Inhibitory basket cell synaptic input to layer IV simple cells in cat striate visual cortex (area 17): A quantitative analysis of connectivity

In the absence of a direct and specific marker for basket cells, the aim of this paper was to use available data to estimate the density of basket cel l synaptic input to smooth and spiny neurons within layer IV of cat striate visual cortex (area 17). A linear quantitative analysis of layer IV basket cell connectivity data suggests that on average basket cells (1) comprise 25-35% of all GABAergic neurons in layer IV (3552-4736 cells mm(-3)). (2) a ccount for 30-41% of all putative inhibitory dendritic synapses of layer IV spiny stellate cells (145-195 synapses cell(-1)) and a similar proportion of layer IV basket cells (25-37%, 71-107 synapses cell(-1)), and (3) provid e each layer IV spiny cell with 13-45 axons and each layer IV basket cell w ith 6-29 arena. These estimates suggest that basket cells may be less commo n and provide a smaller proportion of the dendritic synaptic input to layer IV spiny and smooth neurons than previously thought. In addition, the anal ysis indicates that a layer IV spiny stellate cell may receive on average a s many synapses and axons from layer IV basket cells as from lateral genicu late relay cells. Based on this potential numerical similarity, a geniculat e-basket synaptic pairing in a spine-shaft microcircuit is hypothesized. Th is microcircuit could implement a type of local (dendritic) push-pull inter action underlying subfield antagonism.