Development of gustatory organs and innervating sensory ganglia.

Taste function requires neural circuits to transmit gustatory information from taste receptor cells in taste buds, via afferent nerves to the soma of ganglion neurons, and through central ganglion processes into the brainstem. During initial formation, the sensory ganglion neurons have a key situation in establishing receptive fields by extending neurites bidirectionally, to the peripheral taste organs and to central taste nuclei. Our laboratory is studying functional differentiation of sensory ganglia that innervate the tongue, and morphogenesis and patterning of the tongue and papilla organs. The lingual ganglia and taste papillae initially develop independently, but then become reciprocally dependent as ganglia derive molecular support from gustatory papillae and the papillae require sensory innervation for growth and morphogenesis (Mistretta, 1998). Currently our focus is on the geniculate and trigeminal ganglia, which innervate anterior tongue, and the fungiform papilla taste organs innervated by these ganglia. Geniculate and trigeminal ganglia innervate spatially contiguous, but functionally distinct, sensory organs of the fungiform papilla: the trigeminal neurons innervate lateral papilla epithelium and subserve somatosensation and nociception, whereas the geniculate axons project to central apical papilla epithelium to innervate cells that will form taste buds for gustatory sensation (Mistretta and Hill, 2003). In this brief paper we summarize some recent work on development of tongue and taste regions, and on early functional phenotypes of the geniculate and trigeminal ganglia.