Role of the Membrane Transport Mechanism in Electrochemical Nitrogen Reduction Experiments.

The electrochemical synthesis of ammonia through the nitrogen reduction reaction (NRR) is receiving much attention, since it is considered a promising alternative to the Haber-Bosch process. In NRR experiments, a Nafion membrane is generally adopted as a separator. However, its use is controversial since ammonia can be trapped in the membrane, to some extent, or even pass through it. We systematically investigate the interaction of a Nafion membrane with ammonia and with an electrolyte and compare it with Zirfon as a possible alternative separator. We show that Nafion containing ammonia can easily release it when immersed in a 0.1 M Na2SO4 ammonia-free electrolyte, due to the cation exchange mechanism (Na+-NH4+). Since Na2SO4 is a commonly adopted electrolyte for NRR experiments, this may cause serious measurement errors and non-reproducible results. The same experiments performed using the polysulfone Zirfon separator clearly show that it is immune to interactions with ammonia, because of its different ion conduction mechanism. The findings provide a deeper understanding of the choice of membrane and electrolyte to be adopted for NRR tests, and may allow one to obtain more accurate and reliable results.

Cryoablation of small renal tumors in patients with solitary kidneys: initial experience.

Introduction. The purpose of this study was to evaluate the role of renal cryoablation in patients with solitary kidneys with the goals of tumor destruction and maximal renal parenchymal preservation. Methods. Eleven patients with single tumors were treated with cryoablation, of which 10 patients had solitary kidneys and 1 had a nonfunctioning contralateral kidney. All procedures were performed via an open extraperitoneal approach; ten tumors were treated with in-situ cryoablation and 1 tumor was treated with cryo-assisted partial nephrectomy. Results. Cryoablation was successfully performed without any preoperative complications. Mean patient age was 62.4 years (range 49-79), tumor location included: 6 (upper pole), 2 (mid-kidney), 3 (lower pole). The mean and median tumor size was 2.6 cm and 2.8 cm (range 1.2-4.3 cm), mean operative time 205 minutes (range 180-270 minutes), blood loss 98.5 ml (range 40-250 ml), and hospitalization 4.6 days (range 3-8 days). Creatinine values included: preoperative 1.43 mg/dL (range 1.2-1.9), postoperative 1.67 mg/dL (range 1.5-2.5), and nadir 1.57 mg/dL (range 1.3-2.1). All patients were followed postoperatively with magnetic resonance imaging for surveillance. At a median follow-up of 43 months, 9 patients had no evidence of recurrence, 1 patient has an enhancing indeterminate area, and 1 patient was lost to follow-up. Conclusion. Intermediate-term results suggest that renal cryoablation offers a feasible alternative for patients that require a maximal nephron-sparing effort with preservation of renal function and minimal risk of tumor recurrence.

Impact of laparoscopic donor nephrectomy on allograft function in pediatric renal transplant recipients: a single-center report.

Laparoscopic donor nephrectomy (LDN) is rapidly becoming the preferred technique for the procurement of living donor kidneys. An association of this technique with delayed graft function and higher risk for rejection has been reported in pediatric recipients. We reviewed our experience of 17 pediatric patients who received a living donor kidney, from 2002 to 2004, procured by LDN, and compared it with a matched group that received living donor kidneys harvested by the open technique. Patient demographics, etiology of renal failure, intra-operative events, length of stay, serum creatinine decline, and graft function were reviewed. Our experience confirmed the findings of earlier reports specifically in small pediatric recipients. The LDN group showed a significantly slower decline in creatinine in the immediate post-operative period and longer intra-operative time. However, there was no difference between the two groups in the length of hospital stay, and creatinine clearances at discharge, six, 12 and 24 months post-operatively. The incidence of acute rejection was similar in both groups. LDN is a safe procurement modality for pediatric patients. The risk for prolonged OR time and delay graft function has to be considered during the evaluation process.

Anisotropic representation of forelimb position in the cerebellar cortex and nucleus interpositus of the rat.

The relationship between the spatial location of limb and the activity of cerebellar neurons has received little attention and its nature still remains ambiguous. To address this question we studied the activity of Purkinje and nucleus interpositus cells in relation to the spatial location of rat forelimb. A computer-controlled robot arm displaced the limb passively across 15 positions distributed on a parasagittal plane. The limb was upheld for 8 s in each position, which was identified by the Cartesian coordinates of the forepaw. We selected the neurons whose activities were significantly modulated by forepaw position and found that the majority represented preferentially one spatial dimension of the Cartesian plane both in the cerebellar cortex and nucleus interpositus. In particular, the antero-posterior axis was best represented in cerebellar neuronal discharges. This result suggests that the intermediate part of the cerebellum might encode limb position by way of an anisotropic representation of the spatial coordinates of the limb end-point.