Biomedical subjects

G T Marczynski

Publications and source records attributed to G T Marczynski.

22 records · Page 2Linked to original sources

PubMed1985

A transcription map of a yeast centromere plasmid: unexpected transcripts and altered gene expression.

YCp19 is a yeast centromere plasmid capable of autonomous replication in both yeast and E. coli (J. Mol. Biol., 158: 157-179, 1982). It is stably maintained as a single copy in the yeast cell and is therefore a model yeast "minichromosome" and cloning vector. We have located the positions and measured the abundance of the in vivo yeast transcripts from YCp19. Transcripts from the selectable marker genes TRP1 and URA3 were present at increased levels relative to chromosomal copies of the genes. Unanticipated transcripts from the yeast CEN4 and E. coli pBR322 sequences were also found. Although much of the plasmid vector is actively transcribed in vivo, the regions around the most useful cloning sites (BamHI, EcoRI, SalI) are free of transcripts. We have analyzed transcription of BamHI inserts containing promoter variants of the HIS3 gene and determined that although initiation events are accurate, plasmid context may alter levels of gene expression.

Centromere↗

PubMed1983

Algorithm for calculating theoretical probabilities of patterns generated by sequential inequality testing.

Temporal patterns of extracellularly monitored single neuronal impulses or 'spike' trains can be viewed as stochastic point processes that carry information from one neuron to another. There are indications that the dependencies among sequential spike intervals, if treated as sequential inequality patterns, encompass much more than 7 spike intervals. Hence, to fill the gap between the available knowledge and the experimental need, a limited stochastic model of inequality patterns was reviewed and its inherent symmetries were explored. The symmetric attributes of the model, based on three through seven spike intervals, led to an algorithm which allows one to readily compute the theoretical distribution of inequality patterns of considerable complexity and length suitable for studying neuronal responses and other phenomena.

Action Potentials↗

PubMed1982

Visual attention and neuronal firing patterns in the feline pulvinar nucleus of thalamus.

In behaving cats, temporal patterns of neuronal firing were studied during slow wave sleep (SWS), motionless quiet wakefulness (QW) coupled with specific direction of the animal's attention, and during bar pressing performance (BP) for milk reward. The analysis was based on relative relations between sequential spike intervals. The strength of the method is based on the fact that the probabilities of occurrence of patterns are determined by the history of a spike train. During SWS, the neuronal firing modes closely followed the theoretical model of independent distribution of intervals, whereas during QW and BP specific for each neuron departures from the model, i.e., patterning was observed. Most importantly, in seven chronically studied neurons idiosyncratic patterns were related to direction of the animal's attention, and, very likely, to the visual forms the animals gazed at, because the patterns disappeared in the dark and during SWS without major changes in the mean firing rate. The replications of patterns upon recurrence of a particular direction of attention was proven statistically. The constancy and idiosyncrasy of these patterns were apparent even though the comparable episodes occurred several hours apart, and the animals slept and/or ate in between, and the distance, i.e., the retinal size of visual forms varied from one episode to another. On the basis of correlative evidence, it was argued that, compared to more abstract modes of information processing, the identification and quantification of patterns based on relative relations between intervals require the least amount of storage of intermediate results. Hence, these patterns are likely to represent a simple and phylogenetically old principle of communication between neurons. It was postulated that the idiosyncrasy and invariance of patterns may play a role in constancy of feature extraction and Gestalt perception.

Animals↗

PubMed1980

Neuronal firing patterns in the feline hippocampus during sleep and wakefulness.

The study addressed the problem of information transmission in mammalian brain as reflected in the emergence or disappearance of temporal patterns in extracellularly monitored single action potentials from the dorsal hippocampus of unrestrained cats during slow wave sleep (SWS), rapid eye movement sleep (REM), and motionless quiet wakefulness (QW). The spike trains were analyzed with a nonparametric technique. Chi-square statistics were used to measure deviation of firing patterns from the theoretical model which is based on the assumption that the intervals are random and/or independent from each other. The plots of the chi-square values for a given set of patterns represented the neuronal 'signatures' characteristic of a behavioral state. During SWS most neurons followed the theoretical model, i.e. their 'signatures' were flat and statistically non-significant. However, during REM sleep and QW their firing modes showed specific deviations from the theoretical model: some patterns occurred more often while others less often than expected, thus generating large and statistically significant 'signatures'. During REM sleep some neurons shared similar tendencies in their departures from the theoretical model. However, during QW the same neurons developed their individual 'signatures' which were significantly different from each other. Hence, the QW episodes were characterized by a greater differentiation of neuronal firing patterns. The mean firing rate and the shape of the time interval histogram were not necessarily correlated with the emergence of specific temporal patterns in spike trains. The results suggest that information transmission from one neuron to another depends on the emergence of repetitive and specific temporal patterns. The strong tendency of most neurons to lapse during SWS into a firing mode that closely follows the theoretical model constitutes the basis for a working hypothesis which states that the essence of SWS recovery in cognitive systems is the disappearance of temporal patterns, and that the 'noisy' interactions between neurons plays an important role in the recuperative processes.

Animals↗