Pathophysiology of generalized photosensitive epilepsy in the cat.

Feline generalized penicillin-induced epilepsy is a reliable experimental model of epileptic photosensitivity. Binocular photic stimulation at 4-8 flashes/s consistently triggers generalized, bilaterally synchronous spike-and-wave discharges in cats submitted to long-term intramuscular penicillin administration at low dosage (50,000-150,000 IU/kg). The photically induced epileptic activity is first and mainly recorded from the cerebral cortex as compared with the lateral geniculate (GL) body, therefore supporting a cortical onset of epileptic photosensitivity. At this low penicillin dosage, only minimal spontaneous spike-and-wave activity is recorded. Bilateral GL stimulation is more effective than binocular photic stimulation in triggering spike-and-wave discharges, whereas unilateral GL stimulation is grossly ineffective. This observation implies a role of bilateral specific visual thalamocortical volleys in the genesis of epileptic photosensitivity. Five of 12 randomly selected cats receiving long-term penicillin exhibited spontaneous epileptic photosensitivity, a finding that suggests an underlying genetic predisposition of the feline species to this condition.