Considerations for Treating Nonobstetric Diseases in Pregnant Patients in the Emergency Department Setting

OBJECTIVE

To provide nonobstetric practitioners with an overview of key concepts for the pregnant patient and review treatment of 3 common acute nonobstetric diseases encountered in the emergency department setting.

DATA SOURCES

A literature search of PubMed was performed (1997-February 2023) using key search terms related to pregnancy, pain, urinary tract infection (UTI), venous thromboembolism (VTE), and anticoagulants.

STUDY SELECTION AND DATA EXTRACTION

Relevant articles in English and humans were considered.

DATA SYNTHESIS

When caring for a pregnant patient, it is important to utilize appropriate assessments, understand terms used in this population, and recognize how the physiological and pharmacokinetic changes that occur in pregnancy can influence medication use. Pain, UTIs, and VTE are common in this population. Acetaminophen is the most widely used medication for the management of pain during pregnancy and the drug of choice for mild pain in pregnancy not responsive to nonpharmacologic treatment. Pyelonephritis is the most common nonobstetric cause of hospitalization for pregnant patients. Antimicrobial treatment should consider maternal-fetal safety and local resistance patterns. Pregnant and postpartum patients have a 4- to 5-fold increased risk of developing a VTE compared with nonpregnant patients. Low-molecular-weight heparin is the preferred treatment.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Pregnant patients often seek acute care in the emergency department setting for nonobstetric needs. Pharmacists in this setting should understand appropriate assessment questions and terms used within this population, the basics of physiological and pharmacokinetic changes in pregnancy that can impact treatment, and which resources are best to utilize for drug information of the pregnant patient.

CONCLUSION

Practitioners in the acute care setting commonly encounter pregnant patients seeking care for nonobstetric concerns. This article covers key pregnancy-related information for the nonobstetric practitioner and focuses on the management of acute pain, UTI, and VTE during pregnancy.

Curricular Considerations for Preparing Student Pharmacists to Prescribe Hormonal Contraception

In 2014, the pharmacist's role in the United States expanded to include prescribing hormonal contraception, and this practice is currently addressed by policy in 14 states and the District of Columbia. Training and education requirements for this expanded scope of practice vary between states and are changing rapidly. The objective of this review is to examine how student pharmacists are taught to provide contraceptive care, specifically for prescribing ongoing hormonal contraception and emergency contraception, and to identify potential gaps in the United States pharmacy curricula related to contraception. Despite steady adoption into community pharmacy practice, there is sparse literature assessing educational methods used to teach contraceptive care. This review offers recommendations to promote consistent and comprehensive student pharmacist education in providing contraceptive care across institutions, regardless of state policy status.

Comparison of Two Morphine Dosing Strategies in the Management of Neonatal Abstinence Syndrome

OBJECTIVE

The incidence of neonatal abstinence syndrome (NAS) has increased in recent years. Treatment approaches usually involve opioid replacement; however, the optimal treatment strategy is unknown. This study sought to determine the impact of weight- and symptom-based morphine dosing strategies on LOS and medication exposure in patients with NAS.

METHODS

A retrospective review was conducted from May 2015 to June 2017 at 2 NICUs within a health-system using different dosing approaches for NAS. Data were compared using Fisher exact tests for categorical data and t tests and Wilcoxon ranked sums for continuous data.

RESULTS

Baseline demographics were well-matched except for postmenstrual age at morphine initiation (p = 0.04). The weight-based group had a larger initial morphine dose (p < 0.001) and fewer number of steps to maximum morphine dose (p = 0.009). There were no differences between groups in LOS, number of dose adjustments, doses administered, weaning steps, maximum dose, or need to re-escalate dosing. There was also no difference between the first 3 modified Finnegan scores (MFS) after transferring patients to a neonatology service. Neonates with symptom-based dosing had a higher maximum MFS (p = 0.024). Neonates in the symptom-based group required adjunct therapy more often (p < 0.0001).

CONCLUSIONS

Data indicate the dosing strategy impacts number of steps to reach maximum dose and need for adjunctive therapy. Weight-based dosing may decrease the number of steps required to reach the morphine maximum dose and the need for adjunctive therapy by controlling NAS symptoms earlier.

The Influence of the Food and Drug Administration Pregnancy and Lactation Labeling Rule on Drug Information Resources

BACKGROUND

Drug information resources are commonly used by health-care providers answering pregnancy-related medication questions. In 2015, the United States Food and Drug Administration approved a new pregnancy and lactation medication labeling content and format, removing the pregnancy category, and using a narrative. Despite labeling requirements changing, it is unknown if drug information resources updated monographs to reflect these changes.

OBJECTIVE

The primary objective was to evaluate if commonly used drug information resources provide pregnancy information listed similar to the requirements of the Pregnancy and Lactation Labeling Rule (PLLR). Secondary analyses included evaluating the references and inclusion of the pregnancy category rating.

METHODS

Pregnancy recommendations for 23 medications were evaluated in 9 drug information resources (Clinical Pharmacology, Drugs in Pregnancy and Lactation, Epocrates®, First Databank, LexiComp® Online, LexiComp® Online Pregnancy & Lactation, In-Depth, Medi-Span®, Micromedex®, and Multum®). The number of references per drug monograph and most recent reference publication year was obtained.

RESULTS

LexiComp® Online Pregnancy & Lactation, In-Depth mimics the new PLLR structure and consistently had the highest number of and most recent references when the medication was included. Drugs in Pregnancy and Lactation was the next most similar in content with the PLLR and second in most references per monograph; however, the most recent reference was the textbook publication year.

CONCLUSION AND RELEVANCE

LexiComp® Online Pregnancy & Lactation, In-Depth and Drugs in Pregnancy and Lactation provided pregnancy information in a format most similar to the PLLR. However, several drug information resources contained pregnancy categories ratings that were to be removed from medication labeling per the PLLR.

Infertility Management and Pharmacotherapy: What Every Pharmacist Should Know

Infertility is a significant public health concern in the United States. As such, utilization of infertility services, including pharmacotherapeutic treatments, is prevalent, and the role of the pharmacist as part of the health care team is essential. Pharmacists can assist patients by providing education on infertility causes, risk factor mitigation, referrals, nonpharmacologic and pharmacologic management options, navigation of the prescription process, and resource availability for the significant financial burden accompanying infertility treatment. In-depth pharmacotherapeutic information may not be readily available to pharmacists dispensing and counseling on these medications, and infertility management regimens are often varied and complicated requiring more in-depth counseling on use and administration. Given the complexity of infertility management, pharmacists are a valuable patient support and education resource. This article provides an in-depth review of infertility management strategies, both nonpharmacologic and pharmacologic.

Pharmacists’ Perspectives on Prescribing and Expanding Access to Hormonal Contraception in Pharmacies in the United States

Introduction:

Pharmacist prescribing of contraception is becoming increasingly available in selected states. The objective of this study was to assess US community pharmacists’ perspectives on expanding access, barriers, and facilitators since states have begun pharmacist scope of practice expansions for prescribing contraception.

Methods:

A survey study of US community pharmacists’ support for expanded access models, pharmacist prescribing practices and interest, and importance of safety, cost, and professional practice issues for prescribing was conducted.

Results:

Pharmacists are generally supportive of pharmacist prescribing and behind-the-counter models for hormonal contraception and generally opposed to over-the-counter access. A majority (65%) are interested in prescribing hormonal contraception. The top motivation for prescribing contraception is enjoying individual patient contact (94%). Safety concerns (eg, patients not obtaining health screenings) remained most important for pharmacist implementation, followed by cost (eg, lack of payment or reimbursement for pharmacists’ services), and professional practice (eg, pharmacist time constraints and liability) issues.

Conclusion:

This study provides an updated understanding of attitudes toward models of expanded access to hormonal contraception, interest in prescribing, and barriers and facilitators to this service among community pharmacists. Many barriers such as time and reimbursement remain unchanged. This information can inform policy and implementation efforts.

Evaluation of Lactation Compatibility Reference Recommendations

Background: Multiple resources aid the interprofessional health care team when recommending medications for lactating patients. Varying degrees of breastfeeding compatibility and safety are recommended in different resources. New Food and Drug Administration labeling for lactation is being phased in to provide more consistent language in safety recommendations. Objective: The objective of this study is to evaluate lactation recommendations for select medications from different drug information resources to determine the compatibility recommendations for lactating patients. Methods: The breastfeeding recommendations for 19 medications were analyzed in 10 drug information resources. Each drug was reviewed in each resource and the published recommendations evaluated. Results: Medications and Mothers' Milk 18th Edition and LactMed had the most medications listed as compatible with breastfeeding, with Lexicomp Online, Drugs in Pregnancy and Lactation Online, and Epocrates following. LactMed stands out from the group with an average of 15.1 references per medication and number of references ranging from 0 to 58. Date ranges of references used by select resources varied. References to support recommendations ranged from 1979 to 2018 for the select resources. Conclusion and Relevance: Variation continues to exist across resources with regard to recommendations for medication safety in lactation. LactMed represents the most up-to-date and comprehensive review of literature in this review. When making decisions regarding medication use during lactation, health care professionals should consider reviewing data behind the recommendations and consulting multiple resources.

High prevalence of tuberculosis in newly enrolled HIV patients in Zambia: need for enhanced screening approach

SETTING

Tuberculosis (TB) remains a leading cause of morbidity and mortality in sub-Saharan Africa. In Zambia, smear microscopy and chest radiography (CXR) are the primary TB diagnostic tools, and most cases are not bacteriologically confirmed.

OBJECTIVE

We implemented enhanced screening to determine the TB burden among new human immunodeficiency virus (HIV) clinic enrollees.

DESIGN

Consecutive adult HIV clinic enrollees were screened, regardless of symptoms. All underwent microscopy (Ziehl-Neelsen/fluorescence microscopy) on three sputum specimens, physical examination, and digital CXR. Sputum, blood and urine specimens were cultured. Xpert(®) MTB/RIF testing was performed retrospectively.

RESULTS

From July 2011 to April 2012, 399 patients were enrolled. The median age was 34.4 years; body mass index was 20.8 kg/m(2), CD4 count was 202 cells/μl and 86% were symptomatic. Culture-confirmed TB was diagnosed in 72/399 (18%) patients; an additional 31/399 (8%) were culture-negative but diagnosed clinically. Symptom screening for any cough, fever, weight loss or night sweats had high sensitivity (95%) but low specificity (14%) for detecting culture-confirmed cases. Among culture-confirmed cases, 35/72 (49%) were missed clinically and detected only by culture. Xpert was 64% sensitive and 98% specific.

CONCLUSIONS

High TB prevalence was found in Zambians newly enrolled into HIV care. Screening with sensitive diagnostics should be considered with culture when feasible in this population.

Poor continuity of care for TB diagnosis and treatment in Zambian Prisons: a situation analysis

OBJECTIVES

Prisons act as infectious disease reservoirs. We aimed to explore the challenges of TB control and continuity of care in prisons in Zambia.

METHODS

We evaluated treatment outcomes for a cohort of inmates diagnosed with TB during a TB REACH funded screening programme initiated by the Zambia Prisons Service and the Centre for Infectious Disease Research in Zambia.

RESULTS

Between October 2010 and September 2011, 6282 inmates from six prisons were screened for TB, of whom 374 (6.0%) were diagnosed. TB treatment was initiated in 345 of 374 (92%) inmates. Of those, 66% were cured or completed treatment, 5% died and 29% were lost to follow-up. Among those lost to follow-up, 11% were released into the community and 13% were transferred to other prisons.

CONCLUSIONS

Weak health systems within the Zambian prison service currently undermines continuity of care, despite intensive TB screening and case-finding interventions. To prevent TB transmission and the development of drug resistance, we need sufficient numbers of competent staff for health care, reliable health information systems including electronic record keeping for prison facilities, and standard operating procedures to guide surveillance, case-finding and timely treatment initiation and completion.

Neonatal Herpes Simplex Viral Infections and Acyclovir: An Update

Neonatal herpes simplex virus (HSV) infections have high morbidity and mortality rates. Optimization of treatment and prevention strategies are imperative to improve the care and outcomes of neonates infected with HSV. Management of HSV includes reducing neonatal transmission, treating acute infections, and limiting adverse neurodevelopmental outcomes and future cutaneous outbreaks after acute infections. Transmission risk may be affected by route of delivery and maternal suppressive therapy. Neonatal HSV infections are divided into 3 categories: localized skin, eyes, or mouth; localized central nervous system; or disseminated infections. Parenteral acyclovir, the pharmacologic agent of choice, is used when treating each type of infection. However, dosage strategies and durations of therapy may vary based on disease state severity, presentation, and patient characteristics. Oral acyclovir may be used as suppressive therapy after acute treatment completion in specific neonatal populations, reducing long-term adverse neurodevelopmental outcomes and future skin eruptions. The mortality rate remains high even with treatment.

Equine grass sickness, but not botulism, causes autonomic and enteric neurodegeneration and increases soluble N-ethylmaleimide-sensitive factor attachment receptor protein expression within neuronal perikarya

REASONS FOR PERFORMING STUDY

Equine grass sickness (EGS) is of unknown aetiology. Despite some evidence suggesting that it represents a toxico-infection with Clostridium botulinum types C and/or D, the effect of EGS on the functional targets of botulinum neurotoxins, namely the soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins, is unknown. Further, while it is commonly stated that, unlike EGS, equine botulism is not associated with autonomic and enteric neurodegeneration, this has not been definitively assessed.

OBJECTIVES

To determine: 1) whether botulism causes autonomic and enteric neurodegeneration; and 2) the effect of EGS on the expression of SNARE proteins within cranial cervical ganglion (CCG) and enteric neuronal perikarya.

STUDY DESIGN

Descriptive study.

METHODS

Light microscopy was used to compare the morphology of neurons in haematoxylin-eosin stained sections of CCG and ileum from 6 EGS horses, 5 botulism horses and 6 control horses. Immunohistochemistry was used to compare the expression of synaptosomal-associated protein-25, synaptobrevin (Syb) and syntaxin within CCG neurons, and of Syb in enteric neurons, from horses with EGS, horses with botulism and control horses. The concentrations of these SNARE proteins in extracts of CCG from EGS and control horses were compared using quantitative fluorescent western blotting.

RESULTS

EGS, but not botulism, was associated with autonomic and enteric neurodegeneration and with increased immunoreactivity for SNARE proteins within neuronal perikarya. Quantitative fluorescent western blotting confirmed increased concentrations of synaptosomal-associated protein-25, Syb and syntaxin within CCG extracts from EGS vs. control horses, with the increases in the latter 2 proteins being statistically significant.

CONCLUSIONS

The occurrence of autonomic and enteric neurodegeneration, and increased expression of SNARE proteins within neuronal perikarya, in EGS but not botulism, suggests that EGS may not be caused by botulinum neurotoxins. Further investigation of the aetiology of EGS is therefore warranted.

Creating and Assessing Student Perception of an Examination Mastery Score Report for a Pharmacotherapy Course

OBJECTIVE

To compare student-perceived utility of two types of score reports.

METHODS

Assessment standards were followed to create a new examination score report for pharmacotherapy coursework. Student examination scores were returned using the traditional score report, the utility of which students rated along 9 dimensions. A mastery score report was also distributed, and students rated it on the same 9 dimensions. The ratings were compared to determine which the students perceived as more useful.

RESULTS

The students rated the mastery score report significantly better on each of the 9 dimensions and in aggregate.

CONCLUSION

Pharmacy students perceived the mastery score report as more useful in helping them improve their achievement of educational outcomes.

Integrating active tuberculosis case finding in antenatal services in Zambia

SETTING

Three out-patient antenatal care (ANC) clinics in Lusaka, Zambia.

OBJECTIVE

To estimate tuberculosis (TB) prevalence in human immunodeficiency virus (HIV) infected and symptomatic, non-HIV-infected pregnant women and explore the feasibility of routine TB screening in ANC settings.

DESIGN

Peer educators administered TB symptom questionnaires to pregnant women attending their first ANC clinic visit. Presumptive TB patients were defined as all HIV-infected women and symptomatic non-HIV-infected women. Sputum samples were tested using smear microscopy and culture to estimate TB prevalence.

RESULTS

All 5033 (100%) women invited to participate in the study agreed, and 17% reported one or more TB symptoms. Among 1152 presumed TB patients, 17 (1.5%) had previously undiagnosed culture-confirmed TB; 2 (12%) were smear-positive. Stratified by HIV status, TB prevalence was 10/664 (1.5%, 95%CI 0. 7-2.8) among HIV-infected women and 7/488 (1.4%, 95%CI 0.6-2.9) among symptomatic non-HIV-infected women. In HIV-infected women, the only symptom significantly associated with TB was productive cough; symptom screening was only 50% sensitive.

CONCLUSION

There is a sizable burden of TB in pregnant women in Zambia, which may lead to adverse maternal and infant outcomes. TB screening in ANC settings in Zambia is acceptable and feasible. More sensitive diagnostics are needed.

Derivation of a tuberculosis screening rule for sub-Saharan African prisons

SETTING

Lusaka Central Prison, Zambia.

OBJECTIVE

To derive screening rules for tuberculosis (TB) using data collected during a prison-wide TB and human immunodeficiency virus (HIV) screening program.

DESIGN

We derived rules with two methodologies: logistic regression and classification and regression trees (C&RT). We evaluated the performance of the derived rules as well as existing World Health Organization (WHO) screening recommendations in our cohort of inmates, as measured by sensitivity, specificity, and positive and negative predictive values.

RESULTS

The C&RT-derived rule recommended diagnostic testing of all inmates who were underweight (defined as body mass index [BMI] < 18.5 kg/m(2)] or HIV-infected; the C&RT-derived rule had 60% sensitivity and 71% specificity. The logistic regression-derived rule recommended diagnostic testing of inmates who were underweight, HIV-infected or had chest pain; the logistic regression-derived rule had 74% sensitivity and 57% specificity. Two of the WHO recommendations had sensitivities that were similar to our logistic regression rule but had poorer specificities, resulting in a greater testing burden.

CONCLUSION

Low BMI and HIV infection were the most robust predictors of TB in our inmates; chest pain was additionally retained in one model. BMI and HIV should be further evaluated as the basis for TB screening rules for inmates, with modification as needed to improve the performance of the rules.

Pharmacological Management of Obesity in Pediatric Patients

Objective: To review current evidence of pharmacological options for managing pediatric obesity and provide potential areas for future research. Data Sources: A MEDLINE search (1966 to October 2014) was conducted using the following keywords: exenatide, liraglutide, lorcaserin, metformin, obesity, orlistat, pediatric, phentermine, pramlintide, topiramate, weight loss, and zonisamide. Study Selection and Data Extraction: Identified articles were evaluated for inclusion, with priority given to randomized controlled trials with orlistat, metformin, glucagon-like peptide-1 agonists, topiramate, and zonisamide in human subjects and articles written in English. References were also reviewed for additional trials. Data Synthesis: Whereas lifestyle modification is considered first-line therapy for obese pediatric patients, severe obesity may benefit from pharmacotherapy. Orlistat is the only Food and Drug Administration (FDA)-approved medication for pediatric obesity and reduced body mass index (BMI) by 0.5 to 4 kg/m2, but gastrointestinal (GI) adverse effects may limit use. Metformin has demonstrated BMI reductions of 0.17 to 1.8 kg/m2, with mild GI adverse effects usually managed with dose titration. Exenatide reduced BMI by 1.1 to 1.7 kg/m2 and was well-tolerated with mostly transient or mild GI adverse effects. Topiramate and zonisamide reduced weight when used in the treatment of epilepsy. Future studies should examine efficacy and safety of pharmacological agents in addition to lifestyle modifications for pediatric obesity. Conclusions: Lifestyle interventions remain the treatment of choice in pediatric obesity, but concomitant pharmacotherapy may be beneficial in some patients. Orlistat should be considered as second-line therapy for pediatric obesity. Evidence suggests that other diabetes and antiepileptic medications may also provide weight-loss benefits, but safety should be further evaluated.

Ultrastructural evidence for the uptake of a neurotoxic snake venom phospholipase A2 into mammalian motor nerve terminals

A mutant form of ammodytoxin A, a neurotoxic phospholipase A(2) from the venom of the long nosed viper Vipera ammodytes ammodytes, was prepared by site-directed mutagenesis, conjugated to a nanogold particle and inoculated into the antero-lateral aspect of one hind limb of female mice. Eight hours later the mice were killed, the soleus muscles of both ipsi- and contra-lateral hind limbs were removed, exposed to a silver enhancing medium and then prepared for transmission electron microscopy. Silver-enhanced particles were subsequently found concentrated in the peri-synaptic area, particularly within the synaptic gutter and the deep synaptic folds, and in many cases had been taken up into the cytoplasm of the terminal boutons of the motor axon. The results suggest that the presynaptic neurotoxicity of snake venom phospholipases A(2) involves several components of the neuromuscular apparatus, including intracellular organelles of the motor nerve terminal.

Early lessons from the integration of tuberculosis and HIV services in primary care centers in Lusaka, Zambia

BACKGROUND

Zambia faces overlapping tuberculosis (TB) and human immunodeficiency virus (HIV) epidemics; however, care for co-infected patients often occurs through separate, vertical programs.

OBJECTIVE

To establish a program to integrate TB and HIV services in Lusaka primary care centers.

METHODS

In collaboration with the Zambian Ministry of Health, TB-HIV integration activities began in December 2005 and were expanded to seven health centers by March 2007. Principal activities included developing staff capacity to manage co-infected patients, implementing HIV testing within TB departments and establishing referral systems between departments.

RESULTS

Using a provider-initiated approach, 2053 TB patients were offered HIV testing. Seventy-seven per cent agreed to be tested; 69% of those tested were HIV-infected. Of these, 59% were enrolled in HIV care. The proportion of antiretroviral treatment (ART) program enrollees who were TB-HIV co-infected increased by 38% after program implementation. The median CD4 count among co-infected patients was 161 cells/microl, with 88% eligible for ART.

CONCLUSION

Integration of HIV testing and referral services into urban primary care centers identified many co-infected patients and significantly increased the proportion of TB patients among people accessing HIV care. Ongoing challenges include maximizing the number of patients accepting HIV testing and overcoming barriers to enrollment into HIV care.

Envenoming bites by kraits: the biological basis of treatment-resistant neuromuscular paralysis

Beta-bungarotoxin, a neurotoxic phospholipase A2 is a major fraction of the venom of kraits. The toxin was inoculated into one hind limb of young adult rats. The inoculated hind limb was paralysed within 3 h, and remained paralysed for 2 days. The paralysis was associated with the loss of synaptic vesicles from motor nerve terminal boutons, a decline in immunoreactivity of synaptophysin, SNAP-25 and syntaxin, a loss of muscle mass and the upregulation of NaV(1.5) mRNA and protein. Between 3 and 6 h after the inoculation of toxin, some nerve terminal boutons exhibited clear signs of degeneration. Others appeared to be in the process of withdrawing from the synaptic cleft and some boutons were fully enwrapped in terminal Schwann cell processes. By 12 h all muscle fibres were denervated. Re-innervation began at 3 days with the appearance of regenerating nerve terminals, a return of neuromuscular function in some muscles and a progressive increase in the immunoreactivity of synaptophysin, SNAP-25 and syntaxin. Full recovery occurred at 7 days. The data were compared with recently published clinical data on envenoming bites by kraits and by extrapolation we suggest that the acute, reversible denervation caused by beta-bungarotoxin is a credible explanation for the clinically important, profound treatment-resistant neuromuscular paralysis seen in human subjects bitten by these animals.

β-bungarotoxin-induced depletion of synaptic vesicles at the mammalian neuromuscular junction

The neurotoxic phospholipase A(2), beta-bungarotoxin, caused the failure of the mechanical response of the indirectly stimulated rat diaphragm. Exposure to beta-bungarotoxin had no effect on the response of the muscle to direct stimulation. Resting membrane potentials of muscle fibres exposed to the toxin were similar to control values, and the binding of FITC-labelled alpha-bungarotoxin to nAChR at the neuromuscular junction was unchanged. Motor nerve terminal boutons at a third of cell junctions were destroyed by exposure to beta-bungarotoxin leaving only a synaptic gutter filled with Schwann cell processes and debris. At other junctions, some or all boutons survived exposure to the toxin. Synaptic vesicle density in surviving terminal boutons was reduced by 80% and synaptophysin immunoreactivity by >60% in preparations exposed to beta-bungarotoxin, but syntaxin and SNAP-25 immunoreactivity was largely unchanged. Terminal bouton area was also unchanged. The depletion of synaptic vesicles was completely prevented by prior exposure to botulinum toxin C and significantly reduced by prior exposure to conotoxin omega-MVIIC. The data suggest that synaptic vesicle depletion is caused primarily by a toxin-induced entry of Ca(2+) into motor nerve terminals via voltage gated Ca(2+) channels and an enhanced exocytosis via the formation of t- and v-SNARE complexes.

Myotoxic phospholipases A2 and the regeneration of skeletal muscles

The review explains why the myotoxic phospholipases A2 and cardiotoxins are such important tools in the study of the regeneration and maturation of mammalian skeletal muscle. The role of satellite cells as precursors of cell-based regeneration is discussed and recent controversies on the origin of myogenic cells involved in the regeneration of mature skeletal muscle are addressed. This is followed by discussions of sarcomere reconstruction, myosin and sarcoplasmic reticulum ATPase expression, the electrophysiological properties of regenerating muscle, and the reconstruction of the neuromuscular junction. The emphasis throughout is on the plastic changes of major structural and functional proteins that occur during regeneration, and on other influences that determine the final outcome of regenerative activity such as innervation, thyroid status, mechanical work and the functional integrity of the microcirculation. The review closes with a discussion of some of the factors--such as active regeneration--that influence the success of gene-based therapies applied to inherited muscle disease.

Muscle fibre breakdown in venom-induced muscle degeneration

We studied the early stages of the degeneration of skeletal muscles using the venom of Notechis scutatus as the myotoxic agent. The venom was used at a dose equivalent to the LD50 in the mouse. There was no mortality amongst the rats. Electron microscopy was used to show the progressive hypercontraction of sarcomeres and the loss of alignment of myofibrils in individual muscle fibres. Between areas of hypercontraction sarcomeres were torn, shedding loosened myofilaments into the cytosol. Western blotting and Coomassie staining were used to compare the respective rates of loss of desmin, titin, actin, myosin and dystrophin. We showed that desmin and titin were the first proteins to be degraded with a time to 50% loss of approximately 1 h and 3 h, respectively. The loss of major contractile proteins, myosin and actin, was rather slower. The loss of dystrophin was also slower than the loss of desmin and titin. Early damage to the plasma membrane of the muscle fibre caused the cells to depolarize, probably promoting the hypercontraction of the sarcomeres, but actual loss of membrane was incomplete even at 24 h. We suggest that the early degradation of desmin and titin was responsible for the disaggregation of the sarcomeres; the liberated contractile proteins myosin and actin were shed into the cytosol, where they were degraded. Phagocytic cells that had invaded the degenerating muscle fibres were primarily involved in the clearance of damaged mitochondria.

Pharmacological strategies to block rod photoreceptor apoptosis caused by calcium overload: a mechanistic target-site approach to neuroprotection

PURPOSE

Photoreceptor apoptosis and resultant visual deficits occur in humans and animals with inherited, and disease-, injury- and chemical-induced retinal degeneration. Our aims were three-fold: 1) to determine the kinetics of rod apoptosis and Ca2+ overload in Pde6b9rd1) mice and developmentally lead-exposed rats, 2) to establish a pathophysiologically-relevant model of Ca2+ overload/rod-selective apoptosis in isolated rat retina and 3) to examine different mechanistic based neuroprotective strategies that would abrogate or mollify rod Ca2+ overload/apoptosis.

METHODS

Retinal morphometry and elemental calcium content ([Ca]) determined the kinetics of rod apoptosis and Ca2+ overload. A multiparametric analysis of apoptosis including rod [Ca], a live/dead assay, rod oxygen consumption, cytochrome c immunoblots and caspase assays was combined with pharmacological studies of an isolated rat retinal model of rod-selective Ca2+ overload/apoptosis.

RESULTS

Ca2+ overload preceded rod apoptosis in mice and rats, although the extent and kinetics in each differed significantly. The isolated rat model of rod Ca2+ overload/apoptosis showed that blockade of Ca2+ entry through rod cGMP-activated channels with L-cis diltiazem was partially neuroprotective, whereas blockade of Ca2+ entry into rods through L-type Ca2+ channels with D-cis diltiazem or verapamil provided no protection. Inhibition of the mitochondrial Na+/Ca2+ exchanger with D-cis diltiazem provided no protection. CsA and NIM811, mitochondrial permeability transition pore (mPTP) inhibitors, blocked all Ca(2+)-induced apoptosis, whereas the caspase-3 inhibitor DEVD-fmk only blocked the downstream cytochrome c-induced apoptosis.

CONCLUSIONS

The successful pharmacological neuroprotective strategies for rod Ca2+ overload/apoptosis targeted the rod cGMP-activated channels or mPTP, but not the rod L-type Ca2+ channels.

Fulminant hepatic failure due to herpes simplex after hysteroscopy

BACKGROUND

Fulminant hepatic failure due to herpes simplex in healthy adults is a rare condition with a high mortality rate. The lack of specific symptoms and the absence of typical herpetic lesions in a majority of cases contribute to delayed diagnosis.

CASE

We describe a fatal case of fulminant hepatic failure due to herpes simplex in a healthy woman presenting after laparoscopy and hysteroscopy for tubal infertility. The patient lacked evidence of mucocutaneous lesions or jaundice. The surgery likely contributed to viral dissemination.

CONCLUSION

Although rare, disseminated herpes should be considered a possible cause of postsurgical pelvic infections, even in the absence of ulcerative lesions. Until a definitive diagnosis is made, antiviral therapy should be considered in patients with high fever, leukopenia, and abnormal liver function.

Abnormal dendritic spine characteristics in the temporal and visual cortices of patients with fragile-X syndrome: a quantitative examination

Fragile-X syndrome is a common form of mental retardation resulting from the inability to produce the fragile-X mental retardation protein. Qualitative examination of human brain autopsy material has shown that fragile-X patients exhibit abnormal dendritic spine lengths and shapes on parieto-occipital neocortical pyramidal cells. Similar quantitative results have been obtained in fragile-X knockout mice, that have been engineered to lack the fragile-X mental retardation protein. Dendritic spines on layer V pyramidal cells of human temporal and visual cortices stained using the Golgi-Kopsch method were investigated. Quantitative analysis of dendritic spine length, morphology, and number was carried out on patients with fragile-X syndrome and normal age-matched controls. Fragile-X patients exhibited significantly more long dendritic spines and fewer short dendritic spines than did control subjects in both temporal and visual cortical areas. Similarly, fragile-X patients exhibited significantly more dendritic spines with an immature morphology and fewer with a more mature type morphology in both cortical areas. In addition, fragile-X patients had a higher density of dendritic spines than did controls on distal segments of apical and basilar dendrites in both cortical areas. Long dendritic spines with immature morphologies and elevated spine numbers are characteristic of early development or a lack of sensory experience. The fact that these characteristics are found in fragile-X patients throughout multiple cortical areas may suggest a global failure of normal dendritic spine maturation and or pruning during development that persists throughout adulthood.

The neurotoxicity of the venom phospholipases A(2), notexin and taipoxin

The presynaptically active, toxic phospholipases known as notexin and taipoxin are principal components of the venom of the Australian tiger snake and the Australian taipan respectively. The inoculation of the toxins into one hind limb of rats caused, within 1 h, the depletion of transmitter from the motor nerve terminals of the soleus muscle. This was followed by the degeneration of the motor nerve terminals and of the axonal cytoskeleton. By 24 h 70% of muscle fibers were completely denervated. Regeneration and functional reinnervation were almost fully restored by 5 days, but collateral innervation was common in the regenerated muscles, and this abnormality persisted for at least 9 months. The data provide an explanation for both the severity of neuromuscular paralysis that can accompany envenoming bites by tiger snakes and taipans and the difficulty experienced by physicians in managing the envenomed subjects.

Tissue heterogeneity of the FMR1 mutation in a high-functioning male with fragile X syndrome

Few studies have been conducted comparing the FMR1 mutation in multiple tissues of individuals affected with fragile X syndrome. We report a postmortem study of the FMR1 mutation in multiple tissues from a high-functioning male with fragile X syndrome. This man was not mentally retarded and had only a few manifestations of the disorder such as learning disabilities and mild attention problems. Southern blot analysis of leukocytes demonstrated an unmethylated mutation with a wide span of sizes extending from the premutation to full mutation range. A similar pattern was seen in most regions of the brain. In contrast, a methylated full mutation of a single size was seen in the parietal lobe and in most non-brain tissues studied. Therefore, there were striking differences in both FMR1 mutation size and methylation status between tissues. Lack of mental retardation in this individual may have been due to sufficient expression of FMR1 protein (FMRP) in most areas of the brain. Immunocytochemistry showed FMRP expression in regions of the brain with the unmethylated mutation (superior temporal cortex, frontal cortex, and hippocampus) and no expression in the region with the methylated full mutation (parietal). Neuroanatomical studies showed no dendritic spine pathology in any regions of the brain analyzed.

Nerve terminal damage by beta-bungarotoxin: its clinical significance

We report here original data on the biological basis of prolonged neuromuscular paralysis caused by the toxic phospholipase A2 beta-bungarotoxin. Electron microscopy and immunocytochemical labeling with anti-synaptophysin and anti-neurofilament have been used to show that the early onset of paralysis is associated with the depletion of synaptic vesicles from the motor nerve terminals of skeletal muscle and that this is followed by the destruction of the motor nerve terminal and the degeneration of the cytoskeleton of the intramuscular axons. The postjunctional architecture of the junctions were unaffected and the binding of fluorescein-isothiocyanate-conjugated alpha-bungarotoxin to acetylcholine receptor was not apparently affected by exposure to beta-bungarotoxin. The re-innervation of the muscle fiber was associated by extensive pre- and post-terminal sprouting at 3 to 5 days but was stable by 7 days. Extensive collateral innervation of adjacent muscle fibers was a significant feature of the re-innervated neuromuscular junctions. These findings suggest that the prolonged and severe paralysis seen in victims of envenoming bites by kraits (elapid snakes of the genus Bungarus) and other related snakes of the family Elapidae is caused by the depletion of synaptic vesicles from motor nerve terminals and the degeneration of the motor nerve terminal and intramuscular axons.

Silicon analysis of breast and capsular tissue from patients with saline or silicone gel breast implants: II. Correlation with connective-tissue disease

The silicone breast implant controversy rages on. Recent work has demonstrated that normal or baseline breast tissue silicon levels in women who had had no prior exposure to any type of breast implant may be as high as 446 microg/gm of tissue. These data ranged from 4 to 446 microg/gm of tissue, with a median of 27.0 microg/gm of tissue. In addition, numerous other epidemiologic and rheumatologic studies have demonstrated no association between silicone breast implants and any connective-tissue diseases. Despite these reports, the use of silicone implants remains restricted. The present study measured breast and capsular tissue silicon levels from 23 breasts in 14 patients with saline implants, and from 42 breasts in 29 patients with silicone implants. No patient in the saline implant group presented with signs or symptoms of connective-tissue disease. Patients with silicone implants, however, were divided into three groups based on the presence or absence of signs or symptoms of connective-tissue disease: group I, no symptoms or signs; group II, + symptoms, no signs; and group III, + symptoms, + signs. Six patients in group III were diagnosed with a specific connective-tissue disease, including systemic lupus erythematosus, rheumatoid arthritis, or scleroderma. The most common indications for implant removal or exchange were capsular contracture and implant rupture, although 41 percent of patients with silicone implants expressed media-related concern over the implant issue. The most common symptoms described by patients in groups II and III were joint pain and stiffness, arm pain and numbness, and fatigue. In all groups, capsular tissue silicon levels were significantly greater than breast tissue levels. This finding may indicate that the capsule serves as a barrier to the distribution of silicone from the implant into adjacent breast tissue. Although breast tissue silicon levels in patients with silicone implants were not significantly greater than those in patients with saline implants (p = 0.48), capsular tissue levels in patients with silicone implants were, indeed, significantly greater than those in patients with saline implants (p < 0.001). However, no statistically significant differences in tissue silicon levels were observed with relation to the presence or absence of connective-tissue disease signs or symptoms in patients with silicone implants (groups I to III). Therefore, these data strengthen the conclusion that there is no association between tissue silicon levels and connective-tissue disease.

Tuberculosis control in Asia and the western Pacific: a role for computer modelling

Despite the availability of effective treatment, tuberculosis (TB) causes more deaths than any other infection. Most of the world's TB cases and deaths occur in Asia and the Western Pacific, and the growing prevalence of multiple drug-resistant TB and the spread of human immunodeficiency virus (HIV) present ever greater obstacles to effective TB control. The management of TB remains difficult, and epidemiologic studies to assess control programmes require significant time and expense and may not be generalizable to other regions. Computer models are powerful and relatively inexpensive tools for rapidly planning and evaluating TB control strategies. Models have demonstrated the value of targeted chemoprophylaxis strategies for the prevention of TB among HIV-infected individuals, and programmes to ensure that all HIV-infected individuals receive TB chemoprophylaxis should be considered in Asia and the Western Pacific. Though directly observed therapy (DOT) is effective when designed to be attractive to patients, modelling has shown that DOT, if poorly accepted by patients, may lead to fewer patients seeking care and thus to paradoxical rises in TB case rates. Models may be used to make accurate predictions of TB morbidity and programme costs using local epidemiologic and demographic inputs. The use of models in Asia and the Western Pacific offers a low-cost way to compare programmes, to improve the evaluation of programmes, to project future cases, and to examine programme needs while providing insights into TB control helpful to countries in and out of the region.

The effect of palytoxin on neuromuscular junctions in the anococcygeus muscle of the rat

Palytoxin, a highly toxic natural product isolated from zoanthids of the genus Palythoa, is accumulated by a wide range of fishes and marine invertebrates used as food in the Indo-Pacific. It is responsible for many incidents of human morbidity and mortality. The toxin is a potent smooth muscle spasmogen. The cause of the contraction of smooth muscle is unclear, but recent work strongly suggests that it is primarily initiated by the release of neurotransmitters from the motor innervation of the smooth muscle. We show here that palytoxin caused the swelling of the muscle cells and some internal organelles of the anococcygeus muscle of the rat, but no substantial structural damage to the tissue. Axons and Schwann cells were also swollen but the most dramatic feature was the depletion of synaptic vesicles from putative release sites in the axons. Some axons were physically damaged following exposure to the toxin, but this was relatively uncommon (< 10% of all axons studied). In the majority of axons there was no damage to nerve terminal membranes, but there was damage to mitochondria. The depletion of vesicles involved all types-clear, dense-cored, large and small. Our observations and pharmacological data gathered elsewhere, provide a neuropathological basis for the spasmogenic activity of palytoxin.

Abnormal dendritic spines in fragile X knockout mice: maturation and pruning deficits

Fragile X syndrome arises from blocked expression of the fragile X mental retardation protein (FMRP). Golgi-impregnated mature cerebral cortex from fragile X patients exhibits long, thin, tortuous postsynaptic spines resembling spines observed during normal early neocortical development. Here we describe dendritic spines in Golgi-impregnated cerebral cortex of transgenic fragile X gene (Fmr1) knockout mice that lack expression of the protein. Dendritic spines on apical dendrites of layer V pyramidal cells in occipital cortex of fragile X knockout mice were longer than those in wild-type mice and were often thin and tortuous, paralleling the human syndrome and suggesting that FMRP expression is required for normal spine morphological development. Moreover, spine density along the apical dendrite was greater in the knockout mice, which may reflect impaired developmental organizational processes of synapse stabilization and elimination or pruning.

Absence of calpain 3 in a form of limb-girdle muscular dystrophy (LGMD2A)

Antibodies that recognise the muscle-specific calpain 3 (CANP3) were used in a 'blind' study to label blots of skeletal muscle from 12 control subjects and from 12 patients with various muscle diseases. Calpain 3 was clearly detected in all control muscle samples analysed, even though some of the muscle had been at room temperature for over an hour before being dissected and snap-frozen. Calpain 3 was also detected in the muscle biopsies from non-LGMD2A patients, but was absent in samples from 3 patients with LGMD2A. These results show that (i) calpain 3 protein can be detected in whole extracts of human muscle, and (ii) that antibodies can be used to differentiate patients with LGMD2A from those with other muscle diseases. This represents an invaluable diagnostic aid since the limb-girdle dystrophies are very difficult to separate on clinical grounds alone. One possible function that was considered for calpain 3 was the post-translational cleavage of the 97 kDa dystroglycan precursor polypeptide into the mature alpha- and beta-dystroglycan proteins. The beta-dystroglycan band was the correct size on blots of LGMD2A muscle, indicating that calpain 3 is probably not involved in the post-translational processing of dystroglycan.

Determination of silicon in breast and capsular tissue from patients with breast implants performed by inductively coupled plasma emission spectroscopy. Comparison with tissue histology

A method for analysis of silicon in tissue was developed to determine silicon content in breast parenchymal and periprosthetic capsular tissues of patients with silicone or saline implants and to compare levels in tissues from normal (nonaugmented) breasts. It is of interest to determine whether increased silicon content in tissues can be associated with morbidity in patients who have received silicone implants. This manuscript addresses the issues involved in analysis of breast tissue samples for silicon and compares silicon levels with tissue histologic findings and patient morbidity. One hundred sixty tissue samples were obtained for silicon analysis from 72 patients during augmentation, capsulectomy with or without replacement mammoplasty, mastectomy, or biopsy procedures and were frozen in acid-washed polystyrene tubes at 220 degrees C until analysis. Samples were thawed, sectioned to approximately 0.1 g (dry weight), and digested in nitric acid before analysis by inductively coupled plasma emission spectroscopy, monitoring emission intensity at 251.6 nm. Tissue silicon levels (breast parenchymal and periprosthetic capsular tissue) in patients with silicone gel implants were much higher (mean, 9,287 micrograms/g, n = 106) than in patients with saline implants (mean, 196 micrograms/g, n = 37) or nonaugmented breasts (mean, 64 micrograms/g, n = 17). Histologic examination was performed on 54 tissue samples stained with hematoxylin-eosin. Tissue samples were rated as to degree of inflammation and calcification, and amount of giant cells, foamy histiocytes, and vacuoles containing a colorless refractory material. Vacuolization and foamy histiocyte ratings correlated significantly with tissue silicon concentration. No correlations were found between tissue silicon concentration and inflammation, calcification, or giant cell rating. Implant age (number of years an implant was in place before sampling) correlated with capsular tissue silicon concentration in patients with intact implants but not in those with ruptured implants. No difference in tissue silicon concentration was found between patients with or without signs or symptoms of morbidity. Using 0.1 g of tissue, the method was linear to 1,000 micrograms/g, and sensitivity was 3.7 micrograms/g. Precision between runs (mean, 5.1 micrograms/g; coefficient of variance, 13.7%; n = 13) was calculated from multiple analyses of a bovine liver standard (National Bureau of Standards, reference material 1577a). Significant biologic variability (21.4% to 52.5%) was seen in tissues with high silicon levels. Paraffin-embedded, formalin-fixed tissues are not amenable to silicon analysis by this method, because of leaching of silicone from the tissues during preparation. Thus only fresh frozen tissue samples were used.

Oxidative damage to muscle protein in Duchenne muscular dystrophy

The hypothesis that reactive free radical species (ROS) may contribute to the pathogenesis of Duchenne muscular dystrophy (DMD) has been suggested previously, but experimental data obtained in support of the above have to date proved inconclusive. The recent discovery that nitric oxide synthase (required for muscle relaxation) is associated with the sarcolemmal protein dystrophin normally and that both proteins are absent in DMD has heightened interest in the potential role of ROS in this disorder. We therefore investigated oxidative damage to proteins in the quadriceps femoris muscle by quantifying protein carbonyl levels in six patients with DMD and six normal controls. In DMD, the mean protein carbonyl level in the quadriceps femoris muscle was increased by 211% (p < 0.005) compared with the normal control subjects. The data thus support the hypothesis for the role of ROS induced protein oxidation of muscle cell damage in DMD.

Myotoxic activity of the toxic phospholipase, notexin, from the venom of the Australian tiger snake

Notexin is a neurotoxic and myotoxic phospholipase A2 derived from the venom of the Australian tiger snake, Notechis scutatus. Though the phospholipase activity has been implicated in the toxicity of notexin, little is understood of its site and mode of action. In this study we investigated the myotoxicity of notexin on the skeletal muscle of the rat. Using immunogold labeling both in vivo and in vitro, we demonstrated that notexin bound exclusively to the sarcolemma. At the early stages when notexin was injected into the muscle there was no evidence of internalization, though at more advanced degeneration when muscle fibers were necrotic, the toxin was able to penetrate the interior of the fibers to exhibit nonspecific labeling. We also showed the toxin was able to bind to glycolytic muscle fibers, which are known to be resistant to the myotoxic effects of notexin. Electron microscopy confirmed the localization of the binding site to the sarcolemma. Scanning electron microscopy showed that the primary pathological changes associated with exposure to notexin were the appearance of areas of hypercontraction along the muscle fibers associated with small lesions in the sarcolemma. At more advanced stages large tears appeared in the sarcolemma between adjacent areas of hypercontraction, revealing apparently intact myofibrils below. We conclude that the sarcolemma is the binding site for the toxin. We propose that the hydrolytic activity causes the appearance of small lesions in the membrane, the loss of ion gradients, and hypercontraction. The weakened area between sites of hypercontraction is then ruptured, leading ultimately to the degeneration of the muscle fibers.

Differential susceptibility of human skeletal muscle proteins to free radical induced oxidative damage: a histochemical, immunocytochemical and electron microscopical study in vitro

In this study we describe a novel experimental approach to quantify the relative susceptibility of (membrane-associated, contractile and mitochondrial) proteins in normal human muscle tissue sections to oxidative damage by the reactive oxygen species (ROS), hydroxyl (OH.) or superoxide (O2.-) radicals. The latter species were generated under controlled experimental conditions in vitro using a 60Co gamma radiation source, with subsequent analysis of damage to target proteins (dystrophin, beta-dystroglycan, beta-spectrin, fast and slow myosin heavy chain, NADH tetrazolium reductase, succinate dehydrogenase and cytochrome oxidase) via standard histochemistry, immunocytochemistry and electron microscopy of muscle tissue sections. In general terms, each of the proteins listed above was more susceptible to oxidative damage by OH., compared to O2.-. Different proteins (differing in structure, function or intracellular localisation) showed different susceptibility to oxidative damage, with certain mitochondrial proteins (succinate dehydrogenase, cytochrome oxidase) showing particular susceptibility. In addition, the use of monoclonal antibodies to four different regions of dystrophin showed the latter to contain both resistant and susceptible regions to ROS induced oxidative damage. At the ultrastructural level of subcellular organelle damage, mitochondria were identified as being particularly susceptible to ROS induced oxidative damage. We therefore speculate that oxidative damage to mitochondria and/or mitochondrial proteins may represent the principal initial route of free radical-induced damage within skeletal muscle tissue.

Silicon analysis of breast and periprosthetic capsular tissue from patients with saline or silicone gel breast implants

The ubiquitousness of silicon is well known. Recent work has demonstrated measurable baseline levels of silicon in nonaugmented cadavers, subsequent to numerous reports of significant elevations of such levels within patients with silicone breast implants and even more reports alleging a causal relation between silicone gel prostheses and connective-tissue diseases. Despite the lack of scientifically substantiated data that such a relation exists, the calamitous silicone breast implant controversy has ensued. Saline-filled breast implants are constructed with a silicone elastomer envelope that remains in direct contact with periprosthetic capsular tissue following implantation. Although there is no evidence to link saline implants with any disorders, it is important to know if saline breast implants contribute any silicon to human body baseline silicon levels. The present study measured tissue silicon levels in 28 breasts of 16 patients with saline-filled implants to determine if the silicone envelope of these prostheses can contribute to the elevation of such levels. These data were compared with data from 116 breasts of 65 patients with silicone gel-filled prostheses as well as breast tissue from 17 patients (controls) who had never been exposed to either type of implant. Samples of breast tissue and periprosthetic capsular tissue were obtained from patients with both intact and ruptured implants. Silicon levels of breast tissue specimens from patients with saline-filled implants were within the range of the controls if the implants were intact. Silicon levels in periprosthetic capsular tissue from patients with intact saline-filled implants were significantly higher than controls (p < 0.02); however, they were still 100-fold less than capsular tissue levels from patients with intact gel-filled implants. Silicon levels measured in both types of tissue were significantly elevated in patients with silicone gel-filled implants compared with controls (p < 0.01). In the case of ruptured gel implants, breast tissue demonstrated higher silicon levels than did similar specimens from patients with intact implants (p < 0.054); periprosthetic capsular tissue levels also were elevated, although the differences were not statistically significant (p = 0.54). These findings are independent of the implant brand or length of exposure to the particular prosthesis. The finding of elevated levels of silicon in both breast and periprosthetic capsular tissue in patients with silicone gel-filled implants in no way implies or substantiates any claim of a causal relationship between silicone and any reported illnesses.

Mutation detection in the med and medJ alleles of the sodium channel Scn8a. Unusual splicing due to a minor class AT-AC intron

Analysis of a transgene-induced mutation at the mouse med locus led to the identification of the novel voltage-gated sodium channel gene Scn8a (Burgess, D. L., Kohrman, D. C., Galt, J., Plummer, N. W., Jones, J. M., Spear, B., and Meisler, M. H.(1995) Nat. Genet. 10, 461-465). We now report the identification of splicing defects in two spontaneous mutations of Scn8a. The original med mutation was caused by insertion of a truncated LINE element into exon 2 of Scn8a. The med transcript is spliced from exon 1 to a cryptic acceptor site in intron 2. A 4-base pair deletion within the 5' donor site of exon 3 in the medJ allele results in splicing from exon 1 to exon 4. Both mutant transcripts have altered reading frames with premature stop codons close to the N terminus of the protein. Loss of Scn8a expression results in progressive paralysis and early death. Intron 2 of Scn8a is flanked by minor class AT-AC splice sites. The observed splicing patterns of the med and medJ mutant transcripts provide the first evidence for preferential in vivo splicing between donor and acceptor sites of the same class. The apparent functional incompatibility may be a consequence of the different composition of spliceosomes bound to major and minor splice sites.

Comparison of protease and related enzyme activities in snake venoms

We identified the presence of a range of proteolytic enzyme types, normally associated with the process of general intracellular protein catabolism in mammalian tissues, in venom samples from several species of snake and from three subspecies of Russell's viper. Although levels of protease activity in venoms were in general substantially lower than corresponding levels in mammalian tissues, activity levels were comparable with several other classes of enzyme normally considered as significant venom components. Based on the protease types and relative levels of activity present in venom samples, we suggest that a possible function of these enzymes (in addition to their generally held function to increase target tissue permeability to other venom components) may be to interfere with the process of neurotransmission in target tissues, via degradation of neurotransmitter/neuromodulatory oligopeptides; this may be particularly the case for proteases such as leucyl aminopeptidase, the activity of which is greater in some venom types than in mammalian tissues. For the purposes of inter- and intra-species taxonomic classification of snakes, we would suggest that determination of a comprehensive venom protease profile may be of considerable value (particularly for subspecies differentiation) either in conjunction with or in place of more conventionally applied techniques such as analytical electrophoresis.

Neuromuscular effects of Papuan Taipan snake venom

Snakebite is a cause of significant morbidity in Central Province, Papua New Guinea. Three adult patients with clinical evidence of neurotoxicity following envenomation by the Papuan taipan had serial neurophysiological examinations over the course of their subsequent hospitalization. All required artificial ventilation for 2.5 to 5 days. The compound muscle action potential (CMAP) amplitudes declined over the first 2 to 4 days after envenoming and then gradually increased in parallel with clinical recovery. Repetitive stimulation studies revealed a distinctive pattern of abnormality. Activation resulted in brief potentiation of the CMAP followed by significantly greater decrement than observed at rest. This effect lasted up to 30 minutes and was not altered after intravenous edrophonium. Single-fiber electromyographic recordings during the recovery phase of the illness were abnormal with marked blocking and increased jitter. All patients were able to return home.