On the behavior of some associative neural networks

Since Hopfield published his work on an associative memory model, a large number of works have studied the model from several angles and showed in particular its weaknesses, and presented ways to overcome them. Most of the proposed solutions seem to us however not biologically plausible. In this paper we present a simple statistical analysis of two networks similar to the Hopfield net, and show that the usage of positive feedback enhances the net recognizing capability without jeopardizing the stability. We also describe a layered parallel network composed of modules, each module being a modified Hopfield net. We finally present computer simulation results to support our analytical findings. The most important principles of this network are supported by data from the world of neurobiology.     

XY sex reversal syndrome in the mare: clinical and behavioral studies,H-Y phenotype

Summary An inherited genetic disorder causes XY embryos of the horse to develop as mares. On the basis of our study of 38 such mares, we have identified four grades or classes of XY sex reversal according to this scheme: class I, nearly normal female, of which some are fertile; class II, female with gonadal dysgenesis, normal mullerian development; calss III, intersex mare with gonadal dysgenesis, abnormal mullerian development, enlarged clitoris; class IV, virilized intersex characterized by high levels of testosterone. In general, class I and calss II mares were typed H-Y antigen-negative whereas class III and class IV mares were typed H-Y antigen-positive.     

Agyria — pachygyria and Miller-Dieker syndrome: clinical,genetic and chromosome studies

Summary Twelve cases of lissencephaly are reported. A high resolution chromosome study was performed on each in order to detect small chromosomal anomalies, undetectable with routine techniques. Only one case was shown to have an unbalanced karyotype with a microdeletion of the short arm of chromosome 17(del 17p). This child also had symptoms of the Miller-Dieker syndrome, consisting of lissencephaly, characteristic facies, pre- and post-natal growth retardation and other birth defects. As proposed by Dobyns, it seems justifiable to classify lissencephalies into four different groups, according to other clinical manifestations and results of chromosome studies.     

A variation in the structure of the protein-coding region of the human p53 gene

An extensive analysis of genomic DNA preparations from a number of normal and malignant tissues revealed BglII site polymorphism of the human p53 gene. Approximately 10% of p53 gene alleles were found to contain an additional BglII site localized in a region of intron I. This allelic form of p53 gene was also responsible for p53 protein having altered electrophoretic mobility. Molecular cloning and sequencing of both the alleles of p53 gene revealed a base-pair change in codon 72 causing arginine → proline substitution in the allele with the additional BglII site. Both variants of the p53 gene may occur in homozygous state and are therefore functional.     

Establishment of primate lymphoblastic cell lines by coculture with a simian T-cell leukemia virus-1 positive, hypoxanthine-guanine-phosphoribosyltransferase negative Japanese macaque cell line

A cell line (JAMH17+) resistant to 8-azaguanine was established from a human T-cell leukemia virus type 1 related virus (simian T-cell leukemia virus-1) positive Japanese macaque cell line. Lymphoblastic cell lines were established from the peripheral blood mononuclear cells of humans, hominoids, and several species of macaques by coculture with JAMH17+ in hypoxanthine-aminopterin-thymidine medium. HTLV-1 specific antigen was detected in some of the established cell lines. Phenotypic analysis showed that several cell lines of crab-eating macaques expressed Leu11a antigen, which is a marker of human natural killer cells.     

Statistical inference from single channel records: two-state Markov model with limited time resolution

Though stochastic models are widely used to describe single ion channel behaviour, statistical inference based on them has received little consideration. This paper describes techniques of statistical inference, in particular likelihood methods, suitable for Markov models incorporating limited time resolution by means of a discrete detection limit. To simplify the analysis, attention is restricted to two-state models, although the methods have more general applicability. Non-uniqueness of the mean open-time and mean closed-time estimators obtained by moment methods based on single exponential approximations to the apparent open-time and apparent closed-time distributions has been reported. The present study clarifies and extends this previous work by proving that, for such approximations, the likelihood equations as well as the moment equations (usually) have multiple solutions. Such non-uniqueness corresponds to non-identifiability of the statistical model for the apparent quantities. By contrast, higher-order approximations yield theoretically identifiable models. Likelihood-based estimation procedures are developed for both single exponential and bi-exponential approximations. The methods and results are illustrated by numerical examples based on literature and simulated data, with consideration given to empirical distributions and model control, likelihood plots, and point estimation and confidence regions.     

Effects of applying oxytocin to Helix pomatia neurons. II. Hyperpolarization

The ionic mechanisms of hyperpolarization produced by applying oxytocin (OT) were investigated at the membrane of identifiedHelix pomatia neurons. Two types of neuron were known to exist, in one of which hyperpolarization is produced by a reduction in chloride ions at the membrane and a rise in membrane permeability to potassium ions in the other. In the first of these, response to OT had a reversal potential of –40 mV and decreased when furosemide and tolbutamide were added to the external medium. In the second case, the potential of the reversal of the response to OT was –70 mV. Upon doubling of potassium ion concentration in the external solution it was shifted towards depolarization by 15 mV. It is sugested thatHelix pomatia neurons have different types of OT receptors, some of which, when activated, manifest reduced chloride permeability at the membrane (probably through the cell cyclase system) with a rise in potassium permeability at the membrane in others.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 659–666, September–October, 1988.     

Infections with Francisella tularensis biovar palaearctica in hares (Lepus timidus, Lepus europaeus) from Sweden

The occurrence of tularemia was studied in 1,500 hares submitted to the National Veterinary Institute, Uppsala, Sweden for postmortem examination during 1973 through 1985. A total of 109 tularemia cases was recorded based on the fluorescent antibody (FA) test for Francisella tularensis and on the gross and microscopic pathology. Tularemia was diagnosed only in the varying hare (Lepus timidus) and not in the European brown hare (Lepus europaeus). The geographical distribution of the 109 cases indicates that tularemia has not spread in Sweden during the last 45 yr, with the exception of an endemic occurrence of the disease on the island of Stora Karls? in the Baltic sea. The disease was most frequent in the autumn and only a few cases were recorded during winter. Cases were not seen in the spring. The annual prevalence varied, with several cases in 1974 and 1981, but there were no cases in 1976 and 1980. The postmortem findings in hares dying of tularemia in the autumn were characterized by focal coagulative necrosis in liver, spleen and bone marrow, with high numbers of bacteria FA-positive for F. tularensis. In hares dying during winter months, the most characteristic findings were hemorrhagic enteritis and typhlitis, although necrotic lesions could occur in liver, spleen and bone marrow. Diseased hares on the island of Stora Karls? were demonstrated to be infected with ticks, while hares on the mainland of Sweden generally were fed upon by mosquitoes. Twenty-six of the 109 hares with tularemia were examined bacteriologically and F. tularensis biovar palaearctica was isolated from eight. The lung extract antibody test for F. tularensis was performed in 18 of the 109 hares. All were negative. In addition to the field study, an experimental study with F. tularensis biovar palaearctica was performed. Four varying hares and three European brown hares were inoculated. None of the hares died from tularemia, and generalized infection was not demonstrated.     

The low-frequency EEG component in the healthy subject and its changes as affected by acutely developing foci at the level of the diencephalon and brain stem structures

The data are given of the analysis of the low-frequency EEG component (LF EEG--0.2--2.0 Hz) of 34 healthy subjects and 36 patients examined in dynamics in the acute period after operations: ablation of a tumour localized at the level of the diencephalon and the level of the brainstem. The LF EEGs were analyzed by a special program: auto- and crosscorrelation functions and power spectra were estimated. In the norm LF EEGs were characterized by mosaics, various frequencies and periodicity in various cortical areas, they appeared with interhemispheric asymmetry, depended on the EEG type--dominance or lack of the alpha-rhythm. In patients in the post-operative period the LF EEGs were changed; in favourable terminations, at first the period of oscillations and the coefficient of correlation increased, then they tended to normalization. In unfavourable terminations, with gross pathological foci in these areas, the LF EEGs acquired a synchronized character, with a higher frequency than in the norm.