2, 4-dichloro phenoxy acetic acid alters monoamine levels, acetylcholinesterase activity & operant learning in rats.

2, 4-Dichloro phenoxy acetic acid (2, 4-D) was given at 100 mg/kg body weight per day by oral intubation from postnatal days 2 to 25 to assess its effect on the levels of norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) in olfactory bulb (OB), hippocampus (HI), visual cortex (VC), cerebellum (CB) and brainstem (BS). NE levels were increased in OB, HI, VC and BS at 10 days of age. However, by 25 days, NE levels were decreased in OB, HI and VC. DA levels were also increased in OB, HI, VC and CB at 10 days of age and again decreased by 25 days in OB, HI and VC. 5-HT levels were increased in HI, CB and BS at 10 days and in VC and CB at 25 days of age. Reduced acetylcholinesterase (AChE) activity in OB and HI and monoamines in different brain regions at 25 days of age might be responsible for the observed deficits in both acquisition and rate of pedal press response when animals were exposed chronically to 2, 4-D during postnatal brain development.