Cytoarchitecture and fiber pattern of the superior colliculus are disrupted in the Shaking Rat Kawasaki.

Shaking Rat Kawasaki (SRK) is a Reelin-deficient rat, that shows significant cytoarchitectural abnormalities in the cerebral and cerebellar cortices in a similar manner to the reeler malformation. In the present study, we investigated the cytoarchitecture and myeloarchitecture of the superior colliculus (SC) of this mutant rat. The Nissl staining clearly showed that neuronal components in the superficial layers of the SC in SRK rat were intermingled with each other and that the boundaries between these superficial layers were blurred. The MBP immunohistochemistry showed an abnormal fiber pattern in the superficial layers of the SC of this mutant rat. In the normal rat, myelinated fibers passed rostrocaudally through the optic layer, and only a few myelinated fibers were recognized in the uppermost two layers, i.e., the zonal and superficial gray layers. By contrast, in SRK rat, the myelinated fibers were distributed throughout the entire thickness of the superficial layers of the SC. Anterograde labeling of retinotectal fibers with an injection of Cholera Toxin subunit B into the retina revealed that this abnormal fiber pattern was associated with the anomalous course of the retinotectal fibers. No distinct differences in the cytoarchitecture and fiber pattern in the deep layers of the SC were seen. In conclusion, the present study demonstrated that the cytoarchitecture and fiber patterning in the superficial layers of the SC were disrupted in SRK rat, suggesting that Reelin protein regulates the formation of the superficial layers of the SC.