DIFFERENT NEURAL PATHWAYS COORDINATE DROSOPHILA FLIGHT INITIATIONS EVOKED BY VISUAL AND OLFACTORY STIMULI

To determine the role played by the giant fiber interneurons (GFs) in coordinating the jumping stages of visually elicited and olfactory-ind uced flight initiation we have recorded extracellularly from the cervi cal connective nerve during flight initiation, A spike is recorded fro m the cervical connective upon brain stimulation that has the same thr eshold as does activation of the tergotrochanteral muscle (TTM) and do rsal longitudinal muscles (DLMs). A consistent time interval occurs be tween the spike and activation of the TTM, Thus, the spike probably re sults from activity in the GFs. The time intervals between the spike a nd activation of the TTM during GF stimulation and visually elicited f light initiation are similar, These results suggest that the GFs coord inate the activation of the TTM and DLMs during the jumping flight ini tiation. A spike is also recorded from the cervical connective during olfactory-induced flight initiations, but its shape and the time inter val between it and activation of the TTM is different from that observ ed during GF stimulation, Although some olfactory-induced flight initi ations exhibit a pattern of muscle activation indistinguishable from t hat evoked by GF stimulation, our results indicate that, regardless of the pattern of muscle activation, olfactory-induced flight initiation s are not coordinated by the GF circuit, The stereotypic sequence and timing of activation of TTM and DLMs characteristic of the GF pathway can, therefore, be evoked by neurons other than those constituting the GF pathway.