**11. AD-PD-MS (multiple sclerosis)**

In addition to the co-morbid manifestation of neuropsychiatric disorders with neurodegenerative diseases, potential co-morbid occurrence of neurodegenerative diseases such as AD and PD also exists [72]. This might not be very surprising given that the neurobiological substrates of one neurogenerative disease such as mitochondrial dysfunction, oxidative stress and inflammation may be very similar to another disease, except that the anomalies may be confined to specific brain areas and/or circuitries in different diseases. However, when there is an overlap or cross-over of circuitries, similar phenotypes could be manifested. For example, correlation between cholinergic system alterations, oxidative stress-and neuroinflammation in MS has been noted. MS is an autoimmune and demyelinating disease of the central nervous system, characterized by leucocytes infiltration, demyelination, axonal degeneration and neuronal death. As a result of disrupted central communication, different symptoms including vision loss, pain, fatigue, and impaired coordination may be manifested.

The role played by ACh in MS has been recently investigated. Cholinergic alterations may contribute to the dysregulated inflammatory processes of MS [73, 74]. Whether muscarinic or nicotinic receptor manipulation may be of therapeutic potential in MS also, needs to be further investigated.
