The retinohypothalamic tract (RHT) is a neural pathway through which photic time cues are delivered directly to the mammalian circadian pacemaker in the suprachiasmatic nucleus (SCN). Although the excitatory amino acid glutamate is the primary neurotransmitter in the RHT, other substances such as substance P (SP) also have been suggested to play a role. The present study tested the hypothesis that SP participates in retinohypothalamic transmission and selectively modulates either N-methyl-D-aspartate (NMDA) or non-NMDA receptor-mediated neurotransmission. The SP antagonist L-703,606 depressed the excitatory postsynaptic current (EPSC) evoked by optic nerve stimulation in SCN neurons in rat hypothalamic slices. The SP antagonist also had a similar depressive effect on the NMDA and non-NMDA receptor-mediated components of the EPSC. These results suggest that SP is an excitatory neuromodulator contributing to the expression of both the NMDA and non-NMDA receptor-mediated components of retinohypothalamic transmission. Copyright (C) 1999 Elsevier Science Ireland Ltd.
Bibliographical noteFunding Information:
The authors are grateful to Dr. C. Allen for his constructive comments on the earlier drafts of this paper. This research was supported by The Hallym Academy of Sciences, KUMS Institute of Medical Sciences and Korea Research Foundation (1998–001-F00125).
- Circadian rhythm
- Retinohypothalamic transmission
- Substance P
- Suprachiasmatic nucleus
ASJC Scopus subject areas