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At least 541 records · Page 30Linked to original sources
PubMed1998

Resistance reflex that maintains upright head posture in the flesh fly neobellieria bullata (Sarcophagidae)

In flesh flies Neobellieria bullata, we investigated a resistance reflex that maintains upright head posture around the roll axis relative to the thorax. The gain of the reflex depends upon the fly's behavioral state: moving flies immediately correct 90 % of the amplitude of experimentally imposed roll perturbations, returning the head almost to the fully upright position; motionless flies allow perturbations to persist for minutes before correcting only 70 % of perturbation amplitude. To investigate the role of various neural pathways, we examined the control of head posture after sectioning relevant propriosensory or motor nerves. Excision of the prosternal chordotonal organ causes no decrements in the control of head posture. Unilateral deafferentation of a cervical propriosensory organ, the prosternal organ, induces roll towards the cut side. Unilateral section of the frontal nerve, a mixed motor nerve that supplies the neck depressors and levators, leads to unilateral deficits in correcting perturbations towards the contralateral side. After bilateral propriosensory or frontal motor nerve section, approximately 40 % of perturbation amplitude is still corrected. To determine the contributions of the passive elastic properties of the neck skeleto-muscular system, flies were tested under reversible nitrogen anesthesia. They immediately corrected 40 % of perturbation amplitude. Taken together, the results demonstrate that passive elasticity plus active prosternal nerve afference to contralateral depressors innervated by the frontal nerve in combination constitute a sufficient and necessary reflex loop to control head roll posture.

Journal Article↗
PubMed1987

Regeneration of the eighth cranial nerve. II. Physiologic verification in the bullfrog.

Two experiments were performed to document the functional capacity of the regenerated eighth cranial nerve. In experiment 1, the eighth cranial nerve was sectioned preganglionically and allowed to regenerate in a group of bullfrogs with normal contralateral eighth nerve and labyrinth. Posture and reflex to lateral tilt were measured preoperatively and postoperatively for a minimum of 3 months. Similar measures were performed in a second group of bullfrogs in which the eighth nerve had been destroyed by ganglionectomy and in a third with peripheral labyrinthectomies. In experiment 2, the eighth nerve was sectioned and allowed to regenerate in bullfrogs in which the contralateral nerve had previously been destroyed. Posture and reflex to lateral tilt were measured as in experiment 1. Similar measures were performed in a group of bullfrogs that had undergone bilateral nerve destruction. Regeneration of the eighth cranial nerve in bullfrogs in both experiments was documented histologically by labeling the regenerated fibers with horseradish peroxidase (HRP). In both experiments, posture recovered completely only in the bullfrogs in which the eighth cranial nerve was allowed to regenerate. Reflex to lateral tilt recovered more rapidly in the bullfrogs with regenerated nerves than in any of the other bullfrogs.

Animals↗
PubMed2002

Emergency craniotomy in patients worsening due to expanded cerebral hematoma: to what purpose?

BACKGROUND: Supratentorial intracerebral hematomas often are evacuated in rapidly deteriorating patients. Surgery may prevent death but not necessarily disability. The authors studied the outcome of emergent clot evacuation in patients with worsening massive intracerebral hemorrhage. METHODS: The authors reviewed data on 26 consecutive, acutely worsening patients with nontraumatic intracerebral hemorrhage who had surgery for clot evacuation. All patients had clinical (stupor or coma, loss of pontomesencephalic brainstem reflexes, extensor posturing) or radiologic (midline shift of septum pellucidum > or =1 cm downward or obliteration of the ambient and suprasellar cisterns caused by displacement of the temporal uncus) signs of herniation. Outcome was defined using the Glasgow Outcome Scale (GOS). RESULTS: Fifty-six percent of patients died (GOS 1), 22% remained severely disabled (GOS 3), and 22% regained independence (GOS 4-5). Considering findings before surgery, upper brainstem reflexes were preserved more often in survivors (66% vs. 14%; p = 0.01). All patients who had a combination of absent pupillary, corneal, and oculocephalic reflexes and extensor posturing before craniotomy died. No patient lacking corneal or oculocephalic reflexes prior to surgery regained functional independence. CONCLUSIONS: Craniotomy for rapidly worsening patients with supratentorial intracerebral hemorrhage and radiologic signs of brain tissue shift may result in functional independence in approximately a quarter of patients. However, all comatose patients who lost upper brainstem reflexes and had extensor posturing died despite surgery.

Acute Disease↗
PubMed1984

Changes in posturo-kinetic limb responses to cortical stimulation following unilateral neck deafferentation in the cat.

Unilateral neck deafferentation produces in cats a postural asymmetry, characterized by an increase in the extensor activity of the ipsilateral limbs and a decreased activity in the contralateral limbs; moreover, the placing reactions are severely depressed in the ipsilateral limbs. The present experiments were performed to investigate the influence of unilateral section of the cervical dorsal roots C1-C2 or C1-C3 on the postural adjustments occurring during flexion limb movements induced by cortical stimulation in chronically implanted cats. Only weak stimulations were used and motor activity was mainly isometric, to facilitate quantification of responses analyzed by measuring changes in vertical force exerted at the level of each limb in the up-right position of the animal. The results obtained were the following. The general motor behaviour of the animal was not affected by the lesion. In particular, stimulation of the motor cortex evoked not only flexion movement of a contralateral limb but also an initial postural adjustment consisting of a diagonal force pattern. The response threshold of the moving limb increased on the hypertonic side and decreased on the hypotonic side. Moreover, the changes in threshold of the performing limb following unilateral neck deafferentation were coupled with parallel changes in threshold of the limbs involved in the postural adjustment. There were great quantitative modifications both of the movement and the postural adjustment after the neck deafferentation. In fact weight shift latencies increased when the performing limb was ipsilateral to the hypertonic side, while the weight shifts themselves decreased in amplitude and speed. The opposite occurred when the performing limb was ipsilateral to the hypotonic side. Parallel with these changes, the slope of the response curve of the moving limb as well as of the limbs involved in the postural adjustment decreased following stimulation of the motor cortex at different stimulus intensities if the performing limb was ipsilateral to the hypertonic side, but increased if the performing limb was ipsilateral to the hypotonic side. These changes compensated after chronic neck deafferentation. In summary, the results indicate that well coordinated posturo-kinetic responses were still elicited by cortical stimulation in spite of the prominent changes in posture and reflex movements induced by unilateral neck deafferentation. In particular, changes in threshold, latency, amplitude and speed of the force changes under the limb making a movement were coupled with parallel alterations of the force changes under the limbs undergoing postural adjustment.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1989

Inhibition of vestibulospinal reflexes during the episodes of postural atonia induced by unilateral lesion of the locus coeruleus in the decerebrate cat.

1. The spontaneous EMG activity of the forelimb extensor triceps brachii of both sides as well as their responses to roll tilt of the animal at 0.15 Hz, +/- 10 degrees leading to sinusoidal stimulation of labyrinth receptors were tested in precollicular decerebrate cats, before and after unilateral electrolytic lesion of the locus coeruleus (LC). 2. Lesion of the LC of one side decreased the tonic contraction of the ipsilateral limb extensors, but greatly increased the amplitude of modulation and the response gain of the corresponding triceps brachii to animal tilt; however, no change in the phase angle of the responses was observed. A slight increase in the response gain affected also the contralateral triceps brachii. 3. The postural asymmetry described above was followed from time to time by short-lasting episodes of postural atonia, which affected not only the ipsilateral but also the contralateral limb extensors. These episodes were also associated with a suppression of the EMG responses of the triceps brachii of both sides to sinusoidal stimulation of labyrinth receptors. 4. The episodes of postural atonia which appeared after unilateral lesion of the LC were not associated with rapid eye movements; however, the slow horizontal eye movements, which may occur in normal decerebrate animals, increased in amplitude throughout these episodes. Both the postural atonia as well as the related suppression of the vestibulospinal reflexes, which lasted for 5-10 min, disappeared either spontaneously or following acoustic or somatosensory stimulations. 5. Histological controls indicated that unilateral lesions limited to the caudal part of the LC produced only a permanent decrease in postural activity of the ipsilateral limbs, associated with an increase in gain of the vestibulospinal reflex. However, in order to elicit episodes of bilateral postural atonia associated with the suppression of the vestibulospinal reflexes it was necessary to extend the lesion to more rostral aspects of the LC. 6. Since the effects described above were similar to those elicited in decerebrate cats by local injection of cholinergic agonists into the dorsal part of the pontine reticular formation, we postulated that the postural atonia as well as the related suppression of the vestibulospinal reflexes was due to transient release from LC inhibition of these dorsal pontine reticular structures, which might in turn excite the medullary reticulospinal neurons, thus leading to inhibition of the extensor motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗