Static cervical-ocular reflex and optokinetic reflex interaction in rabbits

Summary The effect that tonic eye deviations, induced by angular deviation of the torso, have on the characteristics of optokinetic (OK) nystagmus was studied in rabbits. When the slow component of the OK nystagmus moved in the direction of the tonic eye deviation, the amplitude of the slow and fast components of the nystagmus was decreased and their frequency was increased, whereas when the slow component moved in the opposite direction, the amplitude and the frequency of the nystagmus were not different from those when the head and torso were aligned.Under the influence of neck reflexes, the total range of eye movements was double that when the torso was aligned with the head. The place in the orbit where the fast-component is initiated — the so-called fast-component threshold — was deviated in the direction of the neck-reflex-induced tonic eye deviation. The characteristics of the fast component, however, except for its amplitude, were not affected by the change of location of the fast-component threshold.These data indicate that the OK reflex function, as judged by measurement of the slow component velocity, is not affected by neck-vestibular reflexes. They also show that the fast-component threshold is dependent on parameters other than the actual orbital position and that there must be an internal representation of the range of possible eye movements within the brain to regulate the production of fast components.Abbreviations OK optokinetic - CW clockwise - CCW counterclockwise - CNS central nervous system This work was supported by grants NS07059, NS09823, and NS08335 from the National Institutes of Health     

Consciousness and reflex

In the paper an analogy is drawn between functions of consciousness and scheme of reflex. Consciousness includes afferent part perception of external world, central one--thinking, and efferent one--decision about action and motor command presentation. The basis of higher psychic functions is the junction of reflexes in complicated complexes, singling out in their composition key structures realizing synthesis of qualitatively different information. The centers of integration at realization of afferent functions of consciousness are situated in posterior, and at efferent ones--in anterior brain areas. In the process of thinking predominantly afferent and efferent stages may also be singled out with corresponding localization of foci of interaction. Communicative function of consciousness is provided mainly by centers of the left hemisphere. Breakage between afferent and efferent functions of consciousness may be the basis of some forms of psychic pathology as depression.     

Electrophysiological analysis of facial reflex in monkeys: trigemino-naso-labial reflex]

Electrical stimulation of the awake monkey's supra orbital nerve, elicits two successive reflex discharge in both naso-labialis muscles (NL). The responses have a similar high threshold. Similar responses are also elicited on electrical stimulation of the facial skin, whereas flash, click or tapping on the muscle belly are ineffective. These responses bear some resemblances to those obtained in orbicularis oculi muscles ; but the higher threshold and the different organization of the NL responses would suggest that such reflexes may serve a different function from that of the blink reflex.     

Participation of the beta-adrenergic receptor in the enteroruminal reflex and enteroenteric reflex

In sheep with chronic fistulae of the small intestine and rumen the participation of the beta-adrenergic receptor was investigated in the enteroruminal reflex and enteroenteric reflex using the method of pharmacological analysis. The movements of the segments of the digestive tract with fistulae were recorded by the balloon method. A solution of hydrochloric acid administered into the ileum caused a reflex stimulation of its motor activity and inhibited the movements of the rumen. Intravenous administration of propranolol before instillation of the acid into the intestine abolished or reduced greatly the reflex inhibition of the movements of the rumen and in the small intestine it enhanced significantly the studied reflex reaction. Thus stimulation of the beta-adrenergic receptor plays an important role in the reflex stimulation of the motor activity of the rumen, and stimulation of the motor activity of the small intestine in the enteroenteric reflex is limited by the effects derived from this receptor.     

End-stage reflex sympathetic dystrophy

Reflex sympathetic dystrophy is an automatic dysfunction that occasionally complicates healing after trauma or surgery. The syndrome is characterized by pain, swelling, stiffness, and discoloration often out of proportion to the original injury. Early diagnosis and appropriate treatment are the most important factors in the successful outcome of this disabling condition. A case of longstanding, previously untreated reflex sympathetic dystrophy secondary to a minor injury is presented.     

Methacholine causes reflex bronchoconstriction

To determine whether methacholine causes vagally mediated reflexconstriction of airway smooth muscle, we administered methacholine tosheep either via the bronchial artery or as an aerosol via tracheostomyinto the lower airways. We then measured the contraction of anisolated, in situ segment of trachealis smooth muscle and determinedthe effect of vagotomy on the trachealis response. Administeringmethacholine to the subcarinal airways via the bronchial artery(0.5-10.0 µg/ml) caused dose-dependent bronchoconstriction andcontraction of the tracheal segment. At the highest methacholine concentration delivered, trachealis smooth muscle tension increased anaverage of 186% over baseline. Aerosolized methacholine (5-7 breaths of 100 mg/ml) increased trachealis tension by 58% and airwaysresistance by 183%. As the bronchial circulation in the sheep does notsupply the trachea, we postulated that the trachealis contraction wascaused by a reflex response to methacholine in the lower airways.Bilateral vagotomy essentially eliminated the trachealis response andthe airways resistance change after lower airways challenge (either viathe bronchial artery or via aerosol) with methacholine. We concludethat 1) methacholine causes asubstantial reflex contraction of airway smooth muscle and2) the assumption may not be validthat a response to methacholine in humans or experimental animalsrepresents solely the direct effect on smooth muscle.

     

Role of reflex gain and reflex delay in spinal stability--a dynamic simulation

The goal of this study was to investigate the role of reflex and reflex time delay in muscle recruitment and spinal stability. A dynamic biomechanical model of the musculoskeletal spine with reflex response was implemented to investigate the relationship between reflex gain, co-contraction, and stability in the spine. The first aim of the study was to investigate how reflex gain affected co-contraction predicted in the model. It was found that reflexes allowed the model to stabilize with less antagonistic co-contraction and hence lower metabolic power than when limited to intrinsic stiffness alone. In fact, without reflexes there was no feasible recruitment pattern that could maintain spinal stability when the torso was loaded with 200N external load. Reflex delay is manifest in the paraspinal muscles and represents the time from a perturbation to the onset of reflex activation. The second aim of the study was to investigate the relationship between reflex delay and the maximum tolerable reflex gain. The maximum acceptable upper bound on reflex gain decreased logarithmically with reflex delay. Thus, increased reflex delay and reduced reflex gain requires greater antagonistic co-contraction to maintain spinal stability. Results of this study may help understanding of how patients with retarded reflex delay utilize reflex for stability, and may explain why some patients preferentially recruit more intrinsic stiffness than healthy subjects.