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ANATOMICAL DISTRIBUTION OF INHIBITORY AND EXCITATORY INPUTS TO PINWHEEL CENTERS AND ORIENTATION DOMAINS.

PCLM & Brain Cog Sci, MIT, Cambridge, MA, USA

Orientation selectivity in cat V1 can be refined by excitatory and inhibitory intracortical inputs. At pinwheel centers, cells preferring one orientation are in close proximity to cells with very different orientation preferences.One might predict that locally a greater range of orientations would impinge upon a pinwheel cell. Whole-cell recordings show that they do receive a wider range of subthreshold inputs, yet their spike tuning remains sharp. Thus, heterogeneous excitatory inputs are perhaps balanced by the spread and/or strength of inhibitory inputs. To determine whether the local connectivity is responsible for this effect, we imaged orientation maps in cat V1 and placed small injections of fluorescent CTB at pinwheels and domains. Following a survival of 2 days the brain was cut tangential to the dorsal lateral V1 surface and GABA immunofluorescence was used to identify inhibitory neurons. Digital photos of the retrogradely transported label and GABA positive neurons were merged and the distributions of both the excitatory (tracer transport) and inhibitory (double labeled) neurons were plotted.The pattern of labeled cells was aligned to the orientation map using injection sites, and the blood vessels as landmarks. As predicted, within a 400um radius of the injection site, injections in pinwheel centers labeled neurons over a wide range of orientations, whereas domain injections predominantly labeled cells within the same domain. Furthermore, there was a greater proportion of GABA positive double labeled cells around pinwheel centers compared to domains. When the sampling radius was extended to 800um, the distributions of cells labeled from the injections were less orientation specific for both domains and pinwheels and the proportion of double labeled cells was reduced. Thus, local inhibition (within 400-500 um) may balance the broad excitation to produce narrow spike tuning near pinwheels.
Support Contributed By: NRSA (DL), HHMI (JS), MEC (JM), NIH (MS).

Citation:
D.C. Lyon, J. Schummers, J. Marino, M. Sur. ANATOMICAL DISTRIBUTION OF INHIBITORY AND EXCITATORY INPUTS TO PINWHEEL CENTERS AND ORIENTATION DOMAINS. Program No. 818.8. 2003 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, 2003. Online.