Electrocommunication signals alone are sufficient to increase neurogenesis in the brain of adult electric fish, Apteronotus leptorhynchus

Social interaction can have profound influences on the structure of the adult brain, but little is known about the precise stimulus feature found within social interaction that induces such brain plasticity. We examined the effects of social stimuli on cell addition and radial glial fiber formation in the brains of adult electric fish. These fish communicate primarily through weak, quasi-sinusoidal electric signals. Fish were housed in isolation, paired with another fish or exposed to only the electrocommunication signals of another fish for 7 days. After 3 days of exposure to these stimulus conditions, fish were injected with bromodeoxyuridine (BrdU) to mark newborn cells. We sacrificed the fish 4 days after BrdU injection and used immunohistochemistry to measure cell addition (BrdU+), the fraction of added cells that differentiated into neurons (BrdU+/NeuroTrace+) and the density of radial glia fibers (vimentin+) in the periventricular zone of the diencephalon. Fish that were exposed only to the electrocommunication signals of another fish and no other social stimuli had equivalent levels of cell addition and radial glial fiber density to fish that were housed with full social interaction and higher levels than fish housed in isolation. About 60% of the added cells differentiated into neurons; this fraction did not differ among treatment groups. Artificial sine wave electrical stimuli that mimicked electrocommunication signals were ineffective in increasing cell addition and glia fiber formation above those found in isolated fish. Thus, stimuli through a single modality are sufficient for inducing this brain plasticity, but the waveform or dynamic features of communication signals are crucial for the effect.