Expression of reelin in the dorsal cochlear nucleus of the mouse

The cytoarchitecture of dorsal cochlear nucleus (DCN), characterized by a distinct laminar structure similar to the cerebellar cortex of the normal mouse, is known to be disrupted in the Reelin-deficient mouse, reeler. Here, we have reexamined both the cytoarchitecture and myeloarchitecture of this nucleus and described expression pattern of Reelin protein during perinatal periods. Reelin-immunopositive granule cells were firstly recognized in the external granular layer of the DCN at embryological day 16 (E16). Next, we examined the cytoarchitecture of the DCN of the normal and reeler mice with Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα) immunostaining. CaMKIIα-immunoreactive cartwheel cells were laminarly distributed in the layer II of the normal DCN, but scattered throughout the reeler DCN. Injection of retrograde tracer, Fluoro-Gold (FG) into the inferior colliculus of the reeler mouse resulted in that retrogradely labeled neurons in the DCN were radially scattered instead of being confined to a single layer as seen in the normal mouse. To examine whether CaMKIIα-immunopositive cartwheel cells are neurons projecting to the inferior colliculus or not, double labeling with CaMKIIα immunohistochemistry and retrograde labeling with an injection of FG into the inferior colliculus were made, which revealed that CaMKIIα-immunoreactive cartwheel cells do not send axons to the inferior colliculus. The present findings imply that Reelin may have some roles in the formation of laminar structures of the DCN.