Neuronal and glial reactions following hypophysectomy in developing and adult rats

Abstract

The present study examined response of neurons and glia to axonal injury in the hypothalamo-neurohypophyseal system (HNS) following hypophysectomy in developing and adult rats. Hypophysectomy induced substantial loss of magnocellular neurons of HNS in both developing and adult rats and there was no obvious difference in neuronal survival after the injury between the age groups. In contrast, there was a striking age-dependent regeneration in which robust regeneration was observed following hypophysectomy only in adult but not in immature rats. Reactive astrocytes re-expressed nestin and vimentin and reverted their shape to a more immature stage of radial glial cells in perineuronal areas of magnocellular neurons in the hypophysectomized adult rats but not in the immature ones. Furthermore, ED1 immunoreactivity and morphological transformation of microglia into macrophages can only be observed under conditions of neuronal degeneration in the adult supraoptic and paraventricular nuclei. In summary, hypophysectomy induced a robust regeneration in parallel with an intense microglial and astroglial responses in hypophysectomized adult rats, suggesting that the glial reaction play a positive role on neuronal regeneration after hypophysectomy. The age-related difference in glial reaction in response to the similar extent of neuronal death between the developing and adult rats suggests that mechanism underlying neuronal death between developing and adult may be different. (Supported by the University of Hong Kong).