Effects of pentylenetetrazol-induced seizures on dopamine and norepinephrine levels and on glucose utilization in various brain regions of the developing rat

Heat induced temperature dysregulation and seizures in Dravet Syndrome/GEFS+ Gabrg2+/Q390X mice

It has been established that febrile seizures and its extended syndromes like generalized epilepsy with febrile seizures (FS) plus (GEFS+) and Dravet syndrome have been associated with mutations especially in SCN1A and GABRG2 genes. In patients, the onset of FS is likely due to the combined effect of temperature and inflammation in genetically vulnerable individuals because fever is often associated with infection. Much effort has been spent to understand the mechanisms underlying fever induction of seizures. In addition to the role of cytokines in FS, previous studies in Scn1a^+/- knockout mice, a model of Dravet syndrome, indicated that temperature elevation alone could result in seizure generation, and the effect of elevated temperature inducing seizures was age-dependent. Here, we report the thermal effect in a different mouse model of Dravet syndrome, the Gabrg2^+/Q390X knockin mouse. We demonstrated age-dependent dysregulated temperature control and that temperature elevation produced myoclonic jerks, generalized tonic clonic seizures (GTCSs) and heightened anxiety-like symptoms in Gabrg2^+/Q390X mice. The study indicated that regardless of other inflammatory factors, brief heat alone increased brain excitability and induced multiple types of seizures in Gabrg2^+/Q390X mice, suggesting that mutations like GABRG2(Q390X) may alter brain thermal regulation and precipitate seizures during temperature elevations.

Additional antiepileptic mechanisms of levetiracetam in lithium-pilocarpine treated rats

Several studies have addressed the antiepileptic mechanisms of levetiracetam (LEV); however, its effect on catecholamines and the inflammatory mediators that play a role in epilepsy remain elusive. In the current work, lithium (Li) pretreated animals were administered LEV (500 mg/kg i.p) 30 min before the induction of convulsions by pilocarpine (PIL). Li-PIL-induced seizures were accompanied by increased levels of hippocampal prostaglandin (PG) E2, myeloperoxidase (MPO), tumor necrosis factor-α, and interleukin-10. Moreover, it markedly elevated hippocampal lipid peroxides and nitric oxide levels, while it inhibited the glutathione content. Li-PIL also reduced hippocampal noradrenaline, as well as dopamine contents. Pretreatment with LEV protected against Li-PIL-induced seizures, where it suppressed the severity and delayed the onset of seizures in Li-PIL treated rats. Moreover, LEV reduced PGE2 and MPO, yet it did not affect the level of both cytokines in the hippocampus. LEV also normalized hippocampal noradrenaline, dopamine, glutathione, lipid peroxides, and nitric oxide contents. In conclusion, alongside its antioxidant property, LEV anticonvulsive effect involves catecholamines restoration, as well as inhibition of PGE2, MPO, and nitric oxide.

Effect of saponin fraction from Ficus religiosa on memory deficit, and behavioral and biochemical impairments in pentylenetetrazol kindled mice

In our previous study, the saponin-rich fraction (SRF) of adventitious root extract of Ficus religiosa L. (Moraceae) was shown to have an anticonvulsant effect in acute animal models of convulsions. The present study was envisaged to study the effect of SRF in the pentylenetetrazol (PTZ) kindling mouse model and its associated depression and cognition deficit. Treatment with the SRF (1, 2 and 4 mg/kg; i.p.) for 15 days in kindled mice significantly decreased seizure severity on days 5, 10 and 15 when challenged with PTZ (35 mg/kg; i.p.). Marked protection against kindling-associated depression was also observed on days 10 and 15 in the SRF-treated groups when tested using the tail-suspension test. However, the SRF treatment failed to protect kindling-associated learning and memory impairments in the passive shock avoidance paradigm. The observed behavioral effects were corroborated with modulation in the levels of noradrenaline, dopamine, serotonin, GABA and glutamate in discrete brain regions.

Dietary supplementation with acetyl-l-carnitine in seizure treatment of pentylenetetrazole kindled mice

In spite of the availability of new antiepileptic drugs a considerable number of epilepsy patients still have pharmacoresistant seizures, and thus there is a need for novel approaches. Acetyl-l-carnitine (ALCAR), which delivers acetyl units to mitochondria for acetyl-CoA production, has been shown to improve brain energy homeostasis and protects against various neurotoxic insults. To our knowledge, this is the first study of ALCAR's effect on metabolism in pentylenetetrazole (PTZ) kindled mice. ALCAR or the commonly used antiepileptic drug valproate, was added to the drinking water of mice for 25days, and animals were injected with PTZ or saline three times a week during the last 21 days. In order to investigate ALCAR's effects on glucose metabolism, mice were injected with [1-(13)C]glucose 15 min prior to microwave fixation. Brain extracts from cortex and the hippocampal formation (HF) were studied using (1)H and (13)C NMR spectroscopy and HPLC. PTZ kindling caused glucose hypometabolism, evidenced by a reduction in both glycolysis and TCA cycle turnover in both brain regions investigated. Glutamatergic and GABAergic neurons were affected in cortex and HF, but the amount of glutamate was only reduced in HF. Slight astrocytic involvement could be detected in the cortex. Interestingly, the dopamine content was increased in the HF. ALCAR attenuated the PTZ induced reduction in [3-(13)C]alanine and the increase in dopamine in the HF. However, TCA cycle metabolism was not different from that seen in PTZ kindled animals. In conclusion, even though ALCAR did not delay the kindling process, it did show some promising ameliorative effects, worthy of further investigation.

Dual protective effect of Passiflora incarnata in epilepsy and associated post-ictal depression

ETHNOPHARMACOLOGICAL RELEVANCE

Passiflora incarnata L. (Passifloraceae) has been used for the treatment of epilepsy in several traditional systems of medicine.

AIM OF THE STUDY

The aerial parts of Passiflora incarnata contain multiple bioactive metabolites such as, flavonoids (like, chrysin that show CNS depressant activity by agonizing GABA-benzodiazepine receptor), amino acids (like, GABA), harmala alkaloids (reversible monoamine oxidase-A inhibitor), etc. In view of this, the present study was designed to investigate dual protective effect of the hydroethanolic extract of Passiflora incarnata in pentylenetetrazol (PTZ)-induced seizure and associated post-ictal depression.

MATERIALS AND METHODS

Different groups of mice were administered with repeated subconvulsive doses of PTZ (50mg/kg; i.p.) at an interval of 5 days for 15 days. From 5th to 15th day the animals in different groups were administered daily with varying doses of hydroethanolic extract of Passiflora incarnata (150, 300, and 600mg/kg; i.p.), diazepam (2mg/kg; i.p.) and vehicle. On every 5th day, after PTZ treatment, seizure severity (score) was noted. Following convulsive episodes the locomotor activity (using actophotometer) and immobility period (using forced swim test) were also determined. On 15th day after behavioral assessment, the brain serotonin and noradrenaline levels were determined using spectrofluorometric methods.

RESULTS

Treatment with the extract significantly (p<0.05) reduced the seizure severity and immobility period as compared to vehicle control, in a dose and time-dependent manner. Moreover, the extract treatment retained the serotonin and noradrenaline levels of the brain.

CONCLUSIONS

The results of present study concluded that the hydroethanolic extract of Passiflora incarnata suppress PTZ-induced seizures, and ameliorates its associated post-ictal depression, which has been found to be get worsened with the standard antiepileptic drug, diazepam.

Paradoxical effect of noradrenaline-mediated neurotransmission in the antinociceptive phenomenon that accompanies tonic-clonic seizures: role of locus coeruleus neurons and α(2)- and β-noradrenergic receptors

The postictal state is generally followed by antinociception. It is known that connections between the dorsal raphe nucleus, the periaqueductal gray matter, and the locus coeruleus, an important noradrenergic brainstem nucleus, are involved in the descending control of ascending nociceptive pathways. The aim of the present study was to determine whether noradrenergic mechanisms in the locus coeruleus are involved in postictal antinociception. Yohimbine (an α(2)-receptor antagonist) or propranolol (a β-receptor antagonist) was microinjected unilaterally into the locus coeruleus, followed by intraperitoneal administration of pentylenetetrazole (PTZ), a noncompetitive antagonist that blocks GABA-mediated Cl(-) influx. Although the administration of both yohimbine and propranolol to the locus coeruleus/subcoeruleus area resulted in a significant decrease in tonic or tonic-clonic seizure-induced antinociception, the effect of yohimbine restricted to the locus coeruleus was more distinct compared with that of propranolol, possibly because of the presynaptic localization of α(2)-noradrenergic receptors in locus coeruleus neurons. These effects were related to the modulation of noradrenergic activity in the locus coeruleus. Interestingly, microinjections of noradrenaline into the locus coeruleus also decrease the postictal antinociception. The present results suggest that the mechanism underlying postictal antinociception involves both α(2)- and β-noradrenergic receptors in the locus coeruleus, although the action of noradrenaline on these receptors causes a paradoxical effect, depending on the nature of the local neurotransmission.

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.

Endogenous melatonin and epileptogenesis: facts and hypothesis

In human epilepsy, diurnal variation in seizure phenomena suggests the involvement of a time-dependent biological signal. Clinical evidence indicates that in some cases, temporal clustering of epileptic seizures is in phase with the nocturnal rise in circulating melatonin. Although this hormone has been reported to stabilize the brain against seizure-producing stimuli, these pharmacological doses are not representative of physiological conditions but would nonetheless facilitate widespread inhibitory neurotransmission characteristic of traditional anticonvulsants. Instead, it is proposed that endogenous melatonin contributes to epileptiform activity through inhibitory actions on dopaminergic activity. Dopamine is considered a natural downregulator of seizure activity in a number of species, including humans, and numerous lines of evidence suggest that melatonin is capable of stimulating a decrease in dopamine output within areas of the brain thought to participate in the control of epileptic seizures. Pharmacological manipulation of the endogenous melatonin rhythm may provide a useful therapeutic strategy against the occurrence of seizures during increased hormone production.

Effect of pentylenetetrazol on the expression of tyrosine hydroxylase mRNA and norepinephrine and dopamine transporter mRNA

Seizure activity has been shown to have differential effects on the terminal content of the monoamines, norepinephrine (NE) and dopamine (DA). Induction of seizure activity reduces the terminal content of NE, while DA levels remain unchanged or slightly elevated. This study examined the effect of the chemoconvulsant pentylenetetrazol (PTZ) on the mRNA expression of regulatory proteins which maintain the terminal content of NE and DA (i.e., synthesis and re-uptake). The areas examined were the noradrenergic neurons of the locus coeruleus (LC) and dopaminergic neurons of the substantia nigra pars compacta/ventral tegmentum area (SNpc/VTA) in the rat. In the LC, PTZ increased mRNA expression of the immediate early gene, c-fos, and mRNA expression of the synthesizing enzyme, tyrosine hydroxylase (TH), and the re-uptake protein, norepinephrine transporter (NET). This effect on TH and NET was observed only 1 day after the administration of PTZ. In contrast, PTZ did not alter the expression of c-fos mRNA in the SNpc/VTA, but reduced the expression of the dopamine transporter (DAT) mRNA. This effect was observed only 1 day after the administration of PTZ. TH mRNA expression in dopaminergic neurons was elevated initially in a manner similar to that observed in the LC. However, the effect of PTZ on TH mRNA expression in dopaminergic neurons was more prolonged (still elevated 3 days later). These results indicate that the chemoconvulsant PTZ has differential effects on the mRNA expression of regulatory systems (TH and neurotransporter proteins) in noradrenergic and dopaminergic neurons.

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).