Effects of local application of 5-HT and 8-OH-DPAT into the dorsal and median raphe nuclei on core temperature in the rat.

The core temperature of male Wistar rats was measured after local application of 5-HT (10 micrograms) or 8-OH-DPAT (5 micrograms) into the dorsal (DR) or the median raphe (MR) nuclei. The core temperature was measured by a rectal thermistor probe, 20 and 60 min after the injection procedure started. The injected volume was 0.5 microliter and injections were made by means of 31G needles, at a rate of 0.33 microliter min-1. The raphe nuclei were approached at 30 degrees in order to avoid penetration of the cerebral aqueduct or to avoid the DR with injections aimed for the MR. The application of 5-HT or the 5-HT1A agonist 8-OH-DPAT into the DR produced a marked decrease in core temperature, whereas injections into the MR had no effect. These results demonstrate an important role for the DR in temperature regulation in the rat. The fact that the 5-HT1A agonist 8-OH-DPAT produced a decrease in core temperature, together with the observation that administration of the 5-HT1 antagonist (-)pindolol antagonized the 5-HT as well as the 8-OH-DPAT-induced decrease, indicates the involvement of DR 5-HT1A receptors in rat thermoregulation.