Plasticity in cerebellar tactile maps in the adult rat

We previously demonstrated that the fractured tactile cerebellar map within the crus IIa folia of the cerebellar hemispheres reorganizes after deafferentation of the upper lip in neonatal rats (postnatal day [PND] 1-30). The present study examined the capacity of this map to reorganize after deafferentation in adults and animals late in development (PND 30-89). Several months after cauterization of the infraorbital branch of the trigeminal nerve, the tactile map in the granule cell layer of crus IIa reorganized, with representations of intact structures expanding into the denervated area. The pattern of reorganization was similar to reorganization after neonatal lesions in that (1) all representations were from perioral structures, (2) the reorganized map maintained a fractured somatotopy, and (3) the denervated area was predominantly and consistently invaded by the upper incisor representation. We conclude that the spatial pattern of reorganization is essentially the same regardless of the age of deafferentation. However, we also observed developmental differences in reorganization. First, more areas of crus IIa were nonresponsive in animals lesioned later in development (PND 30-89). Second, we found a surprising degree of variability in the pattern of tactilely evoked cerebellar field potentials of PND 30-40 animals compared with neonates and adults, suggesting that this time period differs from other stages. The pattern of evoked potentials reflects the two primary inputs to the map. Our data show that, although both afferent pathways are capable of reorganization throughout development, their relative contribution to the map appears to differ, depending on the age at which lesion occurs.