Hypothalamic multiunit activity and pulsatile luteinizing hormone release in the castrated male rat

Laboratoire d'Histologie-Embryologie Faculte de Medicine, CNRS, Oullins, France.

Using chronically implanted microelectrodes, multiunit electrical activity (MUA) was recorded from the arcuate nucleus of freely moving gonadectomized male rats. Intermittent increases in MUA activity (MUA volleys) closely associated with luteinizing hormone pulses measured in the peripheral circulation were observed, which confirms that this experimental approach can be used for monitoring the activity of the gonadotropin-releasing hormone-associated hypothalamic pulse generator in the male rat. The mean MUA volley frequency was 22.2 min (range 13-38 min), whereas the mean MUA volley duration was 2.7 +/- 0.8 min (standard deviation). In addition to a large inter-individual variability. MUA volley intervals also showed an important intra-individual variability. This observation suggests that, beside the mean frequency of pulse generator activation, the degree of variability in gonadotropin-releasing hormone-associated pulse generator activity might be an additional relevant parameter in the characterization of the reproductive function in the male rat.