An unusual effect of application of the amino acid L-arginine on cat visual cortical cells.

IONTOPHORETIC application of L-arginine (L-Arg) resulted in a profound decrease in visually elicited and spontaneous activity in 22 of 77 (29%) cells in area 17 of the anaesthetized/paralysed cat. Duration was long, and cells did not recover pre-application activity levels, indicating permanent decline. This effect was obtained without change in the extracellularly recorded waveform, demonstrating that this did not result from depolarization block. In the remaining 55 cells, application of L-Arg alone, at levels capable of eliciting inhibition as described above, was without effect. In 29 cells, L-Arg application was able to reverse the effect of inhibition of nitric oxide (NO) production. Populations of cells showing the depressive effect described above and those affected by NO modulation levels were mutually exclusive.