Hebbian induction of LTP in visual cortex: perforated patch-clamp study in cultured neurons

1. To see whether presynaptic activation paired with postsynaptic depolarization is necessary for the induction of long-term potentiation (LTP) in visual cortex or whether an activation of postsynaptic receptors in conjunction with depolarization is sufficient, we carried out perforated patch-clamp recordings with nystatin from cultured cortical neurons of rats. 2. Recorded neurons were monosynaptically activated either by electrical stimulation of an adjacent neuron or by direct activation of glutamate on "hot spots" of dendrites through iontophoresis or pressure ejection. In experiments in which cultured neurons were stained immunocytochemically with antibody against synaptophysin after electrophysiological recordings, hot spots were found to correspond to probable synaptic sites. 3. Excitatory postsynaptic currents (EPSCs) evoked by test stimulation applied to the adjacent neuron at 0.1 Hz were recorded at a holding potential of -60 or -70 mV for 5-10 min after an establishment of the whole cell recording configuration. Then, stimulation was paired with postsynaptic depolarization (0 mV for 200 ms) at 1 Hz for 30 or 60 s. LTP of EPSCs was induced in 7 of the 15 cells from which stable recordings were obtained for 18-30 min after pairing. 4. When postsynaptic depolarization was paired with direct glutamate application in the absence of presynaptic stimulation in 12 cells, only 1 showed LTP. Postsynaptic depolarization alone did not induce LTP in any of the six cells tested. Also, presynaptic stimulation alone did not induce LTP in any of the five cells tested. 5. These results suggest that the concurrent activation of presynaptic elements with postsynaptic depolarization is necessary for the induction of LTP in visual cortex.     

Statistical Independence as Linear Independence

A contingency table summarizes the conditional frequencies of two attributes and shows how these two attributes are dependent on each other. Thus, this table is a fundamental tool for pattern discovery with conditional probabilities, such as rule discovery. In this paper, a contingency table is interpreted from the viewpoint of granular computing. The first important observation is that a contingency table compares two attributes with respect to the number of equivalence classes. The second important observation is that matrix algebra is a key point of analysis of this table. Especially, the degree of independence, rank plays a very important role in extracting a probabilistic model from a given contingency table.     

Gene expression within cell-sized lipid vesicles

Functional protein synthesis was observed in cell-sized lipid vesicles following encapsulation of a gene-expression system. Expression of rsGFP (red-shifted green fluorescent protein) within individual vesicles was observed by fluorescence microscopy. Interestingly, at the early stage of the reaction, the expression efficiency inside the vesicle was remarkably higher than that in the solution outside. The synthesized rsGFP in individual vesicles is safe from attack by proteinase K added to the external aqueous solution. Studies on cell-sized vesicles expressing protein should contribute to a fundamental understanding of certain aspects of living systems and will be useful for practical applications, such as the construction of microreactors.     

Brain-derived neurotrophic factor enhances long-term potentiation in rat visual cortex

Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), members of the nerve growth factor (NGF) gene family, have been suggested to play a role in experience-dependent modification of neural networks in the developing nervous system. In this study we addressed the question of whether these neurotrophins are involved in long-term potentiation (LTP) in developing visual cortex. We recorded layer II/III field potentials and whole-cell currents evoked by test stimulation of layer IV at 0.1 Hz in visual cortical slices prepared from young rats (postnatal day 15-25) and observed effects of BDNF, NT-3, and NGF on these responses. Then we analyzed the effects of these neurotrophins on LTP induced by tetanic (Theta-burst type) stimulation of layer IV. We found that BDNF at 200 ng/ml potentiated field potentials and EPSCs in most cases and that this potentiation lasted after cessation of the BDNF application. At the concentration of 20 ng/ml, BDNF did not show such an effect, but it enhanced the magnitude of expressed LTP. On the other hand, NT-3 and NGF had none of these effects. Immunohistochemical staining of slices with antibody against BDNF showed that exogenous BDNF penetrated into the whole slice within approximately 5 min of its application. The actions of BDNF were blocked by preincubation of slices with TrkB-IgG fusion protein, a BDNF scavenger, or coapplication of K252a, an inhibitor for receptor tyrosine kinases. TrkB-IgG or K252a itself completely blocked LTP, suggesting that endogenous BDNF or another TrkB ligand plays a role in LTP in the developing visual cortex.     

PRIMEROSE: PROBABILISTIC RULE INDUCTION METHOD BASED ON ROUGH SETS AND RESAMPLING METHODS

Automated knowledge acquisition is an important research issue in machine learning. Several methods of inductive learning, such as ID3 family and AQ family, have been applied to discover meaningful knowledge from large databases and their usefulness is assured in several aspects. However, since their methods are of a deterministic nature and the reliability of acquired knowledge is not evaluated statistically, these methods are ineffective when applied to domains essentially probabilistic in nature, such as medical domains. Extending concepts of rough set theory to a probabilistic domain, we introduce a new approach to knowledge acquisition, which induces probabilistic rules based on rough set theory (PRIMEROSE) and develop a program that extracts rules for an expert system from a clinical database, using this method. The results show that the derived rules almost correspond to those of the medical experts.     

Calorimetric study of mutant human lysozymes with partially introduced Ca2+ binding sites and its efficient refolding system from inclusion bodies

During the process of evolution, ancestral lysozymes evolved into calcium-binding lysozymes by acquiring three critical aspartate residues at positions 86, 91 and 92. To investigate the process of the acquisition of calcium-binding ability, two of the aspartates were partially introduced into human lysozyme at positions 86, 91 and 92. These mutants (HLQ86D, HLA92D and HLQ86D/D91Q/A92D), having two critical aspartates in calcium-binding sites, were expressed in Escherichia coli as non-active inclusion bodies. For the preparation of lysozyme samples, a refolding system using thioredoxin was established. This system allowed for effective refolding of wild-type and mutant lysozymes, and 100% of activity was recovered within 4 days. The calcium ion dependence of the melting temperature (Tm) of wild-type and mutant lysozymes was investigated by differential scanning calorimetry at pH 4.5. The Tm values of wild-type, HLQ86D and HLA92D mutants were not dependent on calcium ion concentration. However, the Tm of HLQ86D/D91Q/A92D was 4 degrees higher in the presence of 50 mM CaCl2 than in its absence, and the calcium-binding constant of this mutant was estimated to be 2.25(+/-0.25)x10(2) M(-1) at pH 4.5. Moreover, the calcium-binding ability of this mutant was confirmed by the result using Sephadex G-25 gel chromatography. These results indicate that it is indispensable to have at least two aspartates at positions 86 and 92 for acquisition of calcium-binding ability. The process of the acquisition of calcium-binding site during evolution of calcium-binding lysozyme is discussed.      

Rule Induction with Grouping Target Concepts based on Rough Sets

One of the most important problems with rule induction methods is that they cannot extract rules, which plausibly represent experts’ decision processes. In this paper, the characteristics of experts’ rules are closely examined and a new approach to extract plausible rules is introduced, which consists of the following three procedures. First, the characterization of decision attributes (given classes) is extracted from databases and the concept hierarchy for given classes is calculated. Second, based on the hierarchy, rules for each hierarchical level are induced from data. Then, for each given class, rules for all the hierarchical levels are integrated into one rule. The proposed method was evaluated on a medical database, the experimental results of which show that induced rules correctly represent experts’ decision processes.