Swimming Training Modulates Nitric Oxide-Glutamate Interaction in the Rostral Ventrolateral Medulla in Normotensive Conscious Rats

Antioxidant therapy reverses sympathetic dysfunction, oxidative stress, and hypertension in male hyperadipose rats

AIMS

The rostral ventrolateral medulla (RVLM) is the main sympathetic output of the central nervous system to control blood pressure. Reportedly, reactive oxygen species (ROS) can increase arterial pressure, leading to hypertension. As ROS increase the sympathetic tone in RVLM and obese animals present grater oxidative stress, it would be important to note this relationship.

MAIN METHODS

Therefore, we evaluated the systemic and central effects (in the RVLM) of vitamin C (vit C, an antioxidant) on the redox balance and cardiovascular and autonomic profiles in hyperadipose male rats. We also evaluated the neurotransmission by L-glutamate (L-glu) and vit C in the RVLM of awake hyperadipose rats.

KEY FINDINGS

Our study confirmed that hyperadipose rats were hypertensive and tachycardic, presented increased sympathetic and decreased parasympathetic modulation of the heart, and had increased plasma lipoperoxidation compared with the control rats (CTR). Oral vitamin C treatment reverted cardiovascular, autonomic, and plasma redox dysfunction. Hyperadipose rats presented a higher blood pressure increase after L-glu microinjection and a lower response to vit C in the RVLM compared with the CTR group. Biochemical analysis of redox balance in RVLM punches showed that hyperadipose rats have increased NBT and T-BARS, and after treatment with vit C, the oxidative profile decreased. The antioxidative activity of vit C reduced the amount of ROS in the RVLM area that might have resulted in lowered blood pressure and sympathetic modulation.

SIGNIFICANCE

Our data suggest central and peripheral benefits of vit C treatment on cardiovascular, autonomic, and oxidative dysfunctions in hyperadipose animals.

Regularly swimming exercise modifies opioidergic neuromodulation in rostral ventrolateral medulla in hypertensive rats

Moderate exercise reduces arterial pressure (AP) and heart rate (HR) in spontaneously hypertensive rats (SHR) and changes neurotransmission in medullary areas involved in cardiovascular regulation. We investigated if regularly swimming exercise (SW) affects the cardiovascular adjustments mediated by opioidergic neuromodulation in the RVLM in SHR and Wistar-Kyoto (WKY) rats. Rats were submitted to 6 wks of SW. The day after the last exercise bout, α-chloralose-anesthetized rats underwent a cannulation of the femoral artery for AP and HR recordings, and Doppler flow probes were placed around the lower abdominal aorta and superior mesenteric artery. Bilateral injection of endomorphin-2 (EM-2, 0.4 mmol/L, 60 nL) into the RVLM increased MAP in SW-SHR (20 ± 4 mmHg, N = 6), which was lower than in sedentary (SED)-SHR (35 ± 4 mmHg, N = 6). The increase in MAP in SW-SHR induced by EM-2 into the RVLM was similar in SED- and SW-WKY. Naloxone (0.5 mmol/L, 60 nL) injected into the RVLM evoked an enhanced hypotension in SW-SHR (-66 ± 8 mmHg, N = 6) compared to SED-SHR (-25 ± 3 mmHg, N = 6), which was similar in SED- and SW-WKY. No significant changes were observed in HR after EM-2 or naloxone injections into the RVLM. Changes in hindquarter and mesenteric conductances evoked by EM-2 or naloxone injections into the RVLM in SW- or SED-SHR were not different. Mu Opioid Receptor expression by Western blotting was reduced in SW-SHR than in SED-SHR and SW-WKY. Therefore, regularly SW alters the opioidergic neuromodulation in the RVLM in SHR and modifies the mu opioid receptor expression in this medullary area.

Reduction of oxidative stress and inflammatory signaling in the commissural nucleus of the solitary tract (commNTS) and rostral ventrolateral medulla (RVLM) in treadmill trained rats

Inflammation has been associated with cardiovascular diseases and the key point is the generation of reactive oxygen species (ROS). Exercise modulates medullary neurons involved in cardiovascular control. We investigated the effect of chronic exercise training (Tr) in treadmill running on gene expression (GE) of ROS and inflammation in commNTS and RVLM neurons. Male Wistar rats (N = 7/group) were submitted to training in a treadmill running (1 h/day, 5 days/wk/10 wks) or maintained sedentary (Sed). Superoxide dismutase (SOD), catalase (CAT), neuroglobin (Ngb), Cytoglobin (Ctb), NADPH oxidase (Nox), cicloxigenase-2 (Cox-2), and neuronal nitric oxide synthase (NOS1) gene expression were evaluated in commNTS and RVLM neurons by qPCR. In RVLM, Tr rats increased Ngb (1.285 ± 0.03 vs. 0.995 ± 0.06), Cygb (1.18 ± 0.02 vs.0.99 ± 0.06), SOD (1.426 ± 0.108 vs. 1.00 ± 0.08), CAT (1.34 ± 0.09 vs. 1.00 ± 0.08); and decreased Nox (0.55 ± 0.146 vs. 1.001 ± 0.08), Cox-2 (0.335 ± 0.05 vs. 1.245 ± 0.02), NOS1 (0.51 ± 0.08 vs. 1.08 ± 0.209) GE compared to Sed. In commNTS, Tr rats increased SOD (1.384 ± 0.13 vs. 0.897 ± 0.101), CAT GE (1.312 ± 0.126 vs. 0.891 ± 0.106) and decreased Cox-2 (0.052 ± 0.011 vs. 1.06 ± 0.207) and NOS1 (0.1550 ± 0.03559 vs. 1.122 ± 0.26) GE compared to Sed. Therefore, GE of proteins of the inflammatory process reduced while GE of antioxidant proteins increased in the commNTS and RVLM after training, suggesting a decrease in oxidative stress of downstream pathways mediated by nitric oxide.

Aquatic Training after Joint Immobilization in Rats Promotes Adaptations in Myotendinous Junctions

The myotendinous junction (MTJ) is the muscle-tendon interface and constitutes an integrated mechanical unit to force transmission. Joint immobilization promotes muscle atrophy via disuse, while physical exercise can be used as an adaptative stimulus. In this study, we aimed to investigate the components of the MTJ and their adaptations and the associated elements triggered with aquatic training after joint immobilization. Forty-four male Wistar rats were divided into sedentary (SD), aquatic training (AT), immobilization (IM), and immobilization/aquatic training (IMAT) groups. The samples were processed to measure fiber area, nuclear fractal dimension, MTJ nuclear density, identification of telocytes, sarcomeres, and MTJ perimeter length. In the AT group, the maintenance of ultrastructure and elements in the MTJ region were observed; the IM group presented muscle atrophy effects with reduced MTJ perimeter; the IMAT group demonstrated that aquatic training after joint immobilization promotes benefits in the muscle fiber area and fractal dimension, in the MTJ region shows longer sarcomeres and MTJ perimeter. We identified the presence of telocytes in the MTJ region in all experimental groups. We concluded that aquatic training is an effective rehabilitation method after joint immobilization due to reduced muscle atrophy and regeneration effects on MTJ in rats.

Swimming training reduces iNOS expression, augments the antioxidant defense and reduces sympathetic responsiveness in the rostral ventrolateral medulla of normotensive male rats

We sought to investigate whether RVLM iNOS activity and oxidative profile may participate in the reduction of sympathetic responsiveness in swimming trained normotensive rats. Sedentary (S) and swimming trained (T) Wistar male rats chronically instrumented with an arterial catheter and guide cannula into the RVLM were submitted to continuous pressure and heart rate (HR) recordings and determination of autonomic control (power spectral analysis) before and after unilateral RVLM iNOS inhibition (aminoguanidine, 250 pmol/100 nL). Other S and T rats received local l-glutamate microinjection (5 nmol/100 nL). In separate S and T groups not submitted to brainstem cannulation, fresh bilateral RVLM punchs were collected for iNOS gene expression (qPCR); reduced glutathione and lipid peroxidation quantification (spectrophotometry); iron-reducing antioxidant (FRAP) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS˙⁺) scavenger assays. iNOS gene expression was confirmed in fixed RVLM slices (immunofluorescence). T rats exhibited resting bradycardia, lower sympathovagal balance, reduced RVLM iNOS gene/protein expression and higher antioxidant capacity. Decreased iNOS expression was positively correlated with reduced HR. Pressor and tachycardic response to l-Glutamate were smaller in T rats. Aminoguanidine microinjection reduced sympathetic activity in S rats but did not change it in T rats expressing reduced RVLM iNOS content. Our data indicate that iNOS, expressed in the RVLM of normotensive male rats, has tonic effects on sympathetic activity and that swimming training is an efficient tool to reduce iNOS expression and augment the antioxidant defense, thus reducing glutamatergic responsiveness and sympathetic drive to cardiovascular effectors.

Remodeling of the skeletal muscle and postsynaptic component after short-term joint immobilization and aquatic training

Joint immobilization is commonly used as a conservative treatment for osteoarticular and musculotendinous traumas. However, joint immobilization might elicit degenerative effects on the neuromuscular system and muscle atrophy. For this reason, the choice of strategies that mitigate these effects is essential in the post-immobilization period. Therefore, this study aimed to investigate the impact of aquatic training on the morphology of muscle fibers and motor endplates of the gastrocnemius muscle in the post-immobilization period. Male Wistar rats (90 days old) were divided into groups: Sedentary: no procedure; Immobilization: joint immobilization protocol (10 days); Immobilization/non-training: joint immobilization protocol (10 days) followed by four weeks without exercise intervention; Immobilization/training: joint immobilization protocol (10 days) and post-immobilization aquatic training (4 weeks). After the procedures, we quantified the cross-sectional area (CSA), volume and numerical density of different myofibers types, and total and stained area and perimeter of the motor endplate. We demonstrate the following main results: (a) short-term joint immobilization resulted in myofibers atrophy; however, we verified a small change in the postsynaptic component; (b) the period of inactivity after immobilization caused severe changes in the motor endplate (lower stained area, stained perimeter, total area, and total perimeter) and maintenance of muscle atrophy due to immobilization; (c) the prescription of post-immobilization exercise proved to be effective in restoring muscle morphology and inducing plasticity in the motor endplate. We conclude that short-term joint immobilization (10 days) results in atrophy type I and II myofibers, in addition to a decline in the total perimeter of the motor endplate. Besides, the post-immobilization period appears to be decisive in muscle and postsynaptic remodeling. Thus, aquatic training is effective in stimulating adjustments associated with muscle hypertrophy and plasticity of the motor endplate during the post-immobilization period.

Role of neuronal nitric oxide synthase on cardiovascular functions in physiological and pathophysiological states

This review describes and summarizes the role of neuronal nitric oxide synthase (nNOS) on the central nervous system, particularly on brain regions such as the ventrolateral medulla (VLM) and the periaqueductal gray matter (PAG), and on blood vessels and the heart that are involved in the regulation and control of the cardiovascular system (CVS). Furthermore, we shall also review the functional aspects of nNOS during several physiological, pathophysiological, and clinical conditions such as exercise, pain, cerebral vascular accidents or stroke and hypertension. For example, during stroke, a cascade of molecular, neurochemical, and cellular changes occur that affect the nervous system as elicited by generation of free radicals and nitric oxide (NO) from vulnerable neurons, peroxide formation, superoxides, apoptosis, and the differential activation of three isoforms of nitric oxide synthases (NOSs), and can exert profound effects on the CVS. Neuronal NOS is one of the three isoforms of NOSs, the others being endothelial (eNOS) and inducible (iNOS) enzymes. Neuronal NOS is a critical homeostatic component of the CVS and plays an important role in regulation of different systems and disease process including nociception. The functional and physiological roles of NO and nNOS are described at the beginning of this review. We also elaborate the structure, gene, domain, and regulation of the nNOS protein. Both inhibitory and excitatory role of nNOS on the sympathetic autonomic nervous system (SANS) and parasympathetic autonomic nervous system (PANS) as mediated via different neurotransmitters/signal transduction processes will be explored, particularly its effects on the CVS. Because the VLM plays a crucial function in cardiovascular homeostatic mechanisms, the neuroanatomy and cardiovascular regulation of the VLM will be discussed in conjunction with the actions of nNOS. Thereafter, we shall discuss the up-to-date developments that are related to the interaction between nNOS and cardiovascular diseases such as hypertension and stroke. Finally, we shall focus on the role of nNOS, particularly within the PAG in cardiovascular regulation and neurotransmission during different types of pain stimulus. Overall, this review focuses on our current understanding of the nNOS protein, and provides further insights on how nNOS modulates, regulates, and controls cardiovascular function during both physiological activity such as exercise, and pathophysiological conditions such as stroke and hypertension.

Moderate Treadmill Exercise Training Improves Cardiovascular and Nitrergic Response and Resistance to Trypanosoma cruzi Infection in Mice

There is evidence suggesting that exercise training (ET) acts as a factor toward resistance to Trypanosoma cruzi infection. However, the effects of mean arterial pressure (MAP), heart rate (HR), and nitric oxide (NO) during the acute phase of infection has not been elucidated yet. Swiss mice were randomly assigned into four groups: sedentary control (SC, n = 30), trained control (TC, n = 30), sedentary infected (SI, n = 30), and trained infected (TI, n = 30). ET was performed on the treadmill for 9 weeks. After training, the mice were infected with 5 × 10³ trypomastigotes of T. cruzi (Y strain) or PBS. We observed resting bradycardia and improved performance in trained animals compared with sedentary ones. On the 20th day post-infection (DPI), we found a decrease in HR in SI animals compared to TI animals (699.73 ± 42.37 vs. 742.11 ± 25.35 bpm, respectively, P < 0.05). We also observed increased production of NO in cardiac tissue on the 20th DPI in the SI group, normalized in TI group (20.73 ± 2.74 vs. 6.51 ± 1.19 μM, respectively). Plasma pro-inflammatory cytokines (IL-12, TNF-α, IFN-γ,) and MCP-1 were increased in SI animals, but decreased in TI animals. The increase in parasitemia on the 15th and 17th DPI in the SI group was attenuated in the TI group. Our results suggest that previous ET plays a preventive role in resistance to T. cruzi infection, modulating cardiovascular aspects, inflammatory reaction, and NO levels of infected mice.