Effects of talipexole on motor behavior in normal and MPTP-treated common marmosets

Pharmacological aspects of anticancer drug-induced emesis with emphasis on serotonin release and vagal nerve activity

Cytotoxic drug-induced nausea and vomiting are the side effects most feared by cancer patients. Emesis is an instinctive defense reaction caused by the somatoautonomic nerve reflex, which is integrated in the medulla oblongata. Emesis caused by cytotoxic drugs such as cisplatin is associated with an increase in the concentration of 5-hydroxytryptamine (5-HT) in the intestine and the brainstem. It is proposed that cytotoxic drugs evoke 5-HT release from the enterochromaffin (EC) cells in the intestinal mucosa and that the released 5-HT stimulates the 5-HT receptors on the adjacent vagal afferent nerves. The depolarization of the vagal afferent nerves stimulates the vomiting center in the brainstem and eventually induces a vomiting reflex. 5-HT released from EC cells seems to mediate the cisplatin-induced emesis sensitive to 5-HT(3) receptor antagonists. The release of 5-HT from the EC cells, however, is regulated by polymodal mechanisms on autoreceptors or heteroreceptors. The precise role of 5-HT on the occurrence of vomiting has not been fully elucidated. The present review aims to describe the role of 5-HT in anticancer drug-induced emesis from the viewpoint of 5-HT release and afferent vagus nerve activity. Various methods for predicting emesis are also evaluated.

Assessment of motor behavior using a video system and a clinical rating scale in parkinsonian monkeys lesioned by MPTP

The best current model of Parkinson's disease is the primate treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Quantification of animal movement is important for the study of severity of parkinsonian syndrome induced by MPTP and response to drug treatments. Both require clinical rating scales that measure motor behavior with well-defined objective items. However, evaluations using these scales depend on the observer scoring the different items, according to his/her experience. The video image analyzer system, which produces an activity curve in correlation with the visual study of animal motor behavior, offers an automatic evaluation method that is observer-independent and reproducible. Using such an system we defined items correlated with those used in clinical rating scales that are sensitive to animal motor changes, decrease in movements with MPTP intoxication and alleviation afforded by levodopa: global locomotor activity and specific activities (climbing, social interactions, eating and drinking behaviors).

A new video/computer method to measure the amount of overall movement in experimental animals (two-dimensional object-difference method)

Evaluation of the amount of overall animal movement is important for investigations of motor control mechanisms in the central nervous system. We describe a new method to quantify overall free movements of an animal without any markers using a video camera and a personal computer equipped with a video-capture board. The operating principle is that the amount of overall movement of an object can be expressed by the difference in total area occupied by the object in two consecutive picture frames. The software for this application operates in real-time. Using this method and with proper setting for the cage and recording view, we can estimate three-dimensional movements of animals. The major advantages are low cost, easy operation and high sensitivity. The experimental results indicate that this method can be applied to various fields of motion analysis.

Effects of anti-Parkinsonian drugs on neurobehavioural changes induced by bilateral 6-hydroxydopamine lesions in rats

1. Effects of anti-Parkinsonian drugs on neurobehavioural changes induced by bilateral lesions of dopaminergic neurons were investigated in rats. 2. Dopaminergic neurons in rats were lesioned bilaterally by injection of 6-hydroxydopamine (6-OHDA; 8 micrograms) into the medial forebrain bundle at the level of the posterolateral hypothalamus. As a result, a decrease in locomotor activity and marked catalepsy and prolongation of grasping time were observed. 3. Levodopa, talipexole, bromocriptine and theophylline dose-dependently antagonized the decrease in locomotor activity induced by bilateral 6-OHDA lesions. These drugs also showed antagonistic effects on the appearance of catalepsy and prolongation of grasping time induced by bilateral 6-OHDA lesions. In contrast, trihexyphenidyl showed no antagonizing effect on the neurobehavioural changes induced by 6-OHDA lesions at any concentration tested. 4. Combined treatment with levodopa and talipexole antagonized the neurobehavioural changes induced by bilateral 6-OHDA lesions, whereas no marked changes were observed when either drug was administered separately. The same findings were noted with the simultaneous use of either levodopa (2 mg/kg) and theophylline (2 mg/kg) or talipexole (0.005 mg/kg) and theophylline (2 mg/kg). 5. These results indicate that this model may be useful for estimating the effects of drugs in the treatment of Parkinson's disease.

Effects of talipexole on contraversive rotation and functional impairment in MPTP-induced chronic hemiparkinsonian monkeys

The effects of talipexole on functional motor improvement in comparison with contraversive circling were studied in five chronic (5-7 years post MPTP-lesioned) hemiparkinsonian Macaca nemestrina monkeys. Talipexole induced contraversive rotations in a dose of 32 microg/kg for about 1 hr after i.m. injection. Larger doses (56 and 100 microg/kg, i.m.) produced less effect due to sedation. Three different rating scales were used to assess functional improvement, including a clinical parkinsonism rating scale, volitional responses to fruit presentations, and number of significant hand movements. The optimal dose of talipexole was 32 microg/kg, i.m. Functional improvement by talipexole, including clinical parkinsonian rating scales and significant hand movements, as well as contraversive circling in hemiparkinsonian monkeys, confirm that this chronic animal model is useful in preclinical testing of drugs for the treatment of human parkinsonism.

Effects of acute or prolonged administration of cabergoline on parkinsonism induced by MPTP in common marmosets

The effects of a single treatment or chronic administration of cabergoline (1-[(6-allylergolin-8beta-yl)carbonyl]-1-[3-(dimethylamino)p ropyl]-3-ethyl-urea), a potent, long-lasting dopamine receptor agonist, on parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in common marmosets were studied. The administration of 0.2 mg/kg or a higer dose of cabergoline began to reverse parkinsonism-like symptoms 60 min after a subcutaneous injection, and showed steady and constant effects throughout the observation period. For prolonged administration, 0.2 mg/kg cabergoline was injected daily for 22 consecutive days. Locomotor activity in MPTP-treated animals increased until it reached its peak on the third day, then it gradually decreased. Akinesia scores, rating the quality of movements, were also improved, and the improvement was sustained up to the last day of chronic administration. None of the animals developed abnormal behaviors after either acute or chronic administration. These results suggest that cabergoline has long-acting effects in the marmoset model of parkinsonism, and that it will be a useful agent for the treatment of Parkinson's disease, particularly in cases with fluctuating motor disabilities.

Talipexole or pramipexole combinations with chloro-APB (SKF 82958) in MPTP-induced hemiparkinsonian monkeys

The effects of two predominant dopamine D2-like receptor agonists, talipexole (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo [4,5-d]-azepine dihydrochloride, B-HT 920 CL2) and pramipexole (S(-)2-amino-4,5,6,7-tetrahydro-6-propyl-aminobenzothiazole dihydrochloride, SND 919 CL2Y), were studied alone and in combination with the selective dopamine D1-like receptor agonist chloro-APB ((+/-)6-chloro-7-8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-benz azepine hydrobromide, SKF 82958) in five chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioned hemiparkinsonian Macaca nemestrina monkeys. Talipexole induced contraversive rotation in a dose-dependent manner up to 32 microg/kg, i.m. Talipexole was more potent than pramipexole (10 vs. 32 microg/kg, i.m.), but pramipexole was more efficacious in producing contraversive rotational behavior and significant hand movements in the afflicted limb. Larger doses of chloro-APB also produced contraversive rotation. Combinations of each dopamine D2-like receptor agonist in a median effective dose with chloro-APB (23.4 and 74.8 microg/kg, i.m.) had synergistic effects, producing either addition or potentiation, depending upon the dose used. The effects noted with these combinations were less than the effect of a large dose (100 microg/kg) of pramipexole. Talipexole, in the largest dose studied (100 microg/kg, i.m.), produced sedation which was not seen with the same dose of pramipexole. No significant extrapyramidal side effects were noted with either agent.

Anti-tremor activity of talipexole produced by selective dopamine D2 receptor stimulation in cynomolgus monkeys with unilateral lesions in the ventromedial tegmentum

The anti-tremor activity of talipexole (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepine dihydrochloride, B-HT 920 CL2, Domin), a non-ergot dopamine D2 receptor agonist which possesses alpha 2-adrenoceptor agonistic and 5-HT3 receptor antagonistic properties, was examined in monkeys with a unilateral lesion in the ventromedial tegmentum. Talipexole dose dependently suppressed the tremor and had ED50 values of 34 micrograms/kg s.c. and 84 micrograms/kg p.o. The anti-tremor effect of talipexole occurred at much lower doses than that of an ergot dopamine receptor agonist, bromocriptine (2-bromo-alpha-ergocryptine mesilate, ED50; 2.5 mg/kg s.c.), and talipexole acted synergistically in combination with L-DOPA (3,4-dihydroxyphenylalanine). In ventromedial tegmentum-lesioned monkeys, anti-tremor doses of talipexole did not cause emetic behavior, but had sedative effects. Conversely, monkeys given bromocriptine exhibited oral movement, salivation and vomiting when anti-tremor effects were observed, but not marked sedative behavior at any of the doses investigated. During repeated administration of talipexole (a daily dose of 50 micrograms/kg s.c. for 21 days), the extent and duration of the anti-tremor effect did not change, but those of the sedative effect decreased gradually. The anti-tremor effect of talipexole was significantly suppressed by sulpiride, but not by SCH 23390 (7-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol) or yohimbine, while the sedative effect was inhibited by sulpiride and yohimbine. The main metabolites of talipexole had no anti-tremor or sedative effects. These results indicate that talipexole exerts its anti-tremor activity via selective dopamine D2 receptor stimulation.

5-HT3 receptor blocking properties of the antiparkinsonian agent, talipexole

1. Talipexole showed moderate displacement activity of 3H-GR 65630 binding to 5-HT3 receptors in both rat cortical and intestinal membrane fractions with Ki values of 0.35 microM and 0.22 microM, respectively. 2. Bromocriptine failed to displace the binding activity in either experimental system even at a concentration of 10 microM. 3. Both talipexole and tropisetron were found to significantly inhibit 5-HT3 receptor-mediated effects of 5-HT in isolated guinea-pig ileum or atrium; however, the effect of talipexole was weaker than that of tropisetron. 4. Bromocriptine, in contrast, had no antagonistic effects on 5-HT3 receptor-mediated activity in guinea-pig ileum or atrium. 5. It was concluded that talipexole might act as an antagonist on 5-HT3 receptors in both brain and intestinal tissues.

Antiparkinsonian activity of talipexole in MPTP-treated monkeys: in combination with L-dopa and as chronic treatment

We examined whether or not the antiparkinsonian activity of talipexole (B-HT 920, 6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]-azepine) could be optimised by combination with L-3,4-dihydroxyphenylalanine (L-dopa). Additionally, the effects of chronic treatment with talipexole on motor behavior were investigated using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated and normal common marmosets. Administration of MPTP (0.5 mg/animal i.v. once or twice) to marmosets induced persistent parkinsonian motor deficits. The antiparkinsonian activity of talipexole (40 micrograms/kg s.c.) was significantly enhanced by its combination with L-dopa (30 mg/kg i.p.). This may further support the postulated postsynaptic dopamine D2 receptor agonist properties of talipexole. Chronic treatment with talipexole (a daily dose of 40 micrograms/kg s.c. for 21 days) did not lead to tolerance to the antiparkinsonian activity in MPTP-treated animals. No obvious dyskinesia was seen throughout the chronic treatment. In contrast, in normal marmosets, talipexole at a dose of 80 micrograms/kg which is a dose sufficient to induce hyperactivity did not increase motor activity during the treatment repeated for 21 days. These results suggest that talipexole is a selective dopamine D2 receptor agonist drug of potential use in the treatment of Parkinson's disease.