Blocker-resistant Ca2+ currents in rat CA1 hippocampal pyramidal neurons

Ca(2+) currents resistant to organic Ca(2+) channel antagonists are present in different types of central neurons. Here, we describe the properties of such currents in CA1 neurons acutely dissociated from rat hippocampus. Blocker-resistant Ca(2+) currents were isolated by combined application of N-, P/Q- and L-type Ca(2+) current antagonists (omega-conotoxin GVIA 2 microM; omega-conotoxin MVIIC 3 microM; omega-agatoxin IVA 200 nM; nifedipine 10 microM) and constituted approximately 21% of the total Ba(2+) current.The blocker-resistant current showed properties similar to R-type currents in other cell types, i.e. voltages of half-maximal inactivation and activation of -76 and -17 mV, respectively, and strong inactivation during the test pulse. In addition, blocker-resistant Ca(2+) currents in CA1 neurons displayed a characteristically rapid deactivation. Application of mock action potentials revealed that charge transfer through blocker-resistant Ca(2+) channels is highly sensitive to action potential shape and changes in resting membrane voltage. Pharmacological experiments showed that these currents were highly sensitive to the divalent cation Ni(2+) (half-maximal block at 28 microM), but were relatively resistant to the spider toxin SNX-482 (8% and 52% block at 0.1 and 1 microM, respectively).In addition to the functional analysis, we examined the expression of pore-forming and accessory Ca(2+) channel subunits on the messenger RNA level in isolated CA1 neurons using quantitative real-time polymerase chain reaction. Of the pore-forming alpha subunits encoding high-threshold Ca(2+) channels, Ca(v)2.1, Ca(v)2.2 and Ca(v)2.3 messenger RNA levels were most prominent, corresponding to the high proportion of N-, P/Q- and R-type currents in these neurons.In summary, CA1 neurons display blocker-resistant Ca(2+) currents with distinctive biophysical and pharmacological properties similar to R-type currents in other neuron types, and express Ca(2+) channel messenger RNAs that give rise to R-type Ca(2+) currents in expression systems.     

Caffeine releasable stores of Ca2+ show depletion prior to the final steps in delayed CA1 neuronal death

In addition to their role in signaling, Ca2+ ions in the endoplasmic reticulum also regulate important steps in protein processing and trafficking that are critical for normal cell function. Chronic depletion of Ca2+ in the endoplasmic reticulum has been shown to lead to cell degeneration and has been proposed as a mechanism underlying delayed neuronal death following ischemic insults to the CNS. Experiments here have assessed the relative content of ryanodine receptor-gated stores in CA1 neurons by measuring cytoplasmic Ca2+ increases induced by caffeine. These measurements were performed on CA1 neurons, in slice, from normal gerbils, and compared with responses from this same population of neurons 54-60 h after animals had undergone a standard ischemic insult: 5-min bilateral occlusion of the carotid arteries. The mean amplitude of responses in the postischemic population were less than one-third of those in control or sham-operated animals, and 35% of the neurons from postischemic animals showed very small responses that were approximately 10% of the control population mean. Refilling of these stores after caffeine challenges was also impaired in postischemic neurons. These observations are consistent with our earlier finding that voltage-gated influx is sharply reduced in postischemic in CA1 neurons and the hypothesis that the resulting depletion in endosomal Ca2+ is an important cause of delayed neuronal death.     

PBN fails to suppress in delayed neuronal death of hippocampal CA1 injury following transient forebrain ischemia in gerbils

Free radicals have been suggested to be involved in the genesis of ischemic brain damage, as shown by the protective effects of alpha-phenyl-N-tert-butyl nitrone (PBN), a spin trapping agent, in ischemic cerebral injury. However, the involvement of free radicals in transient ischemic-induced delayed neuronal death is not fully understood. To clarify this, in the present study, we evaluated the effect of PBN on delayed neuronal death and on the levels of free radicals in hippocampal CA1 region in the gerbil. The administration of PBN (10 mg/kg, i.v.) failed to show any preventive effect on the delayed neuronal death, examined by hematoxylin and eosin staining and the TUNEL method. Furthermore, we observed no free radical formation in delayed neuronal death, determined immunohistochemically using a specific 8-OHdG antibody, after transient ischemic insult. These results suggest that free radical formation may not contribute to the formation of delayed neuronal death.     

Anoxia-evoked intracellular pH and Ca2+ concentration changes in cultured postnatal rat hippocampal neurons.

The ratiometric indicators 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein and Fura-2 were employed to examine, respectively, intracellular pH (pHi) and calcium ([Ca2+]i) changes evoked by anoxia in cultured postnatal rat hippocampal neurons at 37 degrees C. Under both HCO3-/CO2- and HEPES-buffered conditions, 3-, 5- or 10-min anoxia induced a triphasic change in pHi consisting of an initial fall in pHi, a subsequent rise in pHi in the continued absence of O2 and, finally, a further rise in pHi upon the return to normoxia, which recovered towards preanoxic steady-state pHi values if the duration of the anoxic insult was < or = 5 min. In parallel experiments performed on sister cultures, anoxia of 3, 5 or 10 min duration evoked rises in [Ca2+]i which, in all cases, commenced after the start of the fall in pHi, reached a peak at or just following the return to normoxia and then declined towards preanoxic resting levels. Removal of external Ca2+ markedly attenuated increases in [Ca2+]i, but failed to affect the pHi changes evoked by 5 min anoxia. The latency from the start of anoxia to the start of the increase in pHi observed during anoxia was increased by perfusion with media containing either 2 mM Na+, 20 mM glucose or 1 microM tetrodotoxin. Because each of these manoeuvres is known to delay the onset and/or attenuate the magnitude of anoxic depolarization, the results suggest that the rise in pHi observed during anoxia may be consequent upon membrane depolarization. This possibility was also suggested by the findings that Zn2+ and Cd2+, known blockers of voltage-dependent proton conductances, reduced the magnitude of the rise in pHi observed during anoxia. Under HCO3-/CO2-free conditions, reduction of external Na+ by substitution with N-methyl-D-glucamine (but not Li+) attenuated the magnitude of the postanoxic alkalinization, suggesting that increased Na+/H+ exchange activity contributes to the postanoxic rise in pHi. In support, rates of pHi recovery from internal acid loads imposed following anoxia were increased compared to control values established prior to anoxia in the same neurons. In contrast, rates of pHi recovery from acid loads imposed during anoxia were reduced, suggesting the possibility that Na+/H+ exchange is inhibited during anoxia. We conclude that the steady-state pHi response of cultured rat hippocampal neurons to transient anoxia is independent of changes in [Ca2+]i and is characterized by three phases which are determined, at least in part, by alterations in Na+/H- exchange activity and, possibly, by a proton conductance which is activated during membrane depolarization.     

不同时间局灶性脑缺血/再灌损伤时活体脑片Ca2+的变化

目的:通过检测不同时间局灶性脑缺血 /再灌损伤时活体脑片Ca²⁺ 的变化,希望揭示Ca²⁺ 在体水平脑缺血 /再灌损伤机制。方法:用插线法制作局灶性脑缺血 /再灌损伤模型,激光扫描共聚焦显微镜观察活体脑片细胞内Ca²⁺ 的分布及动态变化。结果:①随着缺血时间的延长,皮质及纹状体区域脑片细胞内Ca²⁺ 含量逐渐增加;②缺血1h后再灌注10min可引起脑片纹状体区域细胞内Ca²⁺ 含量明显增加,但将再灌时间延长至 3h,Ca²⁺ 含量较灌注10min为低;③缺血 6h皮质及纹状体区域脑片细胞内Ca²⁺ 含量明显多于缺血1h,再灌注 3h后,细胞内Ca²⁺ 含量有所下降,但仍高于假手术组;④纹状体对缺血 /再灌注损伤比皮质敏感。结论:在脑缺血再灌注损伤中,皮质、纹状体部位的Ca²⁺ 起重要作用.     

Na+/Ca2+ exchanger activity induces a slow DC potential after in vitro ischemia in rat hippocampal CA1 region

In rat hippocampal CA1 neurons recorded intracellularly from tissue slices, a rapid depolarization occurred approximately 5 min after application of ischemia-simulating medium. In extracellular recordings obtained from CA1 region, a rapid negative-going DC potential (rapid DC potential) was recorded, corresponding to a rapid depolarization. When oxygen and glucose were reintroduced after generating the rapid depolarization, the membrane further depolarized and the potential became 0 mV after 5 min. Contrary, the DC potential began to repolarize slowly and subsequently a slow negative-going DC potential (slow DC potential) occurred within 1 min. A prolonged application of ischemia-simulating medium suppressed the slow DC potential. Addition of a high concentration of ouabain in normoxic medium reproduced a rapid but not a slow DC potential. The slow DC potential was reduced in low Na+- or Co2+-containing medium, but was not affected in low Cl-, high K+ or K+-free medium, suggesting that the slow DC potential is Na+-and Ca2+-dependent. Ni2+ (Ca2+ channel blocker as well as the Na+/Ca2+ exchanger blocker) and benzamil hydrochloride (Na+/Ca2+ exchanger blocker) reduced the slow DC potential dose-dependently. These results suggest that the slow DC potential is mediated by forward mode operation of Na+/Ca2+ exchangers in non-neuronal cells, and that reactivation of Na+, K+-ATPase is necessary to the Na+/Ca2 +exchanger activity.     

LAMP-2A ablation in hippocampal CA1 astrocytes confers cerebroprotection and ameliorates neuronal injury after global brain ischemia

Reactive astrogliosis and neuronal death are major features of brain tissue damage after transient global cerebral ischemia/reperfusion (I/R). The CA1 subfield in the hippocampus is particularly susceptible to cell death after I/R. Recently, attention has focused on the relationship between the autophagy–lysosomal pathway and cerebral ischemia. Lysosomal-associated membrane protein type-2A (LAMP-2A) is a key protein in chaperone-mediated autophagy (CMA). However, LAMP-2A expression in astrocytes of the hippocampus and its influence on brain injury following I/R remain unknown. Here, we show that LAMP-2A is elevated in astrocytes of the CA1 hippocampal subfield after I/R and in primary cultured astrocytes after transient oxygen–glucose deprivation (OGD). Conditional LAMP-2A knockdown in CA1 astrocytes inhibited astrocyte activation and prevented neuronal death by inhibiting the mitochondrial pathway of apoptosis after I/R, suggesting that elevated astrocytic LAMP-2A contributes to regional ischemic vulnerability. Furthermore, astrocytic LAMP-2A ablation ameliorated the spatial learning and memory deficits caused by I/R. Conditional astrocytic LAMP-2A knockdown also prevented the loss of hippocampal synapses and dendritic spines, improved the synaptic ultrastructure, and inhibited the reduced expression of synaptic proteins after ischemia. Thus, our findings demonstrate that astrocytic LAMP-2A expression increases upon I/R and that LAMP-2A ablation specifically in hippocampal astrocytes contributes to cerebroprotection, suggesting a novel neuroprotective strategy for patients with global ischemia.     

银杏内酯B对大鼠海马CA1区神经元自发放电的影响(英文)

为了研究银杏内酯B(Ginkgolide B,BN52021)对静息状态下的海马脑片神经元活动的影响。本研究应用细胞外记录单位放电技术观察了银杏内酯B对海马神经元电活动的影响,并分析了相关机制。结果显示:(1)在43个CA1区神经元放电单位给予银杏内酯B(0.1,1,10μmol/L)2min,有42个放电单位(97.67%)放电频率明显降低,且呈剂量依赖性;(2)预先用0.2mmol/L的L-glutamate(L-Glu)灌流海马脑片,10个放电单位放电频率明显增加,表现为癫痫样放电,在此基础上灌流银杏内酯B(1μmol/L)2min,其癫痫样放电全部被抑制;(3)预先用L型钙通道开放剂BayK8644灌流8个海马脑片神经元,8个单位(100%)放电全部增加,在此基础上灌流银杏内酯B(1μmol/L)2min,7个放电单位(87.5%)放电频率明显减低;(4)在8个CA1区神经元,银杏内酯B(1μmol/L)对单位放电的抑制效应可被1mmol/L广泛钾通道阻断剂(tetraethylammonium,TEA)完全阻断。上述结果提示,银杏内酯B可抑制海马CA1区神经元的自发放电,这种作用可能与银杏内酯B抑制L型钙通道有关,而且可能与延迟整流型钾通道(delayed rectifier potassium channel,KDR)有关。银杏内酯B通过降低神经元的活动而发挥对中枢神经元的保护作用。     

Inactivation of a slow Ca2+ current in CA1 neurones of the adult rat hippocampal slice

CA1 neurones of the adult rat hippocampal slice preparation were voltage clamped at or near -40 mV membrane potential using a single electrode clamp method. Depolarizing voltage commands from a holding potential of -40 mV elicited voltage-dependent inward Ca2+ currents comprising a fast and a slow component. The latter one was investigated for its susceptibility to inactivation, which was maximally expressed at around 0 mV membrane potential. When extracellular Ca2+ was replaced by Ba2+, inward currents became much larger and were followed by long tail currents. Similar data were observed in neurones injected with the Ca2+ chelator BAPTA. It is suggested that inactivation of the slow Ca2+ current depends at least partly on the levels of intracellular free Ca2+ in hippocampal neurones.     

Extrusion of intracellular calcium ion after in vitro ischemia in the rat hippocampal CA1 region

Simultaneous recordings of intracellular Ca(2+) ([Ca(2+)](i)) signal and extracellular DC potential were obtained from the CA1 region in 1-[6-amino-2-(5-carboxy-2-oxazolyl)-5-benzofuranyloxy]-2-(2-amino-5-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid penta-acetoxymethyl ester (Fura-2/AM)-loaded rat hippocampal slices. Superfusion with oxygen- and glucose-deprived medium (in vitro ischemia) for 5-6 min produced a rapid rise of the [Ca(2+)](i) level in the stratum radiatum (rising phase of the [Ca(2+)](i) signal), which occurred simultaneously with a rapid negative DC potential (rapid negative potential). When oxygen and glucose were reintroduced, the increased [Ca(2+)](i) signal diminished rapidly (falling phase of the [Ca(2+)](i) signal) during the generation of a slow negative DC potential (slow negative potential), which occurred within 1 min from the onset of the reintroduction. Thereafter, the [Ca(2+)](i) signal partially and the slow negative potential completely returned to the preexposure level approximately 6 min after the reintroduction. The changes in [Ca(2+)](i) signal during and after in vitro ischemia were very similar to the changes in the membrane potential of glial cells. The rising and falling phases of [Ca(2+)](i) signal corresponded to the rapid depolarization and a depolarizing hump, respectively, in the repolarizing phase of glial cells. A prolonged application of in vitro ischemia or a reintroduction of either glucose or oxygen suppressed the falling phase after ischemic exposure. The application of ouabain (30 microM) generated both a rapid negative potential and a rapid elevation of [Ca(2+)](i), but no slow negative potential or rapid reduction in [Ca(2+)](i) were observed. When oxygen and glucose were reintroduced to slices in the Na(+)-free or ouabain- or Ni(2+)-containing medium, the falling phase was suppressed. The falling phase was significantly accelerated in Ca(2+)- and Mg(2+)-free with EGTA-containing medium. In contrast, the falling phase was significantly slower in the Ca(2+)-free with high Mg(2+)- and EGTA-containing medium. The falling phase of the [Ca(2+)](i) signal after ischemic exposure is thus considered to be primarily dependent on the reactivation of Na(+), K(+)-ATPases, while the extrusion of cytosolic Ca(2+) via the forward-mode operation of Na(+)/Ca(2+) exchangers in glial cells is thought to be directly involved in the rapid reduction of [Ca(2+)](i) after ischemic exposure.     

Glutamate-induced disturbances in neurotransmission and ionic homeostasis of extracellular Ca2+ and K+ in CA1 hippocampal area

The effect of various concentrations ofl-glutamate on neurotransmission in the CA1 hippocampal area was studied using hippocampal slices. Three intervals ofl-glutamate concentration were established: ≤1 mM (all studied parameters are completely reversible upon washout, transmission being preserved), from 1 to 10 mM (both responses to frequency stimulation and single population spikes remain partially suppressed after washout), and above 10 mM (more than 50% suppression of transmission persists after washout). Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 124, No. 9, pp. 255–258, September, 1997     

Ca2+ signaling in gerbil CA3 hippocampal neurons following transient in vivo ischemia

Using the gerbil model of post-ischemic neuron death in the hippocampal CA1 region, it was recently shown that there is a strong down-regulation of voltage-gated Ca2+ influx in neurons examined at 2 days after the ischemic insult (Connor, J.A., Razani-Boroujerdi, S., Greenwood, A.C., Cormier, R.J., Petrozzino, J.J. and Lin, R.C., Reduced voltage-dependent Ca2+ signaling in CA1 neurons after brief ischemia in gerbils, J. Neurophysiol., 81 (1999) 299-306). The aim of the present study was to determine whether a similar change occurs in pyramidal neurons of the CA3 region that are relatively resistant to transient ischemia. In vitro intracellular recordings and fluorometric Ca2+ measurements were made from CA3 neurons in coronal slices prepared from controls and 1 or 2 days following in vivo ischemia. In slices from control and post-ischemic animals, the electrophysiological properties of CA3 neurons were consistent with significant voltage-gated Ca2+ influx, leading to spike frequency adaptation. Quantitative results indicated no significant difference in Ca2+ transients evoked by action potential trains. This Ca2+ signaling was compared with responses in CA1 neurons from the same preparations, which showed substantially diminished Ca2+ influx at 2 days post-ischemia. These findings suggest that diminished Ca2+-signaling is not a general feature of pyramidal neurons following ischemia, but is characteristic of neurons destined to die.     

Rat hippocampal CA3 neuronal injury induced by limb ischemia/reperfusion: A possible restorative effect of alpha lipoic acid

Limb ischemia reperfusion (I/R) injury is associated with serious local and systemic effects. Reperfusion may augment tissue injury in excess of that produced by ischemia alone. The hippocampus has been reported to be vulnerable to I/R injury. Alpha lipoic acid (ALA) is an endogenous antioxidant with a powerful antioxidative, anti-inflammatory, and antiapoptotic properties. We studied the probable restorative effect of ALA on limb I/R-induced structural damage of rat hippocampus. Forty adult male albino rats were divided equally into four groups: group I (sham); group II (I/R-1 day) has undergone bilateral femoral arteries occlusion (3 h), then reperfusion for 1 day; group III (I/R-7 days) has undergone reperfusion for seven days; group IV (I/R-ALA) has undergone I/R as group III and received an intraperitoneal injection of ALA (100 mg/kg) for 7 days. I/R groups revealed degenerative changes in the pyramidal neuronal perikarya of CA3 field in the form of dark-stained cytoplasm, dilated RER cisternae, mitochondrial alterations, and dense bodies’ accumulation. Their dendrites showed disorganized microtubules. Astrogliosis is featured by an increased number and increased immunoreactivity of astrocytes for glial fibrillary acid protein. Morphometric data revealed significant reduction of light neurons, surface area of neurons, and thickness of the CA3 layer. Most blood capillaries exhibited narrow lumen and irregular basal lamina. ALA ameliorated the neuronal damage. Pyramidal neurons revealed preservation of normal structure. Significant increase in the thickness of pyramidal layer in CA3 field and surface area and number of light neurons was observed but astrogliosis persisted. Limb I/R had a deleterious remote effect on the hippocampus aggravated with longer period of reperfusion. This work may encourage the use of ALA in the critical clinical settings with I/R injury.     

Subcellular muscarinic enhancement of excitability and Ca2+-signals in CA1-dendrites in rat hippocampal slice

The cholinergic system is involved in Ca2+-dependent models of learning. To study subcellular modulation, we evoked 50-100 microm long dendritic Ca2+-responses by focal pressure application of glutamate. These Ca2+-responses were augmented by +70% by focally applied carbachol. This atropine-sensitive augmentation started within 1 s concurrent to an augmentation of the glutamate-evoked somatic depolarization and firing. Tetrodotoxin reduced the Ca2+-response to glutamate by 60-80% while, after having restored the Ca2+-signal by increasing the application of glutamate, its muscarinic augmentation was reduced from +73 to +30%. Lithium (2 mM, >2 h) slowed and reduced augmentation of Ca2+-signals and blocked augmentation of the glutamate-evoked depolarization and firing, but not suppression of the slow after-hyperpolarization following repetitive discharge. Thus, several mechanisms contribute to muscarinic augmentation of Ca2+-signals.     

Kinetic properties of T-type Ca2+ currents in isolated rat hippocampal CA1 pyramidal neurons.

1. T-type Ca2+ channels producing a transient inward current were studied in pyramidal neurons acutely isolated from the ventral portion of rat hippocampal CA1 region. Membrane currents were recorded by the suction-pipette technique, which allows for internal perfusion under a single-electrode voltage clamp. 2. In all cells superfused with external solution containing 10 mM Ca2+, the T-type Ca2+ current was evoked by step depolarization to potentials more positive than -60 mV from a holding potential of -100 mV and reached a peak in the current-voltage relationship around -30 mV at 20-22 degrees C. 3. Activation and inactivation processes of T-type Ca2+ current were highly potential dependent, and the latter was fitted by a single exponential function. 4. Steady-state inactivation of T-type Ca2+ current could be fitted by a Boltzmann's equation with a slope factor of 6.0 and a half-inactivated voltage of -79 mV. 5. Recovery from inactivation of T-type Ca2+ current was not a single exponent. The major component of recovery (60-90% of total) was voltage sensitive with a time constant of 215 ms at -100 mV. 6. Amplitude of the T-type Ca2+ current depended on the external Ca2+ concentration. The ratio of peak amplitude in the individual current-voltage relationships of Ca2+, Ba2+, and Sr2+ currents passing through T-type Ca2+ channel was 1.0:0.85:1.32. The current kinetics were much the same. 7. All kinetic properties, including activation and inactivation, as well as the amplitude of T-type Ca2+ current, were temperature sensitive with Q10 (temperature coefficient) values of 1.7-2.5.(ABSTRACT TRUNCATED AT 250 WORDS)     

Attenuation of high-voltage-activated Ca2+ current run-down in rat hippocampal CA1 pyramidal cells by NaF

Calcium currents in CA1 neurons from rat hippocampus were studied with the whole-cell, patchclamp technique. Under control conditions high-voltage-activated (HVA) calcium currents activated from membrane potentials of -80 mV and -40 mV underwent run-down. The rate of run-down of the current activated from -40 mV was significantly attenuated by inclusion of the G-protein activator NaF (1 mM) in the pipette and also irreversibly attenuated by brief batch application of NaF (10 mM). This effect was significantly reduced by inclusion of high (10 mM) ethyleneglycoltetraacetate (EGTA) concentrations in the pipette, suggesting an involvement of calcium-dependent processes. It is suggested that activation of guanine nucleotide-binding proteins by NaF leads to a long-lasting attenuation of HVA calcium current run-down in hippocampal CA1 cells.     

Measurement of intracellular Ca2+ concentration using Indo-1 during simultaneous flash photolysis to release Ca2+ from DM-nitrophen

We have constructed a modular instrument to measure intracellular [Ca²⁺] ([Ca²⁺]_i) in single isolated cells while simultaneously imposing step changes in [Ca²⁺]_i using caged Ca²⁺. By combining the outputs of a xenon arc lamp with a frequency-tripled (Nd: YAG) laser, the instrument can operate with low maintained illumination to measure [Ca²⁺]_i using a ratiometric Ca²⁺-sensitive fluorophore and also activate the release of Ca²⁺ from a caged-Ca²⁺ compound with a high energy pulse of ultraviolet light. This instrument is simple to assemble, introduces little electrical noise, provides a wide range of illumination power, produces only moderate photobleaching of the Ca²⁺ indicator and can be readily adapted to diverse cellular preparations. We demonstrate the use of this system to measure step changes in [Ca²⁺]_i in adult rat ventricular myocytes and a human embryonic kidney cell line (293 cells) in culture.     

Selective blockade of Ca2+ permeable AMPA receptors in CA1 area of rat hippocampus

Using whole cell patch-clamp recording from pyramidal cells and interneurons in the CA1 area of hippocampal slices, the effect of IEM-1460, a selective channel blocker of Ca2+ permeable AMPA receptors (AMPARs), on postsynaptic currents (PSCs) was studied. Excitatory postsynaptic currents (EPSCs) were evoked by stimulation of Schaffer collaterals (SCs) in the presence of APV and bicuculline to pharmacologically isolate the EPSCs mediated by AMPAR activation. IEM-1460 (50 microM) did not affect the amplitude of EPSCs in CA1 pyramidal cells but reversibly decreased their amplitude in interneurons of pyramidal layer (15 cells), radiatum (37 cells) and border radiatum-lacunosum-moleculare (R-LM) (55 cells) layers. The ability of IEM-1460 to decrease EPSC amplitude correlated with EPSC rectification properties in CA1 interneurons, providing evidence for synaptic localization of Ca2+ permeable AMPARs at the SC synaptic input. Independent of their localization, the majority of interneurons studied exhibited only modest sensitivity to IEM-1460 (EPSC amplitude decreased by less than 30%), while in 15% of interneurons IEM-1460 induced more than 50% reduction in EPSC amplitude. To reveal possible afferent-specific localization of Ca2+ permeable AMPARs on R-LM interneurons, the effect of IEM-1460 on EPSCs evoked by stimulation of SC was compared with that of perforant path (PP). Although average sensitivities did not differ significantly, in 61% of R-LM layer interneurons, the SC-evoked EPSCs exhibited higher sensitivity to IEM-1460 than the PP-evoked EPSCs. Moreover, in 54% of R-LM layer interneurons the EPSCs evoked by SC stimulation were complex, having an initial peak followed by one or several late components. Kinetics, latency distribution and reversal potential of late components suggest di- and polysynaptic origin of the late components. Late EPSCs were strongly and reversibly inhibited by IEM-1460 indicating that Ca2+ permeable AMPARs are involved in the indirect excitation of R-LM layer interneurons. Despite the ability to decrease the excitatory synaptic input to interneurons, IEM-1460 did not affect interneuron-mediated inhibitory postsynaptic currents (IPSCs) evoked in pyramidal neurons by SC stimulation. These data suggest that interneurons with a synaptic input highly sensitive to IEM-1460 do not contribute specifically to the feed-forward inhibition of hippocampal pyramidal neurons.