Intracerebral administration of 2,4-diclorophenoxyacetic acid induces behavioral and neurochemical alterations in the rat brain

Although, the mechanism of 2,4-dichlorophenoxyacetic acid (2,4-D) neurotoxicity remains unknown, the monoaminergic system appears to mediate some of its effects in rats as we previously reported. In this study, we examined the 2,4-D effects on locomotor activity, circling behavior and monoamine levels after the injection into the basal ganglia of male adult mts. These effects were compared with those induced after selective lesions of dopaminergic neurons with 6-hydroxydopamine (6-OHDA). 2,4-D-injected into one striatum (100 mug/rat) produced a marked depression in locomotor activity and elicited a moderate circling towards the ipsilateral side at 6 and 24 h postinjection. These behavioral changes were accompanied by a decrease and an increase of serotonin (5-HT) and homovanillic acid (HVA) levels, respectively. 2,4-D administration (100 mug/rat) into the nucleus accumbens, induced similar behavioral and neurochemical patterns to the intrastriatal 2,4-D injection, although mts did not present notorious turning. When 2,4-D was injected into one medial forebrain bundle ((MFB, 50 mug/rat), animals presented ipsilateral circling, while locomotor activity was unchanged at 3 and 7 days post-injection. These last rats also exhibited diminished levels of striatal 5-HT: dopamine (DA) and their metabolites without changes in the substantia nigra (SN). Animals sacrificed 3 and 7 days after a 6-OHDA injection into one of the MFB, presented progressive depletion of dopamine in striatum and SN. 2,4-D as well as 6-OHDA treated me into one of the MFB were challenged with low dose (0.05 mg/kg s.c.) of apomorphine (only at 7 days post-injection) to evaluate a possible DA-receptor supersensitivity. Only 6-OHDA treated rats showing a vigorous contralateral rotation activity These results indicate that 2,4-D induced a regionally-specific neurotoxicity in the basal ganglia of rats. The neurotoxic effects of 2,4-D on basal ganglia by interacting with the monoaminergic system depended not only or? the exact location of the 2,4-D injection, brit also on the dose and time period of post-injection. Toxicity produced by 2,4-D appeals to be different in monoaminergic terminals, axonal fibers, and cell bodies. (C) 2001 Elsevier Science Inc. All rights reserved.