Local lateral connectivity of inhibitory clutch cells in layer 4 of cat visual cortex (area 17)

To characterise spatially a major component of the anatomical basis of loca l lateral inhibition in layer 4 of cat visual cortex (area 17), we analysed the lateral distribution of neuronal somata postsynaptic to electrophysiol ogically characterised GABAergic clutch (basket) cell axons (CC1 and CC2). We report two main results. First, the clutch cell axons appear to show iso tropic lateral connectivity near their cell body (less than 50 mum radius), but beyond this core region they show anisotropic lateral connectivity, pr eferring particular angular sectors around their cell body. Second, we esti mated the probability of lateral connection for each axon arbor as a functi on of radial distance from the parent soma. We found that this radial funct ion has a brief rising phase, to a peak at 30-45 mum, and a longer, exponen tial decaying phase, with a space constant of around 50 mum. The shape of t he radial connection probability function suggests that most lateral inhibi tory connections of clutch cells are formed with neurons in nearest-neighbo ur cortical columns. Taken together, the results suggest that these individ ual layer-4 clutch cell axons may inhibit all (isotropic) nearest-neighbour cortical columns with a relatively high probability of connection, but out side this core region may provide a type of anisotropic lateral inhibition of cortical columns with a radially decreasing probability of connection.