Rationale:
Inbred WAG/Rij strain of rats is characterized by episodes of rhythmic activity in the EEG. It is taken as a model of human absences. These types of seizures are typical for school age children. This study aims to find differences elucidating the origin of episodes.
Methods:
Male WAG/Rij and Wistar immature albino rats were used. Two experiments were performed: Pentylenetetrazol (PTZ)-induced convulsions and cortical epileptic afterdischarges (ADs). PTZ was administered subcutaneously in doses of 40, 60 and 80 mg/kg to animals 12, 18 or 25 days old. Rats were placed into Plexiglas boxes and observed for 30 min. Type of seizures, their incidence and latency were registered. ADs were elicited by rhythmic stimulation of sensorimotor cortex (8 Hz for 15 s) using implanted subdural electrodes again in the same age groups of rats. Presence, duration and type of convulsions were registered and evaluated.
Results:
PTZ induced generalized seizures in all rats of either strain if administered in a dose of 80 mg/kg. The significant difference was found after the 60/mg/kg dose. WAG/Rij 18-day-old animals exhibited higher incidence and severity of convulsions than Wistar rats of the same age.
WAG/Rij rats did not exhibit postictal depression of CxADs if stimulation was repeated one minute after the first AD. This phenomenon appears in older (25-day-old) WAG/Rij rats in contrast to Wistar animals where postictal refactoriness was present even at the age of 18 days.
Conclusions:
Marked differences between inbred epileptic WAG/Rij and Wistar rats appear at the age of 18 days, (i.e.at the age when spike-and-wave rhythm appear). It might be developmental stage decisive for generation of absence-like seizures.
Funding:
Supported by grant 23-05274S of the Czech Science Foundation, project National Institute for Neurological Research (Programme EXCELES, ID Project No. LX22NPO5107) (co-supported by EU), grant of Agency for Medical Research NU2004-00389 and Research Project RVO 67985823
.