The role of the chorda tympani nerve in the structural development of brainstem neurons

The brain changes substantially throughout development. In the taste system, brainstem neurons undergo dramatic structural alterations after birth. Most notably, these cells’ dendrites, branch-like projections that that receive sensory input, grow 3-4 times longer by adulthood. It is not clear whether incoming signals about taste are necessary for these structural changes to occur. We have consistently found that when the chorda tympani taste nerve (CT) is cut at an early age in rats, it does not regenerate. With this manipulation, we can permanently limit the amount of taste information that reaches the brain. To determine the role of taste input in shaping brainstem development, we sectioned the CT in five day old rats and characterized the structure of neurons in the brain region that receives taste input, the nucleus of the solitary tract (NTS). Rats were anesthetized at five days of age and the CT was either sectioned or left intact as a control. Approximately 60 days later (when rats are adults), a neural tracer was injected in the parabrachial nucleus (a higher order taste center), and NTS cells that send input to this region were dyed. The tracer transported for three days before brain tissue was collected, sectioned, and processed. We are currently working to quantify cell structure using Neurolucida. We anticipate that NTS neurons in CT cut animals will appear similar to those of newborn rats - with short, stubby dendrites. Results from this project will elucidate the importance of sensory information in shaping the developing brain