Effects of a muramyl dipeptide on the temperature and sleep-wake cycles of the squirrel monkey.

The circadian sleep-wake and body temperature cycles of squirrel monkeys were monitored continuously in an environment free of time cues before and after a 50-nmol injection of a synthetic muramyl dipeptide (MDP) either 1 h after wake-up time (subjective day) or just before sleep time (subjective night). At both phases decreases in percent time awake (relative to saline controls) were observed. After administration of MDP early in the subjective day, the animals exhibited alert wakefulness only 47.4% of the daytime, compared with a mean 86.7% of daytime after a saline control injection. The transitional stage was significantly elevated from 6.2 to 28.7% of time after MDP. Nonrapid-eye-movement (REM) sleep was elevated in four of five animals, but in the fifth animal, which had the least consolidated base-line sleep-wake pattern, a small decrease in non-REM sleep was seen. Regression analysis demonstrated a significant (P less than 0.01) relationship between the degree of sleep-wake consolidation and the effect of MDP on non-REM sleep. Normal sleep behaviors and spontaneous arousals were observed. MDP given at the circadian nighttime of two animals resulted in sleep and transitional episodes occupying 84% of the subjective night vs. 73% of time asleep after control injection. Again, these were mostly transitional and non-REM sleep stages, and they persisted 4-5 h into the predicted circadian daytime. REM sleep appeared to be suppressed in the early hours after injection at either time of day.(ABSTRACT TRUNCATED AT 250 WORDS)