Fetcho, J.R.: New approaches to the function of neuronal circuits that might simplify (a little) studies of the evolution of behavior.

Understanding motor patterns (electromyograms) and their evolution requires understanding the neuronal circuits that produce them and the evolutionary changes in those circuits. This is not easy, which is perhaps why there are not many explicitly comparative studies of the functional organization of motor circuits for feeding or other vertebrate behaviors. Simply identifying which neurons are involved in a particular behavior in even one species is a challenge and doing this in a comparative way has been unrealistic. The problem is even more complicated because over the last decade neurobiological studies have shown how plastic the nervous system really is. Changes in motor output, even within a single animal, can occur in many ways, including changes in synaptic connections, alterations in ion channel expression in neurons, or a restructuring of the function of neuronal circuits by neuromodulators. The challenge is to develop techniques that are easily applicable across species which allow one to identify the active neurons in a behavior and to test their function. Such approaches would then allow for comparative studies of motor circuits in animals with differing motor patterns. We have been applying optical methods and fluorescent indicators to image which neurons are active during behavior of larval fish and to reconstruct their morphology in the live animal. In addition, we have developed approaches to laser kill neurons to test their function in vivo. These approaches, combined with powerful new genetic tools for fluorescently labeling neurons, should allow a more ready attack on the problems of exactly what the motor circuitry is for behaviors such as feeding and how it has changed in conjunction with the evolution of new motor patterns.