8-OH-DPAT-sensitive neurons in the nucleus raphe magnus modulate thermoregulatory output in rats

The nucleus raphe magnus (NRM) is purported to be a relay through which per ipheral thermoafferent information is transmitted to thermointegrative cent ers located in the preoptic/anterior hypothalamus (POAH). Therefore, suppre ssion of neural activity in the NRM should reduce thermoregulatory response s to peripheral thermal challenges, but not affect responses elicited by ma nipulation of POAH temperature. At low ambient temperatures Lidocaine injec tions into the NRM of nonanesthetized rats resulted in decreases in POAH te mperature, oxygen consumption, and electromyographic activity. At a warm am bient temperature, lidocaine injections into the NRM decreased the elevatio ns in oxygen consumption and electromyographic activity elicited by cooling the POAH. The effects of lidocaine injections were duplicated by injection of a 5-HT1A agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) into the N RM. The effect of 8-OH-DPAT was eliminated by pre-treatment with a selectiv e autoreceptor antagonist. These results suggest that NRM 5-HT neurons are modulating the relationship between output of thermointegrative centers and thermoregulatory effector responses rather than processing thermoafferent information. (C) 1999 Elsevier Science B.V. All rights reserved.