GABAergic modulation of gap junction communication in slice cultures of the rat suprachiasmatic nucleus.

We employed morphological and electrophysiological methods in order to elucidate mechanisms which are responsible for communication between cellular oscillators in the cultured rat suprachiasmatic nucleus, the site of the endogenous biological clock that regulates circadian rhythms in mammals. When a gap junction-permeable dye, Lucifer Yellow, was injected into single neurons in the suprachiasmatic nucleus culture, the dye was transferred to neighboring cells in a gap junction blocker-sensitive manner. Optical imaging of neural activity evoked by electrical stimulation in the culture revealed that the spread of depolarization was inhibited by gap junction blockers but not by a blocker of voltage-dependent Na(+) channels. Depolarization propagation was inhibited by muscimol, a GABA(A) receptor agonist, in a dose-dependent manner and the inhibition was reversed by bicuculline, a GABA(A) receptor antagonist. Furthermore, muscimol inhibited dye-transfer between neurons in the suprachiasmatic nucleus culture in a dose-dependent fashion.These independent lines of evidence suggest that the gap junction communication is involved in interneuronal communication in the suprachiasmatic nucleus slice culture and that the coupling state between neurons is not static but dynamically regulated via GABA(A) receptor systems.