INTRANIGRAL ADMINISTRATION OF D-2, DOPAMINE-RECEPTOR ANTISENSE OLIGODEOXYNUCLEOTIDES ESTABLISHES A ROLE FOR NIGROSTRIATAL D-2 AUTORECEPTORSIN THE MOTOR ACTIONS OF COCAINE

Dopamine D-2 autoreceptors found on nigrostriatal dopaminergic neurons are thought to inhibit dopamine release, tyrosine hydroxylase activat ion, and spontaneous firing rate. It is likely that these receptors pl ay an important role in moderating the behavioral response to cocaine, but the lack of potent selective autoreceptor ligands has made it dif ficult to assess this contribution. We have developed an antisense pho sphorothioate oligodeoxynucleotide (ODN) against D-2 receptor mRNA, wh ich was used to reduce levels of D-2 receptors in vitro and in vivo. U nilateral administration of antisense ODN, via intracerebral cannula, into the substantia nigra of rats for several days caused dramatic con tralateral rotational behavior in response to a subcutaneous injection of cocaine. This effect was maximal by 10 min after injection of coca ine and lasted for >30 min; without cocaine, no spontaneous rotational behavior was noted. In striatal slices, the potency of sulpiride, a D -2 antagonist, in enhancing electrically stimulated dopamine release w as significantly reduced on the antisense-treated side; this is consis tent with a decrease in the striatal D-2 autoreceptor population. As m easured by quantitative autoradiography, administration of antisense O DN caused a loss of approximately 40% of nigral D-2 receptor [I-125]io dosulpride binding, compared with the untreated side. In vitro, treatm ent of WERI-27 retinoblastoma cells with D-2 antisense ODN at a concen tration of 1 mu M reduced D-2 receptor levels by 57% after 3 days. The robustness of cocaine-induced rotation and the impaired ability of su lpiride to enhance dopamine release from slices suggest that nigrostri atal D-2 autoreceptors play a direct role in reducing the motor respon se to cocaine administration. Furthermore, the absence of spontaneous rotation in antisense ODN-treated animals suggests that autoreceptor e ffects are masked by compensatory mechanisms during normal behavior.