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Behavioral and neural correlates of postnatal olfactory conditioning: I. Effect of respiration on conditioned neural
R M Sullivan1, D A Wilson, M H Kim
1Department of Psychobiology, University of California, Irvine 92717.
Insights
Early olfactory learning in rats creates a lasting preference for learned odors. This learning enhances olfactory bulb activity, independent of breathing changes during testing, suggesting the olfactory system itself is modified.
Area of Science:
- Neuroscience
- Developmental Biology
- Olfactory Learning
Background:
- Infant rats develop odor preferences after classical conditioning.
- Conditioned odors lead to increased 2-deoxyglucose (2-DG) uptake in the olfactory bulb.
- The role of respiration in this enhanced 2-DG uptake response was previously unclear.
Purpose of the Study:
- To investigate whether altered respiration during testing is necessary for the enhanced olfactory bulb 2-DG uptake observed after olfactory classical conditioning.
- To determine if early olfactory learning modifies the olfactory system directly.
Main Methods:
- Infant rats (postnatal days 1-18) underwent olfactory classical conditioning (Odor-Stroke) pairing an odor with tactile stimulation mimicking maternal contact.
- Control groups received odor or tactile stimulation only.
- On postnatal day 19, pups were tested using a two-odor choice test or an odor/2-DG uptake test, with either normal respiration or experimentally controlled respiration.
Main Results:
- Conditioned pups demonstrated a learned preference for the associated odor.
- Enhanced olfactory bulb 2-DG uptake was observed in Odor-Stroke pups compared to controls under normal respiration.
- This enhanced 2-DG uptake persisted even when respiration was experimentally controlled, with no difference in respiration rate between groups.
Conclusions:
- Modified respiration during testing is not required for the enhanced olfactory bulb response to learned attractive odors.
- Early olfactory learning directly modifies the olfactory system, independent of respiratory changes.
- These findings highlight the plasticity of the olfactory system in response to early life experiences.
Abstract:
Following olfactory classical conditioning, infant rats exhibit a preference for the conditioned odor and exhibit enhanced uptake of focal 14C 2-deoxyglucose (2-DG) within the olfactory bulb. The present experiments assessed the role of respiration on the expression of the enhanced 2-DG uptake response. Pups were conditioned from postnatal day (PN) 1-18 with an olfactory stimulus paired with a reinforcing tactile stimulus which mimics maternal contact (Odor-Stroke). Control pups received odor only or tactile stimulation only. On PN 19, pups received 1 of 3 tests: 1) a two-odor choice test, 2) an odor/2-DG test with normal respiration allowed, or 3) an odor/2-DG test with respiration experimentally controlled. The results indicated that: 1) Odor-Stroke pups learned the conditioned odor preference, 2) Odor-Stroke, normally respiring pups exhibited enhanced olfactory bulb 2-DG uptake when compared to control pups. No difference in respiration rate was detected between groups in normally respiring pups. 3) Odor Stroke pups whose breathing was experimentally controlled exhibited enhanced olfactory bulb 2-DG uptake when compared to control pups with an identical number of respirations. Together, these results demonstrate that modified respiration during testing is not required for the expression of a modified olfactory bulb response to learned attractive odors. Therefore, the data suggest that the olfactory system itself is modified by early learning.