M1 and M4 Receptors Modulate Hippocampal Pyramidal Neurons

Acetylcholine (ACh), acting at muscarinic ACh receptors (mAChRs), modulates the excitability and synaptic connectivity of hippocampal pyramidal neurons. CA1 pyramidal neurons respond to transient (“phasic”) mAChR activation with biphasic responses in which inhibition is followed by excitation, whereas prolonged (“tonic”) mAChR activation increases CA1 neuron excitability. Both phasic and tonic mAChR activation excites pyramidal neurons in the CA3 region, yet ACh suppresses glutamate release at the CA3-to-CA1 synapse (the Schaffer–collateral pathway). Using mice genetically lacking specific mAChRs (mAChR knockout mice), we identified the mAChR subtypes responsible for cholinergic modulation of hippocampal pyramidal neuron excitability and synaptic transmission. Knockout of M1 receptors significantly reduced, or eliminated, most phasic and tonic cholinergic responses in CA1 and CA3 pyramidal neurons. On the other hand, in the absence of other Gq-linked mAChRs (M3 and M5), M1 receptors proved sufficient for all postsynaptic cholinergic effects on CA1 and CA3 pyramidal neuron excitability. M3 receptors were able to participate in tonic depolarization of CA1 neurons, but otherwise contributed little to cholinergic responses. At the Schaffer–collateral synapse, bath application of the cholinergic agonist carbachol suppressed stratum radiatum–evoked excitatory postsynaptic potentials (EPSPs) in wild-type CA1 neurons and in CA1 neurons from mice lacking M1 or M2 receptors. However, Schaffer–collateral EPSPs were not significantly suppressed by carbachol in neurons lacking M4 receptors. We therefore conclude that M1 and M4 receptors are the major mAChR subtypes responsible for direct cholinergic modulation of the excitatory hippocampal circuit.

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Cumulative Effects of Glutamate Microstimulation on Ca2+ Responses of CA1 Hippocampal Pyramidal Neurons in Slice

Journal of Neurophysiology ◽

10.1152/jn.2000.83.1.90 ◽

2000 ◽

Vol 83 (1) ◽

pp. 90-98 ◽

Cited By ~ 14

Author(s):

John A. Connor ◽

Robert J. Cormier

Keyword(s):

Time Course ◽

Pyramidal Neurons ◽

Stratum Radiatum ◽

Neuron Death ◽

Hippocampal Pyramidal Neurons ◽

Ca1 Neurons ◽

Hippocampal Ca1 ◽

High Resolution Images ◽

Stimulation Of

Glutamate stimulation of hippocampal CA1 neurons in slice was delivered via iontophoresis from a microelectrode. Five pulses (∼5 μA, 10 s duration, repeated at 1 min intervals) were applied with the electrode tip positioned in the stratum radiatum near the dendrites of a neuron filled with the Ca2+ indicator fura-2. A single stimulus set produced Ca2+ elevations that ranged from several hundred nM to several μM and that, in all but a few neurons, recovered within 1 min of stimulus termination. Subsequent identical stimulation produced Ca2+ elevations that outlasted the local glutamate elevations by several minutes as judged by response recoveries in neighboring cells or in other parts of the same neuron. These long responses ultimately recovered but persisted for up to 10 min and were most prominent in the mid and distal dendrites. Recovery was not observed for responses that spread to the soma. The elevated Ca2+ levels were accompanied by membrane depolarization but did not appear to depend on the depolarization. High-resolution images demonstrated responsive areas that involved only a few μm of dendrite. Our results confirm the previous general findings from isolated and cell culture neurons that glutamate stimulation, if carried beyond a certain range, results in long-lasting Ca2+ elevation. The response characterized here in mature in situ neurons was significantly different in terms of time course and reversibility. We suggest that the extended Ca2+ elevations might serve not only as a trigger for delayed neuron death but, where more spatially restricted, as a signal for local remodeling in dendrites.

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Threshold Conditions for Synaptically Evoking Ca2+Waves in Hippocampal Pyramidal Neurons

Journal of Neurophysiology ◽

10.1152/jn.00601.2001 ◽

2002 ◽

Vol 87 (4) ◽

pp. 1799-1804 ◽

Cited By ~ 18

Author(s):

Suya Zhou ◽

William N. Ross

Keyword(s):

Pyramidal Neurons ◽

Long Term Potentiation ◽

Threshold Current ◽

Lateral Position ◽

Stratum Radiatum ◽

Tetanic Stimulation ◽

Hippocampal Pyramidal Neurons ◽

Metabotropic Glutamate ◽

Group I ◽

Stimulus Current

Regenerative Ca2+ release from inositol 1,4,5-trisphosphate (IP3)-sensitive intracellular stores in the form of Ca2+ waves leads to large-amplitude [Ca2+]iincreases in the apical dendrites of hippocampal CA1 pyramidal neurons. Release is generated following synaptic activation of group I metabotropic glutamate (mGlu) receptors. We systematically examined the conditions for evoking these waves in transverse slices from 2- to 3-wk-old rats. Using a sharpened asymmetrical bipolar tungsten stimulating electrode placed in the stratum radiatum, we varied the lateral position of the electrode, the number of stimulating pulses, the train frequency, and stimulus current. Several trends were clear. Increasing the frequency of stimulation from 20 to 100 Hz, keeping the total number of pulses constant, lowered the required stimulus current. Stimulation at frequencies below 20 Hz made it difficult to evoke release. Increasing the number of stimulation pulses, keeping the frequency constant, lowered the threshold current. A minimum of five pulses at 100 Hz was required to evoke release reliably, but several examples of success with three pulses were recorded. Theta-burst stimulation was as effective as tetanic stimulation. Placing the point of the stimulation electrode closer to the pyramidal neuron made it easier to evoke release, although stimulation at a lateral distance of 500 μm with unsharpened electrodes was sometimes successful. The simplest explanation for these results is that a bolus of IP3 must be produced quickly in a restricted region of the dendrites to generate Ca2+ waves. The conditions necessary for evoking regenerative Ca2+ release have many parallels (and some differences) with the conditions required to evoke long-term potentiation in these cells following tetanic stimulation.

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Early Ischemia Enhances Action Potential-Dependent, Spontaneous Glutamatergic Responses in CA1 Neurons

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.2009.227 ◽

2009 ◽

Vol 30 (3) ◽

pp. 555-565 ◽

Cited By ~ 15

Author(s):

Hui Ye ◽

Shirin Jalini ◽

Liang Zhang ◽

Milton Charlton ◽

Peter L Carlen

Keyword(s):

Action Potential ◽

Pyramidal Neurons ◽

Glutamate Release ◽

Brain Slices ◽

Spontaneous Release ◽

Ca1 Neurons ◽

Relative Contribution ◽

Hippocampal Ca1 ◽

Ca3 Neurons

Two types of quantal spontaneous neurotransmitter release are present in the nervous system, namely action potential (AP)-dependent release and AP-independent release. Previous studies have identified and characterized AP-independent release during hypoxia and ischemia. However, the relative contribution of AP-dependent spontaneous release to the overall glutamate released during transient ischemia has not been quantified. Furthermore, the neuronal activity that mediates such release has not been identified. Using acute brain slices, we show that AP-dependent release constitutes approximately one-third of the overall glutamate-mediated excitatory postsynaptic potentials/currents (EPSPs/EPSCs) measured onto hippocampal CA1 pyramidal neurons. However, during transient (2 mins) in vitro hypoxia–hypoglycemia, large-amplitude, AP-dependent spontaneous release is significantly enhanced and contributes to 74% of the overall glutamatergic responses. This increased AP-dependent release is due to hyper-excitability in the presynaptic CA3 neurons, which is mediated by the activity of NMDA receptors. Spontaneous glutamate release during ischemia can lead to excitotoxicity and perturbation of neural network functions.

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Inhibition and Disinhibition of Pyramidal Neurons by Activation of Nicotinic Receptors on Hippocampal Interneurons

Journal of Neurophysiology ◽

10.1152/jn.2000.83.5.2682 ◽

2000 ◽

Vol 83 (5) ◽

pp. 2682-2690 ◽

Cited By ~ 171

Author(s):

Daoyun Ji ◽

John A. Dani

Keyword(s):

Nicotinic Acetylcholine Receptors ◽

Pyramidal Neuron ◽

Nicotinic Receptors ◽

Pyramidal Neurons ◽

Hippocampal Slices ◽

Specific Inhibitor ◽

Synaptic Activity ◽

Stratum Radiatum ◽

Local Pressure ◽

Pressure Application

Nicotinic acetylcholine receptors (nAChRs) are expressed in the hippocampus, and their functional roles are beginning to be delineated. The effect of nAChR activation on the activity of both interneurons and pyramidal neurons in the CA1 region was studied in rat hippocampal slices. In CA1 stratum radiatum with muscarinic receptors inhibited, local pressure application of acetylcholine (ACh) elicited a nicotinic current in 82% of the neurons. The majority of the ACh-induced currents were sensitive to methyllycaconitine, which is a specific inhibitor of α7-containing nAChRs. Methyllycaconitine-insensitive nicotinic currents also were present as detected by a nonspecific nAChR inhibitor. The ACh-sensitive neurons in the s. radiatum were identified as GABAergic interneurons by their electrophysiological properties. Pressure application of ACh induced firing of action potentials in ∼70% of the interneurons. The ACh-induced excitation of interneurons could induce either inhibition or disinhibition of pyramidal neurons. The inhibition was recorded from the pyramidal neuron as a burst of GABAergic synaptic activity. That synaptic activity was sensitive to bicuculline, indicating that GABAA receptors mediated the ACh-induced synaptic currents. The disinhibition was recorded from the pyramidal neuron as a reduction of spontaneous GABAergic synaptic activity when ACh was delivered onto an interneuron. Both the inhibition and disinhibition were sensitive to either methyllycaconitine or mecamylamine, indicating that activation of nicotinic receptors on interneurons was necessary for the effects. These results show that nAChRs are capable of regulating hippocampal circuits by exciting interneurons and, subsequently, inhibiting or disinhibiting pyramidal neurons.

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Divergent behavioral consequences of manipulations enhancing pyramidal neuron excitability in the prelimbic cortex

10.1101/2020.06.04.134486 ◽

2020 ◽

Author(s):

Timothy R. Rose ◽

Ezequiel Marron Fernandez de Velasco ◽

Baovi N. Vo ◽

Megan E. Tipps ◽

Kevin Wickman

Keyword(s):

Pyramidal Neuron ◽

Pyramidal Neurons ◽

Fear Learning ◽

Channel Activity ◽

Cocaine Exposure ◽

Gaba Neurons ◽

Neuron Excitability ◽

Girk Channel ◽

Drug Naïve ◽

The Impact

ABSTRACTBackgroundDrug-induced neuroadaptations in the prefrontal cortex are thought to underlie impaired executive functions that reinforce addictive behaviors. Repeated cocaine exposure increased layer 5/6 pyramidal neuron excitability in the mouse prelimbic cortex (PL), an adaptation attributable to a suppression of G protein-gated inwardly rectifying K+ (GIRK/Kir3) channel activity. GIRK channel suppression in the PL of drug-naïve mice enhanced the motor-stimulatory effect of cocaine. The impact of cocaine on PL GABA neurons, key pyramidal neuron regulators, and the behavioral relevance of increased PL pyramidal neuron excitability, remain unclear.MethodsThe effect of repeated cocaine on mouse layer 5/6 PL GABA neurons was assessed using slice electrophysiology. Adaptations enhancing PL pyramidal neuron excitability were modeled in drug-naïve mice using persistent viral Cre ablation and acute chemogenetic approaches. The impact of these manipulations on PL-dependent behavior was assessed in motor activity and trace fear conditioning tests.ResultsRepeated cocaine treatment did not impact GIRK channel activity in, or excitability of, layer 5/6 PL GABA neurons. GIRK channel ablation in PL pyramidal neurons enhanced the motor-stimulatory effect of cocaine but did not impact baseline activity or fear learning. In contrast, direct or indirect chemogenetic activation of PL pyramidal neurons increased baseline and cocaine-induced motor activity and disrupted fear learning. These effects were mirrored by chemogenetic activation of PL pyramidal neurons projecting to the ventral tegmental area.ConclusionsManipulations enhancing the excitability of PL pyramidal neurons, including those projecting to the VTA, recapitulate behavioral hallmarks of repeated cocaine exposure.

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Complex Response to Afferent Excitatory Bursts by Nucleus Accumbens Medium Spiny Projection Neurons

Journal of Neurophysiology ◽

10.1152/jn.00066.2004 ◽

2004 ◽

Vol 92 (3) ◽

pp. 1276-1284 ◽

Cited By ~ 13

Author(s):

Remigijus Lape ◽

John A. Dani

Keyword(s):

Nucleus Accumbens ◽

Pyramidal Neurons ◽

Glutamate Release ◽

Neuronal Population ◽

Synaptic Activity ◽

Projection Neurons ◽

Striatal Slices ◽

Hippocampal Pyramidal Neurons ◽

Stimulus Train

The nucleus accumbens (NAc) of the ventral striatum is involved in attention, motivation, movement, learning, reward, and addiction. GABAergic medium spiny projection neurons that make up ∼90% of the neuronal population are commonly driven by convergent bursts of afferent excitation. We monitored spiny projection neurons in mouse striatal slices while applying stimulus trains to mimic bursts of excitation. A stimulus train evoked a simple, short-lived postsynaptic response from CA1 hippocampal pyramidal neurons, but the train evoked a complex series of excitatory postsynaptic potentials (EPSPs) or currents (EPSCs) from the NAc spiny projection neurons. As is commonly seen with projection neurons, the EPSC amplitudes initially displayed facilitation followed by depression, and that pattern was sensitive to the extracellular calcium concentration. In addition, there were two other novel observations. The spiny projection neurons responded to the stimulus train with a prolonged depolarization that was accompanied by a posttrain increase of spontaneous glutamatergic synaptic activity. Blocking AMPA/kainate glutamate receptors strongly inhibited the evoked EPSP/EPSCs, the posttrain spontaneous synaptic activity, and the prolonged depolarization. A potassium channel inhibitor increased and extended the prolonged postsynaptic depolarization, causing a long-lasting depolarized plateau potential. Our results indicate that burst-like activity along ventral striatal afferents is extended in time by additional spontaneous glutamate release that is integrated by the postsynaptic spiny projection neurons into a prolonged depolarization. The results suggest that the posttrain quantal glutamate release helps to blend and maintain multiple afferent inputs. That convergent excitation is further integrated by the postsynaptic neuron into a prolonged depolarization that may contribute to the depolarized “up state” observed in vivo.

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Metformin Enhances Excitatory Synaptic Transmission onto Hippocampal CA1 Pyramidal Neurons

Brain Sciences ◽

10.3390/brainsci10100706 ◽

2020 ◽

Vol 10 (10) ◽

pp. 706

Author(s):

Wen-Bing Chen ◽

Jiang Chen ◽

Zi-Yang Liu ◽

Bin Luo ◽

Tian Zhou ◽

...

Keyword(s):

Synaptic Transmission ◽

Neuronal Excitability ◽

Pyramidal Neurons ◽

Glutamate Release ◽

Hippocampal Slices ◽

Hippocampal Pyramidal Neurons ◽

Beneficial Effects ◽

Ca1 Pyramidal Neurons ◽

Postsynaptic Currents ◽

Hippocampal Ca1

Metformin (Met) is a first-line drug for type 2 diabetes mellitus (T2DM). Numerous studies have shown that Met exerts beneficial effects on a variety of neurological disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD) and Huntington’s disease (HD). However, it is still largely unclear how Met acts on neurons. Here, by treating acute hippocampal slices with Met (1 μM and 10 μM) and recording synaptic transmission as well as neuronal excitability of CA1 pyramidal neurons, we found that Met treatments significantly increased the frequency of miniature excitatory postsynaptic currents (mEPSCs), but not amplitude. Neither frequency nor amplitude of miniature inhibitory postsynaptic currents (mIPSCs) were changed with Met treatments. Analysis of paired-pulse ratios (PPR) demonstrates that enhanced presynaptic glutamate release from terminals innervating CA1 hippocampal pyramidal neurons, while excitability of CA1 pyramidal neurons was not altered. Our results suggest that Met preferentially increases glutamatergic rather than GABAergic transmission in hippocampal CA1, providing a new insight on how Met acts on neurons.

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Calsyntenin-3 interacts with both α- and β-neurexins in the regulation of excitatory synaptic innervation in specific Schaffer collateral pathways

Journal of Biological Chemistry ◽

10.1074/jbc.ra120.013077 ◽

2020 ◽

Vol 295 (27) ◽

pp. 9244-9262 ◽

Cited By ~ 1

Author(s):

Hyeonho Kim ◽

Dongwook Kim ◽

Jinhu Kim ◽

Hee-Yoon Lee ◽

Dongseok Park ◽

...

Keyword(s):

Neural Circuits ◽

Conditional Knockout ◽

Stratum Radiatum ◽

Excitatory Synapses ◽

Schaffer Collateral ◽

Ca1 Neurons ◽

Electrophysiological Recordings ◽

Presynaptic Differentiation ◽

Collateral Pathways

Calsyntenin-3 (Clstn3) is a postsynaptic adhesion molecule that induces presynaptic differentiation via presynaptic neurexins (Nrxns), but whether Nrxns directly bind to Clstn3 has been a matter of debate. Here, using LC–MS/MS–based protein analysis, confocal microscopy, RNAscope assays, and electrophysiological recordings, we show that β-Nrxns directly interact via their LNS domain with Clstn3 and Clstn3 cadherin domains. Expression of splice site 4 (SS4) insert–positive β-Nrxn variants, but not insert–negative variants, reversed the impaired Clstn3 synaptogenic activity observed in Nrxn-deficient neurons. Consistently, Clstn3 selectively formed complexes with SS4–positive Nrxns in vivo. Neuron-specific Clstn3 deletion caused significant reductions in number of excitatory synaptic inputs. Moreover, expression of Clstn3 cadherin domains in CA1 neurons of Clstn3 conditional knockout mice rescued structural deficits in excitatory synapses, especially within the stratum radiatum layer. Collectively, our results suggest that Clstn3 links to SS4–positive Nrxns to induce presynaptic differentiation and orchestrate excitatory synapse development in specific hippocampal neural circuits, including Schaffer collateral afferents.

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Coincident Glutamatergic and Cholinergic Inputs Transiently Depress Glutamate Release at Rat Schaffer Collateral Synapses

Journal of Neurophysiology ◽

10.1152/jn.01051.2006 ◽

2007 ◽

Vol 97 (6) ◽

pp. 4108-4119 ◽

Cited By ~ 7

Author(s):

Keith E. Gipson ◽

Mark F. Yeckel

Keyword(s):

Acetylcholine Receptors ◽

Glutamate Release ◽

Acetylcholinesterase Inhibitor ◽

Hippocampal Slices ◽

Medial Septum ◽

Network Activity ◽

Stratum Radiatum ◽

Hippocampal Function ◽

Schaffer Collateral ◽

Single Receptor

The mammalian hippocampus, together with subcortical and cortical areas, is responsible for some forms of learning and memory. Proper hippocampal function depends on the highly dynamic nature of its circuitry, including the ability of synapses to change their strength for brief to long periods of time. In this study, we focused on a transient depression of glutamatergic synaptic transmission at Schaffer collateral synapses in acute hippocampal slices. The depression of evoked excitatory postsynaptic current (EPSC) amplitudes, herein called transient depression, follows brief trains of synaptic stimulation in stratum radiatum of CA1 and lasts for 2–3 min. Depression results from a decrease in presynaptic glutamate release, as NMDA-receptor–mediated EPSCs and composite EPSCs are depressed similarly and depression is accompanied by an increase in the paired-pulse ratio. Transient depression is prevented by blockade of metabotropic glutamate and acetylcholine receptors, presumably located presynaptically. These two receptor types—acting together—cause depression. Blockade of a single receptor type necessitates significantly stronger conditioning trains for triggering depression. Addition of an acetylcholinesterase inhibitor enables depression from previously insufficient conditioning trains. Furthermore, a strong coincident, but not causal, relationship existed between presynaptic depression and postsynaptic internal Ca2+ release, emphasizing the potential importance of functional interactions between presynaptic and postsynaptic effects of convergent cholinergic and glutamatergic inputs to CA1. These convergent afferents, one intrinsic to the hippocampus and the other likely originating in the medial septum, may regulate CA1 network activity, the induction of long-term synaptic plasticity, and ultimately hippocampal function.

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