Cerebrovascular melatonin MT1-receptor alterations in patients with Alzheimer's disease.

The pineal hormone melatonin has two major functions: as a transducer of the circadian day-night signal across the seasons, and as a vasoactive substance regulating cerebral circulation. The vasoconstrictive effects of melatonin have been postulated to be mediated by the melatonin 1a-receptor (MT1). The objective of this study was to provide the first immunohistochemical evidence for the localization of vascular MT1 in human control hippocampus compared to Alzheimer's disease (AD) patients, since regional blood flow impairments contribute to the neurodegenerative course of the disease. Both superficial and intrahippocampal arteries revealed MT1 immunoreactivity in adventitia in controls, which was distinctly increased in AD patients. The increased MT1 in AD may indicate a regulatory response to impaired melatonin levels in those patients, contributing to the regulation of cerebral circulation.