Schaffer collateral
Encyclopedia
Schaffer collaterals are axon
collaterals given off by CA3 pyramidal cell
s in the hippocampus
. These collaterals project to area CA1 of the hippocampus and are an integral part of memory
formation and the emotional
network of the Papez circuit
, and of the hippocampal
trisynaptic loop
. It is named after the Hungarian anatomist-neurologist Károly Schaffer
, and It is one of the most studied synapses as well.
In the early stage of long term potentiation Schaffer collaterals release glutamate that binds to AMPA receptor
s of CA1-dendrites.
in terms of storing information. Once those memories are stored, they remain stored in very long time. However, they slowly fade away, which means that there are some roles for the hippocampus when talking to the near cortex in order to prevent diminishing those memories away. It is clear that whatever plastic changes occurring in the hippocampus involve in directing the process by which memories get stored. Schaffer collateral is involved in activity-dependent plasticity and the information processes that always are processed through the hippocampus all the time. Schaffer collateral is clearly affecting whether the target cells fire action potentials or not. However, at the same time, it is triggering the process that takes much longer whereby some synapses get stronger and some get weaker, and overall all the patterns of synaptic strength of the network evolve all over time.
sends the main input to the dentate gyrus
(Perforant pathway). From the granule cells of the dentate gyrus, connections are made to the CA3 regions of the hippocampus via mossy fibers. CA3 sends the information signals to CA1 pyramidal cells via the Schaffer collateral and commissural fibers
from the contralateral hippocampus as well.
(LTP) of synaptic strength at Schaffer collateral synapses has largely been attributed to changes in the number and biophysical properties of AMPA receptors (AMPARs). Neuropsin has a regulatory effect on Schaffer collateral LTP in the rat hippocampus
(LTD) which is a long-lasting decrease in synaptic strength.
can be induced by different patterns of stimulation generating pre- and post-synaptic depolarization
. These synaptic changes can clearly lead to modification in circuit function and to behavioral plasticity. Some patterns of synaptic activity produce an extensive increase in synaptic strength, also known as Long-Term Potentiation (LTP). In the hippocampus, LTP at Schaffer collateral-CA1 modulates the biophysical properties of AMPA receptors. Moreover, SK2
, small-conductance Ca2+-activated K+ channel, changes the shape of excitatory postsynaptic potentials (EPSPs) by coupling with N-methyl D-aspartate (NMDA) receptorsNMDA receptors. The research by Lin MT, et al was designed to investigate whether SK2 channels participate in synaptic changes when an activity-dependent decrease contributes to LTP.
SK2 channels
are ion channels that are activated by an increasing in the concentration of intracellular calcium and as a result of allowing K+ cation to cross the cell membrane. The double immunogold labeling identified that SK2 channels and NMDA cohabit within the postsynaptic density (PSD) of CA1 regions of the hippocampus. The authors used theta-burst pairing (TBP) to produce a rapid potentiation of synaptic strength and to evoke LTP that is induced simultaneously but whose expression levels vary inversely over time, and the result of the TBP induction was compared to the control group. The result showed that the TBP induction of LTP significantly increased EPSPs level. When the stimulus strength was reduced below the action potential threshold, apamin, a neurotoxin, was added to assess the contribution of SK2 activity to EPSPs. It resulted in an increase in the level of EPSPs with blockage of SK2 channels. The TBP induction of LTP abolishes SK2 channel contribution to EPSPs. When the induction of chemical LTP was applied, immunoparticles for SK2 were not found within the PSD of asymmetrical synapses. However, the SK2 immunoparticles were observed within intracellular membranes. The activation of protein kinase A (PKA) downregulates the surface expression of SK2 because PKA regulates the surface expression of AMPA receptors, a non-NMDA-type ionotropic transmembrane receptor, in the hippocampus. Therefore, PKA decreases the activity of LTP-dependent of SK2 channels.
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
collaterals given off by CA3 pyramidal cell
Pyramidal cell
Pyramidal neurons are a type of neuron found in areas of the brain including cerebral cortex, the hippocampus, and in the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cortex and the corticospinal tract. Pyramidal neurons were first discovered and...
s in the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
. These collaterals project to area CA1 of the hippocampus and are an integral part of memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
formation and the emotional
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...
network of the Papez circuit
Papez circuit
Described by James Papez in 1937, the Papez circuit of the brain is one of the major pathways of the limbic system and is chiefly involved in the cortical control of emotion. The Papez circuit plays a role in storing memory....
, and of the hippocampal
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
trisynaptic loop
Trisynaptic loop
The trisynaptic loop is a relay of synaptic transmission in the hippocampus, which is made up of three major cell groups: granule cells, CA3 pyramidal neurons, and CA1 pyramidal cells. The hippocampal relay involves 3 main regions within the hippocampus which are classified according to their...
. It is named after the Hungarian anatomist-neurologist Károly Schaffer
Károly Schaffer
Károly Schaffer was a Hungarian anatomist and neurologist. He was born in Vienna. The axon projection from CA3 to CA1 neurons in hippocampus, Schaffer collateral, is named after him....
, and It is one of the most studied synapses as well.
In the early stage of long term potentiation Schaffer collaterals release glutamate that binds to AMPA receptor
AMPA receptor
The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor is a non-NMDA-type ionotropic transmembrane receptor for glutamate that mediates fast synaptic transmission in the central nervous system . Its name is derived from its ability to be activated by the artificial glutamate analog AMPA...
s of CA1-dendrites.
Development
"Schaffer collateral is the conductor of the orchestra, but not the actual instrument that plays the music" says Dr. Patrick K. Stanton. An individual needs the functional hippocampus to store long-term memories as synaptic plasticitySynaptic plasticity
In neuroscience, synaptic plasticity is the ability of the connection, or synapse, between two neurons to change in strength in response to either use or disuse of transmission over synaptic pathways. Plastic change also results from the alteration of the number of receptors located on a synapse...
in terms of storing information. Once those memories are stored, they remain stored in very long time. However, they slowly fade away, which means that there are some roles for the hippocampus when talking to the near cortex in order to prevent diminishing those memories away. It is clear that whatever plastic changes occurring in the hippocampus involve in directing the process by which memories get stored. Schaffer collateral is involved in activity-dependent plasticity and the information processes that always are processed through the hippocampus all the time. Schaffer collateral is clearly affecting whether the target cells fire action potentials or not. However, at the same time, it is triggering the process that takes much longer whereby some synapses get stronger and some get weaker, and overall all the patterns of synaptic strength of the network evolve all over time.
Location
In the hippocampus, Schaffer collaterals are given off by the CA3 region and project to the CA1 area.Hippocampus
Schaffer collaterals are the axons of pyramidal cells that connect two neurons (CA3 and CA1) and transfer information from CA3 to CA1.Inner Hippocampal Pathways
The entorhinal cortexEntorhinal cortex
The entorhinal cortex is located in the medial temporal lobe and functions as a hub in a widespread network for memory and navigation. The EC is the main interface between the hippocampus and neocortex...
sends the main input to the dentate gyrus
Dentate gyrus
The dentate gyrus is part of the hippocampal formation. It is thought to contribute to new memories as well as other functional roles. It is notable as being one of a select few brain structures currently known to have high rates of neurogenesis in adult rats, .The dentate gyrus cells receive...
(Perforant pathway). From the granule cells of the dentate gyrus, connections are made to the CA3 regions of the hippocampus via mossy fibers. CA3 sends the information signals to CA1 pyramidal cells via the Schaffer collateral and commissural fibers
Commissural fibers
The commissural fibers or transverse fibers connect the two hemispheres of the brain. They include:* the transverse fibers of the corpus callosum* the anterior commissure* the posterior commissure* the lyra or hippocampal commissure....
from the contralateral hippocampus as well.
Hippocampal Synaptic Plasticity
The hippocampus exhibits short and long term synaptic plasticity in terms of a change in the efficiency of synaptic transmission following previous synaptic activity.Short-term Plasticity
Short-term synaptic plasticity undergoes important age-dependent changes that have crucial implications during the development of the nervous systemLong-term Plasticity
Long-term changes in synaptic efficacy in the hippocampus can be induced by different patterns of stimulation generating pre- and postsynaptic depolarizationSchaffer collateral LTP
Long-term potentiationLong-term potentiation
In neuroscience, long-term potentiation is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength...
(LTP) of synaptic strength at Schaffer collateral synapses has largely been attributed to changes in the number and biophysical properties of AMPA receptors (AMPARs). Neuropsin has a regulatory effect on Schaffer collateral LTP in the rat hippocampus
Long-Term Synaptic Plasticity and Schaffer Collaterals
Within the mammalian brain, some patterns of synaptic activity produce long-term potentiation(LTP) which is a long-lasting increase in synaptic strength and long-term depressionLong-term depression
Long-term depression , in neurophysiology, is an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer. LTD occurs in many areas of the CNS with varying mechanisms depending upon brain region and developmental progress...
(LTD) which is a long-lasting decrease in synaptic strength.
LTP at Schaffer collateral-CA1 synapses and "SK2 channel plasticity"
Long-term plasticity in synapses of the hippocampusHippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
can be induced by different patterns of stimulation generating pre- and post-synaptic depolarization
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
. These synaptic changes can clearly lead to modification in circuit function and to behavioral plasticity. Some patterns of synaptic activity produce an extensive increase in synaptic strength, also known as Long-Term Potentiation (LTP). In the hippocampus, LTP at Schaffer collateral-CA1 modulates the biophysical properties of AMPA receptors. Moreover, SK2
SK channel
SK channels are a subfamily of Ca2+-activated K+ channels. They are so called because of their small single channel conductance, ~10 pS. SK channels are a type of ion channel allowing potassium cations to cross the cell membrane and are activated by an increase in the concentration of...
, small-conductance Ca2+-activated K+ channel, changes the shape of excitatory postsynaptic potentials (EPSPs) by coupling with N-methyl D-aspartate (NMDA) receptorsNMDA receptors. The research by Lin MT, et al was designed to investigate whether SK2 channels participate in synaptic changes when an activity-dependent decrease contributes to LTP.
SK2 channels
SK channel
SK channels are a subfamily of Ca2+-activated K+ channels. They are so called because of their small single channel conductance, ~10 pS. SK channels are a type of ion channel allowing potassium cations to cross the cell membrane and are activated by an increase in the concentration of...
are ion channels that are activated by an increasing in the concentration of intracellular calcium and as a result of allowing K+ cation to cross the cell membrane. The double immunogold labeling identified that SK2 channels and NMDA cohabit within the postsynaptic density (PSD) of CA1 regions of the hippocampus. The authors used theta-burst pairing (TBP) to produce a rapid potentiation of synaptic strength and to evoke LTP that is induced simultaneously but whose expression levels vary inversely over time, and the result of the TBP induction was compared to the control group. The result showed that the TBP induction of LTP significantly increased EPSPs level. When the stimulus strength was reduced below the action potential threshold, apamin, a neurotoxin, was added to assess the contribution of SK2 activity to EPSPs. It resulted in an increase in the level of EPSPs with blockage of SK2 channels. The TBP induction of LTP abolishes SK2 channel contribution to EPSPs. When the induction of chemical LTP was applied, immunoparticles for SK2 were not found within the PSD of asymmetrical synapses. However, the SK2 immunoparticles were observed within intracellular membranes. The activation of protein kinase A (PKA) downregulates the surface expression of SK2 because PKA regulates the surface expression of AMPA receptors, a non-NMDA-type ionotropic transmembrane receptor, in the hippocampus. Therefore, PKA decreases the activity of LTP-dependent of SK2 channels.