LTP and LTD

Question 1

What is LTP

Answer 1

long term potentiation - the change in sensitivity in a neurone

Question 2

name a location where LTP is often studies

Answer 2

at CA3 -CA1 hippocampal synapses

Question 3

describe mechanism of LTP at CA3-CA1

Answer 3

at NMDA receptor
remove Mg2+ block by high fequency stimulus and the binding of glutamate
causes depolarisation and influx of Ca2+

Question 4

what 2 ways does Calcium do to increase LTP in neurones

Answer 4

1. stimulates kinas CaMK2 which phosphorylates AMPA receptors to increase their currents so stimultion of neuter more efficient
2. stimulates kinase PKA so moves into nucleus, causes transcription that results in receptor being more sensitive to stimulus

Question 5

what is the mechanism of LTD at purkinje synapses

Answer 5

if stimulate parallel and climbing fibres is causes decresase in the response of the cell

Question 6

role of PKC in LTD in Hippocampus

Answer 6

activated by DAG and calcium, PKC phosphorylates AMPA to decrease its sensitivity

Question 7

what determines if synapse in state of LTP or LTD

Answer 7

the concentration of calcium

Question 8

describe an experiment that was used to test LTP and LTD

Answer 8

monkeys brought up in different environments
some with little stimulation (toys) some with lots
the more enriched the environment the more spines on the dendrites and more synapses

Question 9

what is hebbians synapse

Answer 9

stimulate 1 neurone, causes EPSP in next neurone

Question 10

hippocampus what is role ?

Answer 10

spatial memory formation and initiates storage

Question 11

the hippocampus circuit

Answer 11

Entorhinal to dentate (perforant)
Dentate to CA3 (mossy fibres)
CA3 to CA1 (Schaffer collaterals)
Output via fornix and subiculum

Question 12

what happens if you stimulate CA3

Answer 12

EPSP IN POSTSYNAPTIC CA1

Question 13

if stimulate CA3 with high frequency stimulus what does it do

Answer 13

increase amplitude of EPSP and cause LTP (long term potentiation)

Question 14

how does LTP occur

Answer 14

initiated when postsynaptic neurons become depolarized, NMDA receptor channels are activated, and Ca2 + flows into the postsynaptic neuron

One way to induce LTP is to use high-frequency stimulation to release large amounts of neurotransmitter to depolarize the postsynaptic cell.

Question 15

structure role of NMDA receptors

Answer 15

NMDA receptors have a voltage-dependent Mg2+ block.

need to be indirectly pre-activated by a separate depolar

Question 16

difference between early and late LTP

Answer 16

Early LTP is associated with short-term memory and late LTP with long-term memory

late requires protein synthesis

Question 17

difference between spatial and temporal summation

Answer 17

Spatial summation occurs when multiple presynaptic neurones together release enough neurotransmitter (e.g. acetylcholine) to exceed the threshold of the postsynaptic neurone.

temporal summation occurs when one presynaptic neurone releases neurotransmitter many times over a period of time.

Question 18

what enhances AMPA currents

Answer 18

Phosphorylation enhances AMPA currents.

Question 19

role of cAMP in LTP

Answer 19

triggers the expression of genes as binds to CREB1

Question 20

what mutations all affect aspects of learning

Answer 20

Mutations of CaMKII, NMDARs, cAMP

Question 21

Drugs to enhance memor

Answer 21

Drugs to enhance memory (nootropics) also enhance LTP

AMPAkines - Alzheimer’s – poor success.

Question 22

There are two main types of LTD

Answer 22

Depotentiation- Removal of previous potentiation

LTD de novo- No previous potentiation

Question 23

is LTD hebbian?

Answer 23

LTD may be Hebbian (homosynaptic – like LTP) or non-Hebbian (heterosynaptic – not requiring pre-synaptic activity)

Question 24

what does an LTD often require (but not always )

Answer 24

NMDA receptors
low frequency stimulation (LFS)
Ca2+ influx
activation of serine / threonine phosphatases
glutamate, but also diffuse transmitters e.g. 5-HT

Question 25

what are the inputs and outputs of LTD circuitry

Answer 25

Inputs are +ve mossy and climbing fibres

Output (to DCN) are –ve Purkinje fibres