Effect of manganese treatment on the levels of neurotransmitters, hormones, and neuropeptides: modulation by stress.

Six weeks of daily intraperitoneal injection with manganese chloride (15 mg/kg body wt) reduced the normal weight gain of male Fischer-344 rats. This treatment depressed plasma testosterone and corticosterone levels, but prolactin levels were unaffected. The only significant changes in the levels of a variety of neuropeptides assayed in several regions were increases in the levels of hypothalamic substance P and pituitary neurotensin. Striatal serotonin, dopamine, and their metabolites were unchanged in manganese-exposed rats relative to saline-injected controls. However, the stress of injection combined with the effect of manganese appeared to significantly increase concentrations of striatal monoamines relative to uninjected controls.