Generation of aberrant sprouting in the adult rat brain by GAP-43 somatic gene transfer

The expression of GAP-43 was modulated genetically in the adult rat nigrostriatal or septohippocampal pathway using recombinant adeno-associated virus (rAAV) vectors incorporating the neuron specific enolase (NSE) promoter and either a rat GAP-43 cDNA or the corresponding antisense sequence. Bicistronic expression of green fluorescent protein (GFP) enabled us to evaluate transduced neurons selectively. Single injections of rAAV into the substantia nigra pars compacta (SNc) transduced both dopaminergic and non-dopaminergic neurons stably for the 3-month duration of the study. Transduction with the GAP-43 vector in this region: (1) increased GAP-43 mRNA levels 2-fold compared to controls; (2) led to GAP-43 immunoreactivity in neuronal perikarya, axons, and dendrites that was not observed otherwise; and (3) resulted in GAP-43/ GFP-positive axons that were traced to the striatum where they formed clusters of aberrant nets. The GAP-43 antisense vector, in contrast, decreased neuropil GAP-43 immunoreactivity compared to controls in the SNc. In septum, injections of the GAP-43 expressing vector also caused aberrant clusters of GAP-43 labelled fibers in terminal fields, i.e., fornix and hippocampus, that were not observed in control tissues. It therefore appears that rAAV vectors provide a novel approach for modulating intraneuronal GAP-43 expression in the adult brain.