title: Light responsiveness of the suprachiasmatic nucleus within the island with the retino-hypothalamic tract spared.
abstract: To investigate daily variation in responsiveness of the suprachiasmatic nucleus (SCN) to exposure to light, the evoked change in multiple unit activity of the SCN within the retino-hypothalamic island with the retino-hypothalamic tract (RHT) spared, was measured in the rat at 6 h intervals across a 24 h day. It is found that SCN multiple unit discharge rates increase during a 1 h exposure to light which interrupts constant darkness irrespective of the time of day. A non-parametric statistical analysis did not indicate a significant daily variation in light-responsiveness of the SCN. The present results suggest that the phase-dependent shift of the SCN rhythm after a light exposure is induced not by a rhythm in light-responsiveness of the SCN mediated by the RHT, but by a more complicated machinery within the SCN.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D005074:Evoked Potentials, Visual; D007031:Hypothalamus / Q000502:physiology*; D008027:Light; D008297:Male; D010775:Photic Stimulation; D051381:Rats; D011919:Rats, Inbred Strains; D012160:Retina / Q000502:physiology*; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*