Anterior pituitary prolactin release in vitro after interruption of anterolateral neural connections of the mediobasal hypothalamus in male rats.

These studies examined the effects of surgical interruption of anterolateral neural connections of the medial basal hypothalamus (MBH) on the subsequent ability of the perifused anterior pituitary (AP) to release prolactin (Prl). Anterolateral MBH cuts were made in adult male rats; sham-operated rats served as controls. An in vivo experiment performed at 5 weeks after the two types of surgery showed that the MBH cuts did not alter non-stress plasma Prl concentrations, but this surgery reduced (P less than 0.05) the Prl response to stress. At 4 months after surgery, the perifused APs from rats with MBH cuts released less (P less than 0.001) Prl under basal conditions and when perifused in series with blocks of preoptic-hypothalamic tissue than did APs from the sham-operated controls. The APs from the MBH-cut and control groups released similar amounts of Prl in response to an initial administration of 56 mM potassium (high K+). After 6 h of perifusion, the APs of the group with MBH cuts contained less (P less than 0.001) Prl than did those of the control group. These findings suggest that transecting anterolateral connections of the MBH causes a reduction in Prl synthesis and steady-state release without affecting the pool of Prl that is released in response to high K+.