Hypoxia causes a regulated decrease in body temperature (Tb). There is circumstantial evidence that the
neurotransmitter serotonin (5-HT) in the anteroventral preoptic region (AVPO) mediates this response. However, which
5-HT receptor(s) is (are) involved in this response has not been assessed. Thus, we investigated the participation of the
5-HT receptors (5-HT1, 5-HT2, and 5-HT7) in the AVPO in hypoxic
hypothermia. To this end, Tb of conscious Wistar rats was monitored by biotelemetry before and after intra-AVPO microinjection of
methysergide (a 5-HT1 and 5-HT2 receptor antagonist, 0.2 and 2 microg/100 nL),
WAY-100635 (a 5-HT(1A) receptor antagonist, 0.3 and 3 microg/100 nL), and
SB-269970 (a 5-HT7 receptor antagonist, 0.4 and 4 micro/100 nL), followed by 60 min of
hypoxia exposure (7% O2). During the experiments, the mean chamber temperature was 24.6 +/- 0.7 degrees C (mean +/- SE) and the mean room temperature was 23.5 +/- 0.8 degrees C (mean +/- SE). Intra-AVPO microinjection of vehicle or
5-HT antagonists did not change Tb during normoxic conditions. Exposure of rats to 7% of inspired
oxygen evoked typical
hypoxia-
induced hypothermia after vehicle microinjection, which was not affected by both doses of
methysergide. However,
WAY-100635 and
SB-269970 treatment attenuated the drop in Tb in response to
hypoxia. The effect was more pronounced with the 5-HT7 antagonist since both doses (0.4 and 4 microg/0.1 microL) were capable of attenuating the hypothermic response. As to the 5-HT(1A) antagonist, the attenuation of
hypoxia-
induced hypothermia was only observed at the higher dose. Therefore, the present results are consistent with the notion that
5-HT acts on both 5-HT(1A) and 5-HT7 receptors in the AVPO to induce
hypothermia, during
hypoxia.