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

1. Single taste buds in mouse fungiform papillae consist of similar to 50 e longated cells (TBCs), where fewer than three TBCs have synaptic contacts w ith taste nerves. We investigated whether the non-innervated TBCs were chem osensitive using a voltage-sensitive dye, tetramethylrhodamine methyl ester (TMRM), under in situ optical recording conditions. 2. Prior to the optical recordings, we investigated the magnitude and polar ity of receptor potentials under in situ whole-cell clamp conditions. In re sponse to 10 mM HCl, several TBCs were depolarized by similar to 25 mV and elicited action potentials, while other TBCs were hyperpolarized by similar to 12 mV. The TBCs eliciting hyperpolarizing receptor potentials also gene rated action potentials on electrical stimulation. 3. A mixture of 100 mM NaCl, 10 mM HCl and 500 mM sucrose depolarized six T BCs and hyperpolarized another three TBCs out of 13 identified TBCs in a ta ste bud viewed by optical section. In an optical section of another taste b ud, 1 M NaCl depolarized five TBCs and hyperpolarized another two TBCs out of 11 identified TBCs. 4. The number of chemosensitive TBCs was much larger than the number of inn ervated TBCs in a taste bud, indicating the existence of chemosensitivity i n non-innervated TBCs. There was a tendency for TBCs eliciting the same pol arity of receptor potential to occur together in taste buds. We discuss the role of non-innervated TBCs in taste information processing.