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PubMed1982

Regulation of subcutaneous blood flow during head-up tilt (45 degrees) in normals.

Local and remote regulation of subcutaneous blood flow in the forearm and leg was studied during head-up tilt (45 degrees) in 6 young healthy male subjects. Relative blood flow was estimated by the local 133Xe washout technique. Lowering of a leg to a 51% decrease in its subcutaneous blood flow due to a veno-arteriolar reflex elicited by the increase in venous transmural pressure. During head-up tilt subcutaneous blood flow in the arm remaining at heart level decreased by 27%, in the leg blood flow decreased by 50%. Following proximal nervous blockade, head-up tilt did not induce vasoconstriction in forearm at heart level, but blood flow in distal leg decreased by 45%. Thus there was no difference in the vasoconstrictor response in the leg to head-up tilt or lowering of the labelled area by 40 cm. Since head-up tilt caused neurogenically mediated vasoconstriction in subcutaneous tissue, subcutaneous blood flow in the extremities seems to be regulated by remote (baroreceptor) as well as local sympathetic reflex mechanisms (veno-arteriolar reflex).

Adult↗
PubMed1979

The effects of phenytoin on motor function in awake cats.

Adult cats were monitored for their performance of a variety of motor functions before and after acute administration of phenytoin (5, 10 or 20 mg/kg) in a schedule in which each animal received all drug doses. The only significant loss in motor function was balance and coordination. Half the animals could not balance or walk along a narrow-edged beam after 20 mg/kg of phenytoin although their performance was not impaired at lower drug doses or on wider surfaces. There were no effects of phenytoin on the righting reflex, flexor reflex, muscle strength, the hopping response, the blind placing response or visually aided placing. The data suggest that phenytoin has a selective effect on higher order neuronal systems involved with balance and locomotion rather than simple reflex pathways.

Animals↗
PubMed1997

Anatomy and physiology of the upper esophageal sphincter.

The upper esophageal sphincter (UES) is composed of the cricopharyngeus (CP), thyropharyngeus (TP; inferior pharyngeal constrictor [IPC] in humans), and cranial cervical esophagus. All 3 muscles may at times function to maintain tone in the UES, but only the CP contracts and relaxes in all physiologic states consistent with the UES. The CP is a striated muscle composed of variable-sized small (25-35 microm) muscle fibers that are primarily type I (slow twitch), highly oxidative, and contain abundant (40%) endomysial elastic connective tissue. The fibers may attach to the connective tissue framework, forming a muscular net. In humans and rats, but not other animals, the CP has no median raphe. The optimum length of the CP for development of active tension is about 1.7 times resting length; therefore, in some respects the CP acts more like cardiac than striated muscle. A passive tone in the CP is present and increases through all degrees of stretch. The high compliance of the CP allows it to be opened by distraction of other muscles (e.g., geniohyoideus) or increased intraluminal pressure. The CP is innervated by branches of the vagus nerves: pharyngoesophageal (PE), superior laryngeal (SLN), and recurrent laryngeal (RLN); glossopharyngeal (GPN); and cervical sympathetics. Only the PE and SLN provide motor fibers to the CP. The GLN may be sensory; the sympathetics may innervate the mucosa, blood vessels, and glands; but no functional innervation by the RLN has been identified. Parasympathetic ganglia and various peptides (galanin, cGRP, VIP, neuropeptide Y, substance P, tyrosine hydroxylase) have been found in the CP, but their role in control of the CP is unknown. The motoneurons of the CP are found in the nucleus ambiguus, and the innervation is ipsilateral for animal species in which the CP has a median raphe. These motoneurons are topographically organized with other pharyngeal and laryngeal muscles and the striated muscle esophagus. Pharyngeal motoneurons often have a respiratory rhythm, but not a spontaneous background discharge. Therefore, the CP motoneurons may not generate CP tone. Various reflexes control the tone of the CP. Distension of the esophagus causes contraction of the CP and UES, which is mediated by a vago-vagal reflex. Pressure on the pharyngeal mucosa contracts the CP and UES and is mediated by a glossopharyngo-vagal reflex. Inflation of the lungs causes contraction of the CP and UES, which is mediated by a vago-vagal reflex. The pharyngo-UES and pulmonary-UES reflexes may generate the respiratory rhythm often observed on UES pressure or electromyographic activity. The UES or CP also contracts with arousal or with changes in posture. All of these reflexes and responses and the passive elastic properties of the CP may contribute to the generation of tone in the CP and UES.

Animals↗
PubMed1984

Responses of lateral hypothalamic neurons to simulative hypogravic condition induced by body suspension.

In unanesthetized rats, neuronal activity in the lateral hypothalamic area was recorded during horizontal and head-down tilt suspension. When the rat was raised in the horizontally suspended position, 21 of 44 neurons changed activity as follows: immediate increase (7/21, Type I), immediate decrease (3/21, Type II), and gradual decrease (11/21, Type III). When the rat was raised with a head-down tilt position, the responses were suppressed in about half of the neurons tested. These results showed that the LHA neurons altered their activity in response to low G simulation induced by body suspension. Possible signals which induce the changes in the LHA neuronal activity, and an involvement of the LHA in the autonomic reflexes under hypogravic condition are discussed.

Animals↗
PubMed1991

Cardiovascular responses to tilting in healthy newborn babies.

It has been suggested that newborn infants have immature baroreceptor responses and they are unable to maintain their blood pressure (BP) by appropriate reflex peripheral vasoactivity and heart rate (HR) changes in response to tilting. We have measured simultaneously upper arm and calf systolic and diastolic BP and HR every 30 s using an oscillometric method (Dinamap 847) in quiet and active sleep in 9 term babies. Measurements were performed continuously with 5-min periods in each of three positions; horizontal, 30 degrees head up and 30 degrees head down tilt. The results were analysed using unbalanced analyses of variance and multivariate regression. All responses were proportional to the angle of the tilt. The observed values were very close to those predicted from the model. HR increased and decreased by 3.25 beats/min (bpm) on 30 degrees up and down tilting respectively and by twice this amount when tilting through 60 degrees. Arm systolic and diastolic BP both decreased by 1.3 mmHg when tilting through 60 degrees from down to up and increased correspondingly with down-tilting. Calf systolic BP changed appropriately for the change in hydrostatic pressure (+7.37 mmHg with 30 degrees up tilting), but diastolic BP rose only by 60% of this value. The results showed no individual variation, were independent of day, sleep state, the number of tilts, the starting value of the BP and the direction of the previous tilt. This study shows that the healthy newborn has a well developed baroreceptor reflex.

Blood Pressure↗
PubMed1979

Deficit in the lordosis reflex of female rats caused by lesions in the ventromedial nucleus of the hypothalamus.

1. The effect of electrolytic lesions of the ventromedial nucleus of the hypothalamus (v.m.n.) on the lordosis reflex has been investigated on ovariectomized female rats. Lesions were made through chronically implanted platinum-iridium electrodes. 2. V.m.n. lesions did not disrupt lordosis immediately, but induced a gradual decline in the reflex. Lordosis performance reached it minimum no less than 12 hr after the lesion, and typically after 36--60 hr. 3. The magnitude of the lordosis deficit was related to the amount of v.m.n. damage. Destruction of other hypothalamic regions was without appreciable relation to the deficit. Within v.m.n., lesion size in the lateral, but not medial portion was significantly correlated with lordosis deficit. 4. Because of the slow time courses of v.m.n. lesions and stimulation (Pfaff & Sakuma, 1978) effects, it is postulated that the v.m.n. is not part of the direct reflex-arc for lordosis. Rather, neurones in v.m.n. are likely to exert a tonic hormone-dependent bias on brain stem reflex paths for this behaviour.

Animals↗
PubMed1975

Eye, head and body movements of the guinea pig in response to optokinetic stimulation and sinusoidal oscillation in yaw.

Reflex head and eye movements were observed in the guinea pig subjected to optokinetic stimulation and whole body oscillation in the yaw axis. Optokinetic stimuli induced low velocity head movements in the direction of the stimulus with stepwise movements in the opposite direction. With motion stimuli, the head was well stabilized in space and moved to new positions in stepwise manner; in the absence of vision the head was not able to maintain a stable position. The onset of a stepwise head movement was always synchronized with a saccadic eye movement in the same direction, the coordination being similar to voluntary movement. During good head stabilization, vestibular-ocular nystagmus did not occur. The guinea pig appears to avoid nystagmus by stabilizing its head preferentially. It is likely that the vestibular ocular reflex compensates for head displacement with unity gain in the frequency range of voluntary and stepwise reflex head movement and that a close relationship exists between the control of saccadic eye movements and that of voluntary or reflex head movement.

Animals↗
PubMed1989

Vestibulo-ocular abnormalities in spasmodic torticollis before and after botulinum toxin injections.

In order to establish whether vestibular abnormalities often found in spasmodic torticollis are secondary to the abnormal head posture, the vestibulo-ocular reflex (VOR) was studied in eight patients before and after correction of head posture with botulinum toxin. Eye movements were recorded in the dark during sinusoidal and velocity step rotation. Four patients showed a significantly asymmetric response, with the slow phase of the VOR more active ipsilateral to the torticollis (chin). Despite significant improvement of the head posture in all patients for up to 10 weeks following treatment, no correction of the vestibular asymmetry occurred. This suggests that the VOR abnormalities are not caused by the head posture itself. We interpret the findings as evidence of primary involvement of the vestibular system in torticollis and we postulate a widespread derangement of the sensory-motor mechanisms controlling head posture in this disease.

Adult↗
PubMed1990

Fourier analysis of the relation between the discharge of quadriceps motor units and periodic mechanical stimulation of cat knee joint receptors.

It has been widely assumed that joint receptors contribute to the reflex regulation of movement and posture, although there have been few clear demonstrations of joint-mediated reflex actions on alpha-motoneurones other than those attributable to flexor reflex afferents. The present study extends our recent work on joint-mediated reflexes by using Fourier analysis of spike train interactions to demonstrate that restricted mechanical activation of a small number (one to five) of knee joint receptors by localized indentation of the joint capsule can modify the firing pattern of quadriceps motoneurones in decerebrated cats. The modulation of this discharge pattern can be reversibly abolished by application of droplets of lignocaine directly to the joint nerve and consequently can be attributed unambiguously to articular afferents. Activation of single joint afferents could on occasion produce changes in motor unit firing patterns, but usually activation of two or more was required before secure effects were observed. Increasing the intensity of indentation (resulting in activation of greater numbers of joint receptors) increases the strength of coupling between joint afferent input and motor unit responses, although the relationship is not linear. The relation between the discharge patterns of pairs of motor units was also examined, and it was found that significant coupling occurred at the stimulus frequency, superimposed on a 'background' coupling from unidentified sources. The phase relationship between pairs of motor units was not affected by the periodic stimulus. However, it was observed that if two motor units were firing independently of one another in the absence of capsule probing, maintained capsular indentation produced a striking synchronization between the discharges of the two motor units. These experiments show strong joint-mediated reflex effects on motor unit firing indicating that joint receptors may have an important role to play in motor control.

Action Potentials↗