Paul S. Katz
Speaker of Workshop 1
Will talk about: Comparative neural circuitry in sea slugs; a multiplicity of mechanisms to produce species-specific behaviors
Dr. Katz is interested in understanding how neuronal circuits operate. He uses sea slugs (Mollusca, Gastropoda, Heterobranchia, Nudipleura) because they have fairly simple brains and simple behaviors. His lab determines the neural mechanisms for these behaviors at the cellular level. Furthermore, because there are many species with similar nervous systems, they can compare the neural circuits in these species to learn about the evolution of neural circuits and behavior. Individual animals exhibit variability in behavior and/or variability in circuit properties. It is important to understand the implications of these differences. Sea slugs offer a great opportunity for studying such inter-individual variability because the neurons in neural circuits are individually identifiable. So, one can examine how particular neurons and particular synapses differ between individuals. Furthermore, one can perturb those neurons and synapses to make them more or less similar to each other using techniques like dynamic clamp or expression of exogenous genes. A new direction in the lab involves using Next Generation RNA sequencing to determine all of the genes that are expressed in slug brains, the so-called transcriptome. This has been completed in six different species, allowing the researchers to determine differences and similarities in their genes and then to map those genes onto the neural circuits and the behavior.
Gastropod molluscs, including sea slugs, have highly tractable nervous systems with large, identifiable neurons, allowing neural circuitry to be determined using pair-wise intracellular microelectrode recordings. We have been investigating central pattern generator (CPG) circuitry underlying rhythmic swimming behaviors in six different species. The CPGs contain as few as four neurons in some species, allowing unparalleled control over each neuron in the circuit. Homologous neurons have been identified across species using neurochemical and neuroanatomical criteria. A limitation for identifying homologous neurons has been the paucity of molecular markers. New single-neuron transcriptomic methods promise to provide more markers and thus more readily allow homologous neurons to be identified. We found that species with homologous neurons that exhibit similar behaviors nonetheless used different neural mechanisms to produce the behaviors. This was explored by replacing synapses with computer-generated synapses using the Dynamic Clamp technique and rewiring the CPG of one species into that of another. In addition to synaptic connectivity differing across species, we found differences in neuromodulation, which account for some behavioral differences. Thus, even in these very small brains, there are important species-differences in the neural connectivity and modulation of that connectivity. Our results suggest that the swim CPGs evolved independently using homologous neurons in different configurations thus demonstrating that there are alternate ways to configure a CPG circuit.