Properties of excitatory synaptic connections mediated by the corpus callosum in the developing rat neocortex

Despite the major role of excitatory cortico-cortical connections in mediating neocortical activities, little is known about these synapses at the cellular level. Here we have characterized the synaptic properties of long-range excitatory-to-excitatory contacts between visually identified layer V pyramidal neurons of agranular frontal cortex in callosally connected neocortical slices from postnatal day 13 to 21 (P13-21) rats. Midline stimulation of the corpus callosum with a minimal stimulation paradigm evoked inward excitatory postsynaptic currents (EPSCs) with an averaged peak amplitude of 56.5 +/- 5 pA under conditions of whole cell voltage clamp at -70 mV. EPSCs had fixed latencies from stimulus onset and could follow stimulus trains (1-20 Hz) without changes in kinetic properties. Bath application of 2,3-dihydro-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) abolished these responses completely, indicating that they were mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPARs). Evoked responses were isolated in picrotoxin to yield purely excitatory PSCs, and a low concentration of NBQX (0.1 microM) was used to partially block AMPARs and prevent epileptiform activity in the tissue. Depolarization of the recorded pyramidal neurons revealed a late, slowly decaying component that reversed at approximately 0 mV and was blocked by D-2-amino-5-phosphonovaleric acid. Thus AMPA and N-methyl-D-aspartate receptors (NMDARs) coexist at callosal synapses and are likely to be activated monosynaptically. The peak amplitudes and decay time constants for EPSCs evoked using minimal stimulation (+/-40 mV) were similar to spontaneously occurring sEPSCs. Typical conductances associated with AMPA and NMDAR-mediated components, deduced from their respective current-voltage (I-V) relationships, were 525 +/- 168 and 966 +/- 281 pS, respectively. AMPAR-mediated responses showed age-dependent changes in the rectification properties of their I-V relationships. While I-Vs from animals >P15 were linear, those in the younger (<P16) age group were inwardly rectifying. Although Ca2+ permeability in AMPARs can be correlated with inward rectification, outside-out somatic patches from younger animals were characterized by Ca2+-impermeable receptors, suggesting that somatic receptors might be functionally different from those located at synapses. While the biophysical properties of AMPAR components of callosally-evoked EPSCs were similar to those evoked by stimulation of local excitatory connections, the NMDA component displayed input-specific differences. NMDAR-mediated responses for local inputs were activated at more hyperpolarized holding potentials in contrast with those evoked by callosal stimulation. Paired stimuli used to assay presynaptic release properties showed paired-pulse depression (PPD) in animals <P16, which converted to facilitation (PPF) in older animals, suggesting a developmental transition from low probability of transmitter release to high P(r) at these synapses and/or alterations in the properties of the underlying postsynaptic receptors. Physiologic properties of neocortical e-e connections are thus input specific and subject to developmental changes in their postsynaptic receptors.

Scavenging of reactive oxygen species by chlorophyllin: an ESR study

The antioxidant effects of chlorophyllin (CHL), a water-soluble analog of the green plant pigment chlorophyll, on different reactive oxygen species (ROS) were investigated by electron spin resonance (ESR) spectroscopy. As a standard, we have used the ability of CHL to scavenge the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. CHL inhibits the formation of 5,5-dimethyl-1-pyrroline-N-oxide adduct with hydroxyl radical (DMPO-.OH adduct) generated by gamma-radiation in a dose-dependent manner. At a concentration of 1 mM, CHL caused more than 90% inhibition of ESR signal intensity of this adduct. However, the results obtained with the Fenton reaction were different. We also found evidence for the inhibition of 1O2-dependent formation of the 2,2,6,6-tetramethyl-piperidine oxide (TEMPO) radical during photosensitization of methylene blue with visible light. CHL was also able to inhibit hydrogen peroxide induced oxidation of phenol red. The rate constant of the reaction of CHL with H2O2 was found to be 2.7 x 10(6) M-1 s-1. In conclusion, CHL has potent antioxidant ability involving scavenging of various physiologically important ROS.

Extrusion of actin-positive strands from Hep-2 and Int 407 cells caused by outer membrane preparations of enteropathogenic Escherichia coil and specific attachment of wild type bacteria to the strands

Enteropathogenic Escherichia coli (EPEC) causes persistent infantile diarrhoea. This nontoxigenic E. coli exhibits a complicated pathogenic mechanism in which its outer membrane proteins and type III secretory proteins damage intestinal epithelium and cause diarrhoea. In accordance with this, our previous study using HEp-2 cells demonstrated cytopathic effects caused by cell-free outer membrane preparations of EPEC. In this study, we report the extrusion of actin-positive strands from HEp-2 and Int 407 cells when treated with outer membrane preparations. An interesting observation of this work, perhaps relevant to the characteristic localized three-dimensional colony formation of EPEC, is the attachment of a wild type EPEC strain to these actin-positive strands.

Mechanism of protection against radiation-induced DNA damage in plasmid pBR322 by caffeine

PURPOSE

Caffeine (1,3,7-trimethyl xanthine), a dietary component, has been shown to have widely varying effects on DNA damage induced by UV and ionizing radiation, depending upon pre- or post-irradiation administration and its concentration. Caffeine administered post-UV irradiation is known to inhibit enzymatic repair of DNA lesions, leading to potentiation of damage, whereas its presence before or during irradiation elicits protection in a wide range of test systems: bacteria, cultured human cells, plant seeds and mouse. The purpose of this study is to test whether caffeine present during gamma-irradiation of plasmid DNA, a system devoid of replication and repair, could elicit protection by scavenging free radicals.

MATERIALS AND METHODS

Plasmid pBR322 DNA was exposed to gamma-radiation in the presence or absence of caffeine at a dose-rate of 1.20 Gy min(-1) and damage measured as single-strand breaks. To understand the mechanisms of the observed protection, especially under oxic conditions, reaction of caffeine with superoxide radical (O(2)(-)), hydrogen peroxide (H(2)O(2)) and the deoxyribose peroxyl radical (ROO(*)) were studied.

RESULTS

Irradiation of pBR322 was observed to induce a dose-dependent increase in single-strand breaks. Caffeine itself did not induce strand breaks but reduced radiation-induced strand breaks at micromolar to millimolar concentrations. Caffeine has been shown to react with the radiation-derived oxidants. The reaction rate constants observed were 7.5x10(1) M(-1) s(-1) with O(2)(-) 1.05x10(8) M(-1) s(-1) with ROO(*) and 8.8x10(1) M(-1) s(-1) with H(2)O(2).

CONCLUSIONS

Caffeine effectively protects DNA against ionizing radiation in a system devoid of repair and replication machinery. Thus, DNA protection shown by caffeine is possibly due to the scavenging of radiation-derived primary as well as secondary reactive oxygen species, and this physicochemical protective pathway possibly pre-empts any subsequent inhibitory effect of caffeine on the enzymatic repair of DNA.

Excessive free radical generation in the blood of children suffering from asthma

The aim of the present study is to evaluate the biochemical parameters in blood relevant to oxygen free radicals and antioxidant defenses in children with asthma. A total of 210 asthmatic children, aged 5-18 years, were studied at two different times, once during a severe episode of wheeze (during episode category) and the other after recovery (resting condition). A total of 180 healthy children participated in the study as age and sex matched healthy controls. Superoxide and hydroxyl radical assays were used as a measure of free radical formation. Antioxidant enzymes and free radical scavengers in blood were also assayed. Lipid peroxidation products were assayed in plasma and erythrocytes to evaluate the imbalance (if any) between oxidant (radical) formation and their inactivation. Serum IgE concentrations and peak expiratory flow rate (PEFR) were used as measures of allergic reactions and residual lung capacity, respectively. Excessive production of superoxide and hydroxyl radicals were noted in the blood cells in asthmatics and were correlated to the severity of disease measured as PEFR. Superoxide dismutase and free radical scavengers in blood were significantly lower in asthma, even during resting condition. The present observations endorse the correlation between disease severity and oxygen radical production in asthma subjects. Oxygen metabolites may play a direct or indirect role in the modulation of airway inflammation. Excessive superoxide and hydroxyl radical production may be used as a marker for susceptibility to asthma and for monitoring therapeutic measures.

PALI-a database of Phylogeny and ALIgnment of homologous protein structures

PALI (release 1.2) contains three-dimensional (3-D) structure-dependent sequence alignments as well as structure-based phylogenetic trees of homologous protein domains in various families. The data set of homologous protein structures has been derived by consulting the SCOP database (release 1.50) and the data set comprises 604 families of homologous proteins involving 2739 protein domain structures with each family made up of at least two members. Each member in a family has been structurally aligned with every other member in the same family (pairwise alignment) and all the members in the family are also aligned using simultaneous super-position (multiple alignment). The structural alignments are performed largely automatically, with manual interventions especially in the cases of distantly related proteins, using the program STAMP (version 4.2). Every family is also associated with two dendrograms, calculated using PHYLIP (version 3.5), one based on a structural dissimilarity metric defined for every pairwise alignment and the other based on similarity of topologically equivalent residues. These dendrograms enable easy comparison of sequence and structure-based relationships among the members in a family. Structure-based alignments with the details of structural and sequence similarities, superposed coordinate sets and dendrograms can be accessed conveniently using a web interface. The database can be queried for protein pairs with sequence or structural similarities falling within a specified range. Thus PALI forms a useful resource to help in analysing the relationship between sequence and structure variation at a given level of sequence similarity. PALI also contains over 653 'orphans' (single member families). Using the web interface involving PSI_BLAST and PHYLIP it is possible to associate the sequence of a new protein with one of the families in PALI and generate a phylogenetic tree combining the query sequence and proteins of known 3-D structure. The database with the web interfaced search and dendrogram generation tools can be accessed at http://pauling.mbu.iisc.ernet. in/ approximately pali.

Resistance to arsenite modulates levels of alpha-tubulin and sensitivity to paclitaxel in Leishmania donovani

Tubulin expression is known to alter due to drug resistance. Differentiation of Leishmania promastigotes into infectious amastigotes has been reported to be accompanied by differential tubulin gene expression. In this study, alpha-tubulin expression under various stages of differentiation was measured in an in vitro generated arsenite-resistant L. donovani strain. While levels of expression of alpha-tubulin were similar in wild type and resistant promastigotes, during conversion into axenic amastigotes the changes in the expression levels of alpha-tubulin varied widely between the two strains. Sensitivity of the two strains to paclitaxel (known to promote tubulin assembly) differed, with the resistant strain being two-fold more sensitive than the wild type strain. Paclitaxel was also seen to cause differential effects on alpha-tubulin levels in the two strains.

Effect of vanillin on methylene blue plus light-induced single-strand breaks in plasmid pBR322 DNA

The ability of vanillin (4-hydroxy-3-methoxybenzaldehyde), a naturally occurring food flavouring agent, in inhibiting photosensitization-induced single-strand breaks (ssbs) in plasmid pBR322 DNA has been examined in an in vitro system, independent of DNA repair/replication processes. Photosensitization of DNA with methylene blue, visible light and oxygen, induced ssbs resulting in the production of open circular form (OC form) in a concentration-dependent manner. The yield of OC form induced by photosensitization was increased several-fold by deuteration of the buffer and was found to be inhibited by sodium azide, a scavenger of singlet oxygen (1O(2)). Vanillin, per se, did not induce but inhibited photosensitization-induced ssbs in plasmid DNA, at millimolar concentrations. The inhibitory effect of vanillin was both concentration- and time-dependent. On a molar basis, vanillin was, however, less effective than trolox, a water-soluble analogue of alpha-tocopherol. Photosensitization by methylene blue system generates singlet oxygen, as one of the major components of ROS. Therefore, interaction of singlet oxygen with vanillin was investigated. The rate constant of vanillin with 1O(2) was estimated to be 5.93x10(7)M(-1)s(-1) and that of sodium azide as 2. 7x10(8)M(-1)s(-1). The present investigations show that vanillin can protect against photosensitization-induced ssbs in the plasmid pBR322 DNA, and this effect may partly be due to its ability to scavenge 1O(2).

Supracricoid laryngectomy with Cricohyoidopexy--a clinico oncological & functional experience

Supracricoid laryngectomy with Cricohyoidopexy (CHP) is a procedure that is commonly practiced in France & Canada. Eight such procedures were carried out at Kidwai Memorial Institute of Oncology, Bangalore during the period from 1991 through 1996. Four Glottic, 3 transglottic & one supraglottic cancers were subjected to this procedure. The study comprised of 7 males & 1 female. The average age was 52 years. Two procedures were done as salvage procedures for radiotherapy (RT) failures. The patients have a follow-up ranging from one year to six years, except for one who died soon after discharge from hospital secondary to myocardial infarction. Median follow up was four years. The three year acturial disease free survival was 83%. Six out of 8 (75%) were decannulated, and physiologic deglutition without aspiration was established in all patients. Hospital stay ranged from 11 to 62 days averaging 29 days. The speech was analyzed together with other partial laryngectomies and was found to be qualitatively worse than speech after other partial laryngectomy procedures. In addition speech intensity levels after CHP were lower than in other partial laryngectomy procedures. The speech however allowed normal social interaction. This procedure certainly has distinct oncological advantage in encompassing circumferential horse-shoe lesions with minimal subglottic extension which in the past would have received total laryngectomy and needs to be included in the repertoire of speech restorative surgery in laryngeal cancers.

An intrasubject comparison of two doses of succinylcholine in modified electroconvulsive therapy

The electroconvulsive therapy (ECT) guideline of the Royal College of Psychiatrists recommends a 0.5 mg/kg of succinylcholine for ECT modification. Our clinical experience suggests that this dose is insufficient for Indian patients. The dose recommended by the Royal College of Psychiatrists (0.5 mg/kg) and a larger dose (1 mg/kg) were compared in 50 patients referred for ECT. In one ECT session, patients were equally randomized to receive one of the two doses and in the next session they were switched to the other dose. The extent of motor seizure modification was rated on a five-point scale by two independent raters who were blinded to the succinylcholine dose. The interrater reliability was good (K = 0.85). "Poor" seizure modification occurred in 48% and 12% of patients with the 0.5 and 1 mg/kg doses, respectively. Of the 24 patients who had poor modification with 0.5 mg/kg, 20 had "good" modification in the session with 1 mg/kg (P < 0.001). A small delay (mean = 55 s) occurred in time to recover from the respiratory paralysis with the 1 mg/kg dose of succinylcholine. No patient, however, had prolonged apnea requiring special measures. We recommend 1 mg/kg of succinylcholine dose be used in the first ECT session. For subsequent sessions, the dose may be altered, depending on the response for optimal motor seizure modification.

IMPLICATIONS

The dose of muscle relaxant (succinylcholine) recommended in modified electroconvulsive therapy is not based on empirical research. In the same patients (n = 50), two doses-0.5 mg/kg and 1 mg/kg-were compared during different electroconvulsive therapy sessions. The larger dose was more effective in modifying the peripheral convulsion.

Body piercing in the accident and emergency department

Recently an increasing number of patients with complications related to pierced body jewellery have been seen. Often removal of the jewellery is indicated. Removal of these items may also be required for radiological purposes. If the doctor is familiar with the opening mechanism of the item, removal is not usually difficult. Uninformed attempts at removal may cause unnecessary trauma and distress. In a survey of 28 accident and emergency doctors, only six were able accurately to describe the opening mechanisms of all three commonly used types of jewellery. Descriptions of the types of jewellery currently used are not available in the medical literature. The aim of this article is to familiarize doctors with the types of jewellery used, describe their opening mechanisms, and suggest techniques for their removal. The complications of body piercing and the indications for the removal of body jewellery are also outlined.

Inhibition of radiation-induced DNA damage in plasmid pBR322 by chlorophyllin and possible mechanism(s) of action

Naturally occurring compounds capable of protecting DNA against ionizing radiation and chemical mutagens have considerable potential for prevention of mutation-based health impairment including cancer and other degenerative diseases. Chlorophyllin (CHL), a water-soluble derivative of chlorophyll, has been examined for its ability to protect DNA against radiation induced strand breaks using an in vitro plasmid DNA system. Gamma-radiation, up to a dose of 6 Gy (dose rate 1.25 Gy/min), induced a dose-dependent increase in single-strand breaks (ssbs) in plasmid pBR322 DNA. CHL per se did not induce, but inhibited radiation-induced ssbs in a concentration-dependent manner; 500 microM giving about 90% protection. The protection afforded by CHL was comparatively less than that of trolox, a water-soluble analogue of alpha-tocopherol. To elucidate the underlying mechanism(s), reaction of CHL with the radiation-derived hydroxyl radical (.OH) and deoxyribose peroxyl radical (ROO.) was studied by pulse radiolysis. CHL exhibited a rate constant of 6.1+/-0.4x109 M-1 s-1 with.OH and 5.0+/-1.3x107 M-1 s-1 with ROO. To our knowledge, this is the first report providing direct evidence of free radical-scavenging properties of CHL. The results showed that CHL, effectively protects plasmid DNA against ionizing radiation, in an in vitro system independent of DNA repair or other cellular defense mechanisms. The ability of CHL to scavenge. OH and ROO., may contribute to its protective effects against radiation induced DNA damage in the pBR322 system.

Plasticity of first-order sensory synapses: interactions between homosynaptic long-term potentiation and heterosynaptically evoked dopaminergic potentiation

Persistent potentiations of the chemical and electrotonic components of the eighth nerve (NVIII) EPSP recorded in vivo in the goldfish reticulospinal neuron, the Mauthner cell, can be evoked by afferent tetanization or local dendritic application of an endogenous transmitter, dopamine (3-hydroxytyramine). These modifications are attributable to the activation of distinct intracellular kinase cascades. Although dopamine-evoked potentiation (DEP) is mediated by the cAMP-dependent protein kinase (PKA), tetanization most likely activates a Ca2+-dependent protein kinase via an increased intracellular Ca2+ concentration. We present evidence that the eighth nerve tetanus that induces LTP does not act by triggering dopamine release, because it is evoked in the presence of a broad spectrum of dopamine antagonists. To test for interactions between these pathways, we applied the potentiating paradigms sequentially. When dopamine was applied first, tetanization produced additional potentiation of the mixed synaptic response, but when the sequence was reversed, DEP was occluded, indicating that the synapses potentiated by the two procedures belong to the same or overlapping populations. Experiments were conducted to determine interactions between the underlying regulatory mechanisms and the level of their convergence. Inhibiting PKA does not impede tetanus-induced LTP, and chelating postsynaptic Ca2+ with BAPTA does not block DEP, indicating that the initial steps of the induction processes are independent. Pharmacological and voltage-clamp analyses indicate that the two pathways converge on functional AMPA/kainate receptors for the chemically mediated EPSP and gap junctions for the electrotonic component or at intermediaries common to both pathways. A cellular model incorporating these interactions is proposed on the basis of differential modulation of synaptic responses via receptor-protein phosphorylation.

Use of prokaryotically expressed nucleocapsid protein as positive antigen in ELISA

A cDNA library of Rinderpest vaccine virus was prepared in Zap Express vector (Stratagene). The Rinderpest 'N' gene specific clones were selected, characterized and thereafter expressed in E. coli XLOLR strain. The expressed protein was found to be immunogenic in western blot with hyperimmune sera. It reacted with rinderpest and 'N' protein specific monoclonal antibodies in Enzyme Linked Immunosorbent Assay (ELISA). Prokaryotically expressed 'N' protein also gave precipitin band in counter immunoelectrophoresis test (CIE). The expression of N protein was sufficient for its utility as positive antigen in CIE and ELISA used for rinderpest diagnosis.

Laparoscopic management of a cholecystocutaneous abscess

Spontaneous cholecystocutaneous abscess or fistula is a rare complication of gallbladder disease that has been known since the time of Thilesus in 1670. We describe the case of a 72-year-old white woman who presented with a large subcutaneous abscess in the right upper quadrant of the abdomen accompanied by fever and leukocytosis. There was no history of diabetes or trauma. An abdominal CT scan revealed communication of the abscess cavity with the gallbladder. Laparoscopic cholecystectomy followed by open drainage of the abdominal wall abscess were accomplished without complication. Traditional treatment for a cholecystocutaneous abscess has consisted of abdominal wall incision and drainage followed by staged cholecystectomy. One-stage treatment of the cholecystocutaneous abscess is a preferred option, and a laparoscopic approach appears feasible.

Laparoscopic cholecystectomy in the densely scarred abdomen

Extensive intra-abdominal adhesions are a possible contraindication to laparoscopic cholecystectomy and are known to occur after peritonitis because of perforated hollow viscus or multiple abdominal operations. Four such patients, who had undergone three or more previous abdominal operations, and had additional complicating factors, were successfully treated by laparoscopic cholecystectomy. An initial subxiphoid incision with blunt finger dissection was used to place the primary port. This approach achieves greater success and is safer than the traditional open umbilical dissection, because it avoids extensive lysis of small bowel and transverse colon adhesions from the anterior abdominal wall.

Laparoscopic cholangiography: a new method and device

Laparoscopic cholangiography is invaluable in the detection of bile duct stones, visualization of ductal anomalies and discovery and prevention of iatrogenic injuries to the bile ducts. The use of this procedure is, however, limited by the technical difficulties of cystic duct cannulation. A method of laparoscopic cholangiography that avoids cystic duct cannulation is described. It consists of a Kumar I Cholangiography Clamp that is applied across the gallbladder just above the Hartmann's pouch and divides the gallbladder into a medial and lateral compartment. A Kumar Cholangio Catheter is then introduced through the side-channel of the clamp, puncturing the medial compartment (i.e. the Hartmann's pouch) with a short #22 gauge needle for aspiration, followed by dye injection. Cholangiography was obtained with remarkable ease in 49 of the first 50 cases (98%) without complication.

Continuous infusion of high doses of atropine in the management of organophosphorus compound poisoning

Forty five cases of organophosphorus poisoning were studied to evaluate the results of continuous infusion of high doses of atropine as against the conventional intermittent therapy. A statistically significant reduction in mortality (23.5% to 8.8%; p less than 0.05) was evident in this study as compared to previous years. Pseudocholinesterase levels below 10% of normal were associated with a poor prognosis and increased mortality.

Acute renal failure due to acute diarrhoeal diseases

Fifty four patients with acute renal failure (ARF) due to acute diarrhoeal diseases (ADD) were treated between August 1987 and May 1988. There were 39 males and 15 females. The mean age was 46.25 years. These patients were referred by general practitioners (GP's) and private nursing homes during an epidemic of ADD in Madras city in 1987-'88. Investigations revealed plasma urea (mean +/- SD) 129 +/- 52.8 mg/dl. and plasma creatinine (mean +/- SD) 7.51 +/- 4.3 mg/dl. 42 patients underwent peritoneal dialysis. 3 had haemodialysis. 29 patients died (mortality, 53.7%). The most significant factor for high mortality was the time interval from onset of ADD to diagnosis of ARF which was 5.2 +/- 2.17 days in the patients who survived compared to 8.5 +/- 3.1 days in the patients who died (P less than 0.01). It is concluded that (a) GP's had given inadequate fluid therapy before admission and (b) were initially not aware of renal failure and so referred them late to hospital.

Assessment of progression of chronic renal failure--using reciprocal of serum creatinine

Twenty-seven patients with chronic renal failure (CRF) were studied over a period of 6 to 57 months. The mean serum creatinine (Scr.) was 4 mg/dl. All patients were started on conservative therapy. The rate of progression of renal failure was assessed by least square linear regression analysis using reciprocal of Scr. (1/Scr.) versus time plots. Group I (13 patients) showed steady progression to end-stage renal failure (mean slope 0.013328). 7 of 13 patients had chronic glomerulonephritis. 11 had nephrotic proteinuria. In group II (14 patients), the regression line remained static indicating arrest of progression of renal disease (mean slope 0.0087858). 6 of 14 had nephrosclerosis. 3 had nephrotic proteinuria. We conclude that (1) assessment of progression of CRF by linear regression analysis of 1/Scr. vs time is a useful method. (2) persistent nephrotic proteinuria is an adverse longterm risk factor. (3) conservative therapy has a definite role in the management of CRF.

Dithiocarbamate inhibition of cadmium-induced changes in spermatozoan acetyltransferases

The administration of sodium N-methyl-N-dithiocarboxy-D-glucamine (NaG) subsequent to the administration of CdCl2.2.5H2O to male rats, inhibits the cadmium-induced decreases in spermatozoan acetyltransferase (AT) levels and provides marked protection against the cadmium-induced morphologic testicular changes in the cauda and corpus and partial protection against the changes in the caput.