Disappearance of low affinity adenosine binding sites in aging rat cerebral cortex and hippocampus.

A1 adenosine receptor binding was investigated, using the selective agonist, [3H]cyclohexyladenosine, on membranes prepared from the cerebral cortex and hippocampus of 3- and 24-month-old rats. The Scatchard analysis of the binding results obtained in the cerebral cortex of young animals showed two distinct binding sites with apparent Kd of 2 and 24 nM and Bmax of 259 and 675 fmol/mg protein, respectively. Conversely, in the old rats only one population of high affinity binding sites with a Kd of 2.2 nM and a Bmax of 450 fmol/mg protein was found. Displacement curves of labelled ligand carried out on hippocampal membranes also demonstrate the disappearance of a low affinity subpopulation of A1 receptors in the old rat brain.