Dopamine-beta-hydroxylase immunohistochemical study in the locus coeruleus of neonate rats exposed to 2,4-dichlorophenoxyacetic acid through mother's milk.

Dopamine-beta-hydroxylase (DbetaH), the enzyme that synthesizes noradrenaline from dopamine, was studied in the locus coeruleus (LC) of neonate rats exposed to 2,4-dichlorophenoxyacetic acid (2,4-D) through lactation for 14 days (from PND 9 to 22). Pups (22 days old) were anesthetized and fixed by transcardiac perfusion. Control and treated serial sections from brain stem--which correspond with the LC according to the Paxinos and Watson atlas--were simultaneously processed by an immunohistochemistry method for the DbetaH detection. Using an image analysis system, the immunostaining optical density (OD) was measured as an estimation of the enzyme content, and an OD significant decrease in the LC of 2,4-D-exposed animals was observed. As tyrosine hydroxylase levels in the LC are regulated by serotonin and in a previous study we demonstrated that this neurotransmitter was increased in 2,4-D-exposed pups, an indirect effect through serotonergic inhibition could be involved in the decreased DbetaH synthesis in the LC of these pups.