The visual properties of rat and cat suprachiasmatic neurones
GA Groos, R Mason - Journal of comparative physiology, 1980 - Springer
GA Groos, R Mason
Journal of comparative physiology, 1980•SpringerResponses of single neurones in the suprachiasmatic nuclei (SCN) were recorded in the
anaesthetized rat and cat. Visual SCN units in both species were predominantly present in
the caudal half of the nucleus. The large majority could be classified as either tonically
suppressed or tonically activated according to whether an increase in diffuse adaptation
luminance respectively decreased or increased their mean discharge rate. 2. For both the
cell types the maintained discharge at different luminance levels was a monotonically …
anaesthetized rat and cat. Visual SCN units in both species were predominantly present in
the caudal half of the nucleus. The large majority could be classified as either tonically
suppressed or tonically activated according to whether an increase in diffuse adaptation
luminance respectively decreased or increased their mean discharge rate. 2. For both the
cell types the maintained discharge at different luminance levels was a monotonically …
Summary
- 1. Responses of single neurones in the suprachiasmatic nuclei (SCN) were recorded in the anaesthetized rat and cat. Visual SCN units in both species were predominantly present in the caudal half of the nucleus. The large majority could be classified as either tonically suppressed or tonically activated according to whether an increase in diffuse adaptation luminance respectively decreased or increased their mean discharge rate.
- 2. For both the cell types the maintained discharge at different luminance levels was a monotonically decreasing or increasing function over a large range of light intensities. In both species the threshold for luminance-dependent maintained discharge was high (>−1 log cd·m−2). The observation of either cell type was independent of the phase of the circadian cycle but it was not established whether the same held true for the intensity-response relations.
- 3. A small proportion of suppressed cells in the rat SCN reflected the state of retinal adaptation in their firing rate. After light adaptation these cells attained their steady state dark discharge only very slowly.
- 4. The receptive fields of cat SCN cells tended to be large (> 20°) without a clear antagonistic centre-surround organization. It is proposed that the receptive fields of SCN are the result of the convergence of retinal input from tonic W-cells.
- 5. It is concluded that their characterization as detectors of diffuse temporal luminance gradients makes visual SCN neurones particularly suitable for their function in the photic entrainment of circadian rhythms. This functional specialization is probably common to both the direct retinofugal projection and the indirect visual projection via the ventral lateral geniculate nucleus to the SCN.
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