Abstract
Recently, we have shown that mice with decreased expression of α7-nicotinic acetylcholine receptors (α7) in the olfactory bulb were associated with a deficit in odor discrimination compared to wild-type mice. However, it is unknown if mice with decreased α7-receptor expression also show a deficit in early odor learning preference (ELP), an enhanced behavioral response to odors with attractive value observed in rats. In this study, we modified ELP methods performed in rats and implemented similar conditions in mice. From post-natal days 5–18, wild-type mice were stroked simultaneously with an odor presentation (conditioned odor) for 90 s daily. Control mice were only stroked, exposed to odor, or neither. On the day of testing (P21), mice that were stroked in concert with a conditioned odor significantly investigated the conditioned odor compared to a novel odor, as observed similarly in rats. However, mice with a decrease in α7-receptor expression that were stroked during a conditioned odor did not show a behavioral response to that odorant. These results suggest that decreased α7-receptor expression has a role in associative learning, olfactory preference, and/or sensory processing deficits.
Highlights
Odor learning preference (ELP), a paradigm for classical conditioning, has been associated with behavioral and enhanced olfactory bulb (OB) responses in newborn rats
[2,4,5,7,42,43]) with a few performed in neonatal mice (P0–P6) [11,12,13,14], we modified the methods for use in mice being tested at postnatal day 21 (P21) (Figure 1)
The principal findings of this study are that: 1) early olfactory learning produces a behavioral preference in mice that is similar to previous studies performed in rats, and 2) mice with a decreased a7 nicotinic-receptor expression (i.e., a7+/2 mice) do not develop a behavioral preference for a conditioned odor
Summary
Odor learning preference (ELP), a paradigm for classical conditioning, has been associated with behavioral and enhanced olfactory bulb (OB) responses in newborn rats. ELP has been used in neonatal mice, as young as post-natal day 0 (P0), to determine associative abilities [11,12,13,14]. These mice have similar behavioral responses as those observed in rats, the association is quickly lost (after 5 or 24 hr) as they are tested for odor preference at very young ages (P0–P6). ELP paradigms can determine learning, odor preferences, and other phenotypes of mutant mice at early ages. We tested P21 mice with differing expression of a7-nicotinic acetylcholine receptors (nAChRs, a7) to determine the role of a7 in ELP
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