Involvement of GABAergic and Adrenergic Neurotransmissions on Paraventricular Nucleus of Hypothalamus in the Control of Cardiac Function

Prenatal Morphine Exposure Increases Cardiovascular Disease Risk and Programs Neurogenic Hypertension in the Adult Offspring

BACKGROUND

The opioid overdose and opioid use disorder epidemics are concomitant with increased metabolic and CVD risk. Although opioid use disorder causes adverse pregnancy outcomes, the offspring's cardiovascular health is understudied. We hypothesized that offspring exposed to in utero morphine exposure (IUME) would show increased CVD risk factors and endogenous opioid system dysregulation.

METHODS

Sprague Dawley dams were treated with saline (vehicle, n=10) or escalating doses of morphine (5-20 mg/kg per day, SC, n=10) during gestation. Cardiovascular and metabolic parameters were assessed in adult offspring.

RESULTS

Litter size and pups' birth weight were not different in response to IUME. Female and male IUME offspring showed reduced body length at birth (P<0.05) and body weight from weeks 1 to 3 of life (P<0.05), followed by a catch-up growth effect. By week 16, female and male IUME rats showed reduced tibia length (P<0.05) and fat mass. IUME increases the mean arterial pressure and the depressor response to mecamylamine (5 mg/kg per day, IP) induced by IUME were abolished by a chronic treatment with an alpha-adrenergic receptor blocker (prazosin; 1 mg/kg per day, IP). Although circulating levels of angiotensin peptides were similar between groups, IUME exacerbated maximal ex vivo Ang (angiotensin) II-induced vasoconstriction (P<0.05) and induced endothelial dysfunction in a sex-specific manner (P<0.05). Proenkephalin, an endogenous opioid peptide that lowers blood pressure and sympathetic-mediated vasoconstriction, showed reduced mRNA expression in the heart, aorta, and kidneys from morphine versus vehicle group (P<0.05).

CONCLUSIONS

Among the effects of IUME, neurogenic hypertension, vascular dysfunction, and metabolic dysfunction could be associated with the dysregulation of the endogenous opioid system.

Angiotensin-(1-7) attenuates the negative inotropic response to acetylcholine in the heart

Previous studies have suggested that the Angiotensin-(1-7) [(Ang-(1-7)] can change cardiac function by modulating the autonomic nervous system. However, it is unknown whether the Ang-(1-7) can modulate the effect of acetylcholine (ACh) in ventricular contractility. Thus, this study aimed to investigate whether Ang-(1-7) modifies the amplitude of the cardiac cholinergic effects and if these effects are intrinsic to the heart. In anesthetized Wistar rats, Ang-(1-7) attenuated the effect of ACh in decreasing the left ventricular end-systolic pressure (LVESP), dP/dt_max, and dP/dt_min, but did not modify the hypotensive effect of ACh. Similarly, Ang-(1-7) attenuated the reduction of the LVESP, dP/dt_max, and dP/dt_min evoked by ACh in isolated hearts. These effects were blocked by the Mas receptor antagonist, A-779, but not by the adenylyl cyclase inhibitor MDL-12,330 A. Ang-(1-7) also attenuated the reduction in the maximum contraction and relaxation speeds and the shortening promoted by ACh in isolated cardiomyocytes. These data show that Ang-(1-7) acting through Mas receptor counter-regulates the myocardial contractile response to ACh in an arterial pressure and heart rate-independent manner.

The Role of the Paraventricular-Coerulear Network on the Programming of Hypertension by Prenatal Undernutrition

A crucial etiological component in fetal programming is early nutrition. Indeed, early undernutrition may cause a chronic increase in blood pressure and cardiovascular diseases, including stroke and heart failure. In this regard, current evidence has sustained several pathological mechanisms involving changes in central and peripheral targets. In the present review, we summarize the neuroendocrine and neuroplastic modifications that underlie maladaptive mechanisms related to chronic hypertension programming after early undernutrition. First, we analyzed the role of glucocorticoids on the mechanism of long-term programming of hypertension. Secondly, we discussed the pathological plastic changes at the paraventricular nucleus of the hypothalamus that contribute to the development of chronic hypertension in animal models of prenatal undernutrition, dissecting the neural network that reciprocally communicates this nucleus with the locus coeruleus. Finally, we propose an integrated and updated view of the main neuroendocrine and central circuital alterations that support the occurrence of chronic increases of blood pressure in prenatally undernourished animals.

Hypothalamic GPCR Signaling Pathways in Cardiometabolic Control

Obesity is commonly associated with sympathetic overdrive, which is one of the major risk factors for the development of cardiovascular diseases, such as hypertension and heart failure. Over the past few decades, there has been a growing understanding of molecular mechanisms underlying obesity development with central origin; however, the relative contribution of these molecular changes to the regulation of cardiovascular function remains vague. A variety of G-protein coupled receptors (GPCRs) and their downstream signaling pathways activated in distinct hypothalamic neurons by different metabolic hormones, neuropeptides and monoamine neurotransmitters are crucial not only for the regulation of appetite and metabolic homeostasis but also for the sympathetic control of cardiovascular function. In this review, we will highlight the main GPCRs and associated hypothalamic nuclei that are important for both metabolic homeostasis and cardiovascular function. The potential downstream molecular mediators of these GPCRs will also be discussed.

Ventromedial medullary pathway mediating cardiac responses evoked from periaqueductal gray

Periaqueductal gray (PAG) is a midbrain region that projects to areas controlling behavioral and autonomic outputs and is involved in the behavioral and physiological components of defense reactions. Since Raphe Pallidus (RPa) is a medial medullary region comprising sympathetic premotor neurons governing heart function, it is worth considering the PAG-RPa path. We assessed: i) whether PAG projects to RPa; ii) the amplitude of cardiac responses evoked from PAG; iii) whether cardiovascular responses evoked from PAG rely on RPa. Experiments conducted in Wistar rats (±300 g) were approved by Ethics Committee CEUA-UFG (092/18). Firstly, (n = 3), monosynaptic retrograde tracer Retrobeads was injected into RPa; PAG slices were analyzed. Other two groups (n = 6 each) were anesthetized with urethane (1.4 g/kg) and chloralose (120 mg/kg) and underwent craniotomy, tracheostomy, catheterization of femoral artery and vein and of cardiac left ventricle. In one group, we injected the GABA_A receptor antagonist, bicuculline methiodide (BMI - 40 pmol/100 nL) into lateral/dorsolateral PAG. Another group was injected (100 nL) with the GABA_A receptor agonist muscimol (20 mM) into RPa, 20 min before BMI into PAG. The results were: i) retrogradely labelled neurons were found in PAG; ii) PAG activation by BMI caused positive chronotropism and inotropism, which were accompanied by afterload increases; iii) RPa inhibition with Muscimol reduced heart rate, arterial and ventricular pressures; iv) the subsequent PAG activation still increased arterial pressure, cardiac chronotropy and inotropy, but these responses were significantly attenuated. In conclusion, PAG activation increases cardiac chronotropy and inotropy, and these responses seem to rely on a direct pathway reaching ventromedial medullary RPa neurons.

CoQ10 exerts hepatoprotective effect in fructose-induced fatty liver model in rats

BACKGROUND

Excess dietary sugar is associated with deleterious metabolic effects, liver injury, and coenzyme-Q10 (CoQ10) deficiency. This study investigates the ability of CoQ10 to protect against fructose-induced hepatic damage.

METHODS

Rats were fed tap water or 30% fructose for 12 weeks with or without CoQ10 (10 mg/kg, po). An additional group of rats were allowed to feed on either water or 30% fructose for 12 weeks, followed by four weeks of treatment with either the vehicle or CoQ10.

RESULTS

Fructose-fed rats showed lower CoQ10 levels, increased systolic pressure, increased body weight, higher liquid consumption, decreased food intake and hyperglycemia. Fructose-fed rats also showed deteriorated serum and liver lipid profiles, impaired liver function tests and oxidative status, and lower expression of adiponectin receptor 1 and 2 along with higher GLUT-2 levels. Furthermore, following fructose treatment, tyrosine kinase-PI3K pathway was inhibited. Additionally, there was an increase in the levels of apoptotic markers and serum visfatin and a decrease in the levels of adiponectin and soluble receptor of the advanced glycated end product. Consequently, several histopathological changes were detected in the liver. Concurrent or three months post-exposure administration of CoQ10 in fructose rats significantly reversed or attenuated all the measured parameters and hepato-cytoarchitecture alterations.

CONCLUSION

This study suggests CoQ10 supplement as a possible prophylaxis or treatment candidate for fructose-induced liver injury.

The Lateral Hypothalamus: An Uncharted Territory for Processing Peripheral Neurogenic Inflammation

The roles of the hypothalamus and particularly the lateral hypothalamus (LH) in the regulation of inflammation and pain have been widely studied. The LH consists of a parasympathetic area that has connections with all the major parts of the brain. It controls the autonomic nervous system (ANS), regulates feeding behavior and wakeful cycles, and is a part of the reward system. In addition, it contains different types of neurons, most importantly the orexin neurons. These neurons, though few in number, perform critical functions such as inhibiting pain transmission and interfering with the reward system, feeding behavior and the hypothalamic pituitary axis (HPA). Recent evidence has identified a new role for orexin neurons in the modulation of pain transmission associated with several inflammatory diseases, including rheumatoid arthritis and ulcerative colitis. Here, we review recent findings on the various physiological functions of the LH with special emphasis on the orexin/receptor system and its role in mediating inflammatory pain.

BDNF downregulates β-adrenergic receptor-mediated hypotensive mechanisms in the paraventricular nucleus of the hypothalamus

Brain-derived neurotrophic factor (BDNF) is upregulated in the paraventricular nucleus of the hypothalamus (PVN) in response to hypertensive stimuli such as stress and hyperosmolality, and BDNF acting in the PVN plays a key role in elevating sympathetic activity and blood pressure. However, downstream mechanisms mediating these effects remain unclear. We tested the hypothesis that BDNF increases blood pressure, in part by diminishing inhibitory hypotensive input from nucleus of the solitary tract (NTS) catecholaminergic neurons projecting to the PVN. Male Sprague-Dawley rats received bilateral PVN injections of viral vectors expressing either green fluorescent protein (GFP) or BDNF and bilateral NTS injections of vehicle or anti-dopamine-β-hydroxylase-conjugated saporin (DSAP), a neurotoxin that selectively lesions noradrenergic and adrenergic neurons. BDNF overexpression in the PVN without NTS lesioning significantly increased mean arterial pressure (MAP) in awake animals by 18.7 ± 1.8 mmHg. DSAP treatment also increased MAP in the GFP group, by 9.8 ± 3.2 mmHg, but failed to affect MAP in the BDNF group, indicating a BDNF-induced loss of NTS catecholaminergic hypotensive effects. In addition, in α-chloralose-urethane-anesthetized rats, hypotensive responses to PVN injections of the β-adrenergic agonist isoprenaline were significantly attenuated by BDNF overexpression, whereas PVN injections of phenylephrine had no effect on blood pressure. BDNF treatment was also found to significantly reduce β₁-adrenergic receptor mRNA expression in the PVN, whereas expression of other adrenergic receptors was unaffected. In summary, increased BDNF expression in the PVN elevates blood pressure, in part by downregulating β-receptor signaling and diminishing hypotensive catecholaminergic input from the NTS to the PVN.NEW & NOTEWORTHY We have shown that BDNF, a key hypothalamic regulator of blood pressure, disrupts catecholaminergic signaling between the NTS and the PVN by reducing the responsiveness of PVN neurons to inhibitory hypotensive β-adrenergic input from the NTS. This may be occurring partly via BDNF-mediated downregulation of β₁-adrenergic receptor expression in the PVN and results in an increase in blood pressure.

Contribution of DNA methylation in chronic stress-induced cardiac remodeling and arrhythmias in mice

It is recognized that stress can induce cardiac dysfunction, but the underlying mechanisms are not well understood. The present study aimed to test the hypothesis that chronic negative stress leads to alterations in DNA methylation of certain cardiac genes, which in turn contribute to pathologic remodeling of the heart. We found that mice that were exposed to chronic restraint stress (CRS) for 4 wk exhibited cardiac remodeling toward heart failure, as characterized by ventricular chamber dilatation, wall thinning, and decreased contractility. CRS also induced cardiac arrhythmias, including intermittent sinus tachycardia and bradycardia, frequent premature ventricular contraction, and sporadic atrioventricular conduction block. Circulating levels of stress hormones were elevated, and the cardiac expression of tyrosine hydroxylase, a marker of sympathetic innervation, was increased in CRS mice. Using reduced representation bisulfite sequencing, we found that although CRS did not lead to global changes in DNA methylation in the murine heart, it nevertheless altered methylation at specific genes that are associated with the dilated cardiomyopathy (DCM) (e.g., desmin) and adrenergic signaling of cardiomyocytes (ASPC) (e.g., adrenergic receptor-α1) pathways. We conclude that CRS induces cardiac remodeling and arrhythmias, potentially through altered methylation of myocardial genes associated with the DCM and ASPC pathways.-Zhang, P., Li, T., Liu, Y.-Q., Zhang, H., Xue, S.-M., Li, G., Cheng, H.-Y.M., Cao, J.-M. Contribution of DNA methylation in chronic stress-induced cardiac remodeling and arrhythmias in mice.

GABAB receptors in the hypothalamic paraventricular nucleus mediate β-adrenoceptor-induced elevations of plasma noradrenaline in rats

In the brain, various neurotransmitters such as noradrenaline and GABA regulate peripheral sympathetic functions. Previously, it has been reported that both β-adrenoceptor activation and GABA_B receptor activation in the brain are involved in the elevation of plasma noradrenaline levels. However, it is unknown whether these pathways interact with each other. In the present study, we examined the relationship between the central actions of β-adrenoceptor activation and GABA_B receptor activation with regard to plasma noradrenaline responses using urethane-anesthetized rats. Intracerebroventricular pretreatment with the GABA_A receptor antagonist bicuculline did not affect the β-adrenoceptor agonist isoproterenol-induced elevation of plasma noradrenaline levels. In contrast, pretreatment with the GABA_B receptor antagonist CGP 35348 suppressed the isoproterenol-induced elevation of noradrenaline levels. Intracerebroventricular pretreatment with the β-adrenoceptor antagonist propranolol did not alter the GABA_B receptor agonist baclofen-induced elevation of plasma noradrenaline levels. We next examined the central effects of β-adrenoceptor activation on GABA release in the paraventricular hypothalamic nucleus (PVN), the major integrative center for sympathetic regulation in the brain. Intracerebroventricular administration of isoproterenol increased GABA content in PVN dialysates. In addition, baclofen microinjected unilaterally into the PVN resulted in elevated plasma levels of noradrenaline, but not adrenaline. Finally, unilateral blockade of GABA_B receptors in the PVN suppressed the isoproterenol-induced elevation of plasma noradrenaline level. Our results suggest that activation of β-adrenoceptors in the brain, likely in the PVN, induces GABA release in the PVN, which in turn activates GABA_B receptors in the PVN, leading to elevated plasma noradrenaline.