TONIC EFFECTS OF LIGHT ON THE CIRCADIAN SYSTEM OF THE SQUIRREL-MONKEY

The tonic effects of constant light were examined on the organization of the circadian time-keeping system of squirrel monkeys. The rhythms of feeding, colonic temperature and urinary potassium excretion were measured in chair-restrained animals maintained in 1 lux, 60 lux or 600 lux in isolation chambers at constant temperature with food available ad lib. When compared to previous results from monkeys synchronized by light-dark cycles, there was a reduction in the ranges (R) of all 3 rhythms in constant light. As the intensity of light increased, the computed α/ρ ratio increased for the feeding and temperature rhythms but not for the renal potassium rhythm. The average free-running period (τ) for all three rhythms was approximately 25 h, and long term experiments with unrestrained monkeys showed a small lengthening of τ with brighter light. There was a much broader distribution of τ for the urinary potassium rhythm than for the feeding and temperature rhythms. Spontaneous internal desynchronization between the potassium rhythm and the feeding and temperature rhythms occurred in approximately one-quarter of the experiments, with the light intensity having no influence on the incidence of desynchronization. © 1979 Springer-Verlag.