PubMed Health⌕ Search

Biomedical subjects

J E Levin

Publications and source records attributed to J E Levin.

10 recordsLinked to original sources
PubMed1996

Broadband neural encoding in the cricket cercal sensory system enhanced by stochastic resonance.

Sensory systems are often required to detect a small amplitude signal embedded in broadband background noise. Traditionally, ambient noise is regarded as detrimental to encoding accuracy. Recently, however, a phenomenon known as stochastic resonance has been described in which, for systems with a nonlinear threshold, increasing the input noise level can actually improve the output signal-to-noise ratio over a limited range of signal and noise strengths. Previous theoretical and experimental studies of stochastic resonance in physical and biological systems have dealt exclusively with single-frequency sine stimuli embedded in a broadband noise background. In the past year it has been shown in a theoretical and modelling study that stochastic resonance can be observed with broadband signals. Here we demonstrate that broadband stochastic resonance is manifest in the peripheral layers of neural processing in a simple sensory system, and that it plays a role over a wide range of biologically relevant stimulus parameters. Further, we quantify the functional significance of the phenomenon within the context of signal processing, using information theory.

Action Potentials↗
PubMed1994

Construction and analysis of a database representing a neural map.

We describe the development and analysis of a quantitative database representing the global structural and functional organization of an entire sensory map. The database was derived from measurements of anatomical characteristics of a statistical sample of typical mechanosensory afferents in the cricket cercal sensory system. Anatomical characteristics of the neurons were measured quantitatively in three dimensions using a computer reconstruction system. The reconstructions of all neurons were aligned and scaled to a common standard set of dimensions, according to a highly reproducible set of intrinsic fiducial marks. The database therefore preserves accurate information about spatial relationships between the neurons within the ensemble. Algorithms were implemented to allow the integration of electrophysiological data about the stimulus/response characteristics of the reconstructed neurons into the database. The algorithms essentially map a physiological function onto a "field" representing the continuous distribution of synaptic terminals throughout the neural structure. Subsequent analysis allowed quantitative predictions of several important functional characteristics of the sensory map that emerge from its global organization. First, quantitative and testable predictions were made about ensemble response patterns within the map. The predicted patterns are presented as graphical images, similar to images that might be observed with activity-dependent dyes in the real neural system. Second, the synaptic innervation patterns from the sensory afferent map onto the dendrites of a postsynaptic target interneuron were predicted by calculating the overlap between the interneuron's dendrites with the afferent map. By doing so, several aspects of the stimulus/response properties of the interneuron were accurately predicted.

Animals↗
PubMed1991

What health care cost crisis?

Managed care has inherent limitations that, perhaps out of desperation for some degree of control of health care costs, we tend to disregard. A better understanding of the "crisis" and a host of new strategies become apparent when we separately consider the health care elements and cost elements of the crisis. Managed care is essentially palliative in that it eases symptoms without curing conditions. While this is not a call for the abandonment of managed care, it is a warning that our efforts will prove futile if we do not also address other fundamental elements of impaired health.

Aged↗
PubMed1989

Muscle-specific regulation of a transfected rabbit myosin heavy chain beta gene promoter.

We have examined the transcriptional regulation of the rabbit myosin heavy chain (HC) beta gene by using DNA-mediated transfection experiments. To analyze the activity of the myosin HC beta promoter in a myogenic background, cultured myoblasts from 12-day-old chick embryonic breast muscle were transfected with a chimeric gene containing 781 base pairs of the promoter region fused to the gene for chloramphenicol acetyltransferase (CAT). As indicated by the transient expression of chloramphenicol acetyltransferase, the activity of the promoter in myoblast cultures increased at least 32-fold following differentiation and was selectively inhibited when myogenesis was blocked with 5-bromodeoxyuridine. Furthermore, RNase protection experiments showed that the in vivo myosin HC beta transcriptional initiation (or cap) site was utilized in the transfected skeletal muscle cells and also that the regulation of the exogenous promoter was similar to the induction of the endogenous skeletal alpha-actin gene. The results indicated that the exogenous promoter is regulated in a tissue- and stage-specific manner. By creating progressive 5' deletions of the promoter, we showed that only the region extending -294 base pairs upstream from the cap site is necessary for the muscle-specific expression. Linker-scanner mutagenesis of this region indicated that the positive regulation in differentiated skeletal muscle is mediated by at least two distinct elements within the 5'-flanking region of the myosin HC beta gene.

Animals↗
PubMed1989

Quality of life of adults with growth hormone deficiency: a controlled study.

The quality of life of 23 adults with growth hormone deficiency (GHD) who had received growth hormone (GH) therapy was compared with that of 47 normal individuals in a control group. The GHD group had a poorer quality of life than the control group. Statistically significant differences were found between the groups for social isolation, physical mobility, sleep, and emotional status. More individuals in the control group had a driving licence and were married than in the GHD group.

Adult↗
PubMed1988

Health careers--a method of health education at school for adolescents.

An innovative health education curriculum, "Health Careers", intended for adolescents leaving school, was evaluated using a quasi-experimental pre-/post control group design. The objective of the project was the modification of knowledge, attitudes and behaviour in relation to health. Attempts were made to counteract factors restricting the effect of traditional health education at school. Changes were estimated using questionnaires. Two types of schools were studied, schools A and B, student age averaged 17.3 years and 15.5 years, respectively. The number of students in the experimental groups was 220 and 112, respectively. At school B, in addition, 35 parents participated voluntarily in evening courses arranged by the project staff. Significant improvement was shown in two variables of a possible 60 at school A and in four variables at school B. Analysis by subgroups, however, demonstrated improvements in merely one variable at school B. It is evident that the innovative curriculum did not induce significant behavioural improvement in relation to health. Frame factors of the school--obligatory student participation and teacher role perception--may explain this outcome.

Adolescent↗
PubMed1986

Partial characterization of the human beta-myosin heavy-chain gene which is expressed in heart and skeletal muscle.

A human myosin heavy-chain gene, cloned in gamma Charon 4A phage (and as a clone designated lambda gMHC-1), was shown to code for a cardiac myosin heavy chain of the beta-type. The 5' end of the 14,200-base-pair genomic DNA clone is located in the head region of the myosin chain. The 3' end was shown to extent to the COOH terminus and includes the 3'-nontranslated sequence of the corresponding mRNA. The identification of lambda gMHC-1 as coding for a cardiac beta-myosin heavy chain was achieved by heteroduplex mapping using genomic cardiac myosin heavy-chain DNA of rabbit as a probe and, furthermore, by DNA sequence analysis of three selected subregions of the clones DNA including the 3'-nontranslated sequence. It was demonstrated by the S1 nuclease protection technique that the beta-myosin heavy-chain gene is transcribed in human heart muscle. In addition, we have found by the same technique that it is also expressed in human skeletal muscle.

Animals↗
PubMed1984

Analysis of cloned mRNA sequences encoding subfragment 2 and part of subfragment 1 of alpha- and beta-myosin heavy chains of rabbit heart.

Two cardiac myosin heavy chain cDNA clones, pMHC alpha 252 and pMHC beta 174, were constructed using rabbit ventricular mRNA isolated from adult thyrotoxic and normal hearts, respectively. The complete DNA sequences of the 2.2- and 1.4-kilobase inserts of pMHC beta 174 and pMHC alpha 252, respectively, were obtained. The 736 amino acids specified by pMHC beta 174 begin 439 (1.3 kilobases) residues from the heavy chain NH2 terminus and include a 400-amino acid segment of subfragment 1 and the entire subfragment 2 region. Clone pMHC alpha 252 encodes 465 amino acids encompassing all of subfragment 2 and a portion of light meromyosin. Comparison of these two clones revealed extensive sequence overlap which included 1107 nucleotides specifying a 369-amino acid segment corresponding to subfragment 2. Within this region 78 (7%) base and 32 (8.7%) amino acid mismatches were noted. These differences were clustered within discrete regions, with the subfragment 1/subfragment 2 junctional region being particularly divergent. Structural differences between pMHC alpha 252 and pMHC beta 174 indicate that these two clones represent two similar but distinct myosin heavy chain genes whose expression is responsible for ventricular myosin heavy chain isoforms alpha and beta, respectively. The derived amino acid sequences of both clones exhibit extensive homology (greater than 81%) with sequences obtained by direct analysis of adult rabbit skeletal muscle myosin heavy chain protein. The sequences corresponding to the subfragment 2 region are consistent with an alpha-helical conformation with a characteristic 7-residue periodicity in the linear distribution of nonpolar amino acids. Conversely, subfragment 1 sequences specified by pMHC beta 174 suggest a folded highly irregular structure.

Amino Acid Sequence↗