Advances in Optical Tools to Study Taste Sensation

Abstract

Taste sensation is the process of converting chemical identities in food into a neural code of the brain. Taste information is initially formed in the taste buds on the tongue, travels through the afferent gustatory nerves to the sensory ganglion neurons, and finally reaches the multiple taste centers of the brain. In the taste field, optical tools to observe cellular-level functions play a pivotal role in understanding how taste information is processed along a pathway. In this review, we introduce recent advances in the optical tools used to study the taste transduction pathways.

Keywords: geniculate ganglion; gustation; imaging; insular cortex; optical tools; taste bud.

Fig. 1. The taste transduction pathway from the taste buds on the tongue to the insular cortex in the brain.

The left image is a two-photon microscopic image of the mouse tongue with an inverted look-up table (magenta, autofluorescence; purple, second harmonic generation signal). In the schematic image on the right, the major areas responsible for taste information processing are illustrated. IC, insular cortex; VPM, ventral posteromedial nucleus; PbN, parabrachial nucleus; rNST, rostral nucleus of the solitary tract.

Fig. 2. Representative optical techniques used for studying the taste transduction pathway.

(A) Microfluidics-integrated imaging window for the anterior tongue (µTongue [microfluidics-on-a-tongue]). (B) In vivo imaging preparation for the geniculate ganglion using a microendoscopic gradient refractive index (GRIN) probe. Reproduced from the article of Barretto et al. (2015) (Nature 517, 373-376) with original copyright holder’s permission. (C) Fiber photometry on rostral nucleus of the solitary tract (rNST). Reproduced from the article of Jin et al. (2021) (Cell 184, 257-271.e16) with original copyright holder’s permission. (D) Two-photon imaging of the insular cortex in an awake head-fixed mouse using a prism mirror.