Ontogeny of ethosuximide action against two seizure models in rats is different

Ethosuximide Induces Hippocampal Neurogenesis and Reverses Cognitive Deficits in an Amyloid-β Toxin-induced Alzheimer Rat Model via the Phosphatidylinositol 3-Kinase (PI3K)/Akt/Wnt/β-Catenin Pathway

Neurogenesis involves generation of new neurons through finely tuned multistep processes, such as neural stem cell (NSC) proliferation, migration, differentiation, and integration into existing neuronal circuitry in the dentate gyrus of the hippocampus and subventricular zone. Adult hippocampal neurogenesis is involved in cognitive functions and altered in various neurodegenerative disorders, including Alzheimer disease (AD). Ethosuximide (ETH), an anticonvulsant drug is used for the treatment of epileptic seizures. However, the effects of ETH on adult hippocampal neurogenesis and the underlying cellular and molecular mechanism(s) are yet unexplored. Herein, we studied the effects of ETH on rat multipotent NSC proliferation and neuronal differentiation and adult hippocampal neurogenesis in an amyloid β (Aβ) toxin-induced rat model of AD-like phenotypes. ETH potently induced NSC proliferation and neuronal differentiation in the hippocampus-derived NSC in vitro. ETH enhanced NSC proliferation and neuronal differentiation and reduced Aβ toxin-mediated toxicity and neurodegeneration, leading to behavioral recovery in the rat AD model. ETH inhibited Aβ-mediated suppression of neurogenic and Akt/Wnt/β-catenin pathway gene expression in the hippocampus. ETH activated the PI3K·Akt and Wnt·β-catenin transduction pathways that are known to be involved in the regulation of neurogenesis. Inhibition of the PI3K·Akt and Wnt·β-catenin pathways effectively blocked the mitogenic and neurogenic effects of ETH. In silico molecular target prediction docking studies suggest that ETH interacts with Akt, Dkk-1, and GSK-3β. Our findings suggest that ETH stimulates NSC proliferation and differentiation in vitro and adult hippocampal neurogenesis via the PI3K·Akt and Wnt·β-catenin signaling.

Different effects of postnatal caffeine treatment on two pentylenetetrazole-induced seizure models persist into adulthood

BACKGROUND

Postnatal treatment with caffeine from P7 to P11 (10 or 20 mg/kg daily) resulted in transient changes in two pentylenetetrazole (PTZ)-induced models of epileptic seizures characterized by spike-and-wave EEG rhythm in immature rats. To know if some changes persist into adulthood we studied these models in young adult Wistar rats.

METHODS

Caffeine treatment at a daily dose of 10 and/or 20 mg/kg, sc was executed during postnatal days 7-11. Rhythmic metrazol activity (RMA, model of human absences) was induced in 60-day old rats by two successive doses of PTZ (20 + 20 mg/kg, ip) while for induction of minimal clonic seizures (model of human myoclonic seizures) the second dose of PTZ was 40 mg/kg.

RESULTS

RMA episodes elicited by the 20 + 20 mg/kg dose of PTZ in adult rats exposed to caffeine at P7 to P11 were decreased. This effect was more pronounced in group treated with the higher dose of caffeine. In contrast, the lower dose of caffeine exacerbated minimal clonic seizures (both incidence and intensity were increased). In addition, some animals from the 20-mg/kg caffeine group exhibited transition to generalized tonic-clonic seizures.

CONCLUSION

Different effects of postnatal caffeine exposure persist into adulthood; the seizure ameliorating effects in a model of absences and seizure exacerbating action in a model of myoclonic seizures are dose-specific.

Positive Allosteric Modulator of mGluR4 PHCCC Exhibits Proconvulsant Action in Three Models of Epileptic Seizures in Immature Rats

The activation of metabotropic glutamate receptors subtype 4 (mGluR4) potentiates models of absence seizures in adult rats. These seizures are age-dependent, but data concerning the role of mGluR4 in immature brain is insufficient. N-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1acarboxamide (PHCCC), which is a positive allosteric modulator of these receptors, was used in three different models of seizures in immature rats: 1) convulsions induced by high doses of pentetrazol (PTZ; a model of generalised tonic-clonic seizures); 2) rhythmic electro-encephalographic (EEG) activity induced by low doses of PTZ (a model of absence seizures); and 3) electrically elicited cortical afterdischarges (ADs, a model of myoclonic seizures). We administered four doses of PHCCC (1, 3, 10 and 20 mg/kg) in PTZ-induced convulsions and two doses (3 and 10 mg/kg) in the two electrophysiological models of freely moving rats with implanted electrodes. Every dose and age group consisted from 8 to 10 rats. PTZ-elicited convulsions were not significantly influenced by PHCCC. In contrast, PHCCC potentiated the effect of a subconvulsant dose (60 mg/kg) of PTZ. The 10-mg/kg dose of PHCCC significantly prolonged the duration of PTZ-induced rhythmic activity episodes and shortened the intervals between individual episodes in 25-day-old rats (P25). In contrast, this potentiation was not seen in P18 rats. Cortical ADs were significantly prolonged with repeated stimulations by both doses of PHCCC in P12 and P18 animals. P25 rats exhibited only slightly longer AD durations. In conclusion, we did not find any anticonvulsant effect of PHCCC. On the contrary, proconvulsant action was demonstrated in all three models in immature rats.

Models of epileptic seizures in immature rats

Models of basic types of epileptic seizures are elaborated not only in adult but also in immature rodents. It is important because at least half of human epilepsies starts during infancy and childhood. This paper presents a review of chemically and electrically induced models of generalized convulsive and nonconvulsive (absence) seizures as well as models of partial simple (neocortical) and complex (limbic) seizures in immature rats. These models can also serve as a tool for study the development of central nervous system and motor abilities because the level of maturation is reflected in seizure semiology. Age-dependent models of epileptic seizures (absences and flexion seizures) are discussed. Models of seizures in immature animals should be used for testing of potential antiepileptic drugs.

Ethosuximide: from bench to bedside

Ethosuximide, 2-ethyl-2-methylsuccinimide, has been used extensively for "petit mal" seizures and it is a valuable agent in studies of absence epilepsy. In the treatment of epilepsy, ethosuximide has a narrow therapeutic profile. It is the drug of choice in the monotherapy or combination therapy of children with generalized absence (petit mal) epilepsy. Commonly observed side effects of ethosuximide are dose dependent and involve the gastrointestinal tract and central nervous system. Ethosuximide has been associated with a wide variety of idiosyncratic reactions and with hematopoietic adverse effects. Typical absence seizures are generated as a result of complex interactions between the thalamus and the cerebral cortex. This thalamocortical circuitry is under the control of several specific inhibitory and excitatory systems arising from the forebrain and brainstem. Corticothalamic rhythms are believed to be involved in the generation of spike-and-wave discharges that are the characteristic electroencephalographic signs of absence seizures. The spontaneous pacemaker oscillatory activity of thalamocortical circuitry involves low threshold T-type Ca2+ currents in the thalamus, and ethosuximide is presumed to reduce these low threshold T-type Ca2+ currents in thalamic neurons. Ethosuximide also decreases the persistent Na+ and Ca2+ -activated K+ currents in thalamic and layer V cortical pyramidal neurons. In addition, there is evidence that in a genetic absence epilepsy rat model ethosuximide reduces cortical gamma-aminobutyric acid (GABA) levels. Also, elevated glutamate levels in the primary motor cortex of rats with absence epilepsy (but not in normal animals) are reduced by ethosuximide.

Two different anticonvulsant actions of tiagabine in developing rats

PURPOSE

Our goal was to study the anticonvulsant action of tiagabine (TGB) at different levels of brain maturation in rats.

METHODS

Wistar rats in five age groups (7, 12, 18, 25, and 90 days old) were injected intraperitoneally with TGB at doses of 0.5-32 mg/kg. Thirty minutes later, motor seizures were induced by the subcutaneous adminstration of pentylenetetrazol (PTZ) in a dose of 100 mg/kg for all of the groups except the 18-day-old rat pups, which received a 90-mg/kg dose. The incidence and latency of two types of motor seizures, minimal clonic and generalized tonic-clonic seizures (GTCSs), were evaluated, and the seizure severity was scored. The time profile of TGB action at the 8-mg/kg dose was studied in the 12-and 25-day-old rats.

RESULTS

Minimal clonic seizures were reliably induced in rats 18 days old or older, and the seizures were suppressed by TGB in all of these age groups. Although TGB was very effective against this type of seizure in the 18-day-old rats, the efficacy of the drug decreased with the age of the animal. GTCSs were suppressed by TGB in the adult and 25-day-old rats, and a U-shaped dose-response curve was outlined in these two groups. The 18-and 12-day-old rat pups exhibited a selective suppression of the tonic phase of GTCSs. A mixture of these two effects was observed in the youngest group. TGB demonstrated a markedly longer action in the 12-day-old rats than in the 25-day-old rats.

CONCLUSIONS

TGB exhibits anticonvulsant action against both minimal seizures and GTCSs. Ontogenetic development of these two actions is markedly different.