Long Term Depression (LTD) Flashcards
What is LTD?
Actively evoked, long lasting reduction in synaptic efficacy
Where does LTD occur?
Cerebellum and hippocampus
Types of LTD
Depotentiation
LTD De novo
What is depotentiaion?
Removal of previous potentiation (reversal of LTP)
What is LTD de novo?
Long term depression with no previous potentiation
Is LTD Hebbian?
May be Hebbian (homosynaptic) or non-hebbian (heterosynaptic, not requiring pre-synaptic activity)
LTD requirements
Often rquires NMDA receptors
Often evoked by low frequency stimulation (LFS)
Often requires Ca2+ influx and activation of serine/threonine phosphatases
Often involves glutamate, but also diffuse transmitters like 5-HT
What receptors are involved in cerebellar LTD
Involves metabotropic Glu- receptor, AMPA receptor and voltage activated Ca2+ channels
LTD in cerebellum may help us learn…
Motor skills
Cerebellar LTD mechanism
Climbing fibre activated
Activation of AMPA receptors and voltage gated Ca2+ channels
Ca2+ influx into cell
When parallel fibre stimulated, activation of metabotropic Glutamate-R
Activates cascade involving G protein, phospholipase C, PKC and DAG
PKC phosphorylates AMPA receptors and they are endocytosed
BCM theory
Synapses active when the rest of the cell isn’t become weakened
At a molecular level, how does the cell define whether the synapse undergoes LTP or LTD?
Small increase in Ca2+ trigger more phosphatase action and reduce AMPA efficacy
Large increases activate more protein kinases, which increase AMPA efficacy
What defines whether the synapse undergoes LTP or LTD?
The degree of NMDA receptor activation dictates the probability of inducing LTP or LTD
If stimulated weakly, cell undergoes LTD and vice versa
