Long term effect of teflutixol on apomorphine-induced stereotypy and vomiting in dogs

Pharmacological differentiation of dopamine D-1 and D-2 antagonists after single and repeated administration

In single-dose experiments neuroleptics antagonize dopamine (DA)-agonist-induced stereotypies in animals. The antagonistic potency correlates with their clinical antipsychotic effects. In a series of experiments where DA-agonist-induced stereotyped gnawing in mice and rats was inhibited by neuroleptics it was shown that the antagonistic effect of butyrophenones was greatly attenuated by concomitant treatment with anticholinergics. The effect of phenothiazines was slightly attenuated and that of thioxanthenes and SCH 23390 remained unchanged. After repeated administration a differentiation is also seen in the ability of the antagonists to suppress DA-agonist-induced stereotypies. The differentiation in these experiments is similar to that seen in dopamine D-1 and D-2 receptor binding. The compounds can be classified into three pharmacological subgroups: butyrophenones (e.g., haloperidol) with affinity for D-2 receptors; phenothiazines (e.g., fluphenazine and perphenazine) with affinity for both D-2 and D-1 receptors but with preference for the D-2 receptors; and thioxanthenes (e.g., cis(Z)-flupentixol and cis(Z)-clopenthixol) with equal affinity for D-1 and D-2 receptors, and the selective D-1 antagonist SCH 23390. This compound has the same antistereotypic effect as is seen with the neuroleptics. We have also investigated the effect of the above-mentioned neuroleptics and SCH 23390 after 12 days' treatment and 3-5 days withdrawal. They were given either alone or in combination. When they were given alone a clear differentiation was seen between the groups when mice were tested for methylphenidate antagonism. The thioxanthenes and SCH 23390 retain their ability to antagonize the stereotyped gnawing; the phenothiazines show a reduced effect; and the butyrophenones have almost lost their ability to antagonize the stereotyped behavior.

Effects of S (+)-3-phenethyl-PP, a putative dopamine autoreceptors agonist with greater autoreceptor selectivity than 3-PPP enantiomers

The experiments concerned the pharmacology of the enantiomers of the phenethyl-analogue (3-phenethyl-PP) of the putative dopamine (DA) autoreceptor agonist 3-PPP. In contrast to the almost equipotency of 3-PPP enantiomers, the phenethyl enantiomers showed marked stereoselectivity. S(+)-3-Phenethyl-PP had 25 times higher affinity to D-2 DA receptors in vitro than the R(-)-enantiomer. In vivo a similar potency difference was seen for the inhibition of motility, induction of circling behaviour in 6-OHDA-lesioned rats and emetic effect in dogs. None of the enantiomers induced stereotypy and hypermotility in normal rats or in rats pretreated with reserpine and alpha-methyl-p-tyrosine. In test models for antidopaminergic activity only slight activity of either enantiomer was observed. The S(+)-enantiomer had no antagonistic effect against apomorphine- and amphetamine-induced stereotypies, no cataleptogenic activity and only partially antagonized amphetamine-induced hypermotility. Apomorphine-induced emesis was weakly antagonized. The results indicate a greater and higher selectivity of S(+)-3-phenethyl-PP for DA receptors mediating sedation compared with 3-PPP enantiomers which previously have been shown to exert significant effects on postsynaptic DA receptors. Thus S(+)-3-phenethyl-PP may be a more selective model compound for the differential study of effects elicited by stimulation of pre- and postsynaptic DA receptors.

Pharmacological effects of a specific dopamine D-1 antagonist SCH 23390 in comparison with neuroleptics

Neuroleptics such as thioxanthenes (cis(Z)-flupentixol and cis(Z)-clopenthixol) and phenothiazines (fluphenazine and perphenazine), which block both dopamine (DA) D-1 and D-2 receptors and the butyrophenones (haloperidol and spiroperidol), which block D-2 receptors only, are equipotent both behaviorally and clinically. A new compound SCH 23390 which selectively blocks DA D-1 receptors, resembles many neuroleptics in its pharmacological profile: antistereotypic effects in mice, rats and dogs, cataleptogenic effect and inhibitory effect on amphetamine circling. In contrast SCH 23390 has no effect on apomorphine-induced vomiting in dogs and little effects on 6-OHDA-denervated supersensitive DA receptors, stimulated by the DA agonist 3-PPP. In a series of experiments where methylphenidate-induced stereotyped gnawing in mice was inhibited by neuroleptics, it was shown that concomitant treatment with scopolamine or diazepam attenuated the effect of butyrophenones (D-2 antagonists). The same treatment attenuated the effect of phenothiazines, to a lesser extent, and hardly attenuated the effect of thioxanthenes and SCH 23390 at all. It is concluded that DA D-1 receptors are as important as D-2 receptors for the expression of neuroleptic activity in most animal models believed to be predictive of antipsychotic and extrapyramidal side-effect potential. However, the D-1 antagonist is less sensitive than D-2 antagonists to antimuscarinic compounds and benzodiazepines.

Dopamine receptor agonistic and antagonistic effects of 3-PPP enantiomers

The pharmacological profile of the enantiomers of the proposed selective dopamine (DA) autoreceptor agonist 3-PPP [3-(3-hydroxyphenyl)-N-n-propylpiperidine] has been studied. In vitro both enantiomers showed weak DA agonistic activity, and (--)-3-PPP some DA antagonistic effect on DA-stimulated adenylate cyclase activity. Both enantiomers in low doses had a similar profile in vivo: Inhibition of locomotor activity of mice and rats, induction of contralateral circling behaviour in 6-hydroxy-DA-lesioned rats and an emetic effect in dogs. At higher doses, differential effects of the enantiomers were found: (+)-3-PPP induced hyperactivity, weak stereotyped behaviour and ipsilateral circling in hemitransected rats. (--)-3-PPP had depressant effects in high doses, inhibited d-amphetamine-induced hyperactivity and d-amphetamine-, methylphenidate- and apomorphine-induced stereotyped licking/biting in rats and antagonized apomorphine-induced emesis in dogs. However, (+)-3-PPP also showed a weak antagonistic activity against d-amphetamine-induced hyperactivity and d-amphetamine- and apomorphine-induced stereotypy in rats and inhibited apomorphine-induced emesis in dogs. It is suggested that both enantiomers have significant effects on postsynaptic DA receptors in high doses: (--)-3-PPP with weak antagonistic activity in some test models and (+)-3-PPP with agonistic and antagonistic effect. Since these effects of (+)-3-PPP were of low intensity at high doses, (+)-3-PPP may be a partial DA agonist at postsynaptic receptors in high doses.(ABSTRACT TRUNCATED AT 250 WORDS)