Parasagittal organization of mossy fiber collaterals in the cerebellum of the mouse

Abstract

Abstract We have observed that WGA‐HRP injections in lobule VIII of the mouse result in the labeling of mossy fiber terminals in the anterior lobe (lobules I‐V), which are distributed in five distinct parasagittal bands. Injections in the anterior lobe label mossy fiber terminations in lobules VIII and IX. We interpret these results as indicating that an extensive system of mossy fiber collaterals exists between the anterior lobe and lobule VIII (less so to IX), which terminates as discrete parasagittal bands in the anterior lobe. Intermediate bands are thus occupied by fibers that do not send collaterals to the posterior vermis (VII–IX). In an attempt to identify the source(s) of this collateral system we have used double retrograde tracing techniques. Following injections of one tracer in the anterior lobe and another in lobule VIII we observe large numbers of double retrogradely labeled neurons in the lateral reticular nucleus, the basilar pontine nuclei, and the spinal cord. Thus, these mossy fiber sources are the most likely origins for the banded collateral system. Our studies do not allow us to distinguish whether one, or more than one, of these regions contribute to the system.