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University of Connecticut Graduate School MEDS 371: Systems Neuroscience 2011 Chemosensory Systems Marion E. Frank, Ph.D. Professor Center for Chemosensory Sciences Oral Health & Diagnostic Sciences School of Dental Medicine OLFACTORY SYSTEM Purpose of Smell---Detect, Analyze Valuable or Dangerous Environmental Chemicals Chemicals that Smell: Vapors, Names camphoraceous: hexachloroethane floral: 2-amyl pyridine pepperminty: l-menthol ethereal: diethyl ether Putrid pungent: formic acid putrid: hydrogen sulfide musky: xylene musk Peripheral Labeled Lines Odor Receptors and Mitral Cells in Olfactory Bulb Red = ? Green = ? Blue = ? From Axel and Buck, 2005 1000 GPCR odor receptors (OR) From Buck, 2005 Odor Transduction Adaptation, PKA Rapid Adaptation Species Differences in Olfaction Main Olfactory System -- Vomeronasal System MOE = main olfactory epithelium MOB = main olfactory bulb AON = anterior olfactory nucleus PC = piriform cortex OT = olfactory tubercle LA = lateral amygdala EC = entorhinal cortex VNO = vomeronasal organ AOB = accessory olfactory bulb MeA = medial amygdala Dulac & Wagner, 2006 Rodent Olfactory Bulb OSNs Rapid Adaptation Mixture Suppression Glom = glomerulus, OSN = olfactory sensory neuron Inhibitory Neurons: PG = periglomerular cell, G = granule cell, Output Neurons: M = mitral cell lateral olfactory tract Schoppa and Urban, 2003 Olfactory Epithelium Cells, Turnover, Target in Olfactory Bulb Olfactory Sensory Neuron Generation in Adults Sus = Sustentacular (supporting) cell, HBC = Horizontal Basal Cell GBC = Globose Basal Cell; mpp multipotent progenitor, ta = transit amplifying, inp = immediate neuronal precursor. OSN = Olfactory Sensory Neuron; i = immature, m = mature. Schwob, 2002. Human Nasal Cavity, Sniffing Ortho- vs. Retronasal MOE: Recordings, Apical and Basal Functional Units in Olfactory Bulb Morphological substrates for inhibition. ON = olfactory nerve PG = periglomerular cell M = mitral cell GR = granule cell AON = anterior olfactory nucleus Morphological substrates for specific input-output functions. Responses of Olfactory Bulb Neurons = stimulus delivery N = no response S1, S2 = suppression E1, E2, E3 = excitation At top, phases of electro-olfactogram (EOG) are represented by Roman numerals (I, II, III, IV) (Kauer, 1974). Central Olfactory Pathways: Rodent Rodents: Macrosmic >1000 OR AON: anterior olfactory nucleus, PC: piriform cortex, OT: olfactory tubercle, AM: anterior cortical amygdaloid nucleus, TER: lateral entorhinal cortex ODOR CODING Odor stimuli to test with Monoclonal Nose in Mice. O pungent, orange pine tar, turpentine (+)/(–) Alpha-Pinene Acetophenone O rose-like lily OH (+)/(–) Beta-Citronellol O Ethyl Acetate nail polish, fruity Mice with a “Monclonal Nose”… Fleischmann et al. 2008 ●= control ▲ = transgenic, 95% ORN express M71 (ligand Acetophenone) Go/No-go Fraction Correct Ethyl Acetate, –/+ Citronellol Block of Trials Mice with a “Monclonal Nose”… Fleischmann et al. 2008 ●= control ▲ = transgenic, 95% ORN express M71 (ligand Acetophenone) Go/No-go Fraction Correct Ethyl Acetate, –/+ Pinene Block of Trials Mice with a “Monclonal Nose”… Fleischmann et al. 2008 ●= control ▲ = transgenic, 95% ORN express M71 (ligand Acetophenone) Go/No-go Fraction Correct Acetophenone, Air Block of Trials Mice with a “Monclonal Nose”… Fleischmann et al. 2008 ●= control ▲ = transgenic, 95% ORN express M71 (ligand Acetophenone) Go/No-go Fraction Correct Acetophenone = Air Air Air Air Air Block of Trials See B NATURAL SCENTS 100s of Chemical Components in Scent Representation in Few Glomeruli in Rodents Few Dominant Cues Inhibitory Interactions among Glomeruli Dulac, 2006 Central Olfactory Pathways: Human Humans:Microsmic ~300 OR Odor Mixtures: Humans Single Compound Vanillin Mixture Component Single Compound PEA •V = 5 mM vanillin, v = 1 mM vanillin •R = 5 mM PEA, r = 1 mM PEA. • 0 = water •Gold background highlights correct responses of 10 subjects in each session • The 31 adapt-test pairs were presented to each subject in each session •Average % correct Identification for the 2 sessions is listed at right •PEA = phenethyl alcohol odor Rose ODOR CODING: Rapid Adaptation & Mixture Suppression Single Compounds Controls From Frank et al, 2010 Mixture Components Controls Convergence of Taste and Smell in Orbitofrontal Cortex From Rolls, 2004 Olfactory System Summary Smell is a chemical sense that evaluates vaporous environmental chemicals. We perceive many odor qualities, notes perhaps each associated with one of the hundreds of olfactory receptors (OR). Olfactory sensory neurons (OSN) have dendrites with cilia containing a G-protiencoupled OR and axons that communicate to the olfactory bulb. OSN can regenerate, giving them an unusual ability to recover from injury. OSN located in separate regions use 4 subfamilies of OR, individual OSN express single OR variants, and all OSN expressing one of the hundreds of variants project to a few glomeruli in the olfactory bulb. OSN may respond to many compounds, generating distinct spatial-temporal patterns of neural activity for each odor. Olfactory bulb output neurons, mitral and tufted cells, relay olfactory signals to higher levels, and periglomerular and granule inhibitory neurons, which are generated throughout adult life, modify olfactory signals within the bulb. Olfactory signals are relayed from the olfactory bulb to the olfactory paleo-cortex, then thalamus and cerebral cortex, where odor qualities are discriminated. Projections to the hypothalamus and hippocampus are sites where experience and emotion interact with odor. The End