Trauma related admissions to the PICU at Chris Hani Baragwanath Academic Hospital, Johannesburg.

BACKGROUND: Paediatric trauma is a major cause of morbidity and mortality in low and middle income countries. Data from these regions are scant. We aimed to describe the demographic and injury profile, treatment modality and outcome of trauma admissions to the paediatric intensive care unit at Chris Hani Baragwanath Academic Hospital (CHBAH). METHODS: A retrospective record review of trauma cases admitted to the PICU at CHBAH from 2011 to 2013 was performed. RESULTS: One-fifth of admissions were due to trauma. 58% of admissions were male. Weekends accounted for 49% of admissions. Road traffic injuries (RTI) (66%) and toxin ingestion (TI) (17%) contributed the majority of admissions. Children aged 0-4 years accounted for 45%, 5-9 years 39%, and 10-15 years 16% of admissions. The mortality rate was 9.0% with RTI accounting for 64%. 64% of mortalities occurred in the 0-4 year cohort. Mean age of survivors (5.8 years) was significantly higher than non-survivors (3.4 years) (p < 0.05). 89% of all children required invasive ventilation on PICU admission. Mean length of ventilation in non-survivors (10.2 days) was significantly longer than survivors (4.5 days) (p < 0.05). CONCLUSIONS: RTI accounted for the majority of trauma admissions to our PICU. RTI, female gender and age less than 4 years were all associated with an increased risk for mortality in our study.

Do iatrogenic serosal injuries result in small bowel perforation in a rabbit model?

BACKGROUND: Surgical dogma dictates that serosal injuries should be repaired during laparotomy as these injuries may result in localised areas of bowel ischaemia and may perforate. No study has investigated whether there is a correlation between the extent of serosal injuries and the risk for perforation under normal physiological conditions. We hypothesized that small bowel serosal injuries do not result in early or late perforation at physiological intraluminal pressures regardless of their size. METHOD: An in-vivo rabbit small bowel serosal injury model was developed and two experiments were conducted. The first - to determine whether and at which pressures various lengths and circumferences of serosal injuries in small bowel result in immediate bowel perforation - was performed infusing saline into isolated bowel segments with or without a variety of serosal injuries. In the second study - to determine whether or not serosal injuries result in delayed perforation - a range of injuries was created in rabbits and the effect assessed at re-laparotomy 5 days after the creation of the injury. RESULTS: No perforations were observed at the site of serosal injuries at physiological intraluminal pressures. Perforations occurred at 43.7+ 18.6 cmH2O, 23.3+ 14.4 cmH2O, and 24.4+ 23.9 cmH2O for controls, 4 cm long and 100% circumference serosal injuries respectively (p-value = 0.18 for various lengths and 0.71 for various circumferences). No serosal injuries perforated within 72 or 120 hours after creation. CONCLUSION: Small bowel serosal injuries do not perforate or leak at physiological intraluminal pressures, either at the time of creation or up to 120 hours thereafter.

Neutronics simulations for the design of neutron flux monitors in SPARC.

This paper presents the development and application of high-fidelity neutronic models of the SPARC tokamak for the design of neutron flux monitors (NFM) for application during plasma operations. NFMs measure the neutron flux in the tokamak hall, which is related to fusion power via calibration. We have explored Boron-10 gamma-compensated ionization chambers (ICs) and parallel-plate Uranium-238 fission chambers (FCs). We plan for all NFMs to be located by the wall in the tokamak hall and directly exposed to neutrons streaming through a shielded opening in a midplane port. Our simulations primarily use a constructive solid geometry-based OpenMC model based on the true SPARC geometry. The OpenMC model is benchmarked against a detailed CAD-based MCNP6 model. The B10 ICs are equipped with high-density polyethylene (HDPE) sleeves, borated HDPE housings, and borated aluminum covers to shield out scattered neutrons, optimize detector response levels, and make calibration robust against changes in the tokamak hall. The B10 neutron absorption branching ratio may cause the detectors' responses to be non-linear to neutron flux >200 keV. However, our simulations unveil that, in the SPARC environment and with the proposed housings and sleeves, >99% of the detector responses are induced by <100 keV neutrons. U238's insensitivity to slow neutrons makes this FC a promising candidate for direct fusion neutron measurements. Along with a borated HDPE sleeve, about 60% of the FCs' responses are induced by direct neutrons.

Overview of the early campaign diagnostics for the SPARC tokamak (invited).

The SPARC tokamak is a high-field, Bt0 ∼12 T, medium-sized, R0 = 1.85 m, tokamak that is presently under construction in Devens, MA, led by Commonwealth Fusion Systems. It will be used to de-risk the high-field tokamak path to a fusion power plant and demonstrate the commercial viability of fusion energy. SPARC's first campaign plan is to achieve Qfus > 1 using an ICRF-heated, <10 MW, high current, Ip ∼ 8.5 MA, L-mode fueled by D-T gas injection, and its second campaign will investigate H-mode operations in D-D. To facilitate plasma control and scientific learning, a targeted set of ∼50 plasma diagnostics are being designed and built for operation during these campaigns. While nearly all diagnostics are based on established techniques, the pace of deployment, relative to the first plasma, and the harshness of the thermal, electromagnetic, and radiation environment are unprecedented for medium-sized tokamaks. An overview of the SPARC diagnostic set is given, providing context to further details communicated by the SPARC team in companion publications that are system-specific. The system engineering philosophy for SPARC diagnostics is outlined, and the design and engineering verification process for components inside and outside the primary vacuum boundary are described. Diagnostics are mounted directly to the vacuum vessel as well as housed within a series of eight midplane and 24 off-midplane replaceable port plugs. With limited exceptions, signal conditioning, digitization electronics and cameras as well as lasers and microwave sources are localized to a series of five Diagnostic Lab spaces, totaling ∼350 m2, located >15 m from the center of the tokamak, on the other side of a 2.4 m concrete shielding wall. A series of 31 large-scale penetrations have been included in the SPARC Tokamak Hall to facilitate integration of early campaign diagnostics and to provide upgradability.

Cutaneous lymphocyte antigen and α4ß7 T-lymphocyte responses are associated with peanut allergy and tolerance in children.

BACKGROUND: It is unclear whether the initial route of allergen exposure in early life could influence the subsequent development of allergy, with cutaneous sensitization leading to peanut allergy (PA), and tolerance induced by oral exposure. The skin- and gastrointestinal (GI)-homing markers, cutaneous lymphocyte antigen (CLA) and α4ß7 integrin, are used to determine whether the state of PA correlates with peanut-specific CLA responses, with tolerance associated with predominant α4ß7 responses. METHODS: CLA+ and α4ß7+ memory T cells were isolated and cultured with peanut extract to assess their proliferation. Stimulation indices were compared in peanut allergic and non-allergic (NA) groups, and peanut-specific cytokine production was measured. RESULTS: In peanut allergic patients, peanut-specific proliferation predominates in the skin-homing CLA+ subset, whilst peanut-tolerant groups have a mixed CLA/α4ß7 response (P = 0.008). Comparison with a control food antigen (ovalbumin) showed that these differences are allergen specific. Cytokine responses showed trends towards Th1 skewing in the GI-homing α4ß7+ cells of peanut-tolerant groups and Th2 skewing in the skin-homing CLA+ cells of peanut allergic patients. CONCLUSION: The predominance of the CLA+ response to peanut in peanut allergic patients is consistent with the hypothesis that allergic sensitization occurs through the skin. The predominant α4ß7+ response in peanut-tolerant groups suggests that allergen exposure through the GI tract induces tolerance.

A dual-centre, cohort comparison of open, laparoscopic and robotic-assisted radical cystectomy.

INTRODUCTION: The role of minimally invasive radical cystectomy as opposed to open surgery for bladder cancer is not yet established. We present comparative outcomes of open, laparoscopic and robotic-assisted radical cystectomy MATERIAL AND METHODS: Prospective cohort comparison of 158 patients from 2003-2008 undergoing open radical cystectomy (ORC) (n = 52), laparoscopic radical cystectomy (LRC) (n =58) or robotic-assisted radical cystectomy (RARC) (n = 48) performed by a team of three surgeons at two hospitals. Peri-operative data, complication rates, length of hospital stay, oncological outcome (including lymph node status) and survival were recorded. Statistical analyses were adjusted to account for potential confounding factors such as ASA grade, gender, age, diversion type and final histology. RESULTS: RARC took longer than LRC and ORC. Patients were about 30 times more likely to have a transfusion if they had ORC than if they had RARC (p < 0.0001) and about eight times more likely to have a transfusion if they had LRC compared with RARC (p < 0.006). Patients were four times more likely to have a transfusion if they had ORC as compared with LRC (p < 0.007). Patients were four times more likely to have complications if they had ORC than RARC (p = 0.006) and about three times more likely to have complications with LRC than with RARC (p = 0.02). Hospital stay was mean 19 days after ORC, 16 days after LRC and 10 days after RARC. CONCLUSIONS: Despite study limitations, RARC had the lowest transfusion and complication rates and the shortest length of stay, although taking the longest to perform.

A clinical review of the management of frostbite.

Frostbite is a thermal injury that can occur when temperatures drop low enough for tissue to freeze. On rewarming the tissues, an inflammatory process develops which is often associated with tissue loss. The extent of the tissue loss reflects the severity of the cold exposure and includes factors such as temperature, duration, wind chill, altitude, and systemic hypothermia. This review discusses the epidemiology, the pathophysiological processes involved, and the clinical management of frostbite injuries. Practical advice is given on both the field and hospital management and how to seek expert advice from remote situations. The review also discusses newer developments in frostbite treatment such as intra-vascular thrombolysis and adjunctive treatments such as the use of intravenous vasodilators.

[The German version of the satisfaction with stroke care questionnaire (SASC) for stroke patients]. / Entwicklung der deutschen Version der Patientenzufriedenheits-Skala (SASC) für den Einsatz bei Patienten nach Schlaganfall.

BACKGROUND AND PURPOSE: Patient satisfaction is an important objective to achieve in all parts of the health-care system. Patient satisfaction probably effects adherence to therapy. Until now, German-speaking countries were lacking a reliable instrument to investigate patient satisfaction. The aim of this study was to translate the English Satisfaction with Stroke Care Questionnaire (SASC), validated and created specifically for patients who had a stroke, and to assess the test-retest reliability of the German version. METHODS: The translation of the satisfaction questionnaire followed the protocol of the Medical Outcome Trust. The validation was carried out with continuously admitted inpatients who had suffered an acute stroke and were able to give written consent. Patients received two questionnaires for self-administration three months after hospital admission. The two questionnaires were compared for test-retest reliability. Reliability was measured using AC 1 values. RESULTS: Out of 202 patients continuously admitted to our hospital with the diagnosis of stroke, 33 could not give written informed consent due to aphasia (N = 29) or foreign-language (N = 4) or refused written consent (N = 8) or died during the following 3 months after the event (N = 14). Recall rate at three months was 71 % with 104 of the remaining 147 patients sending both questionnaires back. (Characteristics of responders: NIHSS = 3 [0 - 26], age = 71.5 [31 - 89] years, 40 % female, 48 % with five or more years of secondary school, 66 % paretic, 17 % with aphasia, 26 % with atrial fibrillation). The test-retest reliability of the German version of the self-administered satisfaction questionnaire was substantial (mean AC 1 = 0.612; range from 0.307 to 0.789). CONCLUSION: The German version of the SASC is a reliable tool to test patient satisfaction in stroke patients in the German language.

An analysis of neonates with surgical diagnoses admitted to the neonatal intensive care unit at Charlotte Maxeke Johannesburg Academic Hospital, South Africa.

BACKGROUND: The burden of neonatal surgical conditions is not well documented in low- to middle-income countries (LMICs). These conditions are thought to be relatively common, with a considerable proportion of neonates admitted to the neonatal intensive care unit (NICU) requiring surgical intervention. OBJECTIVES: To review neonates with surgical conditions admitted to the NICU in our hospital setting. METHODS: This was a retrospective, descriptive study of neonates with surgical conditions admitted to the NICU at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH), South Africa, between 1 January 2013 and 31 December 2015. The characteristics and survival of these neonates were described using univariate analysis. The NICU at CMJAH is combined with a paediatric intensive care unit, to a total of 15 beds, and serves as a referral unit. RESULTS: Of 923 neonates admitted to the NICU, 319 (34.6%) had primarily surgical conditions. Of these 319 neonates, 205 survived (64.3%). There were 125/319 neonates (39.2%) with necrotising enterocolitis (NEC), 55 of whom survived (55/125; 44.0%), making the presence of NEC significantly associated with poor outcome (p<0.001). Other significant predictors of poor outcome were the patient being outborn (p=0.029); the presence of late-onset sepsis (p<0.001), with Gram-negative organisms (p=0.005); and lesser gestational age (p=0.001) and lower birth weight (p<0.001). Major birth defects were present in 166/319 neonates (52.0%). The abdomen was the most prevalent site of surgery, with 216/258 procedures (83.7%) being abdominal, resulting in a mortality rate of 76/216 (35.2%). CONCLUSIONS: Neonates with major surgical conditions accounted for one-third of NICU admissions in the present study. The study highlights the considerable burden placed on paediatric surgical services at a large referral hospital in SA. Paediatric surgical services, with early referral and improvement of neonatal transport systems, must be a priority in planned healthcare interventions to reduce neonatal mortality in LMICs.

Frequency and predictors for the risk of stroke recurrence up to 10 years after stroke: the South London Stroke Register.

BACKGROUND: Data estimating the risk of, and predictors for, long-term stroke recurrence are lacking. METHODS: Data were collected from the population-based South London Stroke Register. Patients were followed up for a maximum of 10 years. Kaplan-Meier estimates and Cox proportional hazards models were used to assess the cumulative risk of and predictors for first stroke recurrence. Variables analysed included sociodemographic factors, stroke subtype (defined as cerebral infarction, intracerebral haemorrhage and subarachnoid haemorrhage), stroke severity markers and prior-to-stroke risk factors. RESULTS: Between 1995 and 2004, 2874 patients with first-ever stroke were included. The mean follow-up period was 2.9 years. During 8311 person-years of follow-up, 303 recurrent events occurred. The cumulative risk of stroke recurrence at 1 year, 5 years and 10 years was 7.1%, 16.2% and 24.5% respectively. No differences in stroke recurrence were noted between the stroke subtypes. Factors increasing the risk of recurrence at 1 year were previous myocardial infarction (HR 1.73; 95% CI 1.08 to 2.78) and atrial fibrillation (HR 1.61; 95% CI 1.04 to 4.27); at 5 years, hypertension (HR 1.47; 95% CI 1.08 to 1.99) and atrial fibrillation (HR 1.79; 95% CI 1.29 to 2.49); and at 10 years, older age (p = 0.04), and hypertension (HR 1.38, 95% CI 1.04 to 1.82), myocardial infarction (HR 1.50, 95% CI 1.06 to 2.11) and atrial fibrillation (HR 1.51, 95% CI 1.09 to 2.09). CONCLUSIONS: Very-long-term risk of stroke recurrence is substantial. Different predictors for stroke recurrence were identified throughout the follow-up period. Risk factors prior to initial stroke have a significant role in predicting stroke recurrence up to 10 years.

Cold damage to the extremities: frostbite and non-freezing cold injuries.

The treatment of cold injuries to the periphery has advanced substantially in the last 10 years and optimal outcomes are only likely to be achieved if a multidisciplinary team uses the full range of diagnostic and treatment modalities that are now available. The internet and satellite phones with digital images allow immediate access by patients from remote geographical locations to hospital based specialists who can assess cold injuries and advise on early field care. The severity of frostbite injuries can now be assessed with triple phase bone scanning, allowing early prediction of likely subsequent tissue loss. Early hyperbaric oxygen therapy appears to improve outcome and the use of intravenous drugs such as synthetic prostaglandin analogues infusions and tissue plasminogen activator have been shown to reduce amputation rates. In non-freezing cold injuries the early administration of analgesia, the avoidance of secondary exposure, and the use of infrared thermography to assess the injuries are among newer approaches being introduced.

Correlation of white cell count and CRP in acute appendicitis in paediatric patients.

BACKGROUND: Ten per cent of children who present with abdominal pain at an emergency department are diagnosed with acute appendicitis. The diagnosis of which relies on clinical acumen, but addition of tests such as measurement of the white cell count (WCC) and C-reactive protein (CRP) are needed to decrease the morbidity associated with inappropriate surgical management. This study evaluates the sensitivity, specificity and accuracy of the WCC and CRP separately and when used in combination and evaluates whether an increased WCC and CRP are associated with complicated appendicitis. METHOD: A retrospective record review of all paediatric patients who underwent appendicectomy between June 2010 and December 2016 was conducted. Demographic data, the WCC, CRP and histology results were reviewed. RESULTS: 763 records were reviewed. The sensitivity and specificity of the WCC were 69.6% and 43.1% respectively and of the CRP were 95.4% and 24.5% respectively. The sensitivity was higher when both the CRP and WCC were elevated (97.47%). A normal WCC and CRP had a specificity of 98%, with an odds ratio of 8.69 of a patient not having appendicitis. There was a borderline significance between the WCC and the presence of acute appendicitis (p = 0.0494). The CRP was significant in patient with acute appendicitis (p < 0.0001). The WCC and CRP between uninflamed appendix specimens, uncomplicated appendicitis and complicated appendicitis was significant. CONCLUSION: Both increasing CRP and WCC correlates with an increased likelihood of the presence of complicated appendicitis. The chance of a patient having appendicitis with both normal WCC and CRP is low.

Outcomes of paediatric liver transplant for biliary atresia.

BACKGROUND: Despite the widespread use of Kasai Portoenterostomy (KPE) for biliary atresia, more than two thirds of these patients require liver transplant. Liver transplantation is not widely available in South Africa, and Wits Donald Gordon Medical Centre is one of two centres performing paediatric liver transplantation in the country, and the only centre performing living related donor transplants. METHOD: A retrospective review was performed at the centre. Demographic data were collected, and tabulated. Survival analysis was performed using the Kaplan Meier method. Complication rates were categorised into biliary, vascular and enteric, and classified as early and late. RESULTS: Sixty-seven first time liver transplants were performed for biliary atresia at WDGMC from 2005 to 2017. Sixty-nine percent were female patients and thirty-one percent were male patients. Forty-eight percent of patients under the age of 5 years had a z-score of -2 or worse for mid upper arm circumference (MUAC). One year overall survival of the cohort is 84.5%, and overall graft survival is 82.9%. Overall mortality was 22%, with infection being the most common cause of death. CONCLUSION: Early referral of all patients with biliary atresia to a paediatric liver transplant centre is essential for early assessment of indications, and medical and nutritional optimisation of patients. Primary liver transplant should be considered for a select group of patients with unique clinical indications.

Black and minority ethnic men who have sex with men: a London genitourinary medicine clinic experience.

The aim was to examine sexual behaviour and rates of sexually transmitted infections (STIs) in black and minority ethnic (BME) men who have sex with men (MSM) attending a London genitourinary medicine clinic. A case-note review of BME MSM (n = 203) attending our service between 1 April 2005 and 31 March 2006 was carried out. BME MSM were those who self-identified as being of Black (Caribbean, African or Other), South Asian (Indian, Pakistani, Bangladeshi or Sri Lankan) and Chinese/South-East Asian (Malaysian, Thai, Filipino, Japanese) ethnicities. Consecutively attending self-identified white British (WB) MSM (n = 203) were used as a comparative group. BME MSM were significantly more likely to report unprotected anal intercourse with casual male partners in the preceding three months (P = 0.0016) and were more likely to report female sexual partners (P = 0.0018). Rectal gonorrhoea was more common in WB MSM (P = 0.02). Numbers of other bacterial STIs and HIV infection were similar in both groups. The higher reported rates of risk behaviour in BME MSM are of concern and support the need for focussed sexual health promotion.

The association of post-stroke neurological improvement with risk of subsequent deterioration due to stroke events.

We sought to simultaneously confirm that substantial recovery at day 1 and day 7 after acute ischaemic stroke onset is associated with subsequent neurological deterioration in patients of the Acute Stroke Therapy by Inhibition of Neutrophils randomized clinical trial. Substantial recovery was assessed by improvement in the National Institutes of Health Stroke Score (NIHSS). Neurological deterioration was defined as any stroke event or NIHSS worsening from recovery assessment to day 90. After adjusting for age, t-PA and day 1 NIHSS, there was a non-significant tendency of substantial (pre-specified as 75%) recovery at day 1 to be associated with later deterioration [odds ratio (OR) 2.47; 95% CI, 0.95-6.50]. The corresponding OR for substantial (pre-defined as 65%) recovery at day 7 was 1.84 (0.85-3.96). Other thresholds for recovery were significantly associated with later deterioration: >50%, 80%, 90% and 100% for day 1 and >50%, 60%, 70%, 90% and 100% for day 7. The effect of recovery at day 1 was more important than that of later recovery. This study confirms the association between recovery and subsequent neurological deterioration and is the first to indicate the greater importance of acute recovery at day 1 in comparison with later recovery.

Choledochal malformations: Lessons learnt in Johannesburg.

BACKGROUND: Choledochal malformation (CM) is a well-described and relatively rare condition. CMs may present on antenatal ultrasound screening, through childhood and into adulthood. The aetiology is not well understood but the association with a pancreaticobiliary malunion predisposes to the development of CMs. OBJECTIVES: To review the experience of CMs in the Department of Paediatric Surgery, University of the Witwatersrand, Johannesburg to improve our patient care for this population. METHODS: After institutional ethics approval, a retrospective record review was conducted of patients presenting with CM to the Department of Paediatric Surgery, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg. All patients managed between January 2010 and May 2017 were included. RESULTS: A total of 35 patients underwent surgery for CMs and 2 patients were excluded from the study owing to incomplete records. Most of our patients (83%) presented with jaundice and a median (interquartile range) bilirubin level of 167 (32 - 234) mmol/L. In our cohort of patients those with type IV lesions presented at a younger age and with higher bilirubin and gamma-glutamyl transferase levels, although this finding was not statistically significant. CONCLUSION: Although uncommon, CMs may lead to significant morbidity and malignancy. Specialised care is necessary to improve longterm outcomes in these patients.

Surgery for portal hypertension in children: A 12-year review.

BACKGROUND: Portal hypertension is a common and potentially devastating condition in children. Notwithstanding advances in the nonsurgical management of portal hypertension, surgery remains an important treatment modality in select patients. We report here on our experience in the past 12 years. OBJECTIVES: To describe the profile of, indication for, and complications of shunt surgery in children with portal hypertension. METHODS: Twelve children underwent shunt surgery between 2005 and 2017. Patient records were reviewed. RESULTS: Fourteen procedures were performed on 12 patients during the study period. The median age at surgery was 6.5 (range 1 - 18) years. Six patients were male. Gastrointestinal bleeding that was not amenable to endoscopic control was the most common indication for surgery. Portal vein thrombosis was the most common cause of portal hypertension in our series (n=11). Two-thirds (8/12) of all patients had an identifiable underlying risk factor for portal vein thrombosis. One-third of all patients (4/12) underwent a meso-portal bypass procedure (Rex shunt), while 58% (7/12) were managed with a distal splenorenal shunt. All patients received postoperative thromboprophylaxis. We experienced a single mortality, 1 patient experienced shunt thrombosis that required revision shunt surgery, and 2 patients experienced anastomotic strictures, with one being managed with revision surgery and the other currently awaiting radiological venoplasty. CONCLUSIONS: Surgery is a safe and important tool in the management of children with non-cirrhotic portal hypertension and those with sufficient hepatic reserve who fail to respond to more conservative methods for the treatment of side effects of portal hypertension.

Sulphur-containing excitatory amino acid-evoked Ca(2+)-independent release of D-[3H]aspartate from cultured cerebellar granule cells: the role of glutamate receptor activation coupled to reversal of the acidic amino acid plasma membrane carrier.

Sulphur-containing excitatory amino acid transmitter candidates (500 microM) stimulated the Ca(2+)-independent efflux of exogenously-supplied D-[3H]aspartate from primary cultures of cerebellar granule cells superfused continuously with HEPES-buffered saline containing CoCl2 (1 mM) in place of CaCl2. The stimulated release of D-[3H]aspartate was markedly attenuated by 200 microM 6,7-dinitroquinoxalinedione, a concentration at which the antagonist inhibits both non-N-methyl-D-aspartate and N-methyl-D-aspartate ionotropic excitatory amino acid receptors. The Ca(2+)-independent component of evoked release was also markedly attenuated and, in some cases, abolished by removing NaCl from the superfusion medium. Furthermore, when 700 microM dihydrokainate (demonstrated herein as a mixed/non-competitive inhibitor of the high-affinity dicarboxylic amino acid transporter in cultured granule cells) was included in the superfusion medium, stimulated efflux of D-[3H]aspartate was reduced by between 15-78% of the control response; the extent of inhibition varying with the agonist employed. In constrast, agents which act as competitive inhibitors of the plasma membrane carrier in granule cells, e.g. beta-methylene-D,L-aspartate, potentiated the release of D-[3H]aspartate in a synergistic manner. Taken together, these findings are consistent with a mechanism for the Ca(2+)-independent release of D-[3H]aspartate that is mediated predominantly by activation of excitatory amino acid receptors resulting in a reversal of the high-affinity dicarboxylic amino acid transport system. Although the physiological relevance of such non-vesicular release from the cytosol remains obscure and is still a matter of some debate, this mode of release may be of pathological significance.

L-trans-pyrrolidine-2,4-dicarboxylate and cis-1-aminocyclobutane-1,3-dicarboxylate behave as transportable, competitive inhibitors of the high-affinity glutamate transporters.

The ability of two conformationally restricted analogues of L-glutamate to function as non-transportable inhibitors of plasma membrane L-glutamate transport was investigated in primary cultures of cerebellar granule cells and cortical astrocytes. L-trans-Pyrrolidine-2,4-dicarboxylic acid (L-trans-PDC) and cis-1-aminocyclobutane-1,3-dicarboxylic acid (cis-ACBD) behaved as linear competitive inhibitors of the uptake of D-[3H]aspartate (used as a non-metabolizable analogue of L-glutamate) exhibiting Ki values between 40 and 145 microM; L-trans-PDC being the more potent inhibitor in each preparation. However, both L-trans-PDC and cis-ACBD, over a concentration range of 1 microM-5 mM, dose-dependently stimulated the release of exogenously supplied D-[3H]aspartate from granule cells maintained in a continuous superfusion system. The stimulated release was independent of extracellular calcium ions; essentially superimposable dose-response profiles being obtained in the absence and presence of 1.3 mM CaCl2 and yielding EC50 values of 16-25 microM and 180-220 microM for L-trans-PDC and cis-ACBD, respectively. Stimulated release of D-[3H]aspartate was unaffected by either 300 microM D-(-)-2-amino-5-phosphonopentanoic acid [D-APV; a selective antagonist of the N-methyl-D-aspartate (NMDA) receptor] or by 25 microM 6-cyano-7-nitroquinoxaline-2,3-dione [CNQX; a selective antagonist of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor]. The release of D-[3H]-aspartate following stimulation by either L-trans-PDC or cis-ACBD was however markedly attenuated following substitution in the superfusion medium of sodium ions by choline ions. Taken together, these results support an action of L-trans-PDC and cis-ACBD consistent with that of being competitive substrates rather than non-transportable blockers of the plasma membrane L-glutamate uptake system.

Characterization of the receptor-mediated sulphur amino acid-evoked release of [(3)H]d-aspartate from primary cultures of cerebellar granule cells.

A continuous superfusion system was used to study the release of [(3)H]d-aspartate from primary cultures of mouse cerebellar granule cells. A number of neuroactive acidic sulphur amino acids (viz. cysteine sulphinate, cysteate, homocysteine sulphinate, homocysteate and S-sulpho-cysteine) of endogenous origin were shown to evoke a dose-dependent, saturable and stereospecific release of [(3)H]d-aspartate. Substitution of Ca(2+) in the superfusion medium by Co(2+) (which blocks voltage-gated Ca(2+)-channels) resulted in a marked attenuation of evoked release following stimulation by l-enantiomers of all sulphur amino acids tested, thus demonstrating a "Ca(2+)-dependent" release of [(3)H]d-aspartate. Cysteine sulphinate-evoked release of endogenous glutamate was shown to be Ca(2+)-dependent whereas negligible release of endogenous aspartate was observed. All sulphur amino acids inhibited to varying degrees, the intracellular accumulation of the [(3)H]tetraphenylphosphonium cation, an observation consistent with either partial or complete depolarization of the plasma membrane. The sulphur amino acid-evoked release of [(3)H]d-aspartate from the granule cells was inhibited by a variety of excitatory amino acid receptor antagonists. At a concentration range of antagonist between 0.1-500 ?M, the sulphur amino acid-evoked release of [(3)H]d-aspartate was inhibited by: (i) the selective, competitive N- methyl- d -aspartate receptor antagonists; 3-(+/-)-2-carboxypiperazin-4-yl) propyl-2-phosphonic acid and d-2-amino-5-phosphonopentanoic acid; (ii) the competitive quisqualate/kainate receptor antagonist, 6,7-dinitroquinoxalinedione; and (iii) the broad spectrum excitatory amino acid receptor antagonist, kynurenate. Such observations demonstrate that excitatory sulphur amino acid-evoked release of [(3)H]d-aspartate from primary cultures of cerebellar granule cells occurs primarily by a receptor-mediated event in which both N- methyl- d -aspartate and quisqualate/kainate receptors are involved. The findings of this study provide additional evidence to support the transmitter candidacy of certain endogenous neuroactive sulphur amino acids and furthermore, suggest the mechanism by which their epileptogenic and neurotoxic actions may be explained.