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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., (© 2023 The Authors. The Journal of Physiology © 2023 The Physiological Society.)

Background: In high-risk patients with degenerated aortic bioprostheses, valve-in-valve (ViV) transcatheter aortic valve implantation (TAVI) has emerged as a less invasive alternative to surgical valve replacement. To compare outcomes of ViV and native valve (NV) TAVI procedures., Methods: 34 aortic ViV-TAVI performed between 2012 and 2022 using self-expanding valves, were included in this retrospective analysis. Propensity score matching (1:2 ratio, 19 criteria) was used to select a comparison NV-TAVI group from a database of 1206 TAVI procedures. Clinical and echocardiographic endpoints, short- and long-term all-cause mortality (ACM) and cardiovascular mortality (CVM) data were obtained. Subgroup analyses were completed according to the true internal diameter, dividing patients into a small ( ≤ 19 mm) valve group (SVG) and a large ( > 19 mm) valve group (LVG)., Results: Clinical outcomes of ViV- and NV-TAVI were comparable, including device success [88.2% vs. 91.1%, p = 0.727], major adverse cardiovascular and cerebrovascular events [5.8% vs. 5.8%, p = 1.000], hemodialysis need [5.8% vs. 2.9%, p = 0.599], pacemaker need [2.9% vs. 11.7%, p = 0.265], major vascular complications [2.9% vs. 1.4%, p = 1.000], life-threatening or major bleeding [2.9% vs. 1.4%, p = 1.000] and in-hospital mortality [8.8% vs. 5.9%, p = 0.556]. There was a significant difference in the immediate post-intervention mean residual aortic valve gradient (MAVG) [14.6 ± 8.5 mm Hg vs. 6.4 ± 4.5 mm Hg, p < 0.0001], which persisted at 1 year [ p = 0.0002]. There were no differences in 12- or 30-month ACM [11.8% vs. 8.8%, p = 0.588; 23.5% vs. 27.9%, p = 0.948], and CVM [11.8% vs. 7.3%, p = 0.441; 23.5% vs. 16.2%, p = 0.239]. Lastly, there was no difference in CVM at 1 year and 30 months [11.1% vs. 12.5%, p = 0.889; 22.2% vs. 25.0%, p = 0.742]., Conclusions: Analyzing a limited group (n = 34) of ViV-TAVI procedures out of 1206 TAVIs done at a single institution, ViV-TAVI appeared to be an acceptable approach in patients not deemed appropriate candidates for redo valve replacement surgery. Clinical outcomes of ViV-TAVI were comparable to TAVI for native valve stenosis., Competing Interests: The authors declare no conflict of interest., (Copyright: © 2023 The Author(s). Published by IMR Press.)

Exposure to acute intermittent hypoxia (AIH) induces prolonged increases (long term facilitation, LTF) in phrenic and sympathetic nerve activity (PhrNA, SNA) under basal conditions, and enhanced respiratory and sympathetic responses to hypoxia. The mechanisms and neurocircuitry involved are not fully defined. We tested the hypothesis that the nucleus tractus solitarii (nTS) is vital to augmentation of hypoxic responses and the initiation and maintenance of elevated phrenic (p) and splanchnic sympathetic (s) LTF following AIH. nTS neuronal activity was inhibited by nanoinjection of the GABA A receptor agonist muscimol before AIH exposure or after development of AIH-induced LTF. AIH but not sustained hypoxia induced pLTF and sLTF with maintained respiratory modulation of SSNA. nTS muscimol before AIH increased baseline SSNA with minor effects on PhrNA. nTS inhibition also markedly blunted hypoxic PhrNA and SSNA responses, and prevented altered sympathorespiratory coupling during hypoxia. Inhibiting nTS neuronal activity before AIH exposure also prevented the development of pLTF during AIH and the elevated SSNA after muscimol did not increase further during or following AIH exposure. Furthermore, nTS neuronal inhibition after the development of AIH-induced LTF substantially reversed but did not eliminate the facilitation of PhrNA. Together these findings demonstrate that mechanisms within the nTS are critical for initiation of pLTF during AIH. Moreover, ongoing nTS neuronal activity is required for full expression of sustained elevations in PhrNA following exposure to AIH although other regions likely also are important. Together, the data indicate that AIH-induced alterations within the nTS contribute to both the development and maintenance of pLTF., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Ostrowski, Heesch, Kline and Hasser.)

Surgical aortic valve replacement in the elderly is now being supplanted by transcatheter aortic valve implantation (TAVI). Scoring systems to predict survival after catheter-based procedures are understudied. Both diabetes (DM) and underlying inflammatory conditions are common in patients undergoing TAVI, but their impact remains understudied in this patient group. We examined 560 consecutive TAVI procedures and identified eight pre-procedural factors: age, body mass index (BMI), DM, fasting blood glucose (BG), left-ventricular ejection fraction (EF), aortic valve (AV) mean gradient, C-reactive protein levels, and serum creatinine levels and studied their impact on survival. The overall mortality rate at 30 days, 1 year and 2 years were 5.2%, 16.6%, and 34.3%, respectively. All-cause mortality was higher in patients with DM (at 30 days: 8.9% vs. 3.1%, p = 0.008; at 1 year: 19.7% vs. 14.9%, p = 0.323; at 2 years: 37.9% vs. 32.2%, p = 0.304). The presence of DM was independently associated with increased 30-day mortality (hazard ratio [HR] 5.38, 95% confidence interval [CI], 1.24-23.25, p = 0.024). BG levels within 7-11, 1 mmol/L portended an increased risk for 30-day and 2-year mortality compared to normal BG ( p = 0.001 and p = 0.027). For each 1 mmol/L increase in BG 30-day mortality increased (HR 1.21, 95% CI, 1.04-1.41, p = 0.015). Reduced EF and elevated CRP were each associated with increased 2-year mortality ( p = 0.042 and p = 0.003). DM, elevated BG, reduced EF, and elevated baseline CRP levels each are independent predictors of short- and long-term mortality following TAVI. These easily accessible screening parameters should be integrated into risk-assessment tools for catheter-based aortic valve replacement candidates.

Chronic intermittent hypoxia (CIH) is a model for obstructive sleep apnea. The paraventricular nucleus (PVN) of the hypothalamus has been suggested to contribute to CIH-induced exaggerated cardiorespiratory reflexes, sympathoexcitation and hypertension. This may occur, in part, via activation of the dense catecholaminergic projections to the PVN that originate in the brainstem. However, the contribution of norepinephrine (NE) and activation of its alpha-adrenergic receptors (α-ARs) in the PVN after CIH exposure is unknown. We hypothesized CIH would increase the contribution of catecholaminergic input. To test this notion, we determined the expression of α-AR subtypes, catecholamine terminal density, and synaptic properties of PVN parvocellular neurons in response to α-AR activation in male Sprague-Dawley normoxic (Norm) and CIH exposed rats. CIH decreased mRNA for α 1d and α 2b AR. Dopamine-β-hydroxylase (DβH) terminals in the PVN were similar between groups. NE and the α 1 -AR agonist phenylephrine (PE) increased sEPSC frequency after Norm but not CIH. Block of α 1 -ARs with prazosin alone did not alter sEPSCs after either Norm or CIH but did prevent agonist augmentation of sEPSC frequency following normoxia. These responses to NE were mimicked by PE during action potential block suggesting presynaptic terminal alterations in CIH. Altogether, these results demonstrate that α 1 -AR activation participates in neuronal responses in Norm, but are attenuated after CIH. These results may provide insight into the cardiovascular, respiratory and autonomic nervous systems alterations in obstructive sleep apnea., (Copyright © 2020. Published by Elsevier Inc.)

There is an increase in basal sympathetic nerve activity (SNA) during normal pregnancy; this counteracts profound primary vasodilation. However, pregnancy also impairs baroreflex control of heart rate and SNA, contributing to increased mortality secondary to peripartum hemorrhage. Pregnancy-induced hypertensive disorders evoke even greater elevations in SNA, which likely contribute to the hypertension. Information concerning mechanisms is limited. In normal pregnancy, increased angiotensin II acts centrally to support elevated SNA. Hypothalamic sites, including the subfornical organ, paraventricular nucleus, and arcuate nucleus, are likely (but unproven) targets. Moreover, no definitive mechanisms for exaggerated sympathoexcitation in hypertensive pregnancy have been identified. In addition, normal pregnancy increases gamma aminobutyric acid inhibition of the rostral ventrolateral medulla (RVLM), a key brainstem site that transmits excitatory inputs to spinal sympathetic preganglionic neurons. Accumulated evidence supports a major role for locally increased production and actions of the neurosteroid allopregnanolone as one mechanism. A consequence is suppression of baroreflex function, but increased basal SNA indicates that excitatory influences predominate in the RVLM. However, many questions remain regarding other sites and factors that support increased SNA during normal pregnancy and, more importantly, the mechanisms underlying excessive sympathoexcitation in life-threatening hypertensive pregnancy disorders such as preeclampsia., (Copyright © 2020 Elsevier B.V. All rights reserved.)

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% O 2 ) 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% O 2 , 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.

Key Points: To maintain appropriate blood flow to various tissues of the body under a variety of physiological states, autonomic nervous system reflexes regulate regional sympathetic nerve activity and arterial blood pressure. Our data obtained in anaesthetized rats revealed that glycine released in the rostral ventrolateral medulla (RVLM) plays a critical role in maintaining arterial baroreflex sympathoinhibition. Manipulation of brainstem nuclei with known inputs to the RVLM (nucleus tractus solitarius and caudal VLM) unmasked tonic glycinergic inhibition in the RVLM. Whole-cell, patch clamp recordings demonstrate that both GABA and glycine inhibit RVLM neurons. Potentiation of neurotransmitter release from the active synaptic inputs in the RVLM produced saturation of GABAergic inhibition and emergence of glycinergic inhibition. Our data suggest that GABA controls threshold excitability, wherreas glycine increases the strength of inhibition under conditions of increased synaptic activity within the RVLM., Abstract: The arterial baroreflex is a rapid negative-feedback system that compensates changes in blood pressure by adjusting the output of presympathetic neurons in the rostral ventrolateral medulla (RVLM). GABAergic projections from the caudal VLM (CVLM) provide a primary inhibitory input to presympathetic RVLM neurons. Although glycine-dependent regulation of RVLM neurons has been proposed, its role in determining RVLM excitability is ill-defined. The present study aimed to determine the physiological role of glycinergic neurotransmission in baroreflex function, identify the mechanisms for glycine release, and evaluate co-inhibition of RVLM neurons by GABA and glycine. Microinjection of the glycine receptor antagonist strychnine (4 mm, 100 nL) into the RVLM decreased the duration of baroreflex-mediated inhibition of renal sympathetic nerve activity (control = 12 ± 1 min; RVLM-strychnine = 5.1 ± 1 min), suggesting that RVLM glycine plays a critical role in regulating the time course of sympathoinhibition. Blockade of output from the nucleus tractus solitarius and/or disinhibition of the CVLM unmasked tonic glycinergic inhibition of the RVLM. To evaluate cellular mechanisms, RVLM neurons were retrogradely labelled (prior injection of pseudorabies virus PRV-152) and whole-cell, patch clamp recordings were obtained in brainstem slices. Under steady-state conditions GABAergic inhibition of RVLM neurons predominated and glycine contributed less than 25% of the overall inhibition. By contrast, stimulation of synaptic inputs in the RVLM decreased GABAergic inhibition to 53%; and increased glycinergic inhibition to 47%. Thus, under conditions of increased synaptic activity in the RVLM, glycinergic inhibition is recruited to strengthen sympathoinhibition., (© 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.)

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% O 2 , n = 5) or hypoxia (10% O 2 , 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.

Background: Postmenopausal women represent the largest cohort of patients with heart failure with preserved ejection fraction, and vascular dementia represents the most common form of dementia in patients with heart failure with preserved ejection fraction. Therefore, we tested the hypotheses that the combination of cardiac pressure overload (aortic banding [AB]) and the loss of female sex hormones (ovariectomy [OVX]) impairs cerebrovascular control and spatial memory., Methods and Results: Female Yucatan miniswine were separated into 4 groups (n=7 per group): (1) control, (2) AB, (3) OVX, and (4) AB-OVX. Pigs underwent OVX and AB at 7 and 8 months of age, respectively. At 14 months, cerebral blood flow velocity and spatial memory (spatial hole-board task) were lower in the OVX groups ( P <0.05), with significant impairments in the AB-OVX group ( P <0.05). Resting carotid artery β stiffness and vascular resistance during central hypovolemia were increased in the AB-OVX group ( P <0.05), and blood flow recovery after central hypovolemia was reduced in both OVX groups ( P <0.05). Isolated pial artery (pressure myography) vasoconstriction to neuropeptide Y was greatest in the AB-OVX group ( P <0.05), and vasodilation to the Ca 2+ -activated potassium channel α-subunit agonist NS-1619 was impaired in both AB groups ( P <0.05). The ratio of phosphorylated endothelial nitric oxide synthase:total endothelial nitric oxide synthase was depressed and Ca 2+ -activated potassium channel α-subunit protein was increased in AB groups ( P <0.05)., Conclusions: Mechanistically, impaired cerebral blood flow control in experimental heart failure may be the result of heightened neuropeptide Y-induced vasoconstriction along with reduced vasodilation associated with decreased Ca 2+ -activated potassium channel function and impaired nitric oxide signaling, the effects of which are exacerbated in the absence of female sex hormones., (© 2017 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley.)

Hypoxia results in decreased arterial Po 2 , arterial chemoreflex activation, and compensatory increases in breathing, sympathetic outflow, and neuroendocrine secretions, including increased secretion of AVP, corticotropin-releasing hormone (CRH), adrenocorticotropin hormone (ACTH), and corticosterone. In addition to a brain stem pathway, including the nucleus tractus solitarius (nTS) and the rostral ventrolateral medulla (RVLM), medullary pathways to the paraventricular nucleus of the hypothalamus (PVN) contribute to chemoreflex responses. Experiments evaluated activation of specific cell phenotypes within the PVN following an acute hypoxic stimulus (AH; 2 h, 10% O 2 ) in conscious rats. Retrograde tracers (from spinal cord and RVLM) labeled presympathetic (PreS) neurons, and immunohistochemistry identified AVP- and CRH-immunoreactive (IR) cells. c-Fos-IR was an index of neuronal activation. Hypoxia activated AVP-IR (~6%) and CRH-IR (~15%) cells, but not PreS cells in the PVN, suggesting that sympathoexcitation during moderate AH is mediated mainly by a pathway that does not include PreS neurons in the PVN. Approximately 14 to 17% of all PVN cell phenotypes examined expressed neuronal nitric oxide synthase (nNOS-IR). AH activated only nNOS-negative AVP-IR neurons. In contrast ~23% of activated CRH-IR neurons in the PVN contained nNOS. In the median eminence, CRH-IR terminals were closely opposed to tanycyte processes and end-feet (vimentin-IR) in the external zone, where vascular NO participates in tanycyte retraction to facilitate neuropeptide secretion into the pituitary portal circulation. Results are consistent with an inhibitory role of NO on AVP and PreS neurons in the PVN and an excitatory role of NO on CRH secretion in the PVN and median eminence., (Copyright © 2017 the American Physiological Society.)

Pregnancy is characterized by increased blood volume and baseline sympathetic nerve activity (SNA), vasodilation, and tachycardia. Relaxin (RLX), an ovarian hormone elevated in pregnancy, activates forebrain sites involved in control of blood volume and SNA through ANG II-dependent mechanisms and contributes to adaptations during pregnancy. In anesthetized, arterial baroreceptor-denervated nonpregnant (NP) rats, RLX microinjected into the subfornical organ (SFO; 0.77 pmol in 50 nl) produced sustained increases in lumbar SNA (8 ± 3%) and mean arterial pressure (MAP; 26 ± 4 mmHg). Low-dose intracarotid artery infusion of RLX (155 pmol·ml(-1)·h(-1); 1.5 h) had minor transient effects on AP and activated neurons [increased Fos-immunoreactivity (IR)] in the SFO and in spinally projecting (19 ± 2%) and arginine-vasopressin (AVP)-IR (21 ± 5%) cells in the paraventricular nucleus of the hypothalamus of NP, but not pregnant (P), rats. However, mRNA for RLX and ANG II type 1a receptors in the SFO was preserved in pregnancy. RLX receptor-IR is present in the region of the SFO in NP and P rats and is localized in astrocytes, the major source of angiotensinogen in the SFO. These data provide an anatomical substrate for a role of RLX in the resetting of AVP secretion and increased baseline SNA in pregnancy. Since RLX and ANG II receptor expression was preserved in the SFO of P rats, we speculate that the lack of response to exogenous RLX may be due to maximal activation by elevated endogenous levels of RLX in near-term pregnancy., (Copyright © 2015 the American Physiological Society.)

Brainstem catecholamine neurons modulate sensory information and participate in control of cardiorespiratory function. These neurons have multiple projections, including to the paraventricular nucleus (PVN), which contributes to cardiorespiratory and neuroendocrine responses to hypoxia. We have shown that PVN-projecting catecholaminergic neurons are activated by hypoxia, but the function of these neurons is not known. To test the hypothesis that PVN-projecting catecholamine neurons participate in responses to respiratory challenges, we injected IgG saporin (control; n = 6) or anti-dopamine β-hydroxylase saporin (DSAP; n = 6) into the PVN to retrogradely lesion catecholamine neurons projecting to the PVN. After 2 wk, respiratory measurements (plethysmography) were made in awake rats during normoxia, increasing intensities of hypoxia (12, 10, and 8% O2) and hypercapnia (5% CO2-95% O2). DSAP decreased the number of tyrosine hydroxylase-immunoreactive terminals in PVN and cells counted in ventrolateral medulla (VLM; -37%) and nucleus tractus solitarii (nTS; -36%). DSAP produced a small but significant decrease in respiratory rate at baseline (during normoxia) and at all intensities of hypoxia. Tidal volume and minute ventilation (VE) index also were impaired at higher hypoxic intensities (10-8% O2; e.g., VE at 8% O2: IgG = 181 ± 22, DSAP = 91 ± 4 arbitrary units). Depressed ventilation in DSAP rats was associated with significantly lower arterial O2 saturation at all hypoxic intensities. PVN DSAP also reduced ventilatory responses to 5% CO2 (VE: IgG = 176 ± 21 and DSAP = 84 ± 5 arbitrary units). Data indicate that catecholamine neurons projecting to the PVN are important for peripheral and central chemoreflex respiratory responses and for maintenance of arterial oxygen levels during hypoxic stimuli., (Copyright © 2015 the American Physiological Society.)

Hydrogen peroxide (H₂O₂) is a stable reactive oxygen species and potent neuromodulator of cellular and synaptic activity. Centrally, endogenous H₂O₂ is elevated during bouts of hypoxia-reoxygenation, a variety of disease states, and aging. The nucleus tractus solitarii (nTS) is the central termination site of visceral afferents for homeostatic reflexes and contributes to reflex alterations during these conditions. We determined the extent to which H₂O₂ modulates synaptic and membrane properties in nTS neurons in rat brainstem slices. Stimulation of the tractus solitarii (which contains the sensory afferent fibers) evoked synaptic currents that were not altered by 10-500 μM H₂O₂. However, 500 μM H₂O₂ modulated several intrinsic membrane properties of nTS neurons, including a decrease in input resistance (R(i)), hyperpolarization of resting membrane potential (RMP) and action potential (AP) threshold (THR), and an initial reduction in AP discharge to depolarizing current. H₂O₂ increased conductance of barium-sensitive potassium currents, and block of these currents ablated H₂O₂-induced changes in RMP, Ri and AP discharge. Following washout of H₂O₂ AP discharge was enhanced due to depolarization of RMP and a partially maintained hyperpolarization of THR. Hyperexcitability persisted with repeated H₂O₂ exposure. H₂O₂ effects on RMP and THR were ablated by intracellular administration of the antioxidant catalase, which was immunohistochemically identified in neurons throughout the nTS. Thus, H₂O₂ initially reduces excitability of nTS neurons that is followed by sustained hyperexcitability, which may play a profound role in cardiorespiratory reflexes., (Copyright © 2014 IBRO. Published by Elsevier Ltd. All rights reserved.)

Rupture of a nerve is a debilitating injury with devastating consequences for the individual's quality of life. The gold standard of repair is the use of an autologous graft to bridge the severed nerve ends. Such repair however involves risks due to secondary surgery at the donor site and may result in morbidity and infection. Thus the clinical approach to repair often involves non-cellular solutions, grafts composed of synthetic or natural materials. Here we report on a novel approach to biofabricate fully biological grafts composed exclusively of cells and cell secreted material. To reproducibly and reliably build such grafts of composite geometry we use bioprinting. We test our grafts in a rat sciatic nerve injury model for both motor and sensory function. In particular we compare the regenerative capacity of the biofabricated grafts with that of autologous grafts and grafts made of hollow collagen tubes by measuring the compound action potential (for motor function) and the change in mean arterial blood pressure as consequence of electrically eliciting the somatic pressor reflex. Our results provide evidence that bioprinting is a promising approach to nerve graft fabrication and as a consequence to nerve regeneration.

Hypoxia activates catecholamine neurons in the caudal ventrolateral medulla (CVLM). The hypothalamic paraventricular nucleus (PVN) modulates arterial chemoreflex responses and receives catecholaminergic projections from the CVLM, but it is not known whether the CVLM-PVN projection is activated by chemoreflex stimulation. We hypothesized that acute hypoxia (AH) activates PVN-projecting catecholaminergic neurons in the CVLM. Fluoro-Gold (2%, 60-90 nl) was microinjected into the PVN of rats to retrogradely label CVLM neurons. After recovery, conscious rats underwent 3 h of normoxia (21% O2, n = 4) or AH (12, 10, or 8% O2; n = 5 each group). We used Fos immunoreactivity as an index of CVLM neuronal activation and tyrosine hydroxylase (TH) immunoreactivity to identify catecholaminergic neurons. Positively labeled neurons were counted in six caudal-rostral sections containing CVLM. Hypoxia progressively increased the number of Fos-immunoreactive CVLM cells (21%, 19 ± 6; 12%, 49 ± 2; 10%, 117 ± 8; 8%, 179 ± 7; P < 0.001). Catecholaminergic cells colabeled with Fos immunoreactivity in the CVLM were observed following 12% O2, and further increases in hypoxia severity caused markedly more activation. PVN-projecting CVLM cells were activated following more severe hypoxia (10% and 8% O2). A large proportion (89 ± 3%) of all activated PVN-projecting CVLM neurons were catecholaminergic, regardless of hypoxia intensity. Data suggest that catecholaminergic, PVN-projecting CVLM neurons are particularly hypoxia-sensitive, and these neurons may be important in the cardiorespiratory and/or neuroendocrine responses elicited by the chemoreflex.

The paraventricular nucleus (PVN) of the hypothalamus is an important site for autonomic and neuroendocrine regulation. Experiments in anesthetized animals and in vitro indicate an interaction among gamma-aminobutyric acid (GABA), nitric oxide (NO), and glutamate in the PVN. The cardiovascular role of the PVN and interactions of these neurotransmitters in conscious animals have not been evaluated fully. In chronically instrumented conscious rats, mean arterial pressure (MAP) and heart rate (HR) responses to microinjections (100 nl) in the region of the PVN were tested. Bilateral blockade of ionotropic excitatory amino acid (EAA) receptors (kynurenic acid, Kyn) in the PVN produced small but significant decreases in MAP and HR. GABA(A) receptor blockade (bicuculline, Bic), and inhibition of NO synthase [(NOS), N-(G)-monomethyl-L-arginine, L-NMMA] each increased MAP and HR. The NO donor sodium nitroprusside (SNP) produced depressor responses that were attenuated by Bic. NOS inhibition potentiated both pressor responses to the selective EAA agonist, N-methyl-D-aspartic acid (NMDA), and depressor responses to Kyn. Increases in MAP and HR due to Bic were blunted by prior blockade of EAA receptors. Thus, pressor responses to GABA blockade require EAA receptors and GABA neurotransmission contributes to NO inhibition. Tonic excitatory effects of glutamate in the PVN are tonically attenuated by NO. These data demonstrate that, in the PVN of conscious rats, GABA, glutamate, and NO interact in a complex fashion to regulate arterial pressure and HR under normal conditions.

Peripheral chemoreceptor afferent information is sent to the nucleus tractus solitarii (nTS), integrated, and relayed to other brain regions to alter cardiorespiratory function. The nTS projects to the hypothalamic paraventricular nucleus (PVN), but activation and phenotype of these projections during chemoreflex stimulation is unknown. We hypothesized that activation of PVN-projecting nTS neurons occurs primarily at high intensities of hypoxia. We assessed ventilation and cardiovascular parameters in response to increasing severities of hypoxia. Retrograde tracers were used to label nTS PVN-projecting neurons and, in some rats, rostral ventrolateral medulla (RVLM)-projecting neurons. Immunohistochemistry was performed to identify nTS cells that were activated (Fos-immunoreactive, Fos-IR), catecholaminergic, and GABAergic following hypoxia. Conscious rats underwent 3 h normoxia (n = 4, 21% O(2)) or acute hypoxia (12, 10, or 8% O(2); n = 5 each). Hypoxia increased ventilation and the number of Fos-IR nTS cells (21%, 13 ± 2; 12%, 58 ± 4; 10%, 166 ± 22; 8%, 186 ± 6). Fos expression after 10% O(2) was similar whether arterial pressure was allowed to decrease (-13 ± 1 mmHg) or was held constant. The percentage of PVN-projecting cells activated was intensity dependent, but contrary to our hypothesis, PVN-projecting nTS cells exhibiting Fos-IR were found at all hypoxic intensities. Notably, at all intensities of hypoxia, ∼75% of the activated PVN-projecting nTS neurons were catecholaminergic. Compared with RVLM-projecting cells, a greater percentage of PVN-projecting nTS cells was activated by 10% O(2). Data suggest that increasing hypoxic intensity activates nTS PVN-projecting cells, especially catecholaminergic, PVN-projecting neurons. The nTS to PVN catecholaminergic pathway may be critical even at lower levels of chemoreflex activation and more important to cardiorespiratory responses than previously considered.

The aim of this investigation was to evaluate sex differences in baroreflex and heart rate variability (HRV) dysfunction and indexes of end-organ damage in the TG(mRen2)27 (Ren2) rat, a model of renin overexpression and tissue renin-angiotensin-aldosterone system overactivation. Blood pressure (via telemetric monitoring), blood pressure variability [BPV; SD of systolic blood pressure (SBP)], spontaneous baroreflex sensitivity, HRV [HRV Triangular Index (HRV-TI), standard deviation of the average NN interval (SDNN), low and high frequency power (LF and HF, respectively), and Poincaré plot analysis (SD1, SD2)], and cardiovascular function (pressure-volume loop analysis and proteinuria) were evaluated in male and female 10-wk-old Ren2 and Sprague Dawley rats. The severity of hypertension was greater in Ren2 males (R2-M) than in Ren2 females (R2-F). Increased BPV, suppression of baroreflex gain, decreased HRV, and associated end-organ damage manifested as cardiac dysfunction, myocardial remodeling, elevated proteinuria, and tissue oxidative stress were more pronounced in R2-M compared with R2-F. During the dark cycle, HRV-TI and SDNN were negatively correlated with SBP within R2-M and positively correlated within R2-F; within R2-M, these indexes were also negatively correlated with end-organ damage [left ventricular hypertrophy (LVH)]. Furthermore, within R2-M only, LVH was strongly correlated with indexes of HRV representing predominantly vagal (HF, SD1), but not sympathetic (LF, SD2), variability. These data demonstrated relative protection in females from autonomic dysfunction and end-organ damage associated with elevated blood pressure in the Ren2 model of hypertension.

Through both genomic and nongenomic actions, ovarian hormones and their metabolites have significant effects on the central nervous system to modulate a variety of regulatory systems, including the cardiovascular system. The major metabolite of progesterone, 3α-hydroxy-dihydroprogesterone, is the most potent endogenous positive modulator of GABA(A) receptors known and central nervous system levels of this progesterone metabolite fluctuate with the ovarian cycle and are elevated in pregnant animals. Pregnancy is associated with attenuated arterial baroreflex sympathoexcitation and increased tonic GABAergic inhibition of the rostral ventrolateral medulla (RVLM) likely contributes. The current experiments were performed to determine if the effects of pregnancy on arterial baroreflex control of renal sympathetic nerve activity could be mimicked by microinjection of the neuroactive progesterone metabolite into the RVLM. Compared to control values, 15 min after microinjection of 3α-hydroxy-dihydroprogesterone into the RVLM (n=10), baseline renal sympathetic nerve activity was decreased to 82% of baseline, and the range (157±10 to 131±11%) and maximum nerve activity (164±9 to 136±12%) for the arterial baroreflex curves were decreased. In contrast, microinjection of the inactive isomer, 3β-hydroxy-dihydroprogesterone into the RVLM (n=9), had no effect on baseline nerve activity or the arterial baroreflex nerve activity range or maximum. Thus, although multiple mechanisms likely contribute to pregnancy associated changes in baroreflex function, these experiments suggest that increased levels of 3α-hydroxy-dihydroprogesterone in the RVLM might contribute., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The purpose of this review is to delineate the general features of endocrine regulation of the baroreceptor reflex, as well as specific contributions during pregnancy. In contrast to the programmed changes in baroreflex function that occur in situations initiated by central command (e.g., exercise or stress), the complex endocrine milieu often associated with physiological and pathophysiological states can influence the central baroreflex neuronal circuitry via multiple sites and mechanisms, thereby producing varied changes in baroreflex function. During pregnancy, baroreflex gain is markedly attenuated, and at least two hormonal mechanisms contribute, each at different brain sites: increased levels of the neurosteroid 3alpha-hydroxy-dihydroprogesterone (3alpha-OH-DHP), acting in the rostral ventrolateral medulla (RVLM), and reduced actions of insulin in the forebrain. 3alpha-OH-DHP appears to potentiate baroreflex-independent GABAergic inhibition of premotor neurons in the RVLM, which decreases the range of sympathetic nerve activity that can be elicited by changes in arterial pressure. In contrast, reductions in the levels or actions of insulin in the brain blunt baroreflex efferent responses to increments or decrements in arterial pressure. Although plasma levels of angiotensin II are increased in pregnancy, this is not responsible for the reduction in baroreflex gain, although it may contribute to the increased level of sympathetic nerve activity in this condition. How these different hormonal effects are integrated within the brain, as well as possible interactions with additional potential neuromodulators that influence baroreflex function during pregnancy and other physiological and pathophysiological states, remains to be clearly delineated.

The nucleus tractus solitarius (nTS) of the brainstem receives sensory afferent inputs, processes that information, and sends projections to a variety of brain regions responsible for influencing autonomic and respiratory output. The nTS sends direct projections to the rostral ventrolateral medulla (RVLM), an area important for cardiorespiratory reflexes and homeostasis. Since the net reflex effect of nTS processing ultimately depends on the properties of output neurons, we determined the characteristics of these RVLM-projecting nTS neurons using electrophysiological and immunohistochemical techniques. RVLM-projecting nTS neurons were identified by retrograde tracers. Patch clamp analysis in the horizontal brainstem nTS slice demonstrated that RVLM-projecting nTS cells exhibit constant latency solitary tract evoked excitatory postsynaptic currents (EPSCs), suggesting they receive strong monosynaptic contacts from visceral afferents. Three distinct patterns of action potential firing, associated with different underlying potassium currents, were observed in RVLM-projecting cells. Following activation of the chemoreflex in conscious animals by 3 h of acute hypoxia, 11.2+/-1.9% of the RVLM-projecting nTS neurons were activated, as indicated by positive Fos-immunoreactivity. Very few RVLM-projecting nTS cells were catecholaminergic. Taken together, these data suggest that RVLM projecting nTS neurons receive strong monosynaptic inputs from sensory afferents and a subpopulation participates in the chemoreflex pathway., ((c) 2010 IBRO. Published by Elsevier Ltd. All rights reserved.)

Polarization gratings can be realized by polarization holographic recording in photoanisotropic materials. In this paper, we study two types of polarization gratings. One is recorded with two orthogonally circularly (OC) polarized beams and the other one with two orthogonally linearly (OL) polarized beams. The interference of both cases is explored beyond the small recording angle regime. A novel method is proposed to represent the polarization states of the modulation. The diffraction by polarization gratings is studied with rigorous diffraction theory. Simulations based on the Finite Element Method are performed for both OC and OL polarization gratings at small and large recording angles.

Depressor responses to peripheral or central infusion of Angiotensin II type 1 (AT(1)) receptor antagonists (AT(1)X) are greater in pregnant (P) compared to nonpregnant (NP) animals. AT(1) and ionotropic excitatory amino acid (EAA) receptors contribute to pressor responses to GABA(A) receptor blockade with bicuculline (Bic) in the paraventricular nucleus (PVN) of male rats. Therefore, we hypothesized that GABAergic inhibition is decreased and AT(1) receptors play a greater excitatory role in the PVN of P versus NP rats. Unilateral microinjection of Bic was performed before (Bic(1)), after AT(1)X (Bic(2)), and after AT(1)X + EAA blockade (kynurenate, Kyn) (Bic(3)) in the PVN. Increases in mean arterial pressure (MAP: NP=20+/-2; P=12+/-2 mmHg), heart rate (HR: NP=57+/-6; P=19+/-6 beats/min) and renal sympathetic nerve activity (RSNA: NP=70+/-9; P=33+/-7%) due to Bic (Bic(1)) were attenuated in P rats. Responses to AT(1)X and Kyn alone were insignificant in both groups. In NP rats, AT(1)X attenuated (+12+/-4 mmHg), and AT(1)X + Kyn further decreased the pressor response to Bic in the PVN (+6+/-2 mmHg). In P rats AT(1)X reduced the pressor response to Bic (+5+/-1 mm Hg), and Kyn had no additional effect (+3+/-1 mmHg). Effects of PVN Bic to alter the autospectra of RSNA were suppressed by prior AT(1)X and Kyn in both groups. Thus, tonic GABAergic inhibition is decreased and the contribution of AT(1) receptors in the PVN may be greater in P rats.

Group I metabotropic glutamate receptors (mGluRs) are G-coupled receptors that modulate synaptic activity. Previous studies have shown that Group I mGluRs are present in the nucleus of the solitary tract (NTS), in which many visceral afferents terminate. Microinjection of selective Group I mGluR agonists into the NTS results in a depressor response and decrease in sympathetic nerve activity. There is, however, little evidence detailing which phenotypes of neurons within the NTS express Group I mGluRs. In brainstem slices, we performed immunohistochemical localization of Group I mGluRs and either glutamic acid decarboxylase 67 kDa isoform (GAD67), neuronal nitric oxide synthase (nNOS) or tyrosine hydroxylase (TH). Fluoro-Gold (FG, 2%; 15 nl) was microinjected in the caudal ventrolateral medulla (CVLM) of the rat to retrogradely label NTS neurons that project to CVLM. Group I mGluRs were distributed throughout the rostral-caudal extent of the NTS and were found within most NTS subregions. The relative percentages of Group I mGluR expressing neurons colabeled with the different markers were FG (6.9+/-0.7) nNOS (5.6+/-0.9), TH (3.9+/-1.0), and GAD67 (3.1+/-1.4). The percentage of FG containing cells colabeled with Group I mGluR (13.6+/-2.0) was greater than the percent colabeled with GAD67 (3.1+/-0.5), nNOS (4.7+/-0.5), and TH (0.1+/-0.08). Cells triple labeled for FG, nNOS, and Group I mGluRs were identified in the NTS. Thus, these data provide an anatomical substrate by which Group I mGluRs could modulate activity of CVLM projecting neurons in the NTS.

Pregnancy is characterized by elevated heart rate and decreased total peripheral resistance and arterial blood pressure. Plasma volume is expanded and plasma osmolality is decreased, yet vasopressin secretion in pregnant animals, including humans, is no different than levels in the nonpregnant state. Although reflex compensatory sympathoexcitation is suppressed, baseline sympathetic nerve activity to the heart and vasculature is well maintained or slightly elevated in pregnancy. Clearly there are central nervous system (CNS) adaptations in systems for regulation of cardiovascular and body fluid homeostasis in pregnant animals. The paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus are important CNS sites for control of sympathetic nerve activity and vasopressin secretion. Nitric oxide (NO), an important neuromodulator in these hypothalamic nuclei, contributes to tonic inhibition of neurosecretory and pre-autonomic neurons. Alterations in NO within the PVN and SON could contribute to changes in regulation of vasopressin and sympathetic nerve activity in pregnancy. In the present study, nitric oxide synthase (NOS) activity (NADPH-diaphorase staining), neuronal NOS (nNOS) protein, and nNOS mRNA were assessed in nonpregnant estrus stage and near-term pregnant rats. nNOS mRNA, protein, and activity were greater in the PVN than in the SON. In the PVN only, pregnancy was associated with significant decreases in all three measurements for assessment of nNOS. Thus decreased NO production and relative disinhibition of the PVN may contribute to maintenance of baseline vasopressin secretion and baseline sympathetic nerve activity in the pregnant state.

During baroreceptor unloading, sympathoexcitation is attenuated in near-term pregnant compared with nonpregnant rats. Alterations in balance among different excitatory and inhibitory inputs within central autonomic pathways likely contribute to changes in regulation of sympathetic outflow in pregnancy. Both baroreflex-dependent and baroreflex-independent GABAergic inputs inhibit sympathoexcitatory neurons within rostral ventrolateral medulla (RVLM). The present experiments tested the hypothesis that influence of baroreflex-independent GABAergic inhibition of RVLM is greater in pregnant compared with nonpregnant rats. Afferent baroreceptor inputs were eliminated by bilateral sinoaortic denervation in inactin-anesthetized rats. In pregnant compared with nonpregnant rats, baseline mean arterial pressure (MAP) was lower (pregnant = 75 +/- 6 mmHg, nonpregnant = 115 +/- 7 mmHg) and heart rate was higher (pregnant = 381 +/- 10 beats/min, nonpregnant = 308 +/- 10 beats/min). Pressor and sympathoexcitatory [renal sympathetic nerve activity, (RSNA)] responses due to bilateral GABA(A) receptor blockade (bicuculline, 4 mM, 100 nl) of the RVLM were greater in pregnant rats (delta MAP: pregnant = 101 +/- 4 mmHg, nonpregnant = 80 +/- 6 mmHg; delta RSNA: pregnant = 182 +/- 23% control, nonpregnant = 133 +/- 10% control). Unexpected transient sympathoexcitatory effects of angiotensin AT(1) receptor blockade in the RVLM were greater in pregnant rats. Although excitatory responses to bicuculline were attenuated by prior RVLM AT1 receptor blockade in both groups, pressor responses to disinhibition of the RVLM remained augmented in pregnant rats. Increased influence of baroreflex-independent GABAergic inhibition in RVLM could contribute to suppressed sympathoexcitation during withdrawal of arterial baroreceptor input in pregnant animals.

The caudal ventrolateral medulla (CVLM) provides tonic inhibitory and also excitatory inputs to the rostral ventrolateral medulla (RVLM). These experiments evaluated the role of RVLM gamma-amino butyric acid (GABA) receptor subtypes and glycine receptors in mediating CVLM sympathoinhibition. In Inactin anesthetized female rats, the CVLM and RVLM were functionally defined by pressor and depressor responses to microinjected GABA (500 pmol, 50 nl). Although reduced, pressor and sympathoexcitatory responses due to inhibition of the CVLM with GABA persisted following ipsilateral RVLM GABA(A) receptor blockade (bicuculline, BIC, 400 pmol, 100 nl; n=12) in rats with contralateral nucleus tractus solitarius (NTS) lesion. In the presence of either ipsilateral (+contralateral NTS lesion; n=8) or bilateral (n=6) GABA(A) and GABA(B) receptor blockade of the RVLM (400 pmol BIC+400 pmol CGP35348, 100 nl), inhibition of the CVLM still increased MAP and renal sympathetic nerve activity (RSNA). Thus neither GABA(B) receptors nor a contralateral CVLM to RVLM GABAergic pathway explains residual responses to CVLM blockade. The addition of strychnine (300 pmol, 100 nl) to the RVLM eliminated responses to CVLM inhibition, suggesting that a GABA(A) and GABA(B) independent sympathoinhibitory influence from CVLM to RVLM is mediated by glycine receptors. Decreases in MAP and RSNA due to activation of the CVLM with glutamate (500 pmol, 50 nl) were reversed to increases in the presence of RVLM GABA(A) receptor blockade (n=7). Thus, a sympathoexcitatory pathway from the CVLM can be activated in the presence of RVLM GABA receptor blockade, but sympathoinhibitory influences from the CVLM predominate.

Upon return from spaceflight or resumption of normal posture after bed rest, individuals often exhibit cardiovascular deconditioning. Although the mechanisms responsible for cardiovascular deconditioning have yet to be fully elucidated, alterations within the central nervous system have been postulated to be involved. The paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus are important brain regions in control of sympathetic outflow and body fluid homeostasis. Nitric oxide (NO) modulates the activity of PVN and SON neurons, and alterations in NO transmission within these brain regions may contribute to symptoms of cardiovascular deconditioning. The purpose of the present study was to examine nitric oxide synthase (NOS) activity and expression in the PVN and SON of control and hindlimb unloaded (HU) rats, an animal model of cardiovascular deconditioning. The number of neurons exhibiting NOS activity as assessed by NADPH-diaphorase staining was significantly greater in the PVN but not SON of HU rats. Western blot analysis revealed that neuronal NOS (nNOS) but not endothelial NOS (eNOS) protein expression was higher in the PVN of HU rats. In the SON, there was a strong trend for an increase in nNOS (p=0.052) and a significant increase in eNOS expression in HU rats. Our results suggest that increased nNOS in the PVN contributes to autonomic and humoral alterations following cardiovascular deconditioning. In contrast, the functional significance of increases in nNOS and eNOS protein in the SON may be related to alterations in vasopressin release observed previously in HU rats.

Exposure to a period of microgravity or bed rest produces several physiological adaptations. These changes, which include an increased incidence of orthostatic intolerance, have an impact when people return to a 1G environment or resume an upright posture. Compared with males, females appear more susceptible to orthostatic intolerance after exposure to real or simulated microgravity. Decreased arterial baroreflex compensation may contribute to orthostatic intolerance. We hypothesized that female rats would exhibit a greater reduction in arterial baroreflex function after hindlimb unloading (HU) compared with male rats. Mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded in conscious animals after 13-15 days of HU. Baseline HR was elevated in female rats, and HU increased HR in both genders. Consistent with previous results in males, baroreflex-mediated activation of RSNA was blunted by HU in both genders. Maximum RSNA in response to decreases in MAP was reduced by HU (male control 513 +/- 42%, n = 11; male HU 346 +/- 38%, n = 13; female control 359 +/- 44%, n = 10; female HU 260 +/- 43%, n = 10). Maximum baroreflex increase in RSNA was lower in females compared with males in both control and HU rats. Both female gender and HU attenuated baroreflex-mediated increases in sympathetic activity. The combined effects of HU and gender resulted in reduced baroreflex sympathetic reserve in females compared with males and could contribute to the greater incidence of orthostatic intolerance in females after exposure to spaceflight or bed rest.

New designs of lightguide systems, which emit linear polarized light with a high efficiency for transmissive and transflective LCD applications, are presented. These systems are equipped with nano- and/or micro-structured films or coatings, which emit highly collimated or diffuse linearly polarized light with a high efficiency. The films are based on polarization-selective scattering, reflection, or diffraction of light and their properties can be tuned to a large extent dependent on their envisioned application. For instance, edge-lit lightguide systems are discussed, which combine a range of desirable features such as a high transparency in direct view, a direct emission of light at normal angles to the plane of the lightguide, and a purely unidirectional out-coupling of light towards the LCD-side.

Pregnancy results in attenuated baroreflex mediated sympathoexcitatory responses which may be due to potentiation of gamma-aminobutyric acid (GABA) inhibition in the rostral ventrolateral medulla (RVLM). The major metabolite of progesterone, 3alpha-hydroxy-dihydroprogesterone (3alpha-OH-DHP), which is elevated in pregnancy, is a potent neurosteroid positive modulator of GABA(A) receptors, and sensitivity of GABA(A) receptors to 3alpha-OH-DHP is dependent on the receptor subunit composition. The purpose of this study was to evaluate the GABA(A) alpha(1) and alpha(2) receptor subunit mRNA and protein expression in the RVLM of nonpregnant and late term pregnant rats. Micropunches of RVLM were collected from nonpregnant and late term pregnant rats and the expression levels of GABA(A) alpha(1) and alpha(2) receptor subunits were analyzed using quantitative competitive reverse transcriptase polymerase chain reaction (RT-PCR) and immunoblot techniques. The competitive RT-PCR analysis allows comparison of expression levels between different mRNA, and the mRNA expression level of GABA(A) alpha(1) was several hundred fold greater than GABA(A) alpha(2) in both groups. However, this relative distribution of GABA(A) alpha(1) and alpha(2) receptor subunits protein or mRNA expression was not altered in late term pregnant compared to nonpregnant rats. These data demonstrate, that within the RVLM of both nonpregnant and late term pregnant rats, the relative expression levels of GABA(A) alpha(1,2) receptor subunits favor GABA(A) receptors susceptible to positive modulation by progesterone metabolites.

Attenuated baroreflex-mediated increases in renal sympathetic nerve activity (RSNA) in hindlimb unloaded (HU) rats apparently are due to changes within the central nervous system. We hypothesized that GABA(A) receptor-mediated inhibition of the rostral ventrolateral medulla (RVLM) is increased after hindlimb unloading. Responses to bilateral microinjection of the GABA(A) antagonist (-)-bicuculline methiodide (BIC) into the RVLM were examined before and during caudal ventrolateral medulla (CVLM) inhibition in Inactin-anesthetized control and HU rats. Increases in mean arterial pressure (MAP), heart rate (HR), and RSNA in response to BIC in the RVLM were significantly enhanced in HU rats. Responses to bilateral CVLM blockade were not different. When remaining GABA(A) inhibition in the RVLM was blocked by BIC during CVLM inhibition, the additional increases in MAP and RSNA were significantly greater in HU rats. These data indicate that GABA(A) receptor-mediated inhibition of RVLM neurons is augmented after hindlimb unloading. Effects of input from the CVLM were unaltered. Thus, after cardiovascular deconditioning in rodents, the attenuated increase in sympathetic nerve activity in response to hypotension is associated with greater GABA(A) receptor-mediated inhibition of RVLM neurons originating at least in part from sources other than the CVLM.

The baroreflex function curve is shifted to lower operating pressures, efferent sympathoexcitatory responses are attenuated, and sympathoinhibitory responses are potentiated in pregnant compared with virgin rats. It has been proposed that during pregnancy, elevated levels of 3 alpha-hydroxy-dihydroprogesterone (3 alpha-OH-DHP), a major metabolite of progesterone, may contribute to this difference, because acute intravenous administration of 3 alpha-OH-DHP to virgin female rats mimics the effects of pregnancy on the baroreflex. To determine whether changes in the afferent limb might contribute to these baroreflex responses, the effects of pregnancy and 3 alpha-OH-DHP on aortic depressor nerve activity were assessed in the current study. Baroreceptor discharge curves were obtained in Inactin-anesthetized rats by recording aortic nerve activity during ramp increases and decreases in mean arterial pressure (MAP) [intravenous phenylephrine and nitroprusside infusion] before [(control, C) 15 min (E1), and 30 min (E2) after 3 alpha-OH-DHP (220 microg/kg bolus + 22 microg x kg(-1) x min(-1) infusion iv)]. Baseline blood pressure was significantly lower in pregnant (109 +/- 4.4 mmHg) compared with virgin (122 +/- 2.8 mmHg) rats. The only significant difference in the baroreceptor discharge curves was a decrease in curve midpoint in pregnant rats (virgin = 140 +/- 2.7 vs. pregnant = 124 +/- 3.6 mmHg). 3 alpha-OH-DHP had no effect on afferent baroreceptor discharge curves in either virgin or pregnant groups. These results suggest that pressure-dependent baroreceptor resetting may contribute to a shift in the baroreflex curve to lower operating pressures, but cannot completely explain differences in baroreflex function between virgin and pregnant animals.

Pregnant women often experience orthostatic hypotension, and pregnancy is associated with increased susceptibility to hemorrhagic hypotension. Experiments evaluating arterial baroreflex control of efferent sympathetic nerve activity in virgin and term-pregnant rats revealed that arterial baroreflex sympathoexcitation is attenuated, while sympathoinhibitory responses are well-maintained or potentiated. Following a hypotensive challenge, pregnant animals exhibit attenuated Fos expression in the rostral ventrolateral medulla (RVLM), suggesting that unloading of arterial baroreceptors results in less excitation of presympathetic neurons in the brain stem. Other experiments, in which afferent baroreceptor discharge was recorded, suggest that this was not due to differences in afferent baoreceptor function. GABAergic mechanisms are responsible for tonic inhibition of sympathoexcitatory neurons in the RVLM and the major metabolite of progesterone, 3 alpha-OH-dihydro-progesterone (3 alpha-OH-DHP), which is elevated in pregnancy, is the most potent endogenous positive modulator of CNS GABAA receptor function. Additional experiments revealed that acutely administered 3 alpha-OH-DHP, either intravenously or directly into the RVLM, mimicked the effects of pregnancy on baroreflex control of efferent sympathetic nerve activity and potentiated pressure sensitivity of spinally projecting RVLM neurons. Preliminary experiments using semiquantitative RT-PCR, evaluated the relative expression of three subunits (alpha 1-3) of the GABAA receptor, and suggest that chronic exposure to elevated levels of ovarian hormones can result to changes in GABAA receptor subunit composition. It is likely that changes in control of sympathetic outflow in pregnancy are related to complex interactions between genomic and nongenomic actions of ovarian hormones and metabolites.

Objective: To determine whether there is evidence of platelet activation following in vivo cocaine administration in humans, as cocaine abuse is associated with myocardial infarction and stroke, and platelet activation leading to thrombosis is a possible mechanism., Setting: University hospital., Design and Subjects: Following a randomised, double blind crossover design, 14 healthy volunteers were studied twice, receiving cocaine (2 mg/kg intranasally) once and placebo once. Flow cytometric analysis of P-selectin expression (an alpha granule membrane protein found on the surface of activated platelets), quantification of the platelet specific proteins platelet factor 4 and beta thromboglobulin, and measurement of platelet containing microaggregate and platelet microparticle (fragment) formation were used to assess platelet activation. Circulating von Willebrand factor antigen (vWF) was measured to evaluate a possible role of endothelial stimulation concurrent with platelet activation., Results: There was an increase in both platelet factor 4 (mean (SD), 16 (7) to 39 (22) IU/ml, p = 0. 04) and beta thromboglobulin (70 (20) to 98 (26) IU/ml, p < 0.01) at 120 minutes following cocaine administration. Platelet containing microaggregate formation was increased at 40 minutes (from 47 (3.2)% to 54 (2.0)%, p < 0.001) and 80 minutes (55 (2.5)%, p = 0.04). Bleeding time decreased following cocaine from 10 (1) to 9 (1) minutes (p = 0.07). No changes in any of the measured variables were noted following placebo administration., Conclusions: Cocaine exposure causes platelet activation, alpha granule release, and platelet containing microaggregate formation. These data support the view that cocaine, even at the relatively low doses commonly self administered by occasional abusers, may promote thrombosis and predispose healthy individuals to ischaemic events. Platelet inhibitors should be considered early in any patient with suspected cocaine related ischaemia.

Fos and dopamine beta-hydroxylase immunoreactivity were evaluated in the brain stems of 21-day pregnant and virgin female rats injected with either hydralazine (HDZ; 10 mg/kg iv) or vehicle. HDZ produced significant hypotension in both groups, although baseline blood pressure was lower in pregnant rats (96 +/- 2.5 mmHg) than in virgin female rats (121 +/- 2.8 mmHg). There were no differences in Fos immunoreactivity in the brain stems of pregnant and virgin female rats after vehicle treatment. HDZ-induced hypotension significantly increased Fos expression in both groups; however, the magnitude of the increases differed in the caudal ventrolateral medulla (CVL), the area postrema (AP), and the rostral ventrolateral medulla (RVL). Fos expression after HDZ in pregnant rats was augmented in noncatecholaminergic neurons of the CVL but was attenuated in the AP and in noncatecholaminergic neurons in the RVL. These results are consistent with differences in the sympathetic response to hypotension between pregnant and virgin female rats and indicate that the central response to hypotension may be different in pregnant rats.

The major metabolite of progesterone, 3 alpha-OH-dihydroprogesterone (3 alpha-OH-DHP), is the most potent endogenous positive modulator of central nervous system GABAA receptors. Acute intravenous administration of 3 alpha-OH-DHP to virgin female rats potentiates arterial baroreflex sympathoinhibitory responses. The current experiments tested the possibility that circulating 3 alpha-OH-DHP potentiates central GABAergic influences in the rostral ventrolateral medulla (RVLM). The unit activity of spontaneously active, spinally projecting, and arterial pressure-sensitive neurons was recorded in the RVLM of urethan-anesthetized rats. Arterial pressure sensitivity of RVLM neurons was tested before (control) and 10 min after bolus injection (44 microliters i.v.) of 3 alpha-OH-DHP (1.12 micrograms/kg, n = 19) or vehicle (40% beta-cyclodextrin, n = 8). Both threshold pressure and saturation pressure for inhibition of RVLM neurons were decreased after acute administration of a physiological dose of 3 alpha-OH-DHP (1.12 micrograms/kg i.v.), which produces plasma concentrations similar to those seen during pregnancy (20-30 ng/ml), suggesting potentiated responsiveness to endogenously released GABA. Following suppression by 3 alpha-OH-DHP, high doses of the inactive stereoisomer 3 beta-OH-DHP (112-224 micrograms/kg i.v.; n = 8) restored unit activity, presumably by displacing 3 alpha-OH-DHP from the neurosteroid binding site on GABAA receptors.

Neurosteroids bind to unique sites on the GABA(A) receptor complex and modulate receptor function. The effects of neurosteroids on GABA(A) receptors have been well characterized in forebrain regions. However, little is known about their effects on GABA(A) receptors in the medulla, especially those areas involved in autonomic reflex pathways. Stimulation of [3H]flunitrazepam binding to the GABA(A) receptor by two progesterone metabolites, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha-OH-DHP) and 3beta-hydroxy-5alpha-pregnan-20-one (3beta-OH-DHP), was studied using autoradiographic methods in the medulla and cerebellum of female rats at estrus. [3H]Flunitrazepam binding was enhanced by 3alpha-OH-DHP in every nucleus examined in the medulla and cerebellum. This effect was stereoselective since 3beta-OH-DHP had no effect on binding in any region. No differences were observed in the degree of stimulation of [3H]flunitrazepam binding by 3alpha-OH-DHP among medullary brain regions. However, in the cerebellum, the stimulation of binding was significantly greater in the granular layer than in the molecular layer. Stimulation of [3H]flunitrazepam binding by 3alpha-OH-DHP in nuclei involved in the baroreflex pathways supports previous studies which report that neurosteroids modulate autonomic regulation of blood pressure. These actions may also underlie alterations in autonomic function during pregnancy.

Previous experiments in anesthetized rats suggested that sympathoexcitatory responses were attenuated in pregnant (P) rats. The major progesterone metabolite, 3alpha-hydroxy-dihydroprogesterone (3alpha-OH-DHP), is elevated in pregnancy and reportedly potentiates central gamma-aminobutyric acidergic mechanisms, whereas the 3beta-isomer (3beta-OH-DHP) is inactive. This study obtained baroreflex curves in conscious rats by recording reflex changes in renal sympathetic nerve activity (RSNA) and heart rate (HR) due to perturbations in mean arterial pressure (MAP) [i.v. phenylephrine (PE) and nitroprusside (NTP)] in P rats and in virgin (V) rats before (control) and 15 min after infusion (i.v.) of 3alpha-OH-DHP or 3beta-OH-DHP. Baseline MAP was lower in P rats (P = 102 +/- 2 vs. V = 124 +/- 3 mmHg). Compared with V rats, P rats exhibited less "sympathetic reserve" to respond to a hypotensive challenge, as evidenced by decreased maximum NA and decreased slope of RSNA baroreflex responses to NTP. However, HR baroreflex curves were similar in P and V rats. Acute intravenous administration of 3alpha-OH-DHP to conscious V rats mimicked the effects of pregnancy. Baroreflex sympathoexcitatory responses were decreased, whereas baroreflex control of HR was unaffected. The 3beta-isomer of DHP had no effect on NA or HR baroreflex responses. These results suggest that pregnancy may have differential effects on baroreflex control of sympathetic outflow and HR, and the major metabolite of progesterone, 3alpha-OH-DHP, may contribute to this adaptation of pregnancy.

Acute and chronic cocaine administration has been reported to change endocrine and neurochemical functions in animals and human drug abusers. This study examined the effects of acute cocaine administration on anterior pituitary and gonadal hormones in male human volunteers without a history of drug abuse. Using a double-blind, randomized study design, luteinizing hormone, follicle-stimulating hormone (FSH), prolactin and testosterone levels were measured in 12 healthy men before and after intranasal administration of 2 mg/kg cocaine or placebo. Each subject was studied twice, serving as his own control. Compared to placebo, both luteinizing hormone, and, to a lesser degree, follicle-stimulating hormone levels increased significantly after cocaine, reaching a peak value 60 min after the administration of the study drug. This pattern is consistent with a possible cocaine induced rise in gonadotropin-releasing hormone and subsequent rise in luteinizing hormone and follicle-stimulating hormone due to stimulation of gonadotroph cells in the pituitary gland. Neither cocaine nor placebo induced a change in testosterone levels. Prolactin levels showed a decrease from base line after both placebo and cocaine administration, with a significantly more pronounced decrease after cocaine. This likely reflects the combination of the physiologic diurnal variation in prolactin secretion and an added inhibitory effect on prolactin due to cocaine. These findings show that the acute administration of cocaine significantly alters anterior pituitary hormonal release patterns.

To evaluate whether cocaine administration to human volunteers in vivo increases platelet aggregation, 12 healthy male volunteers were studied twice in a prospective, double-blinded fashion. There was a decrease in aggregation following cocaine exposure compared to placebo, which was most prominent at high doses of adenosine diphosphate.

The current study was performed to determine whether baroreflex resetting after acute administration of converting enzyme inhibitors (CEIs) was dependent on the concomitant decrease in mean arterial pressure (MAP). Reflex changes in lumbar sympathetic nerve activity (LSNA) due to increases and decreases in MAP [i.v. phenylephrine (PE) and nitroprusside infusions] were determined in normotensive and renal hypertensive (1-kidney, 1-clip) anesthetized WKY rats 1) before (control), 2) 15 min after intravenous captopril (2 mg/kg) or enalaprilat (300 micrograms), and 3) 15 min after MAP was returned to pre-CEI levels with intravenous PE. CEIs decreased MAP and caused a leftward shift of the MAP-LSNA curve toward a lower operating pressure range in all hypertensive and in one group of normotensive rats. The baroreflex curve remained shifted to the left even after MAP was restored to pre-CEI levels by infusion of PE. Thus CEIs cause a pressure-independent resetting of baroreflex control of sympathetic outflow within 15 min. This effect of CEIs is most likely due to elimination of a central nervous system effect of circulating angiotensin II and could contribute to the antihypertensive actions of this class of compounds.

Background: OPC-18790 is a water-soluble quinolinone derivative that shares the pharmacological properties of vesnarinone and that may be useful for treating heart failure. We studied the contribution and relative dose sensitivities of the inotropic, lusitropic, and vascular effects of OPC-18790 in patients with dilated cardiomyopathy., Methods and Results: Pressure-volume (PV) analysis was performed in 17 patients who received either 5 micrograms.kg-1.min-1 (low dose, n = 10) or 10 micrograms.kg-1.min-1 (high dose, n = 7) OPC-18790 by 1-hour IV infusion. Right heart pressures and flow and left heart PV relations (conductance catheter) were measured at baseline and every 15 minutes during infusion. Transient inferior vena caval obstruction was used to determine PV relations. Both doses produced venodilation reflected by a 10% decline in left ventricular end-diastolic volume and a 30% fall in atrial and pulmonary artery pressures. Arterial dilation was four times greater at the high dose, with an approximately 40% fall in effective arterial elastance and systemic resistance. Contractility rose by 25% to 100% (depending on PV index) with both doses. Ventricular-arterial coupling (ratio of ventricular end-systolic to arterial elastances) was approximately 0.25 at baseline and doubled (or tripled) at low (or high) dose, correlating with improved efficiency. Isovolumetric relaxation shortened, whereas the diastolic PV relation was generally unchanged. Heart rate was unaltered., Conclusions: OPC-18790 has potent venous and arterial vasodilator effects and moderate inotropic and lusitropic effects without a change in heart rate. These combined actions suggest a unique potential of OPC-18790 for heart failure treatment.

Background: A temporal relationship has been established between cocaine ingestion and myocardial infarction, and a cocaine-induced increase in platelet aggregation has been suggested as a possible explanation. However, the mechanisms of cocaine associated coronary thrombosis have yet to be completely elucidated. For this reason, we examined the in vitro effect of cocaine and its metabolites on platelet aggregation., Methods: Platelet aggregation was tested by obtaining platelet rich plasma from 42 healthy volunteers and incubating the platelet rich plasma in six concentrations of cocaine (ranging from 1.47 to 2940 nmol) for 10 minutes prior to aggregation with ADP 1 microM. The same procedure was used to test the effect of two cocaine metabolites, benzoylecgonine and ecgonine methyl ester, on platelet aggregation. Abnormal results were confirmed by inducing aggregation with ADP at higher concentrations (2.4 and 10 microM) and with arachidonic acid (624 microM)., Results: At increasing concentrations, cocaine progressively inhibited ADP and arachidonic acid induced platelet aggregation. No effect was seen with benzoyl ecgonine or ecgonine methyl ester as compared to saline., Conclusions: These data suggest that under certain conditions cocaine may negatively affect hemostasis by decreasing platelet aggregation.

The effects of acute cocaine administration on the pituitary adrenal axis in humans without a history of drug abuse are unknown. The authors studied 12 male volunteers twice in a double-blinded, placebo-controlled, randomized fashion. After intranasal administration of 2 mg/kg cocaine, cortisol levels were significantly higher than after placebo administration. The authors concluded that acute administration of cocaine to humans increases cortisol secretion.

Although beta blockers have demonstrated a salutary effect on ventricular function in patients with heart failure, it is unclear whether a nonselective third-generation beta blocker produces different hemodynamic and energetic effects than a second-generation beta 1 selective agent. In 30 male patients with heart failure, we retrospectively analyzed hemodynamic data from 2 protocols examining the effects of a nonselective beta antagonist bucindolol (n = 15), and a highly selective beta 1 antagonist metoprolol (n = 15). Both studies were conducted in a similar fashion with patients undergoing cardiac catheterization before and after receiving 3 months of beta blockade. Both groups were matched at baseline in terms of ventricular function. beta blockade resulted in similar reductions in heart rate and similar improvements in ejection fraction, ventricular volumes, stroke and minute work, peak +dP/dt, and isovolumic relaxation in both groups. Only patients taking bucindolol had a significant within-group decrease in resting left ventricular end-diastolic pressure. The metoprolol group had a greater decrease in coronary sinus blood flow and myocardial oxygen consumption. Bucindolol increased cardiac index more than metoprolol, but did not increase stroke volume index more than metoprolol. The bucindolol group had an increase in systolic elastance, whereas the metoprolol group had a parallel left shift in this relation. Thus, metoprolol reduces coronary blood flow and myocardial oxygen consumption more than bucindolol, whereas bucindolol produces slightly more favorable improvements in resting cardiac index and end-diastolic pressure. Otherwise, these 2 agents produced similar hemodynamic changes.

1. Pregnancy is characterized by a 40% increase in blood volume and cardiac output, a decrease in arterial blood pressure and thus a substantial decrease in total peripheral resistance. The aims of the experiments described in this manuscript were: (i) to determine if pregnancy resulted in alterations in baroreflex control of sympathetic outflow; and (ii) to evaluate possible mechanisms for pregnancy-induced changes in control of sympathetic outflow. 2. Arterial baroreflex control of efferent renal sympathetic nerve activity was examined in female pregnant and non-pregnant normotensive Sprague-Dawley and Wistar-Kyoto rats. In both rat strains, pregnancy was associated with a decrease in baseline arterial pressure, a shift in the baroreflex function curve to a lower operating pressure range and an attenuated ability to reflexly increase sympathetic outflow above baseline levels during a hypotensive challenge. Pregnant Sprague-Dawley rats retained their ability to respond to a hypertensive challenge, whereas pregnant Wistar-Kyoto rats exhibited a decreased sensitivity to hypertensive as well as hypotensive challenges. 3. The inhibitory amino acid transmitter, GABA, mediates baroreflex sympatho-inhibition within the rostral ventral lateral medulla (RVLM) of the brainstem. Since 3 alpha-OH dihydroprogesterone (3 alpha-OH-DHP), a major metabolite of progesterone, is elevated in pregnancy and has been reported to potentiate central nervous system GABAA inhibitory responses, experiments were performed to determine if effects of this metabolite of progesterone could contribute to the pregnancy associated changes in control of sympathetic outflow.(ABSTRACT TRUNCATED AT 250 WORDS)