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Biomedical subjects

A Levante

Publications and source records attributed to A Levante.

At least 19 recordsLinked to original sources
PubMed1992

Primary somatosensory cortex in rats with pain-related behaviours due to a peripheral mononeuropathy after moderate ligation of one sciatic nerve: neuronal responsivity to somatic stimulation.

Single-unit recordings were made under moderate gaseous anaesthesia in the hindpaw representation area of the two primary somatosensory motor cortices (SmI) of rats (n = 58) rendered mononeuropathic by four loose ligatures placed around one common sciatic nerve 2-3 weeks beforehand. The rats exhibited clear hyperalgesia and allodynia from the paw with the ligated sciatic nerve, to both mechanical and thermal stimuli. From the tested neuronal population (n = 640), about the same proportion could be activated by somatic stimuli in each cortex: 165/362 (45%) in the cortex contralateral to the ligated sciatic nerve (Cc), 105/278 (37%) in the cortex ipsilateral to the ligated sciatic nerve (Ci). Neurones driven by light touch, exhibited RFs strictly contralateral to the recording sites. Their proportion and response characteristics were similar regardless of recording side. However, the number of neurones with RFs in the sciatic nerve territory was above 95% in the Ci, and was dramatically reduced to 43% in the Cc. By contrast, the number of neurones with RFs supplied by the saphenous nerve reached 57% on this side. Although the RF size of all the neurones appeared roughly normal, there were fewer Cc than Ci neurones with RFs located on the paw itself and with RFs of extremely small size in the sciatic nerve territory. The proportion of neurones responding to a joint stimulus was significantly higher in the Cc than in the Ci. The neuronal responses to joint stimuli of the paw with the ligated sciatic nerve were significantly more sustained than those recorded in the Ci and elicited from the normal paw. The proportion of neurones driven by mechanical stimulation which gave rise to nociceptive reactions in freely moving animals, i.e. "nociceptive" neurones, was comparable in each cortex. However, half of the Cc neurones exhibited paroxysmal discharges occurring without intentional stimulation and of long duration (1 min to several minutes). Only 66% of Cc but 93% of Ci "nociceptive" neurones were exclusively activated by pinch. The remaining Cc neurones were also activated by applying moderate pressure to the paw with the ligated nerve. Pinch responses from the paw with the ligated nerve were often more intense and of longer duration than responses elicited from the intact paw. The "nociceptive" Cc neurones were especially sensitive to thermal stimuli of 39-44 degrees C when the stimuli were applied to the paw with the ligated nerve. They also responded vigorously to a 10 degrees C stimulus applied to this paw.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Further evidence for the involvement of SmI cortical neurons in nociception: modifications of their responsiveness over the early stage of a carrageenin-induced inflammation in the rat.

In this electrophysiological study, changes in the responsiveness of neurons in the primary somatosensory (SmI) cortex in rats were analyzed during the development of carrageenin (CRG)-induced inflammation, an animal model of acute inflammatory hyperalgesia. SmI neurons were characterized as responding to non-noxious light touch, non-noxious articular movement, or noxious pinch. A total of 23 neurons so characterized in three groups were recorded for 60 min (17 of these neurons were recorded for up to 150 min) after an intraplantar injection of CRG. The possible modifications in their background and evoked activities were analyzed over this period of time. After CRG administration, cells responding to noxious pinch stimuli (n = 8) showed a nonsignificant increase in spontaneous activity, but a significant increase in their evoked response to pinch. These results were quite similar to past observations in the ventrobasal nucleus of the thalamus (VB). Cells responding to non-noxious articular stimulation (n = 6) showed variable modifications and no significant increase in the mean evoked response for up to 60 min. These results for articular cells were also quite comparable to results seen for VB responses for similar cells. However, mean spontaneous activity, which showed a highly variable increase, was significantly increased after 60 min. The depressive effect of a local anesthetic, Xylocaine, was tested on the activities of four cells (one pinch, three light touch units) 60 min after CRG administration over a 20-min interval. Xylocaine was found to depress both spontaneous activity and responses to the effective somatic stimulus, thereby implying that the observed central modifications in neuronal discharge are linked to the peripheral inflammation. Modifications observed for each group of cells are compared with past observations in peripheral fibers, in spinal dorsal horn neurons, and especially in the VB under similar inflammatory conditions. These data confirm that the SmI cortex is involved in the nociceptive process. Furthermore, the contrast between some modifications observed at this level and past observations under similar inflammatory conditions suggests a unique role of some cortical neurons, which might partially account for mechanical allodynia.

Afferent Pathways↗
PubMed1983

Electrophysiological and anatomical demonstration of a bulbar relayed pathway towards the medial thalamus in the rat.

In the rat cells antidromically activated by stimulation of the thalamic centrum medianum and centralis lateralis were searched for in the bulbopontine region which receives spinoreticular pathways. Antidromically activated cells were found in the nuclei gigantocellularis and pontis oralis and they possessed peripheral receptive fields that were large, bilateral and often responded to nociceptive stimuli. Injections of horseradish peroxidase or iron-dextran at the same thalamic level revealed retrogradely labelled cells in the same bulbopontine nuclei. Cells retrogradely labelled were also found in the mesencephalic reticular formation, the inferior colliculus and grisea centralis.

Animals↗
PubMed1980

[Anesthesia using methohexital for thermocoagulation of the gasserian ganglion (author's transl)].

The authors report their experience of the treatment of essential trigeminal neuralgia by percutaneous thermocoagulation of the Gasserian ganglion (400 patients). This method has always been performed on anesthetized patients, using an ultra short acting barbiturate: methohexital. Most often, two or three successive coagulations are needed to obtain the desired analgesia. No complications have resulted, although 30 p. cent of our patients were over 70 years old.

Aged↗
PubMed1980

[Air embolism in neurosurgery. General data (author's transl)].

Air embolism in neurosurgery, in the sitting position, are not rare. They depend on the type of surgery (more frequent in operations on the posterior fossa), on the mode of ventilation, and most of all on the criteria for detection (clinical, electrocardiographic, ultrasonic, capnographic of haemodynamia). They depend as well upon the degree of tilt, of intrathoracic and intracardiac pressures (right auricle) and of the gas mixture administered (nitrous oxide increases their size owing to its poor blood solubility). The way of entry is venous, but it is certain that they can pass into the systemic circulation (their passage through the lungs is debated). According to their size, the speed of injection and the subject's previous condition they may affect: --the lungs: precapillary pulmonary artery hypertension, and even pulmonary oedema, --the heart, mainly through the fall of venous return, --the brain anoxia, followed by cerebral oedema, leading to early neurologic disturbances and possibly severe sequellae. Those symptoms are due to the gas embolism itself, but also to microthrombi of fibrin and disturbances of vascular membrane permeability.

Adult↗
PubMed1980

[The technique of anesthesia for the prevention and treatment of gaseous embolism in the neurosurgical sitting position (author's transl)].

The sitting position in neurosurgery gives always three problems for the anaesthesist: --maintain the cerebral perfusion pressure, --not to aggravate intracranial hypertension, --detect gaseous embolism. The clinical signs of air embolism often look like the awakening of the patient. That is why it is necessary to use specific methods to detect them: Doppler, Swan-Ganz catheter, and/or continuous CO2 recording of expired air by capnograph. Among the various methods to prevent air embolism we have used controlled respiration with a positive and expiratory pressure (P.E.E.P.). In our series (45 operations) gas embolism occurred in 13% of the patients operated upon without positive and expiratory pressure, and 0% with P.E.E.P.

Anesthesiology↗
PubMed1979

[Monitoring of extra- and intra-cellular compartment through total body impedance (author's transl)].

To evaluate the extra-cellular space, we measure the impedance (or resistance) of the extra-cellular electrolyte compartment with an alternating current at a fixed frequency of 5 kHz that can't pass through the cellular membrane. Total water is measured by the impedance to a current of 1 MHz which is conducted by extra and intra cellular hydro-electrolytic space. There is a good correlation between electrical impedance measurements and distribution of isotopic markers. The extra-cellular compartment was evaluated by diffusion of D.T.P.A. marked with 99mTc or with 111In and the total water by the diffusion of Antipyrin marked with 1,311 or 1,231. The findings indicate that there is not a significant difference between the results of the size of extra-cellular water measured by electrical impedance and D.T.P.A. diffusion (r = 0.75). Comparable results have been obtained in the determination of total water by electrical impedance measure and diffusion of Antipyrin (r = 0.90). We have also studied by method of electric impedance:--The state of hydratation in head injured patients and after pituitary surgery.--The lean body mass and hydro-electrolyte compartments in pregnancy. Electrical impedance measure seems to be a simple and reliable method to assess the hydric state of patients.

Adult↗
PubMed1978

[Current data on pain pathways].

1--The classical notion attributing the conduction of painful messages to only the A delta and C fibres will be discussed. 2--Spinal cord cells of layers I, V and VIII received painful messages and their physiological properties will be compared. 3--The origin within the cell layers of the spinal cord of the various ascending bundles will be examined. 4--The reticular an thalamic zones (posterior ventra nucleus, mid-line and intralaminar nuclei, GMme posterior group in particular) which receive painful messages have also been studied using activation provoked by pinching, pinprick, the injection of painful substances and stimulation of the dental pulp. The possible role of the different structures thereby brought into action and the limitation of these techniques will be discussed. 5--The existence of metameric controls and controls of central origin active at a spinal, reticular and thalamic level. The absence of inhibitory controls may be responsible for the development of abnormal painful sensations which accompany certain deafferentation procedures. The reestablishment of these controls with the aid of stimulation may result and often results in the improvement of these painful syndromes. 6--Section of the dorsal routes in the chronic animal (rat and cat) may represent an experimental model for deafferentation pain seen in man.

Animals↗
PubMed1977

[Attempt at explaining decompensation of hydrocephalus by modifications of reticular activity].

A correlative study is done between observation of cases of shunted hydrocephalus with mesencephalic signs such as Parinaud's syndrome and a multiunitary recording of mesencephalic and bulbar reticular formation activities during acute and chronic intracranial hypertension in cats. Clinical and experimental data are first separately analysed and then superimposed. This results in analysing the evolution of such intracranial hypertension in three stages: first stage of "tolerance" with minimal clinical signs and no change of reticular activity; second stage of "uncompensation" when mesencephalic signs appear and with increased mesencephalic activity and unchanged bulbar activity; third stage of "exhaustion" where can be noted disorders of consciousness, decerebration fits, and cardiorespiratory disorders; mesencephalic activity falls down to lower levels than basal ones, bulbar activity increases first and then also decreases rapidly. This suggests a mechanism of exhausting stocks of monoamines but also of change of the local cerebral blood flow. Increase and then fall of the reticular activity may be the general way, even without any herniation, of evolution of any intracranial hypertension of traumatic or tumoral origin.

Cerebrospinal Fluid Shunts↗
PubMed1977

[Treatment of essential facial neuralgia by selective thermocoagulation of Gasser's ganglion].

The authors report their experience in the treatment of essential facial neuralgia by differential thermocoagulation of the gasserian ganglion. This method is based upon the fact that small pain fibres (A delta and C) are more sensitive to warmth than large touch fibres. Thus progressive and controlled thermocoagulation of the trigeminal ganglion makes it possible to obtain selective destruction of the small fibres (analgesia without anaesthesia). 76 patients were treated using the method, and in 75 cases the symptoms of neuralgia disappeared immediately. Mortality is nil and morbidity insignificant other than the effects on the trigeminal nerve. The most serious complication (Approximately 10% of cases) was that of marked hypoaesthesia, rather than pure analgesia, in the coagulated area.

Adult↗