The suprachiasmatic nucleus (SCN) has been identified as a mammalian circadian rhythm clock. Treatment with substance P (SP) at zeitgeber time 13- 14 produced phase delays of circadian rhythm in spontaneous neural activity in SCN neurons in vitro. SP-induced phase delays are blocked by treatment with not only SP receptor antagonist, spantide, but N-methyl-D-aspartate receptor antagonist, MK-801. In the biochemical experiment, we demonstrated that SP-induced glutamate release from the SCN slices was observed by the high-performance liquid chromatography assay. The present results suggest that glutamate release may be involved in SP-induced phase delays.
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