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.     

Life Cycle,Host Range,and Reproduction of Heterodera betulae

Heterodera betulae, a cyst-forming nematode, originally recovered from roots of river birch in Arkansas, appears to have a limited host range. Of 80 plant species in 20 families tested, only five species of Betula and Cleome spinosa supported reproduction. The minimum time for a complete life cycle was 52 days at 28 C. No reproduction occurred at 31 C or above, and development was very slow below 20 C. Successful population propagations from single larvae demonstrated that males were not necessary for reproduction.     

The zinc finger transcription factor Gfi1, implicated in lymphomagenesis,is required for inner ear hair cell differentiation and survival

Gfi1 was first identified as causing interleukin 2-independent growth in T cells and lymphomagenesis in mice. Much work has shown that Gfi1 and Gfi1b, a second mouse homolog, play pivotal roles in blood cell lineage differentiation. However, neither Gfi1 nor Gfi1b has been implicated in nervous system development, even though their invertebrate homologues, senseless in Drosophila and pag-3 in C. elegans are expressed and required in the nervous system. We show that Gfi1 mRNA is expressed in many areas that give rise to neuronal cells during embryonic development in mouse, and that Gfi1 protein has a more restricted expression pattern. By E12.5 Gfi1 mRNA is expressed in both the CNS and PNS as well as in many sensory epithelia including the developing inner ear epithelia. At later developmental stages, Gfi1 expression in the ear is refined to the hair cells and neurons throughout the inner ear. Gfi1 protein is expressed in a more restricted pattern in specialized sensory cells of the PNS, including the eye, presumptive Merkel cells, the lung and hair cells of the inner ear. Gfi1 mutant mice display behavioral defects that are consistent with inner ear anomalies, as they are ataxic, circle, display head tilting behavior and do not respond to noise. They have a unique inner ear phenotype in that the vestibular and cochlear hair cells are differentially affected. Although Gfi1-deficient mice initially specify inner ear hair cells, these hair cells are disorganized in both the vestibule and cochlea. The outer hair cells of the cochlea are improperly innervated and express neuronal markers that are not normally expressed in these cells. Furthermore, Gfi1 mutant mice lose all cochlear hair cells just prior to and soon after birth through apoptosis. Finally, by five months of age there is also a dramatic reduction in the number of cochlear neurons. Hence, Gfi1 is expressed in the developing nervous system, is required for inner ear hair cell differentiation, and its loss causes programmed cell death.     

Infra-species Variation in Reactions to Hosts in Heterodera glycines Population

Eighteen hosts were inoculated with each of four races of Heterodera glycines. A discriminant function analysis of the reactions of these races to these hosts demonstrated that these races could be separated but not consistently. Then 33 H. glycines populations collected from 13 states and five obtained from Japan were tested on differential hosts. The number of variants discriminated within these 38 populations depended on the number of differentials and the rating system used. When five differentials were used with a (+) or (-) rating system there were six "races," but when 13 differentials were used with a (+) or (-) system there were 25 physiological groups. If an index rating system was used there were 36 groups. Apparently H. glycines is a very variable species and delineation of races varies with criteria chosen.     

Molecular and behavioral analysis of four period mutants in Drosophila melanogaster encompassing extreme short,novel long,and unorthodox arrhythmic types.

Of the mutationally defined rhythm genes in Drosophila melanogaster, period (per) has been studied the most. We have molecularly characterized three older per mutants-perT, perClk, and per04-along with a novel long-period one (perSLIH). Each mutant is the result of a single nucleotide change. perT, perClk, and perSLIH are accounted for by amino acid substitutions; per04 is altered at a splice site acceptor and causes aberrant splicing. perSLIH exhibits a long period of 27 hr in constant darkness and entrains to light/dark (L/D) cycles with a later-than-normal evening peak of locomotion. perSLIH males are more rhythmic than females. perSLIH''s clock runs faster at higher temperatures and slower at lower ones, exhibiting a temperature-compensation defect opposite to that of perLong. The per-encoded protein (PER) in the perT mutant cycles in L/D with an earlier-than-normal peak; this peak in perSLIH is later than normal, and there was a slight difference in the PER timecourse of males vs. females. PER in per04 was undetectable. Two of these mutations, perSLIH and perClk, lie within regions of PER that have not been studied previously and may define important functional domains of this clock protein.     

Prospective randomised study of an orthopaedic geriatric inpatient service.

A randomised controlled trial of two management regimens was carried out in women patients over 65 years of age with hip fractures. Ninety seven patients were admitted to a designated orthopaedic geriatric unit and 125 to orthopaedic wards. No difference was observed in mortality, length of stay, or placement of patients between the two groups. More medical conditions were recognised and treated in patients in the orthopaedic geriatric unit group. It is concluded that designated orthopaedic geriatric units can provide medical care to these patients and should be administered without additional cost.     

Involvement of the period gene in developmental time-memory: effect of the perShort mutation on phase shifts induced by light pulses delivered to Drosophila larvae

Phases of circadian locomotor activity rhythms of adult Drosophila reared in constant darkness have been shown to be set by a light stimulus delivered as early as the first-instar larval stage. This implies that a circadian clock functions continuously throughout postembryonic development. The clock genes period (per) and timeless (tim) are expressed cyclically in the larval central nervous system of Drosophila, and daily oscillations of per expression persist throughout metamorphosis in a group of cells, which gives rise to the pacemaker cells underlying locomotor activity rhythms of adults. Therefore, PER and TIM cyclings in these neurons may be responsible for the phenomenon of "larval time-memory." In the absence of any evidence for the involvement of these genes in such a developmental clock, and because circadian-pacemaker functions are underanalyzed in terms of the functions during development, the authors tested the time-memory of a fast-clock period mutant. They show that dark-reared perS mutant individuals as well as wild-type flies can be entrained as larvae and that a brief light pulse given to such entrained larvae can induce phase shifts in animals of either genotype. However, the direction and magnitude of phase shifts were different between wild type and perS, suggesting that a clock under the control of period gene participates in the regulation of developmental time-memory. The authors show that the relevant clock can be entrained by two light input pathways, one involving the phospholipase C encoded by the norpA gene, the other mediated by the blue-light receptor cryptochrome. Phase shifts of molecular oscillations during the larval stage were smaller than those measured by adult behavior, suggesting molecularly transient responses during development.     

Morphometric and Serologic Comparisons of a Number of Populations of Cyst Nematodes

Thirty-five populations of Heterodera glycines and populations of 15 other Heterodera, Globodera, and Punctodera species were studied morphometrically and some were compared serologically. There was a wide range of each measurement within each nematode population. Except for one soybean cyst nematode population from Indiana, which was a tetraploid and considerably larger than the others, morphometric measurements overlapped. In a discriminant function comparison most of the populations were closely grouped but at least three were rather distinctly separated. Morphometrically H. fici, H. cruciferae, H. schachtii, and H. trifolii were closely associated with H. glycines. Serology indicated a close relationship between H. glycines, H. lespedezae, H. trifolii, H. schachtii, and the Heterodera sp. from Rumex, while H. betulae appeared to be more distantly related.