Research in brain plasticity and behavior

In this lab, 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 very 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 organisms is classified as electric fish because they 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 and decreases in amplitude of their EOD. Chirps are controlled by simple and well-studied pathway in which electroreceptors send information about environmental stimuli to the prepacemaker 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.

We examine the effect of social stimulation and steroid hormone (cortisol) treatment on behavior and neurogenesis in electric fish. The effect of social stimulation on chirping behavior and neurogenesis is observed by comparing chirping rates and brain cell formation in paired and isolated fish. We have found that pairing fish causes an increase in the chirp rate, and using immuniohistochemistry, we have also observed an increase in cell proliferation and glial fiber formation in the subventricular zone near the region that controls chirping (the PPn).

Cortisol is a naturally occurring hormone produced during stress, which increases during long-term social interaction in electric fish and causes an increase in chirping rate. When we implanted fish with cortisol capsules to determine the effect of this steroid hormone on brain structure, we observed an increase in cell proliferation in the subventricular zone.

The findings of this research into the effects social interaction and hormones on the production of new brain cells could one day be used to create therapies to treat neurodegenerative diseases or brain injury in humans.

E. McCarthey