HOMOGENEITY OF REGIONAL BRAIN LEAD CONCENTRATIONS

It has been proposed that the neurobiological basis of many of the beh avioral manifestations arising in response to Pb exposure may be due t o selective vulnerability of particular brain regions, such as hippoca mpus, a region in which preferential accumulation has been reported in some studies. However, these findings ha ve not been invariant and, i n fact, have been found to vary with dosing parameters. This study exa mined potential regional accumulation of Pb in brain following postnat al exposure of rats to Pb via nursing dams consuming Pb acetate soluti ons of 0, 100, 350, 1000, or 2000 ppm. Offspring were sacrificed at 7, 14, 21, 40 or 60 days of age and brains dissected into 12 regions, in cluding striatum, nucleus accumbens, hypothalamus, thalamus, ventral ( tegmentum) and dorsal (tectum) midbrain, hippocampus, frontal, parieta l/temporal, and occipital cortices, cerebellum and brain stem for regi onal Pb analyses. All brain regions generally accumulated Pb in a simi lar pattern. Regional elimination half-lives, determined for the 350, 1000 and 2000 ppm exposure groups, averaged about 20 days and did not vary between regions. Regional brain Pb levels were not different whet her brains were perfused or not prior to brain Pb determinations. Howe ver, regional differences in brain Pb levels could be introduced by us ing dry, rather than wet weights in the calculation of Pb concentratio ns, and by procedures including soaking in formaldehyde prior to dryin g, probably as a result of the differential fluid volume of different brain regions. Taken together, these data do not support previous find ings of selective regional accumulation of Pb in any brain region, inc luding the hippocampus, at least under conditions of postnatal Pb expo sure and wet weight measures. While there may indeed be differences am ong brain regions in sensitivity to Pb, any differences in response am ong brain regions should probably be ascribed to differences in the in teractions of Pb with biochemical or cellular targets unique or enrich ed in that region rather than to differences in accumulation of Pb. (C ) 1994 Intox Press, Inc.