Abstracts

Rationale: The largest captive baboon colony in the world is housed at the Southwest Foundation for Biomedical Research (SFBR) in San Antonio, Texas. As natural epilepsy (spontaneous seizures) is highly prevalent in this colony, we used EEG to phenotype a large, accurately-pedigreed group of baboons within the colony. Some of the baboons also underwent repeat studies at least one year after their initial evaluation to assess the long-term stability of the electroclinical phenotypes. Methods: Scalp EEG studies were performed in 676 baboons (Papio hamadryas anubis, cynocephalus and their hybrids) using minimal intramuscular ketamine (5-6 mg/kg) to sedate the animals for transfers in and out of a primate chair and electrode placement. Intermittent light stimulation (ILS) was performed on two occasions during the one-hour study, at least fifteen minutes apart at frequencies 3-30 Hz. Each study was between 40-60 minutes in duration. The animals were classified according to conventional electroclinical phenotypes: presence or absence of interictal epileptic discharges (IEDs), seizures and photo-paroxysmal or -convulsive responses during the EEG studies. Effects of age, gender and species on EEG phenotypes were also examined. The present study was approved by the Institutional Animal Care and Use Committees of the UTHSCSA and SFBR. Results: The classification of the animals demonstrates that IEDs were identified in 332 (49%) baboons. Seizures were recorded in 221 (33%) animals, predominantly myoclonic (eyelid, face or body), rarely generalized tonic-clonic or absence, seizures. Photosensitivity was seen in 157 (23%) baboons. Only 42% of baboons with IEDs demonstrated photosensitivity, but photosensitivity was associated with IEDs in 89%, compared to 5% of baboons without IEDs. Repeat studies at mean interval of 3 (range 1-6) years in 30 baboons whose initial studies were performed at 4 years or older were concordant for the presence or absence of IEDs or photosensitivity in 70%, respectively. Conclusions: Spontaneous IEDs and seizures are highly prevalent in this baboon colony. Ketamine, particularly at low doses, may have slightly reduced the IED or seizure threshold. The prevalence of photosensitivity in baboons with IEDs is similar to that associated with juvenile myoclonic epilepsy. Both IEDs and photosensitivity are stable phenotypes in adolescent and adult baboons. The photosensitivity phenotype is strongly associated with the expression of IEDs. The high prevalence of IEDs in this pedigree, and the lack of gender, age or subspecies effects on the EEG phenotypes, strongly suggest that genetic factors must play a role in explaining the observed variability.