Biomedical subjects

E J Walsh

Publications and source records attributed to E J Walsh.

At least 37 records · Page 2Linked to original sources

PubMed1997

A simple program for simulating the responses of neurons with arbitrarily structured and active dendritic trees.

We describe a simple program to simulate neural responses. This program is based on the compartmental approach, in which all compartments of a neuron (i.e. axon, soma or dendrite) are represented by the same basic electrical structure. A parameter file is used to store the model parameters, including the nonlinear channel characteristics of each compartment. The model is then automatically configured according to the values specified in the parameter file. The computation of the conductance of each active channel over time is handled by a unique subroutine optimized according to the kinetics of each channel. The equations for arbitrarily structured trees are solved implicitly using a simple algorithm similar to that of Hines (Hines, M. (1984) Int. J. Biomed. Comput., 15:69-76). The output of the model uses PostScript format. The advantage of this program is that it is small in size, simple to use, efficient, and is platform independent.

Algorithms↗

PubMed1997

Hearing loss in the RBF/DnJ mouse, a proposed animal model of Usher syndrome type IIa.

The Usher syndromes (US) are a group of inherited disorders that feature autosomal recessive neurosensory hearing loss or deafness with retinitis pigmentosa (RP). Moderate to severe non-progressive high frequency hearing loss with RP and normal vestibular function describes Usher syndrome type IIa, which has been localized to 1q41. Severe retinal degeneration in the inbred mouse strain RBF/DnJ is caused by rd3, a recessive gene located on mouse chromosome 1 distal to akp1 in a region which is orthologous to human 1q32-q42. We evaluated rd3 as a candidate for orthology with USH2A by first reducing and refining the relatively broad region in which rd3 is thought to reside. DNA of offspring from an RBF/DnJ x MOLF/Ei backcross was genotyped with PCR markers closely flanking the predicted location of rd3. Our haplotype analysis re-positioned rd3 to a 3.6 cM region between markers D1Mit273 (cen) and D1Mit209 (tel), consistent with the expected position of an USH2A murine orthologue. Consequently, rd3 is a positional candidate for Usher type IIa. Next we assessed the rd3/rd3 audiological phenotype to see how closely it paralleled that of Usher IIa. Audiological evaluation of mice at various ages revealed evidence of high frequency progressive hearing loss, previously unreported in the RBF/DnJ strain. However, this newly discovered hearing deficit was observed to be inherited independently of rd3, establishing that a completely different gene is responsible.

Animals↗

PubMed1997

Influence of medium composition on the growth and antigen expression of Helicobacter pylori.

An evaluation of the ability of various solid and liquid media to support both growth and antigen expression, particularly lipopolysaccharide (LPS) expression, by Helicobacter pylori culture collection strains and clinical isolates was performed. Liquid-based basal media (brain heart infusion, Brucella broth, Mueller-Hinton broth and tryptone soya broth) supported the growth of strains, whereas solid basal media of the same formulation did not support growth. Optimal growth of all strains was obtained on solid and in liquid media containing blood. Supplemented solid media containing supplements other than blood supported growth but only to a small extent. In liquid media excluding blood, serum supplements enhanced growth and horse serum was found to be superior to fetal calf serum. In general, beta-cyclodextrin did not increase growth. Mueller-Hinton broth or tryptone soya broth containing horse serum and a nitrogen source such as yeast extract or proteose peptone no. 3 were found to give optimal growth of H. pylori in a blood-free environment. Strains after cultivation in liquid media, irrespective of composition, maintained production of high-molecular weight (mol. wt) LPS with an O side chain independent of medium composition, whereas subculturing on solid media resulted in production of low-mol. wt LPS. Expression of proteins differed in liquid and on solid media, particularly proteins of 57 and 60 kDa, but qualitatively no differences were observed upon supplementation of basal media.

Antigens, Bacterial↗

PubMed1997

Structural characterization of the lipid A component of Helicobacter pylori rough- and smooth-form lipopolysaccharides.

The chemical structure of free lipid A isolated from rough- and smooth-form lipopolysaccharides (R-LPS and S-LPS, respectively) of the human gastroduodenal pathogen Helicobacter pylori was elucidated by compositional and degradative analysis, nuclear magnetic resonance spectroscopy, and mass spectrometry. The predominant molecular species in both lipid A components are identical and tetraacylated, but a second molecular species which is hexaacylated is also present in lipid A from S-LPS. Despite differences in substitution by acyl chains, the hydrophilic backbone of the molecules consisted of beta(1,6)-linked D-glucosamine (GlcN) disaccharide 1-phosphate. Because of microheterogeneity, nonstoichiometric amounts of ethanolamine-phosphate were also linked to the glycosidic hydroxyl group. In S-LPS, but not in R-LPS, the hydroxyl group at position 4' was partially substituted by another phosphate group. Considerable variation in the distribution of fatty acids on the lipid A backbone was revealed by laser desorption mass spectrometry. In tetraacyl lipid A, the amino group of the reducing GlcN carried (R)-3-hydroxyoctadecanoic acid (position 2), that of the nonreducing GlcN carried (R)-3-(octadecanoyloxy)octadecanoic acid (position 2'), and ester-bound (R)-3-hydroxyhexadecanoic acid was attached at position 3. Hexaacyl lipid A had a similar substitution by fatty acids, but in addition, ester-bound (R)-3-(dodecanoyloxy)hexadecanoic acid or (R)-3(tetradecanoyloxy)hexadecanoic acid was attached at position 3'. The predominant absence of ester-bound 4'-phosphate and the presence of tetraacyl lipid A with fatty acids of 16 to 18 carbons in length differentiate H. pylori lipid A from that of other bacterial species and help explain the low endotoxic and biological activities of H. pylori LPS.

Ethanolamine↗

PubMed1997

Mechanisms of onset responses in octopus cells of the cochlear nucleus: implications of a model.

The octopus cells of the posteroventral cochlear nucleus receive inputs from auditory-nerve fibers and form one of the major ascending auditory pathways. They respond to acoustic and electrical stimulation transiently and are believed to carry temporal information in the precise timing of their action potentials. The mechanism whereby onset responses are generated is not clear. Proposals aimed at elucidating the mechanism range from neural circuitry and/or inhibition, "depolarization block" (or inactivation of Na+ channels), and the involvement of a 4-aminopyridine (4-AP)-sensitive, low-threshold channel (K(LT)). In the present study, we used a compartment model to investigate possible mechanisms. The model cell contains a soma, an axon, and four passive dendrites. Four kinds of ionic channels were included in the soma compartment: the Hodgkin-Huxley-like Na+ and K+ channels, a 4-AP-sensitive, low-threshold channel, K(LT), and a Cs+-sensitive, hyperpolarization-activated inward rectifier, Ih. DC currents and half-wave-rectified sine waves were used as stimuli. Our results showed that an onset response can be generated in the absence of neuronal circuitry of any form, thus suggesting that the onset response in octopus cells is regulated intrinsically. Among the many factors involved, low-input impedance, partly contributed by Ih, appears to be essential to the basic onset response pattern; also, the K(LT) conductance plays a major role, whereas the inactivation of Na+ channels probably plays only a secondary role. The dynamics of Ih also can modify the response pattern, but due to its slow kinetics, its role is probably limited to longer-term regulation under the conditions simulated in this study.

Acoustic Stimulation↗

PubMed1996

Lipopolysaccharide of the Helicobacter pylori type strain NCTC 11637 (ATCC 43504): structure of the O antigen chain and core oligosaccharide regions.

Smooth- and rough-form lipopolysaccharides from phenol-water extraction of cells from Helicobacter pylori type strain NCTC 11637 were isolated as the water-soluble component of high-M(r) and water-insoluble low-M(r) gel. Structural investigations were performed on the intact water-soluble smooth-form lipopolysaccharide, various oligosaccharides formed as chemical and enzymic degradation products, and three oligosaccharide fractions liberated by acetic acid hydrolysis from the water-insoluble rough-form lipopolysaccharide. A structure is proposed for the complete polysaccharide component of the smooth-form lipopolysaccharide comprising the O antigen chain, an intervening region, and the inner core oligosaccharide on the basis of 1H and 13C NMR experiments, fast atom bombardment/mass spectrometry, and methylation linkage analysis of permethylated oligo- and polysaccharide derivatives. The most striking feature of the O antigen region in the lipopolysaccharide is the presence of extended chains with fucosylated and nonfucosylated N-acetyllactosamine (LacNAc) units that mimic human cell surface glycoconjugates in normal human granulocytes. The chains are terminated by di- or trimeric Lewis(x) (Le(x)) determinants, which are also found in tumor-associated carbohydrate antigens in many adenocarcinomas.

Carbohydrate Conformation↗

PubMed1996

Onset and development of auditory brainstem responses in the Mongolian gerbil (Meriones unguiculatus).

The ontogeny of auditory function in the Mongolian gerbil (Meriones unguiculatus) was examined by measuring auditory brainstem response (ABR) thresholds for clicks and tone bursts at frequencies between 0.125 and 32 kHz. ABRs were elicited as early as 10 postnatal days (PND) in a small proportion of animals (28.6%). Three phases of development were identified based on the appearance of frequency-threshold curves: (a) an onset period (10-12 PND) during which ABRs could be elicited only by intense stimuli (95-110 dB SPL) within a restricted range of frequencies (0.25-8 kHz); (b) a transition period (13-14 PND) during which thresholds improved but frequency-threshold curves remained relatively flat; and (c) a refinement period (15-30 PND) during which frequency-threshold curves exhibited an adult-like ('V') shape and thresholds improved steadily to adult-like values. Opening of the external auditory meatus was associated with threshold improvements but not with changes in the frequency region of greatest sensitivity. Between the ages of 13 and 21 PND, low-frequency (0.125-1 kHz) and high-frequency (10-32 kHz) thresholds improved at statistically equivalent rates (4.9 and 5.6 dB/day, respectively), while thresholds for mid-frequency stimuli (2-8 kHz) improved at a significantly faster rate of 9.2 dB/day.

Acoustic Stimulation↗

PubMed1996

Distortion generated by the ear: its emergence and evolution during development.

Physiologically vulnerable active mechanics associated with the transduction of sounds in adults distort cochlear output. Specifically, frequencies not present in the incoming acoustic signal are represented in its output (ie., the spike trains of auditory nerve fibers). The purpose of this investigation was to study the appearance and evolution of intermodulation distortion during development. Established surgical and electrophysiologic techniques were used to record the extracellular electrical activity of individual auditory nerve fibers from developing kittens. Discharge-rate or synchrony-based responses to two tones (f1 and f2) presented simultaneously at various ratios of f2/f1 were recorded. The cubic distortion product (CDP; 2f1-f2, where f1<f2) and the difference tone (f2-f1) were the intermodulation distortion products (DPs) emphasized in the investigation. CDPs were first observed nearly 10 days after the earliest auditory nerve fiber responses to simple tone-burst stimuli could be elicited in neonatal cats. Furthermore, the spectrum of DPs generated in the cochlea changed dramatically during the second postnatal week and achieved adultlike characteristics after the first postnatal month. Findings reported here support the notion that cochlear transduction is initially linear in neonatal cats, possibly representing a critical period of auditory development, and that the content of distortion-related spectral information carried in auditory nerve fiber spike trains increases during development, in concert with other peripheral auditory attributes.

Animals↗

PubMed1996

Effects of stimulus rate on the feline brain-stem auditory evoked response during development. I. Peak latencies.

The effects of stimulation rate on the brain-stem auditory evoked response (BAER) of developing and adult cats were investigated. Age ranged from 10-post-natal days to young adults. Clicks were presented at levels of 90 dB pSPL and 20 dB above each animal's click threshold (20 dB SL). For all animals, a conventional BAER rate series was obtained at rates of 5, 10, 30, 60, and 90 Hz. BAERs were also obtained using pseudorandom pulse sequences called maximum length sequences (MLSs). The minimum time between pulses, the minimum pulse interval (MPI), included 0.5, 1, 2, 4, and 6 ms, which correspond to average rates of 1000, 500, 250, 125, and 83 Hz, respectively. Dependent variables included the latencies of the first four BAER peaks, labeled i through iv. MLS BAERs were indistinguishable from conventional BAERs at all ages studied. In general, for both conventional and MLS BAERs, peak latencies and the i-iv interval increased with increasing stimulus rate. Although absolute peak latencies and the i-iv interval decreased systematically with age, the relative shift in latency and i-iv interval induced by increasing stimulus rate decreased during development. The enhanced sensitivity to stimulus rate observed at younger ages was not the consequence of the threshold improvement that occurs during development since similar observations were made when stimuli were presented at a constant absolute level (90 dB pSPL) or at a constant level above threshold (20 dB SL). In addition, successive BAER peaks exhibited progressively larger latency shifts with increasing stimulus rate at all ages studied. These data suggest that higher stimulus rates produce greater neural adaptation resulting in prolonged BAER peak latencies. Furthermore, the effects of adaptation are cumulative across synapses, and the mechanisms responsible for the acquisition of adult-like adaptation properties develop during the early post-natal period in the cat.

Animals↗

PubMed1996

Effects of stimulus rate on the feline brain-stem auditory evoked response during development. II. Peak amplitudes.

The effects of click rate on brain-stem auditory evoked response (BAER) peak amplitudes were investigated in adult cats and kittens in four age groups: 10, 15, 20, and 30 post-natal days. Conventional BAERs were obtained at rates of 5, 10, 30, 60, and 90 Hz. Maximum length sequences (MLSs) were used to obtain responses at rates of 83, 125, 250, 500, and 1000 Hz. For both techniques, clicks were presented at 90 dB pSPL, and at 20 dB above threshold (20 dB SL). BAERs were observed for all age groups, at all click rates. However, not all peaks could be identified in all animals, with peak absence more common for the youngest kittens at the higher rates. BAER waves i through iv decreased in amplitude with increasing click rate for all age groups. In general, the smallest peak amplitudes were observed for the youngest animals (10- to 15-day-old) studied, while the largest amplitudes were found for the adult, 20- or 30-day-old animals, regardless of rate. When amplitudes were normalized to eliminate the influences of differences in absolute values due to developmental stage (i.e., made proportional to the amplitude observed at 5 Hz), the younger age groups exhibited enhanced sensitivity to the effects of stimulus rate. However, exceptions to this trend were observed. In general, amplitudes of BAER peaks obtained with the MLS procedure were smaller than those obtained using conventional averaging with a similar average click rate, regardless of age. Finally, the most efficient method for obtaining a response at a criterion signal-to-noise ratio was typically by the use of conventional averaging at a rate of 60 or 90 Hz, for all peaks and age groups, Overall, these data suggest that higher stimulus rates produce greater neural adaptation resulting in reduced BAER peak amplitudes. The mechanism responsible for the acquisition of adult-like adaptation properties appears to develop during the early post-natal period in the cat.

Animals↗

PubMed1995

Activity-dependent responses of developing cochlear nuclear neurons to microionophoretically-applied amino acids.

The experimental purpose of this investigation was to determine whether the efficacy of glutamate, N-methyl-D-aspartate (NMDA) and/or GABA is related to the activity state of neurons in the cochlear nuclear complex (CN). The hypothesis tested was that changes in discharge activity produced by glutamatergic and GABAergic ligands are, or may be, greater when neurons are stimulated at moderate to high acoustic levels compared to near threshold stimulation levels, when activity levels are high or low, respectively. All neurons from which discharge rate vs. sound pressure level curves were tested during simultaneous administration of amino acids exhibited characteristics commensurate with an activity-dependent system; at high sound levels, when discharge rates were elevated relative to rates produced by low level stimuli, both glutamate-induced increments and GABA-induced decrements in discharge rate were enhanced. The relationship between discharge rate and amino acid efficacy was a uniform property of neurons sampled throughout the first two postnatal weeks of development. In adults, preliminary indications are that activity-dependent neurotransmitter efficacy is characteristic of some cells, but not others. The activity-dependent nature of endogenous amino acid neurotransmission was demonstrated through the microionophoretic administration of NMDA and GABAA selective antagonists, D-alpha-aminoadipate (D alpha AA) and 2-amino-5-phosphonovalerate (APV), and bicuculline (BIC), respectively. These results suggest that postsynaptic actions elicited by membrane receptors subserving amino acid neurotransmission within the CN are activity-dependent.

2-Amino-5-phosphonovalerate↗

PubMed1995

The development of glycine-like immunoreactivity in the dorsal cochlear nucleus.

Both anatomical and physiological lines of evidence suggest that inhibitory influences are active early in the development of the dorsal cochlear nucleus (DCN). Data from physiological/pharmacological studies suggest that in the adult these inhibitory influences may be mediated at least in part by the neurotransmitter glycine. Using a polyclonal antibody to examine the development of glycine in the DCN, we have observed that glycine-like immunoreactive cell bodies and punctate label are present in the DCN by the day of birth in the hamster and in the kitten at least 10 days prior to birth. In contrast to the development of immunoreactivity for glutamic acid decarboxylase (GAD) (Schweitzer et al., 1993), glycine-like immunoreactivity shows a homogeneous distribution throughout the DCN from the day of birth through adulthood. In addition, glycine immunoreactivity is present earlier than GAD-immunoreactivity and is present well before these brain structures become responsive to air-borne sounds. Thus, glycine is present in the very young animal and may mediate inhibitory effects that occur early in development.

Animals↗

PubMed1994

Responses of peripheral auditory neurons to two-tone stimuli during development: I. Correlation with frequency selectivity.

The responses of peripheral auditory neurons to two-tone stimuli were used to inferentially examine the nature of cochlear processing during development. Rate suppression was not seen in the youngest animals, and was first observed at 77 gestational days, in units exhibiting adultlike frequency selectivity. Suppression was highly correlated with the degree of tuning, and neurons were segregated into three classes based on these responses. Broadly tuned neurons (type IB) with low characteristic frequencies (CFs) did not exhibit suppression, and were observed early in postnatal life. Sharply tuned, but still immature neurons (type IS) exhibited suppression, but to a lesser degree than mature neurons (type M). One interpretation of these results is that basilar membrane mechanics are linear during the final stages of cochlear development, indicating that the immature signal transduction process is fundamentally different from that of adults.

Acoustic Stimulation↗

PubMed1994

Responses of peripheral auditory neurons to two-tone stimuli during development: II. Factors related to neural responsiveness.

In an accompanying paper (Fitzakerley et al., 1994), it was demonstrated that there is a significant developmental correlation between the appearance of tuning and two-tone suppression. However, it was also found that some sharply tuned neurons meeting minimal adult standards did not exhibit suppression. Therefore, in order to investigate other factors that may be related to the demonstration of suppression in peripheral auditory neurons, the relationship of two-tone suppression with various parameters related to neural responsiveness was studied in perinatal kittens. A positive correlation was made between the observance of suppression and driven discharge rate, characteristic frequency (CF), and threshold, all properties which change significantly during the final stages of cochlear differentiation. In older animals, suppression was also observed in higher percentages of neurons having low spontaneous rates (< 1 spk/s). Suppression was evoked less often by test tones placed below CF than above CF in neurons recorded from younger animals, and was generally produced by a narrower range of test tone intensities than those recorded from adults. As a result, the conventional description of suppression as observed in peripheral auditory neurons in mature animals must be extended to include these factors when responses of immature neurons are considered.

Acoustic Stimulation↗

PubMed1994

Responses of peripheral auditory neurons to two-tone stimuli during development: III. Rate facilitation.

Approximately 25% of peripheral auditory neurons having low characteristic frequencies (CFs) and broad tuning, and recorded from immature animals, responded to two-tone stimuli with increases in discharge rate greater than predicted by linear summation of the responses to probe tones (facilitation), in contrast to the two-tone suppression observed in adult animals and in more sharply tuned immature neurons. Facilitation was not seen after 81 gestational days and was not observed when test tones produced a substantial increase in rate when presented alone. The fact that some neural responses were facilitated under conditions of two-tone stimulation during the final stages of cochlear differentiation provides additional evidence that signal transduction is fundamentally different in neonatal kittens than in adults. A linear model of basilar membrane mechanics coupled to nonlinear neural processes is proposed which can account for the production of facilitation.

Acoustic Stimulation↗

PubMed1994

Transportation of Helicobacter pylori cultures by optimal systems.

Cultures of Helicobacter pylori on chocolate agar slants in bijou bottles and on chocolate agar plates inside BBL Campy Pouches were mailed from Dublin to Galway, Ireland; Bordeaux, France; and Beijing, China. Both systems maintained viability of H. pylori for at least 4 days under mailing conditions. Ninety percent of the isolates on the slants survived for 6 days, but only 30% of the isolates in the pouches survived. When the slants were stored at 4 degrees C after arrival, 50% of the isolates were recoverable 10 days after mailing. Failure of recovery was due to coccoid formation by the organisms. Contamination was not a problem in either system. Chocolate agar slants are considered the more suitable system for transporting H. pylori cultures, especially when transport time longer than 4 days is expected.

Agar↗

PubMed1993

Development of GAD-immunoreactivity in the dorsal cochlear nucleus of the hamster and cat: light and electron microscopic observations.

Physiologic and pharmacologic evidence suggests that inhibitory influences are active in the mammalian dorsal cochlear nucleus (DCN) by the onset of hearing, while anatomical evidence suggests that inhibitory synapses are not present until days or weeks later. One inhibitory neurotransmitter in the DCN is gamma aminobutyric acid (GABA) and its presence can be indexed by immunohistochemical localization of its synthetic enzyme glutamic acid decarboxylase (GAD). The present study investigated the ingrowth and synapse formation of GAD-immunoreactive inputs in the DCN of cat and hamster. GAD-immunoreactive puncta are present in the DCN of the cat at birth and of the hamster on postnatal day (PND) 3. Thus, the present data correlate well with the physiologic and pharmacologic evidence. In both species the first labelled puncta are near the dorsal acoustic stria and may originate from efferent axons in the stria. Several days later a band of labelled puncta is found in the fusiform cell layer. This location is equivalent to the termination zone of cartwheel cells, GAD-immunoreactive interneurons in the DCN. Based on this spatiotemporal sequence in the appearance of GAD-immunoreactive puncta, we suggest that sources of GABA extrinsic to the DCN mature first, followed by intrinsic sources.

Animals↗

PubMed1993

Development of glutamate and NMDA sensitivity of neurons within the cochlear nuclear complex of kittens.

1. The effects of glutamate, N-methyl-D-aspartate (NMDA), and NMDA receptor antagonists, D-alpha-aminoadipate (D alpha AA) and 2-amino-5-phosphonovalerate (APV), microionophoretically applied onto neurons in the caudal divisions (posteroventral and dorsal subnuclei) of the cochlear nuclear complex (CN), were investigated during postnatal development in kittens with the use of extracellular techniques. From birth through postnatal day 7, microionophoretically applied glutamate elevated the acoustically evoked discharge rates of nearly 80% of neurons studied. Although fewer neurons were studied with the use of NMDA, approximately 65% of these responded to this glutamatergic agonist, and no developmental changes in the percentage of responsive neurons were observed. The actions of NMDA antagonists were studied in a relatively small number of neurons, and results support the supposition that glutamate, or a glutamate-like substance, acts as a CN neurotransmitter throughout postnatal life. 2. Approximately 64% of CN neurons encountered among neonatal animals were unresponsive to acoustic stimulation, even at the highest output levels available (> 120 dB SPL). That percentage declined monotonically during the next three postnatal days, such that approximately 23% of neurons encountered were unresponsive to acoustic stimulation on the third day. Essentially all encountered neurons were responsive to acoustic stimulation by the middle of the second postnatal week. Under conditions of simultaneous glutamate and acoustic stimulation, neurons in this general class of "acoustically unresponsive" neurons segregated into two groups. Glutamate increased spontaneous discharge rate in 45% of the neurons studied, however, these units remained acoustically unresponsive during combined sound and excitatory amino acid stimulation (group A1). In the second group (A2), 55% of the neurons that were acoustically unresponsive under control (sound alone) conditions responded to the acoustic component of the combined acoustic and glutamate stimulation (the experimental condition) in a frequency-dependent manner. A2 neurons exhibited temporal firing patterns characteristic of acoustically responsive neurons of corresponding age, suggesting that these neurons are functionally connected to the auditory periphery, whereas A1 neurons are not. 3. Dose-response curves were either sigmoidal or linear over the range that measurements were made, and maximum discharge rates evoked by high doses of glutamate in the youngest animals studied tended to be lower than those produced by acoustic stimulation alone in older animals. These results suggest that intrinsic properties contribute to the mechanism(s) that limits neuronal responsiveness. Average dose-response curve slopes were higher for neurons recorded from older animals, also indicating that intrinsic properties regulating dynamic response range are acquired postnatally in the kitten CN.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗