Modulation of presynaptic inhibition and disynaptic reciprocal Ia inhibition during voluntary movement in spasticity

The deep tendon and the abdominal reflexes

The deep tendon reflexes (and the abdominal reflexes) are important physical signs which have a special place in neurological diagnosis, particularly in early disease when they alone may be abnormal. They act as "hard" signs in situations where clinical assessment is complicated by patient anxiety, and become more useful as clinical experience develops.

Modulatory effects of alpha1-,alpha2-, and beta -receptor agonists on feline spinal interneurons with monosynaptic input from group I muscle afferents

Previous studies have shown that monoamines may modulate operation of spinal neuronal networks by depressing or facilitating responses of the involved neurons. Recently, activation of interneurons mediating reciprocal inhibition from muscle spindle (Ia) afferents and nonreciprocal inhibition from muscle spindle and tendon organ (Ia/Ib) afferents in the cat was found to be facilitated by noradrenaline (NA). However, which subclass membrane receptors are involved in mediating this facilitation was not established; the aim of the present experiments was to investigate this. Individual Ia- and Ia/Ib-inhibitory interneurons were identified in the cat lumbar spinal cord, and NA agonists were applied close to these neurons by ionophoresis. The agonists included the alpha1-receptor agonist phenylephrine, the alpha2-receptor agonists clonidine and tizanidine, and the beta-receptor agonist isoproterenol. Effects were measured by comparing changes in the number of extracellularly recorded spike potentials evoked by electrical stimulation of muscle nerves and changes in the latency of these potentials before, during, and after application of the tested compounds. Results show that the facilitatory effect of phenylephrine is as strong as that of NA, whereas the facilitatory effect of isoproterenol is weaker. Clonidine depressed activity of both Ia- and Ia/Ib-inhibitory interneurons, whereas tizanidine had no effect. These findings lead to the conclusion that beneficial antispastic effects of clonidine and tizanidine in humans are unlikely to be associated with an enhancement of the actions of Ia- and Ia/Ib-inhibitory interneurons, and the findings also support previous proposals that these compounds exert their antispastic actions via effects on other neuronal populations.

Spinal interneurones; how can studies in animals contribute to the understanding of spinal interneuronal systems in man?

The first part of this review deals with arguments that the essential properties and organization of spinal interneuronal systems in the cat and in man are similar. The second part is concerned with the possibility that some interneuronal systems may be responsible for motor disturbances caused by spinal cord injuries and that these interneurones may be defined. This possibility is discussed with respect to the hyperexcitability of alpha-motoneurones and the exaggeration of stretch reflexes in spastic patients. To this end, what is known about cat spinal interneurones and about the neuronal basis and pharmacological treatment of spasticity, is put together. Interneurones in di- and trisynaptic reflex pathways from group II muscle afferents are singled out, since they are depressed by the alpha(2) noradrenaline receptor agonists clonidine and tizanidine, which is a critical feature of interneurones expected to contribute to exaggerated stretch reflexes which are reduced by alpha(2) noradrenaline receptor agonists. Recent observations that reflex excitation of extensor motoneurones from group II afferents is enhanced in spastic patients and that the pathologically strong reflex actions of group II afferents are reduced by clonidine and tizanidine support this proposal. On the other hand, a lack of effect of clonidine and tizanidine upon other types of excitatory or inhibitory interneurones argues against any major contribution of such interneurones to the abnormally strong responses of alpha-motoneurones to muscle stretch.

Abnormal conditioning effect of transcranial magnetic stimulation on soleus H-reflex during voluntary movement in Parkinson's disease

OBJECTIVES

The objective of this study is to clarify the participation of cortical motor control abnormality in the motor dysfunction of Parkinson's disease (PD), especially at the onset of movement.

METHODS

Conditioning effects of transcranial magnetic simulation (TMS) on the soleus (SOL) H-reflex evoked with tibial nerve stimulation were examined in 19 patients with PD and 10 normal volunteers. Experiments were done at rest, during tonic plantarflexion (PF), and at PF onset. Stimulus intensity of TMS was maintained at less than 5% of the motor threshold in each situation. Seven patients underwent pallidotomy and were examined twice, once before and once after the operation.

RESULTS

Short latency subthreshold TMS stimulation did not facilitate the SOL H-reflex neither during tonic PF nor at PF onset in the patients with PD, though it was evident in normal subjects. In some patients, paradoxical inhibition appeared at PF onset. The facilitation increase at PF onset, as compared to that at rest, was negatively correlated with the motor part of the unified Parkinson's disease rating scale and with the rigidity grade. Pallidotomy improved both modulation and the clinical scores.

CONCLUSIONS

Cortical activity for the proper execution of reciprocal control between the agonist and antagonist seems to be disturbed in PD.

H reflexes and F waves. Fundamentals, normal and abnormal patterns

H reflexes and F waves have become integral parts of the electrodiagnostic examination in general, and nerve conduction studies in particular. They supplement the sensory and motor conduction studies by assessing the entire nerve segments including proximal portions of the motor and sensory axons. H reflexes and F waves have their own advantages and limitations, similarities and differences. These "late" responses are useful in patients with radiculopathies, plexopathies, and peripheral polyneuropathies, including the Guillain-Barre syndrome. They are also helpful in spinal cord disorders.

Anti-spasticity agents for multiple sclerosis

BACKGROUND

Spasticity is a common problem in MS patients causing pain, spasms, loss of function and difficulties in nursing care. A variety of oral and parenteral medications are available.

OBJECTIVES

To assess the absolute and comparative efficacy and tolerability of anti-spasticity agents in multiple sclerosis (MS) patients.

SEARCH STRATEGY

Randomised controlled trials (RCTs) of anti-spasticity agents were identified using MEDLINE, EMBASE, bibliographies of relevant articles, personal communication, manual searches of relevant journals and information from drug companies.

SELECTION CRITERIA

Double-blind, randomised controlled trials (either placebo-controlled or comparative studies) of at least seven days duration.

DATA COLLECTION AND ANALYSIS

Two independent reviewers extracted data and the findings of the trials were summarised. Missing data were collected by correspondence with principal investigators. A meta-analysis was not performed due to the inadequacy of outcome measures and methodological problems with the studies reviewed.

MAIN RESULTS

Twenty-three placebo-controlled studies (using baclofen, dantrolene, tizanidine, botulinum toxin, vigabatrin, prazepam and threonine) and thirteen comparative studies met the selection criteria. Only thirteen of these studies used the Ashworth scale, of which only three of the six placebo-controlled trials and none of the seven comparative studies showed a statistically significant difference between test drugs. Spasms, other symptoms and overall impressions were only assessed using unvalidated scores and results of functional assessments were inconclusive.

REVIEWER'S CONCLUSIONS

The absolute and comparative efficacy and tolerability of anti-spasticity agents in multiple sclerosis is poorly documented and no recommendations can be made to guide prescribing. The rationale for treating features of the upper motor neurone syndrome must be better understood and sensitive, validated spasticity measures need to be developed.