Figure 6.
The effect of 3 d MI on VGluT2-labeled synapses and the relationship between the direct pupillary reflex and VEPs.
A
, Summary of VGluT2+ synaptic density (mean ± SEM) (C, control; SAL, saline).
B
,
C
, Cumulative probability histograms of PSD lengths (
B
) and VGluT2-positive terminal size (
C
) (gray, saline; red, TTX). The distributions of PSD lengths and synaptic terminal sizes were not significantly different between 3 d MI and control animals (p > 0.05, K-S test).
D
, Experimental timeline and representative traces of the average field potentials evoked by a patterned visual stimulus viewed through the TTX-injected eye. Recordings were made in the binocular region of V1 contralateral to the injected eye. In this example, evoked cortical activity returned after 24 h and was fully restored by 36 h. For the MI experiments used in the EM analysis, a second TTX injection (gray arrow) would have been administered before the appearance of visually evoked activity in V1, maintaining full retinal blockade.
E
, Summary of direct and consensual pupillary reflexes with no TTX (black) and 2 or 20 h after TTX (red). The magnitude of pupillary constriction is represented by the percentage change in the pupil radius on direct light stimulation of a dark-adapted eye. Thus, 0% indicates a nonreflexive pupil (tonically dilated). Pupillary responses >20% would have been excluded from the MI experiments (
E
,
F
, dashed line). Each open circle represents an individual animal, and the filled circles show group means ± SEM [ipsilateral (direct) pupil constriction values: uninjected, 63 ± 3%, n = 8; 2 h TTX, 0 ± 1%, n = 10; 20 h, 27 ± 5%, n = 14; contralateral (consensual) pupil constriction values: uninjected, 24 ± 6%, n = 8; 2 h TTX, −1 ± 2%, n = 10; 20 h, 6 ± 3%, n = 15].
F
, Constriction of the TTX-injected eye evoked by direct stimulation plotted as a function of cortical VEPs (17–22 h after injection, normalized to pre-TTX baseline values). Note that the absence of a direct pupillary reflex in the TTX-injected eye, as described in Materials and Methods, is sufficient to confirm retinal blockade as assessed by the presence of a categorical VEP. Recorded field potentials were classified as containing “no VEP” if the scored amplitude was <2 SDs of the noise (field potentials recorded in response to gray screen). Responses were recorded ∼17–22 h after TTX.