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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↗
PubMed1985

The corneal reflex and the R2 component of the blink reflex.

A reflex contraction of the human orbicularis oculi muscles can be evoked by stimulation of either the supraorbital region ("blink reflex") or the cornea ("corneal reflex"). We found that the latency of the corneal reflex was longer, and the duration was longer than the R2 component of the blink reflex. The absolute refractory period of the R2 component of the blink reflex was longer after supraorbital than after corneal conditioning stimulation. When the R2 component of the blink reflex was habituated by repetitive stimuli, stimulation of the cornea still evoked a reflex, but supraorbital stimulation produced only a depressed R2 response. These findings suggest that the two reflexes do not have identical neural connections.

Adult↗
PubMed1997

Neural reflex regulation of arterial pressure in pathophysiological conditions: interplay among the baroreflex, the cardiopulmonary reflexes and the chemoreflex.

The maintenance of arterial pressure at levels adequate to perfuse the tissues is a basic requirement for the constancy of the internal environment and survival. The objective of the present review was to provide information about the basic reflex mechanisms that are responsible for the moment-to-moment regulation of the cardiovascular system. We demonstrate that this control is largely provided by the action of arterial and non-arterial reflexes that detect and correct changes in arterial pressure (baroreflex), blood volume or chemical composition (mechano- and chemosensitive cardiopulmonary reflexes), and changes in blood-gas composition (chemoreceptor reflex). The importance of the integration of these cardiovascular reflexes is well understood and it is clear that processing mainly occurs in the nucleus tractus solitarii, although the mechanism is poorly understood. There are several indications that the interactions of baroreflex, chemoreflex and Bezold-Jarisch reflex inputs, and the central nervous system control the activity of autonomic preganglionic neurons through parallel afferent and efferent pathways to achieve cardiovascular homeostasis. It is surprising that so little appears in the literature about the integration of these neural reflexes in cardiovascular function. Thus, our purpose was to review the interplay between peripheral neural reflex mechanisms of arterial blood pressure and blood volume regulation in physiological and pathophysiological states. Special emphasis is placed on the experimental model of arterial hypertension induced by N-nitro-L-arginine methyl ester (L-NAME) in which the interplay of these three reflexes is demonstrable.

Animals↗
PubMed1985

Cervicocollic reflex: its dynamic properties and interaction with vestibular reflexes.

Electromyographic activity of dorsal neck muscles elicited by sinusoidal rotations of the body and head was studied in decerebrate cats over a wide range of rotational frequencies and amplitudes. Rotation of the body with the head held fixed in space elicited a cervicocollic reflex (CCR) in the biventer cervicis, complexus, obliquus capitis inferior, rectus capitis major, and splenius muscles. As stimulus amplitude increased, CCR amplitude increased first rapidly and then more slowly, displaying two linear incremental sensitivity ranges. In contrast, the vestibulocollic reflex (VCR) elicited by whole body rotation had a minimum stimulus threshold below which no response was observed, whereas the vestibuloocular reflex (VOR) saturated at intermediate stimulus intensities. When stimulus frequency was varied, the CCR exhibited second-order dynamic behavior. At frequencies below 0.5 Hz, muscle EMG activation was in phase with peak platform angular deviation in the direction that stretched the muscle, and the gain measured as the percent modulation of EMG activity per degree of rotation remained constant. As frequency increased to 3-4 Hz, response phase advanced by 120 deg or more and gain increased with a slope approaching 40 dB/decade. The data were well-fitted by second-order transfer functions containing two zeros. Both the dynamic behavior of the CCR and its high sensitivity to small stimuli resemble the properties of muscle spindle primary afferents, suggesting that the latter may provide the major input responsible for the CCR. Dynamic properties and gains of the CCR and VCR were quite similar at frequencies between 0.2 and 3-4 Hz. Transfer functions of both reflexes contained two zeros whose time constants were correlated in a population of 11 cats, suggesting that reflex dynamics may be matched to the mechanical properties of each animal's head-neck system. Interaction of the CCR and VCR was studied under two conditions. When the head was driven by a servomotor while the body remained stationary, EMG activation by the two reflexes added linearly to produce a large response. When the body was rotated with the head allowed to counterrotate about the C1-C2 joint, the two reflexes combined linearly in an antagonistic fashion: the CCR acted to oppose head rotations produced by the VCR, thus preventing the ratio of head counterrotation to body rotation from exceeding 0.5. The data indicate that the CCR and VCR behave approximately linearly, both individually and in combination. Acting together, the two reflexes assist each other in preventing oscillation of the head on a stationary body.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1999

Comparison of the effects of diazepam on the fear-potentiated startle reflex and the fear-inhibited light reflex in man.

It has been shown previously that the amplitude of the acoustic startle reflex is enhanced, and the amplitude of the light reflex reduced, when subjects anticipate an aversive event, compared to periods when subjects are resting ('fear-potentiated startle reflex' and 'fear-inhibited light reflex'). We examined whether the anxiolytic diazepam would reverse the effects of threat on the startle and pupillary reflexes. Twelve male volunteers participated in three weekly sessions in which they received oral treatment with placebo, diazepam 5 mg and diazepam 10 mg, according to a balanced crossover double-blind design. One hour after ingestion of the treatments, miotic responses to light pulses and electromyographic responses of the orbicularis oculi muscle to sound pulses were elicited during alternating periods in which the threat of an electric shock (electrodes attached to the subject's wrist) was present (THREAT) and absent (SAFE). The THREAT condition was associated with a significant increase in the amplitude of the electromyographic (EMG) response, a significant reduction of the miotic response amplitude, and an increase in self-rated anxiety. Diazepam attenuated all these effects of THREAT. Diazepam did not affect the amplitude of the miotic response under the SAFE condition, but did suppress the EMG response under this condition. These results confirm the validity of the fear-potentiated startle reflex and fear-inhibited light reflex as laboratory models of human anxiety, and reveal some differences between the effects of diazepam on the two reflexes.

Acoustic Stimulation↗
PubMed1975

Genetically-associated variations in the development of reflex movements and synaptic junctions within an early reflex pathway of mouse spinal cord.

The embryonic development of reflex forelimb movements produced by cutaneous stimulation of the forepaw was examined in five inbred strains of the house mouse, Mus musculus. A quantitative electron microscopic study of synapse formation between the neurons that comprise the spinal cutaneous reflex arc was also carried out on specimens from three of the strains subjected to reflex testing. This investigation provides evidence that there is significant genetically-associated variability in the developmental timing of synapse formation within this disynaptic pathway and in the reflex behavior which it mediates. Specifically, it was found that C57BL/6J embryos had greater numbers of synaptic junctions in the reflex pathway at embryonic days 14-16, and they also showed reflex movements earlier than LP/J embryos. C57BL/6J embryos also showed a more rapid increase in the number of boutons during this embryonic period. CBA/CaJ embryos displayed a temporal pattern of development that differed from both C57BL/6J and LP/J. At E15, CBA/CaJ embryos were more similar to LP/J with regard to both reflex activity and synapse number, but by E16, CBA/CaJ values for both of these measures were more similar to C57BL/6J. On the basis of the data detailed in the text, we suggest that the strains differ in the following manner: C57BL/6J embryos develop boutons rapidly but appear to be relatively inefficient in the actual formation of synaptic junctions; CBA/CaJ embryos develop boutons at a slower rate than C57BL/6J but form synaptic junctions more efficiently; LP/J embryos develop boutons slowly and are also relatively inefficient in forming synaptic junctions. The genetic implications of--and some developmental processes which might be responsible for--the observed strain differences in the timing of synaptic development are discussed in the text. There was no detectable genetic variability of the basic sequence in which the neurons of the cutaneous reflex arc develop their synaptic connections. For all three strains examined, the data indicated that synaptic closure occurred in a retrograde sequence with respect to the direction that neurotransmission normally flows between the neurons of this pathway. This finding agrees with results obtained by other investigators from a number of diverse vertebrate species, and such a widespread lack of variability implies that a retrograde sequencing of synapse formation is involved in the development of specific neuronal connectivities.

Age Factors↗