Tyrosine kinase A-nerve growth factor receptor is antigenically present indystrophic neurites from a variety of conditions but not in Alzheimer's disease

Tyrosine kinase A (TrkA), a high affinity receptor for nerve growth factor (NGF), is activated during differentiation and regeneration of selective ne uronal population. We investigated presence, distribution and expression of TrkA in frontal cortex from cases with Alzheimer's disease (AD), normal ag ing and a variety of conditions (AIDS, cystic fibrosis, cerebral infarcts) in which neuroaxonal dystrophy occurs. TrkA was immunocytochemically detect ed in 90% of dystrophic neurites surrounding amyloid deposits in normal agi ng, as well as in all not amyloid-related dystrophic neurites identified by ubiquitin immunoreactivity. Conversely, the amyloid associated dystrophic neurites were not TrkA reactive in AD tissue. The levels of TrkA protein an d mRNA in AD frontal cortex did not significantly differ from those of non- demented aged controls. The absence of TrkA activation in amyloid associate d neurites in AD, but not in normal aging, indicates a different reaction o f neuronal tissue to amyloid (protein (A beta) deposition, and suggests tha t other factors, besides A beta, mediate neuronal degeneration in AD. (C) 1 999 Elsevier Science Ireland Ltd. All rights reserved.