Ambient temperature related sleep changes in rats neonatally treated with capsaicin

Ambient temperature related sleep changes in rats neonatally treated with capsaicin. PHYSIOL BEHAV 00(0) 000-000, 2004. The study was conducted on adult male Wistar rats, neonatally treated with capsaicin to destroy the peripheral warm receptors. The sleep-wakefulness was recorded for 5 h at an ambient temperature (Tamb) of 18, 24, 30 and 33 °C on different days. The rectal temperatures (Tr) of the rats were studied on exposure to 6 and 37 °C for 2 h to assess their thermoregulatory ability. The changes in the behavioral thermoregulation were assessed by noting the thermal preference of rats when they were placed in an environmental chamber with 3 interconnected compartments maintained at 24, 27 and 30 °C. Slow wave (SWS) and rapid eye movement (REM) sleep were decreased at 18 °C and increased at 30 °C, in control rats. There was a decrease in REM sleep and no change in SWS when Tamb was raised from 30 to 33 °C. However, in neonatally capsaicin treated rats, sleep was increased even at 33 °C, though there was no significant change in sleep when Tamb was increased from 18 to 24 °C. Capsaicin treated rats showed thermoregulatory deficiency at 37 °C but the thermal preference was unaltered in these rats. The results suggest that the central warm receptors can produce alteration in sleep at different Tamb, even in absence of peripheral warm receptors. The behavioral thermoregulation was unaffected in these rats, though their ability to defend the body temperature in warm environment was affected.