Figure 3.—

cpo mutants exhibit increased seizure susceptibility without a concomitant increase in single neuron excitability. (A) A representative seizure as recorded from the DLM following a high-frequency brain stimulus of 8 V ECS (depicted as a hatched box) in a cpo^EG1/cpo^cp1 fly. The DLM shows aberrant high-frequency firing approaching 50 Hz during the seizure phase. These high-frequency responses then give way to synaptic failure (not depicted) (calibrations, 10 mV and 200 msec). (B) A cpo^EG1/+ fly shows only a few spikes following an identical 8-V high-frequency stimulus to the brain, since this voltage is below its threshold for seizure. (C) However, seizures are elicited in cpo^EG1/+ flies following administration of 32 V ECS. (D) Comparison of seizure thresholds for various cpo genotypes shows increased seizure susceptibility for cpo mutants (n ≥ 6 for each genotype). (E) Comparison of the firing thresholds of the giant fiber in control flies and cpo mutants reveals no significant differences (n ≥ 6 for each genotype).