Dual information representation with stable firing rates and chaotic spatiotemporal spike patterns in a neural network model

Although various means of information representation in the cortex have been considered, the fundamental mechanism for such representation is not well understood. The relation between neural network dynamics and properties of information representation needs to be examined. We examined spatial pattern properties of mean firing rates and spatiotemporal spikes in an interconnected spiking neural network model. We found that whereas the spatiotemporal spike patterns are chaotic and unstable, the spatial patterns of mean firing rates (SPMFR) are steady and stable, reflecting the internal structure of synaptic weights. Interestingly, the chaotic instability contributes to fast stabilization of the SPMFR. Findings suggest that there are two types of network dynamics behind neuronal spiking: internally-driven dynamics and externally driven dynamics. When the internally driven dynamics dominate, spikes are relatively more chaotic and independent of external inputs; the SPMFR are steady and stable. When the externally driven dynamics dominate, the spiking patterns are relatively more dependent on the spatiotemporal structure of external inputs. These emergent properties of information representation imply that the brain may adopt a dual coding system. Recent experimental data suggest that internally driven and externally driven dynamics coexist and work together in the cortex.

Detection of mutual determinism between a pair of spike trains

A method for detecting mutual deterministic dependence between a pair of spike trains is proposed. When it is assumed that a cell assembly, which is a subgroup of neurons processing a common task, is constituted as a dynamical system, then the mutual determinism between constituent neurons may be directly reflected in functional connectivity in the assembly. The deterministic dependence between two spike trains can be measured with statistical significance using a method of nonlinear prediction. Some examples of simulations are demonstrated in both deterministic and stochastic cases.

Synchronization of pulse-coupled excitable neurons

Collective behavior of pulse-coupled oscillatory neurons has been investigated widely. In many cases, however, real neurons are intrinsically not oscillatory but excitable. The networks of excitable neurons can have their own characteristic dynamics, and they are of interest also from the viewpoint of functional assemblies. In the present paper, the collective behavior of pulse-coupled excitable neurons has been investigated using phase description. It is shown that full synchronization is achieved in networks of excitable leaky integrate-and-fire neurons and discrete-time Nagumo-Sato neurons. The cooperative roles of external spike inputs, decay of internal states, and feedback spikes are explained. Enhancement of synchronization by refractoriness and noise is also reported.

Fractal encoding in a chaotic neural network

We analyze a model of a chaotic neural network consisting of three neurons, namely a chaotically forcing neuron and two neurons comprizing a stable response system with a contraction mapping property, for digital encoding with chaotic dynamics. We show that dynamics of the chaotically forcing neuron is embedded in the form of a code sequence on a fractal attractor of the two-neuron response system. We consider the relation between the state transition of the chaotically forcing neuron and the hierarchical fractal structure on the attractor in the state space of the contracting system. We also report hardware implementation of the presented model with an analog electronic circuit to investigate the fractal attractor of the chaotic neural network as a realistic system.

The 70-kDa peroxisomal membrane protein (PMP70), an ATP-binding cassette transporter

The 70-kDa peroxisomal membrane protein (PMP70) is one of major components of peroxisomal membranes. In rodents, PMP70 is markedly induced by administration of hypolipidemic agents in parallel with peroxisome proliferation and the induction of peroxisomal fatty acid beta-oxidation enzymes. PMP70 is an ATP-binding cassette transporter, identified for the first time in intracellular membranes of eukaryotic cells. The authors' recent studies suggest that PMP70 is synthesized on free polysomes and posttranslationally inserted into peroxisomal membranes, and assembles as dimeric or oligomeric forms on peroxisomal membranes. PMP70 is suggested to be involved in metabolic transport of long-chain acyl-CoA across peroxisomal membranes.

TY-12533, a novel Na+/H+ exchange inhibitor, prevents myocardial stunning in dogs

Anesthetized open-chest dogs were subjected to 15-min myocardial ischemia followed by 2-h reperfusion to induce myocardial stunning. A novel Na(+)/H(+) exchange inhibitor 6,7,8,9-tetrahydro-2-methyl-5H-cyclohepta[b]pyridine-3-carbonylguanidine maleate (TY-12533), administered 10 min before or 10 min after start of ischemia (3 mg/kg/10 min, i.v.), did not affect reductions in regional myocardial wall thickening, blood flow and pH during ischemia, but it significantly improved recovery of the wall thickening and blood flow after reperfusion. These results indicate that TY-12533, even when administered during ischemia, could prevent myocardial stunning without affecting myocardial dysfunction or acidosis induced by brief ischemia.

Solving the binding problem of the brain with bi-directional functional connectivity

We propose a neural network model which gives one solution to the binding problem on the basis of 'functional connectivity' and bidirectional connections. Here, 'functional connectivity' is dynamic neuronal connectivity peculiar to temporal spike coding neural networks with coincidence detector neurons. The model consists of a single primary map and two higher modules which extract two different features shown on the primary map. There exist three layers in each higher module and the layers are connected bi-directionally. An object in the outer world is represented by a 'global dynamical cell assembly' which is organized across the primary map and the two higher modules. Detailed, but spatially localized, information is coded in the primary map, whereas coarse, but spatially extracted information or globally integrated information is coded in the higher modules. Computer simulations of the proposed model show that multiple cell assemblies sharing the same neurons partially can co-exist. Furthermore, we introduce a three-dimensional J-PSTH (Joint-Peri Stimulus Time Histogram) which is capable of tracking such cell assemblies, altering its constituent neurons as in our proposed model.

Successful combination therapy--flunarizine, pentoxifylline, and cholestyramine--for spur cell anemia

Spur cell anemia, a hemolytic anemia observed in patients with alcoholic cirrhosis, is characterized by unusual erythrocyte morphology and an increased ratio of free cholesterol to phospholipid in the erythrocyte membrane. The prognosis of spur cell anemia is usually extremely poor, however, we describe here a patient with spur cell anemia who was successfully treated with combination therapy consisting of flunarizine, pentoxifylline, and cholestyramine. Initial therapy with flunarizine alone for 6 weeks did not significantly decrease the number of spur cells on peripheral blood smears. So pentoxifylline was added to the regimen. The patient recovered from the anemia, showed remarkable improvement with regard to the hyperbilirubinemia, and the changes were accompanied by a significant decrease in the number of spur cells in peripheral blood smears. To correct the hypercholesterolemia, cholestyramine was added to the regimen, which resulted in a reduction in the serum level of free cholesterol and an increase in the molar ratio of free cholesterol to phospholipid in erythrocyte membrane. However, 6 months later a skin eruption developed that was considered an adverse reaction to the drugs, so the flunarizine and pentoxifylline were discontinued. With cholestyramine therapy alone, the remission of spur cell anemia was maintained for more than 11 months. These observations suggest that non-invasive combination therapy with flunarizine, pentoxifylline, and cholestyramine is effective and valuable in the treatment of patients with spur cell anemia.

Molecular mechanism of type I congenital heparin cofactor (HC) II deficiency caused by a missense mutation at reactive P2 site: HC II Tokushima

We found a 66-year-old Japanese patient with type I congenital heparin cofactor (HC) II deficiency manifesting multiple atherosclerotic lesions. To investigate the molecular pathogenesis of our patient, we performed sequencing analysis and expressed recombinant human wild-type and mutant HC II molecules in COS-1 and CHO-K1 cells. Sequencing analysis following amplification of each of all 5 exons and its flanking region showed a single C to T transition at nucleotide position 12,854 in exon 5, which changed a Pro443 codon (CCG) to Leu codon (CTG). Because this mutation generates a new Bhv I site, the Bbv I digestion pattern of the PCR-amplified exon 5 fragments from each family member was analyzed. In all cases, the patterns were consistent with the activities and antigen levels of plasma HC I1 in those members. Transient transfection, metabolic labeling and pulse-chase experiments followed by immunoprecipitation analysis showed that the recombinant mutant HC II molecules were secreted from COS-1 cells in reduced amounts compared with the wild-type, and that an enhanced intracellular association of the mutant molecules with a chaperone, GRP78/BiP, was observed in CHO-K1 cells. Northern blot analysis indicated that the mutant HC I1 mRNA was transcribed at a similar level as that of wild-type. Immunohistochemical staining of the transfected cells revealed that COS-1 cells expressing the mutant HC II molecules were stained mainly in the perinuclear area. We conclude that the impaired secretion of the mutant HC II molecules, due to intracellular degradation, is the molecular pathogenesis of type I congenital HC II deficiency caused by a Pro443 to Leu mutation at reactive P2 site.

Estimating statistics of neuronal dynamics via Markov chains

We present an efficient computational method for estimating the mean and variance of interspike intervals defined by the timing of spikes in typical orbits of one-dimensional neuronal maps. This is equivalent to finding the mean and variance of return times of orbits to particular regions of phase space. Rather than computing estimates directly from time series, the system is modelled as a finite state Markov chain to extract stationary behaviour in the form of invariant measures and average absorption times. Ergodic-theoretic formulae are then applied to produce the estimates without the need to generate orbits directly. The approach may be applied to both deterministic and randomly forced systems.

Chaotic stimulus dependent long-term potentiation in the hippocampal CA1 area

In our previous report [Tsukada, M., Aihara, T., Saito, H., Kato, H., 1996. Neural Netw. 9, 1357-1365], the temporal pattern sensitivity of long-term potentiation (LTP) in hippocampal CA1 neurons was estimated by using Markov chain stimuli (MS) with different values of the serial correlation coefficient rho1 between successive interstimulus-intervals. In this paper, the effect of chaotic stimuli (CS) on induction of LTP in the hippocampal CA1 area was investigated in comparison with that of MS and periodic pattern stimuli (PS). The CS were produced by a modified Bernoulli map, so that interstimulus sequences with various values of rho1 can be generated by changing the parameter B. These stimuli had an identical first order statistics (mean interstimulus-interval), but their higher order statistics such as the serial correlation coefficients were different. The LTP induced by CS at B = 2 was significantly larger in magnitude than that of PS and MS, and also depended on the initial value of CS at B = 2 and 3. These results suggest that chaotic signals play an important role for memory coding in the hippocampal CA1 network.

Associative memory model with temporal spike coding and active dendrite

We propose a neuron model whose internal state is integrated on a two dimensional phase space composed of time and dendritic space. Here, the postsynaptic potential is given as a curved surface on the phase space. Using the proposed neuron model, we introduce a continuous-time associative memory model with spike propagation delay and multiple synaptic sites on the dendrite. We show by numerical simulation that the memory capacity is doubled due to the effects of temporal spike coding and active dendrite compared to the sparse coding associative memory model.

Cardioprotective effect of TY-12533, a novel Na(+)/H(+) exchange inhibitor, on ischemia/reperfusion injury

The effects of 6,7,8, 9-tetrahydro-2-methyl-5H-cyclohepta[b]pyridine-3-carbonylguanidine maleate (TY-12533) on myocardial ischemia/reperfusion injury were evaluated in rats. Inhibitory effects of TY-12533, TY-50893 (the 9-chloro derivative of TY-12533) and cariporide on the platelet Na(+)/H(+) exchanger in vitro were almost equal at pH 6.2 and decreased at pH 6.7; but TY-12533 was four times more potent than TY-50893 and cariporide at pH 6.7. TY-12533, TY-50893 and cariporide administered before ischemia (0.01-1 mg/kg, i.v.) suppressed the ischemia/reperfusion-induced arrhythmias to the same extent in vivo; but TY-12533 was more effective than cariporide and TY-50893 when they were administered during ischemia (0.1-1 mg/kg). Similar results were obtained for the inhibitory effects of these drugs administered before ischemia (0.03-0.1 mg/kg, i.v.) and during ischemia (0.1-1 mg/kg) on the ischemia/reperfusion-induced myocardial infarction. These differences between TY-12533 and the other drugs in vitro and in vivo may be ascribed to the pK(a) values of the guanidinium moiety of TY-12533 (6.93), TY-50893 (6.35) and cariporide (6.28).

No increased risk of thrombosis in heterozygous congenital dysplasminogenemia

To assess the risk of thrombosis in congenital dysplasminogenemia, we studied 10 unrelated families with this disorder. The probands were excluded from the analysis of data to prevent bias in the selection of subjects. Positive thrombotic histories were found in 1 of the 25 family members determined to have heterozygous congenital dysplasminogenemia and in 2 of their 41 biochemically unaffected relatives. The percentages of family members with no history of thrombosis up to a given age among subjects with and without congenital dysplasminogenemia were analyzed by the Kaplan-Meier method. No significant difference between the 2 groups was observed by generalized Wilcoxon test (P = .32) or Cox-Mantel test (P = .62). These findings suggest that heterozygous congenital dysplasminogenemia is not associated with an increased risk of thrombosis.

Synchronization and sensitivity enhancement of the Hodgkin-Huxley neurons due to inhibitory inputs

Recent experimental results imply that inhibitory postsynaptic potentials can play a functional role in realizing synchronization of neuronal firing in the brain. In order to examine the relation between inhibition and synchronous firing of neurons theoretically, we analyze possible effects of synchronization and sensitivity enhancement caused by inhibitory inputs to neurons with a biologically realistic model of the Hodgkin-Huxley equations. The result shows that, after an inhibitory spike, the firing probability of a single postsynaptic neuron exposed to random excitatory background activity oscillates with time. The oscillation of the firing probability can be related to synchronous firing of neurons receiving an inhibitory spike simultaneously. Further, we show that when an inhibitory spike input precedes an excitatory spike input, the presence of such preceding inhibition raises the firing probability peak of the neuron after the excitatory input. The result indicates that an inhibitory spike input can enhance the sensitivity of the postsynaptic neuron to the following excitatory spike input. Two neural network models based on these effects on postsynaptic neurons caused by inhibitory inputs are proposed to demonstrate possible mechanisms of detecting particular spatiotemporal spike patterns.

Analysis of neural spike trains with interspike interval reconstruction

As a method for the analysis of neural spike trains, we examine fundamental characteristics of interspike interval (ISI) reconstruction theoretically with a leaky-integrator neuron model and experimentally with cricket wind receptor cells. Both the input to the leaky integrator and the stimulus to the wind receptor cells are the time series generated from the Rossler system. By numerical analysis of the leaky integrator, it is shown that, even if ISI reconstruction is possible, sometimes the entire structure of the Rössler attractor may not be reconstructed with ISI reconstruction. For analysis of the in vivo physiological responses of cricket wind receptor cells, we apply ISI reconstruction, nonlinear prediction and the surrogate data method to the experimental data. As a result of the analysis, it is found that there is a significant deterministic structure in the spike trains. By this analysis of physiological data, it is also shown that, even if ISI reconstruction is possible, the entire attractor may not be reconstructed.

[Chromophobe cell renal carcinoma: a case report]

Chromophobe cell renal carcinoma is an uncommon subtype of renal cell carcinoma and the number of cases studied is still limited in Japan. We here report a case of chromophobe cell renal carcinoma in a 41-year-old Mexican male. He visited our branch hospital with the symptom of upper abdominal pain. Ultrasound examination showed a left renal mass. He was admitted to our hospital for treatment of a left renal mass. Radiological examinations revealed a hypervascular tumor in the left kidney. Under the clinical diagnosis of possible renal cell carcinoma, left radical nephrectomy was performed. This tumor was diagnosed as chromophobe cell renal carcinoma with a microscopic examination of H & E stained specimens, histochemical staining using Hale's colloidal iron and an ultrastructural study.

Linearization and transposition of circular molecules of insertion sequence IS3

IS3 transposase has been shown to promote production of characteristic circular and linear IS3 molecules from the IS3-carrying plasmid; IS3 circles have the entire IS3 sequence with terminal inverted repeats, IRL and IRR, which are separated by a three base-pair sequence originally flanking either end in the parental plasmid, whereas linear IS3 molecules have three nucleotide overhangs at their 5' ends. Here, we showed that a plasmid carrying an IS3 derivative, which is flanked by different sequences at both ends, generated IS3 circles and linear IS3 molecules owing to the action of transposase. Cloning and sequencing analyses of the linear molecules showed that each had the same 5'-protruding three nucleotide overhanging sequences at both ends, suggesting that the linear molecules were not generated from the parental plasmid by the two double-strand breaks at both end regions of IS3. The plasmid carrying IS3 with a two base-pair mutation in the terminal dinucleotide, which would be required for transposase to cleave the 3' end of IS3, could still generate linear molecules as well as circles. Plasmids bearing an IS3 circle were cleaved by transposase and gave linear molecules with the same 5'-protruding three nucleotide overhanging sequences. These show that the linear molecules are generated from IS3 circles via a double-strand break at the three base-pair intervening sequence. Plasmids carrying an IS3 circle with the two base-pair end mutation still were cleaved by transposase, though with reduced efficiencies, suggesting that IS3 transposase has the ability to cleave not only the 3' end of IS3, but a site three nucleotides from the 5' end of IS3. IS3 circles also were shown to transpose to the target plasmids. The end mutation almost completely inhibited this transposition, showing that the terminal dinucleotides are important for the transfer of the 3' end of IS3 to the target as well as for the end cleavage.

Insulin resistance and angiotensin converting enzyme polymorphism in Japanese hypertensive subjects

Renin-angiotensin system activity has been shown to affect insulin sensitivity. However, the relationship between I/D polymorphism and insulin resistance is controversial. Therefore, we examined the relationship between the ACE genotype and insulin sensitivity in 51 Japanese hypertensive patients using the glucose clamp technique. The ACE genotype distribution in the hypertensive subjects was: 7 subjects with DD, 20 subjects with ID, and 24 subjects with II. Insulin sensitivity in terms of the glucose disposal rate was not significantly different among the three ACE genotypes, although there was a tendency for insulin sensitivity to decrease in the order of II, ID and DD, DD being the lowest. These findings are contrary to previous reports that insulin sensitivity was increased in normotensive subjects with the DD genotype who were Caucasian or African-American. There might be a difference due to race and whether the subjects are hypertensive or obese. We concluded that insulin sensitivity was not different among the ACE genotypes in the Japanese hypertensive subjects, supporting a previous report on the Chinese population. To date, insulin sensitivity has not been found to differ with ACE genotypes in the oriental population.

Similarity and dissimilarity in mode and mechanism of action between YT-146, a selective adenosine receptor A2 agonist, and adenosine in isolated canine hearts

To elucidate the differences in mode and mechanism of action between YT-146, a highly selective adenosine A2 receptor agonist, and adenosine, we compared their effects on coronary circulation and myocardium and modifications of these effects by glibenclamide, a blocker of ATP-sensitive potassium (K) channels, in three kinds of isolated, blood-perfused canine heart preparations. YT-146 and adenosine were injected i.a. In all preparations both YT-146 and adenosine increased coronary blood flow and in this respect YT-146 was about 5 times as potent as adenosine. The increase in blood flow caused by adenosine was transient, whereas that produced by YT-146 was biphasic; the transient increase was followed by a sustained one. In isolated, blood-perfused sinoatrial (SA) node preparations, YT-146 failed to affect sinus rate, whereas adenosine reduced sinus rate by about 38% at its maximum effect. In isolated, blood-perfused atrioventricular (AV) node preparations, when injected into the artery supplying the AV node, YT-146 exerted no effect on AV conduction time, whereas adenosine prolonged AV conduction time by about 17% at the maximum effect. In isolated, blood-perfused papillary muscle preparations, the force of contraction was affected by neither YT-146 nor adenosine. In the same preparations the effect of YT-146 in increasing coronary blood flow was antagonized by glibenclamide in such a manner that the maximum increase was suppressed, but that of adenosine was not. Reactive hyperemia induced by ischemia for 30 seconds was not affected by glibenclamide. These results suggest that although both YT-146 and adenosine produce an increase in coronary blood flow via adenosine A2 receptors, the opening of ATP- or glibenclamide-sensitive K channels is involved in the action of the former, but scarcely in the action of the latter. The opening of ATP- or glibenclamide-sensitive K-channels is less likely involved in reactive hyperemia.

Characterization of the 70-kDa peroxisomal membrane protein, an ATP binding cassette transporter

The 70-kDa peroxisomal membrane protein (PMP70) is one of the major components of rat liver peroxisomal membranes and belongs to a superfamily of proteins known as ATP binding cassette transporters. PMP70 is markedly induced by administration of hypolipidemic agents in parallel with peroxisome proliferation and induction of peroxisomal fatty acid beta-oxidation enzymes. To characterize the role of PMP70 in biogenesis and function of peroxisomes, we transfected the cDNA of rat PMP70 into Chinese hamster ovary cells and established cell lines stably expressing PMP70. The content of PMP70 in the transfectants increased about 5-fold when compared with the control cells. A subcellular fractionation study showed that overexpressed PMP70 was enriched in peroxisomes. This peroxisomal localization was confirmed by immunofluorescence and immunoelectron microscopy. The number of immuno-gold particles corresponding to PMP70 on peroxisomes increased markedly in the transfectants, but the size and the number of peroxisomes were essentially the same in both the transfectants and the control cells. beta-Oxidation of palmitic acid increased about 2-3-fold in the transfectants, whereas the oxidation of lignoceric acid decreased about 30-40%. When intact peroxisomes prepared from both the cell lines were incubated with palmitoyl-CoA, oxidation was stimulated with ATP, but the degree of the stimulation was higher in the transfectants than in the control cells. Furthermore, we established three Chinese hamster ovary cell lines stably expressing mutant PMP70. In these cells, beta-oxidation of palmitic acid decreased markedly. These results suggest that PMP70 is involved in metabolic transport of long chain acyl-CoA across peroxisomal membranes and that increase of PMP70 is not associated with proliferation of peroxisomes.

Numerous huge iron particles appeared around micro blood vessels under intestinal epithelial cells in infant mice fed excess iron with protein

In infant mice (2 weeks old) fed a diet with excess iron for one week, numerous huge iron particles around micro blood vessels under the basement membrane of intestinal epithelial cells were observed by electron microscopy. The frequency of occurrence of these particles (0.24 +/- 0.04 micron diameter) was markedly higher in mice fed a casein-based diet than in mice fed an amino acid-based diet. The quantity of these particles in both groups decreased in proportion to the term of 2 or 3 weeks. Changes in morphological features, such as opening of the intercellular junctions between intestinal epithelial cells, were also observed in these experimental groups. On the other hand, in mice fed the casein-based diet with excess iron, fat globules appeared in the intestinal epithelial tissue (intestinal epithelial cells, interstitial tissue, lympha) and the occurrence of these increased gradually in proportion to the term of feeding. These fat globules were not observed in mice fed the amino acid-based diet with excess iron. These phenomena might be elicited temporally in infant mice fed excess iron together with protein. The mechanisms of fat globule formation remain unclear.