Nerve growth factor phase shifts circadian activity rhythms in Syrian hamsters

Nerve growth factor (NGF) receptors are found in high density in the rodent suprachiasmatic nucleus (SCN), a site which regulates mammalian circadian rhythms. We examined the effects of NGF (40 ng) or vehicle injections into the SCN, at circadian times (CT) 6, 14 or 22 on activity rhythms in hamsters maintained in constant darkness. NGF caused phase advances at CT6 (30.9 min) and CT22 (36.9 min), and phase delays at CT14 (31.2 min). Saline and cytochrome-c administration had no phase-shifting effects at CT6 and CT22, but at CT14 cytochrome-c produced large phase delays, implying that NGF-induced delays at this phase may be non-specific. Similarities between NGF-induced shifts and those elicited by the cholinergic agonist carbachol suggest a common mode of action.