The development of diurnal rhythmicity in fetal suprachiasmatic neurons as demonstrated by Fos immunohistochemistry

Abstract

Using Fos immunohistochemistry as a marker of cellular activity, we have shown that neurons in the suprachiasmatic nucleus of fetal sheep are active by 75 days gestation. From at least 90 days gestation (term is 146 days), these neurons are more active during the day (12.00) than at night (03.00) when pregnant ewes are exposed to a 12-h light-dark cycle with lights on at 07.00. The day-night difference in Fos immunoreactivity persisted when the lighting schedule was extended by 8 h to 03.00, although neurons were now more active at 03.00 than they were in fetuses maintained on the normal difference in Fos immunoreactivity in the fetal suprachiasmatic nucleus was abolished, suggesting that di..