Development and Plasticity of the Gustatory Portion of Nucleus of the Solitary Tract

Excerpt

Developing mammals are highly dependent on the sense of taste to find and choose sources of food. From the earliest postnatal ages, the gustatory system plays a major role in ingestive behaviors and the proper utilization of food in conjunction with homeostatic systems. In addition to discrimination of taste quality and quantity, this sensory system must complement the needs of changing nutritive demands and age-related changes in gastrointestinal function by processing sensory information in a developmentally appropriate way. For example, age-related changes in electrolyte levels determined by gut and renal development [1] may influence age-related changes in gustatory function. Although this hypothesis has not been tested directly, changes in electrolytes, such as plasma sodium levels, occur temporally with increased peripheral taste responses during the first three postnatal weeks in rats [2–5]. Conversely, visceral function is impacted through reflexes triggered by the gustatory system. For example, preabsorptive pancreatic release of insulin in adult animals is triggered by the taste of sugar [6]. Therefore, developmental plasticity in gustatory function, especially plasticity resident to the CNS, may have wide ranging physiological effects beyond sensory coding.

Although the peripheral gustatory system is accurately portrayed as a key site of age-related and experience-related plasticity, primarily because of the ongoing turnover of adult taste bud cells [7–9], it is clear that the nucleus of the solitary tract (NST) also shows an unexpected degree of plasticity during development. In fact, the anatomical and functional studies described in this chapter will demonstrate that the structure-function changes in this first central relay are as impressive as the cortical regions of other sensory systems. As such, the NST provides an ideal location to examine development of the local circuitry and function as well as the development of interactions with brainstem nuclei of other systems (e.g., oromotor).

It is our goal in this chapter to describe the development of the gustatory component of the NST with a particular emphasis on structural and functional plasticity. Interested readers should also examine other recent reviews with differing emphases [10–16].