The present proposal is to record intracellularly from cells in the posteroventral and dorsal cochlear nuclei, parts of the first integrative stage in the mammalian auditory pathway, in brain slice preparations. Brain slice preparations allow stable intracellular recordings to be made while controlled manipulations can be made of: (1) intracellularly injected current, (2) the precise temporal patterning of auditory nerve input, (3) the ionic and pharmacological environment and (4) the physical presence of tissue which might provide synaptic inputs. The voltage changes of cells in response to injected current reveal the intrinsic electrical characteristics of cells. Synaptic responses to electrical stimulation of the auditory nerve show what the properties are of synapses between auditory nerve fibers and postsynaptic cells. If there exists neuronal circuitry in the tissue of the brain slice, the synaptic responses to electrical stimulation of the auditory nerve will consist of short latency responses mediated directly through primary afferent innervation followed by longer latency responses mediated through interneurons. By cutting slices which include different parts of the cochlear nuclear complex, the position of interneurons can be used to separate synaptic inputs. Pharmacological blockers can be used to separate inputs and to obtain clues about the identity of neurotransmitters. Once separated, the characteristics of synaptic inputs can be studied unambiguously. Trains of electrical shocks will be used to give a rough indication of how the various neuronal pathways function in vivo. The physiological characteristics of cells will probably differ. After learning to differentiate cells physiologically, intracellular dye injections will be used to correlate their physiological with their morphological characteristics. To ensure that the tissue is not degenerating, both physiological and anatomical characteristics will be used to assess the tissue. In viable slices, the input resistance of cells should be high and the electrical characteristics and synaptic responses should be stable over hours. Cells injected intracellularly with horseradish peroxidase should look like Golgi-stained tissue fixed in situ.
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