Clinical evidence has demonstrated that there is an upregulation of beta-2 adrenoceptors at the hippocampus and frontal cortex of AD patients, suggesting a compensation for reduced noradrenergic input, while muscarinic M1 receptor densities have been shown to be largely unchanged, suggesting reduced cholinergic innervation as the cause of loss of cholinergic signalling in AD [57]. Here, ADRB2 is linked to Alzheimer disease.