Stress-like responses to common procedures in rats: effect of the estrous cycle.

The objective of this study was to assess cardiovascular and behavioral responses of Sprague-Dawley female rats subjected to or witnessing common husbandry and experimental procedures at various points during the estrous cycle. Heart rate (HR) and mean arterial blood pressure (MAP) were determined using radiotelemetry for 2 h before and 3 h after: cage change, restraint and subcutaneous (s.c.) injection, restraint and tail-vein injection, witnessing decapitation of other rats, smelling urine and feces from stressed rats, and smelling dried rat blood. Home cage behaviors (sleeping, awake, moving, rearing, and grooming) were scored once each minute for 15 min before and 45 min after the incidents. Being subjected to cage change, restraint and injections, and odors significantly increased HR and MAP 60-120 beats per min and 10-20 mm Hg over baseline respectively for 45 to 90 min. Witnessing these procedures also significantly increased HR and MAP but the magnitude was reduced by 20% to 30% compared to that seen in rats subjected to the procedures. Witnessing decapitation of other rats induced cardiovascular responses which were not different from those of rats witnessing other procedures. The cardiovascular responses were not enhanced during proestrus-estrus compared to metestrus-diestrus. There were also no significant effects of the estrous cycle on home cage behavior after these procedures. We conclude that cycling female rats show stress-like effects when they are subjected to or witness common husbandry and experimental procedures, but there is little to no effect of the estrous cycle.

Stress-like responses to common procedures in male rats housed alone or with other rats.

The objective of this study was to assess the cardiovascular function and behavior of male Sprague-Dawley rats housed individually or with one or three cagemates during resting conditions and when subjected to common husbandry and experimental procedures and potentially stressful olfactory stimuli. Heart rate (HR), mean arterial blood pressure (MAP), and movement in the cage were collected by using radiotelemetry for 24 h on an experiment-free day and for 2 h before and 3 h after the following acute procedures: cage change, restraint and subcutaneous injection, restraint and tail-vein injection, exposure to the odor of urine and feces from stressed rats, and exposure to the odor of dried rat blood. Home cage behaviors (sleeping, awake, moving, rearing, and grooming) were scored once each minute for 15 min before and 45 min after the acute procedures. Resting HR and MAP values consistently were lower in rats housed four per cage than animals housed alone or with one cage mate. Compared to that of animals housed individually, general activity was higher during the light phase and lower during the dark phase in rats housed four per cage. Rats housed four per cage showed significantly lower HR and MAP in response to acute husbandry and experimental procedures than rats housed alone, and the HR and MAP of rats housed in pairs were not consistently lower than those of rats housed alone. Procedure-induced arousal behaviors were observed in all housing groups after the acute husbandry and experimental procedures, but rats housed four per cage returned to sleeping behavior more quickly than did rats in the other housing groups. In light of these results, we concluded that under resting conditions, rats housed four per cage were less stressed than were rats housed alone, that common procedures induce noteworthy stress-like responses in male rats, and that the magnitude and duration of these responses are reduced by group housing.