Continuous bilateral infusion of vigabatrin into the subthalamic nucleus: Effects on seizure threshold and GABA metabolism in two rat models

Abstract

The subthalamic nucleus (STN) plays a crucial role as a regulator of basal ganglia outflow but also influences the activity of cortical and limbic structures, so that it is widely used as a therapeutic target in different brain diseases, including epilepsy. In addition to electrical stimulation of the STN, targeted delivery of anti-seizure drugs to the STN may constitute an alternative treatment approach in patients with pharmacoresistant epilepsy. In the present experimental study, we investigated the anti-seizure and adverse effects of chronic infusion of vigabatrin into the STN of rats. Vigabatrin is a clinically approved anti-seizure drug, which acts by increasing brain GABA levels by irreversibly inhibiting GABA-aminotransferase (GABA-T). Based on functional and neurochemical effects of acute STN microinjection, doses for continuous infusion were calculated and administered, using an innovative drug infusion technology. Bilateral infusion of only 10 μg/day vigabatrin over 3 weeks into the STN resulted in an almost complete inhibition of GABA-T and 4-fold increase in GABA in the target region, which was associated with a significant increase in seizure threshold, determined once weekly by i.v. infusion of pentylenetetrazole (PTZ). Lower doses or unilateral infusion were less effective, both on PTZ seizures and on kindled seizures. Bilateral infusion into substantia nigra pars reticulata was less effective and more toxic than STN infusion. In part of the rats, tolerance to the anti-seizure effect developed. The data demonstrate that chronic administration of very low, nontoxic doses of vigabatrin into STN is an effective means of increasing local GABA concentrations and seizure threshold.

Keywords

• Pentylenetetrazole
• GABA aminotransferase
• Substantia nigra
• Basal ganglia
• Pharmacoresistance