Visual acuity deficits following neonatal lead exposure: cholinergic interactions

Clinical reports describe long-term alterations in the spatial resolution properties of the visual system following developmental lead (Pb) exposure. To determine if the spatial resolution limit, visual acuity, of the adult rat was altered following low-level, neonatal Pb exposure psychophysical studies were conducted. To examine possible mechanisms of action (and an additional stressor) the effects of scopolamine were studied in the psychophysical procedure. [3H]-QNB binding was analyzed in retina, superior colliculus, lateral geniculate nucleus and visual cortex. Neonatal hooded rats were exposed to Pb (days 0-21) via the milk of dams drinking 0.2% Pb acetate. Visual acuity was 1.8 cycles/degree in controls compared to 1.3 cycles/degree in the Pb group. Scopolamine caused dose-dependent decreases in spatial resolution with decreases at higher spatial frequencies being greater in the Pb group. Positive controls revealed the effects to be centrally mediated. A decrease in the [3H]-QNB binding was found only in the visual cortex. The results suggest that long-term effects of developmental Pb exposure may be directly on the visual cortex.