Abstract
Separation of neonatal rodent pups from their mothers has been used as a model to study the effects of early life stress (ELS) on behavioral and physiological responses in adults. Using an Induction-Delay-Expression experimental paradigm, our previous studies demonstrate that a wide range of stressors administered during an induction period produces hypertensive response sensitization (HTRS) in response to a subsequent pro-hypertensive stimulus. HTRS is accompanied by activation of the brain renin-angiotensin system (RAS) and CNS inflammation. The present study investigated whether ELS induces HTRS and changes in brain-related underlying mechanisms. Rat neonates from Sprague-Dawley breeders were subjected to ELS by separating them each morning from their mothers for 3 h on postnatal days 2 to 14. Pups from non-handled litters formed control groups. At 10 weeks of age, male rats were used to evaluate blood pressure and autonomic function using telemetric probes and pharmacological methods. In addition, in separate control and ELS groups, the lamina terminalis (LT) structures and the hypothalamic paraventricular nucleus (PVN) were analyzed for mRNA expression of RAS components and proinflammatory cytokines. Adult ELS rats as compared to non-separated controls exhibited 1) HTRS during expression testing using 2 week ANG II infusions (120 ng/kg/min s.c.; ELS animals, Δ45.5±4.5 mmHg vs. controls, Δ22.4±3.1 mmHg); 2) a greater reduction in mean arterial pressure following ganglionic blockade (hexamethonium, 30 mg/kg, ip), 3) increased sympathetic drive to the heart (atenolol, 8 mg/kg, ip), 4) decreased vagal tone (atropine, 8 mg/kg, ip), and 5) increased mRNA expression of several components of the brain RAS and proinflammatory cytokines in the LT and PVN. These results suggest that maternal ELS may predispose individuals to hypertension that is mediated by upregulation of the brain RAS and proinflammatory cytokines and increased sympathetic drive to the cardiovascular system.
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