We will investigate the synaptic bases for processing monaural and binaural information in the inferior colliculus (IC). In order to define the anatomical substrates of neural processing in the IC, we will combine axonal transport, intracellular staining, quantitative methods, and immunocytochemistry at the light (LM) and electron microscopic (EM) levels. Each experiment will address the general hypothesis that neural responses in the IC are a product of functional zones defined by banded inputs and specific cell types. To determine whether the inputs to the IC converge to create specific functional zones, two banded inputs will be labeled in the same experiment. We postulate that bands from different sources overlap to form synaptic domains which are functionally distinct zones of neuropil in the IC. To characterize the synaptic organization of the binaural inputs from the superior olivary complex (SOC), we will use EM autoradiography and test the hypothesis that inputs from the SOC can be identified by their fine structure. We predict these inputs will provide the largest number of excitatory synapses (type 1) to the central nucleus. To identify the inhibitory inputs to the synaptic domains and determine the sources of these synapses, experiments will combine axonal transport methods to determine the inputs and immunocytochemistry at the EM level to detect GABA or glycine. Quantitative analyses will test the hypothesis that the synaptic fine structure depends on the neurotransmitter. If multiple sources of GABA or glycine-containing ending are found, the structure of each inhibitory input to the IC can be investigated. Finally, to define the functional pathways through the IC, retrograde labeling an intracellular staining methods will be used to identify specific cell types in the IC; simultaneously, an anterograde marker will be used to identify a specific ascending input to these cells. We postulate that the content of synaptic domains in relation to specific cell types will create distinct output pathways to process different aspects of auditory information.
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