Ontogenesis of adenosine receptors in the central nervous system of the rat

The ontogeny of adenosine receptors was studied in rat brain and spinal cord using the specific ligand [³H]cyclohexyladenosine ([³H]CHA). The [³H]CHA affinity constant (K_d) and the maximum receptor binding capacity (B_max) were analyzed at all ages and in all CNS regions studied. Throughout development the K_d of [³H]CHA binding remained relatively stable and for cortex, cerebellum, subcortex, midbrain, brainstem and spinal cord ranged from 2.2 ± 0.2 to 5.5 ± 0.6 nM (mean ± S.E.M.). In contrast, the B_max values from 1- and 90-day animals increased by as little as 2-fold in subcortical regions and by as much as 9- and 16-fold in cortex and cerebellum, respectively. The highest density of binding sites was observed in subcortical structures and the lowest in brainstem and midbrain. In cortex, a steady increase in receptor number began at day 1 and stopped at the adult level by 21 days. In cerebellum, maximum receptor proliferation began at about 14 days and continued to adulthood. Other CNS regions showed intermediate rates of receptor development. These differences may reflect both the pattern of postnatal neurogenesis in the rat CNS and the maturation of those neural elements containing adenosine receptors.