PROFILE OF FOS-LIKE IMMUNOREACTIVITY INDUCTION BY LIGHT STIMULI IN THE INTERGENICULATE LEAFLET IS DIFFERENT FROM THAT OF THE SUPRACHIASMATIC NUCLEUS

Light stimuli induce Fos-like immunoreactivity (FLI) in suprachiasmati c nucleus (SCN) and intergeniculate leaflet (IGL). Short pulses of lig ht stimuli that synchronize the circadian rhythms induce FLI in SCN. T he characteristics of light induction of FLI in the IGL were studied u sing immunohistochemistry. In the IGL, at least 2 h of sustained light stimuli were necessary to show an increase of FLI. This FLI persisted while the light was turned on. FLI induction in the IGL by light stim uli was not circadian time specific response. These findings imply tha t the functional significance of Fos activation on circadian rhythms a nd mechanism of FLI induction in IGL would be different from that in S CN.