Severity Of Audiogenic Seizures Research Articles

Suppression of astrocyte BMP signaling improves fragile X syndrome molecular signatures and functional deficits.

Fragile X syndrome (FXS) is a monogenic neurodevelopmental disorder with manifestations spanning molecular, neuroanatomical, and behavioral changes. Astrocytes contribute to FXS pathogenesis and show hundreds of dysregulated genes and proteins; targeting upstream pathways mediating astrocyte changes in FXS could therefore be a point of intervention. To address this, we focused on the bone morphogenetic protein (BMP) pathway, which is upregulated in FXS astrocytes. We generated a conditional KO (cKO) of Smad4 in astrocytes to suppress BMP signaling, and found this lessens audiogenic seizure severity in FXS mice. To ask how this occurs on a molecular level, we performed in vivo transcriptomic and proteomic profiling of cortical astrocytes, finding upregulation of metabolic pathways, and downregulation of secretory machinery and secreted proteins in FXS astrocytes, with these alterations no longer present when BMP signaling is suppressed. Functionally, astrocyte Smad4 cKO restores deficits in inhibitory synapses present in FXS auditory cortex. Thus, astrocytes contribute to FXS molecular and functional phenotypes, and targeting astrocytes can mitigate FXS symptoms.

Radiprodil, a selective GluN2B negative allosteric modulator, rescues audiogenic seizures in mice carrying the GluN2A(N615S) mutation.

GRIN-related disorders are neurodevelopmental disorders caused by mutations in N-methyl-D-aspartate receptor (NMDAR) subunit genes. A large fraction of these mutations lead to a 'gain of function' (GoF) of the NMDAR. Patients present with a range of symptoms including epilepsy, intellectual disability, behavioural and motor. Controlling seizures is a significant unmet medical need in most patients with GRIN-related disorders. Although several hundred GRIN mutations have been identified in humans, until recently none of the mouse models carrying Grin mutations/deletions showed an epileptic phenotype. The two recent exceptions both carry mutations of GluN2A. The aim of this study was to assess the efficacy of radiprodil, a selective negative allosteric modulator of GluN2B-containing NMDARs, in counteracting audiogenic seizures (AGS) in a murine model carrying the GluN2A(N615S) homozygous mutation (Grin2aS/S mice). Grin2aS/S mice were acutely treated with radiprodil at different doses before the presentation of a high-frequency acoustic stimulus commonly used for AGS induction. Radiprodil significantly and dose-dependently reduced the onset and severity of AGS in Grin2aS/S mice. Surprisingly, the results revealed a sex-dependent difference in AGS susceptibility and in the dose-dependent protection of radiprodil in the two genders. Specifically, radiprodil was more effective in female versus male mice. Overall, our data clearly show that radiprodil, a GluN2B selective negative allosteric modulator, may have the potential to control seizures in patients with GRIN2A GoF mutations. Further studies are warranted to better understand the sex-dependent effects observed in this study.

Excessive proteostasis contributes to pathology in fragile X syndrome

In fragile X syndrome (FX), the leading monogenic cause of autism, excessive neuronal protein synthesis is a core pathophysiology; however, an overall increase in protein expression is not observed. Here, we tested whether excessive protein synthesis drives a compensatory rise in protein degradation that is protective for FX mouse model (Fmr1-/y) neurons. Surprisingly, although we find a significant increase in protein degradation through ubiquitin proteasome system (UPS), this contributes to pathological changes. Normalizing proteasome activity with bortezomib corrects excessive hippocampal protein synthesis and hyperactivation of neurons in the inferior colliculus (IC) in response to auditory stimulation. Moreover, systemic administration of bortezomib significantly reduces the incidence and severity of audiogenic seizures (AGS) in the Fmr1-/y mouse, as does genetic reduction of proteasome, specifically in the IC. Together, these results identify excessive activation of the UPS pathway in Fmr1-/y neurons as a contributor to multiple phenotypes that can be targeted for therapeutic intervention.

AntimiR targeting of microRNA-134 reduces seizures in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a severe neurodevelopmental disorder featuring ataxia, cognitive impairment, and drug-resistant epilepsy. AS is caused by mutations or deletion of the maternal copy of the paternally imprinted UBE3A gene, with current precision therapy approaches focusing on re-expression of UBE3A. Certain phenotypes, however, are difficult to rescue beyond early development. Notably, a cluster of microRNA binding sites was reported in the untranslated Ube3a1 transcript, including for miR-134, suggesting that AS may be associated with microRNA dysregulation. Here, we report levels of miR-134 and key targets are normal in the hippocampus of mice carrying a maternal deletion of Ube3a (Ube3am−/p+). Nevertheless, intracerebroventricular injection of an antimiR oligonucleotide inhibitor of miR-134 (Ant-134) reduced audiogenic seizure severity over multiple trials in 21- and 42-day-old AS mice. Interestingly, Ant-134 also improved distance traveled and center crossings of AS mice in the open-field test. Finally, we show that silencing miR-134 can upregulate targets of miR-134 in neurons differentiated from Angelman patient-derived induced pluripotent stem cells. These findings indicate that silencing miR-134 and possibly other microRNAs could be useful to treat clinically relevant phenotypes with a later developmental window in AS.

Remote effects of short-term neonatal hyperthermia in Krushinsky-Molodkina rats prone to audiogenic seizures strain.

Using the audiogenic seizure prone Krushinsky-Molodkina rat strain, it was demonstrated that short-term (5 min) exposure of 14-day-old pups to an elevated temperature (42°C) resulted in a significant decrease in audiogenic seizure severity at the age of 1 month. Presumably, this effect is determined by the activation of the heat-shock protein system (stress proteins).

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".

Developmental PCB Exposure Increases Audiogenic Seizures and Decreases Glutamic Acid Decarboxylase in the Inferior Colliculus.

Previously, we observed that developmental polychlorinated biphenyl (PCB) exposure resulted in an increase in audiogenic seizures (AGSs) in rats. However, the rats were exposed to loud noise in adulthood, and were not tested for AGS until after 1 year of age, either of which could have interacted with early PCB exposure to increase AGS susceptibility. This study assessed susceptibility to AGS in young adult rats following developmental PCB exposure alone (without loud noise exposure) and investigated whether there was a decrease in GABA inhibitory neurotransmission in the inferior colliculus (IC) that could potentially explain this effect. Female Long-Evans rats were dosed orally with 0 or 6 mg/kg/day of an environmentally relevant PCB mixture from 28 days prior to breeding until the pups were weaned at postnatal day 21. One male-female pair from each litter was retained for the AGS study whilst another was retained for Western blot analysis of glutamic acid decarboxylase (GAD) and GABAAα1 receptor in the IC, the site in the auditory midbrain where AGS are initiated. There was a significant increase in the number and severity of AGSs in the PCB groups, with females somewhat more affected than males. GAD65 was decreased but there was no change in GAD67 or GABAAα1 in the IC indicating decreased inhibitory regulation in the PCB group. These results confirm that developmental PCB exposure alone is sufficient to increase susceptibility to AGS, and provide the first evidence for a possible mechanism of action at the level of the IC.

Pharmacological and neuroethological studies of three antiepileptic drugs in the Genetic Audiogenic Seizure Hamster (GASH:Sal)

Epilepsy modeling is essential for understanding the basic mechanisms of the epileptic process. The Genetic Audiogenic Seizure Hamster (GASH:Sal) exhibits generalized tonic–clonic seizures of genetic origin in response to sound stimulation and is currently being validated as a reliable model of epilepsy. Here, we performed a pharmacological and neuroethological study using well-known and widely used antiepileptic drugs (AEDs), including phenobarbital (PB), valproic acid (VPA), and levetiracetam (LEV). The intraperitoneal administration of PB (5–20mg/kg) and VPA (100–300mg/kg) produced a dose-dependent decrease in GASH:Sal audiogenic seizure severity scores. The administration of LEV (30–100mg/kg) did not produce a clear effect. Phenobarbital showed a short plasmatic life and had a high antiepileptic effect starting at 10mg/kg that was accompanied by ataxia. Valproic acid acted only at high concentrations and was the AED with the most ataxic effects. Levetiracetam at all doses also produced sedation and ataxia side effects. We conclude that the GASH:Sal is a reliable genetic model of epilepsy suitable to evaluate AEDs.

Long-lasting effects of minocycline on behavior in young but not adult Fragile X mice

Fragile X Syndrome (FXS) is the most common single-gene inherited form of intellectual disability with behaviors characteristic of autism. People with FXS display childhood seizures, hyperactivity, anxiety, developmental delay, attention deficits, and visual-spatial memory impairment, as well as a propensity for obsessive–compulsive disorder. Several of these aberrant behaviors and FXS-associated synaptic irregularities also occur in “fragile X mental retardation gene” knock-out (Fmr1 KO) mice. We previously reported that minocycline promotes the maturation of dendritic spines – postsynaptic sites for excitatory synapses – in the developing hippocampus of Fmr1 KO mice, which may underlie the beneficial effects of minocycline on anxiolytic behavior in young Fmr1 KO mice. In this study, we compared the effectiveness of minocycline treatment in young and adult Fmr1 KO mice, and determined the dependence of behavioral improvements on short-term versus long-term minocycline administration. We found that 4- and 8-week-long treatments significantly reduced locomotor activity in both young and adult Fmr1 KO mice. Some behavioral improvements persisted in young mice post-treatment, but in adults the beneficial effects were lost soon after minocycline treatment was stopped. We also show, for the first time, that minocycline treatment partially attenuates the number and severity of audiogenic seizures in Fmr1 KO mice. This report provides further evidence that minocycline treatment has immediate and long-lasting benefits on FXS-associated behaviors in the Fmr1 KO mouse model.

Fosinopril and zofenopril, two angiotensin-converting enzyme (ACE) inhibitors, potentiate the anticonvulsant activity of antiepileptic drugs against audiogenic seizures in DBA/2 mice

The renin–angiotensin system (RAS) exists in the brain and it may be involved in pathogenesis of neurological and psychiatric disorders including seizures. The aim of the present research was to evaluate the effects of some angiotensin-converting enzyme inhibitors (ACEi; captopril, enalapril, fosinopril and zofenopril), commonly used as antihypertensive agents, in the DBA/2 mice animal model of generalized tonic–clonic seizures. Furthermore, the co-administration of these compounds with some antiepileptic drugs (AEDs; carbamazepine, diazepam, felbamate, gabapentin, lamotrigine, phenobarbital, phenytoin, topiramate and valproate) was studied in order to identify possible positive interactions in the same model. All ACEi were able to decrease the severity of audiogenic seizures with the exception of enalapril up to the dose of 100mg/kg, the rank order of activity was as follows: fosinopril>zofenopril>captopril. The co-administration of ineffective doses of all ACE inhibitors with AEDs, generally increased the potency of the latter. Fosinopril was the most active in potentiating the activity of AEDs and the combination of ACEi with lamotrigine and valproate was the most favorable, whereas, the co-administrations with diazepam and phenobarbital seemed to be neutral. The increase in potency was generally associated with an enhancement of motor impairment, however, the therapeutic index of combined treatment of AEDs with ACEi was predominantly more favorable than control. ACEi administration did not influence plasma and brain concentrations of the AEDs studied excluding pharmacokinetic interactions and concluding that it is of pharmacodynamic nature. In conclusion, fosinopril, zofenopril, enalapril and captopril showed an additive anticonvulsant effect when co-administered with some AEDs, most notably carbamazepine, felbamate, lamotrigine, topiramate and valproate, implicating a possible therapeutic relevance of such drug combinations.

Anxiety and Predisposition to Audiogenic Epilepsy in Rats of Different Genotypes

We studied plus-maze behavior of inbred Krushinskii-Molodkina, Wistar, and black-hooded rats (originating from the Long-Evans outbred strain) differing by predisposition to audiogenic seizures. The severity of audiogenic seizures partially correlated with anxiety and negatively correlated with the total level of locomotor activity in the elevated plus-maze. The anxiety parameters in Krushinskii-Molodkina rats were evaluated after injection of anticonvulsant levetiracetam and anxiolytic afobazol. Levetiracetam and afobazol somewhat stimulated locomotor activity.

Influence of levetiracetam on the anticonvulsant efficacy of conventional antiepileptic drugs against audiogenic seizures in DBA/2 mice

Levetiracetam (LEV, [S]-alpha-ethyl-2-oxo-1-pyrrolidine acetamide) is a new antiepileptic that has been used as adjunctive therapy to treat patients with intractable epilepsy. Systemic administration of levetiracetam (2.5-30 mg/kg, intraperitoneally (i.p.)) was able to produce a dose-dependent decrease in DBA/2 audiogenic seizure severity score. In combination with conventional antiepileptic drugs, levetiracetam, 5mg/kg, i.p., which per se did not significantly affect the occurrence of audiogenic seizures in DBA/2 mice, potentiated the anticonvulsant activity of some antiepileptic drugs studied against sound-induced seizures in DBA/2 mice. The degree of potentiation induced by levetiracetam was greater, approximately twice, for carbamazepine, diazepam, felbamate, topiramate, gabapentin, and valproate, less for lamotrigine, phenobarbital and phenytoin. This increase was associated with a comparable impairment in motor activity; however, the therapeutic index of combined treatment of antiepileptic drugs with levetiracetam was more favourable than the combination with saline with the exception of lamotrigine, phenytoin and phenobarbital. Since levetiracetam did not significantly influence the total and free plasma and the brain levels of antiepileptics studied. In addition, levetiracetam did not significantly affect the hypothermic effects of the anticonvulsants tested. In conclusion, levetiracetam showed an additive anticonvulsant effect when administered in combination with some classical anticonvulsants, most notably carbamazepine, diazepam, felbamate, gabapentin, topiramate and valproate, implicating a possible therapeutic relevance of such drug combinations.

Effect of chronic consumption of sodium valproate and melatonin on seizure activity in Krushinskii-Molodkina rats

Experiments on Krushinskii-Molodkina rats with hereditary predisposition to audiogenic seizures showed that chronic consumption of aqueous solution of melatonin (50 mg/liter) had no effect on the pattern of seizures induced by 20-fold acoustic stimulation. Sodium valproate (50 mg/liter) insignificantly decreased the seizure response. Combined treatment with sodium valproate and melatonin produced a potent anticonvulsant effect, i.e. increased the latency and decreased the severity of audiogenic seizures. However, myoclonus in animals receiving combined treatment with these drugs developed much more rapidly compared to rats receiving melatonin or sodium valproate monotherapy.

Brainstem Seizure Severity Regulates Forebrain Seizure Expression in the Audiogenic Kindling Model

Although sound-induced (audiogenic) seizures in the genetically epilepsy-prone rat (GEPR) initially occur independent of the forebrain, repeated audiogenic seizures recruit forebrain seizure circuits in a process referred to as audiogenic kindling. In GEPR-3s, audiogenic kindling results in facial and forelimb (F&F) clonic seizures that are typical of forebrain seizures. However, in GEPR-9s, audiogenic kindling produces posttonic all-limb clonus not usually observed during forebrain seizures. We hypothesized that the more severe brainstem seizures of the GEPR-9 prevent the expression of F&F clonic seizures during audiogenic kindling. Therefore attenuation of audiogenic seizures during audiogenic kindling in GEPR-9s should allow F&F clonic seizures to be expressed. Likewise, intensifying audiogenic seizure severity in GEPR-3s should inhibit audiogenically kindled F&F clonic seizures. We have tested this hypothesis in the present study. Lesions of the superior colliculus or treatment with low-dose phenytoin were used to suppress audiogenic seizure severity in GEPR-9s. Depletion of brain serotonin was used to increase the seizure severity in GEPR-3s. All GEPRs were then subjected to audiogenic kindling. Behavioral and electrographic seizures were assessed. Suppression of audiogenic seizure severity during audiogenic kindling in GEPR-9s increased the incidence forebrain seizure behavior. Kindled GEPR-9s that continued to display full tonic seizures did not exhibit forebrain convulsions, but did show posttonic clonus and forebrain seizure activity in the EEG. GEPR-3s chronically depleted of brain serotonin, along with displaying tonic brainstem seizures, tended to display less severe forebrain seizures during audiogenic kindling. These findings support the concept that severe brainstem seizures prevent the behavioral expression of forebrain seizures in audiogenically kindled GEPR-9s. It appears that the severe brainstem seizure of the GEPR-9 does not allow the forebrain seizure to manifest its typical behavioral concomitants despite electrographic evidence that spike-wave discharge is occurring in the forebrain.

Influence of carbenoxolone on the anticonvulsant efficacy of conventional antiepileptic drugs against audiogenic seizures in DBA/2 mice

Carbenoxolone, the succinyl ester of glycyrrhetinic acid, is an inhibitor of 11β-hydroxy steroid dehydrogenase and gap junctional intercellular communication. It is currently used in clinical treatment of ulcer diseases. Systemic administration of carbenoxolone (1–40 mg/kg, intraperitoneally (i.p.)) was able to produce a dose-dependent decrease in DBA/2 audiogenic seizure severity score. Glycyrrhizin, an analogue of carbenoxolone inactive at the gap-junction level, was unable to affect audiogenic seizures at doses up to 30 mg/kg. In combination with conventional antiepileptic drugs, carbenoxolone, 0.5 mg/kg, i.p., which per se did not significantly affect the occurrence of audiogenic seizures in DBA/2 mice, potentiated the anticonvulsant activity of carbamazepine, diazepam, felbamate, gabapentin, lamotrigine, phenytoin, phenobarbital and valproate against sound-induced seizures in DBA/2 mice. This effect was not observed after the combination of glycyrrhizin (10 mg/kg, i.p.) with some conventional antiepileptic drugs. The degree of potentiation induced by carbenoxolone was greater for diazepam, felbamate, gabapentin, phenobarbital and valproate, less for lamotrigine, phenytoin and carbamazepine. This increase was associated with a comparable impairment in motor activity; however, the therapeutic index of combined treatment of antiepileptic drugs with carbenoxolone was more favourable than the combination with glycyrrhizin or saline. Since carbenoxolone did not significantly influence the total and free plasma levels of diazepam, felbamate, gabapentin, lamotrigine, phenytoin, phenobarbital, valproate and carbamazepine, pharmacokinetic interactions are not likely. However, the possibility that carbenoxolone can modify the brain clearance of the anticonvulsant drugs studied may not be excluded. In addition, carbenoxolone did not significantly affect the hypothermic effects of the anticonvulsants tested. In conclusion, carbenoxolone showed an additive anticonvulsant effect when administered in combination with some classical anticonvulsants, most notably diazepam, felbamate, gabapentin, phenobarbital, and valproate, implicating a possible therapeutic relevance of such drug combinations.

A static magnetic field modulates severity of audiogenic seizures and anticonvulsant effects of phenytoin in DBA/2 mice

Rationale: In a search for potential supplements or alternatives to the pharmacological treatment of epilepsy, we examined the effects of static magnetic fields on audiogenic seizures of DBA/2 mice. Methods: Two strains of DBA/2 mice were subjected to auditory stimulation that resulted sequentially in wild running, loss of righting, clonus, tonic hindlimb extension, and death in 80–95% of animals in different experiments. The incidence of seizure stages in groups of animals pretreated with a static magnetic field, phenytoin (PHT) or both was compared to the incidence in sham-exposed control mice. Results: Depending on magnetic flux density and duration of exposure to the field, seizure severity decreased significantly, but not completely, in both strains. However, incidence of five seizure stages was reduced in one strain, with about half of the mice seizure free. Two seizure stages (tonic hindlimb extension and death) were reduced significantly in the other. Magnetic field pretreatment potentiated the effect of PHT. Clonic seizures refractory to PHT or magnetic field pretreatment in DBA/2J mice responded to pretreatment with a combination of PHT and the magnetic field. Conclusions: A static magnetic field had some anticonvulsant effects when employed alone. More robust effects were seen in combination with PHT. Further testing of magnetic fields for anticonvulsant effects and elucidation of mechanisms of action seem to be warranted.

Differential Roles in the Neuronal Network for Audiogenic Seizures Are Observed among the Inferior Colliculus Subnuclei and the Amygdala

The inferior colliculus (IC) is established as the initiation site within the neuronal network for audiogenic seizures (AGS), but the relative importance of the IC subnuclei in AGS is controversial. The lateral and basolateral subdivisions of the amygdala are implicated in the expansion of the AGS network that occurs during AGS kindling. However, the role of the amygdala in the AGS network in nonkindled AGS is unknown. NMDA receptors are implicated in modulation of AGS and in neurotransmission in both the IC and amygdala. Therefore, changes in AGS severity in genetically epilepsy-prone rats (GEPR-9s) were examined after bilateral focal microinjection into IC subnuclei or lateral/basolateral subdivisions of the amygdala of a competitive NMDA receptor antagonist, 3-((+)-2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP). Blockade of AGS in IC central nucleus (ICc) and external cortex (ICx) was observed at identical doses of CPP, but these doses were ineffective in IC dorsal cortex (ICd). Microinjection of CPP into the amygdala did not produce significant changes in AGS severity except at doses 20 times those effective in IC. The latter data contrast with the anticonvulsant effects of amygdala microinjections on seizure severity in kindled AGS reported previously. The present data in concord with neuronal recording studies of these nuclei suggest that the ICc is the most critical site in AGS initiation, the ICx in propagation, and that the ICd plays a lesser role in the AGS network. The amygdala does not appear to play a requisite role in the neuronal network for AGS in animals that have not been subjected to AGS kindling.

In situ hybridization for c-fos mRNA reveals the involvement of the superior colliculus in the propagation of seizure activity in genetically epilepsy-prone rats.

Previous work showed that bilateral lesions made between the inferior and superior colliculi reduced the severity of audiogenic seizures in genetically epilepsy-prone rats (GEPR-9s), and indicated that the connections between these two structures are vital for the propagation of seizure activity. To determine the involvement of the superior colliculus (SC) in seizure propagation, GEPR-9s were given four audiogenic seizures within 1 h by ringing a loud bell, and their brains were processed 30 min later for in situ hybridization for c-fos mRNA. Brain sections from such rats showed dense labeling in both the dorsal cortex and external nucleus of the inferior colliculus. Labeling continued rostrally into the intermediate and deep layers of the SC and the periaqueductal gray region. In addition, other brain regions such as the amygdala, piriform cortex and dorsal endopiriform nucleus showed dense labeling for c-fos mRNA. Comparable increases were not observed in the brains of Sprague-Dawley (SD) rats receiving auditory stimulation or in unstimulated GEPR-9s and SD rats, thereby indicating that increases in stimulated GEPR-9s are seizure-specific. This study provides further evidence that the SC is involved in the propagation of seizure activity in GEPR-9s, and also demonstrates the activation of other brain regions by audiogenic seizures.

Effect of 5,7-dihydroxytryptamine on audiogenic seizures in genetically epilepsy-prone rats.

To further assess the role of 5-HT in the modulation of audiogenic seizures (AGS) in the Genetically Epilepsy-Prone Rat (GEPR), changes in AGS severity after widespread chronic depletion of brain 5-HT by intracerebroventricular administration of 5,7-dihydroxytryptamine (5,7-DHT) were examined in moderate seizure GEPRs (GEPR-3s). Following treatment with 5,7-DHT (150 micrograms/30 microliters), a significant increase in seizure severity was observed at 2, 3 and 4 weeks as compared to vehicle-injected controls. The increase in seizure severity was evidenced by a significant increase in the incidence of tonic convulsions in 5,7-DHT treated animals (53% in treated animals compared to 0% in vehicle treated controls) over the testing period. Interestingly, the latency to wild running was increased in 5,7-DHT treated GEPRs, suggesting that depletion of brain 5-HT may slow initiation of AGS. Neurochemical analysis revealed marked depletion of 5-HT in the cortex (-96%), hippocampus (-94%), thalamus (-80%), hypothalamus (-62%), midbrain (-51%) and pons-medulla (-52%) in animals that received 5,7-DHT. However, no significant reductions in brain norepinephrine content were observed in any of the regions assayed due to the pretreatment of all animals with protriptyline. The present findings lend further support for an inhibitory action of brain 5-HT on audiogenic seizures in GEPRs.

Role of serotonin in the anticonvulsant effect of fluoxetine in genetically epilepsy-prone rats.

This study was designed to demonstrate a role of serotonin in the anticonvulsant effect of fluoxetine, a serotonin reuptake inhibitor, in genetically epilepsy-prone rats. When varied doses of 5-hydroxytryptophan (12.5, 25, 50 mg/kg) were administered i.p. along with a fixed dose of fluoxetine (15 mg/kg) to severe seizure genetically epilepsy-prone rats, the severity of audiogenic seizures was decreased dose-dependently, and the combination treatment also produced a marked potentiation of the anticonvulsant effect when compared with administration of either drug alone. Pretreatment of severe seizure genetically epilepsy-prone rats with p-chlorophenylalanine depleted brain serotonin and reduced the anticonvulsant effectiveness of fluoxetine. By using intracerebral microdialysis, the depletion of serotonin after p-chlorophenylalanine treatment was confirmed by measuring thalamic extracellular serotonin and 5-hydroxyindoleacetic acid concentrations during basal release and in response to a challenge dose of fluoxetine. We concluded that serotonergic transmission may be involved in the anticonvulsant effect of fluoxetine in severe seizure genetically epilepsy-prone rats.