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PubMed1976

Modifications and development of spinal reflexes in the alert baboon (Papio papio) following an unilateral vestibular neurotomy.

Unilateral vestibular neurotomy performed on 6 baboons was followed by the classical postural and locomotor postoperative disorders. Postoperative spinal reflex excitability was studied in these awake baboons by measuring monosynaptic recruitment ratios in soleus motoneuronal pool and the recovery cycle of the monosynaptic response. Vestibular neurotomy induces: (1) asymmetrical spinal reflexes with a decrease of the recruitment on the side of the section and an increase on the opposite side. (2) a modification of phases IV and V of the ipsilateral recovery cycle. The recovery during postoperative days of normal recruitment curves and recovery cycles is described. This recovery is relatively fast and relates closely to the compensation of postural and locomotor disorders. We note the importance of an early active motor exploration on the time-course of recovery: postoperative disorders in posture and locomotion are reduced much later when baboons are submitted to a motor restriction. These findings suggest a combined alpha and gamma-hypoexcitability of the ipsilateral hindlimb. The study of the recovery process suggests that the cerebellum is involved in the compensatory mechanisms. The regression of postural disorders, observed both in restrained and unrestrained baboons, demonstrates the importance of central regulations using proprioceptive afferents for recovery.

Animals↗
PubMed1983

The effect of head position upon jaw reflexes in the rat.

The vestibular apparatus of the decerebrate rat was stimulated by tilting the head dorsally or ventrally, with or without an associated stimulation of neck afferents i.e. either the head alone, or the head and body together, was tilted. The effect of such conditions, upon short latency reflexes elicited in antagonistic jaw and hyoid muscles, was examined. Reflexes in the different jaw and hyoid muscles were affected differently when the head was tilted, whether or not neck movement was permitted. Variations in the pattern of response in different animals were explicable on the basis of the known variable recovery of neck reflexes opposing the influence of the vestibular afferents. Head position can therefore be an important but complex factor which may enhance or depress reflex activity differentially in the different masticatory muscles, at least in the experimental situation.

Animals↗
PubMed1994

Rotational kinematics of the human vestibuloocular reflex. II. Velocity steps.

1. Gain matrices were used to quantify the three-dimensional vestibuloocular reflex (VOR) in five human subjects who were accelerated over 1 s and then spun at a constant 150 degrees/s for 29 s in darkness. Rotations were torsional, vertical and horizontal, about earth-vertical and earth-horizontal axes. 2. Elements on the main diagonal of the gain matrices were much smaller than the optimal value of -1, and torsional gain was weaker than vertical or horizontal. Off-diagonal elements, indicating cross talk, were minimal except for a small but consistent horizontal response to torsional head rotation. 3. Downward slow phases were more than twice as fast as upward at the start of rotation about both earth-vertical and earth-horizontal axes, but the asymmetry vanished later in the rotation. 4. During earth-vertical-axis rotation, all matrix elements decayed to zero. The main-diagonal torsional and vertical gains waned with time constants close to that of the cupula (6.7 and 7.3 s). Velocity storage prolonged the horizontal response to horizontal head rotation (time constant 14.2 s) but not the horizontal response to torsion (7.7 s). A simple explanation is that velocity storage acts on a central estimate of head motion that accurately distinguishes horizontal from torsional and that the inappropriate horizontal eye velocity response to torsion occurs because of cross talk downstream from velocity storage. 5. During earth-horizontal-axis rotation, the torsional, vertical, and horizontal main-diagonal elements declined, with time constants of 7.6, 8.2, and 7.9 s, to maintained nonzero values, all equal to about -0.1. Off-diagonal elements, including the horizontal response to torsion, decayed to zero, so that the otolith-driven reflex, late in the rotation, was equally strong in all dimensions and almost free of detectable cross talk. 6. The difference between gain curves over the course of earth-vertical- and earth-horizontal-axis rotations was not constant but increased with time, suggesting that the VOR response to earth-horizontal-axis rotation is not a simple sum of canal and otolith reflexes.

Acceleration↗
PubMedDate not supplied

The vestibulocollic reflex.

Stabilization of the head is required not only for adequate motor performance, such as maintaining balance while standing or walking, but also for the adequate reception of sensory inputs such as visual and auditory information. The vestibular organs, which consist of three approximately orthogonal semicircular canals (anterior, horizontal, posterior) and two otolith organs (utriculus, sacculus), provide the most important input for the detection of head movement. Activation of afferents from these receptors evokes the vestibulocollic reflex (VCR), which stabilizes head position in space. In this review, which is the outgrowth of a session of the vestibular symposium held in Hawaii in April, 1994, we discuss the neural substrate of this reflex and some aspects of the central processing involved in its production. Some topics are not considered, in particular the important interaction between the VCR and the cervicocollic reflex evoked by activation of neck afferents (70,119), and attempts to model the reflex (69).

Afferent Pathways↗
PubMed1993

The possible effect of periodontal diseases on occlusal function.

This paper raises new questions about the relationship between occlusion and periodontics. Specifically, it raises questions about the effect of periodontal diseases on mechanoreceptors in the periodontal ligament. Periodontal mechanoreceptors transmit information from the periodontium to various reflexes coordinated by the central nervous system. One of these reflexes is the trigemino-neck reflex. Its function is to change the position of the head, neck, and jaws on a moment-to-moment basis, and it powerfully influences the occlusal position. This paper raises questions about the consequences of periodontal diseases on all reflexes that depend on periodontal mechanoreceptors, and specific questions are raised about the effect of periodontal disease on the trigemino-neck reflex because of its extreme importance to the way we analyze and treat occlusion.

Dental Occlusion↗
PubMed1997

The functional effectiveness of neck muscle reflexes for head-righting in response to sudden fall.

Reflex head-righting in normal and labyrinthine-defective (LD) subjects was compared to identify the relative functional effectiveness of vestibular-collic and cervico-collic myotactic reflexes. To restrict stimuli largely to the head and neck, subjects lay supine, supported up to the shoulders on a horizontal bed with their head supported in a sling over the edge. The head fell freely as the sling was released with an electromagnetic catch. Head drops were delivered with the subjects instructed to relax and accept the fall passively or to actively right the head as fast as possible. With both instructions, righting responses in normal subjects commenced with electromyographic (EMG) bursts in the sternocleidomastoid (SCM) at 24.5 ms latency, which was reflected in a deceleration of the downwards head velocity. The latency of the earliest EMG responses in LD subjects was 67.4 ms, accompanied by similar deceleration. It is assumed that the earliest response in normal subjects is vestibular, whereas in LDs the SCM stretch reflex is the earliest response. These reflexes are followed at circa 100 ms by more intense EMG activity due to voluntary movement, but braking of head fall is evident before voluntary activity takes effect. Righting was more effective in normal subjects than in LDs, and when "active" normal subjects made more vigorous righting responses than when "passive"; whereas active righting in LDs was no better than passive. The results demonstrate that reflex responses contribute significantly to head-righting. The vestibular contribution gives an advantage over stretch reflexes alone and also assists in voluntary enhancement of reflex responses.

Acceleration↗
PubMed2004

Investigations on the influence of serum D-lactate levels on clinical signs in calves with metabolic acidosis.

Correlations between the degree of acidosis and clinical signs (changes in posture, behaviour, intensity of suckling reflex) in neonatal diarrhoeic calves have been described in various studies. However, base excess values varied widely in calves exhibiting similar clinical symptoms. The objective of this study was to elucidate whether the clinical picture of acidotic calves with neonatal diarrhoea is influenced more by D-lactate concentration than by degree of acidosis. Eighty calves up to three weeks old that were admitted to the II Medical Animal Clinic with acute diarrhoea and base excess values between -10 and -25 mmol/L were included in the prospective study. Posture, behaviour, suckling and palpebral reflexes, and position of the eyeballs were scored during the initial examination. Base excess and serum D-lactate and urea concentrations were determined in venous blood. In order to quantify the influences of base excess and d-lactate on the clinical parameters, groups of different clinical categories were compared. The results show that variations in behaviour, and in posture can be better explained by elevations of serum D-lactate concentrations than by decreases in base excess. Disturbances of the palpebral reflex appear to be almost completely caused by high levels of D-lactate.

Acid-Base Equilibrium↗
PubMed1988

Improved recovery of nigro-striatally hemitransected rats induced by (Nle4, D-Phe7)alpha-MSH: a central effect.

Rats were subjected to nigro-striatal hemitransection and then intracerebroventricularly infused with the potent and long-acting alpha-MSH analogue, (Nle4, D-Phe7)alpha-MSH, at two different doses (15 or 30 ng/h/rat), or with saline (0.6 microliter/h/rat), continuously for 14 days starting on day 2 after lesion. (Nle4, D-Phe7)alpha-MSH dose-dependently improved the sensorimotor deficit (postural asymmetry, impaired limb reflexes and coordinated limb use, signs of cortical and pyramidal lesion), reduced turning behaviour induced by apomorphine, and increased spontaneous motility in the open field. 3H-Spiperone binding showed that (Nle4, D-Phe7)alpha-MSH treatment caused a down regulation of the striatal DA receptors in the lesioned side, contrary to the supersensitivity developed by the corresponding receptors of saline treated rats. These results indicate that melanopeptides improve the functional recovery of nigro-striatally hemitransected rats, by an action at CNS level.

Animals↗
PubMed1982

Effect of tilting on adipose tissue vascular resistance and sympathetic activity in humans.

To study baroreceptor reflex control of human adipose tissue circulation, head-up tilting (to 80 degrees for 10 min) was performed in eight healthy volunteers. Blood flow in subcutaneous adipose tissue and skeletal muscle on the arm was evaluated by local clearance of 99mTcO4-. The isotope depots were maintained at heart level throughout the experiment. Tilting induced rapid increases in plasma norepinephrine and epinephrine, heart rate, and diastolic but not mean arterial pressure. There was rapid vasoconstriction in both adipose tissue and skeletal muscle followed by vasoconstrictor escape during tilting and a brief period of hyperemia after tilting. The vascular resistance index [mean arterial pressure/disappearance rate (kappa) of 99mTc (%/min)] increased from 16 +/- 2 to 41 +/- 9 U (P less than 0.05) in adipose tissue and from +/- 3 to 44 +/- 15 U (P less than 0.05) in skeletal muscle. Tilting caused an initial decrease followed by an increase in arterial plasma glycerol without concomitant changes in plasma immunoreactive insulin. The vascular and glycerol responses to tilting closely resemble canine subcutaneous adipose tissue responses to sympathetic nerve stimulation. The present experiments show baroreceptor reflex-induced vasoconstriction in human adipose tissue, which presumably is mediated by sympathetic nerve activity.

Adipose Tissue↗
PubMed1991

A case of syndrome of inappropriate secretion of antidiuretic hormone associated with diabetes mellitus.

A 46-year-old man, presenting with headache, nausea, and lassitude, was diagnosed as having diabetes mellitus and hyponatremia, and admitted to Tohoku University Hospital. Insulin treatment improved the hyperglycemia but aggravated hyponatremia, which was proved to be elicited by the inappropriate secretion of antidiuretic hormone (SIADH). An acute water load failed to suppress ADH release in the supine posture but slightly increased plasma atrial natriuretic peptide (ANP). On the other hand, plasma ADH markedly increased in response to an upright posture, accompanied by a fall in blood pressure and a rise in heart rate. After treatment with droxidopa "a sympathomimetic drug", ambulatory blood pressure gradually increased and hyponatremia disappeared. However, blood pressure and ADH responses to upright posture were not improved by treatment with the drug. Moreover, plasma ADH was still not sufficiently suppressed by acute water loading in the supine position, but plasma ANP markedly increased, thereby resulting in urinary dilution and natriuresis. These results suggest that exaggerated ADH release (SIADH) was brought about by the baroreceptor reflex stimulated by the postural hypotension, and also by the impaired osmoregulation associated with diabetic neuropathy, and that droxidopa improved cardiovascular function and increased ANP release with resultant urinary dilution and natriuresis in spite of slightly increased ADH release.

Blood Pressure↗
PubMed1979

Facilitation of the lordosis reflex of female rats from the ventromedial nucleus of the hypothalamus.

1. Effects of electrical stimulation of hypothalamic ventromedial nucleus (v.m.n.) on the lordosis reflex of female rats were examined in ovariectomized and oestrogen-primed animals with chronically implanted electrodes. 2. Lordosis triggered either by manual cutaneous stimulation or by male mounting, was facilitated by electrical stimulation of the v.m.n. 3 A gradual increase in lordosis performance followed a relatively long period of stimulation; never less than 15 min and usually about 1 hr of stimulation was necessary for maximum facilitation. Following the termination of stimulation, the performance returned gradually to the control level during a 5--8 hr period. 4. The optimal frequency of stimulation was between 10 and 30 Hz. Threshold for effective facilitation was, on the average, 12.5 microA. 5. Stimulation tended to induce larger facilitation when applied to the lateral side of v.m.n. 6. Pre-treatment with oestrogen was necessary to obtain facilitation by v.m.n. stimulation. The threshold dosage of oestrogen was 2.5 microgram per animal. 7. Stimulation was effective in adrenalectomized rats, in dexamethasone-primed animals, and in rats pre-treated with exogenous progesterone. Thus, adrenal prodesterone release is not required for the v.m.n. facilitation of lordosis. 8. Medial preoptic stimulation with the same parameters suppressed the lordosis reflex. 9. The v.m.n. participates in the control of lordosis by a facilitatory output. The delay before facilitation implies that the v.m.n. is not in the direct reflex-arc for the execution of lordosis. Rather, a summation or interaction process with an unusually long time course is involved.

Animals↗
PubMedDate not supplied

Can short-latency vestibulospinal reflexes in lower leg muscles be elicited by tapping the head?

A gentle tap on the forehead evoked short-latency motor responses in the sternocleidomastoid muscle, which may be vestibulocollic reflexes with characteristics similar to those elicited by clicks. We tested this paradigm in subjects standing upright, in order to determine the differential effects of taps on the forehead on the patterns and latencies of spinal stretch and vestibulospinal reflexes, which are important for postural control. Taps on the forehead elicited short-latency inhibitory electromyographic responses in both gastrocnemius muscles with a mean latency of 48.3 +/- 3.1 ms (onset) to 98.3 +/- 6.3 ms (end). Taps on the sternum elicited similar responses from the gastrocnemius muscles, indicating that vestibular stimulation is not essential for eliciting these responses. Both responses may play a role in predetermining the strategy for correcting body perturbations. The actual reflex is probably elicited by somatosensory input from the neck, which converges with vestibular input for the multisensory control of posture.

Acceleration↗
PubMed1984

Primary dysfunction of the afferent limb of the arterial baroreceptor reflex system in a patient with severe supine hypertension and orthostatic hypotension.

A 33 year old man with a history of recurrent episodes of orthostatic dizziness since adolescence was noted to have a supine blood pressure of 200/120 mm Hg and a standing blood pressure of 90/60 mm Hg. Results of extensive laboratory studies for secondary hypertension were negative. Studies of the autonomic nervous system function revealed normal plasma catecholamines, cold pressor test and response to 4 minute 30% of maximal static handgrip contraction and an appropriate increase in heart rate on intravenous injection of atropine. In contrast, the heart rate response to phenylephrine and sodium nitroprusside infusion, carotid massage and graded neck suction with an airtight chamber was very abnormal, indicating marked dysfunction of the afferent limb of the arterial baroreceptor reflex system. Methyldopa decreased the supine hypertension and increased the standing blood pressure.

Adult↗
PubMed1989

Pharmacological and metabolic interactions between ethanol and methyl n-butyl ketone, methyl isobutyl ketone, methyl ethyl ketone, or acetone in mice.

Methyl n-butyl ketone (MnBK), methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), and acetone are widely used industrial solvents to which certain groups of workers are exposed. Pharmacological and metabolic interactions between these solvents and ethanol were explored in male CD-1 mice. The effects of these solvents on the duration of ethanol-induced loss of righting reflex and on ethanol elimination in mice were studied. The solvents were dissolved in corn oil and injected intraperitoneally 30 min before ethanol 4 g/kg ip. The four solvents prolonged significantly the duration of ethanol-induced loss of righting reflex when given in the following doses (mmol/kg): MnBK, 3.75 and 5; MIBK, 5; MEK, 5 and 10, acetone, 20 and 40. This prolongation was dose related and increased as the dose of the solvent was increased. The concentrations of ethanol in blood or brain on return of the righting reflex were similar in solvent-treated and control animals, with the exception of the group of mice treated with 40 mmol/kg acetone in which the ethanol concentrations were significantly lower than in control animals. The mean elimination rate of ethanol was markedly reduced in mice treated with MnBK 5 mmol/kg, MEK 15 mmol/kg, and acetone 40 mmol/kg. All four solvents reduced the activity of mouse liver alcohol dehydrogenase in vitro. It is concluded that enhancement of the ethanol-induced loss of righting reflex by these solvents in mice is well correlated to reduced elimination rate of ethanol.

Acetone↗