Browsing by Subject "Neurochemistry"

Now showing 1 - 6 of 6
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    Role of group II metabotropic glutamate receptor subtype 2 (MGluR2) in appetitive and consummatory aspects of ethanol reinforcement
    (2014-12) Windisch, Kyle Allyson; Czachowski, Cristine; Lapish, Christopher; Neal-Beliveau, Bethany S.; Chester, Julia A.
    Background: Group II metabotropic glutamate receptors (mGluR2/3) are predominately presynaptically located Gi/o coupled receptors that are highly expressed in the cortex, nucleus accumbens, amygdala, and hippocampus. Previous studies suggest that group II mGluRs are involved in regulating ethanol (EtOH) consumption and seeking following extinction (Backstrom and Hyytia, 2005; Kufahl, et al., 2011). The sipper tube model, which allows for procedural separation of seeking and consumption, was used to further clarify the role of mGluR2/3 in EtOH-seeking and consumption. The non-selective group II mGluR agonist LY379268 (LY37) and selective mGluR2 positive allosteric modulator (PAM) BINA were used to determine the relative contribution of mGlu2 and mGlu3 receptors on EtOH seeking and consumption. Following characterization of the agonist and PAM on EtOH reinforcement, a microinjection study was performed examining the effect of blockade of nucleus accumbens core mGluR2/3 on systemic agonist induced suppression of EtOH-seeking. Methods: For the systemic agonist/PAM experiments, separate groups of male Wistar rats [n=8-9 group; LY37 (0-2.0 mg/kg) and BINA (0-20 mg/kg)] were trained to complete a response requirement (RR) of 10 lever presses that resulted in access to 10% EtOH or 2% sucrose (in separate groups) for a 20-minute drinking period. For consummatory testing, animals received weekly drug injections with a RR1. The RR was then increased over sessions to a RR20. For appetitive testing, animals received weekly drug injections followed by a non-reinforced extinction session. To determine effects of blockade of NAc core mGluR2/3 receptors on agonist-induced suppression of EtOH-seeking, a separate group of male Wistar rats (n=15) was trained to complete a RR10 for access to 10% EtOH. Animals were surgically implanted with bilateral guide cannulae terminating 1mm above the NAc core. Following recovery, animals received four sets of microinjections in a balanced design (systemic vehicle + core vehicle, systemic LY37 + core vehicle, systemic LY37 + core LY34, and systemic vehicle + core LY34). A final non-balanced microinjection of LY37 was then performed. Results and Conclusions: Systemic administration of the mGluR2/3 agonist LY37 significantly reduced EtOH- and sucrose- seeking with no systematic effect on locomotion. Systemic administration of the selective mGluR2 PAM BINA had no significant effect on either seeking or consumption. These findings suggest that modulation of glutamatergic neurotransmission by a systemic mGluR2/3 agonist, but not allosteric modulation of mGluR2, significantly reduces reinforcer seeking. Intra- accumbens core administration of LY37 significantly reduced EtOH-seeking, suggesting a role of NAc core mGluR2/3 modulation in EtOH-seeking during maintenance drinking. Systemic administration of LY37 was also found to significantly reduce sucrose consumption and body weight 24-hours following systemic administration, meriting further examination of the role of mGluR2/3 receptors on feeding behavior.
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    Sphingosine 1-phosphate enhances excitability of sensory neurons through sphingosine 1-phosphate receptors 1 and/or 3
    (2014) Li, Chao; Vasko, Michael R.; Cummins, Theodore R.; Hudmon, Andrew; Nicol, Grant D.; Quilliam, Lawrence A.
    Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that has proven to be an important signaling molecule both as an extracellular primary messenger and as an intracellular second messenger. Extracellular S1P acts through a family of five S1P receptors, S1PR1-5, all of which are G protein-coupled receptors associated with different G proteins. Previous work from our laboratory shows that externally applied S1P increases the excitability of small-diameter sensory neurons by enhancing the action potential firing. The increased neuronal excitability is mediated primarily, but not exclusively, through S1PR1. This raises the question as to which other S1PRs mediate the enhanced excitability in sensory neurons. To address this question, the expression of different S1PR subtypes in small-diameter sensory neurons was examined by single-cell quantitative PCR. The results show that sensory neurons express the mRNAs for all five S1PRs, with S1PR1 mRNA level significantly greater than the other subtypes. To investigate the functional contribution of other S1PRs in augmenting excitability, sensory neurons were treated with a pool of three individual siRNAs targeted to S1PR1, R2 and R3. This treatment prevented S1P from augmenting excitability, indicating that S1PR1, R2 and/or R3 are essential in mediating S1P-induced sensitization. To study the role of S1PR2 in S1P-induced sensitization, JTE-013, a selective antagonist at S1PR2, was used. Surprisingly, JTE-013 by itself enhanced neuronal excitability. Alternatively, sensory neurons were pretreated with FTY720, which is an agonist at S1PR1/R3/R4/R5 and presumably downregulates these receptors. FTY720 pretreatment prevented S1P from increasing neuronal excitability, suggesting that S1PR2 does not mediate the S1P-induced sensitization. To test the hypothesis that S1PR1 and R3 mediate S1P-induced sensitization, sensory neurons were pretreated with specific antagonists for S1PR1 and R3, or with siRNAs targeted to S1PR1 and R3. Both treatments blocked the capacity of S1P to enhance neuronal excitability. Therefore my results demonstrate that the enhanced excitability produced by S1P is mediated by S1PR1 and/or S1PR3. Additionally, my results indicate that S1P/S1PR1 elevates neuronal excitability through the activation of mitogen-activated protein kinase kinase. The data from antagonism at S1PR1 to regulate neuronal excitability provides insight into the importance of S1P/S1PR1 axis in modulating pain signal transduction.
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