Potentiation of amygdaloid kindling and metrazol-induced seizures by 6-hydroxydopamine in rats

Spike ripples in striatum correlate with seizure risk in two mouse models

Epilepsy biomarkers from electroencephalogram recordings are routinely used to assess seizure risk and localization. Two widely adopted biomarkers include: (i) interictal spikes, and (ii) high frequency ripple oscillations. The combination of these two biomarkers, ripples co-occurring with spikes (spike ripples), has been proposed as an improved biomarker for the epileptogenic zone and epileptogenicity in humans and rodent models. Whether spike ripples translate to predict seizure risk in rodent seizure models is unknown. Further, recent evidence suggests ictal networks can include deep gray nuclei in humans. Whether pathologic spike ripples and seizures are also observed in the basal ganglia in rodent models has not been explored. We addressed these questions using local field potential recordings from mice with and without striatal seizures after carbachol or 6-hydroxydopamine infusions into the striatum. We found increased spike ripples in the interictal and ictal periods in mice with seizures compared to pre-infusion and post-infusion seizure-free recordings. These data provide evidence of electrographic seizures involving the striatum in mice and support the candidacy of spike ripples as a translational biomarker for seizure risk in mouse models.

Behavioral Effects of Neural Transplantation

Considerable evidence suggests that transplantation of fetal neural tissue ameliorates the behavioral deficits observed in a variety of animal models of CNS disorders. However, it is also becoming increasingly clear that neural transplants do not necessarily produce behavioral recovery, and in some cases have either no beneficial effects, magnify existing behavioral abnormalities, or even produce a unique constellation of deficits. Regardless, studies demonstrating the successful use of neural transplants in reducing or eliminating behavioral deficits in these animal models has led directly to their clinical application in human neurodegenerative disorders such as Parkinson's disease. This review examines the beneficial and deleterious behavioral consequences of neural transplants in different animal models of human diseases, and discusses the possible mechanisms by which neural transplants might produce behavior recovery.

Effects of disulfiram and dopamine beta-hydroxylase knockout on cocaine-induced seizures

The antialcoholism drug disulfiram has shown recent promise as a pharmacotherapy for treating cocaine dependence, probably via inhibition of dopamine beta-hydroxylase (DBH), the enzyme that catalyzes the conversion of dopamine (DA) to norepinephrine (NE). We previously showed that DBH knockout (Dbh -/-) mice, which lack NE, are susceptible to seizures and are hypersensitive to the psychomotor, rewarding, and aversive effects of cocaine, suggesting that disulfiram might exacerbate cocaine-induced seizures (CIS) by inhibiting DBH. To test this, we examined CIS in wild-type and Dbh -/- mice following administration of disulfiram or the selective DBH inhibitor nepicastat. We found that Dbh genotype had no effect on CIS probability or frequency, whereas disulfiram, but not nepicastat, increased the probability of having CIS in both wild-type and Dbh -/- mice. Both disulfiram and nepicastat increased CIS frequency in wild-type but not Dbh -/- mice. There were no genotype or treatment effects on serum cocaine levels, except for an increase in disulfiram-treated Dbh -/- mice at the highest dose of cocaine. These results suggest that disulfiram enhances CIS via two distinct mechanisms: it both increases CIS frequency by inhibiting DBH and increases CIS frequency in a DBH-independent manner.

Enaminones and norepinephrine employ convergent mechanisms to depress excitatory synaptic transmission in the rat nucleus accumbensin vitro

We recently reported that anticonvulsant anilino enaminones depress excitatory postsynaptic currents (EPSCs) in the nucleus accumbens (NAc) indirectly via gamma-aminobutyric acid (GABA) acting on GABA(B) receptors [S.B. Kombian et al. (2005)Br. J. Pharmacol., 145, 945-953]. Norepinephrine (NE) and dopamine (DA), both known to be involved in seizure disorders, also depress EPSCs in this nucleus. The current study explored a possible interaction between enaminones and adrenergic and/or dopaminergic mechanisms that may contribute to their synaptic depression and anticonvulsant effect. Using whole-cell recording in rat forebrain slices containing the NAc, we show that NE-induced, but not DA-induced, EPSC depression occludes E139-induced EPSC depressant effect. UK14,304, a selective alpha(2) receptor agonist, mimicked the synaptic effect of NE and also occluded E139 effects. Phentolamine, a non-selective alpha-adrenergic antagonist that blocked NE-induced EPSC depression, also blocked the E139-induced EPSC depression. Furthermore, yohimbine, an alpha(2)-adrenoceptor antagonist, also blocked the E139-induced EPSC depression, while prazosin, a selective alpha(1)-adrenergic antagonist, and propranolol, a non-selective beta-adrenoceptor antagonist, did not block the E139 effect. Similar to the E139-induced EPSC depression, the NE-induced EPSC depression was also blocked by the GABA(B) receptor antagonist, CGP55845. By contrast, however, neither SCH23390 nor sulpiride, D1-like and D2-like DA receptor antagonists, respectively, blocked the E139-induced synaptic depression. These results suggest that NE and E139, but not DA, employ a similar mechanism to depress EPSCs in the NAc, and support the hypothesis that E139, like NE, may act on alpha(2)-adrenoceptors to cause the release of GABA, which then mediates synaptic depression via GABA(B) receptors.

Exacerbation of Seizures in Medial Temporal Lobe Epilepsy Due to an ?1-Adrenergic Antagonist

PURPOSE

We describe the first reported case of a proconvulsant effect of an alpha(1)-adrenergic antagonist in humans.

METHODS

A patient with medial temporal lobe seizures (MTLE) had increased seizure frequency after treatment with tamsulosin, an alpha(1)-adrenergic antagonist.

RESULTS

Experimental evidence suggests that noradrenaline, which has inhibitory effects on the excitatory synaptic response, can act as a powerful anticonvulsant. Mostly, alpha(2)-adrenoreceptors, but also alpha(1)-adrenoreceptors, have been implicated in this effect by different experimental models. Clinical reports of a proconvulsant or anticonvulsant effect of drugs that act through the adrenergic pathway are scarce.

CONCLUSIONS

This is the first report of a proconvulsant effect by an alpha(1)-adrenergic antagonist in humans and suggests that alpha(1)-adrenoreceptors may be involved in modulating noradrenergic activity in the limbic region.

Transcortical cooling inhibits hippocampal-kindled seizures in the rat

PURPOSE

When epileptogenic regions encroach on eloquent brain, surgery may incur unacceptable deficits. Reversible cooling may control seizures while preserving function. We describe the effects of cooling kindled seizures in awake, freely moving rats.

METHODS

We kindled rats after placement of a bipolar electrode and a copper cooling coil in dorsal hippocampus. Fully kindled animals (three consecutive grade 5 seizures) were cooled to one of two target temperatures (24 degrees or 27 degrees C) for 3 min preceding a kindling stimulation and 2 minutes after. We compared seizure score (0-5) and afterdischarge duration (ADD) with and without cooling. Target temperatures were confirmed in identical animals by using a needle thermocouple advanced to the kindling target while circulating coolant.

RESULTS

Circulation of 16 degrees C and 8 degrees C coolant reliably achieved transcortical cooling of the hippocampal target to 27.0 +/- 1.2 degrees C and 23.8 +/- 2.0 degrees C, respectively, by 180 s. Cooling with 16 degrees C coolant (n = 5) significantly reduced seizure scores from 5 to 2.57 +/- 1.56, and ADD from 142 +/- 94.5 s to 45.7 +/- 20.5 s. Cooling with 8 degrees C coolant (n = 5) reduced seizure scores from 5 to 2.0 +/- 0.42, and ADD from 132.3 +/- 29.6 s to 55.5 +/- 25.9 s. In 33.3% of all cooled stimulations, grade 0 seizures resulted; grade 5 seizures recurred during subsequent stimulations when cooling was withheld.

CONCLUSIONS

Fully kindled, tonic-clonic seizures can be suppressed or aborted with periictal cooling of the kindling target. Anticonvulsant activity occurred at temperatures well above those known to result in tissue injury or inhibition of normal neurologic function. These findings have important implications for the potential use of implantable cooling devices in humans with refractory epilepsies in or near eloquent cortex or dominant hippocampal formations.

Genetic deletion of the norepinephrine transporter decreases vulnerability to seizures

Norepinephrine (NE) has been reported to modulate neuronal excitability and act as endogenous anticonvulsant. In the present study we used NE transporter knock-out mice (NET-KO), which are characterized by high levels of extracellular NE, to investigate the role of endogenous NE in seizure susceptibility. Seizure thresholds for cocaine (i.p.), pentylenetetrazol (i.v.) and kainic acid (i.v.) were compared in NET-KO, heterozygous (NET-HT) and wild type (NET-WT) female mice. The dose-response curve for cocaine-induced convulsions was significantly shifted to the right in NET-KO mice, indicating higher seizure thresholds. The threshold doses of pentylenetetrazol that induced clonic and tonic seizures were also significantly higher in NET-KO when compared to NET-WT mice. Similarly, NET-KO mice displayed higher resistance to convulsions engendered by kainic acid. For all drugs tested, the response of NET-HT mice was always intermediate. These data provide further support for a role of endogenous NE in the control of seizure susceptibility.

Amygdala kindling in Proechimys guyannensis rat: an animal model of resistance to epilepsy

PURPOSE

This study examined the effect of amygdala kindling development in Proechimys guayannensis rat, a common rodent of the Amazon basin.

METHODS

Adult male P. guayannensis animals (n = 43) and adult male Wistar rats (n = 14) were submitted to electrical amygdala kindling.

RESULTS

From 43 Proechimys rats submitted to the kindling process, only three animals reached stage 5 of kindling. During the kindling development (stages 4-5), these animals had behavioral alterations different from those observed in Wistar rats. A longer time spent in stages 1-3 and 5 and longer afterdischarge duration in stages 1-4 was observed in the Proechimys group compared with the Wistar group. The number of wet-dog shakes also was reduced in the Proechimys group during the kindling process.

CONCLUSIONS

These findings suggest natural endogenous inhibitory mechanisms in this animal species.

The role of catecholamines in seizure susceptibility: new results using genetically engineered mice

The catecholamines norepinephrine and dopamine are abundant in the CNS, and modulate neuronal excitability via G-protein-coupled receptor signaling. This review covers the history of research concerning the role of catecholamines in modulating seizure susceptibility in animal models of epilepsy. Traditionally, most work on this topic has been anatomical, pharmacological, or physiological in nature. However, the recent advances in transgenic and knockout mouse technology provide new tools to study catecholamines and their roles in seizure susceptibility. New results from genetically engineered mice with altered catecholamine signaling, as well as possibilities for future experiments, are discussed.

Genetic comparison of seizure control by norepinephrine and neuropeptide Y

Epilepsy is a disease of neuronal hyperexcitability, and pharmacological and genetic studies have identified norepinephrine (NE) and neuropeptide Y (NPY) as important endogenous regulators of neuronal excitability. Both transmitters signal through G-protein-coupled receptors, are expressed either together or separately, and are abundant in brain regions implicated in seizure generation. NPY knock-out (NPY KO) and dopamine beta-hydroxylase knock-out (DBH KO) mice that lack NE are susceptible to seizures, and agonists of NE and NPY receptors protect against seizures. To examine the relative contributions of NE and NPY to neuronal excitability, we tested Dbh;Npy double knock-out (DKO) mice for seizure sensitivity. In general, DBH KO mice were much more seizure-sensitive than NPY KO mice and had normal NPY expression, demonstrating that an NPY deficiency did not contribute to the DBH KO seizure phenotype. DKO mice were only slightly more sensitive than DBH KO mice to seizures induced by kainic acid, pentylenetetrazole, or flurothyl, although DKO mice were uniquely prone to handling-induced seizures. NPY contributed to the seizure phenotype of DKO mice at high doses of convulsant agents and advanced stages of seizures. These data suggest that NE is a more potent endogenous anticonvulsant than NPY, and that NPY has the greatest contribution under conditions of extreme neuronal excitability.

Prenatal morphine exposure induces age- and sex-dependent changes in seizure susceptibility

1. Prenatal exposure to morphine induces long-term alterations in seizure susceptibility, which are age-, sex-, and seizure model-specific. 2. Adult male and female rats exposed prenatally to morphine show decreased susceptibility to GABA-regulated seizures. 3. Prenatally morphine-exposed, adult male rats are more sensitive to excitatory amino acid receptor-mediated seizures than control males, control females, or morphine-exposed females.

Acute and chronic administration of clozapine produces greater proconvulsant actions than haloperidol on focal hippocampal seizures in freely moving rats

In this study, we assessed the effects of the acute (a single injection) and repeated (once daily injections for 21 days) administration of the atypical antipsychotic drug clozapine (1.5, 5, or 15 mg/kg i.p.) and the typical antipsychotic drug haloperidol (0.15, 0.5, and 1.5 mg/kg, i.p.) on hippocampal partial seizures generated by low-frequency electrical stimulation in male Wistar rats. The seizure threshold and severity were determined by measuring the pulse number threshold (PNT) and the primary afterdischarge duration (ADD), respectively. A single injection of either 5 or 15 mg/kg of clozapine significantly decreased the PNT and significantly increased the primary ADD, indicating a proconvulsant action. The repeated administration of clozapine (1.5, 5, or 15 mg/kg, i.p.) produced dose-dependent, proconvulsant effects by significantly decreasing the PNT and by significantly increasing the primary ADD. In contrast to clozapine, the acute administration of haloperidol did not significantly alter the PNT or the primary ADD. The repeated administration of haloperidol (0.5 and 1.5 mg/kg, i.p.), unlike clozapine, significantly decreased the primary ADD, but did not alter the PNT. Overall, clozapine produces a greater proconvulsant action than haloperidol in an animal model of hippocampal seizures.

Fos in locus coeruleus neurons following audiogenic seizure in the genetically epilepsy-prone rat: comparison to electroshock and pentylenetetrazol seizure models

Seizures in genetically epilepsy-prone rats (GEPRs) may result from hypoactivity of locus coeruleus (LC) neurons during seizures. This study examined Fos-like-immunoreactivity (FLI) in the LC following audiogenic seizures in two strains of GEPRs (GEPR-9s and -3s), and following pentylenetetrazol (PTZ) or maximal electroshock seizures (MES) in normal rats. After tonic seizure, GEPR-9s showed an identical LC-FLI response to that of normal rats following tonic seizures induced by either PTZ or MES. GEPR-3s, having clonic seizures, had less FLI in the LC. Therefore, stimulus-transcription coupling in the GEPR LC is apparently normo-typic in its FLI response to seizure and thus is not likely the root cause of NE abnormalities in this seizure model.

Alterations in mRNA expression of systems that regulate neurotransmitter synaptic content in seizure-naive genetically epilepsy-prone rat (GEPR): transporter proteins and rate-limiting synthesizing enzymes for norepinephrine, dopamine and serotonin

Two models of genetically epilepsy-prone rat (GEPR) exist, the GEPR-3 and GEPR-9, GEPR-3 and GEPR-9 share a deficiency in presynaptic norepinephrine (NE) and serotonin (5HT) content in specific regions of the central nervous system (CNS). The presynaptic content of dopamine (DA) does not appear to be altered in either adult GEPR strain compared to Sprague-Dawley (SD) rats, the strain from which the GEPR was derived. Presynaptic content of monoamine neurotransmitters, such as NE, 5HT and DA, are maintained by several regulatory proteins which include: synthesis, re-uptake, release, degradation and vesicular transport. To further characterize the monoamine deficiency observed in the GEPR, the mRNA level of the rate limiting enzymes for the synthesis of NE, 5HT and DA and each of the neurotransporter proteins were measured in seizure-naive GEPR-3, GEPR-9 and SD rats. In the locus coeruleus (LC), the major noradrenergic locus, tyrosine hydroxylase (TH) mRNA level was significantly reduced only in GEPR-9 animals compared to SD rats and GEPR-3, while NE transporter (NET) mRNA was significantly elevated in GEPR-3 compared to SD rats and GEPR-9. TH and DA transporter (DAT) mRNA was measured in the dopaminergic neurons of the substantia nigra pars compacta (SNpc), ventral tegmental area (VTA) and zona incerta (ZI), DAT mRNA level was significantly reduced in all dopaminergic neurons in the GEPR-3 compared to SD rats and GEPR-9, while TH mRNA level was significantly elevated in the SNpc/VTA equally in GEPR-3 and GEPR-9 compared to SD rats. In the ZI, TH mRNA level was significantly reduced in GEPR-3 compared to SD rats and GEPR-9. In the dorsal raphe (DR), a major serotonergic locus, tryptophan hydroxylase (TRH) mRNA level was not significantly different from SD in either strain of GEPR; however, 5HT transporter (SERT) mRNA level was significantly reduced in GEPR-9 in the dorsal and lateral regions of the DR compared in SD rats and GEPR-3. These data indicate that two of the regulatory systems that maintain NE, 5HT and DA content are altered in a differential manner in seizure-naive GEPR-3 compared to seizure-naive GEPR-9, with GEPR-3 showing more alterations in dopaminergic neurons. It is uncertain at the present time how these alterations in mRNA level relate to the enhanced seizure susceptibility of these animals. It was apparent that a straightforward correlation between neurotransmitter loss to transcriptional changes in synthesizing enzymes mRNA or to re-uptake protein mRNA was not observed in noradrenergic and serotonergic neurons. Therefore, the decrease in presynaptic NE and 5HT tissue content in these animals may be due to posttranscriptional modification. In contrast, presynaptic DA tissue content which was unaltered in both strains of GEPR, shows an alteration in TH and DAT mRNA level compared to SD rats in all dopaminergic neurons examined. This indicates a possible involvement of DA in regulating the seizure susceptibility of these animals.

The role of dopamine in epilepsy

The clinical benefits of dopamine agonists in the management of epilepsy can be traced back over a century, whilst the introduction of neuroleptics into psychiatry practice 40 years ago witnessed the emergence of fits as a side effect of dopamine receptor blockade. Epidemiologists noticed a reciprocal relationship between the supposed dopaminergic overactivity syndrome of schizophrenia and epilepsy, which came to be regarded as a dopamine underactivity condition. Early pharmacological studies of epilepsy employed nonselective drugs, that often did not permit dopamine's antiepileptic action to be clearly dissociated from that of other monoamines. Likewise, the biochemical search for genetic abnormalities in brain dopamine function, as predeterminants of spontaneous epilepsy, proved largely inconclusive. The discovery of multiple dopamine receptor families (D1 and D2), mediating opposing influences on neuronal excitability, heralded a new era of dopamine-epilepsy research. The traditional anticonvulsant action of dopamine was attributed to D2 receptor stimulation in the forebrain, while the advent of selective D1 agonists with proconvulsant properties revealed for the first time that dopamine could also lower the seizure threshold from the midbrain. Whilst there is no immediate prospect of developing D2 agonists or D1 antagonists as clinically useful antiepileptics, there is a growing awareness that seizures might be precipitated as a consequence of treating other neurological disorders with D2 antagonists (schizophrenia) or D1 agonists (parkinsonism).

Facilitatory effect of olfactory bulbectomy on 2-deoxyglucose uptake in rat amygdala slices

The aim of the present study was to determine whether the 2-deoxyglucose uptake of amygdala slices was affected by olfactory bulbectomy. At 7, 14 and 21 days post-lesion, bilateral olfactory bulbectomized rats exhibited a significant increase of 2-deoxyglucose uptake in amygdala slices, but not in the cerebral cortex. In addition, unilateral olfactory bulbectomized rats showed a high uptake of 2-deoxyglucose uptake in the ipsilateral amygdala, but not in the contralateral amygdala. These results suggest that the enhancement of 2-deoxyglucose uptake is related to the hyperexcitability of amygdala neurons following bulbectomy, and that this enhancement may be responsible for the behavioral changes in olfactory bulbectomized rats.

A crystal-state, solution and theoretical study of the preferred conformation of linear C alpha, alpha-diphenylglycine derivatives and dipeptides with potential anticonvulsant activity

Several linear molecules containing the C alpha, alpha-diphenylglycine residue were prepared as potential anticonvulsants. The conformational preferences of the C alpha, alpha-diphenylglycine residue were assessed in these synthetic derivatives and dipeptides by X-ray diffraction, FTIR absorption and 1H NMR techniques, and by conformational energy computations. Five (out of six) derivatives adopt the fully extended C5 conformation in the crystal state. This intramolecularly H-bonded form is largely populated in chloroform solution in all the derivatives investigated. Conformational energy computations in vacuo support the view that the intramolecularly H-bonded C7-ring form is the most stable structure for these compounds. Only one linear derivative exhibits a (modest) anticonvulsant activity.

Electrical kindling of rats treated discontinuously or continuously with haloperidol

Intermittent as opposed to continuous treatment of rats with haloperidol resulted in a long-lasting potentiation of oral activity. To examine if this behavioural sensitization to discontinuous neuroleptic treatment facilitates seizure development in electrical kindling, rats treated either intermittently or continuously with haloperidol for 15 weeks were kindled in the nucleus amygdala. Development of kindled seizures was significantly faster in the intermittently treated group (P < 0.01) than in controls or continuously treated rats. Furthermore, discontinuously treated animals displayed electroencephalographic afterdischarges in the substantia nigra from the beginning of treatment. The findings of cross-sensitivity between electrical amygdala kindling and pharmacological sensitization and of early appearance of epileptiform nigral activity have implications for the pathogenesis of both conditions. We suggest that depressed gamma-aminobutyric acid activity in substantia nigra could be a common mechanism.

The role of cholinergic neurons in stress-induced increase of interictal discharges in hippocampal-kindled rats

This study aims to clarify the role of cholinergic neurons in the occurrence of epileptic seizures when emotional stress is loaded. The effects of stress and drugs on hippocampal interictal discharges were compared among groups of fully kindled male Wistar rats intraperitoneally given atropine, physostigmine and saline with and without immobilization, or pituitary-adrenocortical hormones without immobilization. Hippocampal interictal discharges increased during immobilization, because hippocampal cholinergic neurons were activated by emotional stress. Pituitary-adrenocortical hormones had no effects on the discharges.

Effect of amygdaloid kindling on [3H]dopamine and [14C]acetylcholine release from rat prefrontal cortex and striatal slices

The involvement of the dopaminergic (DA) systems in the control of limbic kindled seizures is ill defined. The effects of kindling on DA activity may have been overlooked in the past, because of its subtle unilateral occurrence and/or the variance of the endogenous imbalance of DA activity in normal animals. In the present study rats were screened for their endogenous DA imbalance using amphetamine-induced rotational behaviour. Electrical or sham kindling was applied in the hemisphere with the higher endogenous DA activity. Sections of the bilateral prefrontal cortex and dorsal and ventral striatum were dissected either 2 hours or 21 days after the final seizure and the electrically stimulated release of [3H]DA and [14C]acetylcholine (ACh) determined. Release was also measured in the presence of quinpirole or sulpiride to assess the activity of pre- and postsynaptic DA D2-receptors. Long-term effects of kindling consisted of facilitation of ACh release in the ventral striatum contralateral to the kindled amygdala and bilateral depression of DA release in the prefrontal cortex. Kindling therefore produced area specific changes in neurotransmitter systems giving rise to increased pro-convulsive cholinergic activity in the ventral striatum and decreased anti-convulsive dopaminergic activity in the prefrontal cortex.

Bicuculline-induced neocortical epileptiform foci and the effects of 6-hydroxydopamine in developing rats

Catecholamines (dopamine and norepinephrine) are considered to be predominantly inhibitory neurotransmitters in the brain and their depletion produced by 6-hydroxydopamine may result in proconvulsant effects. In our experiments on rats aged 5, 7, 9, 12, 15, 18, 25 and 90 days under urethane anesthesia we demonstrated the development of neocortical epileptic focus evoked by topical application of bicuculline methiodide. In experimental groups aged 7, 12, 18, 25 and 90 days a chronic depletion of catecholamines was induced using pretreatment with 6-hydroxydopamine early postnatally. An epileptogenic focus was induced in all age groups; duration of a single discharge decreased with age in both control and experimental animals. The spread of activity from the primary focus to contralateral frontal cortex via callosal connections was as rapid as in controls. However, the transfer of discharge to occipital regions was delayed and the number of discharges decreased in experimental rats. Our study demonstrated a substantial role of catecholamines for synchronization of focal discharges in neocortex and a promoting role of catecholamines in association pathways within neocortex.

Enhancement of NMDA receptor-mediated synaptic potential evoked in rat medial-amygdala neuron following olfactory bulbectomy

Synaptic potentials evoked in the medial amygdala (m-AMG) neurons were studied in in vitro slice preparations obtained from normal and olfactory bulbectomized rats. Local stimulation induced a sequence of responses: a fast EPSP, a fast IPSP and a slow EPSP. The fast EPSP was suppressed by kynurenic acid (KYN) at a concentration of 1 mM but not by 3-[(+-)-2-carboxypiperazin-4-yl-]-propyl-1-phosphonic acid (CPP) at concentrations up to 20 microM. The slow EPSP was reversibly blocked by both KYN (1 mM) and CPP (5-10 microM). Addition of bicuculline methiodide (50 microM) to the bath suppressed the fast IPSP and augmented both the fast and slow IPSPs leading to burst discharges. In a small population of m-AMG neurons, the slow EPSP was followed by a slow IPSP. The slow IPSP was suppressed by phaclofen (500 microM) but not by bicuculline methiodide (up to 100 microM). In slice preparations obtained from olfactory bulbectomized rats, local stimulation evoked burst discharges, which were similar to those observed when bicuculline methiodide was applied to slice preparations obtained from normal rats. These results suggest that GABAA receptor mediating fast IPSP and N-methyl-D-aspartate (NMDA) receptors mediating slow EPSP regulate activities of m-AMG neurons and that the enhancement of NMDA receptor mediating slow EPSP is responsible for the hyperexcitability of m-AMG neurons following olfactory bulbectomy.

Substantia nigra-mediated anticonvulsant action: a possible role of a dopaminergic component

A number of neural pathways may mediate nigral control of epilepsy. According to the literature, a GABAergic nigrotectal pathway may be responsible for the control exerted by the substantia nigra on the diffusion of discharges toward spinal targets, while the nigrothalamic projection may transfer nigral influence on premotor neocortical epilepsy. Since there is probably an anatomical nigrohippocampal pathway arising from dopaminergic cells in the substantia nigra, we tested the effects of stimulating the substantia nigra pars compacta (SNpc) on focal hippocampal epilepsy induced by penicillin injection in the cat. The possibility of dopamine involvement was further tested by studying the effects of intraperitoneal injection of haloperidol, a dopamine receptor blocking agent on nigrohippocampal influences, while to verify the precise site of action, in other groups of cats, sulpiride and apomorphine (D-receptor antagonist and agonist, respectively) were locally administered in the dorsal hippocampus. Furthermore, modifications of hippocampal epileptiform EEG were studied in control conditions and following SNpc electrolytic lesions. Results showed a strong nigral suppressive effect on focal hippocampal epilepsy. Nigral stimulation induced a significant decrease in both frequency and amplitude of hippocampal spikes, which disappeared either about 10 min after i.p. injection of haloperidol 1 mg/kg or about 5 min after intrahippocampal administration of sulpiride, and did not return during a further hour or more of experimental observation. It should be emphasized that in the absence of nigral stimulation, both haloperidol and sulpiride did not modify hippocampal spike frequency. Apomorphine application to dorsal hippocampus induced a marked reduction of hippocampal epileptiform activity parallel to the effect observed during SNpc stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of regional differences in noradrenergic neuron growth patterns on juvenile kindling

Kindling can be altered by a variety of lesions designed to deplete norepinephrine (NE). However, the effect of the regional alteration in NE concentration on seizure susceptibility has not been studied. Two different concentrations of 6-hydroxydopamine (6-OHDA) were administered to one-day-old rat pups. At age 18 days, rat with significant rostral brain NE loss, due to high dose 6-OHDA, had a faster rate of electrical kindling in the entorhinal cortex than controls. In contrast rats receiving low dose 6-OHDA which resulted in comparable forebrain NE depletion but with a dramatic hindbrain noradrenergic overgrowth showed no enhancement of kindling. These results suggest that in the immature rat the proconvulsant effect of forebrain NE depletion can be overridden by an augmentation of hindbrain NE growth patterns.

Petit mal epilepsy and parkinsonian tremor: hypothesis of a common pacemaker

Rhythmic oscillation in neuronal systems may serve physiological purposes or may interfere with normal functions of the brain. In disorders of petit mal epilepsy and parkinsonian tremor, centrally and peripherally observable rhythmic patterns are due to network oscillations of thalamocortical cells. This article reviews the afferent mechanisms that might be critically involved in controlling the ionic conductances of thalamic neurons in the behaving organism. We propose that during active behavior the subcortical aminergic and cholinergic inputs to the thalamus act as anti-burst and anti-oscillation mechanisms. We suggest further that the thalamopetal GABAergic inputs (pars reticulata of substantia nigra, entopeduncular nucleus, pallidum) are burst- and oscillation-promoting systems, whose output is controlled by the striatum. Experimental or disease-related decrease of the striatal dopamine levels is hypothesized to increase the efficacy of the GABAergic burst-promoting systems resulting in rhythmic network oscillation of thalamocortical neurons during rest. The recognition of the overlapping neuronal mechanisms in petit mal epilepsy and parkinsonian tremor, and the multistage control of thalamic oscillation suggests that drugs effectively used in petit mal attacks may be effective in levodopa-refractory parkinsonian tremor, and conversely, epileptic patients may benefit from drugs acting on the extrapyramidal system.

The effects of perinatal hypoxia on pentylenetetrazol-induced seizures in developing rats

The effects of perinatal hypoxia on susceptibility to seizures due to a single dose (55 mg/kg, i.p.) of pentylenetetrazol (PTZ) were examined, in 15-, 20-, 30-, 60- and 90 to 120-day-old rats. The rats exposed to hypoxia at 10 days of age and the unexposed controls showed similar developmental changes in the types of seizures, ictal electro-encephalograms and severity scores, the last being lowest at 30 days of age. However, the susceptibility to seizures induced by PTZ, which was measured by the mean number of generalized convulsions (GCs) as well as a mean duration of the 1st GC and severity score, was more enhanced in the rats exposed to perinatal hypoxia than in the control group at every age. The present study suggests that hypoxia in rats results in greater seizure susceptibility throughout the developmental period.

Effects of a single or repeated administration of the benzodiazepine inverse agonist FG7142 on behaviour and cortical adrenoceptor binding in the rat

We have reported previously an increase in the number of beta-adrenoceptors in mouse cerebral cortex 7 days after kindling of seizures by repeated once-daily administration of the benzodiazepine receptor inverse agonist, FG7142. In subsequent experiments, an even larger increase in beta-adrenoceptor number was found 7 days after a single injection of this compound. The present experiments investigated whether FG7142-induced changes in adrenoceptor binding are also found in the rat and whether the effects of a single and repeated injections of this drug differ quantitatively. In view of the anxiogenic effects of FG7142, we have also tested for parallel changes in behaviours associated with anxiety and exploration. Nine days after a single injection of FG7142, the number of beta-adrenoceptors in the cerebral cortex was greater than that found after repeated administration of this compound; this difference was statistically significant. There was no difference in beta-adrenoceptor binding to tissues from chronically FG7142-treated and vehicle-injected animals and there were no changes in alpha 2-adrenoceptor binding or noradrenaline levels after either a single or repeated FG7142 treatment. Neither single nor repeated FG7142 treatment modified spontaneous behaviour in either the elevated plus-maze test of anxiety or the holeboard test of exploration. The behavioural effects of yohimbine and clenbuterol in these tests were also unaffected by FG7142. We discuss the possibility that the difference in the effects of a single and repeated administration of FG7142 on beta-adrenoceptor binding is related to the expression of kindled seizures.

Behavioural, electroencephalographic and neuropathological effects of the intrahippocampal injection of the venom of the South American rattlesnake (Crotalus durissus terrificus)

Venom was microinjected into the dorsal hippocampus of rats and electroencephalographic recordings were obtained from the hippocampus and occipital cortex. Behavioural alterations consisted of circling, wet shaking and scratching that evolved to head and body jerks and isolated clonic episodes and then to wild running followed by tonic-clonic generalized seizures and status epilepticus. Electroencephalographic alterations consisted of high frequency and high voltage spikes together with epileptiform seizures beginning in the hippocampus and evolving to the cortex. However there was only a poor electrographic-behavioural correlation between the generalized tonic-clonic seizures preceded by wild running and the electrical recordings from hippocampus and occipital cortex. Histology revealed lesions at the site of injection as well as at distant sites. Severity of neuronal damage was associated with seizure intensity. Damaged areas were almost the same as found within other models of epilepsy. Nevertheless a remarkable difference was the highly lesioned hypothalamus seen in this experiment. We discuss our results in relation to results obtained with other methods of inducing epilepsy. This venom may be a useful tool for studying the nervous system.

Suppression and induction of epileptic activity by neuronal grafts

Fetal rat brain cell suspensions prepared from either the locus coeruleus region or hippocampus were implanted bilaterally into the subcortically denervated seizure-prone hippocampus of adult rats. Animals with locus coeruleus grafts were protected against picrotoxin-induced behavioral seizures and had significantly fewer interictal spikes. In contrast, in rats with fetal hippocampal grafts the incidence of interictal spikes was significantly higher than in lesion-only controls, and spontaneous behavioral seizures occurred in almost half of the animals. We suggest that neuronal grafting offers an alternative method for studying the mechanisms and control of epileptic brain activity.

A function for REM sleep: regulation of noradrenergic receptor sensitivity

We hypothesize that REM sleep serves to upregulate and/or prevent downregulation of brain norepinephrine (NE) receptors. This hypothesis is based on the following observations: (1) NE neurons of the locus coeruleus (LC) are tonically active in waking and non-REM sleep, but the entire population of LC NE neurons is inactive during REM sleep. (2) Continuous presence of NE or adrenoceptor agonists downregulates NE receptors, while a reduction in NE availability upregulates these receptors. (3) The effects of REM sleep deprivation are similar to those of NE receptor downregulation. Recent biochemical studies of NE receptor sensitivity provide strong experimental support for this hypothesis. The functional consequence of enhanced NE receptor 'tone' brought about by REM sleep would be improved signal processing in diverse brain systems, thus endowing the organism with a selective advantage. This hypothesis makes a number of specific predictions which can be tested with currently available techniques, and suggests new ways of understanding the evolution and postnatal development of REM sleep.

Noradrenaline antagonizes and ouabain potentiates the effects of N-methyl-D-aspartate on rat cerebellar cyclic GMP production

Noradrenaline potently antagonizes the effects of N-methyl-D-aspartate (NMDA) (80 microM) on cyclic GMP production in immature rat cerebellar slices in vitro (IC50 = 0.6 microM). The effect is stereospecific (D-noradrenaline, IC50 = 100 microM), and also observed with adrenaline (IC50 = 0.5 microM) and isoprenaline (IC50 = 1.2 microM). The alpha 1-adrenoceptor agonists methoxamine or phenylephrine or the mixed alpha 1/alpha 2 agonists oxymetazoline or xylometazoline (100 microM) do not block the effects of NMDA, but the alpha 2-adrenoceptor agonist clonidine is weakly active (IC50 = 200 microM). Salbutamol and terbutaline were also inactive except at high concentrations (300 microM), as were a number of other catechol and phenylethylamine derivatives. The antagonistic effects of noradrenaline on the NMDA response were insensitive to phentolamine, atenolol, or propranolol (up to 100 microM), but were blocked by the alpha 2 antagonist idazoxan (1-10 microM). The Na+,K+-ATPase inhibitor ouabain (0.1-10 microM) markedly potentiates the effects of NMDA in this model, and also antagonizes and reverses the ability of noradrenaline (10 microM) to block the effects of NMDA. The results suggest that noradrenaline and Na+,K+-ATPase activity have potent modulatory effects on the NMDA response.

Bifunctional roles of catecholamines in the development of amygdala kindling demonstrated by continuous intra-amygdala infusion of 6-hydroxydopamine

Details of seizure stage progression in amygdala kindling were studied in the cat under local denervation of catecholamine input to the amygdala. A chemitrode was used for both electrical stimulation and continuous infusion of 6-hydroxydopamine. The extent of denervation was confirmed by fluorescence histochemistry. The result has indicated that catecholamine afferents to the amygdala exert biphasic roles in normal kindling: inhibitory in the early local and late generalized seizure stages, whereas facilitatory in the intermediate stage.

Formamidine pesticides enhance susceptibility to kindled seizures in amygdala and hippocampus of the rat

Electrical kindling of the amygdala and hippocampus was used to evaluate the effects of two formamidines, chlordimeform (CDF) and amitraz (AMZ), upon seizures susceptibility in the rat. Male Long-Evans rats were implanted with electrodes in the amygdala or dorsal dentate gyrus, and injected IP daily with 40 mg/kg CDF, 50 mg/kg AMZ, or equal volumes of their respective vehicles. Afterdischarge (AD) thresholds were determined after the first injection. Animals were then stimulated twice daily, 2 and 4 hours postinjeciton, at a standard 200 microA stimulus intensity until three stage 5 generalized seizures ensued. Both CDF and AMZ significantly facilitated amygdaloid kindling rate, and CDF also facilitated hippocampal kindling rate. The effects of AMZ on hippocampal kindling were not assessed. AD durations were prolonged in the formamidine-treated groups, but there was no effect on AD thresholds. The alpha-2 adrenergic agonist and/or local anesthetic-like properties of these compounds may be responsible for these seizure enhancing effects.

A possible role for spinal noradrenaline in the mechanisms of 6-hydroxydopamine against pentylenetetrazol induced convulsions in rats

The threshold of the generalized clonic convulsions induced by intravenous infusion of pentylenetetrazol (PTZ) was significantly increased by the intraperitoneal administration of noradrenaline (NA) neurotoxin, 6-hydroxydopamine, which produced no changes in the levels of catecholamines in discrete areas of rat brain, but the effect was accompanied by spinal depletion of NA. Moreover, the anticonvulsant effects of phenobarbitone (PB) and diphenylhydantoin (DPH) against PTZ convulsions were also significantly increased in the animals pretreated with 6-OHDA. These results suggest that the observed elevation of PTZ convulsive threshold and the potentiation of anticonvulsant activity of PB and DPH in 6-OHDA treated rats were possibly mediated through spinal cord depletion of NA.

Grafted noradrenergic neurons suppress seizure development in kindling-induced epilepsy

Norepinephrine-rich cell suspensions, prepared from the locus coeruleus region of rat fetuses, were grafted bilaterally into the hippocampus of rats made hypersensitive to hippocampal kindling by a neurotoxic lesion of the central catecholamine system. The animals with grafts showed a marked suppression of the onset and progression of kindling-induced epilepsy, and this effect was correlated with the degree of graft-derived noradrenergic innervation of the host hippocampal formation. We conclude that grafted neurons can modulate the excitability of epileptic brain regions.

Acute effect of some psychotropic drugs on low-frequency amygdaloid kindled seizures

We assessed the acute effects of some psychotropic drugs on amygdaloid-kindled seizures produced by low-frequency stimulation. We used the number of stimulating pulses required for the induction of epileptic afterdischarge (pulse-number threshold, PNT) as an indicator for the seizure-generating threshold, and the duration of the epileptic afterdischarge (AD duration, ADD) as an indicator for the duration of the induced seizures. Methamphetamine and atropine elevated the PNT and reduced the ADD. Haloperidol reduced the PNT at all tested doses and reduced the ADD at high dosage. Imipramine elevated the PNT at low doses and reduced the PNT at high dosage. Imipramine also reduced the ADD. Reserpine at high dose elevated the PNT without affecting the ADD.

Noradrenergic mechanisms in gamma-hydroxybutyrate-induced seizure activity

The electroencephalographic (EEG) response of 6-hydroxydopamine (6-OHDA)-treated and control rats to gamma-butyrolactone (GBL) the prodrug of gamma-hydroxybutyrate (GHB), was determined. Neonatal treatment with 6-OHDA produced a significant reduction of noradrenaline in cortex and hippocampus while sparing noradrenaline in the hypothalamus. Brain dopamine was unaffected. The electrographic seizure produced by GBL was significantly prolonged and more severe in the 6-OHDA-treated animals. That portion of the hypersynchronous seizure induced by GBL which is pharmacologically sensitive to antipetit mal anticonvulsants, Stage 1, was however shortened in the 6-OHDA-treated animals. Reduction of forebrain noradrenaline seems to have a complex effect on GBL-induced seizure in that it results in a reduction of hypersynchronous EEG activity but in a prolongation of the more severe EEG changes of burst suppression normally seen with higher doses of GBL.

Etiologic and preventive aspects of epilepsy in the child--bridging the gap between laboratory and clinic

Four broad categories of basic phenomena are pertinent to developing ways to prevent epilepsy. These include mechanisms of epileptogenesis, ictal initiation and temporary entrainment by the seizure discharge of normally functioning brain, seizure propagation, and control mechanisms that function both to restrain the cascade of epileptic events culminating in a seizure and to arrest the epileptic event and restore the interictal state. In newborns and children, hypoxia-ischemia is a major factor leading to epileptogenesis, and several schemes are proposed to classify, quantify, and prevent hypoxic-ischemic encephalopathy. Control mechanisms must be better understood in order to develop prophylactic recommendations for epilepsy, and an experimental model of "kindling antagonism" may increase our understanding of these. Programs of prevention of seizures in children will evolve only if basic researchers and clinicians work productively together to develop an adequate understanding of factors important in epileptogenesis and antiepileptogenic control mechanisms.

Amygdala kindling modifies interhemispheric dopaminergic asymmetry

Brain dopamine is known to retard the development of kindled seizures, but it is uncertain whether kindling affects dopamine function. In the present study, rats were screened for cerebral dominance by recording their preferred direction of rotation when injected with d-amphetamine. Bipolar stimulating electrodes were then implanted in the amygdaloid complex of either the dominant or nondominant hemisphere (i.e., respectively, contra- and ipsilateral to the preferred direction of rotation; the dominant hemisphere identified in this way has been shown to contain higher concentrations of dopamine than the nondominant hemisphere). Kindling stimulation (or sham-kindling, in control rats) was applied through the electrodes two or three times daily for 21 days, and the rats were reassessed for amphetamine- and apomorphine-induced rotation, during and after the course of treatment. Kindling of the originally dominant hemisphere caused a diminution of rotational asymmetry as measured in tests 2 to 3 h after stimulation sessions, and in some rats led to a reversal in the preferred direction of amphetamine-induced rotation. Kindling of the nondominant hemisphere tended to accentuate the original amphetamine-induced asymmetry. The direction of rotation induced by a direct postsynaptic DA-receptor agonist (apomorphine) was not significantly affected by kindling of either hemisphere. It appears that kindling stimulation brings about a relatively inferior level of DA function on the stimulated vs. the nonstimulated side of the brain, and that this process depends mainly on changes occurring at a presynaptic level.

Effects of treatment with scopolamine and naloxone, singly and in combination, on amygdala kindling

Scopolamine and naloxone were administered singly and in combination to different groups of rats undergoing electrical kindling of the amygdala. Scopolamine significantly reduced the maximal seizure stage attained during 15 drug sessions and increased the total number of afterdischarges required to kindle a generalized convulsion. Naloxone had a similar but weaker and nonsignificant effect. The results confirm that antagonism of muscarinic receptors by scopolamine retards amygdala kindling.

Kindling antagonism: a role for hindbrain norepinephrine in the development of site suppression following concurrent, alternate stimulation

The concurrent, alternate electrical stimulation of the septal nucleus and the entorhinal cortex results in the development of fully generalized seizures at one site (dominant site) and the lack of development of kindled seizures at the other (suppressed or antagonized site). We have labeled this phenomenon kindling antagonism. Previous work from our laboratory has demonstrated that the whole brain depletion of norepinephrine (NE) eliminates the development of kindling antagonism. In the present study animals were treated with the neurotoxin 6-hydroxydopamine (6-OHDA) as neonates. The neonatal administration of 6-OHDA produced robust increases in brainstem and cerebellar NE levels and depletions of forebrain NE levels when assayed at maturity. Striatal dopamine levels were spared by this treatment. Neonatal 6-OHDA did not alter the development of the kindling antagonism phenomenon which is typically observed following concurrent, alternate stimulation of the septal nucleus and entorhinal cortex. Neonatal 6-OHDA treatment significantly facilitated the rate of kindled seizure development at dominant sites but failed to alter thresholds for the elicitation of afterdischarges (AD) or patterns of development of AD durations. Other characteristics of kindling antagonism were similarly unaffected by 6-OHDA treatment. These data suggest that brainstem and/or cerebellar NE are sufficient to mediate the development of kindling antagonism in the relative absence of forebrain NE.

Alterations in brain catecholamines during pregnancy

During pregnancy mice are more susceptible to flurothyl-induced seizures than are non-pregnant controls. The potential role of brain catecholamines in mediating this behavior was examined in the present study. The concentration and turnover of norepinephrine (NE) and dopamine (DA) were measured in hippocampus, striatum, midbrain and cortex in control, pregnant and delivery-day mice. There were no significant changes from control in DA levels during pregnancy and parturition. The turnover of DA was not altered during pregnancy, except for a small increase in turnover rate in the hippocampus. The concentration of NE decreased during pregnancy, and rose at parturition. This effect was most striking in the hippocampus. The turnover of NE was markedly depressed during pregnancy, with the hippocampus again being most affected. These data imply a role for NE, but not DA in the mediation of increased seizure susceptibility during pregnancy.

Monoaminergic correlates of kindling

High-performance liquid chromatography with electrochemical detection was used to measure the regional concentrations of monoamines and metabolites in the brains of rats killed 2 or 4 weeks after kindling of generalized seizures with amygdaloid stimulation. Each kindled rat was compared to a yoked control that received brief trains of non-convulsive low-frequency stimulation of the amygdala. Two weeks after kindling we found a significant depletion of noradrenaline (NA) in the ipsilateral frontal cortex, a significant depletion of serotonin (5-HT) in the stimulated amygdala and contralateral hypothalamus, and no significant changes in concentration of dopamine (DA). Four weeks after kindling we found significant depletions of NA in the stimulated amygdala and ipsilateral hypothalamus, a significant depletion of 5-HT in the ipsilateral hippocampus, and no significant changes in DA. These findings generally fail to replicate previous reports of monoaminergic correlates of kindling. Furthermore, the alterations in monoamines produced by kindling do not fall into a simple and readily interpretable pattern.

Suppression of amygdala kindling with short interstimulus intervals: effect of norepinephrine depletion

The rate of development of generalized kindled convulsions was profoundly influenced by the interval between amygdala stimulations. With stimulation every 10 min, nearly complete interference with the progression of kindling was observed in most rats, and hourly stimulation precipitated kindling rates three times longer than did once per day. Depletion of norepinephrine (NE), as a result of intracerebroventricular pretreatment with 6-hydroxydopamine, virtually eliminated the interference with kindling development seen in the vehicle control rats. Such depletion of NE, however, had little influence on the generalized responses once developed. At this stage, interference with seizure provocation was observed as truncated electroencephalographic seizures which were usually devoid of motor correlates. This interference was more profound in the shorter interstimulus intervals and was independent of NE depletion. Finally, when changing from the short kindling intervals of 10 min and 1 h to the longer interval of 24 h, an unexpected interference with seizure provocation was observed. The implication of these results for the biochemical basis of kindling and kindling as a model of learning are discussed.

Antagonism of central but not peripheral cholinergic receptors retards amygdala kindling in rats

The effects of antagonism of muscarinic cholinergic receptors on the development of seizures produced by electrical stimulation of the amygdala (kindling) were assessed in three experiments. Rats pretreated with the muscarinic antagonist scopolamine developed seizures more slowly than did untreated rats. Whereas scopolamine retarded the development of seizures in a dose-dependent manner, it did not affect the intensity or duration of seizures when administered to kindled control rats. Pretreatment with methylscopolamine, a quaternary derivative of scopolamine that does not readily cross the blood-brain barrier, did not affect the rate of development of seizures, nor did it affect established seizures. Thus the prophylactic effects of scopolamine are produced in the central nervous system and not in the periphery. The results from these experiments are consistent with the idea that central cholinergic or cholinoceptive neurons are critically involved in amygdala kindling.

The substantia nigra is an important site for the containment of seizure generalization in the kindling model of epilepsy

To investigate the role of the substantia nigra (SN) in kindling, electrical stimulation of the SN was delivered at various times before or after stimulation of the amygdala (AM) or pyriform cortex during or after kindling in rats. The results were as follows: Ipsilateral SN stimulation delivered prior to each AM kindling stimulation for 14 days significantly retarded the appearance of Stage 4 and 5 seizures and shortened the afterdischarge (AD) duration. Bilateral SN prestimulation blocked seizure generalization in some AM- or pyriform cortex-kindled animals, prolonged the latency to bilateral forelimb clonus in others, and shortened the AD duration of the kindled seizure in a current intensity-dependent fashion. These effects were only partially antagonized by haloperidol, but were completely abolished by picrotoxin. The picrotoxin alone significantly reduced the latency. Almost no effect was found when the SN stimulation was delivered after the onset of bilateral forelimb clonus. We conclude that the SN might be an important mediator of the early aspects of seizure generalization from limbic epileptic foci. The relative involvements of GABAergic gamma-aminobutyric acid and dopaminergic systems of the SN in this inhibitory function are discussed.