Spike discharges of skeletomotor neurons during random noise modulated transmembrane current stimulation and muscle stretch

 Spike discharges of skeletomotor neurons innervating triceps surae muscles elicited by white noise modulated transmembrane current stimulation and muscle stretch were studied in decerebrated cats. The white noise modulated current intensity ranged from 4.3 to 63.2 nA peak-to-peak, while muscle stretches ranged from 100 μm to 4.26 mm peak-to-peak. The neuronal responses were studied by averaging the muscle length records centered at the skeletomotor action potentials (peri-spike average, PSA) and by Wiener analysis. Skeletomotor spikes appeared after a sharp peak in PSA of the injected current, preceded by a longer-lasting smaller wavelet of either depolarizing or hyperpolarizing direction. The PSA amplitude was not related to the injected current amplitude nor showed any differences related to the motor unit type. The PSA amplitudes were virtually independent of the stretching amplitude σ, after an initial increase with stretching amplitudes in the range of 15–40 μm (S.D.), or 100–270 μm peak-to-peak.Analyses of cross-spectra indicated a small or absent increase in gain with frequency in response to injected current, but about 20 dB/decade in the range 10–100 Hz in response to muscle stretch. The peaks of both Wiener kernels in response to current injection appear to decrease with the amplitude of injected current, but this decrease was not statistically significant. The narrow first-order kernels suggest that the transfer function between the current input and spike discharge is lowpass with a wide passband, i.e. there is very little change in dynamics. The values of the second-order kernels appear to be nonzero only along the main diagonal. This is characteristic of a simple Hammerstein type cascade, i.e. a zero memory nonlinearity followed by a linear system. Small values of second-order kernels away from the origin and narrow first-order kernels suggest that the linear cascade contributes very little to the overall dynamic response.In contrast to Wiener kernels found in response to current injection, the Wiener kernels in response to stretch showed a decreasing trend with stretch amplitude. The size of the second-order kernels decreased to a somewhat larger extent with input amplitude than that of the first-order kernels, indicating an amplitude-dependent nonlinearity. Overall, the transformation between length and spike output was described as an LNNL cascade with second-order nonlinearities. Received: 1 April 1993/Accepted in revised form: 24 March 1994     

Modulation of Intracellular Cyclic AMP Levels by Different Human Dopamine D4 Receptor Variants

Abstract: To investigate whether polymorphic forms of the human dopamine D4 receptor have different functional characteristics, we have stably expressed cDNAs of the D4.2, D4.4, and D4.7 isoforms in several cell lines. Chinese hamster ovary CHO-K1 cell lines expressing D4 receptor variants displayed pharmacological profiles that were in close agreement with previous data from transiently expressed D4 receptors in COS-7 cells. Dopamine stimulation of the D4 receptors resulted in a concentration-dependent inhibition of the forskolin-stimulated cyclic AMP (cAMP) levels. The potency of dopamine to inhibit cAMP formation was about twofold reduced for D4.7 (EC₅₀ of ∼37 n M ) compared with the D4.2 and D4.4 variants (EC₅₀ of ∼16 n M ). Antagonists block the dopamine-mediated inhibition of cAMP formation with a rank order of potency of emonapride > haloperidol = clozapine ≫ raclopride. There was no obvious correlation between the efficacy of inhibition of forskolin-stimulated cAMP levels and the D4 subtypes. Dopamine could completely reverse prostaglandin E₂-stimulated cAMP levels for all three D4 receptor variants. Deletion of the repeat sequence does not affect functional activity of the receptor. The data presented indicate that the polymorphic repeat sequence causes only small changes in the ability of the D4 receptor to block cAMP production in CHO cells.     

The replication initiator operon of promiscuous plasmid RK2 encodes a gene that complements an Escherichia coli mutant defective in single-stranded DNA-binding protein.

The amino acid sequence of the 13-kDa polypeptide (P116) encoded by the first gene of the trfA operon of IncP plasmid RK2 shows significant similarity to several known single-stranded DNA-binding proteins. We found that unregulated expression of this gene from its natural promoter (trfAp) or induced expression from a strong heterologous promoter (trcp) was sufficient to complement the temperature-sensitive growth phenotype of an Escherichia coli ssb-1 mutant. The RK2 ssb gene is the first example of a plasmid single-stranded DNA-binding protein-encoding gene that is coregulated with replication functions, indicating a possible role in plasmid replication.     

Structure-activity relationships of pyrazole-4-carbodithioates as antibacterials against methicillin–resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of serious hospital-acquired infections and is responsible for significant morbidity and mortality in residential care facilities. New agents against MRSA are needed to combat rising resistance to current antibiotics. We recently reported 5-hydroxy-3-methyl-1-phenyl-1H-pyrazole-4-carbodithioate (HMPC) as a new bacteriostatic agent against MRSA that appears to act via a novel mechanism. Here, twenty nine analogs of HMPC were synthesized, their anti-MRSA structure-activity relationships evaluated and selectivity versus human HKC-8 cells determined. Minimum inhibitory concentrations (MIC) ranged from 0.5 to 64?μg/mL and up to 16-fold selectivity was achieved. The 4-carbodithioate function was found to be essential for activity but non-specific reactivity was ruled out as a contributor to antibacterial action. The study supports further work aimed at elucidating the molecular targets of this interesting new class of anti-MRSA agents.     

Simulation of direct shear tests on rooted and non-rooted soil using finite element analysis

The finite element (FE) method has been used in recent years to simulate overturning processes in trees and to better comprehend plant anchorage mechanics. We aimed at understanding the fundamental mechanisms of root-soil reinforcement by simulating direct shear of rooted and non-rooted soil. Two- (2D) and three-dimensional (3D) FE simulations of direct shear box tests were carried out using readily available software for routine strength assessment of the root-soil composite. Both rooted and non-rooted blocks of soil were modelled using a simplified model of root distribution and root material properties representative of real roots. Linear elastic behaviour was assumed for roots and the soil was modelled as an ideally plastic medium. FE analysis showed that direct shear tests were dependent on the material properties specified for both the soil and roots. 2D and 3D simulations of direct shear of non-rooted soil produced similar results and any differences between 2D and 3D simulations could be explained with regard to the spatial complexity of roots used in the root distribution model. The application of FE methods was verified through direct shear tests on soil with analogue roots and the results compared to in situ tests on rooted soil in field conditions.     

Bone morphogenetic protein (BMP)1-3 enhances bone repair

Members of the astacin family of metalloproteinases such as human bone morphogenetic protein 1 (BMP-1) regulate morphogenesis by processing precursors to mature functional extracellular matrix (ECM) proteins and several growth factors including TGFβ, BMP2, BMP4 and GFD8. We have recently discovered that BMP1-3 isoform of the Bmp-1 gene circulates in the human plasma and is significantly increased in patients with acute bone fracture. We hypothesized that circulating BMP1-3 might have an important role in bone repair and serve as a novel bone biomarker. When administered systemically to rats with a long bone fracture and locally to rabbits with a critical size defect of the ulna, recombinant human BMP1-3 enhanced bone healing. In contrast, neutralization of the endogenous BMP1-3 by a specific polyclonal antibody delayed the bone union. Invitro BMP1-3 increased the expression of collagen type I and osteocalcin in MC3T3-E₁ osteoblast like cells, and enhanced the formation of mineralized bone nodules from bone marrow mesenchymal stem cells. We suggest that BMP1-3 is a novel systemic regulator of bone repair.     

Brain Cytochrome Oxidase in Alzheimer''s Disease

A recent demonstration of markedly reduced (-50%) activity of cytochrome oxidase (CO; complex 4), the terminal enzyme of the mitochondrial enzyme transport chain, in platelets of patients with Alzheimer's disease (AD) suggested the possibility of a systemic and etiologically fundamental CO defect in AD. To determine whether a CO deficiency occurs in AD brain, we measured the activity of CO in homogenates of autopsied brain regions of 19 patients with AD and 30 controls matched with respect to age, postmortem time, sex, and, as indices of agonal status, brain pH and lactic acid concentration. Mean CO activity in AD brain was reduced in frontal (-26%: p less than 0.01), temporal (-17%; p less than 0.05), and parietal (-16%; not significant, p = 0.055) cortices. In occipital cortex and putamen, mean CO levels were normal, whereas in hippocampus, CO activity, on average, was nonsignificantly elevated (20%). The reduction of CO activity, which is tightly coupled to neuronal metabolic activity, could be explained by hypofunction of neurons, neuronal or mitochondrial loss, or possibly by a more primary, but region-specific, defect in the enzyme itself. The absence of a CO activity reduction in all of the examined brain areas does not support the notion of a generalized brain CO abnormality. Although the functional significance of a 16-26% cerebral cortical CO deficit in human brain is not known, a deficiency of this key energy-metabolizing enzyme could reduce energy stores and thereby contribute to the brain dysfunction and neurodegenerative processes in AD.     

Characterization of the Variability of Epstein-Barr Virus Genes in Nasopharyngeal Biopsies: Potential Predictors for Carcinoma Progression

Epstein-Barr virus (EBV) infection is a significant factor in the pathogenesis of nasopharyngeal carcinoma, especially in the undifferentiated carcinoma of nasopharyngeal type (UCNT, World Health Organization type III), which is the dominant histopathological type in high-risk areas. The major EBV oncogene is latent membrane protein 1 (LMP1). LMP1 gene shows variability with different tumorigenic and immunogenic potentials. EBV nuclear antigen 1 (EBNA1) regulates progression of EBV-related tumors; however, the influence of EBNA1 sequence variability on tumor pathogenesis is controversial. The aims of this study were to characterize polymorphisms of EBV genes in non-endemic nasopharyngeal carcinoma biopsies and to investigate potential sequence patterns that correlate with the clinical presentation of nasopharyngeal carcinoma. In total, 116 tumor biopsies of undifferentiated carcinoma of nasopharyngeal type (UCNT), collected from 2008 to 2014, were evaluated in this study. The genes EBNA2, LMP1, and EBNA1 were amplified using nested-PCR. EBNA2 genotyping was performed by visualization of PCR products using gel electrophoresis. Investigation of LMP1 and EBNA1 included sequence, phylogenetic, and statistical analyses. The presence of EBV DNA was significantly distributed between TNM stages. LMP1 variability showed six variants, with the detection of the first China1 and North Carolina variants in European nasopharyngeal carcinoma biopsies. Newly discovered variants Srb1 and Srb2 were UCNT-specific LMP1 polymorphisms. The B95-8 and North Carolina variants are possible predictors for favorable TNM stages. In contrast, deletions in LMP1 are possible risk factors for the most disfavorable TNM stage, independent of EBNA2 or EBNA1 variability. A newly discovered EBNA1 subvariant, P-thr-sv-5, could be a potential diagnostic marker, as it represented a UCNT-specific EBNA1 subvariant. A particular combination of EBNA2, LMP1, and EBNA1 polymorphisms, type 1/Med/P-thr was identified as a possible risk factor for TNM stage IVB or progression to the N3 stage.