title: Photic responses of geniculo-hypothalamic tract neurons in the Syrian hamster.
abstract: The putative neural pacemaker controlling circadian rhythms in mammals is contained in the suprachiasmatic nuclei of the hypothalamus. These nuclei receive a projection, the geniculo-hypothalamic tract (GHT), from neurons in the intergeniculate leaflet (IGL) and portions of the ventral lateral geniculate nucleus (vLGN) of the thalamus. We examined the responses of putative GHT neurons to diffuse illumination using extracellular electrophysiological recordings. The great majority of IGL neurons showed sustained ON responses to diffuse retinal illumination; vLGN neurons showed more variation in their responses. Discharge rates of sustained ON neurons increased monotonically as light intensity was increased and saturated over 2-3 log units of intensity changes. Many IGL neurons had binocular input, and input from the ipsilateral eye was often inhibitory. These results indicate that GHT neurons may provide information about ambient light intensity to the suprachiasmatic nuclei.
authors.affiliation: Department of Psychology, Dalhousie University, Halifax, Nova Scotia.
authors.forename: M E
authors.initials: ME
authors.lastname: Harrington
authors.forename: B
authors.initials: B
authors.lastname: Rusak
mesh_terms: D000818:Animals; D006224:Cricetinae; D004558:Electric Stimulation; D004594:Electrophysiology; D007839:Functional Laterality; D005829:Geniculate Bodies / Q000166:cytology / Q000528:radiation effects*; D007031:Hypothalamus / Q000166:cytology / Q000528:radiation effects*; D008027:Light; D008297:Male; D008647:Mesocricetus; D009474:Neurons / Q000528:radiation effects*; D009799:Ocular Physiological Phenomena; D013493:Suprachiasmatic Nucleus / Q000502:physiology; D015348:Vision, Binocular / Q000502:physiology; D015349:Vision, Monocular / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology