A noninvasive cutaneous delayed type hypersensitivity test is effective for evaluating the effects of handling on immunological stress levels in rats

Abstract

Abstract Rats are a common model for human physiology and psychology, yet routine handling associated with animal maintenance and treatment administration has been shown to impact behavioral and physiological measures in rats, which raises concerns about their use as a model. Adolescent and adult female rats (Sprague-Dawley, n=6 per group) were subjected to handling treatments (restraint, tickling, or playful handling) to evaluate the potential to minimize the physiological impacts of handling stress. Treatments were administered every other day for 21 days, and body weights, blood smears, and ultrasonic vocalizations were collected throughout this time and for 14 subsequent days without handling treatments. A noninvasive delayed type hypersensitivity test was performed by sensitizing rats to 2,4-Dinitrochlorobenzene on abdominal skin and later assessing the response to ear lobe exposure by measuring ear thickness. The greatest increase in lobe thickness was consistently observed at 48 hours post exposure, with few animals showing inflammation that persisted more than 72 hours. Assessments in the middle of the handling period (day 10) and at the end of the handling period (day 21) showed significantly less swelling for adolescent rats receiving the restraint treatment as compared to rats in the tickling or playful handling groups. This effect was observed in both adolescent and adult rats, however the adolescent rats showed more significant changes in circulating blood cell populations and body weight than did adults. No differences were detected outside of the handling treatment period. These results further establish that routine handling can impact immunological measures in rats and demonstrate efficacy of this noninvasive assay.