Prolactin release induced by paired-pulsed stimulation within the preoptic-suprachiasmatic region in male rats: Response to varying interpulse intervals

Abstract

Adult male rats under pentobarbital anesthesia received bilateral electrical stimuli within the preoptic-suprachiasmatic region. Stimulation consisted of paired identical pulses with the following characteristics: monophasic, 100 or 200 μA, 0.5-ms width, 30-s trains on/off applied during 30 min. Several interpulse intervals were tested in different groups of animals: 1.0, 2.5, 5.0, 20.0, and 50.0 ms. Twin pulses were delivered at a mean frequency of 10 Hz through bipolar concentric electrodes. Blood samples were obtained every 30 min starting before the onset of stimulation for a total period of 90 min. Luteinizing hormone (LH) and prolactin concentrations were determined by radioimmunoassay. The LH concentrations at 30 min after stimulation with interpulse intervals of 20.0 and 50.0 ms were significantly higher than control values. Prolactin concentration was higher than in controls at 30 min for all stimulated groups. Prolactin responses did not show significant differences among the various interpulse intervals tested. These results are discussed in terms of the possible differences in the overall neural strategies controlling the release of each hormone.