Effects of 5-HT Denervation of the Suprachiasmatic Nuclei or Lesions of the Median Raphe Nucleus on Daily Torpor in the Djungarian Hamster, <i>Phodopus sungorus</i>

Abstract

In the Djungarian hamster (Phodopus sungorus), using 5,7-dihydroxytryptamine (a specific neurotoxin), depletion of the serotonin (5-HT) fibers innervating the suprachiasmatic nuclei (SCN) was performed in animals displaying torpor bouts. The characteristics of postoperative torpor bouts in lesioned hamsters were similar to those observed before the denervation. 5-HT innervation of the SCN thus seems unnecessary for the expression and temporal organization of daily torpor. After chemical or thermic lesions of the 5-HT neurons of the anterior median raphe nucleus (MR) in hamsters displaying torpor bouts, the phenomenon of torpor was not prevented. In addition, hamsters lesioned on the day of transfer to short photoperiod (SP) displayed their first torpor bouts after the same duration of SP exposure as intact hamsters. These results suggest that, contrary to what is observed in hibernation, 5-HT neurons of the anterior part of the MR are not involved in the mechanisms governing the occurrence and seasonal timing of daily torpor.