The antidepressant effects of anticholinergic drugs.

Acetylcholine is a neurotransmitter that is important for communication between neurons and muscle, is involved in direct neurotransmission in the autonomic parasympathetic nervous system, and has been implicated in cognitive processing, arousal, and attention in the brain. The cholinergic-adrenergic hypothesis of mood disorders states that a given affective state might represent a balance between central cholinergic and adrenergic neurotransmitter activity in those areas of the brain regulating moods. According to this hypothesis, depression would be the clinical manifestation of a state of cholinergic dominance, whereas mania would reflect adrenergic dominance. On the basis of this hypothesis, anticholinergic drugs have been investigated as potential treatments for depression, but study results have not shown consistent antidepressant effects. However, the dosage dependency of scopolamine's effect across different studies and the lack of antidepressant effects with other anticholinergic drugs suggest that a specific muscarinic receptor subtype might be most relevant to the potential antidepressant mechanism of action of anticholinergic drugs.