Practice variation in the diagnosis of acute rejection among pediatric heart transplant centers: An analysis of the pediatric heart transplant society (PHTS) registry.

BACKGROUND: Freedom from rejection in pediatric heart transplant recipients is highly variable across centers. This study aimed to assess the center variation in methods used to diagnose rejection in the first-year post-transplant and determine the impact of this variation on patient outcomes. METHODS: The PHTS registry was queried for all rejection episodes in the first-year post-transplant (2010-2019). The primary method for rejection diagnosis was determined for each event as surveillance biopsy, echo diagnosis, or clinical. The percentage of first-year rejection events diagnosed by surveillance biopsy was used to approximate the surveillance strategy across centers. Methods of rejection diagnosis were described and patient outcomes were assessed based on surveillance biopsy utilization among centers. RESULTS: A total of 3985 patients from 56 centers were included. Of this group, 873 (22%) developed rejection within the first-year post-transplant. Surveillance biopsy was the most common method of rejection diagnosis (71.7%), but practices were highly variable across centers. The majority (73.6%) of first rejection events occurred within 3-months of transplantation. Diagnosis modality in the first-year was not independently associated with freedom from rejection, freedom from rejection with hemodynamic compromise, or overall graft survival. CONCLUSIONS: Rejection in the first-year after pediatric heart transplant occurs in 22% of patients and most commonly in the first 3 months post-transplant. Significant variation exists across centers in the methods used to diagnose rejection in pediatric heart transplant recipients, however, these variable strategies are not independently associated with freedom from rejection, rejection with hemodynamic compromise, or overall graft survival.

Systemic ventricular assist device support in Fontan patients: A report by ACTION.

BACKGROUND: The size of the Fontan population with end-stage heart failure is growing. In this population, heart transplantation has been the only option. This study sought to investigate the efficacy of ventricular assist device (VAD) support in Fontan patients. METHODS: We conducted a retrospective study of Fontan patients in the Advanced Cardiac Therapies Improving Outcomes Network. We evaluated patient characteristics, and the clinical and physiologic outcomes after VAD implantation. RESULTS: We identified 45 Fontan patients implanted with VAD. The average age of patients was 10 years (interquartile range: 4.5-18) and 30% were female. The majority had a morphologic right ventricle (69%), moderate or greater ventricular dysfunction (83%), and moderate or greater atrioventricular valve regurgitation (65%). The majority of implants were as a bridge to transplantation (76%), and the majority of patients were Interagency Registry for Mechanically Assisted Circulatory Support Profile 2 (56%). The most commonly employed device was the Medtronic HeartWare HVAD (56%). A total of 13 patients were discharged on device support, and 67% of patients experienced adverse events, the most common of which were neurologic (25%). At 1 year after device implantation, the rate of transplantation was 69.5%, 9.2% of patients continued to be VAD supported, and 21.3% of patients had died. Hemodynamically, VAD was effective in decreasing both Fontan and ventricular end-diastolic pressures in some individuals. CONCLUSIONS: VAD is effective in supporting patients with end-stage Fontan failure awaiting heart transplantation. Future research should focus on identifying clinical and physiologic characteristics predictive of a favorable response to VAD support.

The impact of flow PRA on outcome in pediatric heart recipients in modern era: An analysis of the Pediatric Heart Transplant Study database.

Data from patients in the Pediatric Heart Transplant Study (PHTS) registry transplanted between 2010 and 2014 were analyzed to determine the association between HLA antibody (PRA) determined by SPA using Luminex or flow cytometry with a positive retrospective cross-match and the post-transplant outcomes of acute rejection and graft survival. A total of 1459 of 1596 (91%) recipients had a PRA reported pretransplant; 26% had a PRA > 20%. Patients with a PRA > 20% were more likely to have CHD, prior cardiac surgery, ECMO support at listing, and waited longer for transplantation than patients with a PRA <20%. Patients with higher PRA% determined by SPA were predictive of a positive retrospective cross-match determined by flow cytometric method (P < .001). A PRA > 50% determined by SPA was independently associated with worse overall graft survival after first month of transplant in both unadjusted and adjusted for all other risk factors. In this large multicenter series of pediatric heart transplant recipients, an elevated PRA determined by SPA remains a significant risk factor in the modern era.

Safety and tolerability of the ß3 -adrenoceptor agonist mirabegron, for the treatment of overactive bladder: results of a prospective pooled analysis of three 12-week randomised Phase III trials and of a 1-year randomised Phase III trial.

AIMS: To evaluate the safety and tolerability of the ß3 -adrenoceptor agonist, mirabegron, in patients with overactive bladder (OAB). METHODS: Tolerability and safety data from three 12-week, randomised, placebo-controlled, double-blind, Phase III trials (Studies 046, 047 and 074) were pooled by treatment group. The three studies were of a similar design, although the assessed doses of mirabegron [25, 50 or 100 mg once daily (qd)] varied, and tolterodine extended release (ER) 4 mg was included as an active-control arm in Study 046 only. Tolerability and safety data from a 1-year, randomised, double-blind, Phase III trial (Study 049) are also presented. Safety variables included the incidence and severity of treatment-emergent adverse events (TEAEs), vital signs and electrocardiogram data. RESULTS: Mirabegron (25, 50 or 100 mg qd) was safe and well-tolerated in patients with OAB over 12-week (n = 2736) and 1-year (n = 1632) periods. The incidence of TEAEs and treatment discontinuations as a result of TEAEs was low; the majority were mild in severity and few were serious. Hypertension, nasopharyngitis and urinary tract infection were the most common TEAEs with mirabegron. The mirabegron tolerability profile was similar to that seen with placebo and tolterodine ER 4 mg, except for dry mouth, which occurred, on average, five times less frequently with mirabegron than tolterodine ER 4 mg. In the pooled 12-week analysis, mirabegron 50 mg was associated with placebo-adjusted mean increases of 0.4-0.6 mmHg in blood pressure and approximately one beat per minute in pulse rate, both reversible upon treatment discontinuation. The incidence of Major Adverse Cardiovascular Events as adjudicated by an independent cardiovascular committee was low and similar across treatment groups. CONCLUSION: The favourable tolerability profile of mirabegron in patients with OAB may allow improved treatment compliance compared with antimuscarinics, with important implications for patient outcomes.

Depressive symptoms and risk of dementia: the Framingham Heart Study.

OBJECTIVES: Depression may be associated with an increased risk for dementia, although results from population-based samples have been inconsistent. We examined the association between depressive symptoms and incident dementia over a 17-year follow-up period. METHODS: In 949 Framingham original cohort participants (63.6% women, mean age = 79), depressive symptoms were assessed at baseline (1990-1994) using the 60-point Center for Epidemiologic Studies Depression Scale (CES-D). A cutpoint of > or = 16 was used to define depression, which was present in 13.2% of the sample. Cox proportional hazards models adjusting for age, sex, education, homocysteine, and APOE epsilon4 examined the association between baseline depressive symptoms and the risk of dementia and Alzheimer disease (AD). RESULTS: During the 17-year follow-up period, 164 participants developed dementia; 136 of these cases were AD. A total of 21.6% of participants who were depressed at baseline developed dementia compared with 16.6% of those who were not depressed. Depressed participants (CES-D >/=16) had more than a 50% increased risk for dementia (hazard ratio [HR] 1.72, 95% confidence interval [CI] 1.04-2.84, p = 0.035) and AD (HR 1.76, 95% CI 1.03-3.01, p = 0.039). Results were similar when we included subjects taking antidepressant medications as depressed. For each 10-point increase on the CES-D, there was significant increase in the risk of dementia (HR 1.46, 95% CI 1.18-1.79, p < 0.001) and AD (HR 1.39, 95% CI 1.11-1.75, p = 0.005). Results were similar when we excluded persons with possible mild cognitive impairment. CONCLUSIONS: Depression is associated with an increased risk of dementia and AD in older men and women over 17 years of follow-up.

Association of parental dementia with cognitive and brain MRI measures in middle-aged adults.

OBJECTIVES: Studies of autosomal dominant Alzheimer disease (AD) have shown structural and cognitive changes in mutation carriers decades prior to clinical disease. Whether such changes are detectable in offspring of persons with sporadic dementia remains unknown. We related prospectively verified parental dementia to brain MRI and cognitive testing in the offspring, within a 2-generational community-based cohort. METHODS: A total of 717 Framingham offspring (mean age: 59 +/- 8 years) were studied. In multivariate analyses, we compared offspring with and without verified parental dementia (and AD) for 1) performance on tests of memory, abstract reasoning, and cognitive flexibility, and 2) volumetric brain MRI measures of total cerebral brain volume (TCBV), hippocampal volume (HV), and white matter hyperintensity volume (WMHV), assessed cross-sectionally and longitudinally. RESULTS: When testing the association of parental dementia and AD with baseline cognitive performance, we observed an interaction of parental dementia and AD with APOE epsilon4 status (p < 0.002). In APOE epsilon4 carriers only (n = 165), parental dementia was associated with poorer scores on tests of verbal memory (beta = -1.81 +/- 0.53, p < 0.001) and visuospatial memory (beta = -1.73 +/- 0.47, p < 0.001). These associations were stronger for parental AD (beta = -1.97 +/- 0.52, p < 0.001, beta = -1.95 +/- 0.48, p < 0.001), equivalent to 14-16 years of brain aging. Among APOE epsilon4 carriers, offspring of participants with dementia were also more likely to show an annual decline in TCBV in the top quartile (odds ratio = 4.67 [1.26-17.30], p = 0.02). Regardless of APOE epsilon4 status, participants with parental dementia were more likely to be in the highest quartile of decline in executive function test scores (odds ratio = 1.61 [1.02-2.53], p = 0.04). CONCLUSIONS: Among middle-aged carriers of the APOE epsilon4 allele, parental dementia and Alzheimer disease were associated with poorer verbal and visuospatial memory and a higher rate of global brain atrophy.

Nociceptin/orphanin FQ decreases serotonin efflux in the rat brain but in contrast to a kappa-opioid has no antagonistic effect on mu-opioid-induced increases in serotonin efflux.

Similar to kappa-opioids, nociceptin/orphanin FQ (OFQ) exerts anti-mu-opioid actions. This may involve interactions within the circuitry controlling 5-HT neurons in the dorsal raphe nucleus (DRN) that project to the nucleus accumbens (NAcc). To test this hypothesis, we compared the effects of OFQ and kappa-opioids on 5-HT efflux in the CNS of freely behaving rats. First, OFQ (30-300 microM) infused into the DRN for 120 min dose-dependently decreased 5-HT efflux in the DRN. The opioid receptor-like 1 (ORL-1) antagonist [Nphe(1)]nociceptin(1-13)NH(2) blocked this effect. Using dual-probe microdialysis we observed that OFQ (300 microM) infused into the DRN for 120 min produced parallel decreases in 5-HT efflux in the DRN and NAcc, suggesting that ORL-1 receptors in the DRN inhibit serotonergic neurons projecting to the NAcc. Also, 5-HT efflux in the NAcc was dose-dependently decreased during OFQ (30-300 microM) infusion into the NAcc. This suggests that OFQ can reduce 5-HT efflux in the NAcc both by inhibiting serotonergic neurons in the DRN and by stimulating ORL-1 receptors in the NAcc. Similar to OFQ, the kappa-opioids U-50,488 (300 microM) and dynorphin A(1-13) (300 microM) infused into the DRN for 120 min decreased 5-HT efflux in the DRN. This effect was blocked only by the kappa-opioid receptor antagonist nor-BNI. Lastly, we compared the ability of OFQ and U-50,488 to block mu-opioid-induced increases in 5-HT. The kappa-opioid U-50,488 (1000 microM) attenuated the increase in 5-HT induced by the mu-opioid agonist endomorphin-1 (300 microM) in the DRN. In contrast, OFQ (300-1000 microM) did not alter mu-opioid-induced increases in 5-HT efflux. In summary, kappa-opioids and OFQ both decreased 5-HT efflux in the CNS. However, in contrast to kappa-opioids, which reversed mu-opioid-induced increases in 5-HT efflux, the anti-mu-opioid effects of OFQ apparently do not involve changes in 5-HT transmission under our experimental conditions.

First-dose success with vardenafil in men with erectile dysfunction and associated comorbidities: RELY-I.

First-dose success of phosphodiesterase type 5 (PDE5) inhibitors may be adversely affected in patients with comorbidities. This article reports first-dose success rates for vardenafil 10 mg in men with erectile dysfunction (ED) and associated comorbidities who participated in the challenge phase of the Reliability--Vardenafil for Erectile Dysfunction I study. This study involved an open-label, single-dose, 1-week challenge period where patients who achieved SEP-2 (penetration) success were randomised to vardenafil 10 mg or placebo for 12 weeks in a double-blind manner. The first-dose success rates for SEP-2 and SEP-3 (maintenance of erection to completion of intercourse) were stratified according to comorbidities. Safety was assessed using adverse events (AEs). Of 600 men who received a single 10 mg dose of vardenafil, 32% had hypertension, 16% had diabetes and 19% had dyslipidaemia. Vardenafil demonstrated overall effectiveness, including first-dose SEP-2 and SEP-3 success rates in patients with and without specific comorbidities. Initial overall success rates for SEP-2 and SEP-3 during the challenge phase were 87% and 74% respectively. First-dose SEP-2 and SEP-3 success rates were 84% and 66% in men with hypertension (n = 191); 84% and 72% in men with dyslipidaemia (n = 116); and 75% and 58% in men with diabetes (n = 95). Vardenafil was well tolerated and most AEs, including the most frequently reported flushing (3.5%), were mild to moderate in intensity. Vardenafil 10 mg is generally well tolerated and efficacious, providing first-dose success with a consistently high rate of reliability of penetration and maintenance of erection in men with ED and associated comorbidities.

Long-term safety and efficacy of oral phentolamine mesylate (Vasomax) in men with mild to moderate erectile dysfunction.

The objectives of this study were to evaluate long-term safety and efficacy of phentolamine mesylate, an orally active, rapid-acting alpha-adrenergic receptor antagonist, for the treatment of men suffering from erectile dysfunction (ED). It was an open-label study involving more than 2000 patients. Men received phentolamine mesylate 40 mg or 80 mg (10 tablets/month) as needed for up to 13 months and self-assessed erectile performance using two validated questionnaires. Treatment with phentolamine mesylate was associated with increases in Erectile Function Domain score of the IIEF, successful vaginal penetrations, and in overall satisfaction. Most adverse events were mild or moderate in severity and consistent with the known pharmacodynamic properties of phentolamine. In conclusion, phentolamine mesylate is safe and effective in the long-term treatment of men with mild to moderate ED.

Depression, pain, exposure to stressful life events, and long-term outcomes in temporomandibular disorder patients.

PURPOSE: This study investigated the role of psychological factors in temporomandibular disorders (TMD). Orofacial pain patients' pretreatment levels of depression, disability caused by pain, and exposure to stressful life events were measured, and differences on these variables between temporomandibular joint (TMJ) disease patients and patients whose pain was of muscular origin (MPD) were evaluated. The use of these variables and patient diagnostic status in predicting response to treatment in a subsample of these patients was also evaluated. PATIENTS AND METHODS: Before undergoing treatment, 258 patients were administered the Beck Depression Inventory (BDI), the Pain Disability Index (PDI), and the Social Readjustment Rating Scale (SRRS). Follow-up data on pain disability, current level of pain, depression, and satisfaction with treatment were obtained on 48 of these patients who were contacted at varying intervals after completing treatment. RESULTS: BDI scores obtained at the outset of treatment were significantly elevated and were positively correlated with SRRS and PDI scores. MPD patients had higher SRRS, BDI depression, and PDI pain disability scores than TMJ patients, and differences between the 2 groups in pain disability were greatest in areas that are often sources of interpersonal stress. Among follow-up patients, PDI scores declined after treatment, with MPD patients showing greater decreases than TMJ patients. Independent of patients' diagnostic status, their pretreatment PDI scores were predictive of their pain level at follow-up and were inversely related to their degree of satisfaction with treatment at follow-up; their pretreatment BDI scores were predictive of their depression level at follow-up. CONCLUSIONS: The findings are consistent with previous research indicating a link between emotional dysfunction and TMD and are largely supportive of the conclusion that psychological factors play a more pronounced role when pain is of muscular origin. Promising behavioral interventions are available for TMD patients in whom psychological factors appear to be playing a significant role.

Sildenafil citrate (VIAGRA) improves erectile function in elderly patients with erectile dysfunction: a subgroup analysis.

BACKGROUND: The prevalence of erectile dysfunction (ED) increases with advancing age, with a particularly high prevalence of ED in elderly patients with diabetes. In the United States it is estimated that approximately 45% of men aged 65 to 69 years have moderate or complete ED. The efficacy and safety of oral sildenafil (VIAGRA) for treating ED in elderly men (aged > or = 65 years or older) were assessed. METHODS: We analyzed data obtained from five double-blind, placebo-controlled studies of the efficacy and tolerability of oral sildenafil taken as required (but not more than once daily) over a 12-week to 6-month period. Two subgroups were evaluated: (i) elderly patients with ED of broad-spectrum etiology (n = 411), and (ii) elderly patients with ED and diabetes (n = 71). Efficacy was assessed using a global efficacy question, questions 3 and 4 of the International Index of Erectile Function (IIEF). and the five sexual function domains of the IIEF. RESULTS: All efficacy assessments indicated that sildenafil significantly improved erectile function both in elderly patients with ED of broad-spectrum etiology and in elderly patients with ED and diabetes. The most common adverse events were mild-to-moderate headache, flushing, and dyspepsia. The rates of discontinuation due to adverse events were low and were comparable to the rates with placebo. CONCLUSIONS: Sildenafil is an efficacious and well-tolerated treatment for ED in elderly men.

Epidemiology and factor analysis of obesity, type II diabetes, hypertension, and dyslipidemia (syndrome X) on the Island of Kosrae, Federated States of Micronesia.

OBJECTIVES: Obesity, type II diabetes, hypertension, and dyslipidemia are major causes of morbidity and mortality throughout the world. Though these disorders often cluster in individuals and families and are collectively known as syndrome X, the basis for this aggregation is not well understood. To further understand the pathogenesis of syndrome X, a comprehensive epidemiological study was undertaken on the Pacific Island of Kosrae, Federated States of Micronesia (FSM). METHODS: The entire adult (>20 years of age) population of Kosrae underwent a clinical evaluation that included a questionnaire that noted the participants' sex, family data including listing of biological parents, siblings, and children, smoking status, village of residence, age and health status. The medical evaluation included: anthropometric measures (weight, height, waist, hip), serum chemistries (leptin, fasting blood sugar (FBS), insulin, total cholesterol (TC), triglycerides (TG), and apolipoproteins B and A-I (apo B and apo A-I) and blood pressure (BP) measurements. RESULTS: Obesity (BMI >/=35) was found in 24%, diabetes (FBS >/=126 or 2-hour oral glucose tolerance test >/=200) in 12%, hypertension (SBP >/=140 or DBP >/=90) in 17%, and dyslipidemia (TC >/=240 or TG >/=200 or apo B >/=120 or apo A-I

Do Patients Want Control over their Own Health Care? A Review of Measures, Findings, and Research Issues.

Across a wide variety of medical settings, patients report that they want detailed information about their condition and their treatment whereas stated desire for input into decision making is skewed more in the direction of physician-only or at least collaborative decision-making. These results, along with the contextual and individual difference factors associated with increased willingness to relinquish control (lower educational level, more serious illness, increasing age), indicate that patients want to assume control if they feel it will be beneficial to them to do so. The findings, however, are based largely on the relationship of patients' mean scores to arbitrarily determined scale midpoints on measures with little or no criterion-related validity. These measures also show insufficient overlap with better validated measures of desire for health care control, which indicate more normally distributed scores and a broader range of individual differences among respondents. Findings are discussed in terms of the need for further research on the structure (dimensionality) and stability of the construct desire for health care control and issues involved in conducting needed criterion-related validational work.

Should patients have control over their own health care?: empirical evidence and research issues.

Available research indicates that purported patient insufficiencies in ability to process information and make rational and reliable decisions have likely been overestimated. Furthermore, data indicate that nonscientific factors often play a role in physician decision-making and that physicians may not value different health outcomes in the same way as patients. Though the data on patient cognitive functioning are limited because of heavy reliance on patient responses in hypothetical versus actual decision-making situations, these findings lend credence to arguments that patients should have increased control over their own health care. Research on the effects of interventions designed to enhance patient control indicates that: (a) patients generally respond positively to increased information, but few studies have evaluated the effects of information as a precursor to decision-making; (b) the few studies using simple behavioral control interventions have shown generally positive effects on a range of patient outcomes; and (c) studies of decisional control (with breast cancer patients) have had experimental confounds which prohibit conclusions regarding effectiveness. Areas in greatest need of research include: (a) further exploration of the utility of noninvasive behavioral control interventions in different settings; (b) measuring the impact of control manipulations on patient perception of control as well as patient control-related behaviors; (c) matching patient differences in desire for control to experimental conditions and to physician differences in receptiveness to patient control; and (d) clinical trials in which patients facing critical decisions in trade-off situations are actually given a choice.

Axial penile rigidity as primary efficacy outcome during multi-institutional in-office dose titration clinical trials with alprostadil alfadex in patients with erectile dysfunction. Alprostadil Alfadex Study Group.

The purpose of the study was to utilize axial penile buckling testing as a primary efficacy variable of erection quality during multi-institutional in-office dose titration testing with alprostadil alfadex, prostaglandin E1 (PGE1)-alpha-cyclodextrin, (EDEX /VIRIDAL, Schwarz Pharma) in patients with erectile dysfunction. In 41 study sites, in three different dose titration studies involving 894 patients with impotence >6 months, a buckling test was performed and repeated every 10 min for up to 60 min, within 30 min following alprostadil alfadex administration, or when two consecutive circumference measurements reached maximum values. The buckling device consisted of a standard weight scale attached to a 2 inch diameter plastic cap with a concavity on its ventral surface (H. Eric Richards, Inc., Canton MA). A positive test was associated with absent penile shaft buckling to a downward force of 1.0 kg, slowly applied to the glans in the axis of the erect shaft. A total of 630 (71%) patients experienced at least one positive buckling test. Three consecutive positive buckling tests, implying a functionally rigid erection for at least 20 min, were noted in 521 (58%) patients. There were high correlations between the presence of three consecutive positive buckling tests following alprostadil alfadex injection and the patient's (83% of cases) and the investigator's (88% of cases) evaluation of adequacy of erection for intercourse. Similarly, there were high correlations between the presence of negative buckling tests and the patient's (95% of cases) and the investigator's (96% of cases) evaluation of inadequacy of erection for intercourse. The axial penile buckling test offers a simple, reliable, and inexpensive method to objectively quantify erectile response following in-office dose titration of intracavernosal alprostadil alfadex. The high correlation to subjective patient/investigator assessment adds to the validity of the test.

Facial frequency manipulation normalizes face discrimination in AD.

People with AD have deficient contrast sensitivity and impaired face discrimination. The authors presented photographs of unfamiliar faces of three different sizes to enhance the low, middle, or high facial frequency information (cycles per face). Patients with AD demonstrated normal discrimination of small faces only, indicating that impaired contrast sensitivity at low facial frequencies contributes to their poor face discrimination.

Differential effect of local infusion of serotonin reuptake inhibitors in the raphe versus forebrain and the role of depolarization-induced release in increased extracellular serotonin.

Systemic administration of selective serotonin reuptake inhibitors (SSRIs) elicits larger increases in serotonin (5-HT) in raphe than in forebrain sites. Because serotonergic neuronal activity is suppressed, the mechanism underlying SSRI-induced increases in extracellular 5-HT is unclear. This study determined whether local infusion of SSRIs also elicited regionally selective increases in extracellular 5-HT, and whether changes depended on serotonergic neuronal depolarization. Conventional microdialysis methods were used to measure 5-HT in dorsal raphe (DRN), median raphe, nucleus accumbens (NAcc), and frontal cortex of unanesthetized rats. During infusion of SSRIs into each site, the maximum response was an approximately 6- to 7-fold increase in 5-HT in NAcc and frontal cortex, and an approximately 20-fold increase in DRN and median raphe. The larger increase in 5-HT in raphe was confirmed using zero-net-flux microdialysis. In NAcc, baseline 5-HT was 0.7 nM, and levels increased to a maximum of 3.1 nM during infusion of the SSRI citalopram. Baseline 5-HT in DRN was greater, 1.3 nM, and increased to 12.4 nM in response to citalopram. Consistent with evidence that autoreceptor activation inhibits serotonergic neuronal discharge, SSRI infusion into DRN produced a moderate decrease in 5-HT in NAcc. However, increases in 5-HT in DRN elicited by SSRI infusion were attenuated by 8-hydroxydipropylaminotetralin and tetrodotoxin. These data indicate that depolarization-dependent 5-HT release was not fully inhibited during SSRI infusion into DRN. In summary, SSRIs produce larger increases in extracellular 5-HT in raphe than in forebrain sites. Increases depend in part on depolarization-induced release, which may be greater in raphe than in forebrain.

Regulation of serotonin release by GABA and excitatory amino acids.

Regulation of serotonin release by gamma-aminobutyric acid (GABA) and glutamate was examined by microdialysis in unanaesthetized rats. The GABA(A) receptor agonist muscimol, or the glutamate receptor agonists kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolaproprionate or N-methyl-D-aspartate were infused into the dorsal raphe nucleus (DRN) while extracellular serotonin was measured in the DRN and nucleus accumbens. Muscimol produced decreases, and the glutamate receptor agonists produced increases in serotonin. To determine if these receptors have a tonic influence on serotonergic neurons, glutamate or GABA(A) receptor antagonists were infused into the DRN. Kynurenate, a nonselective glutamate receptor blocker, produced a small, 30% decrease in serotonin. A similar decrease was obtained with combined infusion of AP-5 and DNQX into the DRN. The GABAA receptor blocker bicuculline produced an approximately three-fold increase in DRN serotonin. In conclusion, glutamate neurotransmitters have a weak tonic excitatory influence on serotonergic neurons in the rat DRN. However, the predominate influence is mediated by GABA(A) receptors.

Serotonin autoreceptor function and antidepressant drug action.

This article briefly summarizes, within the context of a brief review of the relevant literature, the outcome of our recent rat microdialysis studies on (1) the relative importance of serotonin (5-HT)1A versus 5-HT1B autoreceptors in the mechanism of action of 5-HT reuptake blocking agents, including putative regional differences in this regard, and (2) autoreceptor responsiveness following chronic SSRI administration. First, our data are consistent with the primacy of 5-HT1A autoreceptors in restraining the elevation of 5-HT levels induced by SSRIs, whereas nerve terminal 5-HT1B autoreceptors appear to have an accessory role in this regard. Second, there is an important interplay between cell body and nerve terminal 5-HT autoreceptors, and recent findings suggest that this interplay may potentially be exploited to obtain regionally preferential effects on 5-HT neurotransmission in the central nervous system, even upon systemic drug administration. In particular, emerging data suggest that somatodendritic 5-HT1A autoreceptor- and nerve terminal 5-HT1B autoreceptor-mediated feedback may be relatively more important in the control of 5-HT output in dorsal raphe-frontal cortex and median raphe-dorsal hippocampus systems, respectively. Third, 5-HT autoreceptors evidently retain the capability to limit the 5-HT transmission-promoting effect of SSRIs after chronic treatment. Thus, although the responsiveness of these sites is probably somewhat reduced, residual autoreceptor capacity still remains an effective restraint on large increases in extracellular 5-HT, even after prolonged treatment. If a further increase in extracellular 5-HT is crucial to the remission of depression in patients responding only partially to prolonged administration of antidepressants, then sustained adjunctive treatment with autoreceptor-blocking drugs may consequently prove useful in the long term.