Effects of dopamine agonists, catecholamine depletors, and cholinergic and GABAergic drugs on acute dyskinesias in squirrel monkeys

Pediatric Iatrogenic Movement Disorders

The acute development of a movement disorder is often a dramatic and frightening experience for patients and families, often requiring urgent or emergent evaluation by a neurologist. In the assessment of these patients, one relies on the history, physical and neurologic examination to determine the etiology of the condition. We aim to demonstrate that a thorough medication history is an incredibly critical part of this evaluation as iatrogenic movement disorders can arise from exposure not only to psychoactive medications, but from drugs prescribed for a variety of nonneurologic disorders. This comprehensive review is organized by movement disorder semiology so that the reader can more readily develop a differential diagnosis when evaluating a patient with a movement disorder.

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.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Effects of Methamphetamine on Cortisone Concentration, NK Cell Activity and Mitogen Response of T-lymphocytes in Female Cynomolgus Monkeys

As a model for studying methamphetamine (MAP) abuse, which has become a social problem in Japan, we investigated the changes in serum cortisone, NK cell activity and mitogenic response of T-lymphocytes after a single injection of MAP (3.0 mg/kg) in female cynomolgus monkeys. Serum cortisol concentration was significantly elevated to 2.66 times pre-injection levels at 6 h post-injection, and the effect was still observed 24 h later. NK cell activity was significantly elevated at 6 h after MAP injection, but at 24 h after injection had dropped markedly to 49.5% of baseline. Mitogen (PHA) response of lymphocytes was elevated when MAP was injected, and this increased level continued up to 24 h. We speculate that the transient increase in NK cell activity followed by a distinct drop, as well as the changes in T-lymphocytes, may be strongly related to the cortisone concentration.

Antipsychotic drug-induced movement disorders

Very early in the process of diagnosing abnormal involuntary movement (AIM) disorders, one can be rewarded by keeping a high index of suspicion for possible drug-induced causes, not only through a complete list of current medications, but also identification of the drugs the patient used to take and other possible offending medications that might be available from family members and other sources. Among drug-induced movement disorders, antipsychotic drugs and other dopamine receptor blocking agents occupy a central place. Their various acute and tardive motor complications provide the template of this short review. Movement disorders caused by antidepressants, lithium, antiemetics, antiparkinsonian agents, anticonvulsants, calcium channel blockers, sympathomimetics and others are only briefly covered in table form.

Ionotropic and metabotropic GABA and glutamate receptors in primate basal ganglia

The functions of glutamate and GABA in the CNS are mediated by ionotropic and metabotropic, G protein-coupled, receptors. Both receptor families are widely expressed in basal ganglia structures in primates and nonprimates. The recent development of highly specific antibodies and/or cDNA probes allowed the better characterization of the cellular localization of various GABA and glutamate receptor subtypes in the primate basal ganglia. Furthermore, the use of high resolution immunogold techniques at the electron microscopic level led to major breakthroughs in our understanding of the subsynaptic and subcellular localization of these receptors in primates. In this review, we will provide a detailed account of the current knowledge of the localization of these receptors in the basal ganglia of humans and monkeys.

Regional differences in chronic neuroleptic effects on extracellular dopamine activity

The extracellular levels of dopamine (DA) and DA metabolites in the caudate-putamen (CPu) and the nucleus accumbens (NA) of rats following administration of haloperidol (HAL) decanoate and fluphenazine (FLU) decanoate for 8 months were assessed using intracranial microdialysis 1 month after final injection. Both HAL- and FLU-treated animals showed persisting plasma neuroleptic levels at time of sacrifice. Extracellular basal levels of homovanillic acid (HVA) in the CPu were significantly elevated in the FLU-treated animals, while basal levels of 3,4-dihydroxyphenylacetic acid (DOPAC) in the CPu were significantly elevated in the HAL-treated animals. Basal levels of DA and the serotonin metabolite, 5-hydroxyindoleacetic acid (5HIAA) in the CPu were not significantly different between groups. No significant between-group differences were found for basal levels of any of the analytes in the NA. Neuroleptic-treated animals showed an enhanced response to direct infusion through the dialysis probe of amphetamine (1 microM) and nomifensine (10 microM) in the CPu but not the NA. These results suggest that chronic neuroleptic treatment produces enhanced extracellular DA activity in nigrostriatal, but not mesolimbic DA pathways.

Intermittent and continuous haloperidol regimens produce different types of oral dyskinesias in rats

Rats were administered equivalent doses of haloperidol for either 28 days or 8 months using one of two different drug regimens: intermittent (i.e., weekly injections) or continuously (via drinking water and osmotic mini-pumps). Oral movements were determined by human observers and by a computerized video analysis system, which determined number and amplitude of jaw openings and closings (computer-scored movelets "CSMs") as well as the slope (amplitude/duration) and frequency spectrum (fourier transform) of oral activity. The two drug groups developed distinctively different changes over time. Continuous administration resulted in late-onset oral activity changes at 1-3 Hz and withdrawal increases in CSMs, a pattern expected of tardive dyskinesia. Intermittent treatment produced a primed dystonia-like pattern: large amplitude CSMs which had steep onset slopes and a peak energy at 4-7 Hz. These results demonstrate the importance of drug regimen in determining the type of neuroleptic-induced dyskinesias which develop with prolonged neuroleptic treatment in rodents.

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.

The pharmacological characterisation of pilocarpine-induced purposeless chewing behaviour in the rat

Purposeless chewing in rats was induced by the acute administration of the cholinergic agonist pilocarpine or by physostigmine. Pilocarpine-induced chewing was antagonised by the centrally acting anticholinergic drugs scopolamine, benzhexol and secoverine, but not by the peripherally acting anticholinergic drug methylscopolamine. Both benzhexol and secoverine caused dose-dependent inhibition of pilocarpine-induced chewing. The D-2 antagonist sulpiride and the D-1 antagonist SCH 23390 did not inhibit pilocarpine-induced chewing. The non-selective neuroleptics pimozide, trifluoperazine and thioridazine also were inactive. In contrast, clozapine caused a dose-related inhibition of pilocarpine-induced chewing. The alpha-1 antagonist prazosin, the alpha-2 antagonist idazoxan, the beta-antagonists propranolol and metoprolol and the H-1 antagonist mepyramine did not reduce pilocarpine-induced chewing. Purposeless chewing behaviour induced by pilocarpine was reduced in a dose-related manner by the administration of the 5-HT antagonists methiothepin and mianserin, but not by spiperone or ketanserin. These data confirm that pilocarpine-induced chewing behaviour in the rat is a model of central cholinergic activity, but suggest that a serotonergic component may be involved in the mediation of this behaviour.

The anti-emetic properties of 1-sulpiride in a ground-based model of space motion sickness

L-sulpiride, at a dose of 4 mg/kg, essentially abolished motion-induced emesis in a group of 6 squirrel monkeys undergoing horizontal rotation at 25 rpm, a terrestrial model of space motion sickness (SMS). Extrapyramidal side effects were not observed. In the absence of the drug, the usual emetic response returned. In comparison while typical neuroleptics were also strongly anti-emetic, they produced a considerable degree of rigidity and akinesia.

Effects of gamma-hydroxybutyrate on the performance of monkeys in a Go/No-go visual discrimination task

It has been suggested that monkeys, administered gamma-hydroxybutyrate (GHB), manifest a state resembling petit mal status. This implies that an animal would produce erroneous responses immediately prior to, and discontinue behaviors requiring any cognitive effort concurrently with, an episode of GHB-induced generalized 3 cps wave-spike bursts in the EEG. This prediction was not confirmed in the present study. Rhesus macaques (Macaca mulatta) were trained to perform in a visual discrimination Go/No-go test. Thereafter bipolar transcortical electrodes were implanted in the hemisphere contralateral to the preferred hand. All monkeys discontinued to lever-press for water reward when administered GHB (125 or 250 mg/kg, esophageal intubation) and exhibited signs of reduced postural control and somnolence punctuated by episodes of hypermotility about 40-50 min after GHB. However, the monkey's difficulties in completing the program were not associated with the development of generalized hypersynchronous EEG activity. While occasional wave-spike bursts did occur, they were poorly regulated, often 'focal' (i.e. developed only in isolated areas), and had a frequency of 1.5-2 cps. In this state, animals could be easily roused by sensory stimuli. All of them reacted with a characteristic aversive-aggressive display when confronted by a direct gaze. These effects are interpreted to be more consistent with characterization of GHB activity as that of a potent hypnotic rather than a convulsant agent.

D1 dopamine receptor--the search for a function: a critical evaluation of the D1/D2 dopamine receptor classification and its functional implications

The present review focuses on the hypothesized D1/D2 dopamine (DA) receptor classification, originally based on the form of receptor coupling to adenylate cyclase activity. The pharmacological effects of compounds exhibiting putative selective agonist or antagonist profiles at those DA receptors positively coupled to adenylate cyclase activity (D1 DA receptors) are extensively reviewed. Comparisons are made with the effects of putative selective D2 DA receptor agonists and antagonists, and on the basis of this work, the DA receptor classification is critically evaluated. A variety of biochemical, behavioral, and electrophysiological evidence is presented which supports the view that D1 and D2 DA receptors can interact in both an opposing and synergistic fashion. Particular attention is focused on the possibility that D1 receptor stimulation is required to enable the expression of certain D2 receptor-mediated effects, and the functional consequences of this form of interaction are considered. A hypothetical model is presented which considers how both the opposing and enabling forms of interaction between D1 and D2 DA receptors can control behavioral expression. Finally, the clinical relevance of this work is discussed and the potential use of selective D1 receptor agonists and antagonists in the treatment of psychotic states and Parkinson's disease is considered.

Acute dystonic reaction to bethanechol--a direct acetylcholine receptor agonist

Bethanechol is a direct agonist of the acetylcholine receptor that was recently introduced in the therapy of gastro-oesophageal reflux. Acute dystonic reactions to bethanechol were observed in a 10-month-old infant who also demonstrated similar dystonic reactions to dopamine receptor blocking agents of two different classes. This first report of acute dystonic reaction to cholinergic agonists in human is in accord with the current theories of the rôle of acetylcholine and dopamine in the pathogenesis of acute dystonic reactions.

SCH 23390 dissociated from conventional neuroleptics in apomorphine climbing and primate acute dyskinesia models

SCH 23390 induced only a negligible incidence of the acute dyskinetic syndrome, a predictor of neuroleptic-induced extrapyramidal liability, in squirrel monkeys. However, haloperidol-induced dyskinesias were potentiated by SCH 23390 and were blocked by the D-1 agonist, SKF 38393. When administered orally or intraperitoneally to mice, SCH 23390 showed a considerably wider dose separation than did conventional neuroleptics between antagonism of apomorphine climbing and antagonism of stereotyped sniffing. Clinically relevant distinctions may exist between D-1 and D-2 antagonists, with D-1 antagonists (exemplified by SCH 23390) showing lower, although possibly not negligible, potential to cause extrapyramidal side effects.

Methylmercury poisoning of the developing nervous system in the rat: decreased activity of glutamic acid decarboxylase in cerebral cortex and neostriatum

The specific activities of glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) were measured in 6 regions of the central nervous system in young rats, following chronic postnatal administration of methylmercuric chloride. These rats exhibited signs of neurological impairment which included visual deficits, ataxia, spasticity and myoclonus. At the onset of neurological impairment, there was a significant reduction in GAD activity in the occipital cortex (43%), frontal cortex (37%) and caudate-putamen (42%). Preceding the onset of neurological impairment, diminished GAD activity was detected only in the occipital cortex. In the cerebellum, thalamus and spinal cord, GAD activities were normal throughout the experiment. No significant differences in ChAT activity were detected in any of the 6 regions. These results are consistent with a preferential involvement of GABAergic neurons in methylmercury-induced lesions of the cerebral cortex and neostriatum.

Dopamine-receptor agonists: mechanisms underlying autoreceptor selectivity. I. Review of the evidence

The behavioural, biochemical, neuroendocrinological and electrophysiological actions of the enantiomers of the dopamine (DA) analogue 3-(3-hydroxyphenyl)-N-n-propylpiperidine, 3-PPP, are extensively reviewed. (+)-3-PPP acts in a fashion similar to classical direct-acting DA agonists, stimulating both DA autoreceptors and postsynaptic DA receptors, although in some situations the drug appears to exhibit partial agonist activity. (-)-3-PPP exerts a variety of actions in different pharmacological models. Either agonistic, antagonistic or both agonistic and antagonistic activity are observed depending on the anatomical location of the relevant DA receptors and the experimental conditions. The actions of transdihydrolisuride (TDHL) and the trans-fused 7-OH-1,2,3,4,4a,5,6,10b-octahydrobenzo(f)quinoline (HW 165) are also discussed. These agents possess a similar spectrum of action to (-)-3-PPP suggesting a new generation of DA agonists which exhibit variable intrinsic activity at different DA receptors. Finally, evidence is presented indicating that the 3-PPP enantiomers display selectivity for DA receptors.

Pharmacological characterisation of spontaneous or drug-associated purposeless chewing movements in rats

Continuous administration of haloperidol, sulpiride, or cis-flupenthixol, but not of domperidone or apomorphine, to Wistar rats for up to 3 weeks caused an increase in spontaneous purposeless chewing movements. Treatment with physostigmine and pilocarpine, but not neostigmine, for up to 3 weeks increased chewing, whilst scopolamine decreased chewing. Metergoline and cyproheptadine, but not quipazine, increased chewing after only 1 and 7 days but not thereafter. Chewing was not altered following treatment with compounds acting on GABA or noradrenaline systems or by a range of non-neuroleptic agents inducing dystonia in man. The enhancement of chewing induced by neuroleptic and cholinomimetic drugs was reduced by acute treatment with scopolamine, and reverted to control levels following drug withdrawal. Neuroleptic-induced purposeless chewing in Wistar rats appears to be primarily influenced by cerebral dopamine and acetylcholine function and may resemble acute dystonia, rather than tardive dyskinesia.