[ super(3)H]SCH 58261, a selective adenosine A sub(2A) receptor antagonist, is a useful ligand in autoradiographic studies

We have characterized the new potent and selective nonxanthine adenosine A sub(2A) receptor antagonist SCH 58261 as a new radioligand for receptor autoradiography. In autoradiographic studies using agonist radioligands for A sub(2A) receptors ([ super(3)H]CGS 21680) or A sub(1) receptors (N super(6)-[ super(3)H]cyclohexyladenosine), it was found that SCH 58261 is close to 800-fold selective for rat brain A sub(2A) versus A sub(1) receptors (K sub(i) values of 1.2 nM versus 0.8 mu M). Moreover, receptor autoradiography showed that [ super(3)H]SCH 58261, in concentrations below 2 nM, binds only to the dopamine-rich regions of the rat brain, with a K sub(D) value of 1.4 (0.8-1.8) nM. The maximal number of binding sites was 310 fmol/mg of protein in the striatum. Below concentrations of 3 nM, the nonspecific binding was