Radial glia-like cells in the supraoptic nucleus of the adult rat.

Conventional light and confocal microscopy of thick vibratome sections of the hypothalamus of adult male and female rats immunostained for the astrocytic marker glial fibrillary acidic protein (GFAP) revealed that the supraoptic nucleus (SON) contains two morphologically distinct types of astrocytes. One has a stellate form, similar to that of most astrocytes in the adult CNS. The other has a morphology reminiscent of radial glia in the developing CNS: from their cell bodies, located along the ventral glia lamina (VGL), arise one long thick process that spans the SON in the coronal plane, several horizontally-oriented processes that form a dense network in the VGL, and a short process oriented towards the pia. The latter astrocytes are immunoreactive for vimentin, an intermediate filament protein of immature glial cells and a marker for radial glia. The stellate astrocytes showed no vimentin immunoreactivity. The functional significance of each type of supraoptic astrocyte is at present unknown but the presence of radial glia-like cells in this hypothalamic region suggests that the SON retains a certain degree of immaturity during adulthood, that may be linked to its well known capacity to undergo neuronal-glial plasticity under physiological and experimental stimulation.