Receptor alterations in manganese intoxicated monkeys

The density of four different receptors and one marker of dopamine uptake sites were analyzed in monkey brains after manganese exposure (0.1 g manganese per month during 26 months, a dose comparable to that workers might inhale in dusty environments) by means of quantitative receptor autoradiography. The binding of 3H-mazindol to the dopamine uptake sites was reduced by 75% in both the head of the caudate nucleus and putamen, while it remained unchanged in the other regions analyzed. The binding of the D1 receptor ligand 3H-SCH 23,390 was reduced about 45% in the same areas as mazindol binding, while the density of D2 receptors was unaffected. The muscarinic acetylcholine receptors as well as GABAA receptors remained also unchanged in all brain areas analyzed after manganese exposure. Thus the dopaminergic neurons must be considered to be vulnerable to manganese concentrations attainable in the work environment. Our results also indicate that postsynaptic structures containing D1 receptors are sensitive while cells containing D2 receptors are either spared or compensated for by up-regulation of the number of receptors on remaining sites.