Pentylenetetrazole (PTZ)-induced kindling

Rats received multiple intraperitoneal injections of PTZ (Sigma-Aldrich, St. Louis, MO, USA) in a subthreshold dose (30 mg/kg of rat body weight, PTZ dissolved in 0.9% sterile saline) every other day, consecutively up to 5 weeks. 30 mg/kg of PTZ is a nonseizure inducing dose, but after multiple administrations it finally led to a precipitation of seizures and to a gradual progression in their strength and duration. Behavioral seizures were scored according to a modified Racine’s scale [4]. Rats were observed up to 2 h after each injection. Animals were assembled into three groups: control (no PTZ injection, only saline injections instead), partially kindled (only weak seizures after repeated PTZ administrations), and fully kindled (strong seizures during the last three PTZ injections). To differentiate effects related to a single neuronal depolarization from effects related to epileptogenesis, we used additional control in our kindling experiment—rats injected with the single subthreshold PTZ dose. All animals were sacrificed 24 h after the last injection and both hippocampi were collected.