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

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.

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.

Mild Concussion, but Not Moderate Traumatic Brain Injury, Is Associated with Long-Term Depression-Like Phenotype in Mice

Mild traumatic brain injuries can lead to long-lasting cognitive and motor deficits, increasing the risk of future behavioral, neurological, and affective disorders. Our study focused on long-term behavioral deficits after repeated injury in which mice received either a single mild CHI (mCHI), a repeated mild CHI (rmCHI) consisting of one impact to each hemisphere separated by 3 days, or a moderate controlled cortical impact injury (CCI). Shams received only anesthesia. Behavioral tests were administered at 1, 3, 5, 7, and 90 days post-injury (dpi). CCI animals showed significant motor and sensory deficits in the early (1-7 dpi) and long-term (90 dpi) stages of testing. Interestingly, sensory and subtle motor deficits in rmCHI animals were found at 90 dpi. Most importantly, depression-like behaviors and social passiveness were observed in rmCHI animals at 90 dpi. These data suggest that mild concussive injuries lead to motor and sensory deficits and affective disorders that are not observed after moderate TBI.

Juvenile traumatic brain injury evolves into a chronic brain disorder: behavioral and histological changes over 6months

Traumatic brain injury (TBI) refers to physical trauma to the brain that can lead to motor and cognitive dysfunctions. TBI is particularly serious in infants and young children, often leading to long-term functional impairments. Although clinical research is useful for quantifying and observing the effects of these injuries, few studies have empirically assessed the long-term effects of juvenile TBI (jTBI) on behavior and histology. After a controlled cortical impact delivered to postnatal 17day old rats, functional abilities were measured after 3, 5, and 6months using open field (activity levels), zero maze (anxiety-like behaviors), rotarod (sensorimotor abilities, coordination, and balance), and water maze (spatial learning and memory, swim speed, turn bias). Sensorimotor function was impaired for up to 6months in jTBI animals, which showed no improvement from repeated test exposure. Although spatial learning was not impaired, spatial memory deficits were observed in jTBI animals starting at 3months after injury. Magnetic resonance imaging and histological data revealed that the effects of jTBI were evolving for up to 6months post-injury, with reduced cortical thickness, decreased corpus callosum area and CA1 neuronal cell death in jTBI animals distant to the impact site. These findings suggest that this model of jTBI produces long-term impairments comparable to those reported clinically. Although some deficits were stable over time, the variable nature of other deficits (e.g., memory) as well as changing properties of the lesion itself, suggest that the effects of a single jTBI produce a chronic brain disorder with long-term complications.

Traumatic brain injury in young rats leads to progressive behavioral deficits coincident with altered tissue properties in adulthood

Traumatic brain injury (TBI) affects many infants and children, and results in enduring motor and cognitive impairments with accompanying changes in white matter tracts, yet few experimental studies in rodent juvenile models of TBI (jTBI) have examined the timeline and nature of these deficits, histologically and functionally. We used a single controlled cortical impact (CCI) injury to the parietal cortex of rats at post-natal day (P) 17 to evaluate behavioral alterations, injury volume, and morphological and molecular changes in gray and white matter, with accompanying measures of electrophysiological function. At 60 days post-injury (dpi), we found that jTBI animals displayed behavioral deficits in foot-fault and rotarod tests, along with a left turn bias throughout their early developmental stages and into adulthood. In addition, anxiety-like behaviors on the zero maze emerged in jTBI animals at 60 dpi. The final lesion constituted only ∼3% of brain volume, and morphological tissue changes were evaluated using MRI, as well as immunohistochemistry for neuronal nuclei (NeuN), myelin basic protein (MBP), neurofilament-200 (NF200), and oligodendrocytes (CNPase). White matter morphological changes were associated with a global increase in MBP immunostaining and reduced compound action potential amplitudes at 60 dpi. These results suggest that brain injury early in life can induce long-term white matter dysfunction, occurring in parallel with the delayed development and persistence of behavioral deficits, thus modeling clinical and longitudinal TBI observations.

Comparing the predictive value of multiple cognitive, affective, and motor tasks after rodent traumatic brain injury

Controlled cortical impact injury (CCI) is a widely-used, clinically-relevant model of traumatic brain injury (TBI). Although functional outcomes have been used for years in this model, little work has been done to compare the predictive value of various cognitive and sensorimotor assessment tests, singly or in combination. Such information would be particularly useful for assessing mechanisms of injury or therapeutic interventions. Following isoflurane anesthesia, C57BL/6 mice were subjected to sham, mild (5.0 m/sec), moderate (6.0 m/sec), or severe (7.5 m/sec) CCI. A battery of behavioral tests were evaluated and compared, including the standard Morris water maze (sMWM), reversal Morris water maze (rMWM), novel object recognition (NOR), passive avoidance (PA), tail-suspension (TS), beam walk (BW), and open-field locomotor activity. The BW task, performed at post-injury days (PID) 0, 1, 3, 7, 14, 21, and 28, showed good discrimination as a function of injury severity. The sMWM and rMWM tests (PID 14-23), as well as NOR (PID 24 and 25), effectively discriminated spatial and novel object learning and memory across injury severity levels. Notably, the rMWM showed the greatest separation between mild and moderate/severe injury. PA (PID 27 and 28) and TS (PID 24) also reflected differences across injury levels, but to a lesser degree. We also compared individual functional measures with histological outcomes such as lesion volume and neuronal cell loss across anatomical regions. In addition, we created a novel composite behavioral score index from individual complementary behavioral scores, and it provided superior discrimination across injury severities compared to individual tests. In summary, this study demonstrates the feasibility of using a larger number of complementary functional outcome behavioral tests than those traditionally employed to follow post-traumatic recovery after TBI, and suggests that the composite score may be a helpful tool for screening new neuroprotective agents or for addressing injury mechanisms.

Unilateral hemispherectomy at adulthood asymmetrically affects motor performance of male Swiss mice

Evidence exists indicating that cerebral lateralization is a fundamental feature of all vertebrates. In humans, a series of studies demonstrated that the left hemisphere plays a major role in controlling movement. No such asymmetries have been identified in rodents, in spite of the fact that these animals have been frequently used in studies assessing motor behavior. In this regard, here, we used unilateral hemispherectomy to study the relative importance of each hemisphere in controlling movement. Adult Swiss mice were submitted to right unilateral hemispherectomy (RH), left unilateral hemispherectomy (LH) or sham surgery. Fifteen days after surgery, motor performance was assessed in the accelerating rotarod test and in the foot-fault test (in which performance depends on skilled limb use) and in the elevated body swing test (in which performance depends on trunk movements). The surgical removal of the right hemisphere caused a more pronounced impairment in performance than the removal of the left hemisphere both in the rotarod and in the foot-fault tests. In the rotarod, the RH group presented smaller latencies to fall than both LH and sham groups. In the foot-fault test, while both the sham and the LH groups showed no differences between left and right hind limbs, the RH group showed significantly worse performance with the left hind limb than with the right one. The elevated body swing test revealed a similar impairment in the two hemispherectomized groups. Our data suggest a major role of the right hemisphere in controlling skilled limb movements in mice.

The effects of hypertonic saline and nicotinamide on sensorimotor and cognitive function following cortical contusion injury in the rat

Hypertonic saline (HTS) is an accepted treatment for traumatic brain injury (TBI). However, the behavioral and cognitive consequences following HTS administration have not thoroughly been examined. Recent preclinical evidence has suggested that nicotinamide (NAM) is beneficial for recovery of function following TBI. The current study compared the behavioral and cognitive consequences of HTS and NAM as competitive therapeutic agents for the treatment of TBI. Following controlled cortical impact (CCI), bolus administrations of NAM (500 mg/kg), 7.5% HTS, or 0.9% saline Vehicle (1.0 mL/kg) were given at 2, 24, and 48 h post-CCI. Behavioral results revealed that animals treated with NAM and HTS showed significant improvements in beam walk and locomotor placing compared to the Vehicle group. The Morris water maze (MWM) retrograde amnesia test was conducted on day 12 post-CCI and showed that all groups had significant retention of memory compared to injured, Vehicle-treated animals. Working memory was also assessed on days 8-20 using the MWM. The NAM and Vehicle groups quickly acquired the task; however, HTS animals showed no acquisition of this task. Histological examinations revealed that the HTS-treated animals lost significantly more cortical tissue than either the NAM or Vehicle-treated animals. HTS-treated animals showed a greater loss of hippocampal tissue compared to the other groups. In general, NAM showed a faster rate of recovery than HTS without this associated tissue loss. The results of this study reiterate the strengths of NAM following injury and show concerns with bolus administrations of HTS due to the differential effects on cognitive performance and apparent tissue loss.

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.

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.

Motor skill training, but not voluntary exercise, improves skilled reaching after unilateral ischemic lesions of the sensorimotor cortex in rats

BACKGROUND AND PURPOSE

Exercise and rehabilitative training each have been implicated in the promotion of restorative neural plasticity after cerebral injury. Because motor skill training induces synaptic plasticity and exercise increases plasticity-related proteins, we asked if exercise could improve the efficacy of training on a skilled motor task after focal cortical lesions.

METHODS

Female young and middle-aged rats were trained on the single-pellet retrieval task and received unilateral ischemic sensorimotor cortex lesions contralateral to the trained limb. Rats then received both, either, or neither voluntary running and/or rehabilitative training for 5 weeks beginning 5 days postlesion. Motor skill training consisted of daily practice of the impaired forelimb in a tray-reaching task. Exercised rats had free access to running wheels for 6 h/day. Reaching function was periodically probed using the single-pellet retrieval task.

RESULTS

In young adults, motor skill training significantly enhanced skilled reaching recovery compared to controls. However, exercise did not significantly enhance performance when administered alone or in combination with skill training. There was also no major benefit of exercise in older rats. Additionally, there were no effects of exercise in a measure of coordinated forelimb placement (the foot-fault test) or in immunocytochemical measures of several plasticity-related proteins in the motor cortex.

CONCLUSIONS

In young and middle-aged animals, exercise did not improve motor skill training efficacy following ischemic lesions. Practicing motor skills more effectively improved recovery of these skills than did exercise. It remains possible that an alternative manner of administering exercise would be more effective.

No improvement by amphetamine on learned non-use, attempts, success or movement in skilled reaching by the rat after motor cortex stroke

Amphetamine (AMPH) has been proposed as a treatment for post-stroke motor deficits when coupled with symptom-relevant physical rehabilitation. Whereas a number of experimental studies report improvements in endpoint measures of skilled reaching for food by rats, there has been no assessment of whether beneficial effects extend to overcoming learned non-use of the limb in the acute post-stroke period or to the qualitative deficits in movement in the chronic post-stroke period. In addition to evaluating the effects of AMPH on success, these were the objectives of the present study. In three different reaching experiments, groups of rats were pre-trained in skilled reaching for food prior to receiving a motor cortex stroke via pial removal. Postoperatively the rats received periodic AMPH treatment and daily rehabilitation. In the acute post-stroke period, AMPH failed to prevent the development of learned non-use of the limb, and in the acute and chronic period failed to improve recovery of reaching success, and also failed to improve the qualitative aspects of reaching movements. Nevertheless, AMPH did enhance adjunct non-reaching movements of locomotion, rearing and turning. The results are discussed in relation to the idea that the beneficial effects of post-stroke AMPH treatment do not extend to all movements, especially the movements of a forelimb in retrieving and consuming food.

Cortical edema in moderate fluid percussion brain injury is attenuated by vagus nerve stimulation

Development of cerebral edema (intracellular and/or extracellular water accumulation) following traumatic brain injury contributes to mortality and morbidity that accompanies brain injury. Chronic intermittent vagus nerve stimulation (VNS) initiated at either 2 h or 24 h (VNS: 30 s train of 0.5 mA, 20 Hz, biphasic pulses every 30 min) following traumatic brain injury enhances recovery of motor and cognitive function in rats in the weeks following brain injury; however, the mechanisms of facilitated recovery are unknown. The present study examines the effects of VNS on development of acute cerebral edema following unilateral fluid percussion brain injury (FPI) in rats, concomitant with assessment of their behavioral recovery. Two hours following FPI, VNS was initiated. Behavioral testing, using both beam walk and locomotor placing tasks, was conducted at 1 and 2 days following FPI. Edema was measured 48 h post-FPI by the customary method of region-specific brain weights before and after complete dehydration. Results of this study replicated that VNS initiated at 2 h after FPI: 1) effectively facilitated the recovery of vestibulomotor function at 2 days after FPI assessed by beam walk performance (P<0.01); and 2) tended to improve locomotor placing performance at the same time point (P=0.18). Most interestingly, results of this study showed that development of edema within the cerebral cortex ipsilateral to FPI was significantly attenuated at 48 h in FPI rats receiving VNS compared with non-VNS FPI rats (P<0.04). Finally, a correlation analysis between beam walk performance and cerebral edema following FPI revealed a significant inverse correlation between behavior performance and cerebral edema. Together, these results suggest that VNS facilitation of motor recovery following experimental brain injury in rats is associated with VNS-mediated attenuation of cerebral edema.

CNS-active drugs in aging population at high risk of cerebrovascular events: evidence from preclinical and clinical studies

The recovery process following cerebral insults such as stroke is affected by aging and pharmacotherapy. The use of medication including CNS-active drugs has increased in the elderly during recent years. However, surprisingly little is known about how safe they are with respect to severity of sensorimotor and cognitive impairments or recovery of function following possible cerebrovascular accidents. This review examines the experimental and clinical literature, primarily from 1995 onwards, concerning medication in relation to cerebrovascular events and functional recovery. Special attention is directed to polypharmacy and to new CNS-active drugs, which the elderly are already taking or are prescribed to treat emerging, stroke-induced psychiatric symptoms. The neurobiological mechanisms affected by these drugs are discussed.

Repetitive vibrissae-elicited forelimb placing before and immediately after unilateral 6-hydroxydopamine improves outcome in a model of Parkinson's disease

In rodent models of Parkinson's disease (PD), exercise or complex living environments introduced immediately before or during early stages of degeneration can provide beneficial effects on functional and/or neurochemical outcome. The goal of this study was to determine whether or not exposure to repetitive vibrissae-elicited forelimb placing, a dopamine-dependent sensorimotor movement, improves functional outcome in rats infused unilaterally with 6-OHDA. Prior to unilateral 6-OHDA infusions into the medial forebrain bundle, male Sprague-Dawley rats were randomly divided into groups exposed to one of five placing schedules: (1) two consecutive days pre-6-OHDA (PRE), (2) PRE+day 1 post-6-OHDA, (3) PRE+days 1, 2, 3 post-6-OHDA, (4) HANDLE, and (5) Sham infusion+handle. A session consisted of 180 total trials (90 left forelimb and 90 right forelimb trials) including 60 consecutive trials where vibrissae stimulation evoked ipsilateral forelimb movement and 30 consecutive trials where the ipsilateral forelimb was restrained so that vibrissae evoked contralateral forelimb movement (cross-midline placing). All groups were exposed to forelimb placing sessions on post-infusion days 7 and 14. The ability of vibrissae stimulation to elicit an ipsilateral response of the 6-OHDA affected forelimb was assessed on all days. Animals were sacrificed on post-lesion day 15 and substantia nigra tyrosine hydroxylase immunoreactivity (TH-ir) quantified. Repetitive forelimb placing had a significant effect on behavioral performance for all groups compared to the HANDLE group, but only the PRE+123 group was not significantly different from SHAM controls. Only the PRE+123 group showed significant sparing of TH-ir compared to the HANDLE group. These data suggest that extensive repetitive exposure to a sensorimotor task may provide therapeutic effects in an animal model of PD.

Recovery of Function after Vagus Nerve Stimulation Initiated 24 Hours after Fluid Percussion Brain Injury

Recent evidence from our laboratory demonstrated in laboratory rats that stimulation of the vagus nerve (VNS) initiated 2 h after lateral fluid percussion brain injury (FPI) accelerates the rate of recovery on a variety of behavioral and cognitive tests. VNS animals exhibited a level of performance comparable to that of sham-operated uninjured animals by the end of a 2-week testing period. The effectiveness of VNS was further evaluated in the present study in which initiation of stimulation was delayed until 24 h post-injury. Rats were subjected to a moderate FPI and tested on the beam walk, skilled forelimb reaching, locomotor placing, forelimb flexion and Morris water maze tasks for 2 weeks following injury. VNS (30 sec trains of 0.5 mA, 20.0-Hz biphasic pulses) was initiated 24 h post-injury and continued at 30-min intervals for the duration of the study, except for brief periods when the animals were detached for behavioral assessments. Consistent with our previous findings when stimulation was initiated 2 h post-injury, VNS animals showed significantly faster rates of recovery compared to controls. By the last day of testing (day 14 post-injury), the FPI-VNS animals were performing significantly better than the FPI-no-VNS animals and were not significantly different from shams in all motor and sensorimotor tasks. Performance in the Morris water maze indicated that the VNS animals acquired the task more rapidly on days 11-13 post-injury. On day 14, the FPI-VNS animals did not differ in the latency to find the platform from sham controls, whereas the injured controls did; however, the FPI-VNS animals and injured controls were not significantly different. Despite the lack of significant histological differences between the FPI groups, VNS, when initiated 24 h following injury, clearly attenuated the ensuing behavioral deficits and enhanced acquisition of the cognitive task. The results are discussed with respect to the norepinephrine hypothesis.

Axonal plasticity is associated with motor recovery following amphetamine treatment combined with rehabilitation after brain injury in the adult rat

Clinical and laboratory studies have suggested that amphetamine treatment when paired with rehabilitation results in improved recovery of function after stroke or traumatic brain injury. In the present study, we investigated whether new anatomical pathways developed in association with improved motor function after brain damage and amphetamine treatment linked with rehabilitation. Following a unilateral sensorimotor cortex lesion in the adult rat, amphetamine (2 mg/kg) was administered in conjunction with physiotherapy sessions on postoperative days two and five. Physiotherapy was continued twice daily for the first 3 weeks after injury, and then once daily until week six. Performance on skilled forelimb reaching and ladder rung walking was used to assess motor improvement. Our results show that animals with sensorimotor cortical lesions receiving amphetamine treatment linked with rehabilitation had significant improvement in both tasks. Neuroanatomical tracing of efferent pathways from the opposite, non-damaged cortex resulted in the novel finding that amphetamine treatment linked with rehabilitation, significantly increased axonal growth in the deafferented basilar pontine nuclei. These results support the notion that pharmacological interventions paired with rehabilitation can enhance neuronal plasticity and thereby improve functional recovery after CNS injury.

Epidural cortical stimulation enhances motor function after sensorimotor cortical infarcts in rats

This study examined whether epidurally delivered cortical electrical stimulation (CS) improves the efficacy of motor rehabilitative training and alters neuronal density and/or cell proliferation in perilesion cortex following ischemic sensorimotor cortex (SMC) lesions. Adult rats were pre-trained on a skilled reaching task and then received partial unilateral SMC lesions and implantation of electrodes over the remaining SMC. Ten to fourteen days later, rats received daily reach training concurrent with anodal or cathodal 100 Hz CS or no stimulation (NoCS) for 18 days. To label newly generated cells, bromodeoxyuridine (BrdU; 50 mg/kg) was administered every third day of training. Both anodal and cathodal CS robustly enhanced reaching performance compared to NoCS controls. Neuronal density in the perilesion cortex was significantly increased in the cathodal CS group compared to the NoCS group. There were no significant group differences in BrdU-labeled cell density in ipsilesional cortex. Staining with Fluoro-Jade-B indicated that neurons continue to degenerate near the infarct at the time when cortical stimulation and rehabilitation were initiated. These data indicate that epidurally delivered CS greatly improves the efficacy of rehabilitative reach training following SMC damage and raise the possibility that cathodal CS may influence neuronal survival in perilesion cortex.

No effects of enhanced central norepinephrine on finger-sequence learning and attention

RATIONALE

When paired with training, substances that increase monoaminergic transmission in the brain support motor and language learning in healthy subjects and in rehabilitation after brain lesions.

OBJECTIVES

To test the hypotheses that enhancement of central norepinephrine by the selective norepinephrine reuptake inhibitor reboxetine (1) improves skilled motor performance, (2) promotes skilled motor learning, and (3) does not exert these effects by modulation of attention.

METHODS

In a double blind, placebo-controlled, crossover study in healthy, adult subjects (n=16), finger-sequence performance and learning was measured after the stimulation of the central noradrenergic system with a single dose (8 mg) of reboxetine and placebo. Effects on attention were assessed by the standardized continuous performance test "CPT-M".

RESULTS

No differential effects of reboxetine or placebo on finger-sequence performance, learning and parameters of attention were found.

CONCLUSION

Selective stimulation of the central noradrenergic system did not promote skilled motor learning or performance as assessed by finger-sequences. The plasticity-enhancing effect of reboxetine, documented in other studies, appears to be dependent on specific neurophysiological and neuropsychological characteristics of the task, and cannot be generalized to other behavioral paradigms.

D-amphetamine improves cognitive deficits and physical therapy promotes fine motor rehabilitation in a rat embolic stroke model

BACKGROUND AND PURPOSE

The purpose of this study was to examine the effects of D-amphetamine (D-amph) and physical therapy separately or combined on fine motor performance, gross motor performance and cognition after middle cerebral artery thromboembolization in rats.

METHODS

Seventy-four rats were trained in appropriate cognitive and motor behaviours. Thirteen animals were sham-operated and fifty-nine animals were embolized in the right carotid territory. Animals were randomly assigned to five groups: 1) SHAM (non-embolized, saline), 2) CONTROL (embolized, saline), 3) D-AMPH (embolized, D-amph), 4) THERAPY (embolized, saline + physical therapy) and 5) D-AMPH + THERAPY (embolized, D-amph + physical therapy). Rats of the groups 4-5 underwent d-amph or saline treatment on days 1, 3, 5 and 7 after surgery and were re-trained for 1 h starting 60 min after each treatment. During this time, rats were allowed to voluntarily engage in suitable cognitive or motor behaviours in order to obtain food. Animals from all groups were re-tested during days 21-28 after surgery.

RESULTS

No differences in infarct volumes were observed between the groups of embolized animals. When evaluating performances on days 21-28 after surgery, rats of the SHAM and THERAPY groups had better fine motor performance than those of the CONTROL (P < 0.05), whereas rats of SHAM and D-AMPH groups achieved better cognitive performance than CONTROL rats (P < 0.05). No significant differences were observed between any groups regarding gross motor performance.

CONCLUSIONS

After embolization, physical therapy improved fine motor performance and D-amph accelerated rehabilitation of cognitive performance as observed in the rats of the THERAPY and D-AMPH groups. As a result of the administration of a high dose of D-amph, the rats of the D-AMPH + THERAPY combination group failed to engage in physical therapy during D-amph intoxication, thereby limiting any promotion of rehabilitation by combining physical therapy and D-amph.

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.

Effect of atorvastatin on spatial memory, neuronal survival, and vascular density in female rats after traumatic brain injury

Object. Atorvastatin administered after traumatic brain injury (TBI) induced by controlled cortical impact promotes functional improvement in male rats. Note, however, that parallel studies have not been performed in female rats. Therefore, the authors tested the effect of atorvastatin on TBI in female rats.

Methods. Atorvastatin (1 mg/kg/day) was orally administered for 7 consecutive days in female Wistar rats starting 1 day after TBI; control animals received saline. Modified neurological severity scores, the corner turn test, and the Morris water maze test were used to evaluate functional response to treatment. Rats were killed on Day 15 post-TBI, and brain tissue samples were processed for immunohistochemical staining. Atorvastatin administration after brain injury significantly promoted the restoration of spatial memory but did not reduce sensorimotor functional deficits. Treatment of TBI with atorvastatin increased neuronal survival in the CA3 region and the lesion boundary zone and prevented the loss of neuronal processes of damaged neurons in the hippocampal CA3 region but not in the lesion boundary zone on Day 15 after TBI. The protective effect of atorvastatin on the injured neurons perhaps is mediated by increasing the density of vessels in the lesion boundary zone and the hippocampus after TBI.

Conclusions. These data indicate that atorvastatin is beneficial in the treatment of TBI in female rats, although the effect may differ between sexes.

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.

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.

Behavioral and neuroplastic effects of focal endothelin-1 induced sensorimotor cortex lesions

Previous studies have established the usefulness of endothelin-1 (ET-1) for the production of focal cerebral ischemia. The present study assessed the behavioral effects of focal ET-1-induced lesions of the sensorimotor cortex (SMC) in adult rats as well as cellular and structural changes in the contralateral homotopic motor cortex at early (2 days) and later (14 days) post-lesion time points. ET-1 lesions resulted in somatosensory and postural-motor impairments in the contralateral (to the lesion) forelimb as assessed on a battery of sensitive measures of sensorimotor function. The lesions also resulted in the development of a hyper-reliance on the ipsilateral forelimb for postural-support behaviors. In comparison to sham-operated rats, in layer V of the motor cortex opposite the lesions, there were time- and laminar-dependent increases in the surface density of dendritic processes immunoreactive for microtubule-associated protein 2, in the optical density of N-methyl-D-asparate receptor (NMDA) subunit 1 immunoreactivity, and in the numerical density of cells immunolabeled for Fos, the protein product of the immediate early gene c-fos. These findings corroborate and extend previous findings of the effects of electrolytic lesions of the SMC. It is likely that compensatory forelimb behavioral changes and transcallosal degeneration play important roles in these changes in the cortex opposite the lesion, similar to previously reported effects of electrolytic SMC lesions.

Atorvastatin Reduces Neurological Deficit and Increases Synaptogenesis, Angiogenesis, and Neuronal Survival in Rats Subjected to Traumatic Brain Injury

Statins administered postischemia promote functional improvement in rats, independent of their capability to lower cholesterol. We therefore tested the effect of statin treatment on traumatic brain injury (TBI) in rats. Atorvastatin was orally administered (1 mg/kg/day) to Wistar rats starting 1 day after TBI for 7 consecutive days. Control animals received saline. Modified Neurological Severity Scores and Corner tests were utilized to evaluate functional response to treatment. Bromodeoxyuridine (BrdU, 100 mg/kg) was also intraperitoneally injected daily for 14 consecutive days to label the newly generated endothelial cells. Rats were sacrificed at day 14 after TBI, and the brain samples were processed for immunohistochemical staining. Atorvastatin administration after brain injury significantly reduced the neurological functional deficits, increased neuronal survival and synaptogenesis in the boundary zone of the lesion and in the CA3 regions of the hippocampus, and induced angiogenesis in these regions. The results suggest that atorvastatin may provide beneficial effects in experimental TBI.

Dexamphetamine treatment in stroke

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

Upregulation of neurogenesis and reduction in functional deficits following administration of DEtA/NONOate, a nitric oxide donor, after traumatic brain injury in rats

OBJECT

Neurogenesis, which is upregulated by neural injury in the adult mammalian brain, may be involved in the repair of the injured brain and functional recovery. Therefore, the authors sought to identify agents that can enhance neurogenesis after brain injury, and they report that (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA/NONOate), a nitric oxide donor, upregulates neurogenesis and reduces functional deficits after traumatic brain injury (TBI) in rats.

METHODS

The agent DETA/NONOate (0.4 mg/kg) was injected intraperitoneally into 16 rats daily for 7 days, starting 1 day after TBI induced by controlled cortical impact. Bromodeoxyuridine (100 mg/kg) was also injected intraperitoneally daily for 14 days after TBI to label the newly generated cells in the brain. A neurological functional evaluation was performed in all rats and the animals were killed at 14 or 42 days postinjury. Immunohistochemical staining was used to identify proliferating cells.

CONCLUSIONS

Compared with control rats, the proliferation, survival, migration and differentiation of neural progenitor cells were all significantly enhanced in the hippocampus, subventricular zone, striatum, corpus callosum, and the boundary zone of the injured cortex, as well as in the contralateral hemisphere in rats with TBI that received DETA/ NONOate treatment. Neurological functional outcomes in the DETA/NONOate-treated group were also significantly improved compared with the untreated group. These data indicate that DETA/NONOate may be useful in the treatment of TBI.

A double-blind, placebo-controlled study of the use of amphetamine in the treatment of aphasia

BACKGROUND AND PURPOSE

A number of studies suggest that drugs which increase the release of norepinephrine promote recovery when administered late (days to weeks) after brain injury in animals. A small number of clinical studies have investigated the effects of the noradrenergic agonist dextroamphetamine in patients recovering from motor deficits following stroke. To determine whether these findings extend to communication deficits subsequent to stroke, we administered dextroamphetamine, paired with speech/language therapy, to patients with aphasia.

METHODS

In a prospective, double-blind study, 21 aphasic patients with an acute nonhemorrhagic infarction were randomly assigned to receive either 10 mg dextroamphetamine or a placebo. Patients were entered between days 16 and 45 after onset and were treated on a 3-day/4-day schedule for 10 sessions. Thirty minutes after drug/placebo administration, subjects received a 1-hour session of speech/language therapy. The Porch Index of Communicative Ability was used at baseline, at 1 week off the drug, and at 6 months after onset as the dependent language measure.

RESULTS

Although there were no differences between the drug and placebo groups before treatment (P=0.807), by 1 week after the 10 drug treatments ended there was a significant difference in gain scores between the groups (P=0.0153), with the greater gain in the dextroamphetamine group. The difference was still significant when corrected for initial aphasia severity and age. At the 6-month follow-up, the difference in gain scores between the groups had increased; however, the difference was not significant (P=0.0482) after correction for multiple comparisons.

CONCLUSIONS

Administration of dextroamphetamine paired with 10 1-hour sessions of speech/language therapy facilitated recovery from aphasia in a small group of patients in the subacute period after stroke. Neuromodulation with dextroamphetamine, and perhaps other drugs that increase central nervous system noradrenaline levels, may facilitate recovery when paired with focused behavioral treatment.

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.

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

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

Inhalation of low concentrations of toluene induces persistent effects on a learning retention task, beam-walk performance, and cerebrocortical size in the rat

The organic solvent toluene is widely used in industry. The threshold limit value for extended occupational exposure to toluene is presently set to 200 ppm in the United States. We have investigated the effect of an inhalation exposure of 80 ppm for 4 weeks (6 h/day, 5 days/week), followed by a postexposure period of at least 4 weeks, on behavior and brain features in the rat. Toluene exposure appeared to affect spatial memory, since toluene-exposed rats showed a longer time in the correct quadrant in a Morris swim maze. This effect may indicate that the exposed rats used their praxis strategy longer before they started to look for the platform elsewhere. Toluene-exposed rats showed trends for increases in both locomotion and rearing behaviors and a significantly reduced beam-walk performance. The area of the cerebral cortex, especially the parietal cortex, was decreased by 6-10% in toluene-exposed rats, as shown by magnetic resonance imaging of living rats and autoradiograms of frozen brain sections. The K(D) and B(max) values of the dopamine D(3) agonist [(3)H]PD 128907 were not affected by toluene, as measured in caudate-putamen and subcortical limbic area using biochemical receptor binding assays and in caudate-putamen and islands of Calleja using quantitative receptor autoradiography. Hence, previously demonstrated persistent effects by toluene on the binding characteristics of radioligands binding to both D(2) and D(3) receptors seem to indicate a persistent effect of toluene selectively on dopamine D(2) receptors. Taken together, the present results indicate that exposure to low concentrations of toluene leads to persistent effects on cognitive, neurological, and brain-structural properties in the rat.

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.

Enhanced neocortical neural sprouting, synaptogenesis, and behavioral recovery with D-amphetamine therapy after neocortical infarction in rats

BACKGROUND AND PURPOSE

D-Amphetamine administration increases behavioral recovery after various cortical lesions including cortical ablations, contusions, and focal ischemia in animals and after stroke in humans. The purpose of the present study was to test the enhanced behavioral recovery and increased expression of proteins involved in neurite growth and synaptogenesis in D-amphetamine-treated rats compared with vehicle-treated controls after a focal neocortical infarct.

METHODS

Unilateral neocortical ischemia was induced in male spontaneously hypertensive Wistar rats (n=8 per time point per group) by permanently occluding the distal middle cerebral artery and ipsilateral common carotid artery in 2 groups of rats: D-amphetamine treated (2 mg/kg IP injections) and vehicle treated (saline IP injections). To determine the spatial and temporal distribution of neurite growth and/or synaptogenesis, growth-associated protein (GAP-43), a protein expressed on axonal growth cones, and synaptophysin, a calcium-binding protein found on synaptic vesicles, were examined by immunohistochemical techniques, and both density and distribution of reaction product were measured. Since the resulting infarction included a portion of the forelimb neocortex, behavioral assessments of forelimb function using the foot-fault test of Hernandez and Schallert were performed on the same rats used for immunohistochemical studies during the period of drug action and 24 hours later. A Morris water maze and other indices of behavioral assays were also measured similarly. Recovery times were 3, 7, 14, 30, and 60 days postoperatively.

RESULTS

Both GAP-43 and synaptophysin proteins demonstrated statistically significant increases in density and distribution of immunoreaction product as determined by optical density measurements in the neocortex of the infarcted group treated with D-amphetamines compared with vehicle-treated infarcted controls. The GAP-43 was elevated to statistically significant levels in forelimb, hindlimb, and parietal neocortical regions ipsilateral to the infarction only at days 3, 7, and 14. By contrast, the synaptophysin demonstrated no statistically significant changes in expression at 3 or 7 days but demonstrated statistically significant increases at 14, 30, and 60 days in the forelimb, hindlimb, and parietal neocortical regions ipsilateral to the infarction as well as increased distribution in the contralateral parietal neocortex. Behavioral assessment of forelimb function indicated that improved recovery of forelimb placement on the side contralateral to the infarction was statistically significant in the D-amphetamine-treated group compared with the vehicle-treated group (P<0.025). Spatial memory, as measured with the Morris water maze, worsened in the vehicle-treated group compared with the D-amphetamine-treated group at 60 days (P<0.025).

CONCLUSIONS

These data support the occurrence of neurite growth followed by synaptogenesis in the neocortex in a pattern that corresponds both spatially and temporally with behavioral recovery that is accelerated by D-amphetamine treatment. While the specific mechanisms responsible for D-amphetamine-promoted expression of proteins involved in neurite growth and synaptogenesis and of enhanced behavioral recovery are not known, it is suggested that protein upregulation occurs as a result of functional activation of pathways able to remodel in response to active behavioral performance.

Ladder beam and camera video recording system for evaluating forelimb and hindlimb deficits after sensorimotor cortex injury in rats

Hindlimb and forelimb deficits in rats caused by sensorimotor cortex lesions are frequently tested by using the narrow flat beam (hindlimb), the narrow pegged beam (hindlimb and forelimb) or the grid-walking (forelimb) tests. Although these are excellent tests, the narrow flat beam generates non-parametric data so that using more powerful parametric statistical analyses are prohibited. All these tests can be difficult to score if the rat is moving rapidly. Foot misplacements, especially on the grid-walking test, are indicative of an ongoing deficit, but have not been reliably and accurately described and quantified previously. In this paper we present an easy to construct and use horizontal ladder-beam with a camera system on rails which can be used to evaluate both hindlimb and forelimb deficits in a single test. By slow motion videotape playback we were able to quantify and demonstrate foot misplacements which go beyond the recovery period usually seen using more conventional measures (i.e. footslips and footfaults). This convenient system provides a rapid and reliable method for recording and evaluating rat performance on any type of beam and may be useful for measuring sensorimotor recovery following brain injury.

Some functional recovery and behavioral sparing occurs independent of task-specific practice after injury to the rat's sensorimotor cortex

These experiments on rats evaluated whether recovery of competence in certain motor tests could be enhanced by practice begun soon after traumatic brain injury (TBI). Before TBI, rats were pre-trained to cross a flat and a pegged beam. Anesthetized animals received a right sensorimotor cortex TBI. One group began task-specific testing (flat and pegged beams) on day 1 after injury and repeated 13 times in 35 days by which time functional recovery occurred. Paw preference was evaluated eight times during the 35 day period, beginning the third day after injury. A second group of injured rats remained in their home cage without any testing for 35 days after injury. From day 35 they were tested 13 times over the next 35 days on both beam tests and eight times on the paw preference test. At day 35 those rats that remained in their home cage without testing (task-specific practice) performed as well on the flat beam as the rats that began testing 1 day after injury. By day 37, their third test day, the untested rats performed as well as the tested rats on the pegged beam. Paw preference was the same in both groups of rats. These results were compared to sham-operated controls. Post-injury performance as measured by these tests indicated that most of the recovery occurred without task-specific practice. However, task-specific practice was necessary to achieve optimum performance on both beam tests. This implies that neural reorganization occurred independent of any practice. Task specific practice served to 'fine tune' the rat's performance after 35 days.

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.

Neuronal cell loss in the CA3 subfield of the hippocampus following cortical contusion utilizing the optical disector method for cell counting

Unilateral cortical contusion in the rat results in cell loss in both the cortex and hippocampus. Pharmacological intervention with growth factors or excitatory neurotransmitter antagonists may reduce cell loss and improve neurological outcome. The window of opportunity for such intervention remains unclear because a detailed temporal analysis of neuronal loss has not been performed in the rodent cortical contusion model. To elucidate the time course of hippocampal CA3 neuronal death ensuing cortical contusion, we employed the optical disector method for assessing the total number of CA3 neurons at 1 and 6 hours, 1, 2, 10, and 30 days following injury. This stereological technique allows reporting of total cell numbers within a given region and is unaffected by change in the volume of the structure or cell size. A rapid and significant reduction in neurons/mm3 in the ipsilateral CA3 field was observed by 1 h following trauma. However, a significant increase in neurons/mm3 was seen at 30 days postinjury. This surprising finding is a result of CA3 volume shrinkage and redistribution of CA3 neurons. Utilization of the optical disector reveals that regardless of an increase in neurons/mm3 at 30 days following injury, CA3 cell loss reaches 41% of control animals by 1 day posttrauma and remains near that level at all subsequent time points examined. It is estimated that there are about 156,000 neurons in the CA3 region in control animals. By 1 h following cortical contusion the cell population decreases to 93,000 neurons indicating a very rapid cell loss. This suggests a window of less than 24 h for pharmacological intervention in order to save CA3 neurons following cortical contusion.

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.