REM sleep-suppressing effects of atropine in cats vary with environmental temperature

Because the occurrence of rapid eye movement (REM) sleep is critically dependent upon an animal's thermal balance, acute pharmacological treatments may effect REM sleep through effects on thermoregulation. We describe how manipulating ambient temperature (T(a)) alters the REM sleep-suppressing effects of systemically-administered atropine, a muscarinic receptor antagonist, in adult cats. At a T(a) of 23 degrees C , atropine (0.5 mg/kg) produced a significant reduction in REM sleep time that persisted for about 8 h of a 16 h recording period. Hypothalamic temperature fell below control levels for about 4 h following atropine. At a T(a) of 30 degrees C, the same dose of atropinehad no significant effect on REM sleep time, or hypothalamic temperature. These findings indicate the importance of considering the possible role of thermoregulation in drug-induced effects on REM sleep.