Imaging Dedicated and Multifunctional Neural Circuits Generating Distinct Behaviors

TLDR

Central pattern generators (CPGs) control both swimming and crawling in the medicinal leech. The study investigates whether neurons in the leech’s swimming and crawling CPGs are dedicated or multifunctional. Using voltage‑sensitive dye imaging of ~80 % of the ~400 neurons in a segmental ganglion, the authors elicited swimming and crawling in the same preparation to identify neurons active in either rhythm or both, and characterized two previously unidentified interneurons, 255 and 257. The imaging revealed that crawling recruits more than twice as many neurons as swimming, that 93 % of swimming‑oscillating cells also participate in crawling, and that interneuron 255 is multifunctional while 257 is crawling‑specific, demonstrating that both dedicated and multifunctional neurons drive the two behaviors.

Abstract

Central pattern generators (CPGs) control both swimming and crawling in the medicinal leech. To investigate whether the neurons comprising these two CPGs are dedicated or multifunctional, we used voltage-sensitive dye imaging to record from ∼80% of the ∼400 neurons in a segmental ganglion. By eliciting swimming and crawling in the same preparation, we were able to identify neurons that participated in either of the two rhythms, or both. More than twice as many cells oscillated in-phase with crawling (188) compared with swimming (90). Surprisingly, 84 of the cells (93%) that oscillated with swimming also oscillated with crawling. We then characterized two previously unidentified interneurons, cells 255 and 257, that had interesting activity patterns based on the imaging results. Cell 255 proved to be a multifunctional interneuron that oscillates with and can perturb both rhythms, whereas cell 257 is an interneuron dedicated to crawling. These results show that the swimming and crawling networks are driven by both multifunctional and dedicated circuitry.