Feedback in the Rabbit's Central Circadian System, Revealed by the Changes in Its Free-Running Food Intake Pattern Induced by Blinding, Cervical Sympathectomy, Pinealectomy, and Melatonin Administration

Long-term records of the number of food approaches per 30 min were obtained from 16 rabbits in constant light and after blinding. Optic nerve sectioning usually resulted in a shortening of the free-running period (τ; mean reduction = -0.26 hr) of the oscillator governing the rabbit's food intake pattern. Subsequent resection of both superior cervical ganglia always reduced this τ (mean = -0.41 hr), and it could be further shortened (mean = -0.24 hr) by chronic administration of melatonin. These observations led to experiments in which the food intake of 15 blinded rabbits was recorded before and after pinealectomy. This always resulted in a lengthening of τ (mean = +0.27 hr), which was never seen after subtotal or sham pinealectomy in 10 other blinded animals (mean = -0.05 hr). Sympathectomy also reduced τ (mean = -0.50 hr) in the pinealectomized rabbits, whereas it induced a smaller reduction (mean = -0.29 hr) after sham pinealectomy. These results, together with previous observations on the effect of sy...