The primate visual cortex uniquely possesses a regular array of metabolically active, cytochrome oxidase (C.O.)-rich zones (blots or puffs) in the supragranular layers with distinct physiological properties, particularly those related to color processing. Our previous studies indicate that unilateral retinal impulse blockage in the adult severely affects the most metabolically active neurons and induces synaptic reorganization within the puffs. These findings suggest that the mature visual cortex is not static but, rather, responds dynamically to altered functional demands. Besides changes in puffs, our preliminary light microscopic analysis of surrounding C.O.-poor interpuff regions indicate compensatory increases in C.O. levels within zones related to the non-treated eye. Such dynamic changes in the adult are of obvious clinical and functional importance, consequently our initial ultrastructural and quantitative analyses of the puffs will be extended to the interpuff regions. Selective vulnerability of the most metabolically active neurons deserves further investigation, since it appears to implicate a specific neurotransmitter type, GABA. Whether all puff neurons with intense C.O. activity are GABAergic, or whether GABAergic neurons encompass a wide range of oxidative metabolic capacities, will be examined by means of combined C.O. histo- or immunohisto-chemistry and GABA-immunohistochemistry on the same histological section. To directly address the relationship of C.O. levels to physiological activity and visual processing, single neurons will be recorded extracellularly from C.O.-rich and poor zones in normal cortex and during periods of physiological modification: 1) following monocular retinal impulse blockage in the adult and 2) during the critical period of postnatal development, when the innately determined cortical organization undergoes further physiological maturation. To understand the anatomical basis of these changes during development and specifically to explore the dynamics of maturational plasticity, we will examine structural reorganization in developing visual cortical neurons following retinal blockade. In summary, our approach is to combine histochemical, immunohistochemical, ultrastructural, and physiological observations to yield an integrated understanding of metabolic adjustments to altered functional demands within developing and mature neurons of the primary visual cortex.
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