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PubMed1991

Nursing posture is elicited rapidly in maternally naive, haloperidol-treated female and male rats in response to ventral trunk stimulation from active pups.

Maternal responsiveness in rats can be induced in virgin females and males, without hormonal priming, following several days of cohabitation with pups. Because antagonism of dopamine (DA) facilitates nursing behavior in lactating rats, the response of nonlactating, maternally naive rats to effective stimulation of the ventral trunk (ventrum) from pups following similar treatment was investigated. Lactating dams, virgin females and males, both intact and gonadectomized, were treated with a catalepsy-inducing dose of haloperidol (5 mg/kg), a DA receptor antagonist, and tested with hungry pups 1 hr later. Subjects were placed over 8 pups and postures assessed every 3 min for 30 min. The nursing posture occurred in most subjects. Lactating and nonlactating females were similar in occurrence of the nursing crouch, though the intensity was somewhat higher in the former; females scored higher than males in terms of likelihood and intensity of crouching; and there was no effect of gonadectomy. The nursing posture was not elicited in intact virgin females if the stimulus pups were anesthetized or if the subjects were treated with saline instead of haloperidol. There were no sex differences in onset or intensity of catalepsy in response to the dose of haloperidol used. These results suggest that the nursing posture occurs reflexively, is not directly dependent upon ovarian hormones, and is diminished by the effects of androgens, prior and current.

Animals↗
PubMed2004

Paraspinal muscle reflex dynamics.

Neuromuscular control of spinal stability may be represented as a control system wherein the paraspinal muscle reflex acts as feedback response to kinetic and kinematic disturbances of the trunk. The influence of preparatory muscle recruitment for the control of spinal stability has been previously examined, but there are few reported studies that characterize paraspinal reflex gain as feedback response. In the current study, the input-output dynamics of paraspinal reflexes were quantified by means of the impulse response function (IRF), with trunk perturbation force representing the input signal and EMG the output signal. Surface EMGs were collected from the trunk muscles in response to a brief anteriorly directed impact force applied to the trunk of healthy participants. Reflex behavior was measured in response to three levels of force impulse, 6.1, 9.2 and 12.0 Ns, and two different levels of external trunk flexion preload, 0 and 110 N anterior force. Reflex EMG was quantifiable in response to 91% of the perturbations. Mean reflex onset latency was 30.7+/-21.3 ms and reflex amplitude increased with perturbation amplitude. Impulse response function gain, G(IRF), was defined as the peak amplitude of the measured IRF and provided a consistent measure of response behavior. EMG reflex amplitude and G(IRF) increased with force impulse. Mean G(IRF) was 2.27+/-1.31% MVC/Ns and demonstrated declining trend with flexion preload. Results agree with a simple systems model of the neuromechanical feedback behavior. The relative contribution of the reflex dynamics to spinal stability must be investigated in future research.

Adaptation, Biological↗
PubMed1978

Task-dependent genetic influences on behavioral response of mice (Mus musculus) to acetaldehyde.

Acetaldehyde was employed as a pharmacological agent in behavioral tests designed to assess genetic influences upon response to the drug. When used as a poison in a conditioned taste aversion study, acetaldehyde was more effective at inducing aversions in DBA/2J mice than in C57BL/6J mice. In another experiment, however, C57 mice were more affected than were DBA mice by acetaldehyde effects on loss of righting reflex. Implications for postulated genetic control of ethanol preference and neurosensitivity are discussed.

Acetaldehyde↗
PubMed2003

A short latency vestibulomasseteric reflex evoked by electrical stimulation over the mastoid in healthy humans.

We describe EMG responses recorded in active masseter muscles following unilateral and bilateral electrical vestibular stimulation (EVS, current pulses of 5 mA intensity, 2 ms duration, 3 Hz frequency). Averaged responses in unrectified masseter EMG induced by unilateral EVS were examined in 16 healthy subjects; effects induced by bilateral (transmastoid) stimulation were studied in 10 subjects. Results showed that unilateral as well as bilateral EVS induces bilaterally a clear biphasic response (onset latency ranging from 7.2 to 8.8 ms), that is of equal amplitude and latency contra- and ipsilateral to the stimulation site. In all subjects, unilateral cathodal stimulation induced a positive-negative response termed p11/n15 according to its mean peak latency; the anodal stimulation induced a response of opposite polarity (n11/p15) in 11/16 subjects. Cathodal responses were significantly larger than anodal responses. Bilateral stimulation induced a p11/n15 response significantly larger than that induced by the unilateral cathodal stimulation. Recordings from single motor units showed that responses to cathodal stimulation corresponded to a brief (2-4 ms) silent period in motor unit discharge rate. The magnitude of EVS-induced masseter response was linearly related to current intensity and scaled with the mean level of EMG activity. The size of the p11/n15 response was asymmetrically modulated when subjects were tilted on both sides; in contrast head rotation did not exert any influence. Control experiments excluded a possible role of cutaneous receptors in generating the masseter response. We conclude that transmastoid electrical stimulation evokes vestibulomasseteric reflexes in healthy humans at latencies consistent with a di-trisynaptic pathway.

Adult↗
PubMed1999

The influence of experimental muscle pain on the human soleus stretch reflex during sitting and walking.

OBJECTIVES: The stretch reflex is functionally important during human locomotion. Muscle pain has been found to increase the stretch reflex amplitude during sitting, possibly due to an altered fusimotor drive. To further study the importance of altered fusimotor activity due to muscle pain we investigated the combined effect of muscle pain and motor task on the soleus stretch reflex. METHODS: Stretch reflexes were elicited before, during and after experimentally induced muscle pain in soleus (i.m. infusion of 6% saline) in 3 experiments: (1) in the relaxed soleus muscle and before, during and after an isometric ramp contraction (500 ms, 0-10 Nm), (2) at 3 different time periods during walking, and (3) at matched pain intensity and soleus activity during sitting and walking. RESULTS: Infusion of hypertonic saline into the soleus muscle caused a significant facilitated stretch reflex in the relaxed muscle (P<0.01), but not during walking or during sitting and walking at matched soleus EMG and matched pain levels. The infusion of isotonic saline (non-painful) did not cause any changes (P = 0.75). CONCLUSIONS: The main findings of the present study were that experimental muscle pain facilitated the stretch reflex during pain in the relaxed muscle, but caused no changes in stretch reflex amplitude during sitting and walking at higher "functional" background EMG levels.

Adolescent↗
PubMed1985

Comparison of electromyographic activity in the lumbar paraspinal muscles of subjects with and without chronic low back pain.

My purpose, in this study, was to test the reflex-spasm model of chronic pain by comparing the levels of muscle activity in the lumbar paraspinal muscles of subjects with and without chronic low back pain (CLBP). Each group, the CLBP group and the nonpain (NP) group, comprised 11 subjects who were matched by age and sex. I used surface electrodes to record integrated electromyographic (IEMG) activity from each side of the low back. All subjects performed three experimental tasks and a reference (normalizing) task. The three experimental tasks were quiet sitting, standing, and sitting during a repetitive unilateral upper extremity task (active sitting). The CLBP and NP groups showed no significant difference for any of the three experimental tasks. For both groups, the active sitting IEMG levels were significantly higher than the quiet sitting and standing IEMG levels. The quiet sitting and standing IEMG levels were not significantly different from each other. The findings of similar levels of IEMG activity in both the CLBP and NP groups while they performed these tasks suggested that the reflex-spasm cycle was not present and, therefore, was not a cause of pain in the subjects with CLBP.

Adult↗
PubMed1986

Abnormality of circulatory reflex and aldosterone response during head-up tilting in patients with primary aldosteronism.

Abnormality of the circulatory reflexes has been reported in patients with primary aldosteronism. However, changes in blood pressure, heart rate, plasma renin activity (PRA), and plasma aldosterone concentration (PAC) after head-up tilting in primary aldosteronism have not yet been reported. Seven patients with primary aldosteronism were tilted to a 65 degree head-up position which was maintained for 30 min. Systolic blood pressure decreased significantly 5 min after tilting and remained at this level during the period of tilting. Diastolic blood pressure did not change during the tilting. Heart rate increased after 5 min of tilting and this level of heart rate was maintained for 30 min. Plasma renin activity was low and did not change during tilting. However, plasma aldosterone concentration increased significantly 20 min after tilting. Plasma cortisol concentration and plasma ACTH concentration also increased significantly. These results suggest that primary aldosteronism causes abnormalities of the circulatory reflexes. The increase of endogenous ACTH may increase plasma aldosterone concentration in patients with primary aldosteronism.

Adrenocorticotropic Hormone↗
PubMed1989

The Auto-Tilt Test in patients with positional vertigo and Menière's disease.

As a new method of testing the righting reflex, which has been considered to be closely related to the otolith function, we used the Auto-Tilt Test (ATT) on 24 patients with positional vertigo, on 5 patients with Meniere's disease before and after cochlearendolymphatic shunt, and on 10 normal subjects. The subject is required to stand on an electrically driven tilt board with an autoregulating switch in hand, and to perform bilateral tilt swings of 5 degrees and 10 degrees wearing a helmet with a Head Inclinometer or tilt sensor. The result of this test in patients with positional vertigo revealed the patients had an abnormal labyrinthine reflex and significantly excessive tilt in the return swing from the side of the lesion. In addition, we consistently observed an inaccurate righting reflex, coupled with a diminished sensation of tilt, on the side of the lesion. The results in Meniere's disease patients, followed up before and after surgery, showed that the depressed righting reflex toward the affected side and the tendency to list to the healthy side before surgery, improved after surgery.

Adult↗
PubMed1993

Capillary underperfusion in chronic venous insufficiency: a cause for leg ulceration?

Dermal capillaries in the goiter area of the lower leg were examined by video-microscopy before and after the administration of intravenous fluorescein in 13 patients with chronic venous insufficiency (CVI) who were at risk of developing leg ulceration, and in 13 normal controls. The influence of posture on capillary perfusion was determined by viewing the same area of skin with the leg in both the supine and dependent positions. Capillary density was lower in patients than in controls, irrespective of the position of the leg (P < 0.01). Fluorescence angiography studies in normal controls showed a reduction in capillary density with dependency (P < 0.01), but patients with CVI showed no significant change. Fluorescence angiography revealed a greater number of capillaries than seen during native capillaroscopy (P < 0.05). The decreased capillary density, and the loss of the postural vasoconstrictor reflex in patients with chronic venous incompetence may play a role in the pathogenesis of ulceration.

Adult↗
PubMed2005

Cerebellar skew deviation and the torsional vestibuloocular reflex.

BACKGROUND: Skew deviation is typically caused by brainstem damage, and has not been identified with focal cerebellar lesions. This vertical strabismus has been attributed to asymmetric disruption of vestibuloocular reflex (VOR) projections from otolithic receptors of the utricle to ocular motoneurons, but asymmetry of the utriculo-ocular counter-roll reflex has not been detected. METHODS: Lesions localized to the cerebellum were identified by MRI in five patients with vertical strabismus. Their skew deviation was measured by prism cover tests in all patients and by search coils in three patients. The angular VOR was tested in patients and 10 controls during sinusoidal +/- 10 degree torsional, vertical, and horizontal head-on-body rotations at 0.5, 1, and 2 Hz. Static torsional VOR gain was measured by the change in torsional eye position divided by change in head position during maintained head tilt. RESULTS: Static torsional VOR gains were asymmetric in each patient. Three patterns of asymmetry were identified: 1) decreased static gain in one eye in both directions; 2) decreased gains in both eyes in one direction; and 3) asymmetric gain in one direction in one eye alone. Dynamic torsional VOR gains were symmetrically reduced in both directions in both eyes in all patients. CONCLUSIONS: Focal cerebellar lesions can cause skew deviation. The static torsional vestibuloocular reflex (VOR) is linked to cerebellar control of vertical vergence. Asymmetry between the eyes or in direction of the static torsional VOR provides evidence that monocular or binocular imbalance of the utriculo-ocular reflex leads to cerebellar skew deviation.

Adult↗
PubMed1983

Regional blood flow response to orthostasis in patients with congestive heart failure.

To investigate the central and regional circulatory response to orthostasis in congestive heart failure, hemodynamic variables and forearm and hepatic blood flow were measured in 22 patients at supine rest and during a 65 degrees head-up tilt. Results were compared with those in nine normal subjects. Heart rate and mean arterial blood pressure increased during tilt in normal subjects, but not in patients with heart failure. Forearm blood flow decreased in normal subjects from 3.7 +/- 1.1 to 2.7 +/- 1.5 ml/min per 100 g (probability [p] less than 0.02), but did not change from a lower baseline (1.65 +/- 0.78 ml/min per 100 g) in patients. Forearm vascular resistance increased in normal subjects but not in patients. Hepatic blood flow did not change during tilt in either group, but hepatic vascular resistance increased in normal subjects from 0.37 +/- 0.13 to 0.47 +/- 0.15 U, (p less than 0.02). The increase was not seen in patients (1.2 +/- 1.1 to 1.4 +/- 1.0 U, p = not significant [NS] ). Total systemic resistance increased in patients from 1,848 +/- 560 to 2,132 +/- 731 dynes.s.cm-5 (p less than 0.005) indicating that resistance did increase in some vascular beds. Plasma norepinephrine also increased modestly in these patients from 665 +/- 377 to 761 +/- 379 pg/ml (p = 0.035), but individual changes in plasma norepinephrine did not correlate with changes in hepatic or forearm resistance. Thus, both the overall hemodynamic response and the regulation of regional blood flow and resistance differ in several respects in patients with congestive heart failure when compared with normal subjects. Changes in heart rate, blood pressure, forearm flow and forearm and hepatic vascular resistance are all blunted in patients. Reasons for the differences are not yet clear, but may be associated with abnormalities in reflex control of the circulation in patients with congestive heart failure.

Adult↗
PubMed2003

Vestibular activation of sympathetic nerve activity.

AIM: The vestibulosympathetic reflex refers to sympathetic nerve activation by the vestibular system. Animal studies indicate that the vestibular system assists in blood pressure regulation during orthostasis. Although human studies clearly demonstrate activation of muscle sympathetic nerve activity (MSNA) during engagement of the otolith organs, the role of the vestibulosympathetic reflex in maintaining blood pressure during orthostasis is not well-established. Examination of the vestibulosympathetic reflex with other cardiovascular reflexes indicates that it is a powerful and independent reflex. Ageing, which is associated with an increased risk for orthostatic hypotension, attenuates the vestibulosympathetic reflex. The attenuated reflex is associated with a reduction in arterial pressure. CONCLUSION: These findings suggest that the vestibulosympathetic reflex assists in blood pressure regulation in humans, but future studies examining this reflex in other orthostatically intolerant populations are necessary to address this hypothesis.

Aged↗
PubMedDate not supplied

Evidence for a vestibular input contributing to dynamic head stabilization in man.

Horizontal head movements in response to unpredictable horizontal oscillations of the trunk were studied in 6 patients lacking vestibular function and in 6 normal subjects. In order to obtain compensatory (i.e. stabilizing with respect to earth) head movements, all subjects were required to look at an earth-fixed target, using their eyes and head. The turning points (maxima and minima) were determined from head and trunk position records. It was found that normal subjects reversed the direction of head movements in advance of trunk movements (mean lead = 82 ms) whereas the patients reversed head direction after the trunk (mean lag = 169 ms). The coherence function between head and trunk movements, measured with a spectral analyser in an additional labyrinthineless patient, was considerably lower than in normal controls. It is concluded that patients lacking vestibular function have impaired stabilization of the head in space, which can be taken as indirect evidence of the existence of active dynamic vestibulo-collic reflex (VCR) mechanisms in normal man. The lead found in normal subjects, notwithstanding the unpredictability of the stimuli, may reflect the detection of early acceleration signals by the vestibular apparatus to organize compensatory head movements.

Adult↗
PubMed1996

Bilateral vestibulopathy revisited.

Bilateral vestibular failure (BVF) is an often undetected disorder of the peripheral labyrinths or the eighth nerves. Key symptoms are oscillopsia during locomotion or head movements and unsteadiness, particularly in the dark. Diagnosis is made by a bedside test for defective vestibulo-ocular reflex and the absence of nystagmic reaction to both caloric and rotatory pendular testing. Most frequent etiologies include ototoxicity, cerebellar degeneration, meningitis, neuropathies, sequential vestibular neuritis, autoimmune disorders, tumors, and miscellaneous otological diseases. Idiopathic BVF is found in more than twenty percent of the patients. Recovery is possible but mostly incomplete. Somatosensory and visual input largely substitute the vestibular deficit for spatial orientation, postural balance and ocular motor control.

Diagnosis, Differential↗
PubMed2001

Cardiovascular reflex testing contributes to clinical evaluation and differential diagnosis of Parkinsonian syndromes.

The differentiation between Parkinson's disease (PD), progressive supranuclear palsy (PSP), and multiple system atrophy (MSA) may be difficult but is important for prognostic and therapeutic purposes. Varying degrees of autonomic failure have been described in PD and MSA, whereas its involvement in PSP remains controversial. The aim of this study was to investigate autonomic function in patients fulfilling strict clinical diagnostic criteria for the disorders above, to evaluate the diagnostic capacity of laboratory autonomic tests. The study group was consecutively recruited among patients referred to a movement disorder unit. Thirty-four patients with PD, 15 patients with PSP, and 47 patients with MSA were compared with 18 healthy age-matched controls. Autonomic tests included analysis of heart rate variability (HRV) in temporal domain, at rest and during forced respiration, as well as blood pressure (BP) changes during 75 degrees head-up tilt. HRV did not differ between groups during quiet breathing but was significantly reduced during forced respiration in MSA (P < 0.01), while PD and PSP groups did not differ from controls. Hypotensive responses during orthostatic provocation were seen in PD (P < 0.01) and MSA (P < 0.001), whereas BP remained stable in most PSP patients, not differing from the healthy control group. On an individual basis, decreased HRV and severe hypotensive responses were seen in MSA patients regardless of age and disease duration, whereas PD patients showed this combination only at high age and long duration. In PSP, only a few cases with decreased HRV and limited hypotensive responses were found. We conclude that cardiovascular reflex tests can supplement the clinical differentiation of Parkinsonian syndromes.

Aged↗
PubMed1996

Effects of facial cooling on elderly and young subjects: interactions with breath-holding and lower body negative pressure.

1. The effects of convective facial cooling by cold air on arterial blood pressure, heart rate and finger blood flow and on the reflex interactions between facial cooling and respiratory and orthostatic cardiac reflexes have been examined in 28 young adults (20-39 years) and 17 elderly (66-78 years) volunteer subjects. 2. During 2 min facial cooling alone, bradycardia was smaller (P < 0.001) and reduction in finger blood flow smaller (P < 0.001) in elderly subjects than in young subjects. Increases in systolic blood pressure and mean arterial pressure were similar and diastolic pressure increased only in the young subjects. Systolic blood pressure and mean arterial pressure remained elevated in the elderly 1 min after facial cooling, but subsided in the young. 3. Arterial blood pressure increased more during a 30-s breath-hold in expiration than in inspiration (P < 0.001) in both groups, and this was exaggerated by breath-hold in expiration combined with facial cooling. The bradycardia produced by facial cooling and breath-holding in expiration was more pronounced in the young subjects than in the elderly (P < 0.002). 4. Interactions between facial cooling and orthostatic reflexes induced by lower-body negative pressure showed significantly different age-related linear trends. Facial cooling diminished the hypotension induced by lower-body negative pressure in both groups. Facial cooling had a greater effect in diminishing the lower-body negative pressure-induced tachycardia in the young than in the elderly. 5. The mechanism of alteration of the facial cooling response in elderly subjects could be largely impairment of arterial baroreflexes, particularly as a result of reduced cardiac vagal activity as well as impairment of cardiopulmonary reflexes with ageing.

Adult↗
PubMed1983

Contribution of local blood flow regulation mechanisms to the maintenance of arterial pressure in upright position during epidural blockade.

The contribution of local blood flow regulation mechanisms to the maintenance of arterial pressure in upright position was studied in 5 normal subjects. Central sympathetic blockade was induced by epidural anesthesia. Blood flow in anterior tibial muscle in both legs and in brachioradial muscle in one arm was measured by the local 133Xe washout technique. Arterial blood pressure was recorded directly from the radial artery. Slow head-up tilt (about 30 degrees) caused a decrease in blood flow of about 36% in the dependent legs and in arm remaining at heart level. Arterial pressure decreased by about 10%. Blockade of the local sympathetic veno-arteriolar "axon reflex" in one leg by injection of phentolamine into the common femoral artery caused a vasodilatation in the ipsilateral muscle, while muscle blood flow did not change in the other leg or arm. Within 20 s after the injection of phentolamine arterial pressure decreased by about 7%. This cannot be explained by a "systemic" effect because injection of phentolamine into the femoral vein did not effect arterial pressure within the first 40 s. Vasoconstriction due to blood-borne factors is ruled out since preventing the increase in vascular transmural pressure in the leg by inducing counterpressure locally, abolished the vasoconstriction. Thus, the results suggest that the local veno-arteriolar "axon reflex" together with myogenic mechanisms contribute to the maintenance of arterial pressure in the upright position.

Adrenergic alpha-Antagonists↗