抄録
In mammals, the hypothalamic suprachiasmatic nucleus (SCN), a circadian oscillator, receives the retinohypothalamic tract (RHT), which is essential for the synchronization of circadian rhythms by light-dark cycle; and nerve growth factor (NGF) receptors with low affinity have been detected in the SCN. Thus, we examined whether low-affinity NGF receptors (LNGFR) are present in the terminals of the RHT by studies on the LNGFR-like immunoreactive substance (LNGFRLIS) in the SCN of blind rats. LNGFRLIS in the SCN gradually decreased with age in control rats, though it could be observed until 16-20 weeks of age. After bilateral orbital enucleation of 4-week-old rats, the density of the LNGFRLIS gradually decreased on both sides of the SCN from week 4 after the operation, disappearing 7 weeks after the operation. In congenitally blind, hereditary microphthalmic rats, LNGFRLIS was not detectable in the SCN, but in half-blind hereditary microphthalmic rats LNGFRLIS was detectable on both sides of the SCN. 125I-NGF injected into the SCN was found in the optic nerve and the retina. Since NGF is suggested to be retrogradely transported and to support survival of neurons, these findings suggest that LNGFR is present at the terminal of the RHT, and raise the possibility that NGF or other growth factors such as brain-derived neurotrophic factor in or around the SCN plays a role in maintaining the retinal ganglion cells through LNGFR.
