36 Older Surgical Patients Pathway: Improving Care for Frail Older People in General Surgery

Background

The Older Surgical Patients Pathway (OSPP) was established in 2014 and aims to improve care for frail older people on General Surgery (GS) wards at Sheffield Teaching Hospitals NHSFT (STH) by delivering consultant-led Comprehensive Geriatric Assessment (CGA). The OSPP team proactively review frail, surgical patients 75 years or older.

Introduction

Patients over 75 account for 10% of admissions in GS at STH, occupying 33% of bed-nights (14,000/year, costing approximately £4.2 M). They may present a challenge to surgical staff due to multiple co-morbidities, cognitive or mental capacity concerns, leaving them vulnerable to clinical decompensation, with subsequent increased health and care needs. Geriatrician input prior to 2014 was ad hoc and reactive. OSPP was developed to improve and co-ordinate care in this vulnerable group.

Methods

The project team consisted of surgeon, geriatrician, senior nurse with service improvement expertise and data analyst. Stakeholder events were held to raise awareness and target interventions.

Through regular review of outcomes with iterative testing and service redesign, the main interventions have been:

• Introduction of a frailty screening tool.

• Embed a geriatrician into the colorectal unit, providing clinical review and leadership.

• Establish regular, frequent multidisciplinary team meetings.

• Use of eWhiteboard.

• Training for multiple professions in geriatrics and general surgery.

• Gather objective (see table) and subjective outcome measures (staff survey and Foundation Programme feedback).

• Access to CGA for all over 70 year olds who have undergone emergency laparotomy.

Results

The OSPP team review approximately 200 frail older patients per year in detail. The objective results, compared to baseline data from 2014, are in the table.

The reduction in LoS equates to a saving of 700 bed-nights (at £300/bed-night, a total financial saving of £210 k) over 5 years. Thirty six more patients are returned to usual place of residence per annum. Multiple staff groups on the colorectal unit have greater awareness of frailty and its consequences and more than 150 junior doctors have received extra support and training in this area.

Conclusions

OSPP has improved quality of care for frail older people in general surgery in Sheffield in both objective and subjective measures. This template could be used to replicate this service in other surgical specialities with a large cohort of frail older patients.

Ganoderic acid A/DM-induced NDRG2 over-expression suppresses high-grade meningioma growth

PURPOSE

N-myc downstream-regulated gene 2 (NDRG2) is down-regulated in grade-III meningioma [anaplastic meningioma (AM)] and associated with clinically aggressive behavior. Current therapies in the treatment of high-grade meningioma are lacking with limited success. This study aims to validate the effect of NDRG2-targeted therapy using structurally related bioactive triterpene compounds derived from the edible mushroom Ganoderma lucidum (ganoderic acid A:GA-A/ganoderic acid DM:GA-DM) in human AM in relevant pre-clinical models.

METHODS

Tissue samples from the AM tumor regions of three human patients and control non-tumor samples were used to analyze the expression pattern of NDRG2. In vitro cell culture and in vivo cell-line-derived orthotopic xenograft animal models of AM were utilized to assess efficacy of treatment with GA-A/DM.

RESULTS

Downregulation of NDRG2 expression was observed in surgically resected high-grade meningiomas compared to normal brain. These results prompt us to use NDRG2-targeting agents GA-A/DM. In vitro results showed that 72-h treatments of 25 µM GA-A/DM induced AM cell death, upregulate NDRG2 protein expression, downregulate NDRG2 promoter methylation in meningioma cells as compared to azacitidine and decitabine, the most commonly used demethylating agents. Our results also demonstrated that GA-A/DM does not have any detrimental effect on normal human neurons and arachnoid cells. GA-A/DM promoted apoptotic factors (Bax) while suppressing MMP-9, p-P13K, p-AKT, p-mTOR, and Wnt-2 protein expression. RNAi-mediated knockdown of NDRG2 protein expression increased tumor proliferation, while forced expression of wt-NDRG2 decreased proliferation in an in vitro model. Magnetic resonance (MR) imaging and Hematoxylin (H&E) staining demonstrated gross reduction of tumor volume in GA-A/DM treated mice at 5 weeks when compared with saline-treated orthotopic AM xenografted controls. There was an overall decrease in tumor cell proliferation with increased survival in GA-A/DM-treated animals. Enzyme assays showed that GA-A/DM did not negatively impact hepatic function.

CONCLUSION

GA-A/DM may be a promising natural therapeutic reagent in the treatment of AM by suppressing growth via NDRG2 modulation and altering of intracellular signal pathways. We have shown it could potentially be an effective treatment for AM with decreased cellular proliferation in vitro, decreased tumor volume and increased survival in vivo.

Assessment of knee alignment with varus and valgus force through the range of flexion with non-invasive navigation

In image-free total knee arthroplasty (TKA) navigation, infra-red markers are attached to bony landmarks to provide kinematic data intra-operatively, with the aim of improving the precision of implant placement. In non-invasive navigation, infra-red markers are attached to the skin surface, with recent evidence suggesting that this can give repeatable measurements of lower limb mechanical alignment. The aim of our study was to evaluate the use of a non-invasive navigation system in the assessment of mechanical alignment with applied coronal force through the range of flexion. A previously validated non-invasive system (Physiopilot™) was tested on 23 volunteers with healthy knees. Two users performed two registrations of the software workflow on each participant's right and left knees. A force was manually applied to the end-point of varus and valgus knee laxity and the measured change in mechanical alignment was recorded. Force was applied with the knee positioned in increments of flexion from 0 to 90°. In keeping with previous studies, satisfactory values of coefficient of repeatability (CR) of 1.55 and 1.33 were found for intra-observer repeatability in measurement of supine mechanical femoro-tibial angle (MFTA) in extension, with a good inter-observer correlation of intraclass correlation coefficient (ICC) .72. However, when flexion was introduced, intra-observer and inter-observer reliability fell out with acceptable limits. Therefore, the trial did not support use of the Physiopilot™ system as a measure of MFTA when flexion is introduced. It was felt that learning-curve, soft tissue artefacts and lack of force standardisation equipment may have accounted for significant levels of error, with further studies required to address these issues.

Effects of online cone-beam computed tomography with active breath control in determining planning target volume during accelerated partial breast irradiation

PURPOSE

To test if active breath control during cone-beam computed tomography (CBCT) could improve planning target volume during accelerated partial breast radiotherapy for breast cancer.

METHODS

Patients who were more than 40 years old, underwent breast-conserving dissection and planned for accelerated partial breast irradiation, and with postoperative staging limited to T1-2 N0 M0, or postoperative staging T2 lesion no larger than 3cm with a negative surgical margin greater than 2mm were enrolled. Patients with lobular carcinoma or extensive ductal carcinoma in situ were excluded. CBCT images were obtained pre-correction, post-correction and post-treatment. Set-up errors were recorded at left-right, anterior-posterior and superior-inferior directions. The differences between these CBCT images, as well as calculated radiation doses, were compared between patients with active breath control or free breathing.

RESULTS

Forty patients were enrolled, among them 25 had active breath control. A total of 836 CBCT images were obtained for analysis. CBCT significantly reduced planning target volume. However, active breath control did not show significant benefit in decreasing planning target volume margin and the doses of organ-at-risk when compared to free breathing.

CONCLUSION

CBCT, but not active breath control, could reduce planning target volume during accelerated partial breast irradiation.

Association of Lumbar Synovial Cysts with Facet Effusion

To show the frequent association of synovial cysts and facet effusion.

MR studies of 26 patients with lumbar synovial cysts were reviewed for sex/age incidence, anatomic location, multiplicity of cysts and associated pathologies. All studies were reviewed for presence of facet effusion.

26 patients had 39 MRI documented synovial (17 females, 9 males). Age distribution: 41 – 79 years. Location of cysts: L4/5 = 29, L3/4 = 6, L5/S1 = 3, L1/2= −;1. 36 synovial cysts showed facet effusion. 19 patients also had facet effusions at adjoining motion segments or at contralateral joints. Synovial cysts were found in anterior (n=20), posterior (n=13), anterior-posterior (n=3) positions. 18 patients had cysts localized to one single facet joint, 8 patients showed synovial cysts at multiple facet joints.

The frequent coexistence of synovial cysts and facet effusion in our material suggests a causal relationship. External herniation of synovium from a fluid expanded joint space appears to be the most plausible pathologic mechanism.

Preoperative embolization of intracranial meningiomas: efficacy, technical considerations, and complications

BACKGROUND AND PURPOSE

Preoperative embolization for intracranial meningiomas offers potential advantages for safer and more effective surgery. However, this treatment strategy has not been examined in a large comparative series. The purpose of this study was to review our experience using preoperative embolization to understand the efficacy, technical considerations and complications of this technique.

MATERIALS AND METHODS

We performed a retrospective review of patients undergoing intracranial meningioma resection at our institution (March 2001 to December 2012). Comparisons were made between embolized and nonembolized patients, including patient and tumor characteristics, embolization method, operative blood loss, complications, and extent of resection. Logistic regression analyses were used to identify factors predictive of operative blood loss and extent of resection.

RESULTS

Preoperatively, 224 patients were referred for embolization, of which 177 received embolization. No complications were seen in 97.1%. There were no significant differences in operative duration, extent of resection, or complications. Estimated blood loss was higher in the embolized group (410 versus 315 mL, P=.0074), but history of embolization was not a predictor of blood loss in multivariate analysis. Independent predictors of blood loss included decreasing degree of tumor embolization (P=.037), skull base location (P=.005), and male sex (P=.034). Embolization was not an independent predictor of gross total resection.

CONCLUSIONS

Preoperative embolization is a safe option for selected meningiomas. In our series, embolization did not alter the operative duration, complications, or degree of resection, but the degree of embolization was an independent predictor of decreased operative blood loss.

Selected fruits reduce azoxymethane (AOM)-induced aberrant crypt foci (ACF) in Fisher 344 male rats

Phytochemicals contribute to the vibrant colors of fruits and it is suggested that the darker the fruit the higher the antioxidative or anticarcinogenic properties. In this study we investigated the possible effects of blueberries (BLU), blackberries (BLK), plums (PLM), mangoes (MAN), pomegranate juice (POJ), watermelon juice (WMJ) and cranberry juice (CBJ) on azoxymethane (AOM)-induced aberrant crypt foci (ACF) in Fisher 344 male rats. Forty-eight male Fisher 344 rats were randomly assigned to eight groups (n=6). The groups were fed AIN-93G as a control (C) diet, the rats fed fruits received AIN-93G+5% fruits and the groups that were given fruits juices received 20% fruit juice instead of water. The rats received subcutaneous injections of AOM at 16 mg/kg body weight at seventh and eighth weeks of age. At 17th week of age, the rats were killed by CO(2) asphyxiation. Total ACF numbers (mean+/-SEM) in the rats fed CON, BLU, BLK, PLM, MNG, POJ, WMJ and CBJ were 171.67+/-5.6, 11.33+/-2.85, 24.0+/-0.58, 33.67+/-0.89, 28.67+/-1.33, 15.67+/-1.86, 24.33+/-3.92 and 39.0+/-15.31. Total glutathione-S-transferase (GST) activity (mICROmol/mg) in the liver of the rats fed fruits (except BLK) and fruit juices were significantly (p<0.05) higher in the rats fed fruits and fruit juices compared with the control. Our findings suggest that among the fruits and fruit juices, BLU and POJ contributed to significant (P<0.05) reductions in the formation of AOM-induced ACF.

Adenoviral gene transfer of a mutant surfactant enzyme ameliorates pseudomonas-induced lung injury

Surfactant deficiency is an important contributor to the acute respiratory distress syndrome, a disorder that commonly occurs after bacterial sepsis. CTP:phosphocholine cytidylyltransferase (CCTalpha) is the rate-limiting enzyme required for the biosynthesis of dipalmitoylphosphatidylcholine (DPPC), the major phospholipid of surfactant. In this study, a cDNA encoding a novel, calpain-resistant mutant CCTalpha enzyme was delivered intratracheally in mice using a replication-deficient adenovirus 5 CTP:phosphocholine cytidylyltransferase construct (Ad5-CCT(Penta)) in models of bacterial sepsis. Ad5-CCT(Penta) gene transfer produced high-level CCTalpha gene expression, increased alveolar surfactant (DPPC) levels and improved lung surface tension and pressure-volume relationships relative to control mice. Pseudomonas aeruginosa (PA103) decreased DPPC synthesis, in part, via calpain-mediated degradation of CCTalpha. Deleterious effects of Pseudomonas on surfactant were lessened after infection with a mutant strain lacking the type III exotoxin, Exo U. Replication-deficient adenovirus 5 CTP:phosphocholine cytidylyltransferase gene delivery improved lung biophysical properties by optimizing surface activity in this Pseudomonas model of proteinase-mediated lung injury. The studies are the first demonstration of in vivo gene transfer of a lipogenic enzyme resulting in improved lung mechanics. The studies suggest that augmentation of DPPC synthesis via gene delivery of CCTalpha can attenuate impaired lung function in surfactant-deficient states such as bacterial sepsis.

Patient-maintained propofol sedation: a follow up safety study using a modified system in volunteers

Patient-maintained sedation is a mode of patient-controlled sedation during which propofol is administered using a target-controlled infusion, with patient demand increasing the target concentration. A system tested previously for safety in our institution resulted in oversedation. Aiming to improve safety, we modified the system by increasing the lockout period to 4 min,reducing the starting concentration to 0.5 microg x ml(-1) and the increments on demand to 0.1 microg x ml(-1). As in the previous study, healthy volunteers attempted to render themselves unconscious by frequently pressing the demand button. To assess effects on memory, volunteers were given keywords to remember every 15 min. The maximum target concentration reached varied between 1.0 and 2.5 microg x ml(-1). No volunteers lost consciousness, however, one volunteer had a brief period of apnoea and oxygen desaturation. The Cp50 for loss of memory for words was 1.26 microg x ml(-1). Although this version represents an improvement, we conclude that the system is not yet completely suitable for use without anaesthetic supervision.

Normal lumbar vertebrae: anatomic, age, and sex variance in subjects at proton MR spectroscopy--initial experience

Fifty-seven subjects underwent proton magnetic resonance (MR) spectroscopy of the second lumbar vertebra to evaluate single-voxel and multivoxel techniques. Measurements included lipid-to-water ratios, lipid fractions, and line width. These data provide information about vertebral fat content. There was an age-dependent linear increase in fat content and sex dependence. A higher fat concentration was found in men. The observed spectra provide a basis for future study to determine clinical utility of vertebral proton MR spectroscopy.

Contrasting effects of CCR5 and CCR2 deficiency in the pulmonary inflammatory response to influenza A virus

The immune response to influenza A virus is characterized by an influx of both macrophages and T lymphocytes into the lungs of the infected host, accompanied by induced expression of a number of CC chemokines. CC chemokine receptors CCR5 and CCR2 are both expressed on activated macrophages and T cells. We examined how the absence of these chemokine receptors would affect pulmonary chemokine expression and induced leukocyte recruitment by infecting CCR5-deficient mice and CCR2-deficient mice with a mouse-adapted strain of influenza A virus. CCR5(-/-) mice displayed increased mortality rates associated with acute, severe pneumonitis, whereas CCR2(-/-) mice were protected from the early pathological manifestations of influenza because of defective macrophage recruitment. This delay in macrophage accumulation in CCR2(-/-) mice caused a subsequent delay in T cell migration, which correlated with high pulmonary viral titers at early time points. Infected CCR5(-/-) mice and CCR2(-/-) mice both exhibited increased expression of the gene for MCP-1, the major ligand for CCR2(-/-) and a key regulator of induced macrophage migration. These studies illustrate the very different roles that CCR5 and CCR2 play in the macrophage response to influenza infection and demonstrate how defects in macrophage recruitment affect the normal development of the cell-mediated immune response.

2D CSI proton MR spectroscopy of human spinal vertebra: feasibility studies

This report focuses on proton magnetic resonance spectroscopy (1H MRS) of spine vertebra acquired with two-dimensional chemical shift imaging (2D CSI), utilizing the stimulated echo acquisition mode (STEAM) sequence. Both validity and reproducibility studies were performed. To validate the 2D CSI method, its spectra were compared with those obtained with the single-voxel (SV) method. Five normal volunteers were scanned. The reproducibility of 2D CSI was examined by performing spectroscopy on two different occasions, on three normal volunteers. Data show that the STEAM 2D CSI technique results in MRI spectra comparable to those obtained with the STEAM SV method. 2D CSI offers significant time savings and convenient multi-voxel spectral analysis at a substantially higher signal-to-noise ratio. The 2D CSI method was then applied to a patient with a small vertebral hemangioma. The results demonstrated that the voxels containing the hemangioma exhibit different spectra than the neighboring voxels of the same vertebra. Additionally, a case of vertebral osteoporosis was investigated. Results showed a significant increase in the lipid-to-water ratio (LWR). It is suggested that 2D CSI may be powerful in identifying physiological as well as pathological changes of the bone marrow. Furthermore, covering a more extensive area of the vertebral body will maximize the chances of depicting a small focus of pathologic tissue. A more detailed bone marrow pattern was noticed in on one subject whose spectra show more lipid peaks.

Controversies in anaesthesia--designer drugs

In the past, the discovery of new drugs often occurred by chance. Over recent years, an increasing knowledge of the mode of drug action and receptor sites has improved our ability to design new drugs. While the mode of action of volatile and intravenous anaesthetic agents remains unclear, neuromuscular blocking agents and opioids have undergone considerable development and design. Drugs are being tailored to produce fewer side effects and to improve desirable properties. As a result, the introduction of new drugs has helped to improve techniques in anaesthesia. The development of remifentanil is an example of this which is discussed. The application of modern technology with target controlled infusions (TCI) for the administration of remifentanil represents further advancement in techniques which may become available to anaesthetists in the future.

Respiratory abnormalities due to craniovertebral junction compression in rheumatoid disease

OBJECTIVE

To assess the extent and severity of respiratory insufficiency associated with severe rheumatoid atlantoaxial dislocation and its relation to compression of the neuraxis.

METHODS

Twelve patients with severe atlantoaxial dislocation due to rheumatoid disease were studied. Detailed clinical, CT myelography and respiratory assessment including nocturnal oximetry, were performed on all patients.

RESULTS

All patients were severely disabled by their underlying disease but none had symptoms of hypoventilation. All the patients with C1 compression had myelopathic features. Those with medullary deformation (moulding and/or stretch) had abnormal noctural oximetry whilst no significant desaturations were seen in the remaining patients. Post-operative studies showed resolution of noctural desaturations.

CONCLUSION

This study suggests that clinically unsuspected respiratory insufficiency may be common in patients with severe medullary compression associated with rheumatoid atlantoaxial dislocation. It emphasises the importance of careful respiratory monitoring including nocturnal oxygen saturation in patients with major atlantoxial dislocation due to rheumatoid disease.

Validation of rating scales in psychiatry

Statistical analysis of psychiatric research requires the translation of qualitative data into quantitative form. This can be achieved using rating scales. However, the reliability and the validity, i.e. the validation of these scales, presents significant problems; these shall be outlined in this article.

Serum masks the inhibition of thrombin-induced prostacyclin release produced by anticardiolipin antibodies

The effect on thrombin-induced release of prostacyclin from human umbilical vein endothelial cells of preincubation with both serum and serum derived from platelet-poor plasma (PDS) from patients with systemic lupus erythematosus (SLE), systemic sclerosis, the antiphospholipid syndrome (APS) and normal controls was examined. Although no significant differences in thrombin-induced prostacyclin release were found in any of the patient groups, further analysis revealed that PDS from patients with SLE and APS that contained IgG anticardiolipin antibodies produced significant inhibition of prostacyclin release when compared with controls (P = 0.02). The effect was maximal with samples that contained both IgG and IgM anticardiolipin antibodies (P less than 0.01) and which had a significantly higher titre of IgG antibodies than samples which contained solely IgG antibodies (P less than 0.05). The absence of any corresponding inhibition of prostacyclin release by serum samples that contained anticardiolipin antibodies, possibly due to the release of masking stimulatory factors by platelets during coagulation, provides an explanation for the conflicting nature of previous reports.

End-plate ion channel block produced by lincosamide antibiotics and their chemical analogs

Five lincosamide compounds were studied for their effects on end-plate currents (epcs), miniature end-plate currents and acetylcholine-induced current fluctuations in the garter snake costocutaneous nerve-muscle preparation. At high concentrations, lincomycin and clindamycin reduced epc amplitude, but analysis of driving functions showed that only with clindamycin was this due solely to changes in epc quantal content. The effect of lincomycin on epc amplitude was exaggerated by rapid channel block during the rising phase of the epc. Clindamycin produced currents with a single exponential decay and single Lorentzian noise spectra. All the other compounds produced currents which decayed as the sum of two exponential components. For lincomycin and epilincomycin, noise spectra consisted of two Lorentzian components. For epiclindamycin and deoxylincomycin, although epcs and miniature end-plate currents decayed with two components, it was not possible to separate two components in the noise spectra. A kinetic analysis of ion channel blocking actions showed only small differences between the two pairs of stereoisomers studied. End-plate ion channel blocking and unblocking rate constants did not vary greatly among the compounds but the end-plate ion channel unblocking rate constant values for the two lincomycin stereoisomers were larger than those for the two clindamycin stereoisomers. Deoxylincomycin exhibited properties similar to those of the clindamycins. It was concluded that lipid solubility, not stereochemical conformation, plays the greater role in determining the ion channel blocking properties within the series, particularly that of the rate of dissociation of the compound from end-plate ion channels.

Cauda equina syndrome secondary to disseminated zygomycosis

We describe a case of cauda equina syndrome secondary to disseminated zygomycosis. A 52-year-old man had myelodysplastic syndrome, progressive weakness of the lower extremities, and incontinence. Neuroradiological findings were consistent with lumbar stenosis and probable disk herniation. A lung lesion was also discovered on the chest roentgenogram. The patient's condition rapidly deteriorated after surgical decompression. Attempts at determining other etiologies were unsuccessful. At autopsy, disseminated zygomycosis was found affecting the lung and the vasculature of the cauda equina and lumbosacral nerve roots, with resultant focal demyelination of these structures. Ribbon-like hyphal elements were also present in the caudal roots. This opportunistic pathogen is discussed along with the diagnostic challenge presented by its unusual clinical presentation.

Neutrophil influx measured in nasal lavages of humans exposed to ozone

Neutrophils (PMNs) obtained by nasal lavage were counted to determine if ozone, an oxidant air pollutant, induces an acute inflammatory response in the upper respiratory tract (URT) of humans. Background data were obtained by the nasal lavages from 200 nonexperimentally exposed subjects. Then, using a known inflammatory agent for the URT, rhinovirus-type 39, the induction, peak, and resolution of an acute inflammatory response was shown to be documented by the nasal lavage PMN counts. To determined if ozone induces this response, 41 subjects were exposed to either filtered air or 0.5 ppm ozone for 4 hr, on 2 consecutive days. Nasal lavages were taken pre-, immediately post each exposure, and 22 hr following the last exposure. Lavage PMN counts increased significantly (p = .005) in the ozone-exposed group, with 3.5-, 6.5-, and 3.9-fold increases over the air-exposed group at the post 1, pre 2, and post 2 time points, respectively. Ozone induces an inflammatory response in the URT of humans, and nasal lavage PMN counts are useful to assay the inflammatory properties of air pollutants.

Rationalization and computerization of the drug supply to an animal unit

Drug stocks in an animal unit were rationalized by discarding out-of-date or unwanted items and drawing up an approved stock list. A computerized system of stock control which enables a regular and accurate inventory of pharmaceuticals to be made was then established. In addition, the paperwork required for reordering drugs is produced automatically. Pharmaceuticals to a total value of 1650 pounds were discarded during the rationalization phase. The value of drugs stocked in the animal unit then stabilized at about one-third of previous levels. In the first 6 months of operation of the new system drug expenditure fell by about 40% in comparison with the same period 1 year previously. The drug stock control system has proved economical to operate and accurate, and can be run by persons without computer expertise. Valuable savings in both cost and labour have resulted. Effective management of drug expenditure by the animal unit is now possible.

The effects of chloramphenicol isomers on the motor end-plate nicotinic receptor-ion channel complex

Four enantiomers of chloramphenicol have been tested for their effects on end-plate current and miniature end-plate current decay and amplitude characteristics in the voltage-clamped costocutaneous nerve-muscle preparation of the garter snake. All four enantiomers exhibited effects on end-plate current and miniature end-plate current decay at similar concentrations (0.2-1.0 mM), indicating that the measured effect was not related to the antibacterial action of the compounds in which D-threo chloramphenicol is known to be at least 50 times more powerful than the L-threo and D- and L-erythro isomers. The compounds slightly increased end-plate current but not miniature end-plate current amplitude, indicating that they produce an increase in end-plate current quantal content. This effect was verified by an analysis of end-plate current driving functions (see Appendix) for one of the chloramphenicol isomers. In addition to this presynaptic action, all four compounds converted end-plate current and miniature end-plate current decays from single to double exponential functions. This effect was both concentration and voltage dependent. For all four compounds, hyperpolarization resulted in a progressive decrease in tau f and an increase in tau s. The relative amplitudes of the fast and slow decay components were independent of membrane potential. The results are interpreted in terms of the drugs blocking the open form of the acetylcholine-activated receptor-ion channel complex. However, in addition to affecting decay characteristics, all four compounds increased the charge passed during both end-plate and miniature end-plate currents. This effect was concentration but not voltage dependent and is inconsistent with the predictions of the sequential model for open ion channel blockade. By using an extension of Ruff's analysis of the sequential model of open end-plate ion channel blockade, we have been able to show that the action of the chloramphenicols on end-plate current amplitude and time course can be explained by the combination of two distinct mechanisms. First is an open channel block conforming to the sequential model and with calculated channel blocking affinity constants ranging from 0.3-1.0 mM. The channel blocking actions of all four isomers were shown to be independent of membrane voltage. Second is an action to slow channel closing, resulting in prolonged open time and hence increased charge passed during the end-plate current. This effect was strongly concentration dependent, but not voltage dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of the antibiotic, primycin, on spontaneous transmitter release at the neuromuscular junction

The effects of primycin, a potent ionophore in biological membranes, have been studied at the neuromuscular junction of the garter snake. Primycin in concentrations greater than 2 X 10(-7)M produced a time- and concentration-dependent depolarization of twitch muscle fibres. Primycin (10(-7)-5 X 10(-7)M) produced an increased rate of quantal release of acetylcholine, which was not maintained, and a slight reduction in quantal size. Time to onset and to peak effect of primycin were concentration-dependent whereas maximum frequency was not. Absence of extracellular Ca2+ produced a significant delay in the time to onset and to peak effect of primycin, but did not affect the peak miniature endplate potential (m.e.p.p.) frequency. Following 60 min exposure to primycin (5 X 10(-7)M), introduction of a high concentration of potassium (20 mM) produced no further increase in spontaneous release. In cut muscle preparations, exposure to primycin (10(-7)-5 X 10(-7)M) reduced peak endplate current (e.p.c.) amplitude until nerve stimulation resulted in failures or the release of one or two quanta. E.p.c. amplitude was not restored with prolonged washing. The effects of primycin on the nerve terminal are considered to be consistent with its ability to increase the permeability of membranes to calcium ions resulting in an influx of extracellular calcium, an efflux of mitochondrial calcium and eventual depletion of synaptic vesicles.

Comparative effects of clindamycin and lincomycin on end-plate currents and quantal content at the neuromuscular junction

The pre- and postjunctional effects of the lincosamide antibiotics, clindamycin and lincomycin, were studied in voltage-clamped transected twitch fibers of costocutaneous muscles of garter snakes (species Thamnophis). Miniature end-plate currents and end-plate currents (EPCs) were recorded over a wide voltage range for each antibiotic. The amplitude and kinetics of these currents were studied and estimates of the quantal content of evoked transmitter release determined. High concentrations of clindamycin (2 X 10(-4) M) and lincomycin (2 X 10(-3) M) produced significant depression of EPC amplitude and a nonlinearity in the EPC-voltage relationships. The time constant of EPC decay was accelerated in clindamycin and the relationship between the time constant of EPC decay and membrane potential remained a single exponential function with a concentration-dependent loss of the voltage dependence. In contrast to clindamycin, lincomycin produced biphasic EPCs which consisted of two components, one faster and one slower than the control decay rate. The relative amplitude and decay rate of each component was both concentration and voltage dependent. Either increasing the concentration of lincomycin or membrane hyperpolarization decreased the amplitude ratio, iota slow/iota fast, and increased the ratio of the respective time constants, tau slow/tau fast. Clindamycin affected EPC decay amplitude and quantal content in the same concentration range, whereas lincomycin affected EPC decay at concentrations 20 times less than those required to reduce EPC amplitude and quantal content. These results suggest that the neuromuscular blocking effects of clindamycin involve both pre-and postjunctional sites, whereas the effects of lincomycin are primarily on the postjunctional receptor-channel complex.

Identification of Rickettsia rickettsii in a guinea pig model by immunofluorescent and electron microscopic techniques

Moribund guinea pigs infected with Richettsia rickettsii were examined by necropsy, histology, immunofluorescence, electron microscopy, and serology. Untreated animals died at 9 and 10 days after inoculation. Animals given saline subcutaneously survived from 1 to 4 days longer. Prolonged survival was accompanied by more severe lesions: scrotal necrosis; infarction of ears; and swollen, hemorrhagic footpads, epididymis, and cremaster muscle. Histopathologic examination demonstrated that acute, necrotizing vasculitis, perivascular hemorrhage, and focal necrosis were more extensive. Direct immunofluorescence indicated many more rickettsiae in endothelium and vascular wall of saline recipients. Ultrastructurally, typical rickettsiae were present focally in the cytoplasm of endothelial and vascular smooth muscle cells. Cytopathology in infected and adjacent cells included swelling, mitochondrial enlargement with decrease in matrix density and loss of cristae, and increased pinocytosis. In addition, treated animals had more cytonecrosis, thrombosis, extravascular fibrin deposition, prominent inflammatory cells with polymorphonuclear phagocytosis of rickettsiae, and antibody production.

Automated Assay of Hexosaminidases in Serum

In serum there are two classes of hexosaminidase. One of these is heat-labile and is inactive in children with Tay—Sachs disease. Serum from heterozygotes for Tay—Sachs disease has half the normal activity of the heat-labile enzyme. The heat-labile enzyme can be inactivated by heating serum diluted in buffer for 5 min at 60 °C. We have used this property to develop a reliable, fully automated assay for serum hexosaminidases, which can be used for mass carrier screening programs.