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. Author manuscript; available in PMC: 2016 May 1.
Published in final edited form as: Hypertension. 2015 Mar 16;65(5):1126–1133. doi: 10.1161/HYPERTENSIONAHA.114.05112

Pro-inflammatory cytokines upregulate sympathoexcitatory mechanisms in the subfornical organ of the rat

Shun-Guang Wei 1, Yang Yu 1, Zhi-Hua Zhang 1, Robert B Felder 1,2
PMCID: PMC4393369  NIHMSID: NIHMS665821  PMID: 25776070

Abstract

Our previous work indicated that the subfornical organ (SFO) is an important brain sensor of blood-borne pro-inflammatory cytokines, mediating their central effects on autonomic and cardiovascular function. However, the mechanisms by which SFO mediates the central effects of circulating pro-inflammatory cytokines remain unclear. We hypothesized that pro-inflammatory cytokines act within the SFO to upregulate the expression of excitatory and inflammatory mediators that drive sympathetic nerve activity. In urethane-anesthetized Sprague-Dawley rats, direct microinjection of TNF-α (25 ng) or IL-1β (25 ng) into SFO increased mean blood pressure, heart rate and renal sympathetic nerve activity within 15–20 minutes, mimicking the response to systemically administered pro-inflammatory cytokines. Pretreatment of SFO with microinjections of the angiotensin II type 1 receptor (AT1R) blocker losartan (1 µg), angiotensin-converting enzyme (ACE) inhibitor captopril (1 µg) or cyclooxygenase (COX)-2 inhibitor NS-398 (2 µg) attenuated those responses. Four hours after the SFO microinjection of TNF-α (25 ng) or IL-1β (25 ng), mRNA for ACE, AT1R, TNF-α and the p55 TNF-α receptor TNFR1, IL-1β and the IL-1R receptor, and COX-2 had increased in SFO, and mRNA for ACE, AT1R and COX-2 had increased downstream in the hypothalamic paraventricular nucleus. Confocal immunofluorescent images revealed that immunoreactivity for TNFR1 and the IL-1 receptor accessory protein, a subunit of the IL-1 receptor, co-localized with ACE, AT1R-like, COX-2 and prostaglandin E2 EP3 receptor immunoreactivity in SFO neurons. These data suggest that pro-inflammatory cytokines act within the SFO to upregulate the expression of inflammatory and excitatory mediators that drive sympathetic excitation.

Keywords: brain renin-angiotensin system, cyclooxygenase-2, paraventricular nucleus, sympathetic nervous system, cytokine receptors

INTRODUCTION

Pro-inflammatory cytokines (PICs) are increased in cardiovascular disease states,1–3 and studies over the past decade have suggested that blood-borne and brain PICs contribute to the neurohumoral activation in heart failure (HF)4 and in some forms of hypertension (HTN).5 We recently demonstrated that the subfornical organ (SFO), a circumventricular organ that lacks a blood-brain barrier (BBB), is an important central nervous system sensor of peripheral inflammation, mediating the effects of circulating PICs on autonomic and cardiovascular function.6 However, the mechanisms by which PICs act within the SFO to influence neurohumoral excitation have not been examined.

The SFO is rich in angiotensin-converting enzyme (ACE) and in angiotensin II (ANG II) type 1 receptors (AT1R),7, 8 key components of the brain renin-angiotensin system (RAS) that activates SFO neurons 9, 10 and drives sympathetic nerve activity in pathophysiological states like HTN and HF.11, 12 PICs contribute to upregulation of brain RAS activity in the hypothalamic paraventricular nucleus (PVN), another brain region that has been implicated in the sympathetic excitation and cardiovascular dysfunction, in HTN 13 and HF.14 Cyclooxygenase (COX), the key enzyme regulating the production of prostaglandin E2 (PGE2) ,15 is also abundantly expressed in the highly vascularized SFO.16 PGE2 increases the firing rate of SFO neurons by disinhibiting inhibitory gamma-aminobutyric acid inputs.17 ANG II infusion induced HTN is reportedly dependent upon the activity of constitutively expressed COX-1 in the SFO,18 and PIC-dependent induction of COX-2 in perivascular macrophages has been implicated in the pathophysiology of HF.19 Thus, inflammatory mechanisms that increase brain RAS activity or PGE2 production in SFO might be expected to increase sympathetic nerve activity.

The present study was undertaken to determine whether the excitatory effects of PICs on cardiovascular function and sympathetic nerve activity are mediated by PIC-induced upregulation of RAS and COX-2 activity in the SFO. Since the SFO projects directly to the PVN,20 which has been implicated as an important source of augmented sympathetic and neuroendocrine activity in HTN and HF,21, 22 we also examined whether PIC activation of the SFO affects the neurochemical milieu downstream in the PVN.

METHODS

Animals

Adult male Sprague-Dawley rats (300–350g) were purchased from Harlan (Indianapolis, IN). Animals were housed in Animal Care Facility at the University of Iowa and fed rat chow ad libitum. All experimental procedures were approved by the University of Iowa Institutional Animal Care and Use Committee. The experimental protocols were conducted in accordance with the National Institutes of Health “Guide for the Care and Use of Laboratory Animals.”

Experimental protocols

  1. Urethane anesthetized rats underwent electrophysiological and hemodynamic recording studies to determine the sympathetic responses to SFO microinjections of TNF-α (25 ng) or IL-1β (25 ng), preceded 10 minutes by SFO microinjection of vehicle (VEH), the AT1R blocker losartan (1 µg), the ACE inhibitor captopril (1µg) or the COX-2 activity inhibitor NS-398 (2µg).

  2. Urethane anesthetized rats received an SFO microinjection of TNF-α (25 ng) or IL-1β (25 ng) or VEH, and were euthanized 4 hours later to collect SFO and PVN tissue to determine the mRNA expression of AT1R, ACE, COX-2 and COX-1, TNF-α, IL-1β, the p55 TNF-α receptor (TNFR1) and the IL-1β receptor (IL-1R).

  3. Urethane anesthetized rats were transcardially perfused with heparinized saline followed by 4% paraformaldehyde in 0.01M PBS to collect brain tissue for immunofluorescent staining. SFO and PVN were cut into 16-micron coronal sections to determine whether TNFR1 and the IL-1 receptor accessory protein (IL-1RAcP) co-localized with AT1R, ACE, COX-2 and the PGE2 receptor EP3.

Drug Administration

SFO microinjection of TNF-α, IL-1β, losartan, captopril and NS-398 was performed via a 35-gauge cannula inserted in a 30-gauge guide cannula that was placed 0.9 mm posterior to bregma, along the midline of the skull (see the online data supplement for details). TNF-α and IL-1β were purchased from Fitzgerald (Acton, MA) and Millipore (Billerica, MA), respectively. Losartan and captopril were purchased from Sigma (St. Louis, MO). All these drugs were dissolved in artificial cerebrospinal fluid (aCSF) for SFO microinjection. NS-398 was purchased from Tocris (Ellisville, MO), and was first dissolved in dimethyl sulfoxide (DMSO) and then diluted in aCSF to make a 5% final DMSO concentration.

Statistical Analysis

All values are expressed as the means ± SEM. The significance of differences among groups was analyzed by 2-way repeated-measure ANOVA followed by post hoc Fisher’s test. Student's t-test was used to determine statistical significance between paired data for a single comparison. p< 0.05 was considered to indicate statistical significance.

Specific Materials and Methods

Please see the online data supplement (http://hyper.ahajournals.org).

RESULTS

Hemodynamic and sympathetic effects of SFO microinjections

TNF-α

SFO microinjection of TNF-α (n=6, Fig. 1A, E, F, G) elicited significant increases in mean blood pressure (MBP), heart rate (HR) and renal sympathetic nerve activity (RSNA) in the rats pretreated with SFO microinjections of VEH. These excitatory responses began within 15–20 minutes after the TNF-α microinjection. The maximum responses of MBP (19.8 ± 2.7 mmHg), HR (75.2 ± 8.5 bpm) and RSNA (81.9 ± 9.2 % change) occurred 2–3 hours after the TNF-α microinjection and remained at higher than baseline level for at least 5 hours. Pretreatment with SFO microinjection of losartan (Fig. 1B, E, F, G), captopril (Fig. 1C, E, F, G) or NS-398 (Fig. 1D, E, F, G) significantly reduced the MBP (10.9 ± 2.6, 12.7 ± 2.9, 9.5 ± 2.6 mmHg, respectively), HR (44.8 ± 8.5, 48.7 ± 8.6 and 38.8 ± 8.2 bpm, respectively) and RSNA (49.1 ± 9.4, 53.7 ± 6.2 % and 45.1 ± 9.3 % changes, respectively) responses to the TNF-α microinjection. SFO microinjections of an equal volume of vehicle (aCSF) had no noticeable effect on baseline MBP (98.3 ± 2.9 mmHg), HR (323 ± 13 bpm) or integrated RSNA (11.2 ± 3.5 mV).

Figure 1.

Figure 1

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Representative tracings (A–D) showing the effects of SFO microinjection of TNF-α (25 ng) on blood pressure (BP, mmHg), heart rate (HR, bpm) and renal sympathetic nerve activity (RSNA), windowed (spikes/s) and integrated (mV), in rats pretreated with SFO vehicle (VEH) (A), captopril (B), losartan (C) and NS-398 (D). Arrows indicate the timing of the microinjections. Scale Bar: 20 min. Grouped data (E–G) showing changes (D) in mean blood pressure (MBP, E), HR (F), and integrated RSNA (G) as a percent (%) of baseline activity. All values are expressed as the mean ± SE. * p<0.05 compared to baseline. † p<0.05 compared to VEH-pretreated animals.

IL-1β

Microinjection of IL-1β into the SFO (n=6, Fig. 2A, E, F, G) also induced substantial and long-lasting increases in MBP, HR and RSNA in the rats pretreated with SFO microinjections of VEH. The excitatory responses to IL-1β began within 15–20 minutes of the IL-1β microinjection. The peak increase in MBP (20.0 ± 2.5 mmHg) occurred at 1–2 hour and was sustained at a higher than baseline level for the remainder of the 3–5 hour recording period. The peak increase in HR (81.2 ± 10.5 bpm) and RSNA (83.5 ± 10.6 % change) occurred 2–3 hours after the IL-1β microinjection and lasted for at least 5 hours. Pretreatment with SFO microinjection of losartan (Fig. 2B, E, F, G), captopril (Fig. 2C, E, F, G) or NS-398 (Fig. 2D, E, F, G) significantly attenuated the MBP (11.2 ± 2.4, 11.8 ± 2.2, 10.7 ± 2.5 mmHg, respectively), HR (44.0 ± 9.0, 49.7 ± 5.9 and 48.7 ± 8.2 bpm, respectively) and RSNA (42.2 ± 7.3 %, 52.0 ± 9.4 % and 47.5 ± 5.5 % changes, respectively) responses to SFO microinjection of IL-1β.

Figure 2.

Figure 2

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Representative tracings (A–D) showing the effects of SFO microinjection of IL-1β (25 ng) on blood pressure (BP, mmHg), heart rate (HR, bpm) and renal sympathetic nerve activity (RSNA), windowed (spikes/s) and integrated (mV), in rats pretreated with SFO vehicle (VEH) (A), captopril (B), losartan (C) and NS-398 (D). Arrows indicate the timing of the microinjections. Scale Bar: 20 min. Grouped data (E–G) showing changes (D) in mean blood pressure (MBP, E), HR (F), and integrated RSNA (G) as a percent (%) of baseline activity. All values are expressed as the mean ± SE. * p<0.05 compared to baseline. † p<0.05 compared to VEH-pretreated animals.

Histological confirmation of SFO microinjection

At the conclusion of each experiment, SFO microinjection sites were examined by light microscopy. Microinjection sites were confirmed by the presence of Pontamine sky blue throughout the SFO, with no dye present in the 3rd ventricle (Fig. S3).

Effects of SFO microinjections on excitatory milieu of SFO and PVN

TNF-α

Real-time PCR analysis of brain tissue obtained 4 hours after the SFO microinjection of TNF-α revealed that mRNA levels for the RAS components, AT1R and ACE, were significantly increased in the SFO (AT1R: 3.32 ± 0.34 vs 1.03 ± 0.12 fold; ACE: 2.87 ±0.30 vs 1.05 ± 0.13 fold) and PVN (AT1R: 2.18 ± 0.23 vs 1.04 ± 0.10 fold; ACE: 2.21 ± 0.33 vs 1.03 ± 0.11 fold) (Fig. 3A, B), compared to SFO microinjection of VEH. There was also a significant increase in COX-2 mRNA in both SFO (4.07 ± 0.42 vs 1.02 ± 0.09 fold) and PVN (2.98 ± 0.24 vs 1.01 ± 0.08 fold), but not in COX-1 mRNA (SFO: 1.44 ± 0.27 vs 1.02 ± 0.12 fold; PVN:1.39 ± 0.16 vs 1.02 ± 0.11 fold) (Fig. 3C, D).

Figure 3.

Figure 3

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Quantitative analysis by real-time PCR showing the mRNA expression of angiotensin-converting enzyme (ACE, A), angiotensin II type-1 receptor (AT1R, B), cyclooxygenase (COX)-2 (C), COX-1 (D), tumor necrosis factor (TNF)-α (TNF-α, E), interleukin (IL)-1β (IL-1β, F), TNF receptor 1 (TNFR1, G) and IL-1 receptor (IL-1R, H) in cerebral cortex (CTX), subfornical organ (SFO) and paraventricular nucleus of hypothalamus (PVN) in rats treated with SFO microinjection of TNF-α or vehicle (VEH). Values are mean ± SEM (n=6–7 for each group) and expressed as a fold change relative to VEH control. *p<0.05 TNF-α vs VEH.

Similarly, 4 hours after SFO microinjection of TNF-α, TNF-α and IL-1β mRNA levels were significantly increased in the SFO (2.58 ± 0.22 vs 1.00 ± 0.09; 2.30 ± 0.38 vs 1.03 ± 0.09 fold, respectively) and the PVN (2.34 ± 0.16 vs 1.03 ± 0.12; 2.00 ± 0.13 vs 1.01 ± 0.07 fold, respectively), compared with microinjection of VEH (Fig. 3E, F). TNFR1 and IL-1R mRNA levels were also increased in both SFO (2.81 ± 0.25 vs 1.01 ± 0.11 to; 2.11 ± 0.34 vs 1.00 ± 0.09 fold, respectively) and PVN (2.55 ± 0.18 vs 1.03 ± 0.12; 1.83 ± 0.12 vs 1.09 ± 0.11 fold, respectively) compared with SFO microinjection of VEH (Fig. 3G, H).

IL-1β

The IL-1β microinjection, like the TNF-α microinjection, significantly increased AT1R and ACE mRNA in the SFO (AT1R: 3.06 ± 0.32 vs 1.00 ± 0.10; ACE: 2.65 ± 0.27 vs 1.01 ± 0.12 fold) and PVN (AT1R: 2.01 ± 0.23 vs 1.08 ± 0.09; ACE: 2.05 ± 0.30 vs 1.01 ± 0.11 fold) (Fig. 4A, B), compared to the SFO microinjection of VEH. COX-2 mRNA was also significantly increased in both SFO (4.23 ± 0.34 vs 1.03 ± 0.09 fold) and PVN (3.25 ± 0.26 vs 1.05 ± 0.10 fold), but COX-1 mRNA was unaffected (SFO: 1.44 ± 0.27 vs 1.12 ± 0.18 fold; PVN: 1.50 ± 0.27 vs 1.08 ±0.17 fold) (Fig. 4C, D).

Figure 4.

Figure 4

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Quantitative analysis by real-time PCR showing the mRNA expression of angiotensin-converting enzyme (ACE, A), angiotensin II type-1 receptor (AT1R, B), cyclooxygenase (COX)-2 (C), COX-1 (D), tumor necrosis factor (TNF)-α (TNF-α, E), interleukin (IL)-1β (IL-1β, F), TNF receptor 1 (TNFR1, G) and IL-1 receptor (IL-1R, H) in cerebral cortex (CTX), subfornical organ (SFO) and paraventricular nucleus of hypothalamus (PVN) in rats treated with SFO microinjection of IL-1β or vehicle (VEH). Values are mean ± SEM (n=6–7 for each group) and expressed as a fold change relative to VEH control. *p<0.05 IL-1β vs VEH.

TNF-α and IL-1β mRNA were significantly elevated in the SFO (2.39 ± 0.27 vs 1.00 ± 0.10; 3.02 ± 0.43 vs 1.10 ± 0.15 fold, respectively) and the PVN (2.17 ± 0.25 vs 1.03 ± 0.11; 2.33 ± 0.16 vs 1.04 ± 0.16 fold, respectively), compared with VEH (Fig. 4E, F). TNFR1 and IL-1R mRNA levels were also augmented in SFO (2.60 ± 0.23 vs 1.06 ± 0.09; 2.66 ± 0.45 vs 1.10 ± 0.12 fold, respectively) and PVN (2.37 ± 0.17 vs 1.09 ± 0.12; 2.30 ± 0.16 vs 1.00 ± 0.11 fold, respectively) compared with VEH (Fig. 4G, H).

SFO microinjection of TNF-α and IL-1β had no significant effects on the mRNA levels of any of these RAS and inflammatory elements in the cortex (Fig. 3, 4).

Co-localization of PIC receptors and excitatory elements in the SFO

Immunofluorescent studies revealed intense, evenly distributed expression of TNFR1 and IL-1RAcP immunoreactivity in the SFO of normal rats (Figs. 5, S1 and S2). AT1R-like, ACE, COX-2 and EP3 receptor immunoreactivity was also densely expressed in the SFO (Fig. 5, S1 and S2). AT1R immunostaining is reported as AT1R-like to acknowledge the lack of specificity of the AT1R antibody. Confocal immunofluorescent images indicated that TNFR1 and IL-1RAcP immunoreactivity co-localized with ACE, AT1R-like, COX-2 and EP3 receptor immunoreactivity on SFO neurons (Figs. 5, S1 and S2). Some co-localization was also apparent in undefined cellular elements surrounding SFO neurons.

Figure 5.

Figure 5

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Laser confocal images showing the co-localized expression of TNF-α receptor 1 (TNFR1: A, C, E, G) and IL-1 receptor accessory protein (IL-1RAcP: B, D, F, H) with the angiotensin II type-1 receptor-like (AT1R: A, B), angiotensin converting enzyme (ACE: C, D), cyclooxygenase (COX)-2 (E, F) and the prostaglandin E2 receptor EP3 (G, H) immunoreactivity in SFO of normal rats. Red, TNFR1 or IL-1RAcP immunoreactivity; Green: AT1R-like, ACE, COX-2 or EP3 immunoreactivity; Yellow: Merged.

DISCUSSION

Our previous work has demonstrated that blood-borne PICs induce sympathetic activation and a pressor response,6, 23 and that the SFO plays an important role in mediating those effects.6 The present study examined potential mechanisms in the SFO, and downstream in the PVN, that might mediate cardiovascular and autonomic responses to circulating PICs. Novel findings of this study are: 1) localized microinjections of TNF-α and IL-1β into the SFO increase BP, HR and RSNA, closely mimicking the effects of systemically administered TNF-α and IL-1β; 2) pretreating the SFO with microinjections of agents that counter RAS and COX-2 activity attenuates the cardiovascular and sympathetic responses to SFO microinjections of PICs; 3) TNF-α and IL-1β receptor immunoreactivity is co-localized with AT1R-like, ACE, COX-2 and EP3 receptor immunoreactivity on SFO neurons; and 4) SFO microinjections of TNF-α and IL-1β upregulate mRNA for key components of the RAS (ACE and AT1R) and mediators of central inflammation (TNF-α and IL-1β, their receptors and COX-2) in both SFO and PVN. These findings suggest that the SFO-mediated acute sympathoexcitatory response to PICs depends upon the ambient level of RAS and COX-2 activity and that PICs act within the SFO to increase RAS and COX-2 activity. This study provides new insights into the central mechanisms driving neurohumoral excitation in cardiovascular disorders like HF and HTN.

Central nervous system markers of inflammation and RAS activity are dramatically upregulated in cardiovascular autonomic regions of the brain in experimental models of HF 24, 25 and HTN,5, 26, 27 and contribute to the increased sympathetic activity characteristic of those conditions. However, the signals that direct the brain to upregulate these excitatory systems are still poorly understood. Afferent neural and humoral signals relaying compromised cardiac, vascular and renal status likely both contribute. As a forebrain circumventricular organ that is exposed to blood-borne humors and projects directly to cardiovascular autonomic nuclei, the SFO is uniquely positioned to regulate central neural responses to peripheral stresses. Previous work from our laboratory has demonstrated that blood-borne ANG II upregulates AT1R mRNA and protein in the SFO.28 The present study demonstrates that TNF-α and IL-1β can also upregulate AT1R mRNA in the SFO, as well as the mRNA for ACE, TNF-α and IL-1β and their receptors and COX-2, the rate limiting enzyme in the production of PGE2. Thus, in conditions like HTN and HF in which circulating ANG II and PICs are both increased, both may contribute to neuro-excitation in the SFO.

In addition, the present study demonstrates that PICs, acting upon their receptors in the SFO, also increase RAS and COX-2 activity downstream in the PVN, a source of pre-sympathetic neurons innervating preganglionic sympathetic neurons in the intermediolateral column of the spinal cord both directly and indirectly via pre-sympathetic neurons in the rostral ventrolateral medulla. Thus, the effects of PICs in the SFO may increase the excitability of PVN neurons to a variety of ascending and descending neural inputs that ultimately determine the level of sympathetic nerve activity.

The present study demonstrates that PIC receptors are present on SFO neurons expressing RAS components and inflammatory mediators and that mRNA expression of these elements in the SFO and in the PVN is increased when measured 4 hours after local microinjection of PICs. While these changes may well contribute to the increases in sympathetic drive observed in HF and HTN, in which circulating levels of PICs are chronically elevated, they cannot account for the SFO-mediated acute (within 10–20 minutes) increases in sympathetic drive and arterial pressure induced by intravenous,6 intracarotid6 and direct SFO microinjection of PICs in normal rats. There are several potential explanations for these early excitatory responses. PIC binding to G-protein coupled receptors (GPCR) in the SFO may activate G-protein-dependent signaling cascades such as protein kinase A (PKA) and protein kinase C (PKC) to modulate both ionotropic and metabotropic receptors29–31. PICs can activate mitogen-activated protein kinase (MAPK) signaling, which has been reported to have acute and as well as chronic influences on sympathetic nerve activity in normal and pathophysiological conditions.32 For example, extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) can acutely phosphorylate the voltage gated potassium channel (Kv) subunit Kv4.2 in neurons,33 reducing the transient outward potassium current that modulates neuronal excitability.34 PICs may also interact with fast neurotransmitter systems to modulate neuronal excitability and synaptic transmission. TNF-α can increase local glutamate concentration in the synaptic cleft by stimulating glutamate release from microglia or inhibiting the glutamate retake by astrocytes35 and can potentiate glutamate-mediated neuronal excitation by modulating NMDA and GABA receptor function.36 Finally, PICs - like ANG II - may induce ER stress,37 which has been associated with ANG II induced HTN.38 One or more of these mechanisms might account for acute sympathetic and cardiovascular responses to PICs, and all might contribute to chronic sympatho-excitation in pathophysiological states.

A novel finding of this study is the ability of pretreatment with agents that block RAS and COX-2 activity to substantially reduce the acute sympathetic and cardiovascular responses to the SFO PIC microinjections. This effect occurs far too early to be explained by a reduction in the activity of PIC-stimulated production of ACE, AT1R and COX-2. A more likely explanation might be that ambient levels of ANG II and PGE2 sustain a basal level of neuronal excitability that is reduced by pretreatment with the inhibitors of RAS and COX-2 activity, rendering pre-sympathetic neurons less responsive to acutely administered PICs.

Perspectives

The SFO is an active interface between peripheral and central inflammation. We previously demonstrated a critical role for the SFO in the cardiovascular and sympathetic response to blood-borne PICs.6 The present study offers some initial insights into the mechanisms by which PICs, which do not directly activate ion channels to excite neurons, might act within the SFO to induce sympathetic excitation. We found that the acute excitatory response to PICs is substantially reduced by agents that inhibit RAS and COX-2 activity, suggesting that the PIC response is dependent on a basal state of neuronal excitability sustained by these two mechanisms. We also observed co-localization of ACE, AT1R-like, COX-2, and EP3 receptor immunoreactivity with PIC receptor immunoreactivity on SFO neurons, and a PIC-induced upregulation of mRNA for ACE, AT1R, TNF-α, TNFR1, IL-1β, IL-1R and COX-2 not only in the SFO but also downstream in the PVN, suggesting that PICs may act within the SFO to induce a chronic, sustained increase in the production of RAS and inflammatory mediators in these two critical cardiovascular regulatory regions of the brain. By doing so, PICs may render SFO and PVN neurons more sensitive to the effects of other excitatory mediators – e.g. ANG II and aldosterone – that circulate in chronic cardiovascular disease states like HTN and HF. Because it lacks a blood brain barrier, the SFO is potentially an ideal target for systemically administered drugs that can modulate central nervous system mechanisms. Further delineation of the molecular mechanisms by which PICs induce changes in the neurochemical milieu of the SFO may lead to the discovery of new therapeutic agents for HTN, HF and other cardiovascular-related diseases with an inflammatory component.

Supplementary Material

1

Novelty and Significance.

What Is New?

  • SFO microinjection of TNF-α or IL-1β induces pronounced increases in BP, HR and RSNA that are largely reduced by pretreatment with the AT1R blocker losartan, the ACE inhibitor captopril or the COX-2 activity inhibitor NS-398.

  • SFO microinjection of TNF-α or IL-1β increases the mRNA expression of ACE, AT1R, COX-2, TNF-α, IL-1β, TNFR1 and IL-1R in the SFO and PVN.

What Is Relevant?

  • Interaction of PICs with RAS and COX-2/PGE2 in the SFO may be an important mechanism contributing to the neurohumoral activation in HTN and HF.

  • PICs, acting upon SFO, upregulate excitatory and inflammatory mediators downstream in the PVN, a source of presympathetic neurons.

Summary.

The data demonstrate that PICs act within the SFO to elicit a sympathoexcitatory response mediated by the RAS and by COX-2/PGE2, and to upregulate the expression of components of the brain RAS and mediators of inflammation in the SFO and downstream in the PVN. These mechanisms may contribute to the sympathoexcitatory influence of circulating PICs in cardiovascular disease states.

Acknowledgments

SOURCES OF FUNDING

This material is based upon work supported in part by the Department of Veterans Affairs, Veterans Health Administration, Office of Research and Development, Biomedical Laboratory Research and Development and by National Institutes of Health grants R01 HL073986 (to RBF) and RO1 HL096671 (to RBF). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Footnotes

DISCLOSURES

None

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