Optical recordings of taste responses from fungiform papillae of mouse in situ

Abstract

Single taste buds in mouse fungiform papillae consist of ≈50 elongated cells (TBCs), where fewer than three TBCs have synaptic contacts with taste nerves. We investigated whether the non‐innervated TBCs were chemosensitive using a voltage‐sensitive dye, tetramethylrhodamine methyl ester (TMRM), under in situ optical recording conditions. Prior to the optical recordings, we investigated the magnitude and polarity of receptor potentials under in situ whole‐cell clamp conditions. In response to 10 mM HCl, several TBCs were depolarized by ≈25 mV and elicited action potentials, while other TBCs were hyperpolarized by ≈12 mV. The TBCs eliciting hyperpolarizing receptor potentials also generated action potentials on electrical stimulation. A mixture of 100 mM NaCl, 10 mM HCl and 500 mM sucrose depolarized six TBCs and hyperpolarized another three TBCs out of 13 identified TBCs in a taste bud viewed by optical section. In an optical section of another taste bud, 1 M NaCl depolarized five TBCs and hyperpolarized another two TBCs out of 11 identified TBCs. The number of chemosensitive TBCs was much larger than the number of innervated TBCs in a taste bud, indicating the existence of chemosensitivity in non‐innervated TBCs. There was a tendency for TBCs eliciting the same polarity of receptor potential to occur together in taste buds. We discuss the role of non‐innervated TBCs in taste information processing.

Bitter substances suppress afferent responses to an appetitive mixture: Evidence for peripheral integration of chemosensory stimuli

“…Furthermore, biogenic amines and other neurotransmitters have been localized to taste cells and may act as modulators to modify the signal projected to the afferents (Roper, 1992). Clearly the intricate synaptic organization of the taste bud suggests that interactions within the bud itself may shape its final output (Roper, 1992;Ohtubo et al, 2001).…”

Distribution of Gustatory Sensitivities in Rat Taste Cells: Whole-Cell Responses to Apical Chemical Stimulation

“…2 B). Similar approaches have been attempted in the past with some success for intracellular, patch, and optical recording (Roper and McBride, 1989;Béhé et al, 1990a;Yoshii, 1997, 1998;Ohtubo et al, 2001). In the course of the present study, we have used several different designs for this modified Ussing (MU) chamber that all retain the same basic features (Fig.…”

“…Although other labora- tories have used an intact epithelial preparation (Roper and McBride, 1989;Béhé et al, 1990a;Yoshii, 1997, 1998;Ohtubo et al, 2001), there has been limited success in applying a range of stimuli to a sizeable number of cells. For example, Furue and Yoshii (1997) recorded from only five cells in mouse fungiform taste buds that were responsive to one or more of three taste stimuli applied to the apical membrane and Ohtubo et al (2001) applied only NaCl or a taste mixture. The present data are the first to show the distribution of gustatory sensitivities across a large number of mammalian taste receptor cells using patchclamp methods and apically restricted stimuli.…”

Postnatal Development of Membrane Excitability in Taste Cells of the Mouse Vallate Papilla

“…Action potential discharges are regularly recorded from taste cells during chemostimulation in mammals (Béhé et al, 1990;Avenet and Lindemann, 1991;Gilbertson et al, 1992;Cummings et al, 1993;Furue and Yoshii, 1997;Ohtubo et al, 2001). Given the presence of voltage-gated Na ϩ currents, Na/OUT cells are able to fire action potentials (see below).…”

“…Several lines of evidence suggest that taste buds are complex chemosensory structures. For example, not all chemosensitive cells are innervated (Ohtubo et al, 2001), and lateral interactions mediated by gap junctions (electrical synapses) have been documented between taste cells (Bigiani andRoper, 1993, 1995). Accordingly, the sensory output to the nerve terminals most likely represents the integrated activity of a population of cells rather than the activity of single, separate cells (Roper, 1989(Roper, , 1993.…”