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.