L7 GABA & Glycine PDF

@Anurag Pandey & Arturas Volianskis Glycine GABA GABA GABA & Glycine Glycine Glycine...

@Anurag Pandey & Arturas Volianskis Glycine GABA GABA GABA & Glycine Glycine Glycine GABA GABA Glycine Glycine GABA GABA Glycine Glycine GABA GABA Glycine Glycine GABA GABA Glycine Glycine GABA GABA Glycine Glycine GABA GABA Glycine Glycine GABA & Glycine Learning outcomes: 1. Review cocculus indicus and its case in the House of Commons. 2. Discuss synthesis and abundance of GABA, and its receptors, GABAergic transmission and inactivation of GABA action, some of the agonists and antagonists; giving examples of its functional significance. 3. Introduce strychnine, and performance enhancement in sports. 4. Discuss synthesis and abundance of glycine, and its receptors, glycinergic transmission and inactivation of glycine action, some of the agonists and antagonists; giving examples of its functional significance. BI2432: Fundamental neuropharmacology Case story - adulteration “This report, it will be seen, affords experimental confirmation of what was said by Mr. Glover at the Liverpool Workhouse meeting, and it will therefore be interesting to inquire a little further into the matter. Our authorities tell us that the following substances are employed to adulterate beer. "Cocculus indicus multum (an extract of cocculus indicus), colouring, honey, hartshorn- shavings, Spanish juice, orange-powder, ginger, grains of paradise, quassia, liquorice, carraway seeds, copperas, capsicum, mixed drugs.” These, we are told, were seized at different breweries in London, and brewers’ druggists’ laboratories"* in addition, sulphuric acid, alum, salt, Datura stramonium, picric acid, and other substances, are mentioned by different writers. * Report of Committee of the House of Commons. See Watts’s 'Dictionary of Chemistry.’ vol. i, p. 537.” Liverpool Daily Post - Tuesday 05 July 1870, page 6. By 1849, William Black, author of A practical treatise on brewing, was forced to conclude that “however much they may surprise, however pernicious or disagreeable they may appear, he has always found them requisite in the brewing of porter, and he thinks they must invariably be used by those who wish to continue the taste, flavor, and appearance of the beer. And though several Acts of Parliament have been passed to prevent porter brewers from using many of them, yet the author can affirm, from experience, he could never produce the present flavored porter without them. The intoxicating qualities of porter are to be ascribed to the various drugs intermixed with it. It is evident that some porter is more heady than other, and it arises from the greater or less quantity of stupefying ingredients. Malt, to produce intoxication, must be used in such large quantities as would very much diminish, if not totally exclude, the brewer’s profit.” BI2432: Fundamental neuropharmacology GABA is the main inhibitory transmitter in the adult nervous system Ironically, the major excitatory neurotransmitter is the precursor to the main inhibitory transmitter! GABA is synthesised by the enzyme glutamic acid decarboxylase (GAD). GAD (either 65 and/or 67) is localised specifically on GABAergic neurons. GABA is present in highly diverse inhibitory interneurons (e.g basket, stellate, etc) and projection neurons (e.g Purkinje) throughout the brain. Removal of a carboxyl group by GAD turns glutamate into GABA. BI2432: Fundamental neuropharmacology GABA is the main inhibitory transmitter in the adult nervous system Ironically, the major excitatory neurotransmitter is the precursor to the main inhibitory transmitter! GABA is synthesised by the enzyme glutamic acid decarboxylase (GAD). GAD (either 65 and/or 67) is localised specifically on GABAergic neurons. GABA is present in highly diverse inhibitory interneurons (e.g basket, stellate, etc) and projection neurons (e.g. Purkinje) throughout the brain. Terminal Cytosolic s Zhao et al., 2013, Characterization of GABAergic Neurons , PLOS ONE, https://doi.org/10.1371/journal.pone.0073750 Schousboe & Waagepetersen, 2017 2009, GABA, Encyclopedia of Neuroscience, https://doi.org/10.1016/B978-0-12-809324-5.02341-5 BI2432: Fundamental neuropharmacology GABAergic neurotransmission GABA is transported back into GABAergic terminals via dedicated GABA transporters. It is also buffered by astrocytes where it is degraded by GABA GABA-T transaminase (GABA-T). Thus, in GABAergic neurotransmission, there is a net flow of GABA from the neuronal to the astrocytic compartment. This net flow needs to be compensated by a flow of a GABA precursor in the opposite direction. BI2432: Fundamental neuropharmacology GABA-proteins: receptors, transporters, etc. Sofie R. Kleppner, Allan J. Tobin, in Encyclopedia of the Human Brain, 2002 BI2432: Fundamental neuropharmacology  Receptor nomenclature: is there a GABAC? Ionotropic Ionotropic Metabotropic Heteromeric Homomeric Heteromeric Schousboe & Waagepetersen, 2017 2009, GABA, Encyclopedia of Neuroscience, https://doi.org/10.1016/B978-0-12-809324-5.02341-5 BI2432: Fundamental neuropharmacology  Receptor nomenclature: is there a GABAC? Basic pharmacology of GABA receptors Ionotropic (Cl- channel) Metabotropic(GPCR receptor) The distinction between GABAA and GABAC receptors is based only on pharmacological grounds. GABAC receptors are characterized by their activation by cis-4-aminobut-2- enoate (CACA), whereas classic GABAA receptor agonists such as isoguvacine have no effect. Because the GABAC receptor is a homomeric complex of “rho”-subunits sharing a considerable amino acid sequence homology with the remaining GABAA receptor subunits, it may be concluded that this receptor subclass should be termed a pharmacologically distinct GABAA receptor. Schousboe & Waagepetersen, 2017 2009, GABA, Encyclopedia of Neuroscience, https://doi.org/10.1016/B978-0-12-809324-5.02341-5 BI2432: Fundamental neuropharmacology Composition of the GABAA & distribution GABAA receptors are thought to be pentameric complexes, comprised of possibly more than 2000 different subunit combinations (~20 widely expressed; fewer dominant). The most prevalent subunit in the brain is α1, with the major GABAA receptor subtype in brain having a stoichiometry of α1β2γ2. Receptors containing the α2 subunit are most abundant in regions where the α1 subunit is absent or expressed at low levels, such as the hippocampus, striatum, and olfactory bulb. Similarly, the α3 subunit is expressed in regions complementary to the α1 subunit, including the lateral septum, reticular nucleus of the thalamus, and brainstem nuclei. Notably, the α6 subunit is expressed almost exclusively in cerebellum. BI2432: Fundamental neuropharmacology Composition of the GABAA & distribution Splice variants of GABAA receptor subunits 19 different subunits, in eight families. The 𝛼 family comprises 6, 𝛽 - 4, 𝛾 - 3 and 𝜌 - 3 subunits. Remaining 4 subunits (𝛿,𝜀,𝜃,𝜋) have only 1 splice variant identified. 𝛼, 𝛽, 𝛾, 𝛿, 𝜀 subunits can form heteromeric complexes. GABAA/C receptor (expressed in retina) is a homomeric complex of 𝜌-subunits, resistant to both bicuculline and baclofen. 𝜋 subfamily is expressed in reproductive organs. BI2432: Fundamental neuropharmacology  Multiple binding sites on the GABAA receptor Binding sites are for illustration purposes. BI2432: Fundamental neuropharmacology  The GABAB receptor is metabotropic The metabotropic G protein-coupled GABA receptors, originally termed GABAB because they are pharmacologically distinct from GABAA (activated by baclofen and insensitive to the GABAA receptor antagonist bicuculline). Two subtypes, GABAB1 and GABAB2 have to form a heterodimeric complex in order to be functionally active. Postsynaptic GABAB receptors normally produce hyperpolarization due to coupling to K+ channels. Presynaptically, GABAB receptors are coupled to Ca2+ channels, and activation leads to a decrease in Ca2+ conductance, resulting in inhibition of transmitter release. Thus, counterintuitively GABAB agonists can produce muscle relaxation and antagonists act as anti- epileptics. BI2432: Fundamental neuropharmacology GABAB in synaptic transmission Glutamatergic synapse GABAergic synapse GABAB receptor function regulates neurotransmitter release at both GABAergic and glutamatergic terminals. BI2432: Fundamental neuropharmacology GABAA&B receptors in synaptic plasticity Under baseline conditions (a) activation of GABAA and GABAB receptors reduce the postsynaptic depolarisation, preventing NMDAR conductance. During high frequency activation (b), decreased release of GABA results due to activation of presynaptic GABAB receptors leading to reduction of postsynaptic GABAA activation and thereby greater depolarisation and NMDAR conductance. BI2432: Fundamental neuropharmacology Drugs affecting GABAergic transmission Inhibitor/Antagonist Activator/Agonist Refractory complex partial seizure Anticonvulsant Anxiolytic Skeletal muscle relaxant Anticonvulsant Convulsant BI2432: Fundamental neuropharmacology  Case study - fate of ethanol in body BAC = blood alcohol concentration BI2432: Fundamental neuropharmacology Are GABAA receptors the main GABAR target for ethanol? Ethanol enhances GABAergic synaptic inhibition Blocking of GABAB receptor activity enhances EtOH potentiation of hippocampal GABAA currents. Ariwodola and Weiner Ethanol and Presynaptic GABAB Receptors, J. Neurosci., November 24, 2004 24(47):10679 –10686 BI2432: Fundamental neuropharmacology Are GABAA receptors the main GABAR target for ethanol? Aguayo and Pancetti, Ethanol modulation of the gamma-aminobutyric acid JPET 1994, 270 (1) 61-69; BI2432: Fundamental neuropharmacology GABA in disease - modulation of spontaneous neuronal activity GABA may play a role in diverse neuropsychiatric disorders, including epilepsy, Huntington disease, tardive dyskinesia, alcoholism and other addictions, and sleep disorders. BI2432: Fundamental neuropharmacology GABA transaminase (GABA-T) deficiency GABA-transaminase deficiency begins in infancy. These babies have recurrent seizures (epilepsy), uncontrolled limb movements (choreoathetosis), exaggerated reflexes (hyperreflexia), weak muscle tone (hypotonia), and excessive sleepiness (hypersomnolence). GABA-T They may grow faster in length (accelerated linear growth) but may not gain normal weight (failure to thrive), possibly due to associated feeding problems. These children show profoundly impaired development and generally do not achieve normal developmental milestones of infancy such as following others' movement with their eyes or sitting unassisted. Individuals with this disorder usually do not survive past the first 2 years of life, although some may live longer into childhood (UK case 2018). https://medlineplus.gov/genetics/condition/gaba-transaminase- deficiency/#frequency BI2432: Fundamental neuropharmacology GABA is excitatory neurotransmitter in embryonic nervous system During early developmental stages, neurons can display accumulation of intracellular chloride, causing opposite Cl− fluxes to occur in immature neurons. Depolarising effects of GABA are often observed in the embryonic nervous system, a property of GABAergic neurotransmission that very likely is important for CNS development. Ben-Ari & Tyzio, 2009, GABA , Encyclopaedia of Basic Epilepsy Research, https://doi.org/10.1016/B978-012373961-2.00241-1 Schousboe & Waagepetersen, 2017 2009, GABA, Encyclopedia of Neuroscience, https://doi.org/10.1016/B978-0-12-809324-5.02341-5 BI2432: Fundamental neuropharmacology Glycine @Arturas Volianskis Case story - performance enhancement Thomas John Hicks (01.11.1876-01.28.1952) was an American track and field athlete. He won the marathon at the Olympic Games in 1904, in St. Louis, Missouri. Conditions were bad, the course being a dirt track, with large clouds of dust produced by the accompanying vehicles. Hicks was not the first to cross the finish line, trailing Fred Lorz. However, Lorz had abandoned the race after 9 miles. After covering much of the course by car, he re- entered the race 5 miles before the finish. This was discovered by the officials, who disqualified Lorz, who claimed it had been a joke. Had the race been run under current rules, Hicks would also have been disqualified for using strychnine: his assistants had given him a dose of 1/60 of a grain (roughly 1 mg) of strychnine and some brandy because he was flagging badly during the race; the first dose of strychnine did not revive him for long, so he was given another. As a result, he collapsed after crossing the finishing line. Another dose might have been fatal. Strychnine was popularly used as an athletic performance enhancer and recreational stimulant in the late 19th century and early 20th century, due to its convulsant effects. Strychnine is now forbidden for athletes as part of the Olympic rules against doping and its use in an Olympic event has only been attempted once since in 2016. According to Wikipedia. BI2432: Fundamental neuropharmacology Synthesis, release, re-uptake and degradation of glycine 2. Glycine packaged into vesicles by vesicular transporter (unk). 3. Glycine is removed from cleft by uptake transporters on astrocytes 2 and presynaptic terminals (GLYT1 & 4 GLYT2). 3 GLYT1 exists in three isoforms and is expressed in both astrocytes and 3 neurones. GLYT2 is expressed in axons and presynaptic terminals. COOH Both GLYT1 and GLYT2 are H2N CH CH2OH expressed in caudal areas of the brain. Serine GLYT1 is also expressed in the forebrain, where it is likely to regulate SMHT 1 NMDAR transmission. COOH 1. Glycine is synthesised from serine by by 4. Degradation occurs by glycine serine hydroxymethyltransferase (SMHT), H2N CH H cleavage system (GCS) in the a pyridoxal phosphate-dependent enzyme. Glycine mitochondria. P. Legendre, 2001, The glycinergic inhibitory synapse, CMLS, Cell. Mol. Life Sci. 58 (2001) 760–793 BI2432: Fundamental neuropharmacology Vesicular glycine transporter Vesicular GABA transporter is capable of glycine transport and therefore a common vesicular inhibitory amino acid transporter (VIAAT) has been proposed, which function can be controlled by extra-vesicular concentration of the two amino acids. Effectively, glycine has been shown to inhibit GABA uptake and vice versa. However, in some areas of CNS that are rich with GABA and/or glycine - VIAAT is missing, suggesting existence of other transporters. On the other hand, some vesicles contain both glycine and GABA and their co-release, activating dedicated postsynaptic receptors, has also been demonstrated. P. Legendre, 2001, The glycinergic inhibitory synapse, CMLS, Cell. Mol. Life Sci. 58 (2001) 760–793 BI2432: Fundamental neuropharmacology Glycine receptors v Glycine receptors, like GABAA, are believed to possess a pentameric structure (also related to nicotinic cholinergic and 5HT3). v They are composed of α (four subunits) and β (single type) subunits. Only α subunits contain glycine binding site. Receptors can be formed of α subunits alone or in combination with β. v Activated by glycine > β-alanine > taurine > L- and D-alanine > L-serine >> D-serine. v Inhibited competitively by strychnine or non- competitively by picrotoxin. Receptors that contain β subunits are insensitive to picrotoxinin. BI2432: Fundamental neuropharmacology Glycine receptors Receptors are developmentally and regionally regulated. α1 corresponds to strychnine sensitive sites in adults. α2 is expressed early during development and throughout the CNS, but only few places in adults. α3 is expressed in parts of the limbic system and the cerebellum. α4 have not been detected in adult humans. β mRNA is common throughout CNS, but they do not form glycine receptors on their own. P. Legendre, 2001, The glycinergic inhibitory synapse, CMLS, Cell. Mol. Life Sci. 58 (2001) 760–793 BI2432: Fundamental neuropharmacology Glycine is excitatory neurotransmitter in embryonic nervous system Glycinergic synapses become functional early in brain development, and glycine just like GABA can depolarise neurones in embyronic and immature animals. K+/Cl– co-transporter KCC2 is first expressed at 10 days postnatally, which produces a marked negative shift in the Cl– reversal potentials. Chamma et al, Role of the neuronal K-Cl co-transporter KCC2 in inhibitory and excitatory neurotransmission, Front. Cell. Neurosci., 21 February 2012, https://doi.org/10.3389/fncel.2012.00005 BI2432: Fundamental neuropharmacology Glycine receptor are modulated by alcohols and other drugs Glycine receptors are allosterically modulated by alcohols and anaesthetics (e.g. enflurane and isoflurane). They are also affected by cocaine and a number of 5HT3 and NMDAR ligands. P. Legendre, 2001, The glycinergic inhibitory synapse, CMLS, Cell. Mol. Life Sci. 58 (2001) 760–793 BI2432: Fundamental neuropharmacology What are the mechanism of action for alcohol? Aguayo and Pancetti, Ethanol modulation of the gamma-aminobutyric acid JPET 1994, 270 (1) 61-69; BI2432: Fundamental neuropharmacology Hereditary hyperekplexia - a glycinergic condition. Hereditary hyperekplexia (startle disease) is a condition in which affected infants have increased muscle tone (hypertonia) and an exaggerated startle reaction to unexpected stimuli, especially loud noises. Following the startle reaction, infants experience a brief period in which they are very rigid and unable to move. During these rigid periods, some infants stop breathing, which, if prolonged, can be fatal. Infants with hereditary hyperekplexia have hypertonia at all times, except when they are sleeping. Other signs and symptoms of hereditary hyperekplexia can include muscle twitches when falling asleep (hypnagogic myoclonus) and movements of the arms or legs while asleep. Some infants, when tapped on the nose, extend their head forward and have spasms of the limb and neck muscles. Rarely, infants with hereditary hyperekplexia experience recurrent seizures (epilepsy). The signs and symptoms of hereditary hyperekplexia typically fade by age 1. However, older individuals with hereditary hyperekplexia may still startle easily and have periods of rigidity, which can cause them to fall down. They may also continue to have hypnagogic myoclonus or movements during sleep. As they get older, individuals with this condition may have a low tolerance for crowded places and loud noises. People with hereditary hyperekplexia who have epilepsy have the seizure disorder These drawings, based on high-speed films, show throughout their lives. the separate movements of the startle reactions in a Most cases of hereditary hyperekplexia are caused by mutations in the GLRA1 gene. The GLRA1 gene provides patient, from the Dutch hyperekplexia family with instructions for making one part, the alpha (α1) subunit, of the glycine receptor protein. When this protein attaches (binds) to the major form of hyperekplexia. glycine, signaling between cells is stopped. GLRA1 gene mutations lead to the production of a receptor that cannot properly respond to glycine. As a result, glycine is less able to regulate signaling in the spinal cord and brainstem leading to Bakker et al “Startle syndromes” Lancet Neurol increased cells signaling and the signs and symptoms of hereditary hyperekplexia. Mutations in other genes account for 2006; 5: 513–24 the remaining cases of hereditary hyperekplexia. https://medlineplus.gov/genetics/condition/hereditary-hyperekplexia/#causes BI2432: Fundamental neuropharmacology Example question L7: What is the main molecular target of picrotoxin? (A) GABAA receptor (B) NMDA receptor (C) GABAB receptor (D) AMPA receptor (E) GABAC receptor BI2432: Fundamental neuropharmacology Study materials: BI2432: Fundamental neuropharmacology Weekly schedule of the fundamental neuropharmacology Friday 29.11.2024 (13:10-14:00 & 14:10-15:00); C/-1.04 Meyer & Quenzer Psychopharmacology, Nestler, Hyman & Malenka’s Molecular Neuropharmacology L1. Introduction to fundamental neuropharmacology Rang & Dale’s Pharmacology, L2. Basic principles of neuropharmacology I & lecture materials Friday 06.12.2024 (13:10-14:00 & 14:10-15:00); C/-1.04 Meyer & Quenzer Psychopharmacology, Nestler, Hyman & Malenka’s Molecular Neuropharmacology L3. Basic principles of neuropharmacology II Rang & Dale’s Pharmacology L4. Techniques in neuropharmacology & lecture materials Friday 10.12.2024 (13:10-14:00 & 14:10-15:00); C/-1.04 Meyer & Quenzer Psychopharmacology, Nestler, Hyman & Malenka’s Molecular Neuropharmacology L5. Acetylcholine and Glutamate (and a bit of Glycine) Rang & Dale’s Pharmacology L6. Pharmacological dissection of field responses The Hippocampus Book pages 27-30 & lecture materials Meyer & Quenzer Psychopharmacology, Tuesday 07.01.2025 (13:10-14:00);C/-1.04 Nestler, Hyman & Malenka’s Molecular Neuropharmacology L7. GABA and Glycine Rang & Dale’s Pharmacology & lecture materials Friday 10.01.2025 (13:10-14:00 & 14:10-15:00); C/-1.04 Meyer & Quenzer Psychopharmacology, Nestler, Hyman & Malenka’s Molecular Neuropharmacology L8. Catecholamines Rang & Dale’s Pharmacology L9. Serotonin & lecture materials Friday 27.01.2025 (13:00-13:45 & 14:00-14:45); C/-1.04 Meyer & Quenzer Psychopharmacology, Nestler, Hyman & Malenka’s Molecular Neuropharmacology L10. Neuropharmacology of drug dependence and addiction I Rang & Dale’s Pharmacology L11. Neuropharmacology of drug dependence and addiction II & lecture materials Tuesday 21.01.2025 (13:10-14:00); C/-1.04 Tuesday 23.01.2025 Neuroanatomy L12. Exam preparation 2 and Neuropharmacology ICA BI2432: Fundamental neuropharmacology