Lead-induced alterations of apoptosis and neurotrophic factor mRNA in the developing rat cortex, hippocampus, and cerebellum

Abstract

Previous reports have recently shown the prototypic neurotoxicant, lead, to induce apoptosis in the brains of developing organisms. In the current study, timed-pregnant rats were exposed to lead acetate (0.2% in the drinking water) 24 h following birth at postnatal day 1 (PND 1). Dams and pups were continuously exposed to lead through the drinking water of the dam until PND 20. Postnatal exposure in the pups resulted in altered mRNA levels of the following apoptotic and neurotrophic factors: caspase 2 and 3, bax, bcl-x, brain-derived neurotrophic factor (BDNF). Ribonuclease protection assays were conducted to measure the factors simultaneously at the following postnatal time points: 9, 12, 15, 20, 25, days. Our results suggest a brain region- and time-specific response following lead acetate exposure. The region most vulnerable to alterations occurs in the hippocampus with alterations beginning at PND 12, in which caspase 3, bcl-x, BDNF increase with lead exposure. Significant treatment effects were not observed for both the cortex and cerebellum.

Figure 1

Profile of mRNA levels of caspase 2, caspase 3, and bax in the cortex following postnatal lead acetate exposure (0.2% in the drinking water). Samples from 5-6 individual animals per group, both Pb exposed and controls, were examined at postnatal day (PND) 9, 12, 15, 20, and 25. Data are expressed as means ± SEM (n=5-6).

Figure 2

Profile of mRNA levels of bcl-x and BDNF in the cortex following postnatal lead acetate exposure (0.2% in the drinking water). Samples from 5-6 individual animals per group, both Pb exposed and controls were examined at postnatal day (PND) 9, 12, 15, 20, and 25. Data are expressed as means ± SEM (n=5-6) (# denotes p<0.05 as determined by Fisher’s LSD post-hoc analysis following ANOVA significant main effect of PND (for bcl-x (F=3.173, df=4) and BDNF (F=6.616, df=4).

Figure 3

Profile of mRNA levels of caspase 2, caspase 3, and bax in the hippocampus following postnatal lead acetate exposure (0.2% in the drinking water). Samples from 5-6 individual animals per group, both Pb exposed and controls were examined at postnatal day (PND) 9, 12, 15, 20, and 25. Data are expressed as means ± SEM (n=5-6). Asterisk (*) and number sign (#) denote significance at p<0.05 based on Fisher’s LSD post-hoc analysis following ANOVA significant main effect of treatment (F=8.125, df=1) and PND (F=3.858, df=4). For the main effect of PND, PND 20 and PND 25 were significantly decreased compared to other time points.

Figure 4

Profile of mRNA levels of bcl-x and BDNF in the hippocampus following postnatal lead acetate exposure (0.2% in the drinking water). Samples from 5-6 individual animals per group, both Pb exposed and controls were examined at postnatal day (PND) 9, 12, 15, 20, and 25. Data are expressed as means ± SEM (n=5-6). Asterisk (*) and number sign (#) denote significance at p<0.05 based on Fisher’s LSD following ANOVA main effect of treatment (for bcl-x F=30.541, df=1; for BDNF F=9.584, df=1) and PND (for bcl-x F=4.463, df=4; for BDNF F=7.931, df=4) respectively. For the main effect of PND, PND 9 was significantly lower than any other timepoint for both bcl-x and BDNF.

Figure 5

Profile of mRNA levels of caspase 2, caspase 3, and bax in the cerebellum following postnatal lead acetate exposure (0.2% in the drinking water). Samples from 5-6 individual animals per group, both Pb exposed and controls, were examined at postnatal day (PND) 9, 12, 15, 20, and 25. Data are expressed as means ± SEM (n=5-6).

Figure 6

Profile of mRNA levels of bcl-x and BDNF in the cerebellum following postnatal lead acetate exposure (0.2% in the drinking water). Samples from 5-6 individual animals per group, both Pb exposed and controls, were examined at postnatal day (PND) 9, 12, 15, 20, and 25. Data are expressed as means ± SEM (n=5-6).