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Biomedical subjects

M L Johnson

Publications and source records attributed to M L Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Why, when, and how biochemists should use least squares.

One of the most commonly used methods for the analysis of experimental data in the biochemical literature is nonlinear least squares (regression). This group of methods are also commonly misused. The purpose of this article is to review the assumptions inherent in the use of least-squares techniques and how these assumptions govern the ways that least-squares techniques can and should be used. Since these assumptions pertain to the nature of the experimental data to be analyzed they also dictate many aspects of the data collection protocol. The examination of these assumptions includes a discussion of questions like: Why would a biochemist want to use nonlinear least-squares techniques? When is it appropriate for a biochemist to use nonlinear least-squares techniques? What confidence can be assigned to the results of a nonlinear least-squares analysis?

Biochemistry↗
PubMed1992

Frequency domain imaging of absorbers obscured by scattering.

Multiple pixel, frequency domain measurements of phase shift, theta, and modulation, m, in a phantom containing an absorber obscured by a relatively non-absorbing scattering solution are presented in combination with a theory of photon migration imaging. Results employing a single point source show that two dimensional theta measurements made in the presence (theta presence) and in the absence (theta absence) of an absorber can be used to create delta theta images. delta theta (theta absence-theta presence) images can be used to detect as well as locate the three dimensional position of the absorber. Images of mpresence measured in the presence of the absorber normalized by mabsence also provided detection and two dimensional location of its position. Images of % mpresence/mabsence at higher modulation frequencies provided greater resolution as predicted by photon migration theory. Neither theta nor m images alone could be used to detect or locate the presence of the absorber.

Light↗
PubMed1992

Saltation and stasis: a model of human growth.

Human growth has been viewed as a continuous process characterized by changing velocity with age. Serial length measurements of normal infants were assessed weekly (n = 10), semiweekly (n = 18), and daily (n = 3) (19 females and 12 males) during their first 21 months. Data show that growth in length occurs by discontinuous, aperiodic saltatory spurts. These bursts were 0.5 to 2.5 centimeters in amplitude during intervals separated by no measurable growth (2 to 63 days duration). These data suggest that 90 to 95 percent of normal development during infancy is growth-free and length accretion is a distinctly saltatory process of incremental bursts punctuating background stasis.

Aging↗
PubMed1992

Tyrosine hydroxylase expression in non-catecholaminergic cells in cerebellar cultures.

Organotypic cerebellar cultures, some with incorporated portions of brainstem, were immunostained after 12-19 days in vitro with three different antibodies to tyrosine hydroxylase. Similar cultures were reacted with glyoxylic acid and examined for catecholamine histofluorescence. Locus coeruleus and other subcortical neurons were positive for tyrosine hydroxylase, as were Purkinje cells and outgrowth zone astrocytes. By contrast, only locus coeruleus neurons and their axons exhibited catecholamine histofluorescence after reaction with glyoxylic acid. These results confirm previously reported in vivo developmental studies indicating that tyrosine hydroxylase can be expressed in the absence of its normal biosynthetic products, and suggest that tyrosine hydroxylase cannot be considered to be a specific marker for catecholaminergic neurons in vitro, as well as during development in vivo.

Animals↗
PubMed1992

Deconvolution analysis of hormone data.

Deconvolution analysis of hormone data poses special problems in view of the sparse, noisy, and short data series typically available for analysis; the unknown true nature of the underlying secretory event; and potentially large variations in dissipation or clearance kinetics in different settings. Consequently, deconvolution techniques, which concern themselves with the estimation of hormone secretion and/or clearance based on serial circulating hormone concentration measurements, face a particular challenge. Ideal features of deconvolution algorithms are summarized in Table IV. Specific deconvolution techniques available to analyze hormone data include both waveform-defined procedures and waveform-independent algorithms. These approaches should be viewed as complementary rather than antagonistic. All deconvolution techniques are subject to individual limitations and specific strengths. Independently of the method employed, error propagation is necessary so as to define the statistical uncertainty intrinsic to the estimate of secretion and clearance. Such calculations of experimental uncertainty should include error inherent in the sample collection, processing, and assay as well as error in the kinetic constants and/or anticipated departures of the biological process from the algebraic structure of the convolution formulation. Moreover, more complex convolution statements will be required to describe the full range of behavior of hormone data in a systems view. The applications of such newer convolution methods as well as currently available techniques include model synthesis, model testing, and analysis of the interactions among multiple pulse generators.

Algorithms↗
PubMed1992

Fluorescence lifetime imaging of calcium using Quin-2.

We describe the use of a new imaging technology, fluorescence lifetime imaging (FLIM), for the imaging of the calcium concentrations based on the fluorescence lifetime of a calcium indicator. The fluorescence lifetime of Quin-2 is shown to be highly sensitive to [Ca2+]. We create two-dimensional lifetime images using the phase shift and modulation of the Quin-2 in response to intensity-modulated light. The two-dimensional phase and modulation values are obtained using a gain-modulated image intensifier and a slow-scan CCD camera. The lifetime values in the 2D image were verified using standard frequency-domain measurements. Importantly, the FLIM method does not require the probe to display shifts in the excitation or emission spectra, which may allow Ca2+ imaging using other Ca2+ probes not in current widespread use due to the lack of spectral shifts. Fluorescence lifetime imaging can be superior to stationary (steady-state) imaging because lifetimes are independent of the local probe concentration and/or intensity, and should thus be widely applicable to chemical imaging using fluorescence microscopy.

Aminoquinolines↗
PubMed1992

Effects of the anesthetic dibucaine on the kinetics of the gel-liquid crystalline transition of dipalmitoylphosphatidylcholine multilamellar vesicles.

The effects of the anesthetic dibucaine on the relaxation kinetics of the gel-liquid crystalline transition of dipalmitoylphosphatidylcholine (DC16PC) multilamellar vesicles have been investigated using volume-perturbation calorimetry. The temperature and pressure responses to a periodic volume perturbation were measured in real time. Data collected in the time domain were subsequently converted into and analyzed in the frequency domain using Fourier series representations of the perturbation and response functions. The Laplace transform of the classical Kolmogorov-Avrami kinetic relation was employed to describe the relaxation dynamics in the frequency domain. The relaxation time of anesthetic-lipid mixtures, as a function of the fractional degree of melting, appears to be qualitatively similar to that of pure lipid systems, with a pronounced maximum, tau max, observed at a temperature corresponding to greater than 75% melting. The tau max decreases by a factor of approximately 2 as the nominal anesthetic/lipid mole ratio increases from 0 to 0.013 and exhibits no further change as the nominal anesthetic/lipid mole ratio is increased. However, the fractional dimensionality of the relaxation process decreases monotonically from slightly less than two to approximately one as the anesthetic/lipid mole ratio increases from 0 to 0.027. At higher ratios, the dimensionality appears to be less than one. These results are interpreted in terms of the classical kinetic theory and related to those obtained from Monte Carlo simulations. Specifically, low concentrations of dibucaine appear to reduce the average cluster size and cause the fluctuating lipid clusters to become more ramified. At the highest concentration of dibucaine, where n < 1, the system must be kinetically heterogeneous.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1992

Comparison of four computerized models to estimate 24-hour growth hormone secretion in girls with Turner's syndrome.

Daily pituitary growth hormone (GH) secretion can be estimated from a 24-hour GH profile by various methods. We have used four methods to assess GH secretion in 36 girls with Turner's syndrome: the method described by Thompson et al., the Pulsar algorithm combined with the method of Hellman et al. and two deconvolution techniques. The number of detected peaks varied considerably among the methods. The mean (+/- SD) total daily secretion per square meter body surface was 0.53 (0.19) U/m2.day by deconvolution, in contrast to 0.31 (0.17) with the Hellman method and 1.06 (0.37) according to Thompson. The differences are explained by different assumptions about the metabolic clearance rate and various methodological aspects. Assuming a degradation rate of 50%, the growth hormone substitution dosage would be 1-2 IU/m2.day in GH-deficient children. The usual dosage in girls with Turner's syndrome is expected to lead to serum GH levels approximately 4 times higher than in the untreated state.

Adolescent↗
PubMed1992

Genetic divergence between the Wistar-Kyoto rat and the spontaneously hypertensive rat.

A method of restriction fragment length polymorphism (RFLP) analysis was used to estimate the amount of genetic divergence between the spontaneously hypertensive rat (SHR) strain and the Wistar-Kyoto (WKY) strain. DNA from each strain was digested with eight restriction endonucleases and hybridized with six single copy gene sequences. The number of hybridization bands in each digestion was used to estimate the total number of bases analyzed and RFLPs were scored as single mutations. Divergence was then estimated by dividing the number of mutations by the number of bases analyzed. In a total of 808 bases analyzed in WKY rats, a minimum of 13 mutations were scored in SHR, which yields a nucleotide divergence of 1 change per 62 bp. This is an extremely high amount of divergence given the known origin of these two strains and is comparable to the maximum divergence possible between unrelated humans.

Animals↗
PubMed1992

Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men.

Serum GH concentrations are increased in fasted or malnourished human subjects. We investigated the dynamic mechanisms underlying this phenomenon in nine normal men by analyzing serum GH concentrations measured in blood obtained at 5-min intervals over 24 h on a control (fed) day and on the second day of a fast with a multiple-parameter deconvolution method to simultaneously resolve endogenous GH secretory and clearance rates. Two days of fasting induced a 5-fold increase in the 24-h endogenous GH production rate [78 +/- 12 vs. 371 +/- 57 micrograms/Lv (Lv, liter of distribution volume) or 0.24 +/- 0.038 vs. 1.1 +/- 0.16 mg/m2 (assuming a distribution volume of 7.9% body weight), P = 0.0001]. This enhanced GH production rate was accounted for by 2-fold increases in the number of GH secretory bursts per 24 h (14 +/- 2.3 vs. 32 +/- 2.4, P = 0.0006) and the mass of GH secreted per burst (6.3 +/- 1.2 vs. 11 +/- 1.6 micrograms/Lv, P = 0.002). The latter was a result of increased secretory-event amplitudes (maximal rates of GH release attained within a burst) with unchanged secretory burst durations. GH was secreted in complex volleys composed of multiple discrete secretory bursts. These secretory volleys were separated by shorter intervals of secretory quiescence in the fasted than fed state (respectively, 88 +/- 4.2 vs. 143 +/- 14 min, P = 0.0001). Similarly, within volleys of GH release, constituent individual secretory bursts occurred more frequently during the fast [every 33 +/- 0.64 (fasted) vs. every 44 +/- 2.0 min (fed), P = 0.0001]. The t1/2 of endogenous GH was not significantly altered by fasting [18 +/- 2.2 (fasted) vs. 20 +/- 1.5 min (fed), P = 0.47]. Serum insulin-like growth factor I concentrations were unchanged after 56 h of fasting. In conclusion, the present data suggest that starvation-induced enhancement of GH secretion is mediated by an increased frequency of GHRH release, and longer and more pronounced periods of somatostatin withdrawal.

Adult↗
PubMed1992

Attenuation of luteinizing hormone secretory burst amplitude as a proximate basis for the hypoandrogenism of healthy aging in men.

To evaluate the impact of healthy aging on specific features of endogeneous LH secretion and clearance, we applied deconvolution analysis to 24-h serum immunoradiometric LH concentration series obtained in normal men whose ages ranged from 21-73 yr. Deconvolution analysis was employed to quantitate the number, amplitude, duration, and mass of individual LH secretory bursts underlying the serum LH concentration profiles, and simultaneously estimate the half-life of LH in individual men. Plasma total and free testosterone and estradiol concentrations and body mass index (a measure of relative adiposity) were studied as possible significant covariates of age and LH secretion. We found that age was a negative determinant of LH secretory burst amplitude (r = -0.519, P = 0.013), and a positive predictor of LH secretory burst frequency (r = +0.435, P = 0.043) and basal LH secretory rates (r = +0.486, P = 0.029). Increasing age also correlated positively with LH secretory burst half-duration (duration of the secretory event at half-maximal amplitude, r = +0.656, P less than 0.001). In contrast, age did not relate to daily pulsatile LH production rate, the mass of LH secreted per burst, or the mean (24-h) serum concentration of immunoradiometric LH. Age correlated negatively with serum free testosterone (r = -0.622, P = 0.0034) but not estradiol concentrations. The serum free testosterone concentration also declined significantly with increasing body mass index (r = -0.519, P = 0.023). Although there were strong combined effects of age, body mass index, and LH secretory burst amplitude on serum free testosterone concentrations (P = 0.0006, multi-r value 0.820), LH secretory burst amplitude was the most prominent single determinant of blood androgen concentrations.

Adult↗
PubMed1992

Temporal coupling among luteinizing hormone, follicle stimulating hormone, beta-endorphin and cortisol pulse episodes in vivo.

We have applied explicit probability equations to assess possible non-random associations among four distinct hormone series consisting of episodic luteinizing hormone, follicle stimulating hormone, beta-endorphin, and/or cortisol pulses observed under physiological conditions in normal men. Closed-form likelihood functions permitted us to demonstrate significantly coordinated patterns of multiple hormone release. A specific quadruple co-pulsatility pattern was observed, in which the two gonadotropic hormones (luteinizing hormone and follicle stimulating hormone) were co-secreted and coupled by a 10-20 min lag to the later release of beta-endorphin. In turn, beta-endorphin release episodes were followed within 0-30 min by cortisol bursts. Conditional probability analysis allowed us to reject with high statistical confidence the null hypothesis that this unique temporally specified pattern of quadruple hormone release was due to purely random associations among the four pulsatile series. We conclude that discrete hormone release episodes associated with four hormones within the gonadotropic and corticotropic axes in man exhibit significantly lagged non-random temporal coupling in vivo.

Adult↗