Pheromone Processing: Inverts Flashcards
What is the general pathway of odourant processing?
- odourant
- sensilla
- odourant binding protein
- olfactory sensory neuron
- glomeruli (connected by interneurons)
- projection neurons
- kenyon cells (and lateral horn)
What is the general pathway of pheromone processing?
- pheromone
- sensillum
- pheromone binding protein
- olfactory sensory neuron
- macroglomeruli complex (and glomeruli)
- projection neuron
- lateral horn (and kenyon cells)
What is the structure of the sensilla?
- pore
- 2-4 OSNs with dendrites extending up
What are the specializations of the sensilla?
- 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
What are the sensilla types?
- 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
What is needed to get olfactory and pheromone molecules to the binding site?
- needs olfactory or pheromone binding protein in order to travel through lymph
- binding protein also allows for an “off-switch” as it degrades
Where do the odourants bind and what process results?
- bind to 7 transmembrane receptor (g-protein coupled receptor) activating an iontropic and metabotropic pathway
- the n-terminus of the receptor is intracellular
What is the iontropic pathway?
- OR 83B
- results in fast and transient ion conductance
- Na and Ca influx and membrane depolarizes
What is the metabotropic pathway?
- 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
Why are both the iontropic and metabotropic pathways important?
- 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
In what ways are olfactory sensory neurons organized?
- 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)
What are the exceptions in convergence to OSNs?
- 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
What mapping is seen in the antennal lobe?
- glomeruli organized so that similar odours (similar chemical structure) are spatially close to one another
- similarly mapped on the antennal surface by receptor type
What are macroglomerular complex?
- male-specific type of glomeruli in insects that use pheromones
- receive input from sex pheromone specific osns
How is sensitivity increased?
- by the osns converging to glomeruli (30:1)
How is specificity increased?
- 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
What is the general nervous system of arthropods?
- 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
What kinds of sensory receptors/structures do arthropods have?
- 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
What are the important features of projection neurons?
- may connect with many glomeruli
- use complex temporal patterning rather than rate code to respond to different odours (partly due to the inhibitory interneurons)
Where does information from the projection neurons travel to?
- 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
What are the three pairs of fused ganglia in the head called? What processes do they include?
- 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
What processes occur in the lateral horn?
- important for distinguishing between odourant and pheromones
- acute and innate behaviour
- coarse discrimination
What processes occur in the kenyon cells?
- important for learning, memory, integration of multisensory information and fine discrimination
What types of experiments in this field have been conducted and what do they tell us?
- 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
At what levels does convergence and divergence occur?
- convergence of OSNs to glomeruli which increases sensitivity
- divergence and convergence from projection neurons to kenyon cells
What is the cellular mechanism that allows for conditioning?
- 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
