Lab Seminar

We understand relatively little about how interneurons regulate motoneuron activity during different movements. Here, I will present evidence that interneurons are organized differently from motoneurons, using the spinal control of swimming in young zebrafish as a model. Spinal motoneurons follow the size principle, with more and more cells added to the active pool as zebrafish swim faster. This pattern is not only related to the size of motoneurons, but also to their input resistance and their position in the spinal cord. For spinal excitatory interneurons, cells are also recruited topographically according to input resistance, but not to size. In addition, unlike motoneurons there are switches in the pools of active interneurons during increases in speed. More ventral excitatory interneurons are inhibited as more dorsal cells are engaged. This inhibition occurs not only between classes of excitatory interneuron, but also within a single class. Thus, increases in movement intensity are achieved by activating more motoneurons, but different interneurons. I will discuss the relevance of this pattern to other vertebrates.

• McLean et al, (2008). Continuous shifts in the active set of spinal interneurons during changes in locomotor speed. Nature Neuroscience 11, 1419-29.
• McLean et al, (2007). A topographic map of recruitment in spinal cord. Nature 446, 71-5.