Seizures and failures in the giant fiber pathway of Drosophila bang-sensitive paralytic mutants

Abstract

Drosophila bang-sensitive paralytic mutants suffer from hyperactivity and paralysis following a mechanical shock; after recovery from paralysis, they cannot be paralyzed for a refractory period lasting up to 1 hr. Previously, we have shown that in easily shocked (eas), a typical bang-sensitive mutant, electrical shocks delivered to the brain cause seizure-like activity in the dorsal longitudinal flight motor neurons (DLMmns), and failure of giant fiber (GF) stimulation to evoke DLM potentials via the escape response pathway (Pavlidis et al., 1994). Here, we show that seizure and failure in the GF pathway with a refractory period is common to all six members of the bang-sensitive class. This syndrome was not found in any of eight other excitability mutants, including those affecting voltage-gated sodium or potassium-channel function. We show that failure occurs at the synapse between a peripherally synapsing interneuron (PSI) and the DLMmns, while the DLMmn-DLM neuromuscular junctions remain functional. Additionally, failure occurs in all other GF pathway-activated muscles. Failures occurred without seizures in the tergotrochanteral jump muscle (TTM), as was also found in approximately 10% of DLM tests, suggesting that seizures and failures may be independent events. This hypothesis is supported by the finding that, in double mutant combination with mlenapts, which suppresses behavioral bang sensitivity, DLM failures, but not seizures, were reduced.