Although comprising only 1–3% of all striatal neurons, cholinergic interneurons (thought to correspond to the tonically active neurons, TANs) have widespread connections throughout the striatum and provide the sole source of acetylcholine (ACh) to striatum [1]. The striatum contains some of the highest levels of cholinergic biomarkers in the brain, including, muscarinic receptors, cholinesterase and others [2]. As reviewed by Cragg, 2006 and Exley, 2008, [3,4], modulation of ACh and its interaction with dopamine (DA) are critical for normal striatal function [3,4]. Additionally, in a 2007 review, Pisani discussed how dysfunction of cholinergic signaling is associated with pathophysiological changes in movement disorders, such as Parkinson’s disease (PD), Huntington’s disease (HD) and dystonia [5,6].
