Activity dynamics and behavioral correlates of CA3 and CA1 hippocampal pyramidal neurons

The CA3 and CA1 pyramidal neurons are the major principal cell types of the hippocampus proper. The strongly recurrent collateral system of CA3 cells and the largely parallel-organized CA1 neurons suggest that these regions perform distinct computations. However, a comprehensive comparison between CA1 and CA3 pyramidal cells in terms of firing properties, network dynamics, and behavioral correlations is sparse in the intact animal. We performed large-scale recordings in the dorsal hippocampus of rats to quantify the similarities and differences between CA1 (n > 3,600) and CA3 (n > 2,200) pyramidal cells during sleep and exploration in multiple environments. CA1 and CA3 neurons differed significantly in firing rates, spike burst propensity, spike entrainment by the theta rhythm, and other aspects of spiking dynamics in a brain state-dependent manner. A smaller proportion of CA3 than CA1 cells displayed prominent place fields, but place fields of CA3 neurons were more compact, more stable, and carried more spatial information per spike than those of CA1 pyramidal cells. Several other features of the two cell types were specific to the testing environment. CA3 neurons showed less pronounced phase precession and a weaker position versus spike-phase relationship than CA1 cells. Our findings suggest that these distinct activity dynamics of CA1 and CA3 pyramidal cells support their distinct computational roles.     

Passive cable properties of hippocampal CA3 pyramidal neurons

The passive electrical cable properties of CA3 pyramidal neurons from guinea pig hippocampal slices were investigated by applying current steps and recording the voltage transients from 25 CA3 neurons, using a single intracellular microelectrode and a 3-kHz time-share system. Two independent methods were used for estimating the equivalent electrotonic length of the dendrites, L, and the dendritic to somatic conductance ratio, . The first method is similar to that used by Gorman and Mirolli (1972) and gave an average L of 0.96; the average was 2.44. The second method is derived here for the first time and assumes a finite-length cable with lumped soma. It is an exact solution for L and , using the slopes and intercepts of the first two peeled exponentials. The average L was 0.94; the average was 1.51. The results, using both methods, are in close agreement. The average membrane time constant for all 25 CA3 neurons was 23.6 ms, suggesting a large (23,600 cm²) average membrane resistivity. It is concluded that CA3 neurons are electronically short.This work was supported by Grants NS 11535 and NS 15772 from the National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, U.S. Public Health Service.     

Activity-dependent regulation of h channel distribution in hippocampal CA1 pyramidal neurons

The hyperpolarization-activated cation current, I(h), plays an important role in regulating intrinsic neuronal excitability in the brain. In hippocampal pyramidal neurons, I(h) is mediated by h channels comprised primarily of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel subunits, HCN1 and HCN2. Pyramidal neuron h channels within hippocampal area CA1 are remarkably enriched in distal apical dendrites, and this unique distribution pattern is critical for regulating dendritic excitability. We utilized biochemical and immunohistochemical approaches in organotypic slice cultures to explore factors that control h channel localization in dendrites. We found that distal dendritic enrichment of HCN1 is first detectable at postnatal day 13, reaching maximal enrichment by the 3rd postnatal week. Interestingly we found that an intact entorhinal cortex, which projects to distal dendrites of CA1 but not area CA3, is critical for the establishment and maintenance of distal dendritic enrichment of HCN1. Moreover blockade of excitatory neurotransmission using tetrodotoxin, 6-cyano-7-nitroquinoxaline-2,3-dione, or 2-aminophosphonovalerate redistributed HCN1 evenly throughout the dendrite without significant changes in protein expression levels. Inhibition of calcium/calmodulin-dependent protein kinase II activity, but not p38 MAPK, also redistributed HCN1 in CA1 pyramidal neurons. We conclude that activation of ionotropic glutamate receptors by excitatory temporoammonic pathway projections from the entorhinal cortex establishes and maintains the distribution pattern of HCN1 in CA1 pyramidal neuron dendrites by activating calcium/calmodulin-dependent protein kinase II-mediated downstream signals.     

Integrative properties of radial oblique dendrites in hippocampal CA1 pyramidal neurons

Although radial oblique dendrites are a major synaptic input site in CA1 pyramidal neurons, little is known about their integrative properties. We have used multisite two-photon glutamate uncaging to deliver different spatiotemporal input patterns to single branches while simultaneously recording the uncaging-evoked excitatory postsynaptic potentials and local Ca2+ signals. Asynchronous input patterns sum linearly in spite of the spatial clustering and produce Ca2+ signals that are mediated by NMDA receptors (NMDARs). Appropriately timed and sized input patterns ( approximately 20 inputs within approximately 6 ms) produce a supralinear summation due to the initiation of a dendritic spike. The Ca2+ signals associated with synchronous input were larger and mediated by influx through both NMDARs and voltage-gated Ca2+ channels (VGCCs). The oblique spike is a fast Na+ spike whose duration is shaped by the coincident activation of NMDAR, VGCCs, and transient K+ currents. Our results suggest that individual branches can function as single integrative compartments.     

Age-related changes in synaptic vesicle pools of axo-dendritic synapses on hippocampal CA1 pyramidal neurons in mice

The ultrastructure of symmetric (putatively inhibitory) axo-dendritic synapses on the membrane of hippocampal CA1 pyramidal neurons was investigated in young (20-day-old) and adult (1-year-old) mice. It was shown that synapses of adult animals contain, on average, fewer synaptic vesicles (SVs), and resting SVs of the reserve pool are mostly responsible for this difference. At the same time, in the synapses of adult mice SVs are localized closer to active zones, and the readily releasable pool of SVs is larger in these animals than in young mice. The observed changes in the spatial structure of SV pools presumably demonstrate the age-associated adaptation of inhibitory synapses providing the maintenance of adequate functional properties of hippocampal neuronal networks. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 407–411, September–December, 2006.     

成年大鼠海马CA1区锥体细胞KATP通道的特性

为了解成年大鼠海马CA1区锥体细胞KATP通道的特性,实验采用膜片钳技术的内面向外式记录法,在急性分离的CA1区锥体神经元上,研究了可被胞浆侧ATP所抑制的钾离子单通道的特性,当细胞膜内外两侧的K^ 浓度均为140mmol/L时,通道的电导为63pS,翻转电位为1．71mV,通道呈弱向内向整流性,在负钳制电位时,通道开放时常被短时的关闭所打断,而在正钳制电位时,这种短时程的关闭状态明显少于负钳制电位时,但通道开放概率未见明显的电压依赖性,ATP对通道活动的抑制作用呈浓度依赖性,抑制通道活动50％的ATP浓度为0．1mmol/L.KATP通道的特异性阻断剂tolbutamide(甲糖宁,1mmol/L)可完全阻断通道的活动,而KATP通道开放剂diazoxide(二氮嗪,1mmol/L）则不增强通道的活动。     

Gating properties of single SK channels in hippocampal CA1 pyramidal neurons.

The activation of small-conductance calcium-activated potassium channels (SK) has a profound effect on membrane excitability. In hippocampal pyramidal neurons, SK channel activation by Ca2+ entry from a preceding burst of action potentials generates the slow afterhyperpolarization (AHP). Stimulation of a number of receptor types suppresses the slow AHP, inhibiting spike frequency adaptation and causing these neurons to fire tonically. Little is known of the gating properties of native SK channels in CNS neurons. By using excised inside-out patches, a small-amplitude channel has been resolved that was half-activated by approximately 0.6 microM Ca2+ in a voltage-independent manner. The channel possessed a slope conductance of 10 pS and exhibited nonstationary gating. These properties are in accord with those of cloned SK channels. The measured Ca2+ sensitivity of hippocampal SK channels suggests that the slow AHP is generated by activation of SK channels from a local rise of intracellular Ca2+.     

Membrane electrical properties of mouse hippocampal CA1 pyramidal neurons during strong inputs

In this work, we highlight an electrophysiological feature often observed in recordings from mouse CA1 pyramidal cells that has so far been ignored by experimentalists and modelers. It consists of a large and dynamic increase in the depolarization baseline (i.e., the minimum value of the membrane potential between successive action potentials during a sustained input) in response to strong somatic current injections. Such an increase can directly affect neurotransmitter release properties and, more generally, the efficacy of synaptic transmission. However, it cannot be explained by any currently available conductance-based computational model. Here we present a model addressing this issue, demonstrating that experimental recordings can be reproduced by assuming that an input current modifies, in a time-dependent manner, the electrical and permeability properties of the neuron membrane by shifting the ionic reversal potentials and channel kinetics. For this reason, we propose that any detailed model of ion channel kinetics for neurons exhibiting this characteristic should be adapted to correctly represent the response and the synaptic integration process during strong and sustained inputs.     

Inhibitory processes of hippocampal CA1 pyramidal neurons following kindling-induced epilepsy in the rat

To determine the alterations in cellular function which may contribute to the chronic predisposition of neuronal tissue to epileptiform activity, the membrane properties and inhibitory processes of hippocampal CA1 pyramidal cells were investigated using in vitro slices prepared from commissural-kindled rats. No changes were observed in resting membrane potential, input resistance, spike amplitude, and membrane time constant of "kindled" CA1 pyramidal neurons when compared with controls. There were also no differences between control and kindled preparations in the amplitude of recurrent inhibitory postsynaptic potentials (IPSP) and in the duration of inhibition produced by either alvear (Alv) or stratum radiatum (SR) stimulation. Irrespective of group, repetitive stimulation of the Alv reduced the amplitude of the recurrent IPSP but failed to induce seizurelike activity. On the other hand, repetitive stimulation of SR frequently produced a neuronal burst discharge even though the duration and to some extent the amplitude of orthodromic inhibition was increased. On the basis of these data, it may be suggested that chronic changes in CA1 pyramidal cell membrane properties and transient reductions of inhibitory processes do not underlie the enhanced sensitivity of these neurons to seizure activity associated with kindling.     

Ionic mechanisms of endogenous bursting in CA3 hippocampal pyramidal neurons: a model study

A critical property of some neurons is burst firing, which in the hippocampus plays a primary role in reliable transmission of electrical signals. However, bursting may also contribute to synchronization of electrical activity in networks of neurons, a hallmark of epilepsy. Understanding the ionic mechanisms of bursting in a single neuron, and how mutations associated with epilepsy modify these mechanisms, is an important building block for understanding the emergent network behaviors. We present a single-compartment model of a CA3 hippocampal pyramidal neuron based on recent experimental data. We then use the model to determine the roles of primary depolarizing currents in burst generation. The single compartment model incorporates accurate representations of sodium (Na(+)) channels (Na(V)1.1) and T-type calcium (Ca(2+)) channel subtypes (Ca(V)3.1, Ca(V)3.2, and Ca(V)3.3). Our simulations predict the importance of Na(+) and T-type Ca(2+) channels in hippocampal pyramidal cell bursting and reveal the distinct contribution of each subtype to burst morphology. We also performed fast-slow analysis in a reduced comparable model, which shows that our model burst is generated as a result of the interaction of two slow variables, the T-type Ca(2+) channel activation gate and the Ca(2+)-dependent potassium (K(+)) channel activation gate. The model reproduces a range of experimentally observed phenomena including afterdepolarizing potentials, spike widening at the end of the burst, and rebound. Finally, we use the model to simulate the effects of two epilepsy-linked mutations: R1648H in Na(V)1.1 and C456S in Ca(V)3.2, both of which result in increased cellular excitability.     

Distance-dependent differences in synapse number and AMPA receptor expression in hippocampal CA1 pyramidal neurons

The ability of synapses throughout the dendritic tree to influence neuronal output is crucial for information processing in the brain. Synaptic potentials attenuate dramatically, however, as they propagate along dendrites toward the soma. To examine whether excitatory axospinous synapses on CA1 pyramidal neurons compensate for their distance from the soma to counteract such dendritic filtering, we evaluated axospinous synapse number and receptor expression in three progressively distal regions: proximal and distal stratum radiatum (SR), and stratum lacunosum-moleculare (SLM). We found that the proportion of perforated synapses increases as a function of distance from the soma and that their AMPAR, but not NMDAR, expression is highest in distal SR and lowest in SLM. Computational models of pyramidal neurons derived from these results suggest that they arise from the compartment-specific use of conductance scaling in SR and dendritic spikes in SLM to minimize the influence of distance on synaptic efficacy.     

Properties of slow, cumulative sodium channel inactivation in rat hippocampal CA1 pyramidal neurons.

Sodium channels in the somata and dendrites of hippocampal CA1 pyramidal neurons undergo a form of long-lasting, cumulative inactivation that is involved in regulating back-propagating action potential amplitude and can influence dendritic excitation. Using cell-attached patch-pipette recordings in the somata and apical dendrites of CA1 pyramidal neurons, we determined the properties of slow inactivation on response to trains of brief depolarizations. We find that the amount of slow inactivation gradually increases as a function of distance from the soma. Slow inactivation is also frequency and voltage dependent. Higher frequency depolarizations increase both the amount of slow inactivation and its rate of recovery. Hyperpolarized resting potentials and larger command potentials accelerate recovery from slow inactivation. We compare this form of slow inactivation to that reported in other cell types, using longer depolarizations, and construct a simplified biophysical model to examine the possible gating mechanisms underlying slow inactivation. Our results suggest that sodium channels can enter slow inactivation rapidly from the open state during brief depolarizations or slowly from a fast inactivation state during longer depolarizations. Because of these properties of slow inactivation, sodium channels will modulate neuronal excitability in a way that depends in a complicated manner on the resting potential and previous history of action potential firing.     

成年大鼠海马CA1区锥体细胞K_(ATP)通道的特性

为了解成年大鼠海马CA1区锥体细胞KATP 通道的特性 ,实验采用膜片钳技术的内面向外式记录法 ,在急性分离的CA1区锥体神经元上 ,研究了可被胞浆侧ATP所抑制的钾离子单通道的特性。当细胞膜内外两侧的K 浓度均为 14 0mmol/L时 ,通道的电导为 63pS ,翻转电位为 1 71mV ,通道呈弱内向整流性。在负钳制电位时 ,通道开放时常被短时程的关闭所打断 ,而在正钳制电位时 ,这种短时程的关闭状态明显少于负钳制电位时。但通道开放概率未见明显的电压依赖性。ATP对通道活动的抑制作用呈浓度依赖性 ,抑制通道活动 5 0 %的ATP浓度为 0 1mmol/L。KATP 通道的特异性阻断剂tolbutamide (甲糖宁 ,1mmol/L)可完全阻断通道的活动 ,而KATP 通道开放剂diazoxide (二氮嗪 ,1mmol/L)则不增强通道的活动。     

Transient increase in Zn2+ in hippocampal CA1 pyramidal neurons causes reversible memory deficit

The translocation of synaptic Zn(2+) to the cytosolic compartment has been studied to understand Zn(2+) neurotoxicity in neurological diseases. However, it is unknown whether the moderate increase in Zn(2+) in the cytosolic compartment affects memory processing in the hippocampus. In the present study, the moderate increase in cytosolic Zn(2+) in the hippocampus was induced with clioquinol (CQ), a zinc ionophore. Zn(2+) delivery by Zn-CQ transiently attenuated CA1 long-term potentiation (LTP) in hippocampal slices prepared 2 h after i.p. injection of Zn-CQ into rats, when intracellular Zn(2+) levels was transiently increased in the CA1 pyramidal cell layer, followed by object recognition memory deficit. Object recognition memory was transiently impaired 30 min after injection of ZnCl(2) into the CA1, but not after injection into the dentate gyrus that did not significantly increase intracellular Zn(2+) in the granule cell layer of the dentate gyrus. Object recognition memory deficit may be linked to the preferential increase in Zn(2+) and/or the preferential vulnerability to Zn(2+) in CA1 pyramidal neurons. In the case of the cytosolic increase in endogenous Zn(2+) in the CA1 induced by 100 mM KCl, furthermore, object recognition memory was also transiently impaired, while ameliorated by co-injection of CaEDTA to block the increase in cytosolic Zn(2+). The present study indicates that the transient increase in cytosolic Zn(2+) in CA1 pyramidal neurons reversibly impairs object recognition memory.     

Modeling features of induction of long term potentiation in pyramidal neurons in the CA3 hippocampal region

The conditions for inducing the long-term potentiation in the hippocampus were analyzed using the mathematical model of a CA3 pyramidal cell. Their dependence on the physiological characteristics of the neuron, the basic biochemical processes, and inhibitory efficacy was considered. The role of additional membrane depolarization in the origination of the hysteresis of the number of phosphorylated receptors as the basis for the formation of an "intermediate" stage of long-term potentiation was studied.     

Prenatal stress causes dendritic atrophy of pyramidal neurons in hippocampal CA3 region by glutamate in offspring rats

A substantial number of human epidemiological data, as well as experimental studies, suggest that adverse maternal stress during gestation is involved in abnormal behavior, mental, and cognition disorder in offspring. To explore the effect of prenatal stress (PS) on hippocampal neurons, in this study, we observed the dendritic field of pyramidal neurons in hippocampal CA3, examined the concentration of glutamate (Glu), and detected the expression of synaptotagmin‐1 (Syt‐1) and N‐methyl‐D ‐aspartate receptor 1 (NR1) in hippocampus of juvenile female offspring rats. Pregnant rats were divided into two groups: control group (CON) and PS group. Female offspring rats used were 30‐day old. The total length of the apical dendrites of pyramidal neurons in hippocampal CA3 of offspring was significantly shorter in PS than that in CON (p < 0.01). The number of branch points of the apical dendrites of pyramidal neurons in hippocampal CA3 of offspring was significantly less in PS (p < 0.01). PS offspring had a higher concentration of hippocampal Glu compared with CON (p < 0.05). PS offspring displayed increased expression of Syt‐1 and decreased NR1 in hippocampus compared with CON (p < 0.001 and p < 0.01, respectively). The expression of NR1 in different hippocampus subfields of offspring was significantly decreased in PS than that in CON (p < 0.05‐0.01). This study shows that PS increases the Glu in hippocampus and causes apical dendritic atrophy of pyramidal neurons of hippocampal CA3 in offspring rats. The decline of NR1 in hippocampus may be an adaptive response to the increased Glu. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2010     

Proteolytic degradation of glutamate decarboxylase mediates disinhibition of hippocampal CA3 pyramidal cells in cathepsin D-deficient mice

Although of clinical importance, little is known about the mechanism of seizure in neuronal ceroid lipofuscinosis (NCL). In the present study, we have attempted to elucidate the mechanism underlying the seizure of cathepsin D-deficient (CD-/-) mice that show a novel type of lysosomal storage disease with a phenotype resembling late infantile NCL. In hippocampal slices prepared from CD-/- mice at post-natal day (P)24, spontaneous burst discharges were recorded from CA3 pyramidal cells. At P24, the mean amplitude of IPSPs after stimulation of the mossy fibres was significantly smaller than that of wild-type mice, which was substantiated by the decreased level of gamma-aminobutyric acid (GABA) contents in the hippocampus measured by high-performance liquid chromatography (HPLC). At this stage, activated microglia were found to accumulate in the pyramidal cell layer of the hippocampal CA3 subfield of CD-/- mice. However, there was no significant change in the numerical density of GABAergic interneurons in the CA3 subfield of CD-/- mice at P24, estimated by counting the number of glutamate decarboxylase (GAD) 67-immunoreactive somata. In the hippocampus and the cortex of CD-/- mice at P24, some GABAergic interneurons displayed extremely high somatic granular immunoreactivites for GAD67, suggesting the lysosomal accumulation of GAD67. GAD67 levels in axon terminals abutting on to perisomatic regions of hippocampal CA3 pyramidal cells was not significantly changed in CD-/- mice even at P24, whereas the total protein levels of GAD67 in both the hippocampus and the cortex of CD-/- mice after P24 were significantly decreased as a result of degradation. Furthermore, the recombinant human GAD65/67 was rapidly digested by the lysosomal fraction prepared from the whole brain of wild-type and CD-/- mice. These observations strongly suggest that the reduction of GABA contents, presumably because of lysosomal degradation of GAD67 and lysosomal accumulation of its degraded forms, are responsible for the dysfunction of GABAergic interneurons in the hippocampal CA3 subfield of CD-/- mice.     

On the integration of subthreshold inputs from Perforant Path and Schaffer Collaterals in hippocampal CA1 pyramidal neurons

Using a realistic model of a CA1 hippocampal pyramidal neuron, we make experimentally testable predictions on the roles of the non-specific cation current, I _h , and the A-type Potassium current, I _A , in modulating the temporal window for the integration of the two main excitatory afferent pathways of a CA1 neuron, the Schaffer Collaterals and the Perforant Path. The model shows that the experimentally observed increase in the dendritic density of I _h and I _A could have a major role in constraining the temporal integration window for these inputs, in such a way that a somatic action potential (AP) is elicited only when they are activated with a relative latency consistent with the anatomical arrangement of the hippocampal circuitry.     

Phosphorylation of CRMP2 is involved in proper bifurcation of the apical dendrite of hippocampal CA1 pyramidal neurons

The neural circuit in the hippocampus is important for higher brain functions. Dendrites of CA1 pyramidal neurons mainly receive input from the axons of CA3 pyramidal neurons in this neural circuit. A CA1 pyramidal neuron has a single apical dendrite and multiple basal dendrites. In wild‐type mice, most of CA1 pyramidal neurons extend a single trunk, or alternatively, the apical dendrite bifurcates into two daughter trunks at the stratum radiatum layer. We previously reported the proximal bifurcation phenotype in Sema3A?/?, p35?/?, and CRMP4?/? mice. Cdk5/p35 phosphorylates CRMP2 at Ser522, and inhibition of this phosphorylation suppressed Sema3A‐induced growth cone collapse. In this study, we analyzed the bifurcation points of the apical dendrites of hippocampal CA1 pyramidal neurons in CRMP2KI/KI mice in which the Cdk5/p35‐phosphorylation site Ser522 was mutated into an Ala residue. The proximal bifurcation phenotype was not observed in CRMP2KI/KI mice; however, severe proximal bifurcation of apical dendrites was found in CRMP2KI/KI;CRMP4?/? mice. Cultured hippocampal neurons from CRMP2KI/KI and CRMP2KI/KI;CRMP4?/? embryos showed an increased number of dendritic branching points compared to those from wild‐type embryos. Sema3A increased the number of branching points and the total length of dendrites in wild‐type hippocampal neurons, but these effects of Sema3A for dendrites were notobserved in CRMP2KI/KI and CRMP2KI/KI;CRMP4?/?hippocampal neurons. Binding of CRMP2 to tubulin increased in both CRMP2KI/KI and CRMP2KI/KI:CRMP4?/? brain lysates. These results suggest that CRMP2 and CRMP4 synergistically regulate dendritic development, and CRMP2 phosphorylation is critical for proper bifurcation of apical dendrite of CA1 pyramidal neurons. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013