Calcium antagonist, adenosine A1, and muscarinic bindings in rat hippocampus after transient ischemia.

The protective roles of Ca2+ channel blockers against ischemic hippocampal damage are still debated. We used autoradiography to study postischemic L-type Ca2+ channels (1,4-dihydropyridine Ca2+ channel blocker binding), adenosine A1 receptors, and muscarinic cholinergic receptors in the rat hippocampus using [3H]PN200-110 (PN), [3H]cyclohexyladenosine (CHA), and [3H]quinuclidinyl benzilate (QNB), respectively, in 49 rats subjected to 20 minutes of forebrain ischemia. The rats were decapitated after 1 (n = 7), 3 (n = 7), 6 (n = 8), 12 (n = 7), 24 (n = 6), 48 (n = 6), or 168 (n = 8) hours of recirculation; eight control rats were sham-operated but experienced no cerebral ischemia. Reduced receptor binding preceding the delayed death of CA1 pyramidal cells was first observed in the stratum oriens of the CA1 subfield. Significant reductions in [3H]PN, [3H]CHA, and [3H]QNB bindings of this stratum compared with control were noticed after 3 (35%, p less than 0.01), 12 (31%, p less than 0.01), and 1 (10%, p less than 0.05) hours of recirculation, respectively. By 168 hours after ischemia (when the populations of CA1 pyramidal cells were depleted) all strata in the CA1 subfield had lost most of their receptor sites, and [3H]PN, [3H]CHA, and [3H]QNB bindings in the stratum oriens were decreased to 23%, 30%, and 63% of control (p less than 0.01). Although [3H]PN binding in the CA3 subfield did not change significantly during 168 hours after ischemia, the histologically intact dentate gyrus exhibited a 31% loss of binding sites compared with control (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)