PARAVENTRICULAR NUCLEUS ABLATION DISRUPTS DAILY TORPOR IN SIBERIAN HAMSTERS

Siberian hamsters were maintained in a short-day photoperiod (8 h ligh t/day) at 15 degrees C; body temperature (T-b) was telemetrically moni tored at 10-min intervals over the course of 4 months. Animals manifes ting repeated torpor bouts (T-b < 30 degrees C) were subjected to lesi ons of the paraventricular nucleus (PVN) or a sham operation. In the 8 weeks after surgery, 67% of the animals with complete bilateral ablat ion of the PVN failed to express torpor; circadian T-b rhythms, as det ermined by periodo-gram analysis, were normal in all operated and sham -operated animals. Body mass did not change in PVN-ablated animals tha t continued to express torpor; in contrast, rapid and sustained increa ses in body mass were manifested by all hamsters that terminated expre ssion of torpor. Expression of torpor is attenuated in the absence of the PVN; it is suggested that the PVN influences torpor indirectly by regulating body mass or the availability of metabolic fuels.