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PubMed1985

[Circulatory and hormonal changes induced by microgravity].

The absence (or decrease) of the hydrostatic pressure during space flights (microgravity state) or simulations of weightlessness (by immersion, bed rest or head-down tilt) result in a body fluid shift and an engorgement of the central circulation where mechanoreceptors involved in plasma volume regulation are located. Their activation induces the initial (first hours) hormonal response with a decrease in plasma vasopressin, renin and aldosterone and probably an increase in a natriuretic factor (Gauer reflex). Prolonged exposure to microgravity leads to more complex and often hypothetical responses: cardiovascular deconditioning, modifications in secretion and circadian rhythms of above cited hormones. After 24 years of studies on approximately 200 astronauts our knowledge of cardiovascular and hormonal adaptation to space flight is still at the beginning.

Adaptation, Physiological↗
PubMed1985

The effect of nicardipine on blood pressure, its variability and reflex cardiac control.

Eight untreated patients with essential hypertension (average casual blood pressure 180/110 +/- 27/12 mm Hg) were studied following control, acute (a single oral dose of 30 mg nicardipine hydrochloride), and chronic (2 months nicardipine oral therapy) treatment periods. During the 2 month treatment period, ambulatory mean intra-arterial (IABP), measured when the patients were awake, fell from 165/105 +/- 6/12 (control) to 150/96 +/- 14/12 mm Hg (P less than 0.05), but heart rate remained unchanged (84 +/- 12 control vs 80 +/- 9 beats min-1). There was an absolute reduction in blood pressure in response to tilting, the Valsalva manoeuvre, and exercise handgrip, but the percent increase in pressure following nicardipine was not significantly different from that in the control period. There was no change in baroreflex sensitivity after either acute or chronic treatment, but the set point of the reflex was reset to a lower pressure following chronic therapy. Both single and multiple doses of nicardipine significantly reduced intra-arterial pressure. Chronic therapy was associated with return of the heart rate to control values, which was due to resetting of the baroreflex control mechanism.

Adult↗
PubMed1991

Modelling the action of caloric stimulation of the vestibule. II. The mechanical model of the semi-circular canal considered as an inflatable structure.

In order to explain the mechanical effects that arise when a semi-circular canal is thermally stimulated in the horizontal position (i.e. in the absence of gravity effects) a physical model was used. The duct (corresponding to the canal) is deformable, the pressure transducer (corresponding to the ampulla) is not deformable. There is no thermal similarity but a dynamical similarity has been respected, so the mechanical phenomena occurring in the semi-circular canal and in the model are identical. The time scale is close to one. The physical model showed that the relative volume variations (fluid/duct) due to caloric stimulation lead to a pressure variation measured by the pressure transducer at the place of the ampulla and the cupula. The time history and the value of this pressure depend on the mechanical and thermal properties of the duct and the fluid. The qualitative responses of the physical model and of the vestibulo-ocular reflex after caloric stimulation were coherent. A numerical model simulating the same mechanisms yielded a quantitative estimation of the transcupular pressure arising in a horizontal semi-circular canal (i.e. without gravity dependent effects) during caloric stimulation. The physical model and the numerical simulation take no account of the inflating pressure variation.

Caloric Tests↗
PubMed1999

Methionine enhances alcohol-induced narcosis in mice.

Methionine is an essential amino acid that has been used as a therapeutic drug in some disorders. In this study we questioned whether methionine affects ethanol-induced loss of righting reflex (narcosis). One hour after IP methionine administration (60, 120, 240, 480, 720, 960, and 1280 mg/kg), mice were injected with ethanol (4.0 g/kg), and the duration of loss of righting reflex was recorded. Methionine, at the higher doses (960 and 1280 mg/ kg), significantly increased this effect on ethanol-treated animals. A time-course study revealed that methionine increased the duration of the loss of righting reflex induced by ethanol until 4 h after being injected. Because methionine did not affect blood ethanol levels, no change in peripheral alcohol can explain the observed effects. This potentiation was not specific for ethanol because methionine increased 3-methyl-1-butanol (0.6 g/kg) and 1-propanol (2.4 g/kg)-induced loss of righting reflex as well. Therefore, the results obtained in this study suggest the need for further investigation into methionine-ethanol interactions prior to the use of methionine as an agent that can be used as an antidepressant and to prevent damage to organic tissue in alcoholism.

1-Propanol↗
PubMedDate not supplied

[The effect of alcohol (ethanol) on the reactions of the vestibular system].

The influence of ethanol upon dynamics of rotatory (RN) and post-rotatory nystagmus (PRN), trunk pose-tonic reflexes and their vegetative (cardiac, respiratory) components was studied in chronic experiments on rabbits with the help of electronystagmo- and electromyography. Ethanol was administered once intra-abdominally (1 g/kg) and one time a day during 30 days. Alcohol concentration in blood was determined by gas-and-fluid chromatography. The animal which were given isotonic solution of sodium chloride in the same doses and quantities served as a control group. It was established that vestibular oculomotor reflexes are mainly facilitated in an acute period of ethanol administration, then their inhibition occurs. Besides, the changes of PRN are stronger expressed than those of RN. Labyrinth pose-tonic reflexes are more often inhibited under the influence of ethanol; their strongest depression was observed during the first hour after ethanol administration and on the 15th day of chronic alcoholization. In alcoholization the changes of vestibular-vegetative reaction occur; primary short-term weakening of vestibular influences upon cardiac rhythm and respiration with their subsequent increasing.

Alcoholic Intoxication↗
PubMed1984

Tonic cervical influences on eye nystagmus following hemilabyrinthectomy: immediate and plastic effects.

In intact guinea pigs a passive horizontal rotation of the body about the fixed head induces compensatory ocular movements (cervico-ocular reflex). When the static neck deviation is maintained, a significant ocular displacement is observed. In acutely hemilabyrinthectomized animals, static body deviation towards the lesion side tonically alters eye nystagmus. It affects slow phase eye velocity and quick phase amplitude and frequency causing the eye to reach a less eccentric orbital position. Apart from such immediate influences, a plastic effect on eye nystagmus abatement is induced. In the animals restrained with no body-on-head deviation, abatement of nystagmus is delayed with respect to the animals restrained with 35 degrees body deviation towards the lesion side. Thus the head position signal is not only a contributing factor for the correction of postural deficits but also influences the time course of the ocular balancing process following unilateral vestibular damage.

Adaptation, Physiological↗
PubMed2004

Mal de debarquement and posture: reduced reliance on vestibular and visual cues.

OBJECTIVE: The neural mismatch theory assumes that the intersensory conflicts leading to motion sickness are resolved by changes in the relative weighting of the various senses that contribute to orientation. If this sensory rearrangement persists after disembarkment, it might result in mal de debarquement (MD): ataxia and a rocking sensation sometimes felt after landing. The objective of the present study was to examine possible changes in sensory organization in naval crew members with differing susceptibility to MD with computerized dynamic posturography (CDP). STUDY DESIGN: Cross-sectional parallel-group design. METHODS: Seventeen subjects susceptible to MD (SMD) and 17 subjects nonsusceptible to MD (NSMD) (healthy male volunteers aged 18-22) participated in the study. CDP was performed twice with each subject, before and immediately after sailing, using the EquiTest system (NeuroCom, Inc., Clackamas, OR). RESULTS: The SMD group showed a significant reduction in their scores on sensory organization tests 3, 4, and 5 after sailing. Sensory pattern analysis revealed reduced use of inputs from the vestibular and visual systems to maintain balance. Prolonged latencies of the motor responses to unexpected pitch perturbations were also recorded in the postsailing CDP of the SMD group. Reduced performance on the presailing CDP task, which presents the greatest challenge to the vestibular system, was found to control for the presence of MD postsailing. CONCLUSIONS: The results show that MD is associated with postural instability, slower motor reflexes, and larger sways in response to abrupt changes in the body's center of gravity. These findings may be explained by under reliance on vestibular and visual inputs and increased dependence on the somatosensory system for the maintenance of balance.

Adult↗
PubMed1994

[The vestibular system: from structure to function].

The two vestibular receptors, right and left, hidden in the petrous part of the temporal bone with the cochlear receptors, receive information from angular and linear movements of the head and transform them into a nerve message sent to the nuclei of the brainstem, which are connected directly on the one hand to the oculomotor nuclei, at the origin of the oculovestibular reflex (induction of nystagmus), and on the other hand, to the spinal motor neurons, at the origin of the vestibulospinal reflex. These reflexes are associated with responses to visual and somaesthetic information for maintenance or return to the standing position, which characterises the function of equilibrium. Vertigo and disorders of balance reflect a conflict of information between these two labyrinths, or between the vestibular apparatus and the messages issued by other captors, and sometimes also dysfunction of central nervous system treatment of information or a lesion of the effector motor systems.

Ear, Inner↗
PubMed1988

Vestibulo-ocular reflex and gaze functions in a patient with congenital inner ear anomalies.

We report on the vestibulo-ocular reflex (VOR) and gaze functions during horizontal rotations as well as upright locomotions in a fisherman with congenital inner ear anomalies. The finding of a marked gaze disturbance due to low VOR gain during passive rotations resembled that found in early acquired lesions. There was an improvement during active rotations, suggesting an intensified cervico-ocular reflex. Although head oscillations in the horizontal plane were abnormally large during stepping and running, they were compensated for visually even at high frequencies. The absence of complaints of oscillopsia as well as his ability to achieve proper balance seemed to be accomplished by his optokinetic ability, regularly transformed head oscillations and modified perceptive mechanisms at higher cortical levels.

Adult↗
PubMed1974

Relation of neurological findings after cardiac arrest to outcome.

Routine neurological examination of patients one hour after cardiac arrest seems to be of value in determining the prognosis for life and likelihood of intellectual impairment.In 48 patients 53 episodes of cardiac arrest were followed by serial neurological examinations. Patients were divided into two groups according to neurological findings one hour after cardiac arrest. Patients in group 1 were unresponsive or at most responded in a reflex fashion to painful stimuli at one hour; these patients died or survived with intellectual damage. Patients in group 2 responded purposefully at one hour and survived without neurological damage. These patients commonly showed transient confusional states and a variety of other non-focal abnormalities, and focal signs were seen occasionally.

Adult↗
PubMed1975

Responses to load disturbances in human shoulder muscles: the hypothesis that one component is a pulse test information signal.

Human motor control has been investigated by applying displacements acting to rotate the shoulder while the subject was endeavouring to maintain a constant position against a pre-existing force delivered by a system of finite stiffness. Four separate stages of the force response were distinguished. First, for the initial 100 msec, an increase in force which was attributed to the viscoelastic properties of activated muscle. Second, after approximately 100 msec, a "medium latency" increase in force accompanied by an increase in EMG activity. Third, a "long latency" increase in force consistent with voluntary action restored the arm to its original position. Fourth, some 500 msec thereafter and dependent upon the final steady force level, a tremor might develop. No changes of force were seen that were of sufficiently short latency to be attributed either to Ia monosynaptic action or immediately following (within 15 msec) polysynaptic action of muscle mechano-receptors. Even the "medium latency" response was too weak to make an appreciable contribution to restoring the arm to its original position; at the best it provided only 15% of the force required. This response is often considered as a "stretch reflex" responsible for maintaining posture in its own right; for example, by means of a servo-assisted transcortical loop (Marsden et al., 1972). Instead, it is now suggested that it might be a test signal designed to inform the central nervous system of the current loading on the muscle and thus permit the CNS to select an appropriate pre-programmed response from its repertoire of motor actions.

Elasticity↗
PubMed1991

Carotid sinus massage, eyeball compression, and head-up tilt test in patients with syncope of uncertain origin and in healthy control subjects.

To verify the role of abnormal neural mechanisms in unexplained syncopes, we evaluated the results of carotid sinus massage (CSM), eyeball compression (EBC), and head-up tilt test (HUT) in the basal state (B) and during isoproterenol infusion (ISO) in: (1) 100 consecutive patients affected by syncope which, despite careful cardiovascular and neurologic examination, was of uncertain origin (age 60 +/- 18 years; 54 men) and (2) 25 healthy subjects matched 4:1 with the patients of the previous group. All the patients underwent CSM and EBC in the supine and standing position for 10 seconds and HUT at 60 degrees for 60 minutes; if HUT-B was negative (68 cases), it was repeated during ISO (1 to 5 micrograms/min) infusion. In the patients with uncertain syncope, spontaneous symptoms were fully reproduced in 49%, 16%, 32%, and 16% of cases respectively by means of CSM, EBC, HUT, and HUT-ISO; overall positivity for at least one test was observed in 79% of cases. The results of CSM, EBC, or HUT-ISO were linked to age, sex, and underlying heart disease. In the healthy subjects, syncope was induced by CSM, EBC, HUT, and HUT-ISO in one case each; overall positivity was 16%. In conclusion, neural reflex induction tests reproduced spontaneous symptoms in most patients affected by uncertain syncope, while they evoked normal responses in most healthy subjects. Therefore on the basis of results of induction tests, the diagnosis of neurally mediated syncope can be ascribed to most patients affected by syncope of uncertain origin.

Adolescent↗
PubMed1977

beta-Endorphin: endogenous opiate or neuroleptic?

The opiatelike neuropeptide beta-endorphin produces a spectrum of effects that contrasts with that induced by the neuroleptic haloperidol. Rats injected intraventricularly or directly into the periaqueductal gray with beta-endorphin (0.5 to 50 micrograms) exhibited rigid immobility accompanied by the loss of righting reflex; the period of rigidity was preceded or followed (depending upon dose) by a state of hyperactivity. In contrast, no dose of haloperidol tested (0.5 to 12 milligrams per kilogram) produced rigidity, loss of righting reflex, or behavioral excitation. Furthermore, whereas animals injected with haloperidol remained stationary on a vertical grid, rats injected with beta-endorphin typically slid off the grid. Moreover, combined beta-endorphin and haloperidol treatment produced flaccidity in most animals. These results do not support the contention that this opiatelike peptide may be a naturally occurring neuroleptic.

Animals↗
PubMed1997

Experimental benznidazole encephalopathy: I. Clinical-neurological alterations.

Benznidazole (N-benzyl-2-nitro-1-imidazoleacetamide) is an antiprotozoan agent of the nitroimidazole group used extensively in South America to treat Chagas' disease. In humans, its most important side effect is peripheral polyneuropathy, the frequency of which is dose related. To evaluate this effect, we administered benznidazole to adult, male, mongrel dogs at doses ranging from 5 to 40 mg/kg/day (0.5 to 4 times the dose used to treat chagasic patients). Subsequent neurological examination revealed apathy, ataxia, spastic tetraplegia with hyperreflexia of stretching reflexes, balance disorders and asymmetrical gait. These alterations appeared earlier and were more intense at the higher doses. Drug withdrawal also left dose- and time-dependent sequelae like ataxia, hypertonia, hyperreflexia and alterations of balance. No peripheral neuropathy was detected. The present findings suggest that a careful reevaluation of the side effects of benznidazole in humans is necessary.

Animals↗
PubMed1978

Lateralization in normal 6-year-olds as related to later reading disability.

The differentiation of lateral preference in hand, eye, ear, and foot was measured in 110 normal Grade 1 children and reading achievement was tested 3 and 5 years later. No support was found for the widely held belief that delays in early lateralization underlie subsequent reading impairment. Paradoxically, boys with serious reading disability showed a strong degree of early lateral concordance. Male, impaired readers displayed a tendency when they were in Grade 1 to be either uniformly right- or left-preferring across all 4 sensory-motor modalities. The results contradict the popular notion that lateral usage emerges from an undifferentiated state in the direction of greater degrees of specialization. Lateralization may be an expression of reflex constraints bound initially to the infant's tonic-neck posture, with later development less reflex-patterned during the acquisition of more sophisticated information-processing strategies. Such an interpretation implies a progressive discontinuity between lateral usage and neuro-maturational processes. Alternatively, the results can be accounted for by (1) a new maturational delay model in which maturation-dependent lateralization proceeds in graduated stages from a highly specialized beginning toward greater levels of neuromotor integration; or (2) a model that maintains the notion of emergent lateralization but in which delays in the lateralization process are actually beneficial to later performance.

Achievement↗
PubMed1979

Sensorimotor deficits produced by phenytoin and chlorpromazine in unanesthetized cats.

Unanesthetized adult cats were evaluated for suprasegmental reflex activity and motor skills before and after administration of chlorpromazine (0.0625--0.5 mg/kg) alone and in combination with phenytoin (20 mg/kg). The greatest deficits were seen in the tests of balance and corrdination in which half the animals failed to match their control responses after administration of chlorpromazine and phenytoin. The impairment was most noticeable with the most stringent test (walking a 4 cm wide beam), and the effects of the two drugs were additive. Although there was no effect of either drug on muscle strength, the two drugs in combination depressed the animals' motivational state, making them less willing to work against imposed loads. Neither drug, alone or in combination, altered responses to the flexor reflex, blind placing, the hopping response or visually aided placing. It is concluded that the effects of chlorpromazine and phenytoin on motor control are selective for the CNS loci which control balance and coordination. Although the two drugs produce additive responses, the deficits occur only at doses which are well above those needed for clinical efficacy and thus may not pose a problem in their long term clinical use.

Animals↗
PubMedDate not supplied

The pharmacological profile of chlordesmethyldiazepam and other benzodiazepines.

The pharmacological profile of chlordesmethyldiazepam was studied in mice and compared with that of other benzodiazepines (diazepam, lorazepam, clonazepam, nitrazepam, oxazepam, flunitrazepam, medazepam and chlordiazepoxide). All the drugs were administered perorally and their anticonvulsive activity (antagonism towards pentetrazole-induced clonic convulsions), anxiolytic action (the four-plate test), myorelaxant activity (the rota-rod test), sedative effect (inhibition of the locomotor activity) and neurotoxic effect (abolition of the righting reflex) were estimated. Chlordesmethyldiazepam revealed an anticonvulsive action (ED50 = 0.11 mg/kg), anxiolytic activity (MED = 2 mg/kg), myorelaxant action (ED50 = 17.5 mg/kg), sedative effect (ED50 = 34 mg/kg) and neurotoxic action (NTD50 = 190 mg/kg). Considering the potency of action (ED50) in respective tests and the therapeutic indices (NTD50/ED50 ratio), chlordesmethyldiazepam in respect of its profile resembles most lorazepam and diazepam.

Animals↗

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