Pheromone Processing: Inverts

Question 1

What is the general pathway of odourant processing?

Answer 1

• odourant
• sensilla
• odourant binding protein
• olfactory sensory neuron
• glomeruli (connected by interneurons)
• projection neurons
• kenyon cells (and lateral horn)

Question 2

What is the general pathway of pheromone processing?

Answer 2

• pheromone
• sensillum
• pheromone binding protein
• olfactory sensory neuron
• macroglomeruli complex (and glomeruli)
• projection neuron
• lateral horn (and kenyon cells)

Question 3

What is the structure of the sensilla?

Answer 3

• pore

- 2-4 OSNs with dendrites extending up

Question 4

What are the specializations of the sensilla?

Answer 4

• can have multiple pores to increase sensitivity
• oily coating to prevent pore from clogging (inspired solution for nanotool that looks at single molecules)
• different types which are mapped on antennal surface

Question 5

What are the sensilla types?

Answer 5

• trichoid: other pheromones (hair like)
• basiconic: food odours, CO2 (peg like)
• coeloconic: food odours, ammonia, amines, water vapour, alcohols (recessed peg like)
• ampulacea: pore plates

Question 6

What is needed to get olfactory and pheromone molecules to the binding site?

Answer 6

• needs olfactory or pheromone binding protein in order to travel through lymph
• binding protein also allows for an “off-switch” as it degrades

Question 7

Where do the odourants bind and what process results?

Answer 7

• bind to 7 transmembrane receptor (g-protein coupled receptor) activating an iontropic and metabotropic pathway
• the n-terminus of the receptor is intracellular

Question 8

What is the iontropic pathway?

Answer 8

• OR 83B
• results in fast and transient ion conductance
• Na and Ca influx and membrane depolarizes

Question 9

What is the metabotropic pathway?

Answer 9

• OR 22a
• results in activation of g-proteins
• g-alpha subunit stimulates adenylyl cyclase which increases ATP to cAMP production
• cAMP slowly activates a long lasting non-selective cation conductance (CNGCC) which causes influx of Ca and Na and causes depolarization

Question 10

Why are both the iontropic and metabotropic pathways important?

Answer 10

• so the organism can respond right away and maintain the response
• cascades allow for energy/info to be translated so that the system understands
• cascades allow for amplification

Question 11

In what ways are olfactory sensory neurons organized?

Answer 11

• 2-4 per sensilla
• project to glomeruli in the antennal lobe
• each glomeruli will receive multiple inputs from osns with the same receptor type
• stimulus is encoded as firing rates in osns (increase in dose = increase in firing rate)

Question 12

What are the exceptions in convergence to OSNs?

Answer 12

• regularly: multiple osns with same receptor converge onto glomeruli
• co-convergence: osns with different receptor types converge onto same glomeruli
• co-expression: osns with two receptor types converge onto same glomeruli

Question 13

What mapping is seen in the antennal lobe?

Answer 13

• glomeruli organized so that similar odours (similar chemical structure) are spatially close to one another
• similarly mapped on the antennal surface by receptor type

Question 14

What are macroglomerular complex?

Answer 14

• male-specific type of glomeruli in insects that use pheromones
• receive input from sex pheromone specific osns

Question 15

How is sensitivity increased?

Answer 15

• by the osns converging to glomeruli (30:1)

Question 16

How is specificity increased?

Answer 16

• specificity increased via lateral inhibition by local inhibitory neurons
• excitation of one glomeruli will excite an inhibitory interneuron that dampens the excitation of other glomeruli

Question 17

What is the general nervous system of arthropods?

Answer 17

• dorsal, anterior brain
• ventral nerve cord
• if ancestral: one ganglion/segment
• otherwise: fusion of ganglia
• subesophageal ganglion: principle centre for motor control
• 2-4 pairs of lateral nerves/ganglion

Question 18

What kinds of sensory receptors/structures do arthropods have?

Answer 18

• greater diversity of receptors than vertebrates
• chemoreceptors: olfactory and gustatory info (humidity and osmotic)
• mechanoreceptors: sensory spines/hairs, motion receptors, contact receptors, strain receptors
• auditory receptors and gravitational organs
• simple and compound eyes with photoreceptors and temperature receptors

Question 19

What are the important features of projection neurons?

Answer 19

• may connect with many glomeruli
• use complex temporal patterning rather than rate code to respond to different odours (partly due to the inhibitory interneurons)

Question 20

Where does information from the projection neurons travel to?

Answer 20

• projection neurons connect with either kenyon cells in the mushroom bodies or the lateral horn
• information they receive may be unprocessed or processed by lateral interaction between glomeruli

Question 21

What are the three pairs of fused ganglia in the head called? What processes do they include?

Answer 21

• protocerebrum: optic lobes, mushroom bodies (receive sensory input and provides to the central body), central body (central pattern generator), pars intercerebalis
• dentocerebrum: antennal lobes (chemosensory input), dorsal lobe (motor output)
• tritocerebrum: gut activity

Question 22

What processes occur in the lateral horn?

Answer 22

• important for distinguishing between odourant and pheromones
• acute and innate behaviour
• coarse discrimination

Question 23

What processes occur in the kenyon cells?

Answer 23

• important for learning, memory, integration of multisensory information and fine discrimination

Question 24

What types of experiments in this field have been conducted and what do they tell us?

Answer 24

• bioessays: honeybees trained to anticipate a reward when a certain stimulus is presented
• electroantennograms: examine electrical signals from antennae to look at activation caused by different odours
• extracellular recordings: to look at electrical activity to certain scents in alive/intact moths

Question 25

At what levels does convergence and divergence occur?

Answer 25

• convergence of OSNs to glomeruli which increases sensitivity
• divergence and convergence from projection neurons to kenyon cells

Question 26

What is the cellular mechanism that allows for conditioning?

Answer 26

• simultaneous arrival of a conditioned stimulus and unconditioned stimulus through a latent synapse
• synapse between kenyon cells and output neurons is strengthened
• activates the cascade: adenylyl cyclase, production of cAMP, protein kinase A activation, phosphorylates target proteins
• calcium calmodulin and calcium is needed to activate Rut-Ac which phosphorylates K channels (deactivating k channels) and prolonging depolarization