Quantitative distribution of GABAimmunopositive and -immunonegative neurons and syn apses in the monkey striate cortex (area 17

rons and synapses was determined in functionally dis-tinct subregions delineated as rich and poor in cyto-chrome ondase (CO) in the visual cortex of adult macaque monkeys. The average numerical density (number per unit volume, NJ of GABA(+) neurons and synapses was not significantly different between the CO-rich and-poor regions. Twenty percent of the total number of cortical neurons and 17 % of the synapses were GABA(+). On average, each visual cortical neuron re-ceives 3900 synapses, 660 of them being GABA(+). The latter were distributed on the target cell in a pattern that predicts the site of GABA influences in cortex. The major targets of GABA(+) synapses were dendritic shafts, comprising nearly two-thirds of the postsynaptic elements. About every fourth and every eighth G ABA(+) synapse was devoted to dendritic spines and to neurona