Decreased expression of hippocampal Na⁺/Ca²⁺ exchanger isoform-1 by pentylenetetrazole kindling in mice

A New Rat Model of Seizures Suitable for Screening Antiepileptic Electrical Stimulation Therapies

The antiepileptic effects of the electrical stimulation therapies developed for patients with intractable epilepsies depend critically on the stimulation parameters, including the pulse duration, current, and frequency. Consequently, optimization of such therapies requires many animals for testing each of the stimulation parameters alone or in combination, which is costly and time consuming. This drawback could be reduced by testing several stimulation paradigms in each animal, but this requires an animal model of long-lasting seizures allowing such repetitive tests. This study was performed to validate such a model of long-lasting seizures. The present analysis was performed on electrocorticogram and intracortical signals collected from the somatosensory cortex of 11 Sprague Dawley rats. A protocol of controlled intravenous infusion of pentylenetetrazol (PTZ) was developed to induce spike-and-wave (SW) seizures and maintain stable those seizures for the whole experimental time. SW discharges were induced and maintained stable for 2 h in all rats through a two-stage infusion of PTZ. During the first stage, the SW discharges were induced by 2.5 min infusion of 10 mg/kg/min PTZ. During the second stage, the SW discharges were maintained at a stable level of frequency and power for 2 h via a 0.21 mg/kg/min PTZ infusion rate. The proposed animal model of seizures is characterized by SW discharges which remain stable for 2 h. This 2-h long time interval allows repetitive tests with different stimulation parameters in each animal, which may lead to a significant reduction of the number of animals necessary for optimizing electrical stimulation therapies developed to inhibit seizures.

KB-R7943 reduces 4-aminopyridine-induced epileptiform activity in adult rats after neuronal damage induced by neonatal monosodium glutamate treatment

BACKGROUND

Neonatal monosodium glutamate (MSG) treatment triggers excitotoxicity and induces a degenerative process that affects several brain regions in a way that could lead to epileptogenesis. Na+/Ca2+ exchangers (NCX1-3) are implicated in Ca2+ brain homeostasis; normally, they extrude Ca2+ to control cell inflammation, but after damage and in epilepsy, they introduce Ca2+ by acting in the reverse mode, amplifying the damage. Changes in NCX3 expression in the hippocampus have been reported immediately after neonatal MSG treatment. In this study, the expression level of NCX1-3 in the entorhinal cortex (EC) and hippocampus (Hp); and the effects of blockade of NCXs on the seizures induced by 4-Aminopyridine (4-AP) were analysed in adult rats after neonatal MSG treatment. KB-R7943 was applied as NCXs blocker, but is more selective to NCX3 in reverse mode.

METHODS

Neonatal MSG treatment was applied to newborn male rats at postnatal days (PD) 1, 3, 5, and 7 (4 g/kg of body weight, s.c.). Western blot analysis was performed on total protein extracts from the EC and Hp to estimate the expression level of NCX1-3 proteins in relative way to the expression of β-actin, as constitutive protein. Electrographic activity of the EC and Hp were acquired before and after intracerebroventricular (i.c.v.) infusion of 4-AP (3 nmol) and KB-R7943 (62.5 pmol), alone or in combination. All experiments were performed at PD60. Behavioural alterations were also recorder.

RESULTS

Neonatal MSG treatment significantly increased the expression of NCX3 protein in both studied regions, and NCX1 protein only in the EC. The 4-AP-induced epileptiform activity was significantly higher in MSG-treated rats than in controls, and KB-R7943 co-administered with 4-AP reduced the epileptiform activity in more prominent way in MSG-treated rats than in controls.

CONCLUSIONS

The long-term effects of neonatal MSG treatment include increases on functional expression of NCXs (mainly of NCX3) in the EC and Hp, which seems to contribute to improve the control that KB-R7943 exerted on the seizures induced by 4-AP in adulthood. The results obtained here suggest that the blockade of NCXs could improve seizure control after an excitotoxic process; however, this must be better studied.