Abstract
C57BL/6 is the most widely used mouse strain in the laboratories. Two substrains of C57BL/6, C57BL/6J (B6J), and C57BL/6N (B6N) are well-known backgrounds for genetic modification and have been shown difference in quite a few tests, including open field test, rotarod test, and Morris water maze. However, difference between these two substrains in olfaction-dependent behaviors remains unknown. Here, we used olfactory two-alternative choice task, which is modified to have two training stages, to evaluate animals’ ability in instrumental learning and olfactory association. In the first (rule learning) stage, the mice were trained to use the operant chamber to collect water rewards. An odor cue was provided in the procedure, with no indication about reward locations. In the following (discrimination learning) stage, two odor cues were provided, with each indicating a specific water port. The animals were rewarded upon correct port choices following cue deliveries. We found that during young adulthood (7–10 weeks old), proportionally more B6J than B6N mice were able to pass rule learning (58.3% vs. 29.2%) and ultimately acquire this task (54.2% vs. 25%), with the two substrains showing similar pass rates in discrimination learning (92.9% vs. 85.7%). Surprisingly, at a more mature age (17 weeks old), this substrain difference disappeared. Mature B6N mice had a significant improvement in pass percentages of rule learning and overall task, whereas similar improvement was not observed in the B6J counterparts. Instead, mature B6J mice had an improved speed in rule learning and overall task. We further examined behavioral patterns of 8-week-old B6J and B6N mice in the olfactory habituation or dishabituation test. We observed normal olfactory habituation from subjects of both substrains, with the B6J mice exhibiting stronger investigative responses to newly presented odorants. These results reveal for the first time that B6J and B6N mice are different in acquisition processes of a behavioral task that requires instrumental learning and olfactory association, and that maturation appears to employ different effects on these two substrains during these processes. Furthermore, young adult B6J and B6N mice might be similar in olfactory habituation but different in the olfactory aspects of novelty seeking.
Highlights
To survive and enhance reproductive success, animals must be able to recognize environmental chemical signals and generate appropriate behavioral responses
To investigate the effect of substrain on olfactory associative learning, we used olfactory two-alternative choice paradigm to train young adult B6J and B6N mice. This paradigm is composed of rule learning and discrimination learning (Figure 1A)
Using stepwise training paradigms of this task, we further measured their performances in rule learning and olfactory associative learning
Summary
To survive and enhance reproductive success, animals must be able to recognize environmental chemical signals and generate appropriate behavioral responses. Most external chemical signals are perceived through the olfactory system and are odor molecules. Some odors can instinctively evoke behaviors in animals, which suggests that biological interpretation of an odor can be genetically predetermined (Wyatt, 2014). Many odor percepts and their meanings are acquired later in life (Cain et al, 1995; Wilson and Stevenson, 2006). Information regarding olfactory function of more mature adults is lacking. Given that olfactory decline is a salient biomarker that often occurs ahead of major symptoms of numerous neurodegenerative diseases (Doty, 2017), information about olfactory function across adult lifespan is needed for better evaluation of pathological situations that may occur later in life
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
