Acute hypoxia activates neuroendocrine, but not presympathetic, neurons in the paraventricular nucleus of the hypothalamus: differential role of nitric oxide

Molecular Interaction Between Vasopressin and Insulin in Regulation of Metabolism: Impact on Cardiovascular and Metabolic Diseases

Numerous compounds involved in the regulation of the cardiovascular system are also engaged in the control of metabolism. This review gives a survey of literature showing that arginine vasopressin (AVP), which is an effective cardiovascular peptide, exerts several direct and indirect metabolic effects and may play the role of the link adjusting blood supply to metabolism of tissues. Secretion of AVP and activation of AVP receptors are regulated by changes in blood pressure and body fluid osmolality, hypoxia, hyperglycemia, oxidative stress, inflammation, and several metabolic hormones; moreover, AVP turnover is regulated by insulin. Acting on V1a receptors in the liver, AVP stimulates glycogenolysis, reduces synthesis of glycogen, and promotes fatty acid synthesis and acetyl CoA carboxylase activity. Stimulating V1b receptors in the pancreatic islands, AVP promotes release of insulin and glucagon-like peptide-1 (GLP-1) and potentiates stimulatory effects of glucose and ACTH on secretion of insulin. Simultaneously, insulin increases AVP secretion by neurons of the paraventricular nucleus and the supraoptic nucleus. There is strong evidence that secretion of AVP and its metabolic effectiveness are significantly altered in metabolic and cardiovascular diseases. Both experimental and clinical data indicate that inappropriate interactions of AVP and insulin play an important role in the development of insulin resistance in obesity and diabetes mellitus.

Orexin Facilitates the Peripheral Chemoreflex via Corticotropin-Releasing Hormone Neurons Projecting to the Nucleus of the Solitary Tract

We previously showed that orexin neurons are activated by hypoxia and facilitate the peripheral chemoreflex (PCR)-mediated hypoxic ventilatory response (HVR), mostly by promoting the respiratory frequency response. Orexin neurons project to the nucleus of the solitary tract (nTS) and the paraventricular nucleus of the hypothalamus (PVN). The PVN contributes significantly to the PCR and contains nTS-projecting corticotropin-releasing hormone (CRH) neurons. We hypothesized that in male rats, orexin neurons contribute to the PCR by activating nTS-projecting CRH neurons. We used neuronal tract tracing and immunohistochemistry (IHC) to quantify the degree that hypoxia activates PVN-projecting orexin neurons. We coupled this with orexin receptor (OxR) blockade with suvorexant (Suvo, 20 mg/kg, i.p.) to assess the degree that orexin facilitates the hypoxia-induced activation of CRH neurons in the PVN, including those projecting to the nTS. In separate groups of rats, we measured the PCR following systemic orexin 1 receptor (Ox1R) blockade (SB-334867; 1 mg/kg) and specific Ox1R knockdown in PVN. OxR blockade with Suvo reduced the number of nTS and PVN neurons activated by hypoxia, including those CRH neurons projecting to nTS. Hypoxia increased the number of activated PVN-projecting orexin neurons but had no effect on the number of activated nTS-projecting orexin neurons. Global Ox1R blockade and partial Ox1R knockdown in the PVN significantly reduced the PCR. Ox1R knockdown also reduced the number of activated PVN neurons and the number of activated tyrosine hydroxylase neurons in the nTS. Our findings suggest orexin facilitates the PCR via nTS-projecting CRH neurons expressing Ox1R.

K252a Prevents Microglial Activation Induced by Anoxic Stimulation of Carotid Bodies in Rats

Inducing carotid body anoxia through the administration of cyanide can result in oxygen deprivation. The lack of oxygen activates cellular responses in specific regions of the central nervous system, including the Nucleus Tractus Solitarius, hypothalamus, hippocampus, and amygdala, which are regulated by afferent pathways from chemosensitive receptors. These receptors are modulated by the brain-derived neurotrophic factor receptor TrkB. Oxygen deprivation can cause neuroinflammation in the brain regions that are activated by the afferent pathways from the chemosensitive carotid body. To investigate how microglia, a type of immune cell in the brain, respond to an anoxic environment resulting from the administration of NaCN, we studied the effects of blocking the TrkB receptor on this cell-type response. Male Wistar rats were anesthetized, and a dose of NaCN was injected into their carotid sinus to induce anoxia. Prior to the anoxic stimulus, the rats were given an intracerebroventricular (icv) infusion of either K252a, a TrkB receptor inhibitor, BDNF, or an artificial cerebrospinal fluid (aCSF). After the anoxic stimulus, the rats were perfused with paraformaldehyde, and their brains were processed for microglia immunohistochemistry. The results indicated that the anoxic stimulation caused an increase in the number of reactive microglial cells in the hypothalamic arcuate, basolateral amygdala, and dentate gyrus of the hippocampus. However, the infusion of the K252a TrkB receptor inhibitor prevented microglial activation in these regions.

Paraventricular nucleus projections to the nucleus tractus solitarii are essential for full expression of hypoxia-induced peripheral chemoreflex responses

The hypothalamic paraventricular nucleus (PVN) is essential to peripheral chemoreflex neurocircuitry, but the specific efferent pathways utilized are not well defined. The PVN sends dense projections to the nucleus tractus solitarii (nTS), which exhibits neuronal activation following a hypoxic challenge. We hypothesized that nTS-projecting PVN (PVN-nTS) neurons contribute to hypoxia-induced nTS neuronal activation and cardiorespiratory responses. To selectively target PVN-nTS neurons, rats underwent bilateral nTS nanoinjection of retrogradely transported adeno-associated virus (AAV) driving Cre recombinase expression. We then nanoinjected into PVN AAVs driving Cre-dependent expression of Gq or Gi designer receptors exclusively activated by designer drugs (DREADDs) to test the degree that selective activation or inhibition, respectively, of the PVN-nTS pathway affects the hypoxic ventilatory response (HVR) of conscious rats. We used immunohistochemistry for Fos and extracellular recordings to examine how DREADD activation influences PVN-nTS neuronal activation by hypoxia. Pathway activation enhanced the HVR at moderate hypoxic intensities and increased PVN and nTS Fos immunoreactivity in normoxia and hypoxia. In contrast, PVN-nTS inhibition reduced both the HVR and PVN and nTS neuronal activation following hypoxia. To further confirm selective pathway effects on central cardiorespiratory output, rats underwent hypoxia before and after bilateral nTS nanoinjections of C21 to activate or inhibit PVN-nTS terminals. PVN terminal activation within the nTS enhanced tachycardic, sympathetic and phrenic (PhrNA) nerve activity responses to hypoxia whereas inhibition attenuated hypoxia-induced increases in nTS neuronal action potential discharge and PhrNA. The results demonstrate the PVN-nTS pathway enhances nTS neuronal activation and is necessary for full cardiorespiratory responses to hypoxia. KEY POINTS: The hypothalamic paraventricular nucleus (PVN) contributes to peripheral chemoreflex cardiorespiratory responses, but specific PVN efferent pathways are not known. The nucleus tractus solitarii (nTS) is the first integration site of the peripheral chemoreflex, and the nTS receives dense projections from the PVN. Selective GqDREADD activation of the PVN-nTS pathway was shown to enhance ventilatory responses to hypoxia and activation (Fos immunoreactivity (IR)) of nTS neurons in conscious rats, augmenting the sympathetic and phrenic nerve activity (SSNA and PhrNA) responses to hypoxia in anaesthetized rats. Selective GiDREADD inhibition of PVN-nTS neurons attenuates ventilatory responses, nTS neuronal Fos-IR, action potential discharge and PhrNA responses to hypoxia. These results demonstrate that a projection from the PVN to the nTS is critical for full chemoreflex responses to hypoxia.

Vasopressin: a possible link between hypoxia and hypertension

Cardiovascular and respiratory diseases are frequently associated with transient and prolonged hypoxia, whereas hypoxia exerts pro-hypertensive effects, through stimulation of the sympathetic system and release of pressor endocrine factors. This review is focused on the role of arginine vasopressin (AVP) in dysregulation of the cardiovascular system during hypoxia associated with cardiovascular disorders. AVP is synthesized mainly in the neuroendocrine neurons of the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON), which send axons to the posterior pituitary and various regions of the central nervous system (CNS). Vasopressinergic neurons are innervated by multiple neuronal projections releasing several neurotransmitters and other regulatory molecules. AVP interacts with V1a, V1b and V2 receptors that are present in the brain and peripheral organs, including the heart, vessels, lungs, and kidneys. Release of vasopressin is intensified during hypernatremia, hypovolemia, inflammation, stress, pain, and hypoxia which frequently occur in cardiovascular patients, and blood AVP concentration is markedly elevated in cardiovascular diseases associated with hypoxemia. There is evidence that hypoxia stimulates AVP release through stimulation of chemoreceptors. It is suggested that acting in the carotid bodies, AVP may fine-tune respiratory and hemodynamic responses to hypoxia and that this effect is intensified in hypertension. There is also evidence that during hypoxia, augmentation of pro-hypertensive effects of vasopressin may result from inappropriate interaction of this hormone with other compounds regulating the cardiovascular system (catecholamines, angiotensins, natriuretic peptides, steroids, nitric oxide). In conclusion, current literature indicates that abnormal mutual interactions between hypoxia and vasopressin may significantly contribute to pathogenesis of hypertension.

Hypothalamic remodeling of thyroid hormone signaling during hibernation in the arctic ground squirrel

Hibernation involves prolonged intervals of profound metabolic suppression periodically interrupted by brief arousals to euthermy, the function of which is unknown. Annual cycles in mammals are timed by a photoperiodically-regulated thyroid-hormone-dependent mechanism in hypothalamic tanycytes, driven by thyrotropin (TSH) in the pars tuberalis (PT), which regulates local TH-converting deiodinases and triggers remodeling of neuroendocrine pathways. We demonstrate that over the course of hibernation in continuous darkness, arctic ground squirrels (Urocitellus parryii) up-regulate the retrograde TSH/Deiodinase/TH pathway, remodel hypothalamic tanycytes, and activate the reproductive axis. Forcing the premature termination of hibernation by warming animals induced hypothalamic deiodinase expression and the accumulation of secretory granules in PT thyrotrophs and pituitary gonadotrophs, but did not further activate the reproductive axis. We suggest that periodic arousals may allow for the transient activation of hypothalamic thyroid hormone signaling, cellular remodeling, and re-programming of brain circuits in preparation for the short Arctic summer.

Arctic ground squirrels hibernating in darkness activate the pars tuberalis - hypothalamus thyroid hormone signaling pathway, remodel hypothalamic tanycytes, and activate the reproductive axis.

Oxytocin and vasopressin in the hippocampus

Oxytocin (OXT) and vasopressin (AVP) are related neuropeptides that exert a wide range of effects on general health, homeostasis, development, reproduction, adaptability, cognition, social and nonsocial behaviors. The two peptides are mainly of hypothalamic origin and execute their peripheral and central physiological roles via OXT and AVP receptors, which are members of the G protein-coupled receptor family. These receptors, largely distributed in the body, are abundantly expressed in the hippocampus, a brain region particularly vulnerable to stress exposure and various lesions. OXT and AVP have important roles in the hippocampus, by modulating important processes like neuronal excitability, network oscillatory activity, synaptic plasticity, and social recognition memory. This chapter includes an overview regarding OXT and AVP structure, synthesis, receptor distribution, and functions, focusing on their relationship with the hippocampus and mechanisms by which they influence hippocampal activity. Brief information regarding hippocampal structure and susceptibility to lesions is also provided. The roles of OXT and AVP in neurodevelopment and adult central nervous system function and disorders are highlighted, discussing their potential use as targeted therapeutic tools in neuropsychiatric diseases.

Complementary Role of Oxytocin and Vasopressin in Cardiovascular Regulation

The neurons secreting oxytocin (OXY) and vasopressin (AVP) are located mainly in the supraoptic, paraventricular, and suprachiasmatic nucleus of the brain. Oxytocinergic and vasopressinergic projections reach several regions of the brain and the spinal cord. Both peptides are released from axons, soma, and dendrites and modulate the excitability of other neuroregulatory pathways. The synthesis and action of OXY and AVP in the peripheral organs (eye, heart, gastrointestinal system) is being investigated. The secretion of OXY and AVP is influenced by changes in body fluid osmolality, blood volume, blood pressure, hypoxia, and stress. Vasopressin interacts with three subtypes of receptors: V1aR, V1bR, and V2R whereas oxytocin activates its own OXTR and V1aR receptors. AVP and OXY receptors are present in several regions of the brain (cortex, hypothalamus, pons, medulla, and cerebellum) and in the peripheral organs (heart, lungs, carotid bodies, kidneys, adrenal glands, pancreas, gastrointestinal tract, ovaries, uterus, thymus). Hypertension, myocardial infarction, and coexisting factors, such as pain and stress, have a significant impact on the secretion of oxytocin and vasopressin and on the expression of their receptors. The inappropriate regulation of oxytocin and vasopressin secretion during ischemia, hypoxia/hypercapnia, inflammation, pain, and stress may play a significant role in the pathogenesis of cardiovascular diseases.

Vasopressin but Not Oxytocin Responds to Birth Stress in Infants

Context

Birth triggers a large fetal neuroendocrine response, which is more pronounced in infants born vaginally than in those born by elective cesarean section (ECS). The two related peptides arginine vasopressin (AVP) and oxytocin (OT) play an essential role in peripheral and central stress adaptation and have a shared receptor mediating their function. Elevated cord blood levels of AVP and its surrogate marker copeptin, the C-terminal part of AVP prohormone, have been found after vaginal delivery (VD) as compared to ECS, while release of OT in response to birth is controversial. Moreover, AVP, copeptin and OT have not yet been measured simultaneously at birth.

Objective

To test the hypothesis that AVP but not OT levels are increased in infants arterial umbilical cord blood in response to birth stress and to characterize AVP secretion in direct comparison with plasma copeptin.

Methods

In a prospective single-center cross-sectional study, we recruited healthy women with a singleton pregnancy and more than 36 completed weeks of gestation delivering via VD or ECS (cesarean without prior uterine contractions or rupture of membranes). Arterial umbilical cord blood samples were collected directly after birth, centrifuged immediately and plasma samples were frozen. Concentrations of AVP and OT were determined by radioimmunoassay and that of copeptin by ultrasensitive immunofluorescence assay.

Results

A total of 53 arterial umbilical cord blood samples were collected, n = 29 from VD and n = 24 from ECS. Ten venous blood samples from pregnant women without stress were collected as controls. AVP and copeptin concentrations were significantly higher in the VD group than in the ECS group (both p < 0.001), median (range) AVP 4.78 (2.38–8.66) vs. 2.38 (1.79–3.88) (pmol/L), copeptin 1692 (72.1–4094) vs. 5.78 (3.14–17.97), respectively, (pmol/L). In contrast, there was no difference in OT concentrations (pmol/L) between VD and ECS, 6.00 (2.71–7.69) vs. 6.14 (4.26–9.93), respectively. AVP and copeptin concentrations were closely related (Rs = 0.700, p < 0.001) while OT did not show any correlation to either AVP or copeptin. In linear regression models, vaginal delivery and biochemical stress indicators, base deficit and pH, were independent predictors for both AVP and copeptin. OT was not linked to base deficit or pH.

Conclusion

Vaginal birth causes a profound secretion of AVP and copeptin in infants. Whereas AVP indicates acute stress events, copeptin provides information on cumulative stress events over a longer period. In contrast, fetal OT is unaffected by birth stress. Thus, AVP signaling but not OT mediates birth stress response in infants. This unique hormonal activation in early life may impact neurobehavioral development in whole life.

Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction

As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O₂ sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.

AMPK and the Need to Breathe and Feed: What's the Matter with Oxygen?

We live and to do so we must breathe and eat, so are we a combination of what we eat and breathe? Here, we will consider this question, and the role in this respect of the AMP-activated protein kinase (AMPK). Emerging evidence suggests that AMPK facilitates central and peripheral reflexes that coordinate breathing and oxygen supply, and contributes to the central regulation of feeding and food choice. We propose, therefore, that oxygen supply to the body is aligned with not only the quantity we eat, but also nutrient-based diet selection, and that the cell-specific expression pattern of AMPK subunit isoforms is critical to appropriate system alignment in this respect. Currently available information on how oxygen supply may be aligned with feeding and food choice, or vice versa, through our motivation to breathe and select particular nutrients is sparse, fragmented and lacks any integrated understanding. By addressing this, we aim to provide the foundations for a clinical perspective that reveals untapped potential, by highlighting how aberrant cell-specific changes in the expression of AMPK subunit isoforms could give rise, in part, to known associations between metabolic disease, such as obesity and type 2 diabetes, sleep-disordered breathing, pulmonary hypertension and acute respiratory distress syndrome.

Central AT1 receptor signaling by circulating angiotensin II is permissive to acute intermittent hypoxia-induced sympathetic neuroplasticity

Acute intermittent hypoxia (AIH) triggers sympathetic long-term facilitation (sLTF), a progressive increase in sympathetic nerve activity (SNA) linked to central AT1 receptor (AT1R) activation by circulating angiotensin II (ANG II). Here, we investigated AIH activation of the peripheral renin-angiotensin system (RAS) and the extent to which the magnitude of RAS activation predicts the magnitude of AIH-induced sLTF. In anesthetized male Sprague-Dawley rats, plasma renin activity (PRA) increased in a linear fashion in response to 5 (P = 0.0342) and 10 (P < 0.0001) cycles of AIH, with PRA remaining at the 10th cycle level 1 h later, a period over which SNA progressively increased. On average, SNA ramping began at the AIH cycle 4.6 ± 0.9 (n = 12) and was similar in magnitude 1 h later whether AIH consisted of 5 or 10 cycles (n = 6/group). Necessity of central AT1R in post-AIH sLTF was affirmed by intracerebroventricular (icv) losartan (40 nmol, 2 µL; n = 5), which strongly attenuated both splanchnic (P = 0.0469) and renal (P = 0.0018) sLTF compared with vehicle [artificial cerebrospinal fluid (aCSF), 2 µL; n = 5]. Bilateral nephrectomy largely prevented sLTF, affirming the necessity of peripheral RAS activation. Sufficiency of central ANG II signaling was assessed in nephrectomized rats. Whereas ICV ANG II (0.5 ng/0.5 µL, 30 min) in nephrectomized rats exposed to sham AIH (n = 4) failed to cause SNA ramping, it rescued sLTF in nephrectomized rats exposed to five cycles of AIH [splanchnic SNA (SSNA), P = 0.0227; renal SNA (RSNA), P = 0.0390; n = 5]. Findings indicate that AIH causes progressive peripheral RAS activation, which stimulates an apparent threshold level of central AT1R signaling that plays a permissive role in triggering sLTF.NEW & NOTEWORTHY Acute intermittent hypoxia (AIH) triggers sympathetic long-term facilitation (sLTF) that relies on peripheral renin-angiotensin system (RAS) activation. Here, increasing AIH cycles from 5 to 10 proportionally increased RAS activity, but not the magnitude of post-AIH sLTF. Brain angiotensin II (ANG II) receptor blockade and nephrectomy each largely prevented sLTF, whereas central ANG II rescued it following nephrectomy. Peripheral RAS activation by AIH induces time-dependent neuroplasticity at an apparent central ANG II signaling threshold, triggering a stereotyped sLTF response.

Pan-tissue transcriptome analysis of long noncoding RNAs in the American beaver Castor canadensis

BACKGROUND

Long noncoding RNAs (lncRNAs) have roles in gene regulation, epigenetics, and molecular scaffolding and it is hypothesized that they underlie some mammalian evolutionary adaptations. However, for many mammalian species, the absence of a genome assembly precludes the comprehensive identification of lncRNAs. The genome of the American beaver (Castor canadensis) has recently been sequenced, setting the stage for the systematic identification of beaver lncRNAs and the characterization of their expression in various tissues. The objective of this study was to discover and profile polyadenylated lncRNAs in the beaver using high-throughput short-read sequencing of RNA from sixteen beaver tissues and to annotate the resulting lncRNAs based on their potential for orthology with known lncRNAs in other species.

RESULTS

Using de novo transcriptome assembly, we found 9528 potential lncRNA contigs and 187 high-confidence lncRNA contigs. Of the high-confidence lncRNA contigs, 147 have no known orthologs (and thus are putative novel lncRNAs) and 40 have mammalian orthologs. The novel lncRNAs mapped to the Oregon State University (OSU) reference beaver genome with greater than 90% sequence identity. While the novel lncRNAs were on average shorter than their annotated counterparts, they were similar to the annotated lncRNAs in terms of the relationships between contig length and minimum free energy (MFE) and between coverage and contig length. We identified beaver orthologs of known lncRNAs such as XIST, MEG3, TINCR, and NIPBL-DT. We profiled the expression of the 187 high-confidence lncRNAs across 16 beaver tissues (whole blood, brain, lung, liver, heart, stomach, intestine, skeletal muscle, kidney, spleen, ovary, placenta, castor gland, tail, toe-webbing, and tongue) and identified both tissue-specific and ubiquitous lncRNAs.

CONCLUSIONS

To our knowledge this is the first report of systematic identification of lncRNAs and their expression atlas in beaver. LncRNAs-both novel and those with known orthologs-are expressed in each of the beaver tissues that we analyzed. For some beaver lncRNAs with known orthologs, the tissue-specific expression patterns were phylogenetically conserved. The lncRNA sequence data files and raw sequence files are available via the web supplement and the NCBI Sequence Read Archive, respectively.

The PVN enhances cardiorespiratory responses to acute hypoxia via input to the nTS

Chemoreflex neurocircuitry includes the paraventricular nucleus (PVN), but the role of PVN efferent projections to specific cardiorespiratory nuclei is unclear. We hypothesized that the PVN contributes to cardiorespiratory responses to hypoxia via projections to the nucleus tractus solitarii (nTS). Rats received bilateral PVN microinjections of adeno-associated virus expressing inhibitory designer receptor exclusively activated by designer drug (GiDREADD) or green fluorescent protein (GFP) control. Efficacy of GiDREADD inhibition by the designer receptor exclusively activated by designer drug (DREADD) agonist Compound 21 (C21) was verified in PVN slices; C21 reduced evoked action potential discharge by reducing excitability to injected current in GiDREADD-expressing PVN neurons. We evaluated hypoxic ventilatory responses (plethysmography) and PVN and nTS neuronal activation (cFos immunoreactivity) to 2 h hypoxia (10% O2) in conscious GFP and GiDREADD rats after intraperitoneal C21 injection. Generalized PVN inhibition via systemic C21 blunted hypoxic ventilatory responses and reduced PVN and also nTS neuronal activation during hypoxia. To determine if the PVN-nTS pathway contributes to these effects, we evaluated cardiorespiratory responses to hypoxia during selective PVN terminal inhibition in the nTS. Anesthetized GFP and GiDREADD rats exposed to brief hypoxia (10% O2, 45 s) exhibited depressor and tachycardic responses and increased sympathetic and phrenic nerve activity. C21 was then microinjected into the nTS, followed after 60 min by another hypoxic episode. In GiDREADD but not GFP rats, PVN terminal inhibition by nTS C21 strongly attenuated the phrenic amplitude response to hypoxia. Interestingly, C21 augmented tachycardic and sympathetic responses without altering the coupling of splanchnic sympathetic nerve activity to phrenic nerve activity during hypoxia. Data demonstrate that the PVN, including projections to the nTS, is critical in shaping sympathetic and respiratory responses to hypoxia.

Activation of alpha-1 adrenergic receptors increases cytosolic calcium in neurones of the paraventricular nucleus of the hypothalamus

Norepinephrine (NE) activates adrenergic receptors (ARs) in the hypothalamic paraventricular nucleus (PVN) to increase excitatory currents, depolarise neurones and, ultimately, augment neuro-sympathetic and endocrine output. Such cellular events are known to potentiate intracellular calcium ([Ca²⁺ ]_i ); however, the role of NE with respect to modulating [Ca²⁺ ]_i in PVN neurones and the mechanisms by which this may occur remain unclear. We evaluated the effects of NE on [Ca²⁺ ]_i of acutely isolated PVN neurones using Fura-2 imaging. NE induced a slow increase in [Ca²⁺ ]_i compared to artificial cerebrospinal fluid vehicle. NE-induced Ca²⁺ elevations were mimicked by the α₁ -AR agonist phenylephrine (PE) but not by α₂ -AR agonist clonidine (CLON). NE and PE but not CLON also increased the overall number of neurones that increase [Ca²⁺ ]_i (ie, responders). Elimination of extracellular Ca²⁺ or intracellular endoplasmic reticulum Ca²⁺ stores abolished the increase in [Ca²⁺ ]_i and reduced responders. Blockade of voltage-dependent Ca²⁺ channels abolished the α₁ -AR induced increase in [Ca²⁺ ]_i and number of responders, as did inhibition of phospholipase C inhibitor, protein kinase C and inositol triphosphate receptors. Spontaneous phasic Ca²⁺ events, however, were not altered by NE, PE or CLON. Repeated K⁺ -induced membrane depolarisation produced repetitive [Ca²⁺ ]_i elevations. NE and PE increased baseline Ca²⁺ , whereas NE decreased the peak amplitude. CLON also decreased peak amplitude but did not affect baseline [Ca²⁺ ]_i . Taken together, these data suggest receptor-specific influence of α₁ and α₂ receptors on the various modes of calcium entry in PVN neurones. They further suggest Ca²⁺ increase via α₁ -ARs is co-dependent on extracellular Ca²⁺ influx and intracellular Ca²⁺ release, possibly via a phospholipase C inhibitor-mediated signalling cascade.

Chronic Isolation Stress Affects Subsequent Crowding Stress-Induced Brain Nitric Oxide Synthase (NOS) Isoforms and Hypothalamic-Pituitary-Adrenal (HPA) Axis Responses

The nitric oxide (NO) pathway in the brain is involved in response to psychosocial stressors. The aim of this study was to elucidate the role of nNOS and iNOS in the prefrontal cortex (PFC), hippocampus (HIP), and hypothalamus (HYPO) during social isolation stress (IS), social crowding stress (CS), and a combined IS + CS. In the PFC, 3 days of CS increased iNOS but not nNOS protein level. In the HIP and HYPO, the levels of nNOS and iNOS significantly increased after 3 days of CS. In the PFC, IS alone (11 days) enhanced iNOS protein level following 3 days of CS and increased nNOS level in the HIP and HYPO after 14 days of CS. By contrast, in the HIP, IS abolished the subsequent CS-induced increase in nNOS in the HIP and strongly elevated iNOS level after 7 days of CS. In the HYPO, prior IS inhibited nNOS protein level induced by subsequent CS for 3 days, but increased nNOS protein level after longer exposure times to CS. Isolation stress strongly upregulated plasma interleukin-1β (IL-1β) and adrenocorticotropic hormone (ACTH) levels while corticosterone (CORT) level declined. We show that the modulatory action of the NO pathway and ACTH/CORT adaptation to chronic social isolation stress is dependent on the brain structure and nature and duration of the stressor. Our results indicate that isolation is a robust natural stressor in social animals; it enhances the NO pathway in the PFC and abolishes subsequent social CS-induced NOS responses in the HIP and HYPO.

Hydrogen peroxide inhibits neurons in the paraventricular nucleus of the hypothalamus via potassium channel activation

The paraventricular nucleus (PVN) of the hypothalamus is an important homeostatic and reflex center for neuroendocrine, respiratory, and autonomic regulation, including during hypoxic stressor challenges. Such challenges increase reactive oxygen species (ROS) to modulate synaptic, neuronal, and ion channel activity. Previously, in the nucleus tractus solitarius, another cardiorespiratory nucleus, we showed that the ROS H₂O₂ induced membrane hyperpolarization and reduced action potential discharge via increased K⁺ conductance at the resting potential. Here, we sought to determine the homogeneity of influence and mechanism of action of H₂O₂ on PVN neurons. We recorded PVN neurons in isolation and in an acute slice preparation, which leaves neurons in their semi-intact network. Regardless of preparation, H₂O₂ hyperpolarized PVN neurons and decreased action potential discharge. In the slice preparation, H₂O₂ also decreased spontaneous excitatory postsynaptic current frequency, but not amplitude. To examine potential mechanisms, we investigated the influence of the K⁺ channel blockers Ba²⁺, Cs⁺, and glibenclamide on membrane potential, as well as the ionic currents active at resting potential and outward K⁺ currents (I_K) upon depolarization. The H₂O₂ hyperpolarization was blocked by K⁺ channel blockers. H₂O₂ did not alter currents between -50 and -110 mV. However, H₂O₂ induced an outward I_K at -50 mV yet, at potentials more positive to 0 mV H₂O₂, decreased I_K. Elevated intracellular antioxidant catalase eliminated H₂O₂ effects. These data indicate that H₂O₂ alters synaptic and neuronal properties of PVN neurons likely via membrane hyperpolarization and alteration of I_K, which may ultimately alter cardiorespiratory reflexes.

CRHR2 (Corticotropin-Releasing Hormone Receptor 2) in the Nucleus of the Solitary Tract Contributes to Intermittent Hypoxia-Induced Hypertension

This study tested the hypothesis that CRHRs (corticotropin-releasing hormone receptors) in the nucleus of the solitary tract (NTS) contribute to the hypertension induced by intermittent hypoxia (IH) exposure in rats. Initial studies using in situ hybridization revealed low mRNA level of CRHR1 (CRH type 1 receptor) but high mRNA level of CRHR2 (CRH type 2 receptor) in the NTS. Calcium imaging studies on NTS slice preparations using Fura-2-acetoxymethyl ester demonstrated that CRH induced a transient increase of intracellular calcium level. The CRH-induced calcium response was reproduced in the presence of TTX (tetrodotoxin) but was abolished by depletion of extracellular calcium or by the L-type calcium channel blocker Nifedipine. The CRH-induced calcium influx was attenuated by the CRHR2 antagonist K41498 but not by the CRHR1 antagonist NBI-35 965. Calcium influx can be induced by the CRHR2 agonist Urocortin II but not by the CRHR1 agonist Stressin 1. IH exposure did not affect CRHR1 mRNA level but significantly decreased CRHR2 mRNA level and the CRH-induced calcium influx in the NTS. Further in vivo studies showed that intra-fourth ventricle infusion of K41498 did not affect the basal blood pressure but significantly attenuated the IH-induced hypertension; intra-fourth ventricle infusion of Urocortin II significantly increased basal blood pressure and exacerbated the IH-induced hypertension. Collectively, these results suggest that CRHR2 in the NTS contributes to the IH-induced hypertension; downregulation of CRHR2 and CRHR2-mediated calcium influx in the NTS may serve as an adaptive response to protect against the IH-induced hypertension.

Activation of the hypothalamic paraventricular nucleus by acute intermittent hypoxia: Implications for sympathetic long-term facilitation neuroplasticity

Exposure to acute intermittent hypoxia (AIH) induces a progressive increase of sympathetic nerve activity (SNA) that reflects a form of neuroplasticity known as sympathetic long-term facilitation (sLTF). Our recent findings indicate that activity of neurons in the hypothalamic paraventricular nucleus (PVN) contributes to AIH-induced sLTF, but neither the intra-PVN distribution nor the neurochemical identity of AIH responsive neurons has been determined. Here, awake rats were exposed to 10 cycles of AIH and c-Fos immunohistochemistry was performed to identify transcriptionally activated neurons in rostral, middle and caudal planes of the PVN. Effects of graded intensities of AIH were investigated in separate groups of rats (n = 6/group) in which inspired oxygen (O₂) was reduced every 6 min from 21% to nadirs of 10%, 8% or 6%. All intensities of AIH failed to increase c-Fos counts in the caudally located lateral parvocellular region of the PVN. c-Fos counts increased in the dorsal parvocellular and central magnocellular regions, but significance was achieved only with AIH to 6% O₂ (P < 0.002). By contrast, graded intensities of AIH induced graded c-Fos activation in the stress-related medial parvocellular (MP) region. Focusing on AIH exposure to 8% O₂, experiments next investigated the stress-regulatory neuropeptide content of AIH-activated MP neurons. Tissue sections immunostained for corticotropin-releasing hormone (CRH) or arginine vasopressin (AVP) revealed a significantly greater number of neurons stained for CRH than AVP (P < 0.0001), though AIH induced expression of c-Fos in a similar fraction (~14%) of each neurochemical class. Amongst AIH-activated MP neurons, ~30% stained for CRH while only ~2% stained for AVP. Most AIH-activated CRH neurons (~82%) were distributed in the rostral one-half of the PVN. Results indicate that AIH recruits CRH, but not AVP, neurons in rostral to middle levels of the MP region of PVN, and raise the possibility that these CRH neurons may be a substrate for AIH-induced sLTF neuroplasticity.

Role of the Carotid Bodies in the Hypertensive and Natriuretic Responses to NaCl Load in Conscious Rats

Hyperosmotic challenges trigger a hypertensive response and natriuresis mediated by central and peripheral sensors. Here, we evaluated the importance of the carotid bodies for the hypertensive and natriuretic responses to acute and sub-chronic NaCl load in conscious rats. Male Wistar rats (250–330 g) submitted to bilateral carotid body removal (CBX) or sham surgery were used. One day after the surgery, the changes in arterial blood pressure (n = 6–7/group) and renal sodium excretion (n = 10/group) to intravenous infusion of 3 M NaCl (1.8 mL/kg b.w. during 1 min) were evaluated in non-anesthetized rats. Another cohort of sham (n = 8) and CBX rats (n = 6) had access to 0.3 M NaCl as the only source of fluid to drink for 7 days while ingestion and renal excretion were monitored daily. The sodium balance was calculated as the difference between sodium infused/ingested and excreted. CBX reduced the hypertensive (8 ± 2 mmHg, vs. sham rats: 19 ± 2 mmHg; p < 0.05) and natriuretic responses (1.33 ± 0.13 mmol/90 min, vs. sham: 1.81 ± 0.11 mmol/90 min; p < 0.05) to acute intravenous infusion of 3 M NaCl, leading to an increase of sodium balance (0.38 ± 0.11 mmol/90 min, vs. sham: -0.06 ± 0.10 mmol/90 min; p < 0.05). In CBX rats, sub-chronic NaCl load with 0.3 M NaCl to drink for 7 days increased sodium balance (18.13 ± 4.45 mmol, vs. sham: 5.58 ± 1.71 mmol; p < 0.05) and plasma sodium concentration (164 ± 5 mmol/L, vs. sham: 140 ± 7 mmol/L; p < 0.05), without changing arterial pressure (121 ± 9 mmHg, vs. sham: 116 ± 2 mmHg). These results suggest that carotid bodies are important for the maintenance of the hypertensive response to acute hypertonic challenges and for sodium excretion to both acute and chronic NaCl load.

Impaired Hypothalamic Regulation of Sympathetic Outflow in Primary Hypertension

The hypothalamic paraventricular nucleus (PVN) is a crucial region involved in maintaining homeostasis through the regulation of cardiovascular, neuroendocrine, and other functions. The PVN provides a dominant source of excitatory drive to the sympathetic outflow through innervation of the brainstem and spinal cord in hypertension. We discuss current findings on the role of the PVN in the regulation of sympathetic output in both normotensive and hypertensive conditions. The PVN seems to play a major role in generating the elevated sympathetic vasomotor activity that is characteristic of multiple forms of hypertension, including primary hypertension in humans. Recent studies in the spontaneously hypertensive rat model have revealed an imbalance of inhibitory and excitatory synaptic inputs to PVN pre-sympathetic neurons as indicated by impaired inhibitory and enhanced excitatory synaptic inputs in hypertension. This imbalance of inhibitory and excitatory synaptic inputs in the PVN forms the basis for elevated sympathetic outflow in hypertension. In this review, we discuss the disruption of balance between glutamatergic and GABAergic inputs and the associated cellular and molecular alterations as mechanisms underlying the hyperactivity of PVN pre-sympathetic neurons in hypertension.

Regulation of sympathetic vasomotor activity by the hypothalamic paraventricular nucleus in normotensive and hypertensive states

The hypothalamic paraventricular nucleus (PVN) is a unique and important brain region involved in the control of cardiovascular, neuroendocrine, and other physiological functions pertinent to homeostasis. The PVN is a major source of excitatory drive to the spinal sympathetic outflow via both direct and indirect projections. In this review, we discuss the role of the PVN in the regulation of sympathetic output in normal physiological conditions and in hypertension. In normal healthy animals, the PVN presympathetic neurons do not appear to have a major role in sustaining resting sympathetic vasomotor activity or in regulating sympathetic responses to short-term homeostatic challenges such as acute hypotension or hypoxia. Their role is, however, much more significant during longer-term challenges, such as sustained water deprivation, chronic intermittent hypoxia, and pregnancy. The PVN also appears to have a major role in generating the increased sympathetic vasomotor activity that is characteristic of multiple forms of hypertension. Recent studies in the spontaneously hypertensive rat model have shown that impaired inhibitory and enhanced excitatory synaptic inputs to PVN presympathetic neurons are the basis for the heightened sympathetic outflow in hypertension. We discuss the molecular mechanisms underlying the presynaptic and postsynaptic alterations in GABAergic and glutamatergic inputs to PVN presympathetic neurons in hypertension. In addition, we discuss the ability of exercise training to correct sympathetic hyperactivity by restoring blood-brain barrier integrity, reducing angiotensin II availability, and decreasing oxidative stress and inflammation in the PVN.

Hypoxia activates a neuropeptidergic pathway from the paraventricular nucleus of the hypothalamus to the nucleus tractus solitarii

The paraventricular nucleus of the hypothalamus (PVN) contributes to both autonomic and neuroendocrine function. PVN lesion or inhibition blunts cardiorespiratory responses to peripheral chemoreflex activation, suggesting that the PVN is required for full expression of these effects. However, the role of efferent projections to cardiorespiratory nuclei and the neurotransmitters/neuromodulators that are involved is unclear. The PVN sends dense projections to the nucleus tractus solitarii (nTS), a region that displays neuronal activation following hypoxia. We hypothesized that acute hypoxia activates nTS-projecting PVN neurons. Using a combination of retrograde tracing and immunohistochemistry, we determined whether hypoxia activates PVN neurons that project to the nTS and examined the phenotype of these neurons. Conscious rats underwent 2 h normoxia (21% O₂, n = 5) or hypoxia (10% O₂, n = 6). Hypoxia significantly increased Fos immunoreactivity in nTS-projecting neurons, primarily in the caudal PVN. The majority of activated nTS-projecting neurons contained corticotropin-releasing hormone (CRH). In the nTS, fibers expressing the CRH receptor corticotropin-releasing factor receptor 2 (CRFR2) were colocalized with oxytocin (OT) fibers and were closely associated with hypoxia-activated nTS neurons. A separate group of animals that received a microinjection of adeno-associated virus type 2-hSyn-green fluorescent protein (GFP) into the PVN exhibited GFP-expressing fibers in the nTS; a proportion of these fibers displayed OT immunoreactivity. Thus, nTS CRFR2s appear to be located on the fibers of PVN OT neurons that project to the nTS. Taken together, our findings suggest that PVN CRH projections to the nTS may modulate nTS neuronal activation, possibly via OTergic mechanisms, and thus contribute to chemoreflex cardiorespiratory responses.

Enhanced Hypothalamic NMDA Receptor Activity Contributes to Hyperactivity of HPA Axis in Chronic Stress in Male Rats

Chronic stress stimulates corticotrophin-releasing hormone (CRH)-expressing neurons in the paraventricular nucleus (PVN) of the hypothalamus and leads to hypothalamic-pituitary-adrenal (HPA) axis hyperactivity, but the mechanisms underlying this action are unknown. Because chronic stress enhances N-methyl-d-aspartate receptor (NMDAR) activity in various brain regions, we hypothesized that augmented NMDAR activity contributes to the hyperactivity of PVN-CRH neurons and the HPA axis in chronic stress. We performed whole-cell patch-clamp recordings on PVN-CRH neurons expressing CRH promoter-driven enhanced green fluorescent protein in brain slices from rats exposed to chronic unpredictable mild stress (CUMS) and unstressed rats. CUMS rats had significantly higher expression levels of the NMDAR subunits GluN1 in the PVN than unstressed rats. Furthermore, puff NMDA-elicited currents, evoked NMDAR currents, and the baseline frequency of the miniature excitatory postsynaptic currents (mEPSCs) in PVN-CRH neurons were significantly larger in CUMS rats than in unstressed rats. The NMDAR-specific antagonist 2-amino-5-phosphonopentanoic acid (AP5) significantly decreased the frequency of mEPSCs of PVN-CRH neurons in CUMS rats but did not change the frequency or amplitude of mEPSCs in unstressed rats. Bath application of AP5 normalized the elevated firing activity of PVN-CRH neurons in CUMS rats but not in unstressed rats. In addition, microinjection of the NMDAR antagonist memantine into the PVN normalized the elevated corticosterone (CORT) levels in CUMS rats to the levels in unstressed rats, but did not alter CORT levels in unstressed rats. Our findings suggest that synaptic NMDAR activity is enhanced in CUMS rats and contributes to the hyperactivity of PVN-CRN neurons and the HPA axis.

Surge of Peripheral Arginine Vasopressin in a Rat Model of Birth Asphyxia

Mammalian birth is accompanied by a period of obligatory asphyxia, which consists of hypoxia (drop in blood O₂ levels) and hypercapnia (elevation of blood CO₂ levels). Prolonged, complicated birth can extend the asphyxic period, leading to a pathophysiological situation, and in humans, to the diagnosis of clinical birth asphyxia, the main cause of hypoxic-ischemic encephalopathy (HIE). The neuroendocrine component of birth asphyxia, in particular the increase in circulating levels of arginine vasopressin (AVP), has been extensively studied in humans. Here we show for the first time that normal rat birth is also accompanied by an AVP surge, and that the fetal AVP surge is further enhanced in a model of birth asphyxia, based on exposing 6-day old rat pups to a gas mixture containing 4% O₂ and 20% CO₂ for 45 min. Instead of AVP, which is highly unstable with a short plasma half-life, we measured the levels of copeptin, the C-terminal part of prepro-AVP that is biochemically much more stable. In our animal model, the bulk of AVP/copeptin release occurred at the beginning of asphyxia (mean 7.8 nM after 15 min of asphyxia), but some release was still ongoing even 90 min after the end of the 45 min experimental asphyxia (mean 1.2 nM). Notably, the highest copeptin levels were measured after hypoxia alone (mean 14.1 nM at 45 min), whereas copeptin levels were low during hypercapnia alone (mean 2.7 nM at 45 min), indicating that the hypoxia component of asphyxia is responsible for the increase in AVP/copeptin release. Alternating the O₂ level between 5 and 9% (CO₂ at 20%) with 5 min intervals to mimic intermittent asphyxia during prolonged labor resulted in a slower but quantitatively similar rise in copeptin (peak of 8.3 nM at 30 min). Finally, we demonstrate that our rat model satisfies the standard acid-base criteria for birth asphyxia diagnosis, namely a drop in blood pH below 7.0 and the formation of a negative base excess exceeding -11.2 mmol/l. The mechanistic insights from our work validate the use of the present rodent model in preclinical work on birth asphyxia.

Hypothalamic PVN contributes to acute intermittent hypoxia-induced sympathetic but not phrenic long-term facilitation

Blackburn MB, Andrade MA, Toney GM. Hypothalamic PVN contributes to acute intermittent hypoxia-induced sympathetic but not phrenic long-term facilitation. J Appl Physiol 124: 1233-1243, 2018. First published December 19, 2017; doi: 10.1152/japplphysiol.00743.2017 .- Acute intermittent hypoxia (AIH) repetitively activates the arterial chemoreflex and triggers a progressive increase of sympathetic nerve activity (SNA) and phrenic nerve activity (PNA) referred to as sympathetic and phrenic long-term facilitation (S-LTF and P-LTF), respectively. Neurons of the hypothalamic paraventricular nucleus (PVN) participate in the arterial chemoreflex, but their contribution to AIH-induced LTF is unknown. To determine this, anesthetized rats were vagotomized and exposed to 10 cycles of AIH, each consisting of ventilation for 3 min with 100% O₂ followed by 3 min with 15% O₂. Before AIH, rats received bilateral PVN injections of artificial cerebrospinal fluid (aCSF; vehicle) or the GABA-A receptor agonist muscimol (100 pmol in 50 nl) to inhibit neuronal activity. Thirty minutes after completing the AIH protocol, during which rats were continuously ventilated with 100% O₂, S-LTF and P-LTF were quantified from recordings of integrated splanchnic SNA and PNA, respectively. PVN muscimol attenuated increases of SNA during hypoxic episodes occurring in later cycles (6-10) of AIH ( P < 0.03) and attenuated post-AIH S-LTF ( P < 0.001). Muscimol, however, did not consistently affect peak PNA responses during hypoxic episodes and did not alter AIH-induced P-LTF. These findings indicate that PVN neuronal activity contributes to sympathetic responses during AIH and to subsequent generation of S-LTF. NEW & NOTEWORTHY Neural circuits mediating acute intermittent hypoxia (AIH)-induced sympathetic and phrenic long-term facilitation (LTF) have not been fully elucidated. We found that paraventricular nucleus (PVN) inhibition attenuated sympathetic activation during episodes of AIH and reduced post-AIH sympathetic LTF. Neither phrenic burst patterning nor the magnitude of AIH-induced phrenic LTF was affected. Findings indicate that PVN neurons contribute to AIH-induced sympathetic LTF. Defining mechanisms of sympathetic LTF could improve strategies to reduce sympathetic activity in cardiovascular and metabolic diseases.

Combined hypoxia and hypercapnia, but not hypoxia alone, suppresses neurotransmission from orexin to hypothalamic paraventricular spinally-projecting neurons in weanling rats

Both orexin neurons in the lateral hypothalamus and spinally-projecting pre-sympathetic neurons (PSNs) in the paraventricular nucleus of the hypothalamus (PVN) play an important role in the regulation of cardiovascular function under normal conditions and during cardiovascular challenges such as hypoxia and/or hypercapnia. We have previously established, using selective optogenetic excitation of orexin neurons and pathways, there is a heterogeneous neurotransmission from orexin neurons to PSNs in the PVN. This study was undertaken to test whether this pathway is altered by acute exposure to hypoxia alone and/or combined hypoxia and hypercapnia (H/H). To test this hypothesis, we selectively expressed channelrhodopsin-2 (ChR2) in orexin neurons in the lateral hypothalamus and photoactivated ChR2-expressing fibers to evoke postsynaptic currents in spinally-projecting PSNs in an in vitro slice preparation in rats. In accordance with previously published data, two subpopulations of spinally-projecting PSNs were established, including those with glutamatergic or GABAergic inputs from orexin neurons. Hypoxia alone did not alter the peak amplitude of either glutamatergic or GABAergic neurotransmission, however, H/H significantly inhibited both glutamatergic and GABAergic neurotransmission from orexin neurons to SPNs. In conclusion, H/H may modulate cardiovascular function by affecting heterogeneous pathways from orexin neurons to spinally-projecting PSNs in the PVN.

Transcription factor ΔFosB acts within the nucleus of the solitary tract to increase mean arterial pressure during exposures to intermittent hypoxia

ΔFosB is a member of the activator protein-1 family of transcription factors. ΔFosB has low constitutive expression in the central nervous system and is induced after exposure of rodents to intermittent hypoxia (IH), a model of the arterial hypoxemia that accompanies sleep apnea. We hypothesized ΔFosB in the nucleus of the solitary tract (NTS) contributes to increased mean arterial pressure (MAP) during IH. The NTS of 11 male Sprague-Dawley rats was injected (3 sites, 100 nl/site) with a dominant negative construct against ΔFosB (ΔJunD) in an adeno-associated viral vector (AAV)-green fluorescent protein (GFP) reporter. The NTS of 10 rats was injected with AAV-GFP as sham controls. Two weeks after NTS injections, rats were exposed to IH for 8 h/day for 7 days, and MAP was recorded using telemetry. In the sham group, 7 days of IH increased MAP from 99.8 ± 1.1 to 107.3 ± 0.5 mmHg in the day and from 104.4 ± 1.1 to 109.8 ± 0.6 mmHg in the night. In the group that received ΔJunD, IH increased MAP during the day from 95.9 ± 1.7 to 101.3 ± 0.4 mmHg and from 100.9 ± 1.7 to 102.8 ± 0.5 mmHg during the night (both IH-induced changes in MAP were significantly lower than sham, P < 0.05). After injection of the dominant negative construct in the NTS, IH-induced ΔFosB immunoreactivity was decreased in the paraventricular nucleus ( P < 0.05); however, no change was observed in the rostral ventrolateral medulla. These data indicate that ΔFosB within the NTS contributes to the increase in MAP induced by IH exposure. NEW & NOTEWORTHY The results of this study provides new insights into the molecular mechanisms that mediate neuronal adaptations during exposures to intermittent hypoxia, a model of the hypoxemias that occur during sleep apnea. These adaptations are noteworthy as they contribute to the persistent increase in blood pressure induced by exposures to intermittent hypoxia.