The serotonergic system in ageing and Alzheimer's disease.

Alzheimer's disease (AD) is one of the major neurodegenerative diseases that deteriorates cognitive functions and primarily affects associated brain regions involved in learning and memory, such as the neocortex and the hippocampus. Following the discovery and establishment of its role as a neurotransmitter, serotonin (5-HT), was found to be involved in a multitude of neurophysiological processes including mnesic function, through its dedicated pathways and interaction with cholinergic, glutamatergic, GABAergic and dopaminergic transmission systems. Abnormal 5-HT neurotransmission contributes to the deterioration of cognitive processes in ageing, AD and other neuropathologies, including schizophrenia, stress, mood disorders and depression. Numerous studies have confirmed the pathophysiological role of the 5-HT system in AD and that several drugs enhancing 5-HT neurotransmission are effective in treating the AD-related cognitive and behavioural deficits. Here we present a comprehensive overview of the role of serotonergic neurotransmission in brain development, maturation and ageing, discuss its role in higher brain function and provide an in depth account of pathological modifications of serotonergic transmission in neurological diseases and AD.