Spontaneous c-Fos rhythm in the rat suprachiasmatic nucleus: location and effect of photoperiod

Illnerová. Spontaneous c-Fos rhythm in the rat suprachias-matic nucleus: location and effect of photoperiod. Am J Physiol Regulatory Integrative Comp Physiol 279: R2262–R2269, 2000.—A recently reported circadian rhythm in the sponta-neous c-Fos immunoreactivity in the rat suprachiasmatic nucleus (SCN) is expressed mostly in the dorsomedial (dm) SCN, where vasopressinergic cells are located. The aim of the present study is to find out whether day length, i.e., photo-period, affects the dm-SCN rhythm and, if so, how the rhythm adjusts to a change from a long to a short photope-riod. In addition, a question of whether the spontaneous c-Fos production is localized in vasopressin- producing cells or in other cells is also studied to characterize further the dm-SCN rhythmicity. Combined immunostaining for c-Fos and arginine vasopressin (AVP) revealed that most of c-Fo