Showing papers on "Reflex published in 1977"

Comparative study of perceived pain and nociceptive flexion reflex in man

Abstract: The purpose of this study was to compare the amplitude of the flexion reflex of the biceps femoris muscle (BF) with the intensity of the painful sensation elicited by a nociceptive stimulation resulting from application of constant-current either on the sural nerve or on the skin in its distal receptive field. Experiments were carried out on 15 normal volunteers. It was observed that: (1) Stimulation of the sural nerve (either on or through the skin) elicits two different reflex responses in the BF: the first (RII) is of short latency, low threshold and corresponds to a tactile reflex. The second (RIII) is of longer latency and higher threshold, and corresponds to a nociceptive reflex. The threshold of RIII was found to be the threshold of a pain sensation. (2) Stimulation of the skin elicits only a late nociceptive (RIII) response in the BF. The threshold of this response was also found to be that of pain. (3) The threshold of both pain and RIII were found to be higher for sural nerve stimulation (10 mA) than for cutaneous stimulation (5 mA). It was suggested that the large diameter cutaneous fibers could have an inhibitory effect of both pain and the nociceptive reflex. This was supported by the results obtained during a selective ischemic block of the largest diameter fibers in the sural nerve, when a 10 mA stimulation was applied to the nerve. In this case, a decrease of the RII reflex was observed in BF, together with an increase of both RIII and pain sensation. Functional implications of these results are discussed.

Specific patterns of neuronal connexions involved in the control of the rabbit's vestibulo-ocular reflexes by the cerebellar flocculus.

Abstract: 1. In anaesthetized albino rabbits, the occurrence of Purkinje cell inhibition on canal-ocular reflexes was surveyed with a reflex testing method. 2. Test reflexes were elicited by electrical stimulation of the semicircular canals. The results were appaised by recording potentials and tension from extraocular muscles. Twelve reflexes were defined in terms of the receptor canal and the effector muscle. 3. Conditioning electrical stimuli were applied to the flocculus, the inferior olive, and optic pathways at the retinae, optic chiasm, pretectal area and upper medulla. 4. The conditioning stimulation at the ipsilateral flocculus induced depression in six of the twelve canal-ocular reflexes; four of the six arose from the anterior canal and the remaining two from the horizontal canal. 5. The effect of stimulation of the contralateral inferior olive was similar to that of the ipsilateral flocculus, though less clear in two of the four reflexes from the anterior canal because of a contaminating effect. 6. The two reflexes from the horizontal canal were depressed by stimulation of the ipsilateral optic pathway which reached the ipsilateral flocculus via the contralateral pretectal area and inferior olive. 7. The four reflexes from the anterior canal were affected by stimulation of optic pathways in a different manner from each other. One was depressed from the contralateral retina via the ipsilateral pretectal area, while another was depressed from the ipsilateral retina via the contralateral pretectal area, though only occasionally. The third reflex was depressed from the ipsilateral pretectal area but not from the retina. The fourth was affected from neither the retina nor the pretectal area. 8. On the basis of latency measurements, it was concluded that the depression of canal-ocular reflexes was due to inhibition of relay neurones of the testing reflexes by flocculus Purkinje cells which were activated either directly, or indirectly through olivocerebellar climbing fibre afferents. 9. The above conclusion was supported by the observation that the depression induced by stimulation of the inferior olive and optic pathways was abolished by acute destruction of the ipsilateral flocculus. 10. The possible functional significance of the specific patterns of connexions from flocculus Purkinje cells to canal-ocular reflex pathways is discussed, and specialization among flocculus Purkinje cells in relationship with vestibulo-ocular reflexes is postulated.

Cutaneous facilitation of transmission in reflex pathways from Ib afferents to motoneurones.

Abstract: 1. The effect of volleys in low threshold cutaneous afferents upon transmission of synaptic action from Ib afferents to motoneurones has been investigated with intracellular recording from alpha motoneurones to hind limb muscles. 2. There was facilitation from cutaneous afferents of transmission in excitatory and inhibitory reflex pathways from Ib afferents without any evidence for difference in effect on di- and trisynaptic pathways. It is postulated that volleys in cutaneous afferents evoke excitatory action in interneurones of these reflex pathways. 3. The time course of the facilitation suggest that cutaneous afferents have disynaptic excitatory connexions with the interneurones intercalated in the disynaptic Ib inhibitory pathways to motoneurones. 4. Some observations are reported suggesting that interneuronal transmission in Ib inhibitory pathways to motoneurones might be facilitated from Ia afferents. 5. The findings are discussed in relation to the presumed role of Ib reflex action in regulating muscle tension.

Characterization of the responses of oxytocin‐ and vasopressin‐secreting neurones in the supraoptic nucleus to osmotic stimulation

Abstract: 1 Extracellular action potentials were recorded from forty antidromically identified single units in the supraoptic nucleus of lactating, urethane-anaesthetized female rats The activity was monitored both during reflex milk ejection and during an increase of 10-15 m-osmole/kg in plasma osmotic pressure induced by intraperitoneal injection of 1 ml of 15 M-NaCl solution 2 About half (eighteen) the cells showed a burst of activity before reflex milk ejection and were dubbed oxytocin cells Oxytocin cells responded to a hypertonic injection with a smooth sustained threefold increase in firing rate 3 The remainder (twenty-two) showed no burst of activity before reflex milk ejection and were dubbed vasopressin cells Vasopressin cells doubled their firing rate as plasma osmotic pressure increased Neither cell type increased its firing rate after injections of isotonic NaCl 4 A phasic firing pattern was rarely seen in slow firing vasopressin cells (< 2 spikes/sec) but was seen in almost all vasopressin cells (twelve out of fourteen) firing between 3 and 8 spikes/sec Above 8 spikes/sec, some vasopressin cells fired continuously Phasic firing was only once encountered in an oxytocin cell 5 The firing rate of both oxytocin and vasopressin cells decreased when plasma osmotic pressure was reduced 10-15 m-osmole/kg by an intragastric water load of 10 ml 6 Hypothalamic cells lying just outside the supraoptic nucleus did not show a consistent response to injection of hypertonic NaCl 7 Clearly, both oxytocin and vasopressin cells are osmoresponsive, but phasic firing is characteristic of stimulated vasopressin cells Thus, osmotic activation allows discrimination between oxytocin- and vasopressin-secreting neurones

The relationship of voluntary movement to spasticity in the upper motor neuron syndrome.

Abstract: Hyperactive strethch reflexes in the upper motor neuron (UMN) syndrome are frequently cited as an impediment to volitional movement. The assumption is that neural or mechanical activity of the hyperactive antagonist interferes with agonist function. The validity of this assumption was examined by evaluating quantitative and qualitative relationships between stretch reflexes and voluntary movement. Sixteen patients with chronic UMN symptoms and 8 normal volunteers were tested. Joint position and integrated electromyograms from primary flexors and extensors were recorded. Quantitated values of (1) reflex response to controlled passive motion by an automated system, (2) a maximal voluntary isometric contraction, and (3) the time required for ten voluntary rapid repetitive movements (RRM) of alternating elbow flexion and extension were obtained. Passive movement elicited tonic reflexes, which predominated during muscle stretch in patients and during muscle shortening in the volunteers. Ratios of the EMG activity elicited during stretch, shortening, and isometric activity were used as measures of spasticity and were compared with the time for RRM. A positive correlation between elbow flexor spasticity and the time for RRM was shown. Qualitative analysis of the EMG activity during voluntary isotonic movement, however, showed that primary impairment of movement is not due to antagonist stretch reflexes, but rather to limited and prolonged recruitment of agonist contraction and delayed cessation of agonist contraction at the termination of movement.

Reticular reflex myoclonus: aphysiological typeof humanpost-hypoxic myoclonus

Abstract: A patient with post-hypoxic myoclonus, sensitive to therapy with 5-hydroxytryptophan and clonazepam, was subjected to detailed electrophysiological investigation. Brief generalised jerks followed the critical stimulus of muscle stretch. The electroencephalogram showed generalised spikes that were associated with, but not time locked to, the myoclonus. The cranial nerve nuclei were activated upward. Analysis of the findings suggests that the mechanism of the myoclonus is hyperactivity of a reflex mediated in the reticular formation of the medulla oblongata.

Reflex inputs to the cardiovascular and respiratory centers from dynamically working canine muscles. Some evidence for involvement of group III or IV nerve fibers.

Abstract: Reflex inputs to the circulatory and ventilator)' centers from dynamically contracting muscles and their interaction with extramuscular inputs were studied in anesthetized dogs. Dynamic work of hindlimb muscles was evoked by electrical stimulation of sciatic nerve branches (40 tetani/min with square wave pulses: 0.2-1.0 V, 0.3-0.7 msec, 30-100 Hz). These pulses activated group I and II nerve fibers and they affected heart rate (HR), minute ventilation (VE), and mean arterial pressure (MAP) only to a small degree when neuromuscular transmission was blocked by cooling distally from the electrodes. Comparable small changes were obtained if these fibers were excited by their natural stimuli when moving and stretching the legs and muscles, respectively. But these responses disappeared when the legs were moved and the muscles stretched after the dogs had been immobilized with drugs, indicating that they were caused by increased muscle tension and not movement per se. If neuromuscular transmission was restored, muscular contractions were induced which caused great reflexogenifc increases of HR, V t , and MAP. Muscular reflex drives to the centers were then eliminated by cold blockade of nervous transmission in both sciatic nerves proximally from the stimulating electrodes while contractions were not interrupted. Blood metabolically enriched in this way entered the systemic circulation, thereby creating humoral extramuscular drives. Muscular reflex inputs accounted for the major and humoral drives for the minor portion of the total cardiovascular and respiratory responses during onset as well as during steady state of dynamic work, although humoral drives increased with time. The time courses of the reflexly induced changes tallied with those of muscular blood flow, indicating a relation with similar metabolic processes. The reflex drives were abolished if a blocking temperature typical for nonmyelinated or small myelinated group IV or III nerve fibers was reached. Similarly, the main responses were only obtained if electrical stimuli were raised to levels where they activated group III or IV afferents.

The Ocular Motor Defects in Progressive Supranuclear Palsy

Abstract: The results of quantitative infrared horizontal eye movement recordings in 8 patients with progressive supranuclear palsy are presented Some of the patients had total paralysis of vertical movements, but none had completely lost the ability to perform horizontal eye movements All patients had a defect in ocular fixation previously undescribed in this condition: the universal presence of square-wave jerks Analysis of refixation saccades demonstrated hypometria, slow velocity/amplitude relationships, and profound prolongation of duration The pursuit abnormality, characterized clinically by "cogwheel" eye movements, represented the inability to match eye velocity to target velocity The ratio of peak eye velocity to peak target velocity (pursuit gain) was 02 to 05 Defects in the vestibuloocular reflex included inability to increase the gain of the reflex (ratio of peak eye velocity to head velocity) during viewing of a visible, stationary target and failure to suppress the reflex when viewing a target rotating with the head

Reticular reflex myoclonus: a physiological type of human post-hypoxic myoclonus.

Abstract: A patient with post-hypoxic myoclonus, sensitive to therapy with 5-hydroxytryptophan and clonazepam, was subjected to detailed electrophysiological investigation. Brief generalised jerks followed the critical stimulus of muscle stretch. The electroencephalogram showed generalised spikes that were associated with, but not time locked to, the myoclonus. The cranial nerve nuclei were activated upward. Analysis of the findings suggests that the mechanism of the myoclonus is hyperactivity of a reflex mediated in the reticular formation of the medulla oblongata.

Reflex control of locomotion as revealed by stimulation of cutaneous afferents in spontaneously walking premammillary cats

Abstract: 1. Stimulation of different hindlimb nerves in spontaneously walking premammillary cats was used in order to examine the effects of sensory input on the rhythmic motor output. 2. Stimulation of the tibial or sural nerve at low intensities caused the burst of activity in the triceps surae or semimembranosus to be prolonged if stimuli were given during the extension phase. When applied during the flexion phase, the same stimuli shortened the burst of activity in the pretibial flexors and induced an early onset of the extensor activity, except if stimuli were given at the very beginning of the flexion phase, when flexor burst prolongations or rebounds were observed instead. 3. These effects were related to activation of large cutaneous afferents in these nerves since the results could be duplicated by low-intensity stimulation of the tibial nerve at the ankle or by direct stimulation of the pad. 4. In contrast, activation of smaller afferents by high-intensity stimulation resulted prolongations of the flexor burst and/or shortenings of the extensor burst for stimuli applied before or during these bursts, respectively. 5. It was concluded that the large and small cutaneous afferents make, respectively, inhibitory and excitatory connections with the central structure involved in the generation of flexion during walking.

The relationship of voluntary movement to spasticity in the upper motor neuron syndrome.

Abstract: Hyperactive strethch reflexes in the upper motor neuron (UMN) syndrome are frequently cited as an impediment to volitional movement. The assumption is that neural or mechanical activity of the hyperactive antagonist interferes with agonist function. The validity of this assumption was examined by evaluating quantitative and qualitative relationships between stretch reflexes and voluntary movement. Sixteen patients with chronic UMN symptoms and 8 normal volunteers were tested. Joint position and integrated electromyograms from primary flexors and extensors were recorded. Quantitated values of (1) reflex response to controlled passive motion by an automated system, (2) a maximal voluntary isometric contraction, and (3) the time required for ten voluntary rapid repetitive movements (RRM) of alternating elbow flexion and extension were obtained. Passive movement elicited tonic reflexes, which predominated during muscle stretch in patients and during muscle shortening in the volunteers. Ratios of the EMG activity elicited during stretch, shortening, and isometric activity were used as measures of spasticity and were compared with the time for RRM. A positive correlation between elbow flexor spasticity and the time for RRM was shown. Qualitative analysis of the EMG activity during voluntary isotonic movement, however, showed that primary impairment of movement is not due to antagonist stretch reflexes, but rather to limited and prolonged recruitment of agonist contraction and delayed cessation of agonist contraction at the termination of movement.

Reflex control of expiratory airflow and duration.

Abstract: Unanesthetized, unrestrained cats were studied repeatedly after placement of a permanent tracheostomy, catheters for respiratory pressure measurements, and respiratory muscle EMG electrodes. The tr...

Local reflex in microcirculation in human skeletal muscle.

Abstract: The effect of venous stasis of 40 mmHg upon blood flow in human skeletal muscle was studied in four normal subjects and in two chronically sympathectomized patients. Blood flow in skeletal muscle was measured by the local 133Xenon washout technique. Blood flow decreased about 30 per cent during venous stasis of 40 mmHg. In a "passive vascular bed" induced by means of histamine, blood flow decreased only by 16 per cent, indicating that the decrease in blood flow is due to a vasoconstrictor response to increase in vascular transmural pressure. The vasoconstrictor response was unaffected by a spinal sympathetic blockade, but was blocked in areas infiltrated with lidocaine or with phentolamine. The vasoconstrictor response was present in the nonoperated limbs used as a control, but abolished in the denervated arms in the two chronically sympathectomized patients. The findings strongly suggest that the vasoconstrictor response in skeletal muscle is due to a local nervous mechanism involving adrenergic fibres. Thus a local reflex mechanism, most likely a sympathetic axon reflex, seems to be present in human skeletal muscle as in cutaneous and subcutaneous tissue. This indicates that about 45 per cent of the change in total vascular conductance, when a person changes from supine to upright position, is due to this local reflex mechanism operating independently of the central nervous system.

The Variable-Pressure Neck-Chamber Method for Studying the Carotid Baroreflex in Man

Abstract: 1. The variable-pressure neck-chamber method was analysed in ten healthy volunteer subjects to determine its suitability for the study of the carotid baroreceptor reflex in man. 2. Positive and negative pressures applied to the neck (range ± 60 mmHg) were always transmitted linearly to a tissue catheter outside the carotid sinus, but only 86% of positive pressure, and 64% of negative pressure. Tissue pressures were confirmed by simultaneous measurement in the internal jugular vein adjacent to the carotid sinus. 3. Positive and negative pressure changes within the above range did not alter P o 2 of internal jugular venous blood, suggesting that cerebral blood flow was unaltered. 4. Positive pressure changes induced reflex pressor responses of similar magnitude at arterial P o 2 12·8 and 70·1 kPa (96 and 527 mmHg), suggesting that the carotid chemoreceptors were not involved. 5. It is concluded that the variable-pressure neck chamber is a valid method for selectively studying the carotid baroreceptor reflex in man. However, transmission of external pneumatic pressure to the carotid sinus is imperfect and greater for positive than for negative pressure. This must be recognized to avoid underestimation of gain and distortion of shape of the reflex.

Respiratory and baroreceptor reflex interactions in man.

Abstract: Respiratory and arterial baroreceptor reflex interactions were studied in six healthy young adults. Carotid baroreceptors were stimulated with two intensities of neck suction during early inspiration or expiration at 100 or 150% of each subject's normal tidal volume. Sinus node responses to moderate baroreflex stimuli were inhibited by inspiration, but responses to intense stimuli were not influenced by the phase of respiration. Supranormal tidal volume did not diminish responses to inspiratory baroreflex stimuli, but significantly reduced responses to expiratory stimuli. These results provide evidence for a central respiratory baroreceptor reflex interaction in man whose quality is dependent upon the level of afferent baroreceptor activity and the depth of inspiration.

The effect of tracheostomy on the laryngeal closure reflex.

Abstract: The clinical observation of aspiration following prolonged tracheostomy prompted a neurophysiologic investigation of the glottic closure reflex in dogs longitudinally evaluated after permanent tracheostomy. The data support significant alterations in the central organization of the protective closure reflex heretofore considered phylogenetically primitive and therefore physiologically stable over wide ranges of functional demand. The data indicate that chronic upper airway bypass results in: 1. increased threshold of the evoked adductor response; 2. random shifts in its latency; 3. rapid attenuation of the primary evoked response to repetitive SLN stimulation; and 4. reduced after-discharge activity, all of which contribute to a weakened, ill-coordinated closure respons.

Plasticity in the adult vestibulo-ocular reflex arc.

Abstract: Human subjects with maintained reversal of their horizontal field of vision exhibit very substantial adaptive changes in their 'horizontal' vestibulo-ocular reflex (v.o.r.). Short durations (8 min) of vision reversal during natural head movement led to 20% v.o.r. attenuation while long periods (4 weeks) eventually led to approximate reversal of the reflex. The reversed condition is approached by a complex, but highly systematic, series of changes in gain and phase of the reflex response relative to normal. Recovery after return to normal vision exhibits a similar duration, but different pattern, to that of the original adaptation. A chronic cat preparation with long-term optical reversal of vision has now been developed and shows similar adaptive and recovery changes at low test stimulus amplitudes, but different patterns of adaptive response at high amplitudes. An adaptive neural model employing known vestibulo-ocular pathways is proposed to account for these experimentally observed plastic changes. The model is used to predict the adapted response to patterns of stimulation extending beyond the range of experimental investigation.

Circulatory reflexes from carotid and extracarotid baroreceptor areas in man.

Abstract: The carotid sinus baroreceptor reflex was studied in 11 normotensive subjects, using a variable pressure neck chamber and correcting for imperfect pressure transmission to the carotid sinus. Decreased carotid baroreceptor stimulation caused a sustaineded rise in arterial pressure, and increased carotid baroreceptor stimulation caused a sustain fall. The responses were in linear relation to the stimulus, and, after reaching the steady state, greater for the reduced than for the increased baroreceptor stimulation. Thus the carotid sinus baroreceptor reflex of the normotensive man is an effective antihypotensive and antihypertensive feedback system, though the former function may have more sensitivity. The increased and decreased baroreceptor stimulation by the neck chamber also caused bradycardia and tachycardia which were modest in magnitude and often transient. In eight subjects the reflex changes in heart rate induced by the neck chamber were compared with those induced by altering transmural pressure not merely at the carotid sinus but throughout the arterial tree (injection of phenylephrine and trinitroglycerin). The slopes of these relations were 3 times as great in the latter circumstance. Thus the carotid baroreceptors play a lesser role in heart rate control than do extracarotid baroreceptors.

Reflex sympathetic dystrophy in children.

Abstract: Two pediatric patients had reflex sympathetic dystrophy, which has been well described in adults but is rarely recognized in children. The syndrome consists of continuous pain, hyperesthesia, and autonomic symptoms occurring in an extremity, usually following trauma. The various types of presentation, differential diagnosis, and modes of therapy are discussed.

Inhibition of human motoneurones, probably of Renshaw origin, elicited by an orthodromic motor discharge

Abstract: 1. The pattern of variations of a test H-reflex after a conditioning H-reflex was investigated in human subjects by an experimental design in which both reflexes involved the same soleus motoneurones. This was made possible by using a method based upon a collision in the motor axons between the orthodromic conditioning reflex volley and the antidromic volley elicited by a test stimulus supramaximal for the motor axons. 2. The variations of the test reflex amplitude seen when increasing the conditioning reflex discharge were studied. This was made possible by facilitating the conditioning reflex without changing the strength of the afferent volley. This facilitation was obtained through a soleus stretch elicited by a stimulation of the plantar nerves. 3. The amplitude of the test reflex depended only on the size of the conditioning reflex discharge. 4. As long as the conditioning reflex was of low amplitude, all the motoneurones responsible for the conditioning response could be activated by the test volley, even though these motoneurones were undergoing after-hyperpolarization. This indicates that, in man, the after-hyperpolarization of the most excitable motoneurones can be completely overcome by a large Ia afferent volley. 5. Increasing the conditioning reflex beyond a specific value resulted in an absolute decrease in the number of motoneurones involved in the test reflex. The amount of this decrease was related only to the amplitude of the conditioning reflex. 6. This inhibition decreased progressively as the time interval separating the test stimulus from the conditioning stimulus increased. The time course of this inhibition was studied with conditioning reflexes of different amplitudes. The duration of the inhibition increased with the size of the conditioning reflex. 7. These results strongly suggest that Renshaw cells excited by the conditioning reflex are responsible for this inhibition. The results are in agreement with observations made in animals on recurrent inhibition.

Laryngeal spasm: a neurophysiologic redefinition.

Abstract: Within the limits of standard neurophysiologic techniques, we have attempted to redefine laryngeal spasm as distinct from the glottic closure reflex. This distinction is based upon the observation that laryngeal spasm is solely mediated by the superior laryngeal nerve. Stimulation of other afferent nerves, capable of eliciting the glottic closure reflex, produces little adductor after-discharge activity that is characteristic of laryngeal spasm. In this regard, modification of output function from the adductor motoneuron aggregate by means of temporal and spatial summation of sensory input data has been described, and its characteristics further defined in response to varying ventilatory states and barbiturate levels.

Properties of the laryngeal chemoreflex in neonatal piglets.

Abstract: Cardiorespiratory reflex responses to laryngeal chemoreceptor stimulation were studied in 62 piglets of both sexes varying in age from 1 to 79 days. The distal trachea was cannulated to provide a free airway and the proximal end used to introduce fluids into the laryngeal area. Introduction of either water or milk produced apnea, bradycardia, and hypertension. Swab application of test fluids to the laryngeal epithelium produced similar responses. The reflex could be interrupted by flushing the laryngeal region with saline, by cutting the superior laryngeal nerves (SLN) or by anesthetizing the laryngeal epithelium with lidocaine. Electrical stimulation of SLN elicited identical responses. Respiratory inhibition by the reflex was enhanced following central depression with chloralose and overridden by administration of the respiratory stimulant, aminophylline. The relative potency of the laryngeal reflex was estimated to be equivalent to about 40% of the dose of chloralose which produced permanent respiratory arrest. It is concluded that in circumstances where respiratory drive is reduced the laryngeal inhibitory reflex is capable of caused persistent apnea and asphyxial death in the young piglet.

Organization of Invertebrate Motor Systems

Abstract: The sections in this article are: 1 Properties of Muscle 11 Anatomic Organization 12 Contraction Speed 13 Strength and Extent of Contraction 14 Thresholds for Excitation-Contraction Coupling 15 Correlations with Innervation 16 Dependence of Tension on Recent History 2 Motor Neurons and the Motor Unit 21 Motor Neuron Morphology 22 Correlations Between Motor Neuron Morphology and Function 23 Neuromuscular Transmission 24 Excitation-Contraction Coupling 25 Peripheral Motor Unit Organization 26 Matching of Central and Peripheral Properties 27 Ontogeny and Regeneration 3 Reflex Organization 31 Proprioceptive Reflexes 32 Exteroreceptive Reflexes 33 Righting Reflexes 34 Optomotor Reflexes 35 Control of Reflex Excitability 4 Central Organization of Motor Systems 41 Structure of Motor Programs 42 Storage of Motor Programs 43 Release of Motor Programs by Command Elements 44 Central Versus Peripheral Control of Motor Output 45 Development of Pattern-Generating Networks 46 Complex Behavioral Phenomena 5 Conclusion

The action of botulinum A neurotoxin on the inhibition by antidromic stimulation of the lumbar monosynaptic reflex

Abstract: 1. Botulinum toxin type A was injected into gastrocnemius muscles of cats and 2 days later its action on the monosynaptic gastrocnemius reflex and on the recurrent inhibition was investigated. 2. In early local botulism, no significant change in the monosynaptic gastrocnemius reflex was observed. 3. The inhibition by antidromic stimulation of the monosynaptic gastrocnemius reflex was significantly reduced. 4. During the early phases of local botulism an action of botulinum toxin on parts of the soma membrane of the alpha-motoneuron is suggested.