Study of tyrosine hydroxylase immunoreactive neurons in neonate rats lactationally exposed to 2,4-dichlorophenoxyacetic acid

Dopaminergic neurons from the midbrain nuclei substantia nigra (SN; A9) and ventral tegmental area (VTA; A10) were investigated by tyrosine hydroxylase (TH) immunostaining in neonate rat brains exposed to 2,4-dichlorophenoxyacetic acid (2,4-D) through lactation. Dorsal raphe serotonin (5-HT) projections to SN and VTA were also studied by 5-HT transporter (5-HTT) immunostaining and results were quantified by image analysis. Twenty-five-day-old pups exposed to 2,4-D through mothers milk were used. Dams were intraperitoneally administered 70 or 100 mg/kg/day of 2,4-D from the 9th to the 25th postpartum day. After 100 mg/kg of 2,4-D exposure, a 25% diminution in the SN and a 33% diminution in the VTA neurons' TH immunostaining along with a significantly 5-HT fiber density diminution were observed. The present work supports previous reports which suggest that exposure to 2,4-D during development has multiple effects on CNS.