Long Term Potentiation (exam 3)

Associative Learning

•Linkage of two or more unrelated stimuli to elicit a behavioral response

Long-term Potentiation (LTP)

•In response to stimulation at a synapse, changed amplitude of an excitatory postsynaptic potential that lasts for hours to days or longer

•Plays a part in associative learning

•When researchers applied a **tetanus** to the hippocampus, response of postsynaptic neurons changed—

larger EPSPs.

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•**Long-term potentiation** (**LTP**)—

a stable and enduring increase in the effectiveness of synapses.

•Weakening of synaptic efficacy—termed long-term depression—can also encode information.

•The hippocampal formation consists of two interlocking C-shaped structures

•Hippocampus

•CA1

•CA2

•CA3

Dentate gyrus

•Glutamate acts on two different types of receptors on the postsynaptic membrane

•AMPA (alpha-amino-3-hydroxy-5-methylisoa-zole-4-proprionic acid)

•NMDA (N-methyl-D-aspartate)

•Glutamate first activates

AMPA receptors.

•NMDA receptor blocked by Mg2+ ion

•NMDA receptors do not respond until enough AMPA receptors are stimulated, and the neuron is partially depolarized.

•Need Mg2+ to move

What happens after Mg2+ needs to move out?

•Mg2+ driven out, Ca2+ enter

•The large Ca2+ influx activates certain **protein kinases**

•One protein kinase, CaMKII (calcium-calmodulin kinase II), affects AMPA receptors

•AMPA receptors movement, production, insertion

•Increases conductance of Na+ and K+ ions

What do all these effects do?

•These effects all increase the synaptic sensitivity to glutamate

Steps in the Neurochemical cascade during the induction of LTP

•Kinases activate **CREB**—cAMP responsive element-binding protein.

•CREB binds to DNA promoter regions

•Strong stimulation of a postsynaptic cell causes release of a **retrograde messenger**

Travels across the synapse and alters function in the presynaptic neuron

•What neural processes underlie the persistent, long-term changes of learning?

•Ca2+ enters postsynaptic neuron and activates a second messenger

•cAMP alters gene expression in nucleus, which physically alters synapse

•Evidence indicates LTP may be one part of memory formation.

•Correlational observations

•Somatic intervention experiments

•Behavioral intervention experiments

Long Term Depression (LTD)

•Another form of synaptic plasticity

•Neuron becomes less active in response to repeated stimulation

•Involves NMDA receptors

•Requires Ca2+ entry