A new dopamine agonist in dopamine deprived systems: FCE 23884

The D1 receptor-mediated effects of the ergoline derivative LEK-8829 in rats with unilateral 6-hydroxydopamine lesions

1. Previous experiments have suggested a potential atypical antipsychotic activity of the ergoline derivative LEK-8829. In vitro experiments showed a high affinity to 5-HT1A, 5-HT2 and D2 receptors (the ratio of pKi values 5-HT2/D2 = 1.11) and a moderate affinity to D1 receptors. In vivo experiments showed antagonism of dopamine and 5-hydroxytryptamine (5-HT) receptor-linked behaviours. 2. In the present study, the rats with unilateral dopaminergic deafferentation of the striatum, induced by the lesion of the median forebrain bundle with 6-hydroxydopamine (6-OHDA), were used to determine the effects of LEK-8829 on turning behaviour and on striatal c-fos mRNA levels. 3. The administration of LEK-8829 induced a long lasting contralateral turning behaviour that was dose-dependent. It was found that the specific D1 receptor antagonist SCH-23390 but not the D2 receptor antagonist haloperidol or 5-HT1A antagonist pindolol, dose-dependently inhibited the turning behaviour induced by LEK-8829. 4. In an attempt to clarify the D1:D2 receptor interactions involved in the action of LEK-8829 in the 6OHDA model, we used in situ hybridization histochemistry to compare the effect of SCH-23390 pretreatment on striatal c-fos mRNA expression induced either by LEK-8829 or by the typical antipsychotic haloperidol. 5. LEK-8829 induced a bilateral striatal c-fos mRNA expression that was significantly higher in the denervated striatum as compared to the intact striatum and was completely blocked on both sides by pretreatment with SCH-23390. In contrast, haloperidol-induced striatal c-fos mRNA expression was limited to the innervated striatum and was not blocked by SCH-23390. 6. Our data demonstrate an intrinsic activity of LEK-8829 on D1 receptors that is potentiated in the dopamine-depleted striatum. We conclude, therefore, that the putative atypical antipsychotic LEK-8829 may prove useful as an experimental tool for the study of D1:D2 receptor interactions and could have beneficial effects in the treatment of drug-induced psychosis in patients with Parkinson's disease.

Effect of the putative dopamine D1 agonist and D2 antagonist FCE 23884 on Parkinson's disease

The ergoline derivative FCE 23,884 acts as a dopamine D1 agonist in untreated parkinsonian animals and as a D2 antagonist in animals whose dopamine system is intact or levodopa treated. To evaluate whether this dual action might benefit patients with Parkinson's disease (PD) who have developed levodopa-induced dyskinesias, the motor effects of FCE 23,884 were examined in seven such individuals using a double-blind, placebo-controlled design. At doses up to the maximum tolerated dose (3.5 +/- 0.5 mg), FCE 23,884 monotherapy did not affect parkinsonian severity. On the other hand, coadministration of FCE 23,884 with a mildly dyskinetic dose of levodopa, infused intravenously under steady-state conditions, reduced the antiparkinson response by 54 +/- 19% and tended to diminish dyskinesia severity. The results thus fail to suggest any useful role for FCE 23,884 in the symptomatic treatment of PD. Although D2 receptor blockade provided by FCE 23,884 antagonizes both the antiparkinson and dyskinesigenic responses to levodopa, the degree of D1 receptor stimulation appears insufficient to ameliorate parkinsonian symptomatology.