4.2. Project Summary (Abstract): The long-term goal of the proposed research is to understand the role ofthe cholinergic system in manganese (Mn)-induced neurological dysfunction. Today, millions of welders,smelters, and miners in the United States (US) and throughout the world are chronically exposed to Mn-containing fumes, aerosols, and particles on a regular basis. Furthermore, drinking water with naturally highMn concentrations is now recognized as an important source of chronic Mn exposure to large segments of thepopulation in the US and globally. Therefore, the number of humans that are potentially exposed to neurotoxiclevels of Mn worldwide are much larger than previously recognized, making it a public health problem of globalproportion. Exposure to contemporary levels of Mn results in impairments in working memory and executivefunction and produces deficits in fine motor control and postural stability. These neurological effects of chronicMn exposure are likely to have a pathophysiology that involves multiple neuronal systems. Previous studiesfrom our laboratory have shown that chronic exposure to moderate levels of Mn in non-human primatesproduces dysfunction of nigrostriatal dopaminergic (DAergic) neurons by inhibiting striatal dopamine release.We now find a marked loss of striatal cholinergic interneurons (ChI) and these findings challenge the currentdogma of Mn-induced pathophysiology from a solely DAergic perspective to one in which there is disruption ofthe DAergic-Cholinergic balance in the basal ganglia.Cholinergic neurons are important in the physiology of cognition, emotion, compulsive behavior, locomotion,and gait, domains that are affected in Mn-induced neurological dysfunction. Here, we also provide initialevidence that chronic Mn exposure in non-human primates results in an apparent basal forebrain cholinergicneuron loss or injury similar to what is found in Alzheimer's disease and other neurodegenerative disorders.Thus, we propose to rigorously characterize the effect of chronic Mn exposure on choline acetyltransferase(ChAT)-positive cholinergic neurons in the caudate/putamen/nucleus accumbens as well as in the basalforebrain and pedunculopontine nucleus in the non-human primate brain (specific aim 1). These studies willuse rigorous unbiased stereological cell counting and soma size determination methods. We will alsodetermine the effect of chronic Mn exposure on vesicular acetylcholine transporter (vAChT) in cholinergic axonterminals and varicosities (specific aim 2) to assess if chronic Mn exposure produces cholinergic neuronaxonopathy. Finally, we will examine the role of neurotrophic factors on the Mn-induced loss of cholinergicneurons (specific aim 3) by measuring concentrations of Brain-Derived Neurotrophic Factor and Nerve GrowthFactor in relevant brain regions. The proposed studies will provide a more precise mechanistic understandingof Mn-induced pathophysiology that can lead to the development of cholinergic- and/or neurotrophic factor-based therapies for the treatment of Mn-induced neurological dysfunction.