Alterations in trk A, trk B and trk C receptor immunoreactivities in parietal cortex and cerebellum in Alzheimer's disease.
The neurotrophins nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 bind to the tyrosine kinase (trk) receptors trk A, trk B and trk C, respectively, with high affinity. We investigated the expression of the trk receptors in the parietal cortex (PC) and cerebellum of patients with Alzheimer's disease (AD) and age-matched controls. Cortical layers II-VI displayed a distinct cellular immunoreactivity for trk A and C with an emphasis in the pyramidal neurons of layers III and V. Trk B immunoreactivity was primarily located in the deeper cortical layers with a predominance in layer V. There was a decrease in trk A and C immunoreactivity in the PC of AD cases, while trk B density appeared to be unchanged. In addition, cerebellar Purkinje cells revealed a distinct immunoreactivity for trk C both in control and AD cases, suggesting trk C may be important in the maintenance of these cells in the aged brain.