Up-regulation of adenosine A1 receptors in frontal cortex from Pick's disease cases

The adenosine A₁ receptor (A₁R)–adenylyl cyclase (AC) pathway was studied in post-mortem human frontal and occipital cortex from Pick's disease (PiD) cases and age-matched nondemented controls. In frontal cortex, the main brain area affected in PiD, A₁Rs, determined by radioligand binding, Western blotting and real-time PCR assays, were significantly increased in PiD samples, suggesting up-regulation of this receptor. AC activity was determined in basal and stimulated conditions via stimulatory guanine nucleotide binding proteins (Gs) using GTP, or directly with forskolin. Basal AC activity was reduced in brains from PiD cases. This agrees with the decrease in AC type I (AC I) level detected by Western blotting. However, inhibition of forskolin-stimulated AC activity by a selective A₁R agonist was significantly increased in brains from PiD. In occipital cortex, adenosine A₁R numbers were similar in control and PiD cases, and no significant differences were found in A₁R-mediated AC inhibition. These results show that the adenosine A₁R–AC transduction pathway is specifically up-regulated and sensitized in frontal cortex brain in PiD.