Olfaction- Lecture 40

what are chemical sensing pathways?

sensory pathways that respond selectively to different chemicals in the environment (as opposed to pressure, pressure waves, light, temperature)

what are chemical signals important for?

-responding to the environment (eat this, don't eat this, danger)

-communication within or across species

what are the 3 sensory pathways described to chemical signals?

-olfactory (airborne, smell)

-gustatory (non-airborne, taste)

-chemesthesis (hot/ cool)

what are different types of olfactory chemical signals?

-odorants

-pheromones

-allomones

-kairomones

what are odorants?

volatile molecules sensed to give an idea of the chemical environment

what are pheromones?

volatile molecules produced by a species to communicate with other members of the same species

what are allomones?

volatile molecules produced by one species that communicate to a second species for the benefit of the first species (skunks)

what are kairimones?

volatile molecules produced by one species sensed by a second species for the second species benefit (mice react to cat urine)

what is a volatile molecule that is sensed as an odor?

odorant

why is the odor of odorants a highly complex field?

-there are often multiple interactive moieties on each molecule

-a single molecules may interact with multiple olfactory receptors

-most odors are mode up of multiple odor molecules

what do pheromones seem to direct?

produced by individuals in species and seem to direct and regulate social behavior

what is the main olfactory epithelium (MOE) designed to detect?

primarily odorants and information about the chemical environment

what do olfactory sensory neurons in the MOE do?

send axons through the cribriform plate and synapse in glomeruli in the olfactory bulb

what is the vomeronasal organ designed to detect?

pheromones

describe the prevalence of a vomeronasal organ

found in many animals, but not birds, some fish and amphibians or whales; may be absent or significantly regressed in primates and humans

describe the vomeronasal organ in rodents

two layers (apical and basal) expressing different families of receptors --> other animals have one layer

where does the vomeronasal organ connect?

some species have VNO connection to nasal cavity others to oral cavity

where do vomeronasal neurons send axons to?

accessory olfactory bulb

what suggests why the VNO may b isolated from the normal airstream during respiration?

anatomy of the VNO

which animals especially exhibit a curious behavior called flehmen with the vomeronasal organ?

especially ungulates and carnivores with VNO connection to oral cavity

what is flehmen response?

curling the lips and closing the nares

what might flehmen behavior promote?

odorant/ pheromone movement into the VNO for detection

what is Gruenebergs ganglion?

relatively recently identified olfactory center, but has been found in every mammal studied so far

what is the function of Gruenebergs ganglion?

exact function has not been identified yet, but it may sense odors, pheromones, alarm signals, social cues, and/ or cold

where can axon projections from Gruenenbergs ganglion be traced to?

caudal portion of the olfactory bulb

what is the olfactory epithelium made of?

-sustentacular cells

-basal cells

-olfactory sensory neurons (OSN)

in regards to olfactory sensation what is the epithelial layer covered in?

mucus (produced by olfactory (Bowmans) glands)

olfactory sensory neurons project what into the mucus covered in olfactory receptors?

non-motile cilia

what must odorants do before they can interact with olfactory sensory neurons?

odorants in the air enter the nose, but must dissolve in the mucus

what does odorant binding proteins (OBP) facilitate?

dissolution and bring the odorants to the olfactory sensory neurons

what are examples of low selectivity olfactory receptors?

-odorant receptors (OR)

-trace amine associated receptors (TAAR)

what are examples of high selectivity olfactory receptors?

-vomeronasal receptors type 1 (VR1)

-vomeronasal receptors type 2 (VR2)

what is the largest GPCR family?

odorant receptors (OR)

where are odorant receptors (OR) found?

main olfactory epithelium

where are trace amine associated receptors (TAAR) found?

-main olfactory epithelium

-vomeronasal organ

-gruenebergs ganglion

where are vomeronasal receptors type 1 (VR1) found?

-main olfactory epithelium

-vomeronasal organ

where are vomeronasal receptors type 2 (VR2) found?

-vomeronasal organ (basal layer)

-grueneberg ganglion

which animals have odorant receptors (OR)?

all animals

which animals have trace amine associated receptors (TAAR)?

all animals

which animals don't have vomeronasal receptors type 1 (VR1)?

not birds

which animals have vomeronasal receptors type 2 (VR2)?

rodents

what is detected by odorant receptors?

odors

what is detected by trace amine associated receptors?

amine odorants; social or alarm cues?

what is detected by vomeronasal receptors type 1?

pheromones

what is detected by vomeronasal receptors type 2?

pheromones

describe the GPCR of odorant receptors

Golf

describe the GPCR of trace amine associated receptors

Golf

describe the GPCR of vomeronasal receptors type 1

Gi2

describe the GPCR of vomeronasal receptors type 2

G0

describe the Gai2 pathway/ VR1

1. pheromones bind to vomeronasal receptor type 1 (VR1)

2. VR1 recruits and activated Gi2 proteins

3. Gai2 stimulates phospholipase C go produce diacylglycerol (DAG) and IP3

4. DAG potentiates TRPC2 channels which allows Ca2+ into the cell, depolarizing the cell

5. Ca2+ opens calcium-activated chloride channels, releasing chloride from the cell, depolarizing the cell

6. the EPSP travels toward the axon hillock of the olfactory sensory neuron

7. if the EPSP is powerful enough, an AP is generated

Golf act like _______

Gs

Gai2 act like _______

Gq

describe Golf pathway/ OR + TAAR

1. odorant binds to odorant receptor (OR)

2. OR recruits and activates Golf protein

3. Gaolf stimulates adenylate cyclase to produce cAMP

4. cAMP potentiates cyclic nucleotide gates channels which allows Ca2+ (and some Na+) into the cell, depolarizing the cell

5. Ca2+ binds to calcium-activated chloride channels (like ANO2), opening them, releasing chloride from the cell. further depolarizing the cell

6. the EPSP travels toward the axon hillock of the olfactory sensory neuron

7. if the EPSP is powerful enough, an AP is generated

what is macrosmatic?

good sense of smell

what animals are macrosmatic?

-dog

-cat

-sheep

-goat

-cow

-horse

what is microsmatic?

poor sense of smell

what animals are microsmatic?

-primates

-humans

what is anosmatic?

no sense of smell

what animals are anosmatic?

-dolphins

-whales

in regards to the olfactory bulb, OSN in the MOE send to ____________

glomeruli (globular neuropil structures) in the MOB

in regards to the olfactory bulb, in the glomeruli what does the OSN axons synapse with?

dendrites of mitral and tufted cells which perform initial processing of the olfactory signal and then send axons deeper into the brain for further processing

in regards to the olfactory bulb, all axons (several thousand) synapsing in a single glomeruli come from where?

OSN expressing identical odorant receptors

in regards to the olfactory bulb, what is the mitral cells: OSN axons in the glomeruli?

1: 1000

in regards to the olfactory bulb, where do mitral cells in the MOB synapse?

in exactly one glomeruli (homotypic)

in regards to the accessory olfactory bulb, OSN in the VNO send to __________

glomeruli in the AOB

in regards ti the accessory olfactory bulb, in the glomeruli what do OSN axons synapse with?

dendrites of mitral and tufted cells which perform initial processing of the olfactory signal and then send axons deeper into the brain or further processing

in the accessory olfactory bulb, all axons in a single glomeruli come from where?

OSN expressing identical vomeronasal receptors

in regards to the accessory olfactory bulb what is the mitral cells : OSN axons in glomeruli?

1: 100

in regards to the accessory olfactory bulb mitral cells in the AOB synapse where?

in multiple glomeruli (but homotypic)

describe one OSN: one receptor

-each OSN only expresses one unique olfactory receptor, signal from this neuron only come from odorants that interact with this receptor

-any single from an olfactory neuron indicates exactly one odorant receptor activated

describe how odorant interact with different odorant receptors with different affinities

any odorant is likely to activate. wide range of different odor receptors with different levels of activation

describe how Olfactory sensation is the combinatorial measurement of the different ORs activated and their respective levels of activation

This allows the number of odors detectable to far exceed

the number of odor receptors

describe the vomeronasal pathway

sends signals to the limbic system (amygdala/ hypothalamus) for preprogrammed response

describe the main olfactory pathway

sends signals to the primary olfactory cortex for learned response