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PubMed1979

Sympathetic reflex responses during treatment of essential hypertension with hydrallazine and oxprenolol.

1. The short term effects of hydrallazine, oxprenolol and oxprenolol plus hydrallazine were studied in five patients with essential hypertension. 2. The increase in pulse rate caused by hydrallazine was prevented by combined treatment with oxprenolol, which also lowered the high plasma noradrenaline levels, associated with the use of hydrallazine. 3. Plasma renin activity was higher in the supine and standing positions with hydrallazine than with oxprenolol alone and with the patients standing this high renin level was prevented by simultaneous treatment with oxprenolol. With the patients supine, combination of oxprenolol with hydrallazine resulted in a mean plasma renin activity which was less than half that with hydrallazine alone, although this difference was not statistically significant. 4. The combination of oxprenolol with hydrallazine did not lower the blood pressure further, but reduced the increased sympathetic activity which occurred with hydrallazine alone.

Blood Pressure↗
PubMed1979

Neurological development of kittens.

The neurological development of the kitten was studied from birth to 120 days of age. Three motor features present at birth disappeared within the 1st 45 days of life. The labyrinthine head and body righting reactions were present at birth; the latter matured only by 25 days of age when the air righting reaction (mature by 35 days) started to appear. Limb placing reactions developed progressively with proprioceptive components being present at birth whereas tactile components evolved slowly from early contact lifting to forepaws contact placing (60 days) and narrow plank walking (75 days). Standing and walking were well developed by 45 days. Eye opening occurred at 9.5 days and several eyeblink reactions (including blink to light) were present at birth. Adequate binocular coordination was seen by 47 days. Vision progressed parallel to the clearing of the ocular media which were fairly transparent by 32 days. Visually guided paw placing and the visuopalpebral blink reflex matured later (by 37 and 59 days, respectively). The external auditory canal and pinna were fully developed by 12 and 31 days, respectively; spontaneous and tactile pinna movements were present at birth; orienting to animal and nonanimal sounds was well developed by 6.5 and 18 days, respectively; spatial sound localization was developed by 16 days and differential responding to animal sounds matured by 24.5 days. Somatic responses and olfaction were present at birth but matured further thereafter. Playful interactions between kittens started by 10--15 days and well developed play behavior was seen by 36--40 days. In brief, all neurological functions mature progressively during the 1st 3 postnatal months.

Animals↗
PubMed1987

Cardiovascular reflexes during isometric exercise--role of muscle mass and gravitational stress.

Six healthy males performed sustained static contractions of five arm- and leg muscle groups for 2 min at 40% maximum voluntary contraction (MVC) sitting and supine. Delta heart rate, blood pressure, forearm vascular resistance, and cardiac output increased during contraction incrementing increasingly in the following order: dorsi flexion of ankle, plantar flexion, third finger flexion, handgrip, and knee extension. Muscle ischemia during recovery did not change this order. The cardiovascular responses to static contraction did not relate to muscle mass involved in a simple rectilinear manner. The increments in cardiovascular responses were not reduced in the supine position, although the values were at a lower level, probably due to the combination of a decreased sympathetic nervous activity in the supine position and an increased aortic baroreceptor stimulation induced by the increased stroke volume.

Adult↗
PubMed1994

The dynamic head-tilt test and the concept of a supranuclear trochlear palsy.

The "dynamic head-tilt test" introduced in this article examines the influence of the vestibular semicircular canals on the eye muscles during the head tilt. Normally, a rotatory nystagmus results. If under certain pathological circumstances, the vestibulo-ocular reflex is transmitted only to the rectus muscles and not to the obliques, the cyclorotatory nystagmus is converted into a vertical nystagmus. We have found this condition in five cases; in two it was very pronounced. During head tilt to the right, the slow phases of the nystagmus were directed upward in the right eye and downward in the left eye. During head tilt to the left, the nystagmus directions were reversed. Since other signs of oblique muscle palsy such as incomitance and cyclotropia were lacking or inappropriately slight, the author suggests the presence of a supranuclear lesion eliminating the vestibular input to the trochlear nucleus and to the subnucleus of the inferior oblique muscle while leaving the input for voluntary and visual gaze signals intact.

Adult↗
PubMed1993

Three dimensional eye movements of squirrel monkeys following postrotatory tilt.

Three-dimensional squirrel monkey eye movements were recorded during and immediately following rotation around an earth-vertical yaw axis (160 degrees/s steady state, 100 degrees/s2 acceleration and deceleration). To study interactions between the horizontal angular vestibulo-ocular reflex (VOR) and head orientation, postrotatory VOR alignment was changed relative to gravity by tilting the head out of the horizontal plane (pitch or roll tilt between 15 degrees and 90 degrees) immediately after cessation of motion. Results showed that in addition to post rotatory horizontal nystagmus, vertical nystagmus followed tilts to the left or right (roll), and torsional nystagmus followed forward or backward (pitch) tilts. When the time course and spatial orientation of eye velocity were considered in three dimensions, the axis of eye rotation always shifted toward alignment with gravity, and the postrotatory horizontal VOR decay was accelerated by the tilts. These phenomena may reflect a neural process that resolves the sensory conflict induced by this postrotatory tilt paradigm.

Animals↗
PubMed2002

Human otolith-ocular reflexes during off-vertical axis rotation: effect of frequency on tilt-translation ambiguity and motion sickness.

The purpose of this study was to examine how the modulation of tilt and translation otolith-ocular responses during constant velocity off-vertical axis rotation varies as a function of stimulus frequency. Eighteen human subjects were rotated in darkness about their longitudinal axis 30 degrees off-vertical at stimulus frequencies between 0.05 and 0.8 Hz. The modulation of torsion decreased while the modulation of horizontal slow phase velocity (SPV) increased with increasing frequency. It is inferred that the ambiguity of otolith afferent information is greatest in the frequency region where tilt (torsion) and translational (horizontal SPV) otolith-ocular responses crossover. It is postulated that the previously demonstrated peak in motion sickness susceptibility during linear accelerations around 0.3 Hz is the result of frequency segregation of ambiguous otolith information being inadequate to distinguish between tilt and translation.

Adult↗
PubMed1969

Hind leg ataxia of cervical origin and cervico-lumbar spinal interactions with a supratentorial pathway.

1. Unilateral section of the nerves to an extensor muscle of the head, biventer cervicis, leads to an ataxia of the hind legs in cats.2. In chloralose anaesthetized cats, shocks to the central end of the cut biventer cervicis muscle nerves leads to direct discharges over lumbosacral ventral roots, to a facilitation of monosynaptic reflexes in flexor and extensor muscles and to a prolonged inhibition of spino-bulbo-spinal reflexes. Such effects are not unique, but follow stimulation of skin and muscle nerves of the forepaw.3. Supratentorial pathways are involved in descending spinal interactions in the chloralose anaesthetized cat, but are more critical for interactions taking origin in biventer cervicis nerve than in forepaw nerves.4. In non-anaesthetized spinal cats showing interactions from forepaw nerves, no interactions could be found taking origin in biventer cervicis nerves. Descending interactions from forepaw nerves could be reduced or abolished by anaesthetic doses of chloralose.5. The rich pathway from biventer cervicis nerve to the superior colliculus does not appear to be involved in the descending interactions reported here as neither stimulation nor ablation of the superior colliculi has any effect on descending interactions.

Anesthesia, Intravenous↗
PubMed1990

Reflex activation of muscle spindles in human pretibial muscles during standing.

1. Experiments were performed in standing subjects to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the human foot reflexly influence fusimotor neurons innervating pretibial flexor muscles. Recordings were made from 30 identified muscle-spindle afferents, four tendon-organ afferents, and one alpha-motor axon innervating the pretibial flexor muscles. The subjects stood without support or vision on a force platform while trains of electrical stimuli (5 stimuli, 300 Hz) were delivered at nonpainful intensities to the sural nerve or to the posterior tibial nerve at the ankle. 2. Seventeen of the 30 spindle endings had no background discharge, and none was activated by the sural or posterior tibial stimuli. Five silent afferents were given a background discharge by sustained pressure on the relevant tendon, but with two the discharge was dominated by a tremor rhythm obscuring any reflex response to the stimuli. Based on peristimulus time histograms (PSTHs), the sural stimuli then produced increases in discharge of two of the remaining three endings at latencies of 84 and 90 ms. These effects could not be explained by muscle stretch and are presumed to have been fusimotor mediated. 3. When the subjects stood freely without support or vision, 13 muscle-spindle endings had a background discharge, but with three endings tremor developed at the ankle and dominated the spindle discharge. Sural stimuli affected the discharge of five of nine endings unaffected by tremor. With three of these endings, there were changes in discharge that could be explained by muscle stretch.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1980

Autonomic control of cardiovascular reflexes in narcolepsy.

Six male patients with narcolepsy for several years, were studied without and with amphetamine in order to evaluate possible abnormalities in autonomic control of the cardiovascular system. Studies were made of (1) heart rate and blood flow in the resting forearm during contralateral isometric handgrip, (2) respiratory sinus arrhythmia and (3) heart rate response to the Valsalva manoeuvre. The patients had a slow heart rate, a reduced forearm blood flow increase on handgrip, and a subnormal sinus arrhythmia. Only two out of the six patients had an abnormal Valsalva ratio. Amphetamine did not alter the response to handgrip but increased the sinus arrhythmia in three patients and the Valsalva ratio in two. It is concluded that narcolepsy is accompanied by reduced vegetative reactivity in the cardiovascular system. Since this applies to functions mediated by both the sympathetic and parasympathetic systems, and since some parasympathetically-mediated functions are affected while others are not, the functional disturbance found probably is of central origin.

Adult↗
PubMed1990

Vestibular autorotation testing of Menière's disease.

Ten patients with previously confirmed diagnosis of acute-stage Meniere's disease were tested with the Vestibular Autorotation Test (VAT), a portable computerized test that measures the higher-frequency vestibulo-ocular reflex (VOR) to compute gain and phase. Patients were asked to fixate on a target and move their heads in synchrony with a computer-generated, sweep-frequency audible cue (0.5 to 6.0 Hz) through an 18-second test epoch. Head movements in both horizontal (yaw) and vertical (pitch) planes were used separately to test horizontal and vertical VORs, respectively. All subjects easily performed the VAT. Results of the horizontal tests were within normal limits for both gain and phase. The vertical gain was markedly high throughout the 2 to 6 Hz range. Mean vertical phase lags were reduced at higher frequencies. These results imply that the vertical VORs of acute-stage Meniere's patients are hypersensitive to the faster vertical head movements that occur commonly in daily activities.

Adult↗
PubMed2003

Torsional and horizontal vestibular ocular reflex adaptation: three-dimensional eye movement analysis.

This study used visual-vestibular conflict to effect short-term torsional and horizontal adaptation of the vestibulo-ocular reflex (VOR). Seven normal subjects underwent sinusoidal whole-body rotation about the earth-vertical axis for 40 min (+/- 37 degrees/s, 0.3 Hz) while viewing a stationary radial pattern fixed to the chair (x0 viewing). During adaptation and testing in darkness, the head was pitched either up or down 35 degrees to excite both the horizontal and torsional VOR. The eyes were kept close to zero orbital elevation. Eye movements were recorded with a dual search coil in a three-field magnetic system. VOR gain was determined by averaging peak eye velocity from ten cycles of chair oscillation in complete darkness. The gain of the angular horizontal VOR (response to rotation about the head rostral-caudal axis) was significantly reduced after training in both head orientations. Angular torsional VOR gain (head rotation about the naso-occipital axis) was reduced in both head orientations, but this reached statistical significance only in the head down position. These results suggest that torsional and horizontal VOR gain adaptation, even when elicited together, may be subject to different influences depending upon head orientation. Differences between head up and down could be due to the relatively greater contribution of the horizontal semicircular canals with nose-down pitch. Alternatively, different VOR-adaptation processes could depend on the usual association of the head down posture to near viewing, in which case the torsional VOR is relatively suppressed.

Adaptation, Physiological↗
PubMedDate not supplied

[Torsion movements of the human eye. IV. Passive body movements, effect of skeletal muscle reflexes, opticokinetic torsion tracking].

A comparative study of torsional movement of the eye in passive and active tilting of the head and body of the object was carried out. Similarity of torsional movement of the eyes in passive and active movements was shown. It was found by the method of exclusion and selective stimulation of vestibular, cervikal, lumbar optokinetic reflexes, that neither the cervikal, nor lumbar reflexes elicited spontaneous torsional movements of the eyes and had no influence on them. A direct study (coinciding with rotation direction of the stimulus of head rotation) and the reverse (noncoinciding) torsional tracing of a rotating disc and tracing without head movements was investigated. During direct tracing depression of saccades and extention of the slow phase of torsion was found; during the reverse one--a decrease of the eye drist and increase of the amplitude and number of saccades. Phenomena of a seeming acceleration and deceleration of disc rotation etc. have been observed. It was found that with torsional saccades vision was retained. The presence of optokinetic control of phases of torsional eye movements formation has been recorded. Tracing without rotation of the head was accompanied by torsional nistagmus. Possible causes of incomplete stabilisation and optokinetic torsional tracing are discussed.

Eye Movements↗
PubMed1982

Sympathetic reflex control of resistance in collateral arteries in the lower extremities in patients with diabetes mellitus.

The vascular response in the lower extremities to 40 degrees head-up tilt was studied in 5 patients with occlusion of the superficial femoral artery and maturity onset diabetes mellitus with symptoms suggesting autonomic neuropathy. The pressure measurements were performed via catheters placed in the brachial artery, femoral artery and vein and popliteal artery and vein. Relative blood flow was calculated as the relative change in arterio-venous oxygen saturation. Absolute blood flow in the common femoral artery was measured by an indicator dilution technique. Resistance of the collateral arteries increased by 40% during head-up tilt compared with horizontal position. Total leg resistance increased by 24%. Vascular resistance did not change below the knee. Intra-arterial alpha-blockade abolished the increase of vascular constriction in the leg during head-up tilt indicating that alpha-adrenergic tone was present in limbs studied.

Aged↗
PubMed1987

Gain and phase of cat vertical eye movements generated by sinusoidal pitch rotations with and without head tilt.

Vertical EOGs were recorded in cats during sinusoidal head pitch from 0.01 to 4.0 Hz with peak velocities of 50 degrees X s-1. The purpose of the experiments was to determine whether dynamic response properties of the vertical vestibulo-ocular reflex (VOR) elicited by pitch with the animal lying on its side (on-side pitch) differ from those resulting from normal (upright) pitch. During on-side pitch (not changing head position with respect to gravity), the vertical VOR gain was 13.5% less than during upright pitch. Thus, the vertical VOR was more compensatory than during on-side pitch. Phase did not differ between the two conditions. The results indicate the importance of interactions between otolith and vertical canal stimulation for vertical eye movement control. The results imply that in micro-gravity, where head tilt does not lead to otolith stimulation as regards gravity, vertical head and eye movements may not be controlled appropriately, leading to vestibular-visual conflicts at the same time that horizontal eye movement controls are normal.

Animals↗
PubMed2005

Adaptive modification of the cats vestibulospinal reflex during sustained and combined roll tilt of the whole animal and forepaw rotation: cerebellar mechanisms.

In decerebrate cats, the electromyogram (EMG) activity of the forelimb extensor triceps brachii (TB) increases during side-down roll tilt of the whole animal (vestibulospinal reflex, VSR) at about 0.15 Hz. (+/-10 degrees ), while decreases during side up tilt. On the other hand, the TB activity increases during dorsal flexion of the ipsilateral forepaw (0.15 Hz, +/-5 degrees-10 degrees ), but decreases during ventral flexion. In six experiments, these stimuli were synergistically associated (side-down tilt coincided with dorsal flexion of the forepaw), so that the EMG modulation of the TB activity was greater than that induced by the individual stimuli. During a 3-h period of this sustained stimulation, the amplitude of the pure VSR progressively increased to reach the maximum value at the end of the third hour and persisted unmodified during the post-adaptation period (1 h). In three experiments, animal tilt and forepaw rotation were antagonistically associated (side-down tilt coincided with ventral flexion of the forepaw). In these instances the VSR gain remained on the average stable, but, at the end of the 3-h period of combined stimulation, a proportion of TB responses to animal tilt showed a phase reversal. In a digitigrade animal like the cat, a dorsal flexion of the wrist is associated with a decrease in limb length and would occur when the extensor tone is not appropriate to support body weight; we propose, therefore, that somatosensory volleys elicited by wrist rotation modify the gain of VSR so as to maintain postural stability. Inactivation, on the side of muscle recording, of the corticocerebellar region which projects to the lateral vestibular nucleus of Deiters, by local microinjection of the GABA-A agonist muscimol (0.5 microl at 16 microg/microl), decreased the already adapted gain of VSR. In conclusion, the results of this study suggest that somatosensory reafferent inputs to the cerebellar vermis are used to plastically modify the gain of VSR, when external forces produce changes in the final posture of the foot during animal tilt.

Adaptation, Physiological↗
PubMed1999

Dizziness in the elderly and age-related degeneration of the vestibular system.

The peripheral and central vestibular systems exhibit an age-related structural deterioration which may be responsible for vestibular reflex deficits and dizziness in the elderly. However, it seems likely that the central nervous system is capable of compensating for a certain degree of decline in function, since not all elderly people are impaired to the extent that the clinical signs of vestibular dysfunction are apparent. Dizziness and other vestibular disorders may develop only when the degree of deterioration of the vestibular system exceeds the ability of the nervous system to compensate. If dizziness does eventuate, it can have profound psychological consequences, particularly in terms of loss of confidence in independent activity, and may lead to the development of anxiety disorders. Vestibular rehabilitation programs may help to minimise the effects of age-related deterioration of the vestibular system and its psychological impact.

Aged↗
PubMed1985

Autonomic cardiovascular responses in old age.

The effect of age on autonomically mediated cardiovascular responses to certain manoeuvres was studied in 15, healthy, old men and women (60-80 years). The results were compared with groups of healthy young (about 25 years) and middle-aged (about 45 years) subjects. There was no significant reduction in cardiovascular responses between the young and middle-aged groups. Respiratory sinus arrhythmia, and heart rate, blood-pressure and contralateral forearm blood flow increases to isometric hand grip, as well as the heart rate decrease during a dive reflex test, were significantly attenuated in the old age group. The Valsalva ratio, and the heart rate and blood-pressure changes during an 8 min orthostatic test did not differ between the old and the two younger age groups. There seems to be only a moderate attenuation of autonomic cardiovascular responses to about 60 years, after which there is a more rapid decline. The difference in reduction between different responses, even those mediated by the same type of autonomic nerve, suggests that the decreased responses are not due to an isolated impaired function of the peripheral autonomic nerve. The impairment may be due to the receptor organ or a combination of defects in function of several parts of the autonomic nervous system in old age.

Adult↗
PubMed1996

Multiple but different genetic factors underlie enflurane and isoflurane requirements studied through backcross analysis in C57BL and ddN mice.

We performed a classic backcross analysis to examine the basic genetic nature of enflurane (ENF) and isoflurane (ISO) anesthetic requirement in two inbred mice strains, C57BL (BL) and ddN. We have previously reported different ENF and ISO anesthetic requirements in these two strains. BL (n = 22) and ddN (n = 26) mice were used as parents and were reciprocally crossed to produce F1 hybrid mice. Each F1 offspring was crossed to its parent to produce backcross siblings (BF1). Anesthetic end point was determined as the loss of righting reflex. Measurement of anesthetic requirement was performed during 8-12 wk after birth. Although ddN mice showed slightly less resistance to ENF and ISO compared with our previous report, they were more resistant than BL mice. Multivariate regression analysis of parents' and F1 hybrids' data revealed that, while maternal factors and factors on autosomes were related to both anesthetics, the factors on the X chromosome were ENF specific. A wide variation in anesthetic requirements among BF1 progeny suggested multifactorial inheritance. The regression equations obtained did not always predict anesthetic requirement in BF1 progeny. These discrepancies may be due to the epistatic interaction of related genes. We conclude that multiple but different genetic factors are involved in determining ENF and ISO anesthetic requirements in BL and ddN mice.

Anesthetics, Inhalation↗