An in vivo intraneuronal recording/HorseRadish Peroxidase marking study of the dorsal (DCN) and posteroventral (PVCN) cochlear nucleus (CN) is proposed. We will ascertain acoustic and electrotonic response properties of CN neurons in the gerbil. Both anesthetized and unanesthetized, decerebrate preparations will be systematically studied because anesthesia is known to influence unit responses. The morphology of labeled neurons will be characterized according to location, and dendritic and axonal branching patterns for assignment to an anatomically-based neuronal type. Evidence from this laboratory suggests functional interactions between specific classes of units within the DCN. Recent in vitro evidence suggests interaction between neurons of the DCN and PVCN. In order to fully evaluate such interactions in the context of a functioning auditory system, the proposed in vivo studies will directly correlate anatomical neuron type with response properties. We hypothesize that the use of extensive response characteristics (e.g. response maps, noise responses, membrane time constants, etc.), enabled by computerization, will provide unequivocal correlations between unit and neuron types. Although past efforts at such correlations have proven equivocal, the present effort should prove successful because 1.) the preparation is very stable and 2.) correlation is not solely or primarily based on the peristimulus time histogram scheme, rather it will be based on a constellation of response characteristics. Thus the objective within the frame of the present proposal is to discover structure/function relationships in the DCN and PVCN, and to evaluate effects of anesthesia on the CN and, by analogy, other neural systems. Our ultimate goal is to elucidate CN neuronal circuitry, including membrane properties and neural interactions. Mechanisms by which the CN subnuclei play an integrative role in hearing may thus be understood and incorporated into schemes of auditory prostheses.
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