Spatial distribution of long-term potentiation in the surround of visual cortex lesions in vitro.

Focal visual cortex lesions lead to functional changes in the surrounding cortical network, possibly mediated through synaptic long-term potentiation (LTP). Although a post-lesional facilitation of LTP has been observed, nothing is known about the spatial profile of LTP in the normal and focally lesioned visual cortex of rats. We used a 64-multielectrode array to characterise the spread of LTP induced by theta-burst stimulation in layer IV. Measurements were made at comparable distances from the midline in the visual cortex of controls, sham-operated and lesioned animals. In control rats, LTP was elicited in projections to all visual cortex layers. However, we completely failed to observe LTP in sham-operated animals 1-4 days after surgery. At comparable survival times, no LTP could be elicited in the lesion-treated rats in direct vicinity of the border of the injury, while LTP was successfully induced at larger distances from the lesion. The maximal reach of this restored post-lesion LTP was spatially more limited than in controls and equal in all directions, accordingly absolute distance and not maximal length or density of connections seems to rule local lesion-induced functional remodelling.