No-Bridge of Drosophila Melanogaster: Portrait of a Structural Brain Mutant of the Central Complex

Abstract

The mutant no-bridge (nobKS49) has its name from a structural defect in the protocerebral bridge of the central complex. This rod-shaped neuropil in nobKS49 has a large gap at the sagittal midplane, with some of the missing material accumulated more laterally. Mutant nob flies have a reduced maximal and average walking speed. Leg coordination is disturbed during turning but not while walking straight. Motivation for walking is low and steps are small due to slow forward swinging of the legs. Flies spontaneously may pass into an autistic (and possibly spastic) state in which they can move their legs and even perform cleaning movements but do not walk or fly. They spontaneously recover if left undisturbed. Gynandromorph experiments place the focus of the walking defects into the head. Mutant flies have a reduced tendency to escape when mechanically stimulated. In a brightly lit arena they do not avoid a black square above the horizon and they are negatively phototactic. In tethered flight optomotor responses are normal but the amplitude of spontaneous torque modulations as well as the number of torque spikes are reduced. If a single black bar is slowly rotated around the fly, the normal response pattern is observed. It vanishes, however, at moderately fast angular velocity at which the wild type still is fully responsible. The behavioral defects support the notion that the protocerebral bridge is part of a higher center for the regulation of behavior.

Expression of Drosophila mushroom body mutations in alternative genetic backgrounds: a case study of the mushroom body miniature gene (mbm).

“…To provide additional support for this conclusion, we compared walking and orientation of mbm1(CS) and CS flies in Buridan's paradigm (31,37,38) and in fast phototaxis (39) ( Table 2). mbm1(CS) was not significantly different from CS in total track length, mean walking speed, and landmark orientation.…”

“…Walking, landmark orientation, circadian activity rhythms (48), male courtship (49), and flight behavior (12) 0.0094 *Values are mean + SE of 2-to 6-day-old female flies (n = 10). Fly position was sampled every 0.2 s for 15 min (4.5 X 103 measurements per fly) (31,38). All comparisons were not significant.…”

“…Aspects of walking behavior were measured in Buridan's Paradigm (31, 37), as described by Strauss et al (38). Single 2-to 6-day-old flies with wings clipped (at the anterior cross-vein) were tracked and recorded for 15 min using a video scanning device.…”

“…Fast phototaxis (39) was also used as a measure of locomotor activity, as described by Strauss et al (38). Scores for each genotype were calculated from groups of -80 flies as the percent of all possible transitions toward light in a countercurrent device during 5 consecutive 5-s intervals.…”

Improved functional abilities of the life-extended Drosophila mutant Methuselah are reversed at old age to below control levels

“…The distance walked in a fixed period of time has previously been used as a measure of exploratory behavior and locomotor ability in Drosophila (Strauss et al 1992;Hayward et al 1993;Roberts 1998;Petrosyan et al 2007). The current experiment measured average walking distance for both genotypes in a large well-lit arena (60×45 cm).…”