The effects of the application of serotonin, histamine, noradrenaline and dopamine to the bath on field potentials in the suprachiasmatic nucleus evoked by stimulation of the optic nerve were studied using a hypothalamic slice. Stimulation of the contralateral optic nerve evoked fast positive and late large negative waves in the suprachiasmatic nucleus. The monoamines produced a dose dependent suppression of the amplitude of the negative wave but did not affect that of the positive waves, and the order of potency was serotonin > noradrenaline > dopamine ≥ histamine. The negative wave was suppressed by phenylephrine (0.1-10 μ M) in a dose-dependent manner, whereas it was unaffected by isoproterenol (0.1-10 μM). The suppression of the negative wave produced by the application of histamine and noradrenaline was antagonized by the H1-receptor antagonist, diphenhydramine and the α1-receptor antagonists, phenoxybenzamine and phentolamine. Therefore, the suppression of the negative wave by histamine and noradrenaline was mediated by the H1-receptor and α1-receptor, respectively. The present study indicates that monoamines may play an inhibitory role in the regulation of neurotransmission in the retinohypothalamic pathway to the suprachiasmatic nucleus.
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience