No abstract

No abstract

2-Methyl-6-(phenylethynyl)pyridine (3), a potent noncompetitive mGlu5 receptor antagonist widely used to characterize the pharmacology of mGlu5 receptors, suffers from a number of shortcomings as a therapeutic agent, including off-target activity and poor aqueous solubility. Seeking to improve the properties of 3 led to the synthesis of compound 9, a highly selective mGlu5 receptor antagonist that is 5-fold more potent than 3 in the rat fear-potentiated startle model of anxiety.

Voltage-gated calcium channels (VGCCs) play an essential role in controlling neurotransmitter release, neuronal excitability, and gene expression in the nervous system. The distribution of cells that contain mRNAs encoding the auxiliary alpha2delta-1, alpha2delta-2, and alpha2delta-3 subunits of the VGCCs in the central nervous system (CNS) and the dorsal root ganglia (DRG) was examined in rats by using in situ hybridization. Specific labeling of alpha2delta-1, alpha2delta-2, and alpha2delta-3 mRNAs appeared to be largely confined to neurons and was widely, although differentially, distributed in the brain, the spinal cord, and the DRG. Importantly, alpha2delta-2 mRNA was found to be expressed in interneurons in the cortex, the hippocampus, the striatum, and in regions that contain dense cholinergic neurons. Our results suggest that different alpha2delta subunits may exert distinctive functions in the CNS. The alpha2delta-1 subunit mRNA is localized in brain regions known to be involved in cortical processing, learning and memory, defensive behavior, neuroendocrine secretion, autonomic activation, primary sensory transmission, and general arousal. The alpha2delta-2 subunit mRNA is present in brain regions known to modulate the overall activities of the cortex, the hippocampus, and the thalamus. The alpha2delta-2 subunit is also found in brain regions known to be involved in olfaction, somatic motor control, fluid homeostasis, ingestive and defensive behaviors, neuroendocrine functions, and circadian rhythm. In addition to being localized in brain regions that express alpha2delta-1 and alpha2delta-2 subunit mRNAs, alpha2delta-3 subunit mRNA is highly expressed in regions involved in auditory information processing and somatic movement.

In the present study, we describe the characterization of a positive allosteric modulator at metabotropic glutamate subtype 2 receptors (mGluR2). 35 S]GTP␥S stimulation. This effect of LY487479 was also observed to a greater extent on the concentration-response curves to selective hmGluR2/3 agonists. In radioligand binding studies to rat cortical membranes, LY487379 increased the affinity of the radiolabeled agonist, [ 3 H]DCG-IV, without affecting the binding affinity of the radiolabeled antagonist, [ N-(4-(2-Methoxyphenoxy)-phenyl-N-(2,2,2-trifluoroethylsulfonyl)-pyrid-3-ylmethylamine3 H]LY341495. In rat hippocampal slices, coapplication of LY487379 potentiated synaptically evoked mGluR2 responses. Finally, to elucidate the site of action, we systematically exchanged segments and single amino acids between hmGluR2 and hmGluR3. Substitution of Ser688 and/or Gly689 in transmembrane IV along with Asn735 located in transmembrane segment V, with the homologous amino acids of hmGluR3, completely eliminated LY487379 allosteric modulation of hmGluR2. We propose that this allosteric binding site defines a pocket that is different from the orthosteric site located in the amino terminal domain.G-protein-coupled receptors (GPCRs) are a family of membrane bound proteins that play a central role in the recognition and signal transduction of neurotransmitters. It is generally believed that binding of the agonist induces a conformational change in the intracellular domain responsible for G-protein activation, thereby initiating a cascade of signaling events in the cell. In contrast, competitive antagonist binding will stabilize the inactive conformation of the receptor and block agonist-induced conformational changes and signal transduction (Gether and Kobilka, 1998). Although the exact mechanism of receptor/G-protein interaction is still unclear, GPCRs share a common motif of seven transmembrane helices connected by intra-and extracellular loops, an extracellular amino terminus, and a cytoplasmic carboxyl terminus. Based on their sequence homology, GPCRs have been subdivided into five families (Pin et al., 1994). Family 3 comprises the calcium-sensing receptors, pheromones, GABA B , and metabotropic glutamate (mGlu) receptors. To date, eight mGlu receptor subtypes have been cloned and classified into three groups based on their primary sequence, second messenger coupling, and pharmacology. Signal transduction from group I receptor subtypes B.A.R. and S.M. participated equally in this work.