Differential effects of NMDA antagonists microinjections into the nucleus reticularis pontis caudalis on seizures induced by pentylenetetrazol in the rat

Effect of valproate on sleep patterns disturbed by epilepsy

Nocturnal epilepsy is a neurological disease that has a significant effect on sleep. Various treatments have been implemented to help mitigate these effects and improve patients' quality of life. The use of experimental animal models for epilepsy has facilitated efficacy assessment and the development of different medications to treat the symptoms of this disease. The objective of this study was to evaluate the effect of valproate on sleep patterns altered by epilepsy. Chronically implanted Wistar rats were used to study sleep patterns over three consecutive days under different experimental conditions. The animals were separated into two groups. The first day was considered the control recording; on the second day, one group received pentylenetetrazol (PTZ) alone, and the other group received valproate prior to induction of convulsive seizures with PTZ administration. The results show that in addition to its antiepileptic effect, valproate has hypnotic properties. It is considered to facilitate the action of GABAergic mechanisms to mitigate the effect of convulsive seizures and increase the occurrence of sleep.

Effect of gabapentin on sleep patterns disturbed by epilepsy

For a long time, numerous sleep alterations induced by nocturnal epilepsy have been described. Such alterations include sleep fragmentation, decrement of sleep efficiency, increment of the wake time after sleep onset (WASO), increment of light sleep, and decrement of sleep depth. On the other hand, gabapentin (GBP), an antiepileptic drug analog of γ-aminobutyric acid (GABA) used as adjunctive and eventually, as a monotherapeutic treatment, induces a significant improvement in patients with both focal and secondarily generalized partial seizures. In experimental epilepsy models, this drug protects against pentylenetetrazol (PTZ)-induced convulsions. In consideration of such GBP properties, the aim of this work was to investigate its efficacy to protect against sleep disturbances provoked by convulsive seizures induced by the administration of PTZ. Nine-hour (9-hour) polygraphic studies were carried out in chronically implanted male adult Wistar rats separated into 4 different groups of 6 individuals. Control recordings in each group were done after saline administration. One group received a SC Subcutaneous (SC) injection of 50 mg/kg of PTZ alone while the other three groups were injected with either 15, 30, or 60 mg/kg IP Intraperitoneal (IP) of GBP 30 min prior to PTZ (50 mg/kg SC) administration. Animals displayed the whole range of electrophysiological and behavioral manifestations of the disease during the epileptic episodes induced by PTZ administration, and the states of vigilance were significantly altered. Insomnia occurred immediately after PTZ injection preceding the appearance of the first epileptic symptoms. Thus, both slow wave sleep (SWS) and rapid eye movement sleep (REM sleep) were completely inhibited during a relatively long period of time. The disturbing effects of epilepsy on sleep decreased when animals were under GBP treatment. Improvement of sleep was dependent on the administered dose of this antiepileptic drug.

Evaluation of dynamic scaling of growing interfaces in EEG fluctuations of seizures in animal model of temporal lobe epilepsy

Epileptic seizures, as a dynamic phenomenon in brain behavior, obey a scale-free behavior, frequently analyzed by electrical activity recording. This recording can be seen as a surface that roughens with time. Dynamic scaling studies roughening processes or growing interfaces. In this theory, a set of exponents -obtained from scale invariance properties- characterize rough interfaces growth. The aim of the present study was to investigate scaling behavior in EEG time series fluctuations of a chemical animal model of temporal lobe epilepsy, with dynamic scaling to detect changes on seizure onset. We analyzed local variables in different sampling intervals and estimated rough, scaling and dynamic exponents. Results exhibited long-range correlations in interictal activity. Results of renormalization and data collapsing confirmed that each epoch of EEG fluctuations for interictal, preictal and postictal collapse in a curve in different scales, each segment independently; remarkably, we found non-scaling behavior in seizures epochs. Data for the different sampling intervals for ictal period do not collapse in one curve, which implies that ictal activity does not exhibit the same scaling behavior than the other epochs. Statistical significant differences of growth exponent were found between interictal and ictal segment, while for scaling exponent, significant differences were found between interictal and postictal segment. These results confirm the potential of scaling exponents as characteristic parameters to detect changes on seizure onset, which suggests their use as inputs for analysis methods for seizure detection in long-term recordings, while changes in growth exponent are potentially useful for prediction purposes.

Unilateral microinjection of carbenoxolone into the pontis caudalis nucleus inhibits the pentylenetetrazole-induced epileptiform activity in rats

Pontine reticular formation (PRF) is involved in the generation and maintenance of generalized epileptic seizures. Carbenoxolone (CBX) is a gap junction blocker with anticonvulsant properties. Therefore, the present study was designed to explore the effects of CBX microinjected into the pontis caudalis nucleus (PnC) on generalized tonic-clonic seizures (GTCS) and epileptiform activity induced by pentylenetetrazole (PTZ). All control rats presented GTCS after a single dose of PTZ. The microinjection of CBX into the PnC reduced the GTCS incidence induced by PTZ. Moreover, the CBX significantly increased the latency to the first myoclonic jerk. Additionally, CBX significantly decreased the spectral power and the amplitude of the epileptiform activity induced by PTZ. By contrast, the microinjection of a gap junction opener (trimethylamine) did not cause anticonvulsant effects and even increased the duration of the GTCS. These findings suggest that the PnC is a particular nucleus where the CBX could exert its action mechanisms and elicit anticonvulsant effects.

Anticonvulsant effects of mefloquine on generalized tonic-clonic seizures induced by two acute models in rats

Background

Mefloquine can cross the blood–brain barrier and block the gap junction intercellular communication in the brain. Enhanced electrical coupling mediated by gap junctions is an underlying mechanism involved in the generation and maintenance of seizures. For this reason, the aim of this study was to analyze the effects of the systemic administration of mefloquine on tonic-clonic seizures induced by two acute models such as pentylenetetrazole and maximal electroshock.

Results

All the control rats presented generalized tonic-clonic seizures after the administration of pentylenetetrazole. However, the incidence of seizures induced by pentylenetetrazole significantly decreased in the groups administered systematically with 40 and 80 mg/kg of mefloquine. In the control group, none of the rats survived after the generalized tonic-clonic seizures induced by pentylenetetrazole, but survival was improved by mefloquine. Besides, mefloquine significantly modified the total spectral power as well as the duration, amplitude and frequency of the epileptiform activity induced by pentylenetetrazole. For the maximal electroshock model, mefloquine did not change the occurrence of tonic hindlimb extension. However, this gap junction blocker significantly decreased the duration of the tonic hindlimb extension induced by the acute electroshock.

Conclusions

These data suggest that mefloquine at low doses might be eliciting some anticonvulsant effects when is systemically administered to rats.

A mouse model that recapitulates cardinal features of the 15q13.3 microdeletion syndrome including schizophrenia- and epilepsy-related alterations

BACKGROUND

Genome-wide scans have uncovered rare copy number variants conferring high risk of psychiatric disorders. The 15q13.3 microdeletion is associated with a considerably increased risk of idiopathic generalized epilepsy, intellectual disability, and schizophrenia.

METHODS

A 15q13.3 microdeletion mouse model (Df[h15q13]/+) was generated by hemizygous deletion of the orthologous region and characterized with focus on schizophrenia- and epilepsy-relevant parameters.

RESULTS

Df(h15q13)/+ mice showed marked changes in neuronal excitability in acute seizure assays, with increased propensity to develop myoclonic and absence-like seizures but decreased propensity for clonic and tonic seizures. Furthermore, they had impaired long-term spatial reference memory and a decreased theta frequency in hippocampus and prefrontal cortex. Electroencephalogram characterization revealed auditory processing deficits similar to those observed in schizophrenia. Gamma band power was increased during active state, but evoked gamma power following auditory stimulus (40 Hz) was dramatically reduced, mirroring observations in patients with schizophrenia. In addition, Df(h15q13)/+ mice showed schizophrenia-like decreases in amplitudes of auditory evoked potentials. Although displaying a grossly normal behavior, Df(h15q13)/+ mice are more aggressive following exposure to mild stressors, similar to what is described in human deletion carriers. Furthermore, Df(h15q13)/+ mice have increased body weight, and a similar increase in body weight was subsequently found in a sample of human subjects with 15q13.3 deletion.

CONCLUSIONS

The Df(h15q13)/+ mouse shows similarities to several alterations related to the 15q13.3 microdeletion syndrome, epilepsy, and schizophrenia, offering a novel tool for addressing the underlying biology of these diseases.

Effect of magnesium oxide on the activity of standard anti-epileptic drugs against experimental seizures in rats

Objectives:

To study the effect of oral magnesium oxide supplementation alone and on the activity of standard anti-epileptic drugs in the animal models of maximal electroshock seizures (MES) and chemically (pentylenetetrazole [PTZ])-induced seizures.

Methods:

Healthy male albino rats were given magnesium oxide (MgO) supplementation orally in various doses (500, 750 and 1000 mg/kg /day) for 4 weeks (day 1 to day 28). On day 0 and day 29, response to MES (180 mA for 0.2 s) was tested 1 h after pre-administration of phenytoin or carbamazepine orally. Similarly, in the other groups, the response to PTZ 40 mg/kg i.p. was tested 1 h after pre-administration of oral sodium valproate.

Results:

Oral administration of MgO in a low dose (500 mg/kg) for 4 weeks in healthy rats appears to exert protective effect against MES. High oral doses of MgO (750 and 1000 mg/kg) appear to enhance the activity of phenytoin and carbamazepine in the MES model. MgO supplementation was seen to decrease the latency of PTZ-induced seizures.

Conclusion:

The dose of oral MgO appears to have an inverse relation with the protective effect in MES-induced seizure model. High doses of MgO supplementation given orally appear to enhance the activity of standard anti-epileptic drugs in the MES-induced seizure model.

Status epilepticus affects the gigantocellular network of the pontine reticular formation

BACKGROUND

The impairment of the pontine reticular formation (PRF) has recently been revealed to be histopathologically connected with focal-cortical seizure induced generalized convulsive status epilepticus. To elucidate whether the impairment of the PRF is a general phenomenon during status epilepticus, the focal-cortical 4-aminopyridine (4-AP) application was compared with other epilepsy models. The presence of "dark" neurons in the PRF was investigated by the sensitive silver method of Gallyas in rats sacrificed at 3 h after focal 4-AP crystal or systemic 4-AP, pilocarpine, or kainic acid application. The behavioral signs of the developing epileptic seizures were scored in all rats. The EEG activity was recorded in eight rats.

RESULTS

Regardless of the initiating drug or method of administration, "dark" neurons were consistently found in the PRF of animals entered the later phases of status epilepticus. EEG recordings demonstrated the presence of slow oscillations (1.5-2.5 Hz) simultaneously with the appearance of giant "dark" neurons in the PRF.

CONCLUSION

We argue that the observed slow oscillation corresponds to the late periodic epileptiform discharge phase of status epilepticus, and that the PRF may be involved in the progression of status epilepticus.

The NMDAR subunit NR2B expression is modified in hippocampus after repetitive seizures

NMDA receptor is involved in synaptic plasticity, learning, memory and neurological diseases like epilepsia and it is the major mediator of excitotoxicity. NR2B-containing NMDA receptors may be playing a crucial role in epileptic disorders. In the present study the effect of the convulsant drug 3-mercaptopropionic acid (MP) repetitive administration (4-7 days) on the hippocampal NR2B subunit was studied. A significant decrease in NR2B in the whole hippocampus was observed after MP4 with a tendency to recover to normal values in MP7 by western blot assay. Immunohistochemical studies showed a decrease in several CA1 and CA2/3 strata (21-73%). MP7 showed a reversion of the drop observed at 4 days in stratum oriens, pyramidal cell layer in CA1, CA2/3 and CA1 stratum radiatum. A significant fall in the lacunosum molecular layer of both areas and stratum radiatum of CA2/3 was observed. The immunostaining in MP4 showed a decrease in the granulare layer from dentate gyrus (20%), in hillus (71%) and subicullum (63%) as compared with control and these decreases were similar at MP7 values. Results showed decreases in NR2B subunit expression in different areas following repeated MP-induce seizures, suggesting that NR2B expression is altered depending on the diverse hippocampal input and output signals of each region that could be differently involved in modulating MP-induced hyperactivity.

Generalization of seizures parallels the formation of "dark" neurons in the hippocampus and pontine reticular formation after focal-cortical application of 4-aminopyridine (4-AP) in the rat

Distribution and time course of the occurrence of "dark" neurons were compared with the EEG activity and behavior of rats during 4-aminopyridine (4-AP) induced epileptic seizures. A crystal of the K(+) channel blocker 4-AP (0.5 mg/kg) was placed onto the exposed parieto-occipital cortex of Halothane-anesthetized rats for 40 min. Thereafter, the anesthesia was discontinued and the behavioral signs of the epileptic seizure activity were observed. The presence of "dark" neurons was demonstrated by the sensitive silver method of Gallyas in rats sacrificed at 0, 3 and 6 h after the end of the 4-AP crystal application. The EEG activity was recorded in the rats with longer survival times. The EEG analysis revealed the generalization of the epileptic seizures. We found that the formation of "dark" neurons in the hippocampus and the pontine reticular formation paralleled the generalization of the seizures.

Spatiotemporal changes of the N-methyl-d-aspartate receptor subunit levels in rats with pentylenetetrazole-induced seizures

The aim of this study was to examine the expression profiles of N-methyl-D-aspartate (NMDA) receptor subunits in rats during seizure development and kindled process induced by pentylenetetrazole (PTZ). Using quantitative Western blotting, the levels of NR1, NR2A and NR2B subunits were measured in the cortex and hippocampus of rats at different times after PTZ injection. In the early seizure developmental process, both NR1 and NR2A were markedly increased in the cortex, and NR1 was significantly increased in the hippocampus. On the other hand, in the kindled process both NR1 and NR2A decreased in the cortex and hippocampus. However, the NR2B subunit had no appreciable change in both the seizure developmental and kindled process. Therefore, these results showed that expression of NMDA receptors undergoes subunit- and region-related changes in the developmental and kindled seizure of rats induced by PTZ.

Ascorbate modulates pentylenetetrazol-induced convulsions biphasically

Ascorbate is an antioxidant vitamin that is found in high concentrations in the brain which seems to have neuroprotective properties in some experimental models of excitotoxic neurological disorders, including convulsive behavior and reactive species-related damage. In this study we tested whether ascorbate (30, 100 or 300 mg/kg, i.p.) protects against the convulsions, protein carbonylation and inhibition of Na(+),K(+)-ATPase activity induced by pentylenetetrazol (PTZ; 1.8 micromol/striatum), a classical convulsant agent that has been fairly used for the study of epilepsy and screening of new compounds with antiepileptic activity. The intrastriatal injection of PTZ caused convulsive behavior in a dose-dependent manner and an increase in the total protein carbonyl content of the injected striatum. However, duration of PTZ-induced convulsive episodes did not correlate with protein carbonyl content of the injected striatum. Ascorbate, at high doses (300 mg/kg), protected against PTZ-induced convulsions, protein carbonylation and inhibition of Na(+),K(+)-ATPase activity in the rat striatum, further suggesting a anticonvulsant and neuroprotective role for this vitamin. Conversely, intermediate doses of ascorbate (100 mg/kg) potentiated the duration of the convulsive episodes, but had no additive effects on protein carbonylation or Na(+),K(+)-ATPase activity inhibition induced by PTZ. Low doses of ascorbate (30 mg/kg) prevented PTZ-induced increase of total striatal carbonyl protein content, but did not alter PTZ-induced convulsions and Na(+),K(+)-ATPase activity inhibition. Collectively, these data indicate that the anticonvulsant activity of ascorbate is not related to its antioxidant action and support a dual role for this compound as a neuroprotective agent, since while it protects against PTZ-induced cellular oxidative damage, it has a biphasic effect on PTZ-induced convulsions.

MK-801 disrupts acquisition of contextual fear conditioning but enhances memory consolidation of cued fear conditioning

The effects of pre-training or post-training subcutaneous injections of multiple doses of the non-competitive NMDA-receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) on cued and contextual fear conditioning were examined in F344 rats. Pre-training injections of MK-801 (0.3 and 1.0 mg/kg) disrupted contextual fear conditioning but not cued fear conditioning. Post-training injections of MK-801 did not disrupt cued or contextual fear conditioning. In fact, the 0.3 mg/kg dose of MK-801 enhanced cued fear conditioning. Finally, rats were tested for MK-801-induced alterations in sensitivity to pain using the formalin test for nociception. MK-801 did not reduce sensitivity to pain. These results suggest that NMDA receptors are involved in acquisition of contextual fear conditioning but not in memory consolidation of the learned response.