Effects of a cage enrichment program on heart rate, blood pressure, and activity of male Sprague-Dawley and spontaneously hypertensive rats monitored by radiotelemetry

To determine whether a nonsocial enrichment program affects cardiovascular responses of individually housed male Sprague-Dawley (SD) and spontaneously hypertensive (SH) rats under basal conditions and after potentially stressful procedures, we used radiotelemetry to record heart rate (HR), systolic blood pressure (SBP), and activity in the cage. Enrichment comprised a simulated burrow (Rodent Retreat), then a food foraging item ("rat cannoli") 2 days later, and a paper bag of bedding for shredding (Nestpak) after another 2 days. Data were collected under undisturbed conditions and before and after several acute and chronic manipulations mimicking common husbandry, experimental, and stressful procedures. Enrichment often, but not always, reduced HR and SBP in male rats, suggesting decreased arousal and stress, and the effects depended on the parameter measured, strain of rat, and nature of the procedure to which animals were exposed. In general, HR varied more than SBP; enrichment affected SH rats more than SD rats; effects of enrichment were more consistently observed under undisturbed conditions than after manipulations of the rats; moderate responses to acute husbandry and experimental procedures were affected more than the larger changes produced by very stressful procedures; and responses to social interactions were unaffected by the enrichment program. What accounts for these variable effects of enrichment is unclear, and more studies are required to resolve the mechanisms. Whether this enrichment program should be used in an animal facility depends on several factors, particularly the professional judgment of the research, veterinary, and animal care staffs involved.