L19

Question 1

Hebian plasticity refers to what?

Answer 1

The tendency towards a relatively stable equilibrium between independent elements, especially as maintained by physiological processes
LTP/LTD

Question 2

LTP

Answer 2

AMPA-R stimulated to produce large depolarisation-> NMDA Mg2+ block released-> Ca2+ in (post synaptic N)-> large EPSP (Ca2+ essential for LTP)
LTP is destabilising, pushes post synaptic N towards activity saturation

Question 3

What is plasticity needed for?

Answer 3

Growth and consolidation of synaptic connections, learning and memory, regeneration after damage/disease

Question 4

Homeostatic mechanism for plasticity:

Answer 4

Synaptic homeostasis/scaling
Firing rate homeostasis
Presynaptic homeostasis
[moving axon hillock; activity dependent dendritic remodelling]

Question 5

Synaptic homeostasis/scaling

Answer 5

Altering GluR (AMPA) to maintain constant depolarisation
(Info is coded by reliable synaptic connections NOT by increased post synaptic activity)
Occurs during sleep

Question 6

Firing rate homeostasis

Answer 6

Increased synaptic activation -> decreased NaV expression/ AP firing
(Pumilio, an mRNA repressor binds/degrades NaV mRNA

Question 7

Presynaptic homeostasis

Answer 7

(Occurs at NMJ) PhtTx blocks post synaptic GluR (fly)/AchR (mammals) -> compensatory increase in presynaptic release

Question 8

Homeostasis activation:

Answer 8

Calcium activates Mef2 -> expression of mir134 and Pumilio (mir134 is a regulator of Pumilio)

Question 9

Plasticity has been implicated in a number of disorders:

Answer 9

Epilepsy, schizophrenia autism, affective disorders
Pum2-/- KO mice have spontaneous seizures, Pum2 down regulation seen in human temporal lobe epilepsy
Drosophila- increase Pumilio is anticonvulsant in bang sensitive mutants; Tor-OE (overexpression of target Rapamycin) decreases ALS symptoms in ALS fly model