Talking too much? Multiple neurotransmitters and neuropeptides within the taste bud
Scott Herness (College of Dentistry, The Ohio State University)
(May 1, 2003 12:00 PM - 1:00 PM)
Taste buds are collections of 50 to 100 individual taste receptor cells (TRCs). These cells detect the presence of chemical stimuli within the oral cavity and relay this information to the central nervous system via synaptic connections with afferent nerve fibers. The "historical" view of this process describes a single TRC as becoming depolarized when stimulated by tastants by elusive transduction mechanisms and subsequently releasing transmitter onto the afferent nerve. Many TRCs were known not to synapse with the afferent nerve fibers and were believed to be supporting cells. Recent developments in the physiology and molecular biology of TRCs have made it clear that this view is no longer tenable. Classes of recently cloned taste receptor molecules for bitter and sweet stimuli and related transduction enzymes have been localized to TRCs that lack synapses to the afferent nerve. How then do these cells, which possess the machinery to respond to taste stimuli, relay this information to the central nervous system? Our laboratory has discovered several signaling pathways endogenous to the taste bud that can serve as mechanisms for cell to cell communication among the TRCs of the bud. These include classic neurotransmitters, such as norepinephrine and serotonin, and neuropeptides, such as cholecystokinin. For the most part, it appears that certain subsets of TRCs express a signaling agent while other subsets of TRCs express a receptor for this agent. As well, physiological responses can be measured to exogenous application of these agents. Thus these pathways may serve unrecognized manners of information processing and modulation of the gustatory signal prior to afferent nerve stimulation.