A chemosensory role for the zebrafish lateral line system

An important function of the vertebrate nervous system is chemosensation, and the ability to detect and distinguish between harmful and useful compounds and react appropriately. However, the neural mechanisms underlying chemosensory responses in vertebrates are poorly understood. Studies addressing chemosensory mechanisms would be greatly facilitated by using a vertebrate model that is easy to stimulate, has a simple well-characterized nervous system, and in which neural activity can be easily detected. Here, I present evidence for the first time demonstrating that the zebrafish lateral line can act as a chemosensory system. The lateral line is a hydrodynamic sensory system found in fish and amphibians. It is comprised of superficial sensory structures called neuromasts that are innervated by afferent and efferent nuclei in the brain. Using c-fos induction as a marker for neural activity I show that neuromasts, as well as neurons deep in the brain, respond to specific pungent natural compounds normally associated with nociception, or the sensation of pain. We take advantage of the optical transparency of the zebrafish larvae to functionally image the response using an optical imaging approach that we have developed. Using this approach we can detect neural activity in higher order components of the lateral line system in response to noxious stimuli. Our results assign an additional sensory role for the lateral line system in zebrafish and demonstrate the potential of this system for studying neural mechanisms associated with nociception in vertebrates, including humans.