Antispasticity drugs: mechanisms of action

Neurophysiology of gait disorders: present and future applications

This article will review those electrophysiological investigations which have addressed the neuronal mechanisms underlying impaired gait. The aims of the review are to provide further insights to the underlying pathophysiology of impaired gait and also towards the selection of an appropriate treatment. From the patients' point of view the first indication of a central motor system lesion is an impairment of movement, most notably locomotion. These symptoms are characteristic in cases of spasticity, cerebellar lesion or Parkinson's disease. Clinical examination reveals typical changes in tendon tap reflexes and muscle tone which were believed to account for the movement disorder presented. However, we now know that there is only a weak relationship between the physical symptoms observed during clinical examination under passive motor conditions and the altered neuronal mechanisms underlying the impairment during active motion. By recording and analysing electrophysiological and biomechanical parameters during functional movements such as locomotion, the significance of impaired reflex behaviour or the pathophysiology of muscle tone and its contribution to the movement disorder can be reliably assessed. Consequently, the treatment should not be cosmetic, i.e. the correction of an isolated clinical parameter, but should be based on the pathophysiology and significance of those mechanisms underlying the impairment of the patients' movements. Data from electrophysiological and biomechanical investigations of locomotion of patients with spasticity, cerebellar disorder or Parkinson's disease are discussed in this review. The neuronal mechanisms, which are essentially central programs and afferent input, involved in disorders of gait are evaluated on the basis of their function in healthy subjects. The impact of this analysis in deciding an appropriate treatment are discussed with respect to the pathophysiology underlying the gait disorder (spasticity, cerebellar disorder or Parkinson's disease). At the present time we have only a basic understanding of the essential receptor systems, such as leg extensor load receptors, and their interaction with other systems involved in postural control. In the future, the knowledge gained from gait analysis may help in the selection of the appropriate pharmacological and physical treatment required even though the patient may only be at an early stage of motor impairment.

Oral pharmacotherapy for the movement disorders of cerebral palsy

Movement disorders are a well-recognized feature of some patients with cerebral palsy and often require treatment. However, treatments have been symptomatic and empiric, and there have been few pharmacologic studies. The major movement disorders in cerebral palsy are dystonia and the hyperkinesias choreoathetosis and myoclonus. They may occur in combination, often accompanied by spasticity and sometimes by epilepsy. Some drugs are useful treatments for all of these problems, but others may improve one while worsening another. Pitfalls in management include not diagnosing metabolic/degenerative disorders, which may mimic cerebral palsy, or not recognizing reversible complications of cerebral palsy, which may exacerbate symptoms. This review attempts to summarize empiric drug use and recommendations for therapy, drug studies in extrapyramidal cerebral palsy, and prospects for new drugs or models for the problem. Many new pharmacologic agents are available for study in cerebral palsy. Better methods of detecting basal ganglia injury after perinatal injury in asymptomatic infants may allow early intervention in the biologic process of recovery and adaptation.

The effects of the muscle relaxant, CS-722, on synaptic activity of cultured neurones

1. The pharmacological properties of the centrally acting muscle relaxant, CS-722, were studied in cultured hippocampal cells and dorsal root ganglion cells of the rat using the whole-cell variation of the patch clamp technique. 2. CS-722 inhibited the occurrence of spontaneous excitatory and inhibitory postsynaptic currents in hippocampal neurones at concentrations of 100-300 microM, but had no effect on postsynaptic currents evoked by the application of glycine, gamma-aminobutyric acid, glutamate or N-methyl-D-aspartate. 3. CS-722 reduced voltage-gated sodium currents, while shifting the sodium channel inactivation curve to more negative membrane potentials. This effect is similar to that reported for local anaesthetics. Voltage-gated potassium currents were decreased by CS-722 by approximately 20%, whereas voltage-activated calcium currents were inhibited by about 25%. 4. CS-722 inhibited evoked inhibitory postsynaptic currents. However, the spontaneous quantal release of inhibitory transmitter was not affected. 5. The inhibitory effect of CS-722 on spontaneous inhibitory postsynaptic currents and excitatory postsynaptic currents in hippocampal cultures probably results from an inhibition of both sodium and calcium currents. This inhibitory effect is likely to be amplified in polysynaptic neuronal circuits.

Effects of diazepam, baclofen and thiopental on the silent period evoked by transcranial magnetic stimulation in humans

The cortical silent period evoked by magnetic transcranial stimulation and the peripheral silent period were studied in healthy subjects after intravenous injection of diazepam, baclofen or thiopental. None of the drugs tested changed the peripheral silent period. But, unexpectedly, diazepam significantly shortened the cortical silent period, the inhibitory effect lasting about 30 min. In experiments using paired transcranial stimuli, the conditioning shock inhibited the test response to a similar extent with and without diazepam. Although baclofen did not change the cortical silent period, it reduced the size of the H reflex in the forearm muscles. Thiopental also left the duration of the cortical silent period unchanged. These findings show that the cortical silent period can be modified pharmacologically. Diazepam possibly shortens the silent period by modulating GABA A receptors at a subcortical site.

Quantitative clinical measure of spasticity in children with cerebral palsy

OBJECTIVE

This investigation developed an objective measure to quantify the degree of spasticity.

DESIGN

Specifications included a single variable that integrated key elements characterizing spasticity: velocity, range of motion, and resistance to passive motion. A dynamometer at a children's hospital quantified the passive resistance of the hamstrings to knee extension for a range of motion at 4 different speeds for the prospective descriptive investigation.

PATIENTS

A convenience sample of six children with able bodies and 17 children with spastic diplegic cerebral palsy volunteered. DATA PROCESSING: Torque-angle data were processed to calculate the work done by the machine on the children for each speed and then determine the slope of the work-velocity curves. This slope was considered to be the measure of spasticity and it was hypothesized that children with cerebral palsy would have a greater slope than children with able bodies. An independent test determined whether a significant difference existed between groups (p < .05).

RESULTS

Torque-angle data for children with able bodies indicated little change in passive resistance as a function of speed. Similar data for children with cerebral palsy indicated larger resistive torques with increasing speed. Slope from the work-velocity data was close to zero for children with able bodies [.003 J/(degrees/sec)], while the corresponding slope for children with cerebral palsy was approximately 10 times greater [.031 J/(degrees/sec)] and significantly different (p < .05).

CONCLUSION

The slope of the work-velocity data integrates three major components characterizing spasticity, it is a single number that can easily be evaluated and interpreted in a clinical setting, and it utilizes a machine that is available at many centers.

Localised tetanus in two cats after ovariohysterectomy

Localised tetanus was diagnosed in two cats 14 and 21 days after ovariohysterectomy by a left flank surgical approach. The diagnosis in each case was based on their history, clinical signs and diagnostic investigations which excluded other possible diagnoses. Both cats showed scoliosis of the lumbar spine and left hind limb spasticity. One cat's clinical signs were exacerbated after the administration of corticosteroids. One cat was treated with oral amoxycillin and diazepam, and the second cat received penicillin, tetanus antitoxin, methocarbarnol and diazepam. Both cats improved after treatment but recovery was prolonged and the spasticity did not resolve until 12 weeks after diagnosis in one cat. The second cat was lost to follow up after 8 weeks.

Continuous intrathecal baclofen infusion for symptomatic generalized dystonia

Five patients with generalized dystonia who were refractory to oral medications were treated by continuous intrathecal baclofen infusion. Dystonia was related to cerebral palsy in three patients and to Hallervorden-Spatz disease in two. Responsiveness to intrathecally administered baclofen was evaluated after bolus injections in one patient and during continuous infusions via an external micropump in four. Patients who responded to trial injections were subsequently implanted with a programmable pump for continuous infusion of baclofen. Dystonia in the three patients were cerebral palsy was substantially improved by continuous intrathecal baclofen infusion in doses of 500 to 800 micrograms/d. Benefit has persisted for > 19 months of continuous infusion. Dystonia in the two patients with Hallervorden-Spatz disease was not improved, although the screening trial was limited by side effects in one patient and by meningitis in the other. We conclude that continuous intrathecal baclofen infusion is beneficial therapy for some patients with generalized dystonia and that additional investigations are indicated.

Prospective study on the use of bolus intrathecal baclofen for spastic hypertonia due to acquired brain injury

OBJECTIVE

To determine if the intrathecal delivery of baclofen will decrease spastic hypertonia caused by brain injury.

PATIENTS

Eleven patients more than 1 year after their brain injury with disabling lower extremity spastic hypertonia.

SETTING

University tertiary care outpatient rehabilitation clinic.

DESIGN

Patients were a consecutive sample randomized in a double blind, placebo-controlled crossover study.

INTERVENTIONS

Bolus intrathecal injection of either normal saline or 50 micrograms baclofen.

MAIN OUTCOME MEASURES

Data for Ashworth rigidity scores, spasm scores, and deep tendon reflex scores were collected for both the upper extremities (UE) and lower extremities (LE). Changes over time were assessed via Friedman's test. Differences between the placebo and active drug at any given time were assessed via Wilcoxon signed-rank.

RESULTS

Four hours after injection with the active drug (maximum effect) the average LE Ashworth score decreased from 4.2 +/- 0.8 (SD) to 2.2 +/- 0.6 (p = .0033), spasm score from 3.1 +/- 1.0 to 1.0 +/- 0.7 (p = .0032), and reflex score from 3.3 +/- 0.5 to 1.0 +/- 1.3 (p = .0033). The average UE Ashworth score decreased from 3.3 +/- 1.3 to 1.9 +/- 0.8 (p = .0033), spasm score from 1.8 +/- 1.3 to 0.6 +/- 1.0 (p = .007), and reflex score from 2.7 +/- 0.5 to 1.7 +/- 0.6 (p = .0111). No trend was observed over time with placebo administration. There were significant reductions in the average for LE Ashworth (p < .0001), spasm (p < .0001), and reflex (p < .0001) scores and for UE Ashworth (p < .0001) and spasm (p < .0004) scores observed over 4 hours (maximum effect) with active drug administration. No significant differences were noted between the active drug and placebo groups before administration in LE and UE Ashworth, spasm, or reflex scores. There were significant differences between the active drug and placebo groups at 4 hours after administration for LE and UE Ashworth, spasm, and reflex scores (p < or = .0272).

CONCLUSION

Intrathecal injection of baclofen is capable of reducing the spastic hypertonia associated with brain injury.

Multiple sclerosis

Multiple sclerosis is a chronic disease that begins in late adolescence or adulthood. It is highly variable in its expression and severity. It is believed to be autoimmune in nature. The cause is unknown; both genetic and environmental factors have been implicated in the pathogenesis. MS generally presents with the acute or subacute onset of neurologic abnormalities that may wax and wane over many years. Diagnosis is generally made by means of observation of the clinical course in conjunction with a neurologic examination and laboratory tests. These tests may include magnetic resonance imaging of the head and spine, lumbar puncture, and evoked potentials. Treatment is based on general supportive care, the use of corticosteroids for relapses, and symptomatic management of ongoing problems. The frequency of relapses can be reduced with interferon-beta (Betaseron). Copolymer 1 and interferon-beta la are being evaluated by the U.S. Food and Drug Administration for approval for use for reduction in the frequency of relapses in relapsing-remitting MS. Treatment of chronic progression is often attempted with immunosuppressive agents such as corticosteroids, azathioprine, and cyclophosphamide. Use of other agents is being investigated.

Stiff-person syndrome with anti-glutamic acid decarboxylase autoantibodies: complete remission of symptoms after intrathecal baclofen administration

A female patient, aged 61 years, who developed a severe immobilizing stiff-person syndrome in conjunction with insulin-dependent diabetes mellitus, is described. In addition to the typical clinical symptoms, diagnosis was proven by the presence of autoantibodies against glutamic acid decarboxylase in serum and cerebrospinal fluid. Symptomatic treatment with continuous intrathecal application of baclofen administered by a subcutaneous pump resulted in rapid clinical improvement so that the patient became ambulatory. Intermittent withdrawal from intrathecal baclofen therapy led to complete remanifestation of stiff-person syndrome within 18 h; after re-introduction of intrathecal therapy stiffness disappeared completely within 48 h. The clinical course has been stable now for over 24 months and stiffness has completely disappeared. The effect of baclofen in this patient is discussed in the light of the suggested pathophysiological mechanisms in stiff-person syndromes.

The influence of glycine and related compounds on spinal cord injury-induced spasticity

Spasticity is a frequent and complex sequel to spinal cord injury. The neurochemical basis for the origin of spasticity is largely unknown. Glycine is among the most abundant neurotransmitters in the spinal cord. However, the role of glycine and related compounds in spasticity have received little attention. An ischemic spinal cord injury was created in rabbits, by an intraaortic balloon occlusion technique, which produced lower limb spasticity. A catheter was inserted into the cisterna magna and the spinal cord was bathed with 100 microM solutions of glycine, strychnine, D-serine, beta-alanine, MK-801, or artificial CSF for 4 hours at a rate of 10 microliters/min. H-reflexes were monitored before and during infusion by stimulating the posterior tibial nerve and recording from the plantar surface of the foot. Glycine, D-serine, and MK-801 depressed the H wave, strychnine produced a heightened H wave, and beta-alanine caused no significant changes. These results indicate that glycine and related compounds may influence spasticity.

N-methyl-D-aspartate and alpha 2-adrenergic mechanisms are involved in the depressant action of flupirtine on spinal reflexes in rats

In urethane-chloralose anesthetised rats the muscle relaxant activity of flupirtine was investigated on the monosynaptic Hoffmann reflex recorded from plantar foot muscles and on the polysynaptic flexor reflex recorded from tibialis muscle. Intraperitoneal (i.p.; 2.5-25 mumol/kg) and intrathecal (i.t.; 33-330 nmol) administration of flupirtine depressed the polysynaptic flexor reflex in anesthetised rats in a dose-dependent manner without affecting the monosynaptic Hoffmann reflex. Flupirtine produced a similar pattern on spinal reflexes as NMDA receptor antagonists, such as (-)-2-amino-7-phosphonoheptanoic acid (500 nmol i.t.) and memantine (125 mumol/kg i.p.), the benzodiazepines diazepam (18 mumol/kg i.p.) and midazolam (80 nmol i.t.), and the alpha 2-adrenoceptor agonist tizanidine (2 mumol/kg). In contrast, the GABAA receptor agonist muscimol (21 mumol/kg i.p.; 20 nmol i.t.) and the GABAB receptor agonist baclofen (47 mumol/kg i.p.; 2 nmol i.t.) reduced the magnitude of both the flexor and the Hoffmann reflex, whereas the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX; 10 nmol i.t.) depressed the Hoffmann reflex without affecting the flexor reflex. The effect of i.t. injection of flupirtine was prevented by coadministration of the mixed alpha 1/alpha 2-adrenoceptor antagonist yohimbine (10 nmol) and the excitatory amino acid N-methyl-D-aspartate (NMDA; 0.1 nmol), but neither by coadministration of the alpha 1-adrenoceptor antagonist prazosine (10 nmol), the GABAA receptor antagonist bicuculline (1 nmol), the GABAB receptor antagonist phaclofen (100 nmol), the non-NMDA receptor agonist alpha-amino-3-hydroxy-5-tertbutyl-4-isoxazolepropionic acid (ATPA; 0.1 pmol) nor by pre-treatment with the benzodiazepine receptor antagonist flumazenil (16 mumol/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the non-NMDA antagonists NBQX and the 2,3-benzodiazepine GYKI 52466 on different seizure types in mice: comparison with diazepam and interactions with flumazenil

1. GYKI 52466 is a benzodiazepine derivative that has muscle relaxant and anticonvulsant properties thought to be mediated by highly selective, noncompetitive antagonism of non-NMDA receptors. However, recent electrophysiological data showed that, in addition to non-NMDA receptors, the GABAA-receptor associated benzodiazepine site is involved in the depressant effect of GYKI 52466 on spinal reflex transmission. In view of the structural similarities between the 2,3 benzodiazepine derivative GYKI 52466 and 1,4-benzodiazepines such as diazepam, the benzodiazepine site of GABAA receptor complex could also be involved in the anticonvulsant activity of GYKI 52466, which has not yet been proven. This prompted us to study the effect of the benzodiazepine receptor antagonist, flumazenil, on anticonvulsant and adverse effects of GYKI 52466 in different seizure models in mice. The non-NMDA antagonist, NBQX and diazepam were used for comparison. 2. Seizure threshold models for different types of generalized seizures were used. The threshold for maximal (tonic) electroshock seizures (MES) was significantly increased by GYKI 52466 (10-20 mg kg-1), NBQX (80-120 mg kg-1) and diazepam (5 mg kg-1) shortly after i.p. drug administration. The same dose-range of the non-NMDA antagonists also significantly increased the threshold for myoclonic and clonic seizures induced by i.v. infusion of pentylenetetrazol (PTZ), although the magnitude of threshold increases obtained with the respective drugs, differed, at least in part, from that seen in the MES experiments. GYKI 52466 was clearly less potent in increasing PTZ thresholds for myoclonic and clonic seizures than on the MES threshold, while NBQX exerted about the same potency in both models. In contrast to the non-NMDA antagonists, diazepam was capable of increasing themyoclonic and clonic PTZ seizure threshold at much lower doses than the MES threshold. The PTZ threshold for tonic seizures was markedly increased by GYKI 52466, while NBQX and diazepam were clearly less potent in this respect.3. With respect to adverse effects, GYKI 52466 and NBQX induced significant seizure threshold increases in the different seizure models only at doses which caused sedation and ataxia, while diazepam increased the myoclonic and clonic PTZ seizure threshold at doses below those inducing motor impairment.4. Flumazenil (5-20 mg kg-1) antagonized the anticonvulsant and adverse effects of diazepam but not GYKI 52466. Instead, the anticonvulsant effect of GYKI 52466 was potentiated by flumazenil in some experiments. The anticonvulsant activity of NBQX was slightly reduced by flumazenil in the MES model but not in the PTZ test.5. The data indicate that the GABAA receptor-associated benzodiazepine site is not critically involved in anticonvulsant or adverse effects of GYKI 52466. However, both GYKI 52466 and NBQX were unable to increase seizure thresholds at doses below those inducing sedation and motor impairment,thus demonstrating that non-NMDA antagonists lack a selective anticonvulsant action in standard models of generalized seizures.

Centrally acting skeletal muscle relaxants and associated drugs

A review of available studies supports a role for muscle relaxants in the treatment of painful musculoskeletal disorders. The utility of these drugs is limited by sedation and other side effects, as well as by the potential for abuse and dependency. Other drugs can also be used in the treatment of muscle spasm, specifically diazepam, baclofen, dantrolene sodium, and quinine sulfate. The pharmacology of the muscle relaxants and these other agents is discussed and practical suggestions for use are offered.

Dopa-responsive dystonia simulating cerebral palsy

Five patients presented in infancy or early childhood with various combinations of pyramidal and extrapyramidal signs with normal cognitive function. Their perinatal courses were unremarkable. In each patient, initial impressions listed by several examiners included spastic diplegia or cerebral palsy. Later in each course, either extrapyramidal features or progression suggested dopa-responsive dystonia. In 4 of the 5 children, cerebrospinal fluid was obtained and disclosed reduced levels of biopterin, neopterin, and homovanillic acid in all 4. Levodopa therapy resulted in prompt improvement with normal function returning within 6 months. The disappearance of the "spasticity," extensor plantar responses, and extrapyramidal signs, following levodopa therapy, confirmed the diagnosis of doparesponsive dystonia in these patients. Three had apparently sporadic disease; the other 2 were siblings with an affected paternal grandmother. Three had onset in infancy with delayed sitting and walking before the appearance of overt dystonia; infantile onset is infrequent in dopa-responsive dystonia. The other 2 had normal milestones, but developed gait disorders with prominent imbalance in early childhood. The diagnosis of dopa-responsive dystonia should be considered in children with unexplained or atypical "cerebral palsy."

Positive response to oral divalproex sodium (Depakote) in patients with spasticity and pain

Divalproex sodium (DVS; Depakote) is a commonly used antiepileptic agent that increases the levels of gamma aminobutyric acid. Spasticity from different causes may be due to a deficiency of inhibitory transmitters like gamma aminobutyric acid or an excess of excitatory neurotransmitters. Spasticity also may be accompanied by pain. The authors administered DVS orally for pain and spasticity in three patients with a history of spinal cord injury and one patient with a history of head injury. Three patients had marked improvement in spasticity and pain. One patient, who had some symptomatic improvement in spasticity, could not tolerate DVS because of gastric irritation. In contrast to the side effects of sedation and increased motor weakness associated with antispasticity drugs commonly used, no such side effects were detected with DVS. It is suggested that a possible enhancement by DVS of gamma aminobutyric acid-ergic postsynaptic inhibition of motor reflex arc in the spinal cord may represent a new nonsedating, management approach for spasticity as a result of traumatic spinal cord and head injuries.

A comparison of clonidine, cyproheptadine and baclofen in spastic spinal cord injured patients

In twenty-five SCI subjects, antispasticity effects of three putative antispasticity agents [clonidine (an alpha-2 noradrenergic agonist), cyproheptadine (a 5-HT2 antagonist) and baclofen (a GABA-B agonist)] were tested in terms of changes in leg tone as graded by the Ashworth scale (AS), in terms of the vibratory inhibition of the H-reflex (VII) and in terms of the ability of the knee to swing passively in the pendulum test as quantified by video motion analysis. When compared to the no drug period, all three drug treatments showed an antispasticity effect on the AS, the VII and the amplitude of the first swing and the relaxation index of the pendulum test, p. < 0001. Surprisingly, cyproheptadine and baclofen produced a greater reduction in the VII than clonidine, p. < 01. The amplitude of the first swing in the pendulum test correlated well with the AS, r = .88, and the antispasticity effects of the drugs produced improvements in both measures, a reduced AS and increased amplitude of knee swing in the pendulum test. Therefore, video motion analysis of the pendulum test is as valid a measure of spasticity as the Ashworth scale and is not limited by subjectivity of the examiner.

Intrathecal baclofen for severe spasticity secondary to spinal cord injury

OBJECTIVE

To evaluate the use of intrathecal baclofen for the treatment of muscle spasticity in patients with spinal cord injury.

DATA SOURCES

A MEDLINE search was used to identify relevant and pertinent literature. Information was obtained from open-label clinical trials, abstracts, conference proceedings, and review articles. Index terms in the search included baclofen, spasticity, intrathecal drug infusion, spinal cord disease, and neurosurgery.

DATA EXTRACTION

Studies were selected for review if they evaluated intrathecal baclofen in patients with spinal cord injury. Emphasis was placed on human studies published in the English language. Trials were reviewed by dosage regimen, therapeutic response, adverse effects, and complications.

DATA SYNTHESIS

Thus far, intrathecal baclofen administration shows promise in the treatment of spasticity resulting from spinal cord trauma. Few complications and adverse effects have been reported.

CONCLUSIONS

Muscle spasms and spasticity constitute a significant problem in spinal cord injuries, interfering with rehabilitation and leading to inconveniences and complications in these patients. Oral baclofen is the drug of choice for spasticity due to spinal cord trauma. It often is ineffective, however, because of the large dosages required to cross the blood-brain barrier and the subsequent appearance of central nervous system adverse effects. These adverse effects are not tolerated by many patients. Intrathecally administered baclofen has been approved by the Food and Drug Administration (FDA) for the treatment of spasticity in patients with spinal cord injury who are refractory to or cannot tolerate oral baclofen. It is intended for use only in implantable pumps approved by the FDA for the administration of baclofen into the intrathecal space. Intrathecal administration achieves high concentrations in the spinal cord with small dosages, thus reducing the incidence of central nervous system adverse effects. To date, approximately 350 patients with spinal cord injury have been treated with intrathecal baclofen. Reductions in spasticity have been demonstrated in both open-label and placebo-controlled trials. Patients also often make substantial gains in activities of daily living. Few adverse effects and complications have been reported. However, tolerance to the clinical effects of intrathecal baclofen has been reported. Further studies are needed to determine specific patient populations that may benefit most from intrathecal baclofen administration. Individual dosage ranges and follow-up care also need to be defined more completely. In addition, the question of whether tolerance detracts from long-term clinical benefits with intrathecal baclofen needs to be addressed.

Update on multiple sclerosis therapy

Multiple sclerosis is a demyelinating disorder of the central nervous system characterized by exacerbations and remissions of symptoms. This article deals with symptomatic therapy involving treatment of spasticity, fatigue, neurobehavioral disorders, paroxysmal disorders, pain, bladder dysfunction, and cerebellar dysfunction. This article also reviews immunosuppressive therapies including treatment of acute exacerbations or overall progression of the disorder with resultant accumulation of disability.

Electrophysiological findings in a case of severe intrathecal baclofen overdose

Multimodality evoked potentials were examined in a case of serious accidental intrathecal baclofen overdose in a patient who suffered from severe spasticity due to a traumatic brain lesion. Electrophysiological findings during, before and after the intoxication were compared. Transcranial electrical stimulation up to 750 V did not evoke any responses in thenar muscles on the first day of intoxication. An improvement to normal values was observed within 3 days, paralleled by an amelioration of the patient's clinical condition. Cervical electrical stimulation was largely unaffected by baclofen. Median nerve somatosensory and brain-stem acoustic evoked potentials revealed few or no differences during intoxication compared to pre- and post-intoxication responses.

Mechanisms of baclofen action on spasticity

This investigation estimated the mechanisms of baclofen action on spasticity using a battery of electromyographic methods. Thirty patients with old post-stroke spastic hemiparesis took part in the investigation. They were treated with baclofen-mean daily dose 54.3 alpha 11.6 mg for a mean of 26.3 alpha 4.9 days. A questionnaire for assessment of subjective improvement after treatment used a 5-point scale. For standardization of the neurological examination 5-point scales were used to assess muscle tone, muscle force and tendon reflexes. A battery of electromyographic methods was used to analyse different mechanisms of spasticity: for alpha motoneurone activity--the F wave parameters; for gamma motoneurone activity--the T/H reflex amplitude ratio; for presynaptic inhibition--the ratio of H reflex amplitudes before and after vibration on the achilles tendon (Hvibr./Hmax); for common interneurone activity--the flexor reflex parameters. Our results revealed that baclofen reduces spastically increased muscle tone and Babinski sign. It has no influence on muscle force, tendon reflexes and ankle clonus. Baclofen acts by normalizing the altered interneurone activity and decreasing of alpha motoneurone activity. When spasticity has altered interneurone activity and increased motoneurone activity, it is better to treat with baclofen.

Baclofen in the treatment of idiopathic dystonia in children

Baclofen benefits some patients with adult onset dystonia, but few reports document the response to baclofen of children with idiopathic dystonia. Sixteen of 80 patients less than age 21 years with idiopathic dystonia seen by the Movement Disorder Group at Columbia-Presbyterian Medical Center in New York were treated with baclofen. Five had substantial improvement in symptoms, two had moderate improvement, and nine failed to benefit. Three of the improved patients had transient improvement on high dose anticholinergics, but had sustained, dramatic improvement when baclofen was added. At last follow-up, five patients maintained improvement for a mean 3.8 years (19 months-8 years) on a mean 79 mg of baclofen (40-120 mg). Response to baclofen did not correlate with age at onset of dystonia or age at onset of therapy, but did correlate with duration of symptoms before therapy (3 years for those who improved vs 7.8 years for those who did not: p less than .002 by t-test). Baclofen can be an effective treatment for childhood dystonia.

Reflex activity and muscle tone during elbow movements in patients with spastic paresis

Reflex behavior and tension development in upper limb muscles were analyzed and comparisons made between the unaffected and spastic sides of patients with spastic hemiparesis. During sinusoidal (0.3-Hz) isometric or isotonic elbow tracking, with a control either of joint position or of torque, randomly timed displacements were induced (at one of three velocities) stretching either the activated flexor or the extensor muscles. On the spastic side, exaggerated short-latency reflexes were apparent, but in contrast, the amplitude of long-latency electromyography (EMG) responses was reduced. The latter responses were differentially modulated on the unaffected side, predominantly by the acceleration signal during control of position and more by the velocity signal during control of torque, while the mode of muscle contraction (isometric or isotonic) had little influence on this behavior. This difference in reflex modulation was lost on the spastic side. The functional consequence of this reduced EMG modulation could be difficulty in performing finely controlled arm movements. The ratio of torque to EMG activity during displacements was higher for both background and reflex-induced EMG on the spastic limb than on the unaffected side. This effect was more pronounced for the flexor than for the extensor muscles. Consequently, the development of spastic muscle hypertonia cannot be attributed to an increase in EMG activity. It is suggested that secondary to a supraspinal lesion, mechanical muscle properties change in such a way that the activated spastic muscle develops more tension when it is stretched.

H-reflex modulation during walking in spastic paretic subjects

Hoffman (H) reflexes were elicited from the soleus muscle during treadmill walking in 21 spastic paretic patients. The soleus and tibialis anterior muscles were reciprocally activated during walking in most patients, much like that observed in healthy individuals. The pattern of H-reflex modulation varied considerably between patients, from being relatively normal in some patients to a complete absence of modulation in others. The most common pattern observed was a lack of H-reflex modulation through the stance phase and slight depression of the reflex in the swing phase, considerably less modulation than that of normal subjects under comparable walking conditions. The high reflex amplitudes during periods of the step cycle such as early stance seems to be related to the stretch-induced large electromyogram bursts in the soleus in some subjects. The abnormally active reflexes appear to contribute to the clonus encountered during walking in these patients. In three patients who were able to walk for extended periods, the effect of stimulus intensity was examined. Two of these patients showed a greater degree of reflex modulation at lower stimulus intensities, suggesting that the lack of modulation observed at higher stimulus intensities is a result of saturation of the reflex loop. In six other patients, however, no reflex modulation could be demonstrated even at very low stimulus intensities.

Efficacy of dorsal longitudinal myelotomy in treating spinal spasticity: a review of 20 cases

The authors report their experience using dorsal longitudinal myelotomy in treating spasticity in 20 patients with complete spinal cord injuries. These patients suffered from severe painful flexor/extensor spasms that prevented them from wheelchair ambulation and/or their decubitus ulcers healing. All were receiving large doses of various oral drugs, including baclofen, which had failed to control their spasticity, and all underwent a modification of a posterior T-myelotomy as first described by Bischof. All 20 patients enjoyed immediate complete relief of their painful spasms, although two (10%) eventually experienced return of their spasms and are thus classified as long-term failures. Seventeen patients succeeded in markedly reducing, or being completely weaned from, their antispasmodic medications. In 11 of 14 patients, nonhealing decubitus ulcers subsequently healed with treatment. Bladder function was unchanged from the preoperative status in all patients. Chronic intrathecal baclofen infusion has recently been reported as an effective treatment of the spasticity of paraplegia. The results of this study, along with previous reports advocating dorsal longitudinal myelotomy, suggest that this approach is an efficacious alternative to chronic baclofen infusion in reducing spasticity for complete paraplegics. Considering the cost of the infusion pump, along with the fact that chronic intrathecal baclofen therapy necessitates long-term medical supervision, it appears that myelotomy is superior for this select group of patients who have no hope of regaining voluntary motor function.

Intraspinal baclofen in the treatment of severe spasticity and spasms

Ten patients with severe spasticity were evaluated according to a standardized protocol in order to be treated by intraspinal baclofen. Entry criteria in the protocol were the following: 1) Stable central nervous system lesion, 2) Severe spasticity and/or flexo-extensor spasms not controllable by oral treatment, 3) Normal CSF circulation and 4) Informed consent. All patients received a test dose of twenty-five micrograms of baclofen injected intrathecally. At intervals of at least one day, doses were increased in 10-25 microgram steps until total abolition of spontaneous spasms was achieved in complete spinal cord lesions. In patients with residual motor function, doses were titrated until the optimal dose was found that reduced spasms and enabled performance of maximum daily life activities according to the patient's neurological level. In nine patients a multidose reservoir was implanted to deliver intrathecal baclofen. Effective dosage was 60 +/- 31 micrograms in the entire group. Ashworth score was reduced from 4.6 +/- 0.7 to 1.2 +/- 0.4 (mean +/- SD) (p less than 0.0001) and spasms from 3.2 +/- 0.8 to 0.2 +/- 0.4 (p less than 0.0001). Follow-up of the nine patients in whom a reservoir was implanted has been 18 +/- 9 months. Initial dosage requirements and tolerance were significantly different in complete (Frankel's A grade) or incomplete lesions (Frankel's B, C and D grades). Complete spinal cord lesions required a greater initial dose (156 +/- 43) than incomplete lesions (44 +/- 24), these differences being statistically significant (Student's t-test, p less than 0.05). Tolerance was observed only in patients with complete motor and complete sensory lesions. In incomplete lesions, dose increase was insignificant.

Trends in the pathophysiology and pharmacotherapy of spasticity

Spasticity develops after supraspinal or spinal lesions of descending motor systems, with obligate involvement of the corticospinal tract. Spasticity is characterized by an increase in muscle tone, which, in contrast to many other types of enhanced muscle tone, shows a marked velocity-dependent increase when the muscle is passively stretched. The pathophysiological mechanisms underlying this spastic muscle tone remain obscure. Three major causes are currently considered possible: (1) changes in the excitability of spinal interneurones; (2) receptor hypersensitivity; (3) formation of new synapses by sprouting. The latter mechanism could account for the long time course over which spastic muscle tone develops in hemiplegic or paraplegic patients, but there is no experimental evidence for this hypothesis. The electromyographic (EMG) gait analysis of patients with spasticity has thrown doubt on the common belief that the velocity-dependent increase in spastic muscle tone is evoked by stretch reflex activity and has led to the idea that spastic muscle tone resides in the muscle fibres themselves. While such a mechanism may contribute to the slowness of active movements in spastic patients, recent experiments on patients with spastic arm paresis have confirmed the classical view that the spastic muscle tone is related to the EMG activity evoked in the passively stretched muscle. This pathological EMG activity is seen during the entire range of the dynamic phase of the stretch, during which a normal muscle exhibits only an early, phasic burst at the highest stretch velocities employed. For the pharmacological treatment of spasticity, substances with different central or peripheral actions are available. Their assumed receptor actions are described, together with their main indications and side-effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Recovery of amino acid neurotransmitters from the spinal cord during posterior epidural stimulation: a preliminary study

Continuous posterior epidural spinal cord stimulation (SCS) has been an effective method for treating spasticity. The mechanisms of SCS include activation of inhibitory segmental neuronal systems and suprasegmental structures that produce inhibitory descending control. The neurochemical correlates of the mechanism of action have not been clearly defined. Microdialysis of the spinal cord extracellular space in an in vivo preparation during continuous epidural SCS was performed. The recovery of amino acid neurotransmitters, aspartate, glutamate, gamma-aminobutyric acid (GABA), glycine, and taurine from stimulated animals was compared to non-stimulated animals. Evoked potentials from the cortex and spinal cord of the stimulated animals were recorded to insure that there had been adequate epidural stimulation and normal segmental cord function. A significant increase in the concentration of glycine was seen after 90 minutes of continuous stimulation. The levels of the other amino acids were not significantly elevated. These results suggest that amelioration of spasticity with epidural SCS may involve enhanced glycine release, the major inhibitory neurotransmitter of the spinal cord.

Release of segmental amino acid neurotransmitters in response to peripheral afferent and motor cortex stimulation: a pilot study

The role of amino acid (AA) neurotransmitters in the spinal cord has been primarily studied using in vitro preparations and histochemical methods. The technology necessary to estimate AA levels in an intact animal has only recently become available. Such an investigation could yield valuable information regarding the segmental neurochemical environment. We measured the release of AAs into the rabbit lumbar spinal cord in response to sciatic nerve and transcranial stimulation with stereotaxically placed microdialysis catheters. Samples were obtained periodically during 90 minutes of continuous stimulation of either the left or right sciatic nerve, or motor cortex. Quantification of gamma-amino butyric acid (GABA), aspartate, glutamate, glycine, and taurine was performed using high pressure liquid chromatography (HPLC). Adequate neural excitation was verified by recording somatosensory evoked potentials (SSEPs) or corticomotor evoked potentials (CMEPs). Sensory activation at intensities sufficient to activate small and large diameter peripheral fibers of the ipsilateral (to the microdialysis probe) sciatic nerve produced a significant change only in segmental glycine levels. Contralateral sciatic nerve stimulation failed to evoke a significant elevation of AAs. In addition, a significant increase in the release of glycine and taurine was measured after 90 minutes of transcranial stimulation. SSEP and CMEP components repeatedly showed adequate activation of primary afferent, descending motor fiber pathways, and segmental interneuron pools during dialysis sampling. Our data are consistent with the hypothesis that suprasegmental influence over peripheral afferent and motor activity may be, in part, through these amino acid neurotransmitters in the rabbit lumbar spinal cord.

Segmental release of amino acid neurotransmitters from transcranial stimulation

The present study used microdialysis techniques in an intact rabbit model to measure the release of amino acids within the lumbar spinal cord in response to transcranial electrical stimulation. Dialysis samples from the extracellular space were obtained over a stimulation period of 90 minutes and were examined using high pressure liquid chromatography. Neuronal excitation was verified by recording corticomotor evoked potentials (CMEPs) from the spinal cord. A significant increase in the release of glycine and taurine compared to sham animals was measured after 90 minutes of transcranial stimulation. Glutamate and aspartate release was not significantly elevated. GABA concentrations were consistently low. CMEP components repeatedly showed adequate activation of descending fiber pathways and segmental interneuron pools during dialysis sampling. Since glycine, and to a lesser extent taurine, have been shown to inhibit motor neuron activity and are closely associated with segmental interneuron pools, suprasegmental modulation of motor activity may be, in part, through these inhibitory amino acid neurotransmitters in the rabbit lumbar spinal cord.

Substantia nigra: a site of action of muscle relaxant drugs

Sites of action of centrally active muscle relaxant drugs are not well defined. Clinical experience with such drugs suggests that the spinal cord may be one of the important regions from which pathologically increased muscle tone may be relieved. Supraspinal centers that may also be involved in the expression of muscle relaxant action have not yet been defined. We report here that microinjections of therapeutically relevant muscle relaxants into the midbrain tegmentum of genetically spastic rats decrease muscle tone. The substantia nigra is the region from which midazolam, baclofen, and tizanidine (drugs used clinically in the treatment of spasticity), or gamma-vinyl-GABA, (-)-2-amino-7-phosphonoheptanoate, and [D-pro2-D-phe7-D-trp9]-substance P (experimental drugs active in animal models of spasticity), reduce muscle tone in genetically spastic rats and Hoffmann reflexes in normal rats. The effects of muscle relaxant drugs are topographically restricted to the substantia nigra pars reticulata and are receptor specific. These observations disclose a previously unknown function of the substantia nigra in mediating muscle relaxation.

Effects of acute barbiturate administration, tolerance and dependence on brain GABA system: comparison to alcohol and benzodiazepines

Central nervous system depressants, e.g., barbiturates, alcohol and benzodiazepines, have a wide spectrum of activity in humans and animals. Evidence accumulated suggests that some of the pharmacological actions exerted by these agents may be mediated through GABA system by mimicking GABAergic transmission. This review attempts to summarize the evidence available as to how the GABA system plays a part in the barbiturate actions and the development of tolerance to and physical dependence on barbiturates. The comparisons of the effects of alcohol, barbiturates and benzodiazepines at different steps of GABA synapse are also presented. Furthermore, the results which have been reported in the literature are inconsistent. This may be due to differences in: (a) animal models used; (b) brain regions used; (c) protocols (dose, duration, form and route of administration, etc.) used in treating animals and/or (d) techniques (pharmacological, biochemical, physiological, etc.) used.

The entopeduncular nucleus regulates muscle tone in genetically spastic rats: role of substance P and gamma-aminobutyric acid

Microinjections of the substance P (SP) antagonist (D-pro2,D-phe7,D-trp9)-SP, or the gamma-aminobutyric acid (GABA) agonist, muscimol, into the entopeduncular nucleus reduced muscle tone in genetically spastic rats in a dose- and time-dependent manner. Similar injections into the ventral thalamus, zona incerta or amygdala had no effect on muscle tone. The muscle relaxant effect of (D-pro2,D-phe7,D-trp9)-SP injected into the entopeduncular nucleus was blocked by co-injections of SP, and that of muscimol by the GABAA antagonist, bicuculline methiodide. These results suggest that SP- and GABA-dependent mechanisms in the entopeduncular nucleus mediate regulation of the muscle tone.

Membrane transport and disease

Four situations in which membrane transport is altered by disease are discussed: (a) non-specific leaks induced by poreforming agents; (b) glucose transport and cellular stress; (c) Ca2+-ATPase and hypertension; (d) Na+ channels and HSV infection.

Intrathecal baclofen and the H-reflex

Baclofen was given intrathecally to six patients with severe lower limb spasticity due to traumatic spinal cord injury. The effects of the drug on spasticity and the ratio between the maximum amplitude of the H reflex and the M response from the soleus (Hmax/Mmax ratio) were assessed. In each patient, spasticity was reduced following intrathecal baclofen and in four patients there was a reduction in the amplitude of the H reflex and Hmax/Mmax ratio. These results suggest that the Hmax/Mmax ratio may be helpful in establishing optimum drug dosage, particularly when the drug is used on a chronic basis.

Intrathecal baclofen for long-term treatment of spasticity: a multi-centre study

Twenty eight patients with severe, intractable spasticity have been treated by chronic intrathecal administration of baclofen. An implantable programmable drug-administration-device (DAD) was used with a permanent intrathecal catheter. Infusion of 50 to 800 micrograms/day of baclofen completely abolished spasticity. Follow-up was up to two years. Therapeutic effect was documented by clinical assessment of tone, spasms and reflexes and by electrophysiological recordings of mono- and polysynaptic reflex activity. Complications and untoward side-effects of the procedure were few. This procedure is recommended for spasticity of spinal origin refractory to physiotherapy and oral medication. It is a preferable alternative to ablative surgical intervention.