Locomotion and posture development in immature male and female rats (Rattus norvegicus): Comparison of sensory-enriched versus sensory-deprived testing environments

Abstract

The aim of the current study was to provide normative data on spontaneous locomotion and posture behavior in developing rats (Rattus norvegicus), during the first 2 postnatal weeks. Male and female rat pups were tested daily from P1 (postnatal day 1; ∼24 hr after birth) to P15 in a sensory-enriched or sensory-deprived testing environment, which was enclosed in a temperature-controlled incubator. Pups in the sensory-deprived condition were tested individually and placed in a square, Plexiglas box (open-field) for a 20-min test period. Pups in the sensory-enriched condition were placed in the same box with the siblings and bedding from the home cage to provide sensory stimulation that mimicked the home nest. Subjects in this condition were tested two at a time, with an additional two siblings (2 males and 2 females total in box). It was hypothesized that pups in the sensory-enriched testing condition would demonstrate more mature patterns of behavior, given the presence of behavior-activating sensory stimuli in the box. It was found that rat pups exhibited spontaneous pivoting and crawling as early as P1, regardless of sensory stimulation present in the testing environment. These behaviors were shown at least 1 to 3 days earlier than reported in prior studies. Quadrupedal walking occurred as early as P4 but was not reliably expressed until P10/11. These findings suggest that controlling temperature during testing influences the typical age of first occurrence of these behaviors. Finally, there were no sex differences in the duration of locomotion and posture behaviors. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Figure 1.

Sensory-deprived and sensory-enriched testing environments, in which rat pups were placed and their spontaneous posture and locomotion behavior were recorded. The box was located inside of an infant incubator that controlled temperature and humidity. A.) An empty, Plexiglas box was used in the sensory-deprived testing condition. B.) In the sensory-enriched testing condition, nest and bedding material from the home cage and two siblings (X_M, X_F) were placed inside the Plexiglas box as well.

Figure 2.

Body mass and length for male and female subjects. A.) Body mass of male and female rat pups for the first two postnatal weeks. B.) Body length for the first two postnatal weeks. Bars represent means, vertical lines show SEM, asterisks indicate significance at the p <.05 level.

Figure 3.

Percent of subjects exhibiting pivoting on P1 to P15 across each sex/testing condition. A.) Males in the sensory-deprived condition. B.) Males in the sensory-enriched condition. C.) Females in the sensory-deprived condition. D.) Females in the sensory-enriched condition. Bars represent mean percentages, asterisks represent first age of occurrence based on criterion, and dashed line indicates 70% criterion.

Figure 4.

Percent of subjects exhibiting crawling on P1 to P15 across each sex/testing condition. A.) Males in the sensory-deprived condition. B.) Males in the sensory-enriched condition. C.) Females in the sensory-deprived condition. D.) Females in the sensory-enriched condition. Bars represent mean percentages, asterisks represent first age of occurrence based on criterion, and dashed line indicates 70% criterion.

Figure 5.

Percent of subjects exhibiting walking on P1 to P15 across each sex/testing condition. A.) Males in the sensory-deprived condition. B.) Males in the sensory-enriched condition. C.) Females in the sensory-deprived condition. D.) Females in the sensory-enriched condition. Bars represent mean percentages, asterisks represent first age of occurrence based on criterion, and dashed line indicates 70% criterion.

Figure 6.

Duration of locomotion over the first two postnatal weeks, as a function of testing condition. A.) Pivoting duration. B.) Crawling duration. C.) Walking duration. Points represent means, vertical lines represent SEM.

Figure 7.

Duration of posture during the first two postnatal weeks. A.) Head elevation duration. B.) Walking stance duration. Points represent means, vertical lines represent SEM.