Spontaneous pneumomediastinum - Hamman´s syndrome.

This case study presents a rare case of a 29-year-old woman with spontaneous pneumomediastinum who was treated in the emergency department for subjective dyspnea, rhinitis, and a subjectively reported increasing swelling of the throat. The clinical presentation was only characterized by crepitus in the neck and supraclavicular areas. CT scan of the neck and chest revealed massive emphysema of the soft tissues of the neck, chest, the right side of the face, and pneumomediastinum extending to the diaphragm. Based on the clinical presentation and imaging findings, which were consulted with thoracic surgeons, we assessed the condition as benign spontaneous pneumomediastinum. The patient was treated conservatively and discharged from the hospital on the third day of hospitalization with the need of aftercare.

Temperature dependence of N-methyl-D-aspartate receptor channels and N-methyl-D-aspartate receptor excitatory postsynaptic currents.

N-methyl-d-aspartate (NMDA) receptors (NMDARs) are highly expressed in the CNS and mediate the slow component of excitatory transmission. The present study was aimed at characterizing the temperature dependence of the kinetic properties of native NMDARs, with special emphasis on the deactivation of synaptic NMDARs. We used patch-clamp recordings to study synaptic NMDARs at layer II/III pyramidal neurons of the rat cortex, recombinant GluN1/GluN2B receptors expressed in human embryonic kidney (HEK293) cells, and NMDARs in cultured hippocampal neurons. We found that time constants characterizing the deactivation of NMDAR-mediated excitatory postsynaptic currents (EPSCs) were similar to those of the deactivation of responses to a brief application of glutamate recorded under conditions of low NMDAR desensitization (whole-cell recording from cultured hippocampal neurons). In contrast, the deactivation of NMDAR-mediated responses exhibiting a high degree of desensitization (outside-out recording) was substantially faster than that of synaptic NMDA receptors. The time constants characterizing the deactivation of synaptic NMDARs and native NMDARs activated by exogenous glutamate application were only weakly temperature sensitive (Q(10)=1.7-2.2), in contrast to those of recombinant GluN1/GluN2B receptors, which are highly temperature sensitive (Q(10)=2.7-3.7). Ifenprodil reduced the amplitude of NMDAR-mediated EPSCs by approximately 50% but had no effect on the time course of deactivation. Analysis of GluN1/GluN2B responses indicated that the double exponential time course of deactivation reflects mainly agonist dissociation and receptor desensitization. We conclude that the temperature dependences of native and recombinant NMDAR are different; in addition, we contribute to a better understanding of the molecular mechanism that controls the time course of NMDAR-mediated EPSCs.

Pregnenolone sulfate modulation of N-methyl-D-aspartate receptors is phosphorylation dependent.

Pregnenolone sulfate (PS), an endogenously occurring neurosteroid, has been shown to modulate the activity of several neurotransmitter-gated channels, including the N-methyl-D-aspartate receptor (NMDAR). NMDARs are glutamate-gated ion channels involved in excitatory synaptic transmission, synaptic plasticity, and excitotoxicity. To determine the mechanism that controls PS sensitivity of NMDARs, we measured NMDAR responses induced by exogenous agonist application in voltage-clamped HEK293 cells expressing NR1/NR2B NMDARs and cultured rat hippocampal neurons. We report that PS potentiates the amplitude of whole-cell recorded NMDAR responses in cultured hippocampal neurons and HEK293 cells; however, the potentiating effect of PS on NMDAR in outside-out patches isolated from cultured hippocampal neurons and HEK293 cells was lost within 2 min after patch isolation in a neurosteroid-specific manner. The rate of diminution of the PS potentiating effect was slowed by protein phosphatase inhibitors. Treatment of cultured hippocampal neurons with a nonspecific protein kinase inhibitor and a specific protein kinase A (PKA) inhibitor diminished PS-induced potentiation, which was recovered by adding a PKA, but not a protein kinase C (PKC), activator. These results suggest that the effect of PS on NMDARs is controlled by cellular mechanisms that are mediated by dephosphorylation/phosphorylation pathways.

Neurosteroid modulation of ionotropic glutamate receptors and excitatory synaptic transmission.

Ionotropic glutamate receptors function can be affected by neurosteroids, both positively and negatively. N-methyl-D-aspartate (NMDA) receptor responses to exogenously applied glutamate are potentiated or inhibited (depending on the receptor subunit composition) by pregnenolone sulphate (PS) and inhibited by pregnanolone sulphate (3alpha5betaS). While PS effect is most pronounced when its application precedes that of glutamate, 3alpha5betaS only binds to receptors already activated. Synaptically activated NMDA receptors are inhibited by 3alpha5betaS, though to a lesser extent than those tonically activated by exogenous glutamate. PS, on the other hand, shows virtually no effect on any of the models of synaptically activated NMDA receptors. The site of neurosteroid action at the receptor molecule has not yet been identified, however, the experiments indicate that there are at least two distinct extracellularly located binding sites for PS mediating its potentiating and inhibitory effects respectively. Experiments with chimeric receptors revealed the importance of the extracellular loop connecting the third and the fourth transmembrane domain of the receptor NR2 subunit for the neurosteroid action. alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors are inhibited by both PS and 3alpha5betaS. These neurosteroids also affect AMPA receptors-mediated synaptic transmission, however, in a rather indirect way, through presynaptically located targets of action.

Temperature dependence of NR1/NR2B NMDA receptor channels.

N-methyl-D-aspartate (NMDA) receptors are highly expressed in the CNS, mediate the slow component of excitatory transmission and play key roles in synaptic plasticity and excitotoxicity. These ligand-gated ion channels are heteromultimers composed of NR1 and NR2 subunits activated by glycine and glutamate. In this study, patch-clamp recordings were used to study the temperature sensitivity of recombinant NR1/NR2B receptors expressed in human embryonic kidney (HEK) 293 cells. Rate constants were assessed by fitting a six-state kinetic scheme to time courses of transient macroscopic currents induced by glutamate at 21.9-46.5 degrees C. Arrhenius transformation of the rate constants characterizing NMDA receptor channel activity indicates that the most sensitive were the rate constants of desensitization (temperature coefficient Q(10)=10.3), resensitization (Q(10)=4.6) and unbinding (Q(10)=3.6). Other rate constants and the amplitude of single-channel currents were less temperature sensitive. Deactivation of responses mediated by NR1/NR2B receptors after a brief application of glutamate was best fit by a double exponential function (tau(fast): Q(10)=3.7; tau(slow): Q(10)=2.7). From these data, we conclude that desensitization/resensitization of the NMDA receptor and glutamate unbinding are especially temperature sensitive and imply that at physiological temperatures the channel kinetics play an important role in determining amplitude and time course of NMDA receptor-mediated postsynaptic currents and these receptors mediated synaptic plasticity.

Antibiotic resistance in an in vitro subgingival biofilm model.

INTRODUCTION: The purpose of this study was to utilize an in vitro biofilm model of subgingival plaque to investigate resistances in subgingival biofilm communities to antibiotics commonly used as adjuncts to periodontal therapy. METHODS: Biofilms were grown on saliva-coated hydroxyapatite supports in trypticase-soy broth for 4 h-10 days and then exposed for 48 h to either increasing twofold concentrations of tetracycline, amoxicillin, clindamycin, and erythromycin or therapeutically achievable concentrations of tetracycline, doxycycline, minocycline, amoxicillin, metronidazole, amoxicillin/clavulanate, and amoxicillin/metronidazole. RESULTS: Concentrations necessary to inhibit bacterial strains in steady-state biofilms were up to 250 times greater than the concentrations needed to inhibit the same strains grown planktonically. In the presence of therapeutically available antibiotic concentrations, significantly higher proportions of the biofilms remained viable as the biofilms reached steady-state growth. The combinations of amoxicillin/clavulanate and amoxicillin/metronidazole were the most effective in suppressing growth. These combinations were particularly effective against biofilms up to and including 7 days of age and inhibited 90% or more of the bacteria present relative to untreated controls. As the biofilms approached steady state, these combinations were less effective with 50-60% of the bacteria retaining viability. CONCLUSION: Most, but not all, species of subgingival bacteria are considerably more resistant in biofilms than in planktonic cultures. Resistance appeared to be age-related because biofilms demonstrated progressive antibiotic resistance as they matured with maximum resistance coinciding with the steady-state phase of biofilm growth.

Morphology and physiology of lamina I neurons of the caudal part of the trigeminal nucleus.

It has been suggested that in mammals, trigeminal lamina I neurons play a role in the processing and transmission of sensory information from the orofacial region. We investigated the physiological and morphological properties of trigeminal subnucleus caudalis (Sp5C) lamina I neurons in slices prepared from the medulla oblongata of 13- to 15-day-old postnatal rats using patch-clamp recordings and subsequent biocytin-streptavidin-Alexa labeling. Twenty-five neurons were recorded and immunohistochemically stained. The Sp5C lamina I consisted of several types of neurons which, on the basis of their responses to somatic current injection, can be classified into four groups: tonic neurons, which fired throughout the depolarizing pulse; phasic neurons, which expressed an initial burst of action potentials; delayed onset neurons, which showed a significant delay of the first action potential; and single spike neurons, characterized by only one to five action potentials at the very beginning of the depolarizing pulse even at high levels of stimulation intensity. Electrical stimulation of the spinal trigeminal tract evoked AMPA receptor-mediated excitatory postsynaptic currents (EPSC) exhibiting a strong polysynaptic component. AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSC) were characterized by a 10-90% rise time of 0.50+/-0.06 ms and a decay time constant of 2.5+/-0.5 ms. The kinetic properties of NMDA receptor-mediated EPSCs were measured at +40 mV. The 10-90% rise time was 8+/-2 ms and the deactivation time constants were 94+/-31 and 339+/-72 ms, respectively. Intracellular staining and morphological analysis revealed three groups of neurons: fusiform, pyramidal, and multipolar. Statistical analysis indicated that the electrophysiological properties and morphological characteristics are correlated. Tonic and phasic neurons were fusiform or pyramidal and delayed onset and single spike neurons were multipolar. Our results show that both the physiological and morphological properties of Sp5C lamina I neurons exhibit significant differences, indicating their specific integration in the processing and transmission of sensory information from the orofacial region.

An in vitro biofilm model of subgingival plaque.

INTRODUCTION: Numerous biofilm models have been described for the study of bacteria associated with the supragingival plaque. However, there are fewer models available for the study of subgingival plaque. The purpose of this study was to develop and validate a model that closely mimicked the composition of the subgingival flora. METHODS: The model was developed as follows: calcium hydroxyapatite disks were coated overnight with 10% sterile saliva, placed in flat-bottomed tissue culture plates containing trypticase-soy broth, directly inoculated with a small aliquot of dispersed subgingival plaque, incubated anaerobically, and transferred to fresh medium at 48-h intervals until climax (steady-state) biofilms were formed ( approximately 10 days). RESULTS: The model, based on samples from eight periodontitis patients and eight healthy subjects, yielded a multi-species, heterogeneous biofilm, consisting of both gram-positive and gram-negative species, and comprising 15-20 cultivable species associated with the subgingival flora. The species present and their proportions were reflective of the initial cultivable subgingival flora. Comparisons of the initial plaque samples from healthy subjects and the mature biofilms showed 81% similarity in species and 70% similarity in the proportions present. Biofilms formed from samples obtained from periodontally diseased subjects were 69% similar in species and 57% similar in the proportions present. CONCLUSIONS: The biofilm model described here closely reproduces the composition of the cultivable subgingival plaque both in the species present and in their relative proportions. Differences existed between biofilms grown from diseased and non-diseased sites with the former being characterized by the presence of periodontal pathogens at microbially significant levels.

Physiology and pathology of NMDA receptors.

Ionotropic glutamate receptors of the N-methyl-D-aspartate (NMDA) subtype are highly expressed in the central nervous system and are involved in excitatory synaptic transmission and synaptic plasticity. Prolonged activation of NMDA receptors can lead to excitotoxicity, which is implicated in the pathogenesis of neurodegeneration occurring in various acute and chronic disorders of the central nervous system. Recent advances in understanding the function, pharmacology, genetics and structure of NMDA receptors has promoted a search for new compounds that could be therapeutically used. These compounds act on agonist binding sites, either apart from them or directly within the ion channel pore. Members of the last group are called open channel blockers, and some of them, such as memantine and ketamine, are already clinically used. Kinetic modeling of NMDA receptor activity was employed to define the effects of various groups of modulators. Quantifying the action of these substances by kinetic parameters can help us to reveal the molecular mechanism of action at the receptor and to characterize the dependence of its action on the mode of NMDA receptor activation. Two modes are considered: phasic activation, induced by synaptically released glutamate, and tonic activation, which is expected to occur under pathological conditions when low, but sustained levels of glutamate activate NMDA receptors. The aim of our review is to summarize the recent data about the structural and functional properties of NMDA receptors and their role in long-term potentiation and excitotoxicity.

Activation and modulation of ligand-gated ion channels.

Ligand-gated ionic channels are integral membrane proteins that enable rapid and selective ion fluxes across biological membranes. In excitable cells, their role is crucial for generation and propagation of electrical signals. This survey describes recent results from studies performed in the Department of Cellular Neurophysiology, Institute of Physiology ASCR, aimed at exploring the conformational dynamics of the acetylcholine, glutamate and vanilloid receptors during their activation, inactivation and desensitization. Distinct families of ion channels were selected to illustrate a rich complexity of the functional states and conformational transitions these proteins undergo. Particular attention is focused on structure-function studies and allosteric modulation of their activity. Comprehension of the fundamental principles of mechanisms involved in the operation of ligand-gated ion channels at the cellular and molecular level is an essential prerequisite for gaining an insight into the pathogenesis of many psychiatric and neurological disorders and for efficient development of novel specifically targeted drugs.

Hemodialysis access placement with preoperative noninvasive vascular mapping: comparison between patients with and without diabetes.

We retrospectively analyzed data on preoperative vascular mapping in 195 consecutive patients to investigate the common belief that patients with diabetes are poor candidates to have an arteriovenous fistula placed as dialysis access because they lack suitable blood vessels. There was no difference in venous diameter, arterial diameter, and arterial peak systolic velocity measurements between patients with and without diabetes. Patients with diabetes had a greater prevalence of vascular calcifications and greater cuff measurements of systolic segmental arterial pressure. In 140 of 195 patients, subsequent vascular access surgery had been performed in our institution, and 127 of these patients were on hemodialysis therapy at the end of the study period. There was no difference in the prevalence of fistula placement (66% versus 60%; chi-square = 2.6; df = 2; P = 0.28, not significant [NS]) and percentage of functioning fistulae between patients with and without diabetes (67% versus 62%; chi-square = 0.27; df = 1; P = 0.61, NS). The percentage of patients dialyzed through a temporary catheter was equal in patients with and without diabetes (18%). In summary, patients with diabetes seem to be as good candidates for arteriovenous fistula placement as patients without diabetes. Additional studies are required to determine the long-term outcome of fistulae in patients with diabetes.

Relationship between phosphorus and creatinine clearance in peritoneal dialysis: clinical implications.

Elevated serum phosphorus levels are associated with increased morbidity and mortality in dialysis patients. To study the determinants of serum phosphorus levels and phosphorus clearance, we measured phosphorus concentrations in 24-hour collections of dialysate and residual urine output during routine urea kinetics in 56 peritoneal dialysis patients. Dietary records were used to estimate oral phosphorus intake, and the net gastrointestinal absorption of phosphorus was determined measuring the amount of phosphorus excreted in 24 hours. Dialysate to plasma ratios of phosphorus and creatinine were very similar, and the peritoneal clearances of phosphorus and creatinine correlated well and were of the same magnitude. High transporters in the peritoneal equilibration test had greater phosphorus and creatinine clearances than low transporters. In patients with residual urine output, the renal clearances of phosphorus and creatinine also correlated well. Comparing two groups of patients with a similar Kt/V of 2 and greater but different levels of creatinine clearance, either greater or less than 60 L/wk, the patients with the greater creatinine clearance also had a greater phosphorus clearance (7.0 +/- 2.2 versus 4.3 +/- 0.7 mL/min/1.73 m(2)) and significantly lower serum phosphorus levels (4.8 +/- 0.9 versus 5.9 +/- 1.4 mg/dL) despite a greater daily amount of phosphorus absorption (490 +/- 190 versus 336 +/- 100 mg/d). In summary, creatinine clearance measurements provide a good estimate of phosphorus clearance and how much dietary phosphorus and therefore protein can be tolerated.

Carboxyhemoglobin and lactate levels do not correlate in critically ill patients.

Endogenous carbon monoxide (CO) is produced in the degradation of heme by heme oxygenase. Studies have shown that hypoxia induces heme oxygenase production of CO in vascular tissue. Because elevated plasma lactate levels are associated with tissue hypoxia, we determined if there was any correlation between lactate and carboxyhemoglobin (COHb) levels in a group of critically ill patients with a high likelihood of hypoxia. In a 7.5-month period, 5322 simultaneous arterial COHb and lactate measurements were performed routinely on 183 patients with a blood gas analyzer in the Department of Veterans Affairs Medical Center, Bronx, New York, Surgical Intensive Care Unit. Sixty-one percent of the patients had elevated lactate levels (> 2.5mmol/L), and 46% had elevated COHb levels (> 1.5%). Lactate levels ranged from 0.12 to 22.7 mmol/L and COHb levels from 0% to 4.8%. There was no correlation between lactate and COHb levels (r = .07 with P < .0001). Levels of endogenous CO do not increase in situations in which lactate production is increased. It is possible that changes in endogenous production of CO may not significantly affect the circulating level of COHb. Although readily available, COHb levels do not seem to be clinically useful as markers of critical illness.

[Wilms' tumor in adults]. / Wilmsuv nádor u dospelého.

The author analyzes the case of a nephroblastoma in an adult and gives an account of the oncogenetic background of this disease based on new ontogenetic findings. He draws attention to the possible association of nephroblastoma and other congenital defects and the possibility of another nephroblastoma which developed on the same ontogenetic background in the other kidney.