The effect of p-chloroamphetamine on motility in rats after inhibition of monoamine synthesis, storage, uptake and receptor interaction

The Antipsychotic Drug Clozapine Suppresses the RGS4 Polyubiquitylation and Proteasomal Degradation Mediated by the Arg/N-Degron Pathway

Although diverse antipsychotic drugs have been developed for the treatment of schizophrenia, most of their mechanisms of action remain elusive. Regulator of G-protein signaling 4 (RGS4) has been reported to be linked, both genetically and functionally, with schizophrenia and is a physiological substrate of the arginylation branch of the N-degron pathway (Arg/N-degron pathway). Here, we show that the atypical antipsychotic drug clozapine significantly inhibits proteasomal degradation of RGS4 proteins without affecting their transcriptional expression. In addition, the levels of Arg- and Phe-GFP (artificial substrates of the Arg/N-degron pathway) were significantly elevated by clozapine treatment. In silico computational model suggested that clozapine may interact with active sites of N-recognin E3 ubiquitin ligases. Accordingly, treatment with clozapine resulted in reduced polyubiquitylation of RGS4 and Arg-GFP in the test tube and in cultured cells. Clozapine attenuated the activation of downstream effectors of G protein-coupled receptor signaling, such as MEK1 and ERK1, in HEK293 and SH-SY5Y cells. Furthermore, intraperitoneal injection of clozapine into rats significantly stabilized the endogenous RGS4 protein in the prefrontal cortex. Overall, these results reveal an additional therapeutic mechanism of action of clozapine: this drug posttranslationally inhibits the degradation of Arg/N-degron substrates, including RGS4. These findings imply that modulation of protein post-translational modifications, in particular the Arg/N-degron pathway, may be a novel molecular therapeutic strategy against schizophrenia.

Pharmacological Modulation of the N-End Rule Pathway and Its Therapeutic Implications

The N-end rule pathway is a proteolytic system in which single N-terminal amino acids of short-lived substrates determine their metabolic half-lives. Substrates of this pathway have been implicated in the pathogenesis of many diseases, including malignancies, neurodegeneration, and cardiovascular disorders. This review provides a comprehensive overview of current knowledge about the mechanism and functions of the N-end rule pathway. Pharmacological strategies for the modulation of target substrate degradation are also reviewed, with emphasis on their in vivo implications. Given the rapid advances in structural and biochemical understanding of the recognition components (N-recognins) of the N-end rule pathway, small-molecule inhibitors and activating ligands of N-recognins emerge as therapeutic agents with novel mechanisms of action.

A neurostimulant para-chloroamphetamine inhibits the arginylation branch of the N-end rule pathway

In the arginylation branch of the N-end rule pathway, unacetylated N-terminal destabilizing residues function as essential determinants of protein degradation signals (N-degron). Here, we show that a neurostimulant, para-chloroamphetamine (PCA), specifically inhibits the Arg/N-end rule pathway, delaying the degradation of its artificial and physiological substrates, including regulators of G protein signaling 4 (RGS4), in vitro and in cultured cells. In silico computational analysis indicated that PCA strongly interacts with both UBR box and ClpS box, which bind to type 1 and type 2 N-degrons, respectively. Moreover, intraperitoneal injection of PCA significantly stabilized endogenous RGS4 proteins in the whole mouse brain and, particularly, in the frontal cortex and hippocampus. Consistent with the role of RGS4 in G protein signaling, treatment with PCA impaired the activations of GPCR downstream effectors in N2A cells, phenocopying ATE1-null mutants. In addition, levels of pathological C-terminal fragments of TDP43 bearing N-degrons (Arg208-TDP25) were significantly elevated in the presence of PCA. Thus, our study identifies PCA as a potential tool to understand and modulate various pathological processes regulated by the Arg/N-end rule pathway, including neurodegenerative processes in FTLD-U and ALS.

Suppression of behavioral activity by norfenfluramine and related drugs in rats is not mediated by serotonin release

Fenfluramine, a phenalkylamine with serotonin (5-HT) releasing properties, decreases motor activity in rats. The following studies assessed the contribution of 5-HT release to the behavioral effects of fenfluramine and norfenfluramine using a behavioral pattern monitor that simultaneously assesses locomotor and investigatory behavior. First, both fenfluramine and its active metabolite d-norfenfluramine dose-dependently reduced locomotor and investigatory activity. The norfenfluramine-induced reduction in activity was not antagonized by pretreatment with the 5-HT uptake inhibitor fluoxetine or the 5-HT synthesis inhibitor p-chlorophenylalanine, drugs that reduce drug-induced 5-HT release. Second, the d- and l-enantiomers of norfenfluramine were nearly equipotent at reducing behavioral activity, although d-norfenfluramine is more potent as a 5-HT releasing agent. Third, p-chloroamphetamine, a drug that shares the 5-HT releasing properties of fenfluramine produced locomotor hyperactivity in the same paradigm. Previous studies indicate that other 5-HT releasing phenalkylamines have behavioral effects resembling those of p-chloroamphetamine rather than those of fenfluramine. Finally, a structurally related drug, 4-methoxy-5-methyl-aminoindan (MMAI), produced dose-dependent reductions in behavioral activity that are similar to the effects of fenfluramine. The behavioral effects of MMAI were not antagonized by fluoxetine or by the 5-HT receptor antagonist methiothepin. These data suggest that the decrease in activity induced by fenfluramine, norfenfluramine and the related drug MMAI is not related to 5-HT release.

Head-twitch response induced by ergometrine in mice: behavioural evidence for direct stimulation of central 5-hydroxytryptamine receptors by ergometrine

Ergometrine (2.5-80 mg/kg IP) induced head twitches in mice. Pretreatment with cyproheptadine (1.5 and 3 mg/kg), methysergide (5 and 10 mg/kg) and (-)-propranolol (2.5 and 5 mg/kg) significantly decreased the number of head twitches induced by ergometrine. Pretreatment with p-chlorophenylalanine (100 mg/kg/day X 4 days) and clomipramine (5 and 10 mg/kg) significantly decreased the number of head twitches induced by fenfluramine (10 mg/kg) and p-chloramphetamine (5 mg/kg) but had no significant effect on the number of head twitches induced by ergometrine. The results indicate that ergometrine induces head twitches in mice by directly stimulating central 5-hydroxytryptamine receptors.

A comparison of the effect of paroxetine and amitriptyline on the tyramine pressor response test

The effect of single and repeated dosing of paroxetine on the in vivo noradrenaline uptake process, as determined by tyramine pressor response tests, was evaluated in normal healthy subjects. No statistically significant inhibition of the uptake process was observed for paroxetine, nor did it produce sedation or dryness of the mouth, though effects were observed for amitriptyline.

Separation of the associative and non-associative effects of brain serotonin released by p-chloroamphetamine: dissociable serotoninergic involvement in avoidance learning, pain and motor function

p-Chloramphetamine (PCA, 0.63-5 mg/kg IP) injected 30-60 min before testing produced a dose-related impairment of avoidance acquisition, prolonged reaction time in the hot-plate test and increased locomotor activity. Pretreatment with the selective serotonin (5-HT) uptake inhibitor zimeldine (10 mg/kg IP) blocked these behavioral effects. Degeneration of brain 5-HT neurons by a high neurotoxic dose of PCA (2 X 10 mg/kg IP) or inhibition of tryptophan hydroxylase by p-chlorophenylalanine (300 mg/kg IP) also blocked the behavioral effects of PCA. There was a complete blockade of the PCA-induced avoidance deficit following pretreatment with metergoline, a central 5-HT receptor blocking agent. On the other hand, metergoline failed to block the hot-plate analgesia and the increased locomotion caused by PCA. Depletion of brain NA and DA by the tyrosine hydroxylase inhibitor H44/68 did not counteract the PCA effect on avoidance or hot-plate performance, but reduced the locomotor stimulating effect. The selective NA neurotoxin DSP4 (50 mg/kg IP) or the opiate antagonist naloxone (1 mg/kg) failed to affect the PCA-induced modulations of the behaviours studied. In addition, PCA administration in doses that caused avoidance deficits, did not result in motor impairment as assessed by the tread mill test. The above results support the hypothesis that the PCA-induced impairment of active avoidance acquisition does not involve changes in nociception or altered locomotor activity. It is concluded that behavioural processes related to serotonergic neurotransmission can be independently modified, suggesting differences in the underlying 5-HT mechanisms.

Psychopharmacological investigation of the monoamine oxidase inhibitory activity of molindone, a dihydroindolone neuroleptic

24 h pretreatment with molindone enhanced the behavioural effects of L-dopa and 5-HTP, precursors of biogenic amines (catecholamines and 5-HT respectively) preferentially deaminated by MAO-A, confirming that a metabolite of molindone inhibits MAO-A. 24 h pretreatment with molindone enhanced the behavioural effects of tryptamine and antagonized reserpine-induced ptosis, and in molindone-pretreated rats L-tryptophan induced behavioural effects, probably because of the MAO-A inhibitory activity exerted by a metabolite of molindone. Since 24 h pretreatment with molindone, unlike 30 min pretreatment with clomipramine, failed to antagonize fenfluramine and p-chloramphetamine-induced behavioural syndromes, it suggests that molindone and/or its metabolites most probably do not exert 5-HT neuronal uptake blocking activity and the potentiation of 5-HTP-induced behavioural syndrome is due to a metabolite's MAO-A inhibitory activity. As 2 h pretreatment with molindone induced catalepsy and antagonized apomorphine-induced climbing behaviour in mice and stereotypy in rats, while 24 h pretreatment failed to induce catalepsy and to antagonize apomorphine-induced behaviour, it appears that, at 24 h, the tissue levels of molindone are inadequate to block postsynaptic striatal and mesolimbic DA receptors and that, though a metabolite of molindone is biologically active so far as inhibition of MAO-A is concerned, the metabolites are devoid of neuroleptic activity. Further, since 2 h pretreatment with molindone failed to enhance the behavioural effects of L-dopa, it suggests that at 2 h the degree of MAO-A inhibition induced by molindone and/or the metabolite is not sufficient to counteract the neuroleptic activity of the parent compound.

Environmental determinants of parachloroamphetamine toxicity in rats

The present investigation assessed PCA toxicity at 0.0, 5.0, and 10.0 mg/kg, in both social (4 rats per cage) and non-social (acrylic tube-restraint or tube restraint-plus-tail shock) circumstances with 16 rats per drug-environment condition. The results indicated that no dose of PCA alone yielded mortality under individual housing, and similarly no environmental circumstance by itself yielded mortality in the absence of PCA. However, various drug-environment interactions produced a dose-related enhancement of PCA toxicity. For both 5.0 mg/kg and 10 mg/kg parachloroamphetamine dose levels, restraint-plus-shock generated the highest percent mortality, followed by restraint-only, with conspecific aggregation producing a mortality incidence lower still. Further, the mortality displayed under each of these environmental conditions was greater for the 10.0 mg/kg PCA treatment than for the 5.0 mg/kg treatment. The results are discussed in terms of the relative aversiveness of the environmental setting and it is suggested that stress-related drug toxicity may be further analyzed in non-social settings. It is proposed that toxic environment-PCA interactions may result from altered cardiovascular and/or thermoregulatory processes, mediated by enhanced catecholaminergic activity.

A frequency analysis of behavior components of the serotonin syndrome produced by p-chloroamphetamine

A time-sampling frequency analysis was made of criterion behaviors following injection of 2.5--10 mg/kg dosages of p-chloroamphetamine (PCA). Stereotypic behaviors (forepaw treading, circling, head weaving and inching) increased with increasing dosages and normal behaviors (grooming, rearing, and instances of inactivity) decreased. Composite scores of stereotypic behavior were a positive, linear function of PCA dosage. Composite scores of normal behavior showed near maximal inhibition at 5 mg/kg. Splayed hindlimbs is a reliable and sensitive indicator of PCA action, but vocalization, tremors, diarrhea and autonomic signs are not. Preinjection of PCA strongly attenuated the PCA-induec syndrome, as expected, since the preinjection should deplete brain serotonin and reduce the amount released by the second PCA injection.

Influence of the new 5-HT-uptake inhibitor paroxetine on hypermotility in rats produced by p-chloroamphetamine (PCA) and 4,alpha-dimethyl-7-tyramine (H 77/77)

Two different forms of hypermotility produced by the amphetamine derivatives PCA and H 77/77, 5 mg/kg of each, was studied in rats treated s.c. with the new 5-HT uptake inhibitor paroxetine. The substance inhibited the effect of PCA but did not influence that of H 77/77. The 5-HT-uptake inhibitors paroxetine, imipramine, and chlorimipramine were also administered p.o. at various times before PCA. The three substances inhibited PCA-induced hypermotility. Paroxetine 0.5-2 mg/kg, was active at intervals of 1-4 h and 4 mg/kg was active at 18-h interval. Imipramine and chlorimipramine 25-30 mg/kg showed PCA inhibition at treatment intervals of 1-2h, but 80-100 mg/kg or more was required to inhibit PCA at intervals of 4 and 18 h. Previous results have shown that PCA-induced hypermotility is antagonized by substances inhibiting 5-HT synthesis and uptake, whereas H 77/77-induced hypermotility is inhibited by substances blocking NA synthesis, uptake, and receptors. The previous and present results indicate that paroxetine is a selective 5-HT-uptake inhibitor. After oral administration paroxetine presumably produces a more potent and long-lasting 5-HT-uptake inhibition than imipramine and chlorimipramine.

Rapid tolerance to the motor effects of p-chloroamphetamine in rats

Studies were designed to test the hypothesis that tolerance to the effect of p-chloroamphetamine (PCA) on motor activity in rats would develop with repeated injections. In related biochemical studies the effects of single or repeated doses of PCA on the in vitro synaptosomal uptake of 3H-NE and 3H-DA and on the in vivo metabolism of intraventricularly administered 3H-NE and 3H-DA were investigated. The administration of 10 mg/kg of PCA induced a complex behavioral syndrome, which was quantified by scoring specific symptoms after direct observation. In agreement with previous data, this syndrome appears to be mediated by a release of 5-HT since pretreatment with PCA prevented its development on subsequent injection of the drug. After the administration of lower doses of PCA, total motor activity as measured in activity cages increased, and tolerance to this effect also developed rapidly. For example, pretreatment with 5 mg/kg of PCA greatly attenuated the stimulant effect of a subsequent dose of 3 or 5 mg/kg of the drug. Moreover, the degree of tolerance was the same if the time between the 2 injections was 1 day or 2 weeks, suggesting that 5-HT release is also involved in the tolerance to the motor effects of lower doses of the drug. Moreover, biochemical studies of the response of catecholaminergic neurons to PCA suggest that tolerance does not develop to the effects on DA and NE neurons on repeated injection of PCA.

Substituted amphetamine derivatives. II. Behavioural effects in mice related to monoaminergic neurones

The effects of the amphetamine derivatives (+/-)-amphetamine (A), 2-, 3- and 4-chloroamphetamine (CA), 4-methylamphetamine (MA) and chlorphentermine (CP) in producing central stimulation (increase in motor activity), antagonism of the reserpine syndrome, potentiation of 1-dopa and 5-hydroxytryptophan (5HTP) responses in mice were investigated. The inhibitors of the membrane amine uptake despramine (DMI) and chlorimipramine (CI) were also included in the study. It was found that the order in central stimulating potency was A greater than 3-CA = 4-CA greater than MA greater than CP. 2-CA, DMI and CI decreased the motor activity. All the compounds potentiated the 1-dopa response with the order of activity: 4-MA greater than A greater than 2-CA = 3-CA = 4-CA = CI greater than or equal to DMI greater than CP. The decrease in motor activity (sedation) produced by reserpine was only reversed by A greater than or equal to 3-CA greater than 2-CA. alpha-Methyltyrosine but not parachlorophenylalanine, antagonized the reversal effect. Three of the compounds (3-CA, 4-CA and MA) produced head-twitches in the reserpinized mice. The 5-HTP syndrome was potentiated in order of potency by MA = 4-CA greater than CI greater than CP greater than 3-CA whereas A, 2-CA and DMI had no effect.

Effects of alpha methyltyrosine and parachlorophenylalanine on open field behavior in rats given tranylcypromine stereoisomers and lithium carbonate

Parachlorophenylalanine (PCPA) and alpha methyltyrosine (AMT) were used to study the roles of serotonin and catecholamines in hyperactivity produced by the stereoisomers of Tranylcypromine (d-Tc and 1-Tc) in male Wistar rats fed a normal diet (control groups) or a diet containing lithium carbonate (lithium groups). Components of locomotor activity were measured in an open field. Lithium decreased ambulation. d-Tc increased ambulation and caused jerky side-to-side movements. PCPA and AMT prevented the effects of d-Tc on ambulation while only PCPA prevented the effects of d-Tc on movement. 1-Tc increased ambulation. The effects of 1-Tc on ambulation were potentiated by PCPA and prevented by AMT. Rearing was increased by 1-Tc and d-Tc in rats given lithium. PCPA and AMT prevented the effects of 1-Tc and d-Tc on rearing in lithium groups. The findings suggest that the roles of serotoninergic and catecholaminergic mechanisms differ for components of open field behavior in control rats and rats given lithium.

Evidence concerning the involvement of 5-hydroxytryptamine in the locomotor activity produced by amphetamine or tranylcypromine plus L-DOPA

1 Pretreatment of rats with p-chlorophenylalanine (PCPA; 2 X 200 mg/kg) decreased the concentration of 5-hydroxytryptamine (5-HT) in the brain. It also decreased the locomotor activity produced by tranylcypromine plus L-DOPA administration 24 h after the second dose of PCPA. 2 Pretreatment with p-chloroamphetamine, which produced a similar decrease in brain 5-HT concentrations did not decrease the locomotor response to tranylcypromine and L-DOPA. 3 PCPA pretreatment decreased the rise in the concentration of DOPA and dopamine in the brain following tranylcypromine and L-DOPA, suggesting its effect on the dopamine-induced locomotor activity was the result of this drug diminishing dopamine formation in the brain, probably by inhibiting L-DOPA uptake. 4 The locomotor activity produced by tranylcypromine and L-DOPA was not decreased by pretreatment 6 h earlier with disulfiram (400 mg/kg). This argues against the locomotor activity being due to noradrenergic stimulation. 5 PCPA pretreatment did not alter amphetamine-induced stereotypy or the circling behaviour in unilateral nigro-striatal lesioned rats.

Inhibition and potentiation of apomorphine-induced hypermotility in rats by neuroleptics

The effect of apomorphine (ap) was investigated in rats kept in a familiar cage; 0.25-5 mg/kg s.c. produced a short-lasting, abnormal hypermotility consisting mainly of locomotion and sniffing without grooming. Ap was administered to rate pretreated s.c. with various drugs. Ap hypermotility was antagonized by 12 neuroleptics from different chemical groups. The ap inhibitory effect of 5 neuroleptics was decreased when the interval between pretreatment and ap administration was increased from 0.5 to 4 hr. Clozapine was the only neuroleptic showing no inhibition but potentiation at 4 hr. Mepazine, a phenothiazine lacking antipsychotic effects, as well as the NA receptor blockers aceperone and phenoxybenzamine, did not inhibit ap hypermotility. Ap was also given 24 hr after haloperidol and clozapine. At this time both neuroleptics showed ap potentiation. The ap inhibition and potentiation after a single administration of the neuroleptics is presumable due to selective blockade and subsequent supersensitivity of some DA receptors.

Comparative action of fenfluramine on the uptake and release of serotonin and dopamine

The anorectic agent, fenfluramine, proves to be a good inhibitor of serotonin uptake in vitro, in synaptosomes from rat whole brain (IC50 = 8.5 +/- 0.6 X 10(-7) M). After administration in vivo, its inhibitory activity in vitro equals that of chlorimipramine and in contrast to the latter, its effect is of long duration. Fenfluramine is also effective in promoting the release of serotonin from pre-loaded synaptosomes. In comparison, the structurally related compound, amphetamine, has little activity with respect to these serotonin mechanisms. It is, however, active both in inhibiting the uptake of dopamine and in promoting its release, whereas fenfluramine is inactive. The implication of these mechanisms in the serotonin-depleting capacity as well as in the anorectic activity of fenfluramine is discussed.

Acute and chronic effects of 4-chloroamphetamine on monoamine metabolism in the rat brain

The acute administration of 4-chloroamphetamine caused a marked reduction in the concentration of serotonin and 5-hydroxyindoleacetic acid and a rise in dopamine in the rat brain. Following the injection of 3H-tyrosine and 3H-tryptophane into rats treated with 4-chloroamphetamine, there was a reduction in brain levels of 3H-dopamine and 3H-serotonin. Although the endogenous concentration of noradrenaline was not affected by 4-chloroamphetamine, there is evidence that its reuptake into neurones was reduced and its release increased by the drug. Following the administration of 4-chloroamphetamine for 10 days, the concentration of 5-hydroxyindoleacetic acid was reduced; no other changes in amine metabolism were apparent. From this investigation, and those of others, it appears that following acute administration, 4-chloroamphetamine has a neurochemical profile which has a similarity to that of many tricyclic antidepressants. However, there is a marked discrepancy between the acute and chronic effects of 4-CA on brain amine metabolism. Such findings are difficult to reconcile with the widely accepted theory that antidepressant drugs counteract the symptoms of depression by increasing the concentration of noradrenaline and/or serotonin at receptor sites within the brain.

Comparative studies of a new 5HT-uptake inhibitor and some tricyclic thymoleptics

The new 5HT-uptake inhibitor, FG 4963, and some tricyclic thymoleptics antagonized p-chloroamphetamine (PCA)-induced hypermotility in rats. FG 4963 was active in about the same s.c. and p.o. doses as chlorimipramine. FG 4963, imipramine and chlorimipramine potentiated hypermotility induced in mice by the 5HT precursor 5HTP, FG 4963 being slighly more active than chlorimipramine. In contrast to the tricyclic thymoleptics FG 4963 did not potentiate the heart rate increasing effect of NA in pithed rats. The peripheral anticholinergic effect of FG 4963 and of desipramine was almost identical while the other imipramine derivatives were more active. All tricyclic thymoleptics were strong peripheral antihistaminics, but FG 4963 was almost devoid of this action. Acute tests for ECG changes in guinea pigs and toxicity in mice and rats showed that FG 4963 and chlorimipramine were less toxic than imipramine and amitriptyline. FG 4963 is presumably a selective 5HT-uptake inhibitor producing much less potentiation of peripheral sympathetic mechanisms than do the tricyclic antidepressants.