Temperature-related release of serotonin from unrestrained rats' pre-optic area perfused with ethanol

Abstract

The circumscribed effect of ethyl alcohol on the local efflux of serotonin (5-HT) within the thermosensitive region of the anterior hypothalamic, pre-optic area (AH/POA) of the unrestrained rat was examined in relation to core temperature. A single guide cannula for push-pull perfusion was implanted stereotaxically in the AH/POA within coronal planes AP 7.0–8.2. Following 3–4 push-pull perfusions with control artificial CSF of a site identified as reactive to 5-HT, ethanol in a concentration of 2.75 (471 mM) or 5.5 (942 mM) percent was perfused at the same locus over a 5–10 min interval. Successive samples of perfusate were assayed for their content of 5-HT by high performance liquid chromatography using electrochemical detection (HPLC-EC). Within a circumscribed region of the AH/POA of the rat maintained at an ambient temperature of 22°C, ethanol induced either an immediate or delayed hypothermia of short latency or a transient decline followed by an immediate increase in core temperature. In each case, the shift in temperature depended on the anatomical site of push-pull perfusion. Overall, the fall in core temperature was accompanied by an inhibition in the efflux of 5-HT. However, the consequent rise in the rat's core temperature was associated with an enhanced release of 5-HT in the samples of perfusate collected from the AH/POA. These results suggest that serotonergic synapses within the AH/POA are apparently involved in the thermolytic effects of ethanol as well as in the thermogenesis following the interval of heat loss.