MONOAMINERGIC CONTROL OF DEVELOPING VISUAL NEURONS

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The general goal of this study is to establish the link between visual cortical plasticity during the postnatal critical period and the central catecholamine-containing system. As an extension of our previous findings in this topic, we will further explore means of restoring cortical plasticity in the brain which haf lost plasticity either due to the specific depletion of catecholaminergic nerve terminals or simply outgrowing the susceptible period. In order to stimulate Beta-adrenoreceptors or, more directly, adenylate cyclase, various chemical agents will be delivered continuously into the visual cortex through a chronically implanted microperfusion system. In search for a noninvasive way to activate the central norepinephrine-Beta-adrenoreceptors-cyclic AMP system, we will stimulate, electrically and chemically, the norepinephrine-containing cell bodies in the brainstem at the locus coeruleus, leaving the visual cortex totally intact. As a well-established assay for neuronal plasticity in the visual cortex, receptive field properties, binocularity in particular, of single visual cortical cells will be examined following monocular occlusion in kittens and adult cats. These animals will be concurrently subjected to a variety of manipulations of the central catecholamine system as mentioned above. In addition to these primarily physiological studies which are precisely designed to tighten up the link between the central catecholamine system and visual cortical plasticity, we want also to study this plausible link in a much more global scope. We will then study, morphologically as well as biochemically, the postnatal maturation of endogenous catecholamines and related receptors in the cat visual cortex so as to compare ontogeny in the central catecholamine system with the maturation of visual cortical cells and their susceptibility to abnormal visual experience.