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. 2009 Jul 1;29(26):8372–8387. doi: 10.1523/JNEUROSCI.1218-09.2009

Figure 9.

Figure 9.

In the presence of l-AP-4, the isolated LM surround was sensitive to HEPES. A, In the presence of l-AP-4, picrotoxin, and strychnine, the isolated LM input responds to the offset of a 300 μm spot and to the onset of an annulus with a 300 μm inner diameter as indicated by the phase of the voltage responses (top) and spike histograms (bottom). The addition of HEPES to l-AP-4, picrotoxin, and strychnine abolishes the LM ON surround, and the cell responds to the offset of both a spot and annulus. B, Response amplitude (top) and phase (bottom) to annuli stimuli (100% contrast, 4 Hz) of increasing inner diameter measured in the presence of l-AP-4, strychnine, and picrotoxin (open circles); l-AP-4, strychnine, picrotoxin, and HEPES (solid circles); and after wash out of HEPES with l-AP-4, strychnine, and picrotoxin still present (open squares). The isolated LM ON surround response is indicated by the shift in the response phase when the inner diameter reaches at least 150 μm. C, Plot showing the isolated LM receptive field mapped with drifting gratings (4 Hz, 28% and 100% contrast) in the presence of l-AP-4, strychnine, and picrotoxin (open circles), and l-AP-4, strychnine, picrotoxin, and HEPES (solid circles). The bandpass receptive field measured in the presence of l-AP-4 was fit with a difference-of-Gaussians model (solid line) and became low pass with the addition of HEPES (fit with a Gaussian receptive field model, solid line). D, The LM 2D receptive field profiles and Gaussian radii (in micrometers) derived from the spatial frequency responses in C; S and LM Gaussian radii (in micrometers) are indicated. Fits were also made to responses recorded under the same three conditions for two other cells. For the cell with voltage responses shown in A (original LM center radius = 82 μm), in the presence of l-AP-4, strychnine, and picrotoxin, center and surround radii = 62 and 237 μm, respectively. With the addition of HEPES, center radius = 81 μm with no measurable surround. For the third cell (data not shown; original LM center radius = 56 μm), in the presence of l-AP-4, strychnine, and picrotoxin, center and surround radii = 48 and 118 μm, respectively. With the addition of HEPES, center radius = 79 μm with no measurable surround.