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

Noradrenergic antagonists mitigate amphetamine-induced recovery

Brain injury, including that due to stroke, leaves individuals with cognitive deficits that can disrupt daily aspect of living. As of now there are few treatments that shown limited amounts of success in improving functional outcome. The use of stimulants such as amphetamine have shown some success in improving outcome following brain injury. While the pharmacological mechanisms for amphetamine are known; the specific processes responsible for improving behavioral outcome following injury remain unknown. Understanding these mechanisms can help to refine the use of amphetamine as a potential treatment or lead to the use of other methods that share the same pharmacological properties. One proposed mechanism is amphetamine's impact upon noradrenaline (NA). In the current, study noradrenergic antagonists were administered prior to amphetamine to pharmacologically block α- and β-adrenergic receptors. The results demonstrated that the blockade of these receptors disrupted amphetamines ability to induce recovery from hemispatial neglect using an established aspiration lesion model. This suggests that amphetamine's ability to ameliorate neglect deficits may be due in part to noradrenaline. These results further support the role of noradrenaline in functional recovery. Finally, the development of polytherapies and combined therapeutics, while promising, may need to consider the possibility that drug interactions can negate the effectiveness of treatment.

An update on medications and noninvasive brain stimulation to augment language rehabilitation in post-stroke aphasia

INTRODUCTION

Aphasia is among the most debilitating outcomes of stroke. Aphasia is a language disorder occurring in 10-30% of stroke survivors. Speech and Language Therapy (SLT) is the gold standard, mainstay treatment for aphasia, but gains from SLT may be incomplete. Pharmaceutical and noninvasive brain stimulation (NIBS) techniques may augment the effectiveness of SLT. Areas covered: Herein reviewed are studies of the safety and efficacy of these adjunctive interventions for aphasia, including randomized placebo-controlled and open-label trials, as well as case series from Pubmed, using search terms 'pharmacological,' 'tDCS' or 'TMS' combined with 'aphasia' and 'stroke.' Expert commentary: Relatively small studies have included participants with a range of aphasia types and severities, using inconsistent interventions and outcome measures. Results to-date have provided promising, but weak to moderate evidence that medications and/or NIBS can augment the effects of SLT for improving language outcomes. We end with recommendations for future approaches to studying these interventions, with multicenter, double-blind, randomized controlled trials.

A Rehabilomics focused perspective on molecular mechanisms underlying neurological injury, complications, and recovery after severe TBI

The molecular mechanisms underlying TBI pathophysiology and recovery are both complex and varied. Further, the pathology underlying many of the clinical sequelae observed in this population evolve over the acute injury period and encompass the subacute and chronic phases of recovery, supporting the contemporary concept that TBI is a chronic disease rather than a static insult from which limited recovery occurs. TBI related complications can also span from acute care to the very chronic stages of recovery that occur years after the initial trauma. Despite ongoing neurodegeneration, the TBI recovery period is also characterized by a propensity for neuroplasticity and rewiring through multiple mechanisms. This review summarizes key elements of acute pathophysiology, how they link to structural damage and ongoing degeneration, and how this process coincides with a permissive neuroplastic environment. The pathophysiology of selected TBI related complications is also discussed. Each of these concepts is studied through the lens of Rehabilomics, wherein an emphasis is placed on biomarker studies characterizing these pathophysiological mechanisms, and biomarker profiles are assessed in relation to multi-modal outcomes and susceptibility to rehabilitation relevant complications. In reviewing these concepts, implications for future research and theranostic principles for patient care are presented.

The 2009 Feinberg lecture: the continuum of stroke research and policy

BACKGROUND AND PURPOSE

This annual Feinberg Award lecture is intended to present examples of the broad scope of stroke-related research and to show how different investigative approaches can advance the field to improve stroke patient's outcomes. In keeping with one of the objectives of the American Heart/American Stroke Association, this lecture also provides a perspective and highlights opportunities for beginning clinical investigators. Summary of Report- Clinically, the continuum of stroke research and care can be divided into primary prevention, acute interventions, secondary prevention, and poststroke recovery. From a technical/methodological standpoint, fundamental laboratory studies yield insights into basic disease mechanisms and applied laboratory studies further explore the biological basis of disease and evaluate possible therapeutic interventions. The results of these laboratory-based observations can inform clinical study design whereas questions raised by clinical observations can be explored in laboratory experiments (ie, "translational" research). Additional information is gained through observational, interventional, and synthetic (eg, meta-analytic) clinical studies. Outcomes/effectiveness research determines how well interventions perform in different "real-world" settings. The discussion provides examples of how several of these approaches can be used to address various research questions. The importance for stroke investigators to contribute to related public policy issues is also reviewed.

CONCLUSIONS

This is an exciting era for clinical investigators studying stroke and for those at the beginning stages of their careers. Whether taking a broad-based research approach or working on a specific, focused question, our combined efforts are leading to improved outcomes for patients with stroke, the very goal of Bill Feinberg's career.

Motor recovery and axonal plasticity with short-term amphetamine after stroke

BACKGROUND AND PURPOSE

There is considerable debate regarding the efficacy of amphetamine to facilitate motor recovery after stroke or experimental brain injury. Different drug dosing and timing schedules and differing physical rehabilitation strategies may contribute to outcome variability. The present study was designed to ascertain (1) whether short-term amphetamine could induce long-term functional motor recovery in rats after an ischemic lesion modeling stroke in humans; (2) how different levels of physical rehabilitation interact with amphetamine to enhance forelimb-related functional outcome; and (3) whether motor improvement was associated with axonal sprouting from intact corticoefferent pathways originating in the contralesional forelimb motor cortex.

METHODS

After permanent middle cerebral artery occlusion, rats received vehicle or amphetamine during the first postoperative week (2 mg/kg, subcutaneously on Postoperative Days 2, 5, and 8). In both treatment groups, separate cohorts of rats were exposed to different levels of "physical rehabilitation" represented by a control environment, enriched environment, or enriched environment with additional sessions of focused activity. Skilled forelimb performance was assessed using the forelimb reaching task and ladder rung walk test. Anterograde tracing with biotinylated dextran amine was used to assess new fiber outgrowth to denervated motor areas.

RESULTS

All treatment groups showed significant motor improvement as compared with control-housed, vehicle-treated animals. However, animals housed in an enriched environment that received amphetamine paired with focused activity sessions performed significantly better than any other treatment group and was the only group to achieve complete motor recovery (ie, reached preoperative performance) by 8 weeks. This recovery was associated with axonal sprouting into deafferentated subcortical areas from contralesional projection neurons.

CONCLUSIONS

This study suggests that, after stroke, short-term pairing of amphetamine with sufficiently focused activity is an effective means of inducing long-term improvement in forelimb motor function. The anatomic data suggests that corticoefferent plasticity in the form of axonal sprouting contributes to the maintenance of motor recovery.

Norepinephrine depletion facilitates recovery of function after focal ischemia in the rat

Previous studies have suggested that increased norepinephrine plays an important role in recovery of function after brain injury; however, the majority of these studies used drugs that are known to also affect other monoamines to increase or decrease norepinephrine. The purpose of the present study was to determine if norepinephrine is required to promote recovery after ischemia. A form of enriched rehabilitation was used to rehabilitate animals after ischemia and the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine was used to selectively destroy norepinephrine projections from the locus coeruleus. Three sensorimotor tests were used to evaluate the recovery of the animals. Depletion of norepinephrine improved sensorimotor recovery in standard-housed animals and did not impede recovery in the rehabilitation groups. Dopamine beta hydroxylase staining was used to confirm N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine-depleted terminal norepinephrine levels. The amount of norepinephrine terminal staining negatively correlated with recovery of function in the staircase test after ischemia. In addition, enriched rehabilitation increased, but depletion of norepinephrine had no effect on, brain-derived neurotrophic factor protein levels, which have also been linked to improved recovery of function. Together the above findings question the previously postulated role of norepinephrine in recovery of function after stroke.

Pontine and cerebellar norepinephrine content in adult rats recovering from focal cortical injury

Norepinephrine (NE) plays an important role in motor recovery after brain damage. Most studies concerning NE activity have been performed in the cerebellum, while the role of the pons, the site where the norepinephrinergic locus coeruleus is located, has not yet been elucidated. For this work, we studied the changes in cerebellar and pontine NE content in sham-operated (n = 17), motor cortex injured (n = 6) and recovered rats (n = 12). Motor effects were assessed by means of footprint analysis and sensorimotor evaluation. It was found that after cortical brain damage, the stride length decreases while the stride angle increases after 6 h post-surgery, while the sensorimotor evaluation showed an increase in the motor deficit. Recovery was observed after 24 h. NE content increased in the pons after 6 h and returned to normal levels in recovered rats, with no significant changes observed in the cerebellum. Based on the functional remote inhibition, it is possible that NE exerts an autoinhibitory effect in the pons after motor cortical ablation. On the other hand, the absence of an effect in the cerebellum suggests that cerebellar NE activity related to damage and/or recovery is limited to discrete areas of the structure.

Methylphenidate modulates cerebral post-stroke reorganization

OBJECTIVE

We hypothesized that a single dose of methylphenidate (MP) would modulate cerebral motor activation and behavior in patients having suffered a subcortical stroke.

METHODS

Eight men with a single stroke on the corticospinal tract resulting in a pure motor hemiparesia were included in a randomized, cross-over, double-blind, placebo-controlled study. Patients were first evaluated 17 days after stroke onset by validated neurological scales, motor tests and fMRI (flexion/extension of the digits) after 20 mg MP or placebo. Seven days later, the patients underwent the same protocol and received the drug they had not taken at the first evaluation. Each patient was his own control.

RESULTS

Placebo intake did not change performance. MP compared to placebo elicited a significant improvement in motor performance of the affected hand at the finger tapping test. MP induced: (1) a hyperactivation of the ipsilesional primary sensorimotor cortex including the motor hand and face areas and of the contralesional premotor cortex; (2) a hypoactivation of the ipsilesional anterior cingulum. Hyperactivation in the face motor area correlated positively with the improvement in performance.

CONCLUSION

We demonstrated that the reorganized network may efficiently be targeted by the drug and that the effect of MP might partly rely on an improvement in attention/effort through cingulum modulation.

Neurotransmitters and motor activity: effects on functional recovery after brain injury

There are complex relationships among behavioral experience, brain morphology, and functional recovery of an animal before and after brain injury. A large series of experimental studies have shown that exogenous manipulation of central neurotransmitter levels can directly affect plastic changes in the brain and can modulate the effects of experience and training. These complex relationships provide a formidable challenge for studies aimed at understanding neurotransmitter effects on the recovery process. Experiments delineating norepinephrine-modulated locomotor recovery after injury to the cerebral cortex illustrate the close relationships among neurotransmitter levels, brain plasticity, and behavioral recovery. Understanding the neurobiological processes underlying recovery, and how they might be manipulated, may lead to novel strategies for improving recovery from stroke-related gait impairment in humans.

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.

Serotonergic cell signaling in an animal model of aging and depression: olfactory bulbectomy elicits different adaptations in brain regions of young adult vs aging rats

Aging involves neuronal and synaptic loss, and maintenance of function depends on adaptations in cellular responsiveness. We studied olfactory bulbectomy (OBX), a model that recapitulates monoaminergic dysfunction in depression, in 10-week vs 19-month-old rats, and evaluated 5HT (5-hydroxytryptamine, serotonin) mechanisms. OBX elicited little change in 5HT1A receptors in the cerebral cortex or striatum of either age group. In contrast, 5HT2 receptors showed disparate effects, with a decrease in the cerebral cortex of young OBX but not aging OBX rats, whereas the latter group showed a selective decrease in striatal 5HT2 receptors. Greater differences were apparent for 5HT-mediated cell signaling, assessed for the adenylyl cyclase (AC) cascade. In young animals, 5HT had a stimulatory effect on AC that was unaltered by OBX. However, in aging animals, the pattern of 5HT responses showed marked alterations in response to OBX: under basal conditions, stimulatory effects were enhanced but when AC was activated with forskolin, 5HT became markedly inhibitory in the striatum of aged OBX animals. Assessment of the relative AC responses to two direct stimulants that act on different epitopes of the enzyme, forskolin and Mn2+, pointed to a shift in the AC isoform and/or its ability to associate with G-proteins as the mechanism underlying the age-related differences for OBX effects. These data indicate that there are biological distinctions in the response of 5HT systems to OBX in young adult vs aging animals, which, if present in geriatric depression, could provide a mechanistic basis for differences in responses to antidepressants that act on 5HT.

Noradrenergic mechanisms in neurodegenerative diseases: a theory

A deficiency in the noradrenergic system of the brain, originating largely from cells in the locus coeruleus (LC), is theorized to play a critical role in the progression of a family of neurodegenerative disorders that includes Parkinson's disease (PD) and Alzheimer's disease (AD). Consideration is given here to evidence that several neurodegenerative diseases and syndromes share common elements, including profound LC cell loss, and may in fact be different manifestations of a common pathophysiological process. Findings in animal models of PD indicate that the modification of LC-noradrenergic activity alters electrophysiological, neurochemical and behavioral indices of neurotransmission in the nigrostriatal dopaminergic system, and influences the response of this system to experimental lesions. In models related to AD, noradrenergic mechanisms appear to play important roles in modulating the activity of the basalocortical cholinergic system and its response to injury, and to modify cognitive functions including memory and attention. Mechanisms by which noradrenaline may protect or promote recovery from neural damage are reviewed, including effects on neuroplasticity, neurotrophic factors, neurogenesis, inflammation, cellular energy metabolism and excitotoxicity, and oxidative stress. Based on evidence for facilitatory effects on transmitter release, motor function, memory, neuroprotection and recovery of function after brain injury, a rationale for the potential of noradrenergic-based approaches, specifically alpha2-adrenoceptor antagonists, in the treatment of central neurodegenerative diseases is presented.

Neuropharmacology of TBI-induced plasticity

PRIMARY OBJECTIVE

The purpose of this report is to review both fundamental studies in laboratory animals and preliminary clinical data suggesting that certain drugs may affect behavioural recovery after brain injury.

MAIN OUTCOMES AND RESULTS

Laboratory studies show that systemically-administered drugs that affect specific central neurotransmitters including norepinephrine and GABA influence affect recovery in a predictable manner. Although some drugs such as d-amphetamine have the potential to enhance recovery, others such as neuroleptics and other central dopamine receptor antagonists, benzodiazepines and the anti-convulsants phenytoin and phenobarbital may be detrimental. In one study, 72% of patients with traumatic brain injury received one or a combination of the drugs that may impair recovery based on both animal experiments and studies in recovering stroke patients.

CONCLUSIONS

Until the true impact of these classes of drugs are better understood, care should be exercised in the use of medications that may interfere with the recovery process in patients with traumatic brain injury. Additional research needs to be completed before the clinical efficacy of drugs that may enhance recovery can be established.

Should the injured and intact hemispheres be treated differently during the early phases of physical restorative therapy in experimental stroke or parkinsonism?

Over a century ago the intact cortex was proposed to contribute to recovery from unilateral brain injury, but its possible role in functional outcome has become more appreciated in recent years as a result of anatomic, metabolic and behavioral studies. Although use of the contralesional limb is naturally impaired after sensorimotor cortex injury, neural and astrocytic events in the intact hemisphere may give rise to, and may be influenced by, an enhanced ability to compensate for lost motor function. The debate is still open as to whether the neural changes are generally compensatory in nature, with activity in the homotopic cortex leading to greater capability in the nonimpaired limb, or whether they are actually a matter of reorganization in the homotopic cortex leading to connections to denervated targets in the opposite hemisphere, thus allowing the homotopic cortex to control motor programs there. Although both phenomena may occur to some degree, there is mounting evidence in support of the former view. Careful behavioral techniques have been developed that can expose compensatory tricks, and the time course of these behaviors correlates well with anatomic data. Moreover, if the intact cortex sustains a second lesion after recovery from the first, forelimb sensorimotor function specific to the first-impaired side of the body is not worsened. Partial denervation of callosal fibers coming from the injured hemisphere, plus preferential use of the good forelimb caused by a cortical injury, may increase trophic factors in the intact hemisphere. These and related events seem to provide a growth-favorable environment there that permits motor learning in the intact forelimb at a level of skill exceeding that which a normal animal can attain in the same period of time. There are anecdotal cases in human neurologic patients that are consistent with these findings. For example, a colleague of the authors who sustained a unilateral infarction that rendered his dominant right hand severely impaired noticed that soon after the stroke he was able to use his left hand for writing and computers as well as he had ever used his right hand. Cross-midline placing tests also indicate that the structural events observed in the intact cortex may potentiate projections to the damaged hemisphere. These changes may help restore the capacity of tactile information projecting to the intact hemisphere to control limb placing in the impaired forelimb. Neural events in the injured hemisphere can be affected by behavior differently than the neural events in the intact hemisphere. Different therapeutic strategies might well be used on opposing limbs at different times after unilateral sensorimotor cortex injury to optimize recovery (and, indeed, to avoid exaggerating the insult). Finally, the details of reorganization in both hemispheres differ greatly depending on the type of brain injury sustained (eg, in stroke versus Parkinson's disease), suggesting that an approach that considers the role of both hemispheres is likely to be beneficial in research on a broad variety of brain pathologies.

Amphetamines and related drugs in motor recovery after stroke

Studies in laboratory animals indicate that the rate and extent of functional recovery after focal brain injury can be modulated by drugs affecting specific central neurotransmitters. Preliminary clinical studies suggest that similar drug effects may occur in humans recovering from stroke. Combined with principles derived from the laboratory, these clinical studies provide important insights to guide the rational design of trials aimed at determining the clinical use of this approach to improving poststroke recovery.

Differential effects of haloperidol and clozapine on motor recovery after sensorimotor cortex injury in rats

BACKGROUND

A variety of drugs impair motor recovery after sensorimotor cortex (SMCTX) injury in laboratory animals and may have similar effects in humans.

METHODS

Rats (n = 142) underwent unilateral suction-ablation of the hindlimb SMCTX or sham lesion. After 24 hours, rats were given a single dose of placebo, haloperidol (0.1, 1.0, or 10.0 mg/kg, intraperitoneal), or clozapine (0.1, 0.5, 1.0, or 10.0 mg/kg, intraperitoneal), and motor recovery was measured.

RESULTS

Neither haloperidol (analysis of variance [ANOVA] F[3, 12], P = 0.43) nor clozapine (ANOVA F[4, 19], P = 1.00) affected motor performance in controls. Haloperidol impaired motor recovery (ANOVA F[3, 42], P = 0.002) at each tested dose, with no differences between the doses. The effect persisted after 2 weeks. In contrast, although rats given a single dose of clozapine of 1.0 or 10.0 mg/kg had poorer recoveries (ANOVA F[4, 51], P = 0.014), only those given the highest dose differed from controls. The effect was no longer apparent after 2 weeks.

CONCLUSION

Consistent with previous reports, haloperidol retards motor recovery after SMCTX injury in rats. In contrast, there was no detrimental effect of clozapine when given at low doses. The use of low doses of atypical antipsychotics such as clozapine may provide a safer alternative to haloperidol in the treatment of agitated stroke patients.

Differentially altered cerebral metabolism in ischemic rats by alpha2-adrenoceptor blockade and its relation to improved limb-placing reactions

The selective alpha2-adrenoreceptor antagonist, atipamezole, improves behavioural performance of rats subjected to focal cerebral ischemia. The aim of the present study was to investigate whether the facilitatory effect of atipamezole on behaviour is related to altered neuronal activity in specific brain areas. The right middle cerebral artery of rats was occluded for 120 min using the intraluminal filament method. Starting on day 2 after induction of ischemia, atipamezole (1mg/kg, s.c.) or 0.9% NaCl was administered to ischemic or sham-operated rats once a day 30 min before the limb-placing test. [14C]Deoxyglucose ([14C]DG) uptake was used to measure neuronal activity 30 min after atipamezole or 0.9% NaCl administration on day 6 after ischemia. Ischemia induced a significant decrease in [14C]DG uptake in several cortical areas ipsilateral and contralateral to the lesion, in the ipsilateral thalamus, and bilaterally in the cerebellum and spinal cord. Administration of atipamezole normalised [14C]DG uptake particularly in the cerebellum and spinal cord both in sham-operated and ischemic rats and to a lesser extent in the thalamus in sham-operated rats. The pattern of altered cerebral [14C]DG uptake following alpha2-adrenoceptor blockade suggests that plasticity in the cerebellum and spinal cord contributes to the improved performance of ischemic rats in tests assessing tactile/proprioceptive limb-placing reactions.

Fluoxetine modulates motor performance and cerebral activation of patients recovering from stroke

In order to determine the influence of a single dose of fluoxetine on the cerebral motor activation of lacunar stroke patients in the early phase of recovery, we conducted a prospective, double-blind, crossover, placebo-controlled study on 8 patients with pure motor hemiparesia. Each patient underwent two functional magnetic resonance imaging (fMRI) examinations: one under fluoxetine and one under placebo. The first was performed 2 weeks after stroke onset and the second a week later. During the two fMRI examinations, patients performed an active controlled motor task with the affected hand and a passive one conducted by the examiner with the same hand. Motor performance was evaluated by motor tests under placebo and under fluoxetine immediately before the examinations to investigate the effect of fluoxetine on motor function. Under fluoxetine, during the active motor task, hyperactivation in the ipsilesional primary motor cortex was found. Moreover, fluoxetine significantly improved motor skills of the affected side. We found that a single dose of fluoxetine was enough to modulate cerebral sensory-motor activation in patients. This redistribution of activation toward the motor cortex output activation was associated with an enhancement of motor performance.

Biological plasticity: the future of science in neurosurgery

THE FUTURE OF neurosurgery is intimately related to the future of neuroscientific research. Although the field of neuroscience is immense and not subject to brief review, it is clear that certain trends have become critical to future thinking regarding neurosurgery. An important theme that recurs in much of the current research and that will become more prominent in the future is the concept of plasticity. This refers not only to the changes in cortical representation that can occur after a variety of perturbations but also to a wide variety of neurologically relevant biological processes. In this review, we describe three areas of plasticity, i.e., the response of the brain to ischemia, cortical representational changes, and the potential for stem cell biological processes to allow us to manipulate plasticity. We posit that these trends will be crucial to the future of our specialty.

Cellular determinants of reduced adaptability of the aging brain: neurotransmitter utilization and cell signaling responses after MDMA lesions

Senescence is accompanied by the loss of neurons and synapses, and the maintenance of function depends on adaptive change at the levels of synaptic activity and cellular responsiveness. In the current study, we administered the neurotoxin MDMA, to young and aged mice and assessed the effects on indices of neuronal activity and cell signaling mediated through adenylyl cyclase. Young mice given MDMA showed 80% depletion of dopamine in the caudate and 30% depletion in the cerebral cortex; measurements of dopamine turnover indicated a compensatory upregulation of the activity of the remaining neurons in the caudate but downregulation in the cerebral cortex. Serotonin levels were comparatively less affected but serotonin turnover was decreased significantly in both regions. At the level of cell signaling, the young mice showed heterologous upregulation of adenylyl cyclase activity and a consequent enhancement of responses mediated through neurotransmitter receptors. In aged mice, MDMA treatment produced the same degree of lesioning but substantially different changes in neuronal activity and cell signaling. In the cerebral cortex, dopamine turnover was increased, and serotonin turnover decreased, effects opposite in direction to those seen in young mice. In the aged group, MDMA elicited heterologous loss of adenylyl cyclase responses instead of displaying the supersensitivity that had been seen in the young group. The aging brain thus displays maladaptation to the loss of monoaminergic input, effects that may augment the functional impairment associated with neurodegenerative disorders or stroke.

Effects of amphetamines and small related molecules on recovery after stroke in animals and man

Drugs modulating the levels of specific central neurotransmitters may influence both the rate and amount of functional recovery after focal brain injuries such as stroke. Because such drugs may be effective long after brain injury, the "therapeutic window" may be widened beyond the first few hour after stroke and an entirely new avenue for pharmacological intervention may be possible. The impact of drugs affecting norepinephrine and gamma-aminobutyric acid have been among the most extensively studied in the laboratory, and preliminary clinical data suggest similar effects in humans.

Recovery after damage to motor cortical areas

Until recently, the neural bases underlying recovery of function after damage to the cerebral cortex were largely unknown. Recent results from neuroanatomical and neurophysiological studies in animal models have demonstrated that after cortical damage, long-term and widespread structural and functional alterations take place in the spared cortical tissue. These presumably adaptive changes may play an important role in functional recovery.

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.

Norepinephrine and traumatic brain injury: a possible role in post-traumatic edema

Unilateral cerebral contusion is associated with an early (30 min) increase in norepinephrine (NE) turnover followed by a later (6-24 h) depression of turnover which is bilateral and widespread throughout the brain. Blockade of NE function during the first few hours after traumatic brain injury (TBI) impedes subsequent recovery of function without enlarging the size of the lesion. The current studies were carried out to characterize further the timing of the switch from increased to decreased NE turnover and to investigate the pathogenesis of the delayed recovery of function associated with blocking NE function. Adult male rats had unilateral somatosensory cortex contusions made with a 5 mm diameter impact piston. They were killed after 2 h and their brains analyzed for NE turnover by HPLC with electrochemical detection. In general, NE turnover (the ratio of 3-methoxy-4-hyroxyphenylglycol to NE levels) had returned to sham-lesion control levels in most brain regions by 2 h after either left or right sided contusions. The only exceptions were a persistent 87% increase at the lesion site after right-sided contusions and 22% and 32% increases in the contralateral cerebellum after right- and left-sided contusions, respectively. Blockade of alpha1-adrenoceptors by treatment with prazosin (3 mg/ kg, i.p.) 30 min prior to TBI produced edema in the striatum and hippocampus at 24 h which was not seen saline-treated rats nor in rats where NE reuptake was blocked with desmethylimipramine (DMI; 10 mg/kg, i.p.). DMI increased edema at the lesion site at 24 h, however. These data suggest that the early increase in NE release following unilateral cerebral contusion is protective and that this may act to stabilize the blood-brain barrier in areas adjacent to the injury site. Drugs that interfere with this enhanced noradrenergic function might enhance the damage caused by TBI.