Changes in magnocellular neurosecretory activity following septal forebrain lesions: Morphological and biochemical data

Rats with lesions in the medio-ventral septal area undergo acute polyuria and do not develop an appropriate antidiuretic response to various osmotic stimuli which results from their failure to adequately release vasopressin (VP). Studies were carried out to investigate whether changes in the cellular aspects of neurosecretory activity of VPergic neurons may occur in septal damaged rats and to verify whether hormonal level variations paralleled changes in morphological features of these neurons. We have observed that unreleased neurosecretory material is accumulated in the cytoplasm and axons of SON and PVN cells of lesioned rats during dehydration. On the other hand, in the same experimental conditions, normal and sham-lesioned rats show a depletion of neurosecretory granules. Furthermore, the marked increase of the size of cell nuclei and nucleoli of SON and PVN observed in normal and sham-lesioned rats is attenuated in lesioned animals during this acute phase. These morphological data were associated with decreased levels of circulating radioimmunoassayable VP and the usual VP release which occurred in response to dehydration in normal and sham-lesioned rats was markedly blunted in lesioned animals. All these data imply that the mechanisms involved in the synthesis and release of VP are alterated during intracellular dehydration in septal damaged rats.