Exposure to amphetamine after substantia nigra lesion interferes with the process of behavioral recovery

Behavioral and neurochemical responses derived from dopaminergic intrastriatal grafts in hemiparkinsonian rats engaged in a novel motor task

BACKGROUND

Putative treatments derived from in vivo stem cell transplant-derived dopamine (DA) in hemiparkinsonian rats have been assessed via DA-agonist-induced rotations involving imbalanced intra-hemispheric striatal DA receptor stimulation. However, such tests obscure the natural responses of grafts to sensory stimuli, and drug-induced plasticity can modify the circuit being tested. Thus, we propose an alternative testing strategy using a novel water tank swimming apparatus.

NEW METHOD

Microdialysis was used to compare striatal DA levels when rats were: (1) in a rest-phase within a bowl-shaped apparatus, or (2) in an active forced-swim phase within a specially-equipped water tank. Resting-phase DA release levels were compared with active-phase levels obtained while rats were required to swim in the water-tank task. Behavioral variables such as asymmetric circling while swimming (rotations), front-limb strokes, and front-limb reaches were captured by a camera for analysis.

RESULTS AND COMPARISON WITH EXISTING METHODS

Transplanted cells had a very modest effect on percentage of contralateral front-limb strokes, but did not reduce lesion-induced rotational asymmetry in the swim task. Neither striatal DA levels, nor their breakdown products, were significantly different between transplanted and sham-transplanted groups. Our new behavioral test eliminates the need for pharmacological stimulation, enabling simultaneous assessment of DA released in resting and active phases to explore graft control.

CONCLUSIONS

Our new method allows for accurate assessments of stem cell therapy for PD as an alternative to "rotation" tests. Use of natural motivations to engage in sensory-driven motor tasks provides more accurate insights into ongoing graft-derived behavioral support.

The Intersection of Central Dopamine System and Stroke: Potential Avenues Aiming at Enhancement of Motor Recovery

Dopamine, a major neurotransmitter, plays a role in a wide range of brain sensorimotor functions. Parkinson's disease and schizophrenia are two major human neuropsychiatric disorders typically associated with dysfunctional dopamine activity levels, which can be alleviated through the druggability of the dopaminergic systems. Meanwhile, several studies suggest that optimal brain dopamine activity levels are also significantly impacted in other serious neurological conditions, notably stroke, but this has yet to be fully appreciated at both basic and clinical research levels. This is of utmost importance as there is a need for better treatments to improve recovery from stroke. Here, we discuss the state of knowledge regarding the modulation of dopaminergic systems following stroke, and the use of dopamine boosting therapies in animal stroke models to improve stroke recovery. Indeed, studies in animals and humans show stroke leads to changes in dopamine functioning. Moreover, evidence from animal stroke models suggests stimulation of dopamine receptors may be a promising therapeutic approach for enhancing motor recovery from stroke. With respect to the latter, we discuss the evidence for several possible receptor-linked mechanisms by which improved motor recovery may be mediated. One avenue of particular promise is the subtype-selective stimulation of dopamine receptors in conjunction with physical therapy. However, results from clinical trials so far have been more mixed due to a number of potential reasons including, targeting of the wrong patient populations and use of drugs which modulate a wide array of receptors. Notwithstanding these issues, it is hoped that future research endeavors will assist in the development of more refined dopaminergic therapeutic approaches to enhance stroke recovery.

Enhancing Recovery after Stroke with Noradrenergic Pharmacotherapy: A New Frontier?

Despite much progress in stroke prevention and acute intervention, recovery and rehabilitation have traditionally received relatively little scientific attention. There is now increasing interest in the development of stroke recovery drugs and innovative rehabilitation techniques to promote functional recovery after completed stroke. Experimental work over the past two decades indicates that pharmacologic intervention to enhance recovery may be possible in the subacute stage, days to weeks poststroke, after irreversible injury has occurred. This paper discusses the concept of “rehabilitation pharmacology” and reviews the growing literature from animal studies and pilot clinical trials on noradrenergic pharmacotherapy, a new experimental strategy in stroke rehabilitation. Amphetamine, a monoamine agonist that increases brain norepinephrine levels, is the most extensively studied drug shown to promote recovery of function in animal models of focal brain injury. Further research is needed to investigate the mechanisms and clinical efficacy of amphetamine and other novel therapeutic interventions on the recovery process.

Pharmacotherapy in stroke rehabilitation

BACKGROUND

Pharmacotherapy is commonly given to patients recovering from a stroke to prevent further complications (e.g. recurrent stroke, seizures) or enhance recovery. However, some drugs may have a negative impact on neuroplasticity.

OBJECTIVES

This review examines currently used drugs that are believed to promote recovery from motor and cognitive disturbances associated with stroke.

METHODS

Literature regarding the properties, efficacy, safety, and dosing of drugs used to promote recovery after stroke was reviewed.

RESULTS

The data on pharmacotherapy are insufficient to support a claim of significantly improved rehabilitation outcomes. Moreover, a growing body of evidence indicates that some agents can impair functional reorganization and slow the recovery process. However, a few chemicals are reported to be beneficial for stroke rehabilitation. The most promising are noradrenergic and dopaminergic agents, as well as several growth factors; these should be the future focus of extensive randomized clinical trials.

CONCLUSIONS

Currently there is no drug with proven efficacy in enhancing poststroke recovery.

Amphetamine-evoked rotation requires newly synthesized dopamine at 14 days but not 1 day after intranigral 6-OHDA and is consistently dissociated from sensorimotor behavior

Immediately after unilateral, intranigral 6-hydroxydopamine (6-OHDA), amphetamine (AMPH) evokes "paradoxical" contraversive rotation, whereas 14 days later, AMPH evokes the traditional ipsiversive rotation used to model the chronic Parkinsonian state. In this study, the hypothesis was that accelerated dopamine (DA) synthesis ipsilateral to the lesion augments cytoplasmic DA to produce paradoxical rotation. Therefore, the sensitivity to synthesis inhibition of AMPH-evoked rotation at 1 or 14 days after 6-OHDA was assessed. To determine the functional status that might be reflected by paradoxical rotation, sensorimotor abilities were examined at 1 and 14 days following unilateral 6-OHDA using the elevated swing, paw placement, grip strength, ladder walking, somatosensory neglect, and cylinder tests. At 14 days after 6-OHDA when AMPH-evoked ipsiversive rotation is mediated by the intact hemisphere, rotation was dose-dependently reduced by tyrosine hydroxylase (TH) inhibition with alpha-methyl-p-tyrosine (alpha-MPT) or dopa decarboxylase (DDC) inhibition with 3-hydroxybenzyl hydrazine (NSD-1015), indicating dependence upon newly synthesized DA. Conversely, at 1 day after 6-OHDA, paradoxical rotation, presumably mediated by the treated hemisphere, was completely resistant to synthesis blockade, indicating an abundant supply of intracellular DA that is independent from synthesis rates. Sensorimotor behaviors were not correlated with AMPH-evoked rotation. The present data do not support the hypothesis that enhanced DA synthesis is required to express paradoxical rotation. Therefore, alternative mechanisms that may enhance cytoplasmic DA to produce paradoxical rotation are discussed.

Amphetamines for improving recovery after stroke

BACKGROUND

Animal research shows that treatment with amphetamines improves recovery after focal cerebral ischaemia. If the effects are similar in humans, amphetamine treatment could have a major impact on recovery from stroke.

OBJECTIVES

To assess the effects of amphetamine treatment in patients with stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (last searched January 2006), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2006), MEDLINE (1966 to January 2006), EMBASE (1980 to January 2006), CINAHL (1982 to January 2006), CINAHL (1982 to January 2006), Science Citation Index (1992 to March 2005) and registers of ongoing trials. We also checked the reference lists of all relevant articles and reviews, and contacted researchers in the field.

SELECTION CRITERIA

Randomized unconfounded trials comparing amphetamine with placebo.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion and assessed trial quality; one extracted the data.

MAIN RESULTS

Ten studies involving 287 patients were included, but not all trials contributed data to each outcome examined in this review. The quality of the trials varied but was generally high. Based on three trials (106 patients) there was no evidence that amphetamine treatment reduced death or dependence (Peto's odds ratio (Peto OR) 1.5, 95% confidence interval (CI) 0.6 to 3.3). Imbalances at baseline with more serious stroke allocated to amphetamine may account for the trend for more deaths at the end of follow up among amphetamine-allocated patients (Peto OR 2.8, 95% CI 0.9 to 8.6). Based on two trials (73 patients) systolic (weighted mean difference (WMD) 8.4 mm Hg, 95% CI 1.6 to 15.2) and diastolic (WMD 4.9 mm Hg, 95% CI 1.1 to 8.8) blood pressure, as well as heart rate, increased (WMD 10.6 bpm, 95% CI 3.3 to 17.8) in amphetamine-allocated patients. Based on six studies (176 patients) there was evidence of a better relative change from baseline to last follow up in motor function (WMD -6.1 points; 95% CI -10.4 to -1.9) Different results with different analysis approaches emphasize caution in the interpretation of the results.

AUTHORS' CONCLUSIONS

At present, too few patients have been studied to draw any definite conclusions about the effects of amphetamine treatment on recovery from stroke. The suggested benefits on motor function and the non-significant trend towards increased risk of death could be related to imbalances in prognostic variables or other bias in the studies. Further research is therefore justified.

Drugs for Stroke Recovery

Clinical trials of pharmacological agents in stroke have mainly focused on events that need to be modified in the very acute stage, such as restoration of blood flow with thrombolytic therapy or reducing the effects of ischaemia with neuroprotective therapy. Thrombolytic therapy is, however, only effective within the first few hours of stroke onset and so far, no neuroprotective therapy has proven to be efficacious in humans. Thus, there is a great need for new pharmacological strategies to improve outcome after stroke. Accumulating evidence supports the assumption that the brain is plastic and improvements can be expected after permanent injuries. Acute and chronic alterations in neurotransmitter regulation after injury affects plasticity and may thus provide a basis for new pharmacological targets for stroke recovery. The search for pharmacological therapies that affect the recovery process after a permanent injury has been intensified during the last decade. Amphetamines, in combination with training, are currently one of the most promising pharmacological strategies studied for recovery after stroke. Several non-mutually exclusive hypotheses, more or less supported by experimental studies, have tried to explain the mechanisms underlying the facilitation of recovery of function with amphetamine treatment. Amphetamines are believed to hasten the processes in the brain, such as plasticity mechanisms and resolution of diaschisis. The combination of amphetamine and task-specific training seems to be of importance to the outcome. Results from animal studies are consistent between different models and species, and mainly show an increased rate of recovery but there are a few exceptions, with some studies reporting no effect or even a decreased recovery rate. In humans the number of randomised controlled studies of amphetamines is growing rapidly. Results from a Cochrane systematic review indicate a faster motor and language recovery rate with treatment, but the number of studies is too few and studies are too small to draw definite conclusions about the effect on recovery of stroke. Data in the systematic review also indicate that the mortality rate is higher in amphetamine-treated patients compared with placebo-treated patients. However, this is most likely because of baseline imbalances between the treatment groups with patients with more severe strokes being allocated to amphetamine treatment. Further clinical trials are justified, but at present amphetamines should not be used in clinical practice.

Dexamphetamine treatment in stroke

Reducing disability and dependency after a stroke is an important clinical objective. We examine what is known about the use of dexamphetamine in patients recovering from an acute stroke, and consider whether further clinical studies should be undertaken. Dexamphetamine has repeatedly been shown to enhance recovery after experimental brain injury in animals, the best effects being seen when dexamphetamine is combined with lesion-specific motor training or sensory stimulation. Postulated mechanisms for these beneficial effects in animals are in keeping with contemporary theories of neurophysiological rehabilitation in man. There have been few clinical studies of dexamphetamine during rehabilitation after an acute stroke. Four controlled trials demonstrated a tendency to an improved outcome when dexamphetamine was paired with therapy and administered 3-30 days after an ischaemic stroke. However, clinical studies to date have been small, included only highly selected patients, and have not addressed possible confounding effects of the drug on mood and untreated depression. Dexamphetamine has previously been used under supervision in medically ill patients and appears to be safe and well-tolerated. There is a need for well-designed studies to assess further the safety and efficacy of dexamphetamine in rehabilitation after stroke.

Safety of dexamphetamine in acute ischemic stroke: a randomized, double-blind, controlled dose-escalation trial

BACKGROUND AND PURPOSE

Amphetamine is reported to enhance recovery after experimental stroke, but results from the first few trials in humans are inconclusive. Limited information is available on treatment safety. This study intended to investigate the safety and tolerability of dexamphetamine in patients with acute cerebral ischemia.

METHODS

Forty-five patients with cerebral ischemia were enrolled within 72 hours after onset of symptoms. Patients were randomized to 1 of 3 dose levels (2.5, 5, or 10 mg orally twice daily) or placebo for 5 consecutive days. Adverse events, blood pressure, heart rate, body temperature, consciousness level, and functional outcome measures were followed up daily during treatment. Follow-ups were made at day 7 and 1 and 3 months after stroke.

RESULTS

Mean systolic and diastolic blood pressures and heart rate increased 14 mm Hg, 8 mm Hg, and 9 bpm, respectively, with dexamphetamine treatment compared with placebo (P< or =0.01). There was no difference between dexamphetamine and placebo regarding adverse events, body temperature, or consciousness level. During treatment, there was a benefit of dexamphetamine in neurological and functional outcome (P<0.05), but differences were not maintained at follow-up.

CONCLUSIONS

Overall, dexamphetamine was safe and well tolerated by patients with acute cerebral ischemia, but blood pressure and heart rate increased during treatment in comparison to placebo. These observations may be important in the future planning of amphetamine trials because changes in these variables have been observed to interfere with clinical outcome. The suggestions of improvement in outcome must be confirmed in further studies.

Amphetamines for improving recovery after stroke

BACKGROUND

Experimental animal research shows that treatment with amphetamines improves recovery after focal cerebral ischaemia. If the effect were similar in humans, amphetamine treatment could have a major impact on recovery from stroke.

OBJECTIVES

The objective of this review was to assess the effects of amphetamine treatment in patients with stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (last searched November 2002). In addition, we searched the Cochrane Controlled Trials Register (Cochrane Library, Issue 4 2002), MEDLINE (1966-September 2002), EMBASE (1980-November 2002), and Science Citation Index (1992-December 2002). The reference lists of all relevant articles and reviews were checked, and we contacted researchers in the field to identify further published and unpublished studies.

SELECTION CRITERIA

Randomized unconfounded trials comparing amphetamine with placebo.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected trials for inclusion, assessed trial quality and extracted the data.

MAIN RESULTS

Seven studies involving 172 patients were included. The quality of the trials varied but was generally high. Based on two trials (85 patients) there was no evidence that amphetamine treatment reduced death or dependence (Peto's odds ratio, [Peto OR] 1.54; 95% Confidence Interval [CI] 0.64 to 3.73). In these two trials, there were imbalances at baseline, with more serious strokes allocated to amphetamine. This imbalance may account for the trend for more deaths at the end of follow-up among amphetamine allocated patients (Peto OR 3.33; 95% CI 0.99 to 11.24). Based on 4 studies (95 patients) there was evidence of a better relative change in motor function according to the Fugl-Meyer motor scale (Weighted Mean Difference, [WMD] -8.17 points; 95% CI -13.58 to -2.76) and based on 1 study (21 patients) there was evidence of a better change in language function as assessed by the Porch Index of Communicative Ability score (WMD -7.51 points; 95% CI -14.42 to -0.60) in amphetamine allocated patients.

REVIEWER'S CONCLUSIONS

At present, too few patients have been studied to draw any definite conclusions about the effects of amphetamine treatment on recovery from stroke. The suggested benefits on motor and language function, and the non-significant trend towards increased risk of death, could be related to imbalances in prognostic variables or other bias in studies. Further research in this area is therefore justified.

An alpha(2)-adrenergic antagonist, atipamezole, facilitates behavioral recovery after focal cerebral ischemia in rats

Previous studies suggest that enhanced noradrenergic neurotransmission promotes functional recovery following cerebral lesions. The present study investigated whether systemic administration of an alpha(2)-adrenergic antagonist, atipamezole, facilitates recovery following transient focal cerebral ischemia in rats. The effect of atipamezole therapy on recovery from ischemia was compared with the effect of enriched-environment housing in rats. Ischemia was induced by occlusion of the right middle cerebral artery (MCA) for 120 min using the intraluminal filament model. Daily atipamezole treatment (1 mg/kg, subcutaneously) was started on day 2 after ischemia induction and drug administration stopped after 10 days. Another group of rats was housed in an enriched environment from day 2 following ischemia induction until the end of the experiment. Several different behavioral tests were used to measure functional recovery during the 26 days following the induction of focal cerebral ischemia. There was improved performance in the limb-placing test from the beginning of atipamezole treatment to day 8, and in wheel-running in the foot-slip test on days 2 and 4. Enriched-environment housing facilitated recovery in the foot-slip test in a later phase of the test period (days 8 to 10). Discovery of a hidden platform in a water-maze task was also facilitated in rats housed in the enriched environment, but this was probably due to the increased swimming speed of these rats. The present data suggest that the alpha(2)-adrenergic antagonist, atipamezole, facilitates sensorimotor recovery after focal ischemia, but has no effect on subsequent water-maze tests assessing spatial learning and memory, when assessed 11 days after the cessation of drug administration.

Behavioral effects of the alpha(2)-adrenoceptor antagonist, atipamezole, after focal cerebral ischemia in rats

The present study characterized the behavioral effects of the selective alpha(2)-adrenoceptor antagonist, atipamezole, in a rat model of focal cerebral ischemia. Atipamezole (1 mg/kg, s.c.) or desipramine (5 mg/kg, i.p.), a noradrenaline reuptake blocker, was administered either as a single injection 2 days after ischemia induction or for 10 days thereafter (subacute administration). A subacute atipamezole treatment given 30 min before behavioral assessment improved performance in the limb-placing test (days 5, 7, 9, and 11) and in the foot-slip test (days 3 and 7), but not in the beam-walking test. There was no difference between experimental groups in behavioral performance following a single administration of atipamezole or following single or subacute administration of desipramine. The drug treatments did not attenuate the impairment of spatial cognitive performance of ischemic rats in the Morris water-maze test. These results suggest that repeated use-dependent release of noradrenaline by atipamezole facilitates the sensorimotor recovery following focal cerebral ischemia in rats.

Dissociation of kainic acid lesion effects on the asymmetry of rotation and lateral head movements

The present study tested the relationship between horizontal head movement asymmetry and rotation behavior after unilateral kainic acid (KA) lesions of the pontine reticular formation (PRF). In line with previous studies, the lesions decreased the rate of ipsilateral spontaneous head movements and spared contralateral spontaneous head movements. In contrast to previous studies, however, these lesions facilitated ipsilateral rather than contralateral rotation. Histological analysis revealed that the ipsilateral rotation may be accounted for by distant effects of the KA injection in the PRF on the ipsilateral substantia nigra (SN). We conclude that unilateral lesions consisting solely of the PRF lead to a preference for contralateral horizontal head movements which then channel rotated away from the lesioned side. KA injections in the PRF, however, are also associated with distant lesions within the ipsilateral extrapyramidal system which override the channeling effect of the contralateral head movements and induce instead ipsilateral rotation.