Anatomical plasticity in brainstem auditory nuclei following unilateral ablation of the inferior colliculus in neonatal rats

Anatomical plasticity of projections from brainstem auditory structures to the inferior colliculus (IC) was examined in albino rats to determine the effects of unilateral destruction of the IC during early development. The IC in the right hemisphere was destroyed by aspiration on postnatal day 3. Upon reaching adulthood, the rats were examined by retrograde tract tracing methods with fluoro-gold (FG) and [3H]-glycine to determine patterns of brainstem projections to the undamaged left IC. In our FG experiments, the results confirmed the presence of aberrant crossed projections from the right medial superior olive (MSO) to the undamaged left IC. Following injections of [3H]-glycine or FG into the undamaged left IC, however, no other aberrant projections were found in the superior olive, including those from the ipsilateral lateral superior olive (LSO) or the superior paraolivary nucleus (SPN). These results suggest that projections from the MSO to the IC may have the latent ability to create aberrant crossed projections during development. On the other hand, the neurons in LSO and SPN do not form aberrant projections following early unilateral IC lesions.