Processing umami and other tastes in mammalian taste buds

Abstract

Neuroscientists are now coming to appreciate that a significant degree of information processing occurs in the peripheral sensory organs of taste prior to signals propagating to the brain. Gustatory stimulation causes taste bud cells to secrete neurotransmitters that act on adjacent taste bud cells (paracrine transmitters) as well as on primary sensory afferent fibers (neurocrine transmitters). Paracrine transmission, representing cell-cell communication within the taste bud, has the potential to shape the final signal output that taste buds transmit to the brain. The following paragraphs summarize current thinking about how taste signals generally, and umami taste in particular, are processed in taste buds.

Figure 1

Schematic drawing of signal transfer and synaptic transmitters in taste buds. The gray shaded area shows events taking place within the taste bud. The precise targets for 5-HT and NE are not known with confidence, as represented here by question marks.

Figure 2

Cell–cell communication within the taste bud. Receptor (Type II) cells secrete ATP through pannexin 1 hemichannels. ATP acts on primary gustatory afferent fibers as well as on adjacent presynaptic (Type III) taste cells. Presynaptic taste cells release 5-HT and NE, possibly at synaptic sites as well as widely from basolateral membrane sites. The latter may represent paracrine transmission, whereas synaptic release would be consistent with neurocrine transmission.