ACTIVITY-DEPENDENT REFINEMENT OF INHIBITORY CONNECTIONS

Several lines of evidence suggest that excitatory synaptic transmissio n contributes to the maturation of precise neuronal connections. In th e present study we determined whether the specific innervation pattern of single inhibitory arborizations was dependent upon neuronal activi ty during development. A homogeneous group of glycinergic inhibitory n eurons in the central auditory system, the medial nucleus of the trape zoid body (MNTB), was functionally denervated in neonatal gerbils. The anatomical specificity of single MNTB terminal arborizations was subs equently measured along the tonotopic axis of a postsynaptic target, t he lateral superior olive. Here we demonstrate that inhibitory termina l boutons spread a significantly greater distance along the frequency axis of the postsynaptic target following functional denervation. Alth ough total arbor length remained unchanged, there was a significant in crease in the number of branch points, suggesting de novo sprouting. T he results indicate that normal inhibitory synaptic activity contribut es to the developmental refinement of specific neuronal connections.