The Journal of Neurophysiology Vol. 82 No. 6 December 1999, pp. 3160-3167
Copyright ©1999 by the American Physiological Society
Physiological Evidence for the Discrimination of
L-Arginine From Structural Analogues by the Zebrafish
Olfactory System
D. L.
Lipschitz and
W. C.
Michel
Department of Physiology, University of Utah School of Medicine,
Salt Lake City, Utah 84108-1270
Lipschitz, D. L. and
W. C. Michel.
Physiological Evidence for the Discrimination of
L-Arginine From Structural Analogues by the Zebrafish
Olfactory System. J. Neurophysiol. 82: 3160-3167, 1999. Although it is generally assumed that fish are capable of
discriminating amino acid odorants on the basis of differences in side-chain structure, less is known about their ability to discriminate amino acids with modifications to 
-carboxyl and -amino groups. In
this study, the ability of the zebrafish olfactory system to detect and
presumably discriminate analogues of the basic amino acid Arg was
assessed, by using cross-adaptation and activity-dependent labeling
techniques. Electrophysiological recordings established that
esterification (L-arginine methyl ester; AME) or deletion (agmatine or amino-4-guanidobutane; AGB) of the -carboxyl group yielded odorants more potent than Arg, whereas deletion of the -amino group (L-argininic acid; AA) yielded a less
potent analogue. In cross-adaptation experiments, no test-competitor
odorant combination yielded complete cross-adaptation, suggesting the
detection of these Arg analogues by multiple odorant receptors (ORs)
with partially nonoverlapping specificities. Activity-dependent
immunocytochemical labeling of olfactory receptor neurons supported
this conclusion. AGB, an ion-channel-permeant probe (and odorant),
labeled 4.9 ± 0.4% (n = 24) of
sensory epithelium, whereas the addition of Arg, 1-ethylguanidine
sulfate, L--amino-
-guanidinopropionate, or AME to AGB resulted in a significant elevation of labeling (8-14%). This study provides evidence that the olfactory system has
the potential to discriminate among amino acid odorants with modified
-carboxyl and -amino groups.
