Examples of smallmolecule. peptide neurotransmitters

Transcription

1 Examples of smallmolecule and peptide neurotransmitters

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3 Small- molecule transmitters are transported from the cytosol into vesicles or from the synaptic cleft to the cytosol by TRANSPORTERS

4 Unconventional transmitters (ecbs, NO): retrograde signalling

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6 A brief history of cannabinoid and endocannabinoid research

7 Biosynthesis of endocannabinoids

8 Presynaptic action of endocannabinoids

9 Activation and signal transduction of neurotransmitter receptors Direct activation of an ion channel Modulation of an ion channel through intracellular effector enzymes and second messengers

10 The general architecture of ligand-gated ion channels subunit Oligomeric subunit assembly

11 The nicotinic Acetylcholine receptor (nachr) is the best-studied of ionotropic receptors nachr is a cationic channel permeable to Na + e K + The electric organ of the electric ray is an example of preparation in which nicotinic receptors have been extensively studied. On a dissected Torpedo (left) we can see the electric organs and their innervation. These organs constitute electroplax membranes (right) which are modified muscle cells that do not contract. Nicotinic receptors are present on the ventral side of the postsynaptic membrane of the electroplax. The electroplax are simultaneously activated and the summation of their electric discharges can be of the order of 500 V.

12 The nachr of the neuromuscular junction is a cationic channel made of 5 subunits:(2)a, b, g, d (c) a subunit 5 subunits (a) Schematic representation of the primary sequence of the α- (α 1 α 9 ) and non-α- (β 1 β 4, γ, ɛ, and δ) subunits of the nachr. M1 M4, transmembrane domains; CC, Cys-Cys pair found in the α-subunits from both muscleand neuronal-type nachrs. (b) Diagram of the tertiary organization of nachrs. (Left) Schematic representation of the transmembrane organization of a single subunit. (Right) Schematic representation of the oligomeric organization of muscletype nachr. The pentameric nachr is formed by two α- subunits and three non-α-subunits. The two ligand binding sites (L) are located at the interfaces of one α-subunit and one non-α-subunit. (c) Architecture of the extracellular and transmembrane domains of the nachr from electron micrographs at 4 Å (0.4 nm) resolution. Individual subunits are in different colours (α, red; β, green; γ, blue; δ, light blue). The extracellular domains are β-sandwiches formed from two anti-parallel β-sheets perpendicular to the membrane topped by an α-helix. The transmembrane domains of each subunit contain four α-helices. (Right) Plan view from the synaptic cleft. The five subunits form a ring. A water filled vestibule runs through the extracellular domains down to the channel and through the membrane. The four M2 domains (in bright colors) of the four subunits line the channel.

13 Molecular bases of the selective ion permeability of nachr

14 Each ionotropic receptor subtype is made of a combination of different subunits GluA1 GluN1 GluK1 a 1-6 a 1-6 a HT 3A GluA2 GluN2A GluK2 b 1-3 b 5-HT 3B GluA3 GluN2B GluK3 g HT 3C GluA4 GluN2C GluK4 5-HT 3D GluN2D GluK5 e 5-HT 3E GluN3A GluN3B q h

15 Multiplicity of metabotropic receptors

16 At synapses metabotropic receptors have mostly a modulatory role

17 Metabotropic receptors transduction mechanisms

18 Phosphatidylinositide hydrolysis by different phospholipases

19 The GABA A receptor Receptor activity is modulated by a series of molecules (drugs such as sedatives, anxiolitics, anesthetics, ) Benzodiazepines positively modulates GABA A receptors

20 Excitatory actions of GABA during development Neuroscience, Vth edition

21 GABA A receptor subunit distribution is spatially regulated in the brain a1 a3 a 1-6 b 1-3 a6 g 1-3 qh

22 GABA A Rs are made of variable combinations of at least 18 different subunits (each receptor is a heteropentameric Cl - channel) a 1-6 b 1-3 g 1-3 qh Jacob et al., 2008 Many different subunit combinations are theoretically possible; however, only a limited number of these combinations can actually exit the ER and access the neuronal cell surface. The majority of studies agree that most GABA A Rs expressed on the surface of neurons are composed of two a subunits, two b subunits and one g subunit The relative expression of GABA A receptor subunit combinations in the rodent brain. Stephens et al., 2016 Genes Brain Behav. doi: /gbb

23 GABA A R subunit compositions at synaptic sites differ from those located at extra-synaptic sites GABA A Rs composed of a(1 3) subunits together with β and γ subunits are thought to be primarily synaptically localized, whereas a5βγ receptors are located largely at extrasynaptic sites. Both these types of GABA A R are BZ sensitive. By contrast, receptors composed of a(4 or 6)βδ are BZ insensitive and localized at extrasynaptic sites. Jacob et al., 2008

24 cerebellum a1 Expression levels of GABA A receptor subunits are strictly regulated during development a5 synaptic extra-synaptic g2 subunit regulation involves both the transcription rate and the type of splicing occurring at different developmental stages g2s g2l

25 Chromosomal locations of major GABA A receptor gene clusters Syntenic regions for the human clusters occur in the mouse, suggesting a highly conserved organization of these genes. Expression of those genes located on human chr 4 predominate in rodent embryo, but these genes are generally down regulated in the adult rat, except in particular structures (cortical areas, hippocampus, etc..) where they continue to be highly expressed Three of the chr 5 cluster genes encode the most frequently expressed GABA A α1β2γ2 receptor, while the chr 4 genes encode the GABA A receptor subunit group α2β1γ1 that is found almost exclusively in the addiction-related mesolimbic pathways encompassing ventral tegmental area (VTA) and ventral striatal regions, consistent with co-ordinated transcription within clusters Stephens et al., 2016 Genes Brain Behav. doi: /gbb

26 GABA A receptors endocytosis and recycling Comenencia-Ortiz et al. 2014