Asymptomatic neurotoxicity of low-level, environmental lead (Pb) exposure in human fetus, infants, and young children poses a significant public health problem. Epidemiological and experimental studies indicate that lead exposure during development causes lasting cognitive and behavior impairments. The Center for Disease Control estimates 3 million U.S. children have lead concentrations above the danger level of 10 micrograms per decaliter of blood. The long-term goal of this research is to understand the biology of developmental lead-induced brain injury and ultimately develop strategies to ameliorate its consequences. Our studies to date indicate that exposure of perinatal rat to low-doses of Pb selectively compromises the survival and function of cholinergic septohippocampal neurons, resulting in lasting denervation-like effects in the hippocampus. The current project will characterize the cellular and molecular basis of the lesion and its long-term effects on hippocampal physiology. 1. Histo-morphometric analysis will be carried out to correlate the extent of Pb-induced loss of ChAT-immunoreactive neurons in the septum with the reduction of the AChE-positive fiber density and cholinergic presynaptic markers in the rat hippocampus in vivo.
The aim of these experiments is to determine the relationship between Pb exposure dosage, the extent of cholinergic denervation, and subsequent recovery (reinnervation). A related issue that will be examined in the course of these studies concerns the effect of the sympathohippocampal ingrowth on the extent of functional recovery. 2. Electrophysiological analysis of hippocampal electrical activity will be carried out to obtain neurophysiological correlates of Pb-induced cholinergic deficit and its reversal. The functional integrity of cholinergic septohippocampal pathway will be assessed by measuring changes in the atropine-sensitive, type 2 hippocampal theta rhythm. Patch clamp recordings from acutely isolated septal neurons will be employed to analyze the effect of in vivo Pb exposure on the electrophysiology of identified septohippocampal projections neurons. The neurons will be identified by retrograde labeling and immunocytochemical staining. 3. Molecular and cell biological techniques win be employed to test the hypothesis that differential vulnerability of septal cholinergic neurons to Pb results from the disruption of nerve growth factor (NGF)-dependent regulation of cholinergic gene expression and cell survival. Specifically, we will determine if Pb (a) alters expression of the low- and high-affinity receptors (p75 and pl4Otrk), (b) alters ChAT protein and mRNA expression by interfering with NGF-responsive regulatory elements of the rat ChAT gene, and (c) induces cholinergic neuron apoptosis by disrupting the cell survival functions of NGF.
Showing the most recent 10 out of 11 publications
