Absence of direct effects on the dopamine D2 receptor by mGluR2/3‐selective receptor agonists LY 354,740 and LY 379,268

Abstract

We previously reported the absence of high-affinity binding of the group II metabotropic glutamate receptor agonists LY 354,740 and LY 379,268 to the D2L dopamine receptor. A rebuttal to our findings has since been reported (see Introduction section); this study represents our response. Analysis by LCMS of LY 354,740 and LY 379,268 used in this study revealed the correct molecular mass for these compounds. Both LY 354,740 and LY 379,268 exhibited potent agonist activity for mGluR₂ in the ³⁵S-GTPγS assay. Functionally, neither compound displayed antagonist activity in the GTPγS assay with recombinant D₂. At concentrations up to 10 μM, both compounds failed to displace [³H]-raclopride, [³H]-PHNO, or [³H]-domperidone in filter-binding assays under isotonic (120 mM NaCl or N-methyl glucamine) or low-ionic strength (no NaCl or N-methyl glucamine) conditions. Some displacement of [³H]-domperidone (20-40%) was observed at 30 μM of LY 354,740 under low-ionic strength and under isotonic conditions in the absence of NaCl. No displacement of [³H]-domperidone was detected in a two site model at lower (<100 nM) concentrations of either compound. Moreover, no D₂ activity was observed for LY 354,740 or LY 379,268 in the CellKey™ (cellular dielectric spectroscopy) assay. In this communication, we discuss the possible reasons for differences in our study and the previously published work and implications of these studies for mechanisms of antipsychotic action.

Tricyclic Antidepressant Amitriptyline-induced Glial Cell Line-derived Neurotrophic Factor Production Involves Pertussis Toxin-sensitive Gαi/o Activation in Astroglial Cells

“…This study demonstrated that the PTX-sensitive G i/o subunits, especially G o and G i3 , play important roles in the activation of ERK evoked by amitriptyline. The CellKey TM assay confirmed the pharmacological and siRNA findings, in that the pattern of the change in impedance induced by amitriptyline was similar to that of activation of G i/o -coupled receptors, and not of G s -or G q -coupled receptors (13,14,17,18). Although the C6 cells is an astrocyte model cell line derived from rat glioma, activation of the MMP/FGFR/FRS2␣/ERK cascade occurs in both normal human and rat astrocytes as well (9,11), in a PTX-sensitive manner.…”

“…Electrical Impedance-based Biosensors (CellKey TM Assay)-The CellKey TM assay has been described previously (17,18). Cellular dielectric spectroscopy is a novel technology that employs a label-free, real time, cell-based assay approach for the comprehensive pharmacological evaluation of cells that exogenously or endogenously express GPCRs, and nuclear receptors on the same platform without any modification of the cells.…”

Activation of Group II Metabotropic Glutamate Receptors Inhibits the Discriminative Stimulus Effects of Alcohol via Selective Activity Within the Amygdala

“…It could also be argued that the LY379268 doses tested were not high enough to elicit alcohol-like stimulus effects because there were no changes in behavior observed across tested doses. Indeed, the highest dose did not significantly alter response rate (Figure 2b), but acute doses of LY379268 higher than 10 mg/kg produce profound motor impairing effects (Cartmell et al, 2000) and may have nonspecific actions at other receptors (Monn et al, 1999;Seeman and Guan, 2008; but see Fell et al, 2009;Zysk et al, 2011), which would potentially complicate the interpretation of results; therefore, higher doses were not tested in this study.…”

mGluR2/3 mechanisms in primate dorsolateral prefrontal cortex: evidence for both presynaptic and postsynaptic actions

“…However, higher doses of LY379268 eroded the improving effect of low dose on spatial tuning, causing the d′ to fall to the level that was not significantly different from the Control condition ( Supplementary Figure 4b; P40.9), thus compromising the specificity of working memory representations. The nonspecific actions of LY379268 at high doses may arise from its off-target interactions with the dopamine system, 55 but this issue remains controversial 56,57 and there may be other possibilities underlying the mixed effect at high doses. mGluR2/3 antagonist reverses APDC beneficial actions.…”