Preoptic-hypothalamic control of LH and prolactin release in male rats under pentobarbital anesthesia: differential responses to electrical stimulation.

In acute experiments under pentobarbital anesthesia, the brains of adult male rats were stimulated bilaterally with trains of monophasic pulses at different frequencies and current intensities through bipolar, concentric, stainless steel electrodes. Stimulation of the POA-SQ region at 3, 10 (200 muA) or 200 Hz (100 muA) increased plasma prolactin levels within 30 min of the onset of stimulation. Stimulus parameters fully effective when applied to the POA-SQ or ARC-MED. EM. regions were ineffective when applied to the ARC-VMH region. Maximal effects were obtained with 10 Hz (200 muA) stimuli applied to the POA-SQ region. LH levels were increased after stimulation of any of the three regions--POA-SQ, ARC-VMH or ARC-MED. EM. Conversely to the prolactin response, LH levels did not rise after 3 Hz stimulation of the POA-SQ region. In male rats under pentobarbital anesthesia, LH levels seemed to be affected maximally with a stimulus frequency rate of about 50 Hz applied to the POA-SQ region. The results suggest a potential physiological role of frequency discrimination in the functional segregation of LH and prolactin release controls.