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J Arnt

Publications and source records attributed to J Arnt.

At least 73 records · Page 4Linked to original sources

Pharmacology in vivo of the phenylindan derivative, Lu 19-005, a new potent inhibitor of dopamine, noradrenaline and 5-hydroxytryptamine uptake in rat brain.

Behavioural effects on dopaminergic transmission of a phenylindane derivative, Lu 19-005 [(+/-)-trans-3-(3,4-dichlorophenyl)-N-methyl-l-indanamine, HCI], with potent inhibitory effect on dopamine (DA), noradrenaline (NA) and serotonin (5-HT) uptake in rats and the effect on DA, NA and 5-HT activity in mice have been studied and compared with those of other known DA, NA and 5-HT uptake inhibitors with different selectivity ratios. Lu 19-005 induced stereotyped behaviour after parenteral and oral administration with a duration of action of more than 24 h. The stereotyped licking and biting induced by Lu 19-005 was antagonized by reserpine and cis(Z)-flupentixol, but not affected by prazosin, p-chlorophenylalanine and alpha-methyl-p-tyrosine pretreatments. Metergoline slightly facilitated the onset of stereotypy. Lower doses of Lu 19-005 induced ipsilateral circling in unilaterally 6-hydroxy-DA-lesioned rats. Finally, Lu 19-005 antagonized the catalepsy induced by perphenazine. In mice, Lu 19-005 potentiated the apomorphine-induced gnawing, reversed tetrabenazine-induced ptosis and potentiated the behavioural effects of 5-HTP within a similar dose range. The effects of Lu 19-005 were compared with those of other reference compounds. Nomifensine had qualitatively similar effects in rats although of much shorter duration. In mice, nomifensine selectively reversed tetrabenazine-induced ptosis. Weaker effects in all test models were found with bupropion, LR 5182 and GBR 13.069, compounds with inhibitory effect on DA and NA uptake. The DA-, NA- and 5-HT-uptake inhibitor diclofensine, however, had no effect in rats except in the 6-hydroxy-DA-circling test and had low potency in mice. The specific 5-HT- and NA-uptake inhibitors citalopram and talsupram, respectively, were ineffective in all rat models.(ABSTRACT TRUNCATED AT 250 WORDS)

5-Hydroxytryptophan↗

Down-regulation of dopamine D-2, 5-HT2 receptors and beta-adrenoceptors in rat brain after prolonged treatment with a new potential antidepressant, Lu 19-005.

Lu 19-005 is a new phenylindan derivative with strong and equipotent inhibitory effect on dopamine (DA), noradrenaline (NA) and serotonin (5-HT) uptake. The adaptive effects of 2 weeks treatment with Lu 19-005, on receptor binding in vitro and on d-amphetamine responsiveness in vivo have been investigated in rats. One or 3 days after the final dose the number of beta-adrenoceptors and of 5-HT2 and DA D-2 receptors was decreased by 20-30%, whereas alpha 1-adrenoceptor number was slightly decreased only 1 day after withdrawal. The DA D-2 receptor number remained decreased at 7 days withdrawal, but returned to normal after another 3 days. The brain levels of DA, NA and 5-HT were not changed by 2 weeks' Lu 19-005 treatment. The down-regulation of DA D-2 receptors was accompanied by tolerance to d-amphetamine-induced hypermotility (after low doses) and stereotyped licking or biting (after a high dose). The tolerance to d-amphetamine-induced hypermotility was maximal at 3-5 days withdrawal time, and remained significant also 15 days after the last dose. An acute dose of Lu 19-005 did not modify the effects of d-amphetamine. The results are discussed in relation to the effect of prolonged treatment with other antidepressant drugs.

Animals↗

Reduction in locomotor activity of arthritic rats as parameter for chronic pain: effect of morphine, acetylsalicylic acid and citalopram.

Arthritis was induced in rats by plantar injection of a suspension of killed mycobacteria in Viscoleo. Non-treated rats served as controls. The locomotor activities of the rats were measured weekly during the following four weeks. The exploratory activity was determined in the daytime in activity cages and spontaneous locomotor activity was measured during the night in the same cages. From one week to four weeks after treatment in one hind paw the arthritic rats showed significantly lower exploratory activity than the control rats, whereas the spontaneous locomotor activity in the arthritic rats was not significantly reduced. After treatment in two hind paws both activities were significantly smaller in the arthritic group than in the control group. The low exploratory activity level of the arthritic rats was not changed by acetylsalicylic acid but was significantly increased by morphine and citalopram in doses which did not influence the exploratory activity of the control rats. The results suggest that reduction of the locomotor activity of arthritic rats might be a reliable parameter for chronic pain.

Animals↗

Differential inhibition by dopamine D-1 and D-2 antagonists of circling behaviour induced by dopamine agonists in rats with unilateral 6-hydroxydopamine lesions.

The selective dopamine (DA) D-1 antagonist SCH 23390 antagonized the contralateral circling behaviour induced by the DA D-1 agonist SK & F 38393 in rats lesioned unilaterally with 6-hydroxy-DA but had a 600 times weaker effect against the preferential DA D-2 agonist pergolide. The D-2 antagonists clebopride and spiroperidol had the reverse selectivity. The mixed D-1/D-2 antagonists cis(Z)-flupentixol and cis(Z)-clopenthixol blocked the circling induced by either agonist. It is concluded that circling behaviour is mediated by closely related but independent DA D-1 and D-2 receptor sites.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

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.

Adenylyl Cyclases↗

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.

Adrenergic alpha-Antagonists↗

Biochemical effects and drug levels in rats after long-term treatment with the specific 5-HT-uptake inhibitor, citalopram.

The effects in rats of long-term administration of the potent, specific 5-HT uptake inhibitor citalopram have been investigated. Citalopram hydrobromide (MW = 405) was given in the diet, 99 or 25 mumol/kg daily, for 13 days or orally, 49 mumol/kg twice a day, for 14 days. High plasma and brain levels of citalopram were found during the treatment period, whereas negligible amounts were found 24 h after withdrawal. The 5-HT uptake mechanism in blood platelets was completely blocked, since levels of whole blood 5-HT during and shortly (2 days) after treatment were decreased by 75-90%. The drug load after the two highest doses in terms of plasma drug levels was the same as in depressed patients treated with citalopram. Receptor binding technique ex vivo was applied to different brain parts to measure receptor parameters for several neurotransmitters. All data were evaluated by Eadie- Hoffstee analysis. No changes were seen in Bmax and Kd for beta-receptors (3H-dihydroalprenolol) in frontal cortex, occipital + temporal cortex, whole cortex and limbic structures, 5-HT2 receptors (3H-spiroperidol) in frontal and whole cortex, alpha 1-receptors (3H-prazosin) in "rest of brain" and DA D-2 receptors (3H-spiroperidol) in corpus striatum and limbic structures. The uptake mechanism for 5-HT as well as the inhibitory effect of citalopram on this uptake remained unaffected in brain synaptosomes derived from control and from citalopram (99 mumol/kg)-treated rats. Thus long-term treatment with citalopram does not induce changes in neurotransmitter receptors as seen with most tricyclic as well as newer " atypical " antidepressants.(ABSTRACT TRUNCATED AT 250 WORDS)

Amphetamines↗

Changes in rat dopamine- and serotonin function in vivo after prolonged administration of the specific 5-HT uptake inhibitor, citalopram.

The effect of prolonged administration of the potent and specific 5-HT uptake inhibitor citalopram on behavioural measures of dopaminergic and serotonergic activity has been studied in rats. Administration of citalopram in the diet at a daily dose of 99 mumol/kg led to supersensitivity to d-amphetamine-induced hypermotility and stereotypy and to subsensitivity to apomorphine-induced hypomotility 2 h after withdrawal. Forepaw clonus induced by 5-methoxy-N,N-dimethyltryptamine was decreased 2 h and 24 h after withdrawal and the number of head shakes induced by 1-5-HTP and citalopram were decreased 24 h after withdrawal. The d-amphetamine potentiation was still seen after 24 h, whereas the response had returned to normal 3 and 7 days after withdrawal. The content of amphetamine in three different brain regions was about 50% higher compared with controls 24 h after withdrawal of prolonged citalopram administration. At this time citalopram had been eliminated, and citalopram itself could not affect amphetamine metabolism. Other experiments indicated a linear relation between d-amphetamine brain concentration and motility level. Thus, a 50% increase in citalopram-treated rats cannot alone account for 3-fold increase in d-amphetamine-induced motility. Potentiation of d-amphetamine-induced hypermotility was also found after citalopram in a daily dietary dose of 25 mumol/kg for 13 days and after oral bolus injection (49 mumol/kg twice daily for 14 days). Acute citalopram injection had no effect in any of these models. The results suggest increased responsiveness of dopaminergic mechanisms mediating hypermotility, and decreased sensitivity of dopamine receptors mediating sedation (proposed autoreceptors). Sensitivity of 5-HT receptors was also decreased. The mechanisms by which citalopram induces d-amphetamine supersensitivity as well as subsensitivity to apomorphine and 5-HT agonists are presently unknown, since no changes in dopaminergic and serotonergic receptor binding have been found after an identical dose regimen.

5-Hydroxytryptophan↗

Postsynaptic dopamine agonistic effects of 3-PPP enantiomers revealed by bilateral 6-hydroxy-dopamine lesions and by chronic reserpine treatment in rats.

The motor effects of some DA autoreceptor agonists and apomorphine in rats with bilateral 6-hydroxydopamine lesions of the median forebrain bundle were studied. Whereas (-)-3-PPP, (+)-3-phenethyl-PP and EMD 23448 decreased motility in sham-operated controls, a pronounced hypermotility was induced in 6-OHDA-lesioned rats. 3-PPP enantiomers and apomorphine had similar potency as that found in test models for DA autoreceptor activity in normal rats, e.g. motility inhibition. The DA receptor involvement in the effect of (-)-3-PPP was confirmed by neuroleptic antagonism. (-)-3-PPP and EMD 23448 had similar intrinsic activity as apomorphine, whereas (+)-3-phenethyl-PP and (+)-3-PPP had lower maximal effect. However, the DA autoreceptor agonists differed from apomorphine: The development of postsynaptic supersensitivity to these drugs appeared 4-7 days after the lesion compared to 1-2 days for apomorphine and (+)-3-PPP. Furthermore, no active oral stereotypy was induced by the autoreceptor selective compounds in contrast to the effect observed after apomorphine and (+)-3-PPP. In a separate experiment using circling behaviour in unilaterally 6-OHDA-lesioned rats the different time-course of appearance of supersensitivity to (-)-3-PPP, (+)-3-PPP and apomorphine was confirmed. After chronic reserpine treatment a similar postsynaptic supersensitivity to (-)-3-PPP was observed with a development time between 4 and 7 days and with a similar intensity as that observed in 6-OHDA-lesioned rats. In contrast, after chronic neuroleptic treatment for 12 days, (-)-3-PPP was unable to induce hyperactivity 3-7 days after withdrawal. The results indicate that DA autoreceptor agonists are able to stimulate postsynaptic DA receptors in conditions without endogenous transmitter supply for at least 4-7 days, but not after chronic receptor blockade in a similar period. This should lead to consideration of DA autoreceptor agonists as potential antiparkinsonian drugs without stimulant effects on normosensitive postsynaptic DA receptors.

Animals↗

Spinal 5-HT or NA uptake inhibition potentiates supraspinal morphine antinociception in rats.

Spinal injection of the specific uptake inhibitor of 5-hydroxytryptamine (5-HT), citalopram, or of noradrenaline (NA), desipramine, potentiated the antinociception following intracerebroventricular injection of morphine in rats tested on the hot plate. Combined spinal injection of citalopram and desipramine caused a synergistic potentiation. The unselective and less potent inhibitor of both 5-HT and NA uptake, amitriptyline, did not cause potentiation. The results support the suggested involvement of both 5-HT and NA pathways in supraspinal morphine antinociception.

Amitriptyline↗

The citalopram/5-HTP-induced head shake syndrome is correlated to 5-HT2 receptor affinity and also influenced by other transmitters.

Combination of the 5-HT-uptake inhibitor, citalopram, with 1-5-HTP induced a characteristic head shake syndrome in rats. This was blocked by a range of 5-HT antagonists, including the selective 5-HT2 antagonists, ketanserin and pirenperone and was also blocked by the alpha 1-adrenoceptor antagonists, prazosin and WB 4101, and the alpha 2-adrenoceptor agonist, clonidine. 1-5-HTP-antagonistic effect was also recorded for 26 neuroleptic drugs. Their inhibitory potencies showed close correlation to 5-HT2-receptor affinity in vitro and, slightly weaker, to alpha 1-adrenoceptor affinity. In contrast, no correlation to dopamine D-2 receptor affinity was found, indicating that the cataleptogenic and motility-inhibitory properties of neuroleptics did not unspecifically influence 1-5-HTP-induced head shakes. These were not influenced by a histaminic antagonist, muscarinic antagonist or alpha 2-adrenoceptor antagonist, but were inhibited by beta-adrenoceptor blockers, GABA agonists, a benzodiazepine and morphine. The results indicate that 1-5-HTP-induced head shakes are most sensitive to 5-HT2 antagonists, but that the syndrome is influenced by other neuronal systems. Since 5-HT2 affinity and alpha 1-adrenoceptor affinity of many compounds is found concomitantly, caution is needed to evaluate the relative importance of these properties for 1-5-HTP antagonism.

5-Hydroxytryptophan↗

Differential behavioural effects of dopamine agonists in developing rats: a study of 3-PPP enantiomers.

The effect of different dopamine (DA) agonists on spontaneous activity and d-amphetamine-induced hyperactivity was studied in 11, 20 and 30 day old rats. The proposed selective DA autoreceptor agonist 3-PPP induced biphasic hyperactivity at 11 and 20 days of age, whereas only hypoactivity was observed at 30 days of age, as shown previously for adult rats. The enantiomers of 3-PPP had differential effect: (+)-3-PPP increased activity in 11 and 20 day old rats, where (-)-3-PPP had no effect in similar doses but motility decreased at a higher dose. At 30 days of age (+)-3-PPP decreased motility at low doses and increased motility at a high dose, whereas (-)-3-PPP induced a monotonic decrease, as observed in adult rats. The reference DA agonists apomorphine and pergolide induced only hyperactivity at 11 and 20 days of age. At 30 days the usual sedative effect of low doses was seen. These results confirm that DA autoreceptors mediating sedation are developed later than postsynaptic DA receptors mediating hyperactivity and suggest that 3-PPP (by its (+)-enantiomer) stimulates postsynaptically. (-)-3-PPP had no detectable postsynaptic DA stimulating activity and may, in contrast, act as a postsynaptic antagonist at high doses. Racemic-and (-)-3-PPP antagonized the d-amphetamine-induced hyperactivity at all ages, whereas (+)-3-PPP had no effect and apomorphine was effective at 30 days of age only. These results suggest that the d-amphetamine antagonism by (-)-3-PPP cannot be explained solely by DA autoreceptor stimulation but that autoreceptor stimulation may contribute to the inhibitory effect in mature rats.

Age Factors↗

Neuroleptic inhibition of 6,7-ADTN-induced hyperactivity after injection into the nucleus accumbens. Specificity and comparison with other models.

The dopamine agonist 6,7-ADTN induced locomotor stimulation after injection into the nucleus accumbens of rats. This hyperactivity was stereospecifically antagonized by peripheral injection of typical and atypical neuroleptics, except sulpiride, regardless of structural class. The potency of 14 neuroleptics correlated significantly to that in other neuroleptic in vivo models in rats, i.e. cataleptogenic and amphetamine-antagonistic (stereotypy, circling) activity. Sulpiride was inactive after peripheral injection, whereas intraacumbens sulpiride antagonized 6,7-ADTN-induced hyperactivity with a higher potency than that found for locally injected cis-(Z)-flupentixol, haloperidol and clebopride. Blockade of alpha 1-adrenergic receptors by systemic prazosin or locally injected phentolamine also antagonized 6,7-ADTN, whereas antagonists of alpha 2-adrenergic, beta-adrenergic, muscarinic and serotoninergic receptors were without effect. Furthermore, the cis-(Z)-flupentixol and haloperidol-induced 6,7-ADTN blockade was only slightly or not reversed by additional antimuscarinic (scopolamine) or antiserotonergic (methysergide) treatment. It is concluded that antagonism of 6,7-ADTN-induced hyperactivity is a relevant model for detecting neuroleptic activity with minimal influence of anticholinergic and antiserotonergic activity, but that the dopamine receptor within the nucleus accumbens responsible for the locomotor stimulation is similar to that involved in other behavioural effects of neuroleptics. It is suggested that an apparent preferential limbic action of some neuroleptics (e.g. clozapine and chlorprothixene) is more likely to be explainable by their simultaneous blocking effect on dopaminergic, alpha-adrenergic and muscarinic receptors.

Amphetamine↗

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)

Adenylyl Cyclases↗

Pharmacological specificity of conditioned avoidance response inhibition in rats: inhibition by neuroleptics and correlation to dopamine receptor blockade.

The inhibitory effect of 36 neuroleptic compounds on conditioned avoidance response (CAR) and unconditioned escape response (UER) has been studied in rats. All neuroleptics antagonized CAR in doses below those inhibiting UER and below those inducing catalepsy. Stereospecificity was shown in two cases. Significant correlation was found between CAR inhibitory and cataleptogenic potency. Also inhibition of amphetamine induced stereotypy, affinity to 3H-haloperidol binding sites in vitro and clinical potency was significantly correlated to CAR inhibition. CAR and UER inhibition induced by cis(Z)-flupentixol and haloperidol was attenuated by scopolamine, but was only weakly influenced by methysergide and prazosin. Among a wide range of other CNS active compounds tested, CAR was inhibited by alpha 1-adrenergic antagonists, benzodiazepines, a barbiturate, GABA agonists, morphine and a serotonin agonist, but in doses inducing other motor disturbances. It is concluded that CAR inhibition is a sensitive test for dopamine receptor antagonists. However, additional alpha-adrenergic activity found for some neuroleptics (e.g. clozapine, chlorprothixene) may contribute to the CAR inhibitory potency. Additional antimuscarinic activity of neuroleptics may moderately attenuate CAR inhibition whereas serotonin receptor blockade is of minor importance.

Animals↗

Turning behaviour and catalepsy after injection of excitatory amino acids into rat substantia nigra.

Unilateral injection of AMPA ((R,S)-alpha-3-hydroxyl-5-methyl-4-isoxazolepropionic acid), 4-bromohomoibotenic acid, kainic acid and N-methylaspartic acid into the caudal part of substantia nigra induced ipsilateral turning behaviour. AMPA and kainic acid were most potent. Ibotenic acid produced short-lasting ipsilateral turning followed by long-lasting contralateral turning behaviour which was antagonized by the GABA antagonist bicuculline methiodide. The turning induced by AMPA was not blocked by previous 6-hydroxydopamine lesion of the nigrostriatal dopaminergic pathway and was increased by systemic apomorphine. High doses of bilateral intranigral AMPA induced rigid catalepsy. The results are consistent with an involvement of glutamate or aspartate receptors in the regulation of dopamine output systems.

Amino Acids↗