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.
| Original language | English |
|---|---|
| Pages (from-to) | 367-375 |
| Number of pages | 9 |
| Journal | Visual Neuroscience |
| Volume | 2 |
| Issue number | 4 |
| DOIs | |
| Publication status | Published - Apr 1989 |
Bibliographical note
Funding Information:We are indebted to Patricia Dickson, Donna Goguen, and Gordon Troop for their technical assistance, and to Keith Grasse, Max Cynader, Steve Shaw, Jeff Radel, and the late Gerard Groos for their generous help and advice. This research was supported by Grant MA8929 from MRC of Canada, Grant A03O5 from NSERC of Canada, and Research and Development Fund in the Sciences from Dalhousie University. M.E. Harrington was supported by a Killam Memorial Scholarship during part of this study.