We examine the relationship between behavior and brain structural plasticity, particularly cell proliferation and neurogenesis (the formation of new neurons). In complex organisms, such as humans, it is difficult to study these relationships because the neural circuits controlling behavior are so numerous and interconnected. One organism in which the link between brain structure and behavior is more easily investigated is in the electric fish, Apternotus leptorhynchus. These fish produce a weak electric signal, called the electric organ discharge (EOD), that they use for locating objects in the environment and for communication. During aggressive and sexual interactions, they produce modulations in the EOD termed chirps, which are rapid increases in frequency. Chirps are controlled by a simple and well-studied pathway in which electroreceptors send information about environmental stimuli to the pre-pacemaker nucleus (PPn), which then initiates the chirping. The direct link between this brain structure and electrocommunication behavior and a high rate of cell proliferation makes the electric fish an ideal organism in which to study the link between changes in brain structure and behavior.
Another relationship we study is the effects of the predatory environment on brain development. In almost all species, environmental factors influence the development of animals. Here we examine predation (a negative stimulus) on the brains of electric fish and Trinidadian killifish. In many animals, stress of all sorts decreases neurogenesis. In our earlier investigation with electric fish, we simulated predation and found that experimental fish showed significantly reduced levels of brain cell proliferation than undisturbed control fish. This lab study supported findings from the field showing that fish exposed to higher levels of predation risk and tail injuries from predators showed decreased forebrain cell proliferation compared to fish with low levels of predation risk and intact tails. In our current study with Trinidadian killifish, Rivulus hartii, we examine how predators affect the brain by comparing wild populations that live with predators and with populations that do not.
In contrast to our results on electric fish, we found that killifish living with predators have more brain cell proliferation than killifish living without predators. This is likely due to predators influencing the overall growth pattern of both the brain and body. Presently we are performing a common garden experiment, for which we will use the lab-bred F1 generation of wild-caught killifish to test whether there is a genetic component that causes population differences in the brain.
Joshua Corbo, July 2018