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PubMed1999

A neurophysiological approach to brainstem reflexes. Blink reflex.

The blink reflex (BR) is a generalised phenomenon in mammals. Its teleological protective eye function is perhaps the reason why the BR can be provoked by a multitude of stimuli. As corneal and glabellar reflexes, BR has an inveterate use in the neurological exploration. Some of its physiopathological aspects were discussed more than 100 years ago, and soon half a century will have passed since the first electrophysiological study was published. This review focuses on the BR elicited by the electrical stimulation of the trigeminal supraorbital nerve, a controlled and reliable model in clinical neurophysiology. The electrically elicited BR is an exteroceptive-nociceptive reflex recorded on the orbicularis oculi muscle and formed by three components: the two principal ones, R1 and R2, of well-known characteristics, and a third, R3, of increasing interest, to which there is wide mention. The trigeminal afferent limb reaches the facial efferent one by means of a long and quite complex central pathway located at the brainstem bulbopontine level. The anatomical substrate and criteria of the rich topographical lesional semiology of the BR are established. The importance of the suprasegmental influences upon the reflex, coming mainly from the cerebral cortex and basal ganglia, as well as the impairment caused by their damage, will be emphasised. Special attention is paid to the relationship between the reflex and the dopaminergic system, and the consequences of its derangement. The methods of habituation and suppression-recovery of the BR are extensively and critically reviewed. These methods measure its excitability and serve in practice for the pathophysiological study of numerous diseases. The relationship of the BR with the spontaneous blinking is considered, and the existence of a primary inhibitory reflex on levator palpebrae muscles, previous to the active reflex response of the orbicularis, is proposed. The electrophysiological characteristics of the glabellar reflex, the corneal reflex, the acoustic, photic and somatosensory provoked BR, the ontogeny, and some of the common factors influencing the reflex, such as sleep, are also discussed. The strategic position of the neural structures of the BR, in an area involved in the gating of the various sensory-motor systems and the relative ease to its evaluation with common methodology used in clinical neurophysiology, makes the BR an essential tool for the diagnosis and pathophysiological insight into an important number of human neurological disorders.

Animals↗
PubMed1979

The Bezold reflex: a special case of the left ventricular mechanoreceptor reflex.

Our previous finding that increasing myocardial contractility caused reflex systemic hypotension, the left ventricular (LV) mechanoreceptor reflex, suggested that the classical Bezold reflex (systemic hypotension and bradycardia after intracoronary administration of veratrum alkaloids) may be initiated by these same LV mechanoreceptors. In our working LV preparation with the coronary and systemic circulations isolated and perfused separately, intracoronary injection of veratrum alkaloids, like that of catecholamines or ouabain, had a positive inotropic effect which produced the hypotensive response typical of the LV mechanoreceptor reflex. To test directly if veratridine's positive inotropic effect initiates the Bezold reflex, verapamil, which blocks the slow Ca(2+) channels of myocardial cells but leaves intracardiac nerves unaffected, was injected by the intracoronary route to prevent the increased contractility from intracoronary injection of veratridine which also abolished the reflex hypotension, demonstrating conclusively that increasing myocardial contractility and thereby activating LV mechanoreceptors but not chemoreceptors initiates the Bezold reflex. Contrariwise, decreasing contractility or cardiac asystole by administration of tetrodotoxin, verapamil, or EDTA resulted in an increase in the systemic resistance, indicating that changes in the magnitude of the stimulus initiating the LV mechanoreceptor reflex (i.e., changes in myocardial contractility) lead to directionally opposite changes in peripheral resistance, as in the sino-aortic mechanoreflexes. Thus, it is concluded that the Bezold reflex is a special case of the LV mechanoreceptor reflex. The latter, by means of feedback mechanisms, functions normally by continuously matching the peripheral resistance to the LV contractile state so as to maintain the arterial pressure constant, thereby playing an important role in blood pressure regulation.

Animals↗
PubMed2006

Reflex seizures and reflex epilepsy.

Reflex seizures are evoked by a specific afferent stimulus or by activity of the patient and are divided into those characterized by generalized seizures and those principally manifested by focal seizures. Reflex epilepsies are syndromes in which all epileptic seizures are precipitated by sensory stimuli. Three categories of reflex seizures encountered clinically include pure reflex epilepsies, reflex seizures that occur in generalized or focal epilepsy syndromes that are also associated with spontaneous seizures, and isolated reflex seizures occurring in situations that do not necessarily require a diagnosis of epilepsy. Generalized reflex seizures are precipitated by visual light stimulation, thinking, and decision making. These seizures usually respond to valproate treatment. Numerous triggers can induce focal reflex seizures. The triggers include reading, writing, other language functions, startle, somatosensory stimulation, proprioception, auditory stimuli, immersion in hot water, eating, and vestibular stimulation. The classification and characteristics of reflex seizures and epilepsies are described in this review. Findings on EEG and advanced neuroimaging in the reflex seizures and epilepsies, treatment and preventive options, and animal models and mechanisms are also discussed.

Animals↗
PubMed2000

Leg muscle reflexes mediated by cutaneous A-beta fibres are normal during gait in reflex sympathetic dystrophy.

OBJECTIVES: Reflex sympathetic dystrophy (RSD) is, from the onset, characterized by various neurological deficits such as an alteration of sensation and a decrease in muscle strength. We investigated if afferent A-beta fibre-mediated reflexes are changed in lower extremities affected by acute RSD. METHODS: The involvement of these fibres was determined by analyzing reflex responses from the tibialis anterior (TA) and biceps femoris (BF) muscles after electrical stimulation of the sural nerve. The reflexes were studied during walking on a treadmill to investigate whether the abnormalities in gait of the patients were related either to abnormal amplitudes or deficient phase-dependent modulation of reflexes. In 5 patients with acute RSD of the leg and 5 healthy volunteers these reflex responses were determined during the early and late swing phase of the step cycle. RESULTS: No significant difference was found between the RSD and the volunteers. During early swing the mean amplitude of the facilitatory P2 responses in BF and TA increased as a function of stimulus intensity (1.5, 2 and 2.5 times the perception threshold) in both groups. At end swing the same stimuli induced suppressive responses in TA. This phase-dependent reflex reversal from facilitation in early swing to suppression in late swing occurred equally in both groups. CONCLUSIONS: In the acute phase of RSD of the lower extremity there is no evidence for abnormal A-beta fibre-mediated reflexes or for defective regulation of such reflexes. This finding has implications for both the theory on RSD pathophysiology and RSD models, which are based on abnormal functioning of A-beta fibres.

Adult↗
PubMed1972

Orbicularis oculi reflex in the Wallenberg syndrome: alteration of the late reflex by lesions of the spinal tract and nucleus of the trigeminal nerve.

The orbicularis oculi reflex was studied in nine cases with lateral medullary lesions. Diagnosis of the Wallenberg syndrome was made clinically in seven cases and at necropsy in another. The clinical features of one other case were closely allied to but not typical of this syndrome. An afferent delay of the late reflex on the side of the lesion in the presence of a normal early reflex was seen in all but two cases. In one of the latter, the late reflex was normal and in the other, a comatose patient, the late reflex was totally absent. It was concluded that the neurones of the first order responsible for the bilateral late reflex on unilateral stimulation terminate in the ipsilateral spinal nucleus of the trigeminal nerve without significant crossing over to the same structure on the other side. An afferent delay of the late reflex in the presence of a normal or nearly normal early reflex is consistent with a lateral medullary lesion implicating the spinal tract and nucleus. The Wallenberg syndrome is a common clinical entity showing this abnormality of the orbicularis oculi reflex.

Adult↗
PubMed1989

Long latency cutaneous reflex effect on H-reflex recovery in hemiplegics and paraplegics: a longitudinal study for the assessment of motor function.

H-reflex recovery by twin pulses was recorded serially in 10 paraplegics for 5 months and in 23 hemiplegics for 2 months after the lesion. Fifty-one normal subjects acted as controls. The effect of cutaneous tactile stimulation was also studied simultaneously by applying electrical stimuli synchronized with twin pulses to the skin over the lateral border of small toe. In paraplegics, the H-reflex recovery curves recorded serially showed a highly depressed pattern during the first two weeks, an almost normal pattern during the second and third months and a significantly elevated pattern during the fourth and fifth months. Whereas cutaneous stimulation in control subjects produced a highly significant late inhibition of H-reflex recovery between 600 ms and 600 ms, in paraplegics it failed to produce any significant effect, except in two, who besides having a normal H-reflex recovery curve even during the first week, showed a substantial amount of cutaneous inhibition of H-reflex recovery, 4 months after the lesion. A highly depressed pattern of H-reflex recovery was observed on the affected side of the majority of hemiplegics during the first week after the lesion, many of them showing similar pattern on the "unaffected side" also. The serial study showed very good improvement in all hemiplegics both in terms of H-reflex recovery pattern and the amount of cutaneous inhibition. The observations in present study suggest preservation and/or restoration of supraspinal influences in many hemiplegics and in at least two paraplegics. The study also shows that a serial recording of H-reflex recovery curve and the amount of cutaneous reflex effect on it, is a very sensitive method of assessing the supraspinal influences on the spinal motoneurones and so can be of immense help in the diagnosis and prognosis in hemiplegics and paraplegics.

Female↗
PubMed2003

Reflex and non-reflex torque responses to stretch of the human knee extensors.

Reflex responses to unexpected stretches are well documented for selected muscles in both animal and human. Moreover, investigations of their possible functional significance have revealed that stretch reflexes can contribute substantially to the overall stiffness of a joint. In the lower extremity only the muscles spanning the human ankle joint have been investigated in the past. This study implemented a unique hydraulic actuator to study the contributions of the knee extensor stretch reflex to the overall knee joint torque. The quadriceps muscles were stretched at various background torques, produced either voluntarily or by electrical stimulation, and thus the purely reflex mediated torque could be calculated. The stretch had a velocity of 67 degrees /s and an amplitude of 20 degrees. A reflex response as measured by electromyography (EMG) was observed in all knee extensors at latencies of 26 - 36 ms. Both phasic and tonic EMG stretch responses increased with increasing background torques. Lines of best fit produced correlation coefficients of 0.59 - 0.78. This study is the first to examine the reflex contribution of the knee extensors to the total torque at background torques of 0 - 90% MVC. The contribution of the reflex mediated torque is initially low and peaked at background torques of 20 - 40% MVC. In terms of the total torque the reflex contributed 16 - 52% across all levels of background torque. It is concluded that during medium background torque levels such as those obtained during walking, the stretch reflex of the quadriceps muscle group contributes substantially to the total torque around the knee joint.

Adult↗
PubMed1980

Labyrinth and neck reflex modification of the tonic vibration reflex in the decerebrate cat.

The interaction between tonic labyrinth or neck reflexes and the tonic vibration reflex acting on the medial head of triceps in the decerebrate cat is described. Medial triceps was isotonically loaded and reflex actions were measured as changes in muscle length. Natural stimulation of the receptors giving rise to tonic labyrinth or neck reflexes can either enhance or diminish the size of a pre-existing tonic vibration reflex. It is also shown that descending activity from either the labyrinth or neck reflex systems can completely suppress the tonic vibration reflex, whereas the tonic vibration reflex was never observed to suppress an established labyrinth or neck reflex.

Animals↗
PubMed1994

The effect of repeated prepulse-blink reflex trials on blink reflex modulation at short lead intervals.

The amplitude of a blink reflex is inhibited if the reflex eliciting stimulus is preceded by a short prestimulus (e.g. < 250 ms). If the prestimulus duration is longer than 1 s, blink reflex amplitude is facilitated. The present study investigated the effect of repeated presentations of prestimulus-blink eliciting stimulus pairings on blink reflex modulation. Subjects in Experiment 1 (N = 59) were presented with a sequence of 12 blocks of 7 trials. Within each block, one trial was a blink stimulus alone, whereas the blink stimulus was preceded by a prestimulus on the other trials. Prestimulus intervals were 30, 60, 120, 240, 500 and 2000 ms. Prestimuli were presented continuously throughout the prepulse interval. The amount of reflex magnitude inhibition at the 60, 120, 240 and 500 ms lead intervals and reflex latency shortening at 30 and 60 ms decreased over blocks. The amount of reflex facilitation at a lead interval of 2000 ms was not reduced. In Experiment 2 (N = 22), two groups of subjects were presented with a sequence of blink stimulus alone presentations and prestimulus-blink stimulus pairings. The prestimulus lasted for 120 ms in one group and for 200 ms in the second. Blink reflex magnitude inhibition declined in both groups over blocks of trials. However, the groups also differed in responding on the blink stimulus alone control trials. Experiment 3 (N = 24) employed the same design as did Experiment 2. No difference in control responding was found. Similar to Experiment 2, blink inhibition decreased over repeated trials in both groups. The present results indicate that prepulse inhibition reflects a process which is affected by repeated presentation of prestimulus-reflex stimulus pairings. However, the conclusion that the reduction of prestimulus effects reflects habituation seems to be premature.

Adolescent↗
PubMed1996

Subthreshold stimulation of a serotonin 5-HT3 reflex attenuates cardiovascular reflexes.

Volume-sensitive and chemosensitive cardiopulmonary reflexes modulate volume homeostasis via renal sympathetic nerve activity (RSNA). Blunting of volume-sensitive cardiopulmonary reflexes is associated with volume retention, e.g., in hypertension, whereas the role of chemosensitive cardiopulmonary reflexes is largely unknown. To elucidate the possible role of chemosensitive cardiopulmonary reflexes in control of volume homeostasis, we investigated whether subthreshold stimulation of 5-HT3 receptors modulates the control of RSNA by volume-sensitive cardiopulmonary reflexes or the arterial baroreceptor reflex in rats. Phenyl biguanide (PBG) was infused intravenously to stimulate 5-HT3 receptors. Higher doses of PBG lowered RSNA, but a dose of 6 micrograms/min, given as a background infusion throughout the experiment, did not change arterial pressure, heart rate (HR), or RSNA. Ten minutes after beginning the 6 micrograms/min PBG infusion, a 15-min volume expansion (0.9% saline, 5 or 10% body weight) was started to stimulate volume-sensitive cardiopulmonary reflexes. In separate experiments, 5-min ramp infusions of methoxamine and nitroglycerin to stimulate the arterial baroreceptor reflex (evaluated by a 4-parameter logistic regression) were performed 15 min after beginning the PBG background infusion (6 micrograms/min). During PBG infusion, the RSNA responses to volume expansions were significantly impaired (5% body weight: PBG -6 +/- 6%, n = 7 vs. control -39 +/- 9%, n = 6, P < 0.001; 10% body weight: PBG -33 +/- 6%, n = 8 vs. control -52 +/- 5%, n = 7, P < 0.05). The 5-HT3 receptor antagonist odansetron (GR-38032F) abolished these effects of PBG. The maximum HR gain of the arterial baroreceptor reflex was impaired but the arterial baroreceptor control of RSNA was unaffected by PBG background infusion. We conclude that 5-HT3-serotonergic cardiopulmonary chemoreceptors blunt the RSNA decrease to volume loading. This mechanism may facilitate volume retention when cardiac serotonin is increased.

Animals↗
PubMed1996

Preliminary clinical observations on a new trigeminal reflex: the trigemino-cervical reflex.

Short latency trigemino-cervical reflexes can be recorded from sternocleidomastoid muscle after stimulation of the infraorbital branch of the trigeminal nerve. We studied the trigemino-cervical reflexes and the conventional blink reflex in three patients with an isolated lesion in the medulla oblongata, eight patients with multiple sclerosis, and two patients with supratentorial ischemic lesion. The trigemino-cervical response was abnormal in the patients with an isolated lesion in the medulla oblongata and in all multiple sclerosis patients, whereas both components of the blink reflex were preserved in the patients with a lesion in the medulla oblongata and in half of the patients with multiple sclerosis. The trigemino-cervical reflex was preserved in patients with supratentorial lesions, whereas the late component of the blink reflex was abnormal. These findings suggest that central pathways generating the trigemino-cervical reflex are confined to the medulla oblongata and that they are independent from those generating the long latency (R2) component of the blink reflex. The trigemino-cervical reflex may help in disclosing and localizing brainstem lesions.

Adult↗
PubMed1990

Effects of flexor reflex afferent stimulation on the soleus H reflex in patients with a complete spinal cord lesion: evidence for presynaptic inhibition of Ia transmission.

The effects of electrically stimulating the Flexor Reflex Afferent (FRA) on the soleus H reflexes were investigated in 34 paraplegic patients having a clinically complete spinal cord lesion. Conditioning stimuli (5-50 mA) were applied to the ipsilateral or contralateral sural nerve. The conditioning-test interval ranged from 20 to 1000 ms. A late ipsilateral flexor reflex (EMG) was found in all patients. A late contralateral extension reflex was sporadically observed in only 3 patients. The excitability curves usually showed two phases of ipsilateral H reflex inhibition and contralateral H reflex facilitation, one between 50 and 130 ms and the other after over 200 ms. These intervals correspond to early and late flexion reflexes. With high intensity stimulation the early and late ipsilateral inhibition fused. An early low threshold ipsilateral facilitation occurred in 9 patients. The contralateral late facilitation was followed by prolonged inhibition in 10 patients. Changes in presynaptic inhibition were assessed by measuring the heteronymous monosynaptic Ia facilitation from quadriceps to soleus. For methodological reasons, it was only possible to investigate the effect of contralateral conditioning volleys which was performed in 5 patients. A significant and regular reduction of the heteronymous Ia facilitation was found in 4 patients. The reduction is taken to indicate that the FRA evokes presynaptic inhibition of Ia transmission to alpha motoneurones. Presynaptic inhibition was also indicated by the enhancement of a vibratory stimulus induced inhibition in 2 subjects. These results are consistent with the hypothesis that the reflex organization in patients with a spinal cord section is similar to that of the acute spinal cat injected with DOPA.

Adolescent↗
PubMed1957

Reflex depression in rhythmically active monosynaptic reflex pathways.

A study has been made of the depression that occurs when a monosynaptic reflex pathway is subjected to repetitive stimulation. Reflex depression has a dual origin. High frequency or early depression is postsynaptic in origin and results from subnormality in the motoneurons. Low frequency, late, or enduring depression is presynaptic in origin. The conditioning volley-test volley technique and the frequency-mean monosynaptic reflex amplitude relation yield similar information concerning reflex depression. Each method has its advantages and for some purposes one or the other of the methods necessarily must be employed. The results of a variety of experiments are consistent with the proposition that reflex depression in the monosynaptic reflex pathway originates by action in the group IA afferent fibers of muscle origin that are responsible for monosynaptic reflex transmission. Depression is present at a frequency of 0.1 per second (6 per minute) and absent at a frequency of 0.05 per second (3 per minute). Thus it is impractical for most purposes to employ repetition rates that satisfy the requirement for designation as "single shock" stimulations. The temporal course of enduring depression has been determined. It is identical with that for a number of other phenomena observable in monosynaptic reflex pathways, which suggests a common origin. The mechanism of low frequency or enduring depression is discussed in the light of this suggestion.

Depression↗