Lectures 15 and 16

Rachel A. Kaplan and Elbert Heng4.8.14

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• 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