TbhnM18 mutant larvae travel less distance than control larvae.
TbhnM18 mutants are in forward locomotion only ~35% of the time, compared to ~80% for wild-type larvae.
Regular rhythmic activity is less common in TbhnM18 mutants compared to control larvae. Only 25% of TbhnM18 larvae show spontaneous bursting activity (compared to 88% in the revertant TbhrM6 and 85% in wild-type). Instead, there is a high level of tonic nerve activity with very few bursts. These bursts have a similar spindle shape as controls, with larger amplitude neurons firing near the end of the bursts.
Rhythmic nerve bursting activity and muscle contraction waves are rare in TbhnM18 mutants.
Nerve spiking bursts, associated with waves of body-wall contractions, are rare in TbhnM18 mutants compared to wild-type. These locomotive contraction waves are often isolated, not part of a regular rhythmic pattern, as in wild-type. Only occasional intersegmentally co-ordinated bursts are seen, generating an anterior to posterior (or vice versa) contraction wave, consistent with the lack of linear locomotion pattern in TbhnM18 mutant larvae. Most bursts are associated with isolated local, nonpropagated contractions. For bursts associated with propagating waves, there are no obvious differences from wild-type in the co-ordination of activities bilaterally within a single segment or unilaterally from nerves innervating anterior and posterior segments.
Non-rhythmic activity that is not associated with regular waves of body-wall contractions is more frequent in TbhnM18 mutants that have reduced OA and increased TA levels, compared to wild-type. On average, TbhnM18 mutants have 80% fewer bursts per minute than the wild-type larvae and 65% fewer bursts than the TbhnM18 revertants. In addition, bursts in TbhnM18 mutants are less likely to be part of a regular rhythmic pattern.
TbhnM18 mutants express non-rhythmic bursting activities significantly more often than control larvae. TbhnM18 mutants spend approximately 93.6% of the time in non-rhythmic activities, whereas TbhrM6 revertant and wild-type larvae exhibit non-rhythmic activities approximately 46.6% and 34.4% of the time, respectively. TbhnM18 mutants produce regular rhythmic patterns 7% of the time, with these locomotor contraction waves divided equally between posterior-to-anterior and anterior-to-posterior. In contrast, wild-type or revertant larvae are much more likely to generate posterior-to-anterior locomotive waves.
It is very rare for rhythmic bursting activity to persist for >5 or >10 bursts in TbhnM18 mutants, despite this being a common occurence in wild-type.
Segmental nerves of TbhnM18 mutants appear to be bilaterally co-ordinated, but bursts of activity associated with co-ordinated waves of contractions are rare in these mutants.
EJCs recorded from the ventral muscle 6/7, lateral muscle 4, or dorsal muscle 2 are organised into a bursting-like pattern for both wild-type larvae and TbhnM18 mutants. In general, the activity pattern of clustered EJCs is similar for simultaneous recordings from muscle pairs (e.g. ventral muscle 6/7 with lateral muscle 5, and muscle 6/7 with dorsal muscle 2). However, the temporal co-ordination of the muscle pairs appears to be tighter in wild-type larvae than TbhnM18 mutants.
The average number of strides produced by crawling larvae is 10 times lower in TbhnM18 mutants compared to wild-type controls.
Tapping the ventral midline with a silver wire near the head of TbhnM18 mutant larvae produces a dramatic effect. The ongoing nerve activity for all TbhnM18 mutants consists primarily of nonrhythmic spiking activities that are not associated with contraction waves. Touching the head of TbhnM18 mutants with a silver wire produces an extended burst in segmental nerve 3 that is associated with a contraction of the anterior body regions and not a locomotive contraction wave. Most strikingly, the contraction is followed by alternating bursts, in nerves 3 and 7, that are associated with anterior to posterior waves. Touching the tail of TbhnM18 mutant larvae initiates extended contractions and bursts in posterior segments of TbhnM18 larvae. This is followed by a rhythmic nerve activity pattern corresponding to contraction waves that proceed from posterior to anterior body segments. This demonstrates that the CNS of TbhnM18 mutants is capable of generating the motor program necessary for locomotion within a short period after sensory stimulation.