Amphetamine and apomorphine restore tactile placing after motor cortex injury in the cat

Inhibiting metabotropic glutamate receptor 5 after stroke restores brain function and connectivity

Stroke results in local neural disconnection and brain-wide neuronal network dysfunction leading to neurological deficits. Beyond the hyper-acute phase of ischaemic stroke, there is no clinically-approved pharmacological treatment that alleviates sensorimotor impairments. Functional recovery after stroke involves the formation of new or alternative neuronal circuits including existing neural connections. The type-5 metabotropic glutamate receptor (mGluR5) has been shown to modulate brain plasticity and function and is a therapeutic target in neurological diseases outside of stroke. We investigated whether mGluR5 influences functional recovery and network reorganization rodent models of focal ischaemia. Using multiple behavioural tests, we observed that treatment with negative allosteric modulators (NAMs) of mGluR5 (MTEP, fenobam and AFQ056) for 12 days, starting 2 or 10 days after stroke, restored lost sensorimotor functions, without diminishing infarct size. Recovery was evident within hours after initiation of treatment and progressed over the subsequent 12 days. Recovery was prevented by activation of mGluR5 with the positive allosteric modulator VU0360172 and accelerated in mGluR5 knock-out mice compared with wild-type mice. After stroke, multisensory stimulation by enriched environments enhanced recovery, a result prevented by VU0360172, implying a role of mGluR5 in enriched environment-mediated recovery. Additionally, MTEP treatment in conjunction with enriched environment housing provided an additive recovery enhancement compared to either MTEP or enriched environment alone. Using optical intrinsic signal imaging, we observed brain-wide disruptions in resting-state functional connectivity after stroke that were prevented by mGluR5 inhibition in distinct areas of contralesional sensorimotor and bilateral visual cortices. The levels of mGluR5 protein in mice and in tissue samples of stroke patients were unchanged after stroke. We conclude that neuronal circuitry subserving sensorimotor function after stroke is depressed by a mGluR5-dependent maladaptive plasticity mechanism that can be restored by mGluR5 inhibition. Post-acute stroke treatment with mGluR5 NAMs combined with rehabilitative training may represent a novel post-acute stroke therapy.

Supporting Post-Stroke Language and Cognition with Pharmacotherapy: Tools for Each Phase of Care

PURPOSE OF REVIEW

There is enormous enthusiasm for the possibility of pharmacotherapies to treat language deficits that can arise after stroke. Speech language therapy remains the most frequently utilized and most strongly evidenced treatment, but the numerous barriers to patients receiving the therapy necessary to recover have motivated the creation of a relatively modest, yet highly cited, body of evidence to support the use of pharmacotherapy to treat post-stroke aphasia directly or to augment traditional post-stroke aphasia treatment. In this review, we survey the use of pharmacotherapy to preserve and support language and cognition in the context of stroke across phases of care, discuss key ongoing clinical trials, and identify targets that may become emerging interventions in the future.

RECENT FINDINGS

Recent trials have shifted focus from short periods of drug therapy supporting therapy in the chronic phase to longer terms approaching pharmacological maintenance beginning more acutely. Recent innovations in hyperacute stroke care, such as tenecteplase, and acute initiation of neuroprotective agents and serotonin reuptake inhibitors are important areas of ongoing research that complement the ongoing search for effective adjuvants to later therapy. Currently there are no drugs approved in the United States for the treatment of aphasia. Nevertheless, pharmacological intervention may provide a benefit to all phases of stroke care.

No evidence of impediment by three common classes of prescription drugs to post-stroke aphasia recovery in a retrospective longitudinal sample

A number of pharmaceuticals have been identified as potential adjuvants to speech language therapy following stroke, but it is also important to consider which pharmaceuticals may result in a less robust recovery. Here we examine whether post-stroke language recovery was meaningfully impeded by cholinergic, GABAergic, or dopaminergic medications patients received. Eighty participants with left hemisphere stroke were examined retrospectively to see whether the use of one of these three classes of medication prior to admission for acute stroke, during their inpatient stay, or at discharge was associated with differences in recovery on three common measures of language. While prescription of any of the candidate drugs was relatively uncommon, groups were very well matched for many common factors that impact performance. When age, education, and acute lesion volume were controlled, there were no significant differences in performance among those taking cholinergic, GABAergic, or dopaminergic medications and those who were not. Those who experienced a "good recovery" of language (≥10% improvement on any one language measure over time) had similar exposure to these drugs to those with a poor recovery. This work represents a first look at these drug classes with regard to their effects on the recovery of language after stroke and should not be interpreted as resolving all potential for concern, but these results do offer modest reassurance that these common classes of pharmacotherapy, when given for short periods in this population, do not appear to have marked deleterious effects on post-stroke recovery of language.

Better language through chemistry: Augmenting speech-language therapy with pharmacotherapy in the treatment of aphasia

Speech and language therapy is the standard treatment of aphasia. However, many individuals have barriers in seeking this measure of extensive rehabilitation treatment. Investigating ways to augment therapy is key to improving poststroke language outcomes for all patients with aphasia, and pharmacotherapies provide one such potential solution. Although no medications are currently approved for the treatment of aphasia by the United States Food and Drug Administration, numerous candidate mechanisms for pharmaceutical manipulation continue to be identified based on our evolving understanding of the neurometabolic experience of stroke recovery across molecular, cellular, and functional levels of inquiry. This chapter will review evidence for catecholaminergic, glutamatergic, cholinergic, and serotonergic drug therapies and discuss future directions for both candidate drug selection and pharmacotherapy practice in people with aphasia.

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.

The neuroprotective potential of low-dose methamphetamine in preclinical models of stroke and traumatic brain injury

Methamphetamine is a psychostimulant that was initially synthesized in 1920. Since then it has been used to treat attention deficit hyperactive disorder (ADHD), obesity and narcolepsy. However, methamphetamine has also become a major drug of abuse worldwide. Under conditions of abuse, which involve the administration of high repetitive doses, methamphetamine can produce considerable neurotoxic effects. However, recent evidence from our laboratory indicates that low doses of methamphetamine can produce robust neuroprotection when administered within 12h after severe traumatic brain injury (TBI) in rodents. Thus, it appears that methamphetamine under certain circumstances and correct dosing can produce a neuroprotective effect. This review addresses the neuroprotective potential of methamphetamine and focuses on the potential beneficial application for TBI.

Sensorimotor recovery from cortical injury is accompanied by changes on norepinephrine and serotonin levels in the dentate gyrus and pons

Monoamines such as norepinephrine (NE) and serotonin (5-HT) have shown to play an important role in motor recovery after brain injury. The effects elicited by these neurotransmitters have been reported as distal from the area directly affected. Remote changes may take place over minutes to weeks and play an important role in post-stroke recovery. However, the mechanisms involved in spontaneous recovery have not been thoroughly delineated. Therefore, we determined the NE and 5-HT content, in the pons and hippocampal dentate gyrus (DG) as well as motor deficit and spontaneous activity in rats after 3, 10 and 20 days cortical iron injection. Three days post-lesion the pontine NE content diminished, this effect was accompanied by deficient spontaneous activity and impaired sensorimotor evaluation. Ten and twenty days after lesion the NE levels were similar to those of control group, and animals also showed behavioral recovery. Monoamines content on DG 3 days post-lesion showed no differences as compared to controls. Interestingly, ten and twenty days after cortical injury, animals showed increased NE and 5-HT. These results suggest that behavioral recovery after brain damage involve changes on monoamines levels on DG, an important structure to plastic processes. In addition, the results herein support evidence to propose these neurotransmitters as key molecules to functional recovery in the central nervous system.

The Role of Task-Specific Training in Rehabilitation Therapies

Task-oriented therapy is important. It makes intuitive sense that the best way to relearn a given task is to train specifically for that task. In animals, functional reorganization is greater for tasks that are meaningful to the animal. Repetition alone, without usefulness or meaning in terms of function, is not enough to produce increased motor cortical representations. In humans, less intense but task-specific training regimens with the more affected limb can produce cortical reorganization and associated, meaningful functional improvements.

Drug treatment of poststroke aphasia

Impairment of language function (aphasia) is one of the most common neurological symptoms after stroke. Approximately one in every three patients who have an acute stroke will suffer from aphasia. The estimated incidence and prevalence of stroke in Western Europe is 140 and 800 per 100,000 of the population. Aphasia often results in significant disability and handicap. It is a major obstacle for patients to live independently in the community. When recovery from aphasia occurs, it is usually incomplete and patients are rarely able to return to full employment and other social activities. Currently, the main treatment for aphasia is conventional speech and language therapy. However, the effectiveness of this intervention has not been conclusively demonstrated and empirical observations suggest that spontaneous biological recovery may explain most of the improvement in language function that occurs in aphasics. The generally poor prognosis of the severe forms of poststroke language impairment (Broca, Wernicke and global aphasia), coupled with the limited effectiveness of conventional speech and language therapy has stimulated the search for other treatments that may be used in conjunction with speech and language therapy, including the use of various drugs. Dopamine agonists, piracetam (Nootropil), amphetamines, and more recently donepezil (Aricept), have been used in the treatment of aphasia in both the acute and chronic phase. The justification for the use of drugs in the treatment of aphasia is based on two types of evidence. Some drugs, such as dextroamphetamine (Dexedrine), improve attention span and enhance learning and memory. Learning is an essential mechanism for the acquisition of new motor and cognitive skills, and hence, for recovery from aphasia. Second, laboratory and clinical data suggest that drug treatment may partially restore the metabolic function in the ischemic zone that surrounds the brain lesion and also has a neuroprotective effect following acute brain damage. An example of this is the nootropic agent piracetam. Extensive animal studies have demonstrated the beneficial effects of this and other drugs on neural plasticity, but data on humans are still sparse. This review provides a critical analysis of the current evidence of the effectiveness of these drugs in the treatment of acute and chronic aphasia.

Administration of low dose methamphetamine 12 h after a severe traumatic brain injury prevents neurological dysfunction and cognitive impairment in rats

We recently published data that showed low dose of methamphetamine is neuroprotective when delivered 3 h after a severe traumatic brain injury (TBI). In the current study, we further characterized the neuroprotective potential of methamphetamine by determining the lowest effective dose, maximum therapeutic window, pharmacokinetic profile and gene expression changes associated with treatment. Graded doses of methamphetamine were administered to rats beginning 8 h after severe TBI. We assessed neuroprotection based on neurological severity scores, foot fault assessments, cognitive performance in the Morris water maze, and histopathology. We defined 0.250 mg/kg/h as the lowest effective dose and treatment at 12 h as the therapeutic window following severe TBI. We examined gene expression changes following TBI and methamphetamine treatment to further define the potential molecular mechanisms of neuroprotection and determined that methamphetamine significantly reduced the expression of key pro-inflammatory signals. Pharmacokinetic analysis revealed that a 24-hour intravenous infusion of methamphetamine at a dose of 0.500 mg/kg/h produced a plasma Cmax value of 25.9 ng/ml and a total exposure of 544 ng/ml over a 32 hour time frame. This represents almost half the 24-hour total exposure predicted for a daily oral dose of 25mg in a 70 kg adult human. Thus, we have demonstrated that methamphetamine is neuroprotective when delivered up to 12 h after injury at doses that are compatible with current FDA approved levels.

Is there a role for vagus nerve stimulation therapy as a treatment of traumatic brain injury?

This paper aims to review the current literature on vagus nerve stimulation (VNS) use in animal models of traumatic brain injury (TBI) and explore its potential role in treatment of human TBI. A MEDLINE search yielded four primary papers from the same group that demonstrated VNS mediated improvement following fluid percussion models of TBI in rats, seen as motor and cognitive improvements, reduction of cortical oedema and neuroprotective effects. The underlying mechanisms are elusive and authors attribute these to attenuation of post traumatic seizures, a noradrenergic mechanism and as yet undetermined mechanisms. Reviewing and elaborating on these ideas, we speculate other potential mechanisms including attenuation of peri-infarct depolarisations, attenuation of glutamate mediated excitotoxicity, stabilisation of intracranial pressure, enhancement of synaptic plasticity, upregulation of endogenous neurogenesis and anti-inflammatory effects may have a role. Although this data unequivocally shows that VNS improves outcome from TBI in animal models, it remains to be determined if these findings translate clinically. Further studies are warranted.

Amphetamine-enhanced motor training after cervical contusion injury

Individually, motor training, pharmacological interventions, and housing animals in an enriched environment (EE) following spinal cord injury (SCI) result in limited functional improvement but, when combined, may enhance motor function. Here, we tested amphetamine (AMPH)-enhanced skilled motor training following a unilateral C3-C4 contusion injury on the qualitative components of reaching and on skilled forelimb function, as assessed using single-pellet and staircase reaching tasks. Kinematic analysis evaluated the quality of the reach, and unskilled locomotor function was also tested. Animals receiving AMPH and skilled forelimb training performed better than operated control animals on qualitative reaching, but not on skilled reaching. Those that received the combination treatment and were housed in EE cages showed significantly less improvement in qualitative reaching and grasping. Kinematic analysis revealed a decrease in digit abduction during skilled reaching among all groups, with no differences among groups. Kinematics provided no evidence that improved function was related to improved quality of reach. There was no evidence of neuroprotection in the cervical spinal cord. The absence of evidence for kinematic improvement or neuroprotection suggested that AMPH-enhanced motor training is due primarily to supraspinal effects, an enhancement of attention during skilled motor training, or plasticity in supraspinal circuitry involved with motor control.

L-Dopa effect on frequency-dependent depression of the H-reflex in adult rats with complete spinal cord transection

This study investigated whether l-dopa (DOPA), locomotor-like passive exercise (Ex) using a motorized bicycle exercise trainer (MBET), or their combination in adult rats with complete spinal cord transection (Tx) preserves and restores low frequency-dependent depression (FDD) of the H-reflex. Adult Sprague-Dawley rats (n=56) transected at T8-9 had one of five treatments beginning 7 days after transection: Tx (transection only), Tx+Ex, Tx+DOPA, Tx+Ex+DOPA, and control (Ctl, no treatment) groups. After 30 days of treatment, FDD of the H-reflex was tested. Stimulation of the tibial nerve at 0.2, 1, 5, and 10Hz evoked an H-reflex that was recorded from plantar muscles of the hind paw. No significant differences were found at the stimulation rate of 1Hz. However, at 5Hz, FDD of the H-reflex in the Tx+Ex, Tx+DOPA and Ctl groups was significantly different from the Tx group (p<0.01). At 10Hz, all of the treatment groups were significantly different from the Tx group (p<0.01). No significant difference was identified between the Ctl and any of the treatment groups. These results suggest that DOPA significantly preserved and restored FDD after transection as effectively as exercise alone or exercise in combination with DOPA. Thus, there was no additive benefit when DOPA was combined with exercise.

Long-term motor improvement after stroke is enhanced by short-term treatment with the alpha-2 antagonist, atipamezole

Drugs that increase central noradrenergic activity have been shown to enhance the rate of recovery of motor function in pre-clinical models of brain damage. Less is known about whether noradrenergic agents can improve the extent of motor recovery and whether such improvement can be sustained over time. This study was designed to determine if increasing central noradrenergic tone using atipamezole, an alpha-2 adrenoceptor antagonist, could induce a long-term improvement in motor performance in rats subjected to ischemic brain damage caused by permanent middle cerebral artery occlusion. The importance of pairing physical "rehabilitation" with enhanced noradrenergic activity was also investigated. Atipamezole (1 mg/kg, s.c.) or vehicle (sterile saline) was administered once daily on Days 2-8 post-operatively. Half of each drug group was housed under enriched environment conditions supplemented with daily focused activity sessions while the other half received standard housing with no focused activity. Skilled motor performance in forelimb reaching and ladder rung walking was assessed for 8 weeks post-operatively. Animals receiving atipamezole plus rehabilitation exhibited significantly greater motor improvement in both behavioral tests as compared to vehicle-treated animals receiving rehabilitation. Interestingly, animals receiving atipamezole without rehabilitation exhibited a significant motor improvement in the ladder rung walk test but not the forelimb reaching test. These results suggest that a short-term increase in noradrenergic activity can lead to sustained motor improvement following stroke, especially when paired with rehabilitation.

Akathisia after mild traumatic head injury

The authors describe the case of a 13-year-old boy who exhibited progressive disabling motor restlessness, torticollis, urinary symptoms, and confusion following a fall from a bicycle. The differential diagnosis of this striking symptom complex in this clinical context can be problematic. In this case, the symptoms ultimately appeared most consistent with severe akathisia resulting from a single administration of haloperidol used at an outside hospital to sedate the patient prior to a head CT scan. The literature on akathisia in pediatric patients, and especially in patients following acute head injury, is reviewed, with suggestions for an approach to these symptoms in this clinical setting.

Therapeutic approaches for spinal cord injury induced spasticity

Spasticity is evident in both humans and animals following spinal cord injury (SCI) and can contribute to significant functional limitation and disruption in quality of life of patients with this disorder. This mini-review describes a number of preclinical and clinical studies that promise to improve outcomes for, especially in terms of spasticity and hyper-reflexia, patients with SCI. A gold standard for the quantification of spasticity has proved elusive, but the combination of H-reflex frequency dependent depression and a novel stretch reflex (SR) windup protocol have the potential to provide new insights. As the pathophysiology of hyper-reflexia and spasticity continue to be investigated, the documented onset in the animal model of SCI provides critical time points for further study into these complex mechanisms. The positive effects of a passive exercise protocol and several potential pharmacological interventions are reviewed as well as a novel potential mechanism of action. Further work is needed to determine additional mechanisms that are involved in SCI, and how to optimize multiple therapies to overcome some of the deficits induced by SCI.

The effects of amphetamine on recovery of function in animal models of cerebral injury: a critical appraisal

Therapeutic strategies to promote recovery from stroke are now beginning to utilize current knowledge of neural plasticity and the neuromodulatory role of physical rehabilitation. Current interests are also focused on adjuvant therapies that may enhance plasticity associated with recovery and rehabilitation. Amphetamine was one of the earliest pharmacological interventions and continues to show promising results as an adjuvant treatment for recovery of function in pre-clinical animal studies. This drug is a potent modulator of neurological function and cortical excitation, acting primarily through norepinephrine and dopamine mechanisms to enhance arousal and attention, and thus, to facilitate learning of motor skills. Although the results from the pre-clinical studies have been primarily positive, they have not translated well to clinical trials, which have yielded mixed results. This review addresses some of the conflicting evidence from pre-clinical studies conducted between 1982 and 2008 in order to better understand how to optimize the clinical application of amphetamine as an adjuvant therapy for stroke recovery. Among many of the factors that relate to differences in outcome, it is likely that both amphetamine dose and the timing of the intervention with respect to the time of injury affected the outcome.

Acute neuroprotection to pilocarpine-induced seizures is not sustained after traumatic brain injury in the developing rat

Following CNS injury there is a period of vulnerability when cells will not easily tolerate a secondary insult. However recent studies have shown that following traumatic brain injury (TBI), as well as hypoxic-ischemic injuries, the CNS may experience a period of protection termed "preconditioning." While there is literature characterizing the properties of vulnerability and preconditioning in the adult rodent, there is an absence of comparable literature in the developing rat. To determine if there is a window of vulnerability in the developing rat, post-natal day 19 animals were subjected to a severe lateral fluid percussion injury followed by pilocarpine (Pc)-induced status epilepticus at 1, 6 or 24 h post TBI. During the first 24 h after TBI, the dorsal hippocampus exhibited less status epilepticus-induced cell death than that normally seen following Pc administration alone. Instead of producing a state of hippocampal vulnerability to activation, TBI produced a state of neuroprotection. However, in a second group of animals evaluated 20 weeks post injury, double-injured animals were statistically indistinguishable in terms of seizure threshold, mossy fiber sprouting and cell survival when compared to those treated with Pc alone. TBI, therefore, produced a temporary state of neuroprotection from seizure-induced cell death in the developing rat; however, this ultimately conferred no long-term protection from altered hippocampal circuit rearrangements, enhanced excitability or later convulsive seizures.

Mechanisms of working memory dysfunction after mild and moderate TBI: evidence from functional MRI and neurogenetics

Cognitive complaints are a frequent source of distress and disability after mild and moderate traumatic brain injury (TBI). While there are deficits in several cognitive domains, many aspects of these complaints and deficits suggest that problems in working memory (WM) play an important role. Functional imaging studies in healthy individuals have outlined the neural substrate of WM and have shown that regions important in WM circuitry overlap with regions commonly vulnerable to damage in TBI. Use of functional MRI (fMRI) in individuals with mild and moderate TBI suggests that they can have problems in the activation and allocation of WM, and several lines of evidence suggest that subtle alterations in central catecholaminergic sensitivity may underlie these problems. We review the evidence from fMRI and neurogenetic studies that support the role of catecholaminergic dysregulation in the etiology of WM complaints and deficits after mild and moderate TBI.

Increased extracellular concentrations of norepinephrine in cortex and hippocampus following vagus nerve stimulation in the rat

The vagus nerve is an important source of afferent information about visceral states and it provides input to the locus coeruleus (LC), the major source of norepinephrine (NE) in the brain. It has been suggested that the effects of electrical stimulation of the vagus nerve on learning and memory, mood, seizure suppression, and recovery of function following brain damage are mediated, in part, by the release of brain NE. The hypothesis that left vagus nerve stimulation (VNS) at the cervical level results in increased extracellular NE concentrations in the cortex and hippocampus was tested at four stimulus intensities: 0.0, 0.25, 0.5, and 1.0 mA. Stimulation at 0.0 and 0.25 mA had no effect on NE concentrations, while the 0.5 mA stimulation increased NE concentrations significantly in the hippocampus (23%), but not the cortex. However, 1.0 mA stimulation significantly increased NE concentrations in both the cortex (39%) and hippocampus (28%) bilaterally. The increases in NE were transient and confined to the stimulation periods. VNS did not alter NE concentrations in either structure during the inter-stimulation baseline periods. No differences were observed between NE levels in the initial baseline and the post-stimulation baselines. These findings support the hypothesis that VNS increases extracellular NE concentrations in both the hippocampus and cortex.

Pharmakologische Zusatzbehandlung in der Aphasietherapie

Aphasia is one of the most frequent and disabling consequences of stroke. Poor spontaneous recovery and the limited success of conventional speech therapy bring up the question of how current treatment approaches can be improved. Besides increasing training frequency-with daily sessions lasting several hours and high repetition rates of language materials ("massed training")-adjuvant drug therapy may help to increase therapy efficacy. In this article, we illuminate the potential of monoaminergic (bromocriptine, levodopa, d-amphetamine) and cholinergic (donepezil) substances for treating aphasia. For a final evaluation of combined massed training and adjuvant pharmacotherapy, randomized, placebo-controlled (multicenter) clinical trials with sufficient numbers of patients are needed. Furthermore, results of experimental animal studies of functional recovery in brain damage raise hopes that neurotrophic factors or stem cells might find a place in recovery from aphasia in the intermediate future.

Electrical stimulation of the vagus nerve enhances cognitive and motor recovery following moderate fluid percussion injury in the rat

Intermittent, chronically delivered electrical stimulation of the vagus nerve (VNS) is an FDA-approved procedure for the treatment of refractory complex/partial epilepsy in humans. Stimulation of the vagus has also been shown to enhance memory storage processes in laboratory rats and human subjects. Recent evidence suggests that some of these effects of VNS may be due to the activation of neurons in the nucleus locus coeruleus resulting in the release of norepinephrine (NE) throughout the neuraxis. Because antagonism of NE systems has been shown to delay recovery of function following brain damage, it is possible that enhanced release of NE in the CNS may facilitate recovery of function. To evaluate this hypothesis the lateral fluid percussion injury (LFP) model of traumatic brain injury was used and a variety of motor and cognitive behavioral tests were employed to assess recovery in pre-trained stimulated, control, and sham-injured laboratory rats. Two hours following moderate LFP, vagus nerve stimulation (30.0-sec trains of 0.5 mA, 20.0 Hz, biphasic pulses) was initiated. Stimulation continued in each animal's home cage at 30-min intervals for a period of 14 days, with the exception of brief periods when the animals were disconnected for behavioral assessments. Motor behaviors were evaluated every other day following LFP and tests included beam walk, locomotor placing, and skilled forelimb reaching. In each measure an enhanced rate of recovery and /or level of final performance was observed in the VNS-LFP animals compared to nonstimulated LFP controls. Behavior in the Morris water maze was assessed on days 11-14 following injury. Stimulated LFP animals showed significantly shorter latencies to find the hidden platform than did controls. Despite these behavioral effects, neurohistological examination did not reveal significant differences in lesion extent, density of fluorojade positive neurons, reactive astrocytes or numbers of spared neurons in the CA3 subarea of the hippocampus, at least at the one time point studied 15 days post-injury. These results support the idea that vagus nerve stimulation enhances the neural plasticity that underlies recovery of function following brain damage and provides indirect support for the hypothesis that enhanced NE release may mediate the effect. Importantly, since VNS facilitated both the rate of recovery and the extent of motor and cognitive recovery, these findings suggest that electrical stimulation of the vagus nerve may prove to be an effective non-pharmacological treatment for traumatic brain injury.

D-amphetamine enhances skilled reaching after ischemic cortical lesions in rats

Unilateral sensorimotor cortical (SMC) lesions in rats impair reaching and grasping movements of the contralateral forelimb. These impairments can be improved using motor rehabilitative training on a skilled reaching task, but the training may be far from sufficient to return animals to pre-lesion levels of performance. Because D-amphetamine (AMPH) has been found to promote neuroplastic responses to injury and to be very beneficial when combined with some (but not all) types of rehabilitative training, we asked in this experiment whether it could improve the efficacy of rehabilitative training in skilled reaching. Ten to 14 days after unilateral ischemic (endothelin-1 induced) lesions of the SMC, adult rats were given a 3-week regimen of AMPH (1mg/kg) coupled with daily rehabilitative training on a skilled reaching task, the single pellet retrieval task. AMPH treatment not only dramatically improved reaching performance compared with saline-injected controls, the AMPH treated rats surpassed pre-lesion levels of performance by the end of the rehabilitative training period. The greater performance in AMPH compared to saline-treated rats was still evident at 1 month, but not at 2 and 3 months, after the end of rehabilitative training. Thus, AMPH treatment can greatly enhance the efficacy of rehabilitative training on a skilled reaching task after unilateral SMC lesions, but alternate injection and training regimes may be needed to produce permanent improvements.

Working memory deficits after traumatic brain injury: catecholaminergic mechanisms and prospects for treatment -- a review

PRIMARY OBJECTIVE

To review the neural circuitry and neurochemistry of working memory and outline the evidence for working memory deficits after traumatic brain injury, and the evidence for the use of catecholaminergic agents in the amelioration of these deficits. Current knowledge gaps and research needs are identified.

MAIN OUTCOMES AND RESULTS

Impairments in working memory are a core component of the cognitive deficits associated with traumatic brain injury. Recent progress in understanding the neural circuitry and neurochemistry of working memory suggests that catecholamines play a central role in the activation and regulation of working memory and thus lays a framework in which to consider the use of catecholaminergic agents (dopaminergic and alpha-2 adrenergic agonists) in the treatment of specific cognitive deficits after traumatic brain injury.

CONCLUSIONS

The combined methods of cognitive neuroscience, functional brain imaging and neuropharmacology are proposed as an excellent method for studying working memory deficits. A strong rationale exists for the targeted use of catecholaminergic agonists in the treatment of working memory deficits after traumatic brain injury.

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.

Haloperidol, but Not Olanzapine, Impairs Cognitive Performance After Traumatic Brain Injury in Rats

OBJECTIVE

Traumatic brain injury can cause a variety of impairments, including persistent alterations in personality, mood, and cognition. Antipsychotic agents are frequently used to treat pathologic behaviors in traumatic brain injury patients, but the influence of prolonged administration of such drugs on cognition after injury is unknown. The effects of two antipsychotic drugs on cognitive recovery after traumatic brain injury were assessed using the fluid percussion model in rats.

DESIGN

The typical antipsychotic, haloperidol, and the third-generation antipsychotic, olanzapine, were administered via intraperitoneal injection beginning 24 hr after injury and continuing daily for the duration of the study. Morris water maze performance was assessed on days 11-15 postinjury.

RESULTS

Haloperidol, an antagonist acting on D2-like dopamine receptors, exacerbated the cognitive deficits induced by injury, as injured rats treated with 0.30 mg/kg haloperidol performed worse in the Morris water maze than injured rats treated with vehicle.

CONCLUSIONS

Our results demonstrate the importance of the D2 receptor in cognitive recovery after traumatic brain injury. Also, the data illustrate that some classes of antipsychotic drugs may influence cognitive recovery, and further research is needed to determine the optimal pharmacologic treatment of aggression, agitation, and other pathologic behaviors in patients with traumatic brain injury.

The use of atypical antipsychotics in traumatic brain injury

The use of antipsychotic medication in treating individuals with traumatic brain injury (TBI) has been controversial. Much of the caution derives from animal studies (and limited human data) with regard to typical antipsychotics. Of note, however, is that similar assumptions have been made about the newer generation of atypical antipsychotics as well. Because these agents have different mechanisms of action as well as different neurotransmitter targets, this may very well be unwarranted. In this article, mechanisms of action of typical and atypical antipsychotics are discussed, with particular attention paid to their use in TBI. Indications and contraindications are presented, and recommendations are made for the responsible prescribing of antipsychotic medications after TBI.

Modulation of use-dependent plasticity by d-amphetamine

Use-dependent plasticity, thought to contribute to functional recovery after brain injury, is elicited by motor training. The purpose of this study was to determine if administration of d-amphetamine facilitates the effects of motor training on use-dependent plasticity. Healthy human volunteers underwent a training period of voluntary thumb movements under the effects of placebo or d-amphetamine in different sessions in a randomized double-blind, counterbalanced design. Previous work in a drug-naive condition showed that such training causes changes in the direction of thumb movements evoked by transcranial magnetic stimulation and in transcranial magnetic stimulation-evoked electromyographic responses. The endpoint measure of the study was the magnitude of training-induced changes in transcranial magnetic stimulation-evoked kinematic and electromyographic responses in the d-amphetamine and in the placebo conditions. Motor training resulted in increased magnitude, faster development and longer lasting duration of use-dependent plasticity under d-amphetamine compared to the placebo session. These results document a facilitatory effect of d-amphetamine on use-dependent plasticity, a possible mechanism mediating the beneficial effect of this drug on functional recovery after cortical lesions.

Role of adaptive plasticity in recovery of function after damage to motor cortex

Based upon neurophysiologic, neuroanatomic, and neuroimaging studies conducted over the past two decades, the cerebral cortex can now be viewed as functionally and structurally dynamic. More specifically, the functional topography of the motor cortex (commonly called the motor homunculus or motor map), can be modified by a variety of experimental manipulations, including peripheral or central injury, electrical stimulation, pharmacologic treatment, and behavioral experience. The specific types of behavioral experiences that induce long-term plasticity in motor maps appear to be limited to those that entail the development of new motor skills. Moreover, recent evidence demonstrates that functional alterations in motor cortex organization are accompanied by changes in dendritic and synaptic structure, as well as alterations in the regulation of cortical neurotransmitter systems. These findings have strong clinical relevance as it has recently been shown that after injury to the motor cortex, as might occur in stroke, post-injury behavioral experience may play an adaptive role in modifying the functional organization of the remaining, intact cortical tissue.

Enduring vulnerability to transient reinstatement of hemiplegia by prazosin after traumatic brain injury

A single dose of an alpha1-noradrenergic antagonist transiently reinstates hemiplegia after recovery from brain injury, which suggests that noradrenaline (NA) is required to maintain recovery. No systematic studies have determined the postinjury duration of this vulnerability. This study used a within-subject, dose-response design to determine whether prazosin (PRAZ), an alpha1-NA antagonist, or propranolol (PROP), a beta-NA antagonist, would continue to reinstate hemiplegia over time after recovery from weight-drop traumatic brain injury (TBI). PRAZ transiently reinstated hemiplegia as measured by beam walk (BW) score in a dose-dependent manner, with the same degree of symptom reinstatement at 1, 3, 6, and 12 months post-TBI. Between-animal variability in reinstatement of hemiplegia by PRAZ was predicted by severity of deficits in BW ability 24 h after TBI. In contrast, PRAZ did not reinstate tactile placing deficits at 1 month post-TBI suggesting a different mechanism of maintaining recovery for each task. Reinstatement of symptoms are not due to sedation. Only TBI rats receiving PRAZ, not high, sedating doses of PROP or saline (SAL), showed return of hemiplegia. These data indicate that vulnerability to transient reinstatement of hemiplegia on some tasks endures long after functional recovery from TBI.

A Pilot Study of the Effect of L-Threodops on Rehabilitation Outcome of Stroke Patients

We investigated whether L-threodops (L-DOPS), a norepinephrine precursor, improves rehabilitation outcome in patients with initial hemiparetic supratentorial ischemic stroke (2 months post stroke). Five patients who agreed to be treated with L-DOPS received 45-minute physical therapy (PT) and occupational therapy (OT) for 2 months, 3 days a week, with an oral dose of 200 mg L-DOPS 2 hours before each session, followed by PT and OT without L-DOPS for 2 months (DOPS group). Eight patients who disagreed received PT and OT for 4 months (control). Each group demonstrated comparable age, sex, complications, Mini-Mental State Examination, and the baseline Functional Independence Measure (FIM, DOPS/control = 36/42), Fugl-Meyer (F-M) motor scale (30/27), and ambulation endurance (10/9 meters). DOPS group had significantly greater gain than control (p < 0.05, Mann-Whitney U test) in FIM score at 4 (51/45) and 6 months (57/49), ambulation at 4 (66/16) and 6 months (82/24), and F-M score at 4 months (40/29). There were no side effects that required discontinuation of the drug. These results suggest that L-DOPS treatment paired with PT and OT may be effective in improving functional outcome in stroke.

Increasing CNS norepinephrine levels by the precursor L-DOPS facilitates beam-walking recovery after sensorimotor cortex ablation in rats

The present investigation was conducted to document a role of L-threo-3,4-dihydroxyphenylserine (L-DOPS), precursor of L-norepinephrine (NE), in the functional recovery from beam-walking performance deficits in rats after unilateral sensorimotor cortex ablation. L-DOPS was administered simultaneously with benserazide (BSZ; a peripheral aromatic amino acid decarboxylase inhibitor), and the regional contents of NE in the cerebral cortex, hippocampus, and cerebellum were assayed. Behavioral recovery was demonstrated by the rats treated with L-DOPS and BSZ, and the rate of recovery was significantly different from that of either BSZ-treated or vehicle-treated control rats. The NE tissue levels in the three discrete regions of the rat brain were significantly elevated in the experimental rats receiving both L-DOPS and BSZ. The present studies indicate that increasing NE levels by the precursor L-DOPS may be responsible for facilitating behavioral recovery from beam-walking performance deficits in rats, and further suggest that L-DOPS may become one of the candidate compounds for further clinical human trials promoting functional recovery after injuries to the cerebral cortex.

L-DOPS-Accelerated recovery of locomotor function in rats subjected to sensorimotor cortex ablation injury: pharmacobehavioral studies

Central norepinephrine (NE) has been shown to play a beneficial role in amphetamine-facilitated recovery of behavior. To give insight into understanding the mechanism, the present studies were conducted to examine (a) the effects of L-threo-3,4-dihydroxyphenylserine (L-DOPS) combined with benserazide (BSZ; a peripheral aromatic amino acid decarboxylase inhibitor) and L-3,4-dihydroxyphenylalanine (L-DOPA), precursors of NE and dopamine (DA), respectively, on the recovery from beam-walking performance deficits in rats subjected to unilateral sensorimotor cortex ablation injury, and (b) the relationships between the behavioral recovery and the frequency of postoperative training and the size of ablation injury. It was found that the combined treatments with L-DOPS and BSZ promoted the recovery of locomotor function as early as 24 hours after injury. L-DOPA alone, however, did not facilitate behavioral recovery. The results of assay for the tissue levels of NE and its major metabolite (3-methoxy-4-hydoxyphenylethylene glycol; MHPG) in the brain using high-pressure liquid chromotography showed MHPG, but not NE, significantly increased in the cerebellum and the hippocampus. The behavioral recovery was also significantly correlated with the frequency of training subsequent to injury, but inversely with the size of cortex ablation. These results suggest that NE is likely to modulate functional recovery in this rodent model.

A critical maturational period of reduced brain vulnerability to developmental injury. I. Behavioral studies in cats

Groups of cats with resection of the neocortex of the left cerebral hemisphere at postnatal (P) ages (in days) 5-15 (P10), 30 (P30), 60 (P60), 90 (P90), 120 (P120), and in adulthood, were compared using a comprehensive battery of 16 neurobehavioral tests administered when they were at least 6 months post-lesion. For all behaviors, except 3 (including the paw contact placing reaction which never recovered), the performance was significantly better for the cats lesioned between P10 and P30 compared to cats lesioned at older ages. For 10 of the behaviors, the transition from age-at-lesion P30 to P60 was rather abrupt and characterized by a significant increment in impairments. However, cats with the resection at ages P90 and P120 still showed some behavioral advantage over the adult-lesioned animals. Overall, for most of the behaviors tested, there was a significant linear trend for an increase in the magnitude of impairments across the entire age-at-lesion range. We previously reported that cats with a unilateral frontal cortical lesion sustained during the late fetal life showed substantial behavioral impairments, while animals with a similar resection sustained early postnatally exhibited minimal abnormalities. These findings, together with the present results, indicate that the long-term behavioral outcome of neocortical injury is best when the lesion is sustained during a discrete period of the life of the cat. This period extends from about fetal age 55 days (the oldest lesion age in our fetal studies) to about P60, as shown in the present paper. For these reasons, we propose that there is a Critical Maturational Period (CMP) for optimal post injury brain and behavioral restoration. We hypothesize that this span of reduced vulnerability is linked to specific developmental morphological events which occur during the same time period. Since, as discussed, such ontogenetic events also occur in other mammal species (albeit at different chronological ages), we further propose that the timing of the CMP as delineated in cats, can be extrapolated to other higher mammals species including humans.

Effects of dorsal noradrenergic bundle lesions on recovery after sensorimotor cortex injury

Several lines of evidence suggest that the recovery of the ability of rats to traverse a narrow beam after unilateral injury to the sensorimotor cortex is noradrenergically mediated. We tested the hypotheses that the influence of norepinephrine on beam-walking recovery occurs, at least partially, through effects in the contralateral and/or ipsilateral cerebral cortex. Rats had either a selective left or right 6-hydroxydopamine lesion or sham lesion of the dorsal noradrenergic bundle (DNB) 2 weeks before suction-ablation or sham injury of the right sensorimotor cortex. The rats' abilities to perform the beam-walking task were measured over the 10 days following cortex surgery. DNB lesions did not affect the initial severity of the beam-walking deficit and had no effect on the performance of the task in rats with sham cortex injuries. Lesions of the contralateral but not ipsilateral DNB significantly impaired recovery. Further, in cortically lesioned rats with contralateral DNB lesions, norepinephrine content in the cerebral cortex opposite to the sensorimotor cortex lesion was significantly correlated with recovery. These data suggest that the effect of norepinephrine on recovery of beam-walking ability may be partially exerted in the cerebral cortex contralateral to the injury.

Amphetamine and task-specific practice augment recovery of vibrissae-evoked forelimb placing after unilateral sensorimotor cortical injury in the rat

This study investigated the relative contribution of amphetamine administration and task-specific practice during the period of drug action to recovery of forelimb-placing ability after unilateral electrolytic lesions of the sensorimotor cortex (SMC) in rats. Subjects were divided into groups receiving amphetamine plus postinjection forelimb-placing practice, amphetamine only, saline plus postinjection forelimb-placing practice, or saline only. The results revealed that groups of subjects receiving either amphetamine, postinjection practice, or a combination of these treatments exhibited the greatest enhancement of rates of vibrissae-evoked forelimb-placing recovery. These data suggest that these treatments can have an enduring beneficial effect on vibrissae-evoked forelimb-placing recovery without any immediate restorative effect on forelimb-placing ability. The recovery patterns and experimental evidence (see Feeney and Sutton, 1988; Chaouloff, 1989) suggest that the beneficial effect of the two therapies may be mediated by catecholamine release.

Rats with partial striatal dopamine depletions exhibit robust and long-lasting behavioral deficits in a simple fixed-ratio bar-pressing task

It is widely accepted that enduring parkinsonian symptoms are only evident if there are few remaining dopaminergic neurons in the substantia nigra and dopamine levels in the basal ganglia are very low [26,41]. In the present study, partial dopamine depletions were produced by infusing 6-OHDA bilaterally into the ventrolateral striatum as previously described [11,12,44]. Consistent with previous studies, behavioral deficits were detectable in rats with partial lesions with a simple fixed-ratio bar-pressing task. The present study demonstrated that these behavioral deficits were long-lasting, and that the sensitivity of this bar-pressing task could be increased by manipulating the level of difficulty of the task-higher fixed ratios were more sensitive to partial dopamine depletions. Deficits in rats with partial dopamine depletions could also be detected using non-automated neurological tests of parkinsonian symptoms developed for rats with severe unilateral dopamine depletions, but these deficits were transient and not as robust as those detected with the bar-pressing task. Oral Sinemet (L-DOPA:carbidopa) did not attenuate behavioral deficits related to partial dopamine depletions in this simple fixed-ratio bar-pressing task, but the present results suggest that Parkinson's patients might be identifiable earlier in the disease process, at a time when they could benefit from treatment with neuroprotective/neurotrophic agents. In addition, the results of the present study demonstrate that robust behavioral deficits may emerge with age. Mild dopamine depletions that were not detectable behaviorally at the time of the insult became clearly evident 10 months after the lesion with this bar-pressing task, and this may represent a more clinically relevant rodent model of Parkinson's disease.

Lack of delayed effects of amphetamine, methoxamine, and prazosin (adrenergic drugs) on behavioral outcome after lateral fluid percussion brain injury in the rat

This study examined the delayed effects of the administration of d-amphetamine, methoxamine (an alpha1-adrenergic receptor agonist), and prazosin (an alpha1-adrenergic receptor antagonist) on the behavioral outcome of lateral fluid-percussion (FP) brain injury. Rats trained to perform a beam-walking task were subjected to brain injury of moderate severity (2.1 to 2.2 atm). Twenty-four hours after injury, rats were treated with amphetamine, methoxamine, or prazosin at two or three different dose levels. Amphetamine-treated animals displayed no significant improvement in beam-walking ability either during or after drug intoxication (from days 3 to 5 after brain injury). Similarly, neither methoxamine nor prazosin significantly affected beam-walking ability during or after drug intoxication. Neither amphetamine treatment at three different doses nor treatment with methoxamine or prazosin at two different doses affected the spatial learning disabilities of brain-injured animals. These results suggest that (1) unlike amphetamine administration after sensorimotor cortex (SMC) ablation or contusion brain injury models, amphetamine administration at 24 h after concussive FP brain injury does not improve beam-walking performance; (2) unlike amphetamine administration 10 min after concussive FP brain injury amphetamine administration 24 h after injury does not improve cognitive function; and (3) unlike prazosin administration after SMC ablation brain injury, prazosin administration 24 h after concussive FP brain injury does not effect beam-walking performance.

Studies on the influence of enriched-environment housing combined with systemic administration of an alpha2-adrenergic antagonist on spatial learning and hyperactivity after global ischemia in rats

BACKGROUND AND PURPOSE

The purpose of this study was to determine whether an enriched housing environment and/or systemic administration of the alpha2-adrenergic receptor antagonist atipamezole facilitate the rate of spatial learning after global ischemia in rats.

METHODS

Carotid arteries were closed for 20 minutes after permanent cauterization of vertebral arteries on the previous day. Enriched-environment housing and drug/saline treatment were begun 3 days after ischemia. For rehabilitation, housing in an enriched environment was combined with exploration in a labyrinth. Behavioral tests (the open-arena test and water-maze learning set task) were performed after 1-week periods of drug/saline treatment three times. In addition, the open-arena test was performed to evaluate the baseline level of animals 2 days after the induction of ischemia and at the end of the experiment, when the water-maze task was assessed in another room.

RESULTS

Rats housed in an enriched environment after ischemia showed better acquisition of the water-maze learning set task after 1 week of housing. The influence of atipamezole treatment on this parameter did not reach statistical significance. In the open-arena test, ischemic animals were slightly hyperactive; however, this symptom was eliminated by housing in an enriched environment.

CONCLUSIONS

The present data suggest that housing in an enriched environment facilitates the rate of spatial learning in rats with global ischemia. Rehabilitation also alleviated the hyperactivity observed in ischemic animals.

The effects of amphetamine on recovery of function after cortical damage in the rat depend on the behavioral requirements of the task

The effects of amphetamine on the recovery of function following unilateral lesions of the rat somatic sensorimotor cortex (SMC) were examined. Rats with large SMC were tested on two measures of locomotor placing: the beam-walking test and the foot-fault test. Amphetamine produced an immediate and enduring facilitation of recovery on the beam-walking test. In contrast, the drug had no effect on the rats' ability to accurately place the forelimbs on the rungs of the elevated grid during locomotion on the foot-fault test. These data suggest that amphetamine may facilitate recovery when the requirements of the task produce a deficit in the initiation of locomotion but not when the animal is required to use somatosensory and proprioceptive cues to guide performance on the task. A second group of rats with smaller SMC lesions was evaluated with tactile-placing tests and the bilateral-tactile stimulation task. The forelimb placing reaction is elicited by unilateral tactile stimulation of the vibrissae or forelimb, whereas the ipsilateral asymmetry observed on the bilateral-tactile stimulation test has been interpreted as an impairment in processing stimuli presented on both sides of the body. On two measures of forelimb placing amphetamine produced a facilitation of recovery, but restoration of function was not observed during the period of drug intoxication. In contrast, amphetamine had no effect on recovery of function on the bilateral-tactile stimulation test. Taken together, these data suggest that the behavioral requirements of the task are an important factor in determining the facilitatory effects of amphetamine on recovery of function.

Traumatic brain injury enhances the amnesic effect of an NMDA antagonist in rats

The authors have examined the effect of experimental traumatic brain injury on the amnesia produced by the N-methyl-D-aspartate (NMDA) antagonist MK-801. Rats were either subjected to a moderate level of fluid-percussion injury or prepared for injury but not injured ("sham injury"). Nine days following injury or sham injury, the rats were injected either with saline (sham/saline group, nine rats; injured/saline group, nine rats) or with 0.1 mg/kg of MK-801 (sham/MK-801 group, nine rats; injured/MK-801 group, eight rats) 30 minutes before being trained on a passive-avoidance task. Twenty-four hours later, the rats were tested for retention of the passive-avoidance task. Results revealed that the low dose of MK-801 did not significantly affect retention of the passive-avoidance task in the sham-injured group. In injured animals, administration of MK-801 produced a profound amnesia in contrast to the sham-injured animals treated with MK-801 and the injured animals treated with saline. To further investigate this enhanced sensitivity to the amnesic effects of MK-801 exhibited by the injured animals, nine injured and eight sham-injured rats were injected with 0.3 mg/kg of MK-801 15 minutes before injury. Results indicated that the animals treated with MK-801 before injury did not significantly differ from the sham-injured animals in retention of the passive-avoidance task. In addition, test results in the animals treated with MK-801 before injury and reinjected with MK-801 before passive-avoidance testing did not differ from those in untreated injured animals reinjected with saline before passive-avoidance testing. These findings indicate that MK-801 treatment before injury prevented the enhanced sensitivity to MK-801-induced amnesia that follows traumatic brain injury.

Pharmacotherapy of aphasia. A critical review

BACKGROUND

Communication problems are a common sequela of cerebrovascular disease and other central nervous system disorders. Behavioral treatment of these disorders aims to harness uninjured parts of the brain to improve the communicative life of the individual. While pharmacotherapy has held promise for the treatment of aphasia for over 50 years, it has not fulfilled this promise. This article reviews both the promise and the disappointment of aphasia pharmacotherapy.

SUMMARY OF REVIEW

Diverse theories of the underlying neurological deficits in aphasia have led to different pharmacologic rationales for therapy. Animal studies have demonstrated decreased levels of brain catecholamines after cortical stroke and more rapid stroke recovery with therapy aimed at augmenting brain norepinephrine and dopamine. These studies have led to recent attempts to hasten or extend language and sensorimotor rehabilitation after human stroke by administration of catecholaminergic drugs. When used as an adjunct to behavioral therapy, such pharmacotherapy appears to have benefit.

CONCLUSIONS

While drug therapy is unlikely to revolutionize the treatment of aphasia, it nonetheless holds promise as an adjunct to behavioral speech and language therapy to decrease performance variability and consequently to improve mean performance in patients with mild to moderate language dysfunction. Additional studies with carefully designed methods are necessary to assess the full potential of aphasia pharmacotherapy.

Differential effects of amphetamine and haloperidol on recovery after global forebrain ischemia

Gerbils subjected to sham surgery or to bilateral occlusion of the carotid arteries were given an injection, during the recovery period, of saline, d-amphetamine, or haloperidol. The animals were subsequently tested once daily for 50 days in an eight-arm radial maze. Global forebrain ischemia had no effect on learning to avoid unbaited arms (reference memory), but greatly increased the number of times animals reentered previously visited arms (working memory errors). Gerbils made ischemic and treated with amphetamine reduced working memory errors more rapidly than did saline-treated ischemic gerbils; conversely, animals made ischemic and treated with haloperidol made more working memory errors than the ischemic controls. Although all ischemic animals were hyperactive, the differential radial maze behaviors of the ischemic groups cannot be explained on the basis of increased activity.

Neurological and behavioral effects of a unilateral frontal cortical lesions in fetal kittens. I. Brain morphology, movement, posture, and sensorimotor tests

Nine fetal kittens sustained removal of the left frontal cortex during the last third of gestation (E 43-55) and were compared to animals sustaining a similar lesion postnatally (P 8-14) as well as to littermate controls. Starting after 6 months of age the animals received a comprehensive battery of movement, posture and sensorimotor tests. The prenatal-lesioned cats performed worse in practically all 15 tests applied (significantly in 13 of them) compared to the neonatal-lesioned cats. Impairments included contralateral paresis of the limbs and face, defective limb placing reactions (with almost absence of the contact components) and a slight extensor hypertonus; tactile hypoesthesia in the contralateral face and hind paw; a bias not to use the contralateral forepaw in a food retrieval task, and an ipsilateral body turning bias. The neonatal-lesioned animals only showed minor defects in the contact components of the limb placing reactions and a tendency to a body turning bias. Morphologically, the brains of the prenatal-lesioned cats, but not of neonatal-lesioned or intact control cats, showed bilateral disruption of the cortical sulcal and gyral patterns, shrinkage of the ipsilateral hemisphere, and reduction in volume of the ipsilateral thalamus and cortex. We concluded, contrary to expectations, that the consequences of a prenatal brain lesion in the cat are worse than when a similar lesion is sustained neonatally.

Comparison of GM1 ganglioside, AGF2, and D-amphetamine as treatments for spatial reversal and place learning deficits following lesions of the neostriatum

These experiments tested the effectiveness of parenterally administered gangliosides and amphetamine as treatments for spatial learning deficits caused by bilateral lesions of the neostriatum. In Expt. 1, rats were tested postsurgically for 30 days on a shock-avoidance, spatial reversal task. Treatments of gangliosides (GM1 at 30 mg/kg, and AGF2 at 20 mg/kg and 30 mg/kg) and D-amphetamine (2 mg/kg) significantly decreased lesion-induced learning deficits on this task, while treatments of 10 mg/kg AGF2 and the combination of GM1 (30 mg/kg) and D-amphetamine (2 mg/kg) were ineffective. In Expt. 2, rats were given bilateral neostriatal lesions and treated with GM1 (30 mg/kg), AGF2 (20 mg/kg) or D-amphetamine (2 mg/kg) and tested postsurgically for 5 days on a place learning task in the Morris water maze. Only the GM1-treated rats showed a reduction in lesion-induced place learning deficits on this task. Since in both experiments, cell counts near the area of the lesion revealed no differences among any of the brain-damaged groups, it was suggested that the treatments exert their behavioral effects by biochemically activating spared neurons, independent of any ultimate effects they may have on neuronal survival.

Novel pharmacologic therapies in the treatment of experimental traumatic brain injury: a review

Delayed or secondary neuronal damage following traumatic injury to the central nervous system (CNS) may result from pathologic changes in the brain's endogenous neurochemical systems. Although the precise mechanisms mediating secondary damage are poorly understood, posttraumatic neurochemical changes may include overactivation of neurotransmitter release or re-uptake, changes in presynaptic or postsynaptic receptor binding, or the pathologic release or synthesis of endogenous "autodestructive" factors. The identification and characterization of these factors and the timing of the neurochemical cascade after CNS injury provides a window of opportunity for treatment with pharmacologic agents that modify synthesis, release, receptor binding, or physiologic activity with subsequent attenuation of neuronal damage and improvement in outcome. Over the past decade, a number of studies have suggested that modification of postinjury events through pharmacologic intervention can promote functional recovery in both a variety of animal models and clinical CNS injury. This article summarizes recent work suggesting that pharmacologic manipulation of endogenous systems by such diverse pharmacologic agents as anticholinergics, excitatory amino acid antagonists, endogenous opioid antagonists, catecholamines, serotonin antagonists, modulators of arachidonic acid, antioxidants and free radical scavengers, steroid and lipid peroxidation inhibitors, platelet activating factor antagonists, anion exchange inhibitors, magnesium, gangliosides, and calcium channel antagonists may improve functional outcome after brain injury.

Effects of d-amphetamine on the recovery of function following cerebral ischemic injury

Amphetamine with appropriate motor experience has been found to facilitate the recovery of motor function after several different types of brain injuries. We investigated whether amphetamine would hasten the recovery of spatial mapping ability in gerbils previously subjected to a 3-min episode of forebrain ischemia. Amphetamine did not promote behavioral recovery, nor did it attenuate ischemic cell damage of hippocampal CA1 neurons. The beneficial effects of amphetamine after brain injury may be limited to restoration of sensorimotor ability and not to cognitive functions such as memory.