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Biomedical subjects

L Gray

Publications and source records attributed to L Gray.

At least 163 records · Page 9Linked to original sources
PubMed1986

Naturalistic psychophysics: thresholds of ducklings (Anas platyrynchos) and chicks (Gallus gallus) to tones that resemble mallard calls.

Neonatal ducklings and chickens were tested for responsiveness to a pulsing pure tone that was as similar as possible to the mallard maternal alarm call. It is known that ducklings momentarily cease vocalizing when they hear the alarm call and that chicks do the same when they hear pure tones. The duration of peep suppression can thus be used as a measure of whether subjects of either species heard the stimulus. Chicks might not be as sensitive as ducklings to a mallard alarm call because the signal is less significant to them. An adaptive or staircase procedure was used to estimate absolute thresholds, and group psychometric functions were reconstructed for each species from the trial-by-trial data. Ducklings had lower thresholds than chickens as well as steeper psychometric functions to this stimulus. The results suggest that more sensitive and consistent behavioral responses can be elicited by naturalistic sounds than by more arbitrary acoustic stimuli.

Animals↗
PubMed1985

Characterisation of HlyC and mechanism of activation and secretion of haemolysin from E. coli 2001.

In this paper the DNA sequence of the cloned hlyC gene from E. coli 2001 is presented. The gene encodes a protein of 20 kDa which is able to activate the 107 kDa polypeptide encoded by hlyA. This gives rise to a haemolytically active protein which differs from the inactive form in stability and by its migration when analysed by polyacrylamide gel electrophoresis under non-denaturing conditions. We also show that the inactive form is secreted in the presence of the transport functions hlyB and hlyD. This result rules out any role for the hlyC gene product in the transport of HlyA across the inner membrane.

Base Sequence↗
PubMed1985

Regulation of haemolysin synthesis in E. coli determined by HLY genes of human origin.

We have previously reported the secretion of a 107K polypeptide into the medium from a haemolytic E. coli K12 strain (Mackman and Holland 1984a). In addition, we demonstrated that haemolysin production was correlated with the presence of this polypeptide in the growth medium in a large number of E. coli isolates of human and animal origin (Mackman and Holland 1984b). In this paper we confirm that the 107K polypeptide is indeed haemolysin: both haemolytic activity and the 107K polypeptide show a similar pattern of accumulation during the growth cycle; identical levels are produced in three different growth media; they have the same half-life in minimal medium. The results also show that the expression of haemolysin is not influenced by the growth medium or subject to catabolite repression. However, expression is apparently switched off as cells enter the late exponential phase of growth. Finally, we present data indicating that the previously reported variation in haemolysin production in different media is entirely due to the instability of the haemolysin itself. Degradation of the 107K polypeptide in the medium was accompanied by the accumulation of a major breakdown product of 60K.

DNA, Recombinant↗
PubMed1985

Identification of polypeptides required for the export of haemolysin 2001 from E. coli.

We have identified the polypeptides encoded by the haemolysin export genes from a haemolytic determinant 2001 carried by pLG570. This was previously cloned from an E. coli strain, serotype 04 isolated from a human urinary tract infection. Subclones from the recombinant plasmid pLG570 carrying hlyD analysed in vitro and in minicells showed that this gene is transcribed from an independent promoter and encodes a 53 Kd polypeptide. In contrast, detectable levels of the gene products encoded by hlyB were only observed when transcription presumably emanated from a vector promoter. This gene was found to encode at least two polypeptides apparently expressed from alternative translational start sites within a single reading frame. In minicells the major product was a 66 Kd polypeptide whilst after expression in vitro the major product was a 46 Kd polypeptide. Transposon mutagenesis leading to the synthesis of the expected truncated polypeptides was used to confirm the identity of the hlyD and the two hlyB products. Preliminary results suggest that the majority of the 53 Kd polypeptide is located in the inner membrane when cell envelopes from minicells and maxicells were fractionated using sarkosyl, although residual amounts of the 53 Kd polypeptide were also found in the outer membrane.

Bacterial Proteins↗
PubMed1985

Genetical and functional organisation of the Escherichia coli haemolysin determinant 2001.

We have identified gene products corresponding to hlyC, hlyA and hlyD encoded by the Escherichia coli haemolytic determinant 2001 of human origin cloned into the recombinant plasmid pLG570. The product of hlyC is required for the "activation" of the inactive 107K polypeptide encoded by the hlyA gene. The activated 107K protein constitutes the active haemolysin secreted into the medium. hlyB and hlyD are separate regions defined by complementation studies and encode functions essential for the export of haemolysin with hlyD encoding a 53K protein. Complementation studies using subclones and Tn5 insertions into pLG570 have revealed the presence of two major promoters upstream of hlyC and hlyD which transcribe the four hly genes in the same direction. Finally, we were able to reconstitute the complete haemolysin system from three different plasmids encoding hlyC, hlyA and hlyB + hlyD, respectively.

Cloning, Molecular↗
PubMed1985

An avian vocalization detector.

A simple circuit to detect avian vocalizations is described. Adjustments of five different controls (frequency, bandwidth, amplitude, duration and spacing) allow the circuit to accurately detect the vocalizations of different ages and species of birds. Analyses of over 4000 peeps and 500 inter-peep intervals from 40 chicks and 16 ducklings showed that the circuit and an experienced observer agreed closely in the timing and counting of vocalizations.

Animals↗
PubMed1985

Fourier analysis of infantile stridor: preliminary data.

Preliminary data from 3 patients suggest that computerized (Fourier) analysis of infantile stridor can be instructive. Several recordings are quickly collected with a microphone and digital oscilloscope at the patient's bedside. The data are later sent to a computer for spectral analysis. Averaging of several spectra from each patient depicts only those sounds that are consistent from sample to sample. Subtraction of background noise from the averaged stridor removes all but those sounds that are produced by the patient. The results show that the spectra are relatively consistent from sample to sample within the same patient, and that different patients with different pathologies have distinct patterns in their spectra. It thus appears that further acoustical studies of infantile stridor will be productive. We are optimistic that data from a larger series of patients will indicate those spectral patterns which are characteristic of a specific laryngotracheal pathology, and perhaps facilitate rapid diagnosis without invasive procedures. An additional potential of this analysis is that pre- and post-operative spectra can be subtracted to show those sounds that improved or worsened. Such serial comparisons during the management of airway problems could be useful in evaluating treatment.

Female↗
PubMed1985

Reduced capsule formation around soft silicone rubber prostheses coated with solid collagen.

Silicone rubber miniprostheses were coated with solid collagen formed from a fibrillar collagen suspension (Zyderm collagen implant) and then implanted subcutaneously in rats. There was a reduced amount of capsule formation around the coated prostheses, whereas the uncoated control implants all became surrounded by normal capsule. At the interface between the collagen coating and the surrounding tissue, no capsule formation was seen. At the interface between the prosthesis and the collagen coating, no capsule or only slight, locally limited, capsule formation was seen. Furthermore, capsule associated with coated implants was measurably thinner than that around control implants. When capsule appeared around coated implants, it was frequently associated with defects in the continuity of the coating. Host cells, fibroblasts, and round cells progressively invaded the coatings from the periphery inward, frequently along defects in the coating. The difference between coated and control implants became less pronounced between 60 and 120 days after implantation, as the amount of intact coating decreased. This work supports the hypotheses that the collagen coatings, while intact, prevent capsule formation, that the coatings produced by the present method are imperfect and are broken down with time, and that the disappearance of the coatings results in subsequent capsule formation. These hypotheses permit the deduction that development of better, more persistent coatings will permit indefinitely prolonged inhibition of capsule formation.

Animals↗
PubMed1985

Development of absolute thresholds in chickens.

Absolute auditory thresholds were estimated in chickens at 0 and 4 days after hatching. Momentary suppressions of the chicks' regular peeping, following the onset of a tone, were used as indications of stimulus detection. In the first experiment a staircase procedure was used to estimate thresholds. The absolute thresholds of both ages were the same at low frequencies (250-500 Hz), but at higher frequencies (1-2 kHz) 4-day-old chicks had lower thresholds than the 0-day-old chicks. The estimates of thresholds at 1 kHz were corroborated in the second experiment with a method of constant stimuli. A more efficient modified method of limits was used to replicate the age by frequency interaction in the third experiment. These changing thresholds are likely to reflect a developmental process somewhere in the auditory system and not some nonsensory artifact for two reasons: similar thresholds at low frequencies show that developmental differences are not due to differences in the sensitivity of the testing procedure at the two ages and thresholds obtained from the 4-day-old birds are similar to estimates from mature birds. In conclusion, responsiveness to low frequencies develops before responsiveness to higher frequencies, showing that the development of absolute thresholds is correlated with other measures of functional maturation in the auditory system.

Aging↗
PubMed1984

Giant right atrial myxoma with rheumatic mitral valve disease.

A patient with a 456 Gram right atrial myxoma is described. Associated rheumatic mitral valvular heart disease obscured the presence of the tumor and only with presentation of bradyarrhythmias leading to pacemaker implantation was the diagnosis suspected. Successful surgical removal of the tumor and correction of the intracardiac valvular dysfunction were performed. The role of echocardiography in the early detection of these tumors is reinforced.

Bioprosthesis↗
PubMed1984

Possible biomedical applications of antiproton beams: focused radiation transfer.

A calculation of the energy lost by antiprotons stopping in water shows that the radiation transferred is localized within 1 mm of the stopping point. This "focusing" of the radiation is mainly due to heavily ionizing particles emitted from the nuclei on which the annihilation takes place. At present antiproton beams for medical purposes may not be cost effective compared to other charged particle beams, but the sharpness of their radiation transfer combined with antiprotonic radiography are highly attractive and unique features that may invite special applications.

Elementary Particles↗
PubMed1983

Afferent influences on brainstem auditory nuclei of the chicken: n. laminaris dendritic length following monaural conductive hearing loss.

The influence of monaural acoustic deprivation on the size of dendrites in n. laminaris in the chick was examined. Chicks were raised in a controlled acoustic environment with one ear occluded from 2 days prior to hatching until 25 days after hatching by an earplug which provided a conductive hearing loss of approximately 40 dB across the audible frequency range. Each n. laminaris cell receives spatially segregated binaural excitatory innervation; one dendritic field received input from the plugged ear while the other received input from the normal ear. This arrangement allowed comparison of the size (length) of the "deprived" dendrites and the "nondeprived" dendrites for each cell. The tonotopic organization of n. laminaris allowed these comparisons to be made as a function of the frequency organization of the nucleus. We observed systematic changes in dendritic size which differed as a function of the tonotopic position of the neurons. In high-frequency regions the dendrites receiving information from the deprived ear were shorter than those receiving input from the normal ear. Unexpectedly, cells responsive to low frequencies showed the opposite result; the dendrites innervated from the deprived ear were longer than those responsive to the nondeprived ear. These results suggests that a relatively flat conductive hearing loss may cause nonuniform changes in activity impinging on high- and low-frequency areas of the auditory system.

Animals↗
PubMed1983

Strategies for developing a cost-effective pulmonary rehabilitation program.

A cost-effective pulmonary rehabilitation program can be created by using strategic planning, a thorough budgetary process, and then promotion of the program. Strategic planning assesses the need for such a program, develops its overall direction, establishes priorities, assesses economic factors and the presence or absence of similar services already in existence, and identifies the proposed scope of the program. The budgetary process identifies the specific services to be offered and estimates the volume of services, their costs, and revenues. Promotion of the program serves to acquaint potential referring physicians and patients with the services to be offered. If preliminary investigation indicates that a pulmonary rehabilitation program is needed in the community, then strategic planning, careful budgeting, and creative promotion can help assure that the program is financially viable.

California↗
PubMed1982

Developmental and experimental changes in dendritic symmetry in n. laminaris of the chick.

Early acoustic experience affects the structure of neurons in the brainstem of young chickens. In the binaurally innervated cells of the nucleus laminaris the symmetry of the dorsal and ventral dendritic trees normally increases during the embryonic and early postnatal period. Unilateral ear plugs disrupt that development. This study shows that balanced stimulation plays an important role in the development of symmetrical neuronal structures in the central auditory pathway.

Aging↗
PubMed1982

Thermal stimulus thresholds: sources of variability.

Thresholds to warming and cooling by a small Peltier stimulator were measured and remeasured in 24 adults and children aged 7-9. The median thresholds to warming and cooling of the forearm were +1.04 and -.15 degrees C. respectively, and neither age nor sex mattered significantly. The test-retest correlation was significant, suggesting intra-subject reliability, despite a large range of thresholds across subjects-about an order of magnitude. Measurements of skin temperature revealed that the same stimulus can cause a greater degree of warming or cooling in one subject than another. These differences proved reliable on retesting. Surprisingly, however, there was no correlation between this physical variation among people and the size of their psychophysical thresholds. Some compensatory mechanism is suggested by these data; the implication is that people who are less responsive physically may be more sensitive neurally and vice versa.

Adult↗