Effects of enucleations and visual deprivation on adenosine A₁ and A₂ receptor binding in superior colliculus of rat

Adenosine receptors of A₁ and A₂ subtypes on retino-collicular projections in rat were studied using [³H]cyclohexyladenosine ([³H]CHA), [³H]N-ethylcarboxamidoadenosine ([³H]NECA), and [³H]CGS 21680. Unilateral enucleation significantly reduced by 51% [³H]CHA binding to A₁ sites, and by 42% the A₁ component of [³H]NECA binding in contralateral SC. The binding of [³H]CGS 21680 and [³H]NECA to A₂ sites was not significantly affected by enucleation procedures. No significant reductions in adenosine receptor binding were observed in SC from rats exposed to a dark environment for three weeks. The reductions in A₁ but not A₂ adenosine receptor binding strongly suggests that A₁ sites are presynaptically located on retinal projections and are vulnerable to deafferentiation-, but not visual deprivation-induced decreases.