Developmental study of benzodiazepine effects on monosynaptic GABAA-mediated IPSPs of rat hippocampal neurons

1993 ◽  
Vol 70 (3) ◽  
pp. 1076-1085 ◽  
Author(s):  
C. Rovira ◽  
Y. Ben-Ari
Keyword(s):  
Hippocampal Neurons ◽  
Receptor Agonist ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Developmental Study ◽  
Type I ◽  
Gamma Aminobutyric Acid ◽  
Adult Rats ◽  
Young Rats ◽  
In Cells

1. The effects of type I (BZ1) and type II (BZ2) benzodiazepine receptor ligands on monosynaptic gamma-aminobutyric acid (GABA)A-mediated inhibitory postsynaptic potentials (IPSPs) and on responses to exogenously applied GABA were studied using intracellular recordings from CA3 pyramidal cells of rat hippocampal slices taken at different postnatal stages [postnatal day 4 (P4)-P35)]. 2. The effects of midazolam, a BZ1 and BZ2 receptor agonist, were tested on the monosynaptic IPSPs at different stages. Monosynaptic, bicuculline-sensitive IPSPs were evoked by hilar stimulation in presence of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) antagonists [6-cyano-7-nitroquinoxaline-2,3-dione (10 microM) and D(-)2-amino-5-phosphonopentanoic acid (50 microM)]. Midazolam at 300 nM maximally increased the duration and amplitude of monosynaptic GABAA-mediated IPSPs in neurons from pups (P4-P6, n = 6) and young (P7-P12, n = 8) and adult (P25-P35, n = 9) rats. All the effects of midazolam on IPSPs were reversed by the antagonist Ro 15-1788 (10 microM). 3. The effect of midazolam was also tested on the response to exogenously applied GABA (5 mM) in the presence of tetrodotoxine [TTX (1 microM)]. In neurons from young rats (n = 9), midazolam (1 nM-1 microM) did not change the responses to exogenously applied GABA, whereas in adult rats (n = 8) midazolam maximally increased GABA currents at 30 nM. 4. The effect of zolpidem, a BZ1 receptor agonist, was tested on monosynaptic IPSPs and GABA currents at different stages. Zolpidem (10 nM-1 microM) was inactive in cells from young rats (n = 12). In neurons from adult rats, zolpidem maximally increased the duration and amplitude of the monosynaptic IPSPs at 300 nM (n = 5) and the amplitude of GABA current at 30-100 nM (n = 5). 5. Methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) (300 nM), an inverse agonist of BZ1 and BZ2 receptors, decreased the amplitude and duration of monosynaptic IPSPs in neurons from pups (n = 3) and young (n = 4) and adult (n = 5) rats. In all cases, full recovery was obtained after exposure to R0 15-1788 (10 microM). DMCM (300 nM-10 microM) failed to reduce GABA responses in cells from young (n = 3) or adult (n = 7) rats. 6. Results indicate that the regulation by benzodiazepine of GABAA-mediated IPSPs varies with the developmental stage.(ABSTRACT TRUNCATED AT 400 WORDS)

Abundant GFP Expression and LTP in Hippocampal Acute Slices by In Vivo Injection of Sindbis Virus

2001 ◽  
Vol 86 (2) ◽  
pp. 1037-1042 ◽  
Author(s):  
Massimo D'Apuzzo ◽  
Georgia Mandolesi ◽  
Gerald Reis ◽  
Erin M. Schuman
Keyword(s):  
Hippocampal Neurons ◽  
Sindbis Virus ◽  
Fluorescent Protein ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Long Term Potentiation ◽  
Neuronal Structure ◽  
Adult Rats ◽  
Acute Hippocampal Slices

Virus-mediated gene transfer into neurons is a powerful tool for the analysis of neuronal structure and function. Recombinant sindbis virus has been previously used to study protein function in hippocampal neuron cultures as well as in hippocampal organotypic slice cultures. Nevertheless, some concern still exists about the physiological relevance of these cultured preparations. Acute hippocampal slices are a widely used preparation for the study of synaptic transmission, but currently recombinant gene delivery is usually achieved only through time-consuming transgenic techniques. In this study, we show that a subregion of the CA1 area in acute hippocampal slices can be specifically altered to express a gene of interest. A sindbis virus vector carrying an enhanced green fluorescent protein (EGFP) reporter was injected in vivo into the hippocampus of adult rats. After 18 h, rats were killed, and acute hippocampal slices, infected in the CA1 field, were analyzed morphologically and electrophysiologically. Infected slices showed healthy and stable electrophysiological responses as well as long-term potentiation. In addition, infected pyramidal cells were readily recognized in living slices by two-photon imaging. Specifically, the introduction of an EGFP-Actin fusion protein greatly enhanced the detection of fine processes and dendritic spines. We propose this technique as an efficient tool for studying gene function in adult hippocampal neurons.

Electrophysiological evidence from glutamate microapplications for local excitatory circuits in the CA1 area of rat hippocampal slices

1988 ◽  
Vol 59 (1) ◽  
pp. 110-123 ◽  
Author(s):  
E. P. Christian ◽  
F. E. Dudek
Keyword(s):  
Hippocampal Neurons ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Inhibitory Synapses ◽  
Excitatory Synapses ◽  
Recording Site ◽  
Postsynaptic Potentials ◽  
Inhibitory Postsynaptic Potentials ◽  
Ca1 Area ◽  
Transverse Slice

1. Evidence for local excitatory synaptic connections in CA1 of the rat hippocampus was obtained by recording excitatory postsynaptic potentials (EPSPs) intracellularly from pyramidal cells during local microapplications of glutamate. 2. Experiments were performed in hippocampal slices cut parallel to (transverse slice) or perpendicular to (longitudinal slice) alvear fibers. In normal solutions, glutamate microdrops (10–20 mM, 10–20 micron diam) applied in CA1 within 400 micron of recorded cells sometimes increased the frequency of inhibitory postsynaptic potentials for 5–10 s in both transverse and longitudinal slices. Increases in EPSP frequency were also occasionally observed, but only in transverse slices. Tetrodotoxin (1 microgram/ml) blocked glutamate-induced increases in PSP frequency, thus indicating that they were not caused by subthreshold effects on presynaptic terminals. Increases in PSP frequency were interpreted to result from glutamate activation of hippocampal neurons with inhibitory and excitatory connections to recorded neurons. 3. In both slice orientations, local excitatory circuits were studied in more isolated conditions by surgically separating CA1 from CA3 (transverse slices) and by blocking GABAergic inhibitory synapses with picrotoxin (5–10 microM). Microdrops were systematically applied at 200 and 400 micron on each side of the recording site. Significant glutamate-induced increases in EPSP frequency were observed in neurons from both slice orientations to microdrops in at least one of the locations. This provided evidence that excitatory synapses are present in both transverse and longitudinal slices. 4. Substantial increases in EPSP frequency only occurred in neurons from longitudinal slices when glutamate was microapplied 200 micron or less from the recording site. In transverse slices, however, large increases in EPSP frequency were observed to glutamate microapplications at 200 or 400 micron. These data suggest that CA1 local excitatory connections project for longer distances in the transverse than in the longitudinal plane of section. 5. Increases in EPSP frequency, averaged across cells, did not differ significantly in the four microapplication sites in either transverse or longitudinal slices. Thus local excitation in CA1 does not appear to be asymmetrically arranged in the way suggested for CA3. 6. The densities of local excitatory circuits in CA1 versus CA3 were studied by quantitatively comparing glutamate-induced increases in EPSP frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium-dependent current generating the afterhyperpolarization of hippocampal neurons

1986 ◽  
Vol 55 (6) ◽  
pp. 1268-1282 ◽  
Author(s):  
B. Lancaster ◽  
P. R. Adams
Keyword(s):  
Voltage Clamp ◽  
Hippocampal Neurons ◽  
Hippocampal Slices ◽  
Outward Current ◽  
Pyramidal Cells ◽  
Resting Potential ◽  
Tail Current ◽  
Calcium Dependent ◽  
K Current

A single-electrode voltage-clamp technique was employed on in vitro hippocampal slices to examine the membrane current responsible for the slow afterhyperpolarization (AHP) in CA1 pyramidal cells. This was achieved by using conventional procedures to evoke an AHP in current clamp, followed rapidly by a switch into voltage clamp (hybrid clamp). The AHP current showed a dependence on extracellular K+, which was close to that predicted for a K+ current by the Nernst equation. The AHP current could be blocked by Cd2+ or norepinephrine. Although the AHP current showed a requirement for voltage-dependent Ca2+ entry, the current did not show any clear intrinsic voltage dependence. Once activated, AHP current is not turned off by hyperpolarizing the membrane potential. The effects of norepinephrine, Cd2+, and tetraethylammonium (TEA) were used to identify an AHP current component to the outward current evoked by depolarizing voltage commands from holding potentials that approximate to the resting potential for these cells. The AHP current can contribute significantly to the outward current during the depolarizing command. Upon repolarization it is evident as a slow outward tail current. This slow tail current had the same time constant as AHP currents evoked by hybrid clamp. Fast components to the tail currents were also observed. These were sensitive to Cd2+ and TEA. They probably represent a voltage-sensitive gKCa, sometimes termed C-current. The strong sensitivity to voltage and TEA displayed by the conventionally described gKCa (IC) are properties inconsistent with the AHP. It seems likely that the AHP current (IAHP) represents a Ca2+-activated K+ current separate from IC and that these two currents coexist in the same cell.

The K+ channel opener diazoxide enhances glutamatergic currents and reduces GABAergic currents in hippocampal neurons

1993 ◽  
Vol 69 (2) ◽  
pp. 494-503 ◽  
Author(s):  
V. Crepel ◽  
C. Rovira ◽  
Y. Ben-Ari
Keyword(s):  
Intracellular Recording ◽  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Reversal Potential ◽  
Input Resistance ◽  
Katp Channels ◽  
K Channel ◽  
Gamma Aminobutyric Acid ◽  
Postsynaptic Potentials

1. The effect of diazoxide, an opener of ATP-sensitive K+ channels (KATP channels) has been investigated in the rat hippocampal slices by the use of extracellular and intracellular recording techniques. 2. In control solution, diazoxide enhanced the CA1 and CA3 field excitatory postsynaptic potentials (EPSPs) and produced interictal activities in CA3. These effects were neither prevented by KATP blockers, including glibenclamide (3-30 microM) or tolbutamide (500 microM), nor mimicked by another KATP opener such as galanine (1 microM); thus these effects are probably not mediated by KATP channels. 3. Using intracellular recording, we then studied, in CA3 pyramidal neurons, the effect of diazoxide on the EPSPs and the fast and slow inhibitory postsynaptic potentials (IPSPs). 4. In presence of bicuculline (10 microM) and phaclofen (50 microM), to block, respectively, fast and slow IPSPs, diazoxide reversibly enhanced the EPSPs. 5. In presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM), to block EPSPs, diazoxide reversibly decreased both fast and slow IPSPs. 6. These effects of diazoxide on the EPSPs and fast and slow IPSPs were associated neither with a change of the reversal potential of the EPSPs or the fast and slow IPSPs nor with a change of the input resistance and membrane potential. 7. Using single electrode voltage-clamp technique, we then tested the effects of diazoxide on the currents generated by applications of glutamate or gamma-aminobutyric acid (GABA) -A and -B analogues. 8. In presence of tetrodotoxin (TTX; 1 microM), diazoxide reversibly enhanced the peak currents evoked by alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionate (AMPA; 3-5 microM), quisqualate (5-10 microM) and N-methyl-D-aspartate (NMDA; 10 microM), but not those evoked by kainate (1-3 microM). 9. In presence of TTX (1 microM), diazoxide reversibly decreased the GABA- (1-5 mM), isoguvacine- (30-60 microM), and baclofen- (10-30 microM) mediated peak currents. 10. It is concluded that, in the hippocampus, diazoxide enhances the excitatory glutamatergic currents and reduces the GABAergic inhibition, thus generating paroxystic activities. We suggest that these effects are mediated by second messenger cascades.

On the synchronous activity induced by 4-aminopyridine in the CA3 subfield of juvenile rat hippocampus

1993 ◽  
Vol 70 (3) ◽  
pp. 1018-1029 ◽  
Author(s):  
M. Avoli ◽  
C. Psarropoulou ◽  
V. Tancredi ◽  
Y. Fueta
Keyword(s):  
Nmda Receptor ◽  
Gabaa Receptor ◽  
Action Potentials ◽  
Hippocampal Slices ◽  
Field Potential ◽  
Pyramidal Cells ◽  
Occurrence Rate ◽  
Gamma Aminobutyric Acid ◽  
Synchronous Activity ◽  
Ca3 Pyramidal Cells

1. Extracellular field potential and intracellular recordings were made in the CA3 subfield of hippocampal slices obtained from 10- to 24-day-old rats during perfusion with artificial cerebrospinal fluid (ACSF) containing the convulsant 4-aminopyridine (4-AP, 50 microM). 2. Three types of spontaneous, synchronous activity were recorded in the presence of 4-AP by employing extracellular microelectrodes positioned in the CA3 stratum (s.) radiatum: first, inter-ictal-like discharges that lasted 0.2-1.2 s and had an occurrence rate of 0.3-1.3 Hz; second, ictal-like events (duration: 3-40 s) that occurred at 4-38 x 10(-3) Hz; and third, large-amplitude (up to 8 mV) negative-going potentials that preceded the onset of the ictal-like events and thus appeared to initiate them. 3. None of these synchronous activities was consistently modified by addition of antagonists of the N-methyl-D-aspartate (NMDA) receptor to the ACSF. In contrast, the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 2-10 microM) reversibly blocked interictal- and ictallike discharges. The only synchronous, spontaneous activity recorded in this type of medium consisted of the negative-going potentials that were abolished by the GABAA receptor antagonists bicuculline methiodide (5-20 microM) or picrotoxin (50 microM). Hence they were mediated through the activation of the GABAA receptor. 4. Profile analysis of the 4-AP-induced synchronous activity revealed that the gamma-aminobutyric acid (GABA)-mediated field potential had maximal negative amplitude in s. lacunosum-moleculare, attained equipotentiality at the border between s. radiatum and s. pyramidale, and became positive-going in s. oriens. These findings indicated that the GABA-mediated field potential presumably represented a depolarization occurring in the dendrites of CA3 pyramidal cells. 5. This conclusion was supported by intracellular analysis of the 4-AP-induced activity. The GABA-mediated potential was reflected by a depolarization of the membrane of CA3 pyramidal cells that triggered a few variable-amplitude, fractionated spikes or fast action potentials. By contrast, the ictal-like discharge was associated with a prolonged depolarization during which repetitive bursts of action potentials occurred. Short-lasting depolarizations with bursts of action potentials occurred during each interictal-like discharge. 6. The GABA-mediated potential recorded intracellularly in the presence of CNQX consisted of a prolonged depolarization (up to 12 s) that was still capable of triggering a few fast action potentials and/or fractionated spikes.(ABSTRACT TRUNCATED AT 400 WORDS)

Classical conditioning reduces amplitude and duration of calcium-dependent afterhyperpolarization in rabbit hippocampal pyramidal cells

1989 ◽  
Vol 61 (5) ◽  
pp. 971-981 ◽  
Author(s):  
D. A. Coulter ◽  
J. J. Lo Turco ◽  
M. Kubota ◽  
J. F. Disterhoft ◽  
J. W. Moore ◽  
...  
Keyword(s):  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Channel Blockers ◽  
Calcium Spikes ◽  
Calcium Dependent ◽  
Current Threshold ◽  
The Difference ◽  
And Control ◽  
Hippocampal Pyramidal Cells ◽  
In Cells

1. The afterhyperpolarization (AHP) that follows action potentials was studied in CA1 hippocampal pyramidal cells from classically conditioned and control rabbits. Measurements of the AHP were obtained with intracellular recordings from CA1 cells within hippocampal slices. 2. The AHP of rabbit CA1 pyramidal cells was found to be accompanied by a conductance increase. The AHP was reduced by bath applications of the calcium channel blockers, cadmium and cobalt, by bath application of the cholinergic agonist, carbamylcholine chloride, and intracellular injection of the calcium chelator, ethylene glycol-bis(B-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). 3. The AHP was markedly reduced in cells from rabbits that were well-trained with the nictitating membrane conditioning procedure, as compared with cells from pseudoconditioned or naive control animals. The difference in AHP amplitudes between conditioned and control groups increased as the number of spikes elicited by the stimulation pulse increased from one to four. Both the duration (measured as the time constant of AHP decay) and amplitude of the AHP were reduced in cells from conditioned animals. 4. The reduced AHP in cells from conditioned animals remained reduced in a medium that contained 0.5 microM tetrodotoxin (TTX) and 5.0 mM tetraethylammonium chloride (TEA); the AHP following calcium spikes was measured under these conditions. Since this medium eliminated synaptic transmission elicited by Schaeffer collateral stimulation, the AHP reduction in pyramidal cells from conditioned animals was not due to a modification in synaptic properties. There were no significant differences in the mean voltage thresholds, amplitudes, or durations of calcium spikes between cells from animals in the three groups. Thus the AHP reduction appears to be due to a modification of a Ca2+ -dependent K+ conductance and was not due to a secondary effect of reductions in calcium conductances underlying the spike. 5. In medium containing TTX and TEA, the amount of injected current required to elicit a calcium spike (current threshold) was significantly greater in cells from conditioned animals than in cells from control animals. This increase in current threshold persisted in 4-aminopyridine (4-AP)-containing medium and so cannot be attributed entirely to conditioning-specific increases in the A-current. 6. The conditioning-specific AHP reduction resulted in increased excitability in cells from conditioned animals versus pseudoconditioned control animals. Cells from conditioned animals fired more spikes to trains of 100-ms depolarizing current pulses than did cells from controls.

Role of EPSPs in initiation of spontaneous synchronized burst firing in rat hippocampal neurons bathed in high potassium

1990 ◽  
Vol 64 (3) ◽  
pp. 1000-1008 ◽  
Author(s):  
N. L. Chamberlin ◽  
R. D. Traub ◽  
R. Dingledine
Keyword(s):  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Burst Firing ◽  
Interictal Spikes ◽  
High Potassium ◽  
Synaptic Excitation ◽  
Ca3 Neurons

1. Spontaneous discharges that resemble interictal spikes arise in area CA3 b/c of rat hippocampal slices bathed in 8.5 mM [K+]o. Excitatory postsynaptic potentials (EPSPs) also appear at irregular intervals in these cells. The role of local synaptic excitation in burst initiation was examined with intracellular and extracellular recordings from CA3 pyramidal neurons. 2. Most (70%) EPSPs were small (less than 2 mV in amplitude), suggesting that they were the product of quantal release or were evoked by a single presynaptic action potential in another cell. It is unlikely that most EPSPs were evoked by a presynaptic burst of action potentials. Indeed, intrinsic burst firing was not prominent in CA3 b/c pyramidal cells perfused in 8.5 mM [K+]o. 3. The likelihood of occurrence and the amplitude of EPSPs were higher in the 50-ms interval just before the onset of each burst than during a similar interval 250 ms before the burst. This likely reflects increased firing probability of CA3 neurons as they emerge from the afterhyperpolarization (AHP) and conductance shunt associated with the previous burst. 4. Perfusion with 2 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a potent quisqualate receptor antagonist, decreased the frequency of EPSPs in CA3 b/c neurons from 3.6 +/- 0.9 to 0.9 +/- 0.3 (SE) Hz. Likewise, CNQX reversibly reduced the amplitude of evoked EPSPs in CA3 b/c cells. 5. Spontaneous burst firing in 8.5 mM [K+]o was abolished in 11 of 31 slices perfused with 2 microM CNQX.(ABSTRACT TRUNCATED AT 250 WORDS)

Agent-selective Effects of Volatile Anesthetics on GABAAReceptor–mediated Synaptic Inhibition in Hippocampal Interneurons

2001 ◽  
Vol 94 (2) ◽  
pp. 340-347 ◽  
Author(s):  
Koichi Nishikawa ◽  
M. Bruce MacIver
Keyword(s):  
Gabaa Receptor ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Volatile Anesthetics ◽  
Stratum Radiatum ◽  
Synaptic Inhibition ◽  
Gamma Aminobutyric Acid ◽  
Ca1 Region ◽  
Whole Cell Patch Clamp ◽  
Cortical Regions

Background A relatively small number of inhibitory interneurons can control the excitability and synchronization of large numbers of pyramidal cells in hippocampus and other cortical regions. Thus, anesthetic modulation of interneurons could play an important role for the maintenance of anesthesia. The aim of this study was to compare effects produced by volatile anesthetics on inhibitory postsynaptic currents (IPSCs) of rat hippocampal interneurons. Methods Pharmacologically isolated gamma-aminobutyric acid type A (GABAA) receptor-mediated IPSCs were recorded with whole cell patch-clamp techniques in visually identified interneurons of rat hippocampal slices. Neurons located in the stratum radiatum-lacunosum moleculare of the CA1 region were studied. The effects of clinically relevant concentrations (1.0 rat minimum alveolar concentration) of halothane, enflurane, isoflurane, and sevoflurane were compared on kinetics of both stimulus-evoked and spontaneous GABAA receptor-mediated IPSCs in interneurons. Results Halothane (1.2 vol% approximately 0.35 mm), enflurane (2.2 vol% approximately 0.60 mm), isoflurane (1.4 vol% approximately 0.50 mm), and sevoflurane (2.7 vol% approximately 0.40 mm) preferentially depressed evoked IPSC amplitudes to 79.8 +/- 9.3% of control (n = 5), 38.2 +/- 8.6% (n = 6), 52.4 +/- 8.4% (n = 5), and 46.1 +/- 16.0% (n = 8), respectively. In addition, all anesthetics differentially prolonged the decay time constant of evoked IPSCs to 290.1 +/- 33.2% of control, 423.6 +/- 47.1, 277.0 +/- 32.2, and 529 +/- 48.5%, respectively. The frequencies of spontaneous IPSCs were increased by all anesthetics (twofold to threefold). Thus, the total negative charge transfer mediated by GABAA receptors between synaptically connected interneurons was enhanced by all anesthetics. Conclusions Volatile anesthetics differentially enhanced GABAA receptor-mediated synaptic inhibition in rat hippocampal interneurons, suggesting that hippocampal interneuron circuits are depressed by these anesthetics in an agent-specific manner.

scholarly journals Neurosteroid Effects on GABAergic Synaptic Plasticity in Hippocampus

2003 ◽  
Vol 89 (4) ◽  
pp. 1929-1940 ◽  
Author(s):  
Fu-Chun Hsu ◽  
Robert Waldeck ◽  
Donald S. Faber ◽  
Sheryl S. Smith
Keyword(s):  
Time Constant ◽  
Decay Time ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Hormone Treatment ◽  
Bimodal Distribution ◽  
Decay Time Constant ◽  
Decay Kinetics ◽  
Adult Rats ◽  
Bath Application

We have previously reported that short-term (48–72 h) exposure to the GABA-modulatory steroid 3α-OH-5α-pregnan-20-one (3α,5α-THP) increases expression of the α4 subunit of the GABAA receptor (GABAR) in the hippocampus of adult rats. This change in subunit composition was accompanied by altered pharmacology and an increase in general excitability associated with acceleration of the decay time constant (τ) for GABA-gated current of pyramidal cells acutely isolated from CA1 hippocampus similar to what we have reported following withdrawal from the steroid after chronic long-term administration. Because GABAR can be localized to either synaptic or extrasynaptic sites, we tested the hypothesis that this change in receptor kinetics is mediated by synaptic GABAR. To this end, we evaluated the decay kinetics of TTX-resistant miniature inhibitory postsynaptic currents (mIPSCs) recorded from CA1 pyramidal cells in hippocampal slices following 48-h treatment with 3α,5α/β-THP (10 mg/kg, ip). Hormone treatment produced a marked acceleration in the fast decay time constant (τfast) of GABAergic mIPSCs. This effect was prevented by suppression of α4-subunit expression with antisense (AS) oligonucleotide, suggesting that hormone treatment increases α4-containing GABAR subsynaptically. This conclusion was further supported by pharmacological data from 3α,5β-THP-treated animals, demonstrating a bimodal distribution of τs for individual mIPSCs following bath application of the α4-selective benzodiazepine RO15–4513, with a shift to slower values. Because 40–50% of the individual τs were also shifted to slower values following bath application of the non–α4-selective benzodiazepine agonist lorazepam (LZM), we suggest that the number of GABAR synapses containing α4 subunits is equivalent to those that do not following 48-h administration of 3α,5β-THP. The decrease in GABAR-mediated charge transfer resulting from accelerated current decay may then result in increased excitability of the hippocampal circuitry, an effect consistent with the increased behavioral excitability we have previously demonstrated.

Electrophysiological and pharmacological characterization of perforant path synapses in CA1: mediation by glutamate receptors

1992 ◽  
Vol 68 (1) ◽  
pp. 1-8 ◽  
Author(s):  
C. M. Colbert ◽  
W. B. Levy
Keyword(s):  
Hippocampal Slices ◽  
Field Potential ◽  
Perforant Path ◽  
Gamma Aminobutyric Acid ◽  
Receptor Antagonists ◽  
Adult Rats ◽  
Pharmacological Characterization ◽  
Schaffer Collaterals ◽  
Perforant Pathway ◽  
Bath Application

1. With the use of hippocampal slices from adult rats, we studied monosynaptic potentials in CA1 evoked by stimulating either the perforant pathway or the Schaffer collaterals. Excision of region CA3 and the dentate gyrus prevented polysynaptic excitation of CA1 and facilitated interpretation of the extracellular potentials. 2. Laminar profiles distinguished the population excitatory postsynaptic potentials (pEPSPs) in CA1 evoked by stimulating the Schaffer collaterals and the perforant path. Stimulating the perforant path evoked short-latency negative-going pEPSPs in s. lacunosum-moleculare of CA1 and positive-going pEPSPs in s. radiatum. Stimulating the Schaffer collaterals evoked negative-going pEPSPs in s. radiatum. 3. A pharmacological manipulation also distinguished the two pathways in CA1. The selective GABAB agonist baclofen greatly decreased the slope of pEPSPs evoked by stimulating the Schaffer collaterals but did not decrease the slope of pEPSPs evoked by stimulating the perforant path. 4. Combined bath application of the glutamate receptor antagonists 6,7-dinitroquinoxaline-2,3-dione (DNQX) and 2-amino-5-phosphonopentanoic acid (APV) abolished the negative-going pEPSPs in s. lacunosum-moleculare evoked by stimulating the perforant pathway. This application of DNQX and APV revealed a positive-going field potential that was blocked by bath application of the gamma-aminobutyric acid (GABA) receptor antagonists picrotoxin or bicuculline. 5. Although the glutamate-mediated component of the response evoked by stimulating the perforant path was apparently excitatory, we never observed a population spike in s. pyramidal evoked by stimulating the perforant path.(ABSTRACT TRUNCATED AT 250 WORDS)

Sign in / Sign up

Export Citation Format

Share Document