Selective desensitization of serotonin (5-HT) receptor-mediated hyperthermia by mianserin and other 5-HT antagonists

Hyperthermic responses to 6-chloro-2-(1-piperazinyl)-pyrazine (MK-212) and hypothermic responses to 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) were assessed in rats as an in vivo index of the responsiveness of 5-HT2 and 5-HT1A receptors, respectively. Forty-eight hours after a single injection of mianserin, there was a shift to the right in the dose-response relationship for MK-212-induced hyperthermia. The hyperthermic response to MK-212 was attenuated 1 hr and 48 hr (but not 8, 24 or 96 hr) after the administration of mianserin. The hyperthermic effect of 5-methoxy-N,N-dimethyltryptamine (5MeODMT) also was diminished 48 hr after administration of mianserin. However, mianserin did not alter the hypothermic response to 8-OH-DPAT. A diminished hyperthermic effect of MK-212 also was observed 48 hr after a single injection of loxapine, methysergide, pizotifen and ketanserin. It is concluded that there is a selective decrease in the responsiveness of the 5-HT2 receptors mediating MK-212-induced hyperthermia, 48 hr after a single injection of mianserin or other selected 5-HT antagonists. Moreover, MK-212-induced hyperthermia appears to be a functional measure of the reported decrease in the number of 5-HT2 receptors, 48 hr after a single injection of mianserin.