Effects of Neuropeptide Y on the Behavioral Circadian Rhythm of the Locomotor Activity in Rats
In the experiments on male Wistar rats, the effects of threefold intranasal administration of 0.85 pg neuropeptide Y at different points of the projected daily cycle (ZT = 2, ZT = 6, ZT = 10, ZT = 14, ZT = 18, and ZT = 22) on the circadian rhythm of the voluntary locomotor activity (wheel running) were studied. Neuropeptide Y administration at ZT = 22 induced a statistically significant phase advance of the rhythm by 1.54 hr. Intranasal administration of neuropeptide Y at the other points of the projected daily cycle did not induce statistically significant phase-shifts of the locomotor activity rhythm. Neuropeptide Y did not cause changes in the duration of the circadian rhythm period and daily gross locomotor activity independently of the administration time. The obtained data confirm the important role of endogenous neuropeptide Y as a synchronising factor for the circadian oscillator in absence of main physiological zeitgeber - cyclic afferentation from photoreceptors of the retina.