Neurophysiological Studies of the SCN in the Rat and in the Java Sparrow

Abstract

Lesion experiments of the suprachiasmatic nucleus (SCN), a tiny nucleus in the hypothalamus, revealed abolishment of circadian rhythms of various physiological and behavioral activities in the rat. Stephan and Zucker (1972) indicated elimination of circadian rhythms of drinking and eating behavior as well as wheel-running activity in the rat after bilateral lesions of the SCN. Moore and Eichler (1972) reported the abolishment of the adrenal corticosterone rhythms after lesions of the SCN. Later on, we also observed that lesions of the rat SCN abolished the circadian rhythm of sleep and wakefulness in this nocturnal animal without changing the total amount of slow wave sleep and paradoxical sleep in a day (Ibuka and Kawamura 1975). Distribution of sleep during daytime and nighttime became even after lesions of the SCN. These studies suggested that the nucleus contains an endogenous oscillator generating circadian rhythms. Alternatively, this nucleus could be a coupler of many circadian rhythm oscillators within the brain. From such lesion experiments alone, it is difficult to conclude that the SCN really generates a circadian rhythm. For such a conclusion, we should obtain a tissue culture preparation of the SCN demonstrating that cellular metabolic or physicochemical activity of the SCN in vitro shows a circadian rhythm. However, presently, the in vitro culture of adult mammalian brain tissue is technically difficult. Therefore we developed a method for the in vivo isolation of a part of the hypothalamus containing the SCN as an island using a modified Halasz technique. We succeeded in making a relatively intact island in the anterior hypothalamus (Inouye and Kawamura 1979).