Getting a handle on rat familiarization: The impact of handling protocols on classic tests of stress in Rattus norvegicus.

Experimenter familiarization with laboratory rodents through handling prior to experimentation is an important practice in neurobehavioral research and is implicated in stress, study variability, and replicability. Unfortunately, different handling protocols have not been thoroughly examined. Determining optimal experimenter familiarization protocols is expected to reduce animal stress and thus improve welfare and data consistency. The impact of different handling protocols was determined through behavioral assessments (i.e. elevated plus maze, light/dark box, open field) as well as via analysis of fecal boli counts, ultrasonic vocalizations, and blood corticosterone. Male and female Sprague Dawley rats were distributed among three groups: never handled, picked-up, and handled for 5 min once daily over five days. Handled and picked-up rats spent more time in open arms and less time in closed arms of the elevated plus maze and more time in the center and less time at the perimeter of the open field compared to rats that were never handled, indicating that handled and picked-up rats were less anxious than those that were never handled. Male rats consistently defecated more frequently throughout the handling process and throughout behavioral testing, whereas females showed greater concentrations of blood corticosterone. Female rats were found to emit more 50-kHz calls and fewer 22-kHz calls compared to males. The results observed suggest that picking animals up may suffice as a handling method compared to time-intensive handling procedures, and that there are significant sex differences in response to handling.

The Effects of Rearing in a Shelved Environment on Behavioral and Physiological Markers of Welfare in Rats (Rattus norvegicus).

Early-life experiences are critical modifiers of development. An important component of early-life experience is the nature of maternal interactions, which can be modified by stress. During rearing, mothers are typically allocated to single-level cages where they are readily accessible to pups, a potentially stressful scenario not reflective of nature. Accordingly, mothers regularly removed from the rearing environment interact differently with their offspring, leading to long-term changes in offspring physiology and behavior. Such changes commonly include modifications within the hypothalamic-pituitary-adrenal axis, of which corticosterone is a major component. Modifications in the hypothalamic-pituitary-adrenal axis may also be manifested through changes in affective behavior and assessed via tests such as the open field and elevated plus maze as well as via ultrasonic vocalization (USV) analysis. As a means of assessing the impact of rearing in a shelved environment, we allocated mothers to standard single-level cages or cages with an integrated shelf, which allowed the mother to temporarily escape pups. While there were no differences in fecal cortico-sterone, behavior in the elevated plus maze, or USVs, male rats reared in standard cages weighed more, and all standard single-level housed rats spent more time in the center of the open field. The observed differences indicate that allocating nursing mothers to shelved environments throughout the postnatal period has long-lasting effects on offspring behavior that must be considered when establishing dam enrichment protocols.