Field potential and single unit analyses of the avian dorsal motor nucleus of the vagus and criteria for identifying vagal cardiac cells of origin

The compound action potential components and their associated fiber contingents were investigated in the pigeon vagus nerve with a view toward identifying the vagal cardioinhibitory fibers. In the cervical vagus, the compound action potential evoked by electrical stimulation included four major components that conducted at 17.0-30.0 (A-wave), 8.0-14.5 (B2-wave) and 0.8-2.0 (C-wave) m/sec. Cardiac slowing was not elicited until activation of the Bl-wave, and the bradycardic response was maximal when this component was maximized. Electron microscopic analysis of the cervical vagus revealed myelinated fibers 1.1-6.8 micron in diameter and unmyelinated fibers 0.3-1.4 micron in diameter. A contingent of myelinated fibers approximately 2-4 micron in diameter apparently generated the Bl-wave, while the prominent unmyelinated fiber contingent (37%) accounted for the C-wave. Analysis of various vagal branches indicated that approximatley 20% of the cervical vagal fibers exit the main trunk between cervical and mid-thoracic levels, but few of these are the larger myelinated fibers greater than 2 micron in diameter. The upper abdominal vagus consists largely of unmyelinated and small myelinated fibers, and consequently the vast majority of larger myelinated fibers found in the cervical vagus exit between mid-thoracic and upper abdominal levels, presumably in the cardiac branches. Direct examination of the cardiac branches confirmed this. Thus, it is concluded that the Bl-wave of the compound action potential is uniquely associated with cardiac slowing, that this component is generated by myelinated fibers ranging from 2 to 4 micron in diameter, and that almost all such fibers are destined for the cardiac branches of the vagus.     

Administration of L-3,4-dihydroxyphenylalanine to rats after complete hepatectomy-II. Excretion of metabolites

The excretion of metabolites of l-[3-¹⁴C]dihydroxyphenylalanine (l-[3-¹⁴C]DOPA) was studied after its injection into rats with complete hepatectomies and into control rats. Approximately 60 per cent of the dose (11 mg/kg; 20 μCi) of injected [¹⁴C]DOPA was excreted in urine in 24 hr by the control rats, and 11 per cent in bile. Although a similar percentage of the dose (69.4 per cent) was excreted by the hepatectomized rats into urine, excretion was at a slower rate. Decarboxylation of injected [¹⁴C]DOPA within 24 hr appeared to be as great in the hepatectomized rats as in the controls, but metabolism of 3,4-dihydroxyphenylethylamine (dopamine, DA) to norepinephrine was less. In the operated animals most of the DA was metabolized to 3,4-dihydroxyphenylacetic acid or to homovanillic acid. Little radioactivity was present in tissues at 24 hr after injection of l-DOPA into control rats or into hepatectomized rats; however, some radioactivity appeared to be bound to protein in some tissues in both groups of rats.     

Reproducibility of the heart rate variability responses to graded lower body negative pressure

The reproducibility of heart rate variability (HRV) measures during graded lower body negative pressure (LBNP) have not been studied in sufficient detail. Active college age men (n=14) underwent an orientation exposure and two trials of graded LBNP to presyncope or –100 mmHg, separated by 1 week. Heart rate, stroke volume (impedance cardiography), blood pressure (Finapres), and forearm blood flow were assessed, as was HRV in both time and frequency domains. The trial-to-trial responses to LBNP common to all subjects (LBNP–60 mmHg and at test termination) showed parallel changes, suggesting similar responses between both trials. Good reproducibility estimates were found for the resting HRV data (lowest: R=0.62 for low frequency/high frequency ratio; highest: R=0.94 for standard deviation of normal R-R intervals). During LBNP, reproducibility estimates varied but were generally similar to that seen at rest. At test termination, they were unacceptably low (R<0.41) for the HRV data assessed in the frequency domain and expressed in absolute units. LBNP tolerance was lower in the first trial [LBNP tolerance index: 404 (21) versus 437 (15) mmHg min^–1; P<0.05] but the intraclass correlation coefficient was high (R=0.87). These data suggest that (1) HRV responses to submaximal LBNP up to –60 mmHg are consistent across trials, (2) the considerable variability seen in the HRV parameters at maximal LBNP can be reduced by expressing these data in either the time domain or using normalized units in the frequency domain, and (3) cardiovascular responses to sub- and maximal LBNP are reproducible. Data are presented as mean (SEM) unless otherwise stated.     

Prediction of mortality in an Indian intensive care unit

Objective To compare hospital outcome prediction using an artificial neural network model, built on an Indian data set, with the APACHE II (Acute Physiology and Chronic Health Evaluation II) logistic regression model.Design Analysis of a database containing prospectively collected data.Setting Medical-neurological ICU of a university hospital in Mumbai, India.Subjects Two thousand sixty-two consecutive admissions between 1996 and1998.Interventions None.Measurements and results The 22 variables used to obtain day-1 APACHE II score and risk of death were recorded. Data from 1,962 patients were used to train the neural network using a back-propagation algorithm. Data from the remaining 1,000 patients were used for testing this model and comparing it with APACHE II. There were 337 deaths in these 1,000 patients; APACHE II predicted 246 deaths while the neural network predicted 336 deaths. Calibration, assessed by the Hosmer-Lemeshow statistic, was better with the neural network (=22.4) than with APACHE II (=123.5) and so was discrimination (area under receiver operating characteristic curve =0.87 versus 0.77, p=0.002). Analysis of information gain due to each of the 22 variables revealed that the neural network could predict outcome using only 15 variables. A new model using these 15 variables predicted 335 deaths, had calibration (=27.7) and discrimination (area under receiver operating characteristic curve =0.88) which was comparable to the 22-variable model (p=0.87) and superior to the APACHE II equation (p<0.001).Conclusion Artificial neural networks, trained on Indian patient data, used fewer variables and yet outperformed the APACHE II system in predicting hospital outcome.Electronic Supplementary Material Supplementary material is available in the online version of this article at Part of this work was presented at the Sixth Annual Critical Care Congress of the Indian Society for Critical Care Medicine, Bangalore, India     

Effects of simulated environmental conditions on glucocorticoid metabolite measurements in white-tailed deer feces

Environmental conditions may influence fecal glucocorticoid metabolite measurements if feces cannot be collected immediately after deposition. To evaluate the influence of environmental conditions on fecal glucocorticoid metabolite concentrations, we exposed fresh fecal samples to 1 of 5 simulated conditions: (1) room temperature (22 degrees C), (2) high heat (38 degrees C), (3) alternating high heat and room temperature cycle, (4) alternating freezing (-20 degrees C) and room temperature cycle, and (5) simulated rainfall (0.85 cm every other day at 22 degrees C) for 7 days. We collected fresh white-tailed deer (Odocoileus virginianus) feces at various times pre- and post-adrenocorticotropin injection to provide samples with initially low (n=5), medium (n=5), and high (n=5) glucocorticoid concentrations. Feces were mixed thoroughly and then allocated into five 10-g samples. Also, a 5-g sub-sample was taken from each fecal mass prior to treatment and stored at -20 degrees C until assayed. We subsampled from all treatments once every 24-h for 7 days. Fecal samples were assayed using [125I]corticosterone radioimmunoassay kits. Fecal glucocorticoid metabolites in all three groups in the simulated rainfall treatment and the low group in the alternating freezing and room temperature treatment increased significantly over the 7-day period. We believe increased microbial metabolism of fecal glucocorticoids may partly explain these results. Other biochemical processes (e.g., cleavage of conjugate side groups from hormone metabolites by non-microbial action or release of glucocorticoids from lipid micelles) may also have increased fecal glucocorticoid measurements. Our findings suggest that fecal samples exposed to rainfall for one week may artificially inflate fecal glucocorticoid measurements. Thus, researchers should recognize the potential bias when collecting fecal samples exposed to rainfall. Non-fresh samples may prove useful when care is taken to address the elevation in immunoreactive glucocorticoid concentrations.     

Anatomy and function of the subdeltoid bursa

An anatomical study was undertaken on 40 non-embalmed normal cadaver shoulders to determine the attachments, boundaries and macroscopic nerve supply of the subdeltoid bursa. Two areas of attachment were observed, one (proximal and superficial) along the free border of the coracoacromial ligament and adjacent deep surface of deltoid, the other (distal and deep) to the humerus distal to the supraspinatus tendon there were no posterior or anterior attachments. In addition, two blind pouches were observed, one proximal under the coracoacromial ligament and the other beyond the distal attachment. The continuity observed between the lateral border of the coracoacromial ligament and the subdeltoid bursa provides a smooth surface, thereby casting doubt on the aggressive action of the ligament on the rotator cuff.     

贝尔纳的生命观对现代生理学的影响

19世纪下半叶,机械还原论主导生理学领域。然而,贝尔纳却大力提倡有机、整体的生命观,并提出了生物内环境的概念。他的思想和方法,对20世纪初期生理学的发展产生了重要的影响。     

留学生生理学实验教学的探索与思考

本文探讨了留学生生理学实验教学的教学模式和方法。通过采取与留学生充分交流，自编英文教材，认真备课，实行启发式、互动式教学，激发学生内在学习动机，启发学生思维等措施，显著地提高了教学质量和效果。