**2. Brain ACh pathways and their significance**

An extensive local interneuron network in brain areas involved in motor, cognitive and reward activities such as the striatum, nucleus accumbens, and neocortex utilize ACh as a neurotransmitter. In addition, cholinergic pathways connecting the basal forebrain, a complex of 4 cholinergic nuclei that project to: cerebral cortex, hippocampus, amygdala and the olfactory bulb, are critical in regulating cognition, motivation, hedonic state and reinforcement. Cholinergic input to the substantia nigra pars compacta (SNpc), ventral tegmental area (VTA), thalamus and hypothalamus, areas critical in regulating motor, reward and endocrine systems are provided by the pedunculopontine nucleus (PPN) and laterodorsal tegmental nucleus (LDTN) [1]. Moreover, lateral habenula (LatH), part of a complex nucleus which connects the midbrain to the limbic forebrain and uses ACh, has received considerable attention because of its potential role in cognition and in the pathogenesis of various psychiatric disorders. The medial habenula (MedH), which can be further subdivided into a dorsal region containing non-cholinergic excitatory neurons such as tachykinin and substance P and a ventral region containing dense cholinergic neurons, has recently been investigated more thoroughly. It is now believed that cholinergic projections of MedH is involved in mood regulation as well as drug addiction and that manipulation of this system may be therapeutically exploited [2].
