Cortical Plasticity Induced by Spike-Triggered Microstimulation in Primate Somatosensory Cortex

Electrical stimulation of the nervous system for therapeutic purposes, such as deep brain stimulation in the treatment of Parkinson’s disease, has been used for decades. Recently, increased attention has focused on using microstimulation to restore functions as diverse as somatosensation and memory. However, how microstimulation changes the neural substrate is still not fully understood. Microstimulation may cause cortical changes that could either compete with or complement natural neural processes, and could result in neuroplastic changes rendering the region dysfunctional or even epileptic. As part of our efforts to produce neuroprosthetic devices and to further study the effects of microstimulation on the cortex, we stimulated and recorded from microelectrode arrays in the hand area of the primary somatosensory cortex (area 1) in two awake macaque monkeys. We applied a simple neuroprosthetic microstimulation protocol to a pair of electrodes in the area 1 array, using either random pulses or pulses time-locked to the recorded spiking activity of a reference neuron. This setup was replicated using a computer model of the thalamocortical system, which consisted of 1980 spiking neurons distributed among six cortical layers and two thalamic nuclei. Experimentally, we found that spike-triggered microstimulation induced cortical plasticity, as shown by increased unit-pair mutual information, while random microstimulation did not. In addition, there was an increased response to touch following spike-triggered microstimulation, along with decreased neural variability. The computer model successfully reproduced both qualitative and quantitative aspects of the experimental findings. The physiological findings of this study suggest that even simple microstimulation protocols can be used to increase somatosensory information flow.     

Purification and spectroscopic properties of 124-kDa oat phytochrome

A simplified procedure for the isolation and purification of 124-kDa phytochrome from etiolated Avena seedlings has been developed using the method of ammonium sulfate back-extraction. After hydroxyapatite chromatography of seedling tissue extracts, the pooled phytochrome was subjected to ammonium sulfate back-extraction instead of the usual application to an Affi-Gel Blue column. The resulting phytochrome had specific absorbance ratios (SAR = A666/A280) ranging from 0.85 to 0.95. Subsequent Bio-Gel filtration chromatography yielded highly pure 124-kDa phytochrome with SAR values ranging from 0.99 to 1.13. The absorption maxima of 124-kDa phytochrome were at 280, 379, and 666 nm for the red absorbing form of phytochrome (Pr) and at 280, 400 and 730 nm for the far-red absorbing form (Pfr). The A730/A673 ratio in Pfr was found to be 1.5 to 1.6. The mole fraction of Pfr under red light photoequilibrium was 0.88. No dark reversion was detected within 5 h at 3 degrees C. A photoreversible far-uv-circular dichroism was observable with all phytochrome preparations examined. Fluorescence and phosphorescence lifetimes were measured to further characterize the differences between the phytochromes prepared under different conditions. The Trp fluorescence and phosphorescence lifetimes of Pr and Pfr with the chromophore "X", probably polyphenolic in nature, were significantly shorter than those of phytochrome without the contaminant X. The short lifetime of the fluorescence of the Pr chromophore is attributable to X in the former.     

Preparation of base-modified nucleosides suitable for non-radioactive label attachment and their incorporation into synthetic oligodeoxyribonucleotides.

A very mild and efficient procedure has been developed for the preparation of C-5 substituted deoxyuridines. The substituent carries a masked primary aliphatic amino group. These compounds are readily converted into their phosphoramidites and can be used to prepare oligonucleotides carrying one or more aliphatic amino groups. Fluorescein isothiocyanate coupled to these compounds gives oligonucleotide probes carrying multiple fluorescein labels. These compounds have a free 5'-hydroxy group enabling additional 5'- end radioactive labelling for evaluation of their hybridization characteristics. It was found that oligonucleotides carrying a long (11 atom) linker arm to the fluorescein hybridize more efficiently to mRNA than those carrying a short (4 atom) arm. The long linker arm derivatives are comparable to underivatized oligonucleotides in hybridizing to mRNA.     

龟鳖类寄生血簇虫六新种

血簇虫(Haemogregarina Danilewsky,1885)属真球虫目(Eucoccidia)血簇虫科(Haemogregarinidae),这一属的寄生虫,其寄主以爬行动物为主,两栖动物和鱼类也有寄生。至今已记载有300余种。龟鳖类的血簇虫研究,国内尚无报道。作者在1984年3月—1985年3月,对我国龟鳖类寄生的血簇虫进行了调查研究,共解剖检查了中华     

Chromosomes and their relationship to nuclear components during the cell cycle in Chinese hamster cells

Summary Chromosomes and their relationship to nuclear components during various phases of the cell cycle were studied with different fixation, embedding, and enzyme techniques. The results showed that interphase chromosomes may have oriented in such a way that a given locus became associated with the nuclear membrane. Some chromosomes also appeared to interact with the nucleolus. The nuclear matrix materials, however, were distributed between the chromosomes and formed a delineating boundary for the chromosomes. These matrix materials, furthermore, formed channel-like structures within the nucleus and towards the cytoplasm through their interaction with nuclear pore complexes. During mitosis, chromosomes were encapsulated with material that appeared to be derived from the matrix, disintegrated residues and fragments of the nuclear envelope, the lamina, and nucleolar material. These chromosome-associated materials seen in mitosis appeared to serve as foci for formation of new nuclear components in subsequent interphase.     

寡糖的荧光标记高效液相色谱分析

 利用氨化还原的方法把高量子产率的荧光标记物——α-萘胺,接到异麦芽糖寡糖的还原端。用硅胶薄层色谱、荧光光谱及快原子轰击质谱证实反应物的完全性及其结构。高效液相色谱用Micropak si5硅胶柱,以乙腈-水(含0.05％三乙胺)为梯度洗脱液可使含有二到九个糖残基的异麦芽糖寡糖的α-萘胺衍生物全部分离。本法对异麦芽糖二糖的荧光检测灵敏测度为2.35Pmol。     

Comparison of theN-glycoloylneuraminic andN-acetylneuraminic acid content of platelets and their precursors using high performance anion exchange chromatography

N-Acetylneuraminic acid (Neu5Ac) andN-glycoloylneuraminic acid (Neu5Gc) are distributed widely in nature. Using a Carbopac PA-1 anion exchange column, we have determined the ratios of Neu5Ac and Neu5Gc in hydrolysates of platelets and their precursors: a rat promegakaryoblastic (RPM) cell line and a human megakaryoblastic leukemia cell line (MEG-01). The ratio of Neu5Gc:Neu5Ac in cultured RPM cells is 16:1, whereas in platelet rich plasma and cultured MEG-01 cells it is 1:38 and 1:28, respectively. The nature of these sialic acids from RPM cells was verified using thin layer chromatography and liquid secondary ion mass spectrometry. The relevance of increased Neu5Gc levels in early stages of development is discussed.Abbreviations Neu5Ac N-acetylneuraminic acid - Neu5Gc N-glycoloylneuraminic acid - RPM rat promegakaryoblast - MEG-01 human megakaryoblastic leukaemia cell line - PAD pulsed amperometric detection - WGA wheat germ agglutinin - FCS foetal calf serum - PPEADF phosphatidylethanolamine dipalmitoyl - LSIMS liquid secondary ion mass spectrometry - HPAEC high performance anion exchange chromatography - TBA thiobarbituric acid     

A photoreversible conformational change in 124 kDa Avena phytochrome

Tryptophan (Trp) fluorescence quenching of phytochrome has been studied using anionic, cationic and neutral quenchers, I-, Cs+ and acrylamide, respectively, in an effort to understand the molecular differences between the Pr and Pfr forms. The data have been analyzed using both Stern-Volmer and modified Stern-Volmer kinetic treatments. The anionic quencher, I-, was proven to be an ineffective quencher with Stern-Volmer constants, Ksv, of 0.60 and 0.63 M-1, respectively, for the Pr and Pfr forms of phytochrome. The cationic quencher, Cs+, showed about a 2-fold difference in the Ksv of Pr and Pfr, indicating a significant change in the fluorescent Trp environments during the Pr to Pfr phototransformation. However, only 25-37% of the fluorescent Trp residues were accessible to the cationic quencher. Most of the fluorescent Trp residues were accessible to acrylamide, but the quenching by acrylamide was indistinguishable for the Pr and Pfr forms. An additional quenching by acrylamide after a saturated quenching with Cs+ showed more than 40% increase in the Ksv of Pfr over Pr. These observations, along with the finding of two distinct components in the Trp fluorescence lifetime, indicate the existence of Trp residues in at least two different sets of environments in the phytochrome protein. The two components of the fluorescence had lifetimes of 1.1 ns (major) and 4.7 ns (minor) for Pr and 0.9 ns (major) and 4.6 ns (minor) for Pfr. Fluorescence quenching was found to be both static and dynamic as the Stern-Volmer constants for the steady-state fluorescence quenching were higher than for the dynamic fluorescence quenching. Based on the quenching results, in combination with the location of Trp residues in the primary structure, we conclude that the Pr to Pfr phototransformation involves a significant conformation change in the phytochrome molecule, preferentially in the 74 kDa chromophore-bearing domain.     

Segregation of Deoxyribonucleic Acid in Bacteria: Association of the Segregating Unit with the Cell Envelope

Cells of the gram-positive organism Lactobacillus acidophilus R-26 were labeled with ³H-thymine to measure the segregation of radioactive deoxyribonucleic acid (DNA) into daugher cells. Such cells were found to contain 8 conserved units of DNA which would correspond to two replicating chromosomes per cell. Fluorescent antibody (FA) against this organism was used to demonstrate that portions of the cell surface (2 to 4 units per cell) were conserved during growth and division. The permanent association of DNA with these conserved cell surface units was measured by combining autoradiography with FA techniques. DNA synthesized immediately before FA labeling was not associated with the fluorescent cell surface, whereas DNA synthesized a generation previously was. The results are consistent with a model in which DNA becomes permanently fixed to the cell surface when it is first used as a template.