Recordings were made from olfactory receptor neurons of Xenopus laevis tadpoles using the patch-clamp technique to investigate the responses of these cells to odorants. Four amino acids (glutamate, methionine, arginine and alanine) both individually and as a mixture were used as stimuli. Of the 156 olfactory neurons tested, 43 showed a response to at least one of the stimuli. Of the cells tested, 19 % responded to glutamate, 16 % to methionine, 12 % to arginine and 10 % to alanine. Each amino acid was able to induce both excitatory and inhibitory responses, although these occurred in different cells. Each amino acid produced approximately equal numbers of inhibitory and excitatory responses. Inhibitory responses could best be observed in the perforated-patch configuration using gramicidin as an ionophore and a recording configuration that is a current-clamp for fast signals and a voltage-clamp for slow signals. The diversity of the odorant responses, in particular the existence of excitatory and inhibitory responses, is not consistent with a single transduction pathway in olfactory neurons of Xenopus laevis tadpoles.

REFERENCES

Ache
B. W.
(
1994
).
Towards a common strategy for transducing olfactory information
.
Cell Biol
5
,
55
–.
Chiu
D.
,
Nakamura
T.
,
Gold
G. H.
(
1988
).
Ionic composition of toad mucus measured with ion selective microelectrodes
.
Chem. Senses
13
,
677
–.
Derby
C. D.
,
Girardot
M.-N.
,
Harpaz
S.
(
1988
).
Inhibition in the periphery: occurrence in olfaction and gustatory receptor cells of aquatic crustaceans, correlation with mixture suppression and effect on quality coding
.
Chem. Senses
13
,
683
–.
Dionne
V. E.
(
1990
).
Excitatory and inhibitory responses induced by amino acids in isolated mudpuppy olfactory receptor neurons
.
Chem. Senses
15
,
566
–.
Dionne
V. E.
(
1992
).
Chemosensory responses in isolated olfactory receptor neurons from Necturus maculosus
.
J. Gen. Physiol
99
,
415
–.
Dionne
V.
,
Dubin
A. E.
(
1994
).
Transduction diversity in olfaction
.
J. Exp. Biol
194
,
1
–.
Dubin
A. E.
,
Dionne
V. E.
(
1994
).
Action potentials and chemosensitive conductance in the dendrites of olfactory neurons suggest new features for odor transduction
.
J. Gen. Physiol
103
,
181
–.
Freitag
J.
,
Krieger
J.
,
Strotmann
J.
,
Breer
H.
(
1995
).
Two classes of olfactory receptors in Xenopus laevis
.
Neuron
15
,
1383
–.
Gesteland
R. C.
,
Adamek
G. D.
(
1987
).
Adaption and mixture component suppression in olfaction
.
Chem. Senses
12
,
657
–.
Getchell
T. V.
(
1986
).
Functional properties of vertebrate olfactory receptor neurons
.
Physiol. Rev
66
,
772
–.
Hamill
O. P.
,
Marty
A.
,
Neher
E.
,
Sakmann
B.
,
Sigworth
F. J.
(
1981
).
Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches
.
Pflugers Arch
391
,
85
–.
Horn
R.
,
Marty
A.
(
1988
).
Muscarine activation of ionic currents measured by a new whole-cell recording method
.
J. Gen. Physiol
92
,
145
–.
Kaissling
K. E.
(
1986
).
Chemo-electrical transduction in insect olfactory receptors
.
Annu. Rev. Neurosci
9
,
121
–.
Kang
J.
,
Caprio
J.
(
1995
).
In vivo responses of single olfactory receptor neurons in the channel catfish, Ictalurus punctatus
.
J. Neurophysiol
73
,
172
–.
Kang
J.
,
Caprio
J.
(
1995
).
Electrophysiological responses of single olfactory bulb neurons to amino acids in the channel catfish, Ictalurus punctatus
.
J. Neurophysiol
74
,
1421
–.
Kurahashi
T.
,
Yau
K.-W.
(
1993
).
Co-existence of cationic and chloride components in odorant-induced current of vertebrate olfactory receptor cells
.
Nature
363
,
71
–.
Lynch
J. W.
,
Barry
P. H.
(
1989
).
Action potentials initiated by single channels opening in a small neuron (rat olfactory receptor)
.
Biophys. J
55
,
755
–.
McClintock
T. S.
,
Ache
B. W.
(
1989
).
Hyperpolarizing receptor potentials in lobster olfactory receptor cells: implications for transduction and mixture suppression
.
Chem. Senses
14
,
637
–.
Michel
W. C.
,
Ache
B. W.
(
1994
).
Odor-evoked inhibition in primary olfactory receptor neurons
.
Chem. Senses
19
,
11
–.
Michel
W. C.
,
McClintock
T. S.
,
Ache
B. W.
(
1991
).
Inhibition of lobster olfactory receptor cells by an odor-activated potassium conductance
.
J. Neurophysiol
65
,
446
–.
Minor
A. V.
,
Bykov
K. A.
,
Dmitriev
A. V.
,
Skachkov
S. N.
(
1992
).
Extracellular ion concentrations in the olfactory epithelium: steady state and changes during excitation
.
Chem. Senses
17
,
864
–.
Miyamoto
T.
,
Restrepo
D.
,
Cragoe
E. J.
,
Teeter
J. H.
(
1992
).
IP3-and cyclic AMP-induced responses in isolated olfactory receptor neurons from the channel catfish
.
J. Membr. Biol
127
,
173
–.
Miyamoto
T.
,
Restrepo
D.
,
Teeter
J. H.
(
1992
).
Voltage-dependent and odorant-regulated currents in isolated olfactory receptor neurons of the channel catfish
.
J. Gen. Physiol
99
,
505
–.
Morales
B.
,
Bacigalupo
J.
(
1996
).
Chemical reception in vertebrate olfaction: evidence for multiple transduction pathways
.
Biol. Res
29
,
333
–.
Morales
B.
,
Labarca
P.
,
Bacigalupo
J.
(
1995
).
A ciliary K+conductance sensitive to charibdotoxin underlies inhibitory responses in toad olfactory receptor neurons
.
FEBS Lett
359
,
41
–.
Morales
B.
,
Ugarte
G.
,
Labarca
P.
,
Bacigalupo
J.
(
1994
).
Inhibitory K+current activated by odorant in toad olfactory neurons
.
Proc. R. Soc. Lond. B
257
,
235
–.
Restrepo
D.
,
Miyamoto
T. C.
,
Bryant
B.
,
Teeter
J. H.
(
1990
).
Odor stimuli trigger influx of calcium into olfactory neurons of the channel catfish
.
Science
249
,
1166
–.
Restrepo
D.
,
Teeter
J. H.
(
1990
).
Olfactory neurons exhibit heterogeneity in depolarization-induced calcium change
.
Am. J. Physiol
258
,
1051
–.
Schild
D.
,
Gennerich
A.
,
Schultens
H. A.
(
1996
).
Microcontrollers as inexpensive pulse generators and parallel processors in electrophysiological experiments
.
Med. Biol. Eng. Comput
34
,
305
–.
Schild
D.
,
Restrepo
D.
(
1998
).
Transduction mechanisms in vertebrate olfactory receptor cells
.
Physiol. Rev
78
,
429
–.
Zhainazarov
A. B.
,
Ache
B. W.
(
1995
).
Odor-induced currents in Xenopus olfactory receptor cells measured with perforated-patch recording
.
J. Neurophysiol
74
,
479
–.
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