REACTIVE CHANGES IN THE ADULT-RAT SUPERIOR COLLICULUS AFTER DEAFFERENTATION

We have recently shown that optic nerve transection is followed by a d elayed appearance (7-14 days after lesion) of putative guidance activi ties for retinal axons in the superior colliculus (SC) of adult rats. In the present study we analysed with immunohistological methods wheth er there is a correlation between localized reactive changes in the ce llular compartment of the SC after deafferentation and the reappearanc e of putative guidance activities. The optic nerve of adult female Spr ague-Dawley rats was transected. After 1 day to 1 year the contralater al SC was sectioned sagitally and examined with antibodies directed ag ainst Vimentin and glial fibrillary acidic protein (GFAP) to label ast rocytes, myelin basic protein (MBP) to detect oligodendrocytes, OX-42 to stain microglia and SMI-31 to determine degeneration of afferent re tinal ganglion cell axons. These stainings were performed in order to detect differences in the cellular composition of macro- and microglia l cells between the anterior and posterior regions of the SC. All cell populations we examined in the SC showed reactive changes after optic nerve transection. Microglia activation occurred as soon as 2 days af ter optic nerve transection in the anterior part of the SC. After 4 da ys, a homogeneous distribution of activated microglia was seen in the whole SC. GFAP upregulation occurred without a specific regional distr ibution. Only Vimentin-expressing astrocytes appeared with a delay of 1-2 weeks after deafferentation and were strongly restricted to the af ferent optic tract and the very anterior region of the SC. In conclusi on, a temporo-spatial correlation between the re-expression of guidanc e activities and changes in the cellular compartment of the SC exists in the delayed re-expression of Vimentin in astrocytes and their stron g spatial restriction. Activated microglia might be involved in trigge ring regional changes in an anterior-posterior graded fashion in the d eafferented SC.