Study objective: Neuropeptide B (NPB) and neuropeptide W (NPW) are two recently identified neuropeptides that act as endogenous ligands to orphan G protein coupled receptors, GPR7 and GPR8. In rodents, the GPR8 ortholog is absent and both NPB and NPW function exclusively through GPR7. Although NPB and NPW are implicated in the regulation of feeding behavior, endocrine function, and pain sensation, their physiological role is incompletely understood.
Design: NPB or saline was administered into the lateral ventricle of mice during both the light and dark periods. In separate experiments, spontaneous locomotor activity or EEG and EMG were recorded after intracerebroventricular (i.c.v). injection. To confirm the involvement of GPR7 in NPB-induced responses, GPR7 knockout mice were also subjected to i.c.v. injections.
Measurements and results: NPB injections reduced locomotor activity during the dark period, but not during the light period. EEG and EMG recordings in freely moving mice revealed that NPB injection decreased the time spent in the waking state and increased the time spent in slow wave sleep (SWS) during the dark period. The time spent in paradoxical sleep was unaffected. The spectral power of NPB-induced SWS was indistinguishable from that of physiological SWS. The NPB-induced increase in SWS was not observed in GPR7 knockout mice.
Conclusion: These results suggest that NPB induced physiological SWS through GPR7 and that NPB and GPR7 may have a role in modulating the occurrence of sleep and wakefulness.
Keywords: GPR7; GPR7 knockout mice; Neuropeptide B; intracerebroventricular injection; locomotor activity; neuropeptide W; slow wave sleep.