Lecture 20 (no lecture 19, prof took up test instead)

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Cell and Systems Biology
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Melanie Woodin

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CSB332H1S L20 (no L19, prof took up test instead); March.28, 2012  Some anosmics suffer from depression& quality of life severely Sensory Systems affected – atm little that can be done to help o Since regulates emotional bhvr in significant way Transduction in Olfactory Cilia TASTE (GUSTATION)  Taste & Smell often associated o 1 reason: Both senses activated by external chemical stimuli  Some taste stimuli (tastants) also act on G-prot coupled recs similar to odorants o Structural similarities  Other tastants act directly on membrane conductances  75% of what we perceive as taste comes from sense of smell o Odorants can’t go form mouth to nose when have a cold  lost hald of odorant info in nasal cavity; have a lot of mucus Taste Receptor Cells  Taste Rs = ciliated neuroepithelia cells found in taste buds  Regenerated throughout life  Signal transduction cascade  Don’t have axons o Short recs  Increases [cAMP]  influx of Ca, Na  Form chemical synapses w afferent neurites in taste bud  Ca influx  opens Cl channel  Cl leaves  more depolarization  Microvilli project from taste cell into taste bud where they are Chemical Amplification bound by tastants (dissolved in saliva)  Olfaction depends upon chemical amplification in order to yield Tastants are divided into: 1. Salt sensitivity 2. Sour  Chemical amplification - 2 msger pathways in which enzymatic cascades produce large #s of intermediate products to be activated (ex. 3. Bitter cAMP) 4. Sweet   increasing by 1000x the effect of one activated rec molec 5. Umami o (MSG – amino acid taste) Odorant Specificity  Humans can discriminate odors due to 1000s of dif olfactory recs 2 broad categories of transduction mechanisms for these 5 tastants:  Each olfactory rec recognizes spectrum of odors rather than being 1. Direct action on ion channels highly selective nd 2. 2 messenger activation  Each particular odorant rec is found in restricted area of olfactory epithelium Salt & Sour o Dif families of R genes expressed in zones extending along  Taste of salt  direct flux of Na+ thru channels in apical length of epithelium membrane of outside of taste cell Central olfactory pathways  Salty foods contain high [Na+] o Diffuses down conc grad into taste cells  Neurons from lateral olfactory tract project to; o  Salt induced depolarization  transmitter release from 1. Limbic system (amygdala, entorhinal cortex, hippocampus, taste cell onto afferent neurons  act pot subiculum). Ancient region of brain (motivation, emotion, certain kinds of memory) o Cues to lay down & recall these memories 2. Thal  frontal cortex for recognition. o To primary olfactory region for processing Olfaction & Gender  Olfactory sensitivity can be induced in humans o Ex. humans who were initially unable to smell volatile steroid  Salts & acids can permeate ion channels in sensitive ending or block normally open K+ channels androstenone developed ability after repeated brief exposure  Sour taste  high [proton] in acidic foods  Humans can show enhanced sensitivity to odors they could previously  Sometimes Protons block K+ channels  depolarization detect o Avg increase of 5-fold only observed in females of reproductive age o Suggests greater olfactory sensitivities among females may be associated w female reproductive bhvrs such as pair bonding & kin recognition  Also in mice, rats  Nature Neuroscience 2002 Volume 5 p. 20 Anosmia  A condition where sense of smell is reduced
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