Lead-induced alterations of glial fibrillary acidic protein (GFAP) in the developing rat brain

Abstract

The developing nervous system is preferentially vulnerable to lead exposure with alterations in neuronal and glial cells of the brain. The present study examined early lead-induced alterations in the developing astrocyte population by examination of the developmentally regulated astrocyte specific protein, glial fibrillary acidic protein (GFAP). A developmental profile (Postnatal Day (PND) 6, 9, 12, 15, 20, and 25) for GFAP mRNA was generated for the cortex and hippocampus of developing Long-Evans hooded male rats under various lead exposure conditions: (1) prenatal (Gestational Day 13 to birth), (2) postnatal (Postnatal Day 1 to Postnatal Day 20), or (3) perinatal (Gestational Day 13 to Postnatal Day 20) exposure to lead acetate (0.2% in the drinking water of the dam). Control GFAP mRNA levels displayed a developmentally regulated profile of expression. In the cortex this was characterized by a transient elevation in peak level between PND 9 and PND 15 followed by a decline to within adult levels by PND 25. Under all lead acetate exposure conditions, the cortex showed an increase in the peak level of expression and extended the time of elevation of GFAP mRNA until PND 20. Levels of GFAP were elevated at PND 60 but not as early as PND 28. In the control hippocampus, levels of GFAP mRNA gradually increased until PND 20 followed by a sharp decline at PND 25. Postnatal and perinatal lead exposure followed a similar pattern; however, levels declined earlier at PND 20. Following prenatal lead exposure, levels of GFAP mRNA showed an earlier peak at PND 12 and a decrease as early as PND 15. By PND 60 protein level for GFAP was elevated in the postnatal lead exposure group only. As demonstrated by GFAP immunoreactivity, these lead-induced elevations were not associated with astrocyte hypertrophy. Following a physical injury in the cortex, astrocyte reactivity was similar between lead-exposed and control rats. These data suggest an alteration in the timing of astrocyte differentiation and maturation in the brain following developmental lead exposure.