Influence of Bilateral Cochlear Ablation on Segregation of Afferent Projections of the Dorsal Nucleus of the Lateral Lemniscus in the Rat Inferior Colliculus

Abstract

Parallel ascending auditory inputs to the inferior colliculus are integrated in multiple synaptic compartments within fibrodendritic layers of the central nucleus of the inferior colliculus (CNIC). Early competitive interactions within the CNIC may influence development of synaptic compartments even before onset of hearing (approximately postnatal day 12 in rat). Previous studies in our laboratory showed that unilateral cochlear ablation on either P2 or P9 disrupt the development and maintenance of banded afferent projections from the dorsal nucleus of the lateral lemniscus (DNLL) to the CNIC. Bilateral cochlear ablations (BCA) were performed in P9 rat pups to address if a perturbation of the cochlea would affect competitive segregation of DNLL afferent bands in CNIC. Three days following BCA, animals were sacrificed and pins coated with the carbocyanine dye, DiI, were placed in the DNLL commissure to label afferent axons projecting to both CNICs. DiI labeled axons symmetrically filled the CNIC on each side and distributed along layers. Analysis of the spatial distribution of the labeled DNLL afferent axons indicated a pattern of dense and light terminal fields in CNIC that varied from the regular spacing of banded label in CNIC of surgical controls. These findings suggest that plastic changes have taken place in the banded pattern of DNLL projections just three days after BCA. These results, together with previous data from unilateral cochlear ablation, lead us to propose that activity dependent competition assists in the formation of synaptic compartments within fibrodendritic layers in the CNIC. Supported by NIH NIDCD grant DC 004412