MH - Neur 3206 - Lecture 3 Handout.pptx

MH - Neur 3206 - Lecture 3 Handout.pptx - Lecture 3...

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Lecture 3: Olfaction – Transduction, Discrimination and Perception
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Announcements Reading 1 due in one week Today’s text: Chapter 8, 2 nd half
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What are we going to do today? Olfactory transduction Olfactory processing in the olfactory bulb Olfactory processing in higher brain centers Mechanisms of odor discrimination and perception Olfaction, memory and emotion
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Olfactory cilia – site of transduction How are receptor potentials generated by specific odorant compounds in a given OSN?
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Olfactory receptors The olfactory system is the only one of our sensory systems that was deciphered primarily using molecular techniques: Linda Buck and Richard Axel, Nobel Prize in 2004 described a large family of “orphan receptor” genes (~1500 in mice) that code for odorant receptors olfactory receptors http://www.nobelprize.org/nobel_prizes/medicine/laureate s/2004/press.html
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Diversity of olfactory receptors Olfactory receptors are G-protein coupled receptors with extracellular odorant binding sites Olfactory receptors are the largest known single gene family represent 3 – 5% of the genome! But , 60% of olfactory receptors genes in humans not transcribed/translated, due to molecular changes pseudogenes Each functional receptor type detects (is activated by) a specific set of odorant molecules
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Time Out – G-Protein Coupled Receptors Olfactory receptors are G-protein coupled receptors with extracellular odorant binding sites GPCRs are 7 transmembrane domain membrane proteins activated by specific ligand Ligand binding causing phosphorylation-dependent activation of associated G-proteins Activated G-proteins dissociate from receptor to act on channels and/or enzymes in the membrane or cytoplasm (or ligand) (or ligand) Fig. 5.17 G alpha G beta gamma
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Olfactory transduction Most mammalian OSNs typically express one olfactory receptor gene (e.g. – M71 from Reading 1), with the transcribed receptors localized to olfactory cilia Fig. 8.10
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Olfactory transduction Odorant-bound receptor proteins activate an intracellular signalling cascade: Activation of heterotrimeric G- protein, causing G  subunit (G olf ) to dissociate G olf -mediated activation of adenylate cyclase enzyme, which synthesizes cAMP Increase in cAMP, causing opening of cationic cyclic nucleotide-gated channels graded depolarization of OSN Increased intracellular Ca 2+ (due to influx through cAMP channels) opens Ca 2+ –activated Cl - channels further graded depolarization of OSN (due to high intracellular Cl - in Fig. 8.10
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From receptor potentials to APs
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