Effect of anterior of posterior deafferentation of the hypothalamus on unit activity in the paraventricular nucleus of ovariectomized female rats with or without estrogen treatment.

Extracellular recordings of action potentials were made and their firing rates were determined from 345 paraventricular neurosecretory cells in ovariectomized rats with or without estrogen treatment. And the effect of anterior or posterior deafferentation of the hypothalamus on the firing rates was studied. In both non-treated and estrogen-treated rats the anterior deafferentation reduced the firing rates significantly (P less than 0.05 in the non-treated rats and P less than 0.01 in the estrogen-treated rats), while the posterior deafferentiation did not change the firing rates significantly. Comparisons between firing rates in estrogen-treated rats and those in non-treated ones revealed what neurosecretory neurones with intact afferent connections and with damaged posterior connections showed a facilitatory response to estrogen but that the neurones with damaged anterior connections failed to show the response. The frequency distribution of the firing rates in each of the experimental groups showed an exponential form. In conclusion, these findings suggest that the extrahypothalmic inputs from the rostral brain regions are important factors in the maintenance of the basal activity of the paraventricular neurosecretory cells. It is also indicated that estrogen stimulates the neurosecretory cell activity indirectly via afferent inputs from the rostral cerebral structures.