Elsevier

Neuroscience Letters

Volume 422, Issue 1, 5 July 2007, Pages 59-63
Neuroscience Letters

Gastrin releasing peptide and neuropeptide Y exert opposing actions on circadian phase

https://doi.org/10.1016/j.neulet.2007.06.003Get rights and content

Abstract

Microinjection of gastrin releasing peptide (GRP) into the third ventricle or the suprachiasmatic nucleus (SCN) induces circadian phase shifts similar to those produced by light. Administration of GRP during the day does not alter circadian phase. In contrast, neuropeptide Y (NPY) induces phase shifts of circadian rhythms during the day but has little effect when administered at night, similar to the effects of most non-photic stimuli. NPY inhibits the phase shifting effects of light, and GRP is thought to be part of the photic signaling system within the SCN. This experiment was designed to test whether GRP and NPY inhibit each other's effects on circadian phase. Adult male Syrian hamsters equipped with guide cannulas aimed at the SCN were housed in constant darkness until stable free-running rhythms of wheel running activity were apparent. Microinjection of GRP during the early subjective night induced phase delays that were blocked by simultaneous administration of NPY. During the middle of the subjective day, microinjection of NPY caused phase advances that were blocked by simultaneous administration of GRP. These data suggest that GRP and NPY oppose each other's effects on the circadian clock, and that the actions of NPY on the photic phase shifting mechanism in the SCN occur at least in part downstream from retinorecipient cells.

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Acknowledgements

The authors would like to thank Veronica Porterfield and Erin Gilbert for their assistance. This research was supported by NIH Grant NS043155 and the Kent State Department of Biological Sciences

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Cited by (15)

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    Furthermore, NPY release into the SCN has been shown to produce non-photic phase shifts during the day, and the application of glutamate (as a mimic of photic input) blocks this non-photic phase shifts in vitro (Biello et al., 1997). Finally, application of gastrin releasing peptide (GRP) blocks these non-photic phase shifts in vivo (Kallingal and Mintz, 2007). This further supports the idea of light dependent modulation of SCN rhythms by non-photic signals.

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    Conversely, an NMDA antagonist does not attenuate GRP-induced phase shifts 15 min after central administration of GRP. Previous studies have shown that exposure to light (DeCoursey, 1960), or GRP administration into the third ventricle (Antle et al., 2005a; Kallingal and Mintz, 2006) or near the SCN (Albers et al., 1991; Kallingal and Mintz, 2007; Piggins et al., 1995) can induce shifts of circadian rhythms during the subjective night. The responses to light (Colwell and Menaker, 1992) and GRP (Kallingal and Mintz, 2006) can be attenuated by administration of glutamate receptor antagonists.

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