Ethanol and opioid receptor signalling

Summary Ethanol may modulate endogenous opioid systems by disrupting opioid receptor signalling. Low concentrations of ethanol slightly potentiate -opioid receptor binding by increasing receptor B_max, and, in some cases, chronic ethanol exposure decreases the density or affinity of the -opioid receptors. By contrast, high concentrations of ethanol acutely decrease -opioid receptor binding by decreasing receptor affinity, whereas chronic exposure of animals and neuronal cell lines to lower concentrations of ethanol leads to possibly adaptive increases in the density or affinity of the -opioid receptors. In the neuronal cell line NG108-15, ethanol does not up-regulate the -opioid receptor by blocking receptor degradation or endocytosis, but protein synthesis is required for this response. Up-regulation of the -opioid receptor renders ethanol-treated NG108-15 cells 3.5-fold more sensitive to opioid inhibition of adenylyl cyclase. Long-term treatment with ethanol also increases maximal opioid inhibition in NG108-15 cells, possibly by decreasing levels of G_s and its mRNA. Ethanol differentially modulates signal transduction proteins in three additional neuronal cell lines, N18TG2, N4TG1, and N1E-115. Ethanol-treated N18TG2 cells show the least up-regulation of the -opioid receptor, little heterologous desensitization of adenylyl cyclase, and no changes in G_s or G_i. By contrast, ethanol-treated N1E-115 cells show the largest up-regulation of the -opioid receptor, the most heterologous desensitization of adenylyl cyclase, and concentration-dependent decreases in G_s and increases in G_i. Further analysis of these related neuronal cell lines may help to identify the molecular elements that endow some, but not all, neuronal cells with the capacity to adapt to ethanol.     

Ethanol and opioid receptor signalling

Ethanol may modulate endogenous opioid systems by disrupting opioid receptor signalling. Low concentrations of ethanol slightly potentiate mu-opioid receptor binding by increasing receptor Bmax, and, in some cases, chronic ethanol exposure decreases the density or affinity of the mu-opioid receptors. By contrast, high concentrations of ethanol acutely decrease delta-opioid receptor binding by decreasing receptor affinity, whereas chronic exposure of animals and neuronal cell lines to lower concentrations of ethanol leads to possibly adaptive increases in the density or affinity of the delta-opioid receptors. In the neuronal cell line NG108-15, ethanol does not up-regulate the delta-opioid receptor by blocking receptor degradation or endocytosis, but protein synthesis is required for this response. Up-regulation of the delta-opioid receptor renders ethanol-treated NG108-15 cells 3.5-fold more sensitive to opioid inhibition of adenylyl cyclase. Long-term treatment with ethanol also increases maximal opioid inhibition in NG108-15 cells, possibly by decreasing levels of G alpha s and its mRNA. Ethanol differentially modulates signal transduction proteins in three additional neuronal cell lines, N18TG2, N4TG1, and N1E-115. Ethanol-treated N18TG2 cells show the least up-regulation of the delta-opioid receptor, little heterologous desensitization of adenylyl cyclase, and no changes in G alpha s or G alpha i. By contrast, ethanol-treated N1E-115 cells show the largest up-regulation of the delta-opioid receptor, the most heterologous desensitization of adenylyl cyclase, and concentration-dependent decreases in G alpha s and increases in G alpha i. Further analysis of these related neuronal cell lines may help to identify the molecular elements that endow some, but not all, neuronal cells with the capacity to adapt to ethanol.     

The roles of cannabinoid and dopamine receptor systems in neural emotional learning circuits: implications for schizophrenia and addiction

Cannabinoids represent one of the most widely used hallucinogenic drugs and induce profound alterations in sensory perception and emotional processing. Similarly, the dopamine (DA) neurotransmitter system is critical for the central processing of emotion and motivation. Functional disturbances in either of these neurotransmitter systems are well-established correlates of the psychopathological symptoms and behavioral manifestations observed in addiction and schizophrenia. Increasing evidence from the anatomical, pharmacological and behavioral neuroscience fields points to complex functional interactions between these receptor systems at the anatomical, pharmacological and neural systems levels. An important question relates to whether these systems act in an orchestrated manner to produce the emotional processing and sensory perception deficits underlying addiction and schizophrenia. This review describes evidence for functional neural interactions between cannabinoid and DA receptor systems and how disturbances in this neural circuitry may underlie the aberrant emotional learning and processing observed in disorders such as addiction and schizophrenia. Received 20 January 2006; received after revision 14 March 2006; accepted 29 March 2006     

Effects of selective dopamine D1 and D2 antagonists on male rat sexual behavior

The effects of selective dopamine (DA) D1 and D2 antagonists on male rat sexual behavior were investigated. The D1 antagonist (+)SCH-23390, 25-100 micrograms kg-1 s.c. -20 min, and the D2 antagonist raclopride, 0.1-1.6 mg kg-1 s.c., -20 min, decreased both the number of mounts and intromissions preceding ejaculation. No statistically significant effects in the time up to ejaculation or in the time up to the first intromission were noted, whereas both compounds produced a statistically significant increase in the post-ejaculatory interval. The effect can generally be characterized as psychomotor inhibition, and no evidence was obtained for a specific role of DA D1 or D2 receptors in the mediation of male rat sexual behavior.     

Effects of selective dopamine D1 and D2 antagonists on male rat sexual behavior

Summary The effects of selective dopamine (DA) D₁ and D₂ antagonists on male rat sexual behavior were investigated. The D₁ antagonist (+)SCH-23390, 25–100 g kg^–1 s.c. –20 min, and the D₂ antagonist raclopride, 0.1–1.6 mg kg^–1 s.c., –20 min, decreased both the number of mounts and intromissions preceding ejaculation. No statistically significant effects in the time up to ejaculation or in the time up to the first intromission were noted, whereas both compounds produced a statistically significant increase in the post-ejaculatory interval. The effect can generally be characterized as psychomotor inhibition, and no evidence was obtained for a specific role of DA D₁ or D₂ receptors in the mediation of male rat sexual behavior.The expert technical assistance of Ms Elisabeth Wallin is gratefully acknowledged. The figures were skilfully prepared by Ms Madelene Kröning at the Department of Psychology. This study received support from the Bank of Sweden tercentenary Foundation, The Swedish MRC and Wilhelm and Martina Lundgren Foundation.     

Modulation of protein biophysical properties by chemical glycosylation: biochemical insights and biomedical implications

Glycosylation constitutes one of the most important posttranslational modifications employed by biological systems to modulate protein biophysical properties. Due to the direct biochemical and biomedical implications of achieving control over protein stability and function by chemical means, there has been great interest in recent years towards the development of chemical strategies for protein glycosylation. Since current knowledge about glycoprotein biophysics has been mainly derived from the study of naturally glycosylated proteins, chemical glycosylation provides novel insights into its mechanistic understanding by affording control over glycosylation parameters. This review presents a survey of the effects that natural and chemical glycosylation have on the fundamental biophysical properties of proteins (structure, dynamics, stability, and function). This is complemented by a mechanistic discussion of how glycans achieve such effects and discussion of the implications of employing chemical glycosylation as a tool to exert control over protein biophysical properties within biochemical and biomedical applications. Received 15 December 2006; received after revision 28 March 2007; accepted 25 April 2007     

The cross-talk between the urokinase receptor and fMLP receptors regulates the activity of the CXCR4 chemokine receptor

The receptor (CXCR4) for the stromal-derived factor-1 (SDF1) and the urokinase-receptor (uPAR) are up-regulated in various tumors. We show that CXCR4-transfected cells migrate toward SDF1 on collagen (CG) and do not on vitronectin (VN). Co-expression of cell-surface uPAR, which is a VN receptor, impairs SDF1-induced migration on CG and allows migration on VN. Blocking fMLP receptors (fMLP-R), alpha-v integrins or the uPAR region capable to interact with fMLP-Rs, impairs migration of uPAR/CXCR4-transfected cells on VN and restores their migration on CG. uPAR co-expression also reduces the adherence of CXCR4-expressing cells to various components of the extracellular matrix (ECM) and influences the partitioning of beta1 and alpha-v integrins to membrane lipid-rafts, affecting ECM-dependent signaling. uPAR interference in CXCR4 activity has been confirmed in cells from prostate carcinoma. Our results demonstrate that uPAR expression regulates the adhesive and migratory ability of CXCR4-expressing cells through a mechanism involving fMLP receptors and alpha-v integrins.     

Biological properties of synthetic Ser4-Arg8-oxytocin (Ile3-Ser4-Arginine vasopressin): Role of the residue No. 4 in the hormone-pressor receptor interaction

Résumé Les propriétés pharmacologiques de la Ser⁴-Arg⁸-ocytocine (Ser⁴-vasotocine) synthétique ont été étudiées. La substitution en position 4 de la glutamine par la sérine diminue considérablement l'activité pressique de la vasotocine, ce qui montre l'importance de cette position dans les interactions entre les hormones neurohypophysaires et le récepteur vasopressique.

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The authors are indebted to Dr.Albert Jöhl (Ciba-Geigy Laboratories) for a sample of synthetic Ser⁴-Arg⁸-oxytocin. They thank Mrs.Christine Gaullier for ther skilled technical assistance.     

Ras proteins: paradigms for compartmentalised and isoform-specific signalling

Ras GTPases mediate a wide variety of cellular processes by converting a multitude of extracellular stimuli into specific biological responses including proliferation, differentiation and survival. In mammalian cells, three ras genes encode four Ras isoforms (H-Ras, K-Ras4A, K-Ras4B and N-Ras) that are highly homologous but functionally distinct. Differences between the isoforms, including their post-translational modifications and intracellular sorting, mean that Ras has emerged as an important model system of compartmentalised signalling and membrane biology. Ras isoforms in different subcellular locations are proposed to recruit distinct upstream and downstream accessory proteins and activate multiple signalling pathways. Here, we summarise data relating to isoform-specific signalling, its role in disease and the mechanisms promoting compartmentalised signalling. Further understanding of this field will reveal the role of Ras signalling in development, cellular homeostasis and cancer and may suggest new therapeutic approaches.     

The occurrence of dopamine and noradrenaline in the tubero-hypophysial system

Zusammenfassung Mit chemischer Methode wurden bei grösseren Tierarten die Mengen von Dopamin und Noradrenalin im Eminentia-mediana-Infundibulum-Gebiet, im mediobasalen Hypothalamus und im Endteil des Hypothalamus bei Mensch, Schwein und Rind genau bestimmt. Die höchste Konzentration von Dopamin wurde in Eminentia mediana und die höchste Konzentration von Noradrenalin im mediobasalen Hypothalamus gefunden.

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Aided by a grant from the Sigrid Jusélius Stiftelse.     

MAP kinase signalling: interplays between plant PAMP- and effector-triggered immunity

In plants, mitogen-activated protein kinase (MAPK) cascades are involved in regulating many biological processes including immunity. They relay signals from membrane-residing immune receptors to downstream components for defense activation. Arabidopsis MPK3/6 and MPK4 are activated in two parallel MAPK cascades during PAMP-triggered immunity. MPK3/6 have been implicated in the activation of various immune responses and their inactivation leads to compromised defense against pathogens. On the other hand, the MEKK1-MKK1/2-MPK4 cascade plays critical roles in basal resistance. Disruption of this MAPK cascade results in constitutive defense responses mediated by the NB-LRR protein SUMM2. Interestingly, SUMM2 guards the MEKK1-MKK1/2-MPK4 cascade activity indirectly through monitoring the phosphorylation status of CRCK3, which is a substrate of MPK4. From the pathogens’ side, a number of effectors are shown to target various components of MAPK cascades in plants. Inactivation of MPK4 by the Pseudomonas effector HopAI1 triggers SUMM2-mediated immunity. Together, these findings suggest intricate interplays between PAMP-triggered immunity and effector-triggered immunity via MAPK signaling.