CNS adenosine A1 receptors are altered after the administration of convulsant 3-mercaptopropionic acid and cyclopentyladenosine: an autoradiographic study.

Rat CNS adenosine A1 receptors were studied by quantitative autoradiography after the administration of convulsant 3-mercaptopropionic acid (MP) and an adenosine analogue cyclopentyladenosine (CPA), using 2-chloro-N6-[cyclopentyl-2,3,4,5-3H adenosine]-([3H]CCPA) as radioactive ligand. Specific binding was quantified in hippocampus, cerebellum, cerebral cortex, thalamic nuclei, superior colliculus and striatum, and the highest densities were found in CA1, CA2, and CA3 hippocampus subareas and the lowest levels in superior colliculus and striatum. MP administration (150 mg/kg, i.p.) produced significant increases in [3H]CCPA binding in CA1 subarea at seizure (15%) and postseizure (21%) and in CA2 at seizure (15%) but a tendency to decrease in dentate gyrus. There was an increase in cerebellum at seizure (18%) but no significant changes in the other studied regions. CPA injection (2 mg/kg, i.p.) enhanced [3H]CCPA binding in CA1 and CA2 areas (17-18%) but not in CA3 area of the hippocampus. When CPA was administered before MP, which delayed seizure onset, an increase in [3H]CCPA binding in CA1 hippocampus subarea (19%) and cerebellum (28%) was also observed. Results showed that the administration of convulsant MP and adenosine analogue CPA exerts differential effects on adenosine A1 receptors in CNS areas; hippocampus is the most affected area with all treatments, specially CA1 subarea, supporting an essential role in convulsant activity as well as in seizure prevention.