MK-801 prevents chemical kindling induced by pentylenetetrazol in rats

Comparing the synaptic potentiation in schaffer collateral-CA1 synapses in dorsal and intermediate regions of the hippocampus in normal and kindled rats

There is growing evidence that the hippocampus comprises diverse neural circuits that exhibit longitudinal variation in their properties, however, the intermediate region of the hippocampus has received comparatively little attention. Therefore, this study was designed to compared short- and long-term synaptic plasticity between the dorsal and intermediate regions of the hippocampus in normal and PTZ-kindled rats. Short-term plasticity was assessed by measuring the ratio of field excitatory postsynaptic potentials' (fEPSPs) slope in response to paired-pulse stimulation at three different inter-pulse intervals (20, 80, and 160 ms), while long-term plasticity was assessed using primed burst stimulation (PBS). The results showed that the basal synaptic strength differed between the dorsal and intermediate regions of the hippocampus in both control and kindled rats. In the control group, paired-pulse stimulation of Schaffer collaterals resulted in a significantly lower fEPSP slope in the intermediate part of the hippocampus compared to the dorsal region. Additionally, the magnitude of long-term potentiation (LTP) was significantly lower in the intermediate part of the hippocampus compared to the dorsal region. In PTZ-kindled rats, both short-term facilitation and long-term potentiation were impaired in both regions of the hippocampus. Interestingly, there was no significant difference in synaptic plasticity between the dorsal and intermediate regions in PTZ-kindled rats, despite impairments in both regions. This suggests that seizures eliminate the regional difference between the dorsal and intermediate parts of the hippocampus, resulting in similar electrophysiological activity in both regions in kindled animals. Future studies should consider this when investigating the responses of the dorsal and intermediate regions of the hippocampus following PTZ kindling.

From Inhibition of GABA-A Receptor-Mediated Synaptic Transmission by Conventional Antidepressants to Negative Allosteric Modulators of Alpha5-GABA-A Receptors as Putative Fast-Acting Antidepressant Drugs: Closing the Circle?

The present perspective paper shortly and specifically addresses the issues of whether inhibition of GABA-A receptor-mediated synaptic transmission may be involved in antidepressant-like actions and the therapeutic effects of conventional antidepressant (AD) drugs, and whether the recent development of negative allosteric modulators (NAMs) of the alpha5-GABA-A receptor may constitute significant progress in our knowledge on the neurobiology and the treatment of depression.

Antiepileptic effects of antioxidant potent extract from Urtica dioica Linn. root on pentylenetetrazole and maximal electroshock induced seizure models

Urtica dioica Linn. (Urticaceae) is a medicinal plant that has shown various therapeutic utilities in folklore medicine along with its use in the treatment of epilepsy. The entire plant has a sensible reservoir of nutritional elements and micronutrients. The purpose of the present study was to investigate the antiepileptic effect of antioxidant potent extract of Urtica dioica root on animal models. Antioxidant activity of various solvent extracts i.e. Petroleum ether extract (PEE), Ethyl acetate extract (EAE), Chloroform extract (CE) and Ethanolic extract (EE) were screened by DPPH radical scavenging assay using Ascorbic acid as the standard. Further the most potent antioxidant extract was subjected to antiepileptic activity against MES and PTZ model. The IC₅₀ values of different Urtica dioica extracts (PEE, CE, EAE, and EE) in antioxidant assay were found to be 167.54 ± 1.97, 134.41 ± 0.82, 88.15 ± 1.39 and 186.38 ± 1.91 μg/ml in DPPH radical scavenging assay, respectively. The EAE has showed the potent antioxidant activity. In experimental study the EAE (100 and 200 mg/kg, p.o) has found to be effective and significant against MES and PTZ induced seizures. The present study also suggested that antioxidant potent extract (EAE) of Urtica dioica root has antiepileptic effect against MES and PTZ induced seizures. However, further research studies will investigate the active component(s) of Urtica dioica responsible for the observed anticonvulsant effects.

Interleukin-10 inhibits interleukin-1β production and inflammasome activation of microglia in epileptic seizures

BACKGROUND

Microglia are important for secreting chemical mediators of inflammatory responses in the central nervous system. Interleukin (IL)-10 and IL-1β secreted by glial cells support neuronal functions, but the related mechanisms remain vague. Our goal was to demonstrate the efficacy of IL-10 in suppressing IL-1β and in inflammasome activation in mice with epileptic seizure based on an epileptic-seizure mouse model.

METHODS

In this study, mice in which epileptic seizures were induced by administering picrotoxin (PTX) were used as a case group, and mice injected with saline were employed as the control group. The expression of nucleic acids, cytokines, or signaling pathways was detected by reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), flow cytometry, and Western blotting.

RESULTS

Our results demonstrated that IL-10 inhibits IL-1β production through two distinct mechanisms: (1) Treatment with lipopolysaccharides (LPS) results in IL-10 overexpression in microglia and reduced NLRP3 inflammasome activity, thus inhibiting caspase-1-related IL-1β maturation; (2) next, autocrine IL-10 was found to subsequently promote signal transducer and activator of transcription-3 (STAT-3), reducing amounts of pro-IL-1β.

CONCLUSIONS

Our results indicate that IL-10 is potentially effective in the treatment of inflammation encephalopathy, and suggest the potential usefulness of IL-10 for treating autoimmune or inflammatory ailments.

Anticonvulsant effect of the hydroethanolic leaf extract of Psydrax subcordata (DC.) Bridson in murine models

ETHNOPHARMACOLOGICAL RELEVANCE

Psydrax subcordata (DC.) Bridson is a tropical medicinal plant used traditionally for the management of epilepsy. However, there is little scientific evidence to support its use.

AIM OF STUDY

The current study investigated the anticonvulsant properties of the hydroethanolic leaf extract of Psydrax subcordata (PSE) in animal models.

MATERIALS AND METHODS

The anticonvulsant effects were evaluated in mouse models of acute seizures (pentylenetetrazole-, picrotoxin-, 4-aminopyridine-, strychnine- and maximal electroshock-induced seizure tests) and status epilepticus (Lithium/pilocarpine-induced SE). The role of GABAergic mechanisms in the actions of the extract was also examined by pre-treatment of animals with flumazenil in the pentylenetetrazole test.

RESULTS

The extract (30, 100 and 300mg/kg, p.o.) significantly delayed the onset and decreased the duration and frequency of pentylenetetrazole- and picrotoxin-convulsions. PSE also reduced the duration of tonic hind limb extensions in the maximal electroshock-induced seizure test. Furthermore, PSE pre-treatment significantly delayed the onset of seizures and improved survival in the 4-aminopyridine-induced seizure test. In the strychnine-induced seizure test, PSE treatment did not significantly affect the latency to convulsions and time until death when compared to controls. PSE exhibited anticonvulsant effects in the lithium/pilocarpine test by delaying the onset of seizures and status epilepticus as well as reducing the severity of seizures and mortality of mice. Again, the anticonvulsant effect of PSE (100mg/kg, p.o.) was blocked by pre-treatment with flumazenil in the PTZ test.

CONCLUSION

PSE has anticonvulsant activity in animal models, and this effect may be mediated, at least partly, through GABAergic mechanisms.

Potential functional and pathological side effects related to off-target pharmacological activity

Most pharmaceutical companies test their discovery-stage proprietary molecules in a battery of in vitro pharmacology assays to try to determine off-target interactions. During all phases of drug discovery and development, various questions arise regarding potential side effects associated with such off-target pharmacological activity. Here we present a scientific literature curation effort undertaken to determine and summarize the most likely functional and pathological outcomes associated with interactions at 70 receptors, enzymes, ion channels and transporters with established links to adverse effects. To that end, the scientific literature was reviewed using an on-line database, and the most commonly reported effects were summarized in tabular format. The resultant table should serve as a practical guide for research scientists and clinical investigators for the prediction and interpretation of adverse side effects associated with molecules interacting with components of this screening battery.

Comparison and effects of acute lamotrigine treatment on extracellular excitatory amino acids in the hippocampus of PTZ-kindled epileptic and PTZ-induced status epilepticus rats

In this communication, the effect of acute treatment with lamotrigine (LTG) was investigated on release of main excitatory amino acids (EAA) such as glutamate (Glu) and aspartate (Asp) in the hippocampus of pentylenetetrazol (PTZ)-induced and PTZ-kindled freely moving rats using micro dialysis. The results show that, levels of Glu and Asp significantly increased in the rat hippocampus during the seizure/interical periods for PTZ-status epilepticus (SE) and PTZ-kindled epileptic (EP) rats. The levels of Glu and Asp increased more in EP rat hippocampus than in SE rat hippocampus. After administration of 20 mg/kg LTG, the levels of Glu and Asp significantly decreased in the SE and EP rat hippocampus. The results indicate that: (a) excitability of the PTZ-kindled epileptogenic model is higher than that of the status epilepticus model; (b) the modulation of LTG on the EAA neurotransmitters certainly plays an important role in antiepileptic efficacy, especially in PTZ-kindled epileptic model where the release of EAA was influenced more markedly by acute application of 20 mg/kg LTG.

The effect of PTZ-induced epileptic seizures on hippocampal expression of PSA-NCAM in offspring born to kindled rats

BACKGROUND

Maternal epileptic seizures during pregnancy can affect the hippocampal neurons in the offspring. The polysialylated neural cell adhesion molecule (PSA-NCAM), which is expressed in the developing central nervous system, may play important roles in neuronal migration, synaptogenesis, and axonal outgrowth. This study was designed to assess the effects of kindling either with or without maternal seizures on hippocampal PSA-NCAM expression in rat offspring.

METHODS

Forty timed-pregnant Wistar rats were divided into four groups: A) Kind+/Seiz+, pregnant kindled (induced two weeks prior to pregnancy) rats that received repeated intraperitoneal (i.p.) pentylenetetrazol, PTZ injections on gestational days (GD) 14-19; B) Kind-/Seiz+, pregnant non-kindled rats that received PTZ injections on GD14-GD19; C) Kind+/Seiz-, pregnant kindled rats that did not receive any PTZ injections; and D) Kind-/Seiz-, the sham controls. Following birth, the pups were sacrificed on PD1 and PD14, and PSA-NCAM expression and localization in neonates' hippocampi were analyzed by Western blots and immunohistochemistry.

RESULTS

Our data show a significant down regulation of hippocampal PSA-NCAM expression in the offspring of Kind+/Seiz+ (p = 0.001) and Kind-/Seiz+ (p = 0.001) groups compared to the sham control group. The PSA-NCAM immunoreactivity was markedly decreased in all parts of the hippocampus, especially in the CA3 region, in Kind+/Seiz+ (p = 0.007) and Kind-/Seiz+ (p = 0.007) group's newborns on both PD1 and 14.

CONCLUSION

Our findings demonstrate that maternal seizures but not kindling influence the expression of PSA-NCAM in the offspring's hippocampi, which may be considered as a factor for learning/memory and cognitive impairments reported in children born to epileptic mothers.

The NMDA receptor complex as a therapeutic target in epilepsy: a review

A substantial amount of research has shown that N-methyl-D-aspartate receptors (NMDARs) may play a key role in the pathophysiology of several neurological diseases, including epilepsy. Animal models of epilepsy and clinical studies demonstrate that NMDAR activity and expression can be altered in association with epilepsy and particularly in some specific seizure types. NMDAR antagonists have been shown to have antiepileptic effects in both clinical and preclinical studies. There is some evidence that conventional antiepileptic drugs may also affect NMDAR function. In this review, we describe the evidence for the involvement of NMDARs in the pathophysiology of epilepsy and provide an overview of NMDAR antagonists that have been investigated in clinical trials and animal models of epilepsy.

Experimental re-evaluation of flunarizine as add-on antiepileptic therapy

Background:

Experimental studies have found several calcium channel blockers with anticonvulsant property. Flunarizine is one of the most potent calcium channel blockers, which has shown anticonvulsant effect against pentylenetetrazole (PTZ) and maximal electroshock (MES)-induced seizures. However, further experimental and clinical trials have shown varied results. We conducted a PTZ model experimental study to re-evaluate the potential of flunarizine for add-on therapy in the management of refractory epilepsy.

Materials and Methods:

Experiments were conducted in PTZ model involving Swiss strain mice. Doses producing seizures in 50% and 99% mice, i.e. CD₅₀ and CD₉₉ values of PTZ were obtained from the dose-response study. Animals received graded, single dose of sodium valproate (100–300 mg/kg), lamotrigine (3–12 mg/kg) and flunarizine (5–20 mg/kg), and then each group of mice was injected with CD₉₉ dose of PTZ (65mg/kg i.p.). Another group of mice received single ED₅₀ dose (dose producing seizure protection in 50% mice) of sodium valproate and flunarizine separately in left and right side of abdomen. Results were analysed by Kruskal–Wallis ANOVA on Ranks test.

Results:

As compared to control, sodium valproate at 250 mg/kg and 300 mg/kg produced statistical significant seizure protection. At none of the pre-treatment dose levels of lamotrigine, the seizure score with PTZ differed significantly from that observed in the vehicle-treated group. Pre-treatment with flunarizine demonstrated dose-dependent decrease in the seizure score to PTZ administration. As compared to control group, flunarizine at 20 mg/kg produced statistical significant seizure protection.

Conclusion:

As combined use of sodium valproate and flunarizine has shown significant seizure protection in PTZ model, flunarizine has a potential for add-on therapy in refractory cases of partial seizures. It is therefore, we conclude that further experimental studies and multicenter clinical trials involving large sample size are needed to establish flunarizine as add-on therapy in refractory epilepsy.

Correlation of seizures and biochemical parameters of oxidative stress in experimentally induced inflammatory rat models

The role of oxidative stress in the pathogenesis of various conditions including epilepsy, inflammatory bowel disease and rheumatoid arthritis is evolving. The aim of this study was to find out the correlation between various inflammatory models with seizures and antioxidant parameters. Fifty-four male rats were divided into three groups of colitis, adjuvant arthritis and cotton wool granuloma (CWG). Each group had three subgroups of control, model and treatment. Thalidomide was used as treatment in colitis and arthritis group, whereas etoricoxib was used in CWG group. In colitis and arthritis groups, thalidomide was administered for 3 and 17 days, respectively, whereas etoricoxib was administered for 7 days in CWG group. At the end of treatment protocols, a subconvulsive dose of pentylenetetrazole (PTZ) (40 mg/kg i.p.) was injected intraperitoneally to note seizure onset and score. After confirming the presence of inflammation by morphological and histological studies, plasma and brain biochemical parameters of oxidative stress were estimated. The models of colitis, arthritis and CWG were effectively produced as evidenced by morphological scores (P < 0.001). Thalidomide reduced the morphological score (P < 0.002) and seizure grade (P < 0.001), whereas increased seizure onset (P < 0.001) in the arthritis group. There was an increase in malondialdehyde levels in the brain of thalidomide-treated groups (P < 0.002) and a significant decrease in superoxide dismutase (SOD) and glutathione peroxidase (GPx) levels. There was neither improvement in seizure nor any significant changes in lipid peroxidation and antioxidant enzyme levels in etoricoxib-treated group. Thalidomide was effective in reducing the extent of arthritis as well as reducing the seizure scoring and increasing seizure onset in the adjuvant arthritis group. As it increased lipid peroxidation and reduced SOD and GPx, further evaluation is necessary with respect to oxidative stress.

Neuroprotective effect of progesterone on acute phase changes induced by partial global cerebral ischaemia in mice

The possible neuroprotective effect of progesterone, a steroid hormone, on acute phase changes in a mouse model of cerebral ischaemia induced by bilateral common carotid artery occlusion (BCAO) was studied. A total of 72 male mice were included in the study. The BCAO model was used to induce partial global cerebral ischaemia. Morphological assessment included measurement of infarct size and brain oedema. Post-ischaemic seizure susceptibility was assessed using a subconvulsive dose of pentylenetetrazole (30 mgkg−1 i.p.). Biochemical estimations included tumour necrosis factor α (TNF-α) levels and enzyme parameters such as lipid peroxidation, superoxide dismutase, catalase and glutathione peroxidase, and protein estimation. BCAO induced a significant infarct size and oedema in the saline-treated control group, along with an increase in oxidative stress, indicated by increased lipid peroxidation and decreased levels of antioxidants such as superoxide dismutase, catalase and glutathione peroxidase. Progesterone (15 mgkg−1 i.p.) administration showed a neuroprotective effect by significantly reducing the cerebral infarct size as compared with the control group. Post-ischaemic seizure susceptibility was also reduced as the number of positive responders decreased. Brain oedema subsided, but not significantly. Progesterone significantly reduced TNF-α levels compared with the ischaemia group. Progesterone improved levels of all the anti-oxidants, indicating activity against oxidative stress induced by BCAO. The results demonstrate the neuroprotective effect of progesterone against ischaemic insult, suggesting a role for the steroid as a neuroprotective agent.

Allopregnanolone, the active metabolite of progesterone protects against neuronal damage in picrotoxin-induced seizure model in mice

Progesterone exerts anti-seizure effect against several chemoconvulsants. However, there is no published report on the interaction between progesterone and picrotoxin (PTX). The present study evaluated the effects of progesterone and its active metabolite, allopregnanolone against PTX-induced seizures, brain lipid peroxidation and DNA fragmentation in male mice. Finasteride, a 5alpha-reductase inhibitor and indomethacin, an inhibitor of 3infinity-hydroxysteroid dehydrogenase were assessed against progesterone's effects on PTX-induced seizures, brain lipid peroxidation and DNA fragmentation. PTX produced clonic-tonic seizures in mice with CD50 and CD97 of 2.4 and 4.0mg/kg, i.p. respectively. Progesterone significantly countered PTX-induced seizures, with ED50 of 78.30mg/kg and ED97 of 200mg/kg. Progesterone antagonized PTX-induced DNA fragmentation. Finasteride (200mg/kg) and indomethacin (1mg/kg) reversed the anti-seizure and anti-DNA fragmentation effects of progesterone. Allopregnanolone, also protected against PTX-induced seizures and DNA fragmentation. There was no significant change in the brain lipid peroxidation parameters in any of the treatment groups. It may be concluded that progesterone protects against PTX-induced seizures and DNA fragmentation through its active metabolites allopregnanolone and 5alpha-pregnan-3,20-dione. However, it appears from the present study that, the neuroprotection with progesterone is primarily on account of allopregnalone. The therapeutic potential of allopregnanolone deserves to be evaluated clinically.

Experimentally induced various inflammatory models and seizure: understanding the role of cytokine in rat

BACKGROUND

The mechanism of epileptogenesis is not well established. There is higher incidence of seizures among patients with chronic inflammatory disease. Cytokines are rapidly induced in the brain after a variety of stimuli including inflammation. Aim of this study was to produce various inflammatory models and seizure to understand the role of TNFalpha in above mentioned models.

MATERIALS AND METHODS

A total of 54 male rats were included in the study. Animals were divided into 3 groups of colitis, arthritis, and cotton wool granuloma. Each group had 3 subgroups of control, model and treatment. At the end of 3 days in colitis, 17 days in arthritis and 7 days in cotton wool granuloma groups a subconvulsive dose of PTZ (40 mg/kg i.p) was injected to note seizure onset and seizure score. Brain samples were subjected to DNA fragmentation testing. Presence of inflammation was confirmed by morphology and histology. Plasma and brain TNFalpha levels were measured.

RESULTS

The models of colitis, arthritis and CWG were effectively produced as evidenced by morphology and histology scores (p<0.001). Seizure onset was reduced and grade was increased (p<0.001). Thalidomide reduced the morphological, histological (p<0.002), DNA fragmentation and seizure grade (p<0.001) while increased seizure onset (p<0.001) in the arthritis group. TNFalpha levels in both plasma and brain were reduced following thalidomide treatment (p<0.002) in arthritis group. There were no significant findings in colitis or cotton wool granuloma groups.

CONCLUSION

Inflammation was associated with decreased threshold to PTZ induced seizure. Thalidomide is effective in reducing the extent of arthritis as well as reducing the seizure scoring and increasing seizure onset in the adjuvant arthritis group. Thalidomide was also effective in reducing TNFalpha levels thus contributing to its antiepileptic activity.

Adenosine receptor agonists attenuate the development of diazepam withdrawal-induced sensitization in mice

In the present study, the effects of adenosine agonists on the development of sensitization to withdrawal signs precipitated after sporadic treatment with diazepam, in mice, were investigated. To obtain the sensitization, the animals were divided into groups: continuously and sporadically treated with diazepam (15.0 mg/kg, s.c.). The adenosine receptor agonists (CPA, CGS 21,680 and NECA) were administered in sporadically diazepam treated mice during two diazepam-free periods. Concomitant administration of pentetrazole (55.0 mg/kg, s.c.) with flumazenil (5.0 mg/kg, i.p.) after the last injection of diazepam or vehicle, induced the withdrawal signs, such as clonic seizures, tonic convulsion and death episodes. The major finding of our experiments is attenuation of withdrawal signs in sensitized mice, inducing by all adenosine agonists. Only higher dose of CPA produced significantly decreased the number of withdrawal incidents, while both used doses of CGS 21,680 and NECA produced more clear effects. These results support the hypothesis that adenosinergic system is involved in the mechanisms of sensitization to the benzodiazepine withdrawal signs, and adenosine A(2A) receptors play more important role in that process.

Offsetting of aberrations associated with seizure proneness in rat hippocampus area CA1 by theta pulse stimulation-induced activity pattern

Epileptiform activity induces long term aberrations in hippocampal network functions. This study was conducted in pentylenetetrazol (PTZ) -kindled rats to examine offsetting of aberrations associated with seizure proneness in hippocampus area CA1 by theta pulse stimulation (TPS: 5 Hz trains for 3 min) -induced activity pattern. In hippocampal slices from both control and kindled rats, the field excitatory postsynaptic potentials (fEPSP) and population spikes (PS) were simultaneously recorded through electrodes in the apical dendrites and stratum pyramidale, respectively. The following changes in kindled vs. control slices were observed. The fEPSP needed to be greater to produce the PS recorded in the cell body layer. The fEPSP was reduced by paired stimuli whereas the PS amplitude was increased. TPS selectively depressed the PS in a lasting fashion, and shifted the fEPSP slope and the PS amplitude relation toward what was observed in controls. Both the fEPSP and PS were increased by paired stimuli at 60 min after TPS application. The lasting depressive effect of TPS on the PS amplitude was converted into facilitation by adenosine A1 receptor antagonist 8-cyclopentyl-1, 3-dipropylxanthine (CPX). Potentiation of the PS amplitude by TPS in the presence of CPX was blocked by an N-methyl-d-aspartate receptor antagonist AP5. We hypothesize that the extracellular adenosine spillover, acting through adenosine A1 receptors, during TPS-induced activity pattern could trigger a homeostatic process for correcting network imbalances caused by epileptiform activity.

Epileptogenic insult causes a shift in the form of long-term potentiation expression

The relationship between epilepsy, modeled here by pentylenetetrazol kindling, and learning deficits, modeled here by long-term potentiation (LTP), was studied. The field excitatory postsynaptic potentials and population spikes (PS) were recorded from strata radiatum and pyramidale, respectively, in urethane-anesthetized rat dorsal hippocampus CA1 area upon stimulation of Schaffer collaterals. To induce LTP, a 100 Hz primed-burst stimulation protocol was used. Experiments were carried out at approximately 30 days after the last pentylenetetrazol dose. The effects of voltage dependent calcium channel blocker verapamil and N-methyl-D-aspartate receptor antagonist MK-801 on LTP expression were examined. Tetanic stimulation elicited both field excitatory postsynaptic potential LTP and PS LTP in control animals, and LTP-induction of the PS in control animals was attenuated by MK-801, but not by verapamil. By contrast, kindled rats showed LTP of the PS only. MK-801 reduced the extent of potentiation of PS amplitude and verapamil inhibited the PS amplitude potentiation, completely. The results suggest that seizure induction modifies mechanisms underlying LTP induction and causes a shift in the form of LTP expression. The pentylenetetrazol-kindling-induced increase in PS LTP is sensitive to verapamil and not to MK-801 and therefore primarily dependent on activation of voltage dependent calcium channels rather N-methyl-D-aspartate receptors. Kindling may lead to a shift in synaptic plasticity thresholds much like the shift that occurs during aging, and such alterations may contribute to deficits in learning and memory.

Posttraining administration of pentylenetetrazol dissociates gabapentin effects on memory consolidation from that on memory retrieval process in mice

Gabapentin (GBP), an anticonvulsant drug, 10 mg/kg, i.p., but not 100 mg/kg, i.p., enhanced retention of an inhibitory avoidance task when given 20 min after training, as indicated by retention performance 48 h later. The immediate post-training administration of pentylenetetrazol (PTZ, 45 mg/kg, i.p.) impaired retention performance. The amnesic effects of the convulsant drug PTZ were not influenced by GBP at any level of doses. However, GBP 100 mg/kg, but not 10 mg/kg, delayed the latency to first clonic body seizures and decreased the duration of convulsion induced by PTZ. The enhancing effect of GBP on retention was not prevented by the opiate receptor antagonist, naltrexone (0.01 mg/kg, i.p.), which completely prevented the impairment of retention caused by PTZ. Further, naltrexone did not modify the convulsions induced by PTZ. In mice pretreated with naltrexone and that received PTZ, the administration of GBP again, enhanced retention performance during the retention test. Since previous results indicate that the amnesic action of PTZ are due to an effect on memory retrieval, the present results provide additional pharmacological evidence suggesting that GBP influenced memory consolidation and not memory retrieval of an inhibitory avoidance task in mice.

Dynamic release of amino acid transmitters induced by valproate in PTZ-kindled epileptic rat hippocampus

In the present communication, the dynamic release of amino acid (AA) transmitters induced by valproate (VPA) in pentylenetetrazol (PTZ)-kindled freely moving rats hippocampus has been determined. The results showed that glutamate and aspartate release were significantly increased during the seizure/interical periods, and markedly decreased after the application of 200mg/kg valproate. In contrast, gamma-aminobutyric acid and taurine release were markedly decreased during interical period, and significantly increased during the seizure period. Glycine release was similar to the case of glutamate and aspartate release. The increase of either gamma-aminobutyric acid/taurine or glycine releases during the seizure period could be inhibited by the application of valproate likewise. The results indicate that: (a) the imbalance between excitatory and inhibitory neurotransmitters is really involved in epilepsy; (b) the modulation of valproate on the major amino acid neurotransmitters certainly plays one of important roles on antiepilepsy efficacy; (c) the pentylenetetrazol-kindled epileptogenesis model is a fit one for approaching the mechanisms of valproate modulating amino acid neurotransmitters.

FK506 facilitates chemical kindling induced by pentylenetetrazole in rats

To clarify the possible role played by calcineurin in kindling development, we examined the effects of pretreatment with FK506, a selective calcineurin inhibitor, on pentylenetetrazole (PTZ) kindling in rats. FK506 facilitated the speed of kindling induced by repeated administration of 30-mg/kg PTZ, while FK506 did not ameliorate acute seizure manifestations after a single injection of PTZ. Our results suggested that calcineurin might exert an inhibitory effect on PTZ kindling.

Differential effects of pentylenetetrazol-kindling on long-term potentiation of population excitatory postsynaptic potentials and population spikes in the CA1 region of rat hippocampus

The effects of pentylenetetrazol-kindling on synaptic transmission and the effectiveness of &theta; pattern primed-bursts (PBs) for the induction of long-term potentiation (LTP) of population excitatory postsynaptic potentials and population spikes were investigated in hippocampal CA1 of pentylenetetrazol-kindled rats. Experiments were carried out in the control and kindled animals at two post-kindling periods, i.e., 48-144 h (early phase) and 30-33 days (long lasting phase). Field potentials (population excitatory postsynaptic potentials, pEPSPs; and population spikes, PSs) were recorded at the stratum radiatum and the stratum pyramidale following stimulation of the stratum fibers, respectively. PBs were delivered to stratum fibers and PB potentiation was assessed. The results showed that 48-144 h after kindling there was no significant difference for pEPSP slope and PS amplitude between two groups. But at 30-33 days after kindling, the pEPSP slope in the stratum radiatum of kindled animals decreased, whereas the amplitude of PSs increased compared to those of controls. Shortly after kindling, control animals had normal LTP of pEPSP slope and PS amplitude in response to PBs, but kindled rats lack LTP of pEPSP slope and PBs induced LTP of PS amplitude in most of kindled animals. In 30-33 days after kindling, PB potentiation was not observed in the stratum radiatum of kindled animals but PBs induced LTP of PS amplitude, which was significantly greater than that of control animals. The effect is compatible with the hypothesis, which postulates kindling-associated functional deficit in hippocampus, especially CA1, as an explanation for the behavioral deficits seen with the kindling model of epilepsy.

4-Hydroxybenzaldehyde from Gastrodia elata B1. is active in the antioxidation and GABAergic neuromodulation of the rat brain

Ether fraction of G. elata methanol extract significantly inhibited the recovery time and severity induced by pentylenetetrazole (PTZ) treatment. Pretreatment of ether fraction of G. elata methanol extract successfully prevented diminution of brain GABA level in subconvulsive dose of PTZ-treated rats. 4-Hydroxybenzaldehyde, an analogue of p-hydroxybenzyl alcohol, showed an inhibitory effect on the GABA transaminase, and its inhibitory activity was higher than that of valproic acid, a known anticonvulsant. In the brain of PTZ-treated rats, brain lipid peroxidation was significantly increased, while it recovered to the control level after treatment with 4-hydroxybenzaldehyde. It may be concluded that antioxidation and positive modulation of GABAergic neuromodulation of 4-hydroxybenzaldehyde partially contribute to an antiepileptic and anticonvulsive activity of G. elata B1.

Primed-burst potentiation occludes the potentiation phenomenon and enhances the epileptiform activity induced by transient pentylenetetrazol in the CA1 region of rat hippocampal slices

The effects of pentylenetetrazol (PTZ) following induction of long-term potentiation (LTP) on population spikes in CA1 of hippocampal slices were investigated. Population spikes were evoked by activation of Schaffer collaterals with a range of stimulation intensities. LTP was induced using &theta;-pattern primed burst tetanic stimulation. Changes in the population spike amplitude and number of population spikes were used as indices to quantify the effects of PTZ exposure in the control (non-tetanized) and LTP (tetanized) conditions. The amplitude of population spike was measured 20 min before, during 20 min chemical application (3 mM), and also after 30 or 60 min washout period. In non-tetanized slices, the population spike input-output curve was significantly increased 20 min after PTZ application and persisted at least for 60 min. Multiple population spikes or after potentials also appeared, but did not persist. When PTZ was applied on tetanized slices, 60 min after LTP induction, the amplitude increase produced by PTZ was smaller than the increase seen in the control condition. Also LTP induction preceding PTZ exposure increased the number of population spikes evoked by stimulation of Schaffer collaterals. It is concluded that a transient PTZ application produces a long-lasting increase in population spike amplitude. Primed burst LTP occludes PTZ-induced potentiation while also increasing the epileptogenic effect of PTZ.

Kindling induced by pentylenetetrazole in rats is not directly associated with changes in the expression of NMDA or benzodiazepine receptors

Repeated injections of a subconvulsant dose of pentylenetetrazole (PTZ, 30 mg/kg IP three times weekly for 13 injections) in Wistar and hooded Lister rats resulted in kindled seizures, the extent of which varied between strains. Wistar rats achieved stage 4 of clonic-tonic seizures, whereas hooded Lister rats only reached stage 2 of convulsive waves axially through the body. Rats were killed 10 days after their final injection, and radioligand binding was used to measure the expression of NMDA receptors in cortex and hippocampus using [3H]MK-801 and [3H]L-689,560, the latter binding specifically to the NR1 subunit. [3H]Ro 15-1788 measured expression of GABA(A)-benzodiazepine binding sites containing alpha1, alpha2, alpha3, or alpha5 subunits. Specific analysis of GABA(A) receptors containing the alpha5 subunit, which are preferentially localized in the hippocampus, was assessed with [3H]L-655,708. In the cortex, there was no effect of strain or treatment on the K(D) or B(max) of any of the ligands. Similarly, there was no effect of strain or treatment on hippocampal [3H]L-689,560 or [3H]Ro 15-1788 binding. However, in the hippocampus there was a significant, albeit modest, effect of treatment on the B(max) of [3H]MK-801 binding and the B(max) and K(D) of [3H]L-655,708 binding, i.e., PTZ-treated rats had fewer [3H]MK-801 and [3H]L-655,708 binding sites (NMDA and alpha5-containing GABA(A) receptors, respectively), but, these reductions were significant only in the relatively seizure-insensitive hooded Lister strain. This suggests that the increased susceptibility to kindling in Wistar rats is not directly related to alterations in the expression of NMDA or GABA(A) receptors.

The effect of pentylenetetrazole-kindling on the extracellular glutamate and taurine levels in the frontal cortex of rats

We studied the extracellular concentration of glutamate and taurine in the frontal cortex of freely-moving pentylenetetrazole (PTZ) kindled rats using an in vivo microdialysis. A significant and sustained increase in the glutamate level was observed in the kindled rats, in contrast, a slight and delayed increase was observed in the non-kindled rats when the same grade seizure was induced by PTZ. The convulsive dose of PTZ administration caused a decrease in taurine levels in the controls, however, no significant changes were found in the kindled rats.

Enhanced susceptibility to cocaine- and pentylenetetrazol-induced seizures in prenatally cocaine-treated rats

We previously reported that prenatal cocaine exposure increased susceptibility to cocaine-induced seizures later in life. Here we examine whether this enhanced susceptibility to seizures generalizes to other chemoconvulsants, and whether postnatal cocaine treatment similarly increases susceptibility. Following prenatal cocaine treatment (40 mg/kg; E10-20), both male and female rats were more likely to seize to a dose of 30 mg/kg pentylenetetrazol (PTZ) at 2 months of age, although the severity of the seizures observed was increased only in females. Daily cocaine injections (10-20 mg/kg SC) during the first 10 days after birth also produced effects that were dependent on the sex of the animal. Postnatally cocaine-treated female rats showed no greater incidence of seizures in response to an acute high dose of cocaine, but did exhibit an increased susceptibility to cocaine-kindled seizures. Male, but not female, postnatally cocaine-treated rats were more susceptible to PTZ-induced seizures. The increased susceptibility to seizures induced by two different chemoconvulsants after prenatal cocaine treatment suggests that developmental cocaine exposure, particularly during the second trimester equivalent, alters the balance between excitation and inhibition in the brain.

Involvement of nitric oxide in pentylenetetrazole-induced kindling in rats

We investigated the role of nitric oxide (NO) and brain-derived neurotrophic factor (BDNF) in the pentylenetetrazole (PTZ)-induced kindling in rats. Seizures were induced by single administration of PTZ, which was associated with an increase in levels of NO metabolites (NOx) in the hippocampus. Pretreatment with a neuronal NO synthase inhibitor, 7-nitroindazole (7-NI), diminished the PTZ-induced increase in NOx levels without affecting the seizure intensity. Repeated administration of PTZ produced a gradual increase in the seizure intensity, leading to the development of kindling. In the kindled rats, PTZ at a dose of 40 mg/kg increased NOx levels in the hippocampus, whereas it had no effect in control animals. Cotreatment of 7-NI with PTZ blocked the development of kindling and attenuated the PTZ-induced increase in NOx levels. A significant increase in BDNF levels was observed in the hippocampus of the kindled rats, which returned to the control levels following seizures induced by PTZ. 7-NI reduced the hippocampal BDNF levels in control rats and suppressed the increase of BDNF levels in the kindled rats. Our findings suggest that NO plays a role in the development of PTZ-induced kindling and that BDNF may contribute to the NO-dependent plastic changes in neuronal excitability.

Effects of nicardipine, an antagonist of L-type voltage-dependent calcium channels, on kindling development, kindling-induced learning deficits and hippocampal potentiation phenomena

Kindling is considered to be a useful experimental model for investigating drug effects on the convulsive component of epilepsy and related alterations at the behavioural level. It was demonstrated that pentylenetetrazol (PTZ)-kindled rats show diminished learning performance in shuttle-box training. We used this model to study the influence of nicardipine, an antagonist of L-type voltage-dependent calcium channels, on kindling seizure development as well as related learning impairments. Additionally, we tested the influence of nicardipine on kindling-induced potentiation, a special form of long-term enhancement of evoked potentials in the dentate gyrus after kindling. Therefore, monosynaptic evoked field potentials in the dentate area upon test stimuli to the perforant pathway were recorded in freely moving kindled and control rats at different times after injection of PTZ. The results indicate that the blockade of L-type voltage-dependent Ca2+-channels during the kindling procedure attenuates PTZ-kindling, antagonizes a kindling-induced learning deficit in an active avoidance test and decreases a novel form of kindling-related potentiation, the long-lasting amplitude enhancement of the monosynaptic evoked field potential in the dentate gyrus after injection of a small test dose of PTZ. This potentiation can also be prevented in kindled animals by nicardipine injection in an acute experiment.

Amygdala-kindled and pentylenetetrazole-induced seizures in glutamate transporter GLAST-deficient mice

The glutamatergic system has been shown to be important for the induction of epileptiform activity and the development of epileptogenesis. To investigate the role of the astroglial glutamate transporter GLAST in epileptogenesis, we examined amygdala (AM)-kindled and pentylenetetrazole (PTZ)-induced seizures in GLAST-deficient mice (GLAST(-/-)) and compared them to those observed in wild-type mice (GLAST(+/+)) and maternal C57Black6/J (C57) mice. AM-kindling resulted in no significant differences in afterdischarge threshold or in the seizure responses induced by first stimulation between these groups. In addition, although no significant differences were seen in kindled seizure development, the generalized seizure duration of AM-kindled seizures in GLAST(-/-) mice was significantly prolonged (approximately 35%) compared with that of C57 mice. Furthermore, GLAST(-/-) mice showed more severe stages of PTZ-induced seizures than GLAST(+/+) mice, and the latency to the onset of seizures was significantly shorter for the mutant mice. These results indicate that GLAST is one of factors determining seizure susceptibility.

Effects of anticonvulsive drugs on pentylenetetrazol kindling and long-term potentiation in freely moving rats

Drugs with anticonvulsive properties and different mechanisms of action were compared for their influence on long-term potentiation and pentylenetetrazol kindling in freely moving animals. Rats were chronically implanted with a stimulation electrode in the angular bundle and a recording electrode in the dentate gyrus. Field potentials in the dentate gyrus were elicited and long-term potentiation was induced by stimulation of the perforant pathway. The clinically used drugs or the potentially anticonvulsive drugs, diphenylhydantoin (50 mg/kg), diazepam (0.5 mg/kg), pentobarbital (10 mg/kg), dizocilpine (MK 801, 0.2 mg/kg) and CGP 43487 (2-amino-4-methyl-5-phosphono-3-pentenoic acid-carboxyethylester, 10 mg/kg), were injected before tetanization. In behavioural experiments pentylenetetrazol kindling was performed with pretreatment with the substances in dosages indicated above (except MK 801, 0.3 mg/kg). Field potentials recorded in the interval between drug administration and tetanization were influenced only by diphenylhydantoin which enhanced the population spike amplitude to 128% of control values. However, the substances showed different effects on long-term potentiation. MK 801, CGP 43487 and pentobarbital depressed potentiation; diazepam was without effect. Diphenylhydantoin had a minor influence on induction but significantly impaired maintenance of long-term potentiation. Furthermore, MK 801, CGP 43487, diazepam and pentobarbital differentially depressed kindling whereas phenytoin only slightly influenced it. The consequences as to hypothetical common cellular mechanisms for kindling development and long-term potentiation are discussed.

A neuropharmacological analysis of PTZ-induced kindling in mice

1. Glutamate seems to play a central role in epilepsy, and kindling is considered the most useful experimental model in revealing plastic changes associated with epileptic features. 2. The aim of this study was to optimize pentylenetetrazol (PTZ)-kindling conditions in mice and analyze glutamatergic changes associated with this phenomena. 3. A significant increase (85.7%) in seizuring animals was observed after four PTZ administrations, with all subjects presenting full seizures after five administrations. 4. PTZ kindling, but not acute seizure, significantly increased (169.8%) the specific binding of [3H]glutamate in the cerebral cortex. 5. The development of PTZ-induced kindling in mice was prevented by the coadministration of phenobarbital or diazepam. 6. This study indicates that mice can be used in a reliable model of PTZ-induced kindling and that, as in rats, the kindling increases the specific [3H]glutamate binding in the cerebral cortex, therefore allowing for screening new drugs that can interfere in the plastic changes believed to underlie epileptic phenomena.

NMDA receptor antagonists potently suppress the spontaneous withdrawal signs induced by discontinuation of long-term diazepam treatment in Fischer 344 rats

The present study investigated the effects of the NMDA receptor antagonists dizocilpine (MK-801) and ifenprodil on the appearance of diazepam withdrawal signs caused by discontinuation of long-term diazepam treatment using a drug-admixed food (DAF) method in Fischer 344 rats. The total withdrawal score was significantly decreased by after-withdrawal treatment with dizocilpine or ifenprodil. Dizocilpine, in particular, markedly suppressed the motor withdrawal signs and body weight loss, while ifenprodil suppressed the motor and emotional withdrawal signs. Furthermore, the decrease in the food intake during withdrawal (anorexia) was significantly reduced by dizocilpine, but not by ifenprodil. These behavioral results indicated that the activation of NMDA receptors during withdrawal may play an important role in the appearance of withdrawal signs (in particular motor withdrawal signs) caused by discontinuation of chronic diazepam treatment, and that inhibitory agents for NMDA receptors may be effective in alleviation of the appearance of benzodiazepine withdrawal signs.

Evidence for a role of bradykinin neurons in the control of gonadotropin-releasing hormone secretion

The present study provides evidence of a novel neuronal pathway for the control of GnRH secretion involving bradykinin neurons. Bradykinin neurons were shown by immunohistochemistry to be densely localized in several regions of the brain including the cortex, hippocampus and supraoptic nucleus, as well as two regions critical in the control of GnRH secretion, the organum vasculosum of the lamina terminalis and arcuate nucleus. Bradykinin dose-dependently stimulated GnRH release from male and proestrous female rat hypothalami in vitro. Antagonist studies revealed that bradykinin effects are mediated by the bradykinin B2 receptor. The effect of bradykinin on GnRH release is not mediated by the classical major transmitter, glutamate, as glutamate antagonists had no effect on bradykinin stimulation of GnRH release. Rather, bradykinin appears to act directly on the GnRH neuron as bradykinin stimulated GnRH release directly from immortalized GnRH (GT1-7) neurons in vitro, and immunoblot studies revealed that the bradykinin B2 receptor is present in GT1-7 neurons. The bradykinin B2 receptor was also demonstrated in the rat hypothalamus and pituitary by immunoblotting. Bradykinin-induced exocytosis of GnRH appears to involve activation of the PKC signaling pathway, as a PKC inhibitor blocked bradykinin-induced GnRH release. Finally, bradykinin neurons appear to be important mediators of steroid signals in the hypothalamus to produce the LH surge, as central administration of a B2 antagonist, but not a B antagonist, significantly attenuated the steroid-induced LH surge in the ovariectomized female rat.

Dose-finding study with nimodipine: a selective central nervous system calcium channel blocker on aminophylline induced seizure models in rats

Nimodipine, a dihydropyridine derivative central nervous system (CNS) selective calcium channel blocker was studied at four different dosage schedules in five different models of seizures in rats. At a dose of 5 mg/kg, i.p. with pretreatment time of 15 min, nimodipine significantly antagonized aminophylline (175 and 200 mg/kg, i.p.), electroshock (150 mA for 0.2 s), pentylenetetrazole (60 and 75 mg/kg, i.p.), aminophylline (100 mg/kg i.p.) + electroshock (66mA for 0.2 s), and aminophylline (100 mg/kg, i.p.) + pentylenetetrazole (40 mg/kg, i.p.) induced seizures in rats. No hemodynamic alteration was observed with this dose of nimodipine. However, 2 mg/kg, i.p. (pretreatment time of 15 min and 30 min) and 5 mg/kg, i.p. (pretreatment time of 30 min) doses of nimodipine failed to demonstrate any significant anticonvulsant effect. The study highlighted the critical role of calcium ion flux into the neurons for the genesis of seizure activity to aminophylline, electroshock, and pentylenetetrazole in rats. Furthermore, the critical dose requirement for nimodipine could be explained on the basis of its short half-life and shorter duration of protection against seizures. Therefore, nimodipine may be tried clinically as an anticonvulsant in patients who are on aminophylline because of bronchial asthma or chronic obstructive pulmonary disease, when such patients have concomitant epilepsy or other seizure prone neurological deficits or are scheduled to undergo electroshock therapy.

Pentylenetetrazol kindling changes the ability to induce potentiation phenomena in the hippocampal CA1 region

The present study describes changes of response enhancement of hippocampal field potentials in slices of kindled rats using different methods to induce long-lasting potentiation. Eight-week-old male Wistar rats were subjected to pentylenetetrazol (PTZ) kindling induced by intraperitoneal injection of 45 mg/kg once every 48 h until the occurrence of seizure stages 4-5. Eight to 12 days after the last kindling session, transverse hippocampus slices were prepared and maintained in an artificial medium. Evoked-field potentials were recorded in the CA1 region upon stimulation of the Schaffer collaterals. Potentiation was induced: 1. By moderate tetanic stimulation of the Schaffer collaterals, 2. by changing the perfusion medium to 0-magnesium for 30 min, and 3. by changing the medium to 4 mM Ca2+ for 7 min. In slices from kindled rats, long-term potentiation (LTP) after tetanic stimulation and increase of the evoked potential by 0-magnesium were significantly enhanced in comparison to slices from sham-kindled rats. However, Ca(2+)-induced LTP could not be induced in slices from kindled rats. The results support the assumption that PTZ kindling also induces lasting changes in the responsiveness of hippocampal structures, expressed as an enhanced ability to induce potentiation. An alteration of N-methyl-D-aspartate (NMDA) receptor-coupled processes can be assumed. The inability to induce Ca(2+)-induced LTP points to more complex effects of PTZ, perhaps also on nonNMDA coupled ionic channels.

Co-variation of free amino acids in brain interstitial fluid during pentylenetetrazole-induced convulsive status epilepticus

Effects of pentylenetetrazole (PTZ)-induced convulsive status epilepticus on free amino acids changes in venous blood, CSF and interstitial fluid (IF) of the brain were examined in dogs. A volume of brain IF sufficient for analysis was obtained by chronically implanted tissue cages. The onset of PTZ-induced convulsive seizures seemed mainly related to a marked increase of glutamate, aspartate, taurine, glycine and phosphoserine while, the maintenance and frequency of seizures seemed related to a marked increase of serine and glycine, in combination with a moderate rise of glutamate. L-alpha-Aminoadipate was recovered in moderate amount in epileptic brain IF, while, in controls, this compound was present in minimal amount. The observed complex temporal variation of the amino acidic pattern may play a role in PTZ-induced seizures and, possibly, in pharmacological kindling and brain structural alterations induced by PTZ.

A comparative study of aminophylline- and acepifylline-induced seizures and death in the chemoconvulsion model in rats

The convulsive, pro-convulsive and lethal effects of two theophylline-containing bronchodilating agents, aminophylline and acepifylline, have been evaluated in rats. Aminophylline (theophylline ethylenediamine) caused seizures and death in a dose-dependent manner; an intraperitoneal dose of 250 mg kg-1 caused seizures and death in all rats. Intraperitoneal doses of acepifylline (theophylline ethanoate of piperazine) up to 1000 mg kg-1, however, did not cause seizure or death. Further, pre-treatment of the rats by intraperitoneal administration of a subconvulsive dose (100 mg kg-1) of aminophylline caused a significant decrease in CD50 and LD50 values for pentylenetetrazole and a significant increase in the number of positive responders (i.e. rats with a pentylenetetrazole-induced seizure score of 3 or more on a seizure scale ranging from 0 to 6) and death rate compared with those obtained for rats pre-treated with an equivalent intraperitoneal dose (140 mg kg-1) of acepifylline ('equivalent dose' referred to here denotes the theophylline content of the two preparations). The study has established the neurosafety profile of acepifylline and documents a safer alternative to aminophylline for use in asthmatics suffering from concomitant epilepsy or other seizure-prone neurological defects.

Examination of persistent effects of repeated administration of pentylenetetrazol on rat hippocampal CA1: evidence from in vitro study on hippocampal slices

The early and long-lasting effects of pentylenetetrazol-kindling on hippocampal CA1 synaptic transmission were investigated. Experiments were carried out in the hippocampal slices from control and kindled rats at two post-kindling periods, i.e. 48-144 h (early phase) and 30-33 days (long-lasting phase). Field potentials, i.e. population excitatory postsynaptic potential (pEPSP) and population spike (PS) were recorded at the stratum pyramidale following stimulation of the stratum radiatum. Kindling-induced changes in synaptic transmission were assessed by stimulus-response functions and paired-pulse responses. The results showed that 48-144 h after kindling, the PS amplitude in the CA1 of kindled slices enhanced, and a second PS appeared compared to control slices. But at 30-33 days after kindling, the pEPSP slope in the CA1 of kindled slices enhanced without any change in the PS compared with those in the control slices. Evaluation of paired-pulse responses showed a significant reduction in paired-pulse inhibition for PS 48-144 h after kindling and a significant increase in paired-pulse inhibition for pEPSP 30-33 days after kindling. Our results suggest that pentylenetetrazol-kindling is accompanied by enhanced excitability and a reduction of paired-pulse inhibition in hippocampal CA1. The increased paired-pulse inhibition one month after kindling, may be interpreted as an adaptive process to cope with subsequent seizures.

Regional excitatory and inhibitory amino acid concentrations in pentylenetetrazol kindling and kindled rat brain

We determined regional concentrations of excitatory and inhibitory amino acids in pentylenetetrazol (PTZ) kindling and kindled rat brains in order to investigate the mechanisms responsible for the PTZ kindling process and kindled state. Compared with control rats, PTZ kindling rats had significantly higher concentrations of aspartate in the striatum and the temporal cortex 24 h after the 14th injection of PTZ. Glutamate and GABA concentrations were also significantly higher in the brainstem of PTZ kindling rats 24 h after the 14th injection of PTZ. These findings suggest that the striatum and temporal cortex may participate in a pathway for propagation of the PTZ kindling process, and that the brainstem may be a primary site of PTZ kindling epileptogenesis or a part of the pathways for propagation. On the other hand, the concentrations of amino acids in PTZ kindled rats and controls did not differ 4 weeks after the 14th injection. This suggests that the alterations we detected in amino acid metabolism are not related to retention of the PTZ kindled state, and that some other mechanism for it must exist.

NMDA receptor dependence of kindling and mossy fiber sprouting: evidence that the NMDA receptor regulates patterning of hippocampal circuits in the adult brain

The NMDA receptor plays an important role in patterning neural connectivity in the developing brain. In the adult brain, repeated kindling stimulation of limbic pathways increases the NMDA-dependent component of synaptic transmission in granule cells of the dentate gyrus (DG) and also induces sprouting of the mossy fiber axons of granule cells that reorganizes synaptic connections in the DG. Because the NMDA antagonist MK801 impedes the progression of kindling, it was of interest to determine whether MK801 also modified mossy fiber sprouting. Low doses of MK801, which had no antiseizure effect, impaired the progression of kindling and development of mossy fiber sprouting during the initial and also more advanced stages of kindling. These observations demonstrate that the NMDA receptor is a component of a molecular pathway that influences the progression of kindling and mossy fiber sprouting and suggest that NMDA-dependent gene expression may play a role in the development of long-term structural and functional alterations induced by seizures in hippocampal circuitry. The NMDA receptor appears to play a continuing role in modifying the organization and patterns of connectivity in hippocampal circuits of the adult brain.

Repeated administration of pentylenetetrazol alters susceptibility of rat hippocampus to primed-burst stimulation: evidence from in vitro study on CA1 of hippocampal slices

The effectiveness of theta pattern primed-bursts (PBs) on development of primed-burst (PB) potentiation was investigated in hippocampal CA1 of pentylenetetrazol-kindled rats. Experiments were carried out in the hippocampal slices from control and kindled rats at two post-kindling periods, i.e., 48-144 h (early phase) and 30-33 days (long-lasting phase). Field potentials (population excitatory post-synaptic potential, pEPSP) were recorded at stratum radiatum following stimulation of the stratum fibers. theta pattern primed-bursts were delivered to stratum radiatum and PB potentiation was assessed. The results showed that 48-144 h after kindling, PB potentiation in CA1 of kindled slices is significantly greater than control slices. In contrast, 30, 33 days after kindling PB potentiation was not observed and the pEPSP slope was depressed after PBs delivery, which lasted at least 60 min. Our results suggest that shortly after kindling, PB potentiation can be more readily induced while one month later, it is more difficult ot elicit. These findings may help to explain the behavioral deficits seen with the kindling model of epilepsy.

Potentiation effects in the dentate gyrus of pentylenetetrazol-kindled rats

The study examines changes in the function of perforant pathway dentate granule cell synapses after pentylenetetrazol (PTZ) kindling. Field potentials evoked in the dentate area by test stimuli to the perforant pathway were recorded in freely moving rats at different times after injection of PTZ. In fully kindled animals, but not in sham-kindled controls, subconvulsive test doses of PTZ induced long-lasting potentiation of the population spike. Also, potentiation was not induced in naive controls injected with equieffective doses of the convulsant. The slope function of the field EPSP was depressed 90-120 min after PTZ administration, in both kindled and control animals, indicating that this was an effect of acute-injected PTZ. Later on, only in kindled animals that showed seizure stages 4 or 5 did it increase in parallel with the population spike potentiation. Finally, when compared to controls the kindled animals showed a greater pop spike potentiation induced by moderate tetanization of the perforant pathway. The model offers the possibility of differentiating between acute effects of the convulsant drug and kindling-related changes in neuronal plasticity.

Nuclear factor-kappa B in rat brain: enhanced DNA-binding activity following convulsant-induced seizures

The DNA-binding protein nuclear factor-kappa B (NF-kappa B) is a pleiotropic transcription factor which regulates the transcription of specific target genes such as cytokines. The existence of NF-kappa B has not been reported in brain tissue. This is the first report demonstrating the expression of NF-kappa B in the rat brain. After pentylene tetrazole (s.c.)-induced clonic-tonic seizures at an LD50 dose of 85 mg/kg, we have shown a gradual increase in NF-kappa B expression reaching a maximum at 24 h, a decrease at 48 h and again increased at 96 and 120 h. A similar time-dependent pattern was observed for the NF-kappa B subunit p50 expression. The NF-kappa B subunit p65 was not expressed at all. These data suggest a possible underlying mechanism of signal transduction and transcriptional regulation of late-response genes after perturbations in the CNS milieu.

Convulsions induced by methyl beta-carboline-3-carboxylate in mice: effects of preceding saline injections

The convulsant effects of a high (5 mg/kg intraperitoneally, i.p.) dose of benzodiazepine (BZD) receptor ligand methyl beta-carboline-3-carboxylate (beta-CCM), whether or not preceded by administration of two lower doses of beta-CCM (0.5 and 1 mg/kg i.p.) or of saline were studied in nine inbred mouse strains. In five of the strains (A/J, BALB/cBy, C3H/HeJ, CBA/H, and DBA/2J), neither saline nor preceding injections of beta-CCM had any effect on subsequent reactivity to the subsequent convulsant dose. In the other 4 strains, such injections induced either tolerance (CPB-K, NZB), or sensitization (C57BL/6J, XLII), whatever the compound subsequently administered (beta-CCM or saline). In these strains, the data rule out any tolerance or sensitization effect due to beta-CCM, but suggest that such effects could be due to injection itself.