Light syncronizes body's circadian rhythms by modulating the master clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. In modern life, the extended and/or irregular light exposure impairs circadian rhythms and consequently promotes feeding and metabolic disorders. However, the neuronal pathway through which light is coupled to feeding behavior is less elucidated. The present study employed the light exposure during dark phase of the day in rats and observed its effect on neuronal activity and feeding behavior. Light exposure acutely suppressed food intake and elevated c-Fos expression in the arginine vasopressin (AVP) neurons of SCN and the oxytocin (Oxt) neurons of paraventricular nucleus (PVN) in the hypothalamus. The light-induced suppression of food intake was abolished by blockade of the Oxt receptor in the brain. Retrograde tracer analysis demonstrated the projection of SCN AVP neurons to PVN. Furthermore, intracerebroventricular (icv) injection of AVP suppressed food intake and increased c-Fos in PVN Oxt neurons. Intra-PVN injection of AVP exerted a stronger anorexigenic effect than icv injection. AVP also induced intracellular Ca2+ signaling and increased firing frequency in Oxt neurons in PVN slices. These results reveal the novel neurocircuit from SCN AVP to PVN Oxt that relays light reception to inhibition of feeding behavior. This light-induced neurocircuit may serve as a pathway for forming the circadian feeding rhythm, and linking irregular light exposure to arrhythmic feeding and consequently obesity and metabolic diseases.
- feeding rhythm
- metabolic disorders
- Copyright © 2017, American Journal of Physiology-Endocrinology and Metabolism