Association Between Biliary Pathogens, Surgical Site Infection, and Pancreatic Fistula: Results of a Randomized Trial of Perioperative Antibiotic Prophylaxis in Patients Undergoing Pancreatoduodenectomy.

OBJECTIVE: To establish the association between bactibilia and postoperative complications when stratified by perioperative antibiotic prophylaxis. BACKGROUND: Patients undergoing pancreatoduodenectomy experience high rates of surgical site infection (SSI) and clinically relevant postoperative pancreatic fistula (CR-POPF). Contaminated bile is known to be associated with SSI, but the role of antibiotic prophylaxis in mitigation of infectious risks is ill-defined. METHODS: Intraoperative bile cultures (IOBCs) were collected as an adjunct to a randomized phase 3 clinical trial comparing piperacillin-tazobactam with cefoxitin as perioperative prophylaxis in patients undergoing pancreatoduodenectomy. After compilation of IOBC data, associations between culture results, SSI, and CR-POPF were assessed using logistic regression stratified by the presence of a preoperative biliary stent. RESULTS: Of 778 participants in the clinical trial, IOBC were available for 247 participants. Overall, 68 (27.5%) grew no organisms, 37 (15.0%) grew 1 organism, and 142 (57.5%) were polymicrobial. Organisms resistant to cefoxitin but not piperacillin-tazobactam were present in 95 patients (45.2%). The presence of cefoxitin-resistant organisms, 92.6% of which contained either Enterobacter spp. or Enterococcus spp., was associated with the development of SSI in participants treated with cefoxitin [53.5% vs 25.0%; odds ratio (OR)=3.44, 95% CI: 1.50-7.91; P =0.004] but not those treated with piperacillin-tazobactam (13.5% vs 27.0%; OR=0.42, 95% CI: 0.14-1.29; P =0.128). Similarly, cefoxitin-resistant organisms were associated with CR-POPF in participants treated with cefoxitin (24.1% vs 5.8%; OR=3.45, 95% CI: 1.22-9.74; P =0.017) but not those treated with piperacillin-tazobactam (5.4% vs 4.8%; OR=0.92, 95% CI: 0.30-2.80; P =0.888). CONCLUSIONS: Previously observed reductions in SSI and CR-POPF in patients that received piperacillin-tazobactam antibiotic prophylaxis are potentially mediated by biliary pathogens that are cefoxitin resistant, specifically Enterobacter spp. and Enterococcus spp.

Piperacillin-Tazobactam Compared With Cefoxitin as Antimicrobial Prophylaxis for Pancreatoduodenectomy: A Randomized Clinical Trial.

Importance: Despite improvements in perioperative mortality, the incidence of postoperative surgical site infection (SSI) remains high after pancreatoduodenectomy. The effect of broad-spectrum antimicrobial surgical prophylaxis in reducing SSI is poorly understood. Objective: To define the effect of broad-spectrum perioperative antimicrobial prophylaxis on postoperative SSI incidence compared with standard care antibiotics. Design, Setting, and Participants: Pragmatic, open-label, multicenter, randomized phase 3 clinical trial at 26 hospitals across the US and Canada. Participants were enrolled between November 2017 and August 2021, with follow-up through December 2021. Adults undergoing open pancreatoduodenectomy for any indication were eligible. Individuals were excluded if they had allergies to study medications, active infections, chronic steroid use, significant kidney dysfunction, or were pregnant or breastfeeding. Participants were block randomized in a 1:1 ratio and stratified by the presence of a preoperative biliary stent. Participants, investigators, and statisticians analyzing trial data were unblinded to treatment assignment. Intervention: The intervention group received piperacillin-tazobactam (3.375 or 4 g intravenously) as perioperative antimicrobial prophylaxis, while the control group received cefoxitin (2 g intravenously; standard care). Main Outcomes and Measures: The primary outcome was development of postoperative SSI within 30 days. Secondary end points included 30-day mortality, development of clinically relevant postoperative pancreatic fistula, and sepsis. All data were collected as part of the American College of Surgeons National Surgical Quality Improvement Program. Results: The trial was terminated at an interim analysis on the basis of a predefined stopping rule. Of 778 participants (378 in the piperacillin-tazobactam group [median age, 66.8 y; 233 {61.6%} men] and 400 in the cefoxitin group [median age, 68.0 y; 223 {55.8%} men]), the percentage with SSI at 30 days was lower in the perioperative piperacillin-tazobactam vs cefoxitin group (19.8% vs 32.8%; absolute difference, -13.0% [95% CI, -19.1% to -6.9%]; P < .001). Participants treated with piperacillin-tazobactam, vs cefoxitin, had lower rates of postoperative sepsis (4.2% vs 7.5%; difference, -3.3% [95% CI, -6.6% to 0.0%]; P = .02) and clinically relevant postoperative pancreatic fistula (12.7% vs 19.0%; difference, -6.3% [95% CI, -11.4% to -1.2%]; P = .03). Mortality rates at 30 days were 1.3% (5/378) among participants treated with piperacillin-tazobactam and 2.5% (10/400) among those receiving cefoxitin (difference, -1.2% [95% CI, -3.1% to 0.7%]; P = .32). Conclusions and Relevance: In participants undergoing open pancreatoduodenectomy, use of piperacillin-tazobactam as perioperative prophylaxis reduced postoperative SSI, pancreatic fistula, and multiple downstream sequelae of SSI. The findings support the use of piperacillin-tazobactam as standard care for open pancreatoduodenectomy. Trial Registration: ClinicalTrials.gov Identifier: NCT03269994.

The past, present and future of ACS NSQIP-Pediatric: Evolution from a quality registry to a comparative quality performance platform.

Quality and process improvement (QI/PI) in children's surgical care require reliable data across the care continuum. Since 2012, the American College of Surgeons' (ACS) National Surgical Quality Improvement Program-Pediatric (NSQIP-Pediatric) has supported QI/PI by providing participating hospitals with risk-adjusted, comparative data regarding postoperative outcomes for multiple surgical specialties. To advance this goal over the past decade, iterative changes have been introduced to case inclusion and data collection, analysis and reporting. New datasets for specific procedures, such as appendectomy, spinal fusion for scoliosis, vesicoureteral reflux procedures, and tracheostomy in children less than 2 years old, have incorporated additional risk factors and outcomes to enhance the clinical relevance of data, and resource utilization to consider healthcare value. Recently, process measures for urgent surgical diagnoses and surgical antibiotic prophylaxis variables have been developed to promote timely and appropriate care. While a mature program, NSQIP-Pediatric remains dynamic and responsive to meet the needs of the surgical community. Future directions include introduction of variables and analyses to address patient-centered care and healthcare equity.

Correlation Between Postoperative Antimicrobial Prophylaxis Use and Surgical Site Infection in Children Undergoing Nonemergent Surgery.

Importance: Use of postoperative antimicrobial prophylaxis is common in pediatric surgery despite consensus guidelines recommending discontinuation following incision closure. The association between postoperative prophylaxis use and surgical site infection (SSI) in children undergoing surgical procedures remains poorly characterized. Objective: To evaluate whether use of postoperative surgical prophylaxis is correlated with SSI rates in children undergoing nonemergent surgery. Design, Setting, and Participants: This is a multicenter cohort study using 30-day postoperative SSI data from the American College of Surgeons' Pediatric National Surgical Quality Improvement Program (ACS NSQIP-Pediatric) augmented with antibiotic-use data obtained through supplemental medical record review from June 2019 to June 2021. This study took place at 93 hospitals participating in the ACS NSQIP-Pediatric Surgical Antibiotic Prophylaxis Stewardship Collaborative. Participants were children (<18 years of age) undergoing nonemergent surgical procedures. Exclusion criteria included antibiotic allergies, conditions associated with impaired immune function, and preexisting infections requiring intravenous antibiotics at time of surgery. Exposures: Continuation of antimicrobial prophylaxis beyond time of incision closure. Main Outcomes and Measures: Thirty-day postoperative rate of incisional or organ space SSI. Hierarchical regression was used to estimate hospital-level odds ratios (ORs) for SSI rates and postoperative prophylaxis use. SSI measures were adjusted for differences in procedure mix, patient characteristics, and comorbidity profiles, while use measures were adjusted for clinically related procedure groups. Pearson correlations were used to examine the associations between hospital-level postoperative prophylaxis use and SSI measures. Results: Forty thousand six hundred eleven patients (47.3% female; median age, 7 years) were included, of which 41.6% received postoperative prophylaxis (hospital range, 0%-71.2%). Odds ratios (ORs) for postoperative prophylaxis use ranged 190-fold across hospitals (OR, 0.10-19.30) and ORs for SSI rates ranged 4-fold (OR, 0.55-1.90). No correlation was found between use of postoperative prophylaxis and SSI rates overall (r = 0.13; P = .20), and when stratified by SSI type (incisional SSI, r = 0.08; P = .43 and organ space SSI, r = 0.13; P = .23), and surgical specialty (general surgery, r = 0.02; P = .83; urology, r = 0.05; P = .64; plastic surgery, r = 0.11; P = .35; otolaryngology, r = -0.13; P = .25; orthopedic surgery, r = 0.05; P = .61; and neurosurgery, r = 0.02; P = .85). Conclusions and Relevance: Use of postoperative surgical antimicrobial prophylaxis was not correlated with SSI rates at the hospital level after adjusting for differences in procedure mix and patient characteristics.

Hyperamylasemia grade versus drain fluid amylase: which better predicts pancreatectomy outcomes?

BACKGROUND: The clinical importance of postoperative hyperamylasemia (POHA) grade is unknown. Our objectives were to evaluate the association of POHA grade with clinically relevant postoperative pancreatic fistula (CR-POPF) and compare its prognostic utility against postoperative day 1 drain fluid amylase (DFA-1). METHODS: Patients who underwent pancreatectomy from January 2019 through March 2020 were identified in the ACS NSQIP pancreatectomy-targeted dataset. POHA grade was assigned using post-operative serum amylase and clinical sequelae. The primary outcome was CR-POPF within 30 days. The association of POHA grade with CR-POPF was assessed using multivariable logistic regression, and c-statistics were used to compare POHA grade versus DFA-1. RESULTS: POHA occurred in 520 patients at 98 hospitals, including 261 (50.2%) with grade A, 234 (45.0%) with grade B, and 25 (4.8%) with grade C POHA. CR-POPFs were increased among patients with grade B (66.2%, OR 9.28 [5.84-14.73]) and C (68.0%, OR 10.50 [3.77-29.26]) versus grade A POHA (19.2%). POHA-inclusive models better predicted CR-POPF than those with DFA-1 alone (p < 0.002) and models with both predictors outperformed POHA alone (p = 0.039). CONCLUSION: POHA grade represents a measure of post-pancreatectomy outcomes that predicts CR-POPF and outperforms DFA-1 but must be aligned with new international definitions.

Optimal hepatic surgery: Are we making progress in North America?

BACKGROUND: The aim of this analysis was to determine whether optimal outcomes have increased in recent years. Hepatic surgery is high risk, but regionalization and minimally invasive approaches have evolved. Best practices also have been defined with the goal of improving outcomes. METHODS: The American College of Surgeons National Surgical Quality Improvement Program database was queried. Analyses were performed separately for partial (≤2 segments), major (≥3 segments), and all hepatectomies. Optimal hepatic surgery was defined as the absence of mortality, serious morbidity, need for a postoperative invasive procedure or reoperation, prolonged length of stay (<75th percentile) or readmission. Tests of trend, χ2, and multivariable analyses were performed. RESULTS: From 2014 to 2018, 17,082 hepatectomies, including 11,862 partial hepatectomies and 5,220 major hepatectomies, were analyzed. Minimally invasive approaches increased from 25.6% in 2014 to 29.6% in 2018 (P < .01) and were performed more frequently for partial hepatectomies (34.2%) than major hepatectomies (14.4%) (P < .01). Operative time decreased from 220 minutes in 2014 to 208 minutes in 2018 (P < .05) and was lower in partial hepatectomies (189 vs 258 minutes for major hepatectomies) (P < .01). Mortality (0.7%) and length of stay (4 days) were lower for partial hepatectomies compared with major hepatectomies (1.9%; 6 days), and length of stay decreased for both partial hepatectomies (5 days in 2014 to 4 days in 2018) and major hepatectomies (6 days in 2014 to 6 days in 2018) (all P < .01). Postoperative sepsis (2.9% in 2014 and 2.4% in 2018), bile leaks (6% in 2014 and 4.8% in 2018), and liver failure (3.7% in 2014 and 3.3% in 2018) decreased for all patients (<.05). On multivariable analyses, overall morbidity decreased for major hepatectomies (OR 0.95, 95% CI 0.91-0.99) and all hepatectomies (OR 0.97, 95% CI 0.94-0.99, both P < .01), and optimal hepatic surgery increased over time for partial hepatectomies (OR 1.05, 95% CI 1.02-1.09) and all hepatectomies (OR 1.04, 95% CI 1.02-1.07, both P < .01). CONCLUSION: Over a 5-year period in North America, minimally invasive hepatectomies have increased, while operative time, postoperative sepsis, bile leaks, liver failure, and prolonged length of stay have decreased. Optimal hepatic surgery has increased for partial and all hepatectomies and is achieved more often in partial than in major resections.

Optimal Pancreatic Surgery: Are We Making Progress in North America?

OBJECTIVE: Our aims were to assess North American trends in the management of patients undergoing pancreatoduodenectomy (PD) and distal pancreatectomy (DP), and to quantify the delivery of optimal pancreatic surgery. BACKGROUND: Morbidity after pancreatectomy remains unacceptably high. Recent literature suggests that composite measures may more accurately define surgical quality. METHODS: The 2013 to 2017 American College of Surgeons National Surgical Quality Improvement Program Participant Use Files were queried to identify patients undergoing PD (N = 16,222) and DP (N = 7946). Patient, process, procedure, and 30-day postoperative outcome variables were analyzed over time. Optimal pancreatic surgery was defined as the absence of postoperative mortality, serious morbidity, percutaneous drainage, and reoperation while achieving a length of stay equal to or less than the 75th percentile (12 days for PD and 7 days for DP) with no readmissions. Risk-adjusted time-trend analyses were performed using logistic regression, and the threshold for statistical significance was P ≤ 0.05. RESULTS: The use of minimally invasive PD did not change over time, but robotic PD increased (2.5 to 4.2%; P < 0.001) and laparoscopic PD decreased (5.8% to 4.3%; P < 0.02). Operative times decreased (P < 0.05) and fewer transfusions were administered (P < 0.001). The percentage of patients with a drain fluid amylase checked on postoperative day 1 increased (P < 0.001), and a greater percentage of surgical drains were removed by postoperative day 3 (P < 0.001). Overall morbidity (P < 0.02), mortality (P < 0.05), and postoperative length of stay (P = 0.002) decreased. Finally, the rate of optimal pancreatic surgery increased for PD (53.7% to 56.9%; P < 0.01) and DP (53.3% to 58.5%; P < 0.001), and alspo for patients with pancreatic cancer (P < 0.01). CONCLUSIONS: From 2013 to 2017, pre, intra, and perioperative pancreatectomy processes have evolved, and multiple postoperative outcomes have improved. Thus, in 4 years, optimal pancreatic surgery in North America has increased by 3% to 5%.

Association of Patient-reported Experiences and Surgical Outcomes Among Group Practices: Retrospective Cohort Study.

OBJECTIVE: The aim of the study was to determine the association of patient-reported experiences (PREs) and risk-adjusted surgical outcomes among group practices. BACKGROUND: The Centers for Medicare and Medicaid Services required large group practices to submit PREs data for successful participation in the Physician Quality Reporting System (PQRS) using the Consumer Assessment of Healthcare Providers and Systems for PQRS survey. Whether these PREs data correlate with perioperative outcomes remains ill defined. METHODS: Operations between January 1, 2014 and December 31, 2016 in the American College of Surgeons' National Surgical Quality Improvement Program registry were merged with 2015 Consumer Assessment of Healthcare Providers and Systems for PQRS survey data. Hierarchical logistic models were constructed to estimate associations between 7 subscales and 1 composite score of PREs and 30-day morbidity, unplanned readmission, and unplanned reoperation, separately, while adjusting for patient- and procedure mix. RESULTS: Among 328 group practices identified, patients reported their experiences with clinician communication the highest (mean ±â€Šstandard deviation, 82.66 ±â€Š3.10), and with attention to medication cost the lowest (25.96 ±â€Š5.14). The mean composite score was 61.08 (±6.66). On multivariable analyses, better PREs scores regarding medication cost, between-visit communication, and the composite score of experience were each associated with 4% decreased odds of morbidity [odds ratio (OR) 0.96, 95% confidence interval (CI) 0.92-0.99], readmission (OR 0.96, 95% CI 0.93-0.99), and reoperation (OR 0.96, 95% CI 0.93-0.99), respectively. In sensitivity analyses, better between-visit communication remained significantly associated with fewer readmissions. CONCLUSIONS: In these data, patients' report of better between-visit communication was associated with fewer readmissions. More sensitive, surgery-specific PRE assessments may reveal additional unique insights for improving the quality of surgical care.

Assessing the influence of experience in pancreatic surgery: a risk-adjusted analysis using the American College of Surgeons NSQIP database.

BACKGROUND: The association between higher surgical volume and better perioperative outcomes after pancreatectomy has been extensively demonstrated. However, how different notions of experience impact outcomes of surgeons operating within high-quality scenarios remains unclear. METHODS: Self-reported experience parameters from ACS-NSQIP HPB-Collaborative surgeons were merged with 2014-2016 ACS-NSQIP clinical data. The association of various experience parameters with outcomes was investigated through uni- and multivariable analyses. Hierarchical regression assessed surgeon performance. RESULTS: 111/151 HPB-Collaborative surgeons provided responses (73.5%). Compared to the other 532 ACS-NSQIP surgeons performing pancreatectomy, HPB-Collaborative surgeons performed 7692/16,239 of the overall pancreatectomies (47.3%), with improved outcomes of serious morbidity, pancreatic fistula, reoperation, duration of stay and readmissions. Median age of respondents was 49 years and 92.8% were fellowship-trained. Median career and annual pancreatectomy volume were 400 and 35, respectively; median annual institutional volume was 100 resections. On unadjusted analyses, several aspects of experience were associated with the outcomes studied, especially for pancreatoduodenectomy; however, none remained significant after multivariable adjustment. Surgeons' profiling showed substantial homogeneity in performance for both pancreatoduodenectomy and distal pancreatectomy. CONCLUSIONS: Contemporary data shows that for surgeons operating in high quality settings clinical outcomes are largely independent of indicators of greater experience.

Wound protectors mitigate superficial surgical site infections after pancreatoduodenectomy.

BACKGROUND: Whether the choice of antibiotic prophylaxis, the type of incision, or the use of wound protectors decreases surgical site infections (SSIs) in patients undergoing pancreatoduodenectomy (PD) remains unknown. METHODS: Patients undergoing open, elective PD between January 1, 2016 and June 30, 2017 were identified from the American College of Surgeons' National Surgical Quality Improvement Program registry. Multivariable logistic regression models were constructed to determine the association of antibiotic prophylaxis type, incision type, and wound protector use on the incidence of any, superficial, and organ/space SSIs, and to profile hospitals. RESULTS: Overall, 5969 patients were included from 140 hospitals. The overall rate of SSI was 20.3% (n = 1213). Superficial SSIs occurred in 432 (7.2%) patients and organ/space SSIs in 841 (14.1%). Wound protector use was associated with 23% lower odds of experiencing any SSIs (OR 0.77, 95% CI 0.60-0.98), reflective of the decreased odds associated with superficial SSIs (OR 0.65, 95% CI 0.44-0.97), but not organ/space SSIs (OR 0.89, 95% CI 0.68-1.17). Highest-performing hospitals frequently utilized broad-spectrum antibiotics, midline incisions, and wound protectors. CONCLUSION: Wound protectors reduced superficial, but not organ/space, infections in patients undergoing pancreatoduodenectomy. Routine use of wound protectors in patients undergoing proximal pancreatectomy is recommended.

Albumin-Bilirubin Score: Predicting Short-Term Outcomes Including Bile Leak and Post-hepatectomy Liver Failure Following Hepatic Resection.

INTRODUCTION: Post-operative bile leak (BL) and post hepatectomy liver failure (PHLF) are the major potential sources of morbidity among patients undergoing liver resection. We sought to define the incidence of BL and PHLF among a large cohort of patients, as well as examine the prognostic impact of model for end-stage liver disease (MELD) and albumin-bilirubin (ALBI) scores to predict these short-term outcomes. MATERIALS AND METHODS: Patients who underwent a hepatectomy between January 1, 2014 and December 31, 2014 were identified using the National Surgical Quality Improvement Program (NSQIP) liver-targeted database. Risk factors for BL and PHLF were identified using multivariable logistic regression. RESULTS: Among the 3064 patients identified, median age was 60 years (IQR 50-68). Most patients underwent surgery (78.9 %) for malignant lesions. Post-operatively, 250 (8.5 %) patients experienced a BL while PHLF occurred in 149 cases (4.9 %). Both MELD (MELD <10 4.9 %; MELD ≥10, 10 %; P = 0.001) and ALBI (grade 1, 4.0 %; grade 2, 7.2 %; grade 3, 10.0 %; P = 0.001) were associated with PHLF occurrence, while only ALBI predicted PHLF severity (P = 0.008). Moreover, ALBI was associated with BL (grade 1, 7.1 %; grade 2, 11.5 %; grade 3, 14.0 %; P < 0.001), whereas MELD was not (MELD <10, 8.4 %; MELD ≥10, 11.2 %; P = 0.13). On multivariable analysis, ALBI grade 2/3 was associated with PHLF (OR 1.57, 95 % CI 1.08-2.27; P = 0.02), PHLF severity (OR 3.06, 95 % CI 1.50-6.23; P = 0.003), and the development of a BL (OR 1.35, 95 % CI 1.02-1.80; P = 0.04). CONCLUSION: The ALBI score was associated with short-term post-operative outcomes following hepatic resection and represents a useful pre-operative risk-assessment tool to identify patients at risk for adverse post-operative outcomes.

Patterns of hepatic resections in North America: use of concurrent partial resections and ablations.

BACKGROUND: National registries have not adequately captured concurrent partial hepatic resections or ablations. Therefore, the aim of this analysis was to describe the patterns of concurrent partial resections and ablations in North America. METHODS: Patients undergoing a hepatic resection were identified using the American College of Surgeons-National Surgical Quality Improvement Program Targeted Hepatectomy database. Perioperative outcomes were compared for patients undergoing concurrent "wedge" resections and/or ablations and other subsets. RESULTS: A total of 2714 patients were identified who met inclusion criteria. Major hepatectomy was performed in 1037 patients (38.2%) while partial lobectomy was performed in 1677 (61.8%) patients. Concurrent "wedge" hepatic resections and ablations were undertaken in 56.0% and 14.2% of patients, respectively, and were more frequently performed among patients undergoing a partial lobectomy and among patients undergoing surgery for colorectal liver metastasis (both p < 0.001). While associated with a decreased incidence of postoperative complications (p = 0.027) and liver failure (p = 0.031) among patients undergoing a major hepatectomy, concurrent therapies were associated with comparable 30-day outcomes for patients undergoing partial lobectomy. CONCLUSION: Concurrent "wedge" hepatic resections and ablations are performed in 56.0% and 14.2%, respectively of patients undergoing hepatectomy. Concurrent procedures were not associated with worse clinical outcomes.

Greater glucocorticoid receptor activation in hippocampus of aged rats sensitizes microglia.

Healthy aging individuals are more likely to suffer profound memory impairments following an immune challenge than are younger adults. These challenges produce a brain inflammatory response that is exaggerated with age. Sensitized microglia found in the normal aging brain are responsible for this amplified response, which in turn interferes with processes involved in memory formation. Here, we examine factors that may lead aging to sensitize microglia. Aged rats exhibited higher corticosterone levels in the hippocampus, but not in plasma, throughout the daytime (diurnal inactive phase). These elevated hippocampal corticosterone levels were associated with increased hippocampal 11ß-hydroxysteroid dehydrogenase type 1 protein expression, the enzyme that catalyzes glucocorticoid formation and greater hippocampal glucocorticoid receptor (GR) activation. Intracisternal administration of mifepristone, a GR antagonist, effectively reduced immune-activated proinflammatory responses, specifically from hippocampal microglia and prevented Escherichia coli-induced memory impairments in aged rats. Voluntary exercise as a therapeutic intervention significantly reduced total hippocampal GR expression. These data strongly suggest that increased GR activation in the aged hippocampus plays a critical role in sensitizing microglia.

The role of hepatic and splenic macrophages in E. coli-induced memory impairments in aged rats.

Bi-directional communication between the peripheral and central nervous systems has been extensively demonstrated. Aged rats exhibit a prolonged proinflammatory response in the hippocampus region of the brain following a peripheral bacterial infection, and this response in turn causes robust memory declines. Here we aimed to determine whether hepatic or splenic macrophages play a role in the maintenance of this central response. Proinflammatory cytokines measured in liver and spleen four days following an Escherichia coli infection revealed a potentiated proinflammatory response in liver, and to a lesser extent in spleen, in aged relative to young rats. To determine whether this potentiated response was caused by impaired bacterial clearance in these organs, E. coli colony forming units in liver and spleen were measured 4 days after infection, and there were no difference between young and aged rats in either organ. No E. coli was detected in the hippocampus, eliminating the possibility that the aged blood brain barrier allowed E. coli to enter the brain. Depletion of hepatic and splenic macrophages with clodronate-encapsulated liposomes effectively eliminated the proinflammatory response to E. coli at four days in both organs. However, this treatment failed to reduce the proinflammatory response in the hippocampus. Moreover, depletion of peripheral macrophages from liver and spleen did not prevent E. coli-induced memory impairment. These data strongly suggest that hepatic and splenic macrophages do not play a major role in the long-lasting maintenance of the proinflammatory response in the hippocampus of aged rats following a bacterial infection, or the memory declines that this response produces.

Influence of Pre-Training Predator Stress on the Expression of c-fos mRNA in the Hippocampus, Amygdala, and Striatum Following Long-Term Spatial Memory Retrieval.

We have studied the influence of pre-training psychological stress on the expression of c-fos mRNA following long-term spatial memory retrieval. Rats were trained to learn the location of a hidden escape platform in the radial-arm water maze, and then their memory for the platform location was assessed 24 h later. Rat brains were extracted 30 min after the 24-h memory test trial for analysis of c-fos mRNA. Four groups were tested: (1) Rats given standard training (Standard); (2) Rats given cat exposure (Predator Stress) 30 min prior to training (Pre-Training Stress); (3) Rats given water exposure only (Water Yoked); and (4) Rats given no water exposure (Home Cage). The Standard trained group exhibited excellent 24 h memory which was accompanied by increased c-fos mRNA in the dorsal hippocampus and basolateral amygdala (BLA). The Water Yoked group exhibited no increase in c-fos mRNA in any brain region. Rats in the Pre-Training Stress group were classified into two subgroups: good and bad memory performers. Neither of the two Pre-Training Stress subgroups exhibited a significant change in c-fos mRNA expression in the dorsal hippocampus or BLA. Instead, stressed rats with good memory exhibited significantly greater c-fos mRNA expression in the dorsolateral striatum (DLS) compared to stressed rats with bad memory. This finding suggests that stressed rats with good memory used their DLS to generate a non-spatial (cue-based) strategy to learn and subsequently retrieve the memory of the platform location. Collectively, these findings provide evidence at a molecular level for the involvement of the hippocampus and BLA in the retrieval of spatial memory and contribute novel observations on the influence of pre-training stress in activating the DLS in response to long-term memory retrieval.