High frequency UV-Vis sensors estimate error in riverine dissolved organic carbon load estimates from grab sampling

High frequency ultraviolet - visible (UV-VIS) sensors offer a way of improving dissolved organic carbon (DOC) load estimates in rivers as they can be calibrated to DOC concentration. This is an improvement on periodic grab sampling, or the use of pumped sampling systems which store samples in-field before collection. We hypothesised that the move to high frequency measurements would increase the load estimate based on grab sampling due to systemic under-sampling of high flows. To test our hypotheses, we calibrated two sensors in contrasting catchments (Exe and Bow Brook, UK) against weekly grab sampled DOC measurements and then created an hourly time series of DOC for the two sites. Taking this measurement as a 'true' value of DOC load, we simulated 1,000 grab sampling campaigns at weekly, fortnightly and monthly frequency to understand the likely distribution of load and error estimates. We also performed an analysis of daily grab samples collected using a pumped storage sampling system with weekly collection. Our results show that: a) grab sampling systemically underestimates DOC loads and gives positively skewed distributions of results, b) this under-estimation and positive skew decreases with increasing sampling frequency, c) commonly used estimates of error in the load value are also systemically lowered by the oversampling of low, stable flows due to their dependence on the variance in the flow-weighted mean concentration, and d) that pumped storage systems may lead to under-estimation of DOC and over estimation of specific ultra-violet absorbance (SUVA), a proxy for aromaticity, due to biodegradation during storage.

Electrical and Immunohistochemical Properties of Cochlear Fibrocytes in 3D Cell Culture and in the Excised Spiral Ligament of Mice

Fibrocyte degeneration in the cochlear lateral wall is one possible pathology of age-related metabolic hearing loss (presbycusis). Within the lateral wall fibrocytes play a role in potassium recycling and maintenance of the endocochlear potential. It has been proposed that cell replacement therapy could prevent fibrocyte degeneration in the CD/1 mouse model of hearing loss. For this to work, the replacement fibrocytes would need to take over the structural and physiological role of those lost. We have grown lateral wall fibrocytes from neonatal CD/1 mice in a 3D-collagen gel culture with the aim of assessing their functional similarity to native lateral wall fibrocytes, the latter in a slice preparation and in excised spiral ligament pieces. We have compared cultured and native fibrocytes using both immuno-labelling of characteristic proteins and single cell electrophysiology. Cultured fibrocytes exhibited rounded cell bodies with extending processes. They labelled with marker antibodies targeting aquaporin 1 and calcium-binding protein S-100, precluding an unambiguous identification of fibrocyte type. In whole-cell voltage clamp, both native and cultured fibrocytes exhibited non-specific currents and voltage-dependent K⁺ currents. The non-specific currents from gel-cultured and excised spiral ligament fibrocytes were partially and reversibly blocked by external TEA (10 mM). The TEA-sensitive current had a mean reversal potential of + 26 mV, suggesting a permeability sequence of Na⁺  > K⁺. These findings indicate that 3D-cultured fibrocytes share a number of characteristics with native spiral ligament fibrocytes and thus might represent a suitable population for transplantation therapy aimed at treating age-related hearing loss.

A micro-fabricated in vitro complex neuronal circuit platform

Developments in micro-manufacture as well as biofabrication technologies are driving our ability to create complex tissue models such as ‘organ-on-a-chip’ devices. The complexity of neural tissue, however, requires precisely specific cellular connectivity across many neuronal populations, and thus there have been limited reports of complex ‘brain-on-a-chip’ technologies modelling specific cellular circuit function. Here we describe the development of a model of in vitro brain circuitry designed to accurately reproduce part of the complex circuitry involved in neurodegenerative diseases; using segregated co-culture of specific basal ganglia (BG) neuronal subtypes to model central nervous system circuitry. Lithographic methods and chemical modification were used to form structured micro-channels, which were populated by specifically cultured neuronal sub-types to represent parts of the inter-communicating neural circuit. Cell morphological assessment and immunostaining showed connectivity, which was supported by electrophysiology measurements. Electrical activity of cells was measured using patch-clamp, showing voltage dependant Na⁺ and K⁺ currents, and blocking of Na⁺ current by TTX, and calcium imaging showing TTX-sensitive slow Ca²⁺ oscillations resulting from action potentials. Monitoring cells across connected ports post-TTX addition demonstrated both upstream and downstream changes in activity, indicating network connectivity. The model developed herein provides a platform technology that could be used to better understand neurological function and dysfunction, contributing to a growing urgency for better treatments of neurodegenerative disease. We anticipate the use of this advancing technology for the assessment of pharmaceutical and cellular therapies as a means of pre-clinical assessment, and further for the advancement of neural engineering approaches for tissue engineering.

Reservoirs as hotspots of fluvial carbon cycling in peatland catchments

Inland water bodies are recognised as dynamic sites of carbon processing, and lakes and reservoirs draining peatland soils are particularly important, due to the potential for high carbon inputs combined with long water residence times. A carbon budget is presented here for a water supply reservoir (catchment area~9km²) draining an area of heavily eroded upland peat in the South Pennines, UK. It encompasses a two year dataset and quantifies reservoir dissolved organic carbon (DOC), particulate organic carbon (POC) and aqueous carbon dioxide (CO₂(aq)) inputs and outputs. The budget shows the reservoir to be a hotspot of fluvial carbon cycling, as with high levels of POC influx it acts as a net sink of fluvial carbon and has the potential for significant gaseous carbon export. The reservoir alternates between acting as a producer and consumer of DOC (a pattern linked to rainfall and temperature) which provides evidence for transformations between different carbon species. In particular, the budget data accompanied by ¹⁴C (radiocarbon) analyses provide evidence that POC-DOC transformations are a key process, occurring at rates which could represent at least ~10% of the fluvial carbon sink. To enable informed catchment management further research is needed to produce carbon cycle models more applicable to these environments, and on the implications of high POC levels for DOC composition.

Effects of Simultaneous Dietary Exposure to 2,2′,4,4′,5,5′-Hexabromobiphenyl and 3,3′,4,4′,5,5′-Hexachlorobiphenyl on Hepatic Tumor Promotion in Rats

Female Sprague-Dawley rats were partially hepatectomized, initiated with diethylnitrosamine (DEN), and fed diets containing 2,2′,4,4′,5,5′-hexabromobiphenyl (245-HBB), 3,3′,4,4′,5,5′-hexachlorobiphenyl (345-HCB), or combinations of 245-HBB and 345-HCB to determine the tumor-promoting ability of these compounds in a two-stage (initiation/promotion) hepatocar-cinogenesis system. Tumor-promoting ability was assessed by measuring hepatic foci positive for gamma glutamyl transpeptidase (GGT) activity. Concentrations of 10 or 100 mg 245-HBB/kg of diet caused significantly increased numbers of GGT-positive hepatic foci. When 245-HBB and 345-HCB were fed simultaneously, an additive effect on tumor-promoting ability was observed at dietary concentrations of 10 mg/kg 245-HBB and 0.1 mg/kg 345-HCB. However, an inhibitory effect on tumor promotion occurred when dietary concentrations of 100 mg/kg 245-HBB and 1.0 mg/kg 345-HCB were fed simultaneously. These results suggest that the tumor-promoting ability of simultaneous exposure to 245-HBB and 345-HCB can be additive or inhibitory depending upon the concentration of each congener in the diet.

High fluvial export of dissolved organic nitrogen from a peatland catchment with elevated inorganic nitrogen deposition

This study investigates seasonal concentrations and fluxes of nitrogen (N) species under stormflow and baseflow conditions in the peat dominated Kinder River catchment, south Pennines, UK. This upland region has experienced decades of high atmospheric inorganic N deposition. Water samples were collected fortnightly over one year, in combination with high resolution stormflow sampling and discharge monitoring. The results reveal that dissolved organic nitrogen (DON) constitutes ~54% of the estimated annual total dissolved nitrogen (TDN) flux (14.3 kg N ha(-1) yr(-1)). DON cycling in the catchment is influenced by hydrological and biological controls, with greater concentrations under summer stormflow conditions. Dissolved organic carbon (DOC) and DON are closely coupled, with positive correlations observed during spring, summer and autumn stormflow conditions. A low annual mean DOC:DON ratio (<25) and elevated dissolved inorganic N concentrations (up to 63μmoll(-1) in summer) suggest that the Kinder catchment is at an advanced stage of N saturation. This study reveals that DON is a significant component of TDN in peatland fluvial systems that receive high atmospheric inputs of inorganic N.

Meeting report: Emerging respiratory viral infections and nonhuman primate case reports

A workshop on Emerging Respiratory Viral Infections and Spontaneous Diseases in nonhuman primates was sponsored by the concurrent Annual Meetings of the American College of Veterinary Pathologists and the American Society for Veterinary Clinical Pathology, held December 1-5, 2012, in Seattle, Washington. The session had platform presentations from Drs Karen Terio, Thijs Kuiken, Guy Boivin, and Robert Palermo that focused on naturally occurring influenza, human respiratory syncytial virus, and metapneumovirus in wild and zoo-housed great apes; the molecular biology and pathology of these viral respiratory diseases in nonhuman primate (NHP) models; and the therapeutic and vaccine approaches to prevention and control of these emerging respiratory viral infections. These formal presentations were followed by presentations of 14 unique case studies of rare or newly observed spontaneous lesions in NHPs (see online files for access to digital whole-slide images corresponding to each case report at http://scanscope.com/ACVP%20Slide%20Seminars/2012/Primate%20Pathology/view.apml). The session was attended by meeting participants that included students, pathology trainees, and experienced pathologists from academia and industry with an interest in respiratory and spontaneous diseases of NHPs.

Sciatic nerve regeneration is not inhibited by anti-NGF antibody treatment in the adult rat

Elevated nerve growth factor (NGF) is believed to play a role in many types of pain. An NGF-blocking antibody (muMab 911) has been shown to reduce pain and hyperalgesia in pain models, suggesting a novel therapeutic approach for pain management. Since NGF also plays important roles in peripheral nervous system development and sensory nerve outgrowth, we asked whether anti-NGF antibodies would adversely impact peripheral nerve regeneration. Adult rats underwent a unilateral sciatic nerve crush to transect axons and were subcutaneously dosed weekly for 8weeks with muMab 911 or vehicle beginning 1day prior to injury. Plasma levels of muMab 911 were assessed from blood samples and foot print analysis was used to assess functional recovery. At 8-weeks post-nerve injury, sciatic nerves were prepared for light and electron microscopy. In a separate group, Fluro-Gold was injected subcutaneously at the ankle prior to perfusion, and counts and sizes of retrogradely labeled and unlabeled dorsal root ganglion neurons were obtained. There was no difference in the time course of gait recovery in antibody-treated and vehicle-treated animals. The number of myelinated and nonmyelinated axons was the same in the muMab 911-treated crushed nerves and intact nerves, consistent with observed complete recovery. Treatment with muMab 911 did however result in a small decrease in average cell body size on both the intact and injured sides. These results indicate that muMab 911 did not impair functional recovery or nerve regeneration after nerve injury in adult rats.

Ammonium release from a blanket peatland into headwater stream systems

Hydrochemical sampling of South Pennine (UK) headwater streams draining eroded upland peatlands demonstrates these systems are nitrogen saturated, with significant leaching of dissolved inorganic nitrogen (DIN), particularly ammonium, during both stormflow and baseflow conditions. DIN leaching at sub-catchment scale is controlled by geomorphological context; in catchments with low gully densities ammonium leaching dominates whereas highly gullied catchments leach ammonium and nitrate since lower water tables and increased aeration encourages nitrification. Stormflow flux calculations indicate that: approximately equivalent amounts of nitrate are deposited and exported; ammonium export significantly exceeds atmospheric inputs. This suggests two ammonium sources: high atmospheric loadings; and mineralisation of organic nitrogen stored in peat. Downstream trends indicate rapid transformation of leached ammonium into nitrate. It is important that low-order headwater streams are adequately considered when assessing impacts of atmospheric loads on the hydrochemistry of stream networks, especially with respect to erosion, climate change and reduced precipitation.

Arsenic retention and release in ombrotrophic peatlands

Organic matter can play an important role in the mobility and fate of As in the environment, but there is a lack of data on As biogeochemistry in ombrotrophic peatlands. The aim of this study was to investigate As retention and release in atmospherically contaminated ombrotrophic peat soils in the Peak District National Park (UK). Solid phase As concentrations in the peat soils exceed 25 mg kg(-1). Solid phase As and Fe concentrations are closely correlated at sites where the peat is subjected to drying and oxic conditions. In a wetter zone of the bog, solid phase As and Fe distributions are decoupled, suggesting that As retention in these systems is not solely controlled by the presence of Fe oxides. Comparison of solid phase As and Pb distributions reveals that As has been subjected to post-depositional mobility in areas of water table fluctuation. Conversely, at permanently waterlogged locations As is immobile. Detailed stream water sampling reveals that As is released from the organic-rich uplands soils into the fluvial system. Dissolved As concentrations are highly variable, with values ranging from 0.20 to 7.28 microg l(-1). Stream water As concentrations are elevated during late summer stormflow periods when there has been re-wetting of the peat after significant water table draw-down. Dissolved As is strongly correlated to dissolved organic carbon under stormflow and baseflow. The results of this study suggest that organic matter plays an important role in As dynamics in ombrotrophic peatlands, but further work is needed to identify the exact As binding and release mechanisms. Drying and re-wetting of ombrotrophic peat soils and associated changes in redox status has the potential to lead to increased As mobility. Further work is needed to provide information on how predicted climate change will influence As cycling at sites containing a legacy of atmospheric contamination.

Sulphur leaching from headwater catchments in an eroded peatland, South Pennines, U.K

A detailed investigation into sulphur leaching in peatland headwater catchments in the South Pennines, UK shows that, despite significant reductions in sulphur emissions, sulphur remains a key acidifier. This sulphur can be considered as legacy atmospheric pollution, stored within the peat by processes of dissimilatory sulphate reduction and now being leached into the region's surface waters. Persistently lower water tables at gully edge locations define a thick erosional acrotelm that is vulnerable to aeration, oxidation and flushing throughout the year, and not solely confined to periods of drought. Stream discharge behaves as a two-end member system, whereby pre-event water, rich in DOC and sulphate, is diluted by event water as a result of event water flowing through fast flow pathways such as macropores and overland flow. A rapid increase in water table elevation during the storm and a decrease in elevation after the storm indicate that event water has infiltrated the peat and has then been released into the stream. Streamwaters in peat dominated upland catchments with high densities of gullying have high concentrations of sulphate and low concentrations of DOC, whereas the reverse is true for those catchments with low densities of gullying. This is consistent with the concept that high concentrations of sulphate can suppress the solubility of DOC. A significant store of sulphate exists within South Pennine peats, and continued gully erosion will enhance sulphur leaching meaning that the timescale involved for any depletion is uncertain. It is therefore important that models predicting recovery from acidification in these upland systems include an understanding of how this stored sulphur is being leached, especially with respect to gully erosion, climate change and reduced precipitation.

Impact of land drainage on peatland hydrology

There is a long history of drainage of blanket peat but few studies of the long-term hydrological impact of drainage. This paper aims to test differences in runoff production processes between intact and drained blanket peat catchments and determine whether there have been any long-term changes in stream flow since drainage occurred. Hillslope runoff processes and stream discharge were measured in four blanket peat catchments. Two catchments were drained with open-cut ditches in the 1950s. Ditching originally resulted in shorter lag times and flashier storm hydrographs but no change in the annual catchment runoff efficiency. In the period between 2002 and 2004, the hydrographs in the drained catchments, while still flashy, were less sensitive to rainfall than in the 1950s and the runoff efficiency had significantly increased. Drains resulted in a distinctive spatial pattern of runoff production across the slopes. Overland flow was significantly lower in the drained catchments where throughflow was more dominant. In the intact peatlands, matrix throughflow produced by peat layers below 10 cm was rare and produced <1% of the runoff. However, in drained peatlands, matrix throughflow in deeper peat layers was common and provided around 23% of the runoff from gauged plots. Macropore flow, the density of soil piping, and pipeflow were significantly greater in drained peatlands than in intact basins. Gradual changes to peat structure could explain the long-term changes in river flow, which are in addition to those occurring in the immediate aftermath of peatland drainage.

Safety profile of thalidomide after 53 weeks of oral administration in beagle dogs

Fifty-six adult beagle dogs (28 male, 28 female) were orally administered thalidomide at 43, 200, or 1000 mg/kg/day for 53 weeks. Sixteen (2/sex/dose group) and 32 (4/sex/dose group) dogs were euthanized and necropsied after 26 and 53 weeks of dosing, respectively. The remaining 8 animals (2/sex/group; high-dose and control groups) were dosed for 53 weeks, euthanized, and necropsied at 58 weeks after a 5-week recovery period. There were no deaths during the study. The only observed clinical signs attributable to thalidomide administration were green-colored urine, white-colored fecal residue presumed to be unchanged thalidomide, enlarged and/or blue coloration of female mammary tissue, and prolonged estrus. There were no thalidomide-related changes in body weights, food consumption, electrocardiography, ophthalmoscopy, neurological function, and endocrine function. The mostly slight and/or transient variations observed in some hematology and blood chemistry values of dosed dogs were considered to be toxicologically insignificant and were supported by the lack of histopathologic correlates. The only gross finding attributable to thalidomide was a yellow-green discoloration of the femur, rib, and/or calvarium that was observed at each euthanization interval including recovery. There was no microscopic correlate for this finding. No thalidomide-related microscopic changes were seen in any of the organs and tissues at 26 weeks. Mammary duct dilatation and/or glandular hyperplasia observed in females at 53 and 58 weeks and hepatic bile pigment exhibited by high-dose males at 53 weeks were microscopic changes considered to be thalidomide-related. There was no gross and histopathologic evidence of any tumors. In summary, thalidomide at up to 1000 mg/kg/day for 53 weeks did not induce any major systemic toxicity or tumors in dogs. The NOAEL was 200 mg/kg/day.

Cholinergic control of membrane conductance and intracellular free Ca2+ in outer hair cells of the guinea pig cochlea

We have studied the action of cholinergic agonists on outer hair cells, both in situ and isolated from the cochlea of the guinea pig, combining new fast CCD technology for Ca2+ imaging and conventional patch-clamp methods. Carbachol (1 mM) activated a current with a reversal potential near -70 mV and a bell-shaped I-V curve, suggesting that it was a Ca2+ activated K+ current. In a few cells, this current was preceded by a transient inward current, probably owing to an influx of Ca2+ and other cations through the acetylcholine (ACh) receptors. The amplitude of the Ca2+ signal was maximal in a circumscribed region at the basal pole of the cell and decreased steeply towards the apical pole, compatible with Ca2+ influx and/or Ca2+ induced Ca2+ release at the cells base. The time course of the Ca2+ rise was fastest at the base, but it was still slightly slower, and more rounded, than that of the K+ current. In some recordings the K+ current was observed without any measurable change of intracellular Ca2+. The K+ current was potentiated (18%) by caffeine (5 mM), and decreased (19%) by ryanodine (0.1 mM) in the majority of cells tested. The results are discussed in terms of a labile intracellular Ca2+ store located at the base of the cell, close to the Ca2+ permeable ACh receptor channels and Ca2+ activated K+ channels, whose contribution to the Ca2+ rise occurring in the region of the channels is variable, and probably dependent on its ability to refill with Ca2+.

Fetus-in-fetu presenting as cystic meconium peritonitis: diagnosis, pathology, and surgical management

Fetus-in-fetu (FIF), a rare congenital anomaly, is a fetus incorporating the well-differentiated tissue of its twin. The authors describe a newborn who presented with massive abdominal distension and severe respiratory distress. Abdominal x-rays showed multiple calcifications. The diagnosis of meconium pseudocyst was made. At emergency laparotomy an irregular fetiform mass was found in the retroperitoneum lying within a fluid-filled amniotic sac. It contained a vertebral column, 10 limblike structures, and cranial and caudal ends, supporting the diagnosis of fetus-in-fetu. This case highlights several important points. FIF often is overlooked in the differential diagnosis of a newborn abdominal mass and, as in this case, may be confused with meconuim pseudocyst. FIF should be differentiated from a teratoma because of the latter's malignant potential. Because this diagnosis is not made until pathological analysis, all parts of the mass should be removed to prevent malignant recurrence.

The behavioural outcomes of quality improvement teams: the role of team success and team identification

This study investigates the relationship between hospital quality improvement (QI) team success and changes in empowerment, 'organizational commitment, organizational citizenship behaviour' (OCB) and job behaviour related to QI. Data were collected from administrative staff, healthcare professionals and support staff from four community hospitals. The study involved a field investigation with two data collection points. Structured questionnaires and interviews with hospital management were used to collect data on the study variables. High scores were observed for organizational commitment, OCB and job behaviour related to QI when individuals identified with teams that were successful. Low scores were observed when individuals identified with teams that were unsuccessful. Empowerment was positively related to job behaviour associated with QI. It is concluded that participation on QI teams can lead to organizational learning, resulting in the inculcation of positive 'extra-role' and 'in-role' job behaviour.

Measurement of staff empowerment within health service organizations

A measure of empowerment was developed and its psychometric properties evaluated. Employees (n = 52) of two hospitals participated in semistructured interviews and a pilot test of the research instrument. A second study was undertaken with professional, support, and administrative staff (n = 405) of four community hospitals. Psychometric evaluation included factor analysis, reliability estimation, and validity assessment. Subjects responded to questionnaires measuring empowerment, leadership behavior, organizational citizenship behavior and job behaviors related to quality improvement. Factor analysis indicated three dimensions of empowerment: behavioral, verbal, and outcome empowerment. Coefficient alphas ranged from .83 to .87. The three dimensions were positively related to leadership behavior that encouraged self-leadership and negatively related to directive leadership. The three dimensions discriminated between the empowerment level of managers compared to that of nonmanagement staff. Empowerment predicted organizational citizenship behavior and job behaviors related to quality improvement.

Kinetics of activation of a Ca2+-dependent K+ current induced by flash photolysis of caged carbachol in isolated guinea-pig outer hair cells

It has been shown that the application of acetylcholine activates a Ca2+-dependent K+ current in outer hair cells, and the resulting hyperpolarization is thought to be an important part of the inhibition mediated by cholinergic efferent nerve fibres to the cochlea. In order to study the kinetics of the current, flash photolysis has been used to apply a cholinergic agonist, carbachol, rapidly to isolated outer hair cells. A delay in the onset of the outward potassium current following photorelease of carbachol was consistently observed, and the activation phase of the response could be described by a sigmoidal-like function with a mean delay of 59 ms and time constant of 71 ms. The sum of these values lies within the time scale reported for the onset of the inhibition following electrical stimulation of the efferent nerves. Although a distinct current attributable to an acetylcholine receptor was not visible in these experiments, indirect evidence for a carbachol-induced influx of Ca2+ was obtained.

No evidence for functional GABA receptors in outer hair cells isolated from the apical half of the guinea-pig cochlea

Outer hair cells, isolated from the apical cochlear turns, did not respond to GABA during whole-cell recording. A few cells did respond to acetylcholine. Thus we have no evidence to suggest that GABA acts as an efferent neurotransmitter in the cochlea.

Hydrops fetalis and pulmonary sequestration

The development of fetal hydrops in conjunction with intrathoracic pathology has been described, but rarely in association with pulmonary sequestration. The current report presents three cases of antenatally identified nonimmune hydrops fetalis, seen in association with pulmonary sequestrations. In one case, a left-sided chest mass also was defined. One infant was born by emergency cesarean section because of fetal distress at 34 weeks' gestation; the other two were delivered vaginally at 30 and 36 weeks. Two of the newborns were severely hydropic and required aggressive cardiorespiratory resuscitation that included bilateral chest tubes for massive pleural effusions. The third infant was stable at the time of birth, but thereafter respiratory distress developed, and intubation and ventilation became necessary. Two of the infants had a left-chest mass and the other had a right-sided mass, all identified by chest x-ray. Subsequent ultrasonography showed a chest mass and an identifiable systemic feeding artery in two of the patients. For the third, a specific diagnosis was not made before surgery. After resolution of hydrops, all three infants had successful removal of their intrathoracic pulmonary sequestrations. Two of these were found to be extralobar, and the other was an intralobar sequestration of the left lower lobe.

Optimal elective management of patent ductus arteriosus in the older child

Open surgical ligation has proven to be a safe and effective method to bring about closure of the patent ductus arteriosus (PDA). Recent studies have suggested that percutaneous transcatheter and video-assisted thorascopic closure may be better and more cost-effective techniques for PDA closure. The authors reviewed their experience with open thoracotomy for the elective ligation of PDA in 42 children over a 3-year period. The male:female ratio was 1.6:1; the age of the patients (mean +/- SD) was 2.8 +/- 2.3 years and their weight was 14 +/- 7 kg. In all cases the diagnosis was confirmed preoperatively by echocardiography. Open ligation of the PDA was performed through a limited left posterolateral thoracotomy with exposure, by an extrapleural approach. Closure was established with two silk ligatures or a silk ligature and clip, and drainage of the extrapleural space was not used. The operating time was 85 +/- 12 minutes. The total duration of hospitalization was 3.1 +/- 0.8 days. There were no deaths. Successful closure was confirmed by auscultation in 39 children and by subsequent echocardiography in three patients. No surgical complications occurred, and no transfusions were required. Minor respiratory symptoms occurred in two patients postoperatively. Transient systemic hypertension was seen in two patients, and one wound infection occurred.

Acetylcholine activates two currents in guinea-pig outer hair cells

1. Whole-cell voltage clamp recordings were made from outer hair cells (OHCs) isolated from the basal and middle regions of the cochlea. The current produced when acetylcholine (ACh) was applied to the basal pole was investigated. 2. Acetylcholine (50-70 microM) activated an early inward current followed by a late outward current in most cells at -70 mV. The activation of the early current was very rapid, with no delay. 3. The late outward current was a K+ current and was the major component of the total ACh-sensitive current at negative voltages. 4. The ACh-sensitive current was voltage dependent. From tail current measurements, the current was maximal at -55 mV and declined steeply at more positive potentials. On average, 50% of the current was active at -22 mV and 10% was active at 0 mV. This decline was caused by a reduction in the K+ current with depolarization. Between +20 and +40 mV, the major component of the ACh-sensitive current was the early current. 5. The steady-state I-V curve for the ACh-sensitive current was N-shaped, with a peak at -36 mV. The instantaneous I-V curve for the ACh-sensitive current taken from measurements just after a voltage step was outwardly rectifying and did not show this peak. This difference occurred because the voltage dependence was time dependent. 6. The reversal potential for the early current was estimated to be close to+13 mV, in accordance with it being a non-specification current. 7. The K+ current was abolished by the removal of external Ca2+. The effect occurred with no measurable delay. When external Ca2+ was lowered to 0.4 mM, the peak of the steady-state I-V curve for the ACh-sensitive current shifted by up to -20 mV and its amplitude was reduced. These results suggested that the K+ current was dependent on Ca2+ influx. 8. The inward current usually remained when the K+ current was abolished or greatly reduced by removing external Ca2+ or by dialysing the cells with BAPTA (5-10 mM). 9. Both early and late currents were reversibly blocked by alpha-bungarotoxin (0.2 microM) and curare (1 microM). 10. A simple scheme is proposed to account for the response. ACh, binding to a nicotinic receptor, directly gates the early cation current. Part of this current is carried by Ca2+, which once inside the cell leads to the activation of a Ca(2+)-dependent K+ current.

Water soluble inhibitors of topoisomerase I: quaternary salt derivatives of camptothecin

Eleven water soluble 7-substituted quaternary ammonium salt derivatives of 10,11-(methylenedioxy)- and 10,11-(ethylenedioxy)-(20S)-camptothecin were synthesized via the Friedlander reaction followed by nucleophilic displacement with an aromatic amine. All of these compounds were more potent than camptothecin in the in vitro cleavable complex assay. These inherently charged camptothecin derivatives were cytotoxic against three different human tumor cell lines (SKOV3, an ovarian adenocarcinoma; SKVLB a multidrug resistant ovarian adenocarcinoma; and HT-29, a colon carcinoma). A selected group of five compounds was evaluated in the nude mouse HT-29 xenograft model. Two of these quaternary salts (17 and 18) were more efficacious than Topotecan in delaying tumor growth. In an extended in vivo model, 18 demonstrated tumor regression.

Lumbar vein malposition of inferior vena cava catheters

The authors report on a 1 year old who suffered permanent paralysis as a complication of a malpositioned inferior vena cava catheter. A simple protocol to avoid such neurological complications is presented.

Job satisfaction and turnover among nurses: integrating research findings across studies

A meta-analytic study investigated the causal relationships among job satisfaction, behavioral intentions, and nurse turnover behavior. A theoretical model was proposed in which behavioral intentions were viewed as a direct antecedent to turnover behavior. Job satisfaction was expected to be indirectly related to turnover by virtue of the mediating role of behavioral intentions. Consistent with these expectations, a strong positive relationship was indicated between behavioral intentions and turnover; a strong negative relationship between job satisfaction and behavioral intentions; and a small negative relationship between job satisfaction and turnover. The results of the modifier analysis suggested that effect sizes are fairly robust to differences in study designs, response rates, and methods of measuring job satisfaction, but the manner in which behavioral intentions were operationalized appeared to moderate the relationship between behavioral intentions and turnover and job satisfaction. Of variables related to nursing job satisfaction, work content and work environment had a stronger relationship with job satisfaction than economic or individual difference variables.

Subchronic inhalation toxicity of 1,1,1,3-tetrachloropropane in rats

The purpose of this study was to evaluate the inhalation toxicity of 1,1,1,3-tetrachloropropane (TCP), an intermediate in the production of chlorinated silicone fluids. Male and female Sprague-Dawley rats were exposed 6 hr/day, 5 days/week, for 90 days to TCP at concentrations of 0, 25, 75, or 225 ppm (Phase I study) and to 0, 1, 5, or 10 ppm (Phase II study). Phase II of the study was conducted because a no-observed-effect level was not achieved in Phase I. No animals died during the study. Clinical signs of toxicity included oral, nasal, and/or ocular discharge. No statistically significant differences were observed in either body weights or food consumption between exposed and control animals. Clinical pathology did not indicate any treatment-related effects. Absolute and relative liver and kidney weights were increased in male and female rats exposed to 225 ppm TCP, and heart weights were increased in male rats exposed to 225 ppm TCP. The liver and heart weight changes were supported by the findings of microscopic lesions in these organs. These lesions consisted of multifocal/focal myofiber degeneration necrosis with adjacent chronic myocarditis in the heart and multifocal single-cell necrosis in the liver parenchyma. The liver lesions had essentially resolved at the end of a 28-day recovery period but the heart lesions were still present in male rats in the recovery group exposed to 225 ppm TCP. No treatment-related effects were observed in animals exposed to 1, 5, or 10 ppm TCP.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and antitumor activity of novel water soluble derivatives of camptothecin as specific inhibitors of topoisomerase I

The synthesis and antitumor activities of the novel water soluble camptothecin derivatives 7-[(4-methylpiperazino)methyl]-10,11-(methylenedioxy)-(20S)-campto thecin trifluoroacetate (6) and 7-[(4-methylpiperazino)methyl]-10,11-(ethylenedioxy)-(20S)-camptot hecin trifluoroacetate (7) are described. The solubilities of compounds 6 and 7 were measured to be 4.5 and 5.8 mg/mL, respectively, in pH 5 acetate buffer in contrast to < 0.003 mg/mL for camptothecin in the same buffer. In the purified topoisomerase I cleavable complex enzyme assay, compounds 6 and 7 demonstrated potent inhibition of topoisomerase I with IC50's of 300 and 416 nM, respectively, in comparison to 679 nM for camptothecin and 1028 nM for topotecan. In human tumor cell cytotoxicity assays, compounds 6 and 7 demonstrated potent antitumor activity against ovarian (SKOV3), ovarian with upregulated MDRp-glycoprotein (SKVLB), melanoma (LOX), breast (T47D), and colon (HT29) with IC50's ranging from 0.5 to 102 nM. Compounds 6 and 7 induced tumor regressions in the HT29 human colon tumor xenograft model and demonstrated similar rank order of potency compared to in vitro assay results.

In vivo antitumor activity of two new seven-substituted water-soluble camptothecin analogues

The development of camptothecin-like compounds as inhibitors of topoisomerase I for the treatment of resistant tumors has generated clinical excitement in this new class of drugs. We have developed two novel water-soluble camptothecin analogues which are specific inhibitors of topoisomerase I and are potent cytotoxins with significant antitumor activity. We added water-solubilizing groups off position 7 in the B ring of either 10,11-ethylenedioxy- or 10,11-methylenedioxy-20(S)-camptothecin. These water-soluble camptothecin analogues were demonstrated to be nanamolar inhibitors of the topoisomerase I enzyme in the cleavable complex assay. The compounds, GI147211 [7-(4-methylpiperazinomethylene)-10,11-ethylenedioxy-20(S)-camp tot hecin], and GI149893 [7-(4-methylpiperazinomethylene)-10,11-methylenedioxy-20(S)-cam pto thecin], were compared to topotecan, a known water-soluble inhibitor of topoisomerase I. Both GI compounds were found to be slightly more potent than topotecan as inhibitors of topoisomerase I in the cleavable complex assay and were 1.5-2 times more soluble. Tumor cell cytotoxicity assays using 5 separate cell lines demonstrated that both GI compounds were 5-10 times more potent than topotecan, although by comparison all three topoisomerase I inhibitors were unaffected by the multidrug resistance P-glycoprotein. The antitumor activity of all three topoisomerase I inhibitors was compared concomitantly in two human colon xenograft models. In both models, GI147211 and GI149893 were able to induce regression of established HT-29 and SW-48 colon tumors by as much as 60%. The antitumor activity of both compounds were also demonstrated in the MX-1 and PC-3 xenografts. Microscopic examination of selected tissues indicated that drug-induced toxicity was primarily limited to the gastrointestinal tract and was comparable among the three compounds. Further clinical development of this class of compounds is ongoing.

Spontaneous ovarian choriocarcinoma, yolk sac carcinoma, and teratoma in B6C3F1 mice: a case report

Three ovarian neoplasms (choriocarcinoma, yolk sac carcinoma, and teratoma) were diagnosed in a 2 yr carcinogenicity study involving B6C3F1 mice. The yolk sac carcinoma and the teratoma occurred in opposite ovaries of a single female mouse that was sacrificed in extremis on study day 725. The choriocarcinoma occurred in a female mouse that was sacrificed in extremis on study day 565. These neoplasms were considered to be spontaneous in origin.

Pleomorphic adenoma arising in a salivary rest in childhood

Two children with pleomorphic adenomas developing in heterotopic salivary tissue are presented. These are unusual lesions, rarely seen in adults and not previously described in the pediatric age group.

Transplantation of purified frozen/thawed canine pancreatic islet allografts with cyclosporine

We studied the survival of defined volumes of highly purified frozen/thawed islets transplanted into the spleen of 4 groups of apancreatic mongrel dogs (total, 21), with or without cyclosporine from day -4 to day 30: group 1 (controls), without CsA, autograft of mean (+/- SE) islet volume 5 +/- 1 microliters/kg body weight; group 2, single-donor allograft, and group 3, multiple-donor allograft (both, 6 +/- 1 microliters/kg), both with CsA; and group 4, large-volume multiple-donor allograft (24 +/- 1 microliters/kg) with CsA. Grafts were cooled slowly to -40 degrees C, stored at -196 degrees C, and thawed rapidly. The CsA dose was adjusted to maintain whole-blood trough values of 600-800 micrograms/L, and allograft recipients manifesting early hyperglycemia were given insulin to maintain plasma glucose concentration below 150 mg/dl. In group 1, two dogs died early (graft failure in 1, intussusception in 1), but the remaining five were normoglycemic at 30 days. In groups 2 and 3, hyperglycemia ensued from about day 2.5, but 4 of 5 grafts in group 2 and all grafts in group 3 secreted insulin into the splenic vein at 30 days. In group 4, normoglycemia ensued within 24 hr of transplantation and was maintained in all 6 dogs for 30 days; the grafts failed 15 +/- 2 days after CsA was stopped. The data demonstrate prolonged function of purified frozen/thawed islets after transplantation into these outbred dogs but indicate a need for a greater volume of allogeneic islets from multiple donors than of autologous islets to achieve normoglycemia.

The actions of calcium on the mechano-electrical transducer current of turtle hair cells

1. Mechano-electrical transducer currents evoked by deflections of the hair bundle were recorded in turtle isolated hair cells under whole-cell voltage clamp. The outcome of perfusing with solutions of reduced Ca2+ concentration was investigated. 2. The transducer current was roughly doubled by lowering the concentration of divalent cations from normal (2.2 mM-Mg2+, 2.8 mM-Ca2+) to 0 Mg2+, 0.5 mM-Ca2+. No significant effects on the current's kinetics or reversal potential, or on the current-displacement relationship, were noted. 3. If the Ca2+ concentration was lowered to 50 microM (with no Mg2+), there was about a threefold increase in the maximum current but other changes, including loss of adaptation and a decreased slope and negative shift in the current-displacement relationship, were also observed. As a result, more than half the peak transducer current became activated at the resting position of the hair bundle compared to about a tenth in the control solution. 4. The extra changes manifest during perfusion with 50 microM-Ca2+ had also been seen when the cell was held at positive potentials near the Ca2+ equilibrium potential. This supports the view that some consequences of reduced external Ca2+ stem from a decline in its intracellular concentration. 5. With 20 microM-Ca2+, a standing inward current developed and the cell became unresponsive to mechanical stimuli, which may be explained by the transducer channels being fully activated at the resting position of the bundle. 6. The results are interpreted in terms of a dual action of Ca2+: an external block of the transducer channel which reduces the maximum current, and an intracellular effect on the position and slope of the current-displacement relationship; the latter effect can be modelled by internal Ca2+ stabilizing one of the closed states of the channel. 7. During perfusion with 1 microM-Ca2+, the holding current transiently increased but then returned to near its control level. There was a concomitant irreversible loss of sensitivity to hair bundle displacements which we suggest is due to rupture of the mechanical linkages to the transducer channel. 8. Following treatment with 1 microM-Ca2+, single-channel currents with an amplitude of -9 pA at -85 mV were sometimes visible in the whole-cell recording. The probability of such channels being open could be modulated by small deflections of the hair bundle which indicates that they may be the mechano-electrical transducer channels or conductance about 100 pS. 9. Open- and closed-time distributions for the channel were fitted by single exponentials, the mean open time at rest being approximately 1 ms. The mean open time was increased and the mean closed time decreased for movements of the hair bundle towards the kinocilium.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium currents in hair cells isolated from the cochlea of the chick

1. Calcium currents were characterized in tall hair cells isolated from the chick's cochlea to determine what types of Ca2+ channels existed and if these varied in cells with differing voltage responses to current injection. 2. Whole-cell, tight-seal recordings showed that the current-voltage relation of cochlear hair cells of the chick was dominated by K+ current. However, when outward K+ current was blocked it was found that all hair cells had a smaller, maintained inward current. 3. This inward current was a Ca2+ current since it required Ca2+ in the external medium, could also be carried by Ba2+, and was blocked reversibly by 5 mM-Co2+ and by Ni2+ and Cd2+ at micromolar concentrations. The Ca2+ channels were opened at membrane potentials positive to -50 mV, and the current was maximal near 0 mV. 4. The dihydropyridine BayK8644 (0.5 microM) produced a voltage-dependent increase of inward current. Ten micromolar nifedipine partially blocked the inward current. The outward Ca2(+)-activated K+ current was also reduced in the presence of 10 microM-nifedipine. These effects of dihydropyridines were completely reversible. 5. The Ca2+ current had rapid activation kinetics, reaching steady-state levels within 1 ms. If all outward currents were completely blocked the Ca2+ current showed no inactivation during depolarization lasting 200 ms. 6. No differences in voltage activation range, pharmacology, or kinetics of the Ca2+ current were found in tall hair cells from apical and basal regions of the cochlea. This is in contrast to the marked differences in K+ currents amongst cells from these two widely separated regions of the cochlea.

Potassium currents in hair cells isolated from the cochlea of the chick

1. Potassium currents were characterized in tall hair cells of the chick's cochlea. Outward potassium currents were found to flow through two distinct classes of channels. 2. Individual hair cells were isolated from 200 microns long segments of the apical half of the chick's cochlea. Whole-cell voltage-clamp and current-clamp recordings were made from these cells. 3. Voltage responses to injected current ranged from high-frequency (100-250 Hz) oscillations in some cells, to slowly repetitive Ca2+ action potentials or slow oscillations (5-20 Hz) in others. 4. Ionic currents recorded in voltage clamp also varied in different hair cells. Cells with high-frequency voltage oscillations had rapidly activating Ca2(+)-dependent outward K+ current, IK(Ca). Cells that generated action potentials had slow delayed rectifier outward K+ current, IK, and inward rectifier current, IIR. All hair cells had inward Ca2+ current. 5. IK(Ca) activated positive to -45 mV. Tail currents reversed at the K+ equilibrium potential. This current was eliminated in Ca2(+)-free solutions, or when exposed to 10 mM-TEA. This outward current was fully activated within 1-3 ms at 0 mV. The whole-cell current was noisy and ensemble variance analysis suggested a single-channel conductance of 63 pS near 0 mV. 6. IK activated positive to -50 mV. Tail currents reversed at the K+ equilibrium potential. This current was not eliminated in Ca2(+)-free solutions, and was relatively resistant to external TEA. IK activated slowly, reaching peak values in 10-20 ms at 0 mV. This current showed little variance and the average single-channel conductance based on macroscopic noise near 0 mV was 8 pS. 7. External tetraethylammonium (TEA) or Ca2(+)-free saline eliminated the high-frequency voltage oscillations seen in many basal cells. In contrast TEA had little effect on slow action potentials (or low-frequency oscillations) seen in cells with IK. 8. IK(Ca) was prominent in hair cells originating 1.0-2.0 mm from the cochlear apex. IK and IIR dominated the membrane conductance of tall hair cells originating within 0.5 mm of the cochlear apex. 9. The frequency of voltage oscillation in apical cells was temperature-dependent, nearly doubling for each 10 degrees C rise in temperature. 10. IIR activated at membrane potentials negative to -75 mV. The average time constant of activation at -100 mV was 2 ms. Tail currents reversed at the K+ equilibrium potential and did not depend on the external Na+ concentration. IIR was blocked by 5 mM-Cs+ or 100 microM-Ba2+ in the external saline.

Comparison of automated and manual methods for islet isolation

The authors used the principal features of a collagenase perfusion technique and an automated dissociation technique to determine if islets could be isolated from the large mammal pancreas and to compare the effects of the two methods on isolated islets. The pancreases of 16 dogs were cannulated and perfused with collagenase at 4 degrees C, then warmed to 37 degrees C. Group 1 (eight) pancreases were perfused at 37 degrees C until digested, then dissociated manually by teasing and trituration. Group 2 (eight) pancreases were transferred to a closed chamber for continued collagenase digestion and dissociation at 37 degrees C. Islets were purified using identical Ficoll gradients. Aliquots were stained with dithizone and evaluated for number, size and purity. Total islet volume was calculated. Group 2 pancreases were thoroughly digested leaving only a few residual ducts, but undigested fragments persisted in group 1 pancreases. Islet size was similar in both groups. There was a greater islet volume before and after Ficoll purification in group 2, but the difference was not significant. Purity was greater than 90% in both groups. Perifusion with 28 mM glucose elicited a biphasic insulin release from islets in both groups. The data show that the combined protocol enables mass isolation of purified islets from the canine pancreas. Compared with the manual technique, the automated protocol for pancreas dissociation tends to improve the yield of islets without compromising islet size and viability. It provides the advantages of a closed system with increased control over the extent of collagenase digestion.

Reversal of diabetes in dogs by transplantation of pure cryopreserved islets

We have autotransplanted highly purified cryopreserved canine islets into pancreatectomized dogs. Islets were frozen by slow cooling (0.25 degrees C/min) to -40 degrees C, stored at -196 degrees C and thawed rapidly (200 degrees C/min). A total of 7868 +/- 665 (means +/- SE) cryopreserved islets/kg body weight were implanted to the spleen (n = 7) by venous reflux, and seven other control dogs received 6811 +/- 653 fresh islets/kg (P versus cryo., NS). Fasting plasma glucose [( PG] mg/dl, +/- SEM) and intravenous glucose tolerance were determined before and at 1 and 3 months postimplantation. Six dogs that received cryopreserved islets and all seven control animals promptly became normoglycemic, with PGs of 133 +/- 23 and 110 +/- 4, respectively, at 1 week postimplantation (NS). During follow-up one normoglycemic animal from each group died due to small bowel volvulus and one recipient of fresh islets became diabetic at 14 days. The remaining dogs remained normoglycemic with PGs of 89 +/- 3 and 92 +/- 3 in dogs receiving cryopreserved and fresh islets, respectively, at 3 months postimplantation (NS). Mean K value (decline of glucose, %/min +/- SEM) at ivGTT for all dogs was 2.5 +/- 0.3 preoperatively. At 1 and 3 months postimplantation, the K values of dogs receiving cryopreserved islets were 1.3 +/- 0.1 and 1.4 +/- 0.2, respectively, compared with 1.3 +/- 0.2 and 2.0 +/- 0.2 for control dogs (NS). These data demonstrate prompt and sustained function of a defined quantity of frozen-thawed purified islets in a large mammal. Cryopreservation is an effective method for the long-term storage of purified islet tissue.

Evolution of the MHC class I genes of a New World primate from ancestral homologues of human non-classical genes

The products of the classical human major histocompatibility complex (MHC) class I genes (HLA-A, -B, -C) are highly polymorphic molecules that bind peptides and present them to T lymphocytes. The non-polymorphic, non-classical MHC class I gene products (HLA-E, -F, -G) are not restricting elements for the majority of T lymphocytes. The evolutionary relationship of the non-classical and classical MHC class I genes is unclear. Here we present the cloning and sequencing of the MHC class I genes of a New World primate, the cotton-top tamarin (Saguinus oedipus). The expressed MHC class I genes of this species are more closely related to the human non-classical HLA-G gene than they are to genes of the human classical HLA-A, -B, and -C loci. These observations imply that classical and non-classical genes do not necessarily constitute mutually exclusive groups over evolutionary time.

Prolonged function of canine pancreatic fragments autotransplanted to the spleen by venous reflux

The long-term viability and function of pancreatic islets transplanted as nonvascularized dispersed grafts has not been well established. We report maintenance of nondiabetic carbohydrate metabolism for up to 36 months (17.8 +/- 1.4 months) in 77% of 40 consecutive canine recipients of nonpurified islet grafts transplanted to the spleen by venous reflux. Spontaneous loss of graft function occurred in 9 dogs during the follow-up period. Failure usually occurred within 1 year of implantation and was predicted by low K value and low insulin output on intravenous glucose tolerance tests 1 and 3 months postimplant. High K values and insulin output correlated strongly with maintenance of function beyond 24 months. A sufficient mass of implanted islets can provide satisfactory metabolic control for prolonged periods.

Islet isolation from human pancreas stored in UW solution for 6 to 26 hours

1. Viable and functional islets can be recovered from human pancreata stored for prolonged periods (up to 18 hours) with either the UW solution or EC. 2. Function of islets from pancreas stored in UW solution appeared superior. However, the difference in these preliminary studies does not appear nearly so dramatic as in transplantation of vascularized pancreas. 3. Function of islets from human pancreas stored for longer than 18 hours after UW in situ flush was uniformly poor. 4. Considerable room for improvement in the storage of human pancreas before isolation exists. Progress in this area will be important for the development of any large-scale program of clinical islet transplantation.

Activation and adaptation of transducer currents in turtle hair cells

1. Transducer currents were recorded in turtle cochlear hair cells during mechanical stimulation of the hair bundle. The currents were measured under whole-cell voltage clamp in isolated cells that were firmly stuck to the floor of the recording chamber. 2. Stimuli were calibrated by projecting the image of the hair bundle onto a rapidly scanned 128 photodiode array. This technique showed that, while the cell body was immobilized, the tip of the bundle would follow faithfully the motion of an attached glass probe up to frequencies of more than 1 kHz. 3. The relationship between inward transducer current and bundle displacement was sigmoidal. Maximum currents of 200-400 pA were observed for deflections of the tip of the bundle of 0.5 microns, equivalent to rotating the bundle by about 5 deg. 4. In response to a step deflection of the bundle, the current developed with a time constant (about 0.4 ms for small stimuli) that decreased with the size of displacement. This suggests that the onset of the current was limited by the gating kinetics of the transduction channel. The onset time course was slowed about fourfold for a 20 degrees C drop in temperature. 5. For small maintained displacements, the current relaxed to about a quarter of the peak level with a time constant of 3-5 ms. This adaptation was associated with a shift of the current-displacement relationship in the direction of the stimulus. The rate and extent of adaptation were decreased by lowering external Ca2+. 6. Adaptation was strongly voltage sensitive, and was abolished at holding potentials positive to the reversal potential of the transducer current of about 0 mV. It was also diminished by loading cells with 10 mM of the Ca2+ chelator BAPTA. These observations suggest that adaptation may be partly controlled by influx of Ca2+ through the transducer channels. 7. Removal of adaptation produced asymmetric responses, with fast onsets but slow decays following return of the bundle to its resting position; the offset time course depended on both the magnitude and duration of the prior displacement. 8. In some experiments, hair bundles were deflected with a flexible glass fibre whose motion was monitored using a dual photodiode arrangement. Positive holding potentials abolished adaptation of the transducer currents, but had no influence on the time course of motion of the fibre. We have no evidence therefore that adaptation is caused by a mechanical reorganization within the bundle.