ACTH release after tuberal electrical stimulation in rats with various cuts around the medial basal hypothalamus.

After the combined treatment with dexamethasone, morphine and pentobarbitone, the electrical stimulation in the rat tuber cinereum induces a rise in plasma corticosterone (CS) level, probably by direct stimulation of the corticoliberin-producing neural elements and the consecutive ACTH release. We have attempted to locate these corticoliberin-containing neural elements by electrical stimulation in rats with various surgical cuts (deafferentations) around the medial basal hypothalamus (MBH). Seven to eight days after the complete circumsection of the MBH, the electrical stimulation of the isolated region did not affect plasma CS level. Also, the electrical excitation proved to be ineffective after antero-lateral or only lateral sections that interrupted the fibers running through the lateral region of the retrochiasmatic area. In contrast, a rise in CS level followed electrical stimulation of rats with anterolateral transections, provided the basal part of the lateral retrochiasmatic area stayed intact. We suggest that fibers traversing the basal region of the lateral retrochiasmatic area have a major role in the release of corticoliberin from the median eminence (ME).