Abstract
Introduction: SJL/J (SJL) mice have elevated (80beats/min) heart rate (HR) compared to C3HeB/FeJ (C3HeB) mouse strain then measured by tail-cuff plethysmography. SJL and C3HeB are differed in behavioral phenotypes. The goal of this study was to investigate hemodynamic responses to normal and stress conditions between SJL and C3HeB inbred mouse strains. Methods and Results: Radio telemetry was used for continuous recordings of HR and systolic blood pressure (SBP) in C3HeB (n=5-10) and SJL (n=4-10) mice. We found that both strains showed normal circadian rhythms with little differences in HR and SBP. However, a locomotor activity (LA) of SJL was lower compared to C3HeB (7.8±0.4 vs. 10.0±0.1counts) during the lights off period. A correlation between LA and HR was reduced in SJL (R 2 =0.27) compared to C3HeB (R 2 =0.67) during the lights off period. After a mild stress (transfer to a cage) SJL had a slight HR elevation (70 beats/min) compared to C3HeB in first 5min. LA and SBP were similar between inbred strains after a novel cage test. The HR changes were significantly higher (2.5-fold, p<0.05) in SJL vs. C3HeB during first 5min (30min of restraining period) on the first day of tail-cuff training. Five days of tail-cuff procedures resulted in 2-fold elevation of HR in SJL compared to C3HeB for 30min restraining period. Interestingly, changes in SBP were similar between mouse strains on first day, while SBP showed a trend to be 2-fold higher in SJL vs. C3HeB for 30min on day five. Autonomic control of HR was determined by pharmacological blockages in mice. Atropine (1mg/kg, i.p.) caused significantly greater increases in HR in SJL (160+8beats/min, p<0.05) compared to C3HeB (62+11beats/min). Administration of propranolol (4mg/kg, i.p.) resulted in similar HR reductions between these strains. Conclusions: We found that SJL mice are susceptible to elevation of hemodynamic parameters after chronic stress. An increase in sympathetic nervous system activity may explain HR differences between SJL and C3HeB inbred strains. This study was supported in part by funds from Russian Program "Scientific and scientific-pedagogical personnel of innovative Russia" for 2009-2013 GK№14.740.11.0923 and HL105623 (VAK)
Published Version
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