Light augments FOS protein induction in brain of short-term enucleated hamsters

FOS protein is synthesized in neuronal nuclei in response to a variety of e nvironmental stimuli and has been used as a marker of stimulus-specific bra in function. The present studies were initiated to examine the effects of u ltraviolet light on the induction of FOS protein immunoreactivity (FOS-IR) in several brain regions of adult male hamsters. Experiment 1 confirmed pre vious observations of FOS-IR induced in visual cortex in response to ultrav iolet light. However. protein was also induced by ultraviolet or white ligh t in a variety of other areas and induction occurred in both sighted and en ucleated animals. Therefore, experiments were conducted to evaluate the eff ects of a 514 nm light on FOS-IR induction in blind or sighted animals. Exp eriments 2 and 3 were performed during the early subjective night and mid-s ubjective day, respectively, using animals about 4 days after bilateral enu cleation or sham surgery. In Experiment 2, light and enucleation independen tly and interactively resulted in increased FOS-IR neuronal nuclei counts. In Experiment 3, there was a main effect of enucleation and an interaction between enucleation and light condition, but no main effect of light. In Ex periment 3. conducted during the early subjective night using animals enucl eated 60 days earlier, there were neither effects of light or enucleation. The results support the view that, under certain conditions related to subj ective time of day and time since enucleation, light can act through unknow n extraocular mechanisms to modify brain activity. Further. short term enuc leation itself induces widespread alteration in brain function as indicated by increased FOS-IR expression. The results specifically do not support a role for extraretinal photoreception with respect to direct circadian rhyth m regulation. (C) 2001 Elsevier Science B.V. All rights reserved.