Excitatory amino acid receptors appear to mediate paroxysmal depolarizing shifts in rat neocortical neurons in vitro

NMDA receptor binding in focal epilepsies

OBJECTIVE

To demonstrate altered N-methyl-d-aspartate (NMDA) receptor availability in patients with focal epilepsies using positron emission tomography (PET) and [(18)F]GE-179, a ligand that selectively binds to the open NMDA receptor ion channel, which is thought to be overactive in epilepsy.

METHODS

Eleven patients (median age 33 years, 6 males) with known frequent interictal epileptiform discharges had an [(18)F]GE-179 PET scan, in a cross-sectional study. MRI showed a focal lesion but discordant EEG changes in two, was non-localising with multifocal EEG abnormalities in two, and was normal in the remaining seven patients who all had multifocal EEG changes. Individual patient [(18)F]GE-179 volume-of-distribution (VT) images were compared between individual patients and a group of 10 healthy controls (47 years, 7 males) using Statistical Parametric Mapping.

RESULTS

Individual analyses revealed a single cluster of focal VT increase in four patients; one with a single and one with multifocal MRI lesions, and two with normal MRIs. Post hoc analysis revealed that, relative to controls, patients not taking antidepressants had globally increased [(18)F]GE-179 VT (+28%; p<0.002), and the three patients taking an antidepressant drug had globally reduced [(18)F]GE-179 VT (-29%; p<0.002). There were no focal abnormalities common to the epilepsy group.

CONCLUSIONS

In patients with focal epilepsies, we detected primarily global increases of [(18)F]GE-179 VT consistent with increased NMDA channel activation, but reduced availability in those taking antidepressant drugs, consistent with a possible mode of action of this class of drugs. [(18)F]GE-179 PET showed focal accentuations of NMDA binding in 4 out of 11 patients, with difficult to localise and treat focal epilepsy.

Epilepsy: new drug targets and neurostimulation

Despite advances in the medical and surgical therapy for epilepsy, about 30% of patients do not achieve full seizure control. In the past 5 years new antiepileptic drugs have been approved for clinical use. Some of these drugs have unique, novel mechanisms of action. Overall efficacy of these agents, however, seems similar to other antiepileptic drugs. Vagus nerve stimulation is a well-established palliative therapy for medically resistant epilepsy. Neurostimulation, with newer devices and targets becoming available, is a rapidly expanding field in epileptology. Considerable development and research are still necessary before these newer techniques become the standard of care for the treatment of epilepsy.

Tolerability and safety of perampanel: two randomized dose-escalation studies

OBJECTIVES

To evaluate, for the first time in patients with epilepsy, the tolerability and safety of escalating doses of oral perampanel, a novel, selective, non-competitive AMPA antagonist, as adjunctive therapy for refractory partial-onset seizures.

MATERIALS AND METHODS

Two consecutive, randomized, double-blind, dose-escalation studies recruited adults (18-70 years) with uncontrolled partial-onset seizures receiving one to three concomitant antiepileptic drugs. In study 206, patients were treated for 12 weeks (8-week dose-titration, 4-week dose-maintenance) with placebo or perampanel (up to 4 mg/day, dosed once- or twice-daily). In study 208, patients received placebo or perampanel once-daily (up to 12 mg) for 16 weeks (12-week titration, 4-week maintenance).

RESULTS

Overall, 153 patients were randomized into study 206 (perampanel twice-daily, n = 51; perampanel once-daily, n = 51; placebo, n = 51). Study 208 included 48 patients (perampanel once-daily, n = 38; placebo, n = 10). The highest dose in study 206 - 4 mg/day - was well tolerated, with similar proportions of patients tolerating once-daily (82.4%) and twice-daily (82.4%) perampanel and placebo (82.4%) treatments. In study 208 most patients tolerated doses of ≥ 6 mg perampanel once-daily in a Kaplan-Meier analysis. In both studies, the most common adverse events were CNS-related; most were of mild/moderate severity.

CONCLUSIONS

Perampanel was well tolerated across doses of 4-12 mg/day. The studies showed preliminary evidence of efficacy and identified doses to be evaluated in larger clinical studies.

Long-lasting changes in the origin of spontaneous discharges from amygdala-kindled rats: piriform vs. perirhinal cortex in vitro

The origin of spontaneous field potentials in coronal slices of the amygdala-piriform-perirhinal area (A-P area) from amygdala-kindled and control rats was assessed. In Expt. 1, the field potentials initially originated in the perirhinal (PRh) cortex of control tissue while they originated in the piriform (Pir) cortex of amygdala-kindled tissue. In Expt. 2, this kindling-based change was observed in the A-P area ipsilateral but not contralateral to the kindled amygdala. In both experiments, subsequent exposure to perfusion medium containing 0 Mg2+ resulted in the genesis of strong discharges in both control and kindled tissues. After 2-3 h of such treatment, the origin of spontaneous discharges in control tissue changed from the PRh to the Pir area and persisted in a reduced form during reperfusion with medium containing Mg2+. This change in origin of the discharges in control tissue appeared similar to that seen in previously kindled tissue. In Expt. 3, during exposure to 0 Mg2+, the response of the basolateral amygdala (BLA) was compared with the Pir and PRh areas. Independent of the PRh discharge, the BLA discharge closely followed the Pir discharge both in time and morphology. These lasting changes in the ipsilateral A-P area in vitro must be related in vivo to the change which allows the kindled A-P area to participate in the triggering of generalized limbic-kindled convulsions.