Evidence for in vivo thermosensitivity of serotonergic neurons in the rat dorsal raphe nucleus and raphe pallidus nucleus implicated in thermoregulatory cooling.
The ability to sense and respond appropriately to increases in ambient and body temperatures is critical for the survival of all animals. Although evidence suggests that brain serotonergic systems play a role in thermoregulation, including thermoregulatory cooling, evidence for activation of brainstem serotonergic neurons in vivo, in unanesthetized animals, during heat exposure is lacking. In this experiment we tested the hypothesis that populations of serotonergic neurons in the midbrain and medullary raphe complex are activated following exposure to warm ambient temperature. Rats were exposed to an incubation chamber at either warm ambient temperature (37°C) or room temperature (RT; 23°C) for 105 min. Brains then were removed and processed for immunohistochemical detection of the protein product of the immediate-early gene c-fos (as a marker of neuronal activation) and tryptophan hydroxylase (as a marker of serotonergic neurons). Exposure to warm ambient temperature increased body temperature and c-Fos expression in topographically organized populations of serotonergic neurons in the dorsal raphe nucleus. Activation of the dorsal raphe nucleus serotonergic system was positively correlated with body temperature following exposure to the incubation chamber. In the medulla, exposure to warm ambient temperature, compared with exposure to RT, decreased c-Fos expression in serotonergic neurons in the raphe pallidus nucleus and in non-serotonergic cells in the rostral ventrolateral medulla. Together, these results provide evidence for multiple but anatomically discrete thermosensitive serotonergic systems that may have implications for the regulation of body temperature, as well as, via projections to forebrain targets, cognitive and affective functions.
Department of Integrative Physiology and Center for Neuroscience, University of Colorado, Boulder, CO 80309-0354, USA.
Matthew W
MW
Hale
Kathleen F
KF
Dady
Andrew K
AK
Evans
Christopher A
CA
Lowry
D000818:Animals; D001831:Body Temperature / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology*; D019317:Evidence-Based Medicine; D008297:Male; D009434:Neural Pathways / Q000737:chemistry / Q000378:metabolism; D009474:Neurons / Q000737:chemistry / Q000378:metabolism*; D011903:Raphe Nuclei / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism*; D014365:Tryptophan Hydroxylase / Q000378:metabolism
D012701:Serotonin; D014365:Tryptophan Hydroxylase