Figure 5.—

Transmission defects in the GF-DLM pathway of cpo adults. (A) DLM4 and DLM5 responses to brain stimulation in a cpo fly (cpo^EG1/cpo^cp1). Shown are responses to three consecutive 0.2-sec pulses administered near the following frequency threshold of 22 ± 9.2 Hz in cpo^EG1/cpo^cp1 mutants. The response of DLM4 is invariant, while the DLM5 response shifts in latency and then fails independent of DLM4. Independent failure between DLM4 and DLM5 implicates a defect distal to the PSI as the likely labile site in the GF-DLM pathway. (B) DLM5 and DLM6 responses to brain stimulation in the same cpo fly (cpo^EG1/cpo^cp1). Three consecutive 0.2-sec pulses administered near the following frequency threshold do not produce independent failure between DLM5 and DLM6, which are innervated by the same motoneuron, DLMn5. Instead both show identical shifts in latency before eventually failing together. This synchronous firing and failing between DLM5 and DLM6 tends to rule out the DLM NMJ as the labile site in the GF-DLM circuit. Thus, the labile site in the GF-DLM pathway appears to be synapses between the PSI and DLM motoneurons (calibrations, 20 mV and 1 msec).