In human brain tissues from patients dying with cerebral infarction, hypert
ensive encephalopathy, Alzheimer's disease, Huntington's disease, frontotem
poral dementia, and Creutzfeld-Jakob disease there is an activation of astr
ocytes. Such activated astrocytes display GFAP and strong 5-HT2A, but not 5
-HT2B or 5-HT2C, receptor immunoreactivity; this 5-HT2A reaction has not be
en observed in normal, nonactivated astrocytes. It is suggested that an up-
regulation of 5-HT2A receptors may be part of an early response reaction in
astrocytes, possibly designed to maintain homeostasis or to induce seconda
ry message pathways involving trophic factors or glycogenolysis. (C) 1999 A
cademic Press.