Amino acids as taste stimuli. II. Quality coding

Brain Res. 1982 Dec 16;253(1-2):93-104. doi: 10.1016/0006-8993(82)90676-x.

Abstract

Two experiments were performed in rats to evaluate the relative taste qualities of 12 L-amino acids, each at a concentration which evoked half the maximum response for that chemical. The first study involved recording the activity of 40 individual chorda tympani fibers to the stimulus series. Only 34% of the evoked responses resembled the short latency phasic-tonic activity which characterizes gustatory responses to inorganic salts and acids. 32% had latencies exceeding 1 s; another 27% consisted of only a phasic burst lasting less than 1 s. The remaining 7% were inhibitory. Both long latency and purely phasic activity were stimulus selective: 61% of the former were in response to Gly or Pro while 69% of the latter were evoked by Cys-HCl, Lys-HCl or His. Response inhibition was not associated with either specific fibers or stimuli. Thus amino acids, which to humans represent a class of perceptually complex stimuli, show a corresponding complexity of evoked neural properties in the rat. The second study employed a conditioned taste aversion paradigm to assess the qualitative similarity of each amino acid to the others and to the 4 prototypical taste stimuli; NaCl, HCl, quinine-HCl and sucrose. Some amino acids showed strong generalization to a single gustatory prototype (Pro and Gly to sucrose; Cys-HCl to HCl); others generalized well to multiple prototypes (e.g. Arg to sucrose and NaCl). Several showed poor generalization to all 4 prototypical tastes, calling into question the assumption that these 4 totally encompass the gustatory domain.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Avoidance Learning / physiology
  • Axons / physiology
  • Chorda Tympani Nerve / physiology*
  • Conditioning, Classical / physiology
  • Evoked Potentials, Somatosensory
  • Generalization, Stimulus / physiology
  • Male
  • Neural Inhibition
  • Neurons / physiology
  • Rats
  • Rats, Inbred Strains
  • Reaction Time / physiology
  • Synaptic Transmission
  • Taste / physiology*
  • Taste Threshold / physiology