The dorsal hippocampus modifies the negative feedback effect of glucocorticoids on the adrenocortical and median eminence CRF-41 responses to photic stimulation.

In the present study we have evaluated the role of the dorsal hippocampus on the negative feedback effect of glucocorticoids (GC) following photic stimulation. In hippocampectomized rats the recovery of serum corticosterone (CS) to basal levels following photic stimulation, was significantly attenuated in relation to sham hippocampectomized rats. The inhibitory effect of either systemic dexamethasone administration or CS implanted in the paraventricular nucleus (PVN), on the adrenocortical responses to photic stimulation, was completely prevented in hippocampectomized rats in comparison to sham operated animals. In rats with sham operation, the depletion of median eminence CRF-41 induced by photic stimulation, was prevented by pretreatment with CS PVN implants or systemic dexamethasone. These effects were reversed in rats with dorsal hippocampectomy. The results suggest that the dorsal hippocampus modulates the negative feedback of GC on the adrenocortical response following photic stimulation at the PVN level and this effect is mediated by median eminence CRF-41.