Novel mechanism within the paraventricular nucleus reduces both blood pressure and hypothalamic pituitary-adrenal axis responses to acute stress

Effect of Short-Term Restraint Stress on the Hypothalamic Transcriptome Profiles of Rats with Inherited Stress-Induced Arterial Hypertension (ISIAH) and Normotensive Wistar Albino Glaxo (WAG) Rats

Emotional stress is one of the health risk factors in the modern human lifestyle. Stress exposure can provoke the manifestation of various pathological conditions, one of which is a sharp increase in the blood pressure level. In the present study, we analyzed changes in the transcriptome profiles of the hypothalamus of hypertensive ISIAH and normotensive WAG rats exposed to a single short-term restraint stress (the rat was placed in a tight wire-mesh cage for 2 h). This type of stress can be considered emotional stress. The functional annotation of differentially expressed genes allowed us to identify the most significantly altered biological processes in the hypothalamus of hypertensive and normotensive rats. The study made it possible to identify a group of genes that describe a general response to stress, independent of the rat genotype, as well as a hypothalamic response to stress specific to each strain. The alternatively changing expression of the Npas4 (neuronal PAS domain protein 4) gene, which is downregulated in the hypothalamus of the control WAG rats and induced in the hypothalamus of hypertensive ISIAH rats, is suggested to be the key event for understanding inter-strain differences in the hypothalamic response to stress. The stress-dependent ISIAH strain-specific induction of Fos and Jun gene transcription may play a crucial role in neuronal activation in this rat strain. The data obtained can be potentially useful in the selection of molecular targets for the development of pharmacological approaches to the correction of stress-induced pathologies related to neuronal excitability, taking into account the hypertensive status of the patients.

Cerebral Blood Flow Autoregulation in Offspring From Experimentally Preeclamptic Rats and the Effect of Age

Preeclampsia is a hypertensive disorder of pregnancy that causes significant, long term cardiovascular effects for both the mother and offspring. A previous study demonstrated that middle cerebral arteries in offspring from an experimental rat model of preeclampsia were smaller, stiffer, and did not enlarge over the course of maturation, suggesting potential hemodynamic alterations in these offspring. Here we investigated the effect of experimental preeclampsia on cerebral blood flow autoregulation in juvenile and adult offspring that were born from normal pregnant or experimentally preeclamptic rats. Relative cerebral blood flow was measured using laser Doppler flowmetry, and cerebral blood flow autoregulation curves were constructed by raising blood pressure and controlled hemorrhage to lower blood pressure. Immunohistochemistry was used to assess middle cerebral artery size. Heart rate and blood pressure were measured in awake adult offspring using implanted radiotelemetry. Serum epinephrine was measured using enzyme-linked immunosorbent assay. Offspring from both groups showed maturation of cerebral blood flow autoregulation as offspring aged from juvenile to adulthood as demonstrated by the wider autoregulatory plateau. Experimental preeclampsia did not affect cerebral blood flow autoregulation in juvenile offspring, and it had no effect on cerebral blood flow autoregulation in adult offspring over the lower range of blood pressures. However, experimental preeclampsia caused a right shift in the upper range of blood pressures in adult offspring (compared to normal pregnant). Structurally, middle cerebral arteries from normal pregnant offspring demonstrated growth with aging, while middle cerebral arteries from experimentally preeclamptic offspring did not, and by adulthood normal pregnant offspring had significantly larger middle cerebral arteries. Middle cerebral artery lumen diameters did not significantly change as offspring aged. Serum epinephrine was elevated in juvenile experimentally preeclamptic offspring, and a greater degree of hemorrhage was required to induce hypotension, suggesting increased sympathetic activity. Finally, despite no evidence of increased sympathetic activity, adult experimentally preeclamptic offspring were found to have persistently higher heart rate. These results demonstrate a significant effect of experimental preeclampsia on the upper range of autoregulation and cerebrovascular structure in juvenile and adult offspring that could have an important influence on brain perfusion under conditions of hypo and/or hypertension.

Interplay between traumatic brain injury and intimate partner violence: data driven analysis utilizing electronic health records

Background

It is estimated that a majority of intimate partner violence (IPV) victims suffer from blunt force to the head, neck and the face area. Injuries to head and neck are among the major causes for traumatic brain injury (TBI).

Methods

In this interdisciplinary study, we aimed to characterize the key associations between IPV and TBI by mining de-identified electronic health records data with more than 12 M records between 1999 to 2017 from the IBM Explorys platform. For this purpose, we formulated a data-driven analytical framework to identify significant health correlates among IPV, TBI and six control cohorts. Using this framework, we assessed the co-morbidity, shared prevalence, and synergy between pairs of conditions.

Results

Our findings suggested that health effects attributed to malnutrition, acquired thrombocytopenia, post-traumatic wound infection, local infection of wound, poisoning by cardiovascular drug, alcoholic cirrhosis, alcoholic fatty liver, and drug-induced cirrhosis were highly significant at the joint presence of IPV and TBI.

Conclusion

To develop a better understanding of how IPV is related to negative health effects, it is potentially useful to determine the interactions and relationships between symptom categories. Our results can potentially improve the accuracy and confidence of existing clinical screening techniques on determining IPV-induced TBI diagnoses.

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.

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.

Inhibition of BDNF signaling in the paraventricular nucleus of the hypothalamus lowers acute stress-induced pressor responses

Brain-derived neurotrophic factor (BDNF) expression increases in the paraventricular nucleus of the hypothalamus (PVN) during stress, and our recent studies indicate that BDNF induces sympathoexcitatory and hypertensive responses when injected acutely or overexpressed chronically in the PVN. However, it remained to be investigated whether BDNF is involved in the mediation of stress-induced cardiovascular responses. Here we tested the hypothesis that inhibition of the high-affinity BDNF receptor TrkB in the PVN diminishes acute stress-induced cardiovascular responses. Male Sprague-Dawley rats were equipped with radiotelemetric transmitters for blood pressure measurement. BDNF-TrkB signaling was selectively inhibited by viral vector-mediated bilateral PVN overexpression of a dominant-negative truncated TrkB receptor (TrkB.T1, n = 7), while control animals ( n = 7) received green fluorescent protein (GFP)-expressing vector injections. Rats were subjected to acute water and restraint stress 3-4 wk after vector injections. We found that body weight, food intake, baseline mean arterial pressure (MAP), and heart rate were unaffected by TrkB.T1 overexpression. However, peak MAP increases were significantly reduced in the TrkB.T1 group compared with GFP both during water stress (GFP: 39 ± 2 mmHg, TrkB.T1: 27 ± 4 mmHg; P < 0.05) and restraint stress (GFP: 41 ± 3 mmHg, TrkB.T1: 34 ± 2 mmHg; P < 0.05). Average MAP elevations during the poststress period were also significantly reduced after both water and restraint stress in the TrkB.T1 group compared with GFP. In contrast, heart rate elevations to both stressors remained unaffected by TrkB.T1 overexpression. Our results demonstrate that activation of BDNF high-affinity TrkB receptors within the PVN is a major contributor to acute stress-induced blood pressure elevations. NEW & NOTEWORTHY We have shown that inhibition of the high-affinity brain-derived neurotrophic factor receptor TrkB in the paraventricular nucleus of the hypothalamus significantly reduces blood pressure elevations to acute stress without having a significant impact on resting blood pressure, body weight, and food intake.

Activin A increases arterial pressure in the hypothalamic paraventricular nucleus in rats by angiotension II

Activin A, a member of the transforming growth factor β superfamily, plays an important role in the central nervous system as a neurotrophic and neuroprotective factor. The hypothalamic paraventricular nucleus (PVN) in the central nervous system is characterized as an important integrative site to regulate arterial pressure (AP). However, whether activin A in the PVN is involved in the regulation of AP is not well characterized. This study aimed to determine the effect of activin A on AP in the PVN in rats. The results showed that activin βA, activin type IIA and IIB receptors (ActRIIA and ActRIIB), and Smad2 and Smad3 mRNA expressions were detectable in the PVN of WKY rats by reverse-transcription PCR, and the expression of ActRIIA protein in the PVN was further confirmed by immunohistochemical staining. A microinjection of angiotensin II (AngII) (0.1 nmol/100 nl) or activin A (2 ng/100 nl) into the PVN increased AP significantly in WKY rats (P<0.05). Moreover, activin A (5 ng/ml) promoted AngII release from the primary cultured PVN neurons that can increase AP and upregulated the expressions of ActRIIA and Smad3 mRNA in the primary cultured PVN neurons (P<0.05). These data suggest that activin A can regulate AP in the PVN in an autocrine or a paracrine manner, which is related to AngII release and the ActRIIA-Smad3 signal pathway.

The Frequency-Dependent Aerobic Exercise Effects of Hypothalamic GABAergic Expression and Cardiovascular Functions in Aged Rats

A decline in cardiovascular modulation is a feature of the normal aging process and associated with cardiovascular diseases (CVDs) such as hypertension and stroke. Exercise training is known to promote cardiovascular adaptation in young animals and positive effects on motor and cognitive capabilities, as well as on brain plasticity for all ages in mice. Here, we examine the question of whether aerobic exercise interventions may impact the GABAergic neurons of the paraventricular nucleus (PVN) in aged rats which have been observed to have a decline in cardiovascular integration function. In the present study, young (2 months) and old (24 months) male Wistar rats were divided into young control (YC), old sedentary, old low frequency exercise (20 m/min, 60 min/day, 3 days/week, 12 weeks) and old high frequency exercise (20 m/min, 60 min/day, 5 days/week, 12 weeks). Exercise training indexes were obtained, including resting heart rate (HR), blood pressure (BP), plasma norepinephrine (NE), and heart weight (HW)-to-body weight (BW) ratios. The brain was removed and processed according to the immunofluorescence staining and western blot used to analyze the GABAergic terminal density, the proteins of GAD67, GABA_A receptor and gephyrin in the PVN. There were significant changes in aged rats compared with those in the YC. Twelve weeks aerobic exercise training has volume-dependent ameliorated effects on cardiovascular parameters, autonomic nervous activities and GABAergic system functions. These data suggest that the density of GABAergic declines in the PVN is associated with imbalance in autonomic nervous activities in normal aging. Additionally, aerobic exercise can rescue aging-related an overactivity of the sympathetic nervous system and induces modifications the resting BP and HR to lower values via improving the GABAergic system in the PVN.

Central TrkB blockade attenuates ICV angiotensin II-hypertension and sympathetic nerve activity in male Sprague-Dawley rats

Increased sympathetic nerve activity and the activation of the central renin-angiotensin system are commonly associated with cardiovascular disease states such as hypertension and heart failure, yet the precise mechanisms contributing to the long-term maintenance of this sympatho-excitation are incompletely understood. Due to the established physiological role of neurotrophins contributing toward neuroplasticity and neuronal excitability along with recent evidence linking the renin-angiotensin system and brain-derived neurotrophic factor (BDNF) along with its receptor (TrkB), it is likely the two systems interact to promote sympatho-excitation during cardiovascular disease. However, this interaction has not yet been fully demonstrated, in vivo. Thus, we hypothesized that central angiotensin II (Ang II) treatment will evoke a sympatho-excitatory state mediated through the actions of BDNF/TrkB. We infused Ang II (20ng/min) into the right lateral ventricle of male Sprague-Dawley rats for twelve days with or without the TrkB receptor antagonist, ANA-12 (50ng/h). We found that ICV infusion of Ang II increased mean arterial pressure (+40.4mmHg), increased renal sympathetic nerve activity (+19.4% max activity), and induced baroreflex dysfunction relative to vehicle. Co-infusion of ANA-12 attenuated the increase in blood pressure (-20.6mmHg) and prevented the increase in renal sympathetic nerve activity (-22.2% max) and baroreflex dysfunction relative to Ang II alone. Ang II increased thirst and decreased food consumption, and Ang II+ANA-12 augmented the thirst response while attenuating the decrease in food consumption. We conclude that TrkB signaling is a mediator of the long-term blood pressure and sympathetic nerve activity responses to central Ang II activity. These findings demonstrate the involvement of neurotrophins such as BDNF in promoting Ang II-induced autonomic dysfunction and further implicate TrkB signaling in modulating presympathetic autonomic neurons during cardiovascular disease.

Nesfatin-1: a new energy-regulating peptide with pleiotropic functions. Implications at cardiovascular level

Nesfatin-1 is a new energy-regulating peptide widely expressed at both central and peripheral tissues with pleiotropic effects. In the last years, the study of nesfatin-1 actions and its possible implication in the development of different diseases has created a great interest among the scientific community. In this review, we will summarize nesfatin-1 main functions, focusing on its cardiovascular implications.