Novel effects of light on central nervous system-Characteristics of non-visual photoactions and retinosuprachiasmatic complex

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The present study demonstrates a variety of light effects on the central nervous system other than vison, which are medicated by the retina and retinohypothalamic tract. The effects are divided essentially to two categories described as follows :1) Photic action on biological clock :Most peptidergic neuronsd (AVP,VIP,SOM) in the rat SCN were GABAnergic and arhythmic VIPmRNA expression in the SCN became rhythmic after serotonin deprivation (Ibata). Electrical stimulation of optic nerve increased and Ca ion deplivation decreased VIP secretion in the rat SCN slice culture (Shibata). Fos gene induction in the chipmunk SCN by light was not necessarily accompanied by phase-shifts of circadian locomotor rhythm (S.Honma.). Fos gene expression was generally decreased by aging in rats, but light-induced Fos expression was not altered significantly by aging (Yamaoka). REM sleep propencity in sleep structure was systematically changed in humans by changing the light-dark cycles abruptly, which may explain partly jet-lag syndrome (Sasaki). Lights brighter than 500 lux suppressed the nocturnal melatonin rise in humans. but did not shift the phase of melatonin rhythm under entrained condition (K.Honma).2) Photic action on functions other than biological clock :2-DG induced hyperglycemia was blocked by administration of VIP antibody, and VIP neurons in the SCN mediated the reaction to autonomic nerves innervating the liver, kidney and thymus (Nagai). Bright light stimulated or subsided the neuronal activities of autonomic nervous system in rats and enhanced immunoreactivity, which were abolished by bilateral SCN lesion (Niijima). Photoperiodic reactions of testis in hamsters are modified by nutritional state and stress (Ibuka). Behavioral thermoregulation to cold in young women is modifies by prior bright light exposure and menstrual cycle (Tokura).