Figure 1.
Daily BMI injection effectively blocked GABAergic activities.
A, B: Retino-geniculate projection in control animal visualized by intraocular injection of CTB. C, D: Disrupted retino-geniculate projection showing much expanded ipsilateral and contralateral projection of the injected eye (green) and clearly reduced innervations of the uninjected eye (red). Scale bar: 200 µm. E: Comparison of the ipsilateral projection between intact and treated eye. N = 10, Data were analyzed using one way ANOVA, and presented in AVG±SE. *: p<0.05. The BMI group received monocular BMI injection. F: Vitreous extracts from an eye injected 24 h earlier completely blocked the inhibitory inputs of a DSGC in a control retina, showing lasting effectiveness of the BMI. G: In a retina receiving 19 consecutive BMI injections, the inhibitory inputs to a DSGC were blocked by 20 µM BMI, showing no tolerance was induced by repeated injection.
Figure 2.
Normal DSGCs can be found in retinas receiving 16 to 19 daily BMI injections.
A: A DSGC responded to the onset and termination of a stationary flashing spot. B: Directional responses to a rectangle moving in 12 directions. The preferred direction is represented by the arrow in the middle of polar plot surrounded by traces of action potentials. C: Asymmetrical synaptic inputs recorded when membrane potential was held at −65 mV and 0 mV, respectively. Much larger inhibitory inputs were observed when visual stimulus was moving in the null direction. D: Dendritic morphology of the recorded cell. A section of the dendritic field was enlarged showing clear ON (E) and OFF (F) segregation. Tight costratification with cholinergic plexus was clear (G). Scale bar: 30 µm.
Figure 3.
Comparison of DSI and turning width.
Population data comparing direction selective index (A) and the width of direction tuning curves (B) of DSGCs in control retina and retinas treated with BMI, Epb, TTX and the mixture of Epb and TTX. Data were analyzed using one way ANOVA, and presented in AVG±SE. *: p<0.05. Cell number is described in parentheses.
Figure 4.
Homeostatic properties of DSGCs in BMI and Epb plus TTX treated retinas.
A: DSGCs with preferred direction falling into all four subtypes were observed. The length of the lines represents normalized response magnitude (vector sum divided by total number of spikes), the angle preferred direction. B: Clear directional responses to square wave gratings with contrast as low as 20%, normalized data are shown in C (numbers in corresponding color represent DSI of treated DSGCs). D: Responses to a stationary flashing spot of different size. Although cells in treated retina generally exhibit lower firing rate, clear center-surround interaction can be seen especially in normalized data in E. Black: Intact; Blue: Saline; Green: BMI; Red: Epb+TTX. Numbers in parentheses indicate the cell number.
Figure 5.
A DSGC in the retina treated with Epb for 15 days.
A: To a stationary flashing spot, the cell responded to both the onset and termination. B: To a rectangle moving in 12 directions, highly asymmetrical responses could be observed. Polar plot shown in the middle of response traces with the vector sum represented by the arrow and the tuning curve by the circle. C: Excitatory and inhibitory synaptic inputs recorded when membrane potential was held at −65 mV and 0 mV, respectively. D: Dendritic morphology of the recorded cell. E–G: High magnification of the region indicated by the white square in D. E and F: Showing dendrites in the ON and OFF sublamina, respectively. G: Side view, showing costratification with ChAT bands. Scale bar: 30 µm.
Figure 6.
Normal DS in TTX treated retina.
A: Clear ON and OFF responses to a flashing spot. B: Responses to a moving rectangle exhibiting strong directional selectivity. C: Voltage clamp responses to null and preferred direction motion. Membrane potential was held at −65 mV and 0 mV, respectively. D: Dendritic arbor of the recorded cell. E–G: The region indicated by the white square in D. E and F: Dendrites in the ON and OFF sublaminae. G: The side view showing clear costratification with cholinergic bands. Scale bar: 30 µm.
Figure 7.
Normal DS in the retina treated by TTX plus Epb.
A: ON and OFF responses were elicited by a flashing spot. B: Responses to a rectangle moving in 12 directions. Clear direction selectivity could be observed. C: Asymmetric input evoked by motion from null and preferred directions. Membrane potential was held at −65 mV and 0 mV, respectively. D: Dendritic morphology of the recorded cell. E–G: The region indicated by the white square in D. The dendrites in the ON and OFF sublaminae are shown in E and F. G: The side view showing costratification of DSGC dendrites and cholinergic bands. Scale bar: 30 µm.