Announcements Mid term room assignments posted to webpage A – HoS361 (Pavilion) Hoang – LischkaS309 Lishingham - NguiS143 Nguyen – SeguinS128 Sek – Zia H305 ( correction) Lecture 02S319 Lecture 01

Office hours: today 2-4pm, Wed TA Office hours: Wed 12-1 Tutorial Thurs – extra office hours only Answers to practice questions will be posted later today Bring a calculator to the midterm test –Scientific OK ; Not programmable Midterm schedule conflicts –Wednesday 5pm deadline – bring your ROSI timetable Material on midterm – end of today’s lecture

Last Lecture –Synaptic integration Spatial & Temporal Summation Today –Synaptic Plasticity

Soma and dendrites Synaptic inputs Axon Hillock Passive current flow Above threshold? Yes No Action Potential Passive Current Decays to zero Summation Synaptic Plasticity

Changes in the strength of synaptic transmission associated with activity or experience Basis for behaviour such as learning and memory

1.Heterosynaptic Modulation 2.Long-term Potentiation 3.Homosynaptic Modulation 1.Facilitation 2.Post-tetanic Potentiation Types of synaptic plasticity

Heterosynaptic facilitation Aplysia californica (sea slug)

Tap the tail and the gill is withdrawn weakly Tap the head and then the tail the gill is withdrawn strongly Aplysia (sea slug) gill withdrawal reflex

Heterosynaptic facilitation Aplysia (sea slug) gill withdrawal reflex Gill Muscle Motor neuron Sensory neuron tail Head interneuron Sensory neuron serotonin

Heterosynaptic facilitation 1.Serotonin released from interneuron 2.  cAMP in sensory nerve terminal 3.Closes potassium channels 4.Delays repolarization of action potentials 5.Allows more Ca++ to enter the nerve terminal 6.More transmitter release

Tail Sensory Neuron Action potential After Serotonin Motor Neuron Synaptic potential Broader AP allows more Ca++ in

Long-term Potentiation Mammalian hippocampus, and other brain regions Hippocampus is a structure that is important for learning, especially spatial learning

Long-term Potentiation Long-lasting increase (hours to days) in synaptic strength following short high frequency stimulation EPSP Amplitude Time 100% 200% 100 Hz 2 hours

Long-term potentiation Depends on two types of glutamate receptors 1.AMPA permeable to Na+, K+ Function under all conditions 2.NMDA Permeable to Na+, K+, and Ca++ BUT normally blocked by Mg++ Only operate under high frequency stimulation

Na+ NMDA AMPA Mg++ Normal Stimulation

Ca++ Na+ Depolarization Ca++ NMDA AMPA Ca++ Ca++ activates second messenger Mg++ Strong Stimulation

NMDA receptor Key Points 1.Normally blocked by Mg++ 2.Strong depolarization removes Mg++ and allows Ca++ to enter postsynaptically 3.Ca++ activates second messenger pathways that strengthen synaptic transmission Probably activates more AMPA receptors

Homosynaptic Modulation Facilitation Use-dependent increase in synaptic transmission eg. two stimuli are applied to a motor nerve in rapid succession, the second response is bigger than the first Not the same as temporal summation

Synaptic potentials Stimuli close together 1 2 Facilitation Amplitude of 2 is greater than amplitude of 1 Stimuli farther apart – amplitudes are the same

Why get facilitation? If two stimuli are close together there is an accumulation of Ca++ inside the presynaptic nerve terminal –Called residual calcium If the two stimuli are far apart the Ca++ from first stimulus dissipates before second stimulus Lasts for seconds

Ca++ Na+ Depolarization

Ca++ Na+ Depolarization Ca++

Post-tetanic potentiation Tetanic stimulation  high frequency (50 – 100 times per second) Lasts for minutes

EPSP Amplitude Test stimuli 1 / 30 sec 50 Hz for 1 min Potentiation 10 minutes 0 Time Normal Ca++ saline depression

Initial test stimuliestablish baseline During tetanus High release  depletion of vesicles Accumulation of internal Ca++ Post-tetanus Replenishment of Vesicles by recycling Greater release due to high internal Ca++ Post-tetanic potentiation

Summary Synaptic plasticity is a use-dependent change in synaptic strength Heterosynaptic plasticity – one synapse modulates another –Aplysia gill withdrawal reflex Homosynaptic plasticity includes: facilitation and potentiation –Both depend on calcium