Properties Of CA1 Pyramidal Neurons Research Articles

Electrical Low Frequency Stimulation of the Kindling Site Preserves the Electrophysiological Properties of the Rat Hippocampal CA1 Pyramidal Neurons From the Destructive Effects of Amygdala Kindling: The Basis for a Possible Promising Epilepsy Therapy

BackgroundDeep brain stimulation (DBS) has emerged as a potential therapeutic strategy in the treatment of neurological disorders including epilepsy. However, the cellular mechanism responsible for the effects of DBS remains largely undefined. Therefore, using electrophysiological approach, we aimed to determine the antiepileptic effects and restorative potential of low frequency stimulation (LFS) on amygdala kindling-induced changes in electrophysiological properties of rat hippocampal CA1 pyramidal neurons. MethodsAnimals were kindled by electrical stimulation of amygdala in a rapid kindling manner (12 times per day). In one group of animals, immediately after termination of daily 12 rapid kindling stimulations, the kindling site was subjected to 4 packages of LFS at intervals of 5 min (each package contained 200 monophasic square-wave pulses, 0.1 ms pulse duration at 1 Hz). Whole cell patch clamp recording under current clamp conditions was performed on visually identified pyramidal neurons in hippocampal slice preparations obtained from amygdala-kindled rats and the rats receiving LFS. ResultsKindling of the right basolateral amygdala profoundly affected spontaneous firing behavior and repetitive discharge characteristics of pyramidal neuronal electrophysiological properties. Application of LFS at the kindling site almost completely prevented the development of epilepsy and the disruptive effects of kindling on neuronal electrical activity through restoration of the normal electrophysiological characteristics. ConclusionsThe results of this study implied that application of LFS during kindling acquisition prevents the kindling induced changes in functional electrical properties of CA1 pyramidal neurons, suggesting that this action may be involved in the antiepileptogenic mechanism of LFS.

Protective effect of cannabinoid CB1 receptor activation against altered intrinsic repetitive firing properties induced by Aβ neurotoxicity

The amyloid β (Aβ) protein is believed to be the key pathological mediator of Alzheimer's disease (AD) which is the first and most well known type of dementia. Despite a growing body of evidence indicating that Aβ neurotoxicity induces changes in synaptic function, little effort, if any, has been made to investigate the effect of in vivo Aβ treatment on intrinsic neuronal properties. The present study was designed to examine the effects that in vivo Aβ treatment have on the intrinsic repetitive firing properties of CA1 pyramidal neurons, using whole cell patch clamp recording. Protective effect of cannabinoid CB1 receptor activation was also investigated against Aβ-induced alterations in evoked electrophysiological activities. The findings from present study demonstrated that a bilateral injection of Aβ into the prefrontal cortex causes robust changes in activity-dependent electrophysiological responses in hippocampal CA1 pyramidal neurons. The effects of Aβ treatment alone was almost completely prevented by combined treatment with Aβ and ACEA, a selective CB1 receptor agonist. It can be concluded Aβ treatment reduces evoked neuronal activity and activation of CB1 cannabinoid receptors may have beneficial preventative effects on Aβ-induced electrophysiological changes.

Altered synaptic and non‐synaptic properties of CA1 pyramidal neurons in Kv4.2 knockout mice

Back-propagating action potentials (bAPs) travelling from the soma to the dendrites of neurons are involved in various aspects of synaptic plasticity. The distance-dependent increase in Kv4.2-mediated A-type K(+) current along the apical dendrites of CA1 pyramidal cells (CA1 PCs) is responsible for the attenuation of bAP amplitude with distance from the soma. Genetic deletion of Kv4.2 reduced dendritic A-type K(+) current and increased the bAP amplitude in distal dendrites. Our previous studies revealed that the amplitude of unitary Schaffer collateral inputs increases with distance from the soma along the apical dendrites of CA1 PCs. We tested the hypothesis that the weight of distal synapses is dependent on dendritic Kv4.2 channels. We compared the amplitude and kinetics of mEPSCs at different locations on the main apical trunk of CA1 PCs from wild-type (WT) and Kv4.2 knockout (KO) mice. While wild-type mice showed normal distance-dependent scaling, it was missing in the Kv4.2 KO mice. We also tested whether there was an increase in inhibition in the Kv4.2 knockout, induced in an attempt to compensate for a non-specific increase in neuronal excitability (after-polarization duration and burst firing probability were increased in KO). Indeed, we found that the magnitude of the tonic GABA current increased in Kv4.2 KO mice by 53% and the amplitude of mIPSCs increased by 25%, as recorded at the soma. Our results suggest important roles for the dendritic K(+) channels in distance-dependent adjustment of synaptic strength as well as a primary role for tonic inhibition in the regulation of global synaptic strength and membrane excitability.

Conditional Knock-Out of Kir4.1 Leads to Glial Membrane Depolarization, Inhibition of Potassium and Glutamate Uptake, and Enhanced Short-Term Synaptic Potentiation

During neuronal activity, extracellular potassium concentration ([K+]out) becomes elevated and, if uncorrected, causes neuronal depolarization, hyperexcitability, and seizures. Clearance of K+ from the extracellular space, termed K+ spatial buffering, is considered to be an important function of astrocytes. Results from a number of studies suggest that maintenance of [K+]out by astrocytes is mediated by K+ uptake through the inward-rectifying Kir4.1 channels. To study the role of this channel in astrocyte physiology and neuronal excitability, we generated a conditional knock-out (cKO) of Kir4.1 directed to astrocytes via the human glial fibrillary acidic protein promoter gfa2. Kir4.1 cKO mice die prematurely and display severe ataxia and stress-induced seizures. Electrophysiological recordings revealed severe depolarization of both passive astrocytes and complex glia in Kir4.1 cKO hippocampal slices. Complex cell depolarization appears to be a direct consequence of Kir4.1 removal, whereas passive astrocyte depolarization seems to arise from an indirect developmental process. Furthermore, we observed a significant loss of complex glia, suggestive of a role for Kir4.1 in astrocyte development. Kir4.1 cKO passive astrocytes displayed a marked impairment of both K+ and glutamate uptake. Surprisingly, membrane and action potential properties of CA1 pyramidal neurons, as well as basal synaptic transmission in the CA1 stratum radiatum appeared unaffected, whereas spontaneous neuronal activity was reduced in the Kir4.1 cKO. However, high-frequency stimulation revealed greatly elevated posttetanic potentiation and short-term potentiation in Kir4.1 cKO hippocampus. Our findings implicate a role for glial Kir4.1 channel subunit in the modulation of synaptic strength.

Stability and plasticity of intrinsic membrane properties in hippocampal CA1 pyramidal neurons: effects of internal anions

CA1 pyramidal neurons from animals that have acquired hippocampal tasks show increased neuronal excitability, as evidenced by a reduction in the postburst afterhyperpolarization (AHP). Studies of AHP plasticity require stable long-term recordings, which are affected by the intracellular solutions potassium methylsulphate (KMeth) or potassium gluconate (KGluc). Here we show immediate and gradual effects of these intracellular solutions on measurement of the AHP and basic membrane properties, and on the induction of AHP plasticity in CA1 pyramidal neurons from rat hippocampal slices. The AHP measured immediately after establishing whole-cell recordings was larger with KMeth than with KGluc. In general, the AHP in KMeth was comparable to the AHP measured in the perforated-patch configuration. However, KMeth induced time-dependent changes in the intrinsic membrane properties of CA1 pyramidal neurons. Specifically, input resistance progressively increased by 70% after 50 min; correspondingly, the current required to trigger an action potential and the fast afterdepolarization following action potentials gradually decreased by about 50%. Conversely, these measures were stable in KGluc. We also demonstrate that activity-dependent plasticity of the AHP occurs with physiologically relevant stimuli in KGluc. AHPs triggered with theta-burst firing every 30 s were progressively reduced, whereas AHPs elicited every 150 s were stable. Blockade of the apamin-sensitive AHP current (I(AHP)) was insufficient to block AHP plasticity, suggesting that plasticity is manifested through changes in the apamin-insensitive slow AHP current (sI(AHP)). These changes were observed in the presence of synaptic blockers, and therefore reflect changes in the intrinsic properties of the neurons. However, no AHP plasticity was observed using KMeth. In summary, these data show that KMeth produces time-dependent changes in basic membrane properties and prevents or obscures activity-dependent reduction of the AHP. In whole-cell recordings using KGluc, repetitive theta-burst firing induced AHP plasticity that mimics learning-related reduction in the AHP.

Morphological characteristics and electrophysiological properties of CA1 pyramidal neurons in macaque monkeys

Little is known about the morphological characteristics and intrinsic electrophysiological properties of individual neurons in the nonhuman primate hippocampus. We have used intracellular recording and biocytin-labeling techniques in the in vitro hippocampal slice preparation to provide quantitative evaluation of the fundamental morphological and intrinsic electrophysiological characteristics of macaque monkey CA1 pyramidal neurons. These neurons have previously been studied in the rat in our laboratory. Monkey CA1 pyramidal neurons have an average soma volume of 3578μm 3, 4.71 basal dendrites with 53 terminal branches for a dendritic length of about 10,164μm, 1.13 apical dendrites with 47 terminal branches for a dendritic length of about 10,678μm. In comparison, rat CA1 pyramidal neurons have an average soma volume of 2066μm 3, 3.35 basal dendrites with 29 terminal branches for a dendritic length of about 4,586μm, 1.43 apical dendrites with 62 terminal branches for a dendritic length of about 8,838μm. The basic intrinsic electrophysiological properties of CA1 pyramidal cells are similar in monkeys and rats. Monkey CA1 pyramidal neurons have a resting membrane potential of about −62 mV (rat: −62 mV), an input resistance of 35 MΩ (rat: 34–49 MΩ), a rheobase of 0.17 nA (rat: 0.12–0.20 nA) and an action potential amplitude of 83 mV (rat: 71–89 mV). Although morphological differences such as the increased dendritic length may translate into differences in neural processing between primates and rodents, the functional significance of these morphological differences is not yet clear. Quantitative studies of the primate brain are critical in order to extrapolate information derived from rodent studies into better understanding of the normal and pathological function of the human hippocampus.

Resting and active properties of pyramidal neurons in subiculum and CA1 of rat hippocampus.

Action potentials are the end product of synaptic integration, a process influenced by resting and active neuronal membrane properties. Diversity in these properties contributes to specialized mechanisms of synaptic integration and action potential firing, which are likely to be of functional significance within neural circuits. In the hippocampus, the majority of subicular pyramidal neurons fire high-frequency bursts of action potentials, whereas CA1 pyramidal neurons exhibit regular spiking behavior when subjected to direct somatic current injection. Using patch-clamp recordings from morphologically identified neurons in hippocampal slices, we analyzed and compared the resting and active membrane properties of pyramidal neurons in the subiculum and CA1 regions of the hippocampus. In response to direct somatic current injection, three subicular firing types were identified (regular spiking, weak bursting, and strong bursting), while all CA1 neurons were regular spiking. Within subiculum strong bursting neurons were found preferentially further away from the CA1 subregion. Input resistance (R(N)), membrane time constant (tau(m)), and depolarizing "sag" in response to hyperpolarizing current pulses were similar in all subicular neurons, while R(N) and tau(m) were significantly larger in CA1 neurons. The first spike of all subicular neurons exhibited similar action potential properties; CA1 action potentials exhibited faster rising rates, greater amplitudes, and wider half-widths than subicular action potentials. Therefore both the resting and active properties of CA1 pyramidal neurons are distinct from those of subicular neurons, which form a related class of neurons, differing in their propensity to burst. We also found that both regular spiking subicular and CA1 neurons could be transformed into a burst firing mode by application of a low concentration of 4-aminopyridine, suggesting that in both hippocampal subfields, firing properties are regulated by a slowly inactivating, D-type potassium current. The ability of all subicular pyramidal neurons to burst strengthens the notion that they form a single neuronal class, sharing a burst generating mechanism that is stronger in some cells than others.

Neonatal seizures induced persistent changes in intrinsic properties of CA1 rat hippocampal cells

We investigated the effects of repeated early-life seizures induced by flurothyl inhalation on intrinsic membrane properties of hippocampal pyramidal neurons from young rats (postnatal day 15–20). Intracellular recordings of CA1 and CA3 pyramidal neurons from flurothyl-treated and control rats revealed no significant differences in resting membrane potential, input resistance, membrane time constant, and action potential characteristics. In CA1 pyramidal cells from flurothyl-treated rats, the spike frequency adaptation and afterhyperpolarizing potential following a spike train were markedly reduced when compared with controls. In contrast, no significant alterations in the firing properties of CA3 pyramidal neurons were found. It is concluded that neonatal seizures lead to persistent changes in intrinsic membrane properties of CA1 pyramidal neurons. These alterations are consistent with an increase in neuronal excitability and may contribute to the behavioral deficit and epileptogenic predisposition observed in rats that experienced repeated neonatal seizures. Ann Neurol 2000;47:729–738

Neonatal seizures induced persistent changes in intrinsic properties of CA1 rat hippocampal cells

We investigated the effects of repeated early-life seizures induced by flurothyl inhalation on intrinsic membrane properties of hippocampal pyramidal neurons from young rats (postnatal day 15-20). Intracellular recordings of CA1 and CA3 pyramidal neurons from flurothyl-treated and control rats revealed no significant differences in resting membrane potential, input resistance, membrane time constant, and action potential characteristics. In CA1 pyramidal cells from flurothyl-treated rats, the spike frequency adaptation and afterhyperpolarizing potential following a spike train were markedly reduced when compared with controls. In contrast, no significant alterations in the firing properties of CA3 pyramidal neurons were found. It is concluded that neonatal seizures lead to persistent changes in intrinsic membrane properties of CA1 pyramidal neurons. These alterations are consistent with an increase in neuronal excitability and may contribute to the behavioral deficit and epileptogenic predisposition observed in rats that experienced repeated neonatal seizures.

Dendritic properties of hippocampal CA1 pyramidal neurons in the rat: Intracellular staining in vivo and in vitro

Dendritic morphology and passive cable properties determine many aspects of synaptic integration in complex neurons, together with voltage-dependent membrane conductances. We investigated dendritic properties of CA1 pyramidal neurons intracellularly labeled during in vivo and in vitro physiologic recordings, by using similar intracellular staining and three-dimensional reconstruction techniques. Total dendritic length of the in vivo neurons was similar to that of the in vitro cells. After correction for shrinkage, cell extent in three-dimensional representation was not different between the two groups. Both in vivo and in vitro neurons demonstrated a variable degree of symmetry, with some neurons showing more cylindrical symmetry around the main apical axis, whereas other neurons were more elliptical, with the variation likely due to preparation and preservation conditions. Branch order analysis revealed no difference in the number of branch orders or dendritic complexity. Passive conduction of dendritic signals to the soma in these neurons shows considerable attenuation, particularly with higher frequency signals (such as synaptic potentials compared with steady-state signals), despite a relatively short electrotonic length. Essential aspects of morphometric appearance and complex dendritic integration critical to CA1 pyramidal cell functioning are preserved across neurons defined from the two different hippocampal preparations used in this study.

Dendritic electrogenesis in rat hippocampal CA1 pyramidal neurons: functional aspects of Na+ and Ca2+ currents in apical dendrites.

The regenerative properties of CA1 pyramidal neurons were studied through differential polarization with external electrical fields. Recordings were obtained from somata and apical dendrites in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), DL-2-amino-5-phosphonovaleric acid (APV), and bicuculline. S+ fields hyperpolarized the distal apical dendrites and depolarized the rest of the cell, whereas S divided by fields reversed the polarization. During intradendritic recordings, S+ fields evoked either fast spikes or compound spiking. The threshold response consisted of a low-amplitude fast spike and a slow depolarizing potential. At higher field intensities the slow depolarizing potential increased in amplitude, and additional spikes of high amplitude appeared. During intrasomatic recordings, S+ field evoked repetitive firing of fast spikes, whereas S divided by fields evoked a slow depolarizing potential on top of which high- and low-amplitude spikes were evoked. Tetrodotoxin (TTX) blocked all types of responses in both dendrites and somata. Perfusion with Ca(2+)-free, Co(2+)-containing medium increased the frequency and amplitude of fast spikes evoked by S+ field and substantially reduced the slow depolarizing potential evoked by S+ field and substantially reduced the slow depolarizing potential evoked by S divided by fields. Antidromic stimulation revealed that an all-or-none dendritic component was activated in the distal apical dendrites by back-propagating somatic spikes. The dendritic component had an absolute refractory period of about 4 ms and a relative refractory period of 10-12 ms. Ca(2+)-dependent spikes in the dendrites were followed by a long-lasting afterhyperpolarization (AHP) and a decrease in membrane input resistance, during which dendritic excitability was selectively reduced. The data suggest that generation of fast Na+ currents and slow Ca2+ currents in the distal part of apical dendrites is highly sensitive to the dynamic state of the dendritic membrane. Depending on the mode and frequency of activation these currents can exert a substantial influence on the input-output behavior of the pyramidal neurons.

Effects of trifluoperazine on synaptically evoked potentials and membrane properties of CA1 pyramidal neurons of rat hippocampus in situ and in vitro.

The effects of trifluoperazine (TFP), a phenothiazine antipsychotic, on hippocampal activity were studied in the CA1 subfield, both in situ and in slices. In the extracellular studies in situ and in vitro, both somatic population spikes and dendritic excitatory postsynaptic potentials (EPSP) fields were depressed reversibly by TFP, applied by microiontophoresis or in the bath (50-100 microM). Similar effects were also seen during iontophoretic applications of sphingosine in situ. Like TFP (at micromolar concentrations) sphingosine is a dual Ca2+/calmodulin-dependent kinase and protein kinase C (PKC) inhibitor. In intracellular recordings from slices, 50-100 microM TFP induced a slow depolarization and a decrease in input resistance (RN), probably through a gamma-aminobutyric acid (GABA)-mediated increase in Cl- conductance (GCl). TFP also reduced the slow afterhyperpolarization (AHP) as well as electrically evoked inhibitory postsynaptic potentials (IPSPs), but EPSPs were augmented in both amplitude and duration. When CA1 neurons were voltage clamped, TFP elicited a corresponding inward current (consistent with depolarization), increased the leak conductance, and enhanced excitatory synaptic currents; whereas inhibitory synaptic currents and high-threshold Ca2+ currents were reduced. In conclusion, these effects of TFP--which cannot be readily explained by its potent antidopamine action--are in keeping with other evidence that both Ca2+/calmodulin-dependent kinase and PKC can modulate GCl-conductance and high-threshold Ca(2+)-conductance, as well as inhibitory and excitatory postsynaptic currents.

Kindling-induced persistent alterations in the membrane and synaptic properties of CA1 pyramidal neurons

Intracellular recordings of CA1 pyramidal cells were performed in in vitro hippocampal slices obtained from control and amygdala- or perforant path-kindled rats. Passive membrane properties did not differ between control and kindled cells. Twenty-three percent of kindled cells, however, displayed burst firing with depolarizing current injection, whereas no control cells produced bursts ( P < 0.01). Two different types of voltage-dependent alteration of depolarizing postsynaptic potentials (PSPs) were also evident in kindled cells. The majority (26/29) of these cells showed a smaller increase (type 1, n = 18), or a sudden decrease (type 2, n = 8), in PSP amplitude with passive membrane hyperpolarization when compared to controls ( P < 0.01). The NMDA antagonist D-APV did not markedly alter the overall slope of the PSP/membrane potential function in either ‘type 1’ or ‘type 2’ cells, suggesting that neither behavior was due to a change in the activation characteristics of NMDA receptors. The amplitude of IPSPs was smaller in ‘type 1’ kindled cells ( P < 0.05) than in controls, however, suggesting that the reduced slope of the PSP/membrane function may be accounted for by a change in inhibition.

The induction of corticosteroid actions on membrane properties of hippocampal CA1 neurons requires protein synthesis.

Corticosterone can affect electrical properties of CA1 pyramidal neurons via binding to two corticoid receptor types, the mineralocorticoid (MR) and glucocorticoid receptor (GR). Previously we have shown that MR-activation leads to attenuation of serotonin (5-HT)-induced membrane hyperpolarization, while GR-activation induces an increase in the amplitude of the afterhyperpolarization (AHP) following a short current pulse. In this study we show that the MR- and GR-mediated changes of the membrane properties are prevented in the presence of the protein synthesis inhibitor cycloheximide, thus suggesting a genomic action of the steroids.

Mineralocorticoid receptor-mediated changes in membrane properties of rat CA1 pyramidal neurons in vitro.

Pyramidal neurons in the rat hippocampus contain mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) to which the adrenal steroid corticosterone binds with differential affinity. We have used intracellular recording techniques to examine MR-mediated effects on membrane properties of CA1 pyramidal neurons in hippocampal slices from adrenalectomized rats. Low doses of corticosterone (1 nM) applied by perfusion for 20 min decreased the spike accommodation observed during a depolarizing current pulse (0.5 nA for 500 ms) and the amplitude of the subsequent afterhyperpolarization without affecting other membrane properties tested. The decrease became apparent ca. 15 min after steroid perfusion was started and reached its peak value 10-20 min after the steroid perfusion was terminated. The steroid effect was blocked by the MR antagonist spironolactone and mimicked by the natural MR ligand aldosterone (1 nM). Neurons recorded 30-90 min after termination of aldosterone application still displayed a decreased spike accommodation. However, 30-90 min after corticosterone application, the decrease in spike accommodation/afterhyperpolarization appeared to be reversed. Higher doses of corticosterone (greater than or equal to 30 nM) induced a significant increase in accommodation and amplitude of the afterhyperpolarization, as was previously observed for selective GR ligands. The data indicate that MR and GR activations induce opposite actions on the spike accommodation/afterhyperpolarization of CA1 pyramidal neurons, an important intrinsic mechanism of these neurons to regulate their response to excitatory input. We suggest that occupation of both MR and GR by the endogenous ligand corticosterone will result in an initial MR-mediated enhanced cellular excitability, which is gradually reversed and overridden by a GR-mediated suppression of cellular activity.

Galanin blocks the slow cholinergic EPSP in CA1 pyramidal neurons from ventral hippocampus

Using intracellular recordings from slice preparation, we studied the effects of the peptide galanin on the properties of CA1 pyramidal neurons from rat ventral hippocampus. Galanin, applied in the superfusing medium, had a weak and inconsistent effect on the membrane potential or on the afterhyperpolarization which follows a train of spikes. Galanin, which is localized in some cholinergic neurons of the septo-hippocampal pathway, did not affect the action of acetylcholine or carbachol on CA1 pyramidal neurons. However, it did have a presynaptic inhibitory effect on the cholinergic terminals, blocking the slow cholinergic excitatory post-synaptic potential (EPSP) induced by the release of endogenous acetylcholine on the pyramidal neurons. This effect was reversible and mimicked by atropine. These results suggest that the peptide galanin, colocalized with acetylcholine in some septo-hippocampal neurons might play a role in the control of acetylcholine release.