Figure 4.

(A) MEMRI signal intensity changes in receptor (rec.) and postreceptor (post-rec.) retina in control (C) and sodium iodate (SI)–treated rats measured 4 hours after intraperitoneal systemic administration of MnCl₂ from the regions defined in Figure 1. Open bars: light-adapted groups. Significant differences (*P < 0.05) were noted. Note that the minimum value of the y-axis is set to signal intensity measured in the absence of manganese exposure (i.e., 55).⁵ Error bars represent SEM, and numbers above the bars give the number of animals studied. (B) Plot of BRB PS′versus MEMRI signal intensity changes in receptor (■) and postreceptor (●) for each rat. A significant negative correlation between BRB PS′ and MEMRI signal was found only for the receptor layer (r² = 0.78; P < 0.05) and not the postreceptor layer (r² = 0.25; P > 0.05). The lack of correlation in the postreceptor retina may be attributed to its lower signal-to-noise ratio than in the receptor layer. In any event, after sodium iodate exposure, retinal manganese uptake did not increase with increasing BRB PS′.