Lectures 15 and 16 Rachel A. Kaplan and Elbert Heng

LECTURE 15: SYNAPTIC PLASTICITY

LECTURE 16: BEHAVIORAL NEUROBIOLOGY

Overview What/Why/How Study Animal Behavior? Behavior Examples Considerations Application: Fast Escape Response

Ethology What? – Study of animal behavior Why? – Important: understanding implications of manipulation of animal system (as a model) – Animal models of diseases/mechanism How? – Correlation, sufficiency and necessity let us draw conclusions about neurobiology of behavior

Behaviors Responses to releasing stimuli – e.g. Egg Rolling Stimulus (egg) triggers fixed action pattern – e.g. Seagull Chick Feeding Stimulus (spot color) triggers pecking Supernormal stimuli: allows us to study nature of what an animal is actually responding to in a stimulus

Behaviors Social Behaviors – Also ritualized due to evolutionary pressure Which suggests that behavior has genetic components – e.g. courtship of flies and swans

Considerations Want to study the behaviors as the animals do them Animals are different – Different perceptions/adaptations which means their brain circuitry is different and may not be translatable without modulation/caution Strange animals can give us insight into strange capacities

Behavior: Fast Escape Response Fish sense a stimulus (hunter creates vibrations in water) and have a reflex (neural circuit) to execute the fast escape response behavior. Requirements – FAST – Turn the fish around Turn the fish around Do it the right way And only once

Stimulus  Contralateral Contraction Vibrations stimulate hair cells in ear/lateral line These cells transmit signal via CN VIII to the M cell M cell synapses on motor neuron on contralateral side of fish Motor neuron activation contracts muscle FISH TURNS

Stimulus  Ipsilateral Relaxation Same path to M Cell M Cell synapses on inhibitory interneuron Interneuron inhibits motor neuron on ipsilateral side FISH DOESN’T CONTRACT OTHER SIDE TOO

Preventing Multiple Responses From ipsilateral side stimulus – Feedback inhibition M cell synapses on inhibitory collateral neuron which inhibits M cell via axon cap inhibition From contralateral side – Feedforward inhibition CN VIII synapses on PHP interneurons which directly inhibit M cells bilaterally

Recap of Special Physiology Interneurons: usually present to switch polarity of signal (exciting an inhibitory interneuron will inhibit whatever cell the interneuron synapses on) – PHP cells are interneurons Axon cap: a big high resistance structure of glia and axons of PHP cells. – PHP cells spike, drawing + charges into axon from surrounding axon cap and then out into cap, which makes the axon cap more positive, creating a higher potential across axon cap wall and M cell, hyperpolarizing the M cell.

PPI and M Cell Network Applications of our understanding of the network: – Research on PPI and schizophrenia Drug research