Hippocampal mossy fiber pathway development in normal and postnatally lead-exposed rats

Lead (Pb)-induced alterations in the postnatal development of the hippocampal formation have recently been suggested as underlying many of the behavioral changes observed after early Pb exposure. This study was thus designed to assess hippocampal mossy fiber pathway (MFP) development in both normal and postnatally Pb-exposed animals. From postnatal days 1 (P1) to 25, Long-Evans hooded rat pups were exposed to Pb through the maternal milk of dams fed 4.0% PbCO3, by weight, in ground laboratory chow. Control pups suckled dams receiving a Na2CO3 control diet. On P25 and P60, weight-matched pairs of Pb-treated and control animals were selected for morphometric evaluation of the MFP following Timm's silver sulfide staining. An increase in the overall length, as well as a reduction in width of the MFP in the CA3 region of the hippocampus of control animals were observed between P25 and P60. Examination of the MFP of P25 Pb-exposed animals indicated severe reductions in the development of this pathway for all parameters measured. At P60, significant reductions in MFP development were still observed in Pb-exposed animals; however, a large degree of recovery in the later-forming parts of the MFP was evident.