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Biomedical subjects

K Yan

Publications and source records attributed to K Yan.

At least 73 records · Page 4Linked to original sources
PubMed1986

Visual responses of neurons in the avian nucleus isthmi.

Electrophysiological responses of neurons to visual and auditory stimulation are extracellularly recorded from the pigeon isthmic area. Cobalt sulfide markings show that only visual units are localized within the nucleus isthmi pars parvocellularis (Ipc) and pars magnocellularis (Imc), while visual-auditory bimodal units are localized outside. Visual units respond to black or white targets moving through their receptive fields (RFs). The RF centers are mainly distributed in the contralaterally lower visual field. The rostral Ipc and Imc receive information from the nasal visual field, and the caudal part of the Ipc and Imc corresponds to the temporal field. Therefore, both Ipc and Imc are visual centers instead of auditory centers as described before.

Acoustic Stimulation↗
PubMed1985

The effect of acetylcholine on neurones of the amphibian nucleus isthmi.

In the bird, histochemical and biochemical data suggest that the tectal input into nucleus isthmi is of a cholinergic nature. In the present study the response of toad (Bufo bufo gargarizans) isthmic neurones to acetylcholine was investigated using conventional extracellular recording techniques and ionophoresis. The results show isthmic cells to be strongly excited by acetylcholine (ACh), whereas neurones in the neighbouring areas show minimal sensitivity. Atropine sulphate completely blocked the response to acetylcholine and greatly decreased activity induced by visual stimulus. The present data show that acetylcholine mimics one of the physiological transmitters in the nucleus isthmi.

Acetylcholine↗
PubMed1985

Prevalence and nature of bronchial hyperresponsiveness in subjects with chronic obstructive pulmonary disease.

The prevalence, nature, and severity of bronchial hyperresponsiveness in subjects with chronic obstructive pulmonary disease (COPD) is not known. To determine these factors, a 1 in 4 random sample of adults attending the Busselton population survey was studied. Subjects answered a modified Medical Research Council questionnaire and had spirometric function tested. They were defined as having COPD or asthma from the questionnaire. Bronchial responsiveness to histamine was measured using the rapid method, and results in the subjects with COPD were compared with those in asthmatic subjects with abnormal lung function. Fifty-nine subjects with COPD had a histamine inhalation test, and of these, 27 had bronchial hyperresponsiveness (BHR) (PD20FEV1 less than 3.9 mumol). The position of the dose response curves of the subjects with COPD overlapped considerably with those obtained from the 17 asthmatics. The geometric mean values for PD20FEV1 for these 2 groups were significantly different (p less than 0.001). There was a good correlation between FEV1/FVC and PD20FEV1 values in the subjects with COPD but not in the asthmatic subjects. Pretreatment with 600 micrograms of aerosolized fenoterol significantly improved the PD20FEV1 values in 11 subjects with COPD (1.26 to 6.16 mumol; p less than 0.001). The results suggest that approximately half the subjects with COPD in a general population have BHR but this BHR has different characteristics from that occurring in asthmatic subjects.

Adult↗
PubMed1985

Electrophysiological studies on the nucleus isthmi of the lizards Gekko gekko and Shinisaurus crocodilurus.

This report studies visual responses of the isthmic units in Gekko gekko and Shinisaurus crocodilurus using extracellular recording and cobalt sulfide marking techniques. Our results indicate that: (i) the nucleus isthmi pars magnocellularis (Imc) is a visual center; (ii) there are luxotonic units in Imc; (iii) Imc units respond vigorously to moving contrast targets, of which 35% units burst only at the moment when targets are moving into and out of their receptive fields, none react to either tactile or auditory stimulation; (iv) there exist binocular units in Imc; and (v) visual field is topographically projected onto Imc.

Animals↗
PubMed1984

The action of prazosin and propylene glycol on methoxamine-induced bronchoconstriction in asthmatic subjects.

The effect of 1 mg inhaled prazosin on bronchoconstriction induced by methoxamine was investigated in seven asthmatic subjects. Prazosin caused significant inhibition of the methoxamine-induced bronchoconstriction in six of the seven patients. These findings suggest that methoxamine produces bronchoconstriction in asthmatic subjects via stimulation of alpha-adrenoceptors. In previous studies propylene glycol has been used as a vehicle for delivery of prazosin. This substance was found to cause significant inhibition of methoxamine effects and to shift the dose response curve to histamine to the right in four of seven patients.

Adult↗
PubMed1984

The shape of the dose-response curve to histamine in asthmatic and normal subjects.

In order to determine the shape of the dose-response curves of the human airways to bronchial challenge, changes in forced expiratory volume in one second (FEV1) after inhaled histamine were measured in 8 current asthmatic, 2 mildly asthmatic, and 10 normal subjects. The challenges were continued until a plateau was reached (in all the normal and in the 2 mildly asthmatic subjects), or the FEV1 had fallen by 60%. A sigmoidal equation was fitted to the data points to obtain values for alpha (the position constant) and beta (the slope constant). All the normal and the 2 mildly asthmatic subjects reached a plateau value for fall in FEV1. Current asthmatics were differentiated from normal and mildly asthmatic subjects by the failure to reach a plateau at a 60% fall in FEV1 by higher values for alpha (greater sensitivity to histamine) and by higher values for beta. Ipratropium bromide (an atropinelike drug), in doses that completely inhibited the effects of methacholine, caused no change in the shape or position of the curves in normal or asthmatic subjects. It is concluded that the nature of the airway response to histamine is different in asthmatic from that in normal subjects. It is possible that asthmatics lack a normal mechanism that inhibits severe airway narrowing during histamine challenge.

Adult↗
PubMed1983

Neuroanatomy and electrophysiology of the lacertilian nucleus isthmi.

Horseradish peroxidase (HRP) tracings showed a bidirectional connection between the optic tectum (OT) and the ipsilateral nucleus isthmi (NI) pars magnocellularis (Imc) in nocturnal Gekko gekko and diurnal Shinisaurus crocodilurus. We found that, in addition to a direct neuronal pathway, there is an indirect pathway from OT to Imc via the nucleus profundus mesencephali (NPM). The morphology of cells in OT, NPM and NI was studied. Visual units extracellularly recorded from NI were located within Imc based on cobalt sulphide markings. They responded to moving contrast targets, without reacting to tactile and auditory stimulation. HRP and Golgi-Cox studies showed that Imc is a nucleus independent of its parvocellular partner, Ipc.

Animals↗
PubMed1983

Rapid method for measurement of bronchial responsiveness.

A rapid, simple method for measuring bronchial responsiveness to inhaled histamine is described. The method was used to obtain dose response curves in 50 atopic subjects with varying respiratory and nasal symptoms. The cumulative dose of histamine which caused a 20% fall in the one second forced expiratory volume (PD20-FEV1) varied between 0.046 and greater than 3.9 mumol and correlated with the severity of symptoms. The reproducibility of the PD20-FEV1, determined from duplicate measurements in 15 subjects with varying degrees of bronchial responsiveness was found to be satisfactory. When the PD20-FEV1 from this rapid method was compared with that obtained from the dosimeter method no significant difference was found. The dose delivered by this method was shown to be cumulative.

Adolescent↗
PubMed1983

Effect of aerosol fenoterol on the severity of bronchial hyperreactivity in patients with asthma.

Beta adrenergic agents given by aerosol decrease the responsiveness of the airways to histamine and methacholine in subjects with asthma, causing a shift of the dose response curve to the right. To find out whether the shift is related to the dose of beta adrenergic agent given and to determine the duration of the reduced responsiveness, eight subjects with asthma were given histamine inhalation tests after inhaled saline and after increasing doses of inhaled fenoterol on different days. The histamine inhalation tests were repeated at hourly intervals for five hours after a selected dose of fenoterol. Fenoterol caused a dose related shift to the right of the histamine dose response curve in each subject and in some the dose response relationship reached the "non-symptomatic range." The shift in the dose response curve was short lived and had returned towards the control position within three hours in all subjects. There was no change in shape of the curves at the time of maximal shift. The results show that inhaled fenoterol greatly reduces the airway responsiveness to histamine, but up to 400 micrograms of fenoterol every four to five hours may be needed to keep the responsiveness of the airways in the non-symptomatic range.

Adult↗
PubMed1983

Comparison of in vivo and in vitro responses to histamine in human airways.

The study was designed to compare in vivo responses to histamine in 14 patients prior to thoracotomy with in vitro responses to histamine of both parenchymal and bronchial tissue. Although a wide range of responsiveness occurred in vivo, as measured by the histamine inhalation test, the variation in the in vitro dose-response curves was negligible. There was no correlation between the dose of histamine that resulted in a 20% reduction in forced expiratory volume in one second and the concentration of histamine producing 50% of the maximal response in vitro. These findings raise the possibility that airway hyperresponsiveness may not result from an intrinsic abnormality of airway smooth muscle.

Adult↗
PubMed1983

Methods for assessing bronchial reactivity.

Tests of bronchial reactivity in man may help in understanding the nature of bronchial hyperreactivity which is characteristic of asthmatic subjects. Comparison of published studies is, at present, limited because diverse methods have been used to study and to report the results of bronchial provocation tests. The factors which affect the response include the type of provoking agent used, the method of delivery, the lung function test used, the method of expressing the result and "subject" factors. The effect of each of these factors is reviewed. Histamine and methacholine are the most useful substances for distinguishing normal from asthmatic subjects, the technique of provocation appears to have only a small effect on the results and, the FEV1 appear to be the best test for distinguishing asthmatic from normal subjects. It is recommended that, whenever possible, the whole dose response curve is reported with the percent change in FEV1 plotted against the dose delivered on a log scale.

Allergens↗
PubMed1983

The response of the airways to nasal stimulation in asthmatics with rhinitis.

In twelve subjects with perennial allergic rhinitis and stable asthma nasal obstruction was induced with histamine diphosphate solution introduced onto the nasal mucosa by a nasal atomizer in a cumulative manner starting with a 0.001% solution. The effect on the nose was measured by the change in inspiratory nasal flow resistance and the lung response was determined by the one second forced expiratory volume (FEV1). The test was stopped when there was a greater than 20% fall in FEV1 or when the total dose of histamine diphosphate reached 26 mumoles. All twelve subjects had a greater than six fold increase in inspiratory nasal flow resistance together with other symptoms of rhinitis in response to histamine. Six subjects had a dose related fall of greater than 20% in FEV1. Two others had falls of 10% and 17%. These changes persisted for between five and thirty minutes. In four subjects, aerosol salbutamol was needed for complete reversal of the FEV1. There was no relationship between the fall in FEV1 resulting from nasal stimulation and airway reactivity as measured by histamine inhalation test on a separate day. The results suggest that the airways of some asthmatics narrow in response to nasal stimulation.

Airway Resistance↗
PubMed1982

Nucleus isthmus of toad is secondary visual center.

Visual responses of 148 units have been recorded with micropipettes from the left nucleus isthmus areas of toads (Bufo bufo gargarizans), their auditory and tactile responses also examined, and 122 recording sites marked with cobalt sulphide. This study indicates that: (i) 118 units responding solely to visual stimuli are found within the nucleus, and 4 multisensory units outside, (ii) there exist a visual field map and binocular units in the nucleus, and (iii) response latencies of the isthmic units to a spot of light range from 120 to 540 msec, with no correlation with recording sites.

Animals↗