Responses of dopaminergic and serotonergic systems to triethyllead intoxication

Rats treated with triethyllead (TEL) exhibit a behavioral supersensitivity to challenge with dopamine agonists at 7 days following administration of TEL. In the present series of experiments, some neurochemical mechanisms which may affect this behavioral supersensitivity were detected. Administration of a single dose of TEL chloride (7.88 mg/kg, SC) to male Fischer-344 rats decreased the concentrations of dopamine in hippocampus, and of serotonin in olfactory tubercle, at Day 7 posttreatment. The ratio of 5-hydroxyindoleacetic acid/5-hydroxytryptamine (one estimate of serotonin turnover) was increased in nucleus accumbens (p<0.05), with a similar trend in olfactory tubercle and striatum (p<0.10). No changes were detected in binding of [³H]spiperone to D₂ dopamine receptors in striatum or olfactory tubercle. However, although basal adenylate cyclase activity was unaltered in TEL-treated rats, the V_max for dopamine-stimulated adenylate cyclase activity was significantly elevated in olfactory tubercle. Conversely, TEL at micromolar concentrations markedly attenuated both basal and dopamine-stimulated adenylate cyclase activity in vitro in striatal homogenates. These data suggest the hypothesis that administration of TEL to rats results in an up-regulation of D₁ dopamine receptors in olfactory tubercle, and that the behavioral supersensitivity of TEL-treated animals to dopamine agonists may, in part, be a result of this receptor supersensitivity.