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Leung LS. Long-lasting changes in hippocampal GABA B-receptor mediated inhibition following early-life seizures in kindling-prone but not kindling-resistant rats. Brain Res Bull 2019; 150:231-239. [PMID: 31200097 DOI: 10.1016/j.brainresbull.2019.06.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Revised: 06/04/2019] [Accepted: 06/07/2019] [Indexed: 11/30/2022]
Abstract
The hypotheses that hippocampal GABAB receptor dysfunction is a long-lasting consequence of early-life seizures, and its dependence on genetic background, were tested. Two strains of rats bred to be prone (FAST) or resistant (SLOW) to amygdala kindling were used. On postnatal day (PND) 10, control rats were injected with saline, and seizure rats with kainic acid to induce status epilepticus (SE) for 2 h. A significantly lower dose of kainic acid was found to induce SE in FAST as compared to SLOW rats. Population excitatory postsynaptic potentials (pEPSPs) and population spikes (PSs) were recorded in CA1 of hippocampal slices of adult rats in vitro, following stimulation of stratum radiatum. Input-output relation of the single-pulse pEPSP and PS did not show a significant difference between seizure and control rats, sex, or strain (FAST and SLOW). Paired-pulse PSs were significantly enhanced at 10-50 ms interpulse intervals, in FAST seizure male rats compared to FAST male controls, but not in other groups. In adult FAST but not SLOW rats, significantly lower suppression of pEPSPs at 250-300 ms following heterosynaptic burst stimulation was found in seizure rats compared to control rats; the heterosynaptic suppression of the pEPSP was blocked by selective GABAB receptor antagonist CGP55845A. The results provide evidence that an early-life SE has a long-lasting effect in decreasing GABAB receptor-mediated presynaptic inhibition in the hippocampus, in FAST but not in SLOW rats.
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Affiliation(s)
- L Stan Leung
- Department of Physiology and Pharmacology, Medical Science Building, University of Western Ontario, London, Ontario, N6A 5C1, Canada.
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Leung LS, Jin M, Chu L, Ma J. Positive allosteric modulator of GABAB receptor alters behavioral effects but not afterdischarge progression induced by partial hippocampal kindling. Neuropharmacology 2016; 110:154-164. [DOI: 10.1016/j.neuropharm.2016.07.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Revised: 06/17/2016] [Accepted: 07/15/2016] [Indexed: 12/22/2022]
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Ma J, Leung LS. Dual Effects of Limbic Seizures on Psychosis-Relevant Behaviors Shown by Nucleus Accumbens Kindling in Rats. Brain Stimul 2016; 9:762-769. [PMID: 27267861 PMCID: PMC4980124 DOI: 10.1016/j.brs.2016.05.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 05/11/2016] [Accepted: 05/16/2016] [Indexed: 10/21/2022] Open
Abstract
BACKGROUND A paradox in epilepsy and psychiatry is that temporal lobe epilepsy is often predisposed to schizophrenic-like psychosis, whereas convulsive therapy can relieve schizophrenic symptoms. We have previously demonstrated that the nucleus accumbens is a key structure in mediating postictal psychosis induced by a hippocampal electrographic seizure. OBJECTIVE/HYPOTHESIS The purpose of this study is to test a hypothesis that accumbens kindling cumulating in a single (1-time) or repeated (5-times) convulsive seizures have different effects on animal models of psychosis. METHODS Electrical stimulation at 60 Hz was applied to nucleus accumbens to evoke afterdischarges until one, or five, convulsive seizures that involved the hind limbs (stage 5 seizures) were attained. Behavioral tests, performed at 3 days after the last seizure, included gating of hippocampal auditory evoked potentials (AEP) and prepulse inhibition to an acoustic startle response (PPI), tested without drug injection or after ketamine (3 mg/kg s.c.) injection, as well as locomotion induced by ketamine or methamphetamine (1 mg/kg i.p.). RESULTS Compared to non-kindled control rats, 1-time, but not 5-times, convulsive seizures induced PPI deficit and decreased gating of hippocampal AEP, without drug injection. Compared to non-kindled rats, 5-times, but not 1-time, convulsive seizures antagonized ketamine-induced hyperlocomotion, ketamine-induced PPI deficit and AEP gating decrease. However, both 1- and 5-times convulsive seizures significantly enhanced methamphetamine-induced locomotion as compared to non-kindled rats. CONCLUSIONS Accumbens kindling ending with 1 convulsive seizure may induce schizophrenic-like behaviors, while repeated (≥5) convulsive seizures induced by accumbens kindling may have therapeutic effects on dopamine independent psychosis.
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Affiliation(s)
- Jingyi Ma
- Department of Physiology and Pharmacology, The University of Western Ontario, Medical Sciences Building, London, ON, Canada N6A 5C1.
| | - L Stan Leung
- Department of Physiology and Pharmacology, The University of Western Ontario, Medical Sciences Building, London, ON, Canada N6A 5C1; Graduate Program of Neuroscience, The University of Western Ontario, Medical Sciences Building, London, ON, Canada N6A 5C1
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Ma J, Leung LS. Effects of hippocampal partial kindling on sensory and sensorimotor gating and methamphetamine-induced locomotion in kindling-prone and kindling-resistant rats. Epilepsy Behav 2016; 58:119-26. [PMID: 27070861 DOI: 10.1016/j.yebeh.2016.03.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 03/03/2016] [Accepted: 03/04/2016] [Indexed: 11/26/2022]
Abstract
The effects of hippocampal partial kindling on gating of hippocampal auditory-evoked potentials (AEPs), prepulse inhibition (PPI) to an acoustic startle response, and methamphetamine-induced locomotion were examined in selectively bred kindling-prone (Fast) and kindling-resistant (Slow) rats. Ten electrographic seizures (afterdischarges, ADs) induced by high-frequency stimulation of the hippocampal CA1 region resulted in deficits in gating of hippocampal AEP and PPI in Fast, but not Slow, rats. The increase in AD duration with kindling was similar in Fast and Slow rats. Kindling-induced changes in hippocampal AEP and PPI in Fast rats were abolished by pretest injection of CGP7930 (1mg/kg i.p.), a positive allosteric modulator of GABAB receptors. Injection of haloperidol (0.1mg/kg i.p.) daily before kindling also prevented kindling-induced changes in PPI and hippocampal AEP in Fast rats. Interestingly, methamphetamine-induced hyperlocomotion was enhanced by kindling in Slow, but not Fast, rats. However, the methamphetamine-induced hyperlocomotion in Slow rats was not suppressed by daily injection of 0.1mg/kg i.p. haloperidol before kindling, as compared with kindling without haloperidol. It is concluded that genetic disposition affected the behavioral consequences of repeated seizures. Fast rats required fewer hippocampal ADs to induce sensory (AEP) and sensorimotor (PPI) deficits, while Slow kindled rats were more sensitive to methamphetamine-induced locomotion. Dopaminergic blockade by haloperidol during kindling, or acute injection of CGP7930 before testing, attenuated some of the behavioral deficits induced by repeated hippocampal seizures, suggesting possible therapeutic strategies to treat the schizophrenic-like symptoms associated with temporal lobe epilepsy.
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Affiliation(s)
- Jingyi Ma
- Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario N6A 5C1, Canada.
| | - L Stan Leung
- Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario N6A 5C1, Canada; Graduate Program in Neuroscience, The University of Western Ontario, London, Ontario N6A 5C1, Canada
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Lang M, Moradi-Chameh H, Zahid T, Gane J, Wu C, Valiante T, Zhang L. Regulating hippocampal hyperexcitability through GABAB Receptors. Physiol Rep 2014. [PMID: 24771688 PMCID: PMC4001873 DOI: 10.1002/phy2.278] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Disturbances of GABAergic inhibition are a major cause of epileptic seizures. GABA exerts its actions via ionotropic GABAA receptors and metabotropic G protein‐coupled GABAB receptors. Malfunction of GABAA inhibition has long been recognized in seizure genesis but the role of GABAB receptors in controlling seizure activity is still not well understood. Here, we examined the anticonvulsive, or inhibitory effects, of GABAB receptors in a mouse model of hippocampal kindling as well as mouse hippocampal slices through the use of GS 39783, a positive allosteric GABAB receptor modulator, and CGP 55845, a selective GABAB receptor antagonist. When administered via intraperitoneal injections in kindled mice, GS 39783 (5 mg/kg) did not attenuate hippocampal EEG discharges, but did reduce aberrant hippocampal spikes, whereas CGP 55845 (10 mg/kg) prolonged hippocampal discharges and increased spike incidences. When examined in hippocampal slices, neither GS 39783 at 5 μmol/L nor the GABAB receptor agonist baclofen at 0.1 μmol/L alone significantly altered repetitive excitatory field potentials, but GS 39783 and baclofen together reversibly abolished these field potentials. In contrast, CGP 55845 at 1 μmol/L facilitated induction and incidence of these field potentials. In addition, CGP 55845 attenuated the paired pulse depression of CA3 population spikes and increased the frequency of EPSCs in individual CA3 pyramidal neurons. Collectively, these data suggest that GABABB receptors regulate hippocampal hyperexcitability by inhibiting CA3 glutamatergic synapses. We postulate that positive allosteric modulation of GABAB receptors may be effective in reducing seizure‐related hyperexcitability. GABAB positive modulator GS 39783 attenuated, whereas GABAB antagonist CGP55845 facilitated hippocampal EEG spikes in kindled mice and excitatory field potentials in hippocampal slices. We postulate that GABAB receptors may inhibit CA3 glutamate synapses and hence regulate hippocampal hyperexcitability.
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Affiliation(s)
- Min Lang
- Toronto Western Research Institute; University Health Network; Toronto Ontario Canada
| | - Homeira Moradi-Chameh
- Toronto Western Research Institute; University Health Network; Toronto Ontario Canada
- Department of Physiology; University of Tarbiat Modares; Tehran Iran
| | - Tariq Zahid
- Toronto Western Research Institute; University Health Network; Toronto Ontario Canada
| | - Jonathan Gane
- Toronto Western Research Institute; University Health Network; Toronto Ontario Canada
| | - Chiping Wu
- Toronto Western Research Institute; University Health Network; Toronto Ontario Canada
| | - Taufik Valiante
- Department of Surgery (Division of Neurosurgery); University of Toronto; Toronto Ontario Canada
| | - Liang Zhang
- Toronto Western Research Institute; University Health Network; Toronto Ontario Canada
- Department of Medicine (Division of Neurology); University of Toronto; Toronto Ontario Canada
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Boyce R, Leung LS. Loss of dendritic inhibition in the hippocampus after repeated early-life hyperthermic seizures in rats. Epilepsy Res 2012; 103:62-72. [PMID: 22795321 DOI: 10.1016/j.eplepsyres.2012.06.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Revised: 06/12/2012] [Accepted: 06/20/2012] [Indexed: 11/18/2022]
Abstract
Seizures are relatively common in children and are a risk factor for subsequent temporal lobe epilepsy. To investigate whether early-life seizures themselves are detrimental to the proper function of the adult brain, we studied whether dendritic excitation and inhibition in the hippocampus of adult rats were altered after hyperthermia-induced seizures in immature rats. In particular, we hypothesized that apical dendritic inhibition in hippocampal CA1 pyramidal cells would be disrupted following hyperthermia-induced seizures in early life. Seizure rats were given three hyperthermia-induced seizures per day for three days from postnatal day (PND) 13 to 15; control rats were handled similarly but not heated. At PND 65-75, paired-pulse inhibition in area CA1 was evaluated under urethane anesthesia, using CA3 and medial perforant path (MPP) stimulation to excite the proximal and distal apical-dendrites, respectively, and the evoked field potentials were analyzed by current source density. There was no difference in the CA1 response to single-pulse stimulation of CA3 or MPP. In control rats, a high-intensity CA3 stimulus inhibited a subsequent MPP-evoked CA1 distal dendritic excitatory sink, and the inhibition at 150-200 ms was blocked by a GABA(B) receptor antagonist. Seizure as compared to control rats showed a decrease in a CA3-evoked inhibition of the CA1 distal dendritic excitation, 30-400 ms after the CA3 stimulus. In addition, seizure as compared to control rats showed a reduced early (20-80 ms) inhibition of a CA1 mid-apical dendritic sink following paired-pulse CA3 stimulation. In conclusion, long-term alterations in dendritic inhibition in CA1 were found following early-life seizures.
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Affiliation(s)
- Richard Boyce
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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Long-lasting auditory gating deficit accompanied by GABAB receptor dysfunction in the hippocampus after early-life limbic seizures in rats. Physiol Behav 2012; 106:534-41. [DOI: 10.1016/j.physbeh.2012.03.033] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 02/09/2012] [Accepted: 03/26/2012] [Indexed: 11/20/2022]
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GABA(B) receptor blockade in the hippocampus affects sensory and sensorimotor gating in Long-Evans rats. Psychopharmacology (Berl) 2011; 217:167-76. [PMID: 21484240 DOI: 10.1007/s00213-011-2274-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/07/2010] [Accepted: 03/14/2011] [Indexed: 10/18/2022]
Abstract
RATIONALE Sensory and sensorimotor gating deficits are observed in schizophrenia. GABA(B) receptor deficiency is also detected in the hippocampus of schizophrenic patients. OBJECTIVES The present study tested the hypothesis that GABA(B) receptors in the hippocampus contribute to paired-pulse gating of hippocampal auditory-evoked potentials (AEP) and auditory prepulse inhibition (PPI) in Long-Evans rats. METHODS Gating of hippocampal AEP, or PPI, was examined before and after administration of GABA(B) receptor antagonist, CGP56999A or CGP35348, or saline was administered either systemically (intra-peritoneally (i.p.)) or infused bilaterally into the hippocampus 15 min before gating measurements. RESULTS Systemic injection of CGP56999A, at a dose of 0.2 and 0.4 mg/kg i.p. resulted in reduced gating of hippocampal AEP in a dose-dependent manner. Reduced gating was found at conditioning-test interpulse intervals of 300-500 ms, but not 100-200 ms. Reduced gating of hippocampal AEP also followed bilateral infusion of CGP56999A into the hippocampus (0.1 μg/μL/side). Gating loss was attributed to a decreased conditioning response and an increased test response after systemic or local injection of CGP56999A. Robust PPI was found at prepulse-pulse intervals of 30-100 ms, and this PPI was reduced by hippocampal infusion of CGP56999A in a dose-dependent manner, as compared with saline infusion. CONCLUSIONS Blockade of hippocampal GABA(B) receptors led to deficits in sensory and sensorimotor gating, which are symptoms of schizophrenia.
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Vesselkin NP, Natochin YV. Principles of organization and evolution of systems of regulation of functions. J EVOL BIOCHEM PHYS+ 2011. [DOI: 10.1134/s0022093010060083] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Qu L, Boyce R, Leung LS. Seizures in the developing brain result in a long-lasting decrease in GABAB inhibitory postsynaptic currents in the rat hippocampus. Neurobiol Dis 2010; 37:704-10. [DOI: 10.1016/j.nbd.2009.12.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2009] [Revised: 11/27/2009] [Accepted: 12/09/2009] [Indexed: 11/16/2022] Open
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Leung LS, Peloquin P. Cholinergic Modulation Differs between Basal and Apical Dendritic Excitation of Hippocampal CA1 Pyramidal Cells. Cereb Cortex 2009; 20:1865-77. [DOI: 10.1093/cercor/bhp251] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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The Canadian League Against Epilepsy 2007 Conference Supplement. Can J Neurol Sci 2009. [DOI: 10.1017/s0317167100008805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Leung LS, Peloquin P, Canning KJ. Paired-pulse depression of excitatory postsynaptic current sinks in hippocampal CA1 in vivo. Hippocampus 2008; 18:1008-20. [DOI: 10.1002/hipo.20458] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Kouvaras E, Asprodini EK, Asouchidou I, Vasilaki A, Kilindris T, Michaloudis D, Koukoutianou I, Papatheodoropoulos C, Kostopoulos G. Fentanyl treatment reduces GABAergic inhibition in the CA1 area of the hippocampus 24 h after acute exposure to the drug. Neuropharmacology 2008; 55:1172-82. [PMID: 18706433 DOI: 10.1016/j.neuropharm.2008.07.025] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Revised: 05/27/2008] [Accepted: 07/17/2008] [Indexed: 11/19/2022]
Abstract
The effect of in vivo fentanyl treatment on synaptic transmission was studied in the CA1 area of the rat hippocampus. Animals were treated either with saline or fentanyl (4 x 80 microg/kg, s.c./15 min). Intracellular in vitro recordings were obtained, 24 h after treatment, from CA1 pyramidal neurons. No difference in pyramidal neuron basic membrane properties or postsynaptic membrane excitability was observed between neurons from saline- and fentanyl-treated animals. The peak amplitude of fast (f-) and slow (s-) components of IPSPs elicited in standard ACSF and the peak amplitude and rate of rise of isolated f- and s-IPSPs elicited in the presence of antagonists (CNQX, 10 microM; AP-5, 10 microM; CGP 55845, 1 microM; and bicuculline methochloride, 10 microM), in response to various stimulus intensities, was smaller in fentanyl-treated animals. Conversely, the rising slope of excitatory responses was similar in neurons from saline- and fentanyl-treated animals. Furthermore, in fentanyl-treated animals, lower stimulus strengths were required to elicit subthreshold excitatory responses of the same amplitude suggesting that acute exposure to fentanyl increases susceptibility of pyramidal neurons to presynaptic stimulation. GABA immunohistochemistry revealed lower GABA content in processes and neuronal somata suggesting diminished GABA release onto pyramidal neurons. We conclude that acute in vivo exposure to fentanyl is sufficient to induce long-lasting reduction in GABA-mediated transmission, rather, than enhanced excitatory transmission or modulation of the intrinsic excitability of pyramidal neurons. These findings provide evidence regarding the mechanisms involved in the early stages of tolerance development towards the analgesic effects of opioids.
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Affiliation(s)
- E Kouvaras
- Laboratory of Pharmacology, School of Medicine, University of Thessaly, Faculty of Health Sciences, 22 Papakiriazi Street, 41222 Larissa, Greece
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Tsai ML, Shen B, Leung LS. Seizures induced by GABAB-receptor blockade in early-life induced long-term GABAB receptor hypofunction and kindling facilitation. Epilepsy Res 2008; 79:187-200. [DOI: 10.1016/j.eplepsyres.2008.02.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2007] [Revised: 01/25/2008] [Accepted: 02/11/2008] [Indexed: 02/06/2023]
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Bortolato M, Frau R, Orrù M, Piras AP, Fà M, Tuveri A, Puligheddu M, Gessa GL, Castelli MP, Mereu G, Marrosu F. Activation of GABA(B) receptors reverses spontaneous gating deficits in juvenile DBA/2J mice. Psychopharmacology (Berl) 2007; 194:361-9. [PMID: 17604981 DOI: 10.1007/s00213-007-0845-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Accepted: 05/30/2007] [Indexed: 10/23/2022]
Abstract
RATIONALE Gamma-amino-butyric acid (GABA)(B) receptors play a key role in the pathophysiology of psychotic disorders. We previously reported that baclofen, the prototypical GABA(B) agonist, elicits antipsychotic-like effects in the rat paradigm of prepulse inhibition (PPI) of the startle, a highly validated animal model of schizophrenia. OBJECTIVES We studied the role of GABA(B) receptors in the spontaneous PPI deficits displayed by DBA/2J mice. MATERIALS AND METHODS We tested the effects of baclofen (1.25-5 mg/kg, intraperitoneal [i.p.]) in DBA/2J and C57BL/6J mice, in comparison to the antipsychotic drugs haloperidol (1 mg/kg, i.p.) and clozapine (5 mg/kg, i.p.). Furthermore, we investigated the expression of GABA(B) receptors in the brain of DBA/2J and C57BL/6J mice by quantitative autoradiography. RESULTS Baclofen dose-dependently restored PPI deficit in DBA/2J mice, in a fashion similar to the antipsychotic clozapine (5 mg/kg, i.p.). This effect was reversed by pretreatment with the GABA(B) antagonist SCH50211 (50 mg/kg, i.p.). In contrast, baclofen did not affect PPI in C57BL/6J mice. Finally, quantitative autoradiographic analyses assessed a lower GABA(B) receptor expression in DBA/2J mice in comparison to C57BL/6J controls in the prefrontal cortex and hippocampus but not in other brain regions. CONCLUSIONS Our data highlight GABA(B) receptors as an important substrate for sensorimotor gating control in DBA/2J mice and encourage further investigations on the role of GABA(B) receptors in sensorimotor gating, as well as in the pathophysiology of psychotic disturbances.
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Affiliation(s)
- Marco Bortolato
- Department of Neuroscience "Bernard B. Brodie", University of Cagliari, Cittadella Universitaria, S.S.554 Km 4,500, 09042, Monserrato (CA), Italy.
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Mohammad-Zadeh M, Mirnajafi-Zadeh J, Fathollahi Y, Javan M, Ghorbani P, Sadegh M, Noorbakhsh SM. Effect of low frequency stimulation of perforant path on kindling rate and synaptic transmission in the dentate gyrus during kindling acquisition in rats. Epilepsy Res 2007; 75:154-61. [PMID: 17576049 DOI: 10.1016/j.eplepsyres.2007.05.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2007] [Revised: 04/22/2007] [Accepted: 05/10/2007] [Indexed: 10/23/2022]
Abstract
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.
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Affiliation(s)
- Mohammad Mohammad-Zadeh
- Department of Physiology, School of Medical Sciences, Tarbiat Modares University, Tehran, Islamic Republic of Iran
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Qu L, Liu X, Wu C, Leung LS. Hyperthermia decreases GABAergic synaptic transmission in hippocampal neurons of immature rats. Neurobiol Dis 2007; 27:320-7. [PMID: 17643307 DOI: 10.1016/j.nbd.2007.06.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2007] [Revised: 05/17/2007] [Accepted: 06/04/2007] [Indexed: 11/18/2022] Open
Abstract
The mechanisms underlying the generation of febrile seizures are poorly understood. We suggest that high temperature contributes to febrile seizures and specifically tested the hypothesis that hyperthermia suppressed GABAA-receptor-mediated inhibition in hippocampal neurons using whole-cell patch clamp recordings. We found that heating from a baseline temperature of 32 degrees C to 40 degrees C suppressed the peak amplitude of GABAA-receptor-mediated inhibitory postsynaptic currents (IPSCs) by 50+/-4.7% and decreased the decay time constant of IPSCs by 60.6+/-6.7% in immature CA1 neurons in the rat hippocampus. This inhibitory effect partly results from reduced IPSC conductance and increased GABA uptake, as demonstrated by the fact that GABA uptake blocker N-(4,4-diphenyl-3-butenyl)-3-piperidinecarboxylic acid (SKF89976A) significantly reduced the peak suppression and decay time decrease of the IPSC during hyperthermia. In addition, hyperthermia (40 degrees C) produced a significantly larger depression of the IPSC peak than the slope or peak of the excitatory postsynaptic current (EPSC), and IPSCs recovered slower than EPSCs after hyperthermia. The larger decrease in GABAA-receptor-mediated inhibition during and after hyperthermia, as compared with excitation, may shift the excitation/inhibition balance and contribute to the generation of febrile seizures.
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Affiliation(s)
- Lintao Qu
- Graduate Program in Neuroscience, University of Western Ontario, London, Canada
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19
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Thompson SE, Ayman G, Woodhall GL, Jones RS. Depression of glutamate and GABA release by presynaptic GABAB receptors in the entorhinal cortex in normal and chronically epileptic rats. Neurosignals 2007; 15:202-15. [PMID: 17215590 PMCID: PMC2504722 DOI: 10.1159/000098515] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2006] [Accepted: 11/15/2006] [Indexed: 12/14/2022] Open
Abstract
Presynaptic GABA(B) receptors (GABA(B)R) control glutamate and GABA release at many synapses in the nervous system. In the present study we used whole-cell patch-clamp recordings of spontaneous excitatory and inhibitory synaptic currents in the presence of TTX to monitor glutamate and GABA release from synapses in layer II and V of the rat entorhinal cortex (EC)in vitro. In both layers the release of both transmitters was reduced by application of GABA(B)R agonists. Quantitatively, the depression of GABA release in layer II and layer V, and of glutamate release in layer V was similar, but glutamate release in layer II was depressed to a greater extent. The data suggest that the same GABA(B)R may be present on both GABA and glutamate terminals in the EC, but that the heteroreceptor may show a greater level of expression in layer II. Studies with GABA(B)R antagonists suggested that neither the auto- nor the heteroreceptor was consistently tonically activated by ambient GABA in the presence of TTX. Studies in EC slices from rats made chronically epileptic using a pilocarpine model of temporal lobe epilepsy revealed a reduced effectiveness of both auto- and heteroreceptor function in both layers. This could suggest that enhanced glutamate and GABA release in the EC may be associated with the development of the epileptic condition.
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Affiliation(s)
- Sarah E. Thompson
- Department of Pharmacy and Pharmacology, University of Bath, Bath, BA2 7AY, UK
| | - Göher Ayman
- Department of Pharmacy and Pharmacology, University of Bath, Bath, BA2 7AY, UK
| | - Gavin L. Woodhall
- The Molecular Biosciences Research Group, School of Life and Health Sciences, Aston University, Birmingham B4 7ET, UK
| | - Roland S.G. Jones
- Department of Pharmacy and Pharmacology, University of Bath, Bath, BA2 7AY, UK
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Fernández de Sevilla D, Garduño J, Galván E, Buño W. Calcium-activated afterhyperpolarizations regulate synchronization and timing of epileptiform bursts in hippocampal CA3 pyramidal neurons. J Neurophysiol 2006; 96:3028-41. [PMID: 16971683 DOI: 10.1152/jn.00434.2006] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Calcium-activated potassium conductances regulate neuronal excitability, but their role in epileptogenesis remains elusive. We investigated in rat CA3 pyramidal neurons the contribution of the Ca(2+)-activated K(+)-mediated afterhyperpolarizations (AHPs) in the genesis and regulation of epileptiform activity induced in vitro by 4-aminopyridine (4-AP) in Mg(2+)-free Ringer. Recurring spike bursts terminated by prolonged AHPs were generated. Burst synchronization between CA3 pyramidal neurons in paired recordings typified this interictal-like activity. A downregulation of the medium afterhyperpolarization (mAHP) paralleled the emergence of the interictal-like activity. When the mAHP was reduced or enhanced by apamin and EBIO bursts induced by 4-AP were increased or blocked, respectively. Inhibition of the slow afterhyperpolarization (sAHP) with carbachol, t-ACPD, or isoproterenol increased bursting frequency and disrupted burst regularity and synchronization between pyramidal neuron pairs. In contrast, enhancing the sAHP by intracellular dialysis with KMeSO(4) reduced burst frequency. Block of GABA(A-B) inhibitions did not modify the abnormal activity. We describe novel cellular mechanisms where 1) the inhibition of the mAHP plays an essential role in the genesis and regulation of the bursting activity by reducing negative feedback, 2) the sAHP sets the interburst interval by decreasing excitability, and 3) bursting was synchronized by excitatory synaptic interactions that increased in advance and during bursts and decreased throughout the subsequent sAHP. These cellular mechanisms are active in the CA3 region, where epileptiform activity is initiated, and cooperatively regulate the timing of the synchronized rhythmic interictal-like network activity.
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