Dopamine differently modulates central cholinergic circuits in patients with Alzheimer disease and CADASIL.

[cadasil]

Short -latency afferent inhibition (SAI ) technique gives the opportunity to non-invasively test an inhibitory circuit in the human cerebral motor cortex that depends mainly on central cholinergic activity . Important SAI abnormalities have been reported in both patients with Alzheimer disease (AD ) and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL ), a model of "pure " vascular dementia (VD ). Interestingly , a normalization of SAI was observed in AD after levo-dopa (L-dopa ) administration . We aimed to determine whether the pharmacological manipulation of the dopaminergic system can also interfere with SAI test in CADASIL patients , compared with AD patients and healthy controls . SAI was found to be significantly reduced in both patient groups . L-Dopa significantly increased SAI in the AD patients , while it failed to restore SAI abnormality in CADASIL patients . Therefore , L-dopa-mediated changes on SAI in AD patients seem to be a specific effect . The present study supports the notion that relationship between acetylcholine and dopamine systems may be specifically abnormal in AD . L-Dopa challenge may thus be able to differentiate the patients with AD or a mixed form of dementia from those with "pure " VD .