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The Journal of Neuroscience, May 15, 2002, 22(10):4205-4216
Odor Discrimination and Odor Quality Perception in Rats with
Disruption of Connections between the Olfactory Epithelium and
Olfactory Bulbs
Burton
Slotnick1 and
Natalya
Bodyak2
1 Department of Psychology, American University,
Washington, DC 20016, and 2 Department of Medicine,
Endocrinology Division, Beth Israel Deaconess Medical Center and
Harvard Medical School, Boston, Massachusetts 02215
Rats were trained using olfactometry and operant conditioning to
discriminate among homologous fatty acids, homologous aldehydes, and a
series of unrelated odors. Their memory for the positive and negative
assignment of each odor (tested under extinction) was assessed before
and after they had received selective lesions of the olfactory bulbs or
injection of the olfactory epithelial toxin 3-methyl indole (3-MI).
Response accuracy on the memory test provided a measure of the extent
to which treatments altered the remembered perceptual quality of the
odors. The degree of deafferentation of the bulb by treatment with 3-MI
was assessed using anterograde transport of horseradish peroxidase
applied to the olfactory epithelium. Rats treated with 3-MI had a
detectable reaction product only in varying numbers of glomeruli on the
lateral and, in some cases, posterior medial walls of the olfactory
bulb. Bulbar lesions destroyed the dorsal and dorsomedial bulbar areas that have been identified in optical and electrophysiological studies
as showing responses to fatty acids. Rats with bulbar lesions had good
to near perfect retention on their post-treatment memory test on all
odor pairs, as did 3-MI-treated rats that still had substantial input
to glomeruli on the lateral or posterior medial wall of the bulb.
3-MI-treated rats with substantially fewer afferent connections had
severe retention deficits, particularly for the aldehyde and fatty acid
odors, but this loss was secondary to deficits in the ability to
discriminate among these odors. The results indicate that input to
bulbar areas that are activated by a series of homologous odors may not
be essential for odor discrimination and that deafferentation of the
majority of bulbar glomeruli may be primarily without effect on odor
quality perception as assessed by the memory test. These outcomes point
to a much higher degree of redundancy within the olfactory bulb than
that envisioned by current combinatorial or odotopic hypotheses of odor
quality coding or, alternatively, to mechanisms of odor coding used in
the awake behaving animal that have not yet been elucidated.
Key words:
odor coding; odor quality; olfactory bulb; olfactory
memory; olfactory discrimination; olfatoxin
Copyright © 2002 Society for Neuroscience 0270-6474/02/22104205-12$05.00/0
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