COMPARATIVE-EVALUATION OF [H-3] WIN-35428 AND [H-3] GBR-12935 AS MARKERS OF DOPAMINE INNERVATION DENSITY IN BRAIN

WIN 35428 and GBR 12935, two uptake blocker Ligands of the membrane tr ansporter for dopamine (DA), were evaluated as quantitative markers of DA innervation density in CNS tissue. From alternate rat brain slices respectively processed for either light microscope or film autoradiog raphy, counts of DA axon terminals (varicosities) labeled by uptake/st orage of [H-3]DA were matched with densitometric measurements of the s pecific binding of [H-3]WIN 35428 and [H-3]GBR 12935 in the same anato mical areas. The relation between the two parameters was examined in 1 ) the normal cingulate cortex; 2) the neostriatum severely DA-denervat ed by unilateral intramesencephalic injections of 6-hydroxydopamine; a nd 3) the neostriatum, partly DA-reinnervated by an intrastriatal graf t of fetal mesencephalic neurons after prior 6-hydroxydopamine lesion. For technical reasons, the hyperdense DA innervation of normal striat um was not amenable to such correlative testing. Data were subjected t o multilevel analysis. Specific [H-3]WIN binding at 37 degrees C was t ightly and linearly correlated with the number of DA varicosities over the full range of DA innervation densities tested. The regression lin es for intact cortex and for DA-denervated as well as DA-reinnervated neostriatum had the same slope and crossed the ordinate near zero. In contrast, [H-3]GBR 12935 binding at 37 degrees C showed no correlation with the number of DA varicosities. A linear correlation could be obt ained after incubation with [H-3]GBR 12935 at 4 degrees C in the prese nce of ZnSO4, but the intercept of this regression line remained signi ficantly above zero at origin, indicating extraneous binding to non-DA transporter sites. Providing that the hyperdense DA innervation of th e normal neostriatum does not generate a particular problem in vivo as it does in vitro, WIN 35428, but not GBR 12935, might satisfy the sel ectivity and sensitivity requirements of a quantitative marker of DA i nnervation density for eventual use in positron emission tomographic s tudies. (C) 1997 Wiley-Liss, Inc.