Principle projection neurons in the HC
Pyramidal cells and Granule cells
Three main excitatory pathways/ synaptic connections
- Perforant Path from EC to dentate gyrus
- Mossy fibers from DG granule cells to CA3, ending in stratum lucidum
- Schaffer collaterals from CA3 pyramidal cells to CA1 pyramidal cells
CA1 then projects to layer 5 of the EC
Where are new neurons born?
. dentate gyrus
b. hippocampal formation
c. molecular layer
d. CA1
a. dentate gyrus
Initially (first 2.5 weeks), GABAergic input is
a. inhibitory
b. excitatory
b. excitatory
how will the response of an immature cell differ to a mature one to a depolarizing current?
less spiking in immature cell due to sodium channel expression, overexpression of CA2+ channels and different arrangement
immature cell= smaller, so lower capacitance and higher resistance
mature cell= higher capacitance, lower resistance
During recording in CA1 stratum radiatum (multiple answers)
a. exploratory activity is related to theta waves
b. exploratory activity is related to delta waves
c. during awake immobility, monophasic sharp waves and ripples are recorded
d. during immobility, theta waves are recorded
a and c
Characteristics of the stratum radiatum?
primarily dendrites of pyramidal cells, receives input from Schaffer collaterals
choose correct one:
a. Ca1 projects to postcomissural fornix, CA3 to precomissural fornix
b. Ca1 projects to precomissural fornix, CA3 projects to postcomissural fornix
a. correct
3 Main types of inhibition in the HC
- Feedforward inhibition
- regulates flow of information within the hippocampus
- inhibitory neurons activated slightly before the excitatory neurons
-> so when neurons start transmitting their signals, the inhibitory neurons have already begun to inhibit their activity - Feedback inhibition:
-inhibitory cell reacts to cells excessive firing and causes excitatory cell to reduce its activity - Lateral inhibition:
- neighboring neurons/neural circuits can inhibit each others activity
- sharpening contrast / perception
- for single cells or columnar organization
4 types of interneurons in the HC
- OLMC (cell body in str. oriens, synapse to lac-mol)
- Bistratified cells (cell bodies in str. radiatum, target proximal and distal apical dendrites)
- Basket cells (cell bodies in pyr. layer and synapse on soma of pyr cells in pyr. layer)
- Axo-axonic cells (cell body in o.r., synapse on axons)
which type of cells are born first?
a. pyramidal cells
b. interneurons
b. correct
Reason for GABA being depolarizing perinatally
high intracellular CL- concentration mediated by higher expression of NKCC1 (chloride transporter) in immature neurons, causing a more positive equilibrium potential for Chloride than the membrane potential
upon GABA binding, influx of chloride causes a shift of the membrane potential to be less negative
During delivery, GABA..
a. does not excite hippocampal neurons
b. hyperexcites HC neurons
c. only slightly excites HC neurons
a. correct
How can transient loss of excitability ability of GABA in immature neurons be blocked?
a. GABA inverse agonist
b. oxytocin antagonist
c. NKCC1 antagonist
b. correct
Interneurons during oscillations
a. Basket cells
b. Bistratified cells
c. O-LMC
a. more active when moving (theta oscillations
b. some more active during moving (theta), others while asleep/still, each cell has a preferred timing
c. less active when animals are moving and REM sleep, more active when animal are still/deep sleep, no synchrony with theta waves
pyramidal cells and basket cells firing during ripples and sw
- firing happens during ripples and decaying phase for PC
- firing happens before & during but firing does not always result in an AP
- Basket cells have an increase in burst firing during sharp wave, crucial role in synchronization of PC activity
During sharp waves/ripple oscillations….
BC and BIC…..
O-LMC…..
Descending phase ……
Peak….
Trough…..
BC and BIC more active
O-LMC less active
Descending phase: Basket cell
Peak: AAC
Trough: BIC& O-LMC
-> basket cells phase-lock and synchronize pyramidal cell firing in CA1 area
four factors for axon guidance
- diffusible repellent factors
- diffusible attractive factors
- local repellent factors
- local attractive factors
Reelin signals via…
a. ApoLT and VDLDL
b. KCC1
c.ApoER and VLDLR
c. correct
Reelin k.o. can only be rescued by..
a. endogenous reelin
b. heterotypic organotypic co-culture
c. homotypic organotypic co-culture
b.
Reelin
Reelin is a positional signal, exact localization of it is necessary so that proper lamination occurs and the neurons stop migrating, reelin provides stop/pause signal that regulated movement of migrating neurons
-> needs to be replicated to rescue, ie. co-culturing causes formation of DG, HC morphology restored
Entorhinal fibers ..
a. do not innervate the outer molecular plate when there are no DG cells
b. innervate the outer mol. plate even when there are no DGcells
b. innervate the outer mol. plate even when there are no DGcells (helps position them)
There is /are….. type(s) of afferents in the startum radiatum
a. only one
b. different
b. Gluergic, Gabaergic, silent innervation
Layers of the Hippocampus
- Alveus
2 stratum oriens
3 pyramidal layer
4 startum radiatum + stratum lucidum
5 molecular layer
