Comparative fos immunoreactivity in the brain after forebrain, brainstem, or combined seizures induced by electroshock, pentylenetetrazol, focally induced and audiogenic seizures in rats

To help discern sites of focal activation during seizures of different phenotype, the numbers of Fos immunoreactive (FI) neurons in specific brain regions were analyzed following "brainstem-evoked," "forebrain-evoked" and forebrain/brainstem combination seizures induced by a variety of methods. First, pentylenetetrazol (PTZ, 50 mg/kg) induced forebrain-type seizures in some rats, or forebrain seizures that progressed to tonic/clonic brainstem-type seizures in other rats. Second, minimal electroshock induced forebrain seizures whereas maximal electroshock (MES) induced tonic brainstem-type seizures in rats. Third, forebrain seizures were induced in genetically epilepsy-prone rats (GEPRs) by microinfusion of bicuculline into the area tempestas (AT), while brainstem seizures in GEPRs were induced by audiogenic stimulation. A final set was included in which AT bicuculline-induced forebrain seizures in GEPRs were transiently interrupted by audiogenic seizures (AGS) in the same animals. These animals exhibited a sequence combination of forebrain clonic seizure, brainstem tonic seizure and back to forebrain clonic seizures. Irrespective of the methods of induction, clonic forebrain- and tonic/clonic brainstem-type seizures were associated with considerable Fos immunoreactivity in several forebrain structures. Tonic/clonic brainstem seizures, irrespective of the methods of induction, were also associated with FI in consistent brainstem regions. Thus, based on Fos numerical densities (FND, numbers of Fos-stained profiles), forebrain structures appear to be highly activated during both forebrain and brainstem seizures; however, facial and forelimb clonus characteristic of forebrain seizures are not observable during a brainstem seizure. This observation suggests that forebrain-seizure behaviors may be behaviorally masked during the more severe tonic brainstem seizures induced either by MES, PTZ or AGS in GEPRs. This suggestion was corroborated using the sequential seizure paradigm. Similar to findings using MES and PTZ, forebrain regions activated by AT bicuculline were similar to those activated by AGS in the GEPR. However, in the combination seizure group, those areas that showed increased FND in the forebrain showed even greater FND in the combination trial. Likewise, those areas of the brainstem showing FI in the AGS model, showed an even greater effect in the combination paradigm. Finally, the medial amygdala, ventral hypothalamus and cortices of the inferior colliculi showed markedly increased FND that appeared dependent upon activation of both forebrain and brainstem seizure activity in the same animal. These findings suggest these latter areas may be transitional areas between forebrain and brainstem seizure interactions. Collectively, these data illustrate a generally consistent pattern of forebrain Fos staining associated with forebrain-type seizures and a consistent pattern of brainstem Fos staining associated with brainstem-type seizures. Additionally, these data are consistent with a notion that separate seizure circuitries in the forebrain and brainstem mutually interact to facilitate one another, possibly through involvement of specific "transition mediating" nuclei.

First demonstration of a functional role for central nervous system betaine/{gamma}-aminobutyric acid transporter (mGAT2) based on synergistic anticonvulsant action among inhibitors of mGAT1 and mGAT2

In a recent study, EF1502 [N-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]-3-hydroxy-4-(methylamino)-4,5,6,7-tetrahydrobenzo [d]isoxazol-3-ol], which is an N-substituted analog of the GAT1-selective GABA uptake inhibitor exo-THPO (4-amino-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol), was found to inhibit GABA transport mediated by both GAT1 and GAT2 in human embryonic kidney (HEK) cells expressing the mouse GABA transporters GAT1 to 4 (mGAT1-4). In the present study, EF1502 was found to possess a broad-spectrum anticonvulsant profile in animal models of generalized and partial epilepsy. When EF1502 was tested in combination with the clinically effective GAT1-selective inhibitor tiagabine [(R)-N-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]nipecotic acid] or LU-32-176B [N-[4,4-bis(4-fluorophenyl)-butyl]-3-hydroxy-4-amino-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol], another GAT1-selective N-substituted analog of exo-THPO, a synergistic rather than additive anticonvulsant interaction was observed in the Frings audiogenic seizure-susceptible mouse and the pentylenetetrazol seizure threshold test. In contrast, combination of the two mGAT1-selective inhibitors, tiagabine and LU-32-176B, resulted in only an additive anticonvulsant effect. Importantly, the combination of EF1502 and tiagabine did not result in a greater than additive effect in the rotarod behavioral impairment test. In subsequent in vitro studies conducted in HEK-293 cells expressing the cloned mouse GAT transporters mGAT1 and mGAT2, EF1502 was found to noncompetitively inhibit both mGAT1 and the betaine/GABA transporter mGAT2 (K(i) of 4 and 5 muM, respectively). Furthermore, in a GABA release study conducted in neocortical neurons, EF1502 did not act as a substrate for the GABA carrier. Collectively, these findings support a functional role for mGAT2 in the control of neuronal excitability and suggest a possible utility for mGAT2-selective inhibitors in the treatment of epilepsy.

Alzheimer's disease and Down syndrome rodent models exhibit audiogenic seizures

Amyloid-beta protein precursor (AbetaPP) is overexpressed in Alzheimer's disease (AD), Down syndrome (DS), autism, and fragile X syndrome. Seizures are a common phenotype in all of these neurological disorders, yet the underlying molecular mechanism(s) of seizure induction and propagation remain largely unknown. We demonstrate that AD (Tg2576) and DS (Ts65Dn) mice exhibit audiogenic seizures, which can be attenuated with antagonists to metabotropic glutamate receptor 5 (mGluR5) or by passive immunization with anti-amyloid-beta antibody. Our data strongly implicates AbetaPP or a catabolite in seizure susceptibility and suggests that mGluR5 mediates this response.

Differential dietary ethanol intake and blood ethanol levels in adolescent and adult rats: effects on anxiety-like behavior and seizure thresholds

BACKGROUND

Adult rats exhibit increased anxiety-like behavior after exposure to repeated cycles of chronic ethanol and withdrawal. While adolescent rats have differential responses to both acute and chronic ethanol treatments, the potential differences in the effects of repeated withdrawals in this population have yet to be determined.

METHODS

Male adult and adolescent rats received three 5-day cycles of either a 4.5% or 7% ethanol diet (ED) separated by two 2-day withdrawal periods. Five hours into the final withdrawal, rats were tested for social interaction (SI) deficits (an index of anxiety-like behavior) and then assessed for seizure thresholds (audiogenic and bicuculline-induced). Ethanol intake was monitored throughout, and blood ethanol concentrations (BEC) were obtained from a separate group of rats.

RESULTS

Adolescent rats have reduced SI during the final withdrawal from either ED and exhibit a greater reduction in SI compared to adult rats when exposed to a 7%ED. Audiogenic seizures were not increased during withdrawal from either ED in adult rats, but adolescent rats that received 7%ED displayed increased seizures. The bicuculline seizure thresholds were decreased in both ages exposed to a 7%ED, but only adolescent rats showed this decreased threshold after 4.5%ED. Ethanol intakes and BECs were higher in adolescent rats compared to similarly treated adults. However, ethanol intakes and BECs were comparable between 4.5%ED-treated adolescent and 7%ED-treated adult rats.

CONCLUSIONS

Behavioral results from the 7%ED-treated groups suggested that adolescent rats may be more vulnerable to repeated withdrawals from ethanol than adults; however, differences in ethanol intake and BECs may be at least in part responsible. When ethanol intakes and BECs were similar between 4.5%ED-treated adolescent and 7%ED-treated adult rats, behavioral effects were not different. Importantly, these data illustrated that adolescent rats can exhibit anxiety and reduced seizure thresholds following this repeated withdrawal paradigm.

The intrahippocampal administration of the neurosteroid allopregnanolone blocks the audiogenic seizures induced by nicotine

Allopregnanolone (AlloP), GABA(A) positive modulator, has efficacy as anticonvulsant. In contrast, nicotine and pregnenolone sulfate (PregS) act as potent convulsants. The present study aims to evaluate whether a promnesic dose of PregS and/or an anxiolytic dose of AlloP administered in the hippocampus can affect the audiogenic seizures induced by nicotine administration. Rats were assigned at random to six groups that received two consecutive intrahippocampal (dorsal CA1) injections once a week during three consecutive weeks. First injection: nicotine (4.6 microg, 20 mM) or saline, second injection: PregS (5 ng, 24 microM), AlloP (0.2 microg, 1.26 microM) or saline. After the last injections, locomotor activity and audiogenic seizures were tested. AlloP decreased the horizontal and vertical activity, suggesting sedative effects. Nicotine induced behavioral convulsions and AlloP acted as an anticonvulsant. AlloP reversed the seizures induced by nicotine and decreased the audiogenic convulsions in comparison with the controls. PregS also reversed the nicotine-induced audiogenic seizures in the nicotine group but not in the control group. These results suggest that anticonvulsive effects of AlloP and PregS are mediated by different action mechanisms such as GABA(A) positive modulation, or negative modulatory action on neural nicotinic acetylcholine receptors. Even though several brain structures could be involved, these results highlight the important role played by hippocampal cholinergic and GABAergic activities, as well as neurosteroids, especially AlloP, in preventing convulsive behavior.

Audiogenic seizure susceptibility is induced by termination of continuous infusion of gamma-aminobutyric acid or an N-methyl-D-aspartic acid Antagonist into the inferior colliculus

The inferior colliculus (IC) is strongly implicated in seizure initiation in a genetic form of audiogenic seizures (AGS) and in AGS observed during ethanol withdrawal (ETX). Ethanol is known to block the actions of excitatory amino acids (EAA) and enhance the actions of gamma-aminobutyric acid (GABA) in several brain areas, including the IC. The present study investigated the effects on susceptibility to AGS following withdrawal from continuous blockade of N-methyl-D-aspartic acid (NMDA) receptors or continuous activation of GABA receptors in the IC. This involved infusion of GABA (1 M) or a competitive NMDA antagonist, DL-2-amino-7-phosphonoheptanoic acid (AP7, 1 mM), at 0.25 microl/h for 7 days using an Alzet osmotic minipump. Following abrupt termination of the infusion, AGS susceptibility began at 30 min. The incidence of AGS was 38.9 and 56.3% following GABA and AP7 withdrawal, respectively. The AGS behaviors observed during withdrawal, which included wild running and bouncing clonus, were very similar to those evoked by acoustic stimuli during ETX. AGS susceptibility lasted for several hours and in 13% of animals persisted for up to 6 months. The current results support diminished GABAergic and elevated glutamatergic function in the IC as the critical mechanisms and sites for AGS initiation. The present study, coupled with previous evidence that chronic ethanol exposure reduced GABA-mediated inhibition and enhanced EAA-mediated excitation, suggests that these amino acid receptor-mediated alterations in the IC are key elements in initiating AGS during ethanol withdrawal.

3D pharmacophore models for 1,2,3,4-tetrahydroisoquinoline derivatives acting as anticonvulsant agents

A 3D pharmacophore model predicting anticonvulsant activity was obtained for a series of 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline derivatives recently disclosed as a new class of noncompetitive AMPA receptor antagonists. The training set included 17 compounds with varying potency against audiogenic seizures in DBA/2 mice. The best statistical hypothesis, generated with the HypoGen module of Catalyst 4.9, consisted of five features: two hydrogen bond acceptors, two hydrophobic features, and one hydrophobic aromatic region, providing a model with a correlation coefficient of 0.919. The obtained model was an efficient tool in the design of some new anticonvulsant agents containing the tetrahydroisoquinoline scaffold. Moreover, in order to explain the different degree of efficacy of the newly designed N-substituted derivatives, excluded volumes were also considered.

Effects of N-methyl-D-aspartate receptor subunit antagonists on regulation of susceptibility to audiogenic seizures in rats

Rats become susceptible to audiogenic seizures (AS) when they are exposed to intense noise during a certain critical period of development (priming). Antagonism of N-methyl-D-aspartate (NMDA) receptor NR2B subunit by injecting an antagonist ifenprodil at priming enhanced the later susceptibility to AS. An weak NR2A antagonist, dextromethorphan, did not show such effects while it significantly suppressed the manifestation of AS in already susceptible post-weaning (primed) rats. These results indicate that NR2B plays an important role in the developmental regulation of the auditory system involved in AS but this subunit has a minor relevance to the manifestation of AS in the later life.

Role of central histaminergic system in lorazepam withdrawal syndrome in rats

Effects of histaminergic agonists and antagonists were investigated on withdrawal signs in lorazepam-dependent rats. Physical dependence was developed by giving lorazepam admixed with the food in the following dose schedule (in mg/kg given daily x days): 10 x 4, 20 x 4, 40 x 4, 80 x 4, and 120 x 7. The parameters observed during the periods of administration of lorazepam and after its withdrawal were spontaneous locomotor activity (SLA), reaction time to pain, foot shock aggression (FSA), and audiogenic seizures. During the withdrawal period, the rats were divided into groups of 10 each. Control-withdrawal group did not receive any drug. The drugs (in mg/kg administered intramuscularly)--L-histidine (50), histamine-N-methyl (2), promethazine (10), pheniramine (10), astemizole (10), and thioperamide (1)--were given separately in other groups daily during the withdrawal period. The withdrawal signs in control group were hyperkinesia, hyperaggression, and audiogenic seizures. L-Histidine, precursor of histamine, and thioperamide, antagonist of H3 receptor, potentiated hyperkinesia, hyperaggression, and audiogenic seizures. Histamine-N-methyl, agonist of H3 receptor, and H1 receptor antagonists, promethazine and pheniramine, blocked all the withdrawal signs. Astemizole, a peripheral antagonist of H1 receptor, could not affect any withdrawal sign. It may be concluded that histamine H1 receptors are facilitatory and H3 receptors are inhibitory for benzodiazepine (BZD) withdrawal syndrome.

Supplementary motor cortex involvement in reading epilepsy revealed by magnetic source imaging

Reading epilepsy (RE) is an idiopathic reflex epilepsy syndrome characterized by perioral myoclonic jerks (PMJs) during reading associated with left-dominant frontotemporal spike-wave discharges (SWDs). To better understand the pathophysiology of this syndrome, we studied a 45-year-old patient using magnetic source imaging (MSI). The patient underwent two whole-head magnetoencephalography (MEG) recordings (Elekta Neuromag Oy) within 2 months while reading aloud. Forty-two SWDs associated with PMJs were recorded and averaged with respect to SWDs peak power. Epileptic discharges were then reconstructed using conventional equivalent current dipoles (ECDs) modeling, distributed sources sLORETA modeling, and beamformer approach. These methods identified two brain sources located in the left supplementary motor cortex (SMC) and the left primary sensorimotor face area (PSMFA). The spatiotemporal pattern of the sources was characterized by a cross-talk between these two brain regions, with an initial source in the left SMC. This MSI investigation suggests that RE-PMJs are associated with reading-induced activation of hyperexcitable neurons in the left SMC, followed by secondary propagation to the left PSMFA producing the myoclonus.

The effects of delta sleep-inducing peptide on incidence and severity in metaphit-induced epilepsy in rats

The effects of delta sleep-inducing peptide (DSIP) on metaphit- (1-(1(3-isothiocyanatophenyl)-cyclohexyl) (piperidine)-) induced audiogenic seizures in adult male Wistar rats were studied. The animals were divided into four experimental groups: 1. saline injected; 2. metaphit administered (10 mg x kg (-1)); 3. metaphit administered plus DSIP injected (dose range 0.1-1 mg x kg (-1)) and 4. DSIP injected (1 mg x kg (-1)). Upon treatment, the rats were exposed to sound stimulation ( 100 +/- 3 dB, 60 s) at hourly intervals and the incidence and severity (running, clonus and tonus) of seizures were analyzed. In most animals, metaphit led to EEG abnormalities and elicited epileptiform activity recorded as spikes, polyspikes and spike-wave complex and increased power spectra. Time-course studies revealed the peak of convulsive activity 7-12 h after the injection in metaphit-treated rats. DSIP acted as an anticonvulsant and the most potent anticonvulsive dose of 1 mg x kg (-1)significantly increased power spectra of deltawaves (2-11 h) in comparison with the saline-control group and decreased the incidence and duration of convulsive response, as well as mean seizure grade of metaphit-induced convulsions. These results suggest that DSIP should be considered as having potential anticonvulsant activity in this animal model.

ANTICONVULSANT, BUT NOT ANTIEPILEPTIC, ACTION OF VALPROATE ON AUDIOGENIC SEIZURES IN METAPHIT?TREATED RATS

1. The blocking effects of valproate (2-propylpentanoic acid), a standard anti-epileptic drug, on metaphit (1-[1-(3-isothiocyanatophenyl)-cyclohexyl]-piperidine)-induced audiogenic seizures as a model of generalized, reflex audiogenic epilepsy in adult Wistar male rats were studied. 2. Rats were stimulated using an electric bell (100 +/- 3 dB, 5-8 kHz, 60 s) 60 min after i.p. metaphit (10 mg/kg) injection and afterwards at hourly intervals. For power spectra and electroencephalograph (EEG) recordings, three gold-plated screws were implanted into the skull. Different doses of valproate (50, 75 and 100 mg/kg) were injected i.p. into rats with fully developed metaphit seizures after the eighth audiogenic testing. 3. In metaphit-treated animals, the EEG appeared as polyspikes, spike-wave complexes and sleep-like patterns, whereas the power spectra were increased compared with the corresponding controls. 4. Valproate reduced the incidence and intensity of convulsions and prolonged the duration of the latency period in a dose-dependent manner 4 h after administration. 5. The ED(50) of valproate in the first hour after injection was 63.19 mg/kg (95% confidence interval 51.37-77.71 mg/kg). 6. None of the doses of valproate applied eliminated the EEG signs of metaphit-provoked epileptiform activity. 7. Taken together, these results suggest that all doses of valproate examined acted to suppresse behavioural but not epileptic EEG spiking activity in metaphit-induced seizures.

Delta-Sleep-Inducing Peptide Potentiates Anticonvulsive Activity of Valproate against Metaphit-Provoked Audiogenic Seizure in Rats

The effect of delta-sleep-inducing peptide (DSIP) on the anticonvulsive activity of a nonprotective valproate (VPA) dose in a metaphit model of generalized, reflex audiogenic seizures in adult Wistar rats was studied. The animals that received metaphit (10 mg/kg) were exposed to audiogenic stimulation (100 +/- 3 dB, 60 s) at hourly intervals. Metaphit-treated rats displaying seizures in 8 previous tests were i.p. injected with VPA (50 mg/kg) or DSIP (1.0 mg/kg) or their combination. Latency to seizure was behaviorally assessed. The EEGs and power spectra were recorded and analyzed. Neurotoxicity was evaluated by the chimney test. DSIP or VPA alone expressed no significant effect on the latency duration, but their combination significantly prolonged latency to seizure during 6 h after injection, while inducing no significant motor impairment. Neither the applied drugs nor their combination abolished metaphit-provoked EEG epileptiform activity. The results show that DSIP potentiated anticonvulsive effects of a nonprotective VPA dose in a metaphit model of audiogenic seizures without influencing its neurotoxicity.

Antiepileptic activity of delta sleep-inducing peptide and its analogue in metaphit-provoked seizures in rats

PROBLEM

Previous studies have shown that humoral, endogenous and somnogenic, delta sleep-inducing peptide (DSIP) has influence on insomnia, pain, adaptation to stress, epilepsy, etc. We investigated the potential of DSIP and its analogue DSIP-12 (a nonapeptide with alanine in position 2 of DSIP molecule substituted by beta-alanine) to antagonize metaphit (1-[1(3-isothiocyanatophenyl)-cyclohexyl]piperidine) induced generalized, reflex audiogenic seizures in adult male Wistar albino rats.

METHODS

The rats divided in four groups received (i.p.): saline; metaphit; metaphit+DSIP; and metaphit+DSIP-12, respectively. Metaphit-treated animals displaying seizure in eight previous tests received DSIP or DSIP-12 and afterwards audiogenic stimuli were applied at hourly intervals for the next 30 h. The animals were exposed to sound stimulation 60 min after metaphit administration and further on at hourly intervals. Incidence and severity of seizures were behaviorally analyzed. Selected EEGs and power spectra were recorded and analyzed.

RESULTS AND CONCLUSIONS

Metaphit led to hypersynchronous epileptiform activity (polyspikes and spike-wave complexes) and increased power spectra 0.5-30 h after the treatment. Severity of metaphit seizures increased with time to reach the peak 7-12 h after injection. DSIP and DSIP-12 significantly (*P<0.05 and **P<0.01) increased in delta and theta frequency bands and decreased the incidence, mean seizure grade and duration of metaphit convulsions. The results suggest that DSIP and DSIP-12 may be considered as potential antiepileptics in the animal model, DSIP-12 being more efficient than DSIP.

Ontogenetic study of metaphit-induced audiogenic seizures in rats

Ontogenetic differences in susceptibility to metaphit (1-(1-(3-isothiocyanatophenyl)cyclohexyl)-piperidine)-induced audiogenic seizures were examined in young, developing (ages: 12, 18, and 25 days) and adult (90 days old) Wistar albino rats. Metaphit was injected in a dose of 10 mg/kg i.p. and animals were subjected to intense audio stimulation (100 +/- 3 dB, 60 s) at hourly intervals after administration. Audiogenic seizures (AGS) were scored according to a four point descriptive rating scale (0-3). AGS were elicited in all age groups; they were induced for 12, 15, 15, and 30 h in 12-, 18-, 25-day-old, and adult rats, respectively. Younger animals reached a peak incidence and severity of seizures before adult rats. Twenty-five-day-old rats showed greatest incidence and severity of seizures, and shortest latency. Twelve-day-old animals had longest latencies. Besides audiogenic seizures, we observed convulsions induced by metaphit only in the form of running episodes, forelimb clonus, clonic convulsions, and rearing. Results suggest that young rats develop metaphit-induced sound seizures more rapidly, but that adults have longer period of seizure susceptibility. Different susceptibility to seizures is probably due to changes in excitatory and inhibitory pathways, while maturation of blood-brain barrier is less probable, since metaphit has a lipophilic nature.

Convulsive seizures induced by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid microinjection into the mesencephalic reticular formation in rats

Effects of microinjections of a single 2 or 10 nmol dose of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) into the unilateral mesencephalic reticular formation (MRF) on behavior and on the electroencephalogram were examined in rats (n=30) over a 15-min period (Exp. 1); subsequent effects of sound stimulation with key jingling applied at 15, 30, and 45 min after the injection were observed (Exp. 2). The microinjections of a 2 nmol dose of AMPA (n=15) induced hyperactivity (15 of 15 rats) and running/circling (10 of 15 rats) in Exp. 1, and hyperactivity (5 of 15 rats) in Exp. 2. Moreover, the microinjections of a 10 nmol dose of AMPA (n=15) induced hyperactivity (15 of 15 rats), running/circling (13 of 15 rats), generalized tonic-clonic seizures (GTCS) (4 of 15 rats), and amygdala kindling-like seizures (AMKS) (8 of 15 rats) in Exp. 1; electroencephalographic seizure discharges were predominantly observed in the MRF during hyperactivity, running/circling and GTCS, while those predominantly observed in the amygdala were during AMKS. In Exp. 2, hyperactivity (15 of 15 rats), running/circling (14 of 15 rats) and GTCS (6 of 15 rats) were elicited by sound stimulation, although AMKS were not. The control group of rats (n=15) which received a single dose of saline microinjection into the unilateral MRF showed no behavioral or electroencephalographic changes in both Exp. 1 and 2. These findings suggest that potentiation of excitatory amino acid neurotransmission induced by AMPA injection into the MRF plays an important role not only in the development of hyperactivity, running/circling, GTCS and AMKS, but also in the development of audiogenic seizures.

CPP and amlodipine alter the decrease in basal acetylcholine and choline release by audiogenic stimulus in hippocampus of ethanol-withdrawn rats in vivo

Effects of N-methyl-D-aspartate (NMDA) receptor and Ca2+ channel antagonists on extracellular acetylcholine and choline release in the hippocampus of ethanol-withdrawn rats were investigated by in vivo microdialysis. Ethanol was administered to Wistar rats in a liquid diet for 28 days. Basal acetylcholine and choline levels significantly increased at the 24th hour of ethanol withdrawal syndrome (EWS). Either an NMDA receptor antagonist (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) or a calcium channel antagonist amlodipine was administered, and 15 min later, an audiogenic stimulus (100 dB, 1 min) was applied to rats. While audiogenic stimulus increased acetylcholine and had no effect on choline release in control rats, it decreased acetylcholine and increased choline release in ethanol-withdrawn rats. CPP (15 mg/kg) and amlodipine (20 mg/kg) reversed the decrement in acetylcholine and increment in choline release in EW rats. Their effects on acetylcholine and choline release were not different from saline in control rats. Therefore, our findings suggest that, (a) because of adaptive changes in EWS, decrease of the acetylcholine release following audiogenic stimulus may play a role in the triggering of seizures, (b) hippocampal glutamatergic pathway may play a role in the audiogenic stimulus induced decrement of acetylcholine release in EWS, (c) inhibition of this pathway by NMDA receptor and calcium channel antagonists may prevent triggering of the seizures.

Interaction of Delta sleep-inducing peptide and valproate on metaphit audiogenic seizure model in rats

Effects of valproate (VPA), a conventional antiepileptic drug and natural delta sleep-inducing peptide (DSIP) on metaphit (1-[1-(3-isothiocyanatophenyl)-cyclohexyl]-piperidine)-induced audiogenic reflex epilepsy were studied. For the purpose of the study, valproate in the doses of 50 or 75 mg/kg and DSIP (1.0 mg/kg) was i.p. injected either alone or in combination to adult Wistar male rats with fully developed metaphit seizures after eight audiogenic testing. The animals were stimulated using an electric bell (100 +/- 3 dB and 5-8 kHz, for 60 s) 60 min after metaphit injection and afterwards at hourly intervals during the experiment. For EEG recording and power spectra analysis, three gold-plated screws were implanted into the scull. In EEGs of metaphit-treated animals polyspikes, spike-wave complexes and sleep-like patterns were recorded, while the power spectra were increased. Combined treatment of metaphit-induced seizures with valproate and DSIP was more effective than drugs alone especially during 4 h after administration. None of the applied dose combinations eliminated the EEG signs of metaphit-provoked epileptiform activity. Taken together, the results of the present study suggest that the combinations of valproate and DSIP should be considered as beneficial polytherapy in metaphit model of epilepsy.

Audiogenic seizure activity following HSV-1 GAD65 sense or antisense injection into inferior colliculus of Long-Evans rat

Herpes virus technology involving manipulation of GAD65 was used to study effects on audiogenic seizures (AGS). Audiogenic seizure behaviors were examined following injections of replication-defective herpes simplex virus (HSV-1) vectors incorporating sense or antisense toward GAD65 along with 10% lac-Z into the central nucleus of inferior colliculus (CNIC) of Long-Evans rats. In seizure-sensitive animals developmentally primed by intense sound exposure, injection of GAD65 in the sense orientation increased wild running latencies and reduced incidence of clonus compared with lac-Z only, unoperated, and vehicle seizure groups. In contrast, infection of CNIC with GAD65 antisense virus resulted in 100% incidence of wild running and clonus behaviors in AGS animals. Unprimed animals not operated continued to show uniform absence of seizure activity. Administration of GAD65 antisense virus into CNIC produced novel wild running and clonus behaviors in some unprimed animals. Staining for β-galactosidase in all vector animals revealed no differences in pattern or numbers of immunoreactive cells at injection sites. Qualitatively, typical small and medium multipolar/stellate and medium fusiform neurons appeared in the CNIC of vector animals. These results demonstrate that HSV-1 vector constructs implanted into the CNIC can predictably influence incidence and severity of AGS and suggest that viral vectors can be useful in studying GABA mechanisms with potential for therapeutic application in epilepsy. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

[Behavioral and electroencephalographic effects of delta sleep inducing peptide and its analogue on metaphit-induced audiogenic seizures in rats]

INTRODUCTION

Delta sleep inducing peptide (DSIP) is well known natural somnogenic peptide that has many other physiological functions. DSIP analogues representing hepta- and octapeptides (also known as long) as well as tetrapeptide (termed short, used in our experiments) were synthesized with a view to evaluate the peptide specificity in sleep. The effects of DSIP and its analogue DSIP1-4 on metaphit 1-[1(3-isothiocyanatophenylciclohexyl)-piperidine] induced audiogenic seizures were evaluated in rats.

METHODS

Male Wistar albino rats were divided into 4 groups: 1. Saline; 2. Metaphit; 3. Metaphit + DSIP, and 4. Metaphit + DSIP1-4. To examine the blocking effects of DSIP and its analogue on fully developed metaphit seizures, the last two groups were injected after the 8th audiogenic testing. Animals were injected with metaphit (10 mg/kg) intraperitoneally (i.p.) and exposed to sound stimulation (100 +/- 3 dB, 60 s) at hourly intervals. The incidence and severity (running, clonus and tonus) of seizures were analyzed. For electroencephalographic (EEG) recordings, three gold-plated electrodes were used. Convulsive behavior was assessed by incidence of motor seizure and by seizure severity grade, determined by descriptive rating scale ranging from 0 to 3: 0--no response, 1--wild running only; 2--wild running followed by clonic seizures of all four limbs with body rollover; 3--wild running progressing to generalized clonic convulsions followed by tonic extension of fore- and hind legs and tail. Sound onset, seizure events, and sound offset, along with the animal's behavior (convulsive or other) were characterized with EEG changes.

RESULTS

In most animals, the administration of metaphit resulted in electroencephalographic abnormalities, elicited epileptiform activity in the form of spikes, polyspikes and spike-wave complexes. Maximum incidence and severity of metaphit convulsions occurred 8 h after the injection (9/12, 75%), then abated gradually and disappeared 30 h later. Both DSIP and DSIP1-4 significantly increased the power spectra of d waves and decreased the incidence of seizures, mean seizure grade and tonic component of metaphit-induced convulsions.

DISCUSSION

Metaphit has been shown to induce audiogenic seizures after systemic and intracerebroventricular administration and to be truly epileptic in small rodents, although about 8 h after metaphit administration, the power spectra increased and was more intense in the period of sound onset and seizure events. Taken together, DSIP makes an optimal ratio between inhibitory and excitatory amino acid neurotransmitters and may represent one of the endogenous control systems of the brain, thus exerting the protective effect against the seizures. The results obtained throughout the present study corroborate and broaden the data on prolonged antiepileptic DSIP effect.

CONCLUSION

The results of the present study strongly suggest that treatment of adult rats with DSIP and its analogue DSIP1-4 should be considered as potential natural antiepileptics.

Myoclonic and tonic seizures elicited by microinjection of cholinergic drugs into the inferior colliculus

The inferior colliculus (IC) is the initiation site in the neuronal network for the epileptic audiogenic seizure (AGS). The present study investigates the effects of alteration of IC cholinergic transmission on the elicitation of epileptic seizures. Unilateral microinjections of carbachol (3 and 6 micrograms/0.2 microliter) into the IC elicited intense locomotor activity, contraversive rotations and myoclonic seizures. This result indicates that the IC is the initiation site for the induction of myoclonic seizures and suggests that these myoclonic seizures may result from activation of m1 muscarinic receptors. Microinjections of the nicotinic-muscarinic antagonist, gallamine (2 and 6 micrograms/0.2 microliter), into the IC induced AGS susceptibility. However, microinjections of muscarinic antagonists, atropine (15 micrograms/0.2 microliter) and scopolamine (12 and 20 micrograms/0.2 microliter), or the nicotinic antagonist, hexamethonium (12 and 20 micrograms/0.2 microliter), into the IC have no effect. Gallamine-induced AGS susceptibility may result from a selective blockade of m2 muscarinic receptors.

[The delta-sleep inducing peptide and its effect on the electroencephalogram and power spectrum density in rats with metaphit-induced epilepsy]

INTRODUCTION

Sleep has many common features with epilepsy (spontaneously, recurring event and EEG hypersynchrony including EEG potentials that look very similar to epileptiform sharp waves) [1]. Monnier et al. [4] reported the presence of a sleep-inducing factor inducing sleep with predominant EEG activity in the 8 band (1-4 Hz), and it was the reason for the term delta sleep-inducing peptide (DSIP). Metaphit was synthesized by Rafferty et al. (1985) [7] and was shown to increase general brain excitability and induce audiogenic seizures in small rodents. The effects of a natural somnogenic nonapeptide DSIP on metaphit-induced audiogenic epilepsy in rats were studied with the aim of shedding more light on answering the question whether DSIP could be included in the list of antiepileptic agents.

MATERIALS AND METHODS

Adult, 2-month-old male Wistar rats (170-200 g) were used. None of the animals screened for audiogenic susceptibility showed seizure activity. Audiogenic stimulation was used for 60 s using an electric bell (100 +/- 3 dB 5-8 kHz). Rats were divided into four groups: 1. Control, saline-injected (n = 6); 2. metaphit administered (10 mg/kg; n = 12); 3. metaphit + DSIP (1 mg/kg), (n = 14) group, DSIP administered after 8th to investigate blocking effect on fully developed metaphit seizure. 4.DSIP alone (1 mg/kg, n = 6).

RESULTS

In control saline-injected animals AGS provoked no convulsive response. Metaphit injection produced after 30 min initial EEG changes in the form of synchronized spikes and fast high-voltage activity that are typical seizure manifestations, power spectra increased and became more intense in the period of sound onset and seizure events. Our results demonstrate that DSIP acted increasing the EEG output in the 8 range and significantly elevated the mean power spectra in all checked experimental points. Besides, DSIP decreased the incidence and duration of convulsive component, as well as mean seizure grade in metaphit-induced seizures.

DISCUSSION

Metaphit induces a generalized, reflex epilepsy thus providing an experimental model of choice for the studies of the mechanism of epilepsy development and blockade of NMDA/PCP receptors. In our previous studies a competitive NMDA antagonist CPP [9] and a noncompetitive antagonist MK-801 [8] were used. Non-competitive, selective NMDA antagonists MK-801, PCP and ketamin expressed a partial agonist motor action (myoclonic jerks, ataxia and tremor of the whole body) in audiogenic epilepsy prone mice. DSIP produced no harmful effects even when overdosed or any effect over "normality" [4, 5]. DSIP has a capacity of suppressing various forms of convulsive activity in different animal species. It was suggested that it exerts an anticonvulsant action by influencing neurotransmitter (dopaminergic, adrenergic, GABA-ergic) and neuromodulator (peptidergic) brain systems [12, 13].

CONCLUSION

Our results, together with the fact that DSIP penetrates through the blood brain barrier after systemic administration and that overdoses of this natural peptide produce no harmful effects, strongly suggest that it could be an important therapeutic agent for the treatment of sleep disturbances. Also, our data demonstrating reduction in incidence, severity and duration of seizure components, suggest that this agent might be a suitable candidate as an antiepileptic drug.

Metrazol thresholds in inbred and non-inbred audiosensitive mice

Mice of the O'Grady strain which were inbred for susceptibility to audiogenic seizures were found to be more sensitive to pentamethylenetetrazol (Metrazol) convulsions than mice of the parent Swiss-Webster strain from which they were originally derived. A dose of 35 mg/kg Metrazol was required to produce a 50% convulsive response (CD50) in O'Grady mice and 50 mg/kg in the control parent strain. No differences in convulsive thresholds to Metrazol were obtained, however, between untreated Swiss-Webster mice and mice of the same strain made audiosuseptible by rubidium chloride intake or magnesium deficiency.

Inhibition of metaphit-induced audiogenic seizures by APV in rats

The influence of APV ((+/-)-2-amino-5-phosphonovaleric acid) on EEG activity and behavior was studied on a model of epilepsy induced by intraperitoneal administration of metaphit (1-(1-(3-isothiocyanatophenyl)-cyclohexyl)-piperidine). Male Wistar rats received an injection of metaphit (10 mg/kg) and were subjected to intense audio stimulation (100+/-3 dB, 60 s) at hourly intervals during the experiment. The seizures were classified according to a four point scale ranging from 0 (no seizure) to 3 (tonic convulsions). In our report we studied the time course which revealed the maximum incidence and severity of seizures 7-12 h after the injection (10 out of 12 rats, with severity of 2.25+/-0.32). APV (0.05, 0.1, 0.2 and 0.3 micromol) was injected intracerebroventricularly at the time of fully developed convulsions. APV inhibited seizures in a dose-dependent manner. The minimum dose, which completely blocked seizures in all animals, was 0.3 micromol, while ED50 were 0.11, 0.10 and 0.07 micromol against running, clonus and tonus, respectively. In contrast to behavioral inhibition of convulsions, metaphit-provoked epileptiform activity was not abolished by APV, and represented a prerequisite for the reappearance of behavioral seizures. It is suggested that APV is rather an anticonvulsant than an antiepileptic agent in this model of epilepsy.

NEOCORTICAL IMPACT ON THE AUDIOGENIC SEIZURE ACTIVITY DEVELOPMENT

Out of genetically determined epilepsy models a special interest draws the model of audiogenic seizures, which does not require whatever additional intervention (e.g. pharmacological or/and electric stimulation), because epileptic responses are elicited by specific sensory stimulation only. Notwithstanding the fact that different formations of the central nervous system are recruited in audiogenic seizure reactions, critical importance for the manifestation of this type epilepsy is attributed to the inferior colliculus and brainstem reticular nuclei. Significance of the diencephalic structures and the thalamic reticular nucleus, in particular for development and/or modulation of audiogenic seizures is ambiguous. Total of eight Krushinsky- Molodkina (KM) strain rats, weighting 250-300 g, served as the subjects of chronic experiments. The neocortex was bilaterally activated by way of administration of 1 µl strychnine (0.1% solutipon) with a microsyringe through a metal capillary prefixed on the cortical surface. Metal electrodes for recording electrical activity were implanted into the neocortex and brainstem reticular formation. Experiments have shown that against strychnine discharges in the neocortex there occurred an increase in the latency of wild runs and the pause between the first and second wild runs in response to a sound stimulus. Proceeding from the above-said, it can be assumed that activation of the neocortex must stipulate intensification of the thalamic reticular nucleus neuronal activity that, in turn, should have a modulating effect on the audiogenically induced seizure reactions.