Photic regulation of melatonin in rat retina and the role of proteasomal proteolysis

Several investigations have shown that illumination at night reduces melato nin level in the mammalian pineal, but the effect of night illumination on the retina is not known. In this study retinas were cultured in a flow-thro ugh apparatus and then were exposed to light at ZT 18. Light exposure reduc ed melatonin levels to the daytime level within 30 mim The reduction of mel atonin levels was due to a rapid decrease in the activity of the enzyme AA- NAT; AA-NAT mRNA levels were not affected by illumination. Pre-incubation w ith lactacystin (25 muM) prevented light-induced reduction of AA-NAT activi ty and melatonin levels. These results demonstrate that melatonin levels in the mammalian retina are affected by light exposure at night, via proteoso mal proteolysis of AA-NAT. NeuroReport 12:3833-3837 (C) 2001 Lippincott Wil liams & Wilkins.