Effects of Illumination on the Rabbits Eeg During the two Phases of its Circadian Rhythm

Abstract

After exposure to a LD 12:12 regimen for several weeks, rabbits exhibit a programmed circadian rhythm in the RMS values of their occipital and frontal EEG's during 54-hr recordings in constant darkness. Illumination at levels of 80, 160 and 230 Lx raises these RMS values in both phases of the rhythm. The induced rise is large in the phase with low RMS values and small in the other, whereas light-induced changes in spectral composition of the EEG's are slight in either phase. Bilateral optic nerve sectioning results in similar changes in properties of the EEG and in the amplitude of its rhythm. The results are discussed with reference to the influence exerted by steady illumination on the overall-level of retinal maintained "dark" discharge.

Effects of bilateral cervical sympathectomy and subsequent blinding on properties and circadian changes of the rabbit's EEG

“…From further experiments with intact rabbits in the same experimental situation (Bobbert and van Hartevelt, 1986), it appeared that steady illumination induces changes in RMS value of the EEG's and EMG's, and in spectral composition of the EEG's, which are closely similar to those resulting from sympathectomy or blinding, although they are intermediate in size. This suggests that light has a predominantly inhibitory influence on the retinal maintained "dark" discharge.…”

Re‐entrainment of the Rabbit's circadian food intake pattern after inversion of 24‐hr sawtooth illuminations and standard light‐dark alternations

“…Nevertheless, the morphological and electrophysiological correlates of this outline of the factors involved in entrainment of the rabbit's food intake rhythm, and of its rhythm in photic sensitivity of the retina (Bobbert and Brandenburg, 1982;Bobbert et al, 1983;Brandenburg et al, 1983) and, thus, of the ensuing rhythms in the cortical Visually Evoked Potentials (Bobbert et al, 1978) and in the EEG (Bobbert et al, 1985(Bobbert et al, , 1987 are not known with certainty (for reviews see: Meijer and Rietveld, 1989;Moore et al, 1991).It has been established Downloaded by [University of Cambridge] at 17:06 16 June 2016 (Leibowitz, 1980;Mozes et al, 1988) that food intake by mammals is governed by centers located in the hypothalamic part of the reticular formation. The occurrence of a pronounced rhythm in the rabbit's food intake during ad lib-eating in a constant environment, shows that the activity of these hypothalamic centers is strongly modulated by the central circadian mechanism (Kita et al, 1982).…”