[3H]Nipecotic Acid Binding to γ‐Aminobutyric Acid Uptake Sites in Postmortem Human Brain

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Abstract
Binding of [3H]nipecotic acid, a proposed marker for GABAergic neurons, was investigated in postomortem human brain by use of a centrifugation assay. Binding was displaceable, apparently saturable, and to a single site, with typical KD and Bmax values of 1.85 .mu.M and 124.2 pmol/mg of protein in the hippocampus. Regional distribution studies indicated a heterogeneous population of [3H]nipecotic acid binding sites with highest concentrations in the lateral globus pallidus. Putamen tissue from four cases of Huntington''s disease showed a marked reduction in [3H]nipecotic acid binding. Binding correlated with both age and postmortem delay in the hippocampus. There was an effect of agonal state in which prolonged illness before death apparently caused a reduction in binding. Our results indicate that [3H]nipecotic acid may be used successfully as a marker for neuronal GABAergic uptake sites in human brain, but that the effects of variables such as age, postomortem delay, and agonal state must always be taken into account.