Cortical auditory adaptation in the awake rat and the role of potassium currents.

Responses to sound in the auditory cortex are influenced by the preceding history of firing. We studied the time course of auditory adaptation in primary auditory cortex (A1) from awake, freely moving rats. Two identical stimuli were delivered with different intervals ranging from 50 ms to 8 s. Single neuron recordings in the awake animal revealed that the response to a sound is influenced by sounds delivered even several seconds earlier, the second one usually yielding a weaker response. To understand the role of neuronal intrinsic properties in this phenomenon, we obtained intracellular recordings from rat A1 neurons in vitro and mimicked the same protocols of adaptation carried out in awake animals by means of depolarizing pulses of identical duration and intervals. The intensity of the pulses was adjusted such that the first pulse would evoke a similar number of spikes as its equivalent in vivo. A1 neurons in vitro adapted with a similar time course but less than in awake animals. At least two potassium currents participated in the in vitro adaptation: a Na(+)-dependent K(+) current and an apamin-sensitive K(+) current. Our results suggest that potassium currents underlie at least part of cortical auditory adaptation during the awake state.

Temperature modulation of slow and fast cortical rhythms.

In the local cortical network, spontaneous emergent activity self-organizes in rhythmic patterns. These rhythms include a slow one (<1 Hz), consisting in alternation of up and down states, and also faster rhythms (10-80 Hz) generated during up states. Varying the temperature in the bath between 26 and 41 degrees C resulted in a strong modulation of the emergent network activity. Up states became shorter for warmer temperatures and longer with cooling, whereas down states were shortest at physiological (36-37 degrees C) temperature. The firing rate during up states was robustly modulated by temperature, increasing with higher temperatures. The sparse firing rate during down states hardly varied with temperature, thus resulting in a progressive merging of up and down states for temperatures around 30 degrees C. Below 30 degrees C and down to 26 degrees C the firing lost rhythmicity, becoming progressively continuous. The slope of the down-to-up transitions, which reflects the speed of recruitment of the local network, was progressively steeper for higher temperatures, whereas wave-propagation speed exhibited only a moderate increase. Fast rhythms were particularly sensitive to temperature. Broadband high-frequency fluctuations in the local field potential were maximal for recordings at 36-38 degrees C. Overall, we found that maintaining cortical slices at physiological temperature is critical for the generated activity to be analogous to that in vivo. We also demonstrate that changes in activity with temperature were not secondary to oxygenation changes. Temperature variation sets the in vitro cortical network at different functional regimes, allowing the exploration of network activity generation and control mechanisms.

Rhythmic spontaneous activity in the piriform cortex.

Slow spontaneous rhythmic activity is generated and propagates in neocortical slices when bathed in an artificial cerebrospinal fluid with ionic concentrations similar to the ones in vivo. This activity is extraordinarily similar to the activation of the cortex in physiological conditions (e.g., slow-wave sleep), thus representing a unique in vitro model to understand how cortical networks maintain and control ongoing activity. Here we have characterized the activity generated in the olfactory or piriform cortex and endopiriform nucleus (piriform network). Because these structures are prone to generate epileptic discharges, it seems critical to understand how they generate and regulate their physiological rhythmic activity. The piriform network gave rise to rhythmic spontaneous activity consisting of a succession of up and down states at an average frequency of 1.8 Hz, qualitatively similar to the corresponding neocortical activity. This activity originated in the deep layers of the piriform network, which displayed higher excitability and denser connectivity. A remarkable difference with neocortical activity was the speed of horizontal propagation (114 mm/s), one order of magnitude faster in the piriform network. Properties of the piriform cortex subserving fast horizontal propagation may underlie the higher vulnerability of this area to epileptic seizures.

The effects of oral slow-release terbutaline on the circadian variation in spirometry and arterial blood gas levels in patients with chronic airflow obstruction.

The circadian variation of spirometry and blood gases was studied in eight male, normoxemic, patients with chronic air flow obstruction and complaints of early morning dyspnea. The patients were selected for a high amplitude in circadian variation of PEFR. They were treated for eight days with placebo and slow-release terbutaline tablets (5 mg at 8 am and 10 mg at 8 pm). Thereafter, arterial blood gas levels were measured at four-hour intervals over 24 hours. Just after blood sampling, FEV1 measurements were performed. The results on placebo therapy were compared with results in eight healthy volunteers matched for age, sex, and smoking habits. The circadian rhythms of FEV1, PaO2, and SaO2 in these patients showed a higher amplitude than in normal subjects. The decrease of FEV1 in the patient group at 8 am coincided with the decrease in PaO2 and SaO2. In normal subjects no significant nocturnal fall in FEV1, PaO2, or SaO2 occurred. Administration of slow-release terbutaline tablets for eight days, providing comparable diurnal and nocturnal serum levels, prevented the nocturnal decrease of FEV1, PaO2, and SaO2. The increase of the FEV1 at all hours of observation showed a significant correlation with the increase of the PaO2.

Beta-lactamase activity in mycobacteria other than M. tuberculosis.

Beta-lactamase activity was studied in 142 non-tuberculosis mycobacterial strains. The distribution according to species was as follows: four M. avium, 14 M. chelonae, 10 M. fortuitum, 59 M. gordonae, 55 M. kansasii. The spectrum of hydrolysis of the beta-lactamases was screened using an acidimetric method and the characterization was performed by analytical isoelectric focusing.

[Efficiency of tazobactam as inhibitor of beta-lactamases, combined with piperacillin, against resistant strains to this penicillin]. / Eficacia del tazobactam como inhibidor de betalactamasas, asociado a la piperacilina, frente a cepas resistentes a esta penicilina.

We studied the efficacy of tazobactam (YTR 830), a new beta-lactamase inhibitor in combination with piperacillin (P) against 198 Enterobacteriaceae strains. A comparative study of susceptibility (MIC determined on Mueller Hinton agar; inoculum 10(4) cfu) was made with the combination amoxicillin (A) + clavulanic acid (CA). Of 181 strains resistant to P, 79.56% were susceptible to it in the presence of tazobactam (TZ). The characteristics of the beta-lactamases of 37 strains resistant to P + TZ (MIC greater than 40 micrograms/ml) were studied; 11 were hyperproducers of chromosomic beta-lactamase and 7 produced two types of plasmidic beta-lactamase. The MICs of TZ alone were uniform and high (64-128 micrograms/ml), independently of the characteristics of the strains beta-lactamase. Of 17 strains susceptible to P, the efficacy of P + TZ was significant among carriers of plasmidic beta-lactamase; there was practically no change in the P susceptibility among the non carriers. The efficacy of P + TZ was similar to that of A + AC against E. coli strains; it was higher against strains of Enterobacter, Citrobacter and Serratia.

[Loss of antibiotic sensitivity of Pseudomonas aeruginosa strains during treatment]. / Pérdida de sensibilidad a los antibióticos de cepas de Pseudomonas aeruginosa en el curso del tratamiento.

BACKGROUND: Loss of sensitivity to betalactamic, quinolones and aminoglucoside antibiotics has been described during treatment of infections produced by strains of Pseudomonas aeruginosa. Sixteen nosocomial strains isolated over a year during which sensitivity to one or several antibiotics of the above mentioned groups had been lost during the course of treatment were studied. METHODS: The strains were identified by conventional techniques. Sensitivity to antibiotics was studied by determination of the minimum inhibitory concentration in solid medium, according to the guidelines of the National Committee for Clinical Laboratory Standards. Plasmidic beta-lactamases were identified by analytic isoelectric focusing. Hyperproduction of chromosomic lactamase was studied by a qualitative technique. The 0 antigens were studied against rabbit antisera. The pyocinetype was determined according to the Fyfe method. Plasmids were detected by alkaline lysis extraction and electrophoresis in agarose gel. RESULTS: The 16 strains in which changes in sensitivity were observed during the course of treatment represent 4.47% of all P. aeruginosa isolates during one year. Loss of sensitivity to betalactamic antibiotics was observed in 10 strains, in one to aminoglucosides, in two to ciprofloxacin, simultaneously to aminoglucosides and ciprofloxacin in one and to betalactamic and ciprofloxacin in another two. Six of the 13 patients (46%) required a change in antibiotic treatment. CONCLUSIONS: The convenience of following the sensitivity of the strains of Pseudomonas aeruginosa isolated in a patients is suggested to thereby avoid therapeutic failure and the potential danger of clonal dissemination of the strains which have lost sensitivity.

[Characterization of Haemophilus influenzae's resistance to ampicillin]. / Caracterización de la resistencia de Haemophilus influenzae a la ampicilina.

BACKGROUND: The resistance of Haemophilus influenzae to ampicillin is nearly always dependent on plasmid-mediated betalactamase production. The betalactamase type most frequently identified was TEM-1; type ROB has occasionally been identified. The presence of plasmid-mediated betalactamase has been studied in H. influenzae strains moderately susceptible or resistant to ampicillin. METHODS: The test used in the detection of the presence of betalactamase was nitrocefin hydrolysis; the enzyme type was identified by analytic isoelectric focusing; the codifying gene of this betalactamase was identified by hybridisation with a TEM-1 probe labeled with digoxigenine. Strains studied were 110, obtained during the period 1987 to 1989 and isolated from four Hospitals of the Vallés area of Barcelona. RESULTS: Enzyme production was detected in 105 of 110 strains studied; TEM-1 type betalactamase was identified in 108 and positive hybridisation was obtained in these strains with the TEM-1 probe. CONCLUSIONS: Nitrocefin hydrolysis is a reliable test for the detection of betalactamase production, although it may be unable to detect it (falses negatives) when the production is low. The only betalactamase type identified was TEM-1. The frequency of the strains with non-enzymatic resistance was 1.8%.

[Failure of a cyclophosphamide-dexamethasone combination in paraquat poisoning]. / Fracaso de la combinación ciclofosfamida-dexametasona en la intoxicación por paracuat.

A 37-year-old female deliberately ingested a 20% solution of paraquat in water. One hour later gastric lavage was carried out and bentonite was administered. Five hours later cyclophosphamide (5 mg/kg/day) and dexamethasone (24 mg/day) were started and a continuous intestinal lavage was carried out; four hours later, hemodialysis was begun. After 36 hours, features of renal and respiratory failure developed, with a rapid progress to respiratory distress. The patient died 94 hours after the ingestion of the poison. Despite early therapy with dexamethasone and cyclophosphamide, this patient's evolution does not support the presumed effectiveness of this drug association for paraquat poisoning.

[The radiological findings in poisonings by metals]. / Hallazgos radiológicos en intoxicaciones por metales.

We present four cases of heavy metal poisoning (mercury, lead, bismuth and arsenic) in which plain chest and/or abdominal assisted in the differential diagnosis of the clinical picture manifested upon admission at our Emergency Department. The patients suffering from mercury, lead, and bismuth poisoning recovered some weeks after treatment was started. However, the patient with arsenic trioxide poisoning developed cardio-circulatory collapse leading to death three days after admission.

[Benign encephalitis of the brain stem]. / Encefalitis benigna de tronco cerebral.

INTRODUCTION: The secondary encephalitis disorders are due to an immunological mechanism which causes demyelinating lesions of the central and peripheral nervous systems, with very variable clinical features. The pathogenesis and localization of benign encephalitis of the brain stem and the Miller Fisher syndrome (MFS) are still subject to debate. It is suggested that they may both belong to different extremes of the same nosological spectrum known as the ophthalmoplegia-ataxia-areflexia syndrome. CLINICAL CASE: We report the case of an 11 year old boy with encephalitis of the brain stem who had electromyographic alterations compatible with the Guillain-Barré syndrome, and MR images characteristic of an acute demyelinating disorder of the brainstem. CONCLUSIONS: The encephalitis of the brain stem is an uncommon condition in children which leads to diagnostic difficulty at its onset, since this is similar in other disorders such as MFS, tumours, cerebrovascular accidents and less often in the initial stages of multiple sclerosis. The clinical course is very useful to distinguish between these conditions. MR is the imaging technique of choice for diagnosis in these patients. Although there is currently no specific treatment for post-infectious encephalitis, the use of high doses of immunoglobulins may be justified in view of the physiopathological origin of the condition.

[Infantile bilateral striate necrosis]. / Necrosis estriatal bilateral infantil.

INTRODUCTION: Necrosis of the basal ganglia (NBG) is an uncommon condition in childhood. Cases of NBG have been reported in connection with metabolic disorders, infections, degenerative conditions, intoxications, head injuries and hypoxic-ischemic encephalopathies. The commonest clinical features include alteration of consciousness, chorea-athetoic or dystonic movements, spasticity, contractures of the limbs and convulsions. CLINICAL CASE: We describe the case of an eight year old girl, who after having clinical gastroenteritis, developed acute neurological dysfunction, associated with images on cranial computerized axial tomography (CAT) showing a possible intracranial tumour and magnetic resonance (MR) studies showing bilateral hypodensity of the basal ganglia. Three months later magnetic resonance showed that these lesions had almost completely disappeared. This supports the diagnosis of post-infectious lesions. CONCLUSIONS: The clinical course is very variable. Cases with a previous history of infection have a better prognosis. In our patient treatment was started with corticosteroids. She made a good recovery and was sent home with no sequelae five days later. The new imaging techniques (CAT and MR) have led to more cases of selective involvement of the basal ganglia being diagnosed. MR is the most specific technique for diagnosis in these patients. Although there is no effective specific treatment, treatment with biperidine, thyrotropic hormone and corticosteroids have been used with no apparent effect on the course of the disorder.

[Paraquat poisoning: clinical and anatomopathologic aspects in 3 cases]. / Intoxicación por paraquat: aspectos clínicos y anatomopatológicos en tres casos.

3 cases of suicide due to ingestion of 150, 200 and 4 gr. of paraquat, respectively, are presented. Two of them were brothers and agricultural industrialists, the other one was a farmer. The first two cases died 16 and 10 hours after intake. The farmer died 21 days after ingestion. All of them had progressive hypoxemia and renal failure the two brothers had heart conduction system glycemia (23 mg/dl) a few hours after ingestion. The postmortem study showed edema, hemorrhage and congestion of the lungs, alveolitis, fibrosis and lobar atelectasia; renal tubular necrosis adrenal necrosis; colestasia; hepatic steatosis focal miocarditis. The clinical evolution, particularly short in the first two patients, is commented on, as well as the post-mortem findings, comparing them with those described in the literature. Finally, due to the high toxicity of this herbicide, we insist in prompt transport to herbicide, we insist in prompt transport to the hospital in order to apply early treatment.

Fatal hydrogen sulfide poisoning.

Two cases of fatal hydrogen sulfide poisoning are described which occurred during cleaning of a tank that had transported polysulfides. The most characteristic findings of the autopsy were: a blackish-green pigmentation at macroscopic examination; pulmonary edema, steatosis, intrahepatic cholestasis and renal tubular necrosis at microscopic examination. The blood concentration of sulfide ions exceeded 3.5 mg/l. These cases are compared to others described in the literature. The preventive measures that should be adopted to avoid this type of poisoning are stressed.

[Trichloroethylene poisoning. Presentation of 3 cases and review of the literature]. / Intoxicación por tricloroetileno. Presentación de tres casos y revisión de la literatura.

Three cases of occupational poisoning by trichloroethylene, one of them fatal, are presented. The etiologic, clinical and diagnostic aspects of each case are discussed, along with a broad literature review, emphasizing preventive measures and the substitution of this chloric solvent by other, less toxic solvents, as recommended by the U.S. Food and Drug Administration.