Understanding the development of flexible swimming patterns in Xenopus tadpoles

Centre for Neuroregeneration, University of Edinburgh

Background: Animals’ ability to flexibly control the speed of their own rhythmic movements is essential for expression of their full behavioural repertoire and often their survival, paramount for pursuing prey or evading predators. In tadpoles of the African clawed frog, Xenopus laevis, this ability to flexibly control swimming speed develops rapidly; by 72hours post fertilisation (hpf). The spinal networks responsible for rhythmic locomotion, such as walking and swimming, are known as central pattern generators (CPG). Coordination of movements by these networks can occur without sensory, or even descending input from the brain. The mechanisms underlying the flexible control of swimming in Xenopus tadpoles remain unknown, though those responsible are thought to be changes in the descending input from the brain or within the spinal CPG itself.

Methods: This project investigates whether flexible swimming patterns can be produced after (mid)-hindbrain lesion by Xenopus tadpoles at 72hpf, immobilised in α-bungarotoxin. Using ventral root recordings, the activity of populations of motoneurons were recorded 30 minutes before and after lesion, and their firing frequency used as a fictive correlate of swimming speed. Change in motoneuron burst frequency >30% was determined to constitute flexible swimming.

Results: Flexible swimming patterns could still be produced after lesion (n= 3/20 tadpoles); proving that flexible swimming can occur without descending input from higher brain centres.

Conclusions: Mechanisms underpinning flexible swimming can be accounted for by changes in the spinal networks. Future research will investigate changes in the CPG network and test their influence on the development of flexible swimming.