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.

SHV-1 beta-lactamase is mainly a chromosomally encoded species-specific enzyme in Klebsiella pneumoniae.

The nature of the SHV-1 beta-lactamase gene was analyzed in 97 epidemiologically unrelated Klebsiella pneumoniae strains isolated from clinical samples. beta-Lactamase bands that focused at a pI of 7.6 (SHV-1-type) in 74 strains, at a pI of 7.1 (LEN-1-type) in 13 strains, and at a pI of 5.4 (TEM-1-type) in 10 strains were detected by analytical isoelectric focusing (IEF). Among the 74 SHV-1-producing strains, 40 had, in addition to the pI 7.6 band, an additional band on IEF: 20 had a band with a pI of 7.1 and 20 had a band with a pI of 5.4. Most of the 74 SHV-1-producing strains (76.7%) carried plasmids. Transfer of beta-lactam resistance by conjugation was possible in only 9.3% of the strains tested. SHV-1 gene-specific PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of the chromosomal DNA was positive for 93 of the 97 strains and negative for only 4 of the 10 samples with K. pneumoniae TEM-1 producers. In an attempt to approximate the location of the SHV gene locus by endonuclease restriction analysis, RFLP analysis with Southern blotting of chromosomal DNA with a labeled SHV-1 fragment as a probe was used to study the 97 strains. A trial with EcoRI showed at least one positive hybridization band for 96 strains; two bands were detected for 8 strains. The hybridization was negative for only one TEM-1 beta-lactamase-producing strain. DNA sequence analysis showed no differences in promoter regions or extra stop-triplet sequences; only point mutations determined different allelic variants. The novel SHV-type variants are designated SHV-32 and SHV-33. As a result of the RFLP and sequencing analyses, it can be postulated that the loci for SHV-1 and LEN-1 genes are arranged in tandem. Our results strongly support the hypothesis that the ancestor of the SHV-1 beta-lactamase originated from the K. pneumoniae chromosome.

[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.

[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.

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.

[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 plasmids in Escherichia coli strains]. / Caracterización de los plásmidos en cepas de Escherichia coli.

BACKGROUND: Strains of Escherichia coli are frequently plasmid carriers. In this species, resistance to beta-lactam antibiotics is almost always conditioned by the production of enzymes coded by plasmidic genes. The present is a study of the plasmids of 44 ampicillin-sensitive strains and 134 ampicillin-resistant (ampS and ampR). The possibility that the number and size of the plasmids are different and that this data may be added to the information to be considered in these two groups of strains is suggested. METHODS: The 178 strains selected had been isolated from human products. Sensitivity to ampicillin was studied by diffusion and was confirmed with the study of MIC (Mueller-Hinton agar, innoculum: 5 x 10 CFU). The plasmid type beta-lactamases were identified by analytical isoelectrofocus. Characterization of the plasmids was performed according to a variant of the Birnboim and Doly alkaline lysis technique. RESULTS: Among the ampR and ampS strains no plasmid were observed in 9 (6.72%) and 11 (25%) respectively. The mean number of plasmids was 2.53 and 1.57, ranging between 0-10 and 0-5. The number of strains with plasmids larger than, or equal to, 38 Kb was 113 and 27 respectively. The largest plasmids observed in the ampS strains were of 99 Kb and in the ampR of 109 Kb. A total of 3.73% of the ampR strains presented plasmids larger than 99 Kb and 8.20% more than 5 plasmids. CONCLUSIONS: No plasmids, presence of up to five and sizes smaller than or equal to 99 Kb were observed in strains of ampS and ampR. The presence of more than five and/or plasmids larger than or equal to 100 Kb was observed in 11.94% of the ampR.

In vitro antimicrobial production of beta-lactamases, aminoglycoside-modifying enzymes, and chloramphenicol acetyltransferase by and susceptibility of clinical isolates of Acinetobacter baumannii.

Antimicrobial susceptibility testing was performed on 54 epidemiologically unrelated clinical isolates of Acinetobacter baumannii by using a standard agar dilution technique. On the basis of the in vitro activities, imipenem and doxycycline were the most active agents, whereas amikacin, isepamicin, and the new fluorquinolones ciprofloxacin and ofloxacin presented moderate activity. Cephalosporinase activity was found in 98% of the strains, whereas lactamases of TEM type 1 and one with a pI of 7 to 7.5 were present in 16 and 11% of the strains, respectively. Resistance to aminoglycosides was explained by the production of the three classes of aminoglycoside-modifying enzymes, with predominance of aminoglycoside-3'-phosphotransferase VI in 28% of the strains.

A survey of beta-lactamases from 618 isolates of Klebsiella spp.

beta-Lactamases from 618 isolates of Klebsiella spp. (487 Klebsiella pneumoniae and 131 Klebsiella oxytoca) were identified by analytical isoelectric focusing. The strains were consecutive isolates from 618 different patients in five hospital centres between 1980 and 1984. Most of the chromosomal beta-lactamases from the K. pneumoniae isolates had a pI of 7.1, and most of the K. oxytoca isolates had chromosomal beta-lactamases of pIs 7.8, 5.3 and 5.5. Plasmid-mediated beta-lactamases were produced by 91.8% of K. pneumoniae isolates and 9.9% of K. oxytoca isolates. The beta-lactamase types identified most frequently were SHV-1 in the former species, and TEM-1 in the latter species. Of the K. pneumoniae isolates, 101 produced both of these plasmid-mediated beta-lactamases, while one strain produced an extended-spectrum SHV-like beta-lactamase. Of the 131 K. oxytoca isolates, 20 were hyper-producers of chromosomal beta-lactamase. The susceptibility of this genus to beta-lactam antibiotics is controlled almost exclusively by beta-lactamases, the production of which may differ from one strain to another; thus the empirical therapeutic use of beta-lactam antibiotics is not recommended for this genus.

Characterization of penicillinase-producing strains of Neisseria gonorrhoeae.

Twenty-three penicillinase-producing strains of Neisseria gonorrhoeae were characterized. All strains showed hybridization with a TEM-1 probe and production of a TEM-1 type beta-lactamase (pI 5.4) on isoelectric focusing. Eight strains also showed a beta-lactamase band of pI 5.5. The penicillin MICs for the strains producing only TEM-1 were in the range 4-16 micrograms/ml; MICs of the strains with the additional pI 5.5 band were > or = 128 micrograms/ml for seven strains and 4 micrograms/ml for an arginine-hypoxanthine dependent strain. The association of the high MICs with the presence of the pI 5.5 band was statistically significant. The pI 5.5 band could represent a new beta-lactamase type or a TEM-1 mutant.

Clinical and pathological findings in fatal plant oxalosis. A review.

Poisoning by ingestion of oxalate-containing plants, such as raw rhubarb, is infrequent, and such deaths are rare. We present a review of the most important clinical and pathological aspects of oxalate poisoning and recommend that the public be educated about the dangers of eating unknown plants with potentially adverse effects.

[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.