Browsing by Author "Aguayo, Luis G."

Now showing 1 - 4 of 4
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    Influence of nonsynaptic α1 glycine receptors on ethanol consumption and place preference
    (Wiley, 2019-03-18) Muñoz, Braulio; Gallegos, Scarlet; Peters, Christian; Murath, Pablo; Lovinger, David M.; Homanics, Gregg E.; Aguayo, Luis G.; Pharmacology and Toxicology, School of Medicine
    Alcohol abuse leads to great medical, social, and economic burdens throughout the world. It is believed that the rewarding actions of alcohol are mediated by alterations in the mesolimbic dopaminergic system leading to increased levels of dopamine in the nucleus accumbens (nAc). Little is known about the role that ligand gated ion channels (LGIC), such as glycine receptors (GlyR), have in regulating levels of ethanol intake and place preference. In this study, we used Knock-in (KI) mice that have ethanol insensitive α1 GlyRs (KK385/386AA) and a combination of electrophysiological and behavioral approaches to examine how expression of ethanol resistant α1 GlyRs in brain neurons might affect binge drinking and conditioned place preference. Data show that tonic α1 GlyR-mediated currents that modulate accumbal excitability were exclusively sensitive to ethanol only in WT mice. Behavioral studies showed that the KI mice have a higher intake of ethanol upon first exposure to drinking and greater conditioned place preference to ethanol, suggesting that α1 GlyRs in the brain have a protective role against abuse. This study suggests that non-synaptic α1 containing GlyRs have a role in motivational and early reinforcing effects of ethanol and opens a novel opportunity for pharmacotherapy development to treat alcohol use disorders.
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    Modulation of glycine receptor single-channel conductance by intracellular phosphorylation
    (Springer Nature, 2020) Moraga-Cid, Gustavo; San Martín, Victoria P.; Lara, Cesar O.; Muñoz, Braulio; Marileo, Ana M.; Sazo, Anggelo; Muñoz-Montesino, Carola; Fuentealba, Jorge; Castro, Patricio A.; Guzmán, Leonardo; Burgos, Carlos F.; Zeilhofer, Hanns U.; Aguayo, Luis G.; Corringer, Pierre-Jean; Yévenes, Gonzalo E.; Pharmacology and Toxicology, School of Medicine
    Glycine receptors (GlyRs) are anion-permeable pentameric ligand-gated ion channels (pLGICs). The GlyR activation is critical for the control of key neurophysiological functions, such as motor coordination, respiratory control, muscle tone and pain processing. The relevance of the GlyR function is further highlighted by the presence of abnormal glycinergic inhibition in many pathophysiological states, such as hyperekplexia, epilepsy, autism and chronic pain. In this context, previous studies have shown that the functional inhibition of GlyRs containing the α3 subunit is a pivotal mechanism of pain hypersensitivity. This pathway involves the activation of EP2 receptors and the subsequent PKA-dependent phosphorylation of α3GlyRs within the intracellular domain (ICD), which decrease the GlyR-associated currents and enhance neuronal excitability. Despite the importance of this mechanism of glycinergic dis-inhibition associated with dysfunctional α3GlyRs, our current understanding of the molecular events involved is limited. Here, we report that the activation of PKA signaling pathway decreases the unitary conductance of α3GlyRs. We show in addition that the substitution of the PKA-targeted serine with a negatively charged residue within the ICD of α3GlyRs and of chimeric receptors combining bacterial GLIC and α3GlyR was sufficient to generate receptors with reduced conductance. Thus, our findings reveal a potential biophysical mechanism of glycinergic dis-inhibition and suggest that post-translational modifications of the ICD, such as phosphorylation, may shape the conductance of other pLGICs.
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    Modulatory Actions of the Glycine Receptor β Subunit on the Positive Allosteric Modulation of Ethanol in α2 Containing Receptors
    (Frontiers Media, 2021-11-18) Muñoz, Braulio; Mariqueo, Trinidad; Murath, Pablo; Peters, Christian; Yevenes, Gonzalo E.; Moraga-Cid, Gustavo; Peoples, Robert W.; Aguayo, Luis G.; Pharmacology and Toxicology, School of Medicine
    Alpha1-containing glycine receptors (GlyRs) are major mediators of synaptic inhibition in the spinal cord and brain stem. Recent studies reported the presence of α2-containing GlyRs in other brain regions, such as nucleus accumbens and cerebral cortex. GlyR activation decreases neuronal excitability associated with sensorial information, motor control, and respiratory functions; all of which are significantly altered during ethanol intoxication. We evaluated the role of β GlyR subunits and of two basic amino acid residues, K389 and R390, located in the large intracellular loop (IL) of the α2 GlyR subunit, which are important for binding and functional modulation by Gβγ, the dimer of the trimeric G protein conformation, using HEK-293 transfected cells combined with patch clamp electrophysiology. We demonstrate a new modulatory role of the β subunit on ethanol sensitivity of α2 subunits. Specifically, we found a differential allosteric modulation in homomeric α2 GlyRs compared with the α2β heteromeric conformation. Indeed, while α2 was insensitive, α2β GlyRs were substantially potentiated by ethanol, GTP-γ-S, propofol, Zn2+ and trichloroethanol. Furthermore, a Gβγ scavenger (ct-GRK2) selectively attenuated the effects of ethanol on recombinant α2β GlyRs. Mutations in an α2 GlyR co-expressed with the β subunit (α2AAβ) specifically blocked ethanol sensitivity, but not propofol potentiation. These results show a selective mechanism for low ethanol concentration effects on homomeric and heteromeric conformations of α2 GlyRs and provide a new mechanism for ethanol pharmacology, which is relevant to upper brain regions where α2 GlyRs are abundantly expressed.
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    Presence of ethanol-sensitive and ethanol-insensitive glycine receptors in the ventral tegmental area and prefrontal cortex in mice
    (Wiley, 2021) Araya, Anibal; Gallegos, Scarlet; Viveros, Rodrigo; San Martin, Loreto; Muñoz, Braulio; Harvey, Robert J.; Zeilhofer, Hanns U.; Aguayo, Luis G.; Pharmacology and Toxicology, School of Medicine
    Background and purpose: Glycine receptors composed of α1 and β subunits are primarily found in the spinal cord and brainstem and are potentiated by ethanol (10-100 mM). However, much less is known about the presence, composition and ethanol sensitivity of these receptors in higher CNS regions. Here, we examined two regions of the brain reward system, the ventral tegmental area (VTA) and the prefrontal cortex (PFC), to determine their glycine receptor subunit composition and sensitivity to ethanol. Experimental approach: We used Western blot, immunohistochemistry and electrophysiological techniques in three different models: wild-type C57BL/6, glycine receptor subunit α1 knock-in and glycine receptor subunit α2 knockout mice. Key results: Similar levels of α and β receptor subunits were detected in both brain regions, and electrophysiological recordings demonstrated the presence of glycine-activated currents in both areas. Sensitivity of glycine receptors to glycine was lower in the PFC compared with VTA. Picrotoxin only partly blocked the glycine-activated current in the PFC and VTA, indicating that both regions express heteromeric αβ receptors. Glycine receptors in VTA neurons, but not in PFC neurons, were potentiated by ethanol. Conclusion and implications: Glycine receptors in VTA neurons from WT and α2 KO mice were potentiated by ethanol, but not in neurons from the α1 KI mice, supporting the conclusion that α1 glycine receptors are predominantly expressed in the VTA. By contrast, glycine receptors in PFC neurons were not potentiated in any of the mouse models studied, suggesting the presence of α2/α3/α4, rather than α1 glycine receptor subunits.