Physiological studies on umami taste.

Area of Science:

• Neuroscience
• Sensory Science
• Taste Physiology

Background:

• Electrophysiological studies on umami taste in rats and cats showed limited synergism between monosodium glutamate (MSG) and nucleotides (GMP, IMP), with responses indistinguishable from salt.
• Canine taste systems exhibit significant umami taste synergism between MSG and nucleotides, suggesting a distinct pathway.
• Umami substances do not enhance other basic tastes, and their responses are independent of sodium chloride (NaCl) taste, as shown by amiloride inhibition studies.

Purpose of the Study:

• To investigate the physiological basis of umami taste perception.
• To determine if umami taste is mediated by a unique receptor system.
• To compare the taste profiles of umami agonists with known glutamate receptor agonists.

Main Methods:

• Electrophysiological recordings from taste nerves and neurons in various animal models (rats, cats, dogs, mice, monkeys).
• Analysis of taste nerve responses to umami substances, salt, and their combinations.
• Comparison of human taste responses to umami substances and agonists of brain glutamate receptors.

Main Results:

• Canine taste responses to umami substances show strong synergism with nucleotides, unlike rats and cats.
• Umami taste responses are independent of salt taste pathways and other basic tastes.
• In humans, glutamate, ibotenate, L-AP4, and ACPD elicited umami taste, while kainate, NMDA, and AMPA did not, indicating the umami receptor is not a known ionotropic glutamate receptor.

Conclusions:

• Umami taste is a distinct fifth basic taste mediated by a unique receptor.
• The umami receptor is not identical to known brain glutamate receptors.
• Electrophysiological and behavioral evidence supports a specialized umami taste system.