Neural correlates of flight loss in a Mexican grasshopper, Barytettix psolus. II. DCMD and TCG interneurons.

Comparison of the nervous systems of a flightless grasshopper (Barytettix psolus), and locusts (Schistocerca) is extended to include two large interneurons, the descending contralateral movement detector (DCMD) and the tritocerebral commissure giant (TCG). These interneurons are thought to play a role in locust flight. Both were visualized in Barytettix with cobalt staining techniques. Most features of the two neurons are similar in both locusts and Barytettix. Yet, several differences were noted. In locusts, the dorsal DCMD branch in its metathoracic projection terminates in dorsolateral neuropile and synapses with flight motorneurons (Pearson and Goodman, '79). In Barytettix, no branch terminates in the corresponding region. Of the animals examined, 52% lacked branches corresponding to locust dorsal branches. When present, they all had abnormal projections by comparison to their counterparts in locusts. The maintenance of the TCG in Barytettix with so similar a form to that of locusts suggests that the role of the cell in behavior other than flight should be examined. The differences in DCMD projection suggest that a discrete set of output connections may have been modified in Barytettix by the alteration of a single first-order axonal branch.