Properties of the two circadian oscillators influencing the rabbit's food intake pattern

Continuous recordings of the pattern in food approaches during ad libitum-feeding were obtained from 15 rabbits which were exposed, for periods of 3-7 months, to continuous illumination (200-250 Lux), total darkness, light-dark alternations of L1:D23 h and L12:D12h and were blinded afterwards. It appears that the circadian pattern in food intake differs markedly in these circumstances and that it is governed by 2 loosely coupled circadian oscillators. These widely diverge in their effect on the eating pattern, in the response of their free-running periods to changes in steady state condition of the retina, and in their entrainment to either the onset or the ending of the illumination phases of 24-h LD regimens. The results indicate that the hypothalamic centres controlling the rabbit's food intake pattern must be strongly influenced by the retinal maintained 'dark' discharge.