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Biomedical subjects

J Montgomery

Publications and source records attributed to J Montgomery.

At least 73 records · Page 4Linked to original sources
PubMed1994

Function and evolution of superficial neuromasts in an Antarctic notothenioid fish.

Extracellular recording techniques were used to measure frequency response functions of anterior and posterior lateral line nerve fibers innervating superficial neuromasts at five different locations on the head and trunk of an antarctic notothenioid fish, Trematomus bernacchii. Scanning electron microscopy was used to measure neuromast size according to location. Fibers innervating neuromasts from all locations were similar in showing equal responsiveness in the 10-30 Hz range to equal pk-pk velocity levels of a sinusoidally vibrating sphere. The mean cut-off frequency (CF) at which responsiveness declined to 50% of maximum was 46 Hz for all fibers combined. Superficial neuromasts located on the ventral trunk line were three to six times larger in surface area than most other neuromasts. The mean CF for fibers innervating these large neuromasts was 7-18 Hz lower than mean CF's corresponding to other superficial neuromast locations, but small differences in mean CF's were not consistently related to neuromast size. It is argued that fiber responses from different superficial neuromasts are more similar than dissimilar and that the evolution of large superficial neuromasts on the ventral trunk line is linked to a general paedomorphic trend among notothenioid fishes that may be essentially non-adaptive for the lateral line.

Afferent Pathways↗
PubMed1994

Form and function relationships in lateral line systems: comparative data from six species of Antarctic notothenioid fish.

The structure and physiology of the anterior lateral line canal systems were studied in six species of fish belonging to two different families within the suborder of antarctic fish Notothenioidei. Many of the canals within the species belonging to the genus Trematomus are relatively straight sided tubes with diameters around 0.4 mm. Some of the canals in Trematomus, and most of the canals in the icefishes (family Channichthyidae) are more complex. Relatively small pores lead into large tubules, the walls of which appear partially membranous, and the canals not much more than constrictions between adjacent tubules. Dissostichus mawsoni, a large species, has canals with distinctive wide and narrow sections, 1.8 mm and 0.48 mm, respectively. Despite these morphological differences the frequency response characteristics of anterior lateral line units are remarkably similar in all six species. In the case of D. mawsoni, this functional similarity results from narrow sections of the canals, which provide the viscous resistance to flow that preserves the mechanical filtering properties of the canal despite the huge size difference between D. mawsoni and the other species. It is argued that the most appropriate way to view canals is as high pass filters which attenuate lower frequencies, and that this effect is best illustrated by comparing the frequency response characteristics of superficial and canal neuromasts using a sinusoidal stimulus that has a constant peak-to-peak velocity. The functional contribution of canals is to attenuate low frequencies and improve the signal-to-noise ratio for biologically important signals in the presence of low frequency noise produced, for example, by the animal's own movements.

Animals↗
PubMed1993

Identification of an ethylene-responsive region in the promoter of a fruit ripening gene.

Transcription of the E4 gene is controlled by an increase in ethylene concentration during tomato fruit ripening. To investigate the molecular basis for ethylene regulation, we have examined the E4 promoter to identify cis elements and trans-acting factors that are involved in E4 gene expression. In transgenic tomato plants a chimeric gene construct containing a 1.4-kilobase E4 promoter fused to a beta-glucuronidase reporter gene is rapidly induced by ethylene in ripening fruit. Deletion of E4 promoter sequences to 193 base pairs reduces the level of GUS activity but does not affect ethylene induction. Transient expression of E4 promoter-luciferase chimeric gene constructs containing various deletions, introduced into tomato fruit pericarp by particle bombardment, indicates that a positive ethylene-responsive region is localized between nucleotides -161 and -85 relative to the transcription start site. DNase I footprint analysis shows that a nuclear factor in unripe fruit interacts specifically with sequences in this element, from -142 to -110, which are required for the ethylene response. The DNase I footprint of this factor is reduced in ethylene-treated unripe fruit and undetectable in ripe fruit. Based on the correlation of a nuclear factor binding site with promoter sequences required for ethylene induction, we propose that this in vitro DNA-binding activity may represent a factor that is involved in ethylene-regulated E4 gene expression.

Base Sequence↗
PubMed1993

Acquisition and invasiveness of different serotypes of Streptococcus pneumoniae in young children.

Rates of acquisition and mean duration of nasal carriage of different serotypes of Streptococcus pneumoniae have been estimated by fitting a stochastic model to longitudinal carriage data in children from Papua New Guinea. Immunogenicity and two indices of relative invasiveness were determined for each serotype. Immunogenic serotypes were less frequently acquired and were carried for shorter periods, but no relationship between immunogenicity and invasiveness was apparent using either index of invasiveness. Frequent invasion was associated with a high acquisition rate and high frequency and prolonged duration of carriage. Carriage studies can provide a broad indication of which serotypes cause invasive disease but not the proportion of disease due to individual serotypes; some serotypes which cause invasive disease (e.g. serotype 46) are not found even in extensive carriage studies. The antibiotic resistance of carriage organisms, however, does approximate the resistance patterns of invasive organisms and thus may be used to monitor changing patterns of antimicrobial susceptibility in the community.

Antibodies, Bacterial↗
PubMed1993

Levels of anti-pneumococcal antibodies in young children in Papua New Guinea.

Anti-pneumococcal polysaccharide antibody (anti-PPS) levels were measured in 153 serum samples collected from children aged between 2 and 47 months living in the highlands of Papua New Guinea (PNG). Fifty-seven of the samples were collected during acute episodes of lower respiratory tract infection (ALRI). Total IgA and IgG increased steadily with age; however, no association was found between the levels of these antibodies and the health status of the child. Total IgM levels showed little relationship to the age of the child but under 12 months of age levels were somewhat higher on average in children with pneumonia. For most of eight pneumococcal serotypes tested, specific IgG levels were found to decline rapidly in the first 6-8 months, reaching a minimum at approximately 12 months of age. Serotype 3 was exceptional in having very low titres in the youngest children. A separate analysis of 24 cord sera suggested that antibodies to this serotype do not usually cross the placenta in PNG. Children with pneumonia tended to have lower levels of specific IgG than healthy controls of the same age. Specific anti-PPS IgA levels were found to increase steadily with age, but were not associated with health status.

Age Factors↗
PubMed1993

Antigenuria in healthy Papua New Guinean children with nasal Haemophilus influenzae type b carriage.

In 100 healthy children under the age of 3 years living in the vicinity of Goroka, Papua New Guinea, the nares were cultured for Haemophilus influenzae type b (Hib), and a urine sample was obtained for measurement of Hib polysaccharide (PS) by ELISA. Hib carriage was detected in nine children and Hib PS was detected in the urine of 11. Hib PS was found in seven of nine Hib nasal carriers compared with four of 91 healthy children without Hib in their nares (p < 0.001). The range of urine antigen concentrations in the two groups was similar (0.6 to 2.7 ng/ml). The relative risk of antigenuria in the carriers, compared with the children with negative nares cultures, was 58 (95% confidence interval, 10.5-324). These data extend previous observations from Hib carriers studied in the United States and show that Hib carriage in children from a developing country is associated with antigenuria. Further studies are needed to determine whether carriers and patients can be differentiated by differences in the magnitude of the concentration of Hib PS excreted in urine.

Antigens, Bacterial↗
PubMed1993

Positive and negative regulatory regions control the spatial distribution of polygalacturonase transcription in tomato fruit pericarp.

The tomato fruit consists of a thick, fleshy pericarp composed predominantly of highly vacuolated parenchymatous cells, which surrounds the seeds. During ripening, the activation of gene expression results in dramatic biochemical and physiological changes in the pericarp. The polygalacturonase (PG) gene, unlike many fruit ripening-induced genes, is not activated by the increase in ethylene hormone concentration associated with the onset of ripening. To investigate ethylene concentration-independent gene transcription in ripe tomato fruit, we analyzed the expression of chimeric PG promoter-beta-glucuronidase (GUS) reporter gene fusions in transgenic tomato plants. We determined that a 1.4-kb PG promoter directs ripening-regulated transcription in outer pericarp but not in inner pericarp cells, with a sharp boundary of PG promoter activity located midway through the pericarp. Promoter deletion analysis indicated that a minimum of three promoter regions influence the spatial regulation of PG transcription. A positive regulatory region from -231 to -134 promotes gene transcription in the outer pericarp of ripe fruit. A second positive regulatory region from -806 to -443 extends gene activity to the inner pericarp. However, a negative regulatory region from -1411 to -1150 inhibits gene transcription in the inner pericarp. DNase I footprint analysis showed that nuclear proteins in unripe and ripe fruit interact with DNA sequences within each of these three regulatory regions. Thus, temporal and spatial control of PG transcription is mediated by the interaction of negative and positive regulatory promoter elements, resulting in gene activity in the outer pericarp but not the inner pericarp of ripe tomato fruit. The expression pattern of PG suggests that, although they are morphologically similar, there is a fundamental difference between the parenchymatous cells within the inner and outer pericarp.

Base Sequence↗
PubMed1992

Iron deficiency.

Explore the source record for details and available documents.

Child↗
PubMed1992

Physiological characterization of lateral line function in the Antarctic fish Trematomus bernacchii.

The Antarctic notothenioids are a monophyletic radiation of fishes that have evolved under conditions of low light and cold, where non-visual sensory systems, such as the mechanosensory lateral line system, would be of importance. As part of a study of the structure and function of the mechanosensory lateral line system in these fishes we systematically characterized the function of the anterior lateral line system in one of the common benthic species, Trematomus bernacchii. Frequency-response and threshold-tuning curve methods yield similar functional characterizations of single afferent fibre responses to vibrational stimulation. Curve fitting of generalized transfer function to frequency-response curves allows an objective splitting of responses into velocity and acceleration sensitive populations thought to correspond to superficial and canal neuromasts, respectively. Both response types are characterized by a low-pass frequency-response curve, with a relatively low upper frequency cut-off when compared with data from temperate species. The sensitivity of the lateral line system of T. bernacchii is comparable to that of the mottled sculpin Cottus bairdi.

Acceleration↗
PubMed1992

Fibers innervating different parts of the lateral line system of an Antarctic notothenioid, Trematomus bernacchii, have similar frequency responses, despite large variation in the peripheral morphology.

Regional differences in the architecture and size of lateral line canals and neuromasts were measured in an Antarctic fish, Trematomus bernacchii, and the data were used in models of canal and cupular mechanics to predict the frequency response of these two peripheral structures. These modeled predictions were then compared to frequency response functions measured with single unit recording techniques from anterior and posterior lateral line fibers innervating different canals on the head and trunk of fish of various sizes. Despite large variations in the peripheral morphology of head and trunk canals in fish of different sizes, lateral line fibers were relatively homogeneous in their frequency response properties. In response to stimuli of equal pk-pk acceleration levels, all canal neuromast fibers responded with equal and maximum responsiveness in the 10-45 Hz range, after which responsiveness fell off at about 18 dB/octave. Whereas the biomechanical models of cupular and canal responsiveness predicted the region of equal and maximum responsiveness in the 10-45 Hz range, they did not predict the high frequency cutoff nor the slope. Rather, these models predicted responsiveness out to at least 540 Hz, and a high frequency slope of 12 dB/octave. In terms of the frequency response of peripheral fibers, we conclude that (1) there can be considerable morphological variability, with little consequence for function, as long as some minimum standards for maintaining constant acceleration responsiveness in the 10-45 Hz range are met, and (2) there must be additional filters between the cupula and primary afferent fibers.

Acceleration↗
PubMed1992

A case of spontaneous hypothermia.

It is important to recognise any condition, however rare, which can be cured. We report a case of chronic hypothermia and its dramatic response to treatment.

Aged↗
PubMed1991

Leptospires isolated from toads and frogs on the Island of Barbados.

Four pathogenic strains of leptospires were isolated from the kidneys of toads (Bufo marinus) and seven from frogs (Eleutherodactylus johnstonei). Isolates from two toads and one frog belonged to serovar bim, the causative agent of most cases of severe leptospirosis on Barbados. The other eight strains belonged to a new serovar within the Australis serogroup. The name bajan is proposed for this new serovar of Leptospira interrogans.

Agglutination Tests↗
PubMed1991

The bacteriology of acute pneumonia and meningitis in children in Papua New Guinea: assumptions, facts and technical strategies.

Acute respiratory infections in children aged less than 5 years in the Eastern Highlands of Papua New Guinea were investigated bacteriologically for 10 years from November 1978. Haemophilus influenzae and Streptococcus pneumoniae were responsible for 73% of all bacteria cultured from lung aspirate (83 samples), 85.5% from blood (1024 samples) and 92% from cerebrospinal fluid (155 samples). Nonencapsulated H. influenzae was carried by up to 90% of children and was the predominant haemophilus type cultured from lung tissue. Mixed infections of the lung with two types of H. influenzae (8 cases) and both H. influenzae and S. pneumoniae (18 cases), commonly together with other organisms of questionable pathogenicity, reflected the proximity of this organ to the upper respiratory tract. Serotype b accounted for 62% and 82% of H. influenzae isolated from bacteraemic pneumonia and meningitis cases, respectively. Polymicrobic bacteraemic pneumonia occurred in 16 children. Both H. influenzae and S. pneumoniae establish dense, unregulated long-term colonization in the nasopharynx during the neonatal period. Each inhibit autochthonous microflora by mechanisms that are currently unclear. Infections with two or more types occur in 30% (S. pneumoniae) and 60% (H. influenzae) of carriage-positive children. 70-75% of H. influenzae and S. pneumoniae isolates from blood concomitantly colonize the upper respiratory tract. Intense exposure of Papua New Guinean children to penicillin at all levels of health care since the 1940s has resulted in widespread relative resistance among pneumococci to this antibiotic. Resistant strains are now found in 32 serotypes, and in children penicillin resistance is present in 75% of all carriage strains and 52% and 22% of blood and cerebrospinal fluid isolates, respectively. Penicillin-susceptible and resistant pneumococcal serotypes commonly coexist in multiply populated carriage sites. Resistance to betalactam antibiotics is rare among H. influenzae strains and resistance has not been detected in either H. influenzae or S. pneumoniae to chloramphenicol, erythromycin, tetracycline or cotrimoxazole. It should not be assumed that the technology of respiratory bacteriology as it is practised in developed countries can be transferred to the third world for utilization in paediatric aetiology and carriage studies. Respiratory bacteriology strategies as they evolved in Goroka were subject to diverse influences. The type distribution of the major causative agents defied fashionable beliefs, generated the need for more precise epidemiological differentiation and, by virtue of their carriage density, cultural properties and response to commonly used antibiotics, required the introduction or development of compatible diagnostic procedures.

Acute Disease↗
PubMed1990

Antimicrobial susceptibility patterns of Haemophilus isolates from children in eleven developing nations. BOSTID Haemophilus Susceptibility Study Group.

The antimicrobial susceptibilities of 426 isolates of Haemophilus species, which were collected as part of a worldwide study of the etiology of acute respiratory disease in children in selected developing countries, were determined. Eleven antibiotics were tested using the recently described Haemophilus Test Medium. There was a low prevalence of antibiotic resistance; 6% of strains were resistant to ampicillin, and 1.6% were resistant to chloramphenicol. Strains resistant to both ampicillin and chloramphenicol were recovered only from Thailand. Susceptibility to penicillin G was also determined; the minimum inhibitory concentrations for penicillin and ampicillin were concordant within one 2-fold dilution in 97% of the isolates. Thus, Haemophilus isolates were as susceptible to penicillin G as they were to ampicillin, and penicillin resistance was infrequent overall. These data provide support for the current protocols for the management of acute respiratory infections in children in developing countries, in which penicillin G is a first-line agent.

Anti-Bacterial Agents↗