Kynurenic acid blocks suprachiasmatic nucleus responses to optic nerve stimulation.

An in vitro slice preparation of the mouse hypothalamus was used to determine the effects of pharmacological agents on the field potentials that are evoked in the suprachiasmatic nucleus (SCN) by stimulation of the optic nerve. Postsynaptic components of these responses were identified by lowering the concentration of calcium in the superfusate. Bath application of kynurenate, an antagonist of excitatory amino acid neurotransmission, reversibly blocked postsynaptic responses in the SCN. The evoked responses in the SCN were not affected by the acetylcholinergic agents (+)-tubocurarine, scopolamine, physostigmine, or carbachol. These results suggest that excitatory amino acid receptors mediate responses of SCN neurons to retinal input, but do not support a role for acetylcholine.