Blockade of pre-and post-synaptic 5-HT1A receptors does not modify the effect of fluoxetine or 5-hydroxytryptophan on ethanol and food intake in rats

Selective serotonin reuptake inhibitors (SSRIs) or serotonin precursors inhibit ethanol and food intake by increasing the synaptic availability of 5-HT in the central nervous system. However, these agents can also increase 5-HT levels at somatodendritic 5-HT_1A autoreceptors, with negative effects on serotonergic transmission. (+)WAY100135 [N-ter-butyl 3-4-(2-methoxy-phenyl) piperazin-1-yl-2-phenylpropa-namide dihydrochloride] is a selective antagonist both at pre-and post-synaptic 5-HT_1A receptors. The present study investigated the effect on ethanol and food intake of (+)WAY100135, given alone or coadministered with the SSRI fluoxetine or the 5-HT precursor 5-hydroxytryptophan (5-HTP) in genetically selected alcohol-preferring rats. Blockade of presynaptic 5-HT_1A receptors after injection of (+)WAY100135, 0.1 or 1 μg/rat, into the dorsal raphe did not significantly modify ethanol, food or total fluid intake. The same doses of (+)WAY100135 did not modify the inhibition of ethanol and food intake induced by intraperitoneal (IP) injection of fluoxetine, 5 mg/kg. Subcutaneous (SC) administration of (+)WAY100135 (1 or 10 mg/kg) did not affect the 3-h, or the overnight intake of ethanol, food or total fluids. Given together with IP fluoxetine (5 mg/kg) or SC 5-HTP (100 mg/kg plus carbidopa, 12.5 mg/kg), the same SC doses of (+)WAY100135 did not modify their inhibitory effect on ethanol and food consumption. Present findings suggest that blockade either of pre-or of pre-and postsynaptic 5-HT_1A receptors does not potentiate the inhibitory effect of fluoxetine or 5-HTP on ethanol and food intake. Received: 2 November 1996/Final version: 23 April 1997