14 Olfaction 2012-1
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Chemoreception
Nasal Chemoreception
(Smell)
GustationOlfaction
VomeronasalChemoreception
Chemesthesis(Trigeminal Chemoreception)
OralChemoreception
(Taste)
Chemesthesis(Trigeminal Chemoreception)
Introductory Neurobiology 2012
-receptor cells are neurons-long distance -chemesthesis refers to ability to detect irritating stimuli-vomeronasal requires contact w/stimuli; important for mammals, but not for primates
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Olfaction, The Common Chemical Sense and
Vomeronasal Chemoreception
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-nasal cavity is where we sense odors-two routes: sniffing directly through the nose or through the nasal cavity
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Rodriguez. Nat. Neuro.(2003)
Chemosensory Systems in Mammalian Nose:
•Main Olfactory -general odorants
•Accessory Olfactory (Vomeronasal) -pheromones
•Trigeminal (Chemisthesis) -irritating/pungent volatiles
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-pheromones are instinctual, but not entirely-detecting predators, aggressive displays, maternal behavior, finding mates, provides direct input to amygdala
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Olfaction (Smell)
Introductory Neurobiology 2012
-hyposmia: reduced sense of smell-anosmia: no sense of smell; can have a general or specific (lose ability to smell specific odors)-cacosmia: having olfactory hallucinations [smelling things that aren't there]
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The Importance of Olfaction
Introductory Neurobiology 2012
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Our Sense of SmellCan really influence and alter our moodCan influence how long we stay in a roomSharpens our awareness of other people places and things.Can influence who we talk to and who we want to talk again (if histocompatability group is different, better chance of bonding)
• Can be a warning systemIntroductory Neurobiology 2012
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Early warning system
Introductory Neurobiology 2012
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“The Dogtor is in”(Pet Scans)
Moles-melanoma
Breast cancer
Lung cancer
Introductory Neurobiology 2012
-sense odor from body
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Specificity and intensity of dog responses to breath/urine
99% accurate vs biopsies!
Introductory Neurobiology 2012
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Flavor
BitterBitterSweetSweetSour Sour SaltySalty
Umami Umami (MSG)(MSG)
Introductory Neurobiology 2012
-majority of flavor is smell, predominantly retronasal smell-olfactory bulb in human is less than size of pinky nail
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MemoriesMemoriesEmotionsEmotions
Introductory Neurobiology 2012
-olfactory memories are very strong -Several branches of olfactory nerve going to olfactory bulb -olfactory bulb provides direct input to the amygdala; also involves memory
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Odor and Memories
Recall
Vision: 50% accurate after only 3 months
Smell: 65% accurate after a year
Introductory Neurobiology 2012
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Structure of the Nose
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-crib inform plate separates nasal cavity from brain; olfactory nerves terminate in olfactory epithelium-receptor cells are neurons-first synapse is in the brain; in olfactory bulb-neurons terminate in cilia
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The Olfactory Epithelium
The nose is the gateway to the brain (problem if wacked in nose, can get brain infections; diseases by amebas get into nerve and go to brain)
Potential risks of trauma to the nose
Introductory Neurobiology 2012
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Linda BuckIntroductory Neurobiology 2012
-cilia is where initial events in sensory transduction take place
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Introductory Neurobiology 2012
-plate is very thin bone-neurons can regenerate, but there is a lot of scar tissue that can prevent neurons from going back to place
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Introductory Neurobiology 2012
-first synapse is in olfactory bulb-neurons will go to glomerulus-there is a specificity in glomeruli
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Linda BuckIntroductory Neurobiology 2012
-pathway is from OE to OB to OC-sense of smell goes through cortex then the thalamus
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Rodriguez. Nat. Neuro.(2003)
Transduction Mechanisms in Mammalian Nose
Introductory Neurobiology 2012
-g-protein is Golf-cAMP will open ion channel that allows Na and Ca to come in-Ca will open Cl channel to leave neuron to further depolarize-same tranduction pathways for smells, difference in receptor-~300 different receptors
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The Olfactory Receptor Neuron
Introductory Neurobiology 2012
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From: S. Ramon y Cajal y J.F. Tello y Muñoz. 1931
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-when we stimulate neuron, we generate receptor potential-if receptor potential is sufficient, it will generate AP
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A.~ 300B.~ 1, 000C.~ 10, 000D.~ 1 million
How many different odors can Humans discriminate?
Introductory Neurobiology 2012
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Common Odors
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
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Mechanisms of Olfactory Transduction
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-each olfactory receptor expresses only one of the receptors
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Olfactory Coding
Glomeruli
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-there is coding by glomeruli-all same receptor cells send their axons to the same glomeruli-individual receptors tend to go to individual glomeruli
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Introductory Neurobiology 2012
-receptor 1 responds to moer than one odor but respond to differnt intensity-coding is combination of labeled-line and cross fiber coding
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Olfactory Receptor Genes
• Approximately 1000 genes in rodents
• Each olfactory receptor neuron expresses only 1 olfactory receptor
• These same receptors are expressed in the testis on sperm cells
Introductory Neurobiology 2012
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Nobel Prize in Physiology or Medicine 2004
RICHARD AXEL LINDA BUCK
Protein must be able to detect a large number of odorants
One gene, multiple combinations (like immunity)
A large family of genes each encoding a different receptor
Discovered the Odorant Receptor Gene family (in 1991)
Introductory Neurobiology 2012
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Odorant Receptor GenesHUGE gene family
Large fraction of our genome
Scattered throughout all of our chromosomes
Each odorant gene codes for a protein that is sensitive to a particular chemical structure(s)
• combinattion of receptors (1625)
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-how single glomerulus receives axons from neurons expressing one receptor-one receptor one glomerulus
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Introductory Neurobiology 2012
-similar receptors are not distributed randomly, located in zones-specificity of zonation for olfactory receptor neurons
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Linda BuckIntroductory Neurobiology 2012
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Linda BuckIntroductory Neurobiology 2012
-olfactory epithelium is like a mosaic of different receptor neurons expressing different individual receptors
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* ~ 1000 OR types * One OR type per cell * Subset of OR types per zone * Zone to Zone projection * Cells of the same type project to a small number of fields (glomeruli) * Different odors activate different fields
Mori K. et al. Science (1999)
Introductory Neurobiology 2012
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Linda BuckIntroductory Neurobiology 2012
-shows convergence
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Linda BuckIntroductory Neurobiology 2012
-shows zone in olfactory epithelium and axons projecting to different glomeruli
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Linda Buck
Introductory Neurobiology 2012
-4 receptor and odorants-multitude of combinations are possible-w/300 different receptors and 10000 different odors
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Linda BuckIntroductory Neurobiology 2012
-combinatorial coding is superimpozed on zonal label line coding
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The Common Chemical Sense(Chemisthesis)
The importance of the common chemical sense
Introductory Neurobiology 2012
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The Common Chemical Sense (Chemisthesis)
Receptors
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-receptors for CCS are neurons; primary sensory neurons-form synapses in spinal cord
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Introductory Neurobiology 2012
-trigeminal nerve is the fifth cranial nerve-burning sensation
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The Common Chemical Sense (Chemisthesis)
Mechanism of transduction:
Activation of TRP channels
Introductory Neurobiology 2012
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Trigeminal Chemoreception
Heat measured in Scovill units
Introductory Neurobiology 2012
TRP channels are located directly on trigeminal nerve
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Introductory Neurobiology 2012
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Trigeminal Ganglion Peripheral Nerve
Peripheral Terminal
Eye, Nose, or MouthACUTE TREATMENT
CHRONIC TREATMENT
NEONATAL TREATMENT
To Brain Stem
vanillyl alkyl chainaclyamide
Capsaicin desensitization
Introductory Neurobiology 2012
-if acute stimulation, nerve is stimulted-if chronic, nerve will become desensitized-if neonateal, nerve can be killed and not recover
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Figure 3 VR1 responds to purified vanilloids and pepper extracts.. c, Responses to capsaicin (10 M) and extracts derived from four varieties of peppers in oocytes expressing VR1 (30 s application). Bottom right, relative potencies of each pepper extract are plotted (mean s.e.m., n = 3). Values were normalized in each cell to responses obtained with capsaicin (10 M). Extracts evoked no responses in water-injected cells. Reported pungencies for pepper varieties (in Scoville units) are: Habanero (H), 100,000–300,000; Thai green (T), 50,000–100,000; wax (W), 5,000–10,000; and Poblano verde (P), 1,000–1,500 (ref. 23). Capsaicin (C) is rated as 16x106 units.
From Caterina et al., Nature 389, 816 - 824 (23 Oct 1997) Introductory Neurobiology 2012
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Relative “burn” of some common peppers
• Bell pepper 0• Jalapeño 2,000 - 5,000 units• Serrano 5,000 - 15,000 units• Thai 50,000 - 100,000 units• Habañero 100,000 - 300,000 units• Ghost pepper 1-3 million units!!!
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
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Vanilloid receptor 1 (VR1)(TRPV1)
Vanilloid-like receptor 1 (VRL-1)(TRPV2)
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-ligand-gated channel-capsaicin is fat-soluble-makes receptor open up at room temperature
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Cool Receptors(TRPM8)
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-TRPM8 responds to cold and menthol
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TRPA1
• Mustard oil∀ ∆9-tetrahydrocannibinol
• Cinnamaldehyde
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
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Stimulation of Nasal Trigeminal Fibers
• Associated with painful or irritating chemicals (tingling, stinging, burning)
• Examples of physiological reflexes– decreased respiration– increased nasal secretion– closure of nares and glottis– sneezing
• Effects of noxious stimulus is minimized and the individual is protected from further exposure
Introductory Neurobiology 2012
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Vomeronasal Chemoreception and Pheromones
Introductory Neurobiology 2012
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PheromonesDefinition: any chemical or set of chemicals produced by a living organism that transmits a message to other members of the same species.
Naive response, not learned
e.g. pups suckle, males fight, and estrus cycles are altered.
Their precise nature remains somewhat controversial
• males have more whisker growth
Introductory Neurobiology 2012
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Invertebrate Pheromones
First discovered in silkworm moths
Females secrete a specific blend of odorants that is highly attractive to males
males fly upwind to find the source (as far away as a mile away)
Introductory Neurobiology 2012
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Vertebrate Pheromones
Swabbed HamsterA male hamster swabbed with hamster pheromone (“Aphrodisin”) became sexually attractive to another male hamster
Introductory Neurobiology 2012
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Bruce Effect
Male Urine can induce estrus (heat)
Bruce effect = odor memory
Same mouse: pregnancy maintained
New mouse or urine spike with pheromone: pregnancy terminated
Introductory Neurobiology 2012
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The Importance of the Vomeronasal Organ (VNO)
and Pheromones
Mating behaviorTerritorial behaviorOther conspecific behavior
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
-VNO is located in pit in base of nose-goes to accessory olfactory bulb-projects to medial amygdala
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Vomeronasal OrganSecondary Olfactory System
Sensory neurons synapse onto an Accessory Olfactory Bulb
Mouse: at base of nasal cavity
responds to bodily fluids introduced into the cavity (non-volatile)
The Pheromone detector?MOB detects pheromones as well
– terminate in microvilli
Introductory Neurobiology 2012
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Mating Behavior
Anecdote about male hamster
Androstenone
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
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Behaviors Mediated by Vomeronasal Organ and Main Olfactory Epithelium
From Mombaerts
•Aggressive behavior•Mating partner preference•Vocalizations•Endocrine effects (e.g. puberty delay, synchronization of estrous)
•Discrimination of general odors (instrumental conditioning, habituation/ dishabituation?)
Introductory Neurobiology 2012
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Introductory Neurobiology 2012
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Human Pheromones?
Anecdotal: man’s whisker growth faster in the presence of womenWomen who live together tend to get their period during the same time of the month. Chemicals collected from the armpit and dabbed under the nose have the same effect on women
One chemical will shorten the menstrual cycle by 1.7 daysAnother chemical will lengthen the cycle by 1.4 days
Introductory Neurobiology 2012
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MHC
Major Histocompatibility ComplexIdentified as a major component in tissue graft rejection
Also appears to influence our body odor
Mechanism for detecting people with similar (or different) genotypes?
Introductory Neurobiology 2012
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Human VNO?Human fetus
have a VNO
but connections appear to disappear after ~19 weeks of age
Adult: usually a depression (or pit) in nasal cavity
not always there or on both sides
most human VNO Receptors are pseudogenes... Introductory Neurobiology 2012
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“When, from a long-distant past nothing remains,After the people are dead;after the things are broken and scattered.Still, alone, more fragile,but with more vitality,more insubstantial,but more persistent, more faithful,the smell and taste of things remain poised forever,like ghosts, ready to remind us…
Remembrance of Things Past––––Marcel Proust
Introductory Neurobiology 2012