The purpose of this work is to evaluate Fourphit, an acylating derivative of phencyclidine, as a probe for exploring the biochemical and behavioral relevance of the stimulant binding site on the dopamine transport complex. This proposal is an extension of previous work with Metaphit, an isomer of Fourphit, which has been shown to irreversibly inhibit both stimulant binding and dopamine uptake in vitro, and also to block stimulant behaviors caused by cocaine and other stimulant drugs in vivo. The impetus for this proposal was provided by preliminary studies showing that Fourphit may be more selective than Metaphit for the stimulant binding site. The [3H]methylphenidate radioreceptor assay will be used to study the irreversible inactivation of the stimulant recognition site in rat striatal tissue following both in vitro and in vivo exposure to Fourphit. Parallel experiments will examine the effect of the acylating compound on transport of [3H]dopamine by synaptosomes from the same tissue. The relative selectivity of Fourphit for the dopamine carrier compared to the norepinephrine and serotonin uptake complexes will be assessed by determining its ability to irreversibly inhibit [3H]desipramine and [3H]paroxetine binding, respectively. The selectivity of the compound will be further evaluated by screening it against receptors not associated with transport systems. Antagonism of stimulant-induced locomotor and stereotypical behaviors by Fourphit will be determined. These behaviors, considered to be models for the reinforcing and psychosis-producing properties of stimulant drugs, are thought to be controlled by the mesolimbic and nigrostriatal dopaminergic pathways, respectively. The planned experiments may advance our understanding of the differential responsiveness of these neuronal tracts to stimulant agents. Finally, the potential usefulness of radiolabeled Fourphit for the isolation and purification of the stimulant binding site will be investigated by preparing autoradiograms from slab gels obtained by resolving solubilized [JH]Fourphit-labeled membrane proteins by two-dimensional gel electrophoresis. This work has important implications not only for advancing our understanding of how stimulant drugs affect dopamine uptake, but also for the eventual development of an antagonist to discourage human cocaine abuse.
| Schweri, M M; de Costa, B R; Rice, K C (1998) Fourphit, an acylating phencyclidine derivative, attenuates cocaine-induced hyperactivity in rats. Pharmacol Biochem Behav 60:615-23 |
| Schweri, M M; Thurkauf, A; Mattson, M V et al. (1992) Fourphit: a selective probe for the methylphenidate binding site on the dopamine transporter. J Pharmacol Exp Ther 261:936-42 |
