POTENT COCAINE ANALOGS INHIBIT [H-3] DOPAMINE UPTAKE IN RAT MESENCEPHALIC CELLS IN PRIMARY CULTURES - PHARMACOLOGICAL SELECTIVITY OF EMBRYONIC COCAINE SITES

The cellular localization of the cocaine binding sites in primary cult ures of embryonic rat mesencephalic cells was previously reported to d iffer from that observed in adult rat brain. In order to know whether this different localization was associated with a different pharmacolo gical selectivity, we tested the effect of new cocaine analogs on trit iated dopamine ([H-3]DA) uptake in primary cultures of rat embryonic m esencephalic cells. In these cultures, [H-3]DA was taken up by a nomif ensine-sensitive, but desipramine and fluoxetine-insensitive process, reflecting selective uptake by the dopaminergic transporter. 3beta-(4- Chlorophenyl)tropan-2beta-carboxylic acid methyl ester (RTI-COC-31) wa s by far the most potent inhibitor of the [H-3]DA uptake, presenting a n IC50 of 3.8 nM, while the corresponding analog with an unsubstituted phenyl ring (WIN 35,065-2) was 38 times less potent. The enantiomer o f WIN 35,065-2, namely WIN 35,065-3, was 30 times less potent than the former. A similar pattern was found for the relative ability of these compounds to inhibit binding of the radiolabeled cocaine derivative [ I-125]RTI-55 to membranes prepared from mesencephalic cultures. The or der of potencies found for the three cocaine analogs on mesencephalic cultures was similar to that previously obtained in [H-3] WIN 35,428 b inding experiments and [H-3]DA uptake inhibition in adult rat striatum , suggesting that the pharmacological selectivity of cocaine sites fun ctionally related to the DA transporter in cultured embryonic neurons does not differ from that obtained in adult rat brain.