Early maternal separation has mild effects on cardiac autonomic balance and heart structure in adult male rats

Abstract

Early life adverse experiences have long-term physiologic and behavioral effects and enhance stress sensitivity. This study examined the effects of maternal separation (MS) on cardiac stress responsivity and structure in adulthood. Male Wistar rats were separated from the dams for 3 h per day from postnatal days 2 through 15. When exposed to 5-day intermittent restraint stress (IRS) as adults, MS, and control rats showed similar acute modifications of cardiac sympathovagal balance, quantified via heart rate variability analysis. In addition, MS had no effect on cardiac pacemaker intrinsic activity (as revealed by autonomic blockade with scopolamine and atenolol) and did not affect the circadian rhythmicity of heart rate, neither before nor after IRS. However, MS differed from control rats in cardiac parasympathetic drive following IRS, which was heightened in the latter but remained unchanged in the former, both during the light and dark phases of the daily rhythm. The evaluation of adult cardiac structure indicated that stress experienced during a crucial developmental period induced only modest changes, involving cardiomyocyte hypertrophy, increased density of vascular structures, and myocardial fibrosis. The mildness of these functional–structural effects questions the validity of MS as a model for early stress-induced cardiac disease in humans.

Keywords::

• biological rhythms
• heart rate variability
• heart remodeling
• maternal separation
• parasympathetic nervous system
• restraint

Acknowledgements

This study was supported by grants from the Italian Ministry for Education, University and Research (PRIN2007, 2007WB35CW_004) and from the University of Parma (FIL0757771).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.