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Abstract: Prolonged intrathecal (i.t.) administration of morphine results in tolerance to morphine-induced antinociception. We found that co-administration of selective metabotropic glutamate receptor subtype 5 antagonist MPEP with morphine could suppress the loss of morphine-induced antinociception and inhibit the development of tolerance to morphine-induced antinociceptive effect. Whereas, the specific metabotropic glutamate receptor subtype 5 agonist CHPG does the opposite. As the activation of NMDA receptor after chronic morphine administration has been verified, we suppose there is an enhanced activation of mGluR5 during the development of tolerance to morphine-induced antinociception. Activation of mGluR5 may mobilize the release of intracellular Ca2+ and activate PKC, leading to morphine-induced antinociception suppression. We conclude that mGluR5 contributes to the development of tolerance to morphine-induced antinociception after chronic morphine exposure. [Copyright &y& Elsevier]

Abstract: Many receptors for neurotransmitters and hormones rely upon members of the Gqα family of heterotrimeric G proteins to exert their actions on target cells. Gα subunits of the Gq class of G proteins (Gqα, G11α, G14α and G15/16α) directly link receptors to activation of PLC-β isoforms which, in turn, stimulate inositol lipid (i.e. calcium/PKC) signalling. Although Gqα family members share a capacity to activate PLC-β, they also differ markedly in their biochemical properties and tissue distribution which predicts functional diversity. Nevertheless, established models suggest that Gqα family members are functionally redundant and that their cellular responses are a result of PLC-β activation and downstream calcium/PKC signalling. Growing evidence, however, indicates that Gqα, G11α, G14α and G15/16α are functionally diverse and that many of their cellular actions are independent of inositol lipid signalling. Recent findings show that Gqα family members differ with regard to their linked receptors and downstream binding partners. Reported binding partners distinct from PLC-β include novel candidate effector proteins, various regulatory proteins, and a growing list of scaffolding/adaptor proteins. Downstream of these signalling proteins, Gqα family members exhibit unexpected differences in the signalling pathways and the gene expression profiles they regulate. Finally, genetic studies using whole animal models demonstrate the importance of certain Gqα family members in cardiac, lung, brain and platelet functions among other physiological processes. Taken together, these findings demonstrate that Gqα, G11α, G14α and G15/16α regulate both overlapping and distinct signalling pathways, indicating that they are more functionally diverse than previously thought. [Copyright &y& Elsevier]

Abstract: Defining the underlying causes of psychiatric disorders has provided an ongoing and intractable problem. The analysis of the genetic basis of manic depression, in particular, has been impeded by the absence of a suitable model system and by the lack of candidate causative genes. One recent approach to overcome these problems has involved identifying those genes which control the sensitivity to anti-manic drugs in a model organism. Characterisation of the role of these genes and their encoded proteins in this model has allowed the analysis of their mammalian homologues to elucidate the therapeutic role of these drugs and the possible aetiology of manic depression. This approach has been used successfully with the cellular slime mould, Dictyostelium discoideum. This article introduces the use of model systems for pharmacogenetics research. It describes the identification of prolyl oligopeptidase in D. discoideum as a modulator of inositol phosphate signalling, and the subsequent identification of a common mechanism of action of three anti-manic drugs in mammalian neurons. The use of pharmacogenetics in model systems will provide a powerful tool for the ongoing analysis of both the treatment and cause of psychiatric disorders. [Copyright &y& Elsevier]

Abstract: In the human lens, stimulation of tyrosine-kinase coupled growth factor receptors such as epidermal growth factor receptor (EGFR) can induce calcium release from endoplasmic reticulum (ER) stores. The present study investigated the impact of calcium store inactivation on EGFR signalling, cell growth and death in a well-characterised human lens cell line (FHL124). FHL124 cells were routinely cultured in Eagle''s minimum essential medium (EMEM) supplemented with 10% foetal calf serum (FCS) and seeded on 24-well plates (DNA and protein synthesis), tissue culture dishes (growth assay, western immunoblot), and glass coverslips (immunocytochemistry). DNA and protein synthesis rates were quantified by measuring the incorporation of 3H-thymidine and 35S-methionine into FHL124 cells in serum-free EMEM or EMEM supplemented with thapsigargin (Tg) (100nm and 1μm). Longer-term growth was assessed by quantifying the increase in area over time of a circular patch of seeded cells. EGFR was identified using anti-EGFR mouse monoclonal antibody and visualised by fluorescence microscopy with ALEXA 488 conjugated secondary antibody. Programmed cell death was determined by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay method. Activation of the mitogen-activated protein kinase (MAPK) signalling protein extracellular signal-regulated kinase (ERK) and the cell cycle proteins CDK2 and P27kip1 were detected by western immunoblot techniques. Inactivation by ≥100nm Tg inhibited both protein and DNA synthesis although the effect on the latter was greatest. The cell cycle activator CDK2 was reduced by Tg, while the inhibitor P27kip1 was increased along with the percentage of apoptotic cells. A single, maximal epidermal growth factor (EGF) (10ngml−1) exposure induced receptor internalization and increased ERK phosphorylation. Both internalisation and ERK activation were unaffected by the presence of Tg. However, reduced internalisation and ERK activation followed repeated EGF applications in the presence of Tg. Additionally, ERK activation by submaximal EGF concentrations was reduced by store depletion. An intact endoplasmic reticulum calcium store therefore plays a significant role in human lens cell survival and growth. [Copyright &y& Elsevier]