LTP and Aplysia Flashcards
A closer look at the hippocampus reveals some major structures. Which?
- Dentate gyrus
- CA3
- CA1
Memory processing behins when signals enter the X from the Y via Z.
Memory processing behins when signals enter the dentate gyrus from the enthorinal cortex via axons of the perforant pathway.
Three different types of neurons in the hippocampus synapse onto each other in a line. Which?
Granule neurons within the dentate gyrus synapse onto pyramidal neurons in the CA3 regions. The CA3 axons, referred to as Schaffer Collaterals, connect to the CA1 pyramidal cells.
LTP has been most closely studied where?
In the synapse between the Schaffer Collaterals (the axons of CA3 region neurons) and the CA1 pyramidal cells.
Which receptors are involved in LTP?
AMPA and NMDA-receptors.
What are the specifications of the AMPA receptor?
The AMPA receptor is an ionotropic glutamate receptor. The receptor becomes permeable to cations when activated by glutamate.
What are the specifications of the NMDA receptor?
The NMDA receptor is an ionotropic glutamate receptor. Activation of the receptor results in the opening of an ion channel permeable to cations, calcium in particular. The receptor is voltage-gated in addition to being ligand-gated, because extracellular magnesium and zinc ions can bind to specific sites on the receptor, blocking the passage. Depolarization dislodges and repels the magnesium and zinc ions.
What happens in the CA1 postsynapse after low-frequency action potentials reach the presynaptic terminal of the Schaffer Collateral?
The action potential stimulates the release of glutamate into the synapse, which binds to both NMDA and AMPA receptors. This causes cations to flow throught he open AMPA channel pore, resulting in sufficient polarization for a new action potential. It is however not sufficient for the NMDA magnesium to dislodge, and thus does not cause LTP.
The increase in calcium in the postsynaptic neuron causes two phases of LTP. Which?
- Early phase
2. Late phase
What is the early phase of LTP?
Calcium binds to AMPA-receptors in the cytosol, and transports them to the postsynaptic membrane.
What happens in the late phase of LTP?
Repeated influx of calcium causes an increase in transcription factors, eventually leading to a change in gene expression. This causes a higher synthesis of AMPA receptors, and the release of growth factors that may lead to new receptors.
What is the difference between the sensitization happening in the aplysia and the CA3/CA1-LTP in the hippocampus?
The aplysia neurons depend not on burst firing, but the firing of modulatory interneurons onto the sensory neuron synapse.
Describe the long-term sensitization of gill withdrawal in Aplysia.
Modulatory interneurons release serotonin onto the sensory neuron presynapse.
Serotonin binds to a serotonin receptor
Activated serotonin receptors causes release of g-protein
Released g-proteins activates adenyl cyclase
Adenyl cyclase stimulates the production of cAMP from ATP
cAMP bind to the regulatory subunit of PKA
cAMP causes PKA to release their catalytic subunits
The catalytic subunits activate cAMP response element binding protein (CREB).
CREB binding to the cAMP responsive elements (CREs) in regulatory regions of nuclear DNA increases the rate of transcription of downstream genes.
CREB stimulates the synthesis of the enzyme ubiquitin hydroxylase.
CREB also activates the gene that encodes the protein C/EBP
Ubiquitin Hydroxylase stimulates degradation of the regulatory subunit of PKA, causing a persistent increase in the amount of free catalytic subunit.
C/EBP is a transcription factor (like CREB) and stimulates the production of other unknown genes.
The gene products of the C/EBP activation is thought to be responsible for long-term increases in the number of synapses.
