Effects of serotonergic and anticholinergic drugs in haloperidol-induced dystonia in Cebus monkeys

The Dystonias

Dystonia is a difficult problem for both the clinician and the scientist. It is sufficiently common to be seen by almost all physicians, yet uncommon enough to prevent any physician from gaining broad experience in its diagnosis and treatment. Each case represents a difficult challenge even to the specialist. The basic scientist is faced with investigating a disorder that is without relevant animal models and which is so rare that obtaining suitable tissue for study is a major obstacle. Dystonia may be idiopathic, or associated with lesions from many sources, including a variety of rare diseases. If idiopathic, it may be genetically transmitted or sporadic. If genetically transmitted, it may be generalized or focal, with symptoms varying in different members of the same family. It may be refractory to treatment, or it may respond to any one of a number of individual drugs that have very different mechanisms of action. For idiopathic dystonias, no clear method of genetic transmission has been established and no consistent pathology identified.

The substituted (S)-3-phenylpiperidine (−)-OSU6162 reduces apomorphine- and amphetamine-induced behaviour in Cebus apella monkeys

Low affinity dopamine (DA) D2 antagonists such as the substituted (S)-3-phenylpiperidine (-)-OSU6162 have been proposed to be putative antipsychotic agents not endowed with extrapyramidal side effects (EPS). In the present study we investigated the effects of (-)-OSU6162 on (-)-apomorphine and d-amphetamine-induced behaviours in EPS sensitised Cebus apella monkeys. (-)-OSU6162 was administered subcutaneously in doses of 1, 3, 6 and 9 mg/kg alone and in combination with (-)-apomorphine (0.25 mg/kg) or d-amphetamine (0.5 mg/kg). (-)-OSU6162 inhibited (-)-apomorphine-(1-9 mg/kg) as well as d-amphetamine (3-9 mg/kg)-induced arousal and stereotypy. EPS did not occur when (-)-OSU6162 was administered in combination with (-)-apomorphine or d-amphetamine. However, when (-)-OSU6162 was administered alone, dystonia was observed at high doses (6 and 9 mg/kg) in two out of six monkeys. The present study shows that (-)-OSU6162 can inhibit (-)-apomorphine-induced behaviours in non-human primates at doses that do not cause EPS. When (-)-OSU6162 was tested against d-amphetamine-induced behaviours a separation between dose levels that inhibit d-amphetamine effects and cause EPS was not observed. The data further substantiate a role for low affinity DA D2 antagonists in the pharmacological treatment of psychosis.

Efficacy of nefazodone in the treatment of neuroleptic induced extrapyramidal side effects: a double-blind randomised parallel group placebo-controlled trial

Many atypical antipsychotics show antagonism at both serotonergic and dopaminergic neurones and show fewer extrapyramidal side effects (EPS). Nefazodone blocks postsynaptic 5HT2A receptors and weakly inhibits serotonin reuptake. This study aimed to elucidate the role of nefazodone in the treatment of antipsychotic-induced EPS. The trial was a double-blind, randomised, placebo-controlled trial of patients requiring antipsychotic treatment with haloperidol 10mg daily; from which a subgroup of patients who developed EPS were selected for the study. Patients were randomised to add-on therapy with either placebo (n=24) or nefazodone (n=25) 100mg bd. EPS were measured on days 0, 3 and 7 using the Simpson Angus, Barnes akathisia, abnormal involuntary movement and Chouinard scales. Nefazodone significantly reduced EPS as measured by both the Simpson Angus scale and CGI (p=0.007 and 0.0247, respectively). Akathisia and tardive dyskinesia did not differ between the two groups (p=0.601; p=0.507, respectively). These results suggest the role of 5HT2 antagonism in the mechanism of action of atypical antipsychotics with respect to lowering rates of drug-induced EPS. In addition, a therapeutic role for nefazodone is suggested in the treatment of antipsychotic-induced EPS.

Drug-induced Pisa syndrome (pleurothotonus): epidemiology and management

Long-term administration of antipsychotics occasionally produces persistent dystonia of the trunk, a disorder known as Pisa syndrome (or pleurothotonus). The development of Pisa syndrome is most commonly associated with prolonged treatment with antipsychotics; however, it has also been reported, although less frequently, in patients who are receiving other medications (such as cholinesterase inhibitors and antiemetics), in those not receiving medication (idiopathic Pisa syndrome) and in those with neurodegenerative disorders. Drug-induced Pisa syndrome predominantly develops in females and in older patients with organic brain changes. It sometimes occurs after the addition of another antipsychotic to an established regimen of antipsychotics or insidiously arises in antipsychotic-treated patients for no apparent reason. The condition generally disappears after antipsychotic drugs are discontinued. Although a pharmacological therapy for drug-induced Pisa syndrome has not been established, we have reported that anticholinergic drugs are effective in about 40% of patients who have episodes of Pisa syndrome with the remaining patients responding to the withdrawal or reduction of daily doses of antipsychotic drugs. The characteristics of its development and prognosis indicate that drug-induced Pisa syndrome consists of two types of dystonia. Some patients develop clinical features of acute dystonia, whereas others develop symptoms similar to tardive dystonia. Like that of tardive dystonia, Pisa syndrome responds better than tardive dyskinesia to a relatively high daily dose of an anticholinergic. However, the significant improvement caused by the withdrawal of antipsychotic drugs in Pisa syndrome differentiates it from tardive dystonia. Thus, Pisa syndrome including these features is considered to be an atypical type of tardive dystonia. These clinical characteristics suggest that the underlying pathophysiology of drug-induced Pisa syndrome is complex. A dopaminergic-cholinergic imbalance, or serotonergic or noradrenergic dysfunction, may be implicated. Asymmetric brain functions or neural transmission may also be considered as underlying mechanisms of the development of Pisa syndrome that is resistant to anticholinergic drugs. Idiopathic Pisa syndrome is characterised by an adult-onset, segmental truncal dystonia in patients with no previous exposure to antipsychotics. It occurs rarely but shows a complete resolution with high doses of anticholinergic drugs.

5-HT2 antagonism and EPS benefits: is there a causal connection?

This article examines the hypothesis that 5-HT2 antagonism ameliorates extrapyramidal side effects (EPS) induced by the blockade of D2 dopamine receptors by antipsychotics. Neuroanatomical and neurophysiological data confirm the existence of pathways whereby 5-HT2 antagonism may influence EPS. The experimental data in rodents is marginally positive, but shows that the net effect of 5-HT2 antagonism is dependent upon the precise conditions under which catalepsy is induced. The data in monkeys are mainly negative. Studies in patients who have received adjunct 5-HT2 antagonists in addition to typical neuroleptics lend some support the the hypothesis, but are not conclusive. It is reasoned that 5-HT2 antagonism plays no role in clozapine's freedom from EPS, but it may be responsible for risperidone's decreased propensity to cause EPS. The article concludes that there is support for a conditional role of 5-HT2 in decreasing EPS: 5-HT2 antagonists may delay the onset and decrease the severity of EPS but cannot totally eliminate its occurrence. The implications of these findings for the next generation of combined 5-HT2/D2 antagonists are discussed.

Mechanisms of action of atypical antipsychotic drugs: a critical analysis

Various criteria used to define atypical antipsychotic drugs include: 1) decrease, or absence, of the capacity to cause acute extrapyramidal motor side effects (acute EPSE) and tardive dyskinesia (TD); 2) increased therapeutic efficacy reflected by improvement in positive, negative, or cognitive symptoms; 3) and a decrease, or absence, of the capacity to increase prolactin levels. The pharmacologic basis of atypical antipsychotic drug activity has been the target of intensive study since the significance of clozapine was first appreciated. Three notions have been utilized conceptually to explain the distinction between atypical versus typical antipsychotic drugs: 1) dose-response separation between particular pharmacologic functions; 2) anatomic specificity of particular pharmacologic activities; 3) neurotransmitter receptor interactions and pharmacodynamics. These conceptual bases are not mutually exclusive, and the demonstration of limbic versus extrapyramidal motor functional selectivity is apparent within each arbitrary theoretical base. This review discusses salient distinctions predominantly between prototypic atypical and typical antipsychotic drugs such as clozapine and haloperidol, respectively. In addition, areas of common function between atypical and typical antipsychotic drug action may also be crucial to our identification of pathophysiological foci of the different dimensions of schizophrenia, including positive symptoms, negative symptoms, and neurocognitive deficits.

Extrapyramidal symptoms with selective serotonin reuptake inhibitors

BACKGROUND

Several case reports in the literature suggest that selective serotonin reuptake inhibitors can produce extrapyramidal symptoms.

METHODS

Computerised literature searches were used to identify reports on extrapyramidal symptoms and serotonin reuptake inhibitors. Subsequently, manual searches were made for articles in which there was any indication of the mechanisms responsible for these extrapyramidal symptoms.

RESULTS

Only a few reports could be identified in which serotonin reuptake inhibitors were implicated in extrapyramidal symptoms in some patients.

CONCLUSIONS

Evidence is discussed from preclinical and clinical studies suggesting the interaction between serotoninergic and dopaminergic neurotransmitter system, as a possible mechanism for production of extrapyramidal symptoms.

Motor and mental aspects of acute extrapyramidal syndromes

Acute extrapyramidal syndromes (EPS) are one of the major limitations to effective neuroleptic treatment. These disorders have both motor (objective) and mental (subjective) aspects, which must be considered in any evaluation and differential diagnosis of treatment-related side effects. The disorders of akathisia, acute dystonia and parkinsonism have unique features that are best understood in the context of a careful assessment of patient characteristics, drug factors and temporal aspects. Though acute EPS are commonly explained on the basis of dopamine D2 receptor antagonism, data from several lines of study raise important questions about this hypothesis. The roles of receptor subtype specificity, brain region selectivity and ratios of different receptor subtype antagonism are discussed. New and novel antipsychotic drugs with low rates of EPS are important clinical advancements that will increase patients' ability to participate in therapy and rehabilitation and thus improve their quality of life.

The novel selective and silent 5-HT1A receptor antagonist (+)-WAY-100135 aggravates dystonic movements in a mutant hamster model

Several clinical and experimental findings suggest that abnormal serotonin (5-HT) function may be involved in movement disorders such as dystonia, and it was proposed that selective 5-HT1A receptor antagonists may be of benefit in treating such disorders. In the present study, the novel, highly selective and silent 5-HT1A receptor antagonist (+)-WAY-100135 (N-tert-butyl-3(4-(2-methoxyphenyl)piperazin-1-yl)-2-phenylprop ionamide) was tested in an inbred line of Syrian hamsters with generalized dystonia, i.e. a frequent movement disorder in humans. In order to demonstrate that WAY-100135 acts as a 5-HT1A receptor antagonist in the hamster, the drug was shown to antagonize the behavioural syndrome induced by 8-hydroxy-2-(di-n-propylamino)tetralin. When administered at 5-HT1A receptor antagonistic doses in dystonic hamsters, (+)-WAY-100135 dramatically aggravated the dystonic attacks. The data thus suggest that, in contrast to previous theoretical proposals, 5-HT1A receptor antagonists provide no novel therapeutic approach to involuntary movement disorders such as dystonia.

Treatment of schizophrenia: a clinical and preclinical evaluation of neuroleptic drugs

Forty years after the first clinical report on the effectiveness of chlorpromazine in psychiatric patients, neuroleptic drugs are still the most widely used drugs in the treatment of schizophrenia. Indeed, there are no other drugs which have proven to be as effective in the treatment of this severe psychiatric disorder. Yet, there are still many unresolved problems relating to neuroleptic drugs. The present review gives a comprehensive overview of our knowledge (and our lack of knowledge) with respect to the clinical and preclinical effects of neuroleptic drugs and tries to integrate this knowledge in order to identify the neuronal mechanisms underlying the therapeutic and side effects of neuroleptic drugs.

Serotonergic and dopaminergic aspects of neuroleptic-induced extrapyramidal syndromes in nonhuman primates

Neuroleptic drug-induced acute extra-pyramidal syndromes are one of the major reasons why patients discontinue their antipsychotic medicines. The typical (e.g., haloperidol) neuroleptic drug produces acute extrapyramidal symptoms in the majority of patients, whereas the atypical (clozapine) neuroleptic produces only minimal motor system side effects. Serotonin S2 antagonists often reduce or prevent catalepsy in rodents, but the limited number of studies in nonhuman primates have produced conflicting results. The hypothesis of a high serotonin S2/dopamine D2 antagonism ratio as a mechanism underlying atypical neuroleptic effects in preventing acute extrapyramidal syndromes deserves further evaluation in nonhuman primate models because extrapyramidal symptoms in monkeys closely resemble those in patients. Cebus monkeys (22-28 years old) were tested with compounds that ranged from low to high S2/D2 antagonism ratios. These were haloperidol, fluphenazine, clopenthixol, melperone, tefludazine, setoperone, risperidone, and clozapine. A saline control was included with a wide dose range of each of these drugs that was tested in a once-weekly, blindly-scored random drug administration schedule. Dystonia was scored on four different symptoms by an experienced rater who was blind to drug dosage. All the compounds, with the exception of clozapine, produced clinically indistinguishable dose-related dystonia. The only difference was the dose at which dystonia appeared. In contrast to rodent studies, these nonhuman primate investigations with drugs, spanning a wide range of S2/D2 antagonism ratios, produced clinically similar extrapyramidal symptoms. Thus, adding an S2 antagonism component to neuroleptics does not appear to provide an explanation for the motor side effect profile of atypical neuroleptics, or a method for designing neuroleptic drugs that will be free of extrapyramidal symptoms.

Effect of chronic treatment with NNC 756, a new D-1 receptor antagonist, or raclopride, a D-2 receptor antagonist, in drug-naive Cebus monkeys: dystonia, dyskinesia and D-1/D-2 supersensitivity

When given subcutaneously in gradually increasing doses, up to 1 mg/kg, NNC 756, a dopamine (DA) D-1 antagonist, failed to produce dystonia in eight drug-naive Cebus monkeys. In contrast, raclopride, a DA D-2 antagonist, produced dystonia at low doses (0.010-0.015 mg/kg). Following pre-treatment with raclopride, NNC 756 also induced dystonia at low doses (0.015-0.025 mg/kg), but continued treatment caused tolerance, and increasing doses of NNC 756 could be administered without induction of dystonia. NNC 756 induced a dose-dependent parkinsonism (slow, stiff movements and tremor), and more sedation than raclopride. After treatment for 14 weeks, withdrawal of raclopride (0.01 mg/kg) led to mild oral dyskinesia (tardive dyskinesia), while withdrawal of NNC 756 (1.0 mg/kg) led to a special grooming syndrome, but no dyskinesia. Withdrawal of raclopride as well as NNC 756 led to behavioural D-1 and D-2 dopamine supersensitivity in the form of increased dyskinesia (including grooming after NNC 756) induced by D-1 agonist (SKF 81297) and increased arousal induced by D-2 agonist (quinpirole). These results indicate that D-1 antagonists such as NNC 756 elicit fewer extrapyramidal symptoms (both acute and tardive) than D-2 antagonists such as raclopride, although extremely high doses may cause a special grooming withdrawal syndrome.

Antagonism by 8-OH-DPAT, but not ritanserin, of catalepsy induced by SCH 23390 in the rat

In the present experiments, it was shown that the catalepsy induced by the dopamine D1 antagonist SCH 23390 (0.2 mg kg-1 sc), was completely antagonised by the administration of 8-OH-DPAT (0.1 mg kg-1 sc) for the duration of the effect of SCH 23390 (approx. 120 min). Neither the catalepsy induced by raclopride (16 mg kg-1 sc) nor that induced by SCH 23390 (0.2 mg kg-1 sc) could be antagonised by treatment with the 5-HT2 receptor antagonist ritanserin (0.13-2.0 mg kg-1 sc). Administration of SCH 23390 (0.0125-0.2 mg kg-1 sc) produced a significant suppression of avoidance behavior at all doses, and also produced a significant decrease in the number of intertrial crosses. At the higher doses, 0.05 and 0.2 mg kg-1 sc, there were also escape failures. In contrast to the finding in our previous report that raclopride and 8-OH-DPAT in a synergistic manner produce a suppression of conditioned avoidance behavior, no such interaction was found between 8-OH-DPAT (0.1 mg kg-1 sc) and SCH 23390 (6 micrograms kg-1 sc) in the present study.

Effects of 5-HT1A agonists and 5-HT2 antagonists on haloperidol-induced dyskinesias in squirrel monkeys: no evidence for reciprocal 5-HT-dopamine interaction

Dyskinetic movements and dystonic postures may be induced by neuroleptics in monkeys that have undergone previous neuroleptic treatment, and these motor abnormalities constitute a primate model of drug-induced extrapyramidal symptomatology. In view of previous suggestions that brain serotonergic systems may tonically inhibit dopamine neurons, the effects of several new and selective 5-HT2 receptor antagonists and 5-HT1A receptor agonists were investigated in this model. Setoperone, a dopamine D2 receptor antagonist with extremely potent 5-HT2 antagonism, caused dyskinetic movements. Although ritanserin is a potent 5-HT2 antagonist with very weak dopamine antagonist properties, this drug did not antagonize dyskinesias but induced them when administered at a high dose (30 mg/kg). Buspirone induced dyskinesias and blocked apomorphine-induced climbing, supporting prior reports that it has dopamine antagonist effects. Gepirone, a 5-HT1A agonist with less marked dopamine antagonist properties, induced dyskinesias in only one of six monkeys at 30 mg/kg and did not block haloperidol-induced dyskinesias. 8-OH-DPAT partly attenuated haloperidol-induced dyskinesias, an effect possibly attributable to its weak dopamine agonist properties. Tonic inhibition of brain extrapyramidal dopamine systems by serotonin systems does not appear to characterize neuroleptic-related dyskinesias in squirrel monkeys.

Effects of mianserin in neuroleptic-induced parkinsonism

It has been proposed that serotonin (5-HT) antagonists counteract neuroleptic-induced extrapyramidal symptoms by disinhibition of dopamine activity. The effects of the 5-HT antagonist mianserin, the anticholinergic drug procyclidine and placebo were evaluated in 16 psychiatric patients with chronic neuroleptic-induced parkinsonism in a double-blind cross-over trial. The patients received each drug in random order in 3-week periods separated by washout periods of 2 weeks. The effect of mianserin did not significantly differ from that of placebo, while parkinsonian symptoms were significantly reduced during treatment with procyclidine (P less than 0.05). Although mianserin was ineffective in chronic neuroleptic-induced parkinsonism, it cannot be excluded that 5-HT antagonists may be effective in the treatment of acute extrapyramidal side effects.