Calcium response to retinohypothalamic tract synaptic transmission in suprachiasmatic nucleus neurons

Robert P. Irwin, Charles Allen

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

Glutamate released from retinohypothalamic tract (RHT) synapses with suprachiasmatic nucleus (SCN) neurons induces phase changes in the circadian clock presumably by using Ca2+ as a second messenger. We used electrophysiological and Ca2+ imaging techniques to simultaneously record changes in the membrane potential and intracellular calcium concentration ([Ca2+]i) in SCN neurons after stimulation of the RHT at physiologically relevant frequencies. Stimulation of the RHT sufficient to generate an EPSP did not produce detectable changes in [Ca2+] i, whereas EPSP-induced action potentials evoked an increase in [Ca2+]i , suggesting that the change in postsynaptic somatic [Ca2+]i produced by synaptically activated glutamate receptors was the result of membrane depolarization activating voltage-dependent Ca2+ channels. The magnitude of the Ca2+ response was dependent on the RHT stimulation frequency and duration, and on the SCN neuron action potential frequency. Membrane depolarization-induced changes in [Ca2+]i were larger and decayed more quickly in the dendrites than in the soma and were attenuated by nimodipine, suggesting a compartmentalization of Ca2+ signaling and a contribution of L-type Ca2+ channels. RHT stimulation at frequencies that mimicked the output of light-sensitive retinal ganglion cells (RGCs) evoked [Ca 2+]i transients in SCN neurons via membrane depolarization and activation of voltage-dependent Ca2+ channels. These data suggest that for Ca2+ to induce phase advances or delays, light-induced signaling from RGCs must augment the underlying oscillatory somatic [Ca2+]i by evoking postsynaptic action potentials in SCN neurons during a period of slow spontaneous firing such as occurs during nighttime.

Original languageEnglish (US)
Pages (from-to)11748-11757
Number of pages10
JournalJournal of Neuroscience
Volume27
Issue number43
DOIs
StatePublished - Oct 24 2007

Fingerprint

Suprachiasmatic Nucleus
Synaptic Transmission
Calcium
Neurons
Action Potentials
Retinal Ganglion Cells
Excitatory Postsynaptic Potentials
Membranes
Light
Nimodipine
Synaptic Potentials
Circadian Clocks
Glutamate Receptors
Carisoprodol
Second Messenger Systems
Dendrites
Membrane Potentials
Synapses
Glutamic Acid

Keywords

  • Action potential
  • Calcium
  • Circadian rhythm
  • Retinal ganglion cells
  • Suprachiasmatic nucleus
  • Synaptic transmission

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Calcium response to retinohypothalamic tract synaptic transmission in suprachiasmatic nucleus neurons. / Irwin, Robert P.; Allen, Charles.

In: Journal of Neuroscience, Vol. 27, No. 43, 24.10.2007, p. 11748-11757.

Research output: Contribution to journalArticle

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