Light Exposure Induces Short- And Long-Term Changes in the Excitability of Retinorecipient Neurons in Suprachiasmatic Nucleus

J Neurophysiol. 2011 Aug;106(2):576-88. doi: 10.1152/jn.00060.2011. Epub 2011 May 18.

Abstract

The suprachiasmatic nucleus (SCN) is the locus of a hypothalamic circadian clock that synchronizes physiological and behavioral responses to the daily light-dark cycle. The nucleus is composed of functionally and peptidergically diverse populations of cells for which distinct electrochemical properties are largely unstudied. SCN neurons containing gastrin-releasing peptide (GRP) receive direct retinal input via the retinohypothalamic tract. We targeted GRP neurons with a green fluorescent protein (GFP) marker for whole cell patch-clamping. In these neurons, we studied short (0.5-1.5 h)- and long-term (2-6 h) effects of a 1-h light pulse (LP) given 2 h after lights off [Zeitgeber time (ZT) 14:00-15:00] on membrane potential and spike firing. In brain slices taken from light-exposed animals, cells were depolarized, and spike firing rate increased between ZT 15:30 and 16:30. During a subsequent 4-h period beginning around ZT 17:00, GRP neurons from light-exposed animals were hyperpolarized by ∼15 mV. None of these effects was observed in GRP neurons from animals not exposed to light or in immediately adjacent non-GRP neurons whether or not exposed to light. Depolarization of GRP neurons was associated with a reduction in GABA(A)-dependent synaptic noise, whereas hyperpolarization was accompanied both by a loss of GABA(A) drive and suppression of a TTX-resistant leakage current carried primarily by Na. This suggests that, in the SCN, exposure to light may induce a short-term increase in GRP neuron excitability mediated by retinal neurotransmitters and neuropeptides, followed by long-term membrane hyperpolarization resulting from suppression of a leakage current, possibly resulting from genomic signals.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology*
  • Animals
  • Circadian Clocks / physiology
  • Gastrin-Releasing Peptide / physiology*
  • Guinea Pigs
  • Hypothalamus / physiology
  • Mice
  • Mice, Transgenic
  • Photic Stimulation / methods*
  • Photoperiod*
  • Retina / physiology*
  • Scyphozoa
  • Suprachiasmatic Nucleus / physiology*
  • Time Factors

Substances

  • Gastrin-Releasing Peptide