Prolactin and luteinizing hormone release after diencephalic lesions and stimulation

Adult male rats received sham procedures or retrochiasmatic knife cuts of varying sizes. Ten to twelve days (short term survival) or 90 days (long term survival) later animals were placed under pentobarbital anesthesia and pulsed, monophasic (50 Hz, 200 microA, 0.5 msec width, 30 sec on/off) stimuli were delivered during 30 min through bipolar, concentric electrodes bilaterally placed in the medial preoptic-suprachiasmatic nucleus (MPOA-Sch). Blood samples were taken before and at 30 min intervals after stimulation. Plasma prolactin and LH were measured in the same sample. Penetration of the knife guide tube induced a lesion of cortical and subcortical midline structures (sham procedures) placed at or around AP plane 5.0 of the Atlas of Albé-Fessard et al. This resulted in a short term impairment of LH release induced by MPOA-Sch stimulation, an effect that could not be distinguished from the one observed after frontal cuts made with a knife having a 1.5 mm radius (1.5 FC). Frontolateral retrochiasmatic cuts (LFC) blocked the effects of stimulation on LH release. After 90 days, LH response to MPOA-Sch stimulation improved in sham FC and 1.5 FC groups. Sham procedures did not reduce prolactin response after short term survival. 1.5 FC significantly decreased and LFC blocked prolactin release response. Ninety days after FC there was no improvement of prolactin release response to MPOA-Sch stimulation. In conclusion, long term survival after sham and 1.5 FC surgical procedures allowed for a partial recovery of the LH release response, but not that of prolactin, after MPOA-Sch stimulation.