Eyelid movements before and after botulinum therapy in patients with lid spasm

Orbicularis Oculi Muscle Immunohistochemical, Metabolic, and Morphometric Differences in Affected and Nonaffected Sides in Hemifacial Spasm vs Healthy Subjects

BACKGROUND

Subtle morphological alterations have been reported even in the nonaffected side of the orbicularis oculi muscle in patients with hemifacial spasm. However, no previous study assessed immunohistochemical, metabolic, and morphometric alterations in orbicularis oculi muscle fibers in affected and nonaffected sides in patients with this condition, compared with samples obtained from healthy subjects. The purpose of this study is to objectively assess and compare orbicularis oculi muscle (OOM) samples of hemifacial spasm affected and nonaffected sides and healthy subjects.

METHODS

Orbicularis oculi samples from 8 patients with hemifacial spasm who had not been previously treated and 6 healthy subjects were prepared using hematoxylin and eosin, nicotinamide adenine dinucleotide tetrazolium reductase, cytochrome oxidase, succinate dehydrogenase, Gomori staining, and monoclonal antibodies against myosin slow and myosin fast. A digital image analysis software was used for objective analysis.

RESULTS

OOM fiber area was significantly greater in both affected ( P = 0.0379) and nonaffected sides ( P = 0.0012) of HFS samples when compared with control subjects' fibers. A significantly greater number of oxidative fibers were observed in both affected and nonaffected sides of patients with HFS when compared with control subjects ( P < 0.001 for both). A significantly greater percentage of slow fibers was observed in the affected side of HFS patients ( P = 0.0012) compared with control subjects.

CONCLUSIONS

This study's findings suggest that repeated contractions might lead to OOM fiber hypertrophy, increased mitochondrial metabolism, and possible conversion of fast-twitch orbicularis oculi muscle fibers into slow-twitch fibers in patients with HFS. Alterations were observed in affected and nonaffected sides, confirming initial findings that the nonaffected side is not normal in this unique condition.

[Hemifacial spasm]

Hemifacial spasm (HFS), or facial hemispasm, is a paroxysmal hyperkinetic disorder involving muscles innervated by the facial nerve, mainly on the one hand. The development of HFS is based on neurovascular conflict. However, it is impossible to explain the clinical manifestations of HFS only by nerve compression. Both peripheral and central mechanisms are involved in the generation of HFS, with the formation of ephaptic transmission, antidromic excitation, primary or secondary hyper-excitability of the nuclear and supranuclear level of innervation. Two treatment methods are pathogenetically justified: microvascular decompression (MVD) and botulinum toxin (BTX) injections. The effectiveness of MVD is 95.37% with full or partial recovery. The recurrence rate does not exceed 2.4%. Facial nerve paralysis (2.7-22.5%) and hearing loss (1.9-20%) are the most common complications of treatment with the use of the MVD for HFS with partial or complete cure in most cases. Botulinum toxin injection chemo-denervation is a first-line treatment of primary and secondary HFS. HFS is an officially registered indication for the drug dysport (abobotulotoxin) (ABO) in the Russian Federation. Total doses of ABO ranged from 25 to 150 units for one side depending on the severity of the clinical manifestations. Studies demonstrate the statistically significant benefits of HFC treatment with ABO. ABO is generally well-tolerated. Adverse events (up to 3.6%) are transient and include ptosis, lacrimation, blurred vision, double vision, dry eyes and weak facial muscles.

Animal models for investigating benign essential blepharospasm

The focal dystonia benign essential blepharospasm (BEB) affects as many as 40,000 individuals in the United States. This dystonia is characterized by trigeminal hyperexcitability, photophobia, and most disabling of the symptoms, involuntary spasms of lid closure that can produce functional blindness. Like many focal dystonias, BEB appears to develop from the interaction between a predisposing condition and an environmental trigger. The primary treatment for blepharospasm is to weaken the eyelid-closing orbicularis oculi muscle to reduce lid spasms. There are several animal models of blepharospasm that recreate the spasms of lid closure in order to investigate pharmacological treatments to prevent spasms of lid closure. One animal model attempts to mimic the predisposing condition and environmental trigger that give rise to BEB. This model indicates that abnormal interactions among trigeminal blink circuits, basal ganglia, and the cerebellum are the neural basis for BEB.

Dynamic imaging of paralytic eyelid disorders

PURPOSE

Eyelid dysmotility may result from trauma, tumors, inflammation, infection, and a variety of other conditions. In these cases, a mechanical effect is disrupting a normal neuromuscular apparatus. Dysmotility can also be caused by paralytic eyelid disorders; included in this broad category are neurologic and myogenic disorders of eyelid opening and/or closure. Secondary effects include spastic eyelid closure and synkinesis syndromes. These conditions, by definition, are disorders of movement, and can only be studied adequately using dynamic imaging techniques.

METHODS

A comprehensive literature search was performed on PubMed. Ninety abstracts were reviewed.

RESULTS

Dynamic eyelid imaging has evolved dramatically over the past two decades, at least partially due to the rise of inexpensive digital technology. Magnetic search coil imaging, high- and low-speed videography, electromyography, and high-resolution microscopy coil magnetic resonance imaging each has its advantages and disadvantages, an understanding of which will guide appropriate selection of technology in any given clinical situation.

CONCLUSIONS

Dynamic eyelid imaging is useful to study dysmotility. The optimal technique depends upon the clinical setting and the physiologic or pathologic topic of interest. To our knowledge, a report of this type has not been previously summarized.

Spontaneous eyeblink activity

Spontaneous blinking is essential for maintaining a healthy ocular surface and clarity of vision. The spontaneous blink rate (SBR) is believed to reflect a complex interaction between peripheral influences mediated by the eye surface and the central dopaminergic activity. The SBR is thus extremely variable and dependent on a variety of psychological and medical conditions. Many different methods have been employed to measure the SBR and the upper eyelid kinematics during a blink movement. Each has its own merits and drawbacks, and the choice of a specific method should be tailored to the specific needs of the investigation. Although the sequence of muscle events that leads to a blink has been fully described, knowledge about the neural control of spontaneous blinking activity is not complete. The tear film is dynamically modified between blinks, and abnormalities of the blink rate have an obvious influence on the ocular surface.

Conditioned eyelid movement is not a blink

Based on kinematic properties and distinct substrates, there are different classes of eyelid movement described as eyeblinks. We investigate whether the eyelid movements made in response to a conditioned stimulus (CS) are a category of eyelid movements distinct from blinks. Human subjects received 60 trials of classical eyelid conditioning with a tone as the CS and electrical stimulation of the supraorbital branch of the trigeminal nerve as the unconditioned stimulus (UCS). Before and after training, reflex blinks were elicited with the UCS. The kinematics of conditioned responses (CRs) differed significantly from those of reflex blinks. The slope of the amplitude-maximum velocity function was steeper for reflex blinks than for CRs, and reflex blink duration was significantly shorter than CR duration. Unlike reflex blinks, for which maximum velocity was independent of blink duration, the maximum velocity of CRs depended on CR duration. These quantitative and qualitative differences indicated that CRs were a unique class of eyelid movements distinct from blinks and eyelid movements with vertical saccadic gaze shifts.

Asymmetry of blinking

PURPOSE

Too investigate asymmetry in eyelid movements with blinking, the stability of the asymmetry, and its modifiability in normal humans.

METHODS

Differences in the start time and amplitude between the two eyelids were assessed for voluntary blinks and reflex blinks evoked by supraorbital trigeminal nerve stimulation. These variables were also measured before and up to 18 months after 2 hours of unilateral upper lid restraint.

RESULTS

With voluntary blinks, one eyelid consistently began to close earlier and made a larger eyelid movement than the other eyelid. Stimulation of the supraorbital branch of the trigeminal nerve evoked relatively larger amplitude blinks in one eyelid that correlated with the asymmetries of voluntary blinks. There was a continuum of eyelid asymmetry across all subjects that was stable and independent of other biological asymmetries, such as handedness. Briefly reducing eyelid mobility created a long-lasting change in eyelid asymmetry with blinking.

CONCLUSIONS

Eyelid asymmetry results from differences in the excitability of motoneurons in the left and right facial motor nuclei and does not appear to involve asymmetries in cortical inputs to the brain stem. Because adaptive processes modify the motoneuron excitability that creates eyelid asymmetry, these processes may underlie changes in blinking associated with facial palsy and may play a role in the development of disorders that affect one side of the face, such as hemifacial spasm.

Analysis of blink rate in patients with blepharospasm

The blink rate (BR) during rest, conversation, and reading was assessed in 50 patients with blepharospasm (BS) and in 150 healthy subjects. BR at rest and during conversation was higher in patients with BS. Moreover, 76% of patients had BR higher at rest than during conversation, whereas in 74% of controls, BR was higher during conversation than at rest. The sensitivity and specificity of two parameters (value of BR at rest and pattern rest-BR higher than conversation-BR) in discriminating patients and controls were computed. The best fit was obtained with a rest-BR above 27 blinks per minute. When the two parameters were combined (rest-BR above 27 blinks per minute together with the pattern rest-BR higher than conversation-BR), we obtained a 92.3% sensitivity and a 82.0% specificity in discriminating between BS patients and controls. These findings indicate that specific features of BR can be associated with BS, suggesting that the analysis of BR might be helpful for the diagnosis of BS in early stages.

Botulinum toxin A treatment in patients suffering from blepharospasm and dry eye

BACKGROUND

Many patients with essential blepharospasm also show dry eye signs and symptoms. Botulinum toxin A is an effective treatment for reducing spasms in these patients. In this investigation, the effect of botulinum toxin A injections on tear function and on the morphology of the ocular surface in patients suffering from blepharospasm in combination with a dry eye syndrome was investigated.

METHODS

Botulinum toxin A injections were applied to 16 patients with blepharospasm. All patients complained of dry eye symptoms and had reduced tear break up time values. A subjective questionnaire and ocular examinations including tear break up time, Schirmer test without local anaesthesia, and rose bengal staining were evaluated before, 1 week, 1 month, and 3 months after injection. Impression cytology was performed before, 1 month, and 3 months after botulinum toxin A treatment.

RESULTS

Although all patients were relieved of blepharospasm after botulinum toxin injections, only three noticed an improvement in dry eye symptoms. Eight patients noticed no difference and five complained of worsening. Tear break up time was found to be increased 1 week and 1 month after injections. Schirmer test measurements were reduced up to 3 months. Rose bengal staining slightly increased 1 week after injections. Impression cytology showed no definite change in conjunctival cell morphology 1 month and 3 months after botulinum toxin A injections.

CONCLUSION

In the patients presented here suffering from blepharospasm and dry eye, botulinum toxin A injections were effective in relieving blepharospasm but were not successful in treating dry eye syndrome.

Premotor circuits controlling eyelid movements in conjunction with vertical saccades in the cat: I. The rostral interstitial nucleus of the medial longitudinal fasciculus

Saccadic eye movements in the vertical plane are controlled by the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and the interstitial nucleus of Cajal. Eye movements in the vertical direction are accompanied by concurrent upper eye lid movements. These gaze-related lid movements are produced by the levator palpebrae superioris muscle, whose motoneurons are located in the caudal central subdivision (CCS) of the oculomotor nucleus. The neural circuits that direct such gaze-related lid movements were examined by use of both conventional and dual neuronal tracing methods in the cat. Injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the area of the CCS revealed a distinctive subset of retrogradely labeled neurons located in the caudomedial portion of the riMLF. This subset of riMLF neurons was not labeled when injections were localized within the oculomotor nucleus proper, without involving the CCS. Injections of biotinylated dextran amine (BDA) that included this caudomedial riMLF region anterogradely labeled axons that projected profusely throughout the CCS. Labeled terminals were seen in close association with retrogradely labeled levator palpebrae motoneurons, which were primarily found contralateral to WGA-HRP muscle injections. Ultrastructural examination revealed that most BDA-labeled terminals contained clear spherical vesicles and formed asymmetrical synaptic contacts, primarily on the proximal dendrites of WGA-HRP-labeled motoneurons. A few had pleiomorphic vesicles. In summary, these results strongly suggest that the caudomedial part of the cat riMLF is a premotor center that monosynaptically controls lid movements in conjunction with vertical saccades.

Botulinum toxin improves lid opening delays in blepharospasm-associated apraxia of lid opening

Lid movement and EMG of the orbicularis oculi (OOc) were analyzed in 10 patients with apraxia of lid opening associated with blepharospasm before and after botulinum toxin treatment. The latencies to onset and to complete the eye opening and the time during which eye opening was sustained were studied in relation to OOc activity and compared with control values obtained in 12 healthy subjects. Following treatment there was an improvement of all lid opening measurements, a decrease of the abnormally prolonged OOc activity, and a reduction of the functional disability.

Neuroanatomical identification of mesencephalic premotor neurons coordinating eyelid with upgaze in the monkey and man

Except during blinks, movements of the upper eyelid are tightly coupled to vertical eye movements. The premotor source for the coordination of lid and eye movements is unknown. The present paper provides the anatomical identification of a new premotor cell group in the rostral mesencephalon of the monkey and human, which lies in close proximity to the premotor center for vertical saccades and is thought to participate in lid-eye coordination. After injections of a retrograde transsynaptic tracer (tetanus toxin fragment C or BII(b)) into the levator palpebrae (LP), the superior rectus (SR), or the inferior oblique (IO) muscle of macaque monkeys, a small circumscribed group of premotor neurons was labeled in the central gray of the rostral mesencephalon, but not after superior oblique or inferior rectus muscle injections. This group lies immediately rostral to the interstitial nucleus of Cajal and medial to the rostral interstitial nucleus of the medial longitudinal fasciculus, each of which contain premotor neurons for vertical saccades, and was termed the M-group. Injections of tritiated leucine into the M-group led to afferent labeling primarily over LP motoneurons. In addition, label was present over the SR- and IO-motoneuron subgroups in the oculomotor nucleus and frontalis muscle motoneurons in the facial nucleus. This projection pattern of the M-group suggests a role in the coordination of the upper eyelid and eyes during upgaze. Double-labeling experiments in macaque monkeys revealed that the M-group is strongly parvalbumin immunoreactive and contains high levels of cytochrome oxidase activity. With these two histochemical markers, the homologue of the M-group was identified in the human brain as well.

Spontaneous and reflex activity of facial muscles in dystonia, Parkinson's disease, and in normal subjects

OBJECTIVE

The blink rate is an index which can be easily obtained during the clinical examination, but it has not yet been properly standardised. The present study was undertaken to collect data on the age dependent development of this index and on possible abnormalities in Parkinson's disease and dystonia.

METHODS

The blink rate and the rate of perioral movements were measured in 156 normal controls, 51 patients with Parkinson's disease, 48 patients with spasmodic torticollis, 14 patients with generalised dystonia, and 12 patients with focal hand or leg dystonias and have been correlated with the results of testing the orbicularis oculi reflex, the palmomental reflex, and the perioral reflex.

RESULTS

No age related effects were found for the blink rate and perioral movements but all the reflexes showed age dependent variations. It is sufficient to measure the blink rate for one minute, provided standardised conditions are applied. Blink rate and perioral movement rate were positively correlated in patients and controls. The blink rate was significantly increased in spasmodic torticollis and decreased in Parkinson's disease. In generalised dystonia the blink rate was increased but in hand and leg dystonia the blink rate was normal. The reflex tests did not significantly differ between the subject groups except for the orbicularis oculi reflex, which was hyperexcitable in Parkinson's disease.

CONCLUSION

Measuring the blink rate can assist the diagnosis of extrapyramidal disorders as a soft sign, but is not very sensitive. The group differences found indicate a decrease of the blink rate and perioral movements in hypokinetic and an increase in hyperkinetic extrapyramidal disorders such as spasmodic torticollis and generalised dystonias. This may be of interest for future pathophysiological studies.

Effects of botulinum neurotoxin type A on abducens motoneurons in the cat: alterations of the discharge pattern

The discharge characteristics that abducens motoneurons exhibit after paralysis of the lateral rectus muscle with botulinum neurotoxin type A were studied in the alert cat. Antidromically identified motoneurons were recorded during both spontaneous and vestibularly induced eye movements. A single injection of 0.3 ng/kg produced a complete paralysis of the lateral rectus muscle lasting for about 12-15 days, whereas after 3 ng/kg the paralysis was still complete at the longest time checked, three months. Motoneurons recorded under the effect of the low dose showed differences in their sensitivities to both eye position and velocity according to the direction of the previous and ongoing movements, respectively. These directional differences could be explained by post-saccadic adaptation of the non-injected eye in the appropriate direction for reducing ocular misalignment. Thus, backward and forward post-saccadic drifts accompanied on- and off-directed saccades, respectively. The magnitude of the drift was similar to the magnitude of changes in eye position sensitivity. The discharge of the high-dose-treated motoneurons could be described in a three-stage sequence. During the initial 10-12 days, motoneuronal discharge resembled the effects of axotomy, particularly in the loss of tonic signals and the presence of exponential-like decay of firing after saccades. In this stage, the conduction velocity of abducens motoneurons was reduced by 21.4%. The second stage was characterized by an overall reduction in firing rate towards a tonic firing at 15-70 spikes/s. Motoneurons remained almost unmodulated for all types of eye movement and thus eye position and velocity sensitivities were significantly reduced. Tonic firing ceased only when the animal became drowsy, but was restored by alerting stimuli. In addition, the inhibition of firing for off-directed saccades was more affected than the burst excitation during on-directed saccades, since in many cells pauses were almost negligible. These alterations could not be explained by adaptational changes in the movement of the non-injected eye. Finally, after 60 days the initial stages of recovery were observed. The present results indicate that the high dose of botulinum neurotoxin produces effects on the motoneuron not attributable to the functional disconnection alone, but to a direct effect of the neurotoxin in the motoneuron and/or its synaptic inputs.

Botulinum toxin A injection in the treatment of hemifacial spasm

There are conflicting reports concerning the variation in duration of symptoms relief for patients with hemifacial spasm who have undergone several injections of botulinum A toxin (BOTX-A). We present our experience of BOTX-A injections in Taiwanese patients to analyze this issues, and to inspect whether the efficacy of treatment depends on the pre-injection severity.

MATERIAL AND METHOD

From July 1992 to December 1994, 137 patients received injections of BOTX-A. We used objective and subjective score system to evaluate the efficacy and side effects of BOTX-A injection.

RESULTS

The overall successful rate of substantial relief of spasm was 88%. The mean duration of response was 20 weeks. Patents with more severe spasm tended to have shorter duration of improvement. The effects of consecutive injections remained fairly constant over the first 4 injections.

CONCLUSION

The BOTX-A injection is an effective and safe treatment for patients with hemifacial spasm and the effect could be sustained over the consecutive injections.

Distonias: aspectos terapêuticos

Diversas abordagens terapêuticas são utilizadas em pacientes com distonias. Sempre que possível, causas específicas devem ser identificadas e tratadas. As modalidades de tratamento sintomático podem ser agrupadas em três categorias: tratamento farmacológico, cirúrgico e injeções locais de toxina botulínica. Cada uma dessas modalidades apresenta algumas vantagens e limitações. Formas generalizadas, particularmente as de ocorrência na infância, podem se beneficiar com drogas anticolinérgicas ou, em alguns casos, com a levodopa ou outros agentes tais como antagonistas da dopamina, baclofeno e benzodiazepínicos. As formas focais não respondem adequadamente ao tratamento farmacológico sistêmico mas beneficiam-se significativamente com injeções de toxina botulínica nos grupos musculares acometidos. Cerca de 90% dos pacientes com blefarospasmo e 70% daqueles com distonia cervical apresentam resposta satisfatória a esse tipo de terapia. O tratamento cirúrgico tem sido utilizado em algumas formas de distonias generalizadas (lesões estereotáxicas), axiais (rizotomias) ou focais (miectomias e neurectomias) com resultados variáveis.

Electrophysiological studies in patients with blepharospasm before and after botulinum toxin A therapy

Botulinum toxin (BTX) is the treatment of choice for blepharospasm. To investigate if the locally injected BTX influences the central nervous system and in particular the brain stem, amplitude and latency of compound muscle action potential (CMAP) of orbicularis oculi, blink reflex and brain stem auditory evoked potential were studied in 12 blepharospasm patients before BTX therapy, 9 patients after BTX therapy and 9 age and sex matched healthy controls. The mean amplitude of orbicularis oculi in patients was significantly lower before BTX therapy (p < 0.05) and after BTX therapy (p < 0.02). The amplitudes of R1, R2 and contralateral R2 (CR) was higher in patients than controls but did not reach statistical significance. Following BTX therapy there was a reduction in amplitude of R1, R2 and CR (p < 0.001) and prolongation of latency of R2 and CR (p < 0.05). The ratio of blink reflex amplitude/CMAP amplitude of orbicularis oculi showed a significant decline after BTX therapy (p < 0.01). This small study suggests the involvement of brain stem pathways following BTX therapy in patients with blepharospasm.

Palpebral fissure height and downgaze in patients with Graves upper eyelid retraction and congenital blepharoptosis

PURPOSE

To compare the relation between vertical eyelid fissure height and downgaze in healthy subjects and in patients with Graves upper eyelid retraction and congenital blepharoptosis.

METHODS

With a caliper rule, the authors measured the vertical eyelid fissure height of 25 patients with no previous history of eye disease, 34 patients with Graves disease, and 16 patients with congenital blepharoptosis. All measurements were done at the primary position and at four levels of downgaze (10 degrees, 20 degrees, 30 degrees, and 40 degrees). In 13 patients with Graves disease, vertical phoria was quantified with a Maddox rod and prism.

RESULTS

The relation between vertical eyelid fissure height and downgaze is linear. The slope was identical for the control subjects and for the patients with Graves disease (b = -1.36) but it was almost zero for the patients with congenital blepharoptosis (b = -0.037). When vertical eyelid fissure height was corrected to arc values, the slope of the relation between vertical eyelid fissure height and downgaze was significantly greater for the patients with Graves disease. Vertical phoria was not related to the amount of Graves upper eyelid retraction.

CONCLUSIONS

The data support the hypotheses that upper eyelid retraction secondary to Graves eye disease results from hyperactivity of the levator palpebrae superioris muscle.

Extraocular muscles: basic and clinical aspects of structure and function

Although extraocular muscle is perhaps the least understood component of the oculomotor system, these muscles represent the most common site of surgical intervention in the treatment of strabismus and other ocular motility disorders. This review synthesizes information derived from both basic and clinical studies in order to develop a better understanding of how these muscles may respond to surgical or pharmacological interventions and in disease states. In addition, a detailed knowledge of the structural and functional properties of extraocular muscle, that would allow some degree of prediction of the adaptive responses of these muscles, is vital as a basis to guide the development of new treatments for eye movement disorders.

The effect of phenylephrine on Müller muscle. A blepharogram study of eyelid motion

PURPOSE

The blepharogram technique is used to study the effect of a drug on blinking. The authors show that ocular instillation of phenylephrine, a stimulant of Müller muscle of the eyelid, accelerates the up phase of the blink.

METHODS

Motion of a tiny search coil glued to the eyelid moving in a weak magnetic field modifies an induced alternating current which is amplified and used to display the position of the upper eyelid in degrees on the ordinate of a graph with time in milliseconds on the abscissa. The graph is called a blepharogram. Blepharogram studies and individual blink analysis show the effect of phenylephrine on eyelid motion (blinking).

RESULTS

Instillation of phenylephrine accelerated the up phase of the blink in all ten experimental subjects. In 65% of subjects, phenylephrine also produced or increased newly described N and M blepharogram patterns.

CONCLUSION

This is the first instrumental detection of the effect of a pharmacologic agent on eyelid motion. The blepharogram technique provides insight into eyelid physiology and can be used to study any neuromuscular condition that affects eyelid motion.

Discharge of identified deep cerebellar nuclei neurons related to eye blinks in the alert cat

The activity of identified cerebellar nuclear neurons was recorded in the alert cat during blinks induced by corneal air puffs, light flashes and tones. Eyelid response to air puffs consisted of an early (16.5 +/- 2.7 ms) downward movement followed by two to three late downward steps. Blinks induced by flashes or tones presented longer latencies (52.6 +/- 4.8 and 50.1 +/- 8.0 ms). Type A neurons (n = 86) increased their spike activity in coincidence with the beginning of the blink, regardless of the stimulus modality. The late eyelid downward responses were accompanied by corresponding increases in the firing rate of the neuron. Type A neurons were activated mostly from the red nucleus (48/86) or the restiform body (24/86). Type B neurons (n = 30) fired a brief burst of spikes slightly preceding the blink, followed by a noticeable decrease in their firing rate. As for type A, the discharge response of type B neurons was always the same regardless of the sensory modality. These neurons were activated from the red nucleus (18/30), oculomotor complex (6/30) and restiform body (6/30). Although no precise temporal coupling was found between the beginning of the neuronal response and the start of either the stimulus or the motor response, linear regression analysis demonstrated significant relationships between mean firing rate of type A and B neurons and eyelid position, velocity and/or acceleration. Deep cerebellar nuclei neurons presented here seem to be directly involved in the execution of reflexively induced blinks following the smaller details of eyelid motor performance. The opposite behavior of type A and B cells suggests an interplay of reciprocal actions to determine the ongoing displacements of the lid. Finally, the cerebellum seems to influence blinks through a spread action on many brainstem sites and not exclusively on the red nucleus.

Botulinum A toxin stimulates neurite branching in nerve-muscle cocultures

In addition to skeletal muscle paralysis, type A botulinum toxin commonly causes sprouting of motor axons in various experimental whole-animal systems. The use of type A botulinum toxin in clinical treatment of muscle spasm disorders is becoming increasingly popular. The eventual, unwanted return of involuntary activity in the treated muscles may be a consequence of such axon sprouting. We have developed a coculture model allowing the quantification of botulinum toxin-induced sprouting that shows promise for future studies on its mechanism and control. Chick embryo ciliary ganglion motor neurons were cocultured with chick leg muscle cells. The presence of type A botulinum toxin in the coculture medium was correlated with significantly increased branching frequency of neurites. Toxin-increased branching frequency occurred even when the neurons and muscle cells were separated from each other on the culture dishes, suggesting a presynaptic effect of toxin. Cocultures incubated in the presence of curare, a post-synaptic blocker, had control levels of neurite branching, ruling out the possibility that simple synaptic blockade causes sprouting but again supporting the hypothesis of a pre-synaptic activity of botulinum toxin.

Botulinum toxin paralysis of the orbicularis oculi muscle. Types and time course of alterations in muscle structure, physiology and lid kinematics

In chronically prepared guinea pigs, we investigated the time course of botulinum toxin A's (Bot A) effect on the blink reflex by monitoring lid movements and EMG activity prior to and after Bot A injection into the orbicularis oculi muscle (OOemg), or after nerve crush of the zygomatic nerve. We correlated these alterations with the morphological changes of the orbicularis oculi (lid-closing) muscles of the same animals. After Bot A treatment there was a profound reduction of OOemg activity and blink amplitudes as well as a slowing of maximum blink down-phase velocity. Blink up-phases, however, remained unchanged. Gradual recovery of OOemg magnitude and blink amplitude started around day 6; a functioning blink reflex appeared on day 21, and full recovery of blink amplitude occurred by day 42. Crushing the zygomatic branch of the facial nerve produced similar changes in blink parameters, but recovery was much more rapid (15 days) than for Bot A-treated guinea pigs. The morphological analysis demonstrated that Bot A produced a denervation-like atrophy in the orbicularis oculi. No fiber type-specific alterations were noted, and all muscle fiber types ultimately recovered, with no longstanding consequences of the transient denervation. Our findings support the notion that functional recovery was the result of preterminal and terminal axonal sprouting that subsequently re-established functional innervation. Moreover, differences between the present findings and those seen after injection of Bot A into the extraocular muscles strongly support the hypothesis that the composition in terms of muscle fiber type and the properties of the motor control system of a given muscle greatly influence both how the particular muscle responds to toxin injection, and how effective the toxin is in resolution of neuromuscular disorders that affect a particular muscle. The present findings were consistent with clinical observations that Bot A produces only temporary relief in patients with essential blepharospasm. It is likely that the efficacy of Bot A in treatment of blepharospasm could be improved by using agents that suppress terminal sprouting. The close correspondence of the changes in blink physiology between human patients and guinea pigs after Bot A treatment demonstrate that the guinea pig is an excellent model system for testing strategies to prolong the beneficial effects of Bot A treatment in relieving lid spasms in human subjects.

Types and time course of the alterations induced in monkey blink movements by botulinum toxin

The alterations induced in eyelid movement metrics subsequent to unilateral injections of botulinum toxin type A into the orbicularis oculi muscle were studied in chronic alert monkeys using the search coil technique. Botulinum toxin caused rapid paralysis of blinks in the treated eyelid. The amplitude and peak velocity of blinks generated by this eyelid remained at or below 20% of that of the fellow, untreated eyelid for 10-20 days. Blink amplitude gain increased linearly thereafter, attaining control values by 40-60 days after injection. Recovery of blink peak velocity was slower. The adaptive alterations in blink duration that were observed during the acute phase of toxin paralysis suggest that the mechanisms responsible for blink reflex plasticity may produce bilateral adjustments in eyelid function. Taken together, these data establish a quantitative data base that can be exploited in order to: (1) better understand the neural adaptive mechanisms that operate during eyelid movements and (2) allow quantitative comparisons between current treatment protocols that employ botulinum toxin and protocols that may lead to improvements in the treatment of chronic eyelid spasm (blepharospasm).

Regional differences in the orbicularis oculi muscle: conservation between species

The orbicularis oculi muscle is a complex facial muscle involved in eyelid closure. The central parts of pretarsal and preseptal regions of the palpebral part of the orbicularis oculi muscle in rabbit and cynomolgus monkey lower eyelids were examined histologically and were analyzed for muscle fiber number, muscle fiber cross-sectional area and fiber type composition. Distinct regional differences were seen in the muscle fiber composition in these two regions of the muscle. The pretarsal portion of the muscle, that closest to the eyelid margin, was quite homogeneous and almost completely composed of type 2 fibers. These fibers were the smallest in cross-sectional area. Type 2 fibers also predominated in the preseptal portion of the muscle, but this region contained between 10 and 20% type 1 fibers. They appeared to be a gradient in muscle fiber size, whereby the fiber size increased as a function of the distance from the eyelid margin. The same pattern of regional differences were found in both rabbit and monkey orbicularis oculi. Thus, there is a clear conservation of these regional differences in these two species. While the developmental significance is unknown, the identification of this pattern may facilitate the evaluation of chemomyectomy agents for treatment of eyelid spasms in humans and allow a more accurate analysis of biopsy material from this muscle.