The Experts below are selected from a list of 1935 Experts worldwide ranked by ideXlab platform
Itsuki Jibiki - One of the best experts on this subject based on the ideXlab platform.
-
effects of zotepine on excitatory synaptic responses in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
2002Co-Authors: Itsuki Jibiki, Sonoko KurokawaAbstract:The effects of an atypical antipsychotic drug, zotepine, were examined on excitatory synaptic responses elicited in the dentate gyrus by single electrical stimulation of the Perforant Path and the induction of long-term potentiation in this Pathway in chronically prepared rabbits. Doses of 1.0, 2.0 and 5.0 mg/kg of zotepine intraperitoneally injected had virtually no effect on the excitatory synaptic responses. However, these doses of zotepine dose dependently suppressed the induction of long-term potentiation. According to our previous studies, these results indicate that the effects of zotepine are different from those of the other atypical antipsychotic drugs, clozapine, but are rather similar to those of a typical antipsychotic drug, haloperidol and the 5-HT-dopamine receptor antagonist, risperidone. Furthermore, the zotepine-induced blockade of long-term potentiation induction may be associated with drug-induced cognitive dysfunction such as memory disturbance.
-
effects of risperidone an atypical antipsychotic drug on excitatory synaptic responses in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
2001Co-Authors: Takashi Kubota, Itsuki Jibiki, Sonoko KurokawaAbstract:The effects of an atypical antipsychotic drug, risperidone, were examined on excitatory synaptic responses in the dentate gyrus by single electrical stimulations to the Perforant Path and the induction of long-term potentiation (LTP) in this Pathway in chronically prepared rabbits. Any of 0.5, 1.0 and 2.0 mg/kg doses of risperidone intraperitoneally injected had virtually no effect on the excitatory synaptic responses. However, these three doses of risperidone dose-dependently suppressed the LTP induction.
-
effects of mk 801 on clozapine induced potentiation of excitatory synaptic responses in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
2000Co-Authors: Takashi Kubota, Itsuki Jibiki, Fusako Enokido, Haruo Nakagawa, Kenichiro WatanabeAbstract:We previously found that the atypical antipsychotic drug, clozapine, when intraperitoneally (i.p.) injected, long-lastingly potentiated excitatory synaptic responses elicited in the dentate gyrus by single electrical stimulations to the Perforant Path in chronically prepared rabbits, and called this phenomenon 'clozapine-induced potentiation'. In the present study, we likewise examined whether clozapine-induced potentiation is caused by NMDA receptor-mediated neurotransmission in the Perforant Path-dentate gyrus Pathway of chronically prepared rabbits. The non-competitive NMDA receptor antagonist - 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imino hydrogen maleate (MK-801; 1.0 mg/kg, i.p.) - completely prevented the potentiation of synaptic responses induced by subsequent administration of 20 mg/kg clozapine, whereas the 0.5 mg/kg dose had virtually no effect on the potentiation. These results suggest that the effect of clozapine requires NMDA receptor activation.
-
clozapine induced potentiation of synaptic responses in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
1996Co-Authors: Takashi Kubota, Itsuki Jibiki, Susumu Kishizawa, Kenzo KurokawaAbstract:Abstract To examine the contribution of N -methyl- d -aspartate (NMDA) receptors in the mechanisms underlying the action of antipsychotics, we investigated the effects of a representative atypical antipsychotic, clozapine (CLZ), on the induction of long-term potentiation (LTP) in the Perforant Path-dentate gyrus Pathway in 15 chronically prepared rabbits. Eventually, neither low (10 mg/kg) nor high (20 mg/kg) doses of CLZ intraperitoneally injected had any effects on LTP induction. However, the high dose CLZ always potentiated the ordinary synaptic responses induced by single stimulations before the LTP induction. The present study indicates a new finding, the presence of ‘CLZ-induced potentiation’, although it needs further investigation whether NMDA receptors contribute to this potentiation.
-
carbamazepine induced blockade of induction of long term potentiation in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
1994Co-Authors: Takashi Kubota, Itsuki Jibiki, Kenzo Kurokawa, Toshinobu Fukushima, Nariyoshi YamaguchiAbstract:Abstract We investigated the effects of a representative anti-epileptic or anti-psychotic drug, carbamazepine (CBZ), on the induction of long-term potentiation (LTP) in the Perforant Path-dentate gyrus Pathway in 15 chronically prepared rabbits. Pharmacokinetically injected low-dose CBZ, which produced steady serum levels of 2.2–3.3 μg/ml (mean ± S.D. 2.85 ± 0.40), variably affected the induction of LTP, blocking it or showing almost no effect. The high-dose CBZ, which produced steady serum levels of 6.5–8.6 μg/ml (8.01 ± 0.87), always blocked the induction of LTP. These results indicate that CBZ dose-dependently blocks the induction of LTP. The possible mechanisms underlying this blockade are discussed, especially in association with the possible inhibitory action of CBZ on N- methyl- d -aspartate (NMDA) receptors.
Takashi Kubota - One of the best experts on this subject based on the ideXlab platform.
-
effects of risperidone an atypical antipsychotic drug on excitatory synaptic responses in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
2001Co-Authors: Takashi Kubota, Itsuki Jibiki, Sonoko KurokawaAbstract:The effects of an atypical antipsychotic drug, risperidone, were examined on excitatory synaptic responses in the dentate gyrus by single electrical stimulations to the Perforant Path and the induction of long-term potentiation (LTP) in this Pathway in chronically prepared rabbits. Any of 0.5, 1.0 and 2.0 mg/kg doses of risperidone intraperitoneally injected had virtually no effect on the excitatory synaptic responses. However, these three doses of risperidone dose-dependently suppressed the LTP induction.
-
effects of mk 801 on clozapine induced potentiation of excitatory synaptic responses in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
2000Co-Authors: Takashi Kubota, Itsuki Jibiki, Fusako Enokido, Haruo Nakagawa, Kenichiro WatanabeAbstract:We previously found that the atypical antipsychotic drug, clozapine, when intraperitoneally (i.p.) injected, long-lastingly potentiated excitatory synaptic responses elicited in the dentate gyrus by single electrical stimulations to the Perforant Path in chronically prepared rabbits, and called this phenomenon 'clozapine-induced potentiation'. In the present study, we likewise examined whether clozapine-induced potentiation is caused by NMDA receptor-mediated neurotransmission in the Perforant Path-dentate gyrus Pathway of chronically prepared rabbits. The non-competitive NMDA receptor antagonist - 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imino hydrogen maleate (MK-801; 1.0 mg/kg, i.p.) - completely prevented the potentiation of synaptic responses induced by subsequent administration of 20 mg/kg clozapine, whereas the 0.5 mg/kg dose had virtually no effect on the potentiation. These results suggest that the effect of clozapine requires NMDA receptor activation.
-
clozapine induced potentiation of synaptic responses in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
1996Co-Authors: Takashi Kubota, Itsuki Jibiki, Susumu Kishizawa, Kenzo KurokawaAbstract:Abstract To examine the contribution of N -methyl- d -aspartate (NMDA) receptors in the mechanisms underlying the action of antipsychotics, we investigated the effects of a representative atypical antipsychotic, clozapine (CLZ), on the induction of long-term potentiation (LTP) in the Perforant Path-dentate gyrus Pathway in 15 chronically prepared rabbits. Eventually, neither low (10 mg/kg) nor high (20 mg/kg) doses of CLZ intraperitoneally injected had any effects on LTP induction. However, the high dose CLZ always potentiated the ordinary synaptic responses induced by single stimulations before the LTP induction. The present study indicates a new finding, the presence of ‘CLZ-induced potentiation’, although it needs further investigation whether NMDA receptors contribute to this potentiation.
-
carbamazepine induced blockade of induction of long term potentiation in the Perforant Path dentate gyrus Pathway in chronically prepared rabbits
1994Co-Authors: Takashi Kubota, Itsuki Jibiki, Kenzo Kurokawa, Toshinobu Fukushima, Nariyoshi YamaguchiAbstract:Abstract We investigated the effects of a representative anti-epileptic or anti-psychotic drug, carbamazepine (CBZ), on the induction of long-term potentiation (LTP) in the Perforant Path-dentate gyrus Pathway in 15 chronically prepared rabbits. Pharmacokinetically injected low-dose CBZ, which produced steady serum levels of 2.2–3.3 μg/ml (mean ± S.D. 2.85 ± 0.40), variably affected the induction of LTP, blocking it or showing almost no effect. The high-dose CBZ, which produced steady serum levels of 6.5–8.6 μg/ml (8.01 ± 0.87), always blocked the induction of LTP. These results indicate that CBZ dose-dependently blocks the induction of LTP. The possible mechanisms underlying this blockade are discussed, especially in association with the possible inhibitory action of CBZ on N- methyl- d -aspartate (NMDA) receptors.
-
haloperidol induced blockade of induction of long term potentiation in Perforant Path dentate gyrus Pathway in chronically prepared rabbits
1993Co-Authors: Itsuki Jibiki, Shigeki Wakita, Takashi Kubota, Kenzo Kurokawa, Toshinobu Fukushima, Nariyoshi YamaguchiAbstract:Abstract We investigated the effects of the representative neuroleptic and dopamine receptor antagonist haloperidol (HPD) on the induction of long-term potentiation (LTP) or on the previously induced LTP in the Perforant Path-dentate gyrus Pathway in chronically prepared rabbits. The IP HPD injection of 0.8 mg/kg blocked the induction of LTP when it was given before LTP-inducing tetanic stimulations, although this dose showed virtually no effect on the baseline control responses in the Perforant Path-dantate gyrus Pathway to single shocks. However, neither 0.8-mg/kg nor 1.6-mg/kg HPD doses affected the previously induced LTP. The possible mechanisms underlying these results, notably the HPD-induced blockade of LTP induction, are discussed, especially in association with the inhibitory action of HPD on calmodulin-mediated events rather than dopaminergic function.
Claude G Wasterlain - One of the best experts on this subject based on the ideXlab platform.
-
gaba synapses and the rapid loss of inhibition to dentate gyrus granule cells after brief Perforant Path stimulation
2005Co-Authors: David E Naylor, Claude G WasterlainAbstract:Purpose: To study the pharmacologic and synaptic basis for the early loss of paired-pulse inhibition that occurs in the Perforant-Path stimulation model of status epilepticus. Methods: Hippocampal slices were prepared from mate Wistar rats. Test paired pulses (20- to 50-ms interstimulus interval) of the Perforant Path were used before and after an abbreviated period of Perforant-Path stimulation (1-5 min; 2-Hz continuous with 20 Hz of 10 s/min pulses) while either recording field potentials from the dentate gyrus granule cell layer or directly measuring whole-cell patch-clamp currents from granule cells. Paired-pulse field recordings also were obtained during perfusion of the gamma-aminobutyric acid (GABA)A antagonist bicuculline. Results: Prolonged loss of paired-pulse inhibition occurs after brief (< 5 min) Perforant-Path stimulation in vitro (similar to results in vivo) with the paired-pulse population spike amplitude ratio (P2/P1) increasing from a baseline of 0.53 +/- 0.29 to 1.17 +/- 0.09 after Perforant-Path stimulation (p < 0.05). After perfusion with the GABA(A) antagonist, bicuculline, the P2/P1 ratio also increased from a baseline of 0.52 +/- 0.16 to 1.15 +/- 0.26 (p < 0.05). After 1-2 min of Perforant-Path stimulation, a 22 6% (p < 0.05) decrease occurred in the P2/P1 amplitude ratio of paired-pulse evoked inhibitory postsynaptic currents. Conclusions: Similar to in vivo, loss of paired-pulse inhibition occurs with brief Perforant-Path stimulation in vitro. GABA(A) antagonism causes a similar loss of paired-pulse inhibition, and the effects of Perforant-Path stimulation on Postsynaptic inhibitory currents also are consistent with the involvement of GABA(A) synaptic receptors. The findings suggest that loss of inhibition at GABA synapses may be an important early event in the initiation of status epilepticus.
-
self sustaining status epilepticus after brief electrical stimulation of the Perforant Path
1998Co-Authors: Andrey Mazarati, Claude G Wasterlain, Raman Sankar, Don ShinAbstract:We examined the duration of intermittent Perforant Path stimulation (PPS) needed to induce self-sustaining status epilepticus (SSSE) in rats. Seven-minute PPS did not induce SSSE. Some rats receiving 15 min and all animals after 30 min PPS developed SSSE that continued for hours. The animals killed 3 days after SSSE showed extensive neuronal damage. Those which were allowed to survive for 6 weeks after SSSE displayed spontaneous seizures.
-
blockers of nmda receptors restore paired pulse inhibition in the rat dentate gyrus lesioned by Perforant Path stimulation
1997Co-Authors: Andrey Mazarati, Claude G WasterlainAbstract:Abstract The `dormant basket cell' hypothesis postulates, that after status epilepticus, inhibitory interneurons in the hippocampus are deafferented from their excitatory inputs. We provide evidence for active suppression of hippocampal inhibition. Status epilepticus-like Perforant Path stimulation induced loss of interneurons and loss of inhibition in the rat dentate gyrus. This loss was transiently reversed by antagonists acting at three different sites of the N -methyl- d -aspartate (NMDA) receptor. Intrahippocampal administration of γ -aminobutyric acid (GABA) agonists, which were expected to increase inhibition, resulted in the opposite effect. Although the substrate for the observed effects of pharmacological agents cannot be certainly confined to the `dormant' basket cell, they suggest the expression of hippocampal circuits that actively suppress inhibition through an NMDA synapse.
Seyed Mohammad Noorbakhsh - One of the best experts on this subject based on the ideXlab platform.
-
the role of adenosine a1 receptors in mediating the inhibitory effects of low frequency stimulation of Perforant Path on kindling acquisition in rats
2009Co-Authors: Mohammad Mohammadzadeh, Mohammad Javan, Yaghoub Fathollahi, Javad Mirnajafizadeh, Seyed Mohammad Noorbakhsh, Ali Jahanshahi, Fereshteh MotamediAbstract:Low frequency stimulation (LFS) has an inhibitory effect on rapid Perforant Path kindling acquisition. In the present study the role of adenosine A(1) and A(2A) receptors in mediating this inhibitory effect was investigated. Rats were kindled by Perforant Path stimulation using rapid kindling procedures (12 stimulations per day). LFS (0.1 ms pulse duration at 1 Hz, 200 pulses, and 50-150 muA) was applied to the Perforant Path immediately after termination of each rapid kindling stimulation. 1,3-Dimethyl-8-cyclopenthylxanthine (CPT; 50 muM), a selective A(1) antagonist and ZM241385 (ZM, 200 muM), a selective A(2A) antagonist were daily microinjected into the lateral ventricle 5 min before kindling stimulations. LFS had an inhibitory effect on kindling development. Pretreatment of animals with CPT reduced the inhibitory effect of LFS on kindling rate and suppressed the effects of LFS on potentiation of population EPSP during kindling acquisition. In addition, CPT was able to antagonize the effects of LFS on kindling-induced increase in early (10-50 ms intervals) and late (300-1000 ms intervals) paired pulse depression. ZM pretreatment had no effect on antiepileptogenic effects of LFS in kindling acquisition. In addition, LFS prevented the kindling-induced elevation of cyclic AMP (cAMP) levels in kindled animals. Based on these results, we suggest that the antiepileptogenic effects of LFS on Perforant Path kindling might be mediated through activation of adenosine A(1), but not A(2A) receptors. Moreover, modulation of cAMP levels by LFS may potentially be an important mechanism which explains the anticonvulsant effects of LFS in kindled seizures.
-
The role of galanin receptors in anticonvulsant effects of low-frequency stimulation in Perforant Path-kindled rats.
2007Co-Authors: Mehdi Sadegh, Mohammad Mohammad-zadeh, Javad Mirnajafi-zadeh, Mohammad Javan, Yaghoub Fathollahi, Ali Jahanshahi, Seyed Mohammad NoorbakhshAbstract:Abstract Low-frequency stimulation (LFS) has antiepileptogenic effects on kindled seizures. In the present study, the role of galanin receptors in the inhibitory effect of LFS on Perforant Path kindling acquisition was investigated in rats. Animals were kindled by Perforant Path stimulation in a rapid kindling manner (six stimulations per day). LFS (0.1 ms pulses at 1 Hz, 600 pulses, and 80–150 μA) was applied immediately after termination of each kindling stimulation. M35 (0.5 and 1.0 nM per site), a nonselective galanin receptor antagonist and M871 (1.0 μM per site), a selective galanin receptor type 2 (GalR2) antagonist, were daily microinjected into the dentate gyrus before starting the stimulation protocol. The expression of GalR2 in the dentate gyrus was also investigated using semi-quantitative RT-PCR. Application of LFS significantly retarded the kindling acquisition and delayed the expression of different kindled seizure stages. In addition, LFS significantly reduced the increment of daily afterdischarge duration during kindling development. Intra-dentate gyrus microinjection of both M35 and M871 significantly prevented the inhibitory effects of LFS on kindling parameters. During the focal kindled seizure stages (1–3) M871 had no significant effect. However, during generalized seizure stages (4 and 5), M871 had the same effect as M35. Semi-quantitative RT-PCR also showed that after kindling acquisition, the GalR2 mRNA level decreased in the dentate gyrus but application of LFS prevented this decrease. Obtained results show that activation of galanin receptors by endogenous galanin has a role in mediating the inhibitory effect of LFS on Perforant Path–kindled seizures. This role is exerted through GalR1 during focal- and through GalR2 during generalized-kindled seizures.
-
effect of low frequency stimulation of Perforant Path on kindling rate and synaptic transmission in the dentate gyrus during kindling acquisition in rats
2007Co-Authors: Mohammad Mohammadzadeh, Mohammad Javan, Yaghoub Fathollahi, Javad Mirnajafizadeh, Parviz Ghorbani, Mehdi Sadegh, Seyed Mohammad NoorbakhshAbstract:Low frequency stimulation (LFS) has an inhibitory effect on kindling acquisition. In the present study the effect of the Perforant Path LFS on induction of rapid Perforant Path kindled seizures and synaptic transmission in the dentate gyrus was investigated. Animals were kindled by Perforant Path stimulation in a rapid kindling manner (12 stimulations per day). In one group of animals LFS (0.1 ms pulse duration at 1 Hz, 200 pulses, and 50-150 microA) was applied to Perforant Path, immediately after termination of each rapid kindling stimulation. Application of LFS significantly retarded the kindling acquisition and increased the number of stimulations to achieved different kindled seizure stages. LFS also prevented an increment in the slope of field excitatory postsynaptic potentials and population spike amplitude during kindling. In addition, LFS significantly reduced the marked increase in early (10-50 ms intervals) and late (300-1000 ms intervals) paired-pulse depression induced by kindling. According to obtained results, it may be suggested that LFS of Perforant Path has a significant antiepileptogenic effect through inhibition of synaptic transmission in dentate gyrus. Meanwhile, LFS prevents an increase in the paired-pulse depression during kindling acquisition.
Carolyn W. Harley - One of the best experts on this subject based on the ideXlab platform.
-
idazoxan increases Perforant Path evoked epsp slope paired pulse inhibition and reduces Perforant Path evoked population spike paired pulse facilitation in rat dentate gyrus
2006Co-Authors: John Knight, Carolyn W. HarleyAbstract:Abstract Norepinephrine, acting via β-adrenoceptors, enhances the Perforant Path-evoked potential in dentate gyrus. Using systemic idazoxan to increase norepinephrine, and paired Perforant Path pulses to probe early inhibition, previous investigators reported that idazoxan increased initial spike amplitude and increased somatic feedback inhibition. Here, feedback inhibition was re-examined in idazoxan-treated (5 mg/kg) rats under urethane anesthesia. To control for initial increased spike amplitude after idazoxan, evoked potentials were matched, pre- and post-idazoxan, on initial population spike. Input–output current profiles were also compared pre- and post-idazoxan. Saline- and timolol-filled micropipettes permitted evaluation of a contribution of local β-adrenoceptors. As previously observed, initial spike amplitude was potentiated by idazoxan. Comparable spike potentiation was not seen on the timolol micropipette. Paired pulse inhibition of spike amplitude apparently increased, but input–output curve comparisons revealed a loss of feedback facilitation rather than an increase in feedback inhibition. Initial EPSP slopes were depressed after idazoxan in input–output curve data. EPSP slope feedback ratios were significantly reduced following idazoxan.These data suggest idazoxan has multiple effects on Perforant Path input to the dentate gyrus. Spike potentiation following idazoxan has previously been shown to depend on intact norepinephrine input. Here, the reduction in spike potentiation on the timolol pipette is consistent with other evidence that norepinephrine-mediated potentiation of the Perforant Path-evoked potential is dependent on local β-adrenoceptor activation. The input–output data suggest a decrease in feedback facilitation after idazoxan is likely to account for the apparent increase in feedback inhibition previously reported. Decreased EPSP slope ratios with similar paired pulse intervals have been reported in novel environments. Since exposure to novel environments activates locus coeruleus neurons, norepinephrine may mediate the change in EPSP slope inhibition reported in awake rats.In summary, these results are consistent with the hypothesis that idazoxan potentiates granule cell responses to Perforant Path input in the dentate gyrus via increases in norepinephrine that lead to β-adrenoceptor activation, and, further, that idazoxan reduces paired pulse feedback spike facilitation and enhances EPSP slope, but not spike, feedback inhibition.
-
noradrenergic and locus coeruleus modulation of the Perforant Path evoked potential in rat dentate gyrus supports a role for the locus coeruleus in attentional and memorial processes
1991Co-Authors: Carolyn W. HarleyAbstract:The Perforant Path-dentate gyrus synapse has provided a model system for functional neural plasticity in adult mammalian brain. NMDA-dependent long-term changes in neural connectivity occur at this synapse in response to high-frequency input. Norepinephrine (NE) applied exogenously or released endogenously can initiate both a short- and a long-term potentiation (LTP) of the dentate gyrus response to Perforant Path input. Triggering of the potentiated response depends on beta-receptor activation and does not require a high-frequency stimulus. An increase in locus coeruleus (LC) activity can initiate both short and LTP of the Perforant Path response, although a reduction in LC activity does not alter baseline Perforant Path responses. This chapter considers differences between NE modulation in vitro and in vivo, differences and similarities between NE-LTP and frequency-induced LTP, and the surprising specificity of NE effects at the Perforant Path synapse. Studies of NE in the dentate gyrus support a role for the LC in promoting both short- and long-term enhancement of responses to complex sensory inputs and are consistent with a role for the LC in memorial as well as attentional processes.