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Sex and strain differences in the developmental activity profile of the rat tested over clean vs home cage bedding
Insights
Juvenile rats exhibit a developmental hyperactivity phase, with activity patterns varying by sex and strain. Olfactory cues from home bedding significantly influenced activity in CD males, while bedding condition affected Long-Evans females.
Area of Science:
- Neuroscience
- Developmental Biology
- Animal Behavior
Background:
- Rodent models are crucial for understanding developmental neurobiology and behavior.
- Activity patterns in juvenile rodents are influenced by environmental stimuli and genetic background.
- Previous research suggests a period of heightened activity during early development in rats.
Purpose of the Study:
- To characterize developmental activity patterns in CD and Long-Evans rat pups.
- To investigate the influence of olfactory cues from home bedding on juvenile rat activity.
- To compare activity levels and responses to bedding conditions between male and female rats of two different strains.
Main Methods:
- Two experiments were conducted using CD and Long-Evans rat pups from postnatal Day 10/12.
- Activity was measured in a size-adjustable chamber using a single photodetector.
- Pups were tested over clean bedding (C) or home cage bedding (HC) repeatedly.
- Testing occurred every second or fourth day, with comparisons made between strains and sexes.
Main Results:
- Both CD and Long-Evans rats showed a developmental hyperactivity phase, peaking around postnatal Day 16.
- CD males displayed increased activity with home cage bedding (HC), suggesting olfactory cue influence.
- Long-Evans females showed significant alterations in activity based on bedding condition (C vs HC).
- Significant differences in overall activity and bedding condition effects were observed between CD and Long-Evans strains, varying by sex and age.
Conclusions:
- A general developmental hyperactivity phase is confirmed in isolated juvenile rats.
- Sex and strain-specific differences in activity patterns and responses to olfactory cues exist.
- These findings highlight the complex interplay of genetics, sex, and environment in shaping juvenile rodent behavior.
Abstract:
In the first of two experiments, CD rat litters were used to characterize activity patterns obtained in a size-adjustable, single photodetector chamber. Beginning on postnatal Day 10 or 12, pups were tested repeatedly over clean bedding (C) or over bedding removed from each pup's home cage (HC). In C rats of both sexes and in HC females, short-term activity levels peaked on Day 16. However, HC males displayed an earlier and even greater elevation in activity from Day 12 to 16. This overall pattern was found in rats tested either every second or fourth day. In the second experiment, Long-Evans pups were assigned to each testing condition (C vs HC) and activity measured beginning on Day 12. Peak levels were seen in all Long-Evans rats on Day 16 and only females showed significant alterations as a function of bedding condition. When overall activity levels of the two strains were compared, significant differences were found on Days 12, 24, 30, and 120 in males, and 12, 24, and 30 in females. Significant differences between strains in activity as a function of bedding condition were found in males on Days 12, 20, 24, and 120 and in females on Days 12, 30, and 60. These data confirm the generality of a developmental hyperactivity phase in isolated juvenile rats. However, different patterns of hyperactivity were found in male vs female rats across strains. CD males were more active in the presence of HC olfactory cues, while in Long-Evans rats, female activity was affected more by bedding condition.