From synapses, to neurons, to behavior in a nudibranch sea slug

To understand the neural mechanisms of behavior, we must investigate across scales: synaptic, neuronal, and the whole organism. The nudibranch sea slug Berghia stephanieae is a great model species as it is transparent, matures quickly, produces many offspring, and has a moderate number of neurons. We began looking at the synaptic level using immunohistochemistry. DLG4 is the invertebrate version of PSD95, labeling the post-synaptic region of neurons. We used an antibody for DLG4 to locate the specific regions in the adult nudibranch brain and the juveniles’ whole bodies. Surprisingly, juveniles showed immunoreactivity in the skin as well as the brain. We next used in-situ hybridization to visualize the organization of thousands of neurons in the nudibranch brain based on their gene expression. Berghia stephanieae expresses many neuropeptides, including neuropeptide F (NPF), similar to NPY in humans. We will label neurons expressing NPF and its receptors to understand which neurons are communicating. Finally, we looked at the nudibranch’s behavior. Bergia stephanieae has three sets of sensory appendages (rhinophores, oral tentacles, and palps) that we observed using high resolution video. Future experiments include a 3D maze; we will monitor how long it takes for individuals to find food when challenged with a series of obstacles. We also plan to remove part of the slug’s brain, and/or its appendages, to observe its compensatory capabilities after injury. After injured slugs are studied behaviorally, we will compare them to normal slugs at the two previous levels of analysis. This research was supported by NSF award # OIA-2242771.