Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “REFLEX”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,729 records · Page 96Linked to original sources
PubMed2004

Effects of arousal and natural baroreceptor activation on the human muscle stretch reflex.

The nociceptive flexion reflex is inhibited during systole; this inhibition may be due to increased baroreceptor stimulation. It is yet to be determined whether other spinal reflexes are similarly modulated across the cardiac cycle. There is also evidence that stretch and tendon reflexes are facilitated by increased arousal. This study investigated the effects of phase of the cardiac cycle and arousal on the muscle stretch reflex components M1, M2, and M3. Stretch reflexes were elicited in leg muscles at six intervals across the cardiac cycle during rest, number repetition, and mental arithmetic. Mental arithmetic provoked increased cardiovascular arousal and facilitated both M1 and M2 compared to rest and number repetition. The stretch reflex did not vary with the phase of the cardiac cycle. While the stretch reflex is susceptible to arousal, natural baroreceptor-mediated modulation across the cardiac cycle may be specific to nociception.

Adult↗
PubMed1987

The contributions of mu-, delta- and kappa-opioid receptors to the actions of endogenous opioids on spinal reflexes in the rabbit.

Spinal reflexes in the rabbit are suppressed tonically by endogenous opioids. The contributions made to this suppression by mu-, delta- and kappa-opioid receptors have been investigated by studying the actions of a range of opioid antagonists and agonists on reflexes evoked by sural nerve stimulation in the ankle extensor gastrocnemius medialis (g.m.), and in the knee flexor semitendinosus (s.t.). When given at a total dose of 88.5 micrograms kg-1 i.v., either of the universal opioid receptor antagonists (-)-naloxone and (-)-quadazocine enhanced the g.m. response to more than 7 times the pre-drug control values, and the s.t. reflex to 1.5 times controls. The effects of quadazocine were stereospecific. The selective delta antagonist ICI 174864 (3.5 mg kg-1 i.v. total) also augmented the g.m. reflex but only to twice pre-drug controls. The mu-agonists fentanyl (100 micrograms kg-1) and morphine (50 mg kg-1) suppressed both g.m. and s.t. reflex responses to less than half control levels by a naloxone-reversible mechanism. The kappa-agonists bremazocine (50 micrograms kg-1 total), tifluadom (100 micrograms kg-1), ethylketocyclazocine (200 micrograms kg-1) and U50488H (1 mg kg-1) potentiated the g.m. reflex and had variable effects on the s.t. response. Naloxone usually added to the facilitatory actions of these drugs. kappa-Opioid receptor agonists also caused a profound, naloxone-reversible depression of arterial blood pressure. It may be concluded that the endogenous opioid-mediated suppression of spinal reflexes in the rabbit is mediated mainly, if not exclusively, through mu-receptors. There are no known endogenous ligands which are specific for the mu-receptor, so in the present case it seems that selectivity is determined by the receptor population rather than by the ligand.

Animals↗
PubMed1988

Effects of clonidine and yohimbine on a C-fibre-evoked blood pressure reflex in the rat.

1. The involvement of alpha 2-adrenoceptors in a capsaicin-induced depressor reflex in the rat has been investigated. 2. The reflex fall in blood pressure following an intra-arterial injection of capsaicin was partially blocked by an intrathecal infusion of clonidine (1 microgram) at the spinal cord level L4-L5, an effect which was abolished by the prior intrathecal infusion of yohimbine (5 micrograms). 3. Clonidine (1 microgram) given intracisternally blocked the depressor reflex almost completely; however, it also produced a gradual, prolonged fall in mean carotid pressure. 4. Yohimbine (20 micrograms) given intracisternally did not change mean blood pressure but had a dual effect on the depressor reflex in response to the capsaicin injection: a short period of enhanced reflex response was followed by a long lasting inhibition of the response. 5. It was concluded that alpha 2-adrenoceptors in the spinal cord inhibit the capsaicin-evoked depressor reflex and that pre- and postsynaptic alpha 2-adrenoceptors in the brain stem modulate this reflex.

Animals↗
PubMed1993

5-HT4 receptor mediated facilitation of the emptying phase of the peristaltic reflex in the guinea-pig isolated ileum.

1. The influence of 5-hydroxytryptamine (5-HT) receptor agonists and antagonists on the emptying phase (circular muscle contraction) of the peristaltic reflex was investigated in the guinea-pig isolated ileum. 2. The effect of drug application to the serosal surface was measured as the changes in threshold pressure required to trigger the peristaltic reflex and the interval between the peristaltic strokes. A facilitation or inhibition of peristalsis was defined as a reduction or increase in threshold pressure respectively. 3. Peristalsis was not modified by the inclusion of methysergide (1 microM) and/or ondansetron (2 microM) in the bathing medium. 5-HT (0.1-1.0 microM) caused a facilitation of the peristaltic reflex; the response curve to 5-HT was not altered by the presence of methysergide (1 microM) and ondansetron (2 microM). 4. In the presence of methysergide (1 microM) plus ondansetron (2 microM), 5-HT (7.36 +/- 0.06), 5-methoxytryptamine (7.01 +/- 0.17), 5-carboxamidotryptamine (5.43 +/- 0.06), renzapride (6.09 +/- 0.17), (S)-zacopride (5.99 +/- 0.11), (R)-zacopride (5.61 +/- 0.13) and metoclopramide (4.8 +/- 0.65) caused a concentration-related facilitation of the peristaltic reflex, the pEC50 values (mean +/- s.e.mean) being shown in parentheses. 2-Methyl-5-HT was ineffective up to 10 microM. 5. The administration of SDZ 205-557 (1 microM) alone failed to modify the peristaltic reflex, but caused a parallel dextral shift in the concentration-effect curve to 5-HT (apparent pKB 7.38 +/- 0.30). It failed to modify the effect of acetylcholine to enhance the peristaltic reflex. 6. It is concluded that the rank order of potency of the 5-HT agonists from the indole and substituted benzamide series to facilitate the emptying phase of the peristaltic reflex in the guinea-pig ileum closely correlates with their published actions as 5-HT4 agonists in other systems. An agonist action on the 5-HT4 receptor is also supported by the potency of the 5-HT3/5-HT4 antagonist SDZ 205-557 (but not the 5-HT3 antagonist ondansetron) to inhibit the effects of 5-HT.

4-Aminobenzoic Acid↗
PubMed2005

Repetitive painful stimulation produces an expansion of withdrawal reflex receptive fields in humans.

The aims of the present study were to investigate whether temporal summation of the nociceptive withdrawal reflex depends on the stimulation site on the sole of the human foot, and to characterize the reflex receptive fields (RRF) of lower limb muscles to repetitive stimulation. The cutaneous RRFs were assessed in 15 subjects in sitting position by recording the EMG from five lower leg muscles and the kinematic responses (ankle, knee, and hip joints) to repetitive painful electrical stimulation. The stimulus consisted of a series of five stimuli (frequency: 3 Hz) delivered randomly at 10 different sites on the sole of the foot. The size of the reflexes increased generally between the first and the second stimulus, however, the increment depended on the stimulation site. In tibialis anterior, the RRF covered the distal sole of the foot and gradually expanded during the stimulus train. No expansion toward the heel area was detected. In soleus, the reflexes were facilitated after the second stimulus at all sites and remained in this state until the last stimulus. In vastus lateralis, biceps femoris, and iliopsoas a gradual expansion of the RRF was seen, resulting in RRFs covering the lateral, distal foot, and part of the proximal foot (iliopsoas). Knee and hip flexion were evoked at all sites. Ankle dorsiflexion was evoked at the distal foot, while ankle plantarflexion was evoked at the heel. The enlargement of the RRF reflects spinal temporal summation leading to gradually stronger reflex responses. The degree of temporal summation was dependent on stimulation site. The facilitation of the withdrawal reflex responses due to repetitive stimulation might have potential applications in the rehabilitation engineering field, where these reflexes could be used to assist gait of patients with central nervous system injuries.

Adult↗
PubMed1992

Stretch reflex of quadriceps femoris and its relation to rigidity in Parkinson's disease.

Much evidence suggests that parkinsonian rigidity is due to hyperactivity of a reflex arc. While tendon jerk and H reflex are not modified in Parkinson's disease (PD), the long-latency component of stretch reflex (LLR) shows an increased size in PD. It has been proposed that this modification could account for rigidity. We studied in 14 PD patients and 8 normal subjects the stretch reflex of the quadriceps femoris. The muscle was stretched by a torque motor in two experimental sets: at rest and with voluntary background activity. Latency, duration and size of the reflex were compared in two groups; correlation between size of the reflex and rigidity was investigated. A lower threshold for the reflex was found in PD patients in trials at rest, and LLR showed increased size and duration in trials with background activity. No clear relationships between these data and rigidity were demonstrated.

Adult↗
PubMed1993

The position of the tongue during rooting reflexes elicited in newborn infants before the first suckle.

A common breast-feeding problem is when the infant "places its tongue in its palate" and has difficulties in attaching to its mother's nipple. The aim of this study was to document the position of the tongue in the mouth cavity during rooting reflexes elicited in newborn infants before the first suckle. Eleven healthy, full-term infants were videotaped 101 +/- 31 min after birth during an evoked distinct rooting reflex before the first suckle. The videotaped rooting reflex was analyzed in detail concerning the degree of turning of the head, mouth opening and position of the tongue, in pictures that were "frozen" at specific intervals. "Licking movements" preceded and followed the rooting reflex in the alert infants. In 10 of the 11 infants the tongue was placed in the bottom of the mouth cavity during a distinct rooting reflex (p = < 0.05). It is suggested that forcing the infant to the breast might abolish the rooting reflex and disturb placement of the tongue. A healthy infant should have the opportunity of showing hunger and optimal reflexes, and attach to its mother's nipple by itself.

Breast Feeding↗
PubMed1981

Reflex cardiovascular responses to graded stimulations of low- and high-threshold afferents in the carotid sinus and aortic nerves in the cat.

Reflex responses to electrical stimulation of low-threshold and high-threshold afferents in the aortic and carotid sinus nerves were investigated in chloralose-anesthetized cats. Changes in blood pressure, heart rate and muscle resistance were recorded. Low-threshold stimulation induced depressor responses of moderate magnitude. When stimulation intensity was increased to engage also the high threshold aortic nerve afferents a more pronounced reflex response was seen even with stimulation frequencies less than 10 Hz. Furthermore, stimulation of low- and high-threshold aortic nerve afferents induced different reflex patterns. For a given fall in blood pressure, the low-threshold afferents induced a greater reflex decrease in muscle vascular resistance compared with the high-threshold afferents, which reduced heart rate more. The effects seen at low frequency stimulation of high-threshold aortic nerve afferents were interpreted to reflect activation of the non-medullated baroreceptor afferents, while the depressor reflexes at low-threshold stimulation were induced by medullated baroreceptor afferents. Also the reflex effects of continuous and intermittent stimulation patterns of the various afferents were compared. At the same number of imp/s an intermittent stimulation of the low-threshold afferents induced greater reflex changes in blood pressure and muscle vascular resistance but smaller changes in heart rate. No such difference was observed when high-threshold afferents were similarly stimulated.

Animals↗
PubMed1983

Comparison of electrical thresholds of intradental nerves and jaw-opening reflex in the cat.

In experimental animals the jaw-opening reflex in response to stimulation of pulp nerves has been used as a nociceptive reflex. However, there seems to be only scanty information about the amount and types of pulp nerve fibres that mediate the reflex. In the present work on 8 anesthetized cats electrical thresholds of single functional pulp nerve units were compared to the thresholds of jaw-opening reflex. Monopolar cathodal current pulses were applied to each canine tooth. Reflex responses of the digastric muscle were recorded. The inferior alveolar nerve of the left side in 3 cats was exposed for nerve dissection and responses of pulp nerve units coming from the lower left canine tooth were recorded. The mean threshold of the jaw-opening reflex with 10 ms pulses was 5.9 +/- 3.0 (SD) microA. Below or at the level only part of the fast conducting pulp nerve units could be activated. Thresholds of A- (n = 32) and C- (n = 24) fibres were 9.9 +/- 5.7 and 37.4 +/- 14.5 (SD) microA respectively. Nerves of the periodontal tissues (20 units recorded) were not activated with current pulses of up to 200 microA applied to the tooth. Consequently, at threshold level the jaw-opening reflex in response to the present type of stimulation is mediated by the fast conducting intradental nerve units.

Animals↗
PubMed1979

A clinical study on the detection of strabismus, anisometropia or ametropia of children by simultaneous photography of the corneal and the fundus reflexes.

Twenty two strabismus and 106 straight eyed patients with anatomically normal eyes were first photographed with a conventional camera equipped with a weak 100 mm teleobjective and coaxial flashlight and then examined clinically. The possibility of detecting strabismus, anisometropias and ametropias in the photographs by noting the localisation of the corneal reflexes and examining the appearance and lightness of the fundus reflexes and their possible asymmetry were tested in a double blind study. Even small angled strabismus cases could be found because of the asymmetrical localisation of the corneal reflexes. In 18 of the 22 strabismus cases (82%) there was asymmetrical lightness of the fundus reflexes and the fundus reflex of the deviating eye was lighter than that of the fixating eye. All the straight eyed anisometropias of 3.0 diopters or more (five cases) were observed in the photographs because of the asymmetrical appearance of the fundus reflexes. In straight eyed anisometropias of under 3.0 diopters, the fundus reflexes were symmetrical in 90 cases and asymmetrical in 11 cases (11%). Only three out of eight hyperopias of fomr +4.5 to +6.0 diopters were found because of the light crescent in the low part of the pupil. All myopias of over -4.0 diopters (14 cases) were observed because of the light crescent appearance in the upper part of the pupil. No pupillary crescents appeared with refractions of less than -1.75 diopters myopia or less than +4.5 diopters hyperopia; 172 eyes came within this range. Even a technician can perform, without premedication, the method tested here for rapid and simple screening to detect strabismus and straight eyed anisometropias of 3.0 diopters or more in small children or other patients who do not co-operate well in normal clinical examination. Over -4.0 diopters myopias can also be found. The method was rather unreliable for finding hyperopias, presumably because no cycloplegic drops were used.

Astigmatism↗
PubMed1984

The pinna reflex and its inhibition by clonidine: relationship to sedation and quantitation of central alpha 2-antagonist potency.

The relationship between sedation and pinna reflex inhibition has been measured for a range of centrally acting drugs. Ability to abolish the pinna reflex was not related to sedative activity as assessed by a behavioural method. Thus, at equisedative doses, diazepam, haloperidol, mianserin, prazosin and indoramin failed to abolish the pinna reflex while phenobarbitone and chlorpromazine caused partial- and clonidine complete-inhibition. At the ED50 for pinna reflex inhibition, guanabenz and guanfacine were significantly less sedative than clonidine. Mepyramine, yohimbine, RS-21361, idazoxan and phenylephrine produced little or no sedation and did not inhibit the reflex. When these agents (except for guanabenz and guanfacine) were tested for their ability to prevent clonidine-induced pinna reflex inhibition, all except the drugs with alpha 2-adrenoceptor antagonist activity were inactive. The potency order of the active agents was idazoxan greater than yohimbine greater than RS-21361 = mianserin. Antagonism of clonidine-induced pinna reflex inhibition may therefore prove to be a useful quantitative model for assessing the central potency of alpha 2-adrenoceptor antagonists.

Adrenergic alpha-Antagonists↗
PubMed1989

Reflex actions of selective stimulation of sural nerve C fibres in the rabbit.

Selective electrical stimulation of the non-myelinated C fibres of the sural nerve in the decerebrated, spinalized rabbit evoked long-latency (76-160 ms), long-lasting (greater than 100 ms) reflex responses in the ipsilateral ankle extensor gastrocnemius medialis (GM). Activation of the same fibres elicited little or no response from the ipsilateral knee flexor semitendinosus (ST). Reflex responses were evoked in both GM and ST muscle nerves by stimulation of the A beta afferents of the sural nerve. The A beta-elicited reflex in GM was enhanced, and that in ST depressed by prior activation of sural nerve C fibres. Strychnine, but not picrotoxin or mecamylamine, blocked C fibre-induced inhibition of the flexor reflex. Pinching the heel with serrated forceps produced an immediate reflex discharge in GM motoneurones, whereas ST responded upon termination of the stimulus. Pinching the second toe evoked reflex activity in ST but not in GM. After strychnine (0.5 mg kg-1), both sets of motoneurones responded simultaneously to stimulation of either the heel or the toe. These data show that sural and other afferent fibres from the heel excite ipsilateral GM motoneurones and inhibit ST reflex responses. One interpretation of these findings is that fine sural afferents activate parallel inhibitory and excitatory pathways, of which the former is sensitive to strychnine and therefore probably mediated by glycine.

Afferent Pathways↗
PubMed1998

The effects of skin brushing on H reflex amplitude in normal human subjects.

Experiments were performed on twenty-two neurologically normal subjects in order to investigate the effects of skin brushing on H reflex excitability in triceps surae. H reflex amplitude was observed to decrease during brushing of a 2 cm x 10 cm area of skin overlying triceps surae, returning to control levels when brushing ceased. Alterations in the duration of the brushing period did not affect the magnitude of the H reflex inhibition, although increased frequency of brush strokes per minute slightly increased the amount of inhibition observed. Brushing of smaller skin areas overlying the muscle only sometimes resulted in H reflex inhibition. Brushing over other skin areas of the lower limb produced only slight effects on triceps surae H reflex amplitude. Removal of cutaneous input from the skin overlying triceps surae abolished any effects of brushing in this area on H reflex amplitude. These results demonstrate an inhibitory effect of brushing on H reflex excitability in normal subjects. If such results are confirmed in subjects with neurological deficit, they could have implications for the use of brushing in clinical practice.

Adult↗
PubMed2004

Glutamate and tachykinin receptors in central sensitization of withdrawal reflexes in the decerebrated rabbit.

This study assessed the involvement of NMDA and group I metabotropic glutamate receptors, and tachykinin NK1 and NK3 receptors, in central sensitization of withdrawal reflexes in the decerebrated rabbit. Reflexes evoked in the ankle flexor tibialis anterior and the knee flexor semitendinosus by electrical stimulation at the base of the toes were enhanced for 29-63 min after application of 20% mustard oil to the tips of the toes. Selective antagonists of mGlu1, mGlu5, NMDA and NR2B-subunit-containing NMDA glutamate receptors, as well as NK1, and NK3 receptors, and a non-selective blocker of all tachykinin receptors, were assessed for their effects on the magnitude and duration of the increase in reflexes induced by mustard oil. Dizocilpine, an antagonist of all NMDA receptors (1 mg intrathecal) abolished facilitation of tibialis anterior reflexes and significantly reduced the magnitude and duration of increase of the semitendinosus response. The NR2B-subtype selective antagonist CP-101,606 decreased the magnitude of facilitation of both reflexes but had no effect on duration of enhancement. Selective antagonists for the mGlu1 (CPCCOEt, 1-3 mg intrathecal), mGlu5 (MPEP, 0.2-1 mg intrathecal), NK1 (L-733,060, 0.3 mg intrathecal) or NK3 (SR 142,801, 1 mg kg(-1) i.v.) receptors had no effect on the amplitude or duration of sensitization. However, the non-selective tachykinin receptor blocker ZD-6021 (0.3 mg intrathecal) reduced the amplitude but not the duration of sensitization in the flexor reflexes. Combination of ZD-6021 with CP-101,606 (doses as above) decreased both aspects of the sensitization response. Dizocilpine reduced reflexes evoked from the heel per se, and dizocilpine, CP-101,606 and ZD-6021 reduced arterial blood pressure. Otherwise the drugs used had no effects on baseline variables. The present data confirm the importance of NMDA receptors as a critical part of the process of central sensitization, provide no evidence for a role of metabotropic glutamate receptors, and show that simultaneous blockade of all tachykinin receptors is required to reveal their role in hyperalgesia. The data further indicate that a combined pharmacological approach offers a potential way forward for the development of new antihyperalgesic agents.

Animals↗
PubMed2005

Role of adrenergic receptors in the reflex diuresis in rabbits during pulmonary lymphatic obstruction.

The role of adrenergic receptors in the reflex diuresis in response to pulmonary lymphatic drainage was examined in anaesthetized, artificially ventilated New Zealand White rabbits. Pulmonary lymphatic drainage was obstructed by raising the pressure in a pouch created from the right external jugular vein. This pulmonary lymphatic obstruction results in a reflex increase in urine flow and sodium excretion. This reflex is abolished by renal denervation and by administration of L-NAME, a non-selective inhibitor of nitric oxide synthase. Also, infusion of the relatively selective neuronal nitric oxide synthase blocker, 7-nitroindazole sodium salt, into the renal medulla abolished the reflex diuresis. In this study the effects of adrenergic receptor antagonists on the reflex increase in urine were observed. Both ureters were cannulated in order to determine urine flow from both kidneys separately. Prazosin, an alpha1 adrenergic receptor antagonist, was infused into the renal medulla of the right kidney, while the left kidney acted as control. Administration of prazosin in this manner did not block the reflex diuresis in response to pulmonary lymphatic obstruction in either kidney. However, rauwolscine, an alpha2 adrenergic receptor antagonist, abolished the reflex increase in urine and sodium excretion in the ipsilateral kidney while preserving it in the contralateral kidney. These findings suggest that the increase in urine flow in rabbits caused by pulmonary lymphatic obstruction is dependent upon activation of alpha2 adrenergic receptors within the renal medulla.

Animals↗
PubMed1978

The sacral parasympathetic reflex pathway regulating colonic motility and defaecation in the cat.

1. The sacral parasympathetic outflow to the large intestine of the cat was studied by monitoring simultaneously intestinal motility and the efferent firing in postganglionic fibres on the serosal surface of the mid-distal colon. 2. Increases in efferent firing were noted during the occurrence of spontaneous propulsive activity (tonic pressure waves) or segmental contractions (slow rhythmic pressure waves). The neural discharge was not altered by transection of the lumbar sympathetic innervation to the colon but was blocked by interruption of the sacral parasympathetic outflow. 3. Electrical stimulation of pelvic nerve afferents arising in the colon or distension of the colon or rectum evoked reflex increases in efferent firing and sustained propulsive contractions that were associated with defaecation. Both responses were abolished by transection of the pelvic nerves or sacral dorsal roots. 4. Electrical stimulation of colonic afferent fibres also evoked synchronous reflex discharges in colonic efferents at latencies ranging from 180 to 300 msec. The discharges were enhanced during propulsive contractions, abolished by transection of the pelvic nerves but not altered by transection of the lumbar sympathetic nerves. 5. Sacral reflexes were present in cats with intact spinal cord and in chronic spinal animals (transection at T10-T12). The reflexes recovered within minutes to several hours after acute transection of the spinal cord. 6. Electrophysiological measurements indicated that the sacral reflexes to the large intestine were mediated by non-myelinated afferent and preganglionic efferent fibres. The central delay for the reflex was estimated to be 45-60 msec. 7. It is concluded that the sacral parasympathetic reflexes to the large intestine are mediated via a spinal pathway and have an essential role in the initiation of propulsive activity during defaecation.

Animals↗
PubMed1978

The strength of the reflex response to sinusoidal stretch of monkey jaw closing muscles during voluntary contraction.

1. Rhesus monkeys were trained to exert steady biting forces of 3--60 N for 1--2 sec. This behaviour was well maintained while sinusoidal or step opening and closing movements were imposed on the jaw. 2. The amplitude of the force modulation during sinusoidal stretching was divided by the amplitude of movement to obtain the magnitude of stiffness. This estimate was made at frequencies from 2 to 50 Hz at amplitudes of 100 and 500 micrometer (half the peak-to-peak movement at the incisors). 3. Peak magnitudes of stiffness were seen with frequencies of 8--15 Hz when the amplitude of movement was small; there was a great deal of variation between individual animals. This variation was most striking with mean forces of 25--35 N. The stiffness was greatest in animals that showed considerable spontaneous tremor, and the highest levels of stiffness were often recorded with frequencies near which tremor amplitude was large. A marked phase lag in the force response was often seen during small amplitude stretching at 8--30 Hz. 4. Estimates of stiffness for larger amplitude (500 micrometer) stretching showed less variation; the magnitude of stiffness showed maximum values below 10 Hz and a minimum at 15--30 Hz. Force always showed a phase lead on position although this lead became small in the frequency range where with smaller movement there had been phase lags. The magnitude of stiffness increased with increasing mean force. 5. Bilateral electrolytic lesions were made in the brain stems of three animals; they reduced by over 95% the expected number of cells in the mesencephalic nucleus of the fifth cranial nerve on either side. These lesions interrupted the afferent pathway for the stretch reflex and so abolished excitatory electromyogram (e.m.g.) responses to step stretches of the jaw closing muscles. 6. Such reflex responses as persisted after the lesions were small and inhibitory. E.m.g. silences followed both step stretch and release; the response to release was a 'load compensation' that could not be attributed to spindle afferents. 7. After the lesions the responses to movements of 100 micrometer showed neither negative values for the phase nor marked peaks in the stiffness magnitude at low frequencies; these features therefore take origin in the action of the stretch reflex. The stiffness that was measured after the lesions may be attributed to the non-reflex components resisting stretch, particularly to the properties of the contracting muscles. Thus, the phase of the force response was markedly advanced at all frequencies and the stiffness seen for 100 micrometer was similar to that for 500 micrometer. Stiffness increased with increasing mean force, as before surgery. 8. Vector subtraction of the stiffness seen at each frequency after interrupting the stretch reflex from that seen before doing so gave a quantitative estimate of the strength of the stretch reflex. The reflex activity calculated in this way showed attenuation and progressive phase lag as the frequency increased above 10 Hz...

Afferent Pathways↗
PubMed1979

Development of spinal reflexes in the rat fetus studied in vitro.

1. The onset and development of spinal reflex activity was investigated using the isolated spinal cord of the rat fetus. The potential changes generated in motoneurones were recorded extracellularly from L3 ventral roots. 2. A spike potential was recorded from the ventral root at embryonic day 13.5 in response to stimulation of the cord surface close to the ventral root. The discharge persisted in Ca2+-free solution but was blocked by tetrodotoxin. 3. At embryonic day 14.5, trans-synaptically evoked discharges were detected in motoneurones. 4. Stimulation of the dorsal root was first effective in eliciting reflex discharges at embryonic day 15.5. The reflex response then consisted of a prolonged depolarization upon which were superimposed small spikes, and was probably polysynaptic. 5. A spike potential, presumably a monosynaptic reflex, was generated at the end of fetal life. This discharge appeared first at embryonic day 17.5 in a primitive form. 6. Between embryonic day 16.5 and 17.5, stimulation of the dorsal root of diffferent segments (L1-L6) elicited responses similar to those induced by the corresponding (i.e. L3) dorsal root stimulation. These inter-segmentally induced responses were then reduced in size toward the birth. However, in the presence of strychnine, a train of spike discharges of similar shape to the segmentally induced response was also evoked by stimulation of the dorsal root at L4 or L5. These spikes disappeared during further post-natal development. 7. It is concluded that synapses in the segmental polysynaptic pathway become functional in a retrograde sequence with respect to the direction of normal reflex impulse flow. The reflex responses, elicited by stimulation of the dorsal roots of different segments, are suggested to be suppressed first by the development of inhibitory mechanisms and then by neuronal cell death or by elimination of the synapses responsible for generating the inter-segmental reflexes.

Action Potentials↗