The effects of local perfusion of DAMGO on extracellular GABA and glutamate concentrations in the rostral ventromedial medulla

Electrophysiological data suggest an involvement of rostral ventromedial medulla (RVM) GABA and glutamate (GLU) neurons in morphine analgesia. Direct evidence that extracellular concentrations of GABA or GLU are altered in response to mu opioid receptor (MOP-R) activation is, however, lacking. We used in vivo microdialysis to investigate this issue. Basal GABA overflow increased in response to intra-RVM perfusion of KCl (60 mmol/L). Reverse microdialysis of the MOP-R agonist d -Ala(2),NMePhe(4),Gly-ol(5)]enkephalin (DAMGO) (20–500 μmol/L) produced a concentration-dependent decrease of RVM GABA overflow. Behavioral testing revealed that concentrations that decreased GABA levels increased thermal withdrawal thresholds. A lower agonist concentration that did not increase GABA failed to alter thermal thresholds. DAMGO did not alter GLU concentrations. However, KCl also failed to modify GLU release. Since rapid, transporter-mediated uptake may mask the detection of changes in GLU release, the selective excitatory amino acid transporter inhibitor pyrrolidine-2,4-dicarboxylic acid (tPDC, 0.6 mmol/L) was added to the perfusion medium for subsequent studies. tPDC increased GLU concentrations, confirming transport inhibition. KCl increased GLU dialysate levels in the presence of tPDC, demonstrating that transport inhibition permits detection of depolarization-evoked GLU overflow. In the presence of tPDC, DAMGO increased GLU overflow in a concentration-dependent manner. These data demonstrate that MOP-R activation decreases GABA and increases GLU release in the RVM. We hypothesize that the opposing effects of MOP-R on GLU and GABA transmission contribute to opiate antinociception.     

Control of the AcrAB multidrug efflux pump by quorum-sensing regulator SdiA

SdiA is an Escherichia coli protein that regulates cell division in a cell density-dependent, or quorum-sensing, manner. We report that SdiA also controls multidrug resistance by positively regulating the multidrug resistance pump AcrAB. Overproduction of SdiA confers multidrug resistance and increased levels of AcrAB. Conversely, sdiA null mutants are hypersensitive to drugs and have decreased levels of AcrB protein. Our findings provide a link between quorum sensing and multidrug efflux. Combined with previously published reports, our data support a model in which a role of drug efflux pumps is to mediate cell-cell communication in response to cell density. Xenobiotics expelled by pumps may resemble the communication molecules that they normally efflux.     

Simple sequence repeats reveal uneven distribution of genetic diversity in chloroplast genomes of <Emphasis Type="Italic">Brassica oleracea</Emphasis> L. and (<Emphasis Type="Italic">n </Emphasis>= 9) wild relatives

Diversity in the chloroplast genome of 171 accessions representing the Brassica ‘C’ (n = 9) genome, including domesticated and wild B. oleracea and nine inter-fertile related wild species, was investigated using six chloroplast SSR (microsatellite) markers. The lack of diversity detected among 105 cultivated and wild accessions of B. oleracea contrasted starkly with that found within its wild relatives. The vast majority of B. oleracea accessions shared a single haplotype, whereas as many as six haplotypes were detected in two wild species, B. villosa Biv. and B. cretica Lam.. The SSRs proved to be highly polymorphic across haplotypes, with calculated genetic diversity values (H) of 0.23–0.87. In total, 23 different haplotypes were detected in C genome species, with an additional five haplotypes detected in B. rapa L. (A genome n = 10) and another in B. nigra L. (B genome, n = 8). The low chloroplast diversity of B. oleracea is not suggestive of multiple domestication events. The predominant B. oleracea haplotype was also common in B. incana Ten. and present in low frequencies in B. villosa, B. macrocarpa Guss, B. rupestris Raf. and B. cretica. The chloroplast SSRs reveal a wealth of diversity within wild Brassica species that will facilitate further evolutionary and phylogeographic studies of this important crop genus. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Ectopic expression and dynamics of TPM1alpha and TPM1kappa in myofibrils of avian myotubes

From the four known vertebrate tropomyosin genes (designated TPM1, TPM2, TPM3, and TPM4) over 20 isoforms can be generated. The predominant TPM1 isoform, TPM1alpha, is specifically expressed in both skeletal and cardiac muscles. A newly discovered alternatively spliced isoform, TPM1kappa, containing exon 2a instead of exon 2b contained in TPM1alpha, was found to be cardiac specific and developmentally regulated. In this work, we transfected quail skeletal muscle cells with green fluorescent proteins (GFP) coupled to chicken TPM1alpha and chicken TPM1kappa and compared their localizations in premyofibrils and mature myofibrils. We used the technique of fluorescence recovery after photobleaching (FRAP) to compare the dynamics of TPM1alpha and TPM1kappa in myotubes. TPM1alpha and TPM1kappa incorporated into premyofibrils, nascent myofibrils, and mature myofibrils of quail myotubes in identical patterns. The two tropomyosin isoforms have a higher exchange rate in premyofibrils than in mature myofibrils. F-actin and muscle tropomyosin are present in the same fibers at all three stages of myofibrillogenesis (premyofibrils, nascent myofibrils, mature myofibrils). In contrast, the tropomyosin-binding molecule nebulin is not present in the initial premyofibrils. Nebulin is gradually added during myofibrillogenesis, becoming fully localized in striated patterns by the mature myofibril stage. A model of thin filament formation is proposed to explain the increased stability of tropomyosin in mature myofibrils. These experiments are supportive of a maturing thin filament and stepwise model of myofibrillogenesis (premyofibrils to nascent myofibrils to mature myofibrils), and are inconsistent with models that postulate the immediate appearance of fully formed thin filaments or myofibrils.     

Abnormal sympathoadrenal development and systemic hypotension in PHD3-/- mice

Cell culture studies have implicated the oxygen-sensitive hypoxia-inducible factor (HIF) prolyl hydroxylase PHD3 in the regulation of neuronal apoptosis. To better understand this function in vivo, we have created PHD3(-/-) mice and analyzed the neuronal phenotype. Reduced apoptosis in superior cervical ganglion (SCG) neurons cultured from PHD3(-/-) mice is associated with an increase in the number of cells in the SCG, as well as in the adrenal medulla and carotid body. Genetic analysis by intercrossing PHD3(-/-) mice with HIF-1a(+/-) and HIF-2a(+/-) mice demonstrated an interaction with HIF-2alpha but not HIF-1alpha, supporting the nonredundant involvement of a PHD3-HIF-2alpha pathway in the regulation of sympathoadrenal development. Despite the increased number of cells, the sympathoadrenal system appeared hypofunctional in PHD3(-/-) mice, with reduced target tissue innervation, adrenal medullary secretory capacity, sympathoadrenal responses, and systemic blood pressure. These observations suggest that the role of PHD3 in sympathoadrenal development extends beyond simple control of cell survival and organ mass, with functional PHD3 being required for proper anatomical and physiological integrity of the system. Perturbation of this interface between developmental and adaptive signaling by hypoxic, metabolic, or other stresses could have important effects on key sympathoadrenal functions, such as blood pressure regulation.     

Functional synergy between CD40 ligand and HIV-1 Tat contributes to inflammation: implications in HIV type 1 dementia

HIV type 1 (HIV-1)-associated dementia (HAD) is believed to occur due to aberrant activation of monocyte-derived macrophages and brain-resident microglial cells by viral proteins as well as by the proinflammatory mediators released by infected cells. To investigate the inflammatory aspects of the disease, we examined the levels of soluble CD40L (sCD40L) in paired samples of plasma and cerebrospinal fluid obtained from 25 HIV-infected individuals. A significantly higher level of sCD40L was detected in both cerebrospinal fluid and plasma from HIV-infected patients with cognitive impairment, compared with their nonimpaired counterparts. The contribution of sCD40L to the pathogenesis of HAD was then examined by in vitro experiments. rCD40L synergized with HIV-1 Tat to increase TNF-alpha release from primary human monocytes and microglia, in an NF-kappaB-dependent manner. The mechanistic basis for this synergism was attributed to a Tat-mediated up-regulation of CD40 in monocytes and microglia. Finally, the CD40L-mediated increase in TNF-alpha production by monocytes was shown to be biologically important; immunodepletion experiments revealed that TNF-alpha was essential for the neurotoxic effects of conditioned medium recovered from Tat/CD40L-treated monocytes. Taken together, our results show that CD40 signaling in microglia and monocytes can synergize with the effects of Tat, further amplifying inflammatory processes within the CNS and influencing neuronal survival.     

Extracellular signal-regulated kinase (ERK) participates in the hypercapnia-induced Na,K-ATPase downregulation

Hypercapnia has been shown to impair alveolar fluid reabsorption (AFR) by decreasing Na,K-ATPase activity. Extracellular signal-regulated kinase pathway (ERK) is activated under conditions of cellular stress and has been known to regulate the Na,K-ATPase. Here, we show that hypercapnia leads to ERK activation in a time-dependent manner in alveolar epithelial cells (AEC). Inhibition of ERK by U0126 or siRNA prevented both the hypercapnia-induced Na,K-ATPase endocytosis and impairment of AFR. Moreover, ERK inhibition prevented AMPK activation, a known modulator of hypercapnia-induced Na,K-ATPase endocytosis. Accordingly, these data suggest that hypercapnia-induced Na,K-ATPase endocytosis is dependent on ERK activation in AEC and that ERK plays an important role in hypercapnia-induced impairment of AFR in rat lungs.     

RGS13 regulates germinal center B lymphocytes responsiveness to CXC chemokine ligand (CXCL)12 and CXCL13

Normal lymphoid tissue development and function depend upon directed cell migration. Providing guideposts for cell movement and positioning within lymphoid tissues, chemokines signal through cell surface receptors that couple to heterotrimeric G proteins, which are in turn subject to regulation by regulator of G protein signaling (RGS) proteins. In this study, we report that germinal center B lymphocytes and thymic epithelial cells strongly express one of the RGS family members, RGS13. Located between Rgs1 and Rgs2, Rgs13 spans 42 kb on mouse chromosome 1. Rgs13 encodes a 157-aa protein that shares 82% amino acid identity with its 159-aa human counterpart. In situ hybridization with sense and antisense probes localized Rgs13 expression to the germinal center regions of mouse spleens and Peyer's patches and to the thymus medulla. Affinity-purified RGS13 Abs detected RGS13-expressing cells in the light zone of the germinal center. RGS13 interacted with both Gialpha and Gqalpha and strongly impaired signaling through G(i)-linked signaling pathways, including signaling through the chemokine receptors CXCR4 and CXCR5. Prolonged CD40 signaling up-regulated RGS13 expression in human tonsil B lymphocytes. These results plus previous studies of RGS1 indicate the germinal center B cells use two RGS proteins, RGS1 and RGS13, to regulate their responsiveness to chemokines.