Plasticity in the Hippocampus

Flashcards covering hippocampal anatomy, the trisynaptic pathway, the properties and molecular mechanisms of Long-Term Potentiation (LTP), and related behavioral studies.

Entorhinal Cortex (EC)

The region of the brain that provides the primary input to the hippocampus via the Perforant Path.

Cornu Ammonis (CA3/CA1)

Key subfields of the hippocampus involved in the trisynaptic circuit; CA stands for 'Cornu Ammonis'.

Dentate Gyrus (DG)

A part of the hippocampal formation that receives input from the Entorhinal Cortex and sends output to CA3.

Subiculum (Sub)

The most inferior component of the hippocampal formation, positioned between the entorhinal cortex and the CA1 subfield.

Trisynaptic Pathway

The relay circuit of the hippocampus consisting of: 1. EC to Dentate Gyrus (Perforant Path), 2. Granule Cell to CA3 (Mossy Fibre), and 3. CA3 to CA1 (Schaffer Collateral/Associational Commissural fibres).

Perforant Path (PP)

The axonal pathway from the Entorhinal Cortex to the Dentate Gyrus.

Mossy Fibre (MF)

The axons of the Dentate Gyrus granule cells that synapse onto CA3 pyramidal cells.

Schaffer Collateral Pathway (SC)

The pathway formed by the axons of CA3 pyramidal cells that project to the CA1 region.

Behavioral Inhibition

A function of the hippocampus; animals lacking a hippocampus often display hyperactivity.

Anterograde Amnesia

The inability to form new memories, famously observed in patient HM after the removal of the hippocampus.

Place Cells

Cells in the hippocampus that facilitate a spatial map of the world.

Discovery of LTP

Bliss and Lomo demonstrated that brief raised frequency stimulation of the Perforant Path produced long-term potentiation (LTP) in the dentate gyrus.

Theta Burst Stimulation

A stimulation protocol used to induce LTP in CA1, typically consisting of 10 repeats at $5\,Hz$ of 4 pulses at $100\,Hz$, repeated 3 times at 20s intervals.

Cooperativity

The property where LTP is induced by either a strong tetanic stimulation to one pathway or the joint weak stimulation of more than one pathway.

Associativity

The strengthening of weak inputs when they are co-active with strongly active inputs converging on the same neuron (Hebbian learning).

Input Specificity

The characteristic that LTP is specific only to the active pathway; inactive synapses do not undergo LTP.

Persistence

The property of LTP lasting from minutes to years, with longer-lasting effects requiring protein synthesis.

NMDA Receptor

A tetrameric receptor composed of 2 NR1 and 2 NR2 subunits ($NR2A$, $NR2B$, $NR2C$, or $NR2D$) that acts as a coincidence detector.

Voltage-Dependent Blockade

The mechanism where the NMDA receptor channel is blocked by $Mg^{2+}$ under normal conditions, requiring depolarization to be removed.

Coincidence Detector

A descriptor for the NMDA receptor because it requires both ligand binding (glutamate/glycine) and postsynaptic depolarization ($Mg^{2+}$ removal) to open.

CaMKII (Calmodulin-dependent protein kinase II)

A kinase activated by $Ca^{2+}/calmodulin$ that translocates to the synapse and plays a crucial role in LTP induction.

Stargazin

A protein associated with mobile AMPA receptors; when phosphorylated by CaMKII, it binds to PSD95 to immobilize AMPA receptors at the synapse.

PSD95

A scaffolding protein in the postsynaptic density that anchors STARGAZIN-bound AMPA receptors at the synapse.

Morris Water Maze

A behavioral test used to measure spatial learning and memory in rodents by having them find a hidden platform in a pool.

CA1-KO Mice

Mice with the NR1 subunit selectively deleted in CA1 pyramidal cells, resulting in blocked LTP and impaired spatial memory.

CREB-1

A transcription factor involved in the late phase of LTP and memory formation, regulated by pathways including cAMP, PKA, and MAPK.