Ontogeny of swimming behavior and brain catecholamine turnover in rats prenatally exposed to a mixture of 2,4-dichlorophenoxyacetic and 2,4,5-trichlorophenoxyacetic acids

Rats exposed in utero on gestational days 6-15, to nonfetotoxic and grossly nonteratogenic mixtures (50 or 100 mg/kg) of 2,4-D/2,4,5-T as found in Agent Orange (but without significant contamination with 2,3,7,8 tetrachloro-p-dioxin) manifested subtle developmental neurotoxicity. Maturation of swimming behavior was significantly delayed on postnatal day 7 in both treatment groups. The concentration of norepinephrine (NE) in whole brain was significantly increased on postnatal day 15 in both treatment groups, whereas the concentration of dopamine (DA) was increased on postnatal day 15 at 100 mg/kg. The turnover and efflux rate constant of DA in whole brain were significantly reduced whereas the turnover time increased on postnatal day 3. The efflux rate constant for NE decreased and the turnover time increased significantly on postnatal day 15 at 100 mg/kg. These data indicate the value of ontogenic assessment following exposure to small doses, which result in functional alterations in the absence of overt toxic signs.