BackgroundLow-level developmental lead exposure is linked to cognitive and neurological disorders in children. However, the long-term effects of gestational lead exposure (GLE) have received little attention.ObjectivesOur goals were to establish a murine model of human equivalent GLE and to determine dose–response effects on body weight, motor functions, and dopamine neurochemistry in year-old offspring.MethodsWe exposed female C57BL/6 mice to water containing 0, 27 (low), 55 (moderate), or 109 ppm (high) of lead from 2 weeks prior to mating, throughout gestation, and until postnatal day 10 (PN10). Maternal and litter measures, blood lead concentrations ([BPb]), and body weights were obtained throughout the experiment. Locomotor behavior in the absence and presence of amphetamine, running wheel activity, rotarod test, and dopamine utilization were examined in year-old mice.ResultsPeak [BPb] were < 1, ≤ 10, 24–27, and 33–42 μg/dL in control, low-, moderate- and high-dose GLE groups at PN0–10, respectively. Year-old male but not female GLE mice exhibited late-onset obesity. Similarly, we observed male-specific decreased spontaneous motor activity, increased amphetamine-induced motor activity, and decreased rotarod performance in year-old GLE mice. Levels of dopamine and its major metabolite were altered in year-old male mice, although only forebrain utilization increased. GLE-induced alterations were consistently larger in low-dose GLE mice.ConclusionsOur novel results show that GLE produced permanent male-specific deficits. The nonmonotonic dose-dependent responses showed that low-level GLE produced the most adverse effects. These data reinforce the idea that lifetime measures of dose–response toxicant exposure should be a component of the neurotoxic risk assessment process.

Previously, we investigated ubisemiquinone (SQ) EPR spectra associated with NADH-ubiquinone oxidoreductase (complex I) in the tightly coupled bovine heart submitochondrial particles (SMP). Based upon their widely differing spin relaxation rate, we distinguished SQ spectra arising from three distinct SQ species, namely SQ Nf (fast), SQ Ns (slow), and SQ Nx (very slow). The SQ Nf signal was observed only in the presence of the proton electrochemical gradient (Dl H + ), while SQ Ns and SQ Nx species did not require the presence of Dl H þ . We have now succeeded in characterizing the redox and EPR properties of SQ species in the isolated bovine heart complex I. The potentiometric redox titration of the g z,y,x = 2.00 semiquinone signal gave the redox midpoint potential (E m ) at pH 7.8 for the first electron transfer step [E m1 (Q/SQ)] of À45 mV and the second step [E m2 (SQ/QH 2 )] of À63 mV. It can also be expressed as [E m (Q/QH 2 )] of À54 mV for the overall two electron transfer with a stability constant (K stab ) of the SQ form as 2.0. These characteristics revealed the existence of a thermodynamically stable intermediate redox state, which allows this protein-associated quinone to function as a converter between n = 1 and n = 2 electron transfer steps. The EPR spectrum of the SQ species in complex I exhibits a Gaussian-type spectrum with the peak-to-peak line width of $6.1 G at the sample temperature of 173 K. This indicates that the SQ species is in an anionic Q ÅÀ state in the physiological pH range. The spin relaxation rate of the SQ species in isolated complex I is much slower than the SQ counterparts in the complex I in situ in SMP. We tentatively assigned slow relaxing anionic SQ species as SQ Ns , based on the monophasic power saturation profile and several fold increase of its spin relaxation rate in the presence of reduced cluster N2.The current study also suggests that the very slowly relaxing SQ Nx species may not be an intrinsic complex I component. The functional role of SQ Ns is further discussed in connection with the SQ Nf species defined in SMP in situ.

BackgroundPostnatal lead exposure in children and animals produces alterations in the visual system primarily characterized by decreases in the rod-mediated (scotopic) electroretinogram (ERG) amplitude (subnormality). In contrast, low-level gestational Pb exposure (GLE) increases the amplitude of scotopic ERGs in children (supernormality).ObjectivesThe goal of this study was to establish a rat model of human equivalent GLE and to determine dose–response effects on scotopic ERGs and on retinal morphology, biochemistry, and dopamine metabolism in adult offspring.MethodsWe exposed female Long-Evans hooded rats to water containing 0, 27 (low), 55 (moderate), or 109 (high) ppm of Pb beginning 2 weeks before mating, throughout gestation, and until postnatal day (PND) 10. We measured maternal and litter indices, blood Pb concentrations (BPb), retinal Pb concentrations, zinc concentrations, and body weights. On PND90, we performed the retinal experiments.ResultsPeak BPb concentrations were < 1, 12, 24, and 46 μg/dL in control, low-, moderate- and high-level GLE groups, respectively, at PNDs 0–10. ERG supernormality and an increased rod photoreceptor and rod bipolar cell neurogenesis occurred with low- and moderate-level GLE. In contrast, high-level GLE produced ERG subnormality, rod cell loss, and decreased retinal Zn levels. GLE produced dose-dependent decreases in dopamine and its utilization.ConclusionsLow- and moderate-level GLE produced persistent scotopic ERG supernormality due to an increased neurogenesis of cells in the rod signaling pathway and/or decreased dopamine utilization, whereas high-level GLE produced rod-selective toxicity characterized by ERG subnormality. The ERG is a differential and noninvasive biomarker of GLE. The inverted U-shaped dose–response curves reveal the sensitivity and vulnerability of the developing retina to GLE.

BackgroundGestational lead exposure (GLE) produces novel and persistent rod-mediated electroretinographic (ERG) supernormality in children and adult animals.ObjectivesWe used our murine GLE model to test the hypothesis that GLE increases the number of neurons in the rod signaling pathway and to determine the cellular mechanisms underlying the phenotype.ResultsBlood lead concentrations ([BPb]) in controls and after low-, moderate-, and high-dose GLE were ≤ 1, ≤ 10, approximately 25, and approximately 40 μg/dL, respectively, at the end of exposure [postnatal day 10 (PND10)]; by PND30 all [BPb] measures were ≤ 1 μg/dL. Epifluorescent, light, and confocal microscopy studies and Western blots demonstrated that late-born rod photoreceptors and rod and cone bipolar cells (BCs), but not Müller glial cells, increased in a nonmonotonic manner by 16–30% in PND60 GLE offspring. Retinal lamination and the rod:cone BC ratio were not altered. In vivo BrdU (5-bromo-2-deoxyuridine) pulse-labeling and Ki67 labeling of isolated cells from developing mice showed that GLE increased and prolonged retinal progenitor cell proliferation. TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) and confocal studies revealed that GLE did not alter developmental apoptosis or produce retinal injury. BrdU birth-dating and confocal studies confirmed the selective rod and BC increases and showed that the patterns of neurogenesis and gliogenesis were unaltered by GLE.ConclusionsOur findings suggest two spatiotemporal components mediated by dysregulation of different extrinsic/intrinsic factors: increased and prolonged cell proliferation and increased neuronal (but not glial) cell fate. These findings have relevance for neurotoxicology, pediatrics, public health, risk assessment, and retinal cell biology because they occurred at clinically relevant [BPb] and correspond with the ERG phenotype.