Neural plasticity refers to the ability of central nervous system connections to be modified or rearranged, particularly during a critical period early in development. The overall goal of Dr. Stryker's research over the past several years has been to understand the role of neural activity in mammalian visual system plasticity and development. Much recent evidence from studies of long-term potentiation (LTP) in the hippocampus suggests that the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor plays a crucial role in this neural activity-dependent synaptic plasticity. LTP plasticity is found in both young and adult nervous systems. In this project, Dr. Stryker and his colleagues will conduct several studies to elucidate the role of NMDA receptors in mediating the effects of activity on the plasticity of the cat visual cortex. Plasticity in the visual cortex is only found during an early stage of development. The investigators will infuse NMDA-antagonists into the visual cortex; measure electrophysiologically the specificity of the receptor blockade so produced; record the effects of NMDA- receptor blockade on patterns of neural activity; and study physiologically and anatomically effects on plasticity in development. Dr. Stryker has a long history of making significant contributions to our knowledge of nervous system development. This new work promises to reveal whether the cellular and molecular details of plasticity in the adult central nervous system (LTP), now receiving enormous research attention, apply also to the rearrangement of neuronal connections in brain development.