Ontogeny of sound-induced seizures in the genetically epilepsy-prone rat

Seizure responsiveness of the adult genetically epilepsy-prone rat (GEPR) is well documented. Much less is known about the ontogeny to seizure activity in the GEPR. In the present study, members of the moderate seizure (GEPR-3) and severe seizure (GEPR-9) colonies were tested for susceptibility to sound-induced seizures at 11 different ages ranging from 13 to 45 days post partum. Running episodes first appeared in GEPR-3s at 15 days post partum. Clonic seizures first appeared in GEPR-3s and GEPR-9s at 15 and 16 days post partum, respectively. Seizure incidence reached 100% by post partum day 21 in both colonies. GEPR-3s exhibited a 100% incidence of their characteristic clonic seizure at day 21. GEPR-9s exhibited a 77.3% incidence of clonic seizure and a 22.7% incidence of their adult characteristic tonic seizure at day 21. Tonic seizures first appeared in GEPR-9s at day 18 and increased in incidence over time reaching 100% by day 45. Two unexpected findings occurred in GEPR-3s. First, secondary rearing seizures were detected in all GEPR-3s exhibiting clonic seizures between day 16 and 21. Second, GEPR-3s exhibited a transient susceptibility between 19 and 27 days post partum to the more severe tonic seizures characteristic of adult GEPR-9s. Peak incidence of tonic seizures in GEPR-3s was 70%, occurring at day 23. The adult GEPR-3 pattern of 100% incidence of clonic seizures was restored by day 45.