REGULATION OF CIRCADIAN PHOTIC RESPONSES BY NITRIC-OXIDE

A role for nitric oxide in circadian responses to light has been indic ated in previous studies. To determine the specific function of NO-, t he authors manipulated NO- and nitric oxide synthase (NOS) activity pr ior to light pulses that would normally induce phase shifts. The NOS i nhibitor, L-NAME, selectively attenuated phase advances of locomotor r hythms and had no effect on phase delays. The NO- donor, SNAP, potenti ated both photic responses, and phase delays were larger than the maxi mum responses that could be obtained with Light alone. The data sugges t a model in which NO- participates in the adaptation of the system to environmental lighting conditions by regulating in a phase-dependent manner responsiveness to light.