It, is also quite similar in structure. Yet it is not, a partial agonist. This and a related compound, ACR16, bind to the receptors but, show low affinity for dopamine D2 receptors in vitro. The effect of ACR16 was compared with that, of haloperidol on in vivo displacement in rats of raclopride, a dopamine D2 receptor antagonist, (Figure 6). The doseresponse

curve with ACR16 was much shallower, and it was impossible Inhibitors,research,lifescience,medical to determine when it. would have reached zero. This points to a Selleck GSKJ4 subpopulation of dopamine D2 receptors that is available to haloperidol but less avail ablc-and perhaps not available at all-to dopamine stabilizers. These compounds are dopamine receptor antagonists, able to displace at dopamine receptors, but. not to the same extent as haloperidol. Figure 6. Striatal in vivo occupancy studies: displacement of 3Hradopride binding by ACR16 and haloperidol. (Reprinted with the permission of M. Rigby, Merck Pharmaceuticals, West Dayton, Middlesex, UK). We suggest, Inhibitors,research,lifescience,medical that it is the extrasynaptic subpopulation of dopamine receptors that is available to

Inhibitors,research,lifescience,medical these compounds, and that the synaptic subpopulation is less readily available. Insofar as synaptic function is responsible for basic dopamine activity, stabilizers have an insufficient impact on the dopamine system to produce extrapyramidal side effects and the cognitive repercussions of hypodopaminergia.The receptors that gear up dopamine function to an extent sufficient, to produce psychosis are proposed to be predominantly extrasynaptic. Because partial dopamine antagonists can reach extrasynaptic receptors, including the autoreceptors but, not synaptic receptors, Inhibitors,research,lifescience,medical they can exert antipsychotic activity while simultaneously protecting the synapse. In summary, the hypothetical mechanism of action of dopamine stabilizers or partial antagonists in psychosis is Inhibitors,research,lifescience,medical that they preferentially inhibit extrasynaptic dopaminergic transmission while leaving synaptic transmission and basic dopamine function essentially intact.

Clinical deployment, of these compounds remains largely experimental. Both have displayed documented antipsychotic see more activity and have been studied to similar degrees in small clinical groups. Short-term studies have shown (-)-OSU6162 to be an effective antipsychotic and antidyskinetic. Long-term studies remain to be performed. ACR16 has been found to be safe in phase I studies in healthy volunteers and has shown promising results in early phase II studies in patients with schizophrenia, Parkinson’s disease, and Huntington’s disease. In schizophrenic patients, add-on ACR16 significantly decreased Positive and Negative Syndrome Scale (PANSS) ratings after 2 weeks versus no effect with placebo (Figure 7). Dyskinesia was significantly reduced with both compounds.