GIANT FIBER ACTIVATION OF AN INTRINSIC MUSCLE IN THE MESOTHORACIC LEGOF DROSOPHILA-MELANOGASTER

Cinematographic analysis reveals that an important component of the li ght-elicited escape response of Drosophila melanogaster is the extensi on of the femur-tibia joint of the mesothoracic leg. During the jumpin g phase of the response, this extension works synergistically with ext ension of the femur. Femur extension is generated by contraction of th e tergotrochanteral muscle (TTM), one of four previously described esc ape response muscles. Femur-tibia joint extension in the mesothoracic leg has been thought to be controlled by contraction of the tibial lev ator (TLM), an intrinsic leg muscle. We investigated the activation of the TLM during the escape response. Electrical stimulation of the gia nt fiber interneuron that mediates the escape response results in acti vation of the TLM with a latency of 1.46+/-0.02 ms. The TLM is innerva ted by a motor neuron (TLMn) with a large cell body in the mesothoraci c ganglion. The TLMn has extensive arborizations in the lateral mesoth oracic leg neuromere and has a prominent medially directed neurite. To investigate possible presynaptic inputs activating the TLMn during th e escape response, we analyzed the muscle responses of two mutants, gi ant fiber A1 and bendless. Our analysis suggests that the TLMn is acti vated by a novel pathway.