Cardiovascular reactivity and neuronal activation to stress in Schlager genetically hypertensive mice

Schlager inbred hypertensive mice (BPH/2J) have been suggested to have high blood pressure (BP) due to an overactive sympathetic nervous system (SNS). The brain nuclei associated with the hypertension are also those involved in the integration of the cardiovascular responses to stress. Therefore, in the present study, we hypothesize that BPH/2J mice likely have a greater response to stress that is associated with greater neuronal activation in the limbic system, hypothalamus and medulla in regions known to regulate sympathetic activity. Male hypertensive BPH/2J and normotensive BPN/3J mice were implanted with telemetry devices and exposed to dirty cage-switch, an acute model of aversive stress. Stress exposure caused a 60% greater pressor response in BPH/2J compared with BPN/3J mice and an increase in activity, by contrast the level of tachycardia was less in BPH/2J mice. Stress-induced cardiovascular responses were also associated with greater neuronal activation, as detected by c-Fos expression, in BPH/2J compared with BPN/3J mice in the medial nucleus of the amygdala (MeAm), dorsomedial hypothalamus (DMH) (P<0.001) and marginally in the rostral ventrolateral medulla (RVLM; P=0.7). These findings suggest that hypertension in the BPH/2J mice is associated with greater sympathetic vasomotor responses to central pathways mediating the arousal responses to acute aversive stress in particular the amygdala, hypothalamus and rostral ventrolateral medulla.