Afferent and Efferent Interactions in Taste

Bradley, Robert

Abstract

The long-term goal of this laboratory is to understand the sensory input and brainstem neural circuits involved in processing taste information. A crucial result of taste processing is the reflex secretion of saliva, which in turn plays a pivotal role in taste function. Saliva acts as a solvent, transport medium and source of ions that are essential in the initial events in taste sensation. The secretomotor, parasympathetic neurons controlling the salivary glands lie in the salivatory nuclei which are closely associated the first central relay nucleus in the ascending taste pathway - the nucleus of the solitary tract (NST). The overall goal of the research detailed in this application is to explore the neural mechanisms underlying the taste-initiated salivary reflex, at the level of the brainstem salivatory nuclei. To achieve this goal, whole-cell patch clamp recordings from identified neurons that innervate specific salivary glands, in combination with bath application of drugs and electrical stimulation of the solitary and trigeminal tracts, will be performed. In the first Specific Aim intracellular recordings will be made from secretomotor neurons in the salivatory nuclei that innervate individual salivary glands to test the hypothesis that the biophysical properties of the neurons controlling different glands are dissimilar. In the second Specific Aim details of synaptic connections between the afferent sensory input and the parasympathetic secretomotor neurons will be analyzed. These studies test the hypotheses that excitation may arise either from direct connections of afferent inputs onto salivatory neurons or via NST neurons and, that excitatory and inhibitory inputs are differentially expressed among discrete populations of salivatory neurons. In the third Specific Aim the role of a number of neuropeptides known to be localized on salivatory neurons will be investigated. Specifically the effects of these peptides on the membrane properties and synaptic responses of identified salivatory neurons will be analyzed to determine whether these peptides are excitatory or act as modulators of excitation. The experiments detailed in this proposal will provide important new information on the neural circuits, neurotransmitters and neuromodulators responsible for integrating and modifying the activity of neurons responsible for the control of salivary secretion. Understanding these aspects will provide greater understanding of the role of saliva in taste function.