Performance of ceftazidime/avibactam susceptibility testing methods against clinically relevant Gram-negative organisms.

OBJECTIVES: To ensure the accuracy of susceptibility testing methods for ceftazidime/avibactam. METHODS: The performances of the Etest (bioMérieux), 30/20 µg disc (Hardy diagnostics) and 10/4 µg disc (Mast Group) were evaluated against the reference broth microdilution (BMD) method for 102 clinically relevant Gram-negative organisms: 69 ceftazidime- and meropenem-resistant Klebsiella pneumoniae and 33 MDR non-K. pneumoniae. Essential and categorical agreement along with major and very major error rates were determined according to CLSI guidelines. RESULTS: A total of 78% of isolates were susceptible to ceftazidime/avibactam. None of the three methods met the defined equivalency threshold against all 102 organisms. The Etest performed the best, with categorical agreement of 95% and major errors of 6.3%. Against the 69 ceftazidime- and meropenem-resistant K. pneumoniae, only the Etest and the 10/4 µg disc met the equivalency threshold. None of the three methods met equivalency for the 33 MDR isolates. There were no very major errors observed in any analysis. These results were pooled with those from a previous study of 74 carbapenem-resistant Enterobacteriaceae and data from the ceftazidime/avibactam new drug application to define optimal 30/20 µg disc thresholds using the error-rate bound model-based approaches of the diffusion breakpoint estimation testing software. This analysis identified a susceptibility threshold of ≤19 mm as optimal. CONCLUSIONS: Our data indicate that the Etest is a suitable alternative to BMD for testing ceftazidime/avibactam against ceftazidime- and meropenem-resistant K. pneumoniae. The 30/20 µg discs overestimate resistance and may lead to the use of treatment regimens that are more toxic and less effective.

IL-37 suppresses migration and invasion of gallbladder cancer cells through inhibition of HIF-1α induced epithelial-mesenchymal transition.

OBJECTIVE: Gallbladder carcinoma (GBC) is the seventh most common cancer across the globe and the most common malignancy of the biliary tract. Epithelial-mesenchymal transition (EMT) is an important pre-requisite for tumor metastasis; however, its mechanism in GBC has not yet been defined. In the present study, we investigated the effects of interleukin-37 (IL-37) on the epithelial-mesenchymal transition (EMT) of gallbladder cancer cells. MATERIALS AND METHODS: RT-qPCR and Western blotting were used to determine the expression of IL-37 in GBC cancer cells and non-tumorigenic human intra-hepatic biliary epithelial cell line. Western blotting was also used for detecting the expression of vimentin, Snail, and E-cadherin. RESULTS: Expression level of IL-37 in GBC cells was decreased in GBC cancer cells compared with the non-tumorigenic human intra-hepatic biliary epithelial cell line. Decreased expression of vimentin and Snail and increased expression of E-cadherin were found in the groups which overexpress IL-37 when compared with the control. Mechanism study showed that IL-37 suppressed the expression of HIF1α in cells. However, HIF1α stabilization by CoCl2 could attenuate the function of IL-37. CONCLUSIONS: Our results indicate that IL-37 plays an antitumor role during the progression of gallbladder carcinoma. IL-37 could inhibit HIF1α induced EMT. Our data provide a new strategy for the treatment of gallbladder cancer.

Viral activity and outcome of hepatitis B surface antigen-positive grafts in deceased liver transplantation.

Indications of liver transplantation are extensive, but deceased donation does not meet the demand. Hepatitis B surface antigen (HBsAg)-positive grafts used to be discarded in the past. The aim of this study was to examine viral activity and outcome of HBsAg-positive deceased grafts transplanted to HBsAg-positive recipients. Eleven HBsAg-positive deceased grafts were transplanted to HBsAg-positive patients with acute liver failure (3 patients), hepatocellular carcinoma (6 patients) and repeatedly bleeding varices (2 patients). Postoperatively, hepatitis B virus (HBV) infection was treated by a combination of antiviral nucleoside and nucleotide analogues. HBV DNA and HBsAg were measured periodically. The median (interquartile) model of end-stage liver disease score for the recipients was 19 (16-32) with a range from 11 to 40. HBV DNA was detected in 6 patients with a range from 61 to 1083 IU/mL before transplantation. After transplantation, HBV DNA was detected in 4 patients in the first month and 2 patients in the 6th month and became undetectable for all patients at end of the first year. The quantitative HBsAg ranged from 0.86 to 241.1 IU/mL at 6 months and 0.34 to 238.5 IU/mL at 24 months (P = .135). Three of the patients died in the early phase, and the other patients were followed up for 40.0 ± 19.2 months with normal liver function. In conclusion, HBsAg-positive deceased liver grafts function well with minimal viral activity under treatment of combined antiviral nucleoside and nucleotide analogues. Use of HBsAg-positive deceased grafts is feasible and increases the donor pool to rescue dying patients.

Difficult Situation of Pancreas Transplantation in the Setting of Scarce Organ Donation.

BACKGROUND: Currently, pancreas transplantation has been a promising strategy to restore long-term normoglycemia as well as to improve life quality for patients with insulin-dependent diabetes mellitus (DM). However, the discrepancy between the number of organs needed and the number donated for transplantation is always enormous. Under a setting of scarce organ donations, we examined our limited experience of pancreas transplantation. METHODS: A retrospective review of pancreas transplantations was performed with the use of data from the Taiwan Organ Registry and Sharing Center and the Ministry of Health and Welfare. Pancreas transplantations in the Organ Transplantation Institute of Chang Gung Memorial Hospital also were reviewed. RESULTS: At present, there are 5 medical centers approved for pancreas transplantation in Taiwan. Overall, a total of 156 pancreas transplantations were performed from 2005 to the end of 2016; only 9 of them were performed in the Organ Transplantation Institute of Chang Gung Memorial Hospital. Although the number of organ donations is rising, pancreas transplantation numbers remain low. More than 20 pancreas transplantations were performed in 2016, yet there remained a total of 111 patients registered on the wait list for pancreas transplantation at the end of this study. Thus the gap between organ donation and transplantation is still vast. CONCLUSIONS: With continuing improvements in Taiwanese health policies and public education regarding organ transplantation, organ donation rates have risen steadily in recent years. Moreover, quality control and continuing evolution in organ transplantation is crucial to ameliorate the difficult situation of pancreas transplantation and other solid organ transplantation in the context of low levels of donation.

Pre-Transplantation Immune Cell Distribution and Early Post-Transplant Fungal Infection Are the Main Risk Factors of Liver Transplantation Recipients in Lower Model of End-Stage Liver Disease.

BACKGROUND: The prognosis of patients after liver transplantation (LTx) with high Model of End-Stage Liver Disease (MELD) score (>30) is predicted, but patients with lower MELD scores (<30) have no conclusive studies of pre- and post-transplant risk factors that influence the long-term outcome. METHODS: This retrospective study reviewed 268 recipients with MELD score <30, from 2008 to 2013 in our institution, for evaluation of pre-transplant risk factors including patients' clinical background data, pre-transplant lymphocyte subpopulation, and early post-transplant infection complication as predictors for long-term survival after LTx. RESULTS: The post-transplant patients' survival estimates were 90.7%, 85.1%, and 83.6% at 1, 3, and 5 years, respectively. In multivariate analysis, age >55years, presence of ascites, cluster of differentiation (CD)3 < 93.2 (count/µL), CD4/CD8 <2.4, fungal infection, and more than one site of fungal colonization significantly influenced survival (P = .0003, P = .002, P = .04, P = .004, P < .0001, and P > .0001, respectively). We also noticed that these five factors accumulatively influence the long-term survival rate; this means that in the presence of any two risk factors, the 5-year survival can still be 88.4%, whereas in the presence of any three risk factors, the survival rate dropped to only 57.1%. CONCLUSIONS: Older patients in the presence of pre-transplant low immune cell number and ascites in association with post-transplant fungal infection are the independent risk factors in MELD scores <30 LTx groups for long-term survival. Patients in these groups with any of the three factors had inferior long-term survival results.

Application of CD8+ Cells Count as a Guide of Immunosuppressive Regimen Introduction for Very Sick Patients Undergoing Liver Transplantation.

BACKGROUND: Immunosuppression (IS) protocols should be individualized according to the individual recipient's immunity to minimize adverse effects. The aim of this study was to determine whether preoperative levels of CD8+ T lymphocytes could be used as a guide for the introduction of IS. METHODS: Sixteen adult liver transplantations in our institute were retrospectively analyzed. The immunosuppressive agents were temporarily withheld for 8 patients with a lower (<10%) preoperative percentage of CD8+ cells after transplant (classified as group A). In this group, postoperative immunosuppressive agents had never been used until acute rejection was suspected. Another 8 patients receiving classic IS were classified as group B. We collected their demographic features and analyzed the clinical courses. RESULTS: The postoperative IS-free period of group A was 5 to 120 days (median, 31 days). Our data showed an inverse correlation between CD8+ levels and the severity of liver disease. Although the IS-free protocol did not present a lower incidence of infection-related events, most of them were effectively treated with antibiotics. The 1-, 3-, and 5-year overall patient survival rates were not different between those with a short-term IS-free period and those with regular IS (87.5% vs 100%, 75% vs 100%, and 62.5% vs 87.5%; P = .468). No patient died of graft failure due to acute rejection. CONCLUSIONS: Postoperative immunosuppressive agents can be safely withheld for a period of time to preserve proper immune responses against infections in very sick recipients guided by using the CD8+ levels.

Rhabdomyolysis caused by the moderate CYP3A4 inhibitor fluconazole in a patient on stable atorvastatin therapy: a case report and literature review.

WHAT IS KNOWN AND OBJECTIVE: Rhabdomyolysis is a severe potential adverse drug reaction of statin therapy. We report a case of rhabdomyolysis due to drug-drug interaction (DDI) between atorvastatin and fluconazole and review the literature. CASE SUMMARY: A 70-year-old woman received atorvastatin for hyperlipidaemia without any problem for 4 years. When intravenous fluconazole was added for treating a fungal infection, rhabdomyolysis developed 2 weeks later. Removal of atorvastatin led to the resolution of her rhabdomyolysis. WHAT IS NEW AND CONCLUSION: Our case demonstrates that in some subjects even a moderate CYP3A4 inhibitor such as fluconazole may lead to rhabdomyolysis in subjects receiving a statin.

Peripheral and Central Mechanisms Involved in the Hormonal Control of Male and Female Reproduction.

Reproduction involves the integration of hormonal signals acting across multiple systems to generate a synchronised physiological output. A critical component of reproduction is the luteinising hormone (LH) surge, which is mediated by oestradiol (E2 ) and neuroprogesterone interacting to stimulate kisspeptin release in the rostral periventricular nucleus of the third ventricle in rats. Recent evidence indicates the involvement of both classical and membrane E2 and progesterone signalling in this pathway. A metabolite of gonadotrophin-releasing hormone (GnRH), GnRH-(1-5), has been shown to stimulate GnRH expression and secretion, and has a role in the regulation of lordosis. Additionally, gonadotrophin release-inhibitory hormone (GnIH) projects to and influences the activity of GnRH neurones in birds. Stress-induced changes in GnIH have been shown to alter breeding behaviour in birds, demonstrating another mechanism for the molecular control of reproduction. Peripherally, paracrine and autocrine actions within the gonad have been suggested as therapeutic targets for infertility in both males and females. Dysfunction of testicular prostaglandin synthesis is a possible cause of idiopathic male infertility. Indeed, local production of melatonin and corticotrophin-releasing hormone could influence spermatogenesis via immune pathways in the gonad. In females, vascular endothelial growth factor A has been implicated in an angiogenic process that mediates development of the corpus luteum and thus fertility via the Notch signalling pathway. Age-induced decreases in fertility involve ovarian kisspeptin and its regulation of ovarian sympathetic innervation. Finally, morphological changes in the arcuate nucleus of the hypothalamus influence female sexual receptivity in rats. The processes mediating these morphological changes have been shown to involve the rapid effects of E2 controlling synaptogenesis in this hypothalamic nucleus. In summary, this review highlights new research in these areas, focusing on recent findings concerning the molecular mechanisms involved in the central and peripheral hormonal control of reproduction.

Outcomes of liver resection for hepatocellular carcinoma in liver transplantation era.

AIMS: Surgical treatment for early-stage hepatocellular carcinoma (HCC) is toward transplantation. However, liver resection remains the major surgical treatment for HCC in Asia. This study is to examine the results of liver resection when liver transplantation became an option of treatment for early-stage HCC. METHODS: In this retrospective cohort study, 1639 patients with resectable HCC were reviewed and divided into two groups. In the 1st period (2002-2005), all 679 patients received liver resection. In the 2nd period (2006-2010), 916 patients had liver resection and 44 patients jointed liver transplantation program. The results of treatment in these two periods were analyzed. RESULTS: The characteristics of tumors were the most important factors of tumor recurrence after liver resection. Liver function reserve, characteristics of tumors, and surgeons' endeavor were all independent factors for overall survival after liver resection. When the patients with oligo-nodular tumors or portal hypertension with low platelet count had liver transplantation rather than liver resection in the 2nd period, the survival rates in the 2nd period were improved. When the patients in the 1st period with low platelet count (≤105 × 10(3)/uL) were subtracted, the 5-year survival rate of the patients with one-segmentectomy for small-sized HCC in the 1st period was similar to those in the 2nd period and transplant patients. CONCLUSIONS: The outcomes of liver resection were improved while liver transplantation was performed for the patients with suspicious portal hypertension. Platelet count, 105 × 10(3)/uL, could be a watershed for early stage HCC patients to undergo liver resection or liver transplantation.

Autoshortloop feedback regulation of pulsatile gonadotropin-releasing hormone (GnRH) secretion by its metabolite, GnRH-(1-5).

Given the central role of the decapeptide gonadotropin-releasing hormone (GnRH) in reproductive function, our long-term objective is to delineate the underlying mechanism regulating these reproductive processes. The outcome of GnRH secretion is in part dependent on the proteolytic metabolism of this decapeptide. In contrast to the belief that the metabolism of GnRH serves only as a degradative process that removes excess GnRH, we have shown that a metabolite of the decapeptide, GnRH-(1-5), can directly regulate GnRH gene expression and reproductive behavior. To further characterize the effect of GnRH-(1-5) on GnRH neuronal function, we determined whether GnRH-(1-5) can directly regulate GnRH secretion and pulsatility using an in vitro perifusion system. We compared the effect of GnRH-(1-5) on GnRH secretion in the immortalized GnRH neuron (GT1-7 cell line), whole rat hypothalamic explant, and enzymatically dispersed rat hypothalamic cells. Tissue preparations were perifused continuously for 9 h during which a 3-h challenge with GnRH-(1-5) was administered (4-6 h). The results show that treatment with GnRH-(1-5) increased (p < 0.05) the mean GnRH secretion and the amplitude of the pulses but not the pulse frequency. The present study supports the notion that GnRH-(1-5) is functionally capable of regulating the reproductive neuroendocrine system.

Tuberculous sacroiliitis in a renal transplant recipient: a case report.

Although Mycobacterium tuberculosis (TB) is the predominant infectious disease after solid organ transplantation worldwide, extrapulmonary involvement in the sacroiliac (SI) joint has never been reported in renal transplant patients. Herein we have described a 59-year-old man who presented with left hip pain and fever at 1 year after renal transplantation. He had a positive Patrick's test on the left hip, elevated serum C-reactive protein, and widening of left SI joint on pelvic radiograph. Although the initial workup including blood culture, acid-fast stain, and tumor markers was nonrevealing, whole body bone scan and magnetic resonance imaging were suggestive of left sacroiliitis. Surgical debridement with biopsy confirmed mycobacterium TB infection. After a complete course of anti-TB treatment, his symptoms significantly resolved. Given the inconspicuous and protean symptoms of extrapulmonary TB, a high index of suspicion for TB sacroiliitis in renal transplant recipients with unexplained hip pain is warranted for early diagnosis and prompt treatment.

Threat bias in mice with inactivating mutations of Prkar1a.

Anxiety disorders are associated with abnormalities in the neural processing of threat-related stimuli. However, the neurobiological mechanisms underlying threat bias in anxiety are not well understood. We recently reported that a Prkar1a heterozygote (Prkar1a(+/-)) mouse with haploinsufficiency for the main regulatory subunit (R1α) of protein kinase A (PKA) exhibits an anxiety-like phenotype associated with increased cAMP signaling in the amygdala. Prkar1a(+/-) mice provide a novel model to test the direct effect of altered PKA expression and subsequent anxiety-like behavioral phenotype on the response to threat. We hypothesized that Prkar1a(+/-)mice would exhibit a bias in threat detection since increased amygdala activity during emotional stimuli is associated with a maladaptive response. We measured behavior and PKA activity in brain areas after exposure to predator or control odor exposure in male Prkar1a(+/-) and wild-type (WT) littermates. Indeed, there were significant differences in the behavioral response to threat detection; WT mice showed the expected response of decrease in exploratory behavior during predator vs. control odor exposure, while Prkar1a(+/-) mice did not alter their behavior between conditions. Basal and total PKA activity was independently associated with genotype, with an interaction between genotype and threat condition. Prkar1a(+/-) mice had higher PKA activity in amygdala and ventromedial hypothalamus in response to predator odor. In contrast, WT mice had higher PKA activity in amygdala and orbitofrontal cortex after exposure to control odor. Dysregulated PKA activity in the amygdala-prefrontal cortex circuitry in Prkar1a(+/-) mice is associated with behavioral phenotype of anxiety and a bias for threat. This is likely related to a failure to inhibit the amydgala response, which is an effect of the genotype. These results suggest that the alteration in PKA signaling in Prkar1a(+/-) mice is not ubiquitous in the brain; tissue-specific effects of the cAMP/PKA pathway are related to threat detection and fear sensitization.

Nicotinic acid and DP1 blockade: studies in mouse models of atherosclerosis.

The use of nicotinic acid to treat dyslipidemia is limited by induction of a "flushing" response, mediated in part by the interaction of prostaglandin D(2) (PGD(2)) with its G-protein coupled receptor, DP1 (Ptgdr). The impact of DP1 blockade (genetic or pharmacologic) was assessed in experimental murine models of atherosclerosis. In Ptgdr(-/-)ApoE(-/-) mice versus ApoE(-/-) mice, both fed a high-fat diet, aortic cholesterol content was modestly higher (1.3- to 1.5-fold, P < 0.05) in Ptgdr(-/-)ApoE(-/-) mice at 16 and 24 weeks of age, but not at 32 weeks. In multiple ApoE(-/-) mouse studies, a DP1-specific antagonist, L-655, generally had a neutral to beneficial effect on aortic lipids in the presence or absence of nicotinic acid treatment. In a separate study, a modest increase in some atherosclerotic measures was observed with L-655 treatment in Ldlr(-/-) mice fed a high-fat diet for 8 weeks; however, this effect was not sustained for 16 or 24 weeks. In the same study, treatment with nicotinic acid alone generally decreased plasma and/or aortic lipids, and addition of L-655 did not negate those beneficial effects. These studies demonstrate that inhibition of DP1, with or without nicotinic acid treatment, does not lead to consistent or sustained effects on plaque burden in mouse atherosclerotic models.

Whole-body vibration for functional constipation: a single-centre, single-blinded, randomized controlled trial.

AIM: The aim of this trial was to determine whether whole-body vibration (WBV) induced via a noninvasive oscillation platform could improve symptoms and health-related quality of life (HRQOL) in patients with chronic functional constipation. METHOD: A single-blinded, randomized controlled trial was performed in a single hospital in Taiwan. Patients diagnosed with chronic functional constipation, as per the Rome III diagnostic criteria, were included and randomized to either the WBV treatment or no treatment (control) group. The treatment group received six 15-min sessions of WBV therapy over a 2-week period. Patients received vibrations of 2 mm in amplitude at a frequency of 12 Hz. The primary outcome was whether constipation symptoms improved, assessed by the constipation severity instrument (CSI) and the secondary outcome measure was whether there was an improvement in HRQOL. RESULTS: Whole-body vibration therapy over a 2-week period in patients with chronic functional constipation (n = 14) significantly reduced the total CSI and obstructive defaecation subscale scores compared with control (n = 13). However, WBV did not improve the pain and chronic inertia subscale scores of the CSI or HRQOL. CONCLUSION: These findings suggest that low-intensity WBV induced via a noninvasive oscillation platform may be an effective therapy for reducing symptom severity in patients with chronic functional constipation.

Inhibition of allogenic T-cell cytotoxicity by hepatic stellate cell via CD4⁺ CD25⁺ Foxp3⁺ regulatory T cells in vitro.

BACKGROUND: The liver is considered to be an immune-privileged organ. Several types of liver cells have been implicated in the induction of immunologic tolerance. Hepatic stellate cells (HSCs) seem to participate in hepatic fibrosis and to display immunological properties. MATERIALS AND RESULTS: In this study, HSCs isolated from C3H mice were highly positive for GFAP (98.4%) and α-SMA (95.4%). After stimulation by interferon-γ (IFN-γ), HSCs were more active in morphology with enhanced expression of H2-K(K), I-A(K), CD80, and CD54, similar to mature myelogenic dendritic cells (MDCs). Through allogeneic stimulation, C3H HSCs induced proliferation of both CD8(+) and CD4(+) T cells in B6 mice. However, the T cells activated by allogeneic HSCs produced less INF-γ, interleukin (IL)-4, IL-10, and IL-17, but large amount of transforming growth factor-ß. These T cells expressed immunoregulatory rather than effector functions. Naïve T cells stimulated by allogeneic HSCs expressed Foxp3 compared with MDCs (8.67% vs 2.14%, P < .05). CD8(+) T cells activated by HSCs lost their allogeneic cytotoxicity, and CD4(+) T cells activated in this fashion suppressed the allogeneic cytotoxicity of CD8(+) T cells activated by MDCs. CONCLUSION: HSCs seem to act as liver-resident antigen-presenting cells instructing the generation of Foxp3(+) regulatory T cells, a property suggestion of induction of immunologic tolerance.

Risk factors and clinical outcomes of ventilator-associated pneumonia in patients on the liver transplant waiting list.

BACKGROUND: Prolonged intubation results in ventilator-associated pneumonia (VAP), which contributes to significant mortality among patients on the waiting list. The aim of this study was to determine the risk factors for and clinical outcomes of VAP among patients into the intensive care unit (ICU). METHODS: We enrolled 50 consecutive critically ill patients with end-stage liver disease admitted to the ICU from January 2005 through December 2010. All patients were intubated for more than 4 days; no definite infection was found initially. We evaluated potential risks factors for VAP and clinical outcomes. RESULTS: Smoking, underlying liver disease, and lobar focal consolidations were significant factors for patients with versus without VAP. Fourteen-day mortality rates were 61.5% for VAP versus 40.5% for patients without VAP. Twenty-eight-day mortality rates for both groups were 92.3% and 86.5%, respectively. Multivariate analysis failed to identify independent predictors of early 14-day mortality. CONCLUSIONS: Underlying liver disease and lobar focal consolidations were risks factors for VAP in patients with prolonged intubation. Patients with prolonged intubation have a dismal prognosis even without VAP. The clinical outcomes of patients with versus without VAP were similar. However, early liver transplantation (<14 days of intubation) improves the chance to rescue patients before development of VAP.

The risk factors for early infection in adult living donor liver transplantation recipients.

OBJECTIVE: The high rate of early major infections in liver transplantation recipients is due to their compromised immune-system. We examined the risk factors of early major infection in living donor liver transplantation (LDLT). MATERIALS AND METHODS: From January 2004 to December 2010, 242 patients undergoing LDLT were enrolled in the prospective cohort. We prospectively collected their clinical and demographic variables, operative details, and posttransplant complications. RESULT: One hundred thirty-nine patients (57.7%) experienced 252 episodes of early infection posttransplantation: bloodstream septicemia (n = 46, 18.3%), urinary tract (n = 34; 14.1%), pneumonia (n = 64; 25.4%), peritonitis (n = 62; 25.7%), and catheter related (n = 46; 19%). The most frequent Gram-positive bacteria were coagulase-negative staphylococci (n = 52; 16.9%), followed by Staphylococcus aureus (n = 32; 10.4%). The most common Gram-negative bacteria were Escherichia coli (n = 27; 8.8%); Acinetobacter baumannii (n = 29; 9.4%), Pseudomonas aureos (n = 18; 5.8%), and Sternotrophomonas maltophilia (n = 18; 5.8%). Upon multivariate logistic regression analysis, the risk factors for early major infection were a high creatinine level (odds ratio = 1.481), a long anhepatic arterial phase (1.01), a reoperation (6.417), young age (1.040), and non-hepatocellular carcinoma recipient (2.141). CONCLUSION: Early major infection after LDLT was high with Gram-positive bacteria, the most common etiologies. Prolonged anhepatic arterial phase, renal insufficiency, and reoperation were risk factors for an early major infection.

Hormonal regulation of female reproduction.

Reproduction is an event that requires the coordination of peripheral organs with the nervous system to ensure that the internal and external environments are optimal for successful procreation of the species. This is accomplished by the hypothalamic-pituitary-gonadal axis that coordinates reproductive behavior with ovulation. The primary signal from the central nervous system is gonadotropin-releasing hormone (GnRH), which modulates the activity of anterior pituitary gonadotropes regulating follicle stimulating hormone (FSH) and luteinizing hormone (LH) release. As ovarian follicles develop they release estradiol, which negatively regulates further release of GnRH and FSH. As estradiol concentrations peak they trigger the surge release of GnRH, which leads to LH release inducing ovulation. Release of GnRH within the central nervous system helps modulate reproductive behaviors providing a node at which control of reproduction is regulated. To address these issues, this review focuses on several critical questions. How is the HPG axis regulated in species with different reproductive strategies? What internal and external conditions modulate the synthesis and release of GnRH? How does GnRH modulate reproductive behavior within the hypothalamus? How does disease shift the activity of the HPG axis?