ADRENALECTOMY DOES NOT AFFECT THE NOCTURNAL PEAK OF FOS EXPRESSION WITHIN HYPOTHALAMIC PROOPIOMELANOCORTIN NEURONS

Circulating glucocorticoid (GC) levels are thought to modulate the bas al activity of pro-opiomelanocortin (POMC) neurons within the mediobas al hypothalamus (MBH) of the male rat. In a recent study we demonstrat ed that Fos-immunoreactivity (Fos-IR) was spontaneously induced throug hout the dark phase of the light/dark cycle within a large population of these MBH neurons. Here, we have investigated the effect of adrenal ectomy on the nocturnal expression of Fos protein within POMC neurons. To this aim, groups of intact (IN), adrenalectomized (ADX) and sham-o perated (sham) rats were killed 7 days after surgery (or no surgery) a t times when Fos-IR is known to show either nadir (at light offset) or peak (6 h after light offset) values within h?BH POMC neurons. Brains were processed for Fos- and/or POMC-immunohistochemistry. The results showed that, at both times studied, 7-day adrenalectomy did not affec t the number of POMC/Fos double-stained neurons within the MBH. The ro stro-caudal pattern of distribution of such labeled neurons throughout the MBH of ADX rats was also similar to that of IN or sham rats. The present data demonstrate that the nocturnal induction of Fos within MB H POMC neurons is not controlled via the nychtemeral rhythm of secreti on of the adrenal gland. Furthermore, this study shows that basal leve ls of circulating GC do not alter the nocturnal peak of Fos synthesis within POMC neurons. ((C) Elsevier, Paris).