The effects of glutamate iontophoresis on single cell responses and inter-neuronal interactions in the kitten visual cortex.

We studied the effect of glutamate (Glu) micro-iontophoresis on visual responses (PSTHs) and cross-correlograms of neurones recorded simultaneously in the cortex of 4-6 weeks old kittens. PSTHs and cross-correlograms were tested before, during and after Glu injections and compared with adult cats data from previous experiment. Before the injection cross-correlogram shapes and numbers did not differ in young and adult cats, whereas PSTHs differed dramatically. Glu iontophoresis typically elevated background PSTHs levels rather than peak responses in young kittens. In adult animals the opposite effect predominated. After the termination of iontophoresis visual responses were enhanced in 21% of kitten neurones. In adult cats this effect was not observed. In kittens, a clear increase of cross-correlogram strength was recorded in one neuronal pair (3.6%) after the injection terminated. In adult cats similar effect was also found in 3% of pairs.