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PubMed2001

The effect of betahistine on vestibular habituation: comparison of rotatory and sway habituation training.

This study was designed to investigate the effect of histaminergic agonists and antagonists on the acquisition of vestibular habituation. The experimental animals, pigeons, were subjected to unilateral rotatory and sway habituation training sessions. The habituation of postural reflexes and post-rotatory head nystagmus was assessed. Vestibular habituation in the control group was achieved by adopting the kinetic reflex posture after approximately 9 training sessions, and after 10 and 14 training sessions, respectively for 50% reduction of the total number of beats (TNB) and the duration of post-rotatory head nystagmus. In the sway adaptation test control pigeons needed nearly 15 training sessions while pigeons receiving betahistine adapted after approximately 8 sessions. Administration of histamine and, most notably, betahistine accelerated the process, while both H1 and H2 antagonists (clemastine, cimetidine) tended to retard it, indicating a less significant contribution of H2 receptors. The cholinergic agent physostigmine strongly retarded habituation while the anticholinergic agent scopolamine markedly accelerated it. In addition the adrenomimetic agent ephedrine also accelerated habituation while the adrenolytic agent droperidol retarded reduction of nystagmus beats. The results indicate that histaminergic receptors play a significant role in the vestibular habituation mechanism but are intricately involved with other types of receptors. Betahistine is clearly the agent of choice for attenuating vestibular effects.

Animals↗
PubMed1978

Postural and reflex integration in schizophrenic patients.

The relationship among primitive postural reflexes, postural and bilateral integration, and premorbid adjustment were examined in 29 subjects who were divided into 3 groups: normal, chronic process nonparanoid schizophrenic, and chronic paranoid schizophrenic. Significant differences were found between the normal and szhizophrenic groups on the tonic labyrinthine reflex and on five of the six measures of postural and bilateral integration. No significant differences were found between the two schizophrenic groups on any of the test variables. There were significant positive correlations between the tonic labyrinthine reflex, postural and bilateral integration, and premorbid status in the subjects studied.

Adult↗
PubMed1987

Do antidepressants cause postural hypotension by blocking cardiovascular reflexes?

Postural changes in blood pressure, respiratory sinus arrhythmia, the heart rate response to Valsalva's manoeuvre and to standing, and the blood pressure and heart rate responses to isometric exercise have been measured in seven young women taking antidepressant medication and compared with seven controls. Among the patients there was a significant rank order correlation between the degree of postural hypotension and the daily dose of antidepressant medication. There was a significant impairment among the patients of all cardiovascular reflex responses measured, suggesting both cholinergic and adrenergic blockade. These results suggest that postural hypotension associated with antidepressant medication is caused in large part by a failure of reflex peripheral vasoconstriction.

Antidepressive Agents↗
PubMedDate not supplied

Effect of cigarette smoking on postural muscle tremor.

In a study of the effect of smoking on postural reflexes--specifically postural muscle tremor--in man, amplitude of postural muscle tremor, when tested in 30 subjects, was increased to a significant degree immediately following the smoking of one cigarette. Tremor amplitude continued to be significantly increased one-half hour after smoking ceased. There was no significant change in the frequency of tremor. Measurement was made using a piezo crystal accelerometer attached to the third fingers of both hands. Effects were recorded with a Sanborn Twin Viso Recorder. The findings, that smoking does affect postural reflexes, have implications for the formulation of nursing therapies, particularly in areas such as rehabilitation nursing, where the use of postural reflexes is the primary mode of intervention.

Adult↗
PubMedDate not supplied

Postural stress tests for the clinico-physiological evaluation of cardiovascular reflexes.

Postural stress tests are useful in the assessment of cardiovascular reflex response of normal subjects who may be involved in specialised occupations such as flying; in order to study the effects of physiological stresses such as heat stress, hypoxia, simulation of weightlessness; physiological evaluation of cosmonaut candidates, in patients who may have autonomic neuropathy. Most commonly quiet standing is used but head-up tilt table test and the application of lower body suction may provide a better method of evaluation. These three tests for assessing reflex cardiovascular function are discussed.

Blood Pressure↗
PubMed2005

Postural and eye-blink indices of the defensive startle reflex.

Postural and eye-blink reactions to acoustic startle probes were examined in 24 volunteers, who completed two blocked conditions (baseline, startle). A postural reaction during the startle condition demonstrated a reflexive movement in the anterior-posterior direction, which was not observed during the baseline condition. This reflexive response was positively associated with the eye-blink reflex, such that larger blink magnitude related to greater posterior movement. These findings were not observed for postural movements in the medial-lateral direction. The results suggest that a measurable postural reaction may be observed following a startling acoustic stimulus, which may reflect generalized bodily flexion associated with a preparatory behavioral response.

Acoustic Stimulation↗
PubMed1992

Postural proprioceptive reflexes in standing human subjects: bandwidth of response and transmission characteristics.

1. This study investigated the reflex control of postural sway during human bipedal stance. The experiments were designed to: (i) find evidence for the operation of 'stretch reflex' pathways during quiet stance, (ii) determine the bandwidth of the reflex response, (iii) describe the reflex transmission characteristics in standing subjects, and (iv) assess the ability of subjects to make a task-dependent change in the reflex. 2. A continuous random perturbation that did not threaten stability was applied at waist level to nine standing subjects. The effects of the perturbation on ankle torque, ankle movement and soleus electromyographic activity (EMG) were identified by cross-correlation. The bandwidth of the reflex response and the transmission characteristics of reflexes that respond to ankle movement were identified by spectral analysis. Changes in these reflex responses were investigated when subjects attempted to stand as still as possible, had their eyes closed, or balanced a load equivalent to their own body in a situation in which neither visual nor vestibular reflexes would be activated. 3. When standing, a reflex response coherent with the perturbation was seen in soleus EMG at frequencies up to 5 Hz, with maximal coherence at 1.0-2.0 Hz. Reflex gain increased with frequency, and there was a frequency-dependent phase advance of soleus EMG on ankle movement reaching 135 deg at 3 Hz. When attempting to minimize sway, subjects produced a more coherent reflex response and significantly increased reflex gain. 4. The response and transmission characteristics of the lower limb proprioceptive reflex in freely standing subjects were similar to those in subjects balancing a load at the ankle, a situation in which vestibular and visual inputs could not contribute. 5. It is concluded that reflex feedback related to ankle movement contributes significantly to maintaining stance, and that much of the reflex response originates from lower limb mechanoreceptors stimulated by ankle rotation. Although reflex gain may be relatively low during quiet stance it can be increased when necessary to maintain stability.

Adult↗
PubMed1991

Practical aspects of the estimation of the time of ovulation and of insemination in the bitch.

The aims of this study were to assess the precision of the estimates of the time of ovulation derived by various methods, and to define the most appropriate methods for the determination of the optimal time for insemination of bitches with fresh semen (artificial insemination or natural mating), or with frozen-thawed semen. In 11 Labrador bitches, ovulation was estimated (plasma LH surge + 48 h) to occur 9 to 20 d after the start of the cycle, 0 to +4 d after the onset of positive postural reflexes (2 bitches showed no positive postural reflexes), -4 to +7 d after reaching a vaginal cytological eosinophilic index (EI) of 100%, over a range of 2.5 to 5.5 d based on plasma progesterone concentrations of 4 to 10 ng/ml, over a range of 2 to 3 or 4 d based on 2 indirect methods of estimating the time of the plasma LH surge from plasma progesterone concentrations. Assuming fertilisation occurs 2 to 3 d after ovulation, these findings indicate that for fresh semen (with an estimated lifespan of greater than 4 days) an appropriate procedure would be to inseminate/mate on the day after the onset of positive postural reflexes; then 3 days later. For bitches not showing positive postural reflexes, insemination should occur when the vaginal EI = 90% and then each 3 d until day 1 of dioestrus (D1). For frozen-thawed semen (with a lifespan of less than 24 h) insemination should occur 4 to 5 d after the plasma LH surge.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Primitive reflexes and postural reactions in the neurodevelopmental examination.

The primitive reflexes and the postural reactions comprise one of the earliest, simplest, and most frequently used tools among child neurologists to assess the central nervous system integrity of infants and young children. Infants with cerebral palsy have been known to manifest persistence or delay in the disappearance of primitive reflexes and pathologic or absent postural reactions. The clinical significance of asymmetric tonic neck reflex, Moro, palmar grasp, plantar grasp, Galant, Babinski, Rossolimo, crossed extensor, suprapubic extensor, and heel reflex, alone or in combination, as well as their contribution to the early diagnosis and differential diagnosis of cerebral palsy, have been demonstrated in a number of studies. Moreover, infants with 5 or more abnormal postural reactions have developed either cerebral palsy or developmental retardation as reported in a number of studies. Although a comprehensive neurologic examination in the context of a motor assessment instrument is preferable to an informal list of items, the combined examination of primitive reflexes and postural reactions should be considered by the child neurologist, as a simple but predictive screening test for the early identification of infants at risk for cerebral palsy. It is quick and easy to perform, both in nonhospital environments and in underdeveloped countries, where time and specific recourses are limited. The combined examination is also useful in developed countries because many developmental disorders such as cerebral palsy appear in nonrisk groups whereas others are not detected by metabolic screening programs.

Cerebral Palsy↗
PubMedDate not supplied

Acute effects of L- and T-type calcium channel antagonists on cardiovascular reflexes in conscious rabbits.

1. The effects of the relatively selective T-type voltage- operated calcium channel (VOCC) antagonist mibefradil were compared with verapamil, an L-type VOCC antagonist, on a range of autonomic reflexes in conscious rabbits. 2. Mean arterial pressure (MAP), heart rate (HR), the baroreceptor-HR reflex, postural adaptation reflex (90 degrees head-up tilt), Bezold-Jarisch-like reflex and the vasoconstrictor component of the nasopharyngeal reflex were assessed before and during i.v. infusion of vehicle (saline), mibefradil or verapamil. Doses of mibefradil that gave low (M1; 0.45 +/- 0.02 microg/mL) and high (M2; 0.93 +/- 0.05 microg/mL) plasma concentrations, or verapamil (0.059 +/- 0.004 microg/mL; n = 6 each) were chosen to mimic clinically observed therapeutic levels. 3. At steady state infusion over 30-90 min, MAP was significantly lower in M2 (- 7 mmHg) and verapamil (- 6 mm Hg) treatments, but only verapamil caused a significant tachycardia (+ 31 b.p.m.) compared with vehicle. Mibefradil (M2) and verapamil decreased the HR range of the baroreflex by 27 and 29%, respectively, but neither treatment affected the vagal or sympathetic constrictor components of the Bezold-Jarisch-like and nasopharyngeal reflexes, respectively. 4. In response to 90 degrees tilt, vehicle- and verapamil-treated rabbits responded with small rises in MAP of 4 +/- 2 and 8 +/- 2 mm Hg, respectively, 5 s into the upright posture, while M1 and M2 caused falls in MAP of 6 +/- 4 and 9 +/- 3 mm Hg, respectively, at 5 s. 5. Thus, both L- and T-type VOCC antagonists, at plasma concentrations in the clinical range, lowered MAP in the conscious rabbit, but only mibefradil caused postural hypotension. We conclude that T-type VOCC may play an important role in the venoconstrictor reflex in response to tilt in the rabbit.

Animals↗
PubMed2001

Sensory inputs contribution to vestibulo-ocular reflex and postural response maintaining simultaneously body balance.

We investigated which sensor had dominant contribution to vestibulo-ocular reflex (VOR) and postural sway (PS) for the optimal body balance maintenance under conditions of visual or/and somatosensory input reduction. Healthy subjects were examined in upright stance on stable platform and foam rubber, under following conditions: in quiet stance with eyes open (EO) and closed (EC); during voluntary head movements in horizontal plane at frequency 0.2 - 0.3 Hz with EO (HO) and EC (HC). The results showed that PS increased smaller during HC than during HO on both supports stable and unstable, but particularly on the foam rubber. Mean gain of VOR induced by HO was 1.2 and this one evoked by HC was 0.9 on the two supports. Therefore, when in upright stance the vestibular input is stimulated, the reduction of either or both inputs visual and proprioceptive influences postural stability positively while VOR is affected negligibly. Hence, the vestibular contribution to both VOR and PS is dominant.

Adult↗
PubMed2004

[Influence of the cerebellum on the postural labyrinth reflex--experimental and clinical data].

The subject of the study was to estimate the influence of the cerebellum and the postural labyrinth reflex. The pigeons after hemicerebellectomy or vermis ablation this reflex was analysed during body rotation around sagittal and transversal axis. In the clinical part of observations, stabilometric measure of head motion during balance on the movable platform was performed in patients with supratentorial and cerebellar tumors. The results showed the greatest reflex disturbances in vermis ablation and vermis tumors. In hemispheric tumors of the cerebellum these disorders were slighter, but greater in comparison with supratentorial lesions. The authors stressed the role of the vermis in controlling of the reflex.

Adult↗