Marked and selective suppression of prolactin secretion after interruption of neural connections of the medial basal hypothalamus of the rat.

To study the importance of neural connections of the medial basal hypothalamus (MBH) in mediating the prolactin (Prl) response to stress, adult male rats were subjected to complete, anterior or posterior surgical disconnection of the MBH. Complete MBH disconnection blocked, while anterior MBH disconnection significantly attenuated the effects of leg restraint and ether exposure on Prl responses. Similar effects were noted with regard to Prl responses to morphine and chlorpromazine, two potent stimulators of Prl secretion, indicating that the deficits were not specific for stressful stimuli. None of the surgical procedures significantly compromised the response of growth hormone or corticosterone to morphine, ruling out the possibility of surgically-induced panhypopituitarism. Pituitary stores of Prl were reduced in the groups with complete and anterior MBH disconnection at autopsy at 18 weeks. These results indicate that anterolateral neural connections of the MBH are important for maintaining adequate levels of pituitary Prl or mediating the stimuli for Prl secretory responses. These effects may involve alterations in the regulation of Prl-inhibiting factor or Prl-stimulating factor.