This paper presents a review of the literature on the therapeutic action and the side effects of the two main dopaminergic agents: L-DOPA/decarboxylase inhibitor (L-DOPA/DI) and bromocriptine (Parlodel ®) used either as monotherapy or in combination in patients with Parkinson's disease. The combination of L-DOPA/DI and bromocriptine gives the best therapeutic efficacy (49% improvement) in the total score (bradykinesia, rigidity and tremor). However, treatment by monotherapy or combination gives the same pattern of activity: greatest improvement in tremor, followed by rigidity and bradykinesia. Improvement observed in the short term is not sustained over longer periods of time for monotherapy with either drug. The short-term side effects are similar for each treatment, whereas long-term complications (dyskinesia, end-of-dose deterioration and on-off phenomenon) appear only when levodopa is used, alone (high incidence) or in combination with bromocriptine (low incidence). The overall optimum treatment is obtained with a combination of L-DOPA/DI and bromocriptine.

We have evaluated 5 DA agonists-bromocriptine, lergotrile, lisuride, pergolide, and mesulergine in studies encompassing 278 patients with advanced PD. In most of our patients the DA agonist was added to levodopa. Most of our patients were no longer satisfactorily responding to levodopa. Previous attempts at managing these patients by changing the dose of levodopa (increasing or decreasing it), the treatment schedule, or the ratio of levodopa to carbidopa or by temporarily discontinuing levodopa [drug holiday] were unsuccessful. The majority of our patients had diurnal fluctuations in performance, either “wearing off” or “on-off” phenomena. The addition of a DA agonist resulted in a decrease in parkinsonian disability in most patients and a decrease in the severity of the diurnal fluctuations in performance. Improvement in many patients was maintained for at least 2 years. Adverse effects included mental changes, dyskinesias, orthostatic hypotension, and nausea. All of the adverse effects were reversible when the agonist was decreased or discontinued. As a group the agonists behaved similarly but individual patients often responded better to one agonist than another. The main role of agonists is in combination with levodopa in the treatment of patients with early PD who have not yet developed dyskinesias or diurnal fluctuations in performance.

Since the initiation of bromocriptine therapy for Parkinson's disease several newer dopamine agonists have been developed. Pergolide has reached the stage of Phase 3 clinical trials and will probably be available for general use sometime in the foreseeable future. Lisuride shows most promise in its parenteral form for infusion therapy of patients with severe fluctuations. Mesulergine, another ergot-derivative and ciladopa, a new non-ergot agonist, have been withdrawn from further clinical use due to tumorogenesis in rats. It is questionable how applicable these findings are to the use of the drugs in elderly humans with parkinsonism. Recently a small number of drugs have been found to have postsynaptic dopamine agonist properties only in the setting of denervated supersensitive dopamine receptors. These agents may be particularly effective in the early treatment of patients with Parkinson's disease. This paper will review a number of the dopamine agonists which have been developed since the introduction of bromocriptine therapy. Several of these have shown beneficial effects in early clinical trials while others show promise in preclinical studies of animal models of parkinsonism.

It is postulated that endogenous oxidative mechanisms are a major factor in the continuing death of dopaminergic neurons and the progression of Parkinson's disease. Scientific evidence in support of, and negating, the free radical auto-toxicity and dopamine toxicity concepts is reviewed. There is conflicting evidence whether free radicals are involved in the toxicity of l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and attempts to prevent the toxicity of MPTP with antioxidant therapy have had variable results. The oxidation of dopamine by monoamine oxidase produces toxic metabolites however animal studies with high dose longterm levodopa and MPTP have failed to show clear evidence for autoxidation. Firm supportive evidence is obtained from the monoamine oxidase B inhibitor experience which demonstrated a block of the toxicity of MPTP in animals and probable prolongation of the course of human Parkinson's disease.

The scientific data available is inconclusive but there is significant hope of retarding progressive catecholaminergic neuron degenerative changes by augmenting the free radical scavenging system with antioxidants (such as Vitamin E) and slowing catecholamine oxidation by monoamine oxidase B inhibition. Careful clinical trials with these agents must be performed.

Complex motor fluctuations and dyskinesias (“on-off” phenomenon) in Parkinson's disease can be corrected by parenteral administration of levodopa, levodopa-methyl-ester, lisuride and apomorphine. Levodopa and levodopa-methyl-ester may only be administered intravenously because of their low solubility. Lisuride and apomorphine are readily absorbed after subcutaneous administration. Repeated or continuous intravenous infusions of levodopa have been given for a few days, using a wearable “jacket-like” pump, with good results. So far, lisuride is the only dopamine agonist used for chronic treatment by continuous infusion. The “on-off” effect is adequately controlled in most patients by subcutaneous lisuride administration (plus oral levodopa). However, adverse effects, particularly psychiatric complications, constitute a major limiting factor for routine applications of this form of treatment. Subcutaneous apomorphine infusion is unlikely to become a standard therapeutic procedure in Parkinson's disease, but it is a very valuable research method to gain further insight into the pathophysiology of motor fluctuations in Parkinson's disease.

The vestibulospinal system helps to maintain upright posture and head stability. The semicircular canals and their short latency connections to the neck motoneurons, largely via the medial vestibulospinal tract, respond to angular accelerations so as to stabilize the head in space. The paired otolith organs, the utricles placed approximately horizontally, and the saccules vertically, respond to linear acceleration including gravity. Their influence leads, via the lateral vestibulospinal tract, to excitation of ipsilateral extensor motoneurons of the limbs and trunk, and to inhibition of reciprocal flexor motoneurons. Linear displacement of the otoliths leads to bracing of the limbs and body so as to maintain upright posture, and to extend the limbs so as to help in landing after sudden falls.

Lesions of the upper motor neuron cause: 1. Alterations in segmental reflex activity. For example increased tendon jerks and velocity dependent stretch reflexes ("spasticity"), clonus, the clasp knife response, release of flexion reflexes and extensor plantar reflexes. 2. Impaired ability to activate motoneurons rapidly and selectively. Voluntary movements may also be restrained by co-contraction of antagonists muscles, by segmental reflexes (enhanced during voluntary effort) or by contractures. A combination of these factors may impair overall functional ability. Segmental reflexes, voluntary power and overall functional abilities can be assessed using clinical scoring systems. Recordings of muscle length, tension andEMG offer more objective measures of reflex and voluntary activity and of overall functions such as locomotion, and can separate weakness from co-contraction, spasticity from contracture. Methods are now available for exploring individual (transmitter specific) segmental reflex pathways and descending pathways in man. Lesions of the upper motor neuron are complicated by secondary changes in segmental neurons. Segmental reflex activity and muscle mechanics depend on the immediate past history of events. These factors must be taken into account.

No single clinical electrophysiological test can evaluate disorders of muscle tone. These disorders, symptomatic of a variety of diseases have a multifactorial physiological basis. The several tests used are complimentary each aiming to study different aspects of spinal and supraspinal reflexes which become deranged. The H reflex and F wave (H max/M max and F max/M max ratios) measure motoneuron pool excitability in general. The tendon reflex includes spindle mechanisms bypassed by the H reflex and, with limitations, comparison of H max/M max and T max/M max yields information about the -y system. Tonic vibration of a tendon inhibits the H reflex from the same muscle. The TVR measures autogenous presynaptic inhibition exerted by the la afferents of the muscle. Recurrent inhibition via Renshaw cells is evaluated by studying the effect of collision on the H reflex. Reciprocal inhibition of the la afferents can be assessed by measuring H reflex change induced by stimulating la afferents from antagonists. Changes in the H reflex recovery cycle measure polysynaptic influences on spinal motoneuron excitability. Cutaneomuscular (flexor) reflexes measure poly- and oligosynaptic excitatory drive to spinal motoneurons and the blink reflex evaluates the excitatory drive to brainstem motoneurons. Long loop (segmental) responses can be evaluated by limb pertubation using a torque motor or electrical stimulation applied during voluntary muscle contraction. Finally needle electromyography is a more relevant test in several disorders of muscle tone such as the stiff-man syndrome and Isaacs' syndrome.

We have investigated the influence on the excitability of lumbar motoneurons of 5-hydroxytryptamine (5-HT), substance P and thyrotropin releasing hormone (TRH), three substances which coexist in the same bulbospinal descending pathway and end in large part around motoneurons. We have also studied the effect of clonidine, an alpha 2 noradrenergic agonist. This was done in spinalized rats (T5) treated three weeks before with 5-7-dihydroxytryptamine. Under those circumstances 5-HTP (LP.), 5-HT (intrathecally) TRH (LP. or I.T.) and substance P (I.T.) all elicited a strong excitation of motoneurons as measured by integrated EMG of the hindlimb muscles. Substance P reduced by almost half the subsequent response to 5-HTP, 1 hour and 24 hours later. TRH given acutely did not modify the response to 5-HTP but given chronically for twenty one days by means of Alzet minipump, markedly increased the response to 5-HTP. Clonidine by itself decreased the excitability of motoneurons and antagonized the excitatory effect of 5-HTP and TRH. In a pilot trial, cyproheptadine, a 5-HT antagonist was shown to decrease the manifestations of spasticity in patients with a partial spinal lesion. Clonidine also appears to be of potential use in the treatment of spasticity.

The availability of new antispasticity agents has greatly extended the therapeutic arm of the neurologist and has obviated the need for destructive neurosurgical procedures in many instances. Baclofen remains the single most useful agent, but in certain circumstances, benzodiazepines and dantrolene sodium are useful alternative or adjunctive treatments. Tizanidine has been recently introduced, and early experience with this agent appears to be favourable. A variety of new drugs are awaiting further evaluation. The effective use of these agents demands an understanding of their principal mechanisms of action, knowledge of their predictable side effects, and a familiarity with the underlying neurological disorders. The monitoring of clinical efficacy is difficult and is often dependent upon subjective evaluation. The application of electrophysiological studies might facilitate the monitoring of treatment and the prediction of optimum treatment strategies forindividual patients. The use of these pharmacological agents, from the perspective of a clinician, will be discussed.

Spasticity is a frequent and often disabling symptom in MS patients. Current drugs used as antispastic agents include Dantrolene Sodium, Baclofen and Diazepam. Tizanidine (5-chloro-4-(2imidazolin-2 yl amino) -2, 1, 3-benzothialdiazole) is a new antispasticity agent that has purported central action. A double blind placebo controlled trial was performed to study the efficacy of this drug in MS patients. Sixty-six patients entered an eight week therapeutic trial and fifty-nine completed the trial. Patients were assessed at 0, 2, 3 and 8 weeks of therapy for clinical effects. Electrophysiologic tests were performed at 0 and 8 weeks.

A statistically significant benefit was noted in spastic muscle groups in the legs with concomitant significant reduction in hyperactive stretch reflexes and ankle clonus. Side effects most frequently cited included dry mouth and drowsiness. Two patients developed elevated liver function test that decreased with cessation of therapy. Other clinical details, side effects and electrophysiologic data will be presented.

Tizanidine appears to reduce clinical spasticity and hyperreflexia in MS patients although no change in functional status was detected. Tizanidine may well serve as an alternate antispastic agent, alone or in combination with other agents.

MS could well be a two stage disease. The first stage involves the sequential development of multiple small lesions, mostly inflammatory, that accumulate at a given rate. The second stage could be that of consolidation and confluence of lesions that involves not only demyelination but gliosis. MRI now gives us an opportunity to watch the evolution of these processes and also to monitor treatment effects. It is only after the evolution of this process is understood that we can design rational therapies directed toward the prevention of spasticity in MS.

Dystonia is mysterious and its pathophysiology is uncertain. The fundamental motor abnormality is an abnormality of muscle command signals, such that the wrong agonists may be activated for too long, there is abnormal co-contraction of agonist and antagonists, and there is excessive and misdirected action of synergists and postural fixators. The result is action dystonia. In addition, muscle spasms may occur spontaneously. The peripheral motor apparatus, the corticomotoneurone pathway, and (as far as is known) the proprioceptive feedback machinery, are all intact in primary dystonia. However, a defect of interneuronal machinery has been identified in both the brainstem and spinal cord. In blepharospasm there is hyperexcitability of the lower brainstem interneurones responsible for the R2 component of the blink reflex. In the dystonic arm there is loss of the later phases of la reciprocal inhibition from extensors to flexors. Both deficits may be due to loss of normal basal ganglia inputs onto interneurones. The known sites of focal lesions that may cause symptomatic dystonia all impair basal ganglia output. However, whether such abnormal interneuronal function is sufficient to explain dystonia is not known. Among many unanswered questions are 1) are the cortical instructions for movement specified correctly, and 2) what is responsible for the spontaneous dystonic spasms?

A number of pharmacologic agents have been found to be effective for the dystonias. Anticholinergic drugs have been shown to be the most effective in terms of percentage of subjects who receive moderate to marked benefit. About 50% of children and 40% of adults obtain such improvement. Peripheral adverse effects are usually overcome by pyridostigmine. It may be necessary to utilize pilocarpine eyedrops for blurred vision. Central adverse effects, such as forgetfulness, can be reduced only by a reduction in dosage of the anticholinergic. In comparing trihexyphenidyl and ethopropazine, we found that children tend to have better tolerance of the former and adults tend to have better tolerance of the latter. The antidopaminergics are the group of drugs that were found to be the next most effective agents in terms of percentage of patients who respond. However, these drugs, particularly the dopamine receptor blockers, have the capacity to induce tardive dyskinesia and tardive dystonia. Tardive syndromes are difficult to treat and can persist indefinitely. Other agents that have shown usefulness in controlling dystonia are levodopa, baclofen, carbamazepine, and the benzodiazepines, either alone or in combination with each other and with the anticholinergics. Stereotactic thalamotomy is particularly useful in contralateral hemidystonia. The risk of adverse effects is less than with bilateral thalamotomy, which may need to be employed when generalized dystonia is severely disabling and not responsive to pharmacotherapy.

Fifty-six patients with spasmodic torticollis were treated with local injections of botulinum toxin. The drop out rate was 21%. The remaining 44 patients were followed for a period of 3 to 21 months. Thirty-two patients (76%) had pain relief out of 42 presenting with pain; 37 (66%) improved in the amount of sustained movements of torticollis. The efficacy was reproducible after repeated injections.

A variety of neurotransmitters have been implicated in the pathophysiology of chorea as exemplified by Huntington's chorea. These include dopamine, serotonin, acetylcholine, GABA and a variety of neuropeptides including substance P and somatostatin. Despite biochemical data that suggests that alterations in other neurotransmitters may be of greater significance, pharmacologic data still supports a major role of dopamine in the actual clinical manifestation of chorea.

We studied 112 patients with Tourette's syndrome (TS); the male-to-female ratio was 3.8, the mean age of onset was 7.3 years, and the average duration of symptoms prior to the initial evaluation was 15.2 years. Seventy-nine percent of the patients had at least one family member with motor or vocal tics, and an additional 10 percent had a family member with marked obsessive-compulsive behavior. Simple motor tics occurred as the presenting symptom in about one-third of patients; one-third had multiple motor tics at the onset, and another third started with vocal tics. During the course of the illness all patients developed multifocal motor tics and 86 percent had vocal tics. Verbal and mental coprolalia was present in 44 percent of the patients. Copropraxia was seen in 19 percent of patients, and both coprolalia and copropraxia were more frequent among the males than expected. Attentional deficit disorder was diagnosed in 36 percent of the patients and 32 percent had obsessive-compulsive personality. Sleep disturbances were reported by 62 percent of the patients and polysomnography in 34 patients showed motor and vocal tics during all stages of sleep, sleep apnea, abnormal arousal pattern, and other sleep disturbances. Patients with mild symptoms improved with clonidine or clonazepam, but those with more advanced disorder required fluphenazine, pimozide, haloperidol or tetrabenazine.

Progressive supranuclear palsy (PSP) was first recognized as a distinct morbid entity by Richardson, Steele and Olszewski a quarter century ago. Subsequent experience has confirmed and extended their original observations. PSP has become familiar as a chronic progressive disorder with extrapyramidal rigidity, bradykinesia, gait impairment, bulbar palsy, dementia and a characteristic supranuclear ophthalmoplegia. It is an important cause of parkinsonism. Its etiology remains obscure. Familial concentrations have not been observed.

Some cases exhibit no oculomotor dysfunction. Dementia is usually mild. Recent neuropsychological studies have defined features consistent with frontal lobe cortical dysfunction. Seizures and paroxysmal EEG activity may occur.

CT and MRI scans show midbrain atrophy early and later atrophy of the pontine and midbrain tegmentum and the frontal and temporal lobes. PET scans have shown frontal hypometabolism and loss of striatal D-2 dopamine receptors. Postmortem studies have documented involvment of both dopaminergic and cholinergic systems. Treatment remains palliative and unsatisfactory.