scholarly journals Feedforward inhibition is randomly wired from individual granule cells onto CA3 pyramidal cells

Hippocampus ◽  
2017 ◽  
Vol 27 (10) ◽  
pp. 1034-1039 ◽  
Author(s):  
Máté Neubrandt ◽  
Viktor János Oláh ◽  
János Brunner ◽  
János Szabadics
Keyword(s):  
Granule Cells ◽  
Pyramidal Cells ◽  
Individual Granule ◽  
Ca3 Pyramidal Cells ◽  
Feedforward Inhibition

scholarly journals Separable actions of acetylcholine and noradrenaline on neuronal ensemble formation in hippocampal CA3 circuits

2021 ◽  
Vol 17 (10) ◽  
pp. e1009435
Author(s):  
Luke Y. Prince ◽  
Travis Bacon ◽  
Rachel Humphries ◽  
Krasimira Tsaneva-Atanasova ◽  
Claudia Clopath ◽  
...  
Keyword(s):  
Granule Cells ◽  
Mossy Fiber ◽  
Pyramidal Cells ◽  
Recurrent Network ◽  
Memory Storage ◽  
Neuronal Ensembles ◽  
Hippocampal Ca3 ◽  
Ca3 Pyramidal Cells ◽  
Episodic Memories ◽  
Mossy Fiber Pathway

In the hippocampus, episodic memories are thought to be encoded by the formation of ensembles of synaptically coupled CA3 pyramidal cells driven by sparse but powerful mossy fiber inputs from dentate gyrus granule cells. The neuromodulators acetylcholine and noradrenaline are separately proposed as saliency signals that dictate memory encoding but it is not known if they represent distinct signals with separate mechanisms. Here, we show experimentally that acetylcholine, and to a lesser extent noradrenaline, suppress feed-forward inhibition and enhance Excitatory–Inhibitory ratio in the mossy fiber pathway but CA3 recurrent network properties are only altered by acetylcholine. We explore the implications of these findings on CA3 ensemble formation using a hierarchy of models. In reconstructions of CA3 pyramidal cells, mossy fiber pathway disinhibition facilitates postsynaptic dendritic depolarization known to be required for synaptic plasticity at CA3-CA3 recurrent synapses. We further show in a spiking neural network model of CA3 how acetylcholine-specific network alterations can drive rapid overlapping ensemble formation. Thus, through these distinct sets of mechanisms, acetylcholine and noradrenaline facilitate the formation of neuronal ensembles in CA3 that encode salient episodic memories in the hippocampus but acetylcholine selectively enhances the density of memory storage.

Evidence from simultaneous intracellular recordings in rat hippocampal slices that area CA3 pyramidal cells innervate dentate hilar mossy cells

1994 ◽  
Vol 72 (5) ◽  
pp. 2167-2180 ◽  
Author(s):  
H. E. Scharfman
Keyword(s):  
Pyramidal Cell ◽  
Action Potentials ◽  
Granule Cells ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Probability Of Failure ◽  
Mossy Cells ◽  
Mossy Cell ◽  
Ca3 Pyramidal Cells ◽  
Area Ca3

1. Simultaneous intracellular recordings of area CA3 pyramidal cells and dentate hilar “mossy” cells were made in rat hippocampal slices to test the hypothesis that area CA3 pyramidal cells excite mossy cells monosynaptically. Mossy cells and pyramidal cells were differentiated by location and electrophysiological characteristics. When cells were impaled near the border of area CA3 and the hilus, their identity was confirmed morphologically after injection of the marker Neurobiotin. 2. Evidence for monosynaptic excitation of a mossy cell by a pyramidal cell was obtained in 7 of 481 (1.4%) paired recordings. In these cases, a pyramidal cell action potential was followed immediately by a 0.40 to 6.75 (mean, 2.26) mV depolarization in the simultaneously recorded mossy cell (mossy cell membrane potentials, -60 to -70 mV). Given that pyramidal cells used an excitatory amino acid as a neurotransmitter (Cotman and Nadler 1987; Ottersen and Storm-Mathisen 1987) and recordings were made in the presence of the GABAA receptor antagonist bicuculline (25 microM), it is likely that the depolarizations were unitary excitatory postsynaptic potentials (EPSPs). 3. Unitary EPSPs of mossy cells were prone to apparent “failure.” The probability of failure was extremely high (up to 0.72; mean = 0.48) if the effects of all presynaptic action potentials were examined, including action potentials triggered inadvertently during other spontaneous EPSPs of the mossy cell. Probability of failure was relatively low (as low as 0; mean = 0.24) if action potentials that occurred during spontaneous activity of the mossy cell were excluded. These data suggest that unitary EPSPs produced by pyramidal cells are strongly affected by concurrent synaptic inputs to the mossy cell. 4. Unitary EPSPs were not clearly affected by manipulation of the mossy cell's membrane potential. This is consistent with the recent report that area CA3 pyramidal cells innervate distal dendrites of mossy cells (Kunkel et al. 1993). Such a distal location also may contribute to the high incidence of apparent failures. 5. Characteristics of unitary EPSPs generated by pyramidal cells were compared with the properties of the unitary EPSPs produced by granule cells. In two slices, pyramidal cell and granule cell inputs to the same mossy cell were compared. In other slices, inputs to different mossy cells were compared. In all experiments, unitary EPSPs produced by granule cells were larger in amplitude but similar in time course to unitary EPSPs produced by pyramidal cells. Probability of failure was lower and paired-pulse facilitation more common among EPSPs triggered by granule cells.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Does a Unique Type of CA3 Pyramidal Cell in Primates Bypass the Dentate Gate?

2005 ◽  
Vol 94 (1) ◽  
pp. 896-900 ◽  
Author(s):  
Paul S. Buckmaster
Keyword(s):  
Dentate Gyrus ◽  
Entorhinal Cortex ◽  
Synaptic Input ◽  
Granule Cells ◽  
Molecular Layer ◽  
Pyramidal Cells ◽  
Dendritic Morphology ◽  
Dentate Granule Cells ◽  
Excitatory Synaptic Input ◽  
Ca3 Pyramidal Cells

The predominant excitatory synaptic input to the hippocampus arises from entorhinal cortical axons that synapse with dentate granule cells, which in turn synapse with CA3 pyramidal cells.Thus two highly excitable brain areas—the entorhinal cortex and the CA3 field—are separated by dentate granule cells, which have been proposed to function as a gate or filter. However, unlike rats, primates have “dentate” CA3 pyramidal cells with an apical dendrite that extends into the molecular layer of the dentate gyrus, where they could receive strong, monosynaptic, excitatory synaptic input from the entorhinal cortex. To test this possibility, the dentate gyrus molecular layer was stimulated while intracellular recordings were obtained from CA3 pyramidal cells in hippocampal slices from neurologically normal macaque monkeys. Stimulus intensity of the outer molecular layer of the dentate gyrus was standardized by the threshold intensity for evoking a dentate gyrus field potential population spike. Recorded proximal CA3 pyramidal cells were labeled with biocytin, processed with diaminobenzidine for visualization, and classified according to their dendritic morphology. In response to stimulation of the dentate gyrus molecular layer, action potential thresholds were similar in proximal CA3 pyramidal cells with different dendritic morphologies. These findings do not support the hypothesis that dentate CA3 pyramidal cells receive stronger synaptic input from the entorhinal cortex than do other proximal CA3 pyramidal cells.

scholarly journals Acetylcholine disinhibits hippocampal circuits to enable rapid formation of overlapping memory ensembles

2017 ◽  
Author(s):  
Luke Y. Prince ◽  
Krasimira Tsaneva-Atanasova ◽  
Claudia Clopath ◽  
Jack R. Mellor
Keyword(s):  
Granule Cells ◽  
Mossy Fiber ◽  
Pyramidal Cells ◽  
Cholinergic Receptor ◽  
Receptor Activation ◽  
Cellular Excitability ◽  
Rapid Formation ◽  
Ca3 Pyramidal Cells ◽  
Episodic Memories ◽  
Spiking Neural Network Model

AbstractIn the hippocampus, episodic memories are thought to be encoded by the formation of ensembles of synaptically coupled CA3 pyramidal cells driven by sparse but powerful mossy fiber inputs from dentate gyrus granule cells. Acetylcholine is proposed as the salient signal that determines which memories are encoded but its actions on mossy fiber transmission are largely unknown. Here, we show experimentally that cholinergic receptor activation suppresses feedforward inhibition and enhances excitatory-inhibitory ratio. In reconstructions of CA3 pyramidal cells, this disinhibition enables postsynaptic dendritic depolarization required for synaptic plasticity at CA3-CA3 recurrent synapses. We further show in a spiking neural network model of CA3 how a combination of disinhibited mossy fiber activity, enhanced cellular excitability and reduced recurrent synapse strength can drive rapid overlapping ensemble formation. Thus, we propose a coordinated set of mechanisms by which acetylcholine release enables the selective encoding of salient high-density episodic memories in the hippocampus.

scholarly journals Differential coupling of adult-born granule cells to parvalbumin and somatostatin interneurons

2019 ◽  
Author(s):  
Ayelén I. Groisman ◽  
Sung M. Yang ◽  
Alejandro F. Schinder
Keyword(s):  
Granule Cells ◽  
Pyramidal Cells ◽  
Feedback Loops ◽  
Gabaergic Interneurons ◽  
Connectivity Map ◽  
Efficient Control ◽  
Adult Born Neurons ◽  
Ca3 Pyramidal Cells ◽  
Differential Coupling ◽  
Inhibitory Networks

ABSTRACTThe dentate gyrus of the hippocampus is dominated by a strong GABAergic tone that maintains sparse levels of activity. Adult neurogenesis disrupts this balance through the continuous addition of new granule cells (GCs) that display high excitability while develop and connect within the preexisting host circuit. The dynamics of the connectivity map for developing GCs in the local inhibitory networks remains unknown. We used optogenetics to study afferent and efferent synaptogenesis between new GCs and GABAergic interneurons expressing parvalbumin (PV-INs) and somatostatin (SST-INs). Inputs from PV-INs targeted the soma and remained immature until they grew abruptly in >4-week-old GCs. This transition was accelerated by exposure to enriched environment. Inputs from SST-INs were dendritic and developed slowly until reaching maturity by 8 weeks. Synaptic outputs from GCs onto PV-INs matured faster than those onto SST-INs, but also required several weeks. In the mature dentate network, PV-INs exerted an efficient control of GC spiking and were involved in both feedforward and feedback loops, a mechanism that would favor lateral inhibition and sparse coding. Our results reveal a long-lasting transition where adult-born neurons remain poorly coupled to inhibition, which might enable a parallel streaming channel from the entorhinal cortex to CA3 pyramidal cells.

scholarly journals Dentate Gyrus Mossy Cells Share a Role in Pattern Separation with Dentate Granule Cells and Proximal CA3 Pyramidal Cells

2019 ◽  
Vol 39 (48) ◽  
pp. 9570-9584 ◽  
Author(s):  
Douglas GoodSmith ◽  
Heekyung Lee ◽  
Joshua P. Neunuebel ◽  
Hongjun Song ◽  
James J. Knierim
Keyword(s):  
Dentate Gyrus ◽  
Granule Cells ◽  
Pyramidal Cells ◽  
Pattern Separation ◽  
Dentate Granule Cells ◽  
Mossy Cells ◽  
Ca3 Pyramidal Cells

Characteristics of local excitatory circuits studied with glutamate microapplication in the CA3 area of rat hippocampal slices

1988 ◽  
Vol 59 (1) ◽  
pp. 90-109 ◽  
Author(s):  
E. P. Christian ◽  
F. E. Dudek
Keyword(s):  
Granule Cells ◽  
Mossy Fiber ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Firing Frequency ◽  
Block Transmission ◽  
Inhibitory Circuits ◽  
Axon Terminals ◽  
Stratum Pyramidale ◽  
Ca3 Pyramidal Cells

1. Local neuronal circuits in CA3 of hippocampal slices were studied by recording excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) intracellularly during glutamate microapplication in CA3. Control experiments validated this approach by providing evidence that glutamate microdrops stimulated neurons but not axons-of-passage or axon terminals in CA3. 2. Glutamate microdrops (10-20 mM, 10-20 microns diam) increased the firing frequency of extracellularly recorded dentate granule cells for 5–10 s when applied to their somata but not when applied to their mossy fiber axons and terminals in the hilus and in CA3. 3. Glutamate microapplications to granule cell somata, but not to mossy fiber axons, also increased the frequency of intracellularly recorded EPSPs in CA3 pyramidal cells for 5-10 s. This provided a second line of evidence that glutamate did not cause firing in mossy fiber axons synapsing in CA3. 4. In slices where the CA3 region was surgically separated from the dentate gyrus and CA2, glutamate microdrops placed in the CA3 stratum pyramidale within 400 microns of intracellularly recorded pyramidal cells increased the frequency of EPSPs and IPSPs. Tetrodotoxin (1 microgram/ml) blocked these increases in PSP frequency, indicating that they did not result from glutamate-induced depolarization and associated transmitter release from presynaptic terminals. Increases in PSP frequency were interpreted to reflect glutamate activations of CA3 neurons with local synaptic connections to recorded cells. 5. Low concentrations of picrotoxin (PTX, 5-10 microM) blocked glutamate-induced increases in IPSP frequency and often revealed increases in EPSP frequency where they were not previously observed. This suggests that recurrent inhibitory circuits normally mask or block transmission through recurrent excitatory pathways in CA3. 6. In five experiments following PTX treatment (7.5–10 microM), large and prolonged (up to 2 min) increases in EPSP frequency were observed in CA3 pyramidal cells to glutamate microapplications in CA3. Rhythmic epileptiform bursts eventually occurred in two of these cases, suggesting that the protracted increases in EPSP frequency represent a form of reverberating excitation during a transition from normal to epileptic states. 7. Sixteen CA3 pyramidal cells were recorded in PTX (5-10 microM) during glutamate microapplications at 200 and 400 microns on each side of the recording site. The most consistent glutamate-induced increases in EPSP frequency occurred to microapplications 200 microns from recording sites on the hilar side.(ABSTRACT TRUNCATED AT 400 WORDS)

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