Deficits in drinking and vasopressin secretion after lesions of the nucleus medianus

The effects of ablation of the nucleus medianus on drinking and vasopressin secretion were studied in male Long-Evans rats. The amount of water drunk in 1 h was assessed after subcutaneous injection of 5.8% NaCl (13.34 mosm/kg) or of angiotensin II (1.5 mg/kg). In a separate test with no water available, plasma vasopressin was measured 15 min after the above dose hypertonic saline. Ablation of the nucleus medianus, or the dorsal and anterior portions of the nucleus medianus, blocked drinking to hypertonic saline or angiotensin II and attenuated the vasopressin response to hyperosmolality. Animals with septal or diagonal band lesions showed responses comparable to sham-operated rats. These results indicate that a neural pathway important for fluid balance passes through, or terminates in, the nucleus medianus.