PubMed Health⌕ Search

Biomedical subjects

D Contreras

Publications and source records attributed to D Contreras.

49 records · Page 3Linked to original sources
PubMed1994

Delayed unions and nonunions of open tibial fractures. Correlation with arteriography results.

To investigate the importance of arterial integrity in tibial fracture healing, the authors retrospectively assessed prognosis as a function of arterial injury in a large series of tibial fracture patients. The records of 114 patients who were treated for an open fracture of the tibia at a San Francisco hospital between 1981 and 1991 were selected for review; in each case, the injury had been caused by a blunt trauma, and arteriography had been performed to evaluate a suspected arterial injury in the ipsilateral extremity. Sixty-two patients had had a normal arteriogram and 52 had demonstrated occlusion of one or two of the three arteries that supply the foot. The group of patients who had demonstrated arterial occlusion had a significantly greater incidence of delayed union or nonunion (24 of 52 compared with ten of 62) and notably more cases of osteomyelitis (nine of 52 compared with four of 62); when the patients with osteomyelitis are excluded, the difference between the groups is still significant. This study is the first that indicates that patients with open fractures of the tibia who demonstrate arterial occlusion in their ipsilateral extremity may be more prone to delayed union or nonunion. More vigilant follow-up evaluation may therefore be warranted in such patients to better anticipate the need for exchange rodding or bone grafting.

Adolescent↗
PubMed1993

Electrophysiological properties of intralaminar thalamocortical cells discharging rhythmic (approximately 40 HZ) spike-bursts at approximately 1000 HZ during waking and rapid eye movement sleep.

Thalamocortical neurons located in the large-celled district of the cat intralaminar centrolateral nucleus were found to discharge spike-bursts with unusually high frequencies (800-1000 Hz) during spindle oscillations of the electroencephalogram. In chronically implanted animals, similar spike-bursts were also fired during wakefulness and rapid eye movement sleep, two behavioral states in which other thalamocortical neurons tonically fire single spikes. Such high-frequency spike-bursts recurred with a fast rhythm of 20-40 Hz during waking and rapid eye movement sleep. Intracellular recordings under barbiturate anesthesia showed that, during spindle oscillations, the spike-bursts of intralaminar neurons are generated by brief low-threshold spikes with a much shorter refractory phase than in other thalamocortical cells. Depolarizing pulses from the resting membrane potential triggered fast oscillations (20-80 Hz) crowned by short high-frequency (800-1000 Hz) spike-bursts. During the inter-spindle epochs, the "tonic" firing of these neurons was, in fact, a fast oscillation (30-40 Hz) of the membrane potential leading to single spikes or spike-doublets. Autocorrelograms computed from inter-spindle epochs, at relatively depolarized levels, confirmed the presence of multiple peaks at this fast rhythm. The properties of these neurons make them well suited for the distribution of fast rhythms during arousal and rapid eye movement sleep over the cerebral cortex.

Animals↗
PubMed1993

Electrophysiological properties of cat reticular thalamic neurones in vivo.

1. The electrophysiological properties of neurones of the reticular thalamic (RE) nucleus were studied in acutely prepared cats under urethane anaesthesia. 2. Two main types of neuronal firing were recorded. At the resting membrane potential (-60 to -65 mV) tonic repetitive firing was elicited when the cell was activated synaptically or by current injection. From membrane potentials more negative than -75 mV, synaptic or direct stimulation generated a burst of action potentials. 3. The burst of RE cells consisted of a discharge of four to eight spikes riding on a slowly growing and decaying depolarization. The discharge rate during the burst showed a characteristic increase, followed by a decrease in frequency. 4. The burst response behaved as a graded phenomenon, as its magnitude was modulated by changing the intensity of the synaptic volley or the intensity of the injected current. 5. Spike-like small potentials presumably of dendritic origin occurred spontaneously and were triggered by synaptic or direct stimulation. They were all-or-none, voltage-dependent events. We postulate that these spikes originate in several hot spots in the dendritic arbor, with no reciprocal refractoriness and may generate multi-component depolarizations at the somatic level. 6. Excitatory postsynaptic potentials (EPSPs) evoked by internal capsule stimulation consisted of two components, the late one being blocked by hyperpolarization. Such compound EPSPs were followed by a period of decreased excitability during which a second response was diminished in amplitude. 7. A series of depolarizing waves at the frequency range of spindle oscillations was triggered by internal capsule stimulation. The individual depolarizing waves constituting the spindle oscillation gradually decreased in amplitude when decreasing the intensity of the stimulation. 8. These results, showing that RE cells are endowed with an excitable dendritic tree and a graded bursting behaviour, support the proposed role of RE nucleus as the generator and synchronizer of spindle rhythmicity.

Animals↗
PubMed1993

The slow (< 1 Hz) oscillation in reticular thalamic and thalamocortical neurons: scenario of sleep rhythm generation in interacting thalamic and neocortical networks.

As most afferent axons to the thalamus originate in the cerebral cortex, we assumed that the slow (< 1 Hz) cortical oscillation described in the two companion articles is reflected in reticular (RE) thalamic and thalamocortical cells. We hypothesized that the cortically generated slow rhythm would appear in the thalamus in conjunction with delta and spindle oscillations arising from intrinsic and network properties of thalamic neurons. Intracellular recordings have been obtained in anesthetized cats from RE (n = 51) and cortically projecting (n = 240) thalamic neurons. RE cells were physiologically identified by cortically evoked high-frequency spike bursts and depolarizing spindle oscillations. Thalamocortical cells were recognized by backfiring from appropriate neocortical areas, spindle-related cyclic IPSPs, and hyperpolarization-activated delta oscillation consisting of rhythmic low-threshold spikes (LTSs) alternating with afterhyperpolarizing potentials (AHPs). The slow rhythm (0.3-0.5 Hz) was recorded in 65% of RE neurons. In approximately 90% of oscillating cells, the rhythm consisted of prolonged depolarizations giving rise to trains of single action potentials. DC hyperpolarization increased the synaptic noise and, in a few cells, suppressed the long-lasting depolarizing phase of the slow rhythm, without blocking the fast EPSPs. In approximately 10% of oscillating neurons, the hyperpolarizing phase of the oscillation was much more pronounced, thus suggesting that the slow rhythm was produced by inhibitory sculpturing of the background firing. The slow oscillation was associated with faster rhythms (4-8 Hz) in the same RE neuron. The slow rhythm of RE neurons was closely related to EEG wave complexes recurring with the same frequency, and its strong dependency upon a synchronized state of cortical EEG was observed during shifts in EEG patterns at different levels of anesthesia. In 44% of thalamocortical cells the slow rhythm of depolarizing sequences was apparent and it could coexist with delta or spindle oscillations in the same neuron. The occurrence of the slowly recurring depolarizing envelopes was delayed by the hyperpolarizing spindle sequences or by the LTS-AHP sequences of delta oscillation. The hyperpolarization-activated delta potentials that tended to dampen after a few cycles were grouped in sequences recurring with the slow rhythm. We finally propose a unified scenario of the genesis of the three major sleep rhythms: slow, delta, and spindle oscillations.

Action Potentials↗
PubMed1992

Intracellular evidence for incompatibility between spindle and delta oscillations in thalamocortical neurons of cat.

Recent studies have revealed that the thalamus does not only generate spindle oscillations (7-14 Hz), but that it also participates in the genesis of a slower (less than 4 Hz) rhythm within the frequency range of delta waves on the electroencephalogram. In thalamic cells, delta is an intrinsic oscillation consisting of low-threshold spikes alternating with afterhyperpolarizing potentials. It is known from electroencephalographic recordings in humans and animals that slow or delta waves prevail during late sleep stages, whereas spindle oscillations are characteristic for the early stages of sleep. We studied the dependence of spindles and delta oscillations on membrane potential, as well as the effects of spindles on delta oscillations, in thalamocortical neurons of cats under urethane anesthesia and in cerveau isolé preparations (low collicular transections). Spindles appeared at membrane potentials between -55 and -65 mV, whereas delta oscillations occurred by bringing the membrane potential between -68 and -90 mV. Spindles either evoked by cortical stimulation or occurring spontaneously in cerveau isolé preparations prevented delta oscillations. This effect was probably due to the increase in membrane conductance associated with spindles. Barbiturates also blocked delta activity in thalamocortical neurons, probably through the same mechanism. A certain degree of incompatibility between spindles and delta rhythms in thalamocortical cells may explain the prevalence of these two types of oscillations during different stages of sleep with synchronization of the electroencephalogram.

Animals↗
PubMed1992

The relationship between glucose-induced K+ATP channel closure and the rise in [Ca2+]i in single mouse pancreatic beta-cells.

1. Intracellular calcium [Ca2+]i and channel activity were simultaneously recorded in single, dissociated mouse beta-cells kept in culture for 1-3 days. [Ca2+]i was estimated from microfluorometric ratio methods using Indo-1. Channel activity was measured using the cell-attached configuration of the patch-clamp technique. 2. At low glucose concentrations (0.3 mM), resting K+ATP channel activity was prevalent. Increasing glucose up to 16 mM, produced a gradual decrease in K+ATP channel activity over a time course of 90-120 s (temperature = 23 degrees C) and an increase in [Ca2+]i. 3. In the majority of experiments, glucose elicited biphasic action currents (action potentials) which preceded the rise in [Ca2+]i. There was a close correlation between spike frequency and the levels of [Ca2+]i. 4. The sulphonylurea tolbutamide (1 mM) blocked K+ATP channels in 10-20 s. K+ATP channel blockade was associated with a quick rise in [Ca2+]i. 5. When K+ATP channel activity was stimulated in the presence of diazoxide (100 microM), increasing the glucose concentration from 3 to 16 mM produced a decrease in [Ca2+]i. Only when diazoxide was removed did glucose produce an increase in [Ca2+]i. 6. In a small population of cells, glucose (16 mM) produced a small decrease in K+ATP channel activity but not an increase in [Ca2+]i. In such cells, tolbutamide blocked K+ATP channels and produced an increase in [Ca2+]i. 7. These results demonstrate a close correlation between K+ATP channel activity and [Ca2+]i in beta-cells. The findings are consistent with the model in which glucose metabolism produces a rise in [Ca2+]i through the blockade of K+ATP channels, membrane depolarization and calcium current activation.

Animals↗
PubMed1992

Bursting and tonic discharges in two classes of reticular thalamic neurons.

1. Two types of cat reticular (RE) thalamic cells were disclosed by means of intracellular recordings under urethan anesthesia. The RE neurons were identified by their typical depolarizing spindle oscillations in response to synchronous stimulation of the internal capsule. 2. In type I neurons (n = 41), depolarizing current pulses induced tonic firing at the resting or slightly depolarized membrane potential (Vm) and triggered high-frequency spike bursts at a Vm more negative than -75 mV. As well, these cells discharged rebound bursts at the break of a hyperpolarizing current pulse. Internal capsule stimulation elicited spindle sequences made off by depolarizing waves giving rise to spike bursts. 3. Type II cells (n = 9) did not discharge spike bursts to large depolarizing current pulses even when the Vm reached -100 mV, nor did they fire rebound bursts after long-lasting hyperpolarizing current pulses or spike bursts riding on the rhythmic depolarizing components of spindle sequences. 4. Compared with type I cells, type II cells showed less frequency accommodation during tonic firing. The latter neuronal class discharged at high frequencies (40 Hz) with slight DC depolarization, approximately 8-10 Hz at the resting Vm, and no underlying synaptic or subthreshold oscillatory events could be detected when the firing was blocked by DC hyperpolarization. 5. The presence of two cell classes in the RE nucleus challenges the common view that this nucleus consists of a single neuronal class. We suggest that a different set of conductances is present in type II RE neurons, thus preventing the low-threshold Ca2+ current from dominating the behavior of these cells.

Animals↗
PubMed1990

[Wegener's granulomatosis: clinical and pathological report of 22 cases].

We report clinical and pathologic findings in 22 patients with Wegener's granulomatosis collected from 1966 to 1989. Ten cases were analyzed retrospectively. Organs affected included the lungs (n = 18), upper airways (16), kidneys (15), musculo-skeletal system (10), eyes (8), skin (7) and ear (5). Clinical manifestations of airway involvement included nasal obstruction, dysphonia and epistaxis. Lung involvement was evident in chest X-rays in 18 patients, 14 with a nodular aspects. Histologic study in 14 of these patients showed necrotizing and granulomatous vasculitis. Clinical evidence of nephropathy was evident in 15 patients and led to rapidly progressive renal failure in 8. Biopsy in this group (n = 14) revealed focal glomerulonephritis in 6 and diffuse disease in 8. Overall, 13 patients died: 5 without diagnosis, 4 from renal failure, 2 from sepsis, 1 from a lymphoma developing 3 years after immune suppressive therapy and 1 from unknown causes. Among survivors, one received a renal transplant and one remains in chronic dialysis. The diagnosis of Wegener's granulomatosis is therefore based on clinical findings including rhino pharyngeal, pulmonary and renal manifestations.

Adult↗
PubMed1989

Glucose-induced oscillations of intracellular Ca2+ concentration resembling bursting electrical activity in single mouse islets of Langerhans.

Intracellular Ca2+ levels were monitored in single, acutely isolated mouse islets of Langerhans by dual emission Indo-1 fluorometry. High-frequency (3.1 min-1) [Ca2+]i oscillations with a brief rising time (1-2 s) and 10 s half-width ('fast' oscillations) were detected in 11 mM glucose. Raising the glucose concentration to 16.7 mM increased the duration of these oscillations, which were otherwise absent in 5.5 mM glucose. [Ca2+]i waves of lower frequency (0.5 min-1) and longer rising time ('slow' oscillations) were also recorded. The data indicate that "fast" oscillations are directly related to beta-cell bursting electrical activity, and suggest the existence of extensive networks of electrically coupled cells in the islet.

Animals↗
PubMedDate not supplied

[Experimental models in epilepsy].

INTRODUCTION: Epilepsy is an heterogeneous collection of neurological disorders that have in common a transient and recurrent hypersynchronous activation of large populations of neurons in distinct focal areas or in the entire brain. DEVELOPMENT: Research into the cellular mechanisms of epilepsy focuses on understanding. 1. The alterations on cellular and network excitability, and 2. The mechanisms of hypersynchronization. Several different animal models exist that mimic different types of focal and generalized epilepsy in humans. Hypothesis derived from such models is helping to design more effective therapies.

Anticonvulsants↗
PubMedDate not supplied

[Mechanisms of generation of fast (20 80 Hz) oscillations in thalamocortical circuits].

AIM: This review focuses on the mechanisms of generation of fast (20 80 Hz) oscillations in thalamocortical networks and their possible functional role. DEVELOPMENT: Fast oscillations appear in the electroencephalogram in a transitory fashion, during behavioral tasks that require increased alertness or during responses to optimal sensory stimulation in animals and humans. Fast oscillations also appear spontaneously during activated states (awake state and paradoxical sleep) and during the depolarizing phases of the slow oscillation that characterize slow wave sleep and anesthesia. Fast oscillations are generated in thalamic and cortical circuits as the result of the activity of pacemaker cells, or as the result of the synaptic interactions among excitatory and inhibitory cells. The synchronization of fast oscillations has been proposed as a possible solution to the binding problem. The formation of neuronal ensembles containing specific sets of cells oscillating together would be the code representing sensory input and coordination between sensory and motor activity. However, oscillating neurons coexist with equal numbers of non oscillating neurons. CONCLUSIONS: Understanding the rules of coexistence of these two regimes of network activity is key to understanding information processing in the brain. As a first step, and in order to understand the possible role of fast oscillations, it is necessary to understand the mechanisms by which they are generated.

Electroencephalography↗