EFFECTS OF MATERNAL LEAD-EXPOSURE ON FUNCTIONAL PLASTICITY IN THE VISUAL-CORTEX AND HIPPOCAMPUS OF IMMATURE RATS

We examined the amount of long-term potentiation (LTP) in slices from the visual cortex and hippocampus of pre- and postnatally lead-exposed rats and controls at postnatal days (PND) 12-20. A dietary lead intak e of 750 ppm by the dams resulted in a mean blood lead concentration i n the suckling offspring of about 17 mu g/dl. While high-frequency sti mulation (HFS) of the white matter induced LTP of the field potentials in layers II/III in cortical slices of ten out of the 14 control rats , only three of the twelve lead-exposed rats showed a small amount of LTP. However, in slices from seven of the twelve lead-exposed rats a l ong-term depression was found following HFS. Furthermore, paired-pulse inhibition was weaker in cortical slices from the lead-exposed as com pared to the control rats. In the CA1 hippocampal region the amount of LTP was significantly reduced in the lead-exposed group only in slice s taken from rats at PND 16-20, while no differences were seen in slic es from younger animals. It is concluded that even low level lead expo sure impairs functions of the visual cortex in the immature rat. We su ggest that the developing hippocampus is able to compensate for lead-i nduced functional deficits in the 2nd postnatal week, being more vulne rable at older ages.