Effects of a complex housing environment on heart rate and blood pressure of rats at rest and after stressful challenges.

Housing enrichment for rodents continues to be a discussion topic within the animal care community. The objective of this study was to determine the extent to which a complex housing environment affects heart rate, blood pressure, and activity of rats when undisturbed and after exposure to stressful challenges and whether autonomic controls of heart rate would be affected. Male and female Sprague-Dawley and Wistar rats with radiotelemetry transmitters were evaluated under nonenriched single-housing conditions and after acclimation to a complex environment of dim light and cohabitation with 3 conspecifics in large cages with hiding, food foraging, and nesting items. Telemetry data were collected when rats were undisturbed, after acute challenges (cage change, intraperitoneal injections, restraint), during a forced running protocol, and after cholinergic or adrenergic blockade. The complex environment reduced heart rate and increased activity in undisturbed rats but did not affect blood pressure. Heart rate responses to challenges were unaffected, decreased, or increased by complex housing, depending on the stock and sex of rats. Forced running was either unaffected or decreased, depending on the stock and sex of rats. Heart rate responses to cholinergic or β1-adrenergic blockade were not affected. We conclude that the complex housing did not reduce indices of stress (for example, heart rate) as compared with simpler housing. However, the possibility that some environmental elements interact negatively with each other must be considered in future studies.