Serotonin and sensorimotor adaptation in Drosophila larvae

Locomotion requires specialized neural circuits called central pattern generators (CPGs) that tightly control the movement of specific body parts. These circuits need to control crawling in a potentially changing environment, and in the presence of potential injuries. How these CPGs respond to localized disruptions is not well understood. To address this, we attached a splint to two abdominal segments on the right side of the larva, and observed their crawling behavior. The splint initially causes an exaggerated side-to-side movement in the posterior, characterized by a difference between the left and the right of segment A5 compressing. After four hours, the side-to-side movement is reduced and the left and right of A5 compress at the same time. Larvae are able to deadapt over a very short period of time after the splint was removed. These results indicate that changes in segment connections are capable of occurring in response to different stressors.
Adaptation occurs more rapidly in the presence of increased serotonin, and fails to occur when serotonin levels have decreased. Serotonin’s action in adaptation is dependent upon signaling through the 5-HT7 receptor expressed specifically in glial cells. In addition, we describe an assay that can be used to understand neuromodulators, genetics, and anatomical components of plasticity and change in CPGs and sensorimotor circuits. In an unexpected result, we discovered a temperature-sensitive component to adaptation. Larvae exposed to higher temperature have a reduced asymmetric posterior movement, which returns when larvae are retuned to room temperature.