Types of taste circuits synaptically linked to a few geniculate ganglion neurons

• Published in: Journal of comparative neurology (1911) Vol. 511; no. 6; pp. 753 - 772
• Main Authors: Zaidi, Faisal N., Todd, Krista, Enquist, Lynn, Whitehead, Mark C.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 20-12-2008
• Subjects: Animals; Brain Stem - cytology; Brain Stem - physiology; cell types; connections; Facial Nerve - cytology; Facial Nerve - physiology; Feeding Behavior - physiology; geniculate ganglion; Geniculate Ganglion - cytology; Geniculate Ganglion - physiology; gustatory system; Herpesvirus 1, Suid; Mice; Mice, Inbred C57BL; Neural Pathways - cytology; Neural Pathways - physiology; nucleus of the solitary tract; pathways; Reticular Formation - cytology; Reticular Formation - physiology; Sensory Receptor Cells - cytology; Sensory Receptor Cells - physiology; Solitary Nucleus - cytology; Solitary Nucleus - physiology; Staining and Labeling; Stomatognathic System - innervation; Stomatognathic System - physiology; Synapses - physiology; Synapses - ultrastructure; synaptic organization; taste; Taste - physiology; taste bud; Taste Buds - cytology; Taste Buds - physiology; Taste Perception - physiology; Tongue - innervation; Tongue - physiology; tract tracing; virus; Visceral Afferents - cytology; Visceral Afferents - physiology
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.21869

The present study evaluates the central circuits that are synaptically engaged by very small subsets of the total population of geniculate ganglion cells to test the hypothesis that taste ganglion cells are heterogeneous in terms of their central connections. We used transsynaptic anterograde pseudorabies virus labeling of fungiform taste papillae to infect single or small numbers of geniculate ganglion cells, together with the central neurons with which they connect, to define differential patterns of synaptically linked neurons in the taste pathway. Labeled brain cells were localized within known gustatory regions, including the rostral central subdivision (RC) of the nucleus of the solitary tract (NST), the principal site where geniculate axons synapse, and the site containing most of the cells that project to the parabrachial nucleus (PBN) of the pons. Cells were also located in the rostral lateral NST subdivision (RL), a site of trigeminal and sparse geniculate input, and the ventral NST (V) and medullary reticular formation (RF), a caudal brainstem pathway leading to reflexive oromotor functions. Comparisons among cases, each with a random, very small subset of labeled geniculate neurons, revealed “types” of central neural circuits consistent with a differential engagement of either the ascending or the local, intramedullary pathway by different classes of ganglion cells. We conclude that taste ganglion cells are heterogeneous in terms of their central connectivity, some engaging, predominantly, the ascending “lemniscal,” taste pathway, a circuit associated with higher order discriminative and homeostatic functions, others engaging the “local,” intramedullary “reflex” circuit that mediates ingestion and rejection oromotor behaviors. J. Comp. Neurol. 511:753–772, 2008. © 2008 Wiley‐Liss, Inc.