Subsequent mental development of children with lead encephalopathy, as related to type of treatment

Postnatal lead effects on the development of visual spatial acuity in rhesus monkeys (Macaca Mulatta)

High lead levels adversely affect visual function in humans and laboratory animals. The effects of lower lead levels are less certain. This study compared the development of photopic spatial acuity in rhesus monkeys exposed to lead (n = 43) with monkeys (n = 23) not exposed to lead. Lead exposure began at Day 8 postpartum and continued daily throughout the first 26 weeks of postnatal life achieving target blood lead levels of 35-40 microg/dl by about 15 weeks. Photopic spatial acuity was evaluated by a preferential looking technique used clinically to assess spatial acuity in human infants. Acuity increased rapidly over the first few postnatal weeks achieving the maximum acuity level assessed (26.3 c/deg) by 7 weeks of age for most monkeys. Postnatal lead exposure at the dosages and durations studied did not affect the development of photopic spatial acuity.

A selective decrease of cholinergic muscarinic receptors in the visual cortex of adult rats following developmental lead exposure

The effects of low-level developmental lead (Pb) exposure (postnatal days 0-21) on the binding of [3H]quinuclidinylbenzilate (QNB) and on acetylcholinesterase (AChE) activity in the retina, superior colliculus, lateral geniculate nucleus and visual cortex (VC) were studied in the adult rat. Maximal blood and tissue Pb concentrations (50-60 micrograms %) were reached on day 21 and decreased to control levels (4-5 micrograms %), except in the retina (12 micrograms %) and VC (18 micrograms %; 0.87 microM), by day 90. A large decrease in [3H]QNB binding (-38%) and AChE activity (-29%) was found only in the VC of Pb-exposed rats. Scatchard plots of saturation binding data revealed a decrease in the density (Bmax), but not in the affinity (Kd), of the muscarinic receptors. Pb (10(-4)-10(-9)M) had no effect on [3H]QNB binding or AChE activity in VC membrane preparations from control rats. The mechanism accounting for this selective decrease of cholinergic muscarinic receptors in the VC is presently unknown. These results, in combination with those from our psychophysical and pharmacological studies demonstrating a scopolamine supersensitivity in Pb-exposed rats, suggest that the long-term effects of developmental Pb exposure are due to a direct action of Pb on visual cortex cholinergic neurons.

Perinatal exposure to 60-Hz electric fields: effects on the development of the visual-evoked response in rats

Two independent series of experiments were performed on 114 male Sprague-Dawley-derived, albino rat pups, which represented 61 litters in experimental series I and 53 litters in experimental series II. Animals were exposed for 20 h/day from conception to testing (postnatal days 11-20) to a vertical, 65-kV/m, 60-Hz electric field or sham-exposed. Recordings of the visual-evoked response (VER) were obtained using a small silver ball electrode placed epidurally over the visual cortex. Visual stimuli consisted of 10-microseconds light flashes delivered at 0.2 Hz. Computer-averaged VERs were obtained and power spectral analyses (fast Fourier transform) were performed on the tapered (split cosine-bell window), averaged VERs. The expected age-related changes were clearly evident; however, a detailed analysis of VER component latencies, peak-to-peak amplitude, and power spectra failed to reveal any consistent, statistically significant effect of exposure to 60-Hz electric fields.

Cost effectiveness of lead screening

Lead-screening programs may reduce childhood disabilities, but at what cost? Through a review of the literature, we performed a cost-effectiveness analysis in which the costs, savings, and health benefits of two lead-screening strategies--employing either a free erythrocyte protoporphyrin assay or blood lead measurement--were compared with each other and with a strategy of no screening in a population of three-year-old children. When the prevalence of lead poisoning among the children screened is 7 per cent or more, we estimate that free erythrocyte protoporphyrin screening averts morbidity and results in net savings: It is both better and cheaper than no screening. At prevalences below 7 per cent, the net positive costs from screening and early treatment must be weighed against the noneconomic benefits of improved quality of life and considered in relation to other investments that could be made to benefit society. At all prevalence rates, free erythrocyte protoporphyrin screening is more cost effective than blood lead screening.

Scotopic vision deficits in young monkeys exposed to lead

Rhesus monkeys were reared on diets designed to produce blood lead concentrations of 14 (untreated), 55, or 85 micrograms per 100 milliliters for the first year of life. Eighteen months later, blood lead levels were normal in all animals. At this time, however, visual discrimination performance in the 85-microgram group was impaired under dim light relative both to their own performance under bright light and to the performance of the other groups under all light levels used. We interpret these results to reflect a deleterious, enduring impairment of scotopic visual function (night blindness) as a result of early lead intoxication.

Lead poisoning in childhood

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