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Biomedical subjects

D Wong

Publications and source records attributed to D Wong.

At least 163 records · Page 9Linked to original sources
PubMed1995

Analysis and classification of delay-sensitive cortical neurons based on response to temporal parameters in echolocation signals.

Echolocating bats generate an acoustic image of their target by processing target-reflected echoes of their emitted biosonar pulses. Efforts in building computational models of auditory processing in the bat auditory system, using extensive neurophysiological data from cortical studies are challenged by the intrinsic complexity and the significant variability in neural response to stimuli. In this paper, we use a computerized method for the analysis and classification of delay-sensitive neurons to classify neurons from the auditory cortex of Myotis lucifugus, a species that echolocates with FM signals. The coefficients of the bi-linear fit to the best delay response surfaces (mean R2 = 0.01) were used in classifying the neurons. Six classes were derived that corresponded to the four previously characterized neurophysiologically. The first class corresponded to delay-tuned neurons which exhibited a constant best delay at different pulse repetition rates and pulse durations. Three other classes corresponded to the different subtypes of tracking neurons which changed their best delay to one or both of these stimulus temporal parameters. Two additional classes were differentiated although their best-delay response were similar to either the delay-tuned or the duration and pulse-repetition rate sensitive class. Artificial delay-sensitive neurons built from the parameters of the centroid of each class, will serve a key role in the FM bat auditory system model that we are building.

Acoustic Stimulation↗
PubMed1995

The excitability of human corticospinal neurons is depressed by thiopental.

BACKGROUND: We tested the effect of thiopental on the excitability of the corticospinal-motoneuron axis in normal human subjects. METHODS: Magnetic stimulation was used to excite the neurons in the motor cortex which give rise to the fast conducting corticospinal pathway. The characteristics of the composite excitatory post-synaptic potentials (EPSPs) produced in individual spinal motoneurons by cortical stimulation were derived from changes in the firing probability of voluntarily activated motor units of the first dorsal interosseous muscle. RESULTS: In 5 normal subjects, we found that thiopental, in incremental doses sufficient to sustain drowsiness (total dose 75 to 175 mg), significantly reduced the amplitude of these composite EPSPs. CONCLUSIONS: Thiopental reduced the facilitation of motoneurons from the cortex most likely by depressing cortical neurons.

Adult↗
PubMed1995

Comparison between clinician-assisted and fully automated procedures for obtaining a voice range profile.

A comparison was made between two methods of obtaining a voice range profile. One method was traditional, involving a clinician who gave instructions, motivated the subject to achieve the greatest intensity range, and determined when the goal was achieved. The second method was completely automated, involving the use of a videotape for instruction and a computer for elicitation and evaluation. Ten men and 10 women with normal voices participated as subjects in the study, and a counterbalanced design was used. Results indicated that there is no obvious preference for the use of either method, although considerable individual differences are noted.

Adult↗
PubMed1995

A simple technique for the analysis of positional distribution of fatty acids on di- and triacylglycerols using lipase and phospholipase A2.

A simple technique is described for the analysis of positional distribution of fatty acids on di- and triacylglycerols using lipase and phospholipase A2 that de-esterify fatty acids from specific sn positions. The technique makes use of the fact that methanolic-NaOH methylates only fatty acids esterified to glycerol, while methanolic-HCl methylates both free and esterified fatty acids. After lipase action it is possible to determine the fatty acid released by lipase activity by comparing the fatty acid contents of the two methylation reactions. A computer program has been written to calculate enzyme activity and positional distribution from the results. The new technique is easier to use as it eliminates thin-layer chromatography used in the standard technique and can be performed on smaller samples using less lipase.

Brassica↗
PubMed1995

Immediate skin reactivity in adult asthmatic patients.

BACKGROUND: A high prevalence of positive skin reaction is commonly seen in children with asthma. Very little information is available on the prevalence of immediate skin test reactivity in adult patients with asthma. METHODS: We performed allergen skin tests on 260 patients with asthma and 168 patients with red cedar asthma using a battery of 24 allergens. Immediate skin test reactivity was considered to be present if the subject reacted to at least one allergen. RESULTS: Forty-eight percent of adult asthmatic patients had immediate skin test reactivity. Age, sex, and race were predictors of prevalence of immediate skin test reactivity. The number of allergens used for skin testing also determined the prevalence. More than half the patients who had immediate skin test reactivity reacted to house dust mite allergen. CONCLUSIONS: There was a high proportion of immediate skin test reactivity in adult patients with asthma and half of them had positive skin reactions to house dust mite. As avoidance of house dust mites has been shown to be effective in patients with asthma, allergy evaluation should be included in the management of adult patients with asthma.

Adult↗
PubMed1994

Contact angles of substances used for internal tamponade in retinal detachment surgery.

In order to ascertain the tamponade effect of air and silicone oil we examined the contact angles subtended by ex vivo human retina, Teflon and Perspex to find a suitable experimental material which would mimic the surface properties of the retina at a three-phase interface. Using the captive bubble technique to measure the contact angle, it was found that air subtended a larger contact angle (38.8 degrees) with the retina than did silicone oil (18.2 degrees). On coating the Perspex surface with protein (PCP), it was observed that the surface properties were modified such that PCP subtended contact angles with air (43.0 degrees) and silicone oil (16.4 degrees) similar to those subtended by ex vivo human retina. Using PCP as an experimental material that mimics ex vivo human retina, spherical chambers were employed in order to examine qualitatively and to quantify the arc of contact obtained with air and silicone oil. It was found that air gave a greater arc of contact for the same percentage fill than silicone oil.

Air↗
PubMed1994

Connectionist networks in auditory system modeling.

Understanding how complex sounds, such as speech, are processed and eventually perceived in the brain is essential for building more effective speech processors. The echolocating bat provides an animal model for complex-sound processing of identified stimulus features at higher levels of the auditory pathway. In this paper, we present the use of connectionist models for modeling cortical neurons that play a key role in our auditory system model of a species of FM bat, Myotis lucifugus. The influence of network related parameters on modeling accuracy is presented, and the response of these models is explained in a behavioral context.

Acoustic Stimulation↗
PubMed1994

Effects of proligestone and megestrol on plasma adrenocorticotrophic hormone, insulin and insulin-like growth factor-1 concentrations in cats.

This paper reports changes in adrenocorticotrophic hormone (ACTH), insulin and insulin-like growth factor-1 (IGF-1) concentrations in cats from a previously published study. The cats were given oral megestrol acetate (MA, 5 mg once daily for 14 days), subcutaneous proligestone (PRG, 100 mg on two occasions one week apart) or subcutaneous saline (1 ml as for PRG). In the cats given saline (n = 6), basal ACTH, insulin and IGF-1 did not change significantly throughout the following seven weeks. The cats given MA (n = 7) developed significant suppression of plasma ACTH concentrations and hyperinsulinaemia during treatment and for two to four weeks after MA dosage ceased. In the cats given PRG (n = 7), plasma ACTH concentrations were not significantly altered although three cats had markedly suppressed values for some time after PRG treatment had ceased. Serum insulin concentrations were not significantly altered in the PRG-treated cats. The results suggest PRG may be a preferable alternative to MA in some situations.

Adrenocorticotropic Hormone↗
PubMed1994

The adherence of silicone oil to standard and heparin-coated PMMA intraocular lenses.

During combined cataract extraction and intraocular lens insertion in eyes undergoing removal of silicone oil, we noted that oil became adherent to the implant. This adhesion persisted post-operatively. Although patients seemed not to be symptomatic as a result of this effect, the oil interferes with the fundal examination. Since heparin-coated intraocular lenses are more hydrophilic than unmodified lenses, oil should spread less well on these lenses and therefore be less adherent. This study was conducted to test this hypothesis. Heparin-surface-modified and unmodified polymethylmethacrylate (PMMA) lenses were immersed in 1000 centistoke neat silicone oil and in an emulsion of silicone oil taken from a patient. The lenses were washed with saline solution in an attempt to remove adherent oil. The lenses were photographed for examination and qualitative comparison. It was found that both neat and emulsified silicone oil was strongly adherent to both surface-modified and unmodified lenses, and could not easily be washed off. The heparin-coated lenses showed a tendency for adherence of emulsified oil. It is concluded that heparin coating of intraocular lenses does not prevent, though may reduce, oil adherence. We recommend that care be taken to avoid contact between oil and implant during combined oil removal and cataract extraction.

Adhesiveness↗
PubMed1994

Gemcitabine is an active new agent in previously untreated extensive small cell lung cancer (SCLC). A study of the National Cancer Institute of Canada Clinical Trials Group.

BACKGROUND: The new pyrimidine antimetabolite Gemcitabine has shown preclinical efficacy in a number of solid tumour lines and acceptable toxicity in phase I trials. As part of an ongoing effort to identify active new agents in small cell lung cancer, the NCIC Clinical Trials Group studied Gemcitabine in previously untreated patients with extensive disease. PATIENTS AND METHODS: Twenty-nine newly diagnosed patients with untreated extensive small cell lung cancer and at least one bidimensionally measurable site received Gemcitabine as a 30 minute intravenous infusion weekly x 3 every 4 weeks. The starting dose was 1000 mg/m2/week in the first 17 patients and 1250 mg/m2/week in the remainder. Patients were reevaluated for response every 4 weeks. Those failing to respond after 2 cycles of therapy were to be offered standard chemotherapy. RESULTS: Of the 29 patients entered, all were evaluable for toxicity and 26 for response. One complete and 6 partial responses were seen giving a response rate of 27% (95% CI: 11%-47%). Median response duration was 12.5 weeks and the median survival of the entire population was 12 months. Toxic effects were mild to moderate: in particular serious myelosuppression was uncommon. CONCLUSIONS: Gemcitabine is active in previously untreated small cell lung cancer in doses which produce little toxicity. Combination studies of Gemcitabine with other agents active in this disease are warranted.

Aged↗
PubMed1994

Calcium release by cholecystokinin analogue OPE is IP3 dependent in single rat pancreatic acinar cells.

Cholecystokinin (CCK) and carbachol raise intracellular Ca2+ concentration ([Ca2+]i) in pancreatic acinar cells by elevating inositol 1,4,5-trisphosphate (IP3). CCK analogues JMV-180 and OPE stimulate fully efficacious enzyme secretion and [Ca2+]i oscillations but release Ca2+ from intracellular stores by apparently IP3-independent mechanisms in permeabilized acinar cells. In the present study, we investigated whether OPE mobilizes Ca2+ from IP3-sensitive Ca2+ stores and whether IP3 mediates such responses in single intact cells. OPE and JMV-180 similarly elevated IP3 to low levels compared with those elicited by 10 nM CCK. Depletion of IP3-sensitive stores by elevation of intracellular IP3 using carbachol, microinjection of a nonmetabolizable IP3 analogue, or exposure to thapsigargin, in the absence of extracellular Ca2+, depleted the same Ca2+ stores that were sensitive to OPE. In converse experiments, OPE depleted carbachol- or thapsigargin-sensitive stores, indicating that carbachol-, thapsigargin-, IP3-, and OPE-sensitive Ca2+ stores overlap completely and that stores mobilized by OPE are IP3 sensitive. To determine whether IP3 mediates responses to OPE, cells were microinjected with low-molecular-weight heparin, a competitive inhibited the rise of [Ca2+]i in response to carbachol, OPE, or JMV-180, whereas de-N-sulfated heparin, an inactive heparin, was without effect. These results indicate that CCK analogues release Ca2+ from IP3-sensitive Ca2+ stores by mechanisms involving the IP3 receptor.

Animals↗
PubMed1994

Frequency organization of delay-sensitive neurons in the auditory cortex of the FM bat, Myotis lucifugus.

1. The little brown bat, Myotis lucifugus, employs biosonar pulses containing broadband frequency-modulated (FM) sounds of only one harmonic during the initial phases of echolocation. Neurons throughout the auditory cortex exhibit delay-dependent facilitation to artificial pulses and echoes at particular echo delays. Extracellular unit recordings of these delay-sensitive neurons determined the essential frequency components in the sound pair and their relative timing for evoking maximum facilitation. 2. The entire 60-kHz sweep of both the simulated pulse and echo were divided into four equal spectral quarters (Ist, IInd, IIIrd, and IVth), each linearly sweeping 15 kHz downward in 1 ms, to determine the spectral parts essential for maximal facilitation. Maximal facilitation was evoked equally by pulse-echo pairs in which the sound components consisted of either the entire 60-kHz FM sweeps or only the essential quarters. Most neurons required the IVth quarter of the pulse and the echo for delay sensitivity. This is consistent with the hypothesis that the essential quarters swept excitatory frequencies just above inhibitory frequencies. 3. The spectral and temporal contributions to delay sensitivity were examined independently. The spectral content for each spectral quarter of echo was varied in echo delay, and the sound-pair responses were compared. Maximal facilitation in individual delay-sensitive neurons required both a specific part of the echo spectrum and a specific echo delay. 4. The FM sweeps of the essential pulse and echo quarters were further narrowed to their minimum bandwidth, and the essential pulse frequencies (EPFs) and essential echo frequencies (EEFs) were determined. Both the EPFs and EEFs averaged approximately 8 kHz in FM bandwidth and represented different spectral parts of the echolocation pulse emitted by this FM bat. All neurons showed delay sensitivity to search stimuli in which pulse-echo stimuli consisted of 15-kHz FM pairs. 5. Delay sensitivity in virtually all neurons required pulse and echo components whose essential frequencies differed. However, some spectral overlap was found between the pulse and echo in 39% of these neurons. The majority of neurons (81%) required a pulse and echo in which their mean frequencies differed by < or = 16 kHz. This includes neurons with pulse and echo overlapping spectrally and those with sound components showing no overlap but separated by a relatively small frequency range. 6. The facilitative frequency-tuning curves of individual neurons were measured with their essential pulse and echo frequencies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗