Modification of functional architecture of the visual cortex by a developmental pharmacological method

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Neuronal activity and function of subplate cells have been proposed to be involved in the formation of functional architecture of the visual cortex. We have studied the effects of kainic acid injected locally into the visual cortex of a few-days-old kitten. Electrophysiological and immunohistochemical examinations showed that the synaptic connections for normal visuocortical function was prevented to develop by this pharmacological manipulation. In order to examine in detail about the termination pattern of individual axon of neurons in the lateral geniculate nucleus (LGN) , anterograde tracing experiments using PHA-L were performed. The results clearly indicated that LGN axons extended to layr II-III outside the usual termination layr IV in the visual cortex treated with kainic acid. This abnormal termination pattern of LGN axon is considered as a reason why we could not obtain visual responses in the cortex injected with kainic acid. We also examined the effects of kainic acid inject … More ion on the development of the visual callosal projection. Retrograde tracing experiments have shown that the number of the callosal projection to the visual cortex injected with kainic acid was significantly reduced. Larger number of pyramidal cells were identified as callosal neurons in the contralateral visual cortex to the kainic acid injection. These results first demonstrated that the kainic acid injection in the first week of age affected not only thalamocortical projection but also the callosal projection in kitten visual cortex. It is necessary to examine the specificity of kainic acid injection on subplate cells, however, the present study first demonstrated that the interaction of axons with deep cortical cells, including subplate cells plays an important role for establishing appropriate contact to the post synaptic cells and maintaining them in the visual cortex We continue to study molecular and cellular mechanisms of formation of functional connections in the visual cortex during development. Less