline injections (0.5-mu-l)). The second series explored the effects of DA (40-mu-g), NE (25-mu-g), EPI (25-mu-g), 5-HT (25-mu-g) or AMPH again, in a similar way as described for AMPH in the first series. Linear regression analysis on the first series AMPH effect and the amine effect of the 2nd series showed a positive correlation between both series of AMPH, AMPH and DA, and AMPH and 5-HT. This last correlation was replicated in a different group. No correlation was found between AMPH and NE or AMPH and epinephrine (EPI). These results suggest that LH AMPH anorexia could be mediated through DA and 5-HT release.