ONTOGENY OF RADIAL GLIA, ASTROCYTES AND VASOACTIVE-INTESTINAL-PEPTIDE IMMUNOREACTIVE NEURONS IN HAMSTER SUPRACHIASMATIC NUCLEUS

Circadian rhythmicity of rodents is a property of the suprachiasmatic nucleus (SCN). Such rhythmicity can be demonstrated in the prenatal SCN, yet there is little information about the cells in which rhythmicity is generated. The present study was performed to discover the developmental relationships of SCN glial cells and a class of identifiable SCN neurons. Toward this end, vimentin- (VIM), glial fibrillary acidic protein- (GFAP) and vasoactive intestinal peptide- (VIP) immunoreactivity were investigated in SCN radial glia, astrocytes and neurons, respectively. VIP-IR first appears at embryonic day 13 (E13) and is clearly identifiable in neurons at E14. Substantial axon extension begins at E15 and the postnatal day 10 (P10) SCN is adult-like. VIM-IR radial glia fill the SCN region at E13, but by PO, most are absent. On P3, the remaining processes are beaded suggesting degeneration. The first GFAP-IR elements are visible on E15 with a few clear astrocytes present at P0. The number of astrocytes lateral to and in the SCN continues to increase during the postnatal period achieving an adult-like appearance by P21. The data do not support the view that prenatal circadian rhythmicity is derived from astrocytes. VIP-IR neurons are apparently present sufficiently early to be part of the rhythm generating mechanism. These issues are discussed in the context of development of the SCN.