Electrical activity of the external globus pallidus during generalized tonic-clonic epileptic seizures

Abstract

Generalized tonic-clonic seizures (GTCS) are associated with a lower quality of life, a higher likelihood of sudden death, and poor treatment outcomes. Understanding the circuits involved will offer better alternatives for controlling these seizures.

Generalized electrical discharges in epilepsy have an abrupt onset and offset. This favors the spread of epileptic activity to cortical circuits, which causes abnormal synchronization to subcortical circuits, such as the basal ganglia (BG). In this regard, patients with GTCS have been reported to show atrophy and hyperactivity in the BGs, which is why its anticonvulsant effect has been suggested.

The external globus pallidus (eGP) is a GABAergic hub within the BG circuit that synchronizes the overall activity of the BGs and the BG-thalamus-cortex circuit by controlling electrical activity toward its projection nuclei. Its alteration has been demonstrated in Parkinson's disease; however, its role in epilepsy has received little attention.

This context suggests that the electrical activity of Gpe neurons is modified during CGSTs. Therefore, this study aimed to analyze the electrical activity of Gpe neurons using single-unit extracellular recording in a pharmacological model (50 mg/kg of intraperitoneal pentylenetetrazole) of CGSTs in rodents. The presence of CGSTs was behaviorally assessed using the Racine scale.

Preliminary results showed an increase in Gpe firing frequency of 124.19% during CGSTs. Furthermore, the firing pattern (analyzed by the burst index [RI]) showed an increase (baseline RI 0.22 ± 0.38 vs. 0.56 ± CGST RI). The Gpe firing frequency range was 20 Hz before the CTCG seizure; it increased to above 55 Hz during the seizure. These results suggest the Gpe's active participation during CTCGs and modification of its electrical activity during them.