Lesion-induced axon sprouting in the deafferented striatum of adult rat.

Synaptic replacement in rat striatum following a unilateral cortical lesion was investigated using electron microscopy and the anterograde tracer, biotinylated dextrin amine (BDA). In the deafferented striatum evidence of axon sprouting and synapse replacement was seen at 20 days after the lesion and most newly-formed axon terminals were labeled with BDA injected previously into the contralateral cortex. In addition, BDA-labeled fibers from the contralateral cortex formed multiple asymmetric axospinous synapses with deafferented striatal neurons, a morphological feature rarely seen in unlesioned rats. These data suggest that in response to a unilateral cortex lesion axons from the contralateral cortex sprout and reinnervated the deafferented striatal neurons and that reinnervation by 'like' afferents maybe crucial for the establishment of functional recovery after the unilateral cortex lesion.