Putative role of the NTS in alterations in neural control of the circulation following exercise training in rats

Abstract

Exercise training (ExTr) has been associated with alterations in neural control of the circulation, including effects on arterial baroreflex function. The nucleus tractus solitarius (NTS) is the primary termination site of cardiovascular afferents and critical in the regulation of baroreflex-mediated changes in heart rate (HR) and sympathetic nervous system outflow. The purpose of the present study was to determine whether ExTr is associated with alterations in neurotransmitter regulation of neurons involved in control of cardiovascular function at the level of the NTS. We hypothesized that ExTr would increase glutamatergic and reduce GABAergic transmission in the NTS and that, collectively, these changes would result in a greater overall sympathoinhibitory drive from the NTS in ExTr animals. To test these hypotheses, male Sprague-Dawley rats were treadmill trained or maintained under sedentary conditions for 8-10 wk. NTS microinjections were performed in Inactin-anesthetized animals instrumented to record mean arterial pressure (MAP), HR, and lumbar sympathetic nerve activity (LSNA). Generalized activation of the NTS with unilateral microinjections of glutamate (1-10 mM, 30 nl) produced dose-dependent decreases in MAP, HR, and LSNA that were unaffected by ExTr. Bilateral inhibition of NTS with the GABAA agonist muscimol (1 mM, 90 nl) produced increases in MAP and LSNA that were blunted by ExTr. In contrast, pressor and sympathoexcitatory responses to bilateral microinjections of the ionotropic glutamate receptor antagonist, kynurenate (40 mM, 90 nl), were similar between groups. Bradycardic responses to bilateral microinjections of the GABAA antagonist bicuculline (0.1 mM, 90 nl) were attenuated by ExTr. These data indicate that alterations in neurotransmission at the level of the NTS contribute importantly to regulation of HR and LSNA in ExTr animals. In addition to alterations at NTS, these experiments suggest indirectly that changes in other cardiovascular nuclei contribute to the observed alterations in neural control of the circulation following ExTr.

Exercise changes regional vascular control by commissural NTS in spontaneously hypertensive rats

“…Exercise training for 8 wk or more increases the activity of citrate synthase (29,30,32). Indeed, our exercise protocol was not enough to produce the same metabolic muscular changes observed in trained animals.…”

“…Evidence suggested that the exercise training can reduce tonic GABA-mediated inhibition of intermediate NTS neurons involved in the control of heart rate that could explain the decrease in the resting values (32). Reduction of the resting tail pressure after swimming exercise compared with initial preexercise values could be attributed to blunted baroreflex-mediated sympathoexcitation (12,13,27,28,32).…”

Exercise Training Fails to Modify Arterial Baroreflex Sensitivity in Ovariectomized Female Rats

“…On the other hand, it is unknown whether exercise training could ameliorate the reduction in BRSinc caused by altered central autonomic integration associated with withdrawal of female sex hormones. However, it has been shown that exercise training has potency to modulate intrinsic properties of several autonomic-related nucleus in central nervous system (Jackson et al 2005;Mueller and Hasser 2006). Moreover, it is well known that exercise training increases BRSinc in pathological conditions such as hypertension (Somers et al 1991), myocardial infarction (La Rovere et al 2002), and heart failure (Liu et al 2002).…”

Influence of the hypothalamic paraventricular nucleus (PVN) on heart rate variability (HRV) in rat hearts via electronic lesion

“…Preoperation and sham operation groups were used as control. ventrolateral medulla (RCLM) [16][17][18][19][20][21][22][23][24], the nucleus of solitary tract (NTS) [7,25] and paraventricular nucleus (PVN) [26]. The PVN connects these areas in the brain involved in cardiovascular function, forming important neuroendocrine and autonomic modulation, which further modulates the homeostasis of the body through the brain stem, spinal cord, median eminence and posterior pituitary.…”