PLASTICITY OF THE DEVELOPING MAMMALIAN VISUAL SYSTEM

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1) Permanent ectopic retinal projections to auditory or somatosensory thalamic nuclei can be reliably produced by neurosurgery on newborn Syrian hamsters. Neurophysiological recording and the 2-deoxyglucose metabolic mapping techniques will be used to determine if the anomalous projections drive thalamic neurons or the cortical neurons to which the thalamic neurons project. The receptive field properties of single neurons receiving the anomalous visual input and the retinotopic organization of the ectopic visual pathways will also be studied electrophysiologically. The development of the ectopic projections will be studied by anterograde transport techniques. The results of these studies have fundamental implications for the development of orderly connections and single unit receptive field properties in normal animals and are of potential value in the treatment of central nervous system (CNS) lesions in man. 2) The optic tract and second order somatosensory pathways regrow following transection in neonatal hamsters. Retrograde transport of enzymatic and fluorescent tracers will be used to determine whether this regrowth is due to regeneration of cut axons or to the growth of late-developing uncut axons, across the level of transection. The time course of the regrowth will also be examined. These studies will help to determine the circumstances under which transected CNS axons can regenerate; this is important for the clinical treatment of traumatic injury of the CNS.