Search PubMed⌕ Search

Biomedical subjects

G M Smith

Publications and source records attributed to G M Smith.

At least 91 records · Page 5Linked to original sources
PubMed1995

Synchrony between single-unit activity and local field potentials in relation to periodicity coding in primary auditory cortex.

1. We recorded responses from 136 single units and the corresponding local field potentials (LFPs) from the same electrode at 44 positions in the primary auditory cortex of 25 juvenile, ketamine-anesthetized cats in response to periodic click trains with click repetition rates between 1 and 32 Hz; to Poisson-distributed click trains with an average click rate of 4 Hz; and under spontaneous conditions. The aim of the study is to evaluate the synchrony between LFPs and single-unit responses, to compare their coding of periodic stimuli, and to elucidate mechanisms that limit this periodicity coding in primary auditory cortex. 2. We obtained averaged LFPs either as click-triggered averages, the classical evoked potentials, or as spike-triggered averages. We quantified LFPs by initial negative peak-to-positive peak amplitude. In addition, we obtained trigger events from negativegoing level crossings (at approximately 2 SD below the mean) of the 100-Hz low-pass electrode signal. We analyzed these LFP triggers similarly to single-unit spikes. 3. The average ratio of the LFP amplitude in response to the second click in a train and the LFP amplitude to the first click as a function of click rate was low-pass with a slight resonance at approximately 10 Hz, and, above that frequency, decreasing with a slope of approximately 24 dB/octave. We found the 50% point at approximately 16 Hz. In contrast, the LFP amplitude averaged over entire click trains was low-pass with a similar resonance but a high-frequency slope of 12 dB/octave and a 50% point at approximately 12 Hz. 4. The LFP amplitude for click repetition rates between 5 and 11 Hz often showed augmentation, i.e., the amplitude increased in response to the first few clicks in the train and thereafter decreased. This augmentation was paralleled by an increase in the probability of firing in single units simultaneously recorded on the same electrode. 5. We calculated temporal modulation transfer functions (tMTFs) for single-unit spikes and for LFP triggers. They were typically bandpass with a best modulating frequency of 10 Hz and similar shape for both single-unit spikes and LFP triggers. The tMTF per click, obtained by dividing the tMTF by the number of clicks in the train, was low-pass with a 50% cutoff frequency at approximately Hz, similar to that for the average LFP amplitude. 6. the close similarity of the tMTFs for single-unit spikes and LFP triggers suggests that single-unit tMTFs can be predicted from LFP level crossings.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1995

Effect of stimulation on burst firing in cat primary auditory cortex.

1. Neural activity was recorded extracellularly with two independent microelectrodes aligned in parallel and advanced perpendicular to isofrequency sheets in cat primary auditory cortex. Multiunit activity was separated into single-unit spike trains using a maximum variance spike sorting algorithm. Only units that demonstrated a high quality of sorting and a minimum spontaneous firing rate of 0.2 spikes/s were considered for analysis. The primary aim of this study was to describe the effect of periodic click train and broadband noise stimulation on short-time-scale (< or = 50 ms) bursts in the spike trains of single auditory cortical units and to determine whether stimulation influenced the occurrence, spike count, and/or temporal structure of burst firing relative to a spontaneous baseline. 2. Extracellular recordings were made in 20 juvenile and adult cats from 69 single auditory cortical units during click train stimulation and silence, and from 30 single units during noise stimulation and in silence. In an additional 15 single units the effect of both click train and noise stimulation was investigated. The incidence, spike count, and temporal structure of short-time-scale burst firing in the first 100 ms following stimulus presentation was compared with burst firing in the period starting 500 ms after stimulus presentation and with spontaneous burst firing. In addition, the serial dependence of interspike intervals within a burst was tested during periods of stimulation. 3. Burst firing was present in the stimulation, poststimulation, and spontaneous conditions. Longer bursts (consisting of > or = 3 spikes) were more commonly observed in the poststimulation and spontaneous conditions than in the stimulation condition. This effect was most pronounced during click stimulation. A period of elevated firing activity was present in a subset of units 0.5-1.5 s after stimulus presentation, indicating prolonged effects of stimulation on single-unit firing behavior. 4. For both stimuli, the proportion of single-unit responses composed of bursts was significantly greater in poststimulation and spontaneous periods than during stimulation. Burst rate was higher in post-click-train stimulation and spontaneous periods than during periods of click stimulation. The isolated spike rate was significantly higher during periods of noise and click stimulation than in the poststimulation and spontaneous periods. 5. An examination of the autocorrelograms and higher-order interspike interval histograms of single-unit responses during click train stimulation indicated that 25% of single-unit spike trains contained an excess of brief first-order intervals and 14% of spike trains contained a shortage of long higher-order interspike intervals relative to a spontaneous baseline. During noise stimulation, 10% of single-unit responses contained an excess of short intervals relative to baseline. Interspike intervals of short-duration bursts were not serially dependent during periods of stimulation. 6. A comparison of the autocorrelograms and higher-order interval histograms of single-unit responses in the poststimulation and spontaneous conditions indicated that 20% of single-unit spike trains contained an excess of short first-, second-, and third-order intervals following stimulation. This subgroups of single units could not be distinguished on the basis of the age of the animal or the depth at which the recording was made. 7. The low incidence of burst firing during stimulation opposes the view that bursts serve as a mechanism to emphasize or amplify particular stimulus-related responses in the presence of ongoing spontaneous activity in the primary auditory cortex. Moreover, there is little evidence to support the notion that brief bursts represent neural codes, because intraburst intervals are not serially dependent. It is suggested that pyramidal burst firing may be an effective way to evoke postsynaptic firing in inhibitory interneurons and subsequ

Acoustic Stimulation↗
PubMed1995

Detection of clonal immunoglobulin gene rearrangements in the PBPC harvests of patients with acute lymphoblastic leukaemia.

We have used a fluorescently based PCR technique to detect rearrangements in the immunoglobulin heavy chain (IgH) gene in the presentation BM of five patients with adult ALL and have looked for similar rearrangements in their PBPC. Using this approach we have been able to demonstrate clonal rearrangements in the PBPC of two of five patients. Remission BM samples taken 6-12 weeks prior to leucapheresis failed to show a clonal rearrangement in either patient. The significance of these results is discussed.

Base Sequence↗
PubMed1994

Specificity and localization of lipolytic activity in adult Drosophila melanogaster.

The triacylglycerol lipases present in adult Drosophila melanogaster have been investigated. Different lipase activities are present in various tissues in the fly. In particular, an abundant lipase activity is present in the male accessory gland. An esterase null mutant was used to confirm that the enzyme activity was due to a distinct lipase and not non-specific activity from esterase 6 which is also abundant in accessory glands. The properties of the accessory-gland lipase were investigated, and pH optima and substrate utilization suggest that it has some similarities to vertebrate bile-salt-stimulated lipase. Lipase activity is significantly reduced in males and increased in females shortly after mating. This finding suggests that lipase activity is transferred to the female and may be important in mating and reproduction in Drosophila.

Animals↗
PubMed1994

Stable isotope methods for the study of beta-carotene-d8 metabolism in humans utilizing tandem mass spectrometry and high-performance liquid chromatography.

This report presents analytical methods for the isolation and quantification of all-trans-beta-carotene-d8 in human plasma following a 73 mumol oral dose. Retinol-d4 derived from beta-carotene-d8 was also determined in the same plasma. Plasma samples drawn over a 24 day period were analyzed. beta-Carotene and retinol were isolated and purified for analysis using a solid phase extraction protocol with aminopropyl-bonded silica sorbent. Ratios of beta-carotene-d8/beta-carotene were determined using reversed-phase HPLC with spectrophotometric detection, which fully resolved the isotopomers, and by tandem mass spectrometry (MS/MS) with electron ionization. Results obtained from MS/MS and HPLC analysis showed close agreement and demonstrated improved selectivity relative to analysis using a single mass analyzer. Retinol-d4 was converted to its tert-butyldimethylsilyl ether and analyzed by gas chromatography/mass spectrometry using selected ion monitoring. The ability to resolve the beta-carotene isotopomers by HPLC makes it feasible for investigators without mass spectrometers to investigate the dynamics of absorption and metabolism of beta-carotene-d8 in humans.

Adjuvants, Immunologic↗
PubMed1994

Rapid turnover rate of the hippocampal synaptic NMDA-R1 receptor subunits.

The decrease in the number of synaptic NMDA receptors produced by prior i.c.v. injections of antisense oligonucleotides was examined in the CA1 stratum radiatum of hippocampal slices. Isolated NMDA and AMPA receptor-mediated components of extracellular synaptic responses were compared in slices obtained from control animals and from animals treated for 48 h with an 18-mer phosphorothioate antisense oligodeoxynucleotide directed against NMDA-R1. In slices ipsilateral to the injected hemisphere, the synaptic NMDA component was decreased by 29% compared with the contralateral side and by 34% compared with animals injected with vehicle alone. At the same time, synaptic AMPA receptor-mediated components were not affected. These results are consistent with a rapid turnover rate of synaptic NMDA-R1 and demonstrate the feasibility of antisense oligonucleotide techniques for the depletion of specific synaptic receptor channels.

Animals↗
PubMed1994

Immortalization of immature and mature mouse astrocytes with SV40 T antigen.

The ability of neonatal astrocytes to promote neurite outgrowth in vitro and in vivo diminishes as astrocytes mature. This property correlates with the developmental loss of the central nervous system's ability to regenerate after injury. Cell lines representative of immature and mature astrocytes would be useful for studies to determine differences between these two populations. Previous work on immortalization of bipotential neural/glial precursors and fully differentiated glial cells suggests that immortalization of astrocytes at timed intervals of culture may yield cell lines trapped in different maturation states. To test this, neonatal mouse cortical astrocytes were immortalized by retrovirus-mediated transfer of the SV40 T antigen (Tag) gene at 2, 6 and 17 days of culture. The clonal cell lines express Tag and are contact-inhibited. Three phenotypes that change as a function of astrocyte maturation were examined to determine the fidelity with which the cell lines represent immature and mature astrocytes. These were: (1) cell morphology, growth pattern and size, (2) level of glial fibrillary acidic protein (GFAP) expression, and (3) neurite outgrowth promotion. First, immature and mature lines resemble mortal type 1 astrocytes of corresponding ages with respect to morphology and growth pattern, and retain a quantitative difference in cell size (mature cells are larger). Second, the pattern of GFAP expression is preserved, with immature lines expressing lower levels than mature cell lines, but the overall GFAP levels are significantly lower in immortalized cell lines compared to mortal cells. Finally, promotion of neurite outgrowth from embryonic chick retinal ganglion cells on monolayers of the cell lines was examined. While all neurite outgrowth measures are significantly greater for the immortalized lines than for control 3T3 cells, they are attenuated relative to mortal astrocytes. The age-related pattern of stronger outgrowth support on immature astrocytes is retained for neurite initiation, but not retained for mean neurite length. Thus, SV40 Tag-immortalized astrocytes have a complex phenotype characterized by retention of age-related differences in morphology, growth pattern and cell size, and by a marked attenuation of some astrocyte-specific characteristics but retention of age-related differences in the expression level of these same characteristics, and finally, loss of the ability to support neurite extension at level characteristic of immature astrocytes.

3T3 Cells↗
PubMed1994

Positions of His-64 and a bound water in human carbonic anhydrase II upon binding three structurally related inhibitors.

The 3-dimensional structure of human carbonic anhydrase II (HCAII; EC 4.2.1.1) complexed with 3 structurally related inhibitors, 1a, 1b, and 1c, has been determined by X-ray crystallographic methods. The 3 inhibitors (1a = C8H12N2O4S3) vary only in the length of the substituent on the 4-amino group: 1a, proton; 1b, methyl; and 1c, ethyl. The binding constants (Ki's) for 1a, 1b, and 1c to HCAII are 1.52, 1.88, and 0.37 nM, respectively. These structures were solved to learn if any structural cause could be found for the difference in binding. In the complex with inhibitors 1a and 1b, electron density can be observed for His-64 and a bound water molecule in the native positions. When inhibitor 1c is bound, the side chain attached to the 4-amino group is positioned so that His-64 can only occupy the alternate position and the bound water is absent. While a variety of factors contribute to the observed binding constants, the major reason 1c binds tighter to HCAII than does 1a or 1b appears to be entropy: the increase in entropy when the bound water molecule is released contributes to the increase in binding and overcomes the small penalty for putting the His-64 side chain in a higher energy state.

Carbonic Anhydrase Inhibitors↗
PubMed1994

The multifunctional role of hormone-sensitive lipase in lipid metabolism.

Hormone sensitive lipase (HSL) is an enzyme of relatively broad specificity, having the ability to hydrolyze tri-, di- and mono-acylglycerols as well as cholesterol esters and small water-soluble substrates. This broad specificity allows HSL to perform a variety of functions in several tissues. A key feature of HSL is its ability to be activated via phosphorylation by cyclic AMP-dependent protein kinase. In addition it is phosphorylated at a second site by several kinases, notably AMP-activated protein kinase. Phosphorylation of this site apparently plays a role in rendering the enzyme hormone-insensitive, in that prior phosphorylation at site 2 prevents phosphorylation and activation at site 1 by cyclic AMP-dependent protein kinase. Investigation of the protein phosphatases responsible for dephosphorylation of these sites has indicated that phosphatase 2A plays a predominant role but also that protein phosphatase 2C is a significant phosphatase targeted against both phosphorylation sites. Evidence indicates that HSL has at least three functional domains which contain (a) the phosphorylation sites which control activity, (b) the active site responsible for the catalytic activity and (c) a lipid binding site responsible for anchoring the lipase at the water-lipid interface. Using limited proteolytic studies we have found that it is possible to cleave HSL into several fragments including a stable domain of M(r) approximately 17.6 kDa which contains the active site serine residue. Digestion under similar conditions also generates a stable domain of M(r) approximately 11.5 kDa containing both phosphorylation sites. Furthermore, under appropriate conditions it is possible to digest HSL and retain activity against water-soluble substrates but with the concomitant loss of activity against triacylglycerol, implying that a lipid binding domain is lost during this procedure. HSL is responsible for the neutral cholesterol esterase activity in macrophages and it may play a role in the accumulation of cholesterol esters which occur during the development of foam cells. HSL activity is reduced in macrophage foam cells, at least partly due to increased activity of a cytosolic HSL inhibitor protein. A finding unexplained for many years has been that, although lipolysis can be stimulated 50-100-fold in adipocytes by lipolytic hormones, HSL can apparently only be activated 2-3-fold via phosphorylation in vitro by cyclic AMP-dependent protein kinase. One possibility to explain this discrepancy is that an additional anchoring protein is missing from the in vitro system and indirect evidence is now accumulating for such a protein.

Adipose Tissue↗
PubMed1994

Plasma indicators of muscle damage in a model of nutritional myopathy in weaner sheep.

Subclinical nutritional myopathy was induced in 5-month-old sheep by feeding them a diet low in vitamin E and selenium. Subsequently clinical myopathy was induced by dosing with protected polyunsaturated fatty acids. Plasma activities of creatine kinase (CK), pyruvate kinase, aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase and aldolase, enzymes of muscle origin, all remained above their reference ranges in clinically affected sheep, but fluctuated widely. Similar fluctuations occurred in subclinically affected animals, resulting in some activities being within the reference ranges and some above, at different times. Plasma malondialdehyde, an indicator of lipid peroxidation, proved of no diagnostic value. Terminal plasma CK activities were significantly correlated with microscopic damage in the vastus lateralis (VL), but not the vastus intermedius (VI) or the tensor fascia lata (TFL) muscles. AST was the most highly correlated with damage in VI and VL. In two clinically affected sheep successfully treated with an oral dose of alpha-tocopherol acetate all enzymes decreased steadily to within their reference ranges, at rates probably related to their plasma half-lives. These results suggest that measurement of plasma CK activity would be useful in monitoring recovery of treated sheep.

Animals↗
PubMed1994

Development of experimental respiratory infections in neutropenic rats with either penicillin-resistant Streptococcus pneumoniae or beta-lactamase-producing Haemophilus influenzae.

Acute respiratory infections with penicillin-resistant strains of Streptococcus pneumoniae and a beta-lactamase-producing strain of Haemophilus influenzae were established in neutropenic weanling rats. By use of nonsurgical intrabronchial instillation of the bacteria suspended in molten agar, reproducible, acute respiratory infections suitable for experimental antibiotic efficacy studies were established.

Amoxicillin↗
PubMed1994

Glycine betaine confers enhanced osmotolerance and cryotolerance on Listeria monocytogenes.

Listeria monocytogenes is a gram-positive food-borne pathogen that is notably resistant to osmotic stress and can grow at refrigerator temperatures. These two characteristics make it an insidious threat to public health. Like several other organisms, L. monocytogenes accumulates glycine betaine, a ubiquitous and effective osmolyte, intracellularly when grown under osmotic stress. However, it also accumulates glycine betaine when grown under chill stress at refrigerator temperatures. Exogenously added glycine betaine enhances the growth rate of stressed but not unstressed cells, i.e., it confers both osmotolerance and cryotolerance. Both salt-stimulated and cold-stimulated accumulation of glycine betaine occur by transport from the medium rather than by biosynthesis. Direct measurement of glycine betaine uptake shows that cells transport betaine 200-fold faster at high salt concentration (4% NaCl) than without added salt and 15-fold faster at 7 than at 30 degrees C. The kinetics of glycine betaine transport suggest that the two transport systems are indistinguishable in terms of affinity for betaine and may be the same. Hyperosmotic shock and cold shock experiments suggest the transport system(s) to be constitutive; activation was not blocked by chloramphenicol. A cold-activated transport system is a novel observation and has intriguing implications concerning the physical state of the cell membrane at low temperature.

Adaptation, Physiological↗
PubMed1994

A prominent role for glucosylglycerol in the adaptation of Pseudomonas mendocina SKB70 to osmotic stress.

The mechanism of osmoadaptation in a salt-tolerant (1.2 M NaCl) bacterial isolate identified as Pseudomonas mendocina (N. J. Palleroni, M. Doudoroff, R. Y. Stanier, R. E. Solanes, and R. Mandel, J. Gen. Microbiol. 60:215-231, 1970) was investigated. In response to osmotic stress, this species accumulated a number of compatible solutes, the intracellular levels of which depended on both the osmolarity and the ionic composition of the growth medium. Glucosylglycerol [alpha-D-glucopyranosyl-alpha-(1-->2)-glycerol], N-acetylglutaminylglutamine amide, and L-alpha-glutamate were the major compatible solutes accumulated via de novo biosynthesis. Trehalose was also accumulated, but only in cells grown in the presence of high concentrations of sulfate or phosphate ions. Glycine betaine was accumulated only when supplied exogenously to cells grown at high osmolarity, and its accumulation caused a significant depletion of the intracellular pools of glucosylglycerol and glutamate. Glucosylglycerol was also found to accumulate in the type strains of P. mendocina and P. pseudoalcaligenes. This is the first report demonstrating the pivotal role of glucosylglycerol in osmoadaptation in a nonphotosynthetic microorganism.

Adaptation, Biological↗
PubMed1994

Consequences of adolescent drug use and personality factors on adult drug use.

This study examined the stability of adolescent drug use into young adulthood and explored the possible influence of personality on adolescent and adult drug use. Participants in this longitudinal study (N = 640) completed questionnaires which assessed multiple indicators for latent constructs of tobacco, alcohol, cannabis, and hard drugs, and also for the personality constructs of Socialization. In addition, the effects of obedience and extraversion were examined. Results showed that a general drug use factor in adolescence significantly predicted young adult drug use. A particular effect of adolescent obedience on adult drug use was noted. Within adolescence, obedience, extraversion, and the construct of Socialization were significant predictors of drug use. Early onset of smoking predicted adolescent drug use. The implications of these findings for early drug use education and intervention are discussed. Additional analysis explored the possibility of treating obedience as another indicator of Socialization. This model could not provide as good a fit as the original model. The measure of obedience acted as a better predictor of drug use than an overall factor of Socialization. Gender differences are discussed.

Adolescent↗
PubMed1993

DNA-methylation of the E-selectin promoter represses NF-kappa B transactivation.

E-selectin is an adhesion molecule transiently and specifically expressed on endothelial cells upon stimulation with cytokines. We wished to determine whether methylation could play a role in cell-type specific expression of this gene. We found that the E-selectin promoter in cultured endothelial cells is under-methylated in comparison with non-expressing HeLa cells. Plasmid constructs carrying a reporter driven by the E-selectin promoter and methylated in vitro are no longer transcribed in either an in vitro transcription system or in transiently transfected cells. We identified the NF-kappa B site in the promoter as the likely target for this methylation-mediated repression by testing a minimal promoter carrying only this and an associated element. We conclude that methylation is likely to play a role in blocking E-selectin expression in non-endothelial cells.

Base Sequence↗
PubMed1993

Cyclic AMP has a differentiative effect on an immortalized oligodendrocyte cell line.

We investigated the effects of increasing the concentration of intracellular cyclic adenosine monophosphate (cAMP) on genes associated with oligodendrocyte differentiation in an immortalized glial cell line, 6E12, derived from the spinal cord of an MBP-SV40 large T-antigen transgenic mouse. Raising intracellular levels of cAMP induced expression of oligodendrocyte differentiation antigens recognized by O4 and anti-galactocerebroside antibodies, up-regulated expression of the proteolipid protein (PLP) gene, and down-regulated glial fibrillary acidic protein (GFAP) expression. There was no treatment effect on myelin-associated glycoprotein (MAG) expression. These phenotypic changes are consistent with oligodendrocyte differentiation. Treatment of 6E12 cells with dibutyryl cyclic AMP (DBC) down-regulated myelin basic protein (MBP) gene expression, perhaps, because it also up-regulated expression of a putative MBP repressor SCIP/Tst-1. Moreover, the 6E12 cells expressed high levels of MBP mRNA but no MBP translation products were detected in the presence or absence of DBC. This immortalized glial cell line is proposed as a CNS model for cAMP-modulated myelin gene expression and for post-transcriptional regulation of MBP.

Animals↗