Takashi Yamamoto (1), Takatoshi Nagai (2), Tsuyoshi Shimura (1) and Yasunobu
Yasoshima (1)
(1) Department of Behavioral Physiology, Faculty of Human Sciences, Osaka
University, 1-2 Yamadaoka, Suita, Osaka 565-0871, Japan
(2) Department of Physiology, Teikyo University School of Medicine, Kaga
2-11-1, Itabashi-ku, Tokyo 173-8605, Japan
Abstract: Recent advances in neural mechanisms of taste are reviewed
with special reference to neuroactive substances. In the first section,
taste transduction mechanisms of basic tastes are explained in two groups,
whether taste stimuli directly activate ion channels in the taste cell membrane
or they bind to cell surface receptors coupled to intracellular signaling
pathways. In the second section, putative transmitters and modulators from
taste cells to afferent nerves are summarized. The candidates include acetylcholine,
catecholamines, serotonin, amino acids and peptides. Studies favor serotonin
as a possible neuromodulator in the taste bud. In the third section, the
role of neuroactive substances in the central gustatory pathways is introduced.
Excitatory and inhibitory amino acids (e.g., glutamate and GABA) and peptides
(substance P and calcitonin gene-related peptide) are proved to play roles
in transmission of taste information in both the brainstem relay and cortical
gustatory area. In the fourth section, conditioned taste aversion is introduced
as a model to study gustatory learning and memory. Pharmacobehavioral studies
to examine the effects of glutamate receptor antagonists and protein kinase
C inhibitors on the formation of conditioned taste aversion show that both
glutamate and protein kinase C in the amygdala and cortical gustatory area
play essential roles in taste aversion learning. Recent molecular and genetic
approaches to disclose biological mechanisms of gustatory learning are also
introduced. In the last section, behavioral and pharmacological approaches
to elucidate palatability, taste pleasure, are described. Dopamine, benzodiazepine
derivatives and opioid substances may play some roles in evaluation of palatability
and motivation to ingest palatable edibles.
Keywords: Taste transduction, Taste cell, Neuropeptide, Neurotransmitter,
Neuromodulator, Conditioned taste aversion, Palatability