Ependymal cells of the rat fourth ventricle: response to injury.

The response of ependyma to injury was investigated in rats following placement of bilateral lesions in the floor of the fourth ventricle. Animals were sacrificed from 2-60 days post-operatively and the brains were prepared in the conventional manner for comparative LM, SEM and TEM examination. For LM radioautography, randomly selected lesioned rats received either a single i.p. injection (5 muCi/g BW) or multiple injections (2 muCi/g) of 3H-thymidine prior to sacrifice. Focal disruption of the lining resulted in significant qualitative and quantitative changes in the ependyma at the wound margins. Labelling of normally quiescent ependymal cells occurred from day 2-6 post-operatively, however, the level of turnover was relatively low. Labelling was maximum on day 2 and was greater at the medial than lateral margin of the wound. During the first postoperative week, a gradual increase was observed in the number of ependymal cells per unit length at the margins of the wound concomitant with an abrupt reduction in wound diameter. This was consistent with the assumption that newly formed cells were added to the ependymal sheet at the leading edges of the wound. From 14-60 days after injury, further repair resulted from asymmetrical spreading and thinning of the ependymal sheet in the absence of mitotic activity. Quantitatively, this was reflected in a reduction in cell number at the leading edges of the wound that was most pronounced at the lateral margin. At day 60 neither epithelialization nor wound closure was complete and the normal architecture of the lining had not been fully restored. These results suggest that ependyma in the fourth ventricle of the postnatal rat undergoes a process of only limited repair following injury.