The influence of cortical feature maps on the encoding of the orientation of a short line

The inhomogeneous distribution of the receptive fields of cortical neurons influences the cortical representation of the orientation of short lines seen in visual images. We construct a model of the response of populations of neurons in the human primary visual cortex by combining realistic response properties of individual neurons and cortical maps of orientation and location preferences. The encoding error, which characterizes the difference between the parameters of a visual stimulus and their cortical representation, is calculated using Fisher information as the square root of the variance of a statistically efficient estimator. The error of encoding orientation varies considerably with the location and orientation of the short line stimulus as modulated by the underlying orientation preference map. The average encoding error depends only weakly on the structure of the orientation preference map and is much smaller than the human error of estimating orientation measured psychophysically. From this comparison we conclude that the actual mechanism of orientation perception does not make efficient use of all the information available in the neuronal responses and that it is the decoding of visual information from neuronal responses that limits psychophysical performance. Action Editor: Terrence Sejnowski     

Effects of ovine CRF injections into the dorsomedial, dorsolateral and lateral columns of the periaqueductal gray: a functional role for the dorsomedial column

Corticotropin-releasing factor (CRF) and its receptor subtypes have been implicated in the regulation of endocrine, behavioral and autonomic responses to stress, fear and anxiety. Ovine CRF (oCRF) is a nonspecific CRF receptor agonist that produces anxiogenic-like effects when injected locally into the dorsal aspects of the periaqueductal gray (PAG). This structure is subdivided into four distinct longitudinal columns but their exact functional role is not fully understood. The purpose of the present study was to characterize the effects of oCRF (0.25, 0.5 and 1 microg/0.2 microL) injections into the dorsomedial (dmPAG), dorsolateral (dlPAG) and lateral (lPAG) columns of the PAG using an analysis of the exploratory behavior of rats in the elevated plus-maze (EPM) test. The results showed that microinjections of oCRF intra-dmPAG reduced entries and time spent in the open arms and decreased end-arm exploration and head-dipping. In contrast, oCRF intra-dlPAG or lPAG did not affect the exploratory behavior of the animals in the EPM. These findings point to a columnar specificity for the oCRF effects in the PAG, that is, it increased spatial avoidance measures of the EPM test only in the dmPAG. The proaversive effects of oCRF in the dmPAG gain further relevance when combined with previous immunohistochemical studies showing that CRF-containing projections from the periventricular hypothalamic system arch dorsomedially to the PAG, which could function as an important relay station in the midbrain tectum for avoidance behaviors.     

Impact of gamma-oscillatory inhibition on the signal transmission of a cortical pyramidal neuron

Networks of synchronized fast-spiking interneurons are thought to be key elements in the generation of gamma (γ) oscillations (30–80 Hz) in the brain. We examined how such γ-oscillatory inhibition regulates the output of a cortical pyramidal cell. Specifically, we modeled a situation where a pyramidal cell receives inputs from γ-synchronized fast-spiking inhibitory interneurons. This model successfully reproduced several important aspects of a recent experimental result regarding the γ-inhibitory regulation of pyramidal cellular firing that is presumably associated with the sensation of whisker stimuli. Through an in-depth analysis of this model system, we show that there is an obvious rhythmic gating effect of the γ-oscillated interneuron networks on the pyramidal neuron’s signal transmission. This effect is further illustrated by the interactions of this interneuron network and the pyramidal neuron. Prominent power in the γ frequency range can emerge provided that there are appropriate delays on the excitatory connections and inhibitory synaptic conductance between interneurons. These results indicate that interactions between excitation and inhibition are critical for the modulation of coherence and oscillation frequency of network activities.     

Perivitelline space of marsupial oocytes: Extracellular matrix of the unfertilized oocyte and formation of a cortical granule envelope following the cortical reaction

The purpose of this study was to characterize the structure of the vestments surrounding unfertilized and cortical granule-reacted oocytes from a marsupial, the grey short-tailed opossum Monodelphis domestica and to determine if a cortical granule envelope (CGE) forms in the perivitelline space (PVS) following the cortical reaction. Unfertilized oocytes collected from mature ovarian follicles and oviducal oocytes that had undergone a cortical reaction were fixed for electron microscopy in the presence of ruthenium red which stabilizes extracellular matrices (ECM) and facilitates demonstration of a CGE. Unfertilized oocytes were surrounded by a zona pellucida and had a PVS which contained a thick ECM comprised of granules and filaments. This matrix appeared to attach to the oolemma and was structurally similar to matrices reported previously in the PVS of unfertilized oocytes from eutherian mammals and two other marsupials, the Virginia opossum and the fat-tailed dunnart. The cortex of unfertilized oocytes contained cortical granules which were absent in oocytes recovered from the oviducts of mated females. Oviducal oocytes which lacked cortical granules exhibited a new coat within the PVS between the zona pellucida and the tips of the oocyte microvilli. This coat, the CGE, appeared structurally similar to CGEs described previously around fertilized eutherian oocytes. The CGE of the grey short-tailed opossum is approximately 1 μm thick and is made up of numerous small dense granules. The coats of the opossum oocyte are compared to those present around other marsupial and eutherian oocytes. © 1995 Wiley-Liss, Inc.     

Development of cortical vesicles in Sicyonia ingentis ova: their heterogeneity and role in elaboration of the hatching envelope

In the marine shrimp Sicyonia ingentis, ova lack cortical vesicles at spawning. Previous ultrastructural studies suggested that two different populations of cortical vesicles (dense vesicles and the ring vesicles) appear within 30 min post-spawning. These vesicles undergo sequential exocytosis (exocytosis of the dense vesicles followed by exocytosis of the ring vesicles) that leads to the formation of a hatching envelope around the ovum (see Pillai and Clark: Tissue & Cell 20:941-52, 1988). In the present study, lectins were used as molecular probes to study the development of cortical vesicles subsequent to spawning and the role of these vesicles in formation and elaboration of the hatching envelope. Isolated envelopes were screened with 11 different lectins to determine what group(s) were specific to the envelope glycoconjugates; Concanavalin A (Con A), Griffonia simplicifolia (GS II), Lens culinaris (LCA), and wheat germ agglutinin (WGA) bound to the envelopes. FITC-lectin studies of sectioned ova (fixed at various time points after spawning) utilizing WGA and LCA showed different labelling patterns. Data obtained at the light microscopical level indicated that WGA was specific to the dense vesicles and the outer portion of the envelope, while LCA exhibited specificity for the ring vesicles and the inner portion of the envelope. At the ultrastructural level, gold-LCA labelling was seen associated with the cisternal elements (containing ring-shaped structures), ring vesicles, and the inner layer of the fully formed envelope. These data demonstrated that 1) the ring vesicles are formed by fusion of cisternal elements containing ring-shaped structures; 2) the two species of cortical vesicles are chemically heterogeneous; and 3) the components of each type of vesicle contribute to different integral parts (the outer and inner layers) of the hatching envelope.     

Learning-induced modulation of oscillatory activities in the mammalian olfactory system: The role of the centrifugal fibres

In the mammalian olfactory system, oscillations related to odour representation have been described in field potential activities. Previous results showed that in olfactory bulb (OB) of awake rats engaged in an olfactory learning, odour presentation produced a decrease of oscillations in gamma frequency range (60-90 Hz) associated with a power increase in beta frequency range (15-40 Hz). This response pattern was strongly amplified in trained animals. The aim of this work was twofold: whether learning also induces similar changes in OB target structures and whether such OB response depends on its centrifugal inputs. Local field potentials (LFPs) were recorded through chronically implanted electrodes in the OB, piriform and enthorhinal cortices of freely moving rats performing an olfactory discrimination. Oscillatory activities characteristics (amplitude, frequency and time-course) were extracted in beta and gamma range by a wavelet analysis. First, we found that odour induced beta oscillatory activity was present not only in the OB, but also in the other olfactory structures. In each recording site, characteristics of the beta oscillatory responses were dependent of odour, structure and learning level. Unilateral section of the olfactory peduncle was made before training, and LFPs were symmetrically recorded in the two bulbs all along the acquisition of the learning task. Data showed that deprivation of centrifugal feedback led to an increase of spontaneous gamma activity. Moreover, under this condition olfactory learning was no longer associated with the typical large beta band. As a whole, learning modulation of the beta oscillatory response in olfactory structures may reflect activity of a distributed functional network involved in odour representation.     

Built for speed: strain in the cartilaginous vertebral columns of sharks

In most bony fishes vertebral column strain during locomotion is almost exclusively in the intervertebral joints, and when these joints move there is the potential to store and release strain energy. Since cartilaginous fishes have poorly mineralized vertebral centra, we tested whether the vertebral bodies undergo substantial strain and thus may be sites of energy storage during locomotion. We measured axial strains of the intervertebral joints and vertebrae in vivo and ex vivo to characterize the dynamic behavior of the vertebral column. We used sonomicrometry to directly measure in vivo and in situ strains of intervertebral joints and vertebrae of Squalus acanthias swimming in a flume. For ex vivo measurements, we used a materials testing system to dynamically bend segments of vertebral column at frequencies ranging from 0.25 to 1.00 Hz and a range of physiologically relevant curvatures, which were determined using a kinematic analysis. The vertebral centra of S. acanthias undergo strain during in vivo volitional movements as well as in situ passive movements. Moreover, when isolated segments of vertebral column were tested during mechanical bending, we measured the same magnitudes of strain. These data support our hypothesis that vertebral column strain in lateral bending is not limited to the intervertebral joints. In histological sections, we found that the vertebral column of S. acanthias has an intracentral canal that is open and covered with a velum layer. An open intracentral canal may indicate that the centra are acting as tunics around some sections of a hydrostat, effectively stiffening the vertebral column. These data suggest that the entire vertebral column of sharks, both joints and centra, is mechanically engaged as a dynamic spring during locomotion.     

On the alignment of cellulose microfibrils by cortical microtubules: A review and a model

Summary The hypothesis that microtubules align microfibrils, termed the alignment hypothesis, states that there is a causal link between the orientation of cortical microtubules and the orientation of nascent microfibrils. I have assessed the generality of this hypothesis by reviewing what is known about the relation between microtubules and microfibrils in a wide group of examples: in algae of the family Characeae,Closterium acerosum, Oocystis solitaria, and certain genera of green coenocytes and in land plant tip-growing cells, xylem, diffusely growing cells, and protoplasts. The salient features about microfibril alignment to emerge are as follows. Cellulose microfibrils can be aligned by cortical microtubules, thus supporting the alignment hypothesis. Alignment of microfibrils can occur independently of microtubules, showing that an alternative to the alignment hypothesis must exist. Microfibril organization is often random, suggesting that self-assembly is insufficient. Microfibril organization differs on different faces of the same cell, suggesting that microfibrils are aligned locally, not with respect to the entire cell. Nascent microfibrils appear to associate tightly with the plasma membrane. To account for these observations, I present a model that posits alignment to be mediated through binding the nascent microfibril. The model, termed templated incorporation, postulates that the nascent microfibril is incorporated into the cell wall by binding to a scaffold that is oriented; further, the scaffold is built and oriented around either already incorporated microfibrils or plasma membrane proteins, or both. The role of cortical microtubules is to bind and orient components of the scaffold at the plasma membrane. In this way, spatial information to align the microfibrils may come from either the cell wall or the cell interior, and microfibril alignment with and without microtubules are subsets of a single mechanism.Dedicated to Professor Brian E. S. Gunning on the occasion of his 65th birthday     

Quinone-induced inhibition of urease: elucidation of its mechanisms by probing thiol groups of the enzyme

In this work we studied the reaction of four quinones, 1,4-benzoquinone (1,4-BQ), 2,5-dimethyl-1,4-benzoquinone (2,5-DM-1,4-BQ), tetrachloro-1,4-benzoquinone (TC-1,4-BQ) and 1,4-naphthoquinone (1,4-NQ) with jack bean urease in phosphate buffer, pH 7.8. The enzyme was allowed to react with different concentrations of the quinones during different incubation times in aerobic conditions. Upon incubation the samples had their residual activities assayed and their thiol content titrated. The titration carried out with use of 5,5'-di-thiobis(2-nitrobenzoic) acid was done to examine the involvement of urease thiol groups in the quinone-induced inhibition. The quinones under investigation showed two distinct patterns of behaviour, one by 1,4-BQ, 2,5-DM-1,4-BQ and TC-1,4-BQ, and the other by 1,4-NQ. The former consisted of a concentration-dependent inactivation of urease where the enzyme-inhibitor equilibrium was achieved in no longer than 10min, and of the residual activity of the enzyme being linearly correlated with the number of modified thiols in urease. We concluded that arylation of the thiols in urease by these quinones resulting in conformational changes in the enzyme molecule is responsible for the inhibition. The other pattern of behaviour observed for 1,4-NQ consisted of time- and concentration-dependent inactivation of urease with a nonlinear residual activity-modified thiols dependence. This suggests that in 1,4-NQ inhibition, in addition to the arylation of thiols, operative are other reactions, most likely oxidations of thiols provoked by 1,4-NQ-catalyzed redox cycling. In terms of the inhibitory strength, the quinones studied formed a series: 1,4-NQ approximately 2,5-DM-1,4-BQ<1,4-BQ相似文献   

Pre-MBT patterning of early gene regulation in Xenopus: the role of the cortical rotation and mesoderm induction

Patterning events that occur before the mid-blastula transition (MBT) and that organize the spatial pattern of gene expression in the animal hemisphere have been analyzed in Xenopus embryos. We present evidence that genes that play a role in dorsoventral specification display different modes of activation. Using early blastomere explants (16–128-cell stage) cultured until gastrula stages, we demonstrate by RT-PCR analysis that the expression of goosecoid (gsc), wnt-8 and brachyury (bra) is dependent on mesoderm induction. In contrast, nodal-related 3 (nr3) and siamois (sia) are expressed in a manner that is independent of mesoderm induction, however their spatially correct activation does require cortical rotation. The pattern of sia and nr3 expression reveals that the animal half of the 16-cell embryo is already distinctly polarized along the dorsoventral axis as a result of rearrangement of the egg structure during cortical rotation. Similar to the antagonistic activity between the ventral and the dorsal mesoderm, the ventral animal blastomeres can attenuate the expression of nr3 and sia in dorsal animal blastomeres. Our data suggest that no Nieuwkoop center activity at the blastula stage is required for the activation of nr3 and sia in vivo.     

Phosphorylated MARCKS: a novel centrosome component that also defines a peripheral subdomain of the cortical actin cap in mouse eggs

MARCKS (myristoylated alanine-rich C-kinase substrate) is a major substrate for protein kinase C (PKC), a kinase that has multiple functions during oocyte maturation and egg activation, for example, spindle function and cytoskeleton reorganization. We examined temporal and spatial changes in p-MARCKS localization during maturation of mouse oocytes and found that p-MARCKS is a novel centrosome component based its co-localization with pericentrin and gamma-tubulin within microtubule organizing centers (MTOCs). Like pericentrin, p-MARCKS staining at the MI spindle poles was asymmetric. Based on this asymmetry, we found that one end of the spindle was preferentially extruded with the first polar body. At MII, however, the spindle poles had symmetrical p-MARCKS staining. p-MARCKS also was enriched in the periphery of the actin cap overlying the MI or MII spindle to form a ring-shaped subdomain. Because phosphorylation of MARCKS modulates its actin crosslinking function, this localization suggests p-MARCKS functions as part of the contractile apparatus during polar body emission. Our finding that an activator of conventional and novel PKC isoforms did not increase the amount of p-MARCKS suggested that an atypical isoform was responsible for MARCKS phosphorylation. Consistent with this idea, immunostaining revealed that the staining patterns of p-MARCKS and the active form of the atypical PKC zeta/lambda isoform(s) were very similar. These results show that p-MARCKS is a novel centrosome component and also defines a previously unrecognized subdomain of the actin cap overlying the spindle.     

Telophase-interphase transition in taxol-treatedTriticum root cells: cortical microtubules appear without the prior presence of a radial perinuclear array

Summary Taxol stabilizes phragmoplast microtubules (Mts) in cytokinetic root cells ofTriticum, causing a delay in the rate of cytokinesis. As a result, the daughter nuclei acquire interphase appearance in mid- to late-cytokinetic taxol-affected cells much earlier than in control cells. Cortical Mts in such cells appear directly in the cell cortex, without the prior organization of a radial perinuclear Mt array as in control cells. These observations suggest that: (a) Whether perinuclear Mt assembly occurs or not in post-telophase cells is a matter of timing between the nuclear cycle and cytokinesis, (b) Mt organizing activity on the daughter nuclei surface is temporal, (c) Cortical Mts can be in situ assembled in the cortex of post-telophase cells of flowering plants without any participation of perinuclear Mts.Abbreviations Mt microtubules - MTOC microtubule organizing centre - DMSO dimethyl sulfoxide - EM electron microscope     

Effect of heterogeneity on the characterization of cell membrane compartments: I. Uniform size and permeability

Observations of the motion of individual molecules in the membrane of a number of different cell types have led to the suggestion that the outer membrane of many eukaryotic cells may be effectively partitioned into microdomains. A major cause of this suggested partitioning is believed to be due to the direct/indirect association of the cytosolic face of the cell membrane with the cortical cytoskeleton. Such intimate association is thought to introduce effective hydrodynamic barriers into the membrane that are capable of frustrating molecular Brownian motion over distance scales greater than the average size of the compartment. To date, the standard analytical method for deducing compartment characteristics has relied on observing the random walk behavior of a labeled lipid or protein at various temporal frequencies and different total lengths of time. Simple theoretical arguments suggest that the presence of restrictive barriers imparts a characteristic turnover to a plot of mean squared displacement versus sampling period that can be interpreted to yield the average dimensions of the compartment expressed as the respective side lengths of a rectangle. In the following series of articles, we used computer simulation methods to investigate how well the conventional analytical strategy coped with heterogeneity in size, shape, and barrier permeability of the cell membrane compartments. We also explored questions relating to the necessary extent of sampling required (with regard to both the recorded time of a single trajectory and the number of trajectories included in the measurement bin) for faithful representation of the actual distribution of compartment sizes found using the SPT technique. In the current investigation, we turned our attention to the analytical characterization of diffusion through cell membrane compartments having both a uniform size and permeability. For this ideal case, we found that (i) an optimum sampling time interval existed for the analysis and (ii) the total length of time for which a trajectory was recorded was a key factor.     

Bursts shape the NMDA-R mediated spike timing dependent plasticity curve: role of burst interspike interval and GABAergic inhibition

Spike timing dependent plasticity (STDP) is a synaptic learning rule where the relative timing between the presynaptic and postsynaptic action potentials determines the sign and strength of synaptic plasticity. In its basic form STDP has an asymmetric form which incorporates both persistent increases and persistent decreases in synaptic strength. The basic form of STDP, however, is not a fixed property and depends on the dendritic location. An asymmetric curve is observed in the distal dendrites, whereas a symmetrical one is observed in the proximal ones. A recent computational study has shown that the transition from the asymmetry to symmetry is due to inhibition under certain conditions. Synapses have also been observed to be unreliable at generating plasticity when excitatory postsynaptic potentials and single spikes are paired at low frequencies. Bursts of spikes, however, are reliably signaled because transmitter release is facilitated. This article presents a two-compartment model of the CA1 pyramidal cell. The model is neurophysiologically plausible with its dynamics resulting from the interplay of many ionic and synaptic currents. Plasticity is measured by a deterministic Ca²⁺ dynamics model which measures the instantaneous calcium level and its time course in the dendrite and change the strength of the synapse accordingly. The model is validated to match the asymmetrical form of STDP from the pairing of a presynaptic (dendritic) and postsynaptic (somatic) spikes as observed experimentally. With the parameter set unchanged the model investigates how pairing of bursts with single spikes and bursts in the presence or absence of inhibition shapes the STDP curve. The model predicts that inhibition strength and frequency are not the only factors of the asymmetry-to-symmetry switch of the STDP curve. Burst interspike interval is another factor. This study is an important first step towards understanding how STDP is affected under natural firing patterns in vivo.     

Flexibility of the endogenous progesterone lactonisation pathway in Aspergillus tamarii KITA: transformation of a series of cortical steroid analogues

A range of cortical steroids have been transformed by the fungus Aspergillus tamarii, which has the ability to convert progesterone to testololactone in high yield through a four step enzymatic pathway. 16alpha,17alpha-Epoxyprogesterone underwent a rare epoxide opening resulting in a unique inversion of stereochemistry to give 16beta-hydroxy-17alpha-oxa-D-homo-androst-4-en-3,17-dione. The metabolism of deoxycorticosterone resulted in relatively efficient transformation to testololactone with no other products isolated. Transformation of 17alpha-hydroxyprogesterone yielded 17alpha-oxa-D-homo-androst-1,4-dien-3,17-dione, a lactone not previously isolated from A. tamarii. Cortexolone was transformed to the 20(R)-alcohol with no further transformation observed. Evidence is also presented for the presence of a highly flexible but stereospecific keto-reductase. All metabolites were isolated by column chromatography and were identified by 1H, 13C NMR, DEPT analysis and other spectroscopic data.     

Aggregation pattern of individuals and the outcomes of competition within and between species: Differential equation models

The influence of spatial distribution pattern on the outcomes of intra- and interspecific competition is studied theoretically. The models developed are the generalized logistic andVolterra equations, whereLloyd 's indices of intra- and interspecies mean crowding were incorporated with their assumed linear relationship to mean density in order to express the intensity of crowding which is really effective to the existing individuals. It is shown that while the increasing patchiness of distribution has a pronounced effect of promoting the intraspecific competition and lowering the equilibrium density for individual populations, it generally relaxes the interspecific competition, making it easy for different species sharing the same niche, which would otherwise be incompatible, to coexist stably. These models thus provide a simplest theoretical basis to explain why many insect populations in nature are kept relatively rare in number and why a number of allied species often coexist freely sharing the same resource, against the “competitive exclusion principle” deduced from the originalVolterra equations.     

Detection of Short Protein Coding Regions within the Cyanobacterium Genome: Application of the Hidden Markov Model

The gene-finding programs developed so far have not paid muchattention to the detection of short protein coding regions (CDSs).However, the detection of short CDSs is important for the studyof photosynthesis. We utilized GeneHacker, a gene-finding programbased on the hidden Markov model (HMM), to detect short CDSs(from 90 to 300 bases) in a 1.0 mega contiguous sequence ofcyanobacterium Synechocystis sp. strain PCC6803 which carriesa complete set of genes for oxygenic photosynthesis. GeneHackerdiffers from other gene-finding programs based on the HMM inthat it utilizes di-codon statistics as well. GeneHacker successfullydetected seven out of the eight short CDSs annotated in thissequence and was clearly superior to GeneMark in this rangeof length. GeneHacker detected 94 potentially new CDSs, 9 ofwhich have counterparts in the genetic databases. Four of thenine CDSs were less than 150 bases and were photosynthesis-relatedgenes. The results show the effectiveness of GeneHacker in detectingvery short CDSs corresponding to genes.     

Fine structure of the mammalian renal capsule: The atypical smooth muscle cell and its functional meaning

Summary The present electron microscopic study on the fine structure of the renal capsule of some mammals (mouse, rat, mole, guinea pig and rabbit) shows that, although there are some variations in the structure, the general morphology is the same.The renal capsule of these animals consists of two layers, a connective tissue layer and an atypical smooth muscle cell layer, and is bound to the renal parenchyma by a thin peritubular loose connective tissue. The atypical smooth muscle cell is characterized by the existence of fine cytoplasmic filaments usually arranged along the long axis of the cell, and the cells also show a complicated interlocking among adjacent cells. The atypical smooth muscle cells gradually undergo a transition to fibroblasts of the upper connective tissue layer, losing their similarities to smooth muscle cells.When intrarenal pressure is elevated and the renal capsule is distended, the intercellular space among interdigitating or overlapping atypical smooth muscle cells is extensively dilated.Tracers such as horseradish peroxidase and ferritin injected intravenously or intraperitoneally can transverse the renal capsule.From the present study, it is concluded that the renal capsule of mammals possesses common structures, and contains atypical smooth muscle cells. These morphological characteristics suggest that the renal capsule could play a certain role related to the renal function.The author wishes to acknowledge the helpful advices of Prof. T. Yamamoto     

Trypanosoma lewisi: antibody classes which mediate precipitation, agglutination, and the inhibition of reproduction

Sera from Trypanosoma lewisi-infected and uninfected rats were applied to Protein A-Sepharose CL-4B columns. The absorbed fractions of antisera which contained only IgG molecules were reacted in microimmunodiffusion analyses with the exoantigens of T. lewisi in plasma collected from irradiated infected rats, and formed one precipitin line. These sera were also applied to T. lewisi extract immunoabsorbent columns and bound proteins were eluted and analyzed by immunodiffusion against antisera specific for rat immunoglobulins. IgG₁, IgG_2a, IgG_2b, IgG_2c, and IgM were absorbed by the immuno-absorbent columns. Absorption of the rat antisera with anti-rat IgG or anti-rat IgM removed one of the two precipitin lines against extracts prepared from parasites collected from irradiated infected animals. The absorbed IgG fractions and nonabsorbed fractions of antisera which were collected after Protein A-Sepharose CL-4B column chromatography agglutinated trypanosomes. After treatment of antisera with 2-mercaptoethanol, the agglutinin titers were lower than those of the control antisera suggesting both IgG and IgM are involved in the agglutination. The ablastic activity of the fractions eluted from Protein A-Sepharose CL-4B Chromatographic columns was assayed in cultures of bloodstream forms ofT. lewisi. Ablastic activity of proteins of antisera absorbed by the columns was demonstrated indicating they belonged to the IgG class of antibodies.     

Valproic acid induces functional heat-shock protein 70 via Class I histone deacetylase inhibition in cortical neurons: a potential role of Sp1 acetylation

Neuroprotective properties of the mood stabilizer valproic acid (VPA) are implicated in its therapeutic efficacy. Heat-shock protein 70 (HSP70) is a molecular chaperone, neuroprotective and anti-inflammatory agent. This study aimed to investigate underlying mechanisms and functional significance of HSP70 induction by VPA in rat cortical neurons. VPA treatment markedly up-regulated HSP70 protein levels, and this was accompanied by increased HSP70 mRNA levels and promoter hyperacetylation and activity. Other HDAC inhibitors – sodium butyrate, trichostatin A, and Class I HDAC-specific inhibitors MS-275 and apicidin, – all mimicked the ability of VPA to induce HSP70. Pre-treatment with phosphatidylinositol 3-kinase inhibitors or an Akt inhibitor attenuated HSP70 induction by VPA and other HDAC inhibitors. VPA treatment increased Sp1 acetylation, and a Sp1 inhibitor, mithramycin, abolished the induction of HSP70 by HDAC inhibitors. Moreover, VPA promoted the association of Sp1 with the histone acetyltransferases p300 and recruitment of p300 to the HSP70 promoter. Further, VPA-induced neuroprotection against glutamate excitotoxicity was prevented by blocking HSP70 induction. Taken together, the data suggest that the phosphatidylinositol 3-kinase/Akt pathway and Sp1 are likely involved in HSP70 induction by HDAC inhibitors, and induction of HSP70 by VPA in cortical neurons may contribute to its neuroprotective and therapeutic effects.