[Electrophysiological study of hypothalamic neurons and gonadotropin regulation in rhesus monkey (author's transl)]

The electrical activity of various hypothalamic areas was recorded in anesthetized (sodium pentobartital) (n = 3) and unanesthetized (n = 3) ovariectomized rhesus monkeys. The plasma gonadotropin levels of the animals during the recording sessions were obtained by a chronic cardiac catheter. 1. Sodium pentobarbital greatly affected the electrical activity of most hypothalamic neurons (84%). The mean spontaneous electrical unit activity of neurons in the unanesthetized animals (n = 30) was 1.5 spike/sec. This value decreased to 0.1 spike/sec in the anesthetized group (n = 30). However, a small number of hypothalamic neurons were insensitive to the anaesthetic. 2. The multiunit electrical activity recorded in the median eminence showed marked periodic increases, about 200 sec before LH was observed to rise in the plasma (10/12). This increased firing lasted about 10 min (Fig. 1A). 3. In a few cases (2/12), however, increased firing was not associated with LH release. Since, in this area, multiunit activity represents the summation of a large number of axon terminals, the release of a hypothalamic hormone other than Gn-RH is put foreward as a possible hypothesis. 4. Of 51 neurons recorded in various hypothalamic areas, 3 showed periodic increases of electrical unit activity which corresponded to a rise in plasma LH levels (Fig. 1 B). These neurons are located in the arcuate area. 5. These results are consistent with the hypothesis of a relation between the electrical activity of some hypothalamic neurons and the periodical LH discharges observed in the ovariectomized rhesus monkey.