Mueller maneuver attenuates left atrial phasic volumes and myocardial strain in healthy younger adults.

The left atrium (LA) is a key, but incompletely understood, modulator of left ventricular (LV) filling. Inspiratory negative intrathoracic pressure swings alter cardiac loading conditions, which may impact LA function. We studied acute effects of static inspiratory efforts on LA chamber function, LA myocardial strain, and LV diastolic filling. We included healthy adults (10 males/9 females, 24 ± 4 yr) and used Mueller maneuvers to reduce intrathoracic pressure to -30 cmH2O for 15 s. Over six repeated trials, we used echocardiography to acquire LA- and LV-focused two-dimensional (2-D) images, and mitral Doppler inflow and annular tissue velocity spectra. Images were analyzed for LA and LV chamber volumes, tissue relaxation velocities, transmitral filling velocities, and speckle tracking-derived LA longitudinal strain. Repeated measures were made at baseline, early Mueller, late Mueller, then early release, and late release. In the late Mueller compared with baseline, LV stroke volume decreased by -10 ± 4 mL (P < 0.05) and then returned to baseline upon release; this occurred with a -11 ± 9 mL (P < 0.05) end-diastolic volume reduction. Early diastolic LV filling was attenuated, reflected by decreased tissue relaxation velocity (-2 ± 2 cm/s, P < 0.05), E-wave filling velocity (-13 ± 14 cm/s, P < 0.05), and LA passive emptying volume (-5 ± 5 mL, P < 0.05), each returning to baseline with release. LA maximal volume decreased (-5 ± 5 mL, P < 0.05) during the Mueller maneuver, but increased relative to baseline following release (+4 ± 5 mL, P < 0.05), whereas LA peak positive longitudinal strain decreased (-6 ± 6%, P < 0.05) and then returned to baseline. Attenuated LA and in turn, LV filling may contribute to acute stroke volume reductions experienced during forceful inspiratory efforts.NEW & NOTEWORTHY In healthy younger adults, the Mueller maneuver transiently reduces left atrial filling and passive emptying during the reservoir and conduit phases, respectively. Corresponding reductions are seen in left atrial reservoir and conduit phase longitudinal myocardial strain and strain rate. However, left atrial pump phase active function and mechanics are largely preserved compared with baseline. Rapid changes in LA chamber volumes and myocardial strain with recurrent forceful inspiratory efforts and relaxation may reflect acute LA stress.

Creation of EGD-Derived Gastric Cancer Organoids to Predict Treatment Responses.

Gastric adenocarcinoma (GAd) is the third leading cause of cancer-related deaths worldwide. Most patients require perioperative chemotherapy, yet methods to accurately predict responses to therapy are lacking. Thus, patients may be unnecessarily exposed to considerable toxicities. Here, we present a novel methodology using patient-derived organoids (PDOs) that rapidly and accurately predicts the chemotherapy efficacy for GAd patients. Methods:Endoscopic GAd biopsies were obtained from 19 patients, shipped overnight, and PDOs were developed within 24 h. Drug sensitivity testing was performed on PDO single-cells with current standard-of-care systemic GAd regimens and cell viability was measured. Whole exome sequencing was used to confirm the consistency of tumor-related gene mutations and copy number alterations between primary tumors, PDOs, and PDO single-cells. Results:Overall, 15 of 19 biopsies (79%) were appropriate for PDO creation and single-cell expansion within 24 h of specimen collection and overnight shipment. With our PDO single-cell technique, PDOs (53%) were successfully developed. Subsequently, two PDO lines were subjected to drug sensitivity testing within 12 days from initial biopsy procurement. Drug sensitivity assays revealed unique treatment response profiles for combination drug regimens in both of the two unique PDOs, which corresponded with the clinical response. Conclusions:The successful creation of PDOs within 24 h of endoscopic biopsy and rapid drug testing within 2 weeks demonstrate the feasibility of our novel approach for future applications in clinical decision making. This proof of concept sets the foundation for future clinical trials using PDOs to predict clinical responses to GAd therapies.

Lower-limb resistance training reduces exertional dyspnea and intrinsic neuromuscular fatigability in individuals with chronic obstructive pulmonary disease.

Skeletal muscle atrophy, dysfunction, and fatigue are important complications of chronic obstructive pulmonary disease (COPD). Greater reliance on glycolytic metabolism and increased type III/IV muscle afferent activity increase ventilatory drive, promote ventilatory constraint, amplify exertional dyspnea, and limit exercise tolerance. To investigate whether muscular adaptation with resistance training (RT) could improve exertional dyspnea, exercise tolerance, and intrinsic neuromuscular fatigability in individuals with COPD (n = 14, FEV1 = 62 ± 21% predicted), we performed a proof-of-concept single-arm efficacy study utilizing 4 wk of individualized lower-limb RT (3 times/wk). At baseline, dyspnea (Borg scale), ventilatory parameters, lung volumes (inspiratory capacity maneuvers), and exercise time were measured during a constant-load test (CLT) at 75% maximal workload to symptom limitation. On a separate day, fatigability was assessed using 3 min of intermittent stimulation of the quadriceps (initial output of ∼25% maximal voluntary force). Following RT, the CLT and fatigue protocols were repeated. Compared with baseline, isotime dyspnea was reduced (5.9 ± 2.4 vs. 4.5 ± 2.4 Borg units, P = 0.02) and exercise time increased (437 ± 405 s vs. 606 ± 447 s, P < 0.01) following RT. Isotime tidal volume increased (P = 0.01), whereas end-expiratory lung volumes (P = 0.02) and heart rate (P = 0.03) decreased. Quadriceps force, relative to initial force, was higher at the end of the stimulation protocol posttraining (53.2 ± 9.1 vs. 46.8 ± 11.9%, P = 0.04). This study provides evidence that 4 wk of RT attenuates exertional dyspnea and improves exercise tolerance in individuals with COPD, which in part, is likely due to delayed ventilatory constraint and reduced intrinsic fatigability. A pulmonary rehabilitation program beginning with individualized lower-limb RT may help mitigate dyspnea before performing aerobic training in individuals with COPD.NEW & NOTEWORTHY This study presents the novel finding that 4-wk resistance training (RT) focused specifically on the lower limbs can reduce exertional dyspnea during constant-load cycling, improve exercise tolerance, and reduce intrinsic fatigability of the quadriceps in individuals with COPD.

Finding New Meaning in the Practice of Medicine: A Quality Improvement Project Evaluating the Remote Communication Liaison Program During the Initial COVID Pandemic Surge.

Background: In spring 2020, the COVID-19 pandemic overwhelmed intensive care teams with severely ill patients. Even at the end of life, families were barred from hospitals, relying solely on remote communication. A Remote Communication Liaison Program (RCLP) was established to ensure daily communication for families, while supporting overstretched intensivists. Objectives: To evaluate the effectiveness and impact of the RCLP on participating liaisons and intensivists. Design: Two quality improvement surveys were developed and administered electronically. Setting/Subjects: Based in the United States, all liaisons and intensivists who participated in this program were invited to take the surveys. Measurements: Descriptive statistics were used to analyze the quantitative Likert-scale data, and qualitative analysis was used to assess themes. Results: Among respondents, all (100%) liaisons and more than 90% of intensivists agreed or strongly agreed that the RCLP provided a valuable service to families. More than 70% of intensivists agreed or strongly agreed that the program lessened their workload. More than 90% of liaisons agreed or strongly agreed that participation in the program improved their confidence and skills in end-of-life decision making, difficult conversations, and comprehension of critical care charts. Themes elicited from the liaisons revealed that participation fostered a renewed sense of purpose as physicians, meaningful connection, and opportunities for growth. Conclusions: RCLP successfully trained and deployed liaisons to rapidly develop skills in communication with beleaguered families during COVID-19 surge. Participation in the program had a profound effect on liaisons, who experienced a renewed sense of meaning and connection to the practice of medicine.

Evaluating the Use of Video Modeling With Voiceover Instructions to Train Therapists to Deliver Caregiver Training Through Telehealth.

Caregiver training is an important component of behavioral intervention; however, many barriers exist for in-person training. Alternatively, behavioral therapists may use telehealth as a service delivery method. To effectively train caregivers through telehealth, therapists should receive explicit training, but there has been limited research on effective methods for teaching this skill. The purpose of the current study was to evaluate video modeling with voice-over instruction (VMVO) to train therapists to implement 11 component skills of caregiver training through telehealth to teach confederate caregivers to implement a guided compliance procedure. We measured the therapist's implementation of the component skills during a scripted role-play before and after video-model training within a multiple baseline design across participants. We also conducted maintenance and generalization probes to a novel skill. All seven therapists learned the skill, but three therapists required a feedback component in addition to the VMVO. The results suggest that VMVO may be an efficient and effective method for training therapists to conduct caregiver training via telehealth. Furthermore, results indicate that component skill analyses may be valuable to monitor skills that require remediation.

A Multicenter Phase 1 Trial Evaluating Nanoliposomal Irinotecan for Heated Intraperitoneal Chemotherapy Combined with Cytoreductive Surgery for Patients with Peritoneal Surface Disease.

BACKGROUND: Nanoliposomal irinotecan (nal-IRI) is a promising novel hyperthermic intraperitoneal chemotherapy (HIPEC) agent given its enhanced efficacy against gastrointestinal tumors, safety profile, thermo-synergy, and heat stability. This report describes the first in-human phase 1 clinical trial of nal-IRI during cytoreductive surgery (CRS) and HIPEC. METHODS: Patients with peritoneal surface disease (PSD) from appendiceal and colorectal neoplasms were enrolled in a 3 + 3 dose-escalation trial using nal-IRI (70-280 mg/m2) during HIPEC for 30 min at 41 ± 1 °C. The primary outcome was safety. The secondary outcomes were pharmacokinetics (PK) and disease-free survival. Adverse events (AEs) categorized as grade 2 or higher were recorded. The serious AEs (SAEs) were mortality, grade ≥ 3 AEs, and dose-limiting toxicity (DLT). Irinotecan and active metabolite SN38 were measured in plasma and peritoneal washings. RESULTS: The study enrolled 18 patients, who received nal-IRI during HIPEC at 70 mg/m2 (n = 3), 140 mg/m2 (n = 6), 210 mg/m2 (n = 3), and 280 mg/m2 (n = 6). No DLT or mortality occurred. The overall morbidity for CRS/HIPEC was 39% (n = 7). Although one patient experienced neutropenia, no AE (n = 131) or SAE (n = 3) was definitively attributable to nal-IRI. At 280 mg/m2, plasma irinotecan and SN38 measurements showed maximum concentrations of 0.4 ± 0.6 µg/mL and 3.0 ± 2.4 ng/mL, a median time to maximum concentration of 24.5 and 26 h, and areas under the curve of 22.6 h*µg/mL and 168 h*ng/mL, respectively. At the 6-month follow-up visit, 83% (n = 15) of the patients remained disease-free. CONCLUSIONS: In this phase 1 HIPEC trial (NCT04088786), nal-IRI was observed to be safe, and PK profiling showed low systemic absorption overall. These data support future studies testing the efficacy of nal-IRI in CRS/HIPEC.

The Development of Investigator-Initiated Clinical Trials in Surgical Oncology.

Investigator-initiated trials (IITs) are designed by principal investigators who identify important, unaddressed clinical gaps and opportunities to answer these questions through clinical trials. Surgical oncologists are poised to lead IITs due to their multidisciplinary clinical practice and substantial research background. The process of developing, organizing, and implementing IITs is multifaceted and involves important steps including (but not limited to) navigating regulatory requirements, obtaining funding, and meeting enrollment targets. Here, the authors explore the steps, methodology, and barriers of IIT development by surgical oncologists and highlight the importance of IITs in oncology.

Interaction of immune checkpoint PD-1 and chemokine receptor 4 (CXCR4) promotes a malignant phenotype in pancreatic cancer cells.

Despite recent therapeutic advances, pancreatic ductal adenocarcinoma (PDAC) remains a devastating disease with limited therapeutic options. Immune checkpoint inhibitors (ICIs) have demonstrated promising results in many cancers, but thus far have yielded little clinical benefit in PDAC. Based on recent combined targeting of programmed cell death protein-1 (PD-1) and C-X-C chemokine receptor 4 (CXCR4) in patient-derived xenografts (PDXs) and a pilot clinical trial, we sought to elucidate potential interactions between PD-1 and CXCR4. We observed concomitant expression and direct interaction of PD-1 and CXCR4 in PDAC cells. This interaction was disrupted upon CXCR4 antagonism with AMD3100 and led to increased cell surface expression of PD-1. Importantly, CXCR4-mediated PDAC cell migration was also blocked by PD-1 inhibition. Our work provides a possible mechanism by which prior studies have demonstrated that combined CXCR4 and PD-1 inhibition leads to decreased tumor growth. This is the first report investigating PD-1 and CXCR4 interactions in PDAC cells and our results can serve as the basis for further investigation of combined therapeutic targeting of CXCR4 and PD-1.

Endogenous Pancreatic Cancer Cell PD-1 Activates MET and Induces Epithelial-Mesenchymal Transition to Promote Cancer Progression.

We recently demonstrated that immune checkpoint PD-1 was endogenously expressed in pancreatic ductal adenocarcinoma (PDAC) cells. Our data indicated that PD-1 proteins are not exclusive to immune cells and have unrecognized signal transduction cascades intrinsic to cancer cells. Building on this paradigm shift, we sought to further characterize PD-1 expression in PDAC. We utilized a phospho-explorer array to identify pathways upregulated by PD-1 signaling. We discovered PD-1-mediated activation of the proto-oncogene MET in PDAC cells, which was dependent on hepatocyte growth factor (MET ligand) and not secondary to direct protein interaction. We then discovered that the PD-1/MET axis in PDAC cells regulated growth, migration, and invasion. Importantly, the PD-1/MET axis induced epithelial-to-mesenchymal transition (EMT), a well-established early oncogenic process in PDAC. We observed that combined targeting of PDAC cell PD-1 and MET resulted in substantial direct tumor cell cytotoxicity and growth inhibition in PDAC cell lines, patient-derived organoids, and patient-derived xenografts independent of cytotoxic immune responses. This is the first report of PDAC-endogenous PD-1 expression regulating MET signaling, which builds upon our growing body of work showing the oncogenic phenotype of PD-1 expression in PDAC cells is distinct from its immunogenic role. These results highlight a paradigm shift that the tumor-specific PD-1 axis is a novel target to effectively kill PDAC cells by antagonizing previously unrecognized PD-1-dependent oncogenic pathways.

Current Trends in Cytoreductive Surgery (CRS) and Hyperthermic Intraperitoneal Chemotherapy (HIPEC) for Peritoneal Disease from Appendiceal and Colorectal Malignancies.

Peritoneal carcinomatosis (PC) is a poor prognostic factor for all malignancies. This extent of metastatic disease progression remains difficult to treat with systemic therapies due to poor peritoneal vascularization resulting in limited drug delivery and penetration into tissues. Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) are surgical interventions that directly target peritoneal tumors and have improved outcomes for PC resulting from appendiceal and colorectal cancer (CRC). Despite these radical therapies, long-term survival remains infrequent, and recurrence is common. The reasons for these outcomes are multifactorial and signal the need for the continued development of novel therapeutics, techniques, and approaches to improve outcomes for these patients. Here, we review landmark historical studies that serve as the foundation for current recommendations, recent discoveries, clinical trials, active research, and areas of future interest in CRS/HIPEC to treat PC originating from appendiceal and colorectal malignancies.

Phenotyping Cardiopulmonary Exercise Limitations in Chronic Obstructive Pulmonary Disease.

BACKGROUND: Exercise limitation in chronic obstructive pulmonary disease (COPD) is commonly attributed to abnormal ventilatory mechanics and/or skeletal muscle function, while cardiovascular contributions remain relatively understudied. To date, the integrative exercise responses associated with different cardiopulmonary exercise limitation phenotypes in COPD have not been explored but may provide novel therapeutic utility. This study determined the ventilatory, cardiovascular, and metabolic responses to incremental exercise in patients with COPD with different exercise limitation phenotypes. METHODS: Patients with COPD (n = 95, FEV1:23-113%pred) performed a pulmonary function test and incremental cardiopulmonary exercise test. Exercise limitation phenotypes were classified as: ventilatory [peak ventilation (VEpeak)/maximal ventilatory capacity (MVC) ≥ 85% or MVC-VEpeak ≤ 11 L/min, and peak heart rate (HRpeak) < 90%pred], cardiovascular (VEpeak/MVC < 85% or MVC-VEpeak > 11 L/min, and HRpeak ≥ 90%pred), or combined (VEpeak/MVC ≥ 85% or MVC-VEpeak ≤ 11 L/min, and HRpeak ≥ 90%pred). RESULTS: FEV1 varied within phenotype: ventilatory (23-75%pred), combined (28-90%pred), and cardiovascular (68-113%pred). The cardiovascular phenotype had less static hyperinflation, a lower end-expiratory lung volume and larger tidal volume at peak exercise compared to both other phenotypes (p < 0.01 for all). The cardiovascular phenotype reached a higher VEpeak (60.8 ± 11.5 L/min vs. 45.3 ± 15.5 L/min, p = 0.002), cardiopulmonary fitness (VO2peak: 20.6 ± 4.0 ml/kg/min vs. 15.2 ± 3.3 ml/kg/min, p < 0.001), and maximum workload (103 ± 34 W vs. 72 ± 27 W, p < 0.01) vs. the ventilatory phenotype, but was similar to the combined phenotype. CONCLUSION: Distinct exercise limitation phenotypes were identified in COPD that were not solely dependent upon airflow limitation severity. Approximately 50% of patients reached maximal heart rate, indicating that peak cardiac output and convective O2 delivery contributed to exercise limitation. Categorizing patients with COPD phenotypically may aid in optimizing exercise prescription for rehabilitative purposes.

Development of a Single-Cell Technique to Increase Yield and Use of Gastrointestinal Cancer Organoids for Personalized Medicine Application.

BACKGROUND: Organoids are excellent 3-dimensional in vitro models of gastrointestinal cancers. However, patient-derived organoids (PDOs) remain inconsistent and unreliable for rapid actionable drug sensitivity testing due to size variation and limited material. STUDY DESIGN: On day10/passage 2 after standard creation of organoids, half of PDOs were dissociated into single-cells with TrypLE Express Enzyme/DNase I and mechanical dissociation; and half of PDOs were expanded by the standard technique. Hematoxylin and eosin and immunohistochemistry with CK7 and CK20 were performed for characterization. Drug sensitivity testing was completed for single-cells and paired standard PDOs to assess reproducibility. RESULTS: After 2 to 3 days, >50% of single-cells reformed uniform miniature PDOs (∼50 µm). We developed 10 PDO single-cell lines (n = 4, gastric cancer, [GC]; and n = 6, pancreatic ductal adenocarcinoma, [PDAC]), which formed epithelialized cystic structures and by IHC, exhibited CK7(high)/CK20(low) expression patterns mirroring parent tissues. Compared with paired standard PDOs, single-cells (n = 2, PDAC; = 2, GC) showed similar architecture, albeit smaller and more uniform. Importantly, single cells demonstrated similar sensitivity to cytotoxic drugs to matched PDOs. CONCLUSIONS: PDO single-cells are accurate for rapid clinical drug testing in gastrointestinal cancers. Using early passage PDO single-cells facilitates high-volume drug testing, decreasing time from tumor sampling to actionable clinical decisions, and provides a personalized medicine platform to optimally select drugs for gastrointestinal cancer patients.

Mechanical cardiopulmonary interactions during exercise in health and disease.

The heart and lungs are anatomically coupled through the pulmonary circulation and coexist within the sealed thoracic cavity, making the function of these systems highly interdependent. Understanding of the complex mechanical interactions between cardiac and pulmonary systems has evolved over the last century to appreciate that changes in respiratory mechanics significantly impact pulmonary hemodynamics and ventricular filling and ejection. Furthermore, given that the left and right heart share a common septum and are surrounded by the nondistensible pericardium, direct ventricular interaction is an important mediator of both diastolic and systolic performance. Although it is generally considered that cardiopulmonary interaction in healthy individuals at rest minimally affects hemodynamics, the significance during exercise is less clear. Adverse heart-lung interaction in respiratory disease is of growing interest as it may contribute to the pathogenesis of comorbid cardiovascular dysfunction and exercise intolerance in these patients. Similarly, heart failure represents a pathological uncoupling of the cardiovascular and pulmonary systems, whereby cardiac function may be impaired by the normal ventilatory response to exercise. Despite significant research contributions to this complex area, the mechanisms of cardiopulmonary interaction in the intact human and the clinical consequences of adverse interactions in common respiratory and cardiovascular diseases, particularly during exercise, remain incompletely understood. The purpose of this review is to present the key physiological principles of cardiopulmonary interaction as they pertain to resting and exercising hemodynamics in healthy humans and the clinical implications of adverse cardiopulmonary interaction during exercise in chronic obstructive pulmonary disease (COPD), pulmonary hypertension, and heart failure.

MST1R kinase accelerates pancreatic cancer progression via effects on both epithelial cells and macrophages.

The MST1R (RON) kinase is overexpressed in >80% of human pancreatic cancers, but its role in pancreatic carcinogenesis is unknown. In this study, we examined the relevance of Mst1r kinase to Kras driven pancreatic carcinogenesis using genetically engineered mouse models. In the setting of mutant Kras, Mst1r overexpression increased acinar-ductal metaplasia (ADM), accelerated the progression of pancreatic intraepithelial neoplasia (PanIN), and resulted in the accumulation of (mannose receptor C type 1) MRC1+, (arginase 1) Arg+ macrophages in the tumor microenvironment. Conversely, absence of a functional Mst1r kinase slowed PanIN initiation, resulted in smaller tumors, prolonged survival and a reduced tumor-associated macrophage content. Mst1r expression was associated with increased production of its ligand Mst1, and in orthotopic models, suppression of Mst1 expression resulted in reduced tumor size, changes in macrophage polarization and enhanced T cell infiltration. This study demonstrates the functional significance of Mst1r during pancreatic cancer initiation and progression. Further, it provides proof of concept that targeting Mst1r can modulate pancreatic cancer growth and the microenvironment. This study provides further rationale for targeting Mst1r as a therapeutic strategy.

Effect of Kinesio® Taping on Ankle Complex Motion and Stiffness and Jump Landing Time to Stabilization in Female Ballet Dancers.

Ankle sprain is the most commonly diagnosed injury experienced by ballet dancers with few studies investigating preventive support measures such as Kinesio taping. The need exists to examine the mechanical support characteristics of Kinesio taping and effect of application on ankle motion and performance. This may be important to understanding the mechanical mechanisms attributed to Kinesio ankle taping and justify its use in the prevention and treatment of jump landing injuries in ballet dancers. This study compared Kinesio taping with and without tension and no tape (control) on active and passive measures of ankle complex motion in healthy ballet dancers. A secondary objective was to examine the effect of Kinesio taping on balance using time to stabilization. Participants performed three ballet jumps with single-leg landings on a force plate across three ankle support conditions consisting of Kinesio taping, sham-Kinesio taping, and no tape. Sagittal and frontal plane motion and load-displacement of the ankle complex for each support condition were obtained using an ankle arthrometer. Kinesio taping with tension significantly restricted inversion-eversion rotation and increased inversion stiffness of the ankle complex (p < 0.05). No significant differences were found among the three ankle support conditions for jump landing time to stabilization (p > 0.05). Arthrometric results indicate Kinesio taping significantly restricted ankle complex motion in the frontal plane that is associated with lateral ankle sprain. Objective information on the nature of Kinesio taping support can assist sports medicine practitioners when recommending ankle support to athletes.

Tenuous Inhibitory GABAergic Signaling in the Reticular Thalamus.

Maintenance of a low intracellular Cl- concentration ([Cl-]i) is critical for enabling inhibitory neuronal responses to GABAA receptor-mediated signaling. Cl- transporters, including KCC2, and extracellular impermeant anions ([A]o) of the extracellular matrix are both proposed to be important regulators of [Cl-]i Neurons of the reticular thalamic (RT) nucleus express reduced levels of KCC2, indicating that GABAergic signaling may produce excitation in RT neurons. However, by performing perforated patch recordings and calcium imaging experiments in rats (male and female), we find that [Cl-]i remains relatively low in RT neurons. Although we identify a small contribution of [A]o to a low [Cl-]i in RT neurons, our results also demonstrate that reduced levels of KCC2 remain sufficient to maintain low levels of Cl- Reduced KCC2 levels, however, restrict the capacity of RT neurons to rapidly extrude Cl- following periods of elevated GABAergic signaling. In a computational model of a local RT network featuring slow Cl- extrusion kinetics, similar to those we found experimentally, model RT neurons are predisposed to an activity-dependent switch from GABA-mediated inhibition to excitation. By decreasing the activity threshold required to produce excitatory GABAergic signaling, weaker stimuli are able to propagate activity within the model RT nucleus. Our results indicate the importance of even diminished levels of KCC2 in maintaining inhibitory signaling within the RT nucleus and suggest how this important activity choke point may be easily overcome in disorders such as epilepsy.SIGNIFICANCE STATEMENT Precise regulation of intracellular Cl- levels ([Cl-]i) preserves appropriate, often inhibitory, GABAergic signaling within the brain. However, there is disagreement over the relative contribution of various mechanisms that maintain low [Cl-]i We found that the Cl- transporter KCC2 is an important Cl- extruder in the reticular thalamic (RT) nucleus, despite this nucleus having remarkably low KCC2 immunoreactivity relative to other regions of the adult brain. We also identified a smaller contribution of fixed, impermeant anions ([A]o) to lowering [Cl-]i in RT neurons. Inhibitory signaling among RT neurons is important for preventing excessive activation of RT neurons, which can be responsible for generating seizures. Our work suggests that KCC2 critically restricts the spread of activity within the RT nucleus.