Neuroleptics and dopamine transporters

The effects of neuroleptic treatments on dopamine transporters and on dopamine receptors was investigated in the forebrain of adult rats treated for 21 days with either haloperidol, clozapine or saline. The dopamine D-1 receptors, labeled with [H-3]SCH23390, increased in nucleus accumbens, latero-dorsal rostral neostriatum and substantia nigra, after clozapine but not haloperidol. The dopamine D-2 receptors, studied with [SH]raclopride, increased in nucleus accumbens and in dorsolateral, ventro-medial and dorso-medial quadrants of the rostral neostriatum after either haloperidol or clozapine treatments, and also in latero-ventral rostral neostriatum but only after haloperidol. Haloperidol also up-regulated D-2 receptors in rostral and caudal neostriatum, but clozapine produced a more uneven increase, especially in caudal neostriatum. In contrast, the densities of dopamine uptake sites, or transporters, labeled with [I-125]RTI-121, remained unchanged after both neuroleptic treatments. The observation that dopamine transporters are resistant to treatments that modify D-1 and D-2 receptors indicates that these uptake sites can probably be ruled out as the target of neuroleptic drugs, and that dopamine receptor up-regulations can indeed occur independently of the densities of nerve endings at the terminal fields of innervation.