Coronary microvascular dysfunction assessment: A comparative analysis of procedural aspects.

BACKGROUND: Full adoption of coronary microvascular dysfunction (CMD) assessment faces challenges due to its invasive nature and concerns about prolonged procedure time and increased contrast and/or radiation exposure. We compared procedural aspects of CMD invasive assessment to diagnostic left heart catheterization (DLHC) in patients with chest pain who were not found to have obstructive coronary artery disease. METHODS: A total of 227 patients in the Coronary Microvascular Disease Registry were compared to 1592 patients who underwent DLHC from August 2021 to November 2023. The two cohorts were compared using propensity-score matching; primary outcomes were fluoroscopy time and total contrast use. RESULTS: The participants' mean age was 64.1 ± 12.6 years. CMD-assessed patients were more likely to be female (66.5% vs. 45.2%, p < 0.001) and have hypertension (80.2% vs. 44.5%, p < 0.001), history of stroke (11.9% vs. 6.3%, p = 0.002), and history of myocardial infarction (20.3% vs. 7.7%, p < 0.001). CMD assessment was safe, without any reported adverse outcomes. A propensity-matched analysis showed that patients who underwent CMD assessment had slightly higher median contrast exposure (50 vs. 40 mL, p < 0.001), and slightly longer fluoroscopy time (6.9 vs. 4.7 min, p < 0.001). However, there was no difference in radiation dose (209.3 vs. 219 mGy, p = 0.58) and overall procedure time (31 vs. 29 min, p = 0.37). CONCLUSION: Compared to DLHC, CMD assessment is safe and requires only slightly additional contrast use (10 mL) and slightly longer fluoroscopy time (2 min) without clinical implications. These findings emphasize the favorable safety and feasibility of invasive CMD assessment.

Clinical outcomes of patients with and without chronic kidney disease undergoing endovascular revascularization of infrainguinal peripheral artery disease: Insights from the XLPAD registry.

OBJECTIVES: The purpose of the present study was to define clinical outcomes of chronic kidney disease (CKD) patients undergoing endovascular revascularization of infrainguinal peripheral artery disease (PAD). BACKGROUND: CKD is an established predictor of advanced PAD. However, clinical outcomes for these patients following endovascular revascularization remain inadequately defined. METHODS: Using the ongoing multicenter Excellence in Peripheral Artery Disease (XLPAD) registry (NCT01904851), we analyzed all-cause death, target limb amputation, and need for repeat revascularization for patients with and without CKD undergoing infrainguinal endovascular revascularization between the years 2005 and 2018. RESULTS: Of 3,699 patients, 15.1% (n = 559) had baseline CKD. CKD patients had significantly higher incidence of heavily calcified lesions (48.4% vs. 38.1%, p < .001) and diffuse disease (66.9% vs. 61.5%, p = .007). Kaplan-Meier analysis showed significant differences between CKD and non-CKD patient outcomes at 12 months for freedom from target limb amputation (79.9% vs. 92.7%, p < .001) and all-cause death (90.1% vs. 97.6%, p < .001). However, freedom from target vessel revascularization was similar between the groups. After adjusting for baseline comorbidities in the CKD and non-CKD groups, the hazard ratios for target limb amputation and death at 12 months were 2.28 (95% confidence interval or CI 1.25-4.17, p < .001) and 4.38 (95% CI 2.58-7.45, p < .001), respectively. CONCLUSIONS: Following endovascular revascularization for infrainguinal PAD, CKD was an independent predictor of all-cause death and target limb amputation at 12 months.

The role of antiplatelet therapy in patients with peripheral artery disease and lower extremity peripheral artery revascularization.

PURPOSE OF REVIEW: Although antiplatelet agents are frequently prescribed to patients with lower extremity peripheral artery disease (PAD), there is an overall lack of consensus among published evidence and guidelines with respect to this practice. RECENT FINDINGS: Antiplatelet agents are prescribed to patients with PAD to reduce both cardiovascular and limb-based events during the follow-up period. A large evidence base supports the use of antiplatelet monotherapy with aspirin or clopidogrel in patients with symptomatic PAD or a history of peripheral artery revascularization. However, antiplatelet monotherapy has not proven beneficial in patients with asymptomatic PAD. Dual antiplatelet therapy has not demonstrated a clear benefit in reducing the risk of cardiovascular events in patients with symptomatic PAD. Its role in reducing the risk of adverse limb events following endovascular or surgical revascularization also remains unclear. Recently, the use of vorapaxar in addition to aspirin and/or clopidogrel has been associated with a significant reduction in the need for repeat revascularization procedures and hospitalization for limb ischemia in patients with established PAD. SUMMARY: Eligible patients with symptomatic PAD or with a history of peripheral artery revascularization should be prescribed antiplatelet monotherapy for secondary prevention of both cardiovascular and limb events, using aspirin, clopidogrel, and/or vorapaxar. Given the significant overlap of PAD and coronary artery disease, the evidence presented in this article may have important implications for management of patients with coronary artery disease.

The use of the AVERT system to limit contrast volume administration during peripheral angiography and intervention.

BACKGROUND: The AVERT(TM) Contrast Modulation System (AVERT) (Osprey Medical, MN) is designed to reduce contrast volume administration during angiography. The AVERT provides an adjustable resistance circuit which decreases the pressure head delivering contrast towards the patient. The AVERT has not been previously studied in patients undergoing peripheral digital subtraction angiography (DSA). The purpose of this study was (1) to evaluate contrast savings with the AVERT and (2) to evaluate the ability to generate clinically acceptable DSA images in the process. To better define the mechanism of action in the peripheral circulation, we also developed a bench model to study the effects of the AVERT on the hydrodynamics of contrast delivery. METHODS: Patients undergoing lower extremity DSA (diagnostic or intervention, sheath or catheter) were studied. The following variables were recorded for each injection: starting control syringe contrast volume, contrast volume injected towards patient, contrast volume returned to AVERT reservoir, net contrast administered to the patient and % savings. The AVERT resistance was adjusted manually based on operator's discretion--balancing image quality and contrast savings. RESULTS: About 408 DSA angiographic sequences were obtained in 22 patients undergoing 29 procedures. Almost 68% of the patients had chronic kidney disease. An 82% presented with critical limb ischemia, 18% had claudication. There was an overall 37% ± 14% savings of contrast (31% for diagnostic DSA, 40% for interventional procedures). Overall 91% of all images were acceptable for clinical decision making. Specifically, 94% of diagnostic and 87% of interventional images were acceptable. Injection through a 4 Fr catheter (77% acceptable) resulted in poorer image quality as compared to a 5 Fr catheter (96% acceptable). Image quality for 5, 6, and 7 Fr sheath injections was 86%, 91%, 98%, respectively. The bench model of peripheral angiography demonstrated a significant reduction in reflux of contrast proximal to the end of the catheter without loss of antegrade image quality - confirming the in vivo findings. CONCLUSIONS: We demonstrate that the use of the AVERT device during peripheral angiography results in significant contrast savings without compromising image quality.

Comparison of dual-antiplatelet therapy durations after endovascular revascularization of infrainguinal arteries.

BACKGROUND: The optimal dual-antiplatelet therapy (DAPT) duration after endovascular revascularization of infrainguinal arteries is uncertain. METHODS: This study examines DAPT prescription trends and 12-month major adverse limb events (MALEs; a composite of repeat endovascular or surgical revascularization, acute vessel thrombosis, or amputation of the target limb), major adverse cardiovascular events (MACEs; all-cause mortality, nonfatal myocardial infarction [MI], stroke, or coronary revascularization), fatal bleeding events, and those requiring interruption or discontinuation of DAPT (hemorrhagic complications) for patients enrolled into the Excellence in Peripheral Artery Disease (XLPAD) registry. RESULTS: Data on 368 patients prescribed antiplatelet therapy were analyzed; 8.2% were prescribed antiplatelet monotherapy, 48.6% DAPT for ≤3 months, and 43.2% for >3 months. Patients in the >3 DAPT prescribed group were older, had preexisting coronary artery disease (CAD), and prior MI (all P < 0.001). Overall MALE in the ≤3 and >3-month DAPT prescribed groups were 22.3% and 23.9%, respectively (P = 0.541). Survival analysis showed significantly higher rates of MACE in patients prescribed >3-month DAPT (17.6% vs. 9.5%; P = 0.019). An "as-treated" analysis excluded 10 patients who were prescribed DAPT for >3 months and revealed similar rates of MALE (24.9% vs. 20.8%; P = 0.386) and MACE (12.2% vs. 14.8%; P = 0.443) in patients receiving ≤3 and >3 DAPT. Hemorrhagic complications were similar across all prescribed and "as-treated" DAPT groups. CONCLUSIONS: After infrainguinal endovascular procedures, patients with underlying CAD were prescribed longer (>3 months) duration of DAPT and experienced more cardiovascular events compared with those prescribed ≤3 months of DAPT. Adverse limb events were similar in both groups.

Frequency and outcomes of aortocoronary dissection during percutaneous coronary intervention of chronic total occlusions: a case series and systematic review of the literature.

BACKGROUND: Aortocoronary dissection can complicate percutaneous coronary intervention (PCI) of chronic total occlusions (CTOs). METHODS: We retrospectively examined the frequency and outcomes of aortocoronary dissection among 336 consecutive CTO PCIs performed at our institution between 2005 and 2012 and performed a systematic review of the published literature. RESULTS: Aortocoronary dissection occurred in six patients (1.8%, 95% confidence intervals 0.7%, 3.8%). All aortocoronary dissections occurred in the right coronary artery (CTO target vessel in five patients and donor vessel in one patient). The baseline clinical characteristics of patients with and without aortocoronary dissection were similar. Compared to patients without, those with aortocoronary dissection were more likely to undergo crossing attempts using the retrograde approach (25% vs. 67%, P = 0.036) and experience a major complication (2.4% vs. 33.3%, P = 0.008). Technical and procedural success rates were similar in both groups. Of the six patients with aortocoronary dissection one underwent emergency coronary bypass graft surgery (CABG), four were treated with ostial stenting, and one was treated conservatively without subsequent adverse clinical outcomes. Systematic literature review provided 107 published cases of aortocoronary dissection during PCI, that occurred mainly in the right coronary artery (74.8%) and were treated with stenting (49.5%), emergency CABG (29%), or conservatively (21.5%). CONCLUSIONS: Aortocoronary dissection is an infrequent complication of CTO PCI and although it can be treated with stents in most patients, it may infrequently require emergency CABG.

High-risk percutaneous coronary intervention with or without mechanical circulatory support: Will Impella show superiority in the PROTECT IV randomized trial?

BACKGROUND: PROTECT IV is a current enrolling randomized controlled trial evaluating high-risk percutaneous coronary intervention (HR-PCI) with prophylactic Impella versus no Impella to reduce the composite primary endpoint of all-cause death, stroke, myocardial infarction (MI), or cardiovascular hospitalization. In a PROTECT IV-like cohort of patients who underwent HR-PCI without Impella, we aimed to report the rate of major adverse events to determine whether the trial is adequately powered. METHODS AND RESULTS: A total of 700 patients meeting similar inclusion/exclusion criteria of PROTECT IV who underwent HR-PCI without Impella at a single tertiary center from 2008 to 2022 were included in the analysis. The composite rates of all-cause death, MI, target lesion revascularization, and target vessel revascularization at 1, 2, and 3 years were estimated using the Kaplan-Meier method, and the results were used to calculate the sample size under the constant hazard ratio assumption and expected number of events to be observed used in planning PROTECT IV. The primary endpoint occurred in 30.8 % of patients at 2 years. PROTECT IV assumes a hazard ratio of 0.75 using a multivariate Cox regression, which, under a 5 % level and 90 % power, yields 516 events. This implies a 2-year primary outcome rate of 50 % for the non-Impella arm. CONCLUSION: Therefore, PROTECT IV estimates that a sample size of 1252 patients is required for Impella to be declared superior to the non-Impella group. Using our observed 2-year outcome of 30.8 %, we estimate that PROTECT IV requires 1966 patients, demonstrating that PROTECT IV is probably underpowered.

Bioprosthetic Aortic Valve Thrombosis: Definitions, Clinical Impact, and Management: A State-of-the-Art Review.

Bioprosthetic aortic valve thrombosis is frequently detected after transcatheter and surgical aortic valve replacement due to advances in cardiac computed tomography angiography technology and standardized surveillance protocols in low-surgical-risk transcatheter aortic valve replacement trials. However, evidence is limited concerning whether subclinical leaflet thrombosis leads to clinical adverse events or premature structural valve deterioration. Furthermore, there may be net harm in the form of bleeding from aggressive antithrombotic treatment in patients with subclinical leaflet thrombosis. This review will discuss the incidence, mechanisms, diagnosis, and optimal management of bioprosthetic aortic valve thrombosis after transcatheter aortic valve replacement and bioprosthetic surgical aortic valve replacement.

Differences Between Patients With Intermittent Claudication and Critical Limb Ischemia Undergoing Endovascular Intervention: Insights From the Excellence in Peripheral Artery Disease Registry.

BACKGROUND: There are limited data on differences in angiographic distribution of peripheral artery disease and endovascular revascularization strategies in patients presenting with intermittent claudication (IC) and critical limb ischemia (CLI). We aimed to compare anatomic features, treatment strategies, and clinical outcomes between patients with IC and CLI undergoing endovascular revascularization. METHODS: We examined 3326 patients enrolled in the Excellence in Peripheral Artery Disease registry from 2006 to 2019 who were referred for endovascular intervention for IC (n=1983) or CLI (n=1343). The primary outcome was 1-year major adverse limb events, which included death, repeat target limb revascularization, or target limb amputation. RESULTS: Patients with CLI were older and more likely to have diabetes and chronic kidney disease and less likely to receive optimal medical therapy compared with IC. Patients with IC had higher femoropopliteal artery interventions (IC 87% versus CLI 65%; P<0.001), while below the knee interventions were more frequent in CLI (CLI 47% versus IC 12%; P<0.001). Patients with CLI were more likely to have multilevel peripheral artery disease (CLI 32% versus IC 15%, P<0.001). Patients with IC were predominantly revascularized with stents (IC 48% versus CLI 37%; P<0.001) while balloon angioplasty was more frequent in CLI (CLI 37% versus IC 25%; P<0.001). All-cause mortality was higher in patients with CLI (CLI 4% versus IC 2%; P=0.014). Major adverse limb event rates for patients with IC and CLI were 16% and 26%, respectively (P<0.001) and remained higher in CLI after multivariable adjustment of baseline risk factors. CONCLUSIONS: Patients with IC and CLI have significant anatomic, lesion, and treatment differences with significantly higher mortality and adverse limb outcomes in CLI. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01904851. Graphic Abstract: A graphic abstract is available for this article.

Coronavirus Disease 2019 Catheterization Laboratory Survey.

Background The coronavirus disease 2019 pandemic is expected to affect operations and lifestyles of interventional cardiologists around the world in unprecedented ways. Timely gathering of information on this topic can provide valuable insight and improve the handling of the ongoing and future pandemic outbreaks. Methods and Results A survey instrument developed by the authors was disseminated via e-mail, text messaging, WhatsApp, and social media to interventional cardiologists between April 6, 2020, and April 11, 2020. A total of 509 responses were collected from 18 countries, mainly from the United States (51%) and Italy (36%). Operators reported significant decline in coronary, structural heart, and endovascular procedure volumes. Personal protective equipment was available to 95% of respondents; however FIT-tested N95 or equivalent masks were available to only 70%, and 74% indicated absence of coronavirus disease 2019 pretesting. Most (83%) operators expressed concern when asked to perform cardiac catheterization on a suspected or confirmed coronavirus disease 2019 patient, primarily because of fear of viral transmission (88%). Although the survey demonstrated significant compliance with social distancing, high use of telemedicine (69%), and online education platforms (80%), there was concern over impending financial loss. Conclusions Our survey indicates significant reduction in invasive procedure volumes and concern for viral transmission. There is near universal adoption of personal protective equipment; however, coronavirus disease 2019 pretesting and access to FIT-tested N95 masks is suboptimal. Although there is concern over impending financial loss, substantial engagement in telemedicine and online education is reported.

Five-Year Freedom From Target-Lesion Revascularization Using Excimer Laser Ablation Therapy in the Treatment of In-Stent Restenosis of Femoropopliteal Arteries.

BACKGROUND: Target-lesion revascularization (TLR) and loss of patency remain high following treatment of in-stent restenosis (ISR) of the femoropopliteal (FP) artery. Excimer laser atherectomy (ELA) is effective in reducing TLR and improves patency at 6-month and 1-year follow-up when compared with balloon angioplasty (PTA). The long-term sustainability of these early results is unknown. We present a retrospective analysis from our center on the 5-year outcomes of ELA in the treatment of ISR of the FP arteries. METHODS: Patients who underwent ELA for FP-ISR from February 2005 to April 2010 at a single medical center were included. Demographics, angiographic and procedural variables were included. Major adverse events and 5-year TLR and target-vessel revascularization were obtained from medical records. Descriptive analysis was performed on all variables. Kaplan-Meier survival curves for TLR were plotted censored for death among patients who died before the occurrence of a TLR. RESULTS: Forty consecutive patients (mean age, 67.2 ± 9.0 years; 57.5% males) were included. Angiographic variables included: lesion length, 210.4 ± 104.0 mm; lesion severity, 93.9 ± 8.9%; and number of vessel runoffs, 1.7 ± 1.0. All patients were treated with adjunctive PTA. Acute procedural success was achieved in 92.5% of vessels. Distal embolization requiring treatment was 2.5%. No unplanned amputation occurred. Total deaths occurred in 8/40 (20%). At 5-year follow-up, TLR occurred in 62.5% with the steepest decline in freedom from TLR occurred in the first year followed by a less decline in the subsequent 2 to 3 years. CONCLUSION: ELA for FP-ISR continues to show progressive increase in TLR up to 5-year follow-up, but mostly occurs in the first 3 years after index procedure. These data suggest that a minimum follow-up of 3 years is needed to determine stability of treatment of FP-ISR with laser.

Safety and Effectiveness of the Nav-6 Filter in Preventing Distal Embolization During Jetstream Atherectomy of Infrainguinal Peripheral Artery Lesions.

BACKGROUND: The risk of distal embolization (DE) during infrainguinal peripheral artery interventions (PAI) is often mitigated by the use of embolic protection devices. There are limited data on the use of filters with the Jetstream (JS) atherectomy device, a rotational cutter with aspiration capacity. The Nav-6 filter is uniquely suited for use with the JS due to its wire compatibility and detachment from the filter; however, data on the off-label use of this combination have not been reported. METHODS: Consecutive patients between October 2008 and April 2015 undergoing endovascular infrainguinal PAI with JS were analyzed as part of the Excellence in Peripheral Artery Disease (XL-PAD) registry (NCT01904851). Patients were divided into two subgroups with Nav-6 filter use vs no filter use. Descriptive and univariate analyses were performed. RESULTS: Among 141 patients (mean age, 67.8 ± 10.8 years; 169 lesions) included in this study, the Nav-6 filter was used in 82 (59%). Use of a filter was more frequent in longer lesions (146 ± 106 mm vs 91 ± 72 mm; P=.01), in more severe stenoses (95% vs 87%; P=.04), and in chronic total occlusions (33% vs 8.3%; P=.01). Patients receiving filters had longer procedure duration (102 ± 51 min vs 66 ± 41 min; P=.01) and longer fluoroscopy times (31 ± 16 min vs 21 ± 10 min; P<.001). Use of the Nav-6 filter with the JS during PAI was associated with numerically lower rates of DE (1.8% vs 8%; P=.10) and similar rates of death and amputation. At 12 months, the target-lesion revascularization rate was higher in the filter group (22% vs 2.7%; P=.02), likely secondary to use of the filter in more complex lesions. CONCLUSION: Nav-6 filter during JS atherectomy was predominantly used during complex infrainguinal PAI and was associated with less occurrence of DE.

LDL cholesterol: should guidelines include targets?

Elevated low-density lipoprotein cholesterol (LDL-C) is associated with adverse cardiovascular outcomes. The strategy of target-based LDL-C lowering to reduce the risk of coronary heart disease and secondary event rates is now well established. However, the strategy for treating to a target LDL-C, and whether there is a lower threshold level for LDL-C continues to be debated. We present, and critically analyze the evidence for a target-based LDL-C lowering strategy, and the safety and efficacy of intensive plasma LDL-C-lowering with traditional, and novel LDL-lowering therapies below current guideline targets.

Clinical, angiographic, and procedural predictors of periprocedural complications during chronic total occlusion percutaneous coronary intervention.

OBJECTIVES: To identify clinical, angiographic, and procedural factors associated with increased risk of periprocedural complications during chronic total occlusion (CTO) percutaneous coronary intervention (PCI). BACKGROUND: Successful CTO PCI can provide significant clinical benefit; however, procedural risks have received limited study. We sought to identify factors associated with increased CTO PCI periprocedural risk that could be utilized to guide patient and lesion selection. METHODS: The clinical, angiographic, and procedural records of 336 consecutive CTO PCI procedures performed at a single center from May 2005 through 2012 were reviewed, and data on periprocedural complications were recorded. Logistic regression was performed to identify independent predictors of periprocedural complications during CTO PCI. RESULTS: The incidence of major and minor complications was 3.9% and 10.4%, respectively. Minor bleeding and vascular events were the most common complications (4.8%), followed by perforation (2.4%), contrast-induced nephropathy (1.8%), and transient hypotension (0.6%). Major complications were uncommon: death (0.3%); emergency coronary artery bypass grafting (0.6%); stroke (0.3%); tamponade (0.3%); clinical myocardial infarction (0.9%); donor vessel injury (0.6%); and major bleeding or vascular events (0.9%). Patients who experienced any complication had higher preprocedure troponin levels and were more likely to undergo treatment using the retrograde approach. In multivariable analysis, use of the retrograde approach was independently associated with increased risk of periprocedural complications (odds ratio, 2.057; 95% confidence interval, 1.045-4.051; P=.04). CONCLUSIONS: Major complications of CTO PCI are infrequent, but are more common with use of the retrograde approach.

Significance of an abnormal ankle-brachial index in patients with established coronary artery disease with and without associated diabetes mellitus.

An abnormal ankle-brachial index (ABI) is associated with higher risk for future cardiovascular (CV) events; however, it is unknown whether this association is true in patients with established coronary artery disease (CAD) and associated diabetes mellitus (DM). We evaluated 679 patients with stable CAD enrolled in the Excellence in Peripheral Arterial Disease and Veterans Affairs North Texas Healthcare System peripheral arterial disease databases. ABI and 12-month major adverse CV events (MACEs, a composite of all-cause death, nonfatal myocardial infarction, need for repeat coronary revascularization, and ischemic stroke) were assessed. Cox proportional hazard models were used to assess the association of ABI and DM with subsequent CV events. An abnormal ABI (<0.9 or >1.4) was present in 72% of patients with stable CAD and 68% had DM. Using patients without DM and normal ABI as reference, the adjusted hazard ratio for 12-month MACE was 1.7 (95% confidence interval [CI] 0.71 to 4.06) for patients with DM and normal ABI; 2.03 (95% CI 0.83 to 4.9) for patients without DM with abnormal ABI; and 4.85 (95% CI 2.22 to 10.61) for patients with DM and abnormal ABI. In conclusion, in patients with stable CAD, an abnormal ABI confers an incremental risk of MACE in addition to DM and traditional CV risk factors.

Swim stress excitation of nucleus incertus and rapid induction of relaxin-3 expression via CRF1 activation.

Relaxin-3 (RLX3), a newly identified member of the relaxin peptide family, is distinguished by its enriched expression in GABA projection neurons of the pontine nucleus incertus (NI), which are postulated to participate in forebrain neural circuits involved in behavioural activation and stress responses. In this regard, corticotrophin-releasing factor-1 receptor (CRF(1)) is abundantly expressed by NI neurons; central CRF administration activates c-fos expression in NI; and various stressors have been reported to increase NI neuron activity. In studies to determine whether a specific neurogenic stressor would activate RLX3 expression, we assessed the effect of a repeated forced swim (RFS) on levels of RLX3 mRNA and heteronuclear (hn) RNA in rat NI by in situ hybridization histochemistry of exon- and intron-directed oligonucleotide probes, respectively. Exposure of rats to an RFS (10 min at 23 degrees C, 24 h apart), markedly increased RLX3 mRNA levels in NI at 30-60 min after the second swim, before a gradual return to basal levels over 2-4 h, while RLX3 hnRNA levels were significantly up-regulated at 60-120 min post-RFS, following a transient decrease at 30 min. Systemic treatment of rats with a CRF(1) antagonist, antalarmin (20 mg/kg, i.p.) 30 min prior to the second swim, blunted the stress-induced effects on RLX3 transcripts. Relative levels of RLX3-immunostaining in NI neurons appeared elevated at 3 h post-swim, but not at earlier time points (30-60 min). These results suggest that acute stress-induced CRF secretion can rapidly alter RLX3 gene transcription by activation of CRF(1) present on NI neurons. More generally, these studies support a role for RLX3 neural networks in the normal neural and physiological response to neurogenic stressors in the rat.

Distribution of relaxin-3 and RXFP3 within arousal, stress, affective, and cognitive circuits of mouse brain.

Relaxin-3 (RLN3) and its native receptor, relaxin family peptide 3 receptor (RXFP3), constitute a newly identified neuropeptide system enriched in mammalian brain. The distribution of RLN3/RXFP3 networks in rat brain and recent experimental studies suggest a role for this system in modulation of arousal, stress, metabolism, and cognition. In order to facilitate exploration of the biology of RLN3/RXFP3 in complementary murine models, this study mapped the neuroanatomical distribution of the RLN3/RXFP3 system in mouse brain. Adult, male wildtype and RLN3 knock-out (KO)/LacZ knock-in (KI) mice were used to map the central distribution of RLN3 gene expression and RLN3-like immunoreactivity (-LI). The distribution of RXFP3 mRNA and protein was determined using [(35)S]-oligonucleotide probes and a radiolabeled RXFP3-selective agonist ([(125)I]-R3/I5), respectively. High densities of neurons expressing RLN3 mRNA, RLN3-associated beta-galactosidase activity and RLN3-LI were detected in the nucleus incertus (or nucleus O), while smaller populations of positive neurons were observed in the pontine raphé, the periaqueductal gray and a region adjacent to the lateral substantia nigra. RLN3-LI was observed in nerve fibers/terminals in nucleus incertus and broadly throughout the pons, midbrain, hypothalamus, thalamus, septum, hippocampus, and neocortex, but was absent in RLN3 KO/LacZ KI mice. This RLN3 neural network overlapped the regional distribution of RXFP3 mRNA and [(125)I]-R3/I5 binding sites in wildtype and RLN3 KO/LacZ KI mice. These findings provide further evidence for the conserved nature of RLN3/RXFP3 systems in mammalian brain and the ability of RLN3/RXFP3 signaling to modulate "behavioral state" and an array of circuits involved in arousal, stress responses, affective state, and cognition.