Brexanolone for the treatment of patients with postpartum depression

On March 19, 2019, the United States Food and Drug Administration (FDA) approved Zulresso (brexanolone) for intravenous use for the treatment of postpartum depression (PPD) in adult women. The decision was based on three recent clinical trials following an FDA priority review and breakthrough therapy designation. Brexanolone is now available through a restricted process called the Zulresso Risk Evaluation and Mitigation Strategy Program that requires the drug to be administered by a healthcare provider in a certified healthcare facility. Brexanolone represents an important new treatment option to address treatment-resistant depressive symptoms. In this article, we discuss the current critical need for PPD treatments, the mechanisms of brexanolone action, and the efficacy and drug safety studies that led to FDA approval. Additionally, we discuss some limitations of the current formulation, specific populations of women that might benefit from this treatment, and how new drugs on the horizon may increase the ability to treat PPD in a variety of patient populations.

The involvement of older inpatients in medical student education

Objectives

To examine older inpatients’ experiences with medical student education, their views on future interactions, and to seek their opinion on the most important curricular topics related to geriatric medicine.

Methods

The study involved 112 non-confused inpatients older than 65 years of age, who completed a uniformed questionnaire on the day of their discharge from a teaching hospital.

Results

The mean age was 81 years, with equal number of male and female participants. 57% interacted with the students during their admission, the majority being interviewed and examined. Almost all (92%) of these patients described their experience as positive, some described it as time-consuming (23%), repetitive (19%) and tiresome (9%). 92% of all participants agreed that the older patients should be part of medical students’ education. Dementia, cardiac conditions, cancer, arthritis, isolation/loneliness were highlighted as the most important topics to teach medical students related to geriatric medicine, while patience and listening were listed as important skills. They suggested practical, easily implemented advice for the improvement of the interaction between students and older patients; including allowing more time for interactions and for students to speak louder.

Conclusions

Older patients felt positively about their interactions with medical students, and believed that older patients should be involved in medical student education. As well as medical conditions such as dementia, cardiac disease and cancer, these patients highlighted isolation and loneliness as important topics for undergraduate geriatric medical education, implying that students should learn about broader aspects of older patients’ health and wellbeing.

Evaluation of Metabolic and Synaptic Dysfunction Hypotheses of Alzheimer's Disease (AD): A Meta-Analysis of CSF Markers

BACKGROUND

Alzheimer's disease (AD) is currently incurable and a majority of investigational drugs have failed clinical trials. One explanation for this failure may be the invalidity of hypotheses focusing on amyloid to explain AD pathogenesis. Recently, hypotheses which are centered on synaptic and metabolic dysfunction are increasingly implicated in AD.

OBJECTIVE

Evaluate AD hypotheses by comparing neurotransmitter and metabolite marker concentrations in normal versus AD CSF.

METHODS

Meta-analysis allows for statistical comparison of pooled, existing cerebrospinal fluid (CSF) marker data extracted from multiple publications, to obtain a more reliable estimate of concentrations. This method also provides a unique opportunity to rapidly validate AD hypotheses using the resulting CSF concentration data. Hubmed, Pubmed and Google Scholar were comprehensively searched for published English articles, without date restrictions, for the keywords "AD", "CSF", and "human" plus markers selected for synaptic and metabolic pathways. Synaptic markers were acetylcholine, gamma-aminobutyric acid (GABA), glutamine, and glycine. Metabolic markers were glutathione, glucose, lactate, pyruvate, and 8 other amino acids. Only studies that measured markers in AD and controls (Ctl), provided means, standard errors/deviation, and subject numbers were included. Data were extracted by six authors and reviewed by two others for accuracy. Data were pooled using ratio of means (RoM of AD/Ctl) and random effects meta-analysis using Cochrane Collaboration's Review Manager software.

RESULTS

Of the 435 identified publications, after exclusion and removal of duplicates, 35 articles were included comprising a total of 605 AD patients and 585 controls. The following markers of synaptic and metabolic pathways were significantly changed in AD/controls: acetylcholine (RoM 0.36, 95% CI 0.24-0.53, p<0.00001), GABA (0.74, 0.58-0.94, p<0.01), pyruvate (0.48, 0.24-0.94, p=0.03), glutathione (1.11, 1.01- 1.21, p=0.03), alanine (1.10, 0.98-1.23, p=0.09), and lower levels of significance for lactate (1.2, 1.00-1.47, p=0.05). Of note, CSF glucose and glutamate levels in AD were not significantly different than that of the controls.

CONCLUSION

This study provides proof of concept for the use of meta-analysis validation of AD hypotheses, specifically via robust evidence for the cholinergic hypothesis of AD. Our data disagree with the other synaptic hypotheses of glutamate excitotoxicity and GABAergic resistance to neurodegeneration, given observed unchanged glutamate levels and decreased GABA levels. With regards to metabolic hypotheses, the data supported upregulation of anaerobic glycolysis, pentose phosphate pathway (glutathione), and anaplerosis of the tricarboxylic acid cycle using glutamate. Future applications of meta-analysis indicate the possibility of further in silico evaluation and generation of novel hypotheses in the AD field.

The prevalence of proximal hamstring pathology on MRI in the asymptomatic population

PURPOSE

Injury to the proximal hamstring complex (PHC) is becoming more frequently diagnosed. Patients attending our tertiary referral centre demonstrated 'pathological changes' in the unaffected normal contralateral PHC on MRI. The prevalence of PHC pathology, however, has not been previously documented in the literature in asymptomatic subjects. It is the hypothesis of this study that the natural history of asymptomatic pathological change on MRI in the PHC is not clear. The aim is to quantify the natural history of PHC degeneration.

METHOD

Two hundred and fifty-three consecutive patients with an asymptomatic PHC were reviewed retrospectively between 2009 and 2010. The PHC was assessed in multiple MRI planes by a specialist musculoskeletal consultant radiologist.

RESULTS

Five hundred and six proximal hamstrings complexes were reviewed. Eighty-nine patients (35 %) were radiological normal both sides, median age 51 years (range 13-88). Thirty-four patients (13 %) had unilateral pathology, median age 55 years (range 25-89). Of these, 3 patients (1 %) had presence of a complete tear, median age 81 years (range 72-87). Sixteen patients (7 %) had tendinosis, median age 60 years (range 37-78). Fifteen patients (6 %) had a unilateral partial tear, median age 57 years (range 35-78). One hundred and thirty patients (52 %) had bilateral pathology, median age 65 years (range 25-89). Fifty-three patients (21 %) had the presence of bilateral tendinopathy alone, median age 56 years (range 25-89). Twenty-seven patients (11 %) had a partial tear on one side and tendinosis on the other, median age 68 years (range 38-89). Thirty-nine patients (15 %) had evidence of bilateral partial tears, median age 63 years (range 36-89), with 52 % demonstrating a torn conjoined and semi-membranosus tendon. The remaining 48 % had either an isolated tear of the conjoined or the semi-membranosus (the more commonly injured tendon 74 % of the time). Four patients (2 %) had bilateral complete ruptures with a median age of 68 years (range 59-78). Six patients (2 %) had a complete tear on one side and a partial tear on the other, median age 68 years (range 34-83). One patient had a complete tear on one side and tendinosis on the other, age 81 years.

CONCLUSION

There is a higher prevalence of pathology in the asymptomatic population, 15 % have bilateral partial tears, and 2 % have bilateral complete tears. The semi-membranosus being the most affected, this may help clinically stratify the need for surgical intervention.

LEVEL OF EVIDENCE

I.

Finite element analysis: a comparison of an all-polyethylene tibial implant and its metal-backed equivalent

PURPOSE

The hypothesis of this study is that all-polyethylene (APE) tibial implants offer a biomechanical profile similar to metal-backed tray (MBT). There are significant financial implications, in selected patient groups, if APE can be deemed to perform as well as MBT.

METHODS

Using a finite element analysis of CAD models provided by DePuy (Leeds), stress distributions were investigated for both an APE and MBT tibial implant. The performance was assessed for cancellous bone at 700 MPa (normal) and at 350 MPa (less stiff). Plots were recorded along the length of the tibia, showing the loads carried by the bone (cortical and cancellous), the implant interface, cement interface and the stem. von Mises stress distributions and percentage volumes were used to assess bone resorption and hence potential for failure (fracture).

RESULTS

Higher stress shielding (resorption) occurred around the keel and stem of the MBT revealing greater potential for bone loss in these areas. APE had no areas of bone resorption (being more flexible resulting in less stress shielding). The stiffer MBT carries a higher proportion of the load down the stem. MBT stress in cancellous bone is lower than APE, as load is distributed to the cortical rim. APE has a marginally favourable strain state in cancellous bone and spreads loads more at the cement interface than MBT.

CONCLUSION

Modern-day APE bearings may be superior to previously designed implants due to improvements in manufacturing. In the correct patient group, this could offer substantial cost savings.

Origin of anomalous magnetite properties in crystallographic matched heterostructures: Fe3O4(111)/MgAl2O4(111)

Magnetite films grown on crystallographically matched substrates such as MgAl2O4 are not expected to show anomalous properties such as negative magnetoresistance and high saturation fields. By atomic resolution imaging using scanning transmission electron microscopy we show direct evidence of anti-phase domain boundaries (APB) present in these heterostructures. Experimentally identified 1/4<101> shifts determine the atomic structure of the observed APBs. The dominant non-bulk superexchange interactions are between 180° octahedral-Fe/O/octahedral-Fe sites which provide strong antiferromagnetic coupling across the defect interface resulting in non-bulk magnetic and magnetotransport properties.

The effect of sterile versus non-sterile tourniquets on microbiological colonisation in lower limb surgery

INTRODUCTION

Surgical tourniquets are commonplace in lower limb surgery. Several studies have shown that tourniquets can be a potential source of microbial contamination but have not compared the use of sterile versus non-sterile tourniquets in the same procedures.

METHODS

Patients undergoing elective orthopaedic lower limb surgery were randomised prospectively to use of non-sterile pneumatic tourniquet or sterile elastic exsanguination tourniquet (S-MART™, OHK Medical Devices, haifa, Israel). Samples were taken from the ties of the non-sterile tourniquet prior to surgery and from the sterile tourniquets at the end of the operation in a sterile fashion. These were then sealed in universal containers and immediately analysed by the microbiology department on agar plates, cultured and incubated.

RESULTS

Thirty-four non-sterile tourniquets were sampled prior to surgical application, twenty-three of which were contaminated with several different organisms including coagulase-negative Staphylococcus spp, Staphylococcus aureus, Sphingomonas paucimobilis, Bacillus spp, and coliforms. Thirty-six sterile tourniquets were used, with no associated contamination.

CONCLUSIONS

There was significant contamination of 68% of orthopaedic surgical tourniquets. These are used regularly in procedures involving the placement of prosthesis and metalwork, and can act as a potential source of infection. We recommend the use of sterile single-use disposable tourniquets where possible. The availability of an alternative should now set the new standard of care and we recommend adopting this as a current NICE guideline for control of surgical site infection.

Case report: Liposarcoma of the sinonasal tract

Nasal and paranasal malignant tumours account for less than 5% of all head and neck malignancies. Epithelial malignancies overwhelmingly predominate, with squamous cell carcinomas representing the most frequent histological subtype in this location. Soft-tissue sarcomas of the nasal cavity and paranasal sinuses are exceedingly rare. Here, we report two cases of myxoid liposarcomas that occurred in the nasal and paranasal regions, both of which presented diagnostic challenges and could not be diagnosed definitively from intraoperative frozen sections. These cases reinforce the notion that, while they are uncommon, sarcomas in general and liposarcomas in particular should still be considered as part of the differential diagnosis in patients presenting with obstructive symptoms in the nasal and paranasal sinuses.

Preparation and maintenance of organotypic slice cultures of CNS tissue

Organotypic slice cultures are the in vitro method of choice for applications requiring long-term survival of the preparation and a high degree of cellular differentiation and organization resembling that of the original tissue. Long-term survival is achieved by culturing slices at the air/liquid interface, either by continuously rotating the preparation (roller-tube cultures) or by culturing them on semiporous membranes (stationary interface cultures). Both culture techniques yield nerve cells which are highly differentiated in terms of their morphological and physiological characteristics. Because most of these cultures are prepared from 1-week-old postnatal animals, in which the cellular and tissue organization is already relatively advanced, the original cytoarchitecture is often remarkably well maintained. Moreover, the presence of a full complement of glial and nerve cells is thought to provide a microenvironment facilitating differentiation of neurons. Slice culture also offers unique advantages for recording from pairs of cells, as a consequence of the high degree of connectivity between nerve cells. Recently, new applications have emerged such as the cultivation of slices from knock-out animals with limited postnatal survival time or alteration of gene expression by viral vectors.

Novel 'phage display antibodies identify distinct heparan sulfate domains in developing mammalian lung

Heparan sulfate proteoglycans (HSPGs) are essential to respiratory morphogenesis in species as diverse as Drosophila and mice; they play a role in the regulation of numerous HS-binding growth factors, e.g. fibroblast growth factors. Moreover, an HS analogue, heparin, modulates lung growth in vitro. However, it has been difficult to assess the roles of specific HS structures in lung development due to technical barriers to their spatial localisation. Lungs from Sprague-Dawley rats were harvested between E15.5 and E19.5 and immediately fixed in 4 % (w/v) paraformaldehyde (in 0.1 M phosphate-buffered saline (PBS), pH 7.4). Lungs were washed in PBS, cryoprotected with 20% (w/v) sucrose (in PBS), gelatin embedded [7.5% (w/v) gelatin, 15% (w/v) sucrose in PBS], before being covered in Cryo-M-Bed (Bright, Huntingdon, UK) and snap frozen at -40 degrees C. Cryosections were cut at 8 microm and stained with the HSPG core protein specific antibody 3G10 and a HS 'phage display antibody, EW4G2V. 3G10 and EW4G2V immunohistochemistry highlighted the presence of specific HS structures in lungs at all gestational ages examined. 3G10 strongly labelled airway basement membranes and the surrounding mesenchyme and showed weak staining of airway epithelial cells. EW4G2V, however, was far more selective, labelling the airway basement membranes only. Mesenchymal and epithelial cells did not appear to possess the HS epitope recognised by EW4G2V at these gestational ages. Novel 'phage display antibodies allow the spatial distribution of tissue HS to be analysed, and demonstrate in situ that distinct cellular compartments of a tissue possess different HS structures, possibly on the same proteoglycan core protein. These probes offer a new opportunity to determine the role of HS in the pathogenesis of congenital defects such as congenital diaphragmatic hernia (CDH), where lung development is aberrant, and the resulting pulmonary hypoplasia and hypertension are a primary cause of mortality.

Recovery of Four Novel Potato spindle tuber viroid Sequence Variants from Russian Seed Potatoes

First described in the early 1930s, the limited distribution of potato "gothic" disease made it of little economic significance in European Russia until the early 1970s when meristem-tip culture was widely adopted throughout the former USSR to increase production of virus-free seed potatoes. Shortly thereafter, the yield and quality of Russian seed potatoes began a dramatic decline. Symptoms of potato "gothic" resemble those of Potato spindle tuber viroid (PSTVd) (3), and initial suspicions that in vitro plantlets and seed potatoes might be viroid-infected were later proved correct when Kastalyeva et al. (2) showed that approximately 50 to 70% of in vitro plantlets and tubers collected from different regions of Russia as well as the in vitro germplasm collection maintained by the All-Russian Potato Research Institute (ARPRI) were infected with PSTVd. Measures have since been taken to reduce the incidence of PSTVd infection, and numerous PSTVd isolates were collected from territories of the former USSR; however, none of these isolates have been characterized at the molecular level. Overlapping reverse transcription (RT)-PCR products (1) were generated from four PSTVd isolates maintained in field-grown tubers at the VNIIF using two pairs of primers; PSTVd180F (5'-TCACCCTTCCTTTCTTCGGGTGTC-3') + PSTVd179R (5'-AAACCCTGTTTCGGCGGGAATTAC-3') and PSTVd112F (5'-ACT GGCAAAAAAGGACGGTGGGGA-3') + PSTVd359R (5'-AGGAACC AACTGCGGTTCCAAGGG-3'). Automated sequence analysis of the resulting uncloned PCR products revealed the presence of four previously unknown PSTVd variants (GenBank Accession Nos. EF044302-EF044305). All four tubers were also infected with Potato virus M and Potato virus Y and one tuber also contained Potato virus S. ELISA tests for Potato leaf roll virus were negative. Each isolate appeared to contain only a single 358-359 nt variant differing from PSTVd-intermediate strain (GenBank Accession No. V01465) at 2-5 positions. The three closely related variants originating from Leningradskaya Province (Northwest Russia) contain two to three changes in the variable domain and central conserved region and induced intermediate symptoms in Rutgers tomato. The fourth variant originating from Samarskaya Province (Volga River Region) contains additional changes in the pathogenicity domain and induced mild symptoms. Minor differences among the Leningradskaya variants may represent sequence drift during extended (9 to 11 year) tuber passage. The presence of additional sequence changes in the variant from Samarskaya is consistent with independent origin and/or prolonged separation. Additional studies with a wider range of Russian isolates of PSTVd are currently underway to develop diagnostic methods suitable for future large-scale screening programs. References: (1) Y. Hu et al. Virology 219:45, 1997. (2) T. B. Kastalyeva et al. Vestn. RASKHN 3:22, 1992. (3) Y. A. Leontyeva. Potato spindle tuber ('gothic') as one of the most important diseases in the Volga region. (In Russian.) Ph.D. thesis. Agricultural University of Leningrad, Pushkin, 1971.

Identification of neutral mutants surrounding two naturally occurring variants of Potato spindle tuber viroid

Single point mutations in the pathogenicity domain of Potato spindle tuber viroid (PSTVd) can have a dramatic effect on disease expression, and only three substitutions are required for the spontaneous conversion of the type strain PSTVd-Intermediate to the rapidly replicating, highly pathogenic variant RG1 (Gruner et al., Virology 209, 60-69, 1995). To identify available evolutionary pathways linking these two variants, we mutagenized five positions in an infectious cDNA copy of PSTVd-Intermediate and screened the resulting mixture of 768 sequences for neutral or near-neutral mutants. Numerical simulations based on the bioassay data indicate that the 23 variants recovered represent >80 % of all such sequences. RG1 was the only naturally occurring variant recovered, and the overall pattern of sequence changes observed indicates that PSTVd-Int occupies a comparatively steep peak within the fitness landscape.

Compartmentalized and binary behavior of terminal dendrites in hippocampal pyramidal neurons

The dendritic arbor of pyramidal neurons is not a monolithic structure. We show here that the excitability of terminal apical dendrites differs from that of the apical trunk. In response to fluorescence-guided focal photolysis of caged glutamate, individual terminal apical dendrites generated cadmium-sensitive all-or-none responses that were subthreshold for somatic action potentials. Calcium transients produced by all-or-none responses were not restricted to the sites of photolysis, but occurred throughout individual distal dendritic compartments, indicating that electrogenesis is mediated primarily by voltage-gated calcium channels. Compartmentalized and binary behavior of parallel-connected terminal dendrites can greatly expand the computational power of a single neuron.

Metal-modified nucleobase sextet: joining four linear metal fragments (trans-a2PtII) and six model nucleobases to an exceedingly stable entity

Crosslinking of three different model nucleobases (9-ethyladenine, 9-EtA; 9-ethylguanine, 9-EtGH; 1-methyluracil, 1-MeU) by two linear trans-aPtII (a = NH3 or CH3NH2) entities leads to a flat metal-modified base triplet, trans,trans-[(NH3)2Pt(1-MeU-N3)(mu-9-EtA-N7,N1)Pt(CH3NH2)2(9-EtGH-N7)]3+ (4b). Upon hemideprotonation of the 9-ethylguanine base at the N1 position. 4b spontaneously dimerizes to the metalated nucleobase sextet 5, [(4b)(triple bond)(4b-H)]5+. In this dimeric structure a neutral and an anionic guanine ligand, which are complementary to each other, are joined through three H bonds and additionally by two H bonds between guanine and uracil nucleobases. Four additional interbase H bonds maintain the approximate coplanarity of all six bases. The two base triplets form an exceedingly stable entity (KD = 500 +/- 150 M(-1) in DMSO), which is unprecedented in nucleobase chemistry. The precursor of 4b and several related complexes are described and their structures and solution properties are reported.

Differential control of GABA release at synapses from distinct interneurons in rat hippocampus

1. Paired recordings from monosynaptically connected CA3 interneurons and pyramidal cells of rat hippocampal slice cultures were used to compare the modulation of GABA release at synapses from distinct interneurons. 2. The group II metabotropic glutamate receptor (mGluR) agonist (2S,2'R,3'R)-2-(2',3'-dicarboxylcyclopropyl) glycine (DCG-IV, 5 muM) reduced the amplitude of IPSPs originating from stratum radiatum but not stratum oriens interneurons. In contrast, the GABAB receptor agonist (-)baclofen (10 muM) reduced the amplitude of unitary IPSPs elicited by all interneurons. 3. IPSPs mediated by stratum oriens interneurons were unaffected by the N-type calcium channel blocker omega-conotoxin MVIIA (1 muM) but were suppressed by the P/Q-type blocker omega-agatoxin IVA (200 nM). In contrast, IPSPs mediated by stratum radiatum interneurons were abolished by omega-conotoxin MVIIA. 4. Transmission dynamics were different at synapses from the two groups of interneurons. IPSPs mediated by stratum oriens interneurons showed marked paired-pulse depression (PPD) at intervals of 50 400 ms. IPSPs mediated by stratum radiatum interneurons showed paired-pulse facilitation (PPF) at 50 ms and PPD at longer intervals. 5. The amplitude of unitary IPSPs from all interneurons was unaffected by the GABAB receptor antagonist CGP52432 (2 muM) as was PPD at both 50 and 400 ms intervals. However, CGP52432 did reduce PPD of extracellularly evoked IPSPs. 6. Our results show that two groups of inhibitory synapses impinging onto CA3 pyramidal cells can be distinguished according to their dynamic and modulatory properties.

Synaptic plasticity: Building memories to last

A series of recent studies has provided long-awaited direct evidence that enduring changes in synaptic strength, presumably underlying the formation of persistent memories, may be encoded in a lasting form as a change in synaptic structure.

Heterogeneity of synaptic plasticity at unitary CA3-CA1 and CA3-CA3 connections in rat hippocampal slice cultures

Long-term potentiation (LTP) of unitary EPSPs, generated by pairs of monosynaptically connected CA3 and CA1 pyramidal cells, was compared with LTP of extracellularly evoked, multi-unitary EPSPs in rat hippocampal slice cultures. LTP was induced by repeated, synchronous pairing of low-frequency presynaptic and postsynaptic activity. Three differences were observed. First, LTP of multi-unitary EPSPs displayed two phases: transient (<5 min) and sustained. Potentiation of unitary EPSPs displayed both phases in 42% of experiments; the remainder showed sustained potentiation only. Unitary EPSPs displaying transient-sustained and only sustained potentiation could be recorded from single postsynaptic cells, indicating that excitatory synapses on a given cell are heterogeneous with respect to short-term plasticity. Second, whereas LTP of multi-unitary EPSPs never resulted in greater than twofold increases in amplitude (mean potentiation of 175% of control), maximal LTP of unitary EPSPs was as great as 13-fold (mean potentiation of 250%). Third, LTP could not be induced in 24% of unitary EPSPs. We provide here the first evidence for the coexistence of potentiatable and nonpotentiatable synapses on individual postsynaptic neurons. Thirty-seven percent of connections not displaying LTP exhibited long-term depression (LTD), suggesting that the connections were already maximally potentiated. In the remaining 63% of these pairs, neither LTP nor LTD could be induced, despite the existence of a pharmacologically identified, NMDA receptor-mediated EPSP component. In conclusion, there is considerable heterogeneity in the amplitude and time course of LTP expression at different synaptic connections. A substantial proportion of apparently nonplastic synapses probably accounts for the weaker potentiation displayed by compound EPSPs.

Selective glutamate receptor antagonists can induce or prevent axonal sprouting in rat hippocampal slice cultures

After the transection of the Schaffer collateral pathway in hippocampal slice cultures, reactive sprouting is induced in the CA3 area, and eventually synaptic transmission between areas CA1 and CA3 is restored. Using this model, we have studied the role of ionotropic glutamate receptors in the initiation of axonal sprouting and the regeneration of functional synapses. We show that neither reactive sprouting nor functional recovery of synaptic transmission occur in the presence of the non-N-methyl-D-aspartate (NMDA) receptor antagonist 6-nitro-7-sulfamoylbenzoquinoxaline-2,3-dione (CNQX). In contrast, the NMDA receptor antagonists methyl-10, 11-dihydro-5-H-dibenzocyclohepten-5,10-imine (MK-801) or 3-(RS)-2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP) did not interfere with these processes. Moreover, we observed that the application of NMDA receptor antagonists induced massive axonal sprouting and an increase in the frequency of miniature excitatory postsynaptic currents in unlesioned cultures. Our results thus indicate that NMDA and non-NMDA receptors exert a differential effect on reactive sprouting and the recovery of synaptic transmission after injury in the hippocampus. Activation of non-NMDA receptors appears necessary for these processes to occur, whereas activation of NMDA receptors suppresses growth-associated protein -43 expression and axonal outgrowth.

Activation of intrinsic hippocampal theta oscillations by acetylcholine in rat septo-hippocampal cocultures

1. Oscillatory electro-encephalographic activity at theta frequencies (4-15 Hz) can be recorded from the hippocampus in vivo and depends on intact septal projections. The hypothesis that these oscillations are imposed on the hippocampus by rhythmically active septal inputs was tested using dual intracellular recordings from CA1 and CA3 pyramidal cells in septo-hippocampal cocultures. 2. Septo-hippocampal cocultures displayed spontaneous oscillatory synaptic activity at theta frequencies. In CA3 cells, EPSP/IPSP sequences predominated, whereas only EPSPs were apparent in CA1 cells. Synaptic potentials in CA3 cells preceded those in CA1 cells by 5-10 ms. 3. Oscillatory synaptic activity was blocked in cocultures by the muscarinic antagonist atropine (0.1 microM), facilitated but unchanged in frequency upon application of the acetylcholinesterase inhibitor neostigmine (1 microM), and not seen in hippocampal monocultures. 4. The muscarinic agonist methacholine (5-20 nM) induced oscillatory synaptic activity at 4-15 Hz in hippocampal monocultures, which was identical to that occurring spontaneously in septo-hippocampal cocultures. 5. Synaptic theta activity was observed in cocultures of septal tissue with subdissected hippocampal slices containing area CA3 alone, but not in septo-CA1 cocultures. 6. We conclude that oscillatory synaptic activity at theta frequencies, with similar characteristics to theta activity in vivo, can be generated by the hippocampal network in response to activation of muscarinic receptors by synaptically released acetylcholine from septal afferents. Furthermore, the oscillatory activity is determined by mechanisms intrinsic to the hippocampal circuitry, particularly area CA3. Rhythmic septal input is not required.

Maternal phenylketonuria: a continuing problem

OBJECTIVES

To estimate the number of women of childbearing age in New South Wales whose children are at risk of the maternal phenylketonuria (PKU) syndrome (intellectual disability, microcephaly, congenital malformations).

SETTING

New South Wales, 1996.

DESIGN

Comparison of number of women with PKU aged 15-44 years on the NSW PKU database (observed number) with expected number derived from population data.

MAIN OUTCOME MEASURES

Observed and expected numbers of women with PKU (defined as blood phenylalanine levels > or = 400 mumol/L, and phenylalanine-restricted diet recommended) by age; number with no clinical contact with the PKU service in previous year; outcomes of pregnancies in women with PKU (January 1994 to July 1996).

RESULTS

110 women aged 15-44 years with PKU were listed on the database. The expected number was 145 (95% confidence interval, 122-171). The difference was greatest in the 30-44 years age group (born before comprehensive newborn screening), with only 55% of the expected number listed. Sixteen women who had been diagnosed with PKU at birth were not having regular follow-up, while 18 women had been diagnosed only after investigation of abnormalities in their children. Of 28 pregnancies managed by the NSW PKU service, 19 were considered unaffected by the maternal PKU syndrome and five affected (another three did not reach term; one outcome was unknown). Of 46 unmanaged pregnancies, all were affected.

CONCLUSION

There is an urgent need for better follow-up of women with PKU and for education of health professionals about the MPKU syndrome, its recognition, the risks of untreated pregnancy and the benefits of dietary treatment.

Development of liquid chromatography-electrospray ionization-tandem mass spectrometry methods for determination of urinary metabolites of benzene in humans

To investigate the ways in which different levels of exposure affect the metabolic activation pathways of benzene in humans, and to examine the relationship between urinary metabolites and other biological markers, we have developed two sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays for quantitation of the benzene metabolites trans,transmuconic acid (t,t-MA), S-phenylmercapturic acid (S-PMA), hydroquinone (HQ), catechol (CAT), and for estimation of 1,2,4-trihydroxybenzene (BT). In our first assay, urinary S-PMA and t,t-MA were measured simultaneously by liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring (LC-ESI-MS/MS-SRM) in the negative ionization mode. In this assay, the metabolites [13C6]-S-PMA and [13C6]-t,t-MA were used as internal standards. The efficacy of this specific assay was evaluated in human urine specimens from 28 smokers and 18 nonsmokers serving as the benzene-exposed and nonexposed groups, respectively. The coefficient of variation (CV) of analyses on different days (n = 8) for S-PMA was 7% for samples containing 9.4 micrograms/L urine, and for t,t-MA was 10% for samples containing 0.07 mg/L. The mean levels of S-PMA and t,t-MA in smokers were 1.9-fold (p = 0.02) and 2.1-fold (p = 0.03) higher, respectively, than those in nonsmokers.

Excitatory synaptic transmission and its modulation by PKC is unchanged in the hippocampus of GAP-43-deficient mice

We compared excitatory synaptic transmission between hippocampal pyramidal cells in dissociated hippocampal cell cultures and in area CA3 of hippocampal slice cultures derived from wild-type mice and mice with a genetic deletion of the presynaptic growth associated protein GAP-43. The basal frequency and amplitude of action potential-dependent and -independent spontaneous excitatory postsynaptic currents were similar in both groups. The probability that any two CA3 pyramidal cells in wild-type or GAP-43 knockout (-/-) slice cultures were synaptically connected was assessed with paired recordings and was not different. Furthermore, unitary synaptic responses were similar in the two genotypes. Bath application of phorbol 12,13-diacetate (0.6-3 microM) elicited a comparable increase in the frequency of miniature excitatory synaptic currents in wild-type and GAP-43 (-/-) cultures. This effect was blocked by the protein kinase C inhibitor, bisindolylmaleimide I (1.2 microM). Finally, 3 microM phorbol 12,13-diacetate potentiated the amplitude of unitary synaptic currents to a comparable extent in wild-type and GAP-43 (-/-) slice cultures. We conclude that GAP-43 is not required for normal excitatory synaptic transmission or the potentiation of presynaptic glutamate release mediated by activation of protein kinase C in the hippocampus.

Miniature synaptic events maintain dendritic spines via AMPA receptor activation

We investigated the influence of synaptically released glutamate on postsynaptic structure by comparing the effects of deafferentation, receptor antagonists and blockers of glutamate release in hippocampal slice cultures. CA1 pyramidal cell spine density and length decreased after transection of Schaffer collaterals and after application of AMPA receptor antagonists or botulinum toxin to unlesioned cultures. Loss of spines induced by lesion or by botulinum toxin was prevented by simultaneous AMPA application. Tetrodotoxin did not affect spine density. Synaptically released glutamate thus exerts a trophic effect on spines by acting at AMPA receptors. We conclude that AMPA receptor activation by spontaneous vesicular glutamate release is sufficient to maintain dendritic spines.

Coding sequences of the MHC II beta chain of homozygous rainbow trout (Oncorhynchus mykiss)

Six lines of homozygous rainbow trout (Oncorhynchus mikiss) from different genetic and geographical backgrounds have been produced as aquatic models for biomedical research by the chromosome set manipulation techniques of androgenesis and gynogenesis. Messenger RNA from spleens was extracted. and the MHC II B cDNA sequences, amplified by RT PCR, were cloned into plasmids. Sequences of the MHC II beta2 domains were highly conserved between the different plasmids from the same and different lines of trout. Most of the variability among sequences was found in the amino terminal half of the beta1 domain, which corresponds with the peptide binding region of the MHC II molecule. This diversity suggests that the different lines of trout may exhibit differences in immune response. Rainbow trout MHC II B sequences were similar to the MHC II B sequences of the Pacific salmon (O. gorbuscha, O. tshawytscha, O. nerka, O. miasou, O. kisutch). Southern blot analysis performed on the restricted DNA of the OSU and Hot Creek trout, and the doubled haploid progeny produced by androgenesis from OSU x Hot Creek hybrids indicates that two distinct genes encode the MHC II B sequences and that these genes are unlinked.

Utility of endoscopic biopsy samples to quantitate human duodenal ion transport

Duodenal mucosal bicarbonate secretion (DMBS) prevents acid-peptic damage and facilitates nutrient absorption. DMBS is diminished in patients with duodenal ulcers and is normalized after Helicobacter pylori eradication. The measurement of DMBS in human patients in vivo requires intubation with a multi-lumen balloon tube and permits limited testing with putative agonists and antagonists. Our purpose was to develop a means to investigate transport events in human duodenal biopsy samples in vitro. After validation studies in a modified mini-Ussing chamber were performed, duodenal transport events were examined in proximal endoscopic biopsy samples from normal volunteers (n = 17). Tissues were mounted in modified mini-Ussing chambers (volume 2.5 ml, surface area 3.8 mm2). Short circuit current (Isc), potential difference (PD), and bicarbonate secretion were determined under basal conditions and after stimulation with graded doses of prostaglandin E2 (PGE2)(10(-8) to 10(-4) mol/L) and dibutyryl cAMP (db-cAMP)(10(-4) to 10(-2) mol/L). Duodenal tissues remained viable for at least 2 hours and exhibited stable basal HCO3(-) secretion and electrical parameters. Stimulation with PGE2 and db-cAMP resulted in dose-related increases in both Isc and HCO3(-) secretion (P < .05) that were abolished by ouabain and anoxia. It is concluded (1) that human duodenal bulb biopsy samples maintain their inherent transport function in mini-Ussing chambers and (2) that by using this novel method it will be possible to define the transport events that modulate human duodenal secretion, in particular bicarbonate secretion, in both health and disease.

Effects of diagnosis, race, and puberty on platelet serotonin levels in autism and mental retardation

OBJECTIVE

To reevaluate platelet serotonin (5-HT) levels in autism, measuring and controlling for effects of race and puberty. The specificity of hyperserotonemia for autism versus cognitive impairment is also assessed.

METHOD

Platelet 5-HT levels were measured in 77 individuals, aged 2 through 37 years, with autistic disorder; 65 normal controls; and 22 mentally retarded or otherwise cognitively impaired (MR/CI) prepubertal children. Effects of diagnosis, race, and pubertal status were evaluated by analysis of variance in separate pre- and postpubertal groups. 5-HT levels were expressed as ng/mL blood and ng/microL platelet volume.

RESULTS

Among prepubertal children, significant effects of diagnosis (ng/mL; F2,109 = 5.9, p = .004) and race (F2,109 = 14.7, p < .0005) were found. Autistic youngsters had significantly higher 5-HT concentrations than controls, although the elevation (25%) was less than typically reported; MR/CI children had levels very similar to those of controls. White children had significantly lower 5-HT levels than black or Latino youngsters, regardless of diagnosis. Diagnosis and race effects were nonsignificant in the postpubertal group. Postpubertal subjects had lower 5-HT concentrations than prepubertal subjects (ng/mL; F1,114 = 28.5, p < .0005).

CONCLUSIONS

The data underscore the importance of matching for race and pubertal status in neuropsychiatric research and suggest that the prevalence of hyperserotonemia in autistic individuals may have been overestimated because of a failure to control for both variables. Hyperserotonemia was not found in MR/CI youngsters without autistic features.

Long-term synaptic plasticity between pairs of individual CA3 pyramidal cells in rat hippocampal slice cultures

1. Long-term potentiation (LTP) and depression (LTD) were investigated at synapses formed by pairs of monosynaptically connected CA3 pyramidal cells in rat hippocampal slice cultures. 2. An N-methyl-D-aspartate (NMDA) receptor-mediated component of the unitary EPSP, elicited at the resting membrane potential in response to single action potentials in an individual CA3 cell, could be isolated pharmacologically. 3. Associative LTP was induced when single presynaptic action potentials were repeatedly paired with 240 ms postsynaptic depolarizing pulses that evoked five to twelve action potentials or with single postsynaptic action potentials evoked near the peak of the unitary EPSP. LTP induction was prevented by an NMDA receptor antagonist. 4. Associative LTD was induced when single presynaptic action potentials were repeatedly elicited with a certain delay after either 240 ms postsynaptic depolarizing pulses or single postsynaptic action potentials. The time window within which presynaptic activity had to occur for LTD induction was dependent on the amount of postsynaptic depolarization. LTD was induced if single pre- and postsynaptic action potentials occurred synchronously. 5. Homosynaptic LTD was induced by 3 Hz tetanization of the presynaptic neuron for 3 min and was blocked by an NMDA receptor antagonist. 6. Depotentiation was produced with stimulation protocols that elicit either homosynaptic or associative LTD. 7. Recurrent excitatory synapses between CA3 cells display associative potentiation and depression. The sign of the change in synaptic strength is a function of the relative timing of pre- and postsynaptic action potentials.

An introductory course in computation molecular biology: rationale, history, observations, and course description

A course called "Molecular Biology Computer Techniques" was implemented in 1987 and has been evolving ever since. Currently the semester-long three credit course consists of thirty hours of lecture (three hours/week for the first ten weeks of the semester) and a minimum of 45 hours of laboratory instruction (three hours/week). The lectures survey both bioinformatics and structure based methods. The laboratory has two tracks, one that can be described loosely as "sequence analysis" and the other as "molecular modelling." Most students choose one of the two laboratory tracks, although a small number have done both, either simultaneously or in successive years. For each student, the goal of the course is the completion of a student-initiated research project. The culmination of the course is the presentation of the completed projects at a "Poster Session Final." During this final, which is conducted like a poster session at a typical biological science meeting, students are examined, not only by the instructors in the course, but also by a diverse cross-section of the university community at large, including non-scientists (who are specially invited to attend). Questioning by non-scientists provides opportunity for the students to improve their communication skills with the lay public. In this manuscript we discuss our views regarding the rationale for the development of formal courses in computational molecular biology, relate our experiences in the development of our course, and describe the course as it stood the last time it was taught, which was in the Fall of 1994.

Summary oral reflective analysis: a method for interview data analysis in feminist qualitative research

This article explores an innovative approach to qualitative data analysis called Summary Oral Reflective Analysis (SORA). The method preserves the richness and contextuality of in-depth interview data within a broader feminist philosophical perspective. This multidisciplinary approach was developed in two individual research programs within a cooperative, collaborative arrangement. It represents a creative response to perceived deficiencies in the pragmatics of qualitative data analysis where the maintenance of data contextuality is critical.

Ca2+ or Sr2+ partially rescues synaptic transmission in hippocampal cultures treated with botulinum toxin A and C, but not tetanus toxin

Botulinum (BoNT/A-G) and tetanus toxins (TeNT) are zinc endopeptidases that cleave proteins associated with presynaptic terminals (SNAP-25, syntaxin, or VAMP/synaptobrevin) and block neurotransmitter release. Treatment of hippocampal slice cultures with BoNT/A, BoNT/C, BoNT/E, or TeNT prevented the occurrence of spontaneous or miniature EPSCs (sEPSCs or mEPSCs) as well as the [Ca2+]o-independent increase in their frequency induced by phorbol ester, 0.5 nM alpha-latrotoxin, or sucrose. [Ca2+]o-independent and -dependent release thus requires that the target proteins of clostridial neurotoxins be uncleaved. In contrast, significant increases in mEPSC frequency were produced in BoNT-treated, but not TeNT-treated, cultures by application of the Ca2+ ionophore ionomycin in the presence of 10 mM [Ca2+]o. The frequency of sEPSCs was increased in BoNT-treated, but not TeNT-treated, cultures by increasing [Ca2+]o from 2.8 to 5-10 mM or by applying 5 mM Sr2+. Large Ca2+ and Sr2+ influxes thus can rescue release after BoNT treatment, albeit less than in control cultures. The nature of the toxin-induced modification of Ca2+-dependent release was assessed by recordings from monosynaptically coupled CA3 cell pairs. The paired-pulse ratio of unitary EPSCs evoked by two presynaptic action potentials in close succession was 0.5 in control cultures, but it was 1.4 and 1.2 in BoNT/A- or BoNT/C-treated cultures when recorded in 10 mM [Ca2+]o. Log-log plots of unitary EPSC amplitude versus [Ca2+]o were shifted toward higher [Ca2+]o in BoNT/A- or BoNT/C-treated cultures, but their slope was unchanged and the maximal EPSC amplitudes were reduced. We conclude that BoNTs reduce the Ca2+ sensitivity of the exocytotic machinery and the number of quanta released.

Organotypic slice cultures: a technique has come of age

Slices of CNS tissue prepared from young rodents can be maintained in culture for many weeks to months. The basic requirements are simple: a stable substratum, culture medium, sufficient oxygenation and incubation at a temperature of about 36 degrees C. Under these conditions, nerve cells continue to differentiate and to develop a tissue organization that closely resembles that observed in situ. Several alternative culturing methods have been developed recently. Slices maintained in stationary culture with the interface method are ideally suited for questions requiring a three-dimensional structure, whereas slices cultured in roller-tubes remain the method of choice for experiments that require optimal optical conditions. In this report, three typical experiments are discussed that illustrate the potential of the slice-culture technique. The first example indicates that, due to their high neuronal connectivity, slice cultures provide a very useful tool for studying the properties of synaptic transmission between monosynaptically coupled cell pairs. The other two studies show how long-term application of substances to slice cultures can be used to examine the consequences of epileptic discharges in vitro, as well as the effects of slowly acting clostridial neurotoxins on synaptic transmission.

Action-potential propagation gated by an axonal I(A)-like K+ conductance in hippocampus

Integration of membrane-potential changes is traditionally reserved for neuronal somatodendritic compartments. Axons are typically considered to transmit reliably the result of this integration, the action potential, to nerve terminals. By recording from pairs of pyramidal cells in hippocampal slice cultures, we show here that the propagation of action potentials to nerve terminals is impaired if presynaptic action potentials are preceded by brief or tonic hyperpolarization. Action-potential propagation fails only when the presynaptic action potential is triggered within the first 15-20ms of a depolarizing step from hyperpolarized potentials; action-potential propagation failures are blocked when presynaptic cells are impaled with electrodes containing 4-aminopyridine, indicating that a fast-inactivating, A-type K+ conductance is involved. Propagation failed between some, but not all, of the postsynaptic cells contacted by a single presynaptic cell, suggesting that the presynaptic action potentials failed at axonal branch points. We conclude that the physiological activation of an I(A)-like potassium conductance can locally block propagation of presynaptic action potentials in axons of the central nervous system. Thus axons do not always behave as simple electrical cables: their capacity to transmit action potentials is determined by a time-dependent integration of recent membrane-potential changes.

Lesion-induced axonal sprouting and hyperexcitability in the hippocampus in vitro: implications for the genesis of posttraumatic epilepsy

The delayed development of recurring seizures is a common consequence of traumatic head injury; the cause of such epilepsy is unknown. We demonstrate here that transection of the mature axons of CA3 pyramidal cells in hippocampal slice cultures leads to the formation by CA3 pyramidal cells of new axon collaterals that are immunoreactive with the growth-associated protein GAP-43. Individual CA3 cell axons had an elevated number of presynaptic boutons 14 days after the lesion, and dual intracellular recordings revealed an increased probability that any two CA3 pyramidal cells were connected by an excitatory synapse. Lesioned cultures were hyperexcitable and synaptic responses often displayed unusual prolonged polysynaptic components. We thus demonstrate that recurrent axon collaterals are newly sprouted by pyramidal cells as a consequence of axonal injury and suggest that this underlies the development of posttraumatic epilepsy.

Plasma beta-endorphin, adrenocorticotropin hormone, and cortisol in autism

Plasma levels of the hypothalamo-pituitary-adrenal axis hormones beta-endorphin (BE), adrenocorticotropin hormone (ACTH), and cortisol were measured in autistic (N = 48), mentally retarded/cognitively impaired (MR/CI, N = 16), and normal control (N = 26) individuals. Comparison of log transformed data from the three groups revealed that levels of BE and ACTH were significantly higher (p < .05) in the autistic individuals than in normal controls. The higher means in the autistic group were due to significantly higher plasma levels of BE and ACTH, indices of acute stress response, in the more severely affected individuals. The data support the idea that individuals with severe autism have a heightened response to acute stressors rather than chronic hyperarousal or elevated basal stress response system functioning.

Bidirectional associative plasticity of unitary CA3-CA1 EPSPs in the rat hippocampus in vitro

Associative long-term potentiation (LTP) and depression of compound and unitary CA3-CA excitatory postsynaptic potentials (EPSPs) were investigated in rat hippocampal slice cultures. The induction of LTP with synchronous pairing of synaptic activation and postsynaptic depolarization resulted in an increase in the amplitude of EPSPs to the same absolute level, regardless of whether the input was naive or had been previously depressed by asynchronous pairing of pre- and postsynaptic activity. Saturated LTP of compound and unitary EPSPs was reversed by asynchronous pairing and could be reinduced by synchronous pairing. The likelihood that an action potential in a presynaptic CA3 cell failed to trigger an unitary EPSP in a postsynaptic CA1 cell decreased after induction of associative potentiation and increased after induction of associative depotentiation. These changes in the rate of transmission failures were accompanied by large changes in the amplitude of nonfailure EPSPs. We conclude that the same CA3-CA1 synapses can alternatively undergo associative potentiation and depression, perhaps through opposite changes in a single expression mechanism.

Properties of spontaneous miniature GABAA receptor mediated synaptic currents in area CA3 of rat hippocampal slice cultures

Miniature, gamma-aminobutyric acid A receptor mediated inhibitory postsynaptic currents (mIPSCs) were recorded from CA3 pyramidal cells in hippocampal slice cultures using whole-cell techniques in the presence of tetrodotoxin. The kinetics and amplitudes of the mIPSCs were analyzed with the aim of determining whether subclasses of events arising from distinct populations of presynaptic interneurons could be distinguished. Histograms of mIPSC amplitude, rise time constant, and decay time constant were all positively skewed, but discrete subsets of events could not be distinguished. The positive skew did not appear to result from electrotonic filtering of distal synaptic currents because there was no correlation among mIPSC amplitudes and the kinetic parameters. Analysis of the intervals between mIPSCs indicated that each event occurred independently. The analysis of spontaneous mIPSCs does not provide evidence of the innervation of pyramidal cells by heterogeneous interneurons.

Either N- or P-type calcium channels mediate GABA release at distinct hippocampal inhibitory synapses

Transmitter release at most central synapses depends on multiple types of calcium channels. Identification of the channels mediating GABA release in hippocampus is complicated by the heterogeneity of interneurons. Unitary IPSPs were recorded from pairs of inhibitory and pyramidal cells in hippocampal slice cultures. The N-type channel antagonist omega-conotoxin MVIIA abolished IPSPs generated by interneurons in st. radiatum, whereas the P/Q-type antagonist omega-agatoxin IVA had no effect. In contrast, omega-agatoxin IVA abolished IPSPs generated by st. lucidum and st. oriens interneurons, but omega-conotoxin MVIIA had no effect. After unitary IPSPs were blocked by toxin, transmission could not be restored by increasing presynaptic calcium entry. The axons of the two types of interneurons terminated within distinct strata of area CA3. Thus, GABA release onto pyramidal cells, unlike glutamate release, is mediated entirely by either N- or P-type calcium channels, depending on the presynaptic cell and the postsynaptic location of the synapse.

Calcium-independent actions of alpha-latrotoxin on spontaneous and evoked synaptic transmission in the hippocampus

1. The black widow spider venom component, alpha-latrotoxin (alpha-LTx) (< 0.5 nM), increased the frequency of miniature excitatory postsynaptic currents (mEPSCs) in hippocampal CA3 pyramidal cells 14-fold, without changing their amplitude. 2. This action of alpha-LTx was not affected by application of Ca(2+)-free/ethylene glycol-bis(b-aminoethyl ether)-N,N,N',N'-tetraacetic acid-containing saline, 100 microM Cd2+, or 50 microM Gd3+. The increase in mEPSC frequency was thus not due to an influx of Ca2+ into the axon terminal via voltage-dependent Ca2+ channels or alpha-LTx-induced pores. 3. alpha-LTx did not increase spontaneous release when synaptic transmission had been impaired by botulinum toxin/F. 4. alpha-LTx reduced the amplitude of EPSCs, elicited with stimulation of mossy fibers, without affecting paired-pulse facilitation. 5. The Ca2+ ionophore ionomycin (2-2.5 microM) also enhanced the frequency of mEPSCs, but unlike alpha-LTx, potentiated evoked EPSCs and reduced paired-pulse facilitation. Application of N-methyl-D-aspartate elicited a high frequency of Ca(2+)-dependent, tetrodotoxin-sensitive spontaneous EPSCs, but did not affect evoked EPSC amplitude. Agents that stimulate vesicular release by increasing presynaptic Ca2+ influx thus do not mimic the alpha-LTx-induced depression of evoked EPSCs. 6. We conclude that entry of Ca2+ into presynaptic axon terminals is not responsible for the effects of low concentrations of alpha-LTx on either spontaneous or evoked transmitter release in the hippocampus. 7. Potential presynaptic mechanisms that could mediate the opposing actions of alpha-LTx on spontaneous and evoked transmitter release in the hippocampus (i.e., alpha-LTx-induced ionic pores, depletion of synaptic vesicles, actions on exocytotic proteins) are discussed.

Cooperative interactions in the induction of long-term potentiation and depression of synaptic excitation between hippocampal CA3-CA1 cell pairs in vitro

The requirement for cooperative interactions between multiple synaptic inputs in the induction of long-term potentiation (LTP) and long-term depression (LTD) has been tested at Schaffer collateral synapses with paired recordings from monosynaptically coupled CA3-CA1 cell pairs in rat hippocampal slice cultures. Tetanization of single presynaptic neurons at 50 Hz (repeated 5-7 times for 300-500 ms each) induced only a transient potentiation (< 3 min) of excitatory postsynaptic potentials (EPSPs). Persistent potentiation (> 15 min) was induced only when single presynaptic action potentials were synchronously paired with directly induced postsynaptic depolarizing pulses (repeated 50-100 times). Tetanus-induced potentiation of extracellularly evoked EPSPs lasting > 4 min could only be obtained if the EPSP was > 4 mV. Because unitary EPSP amplitudes average approximately 1 mV, we conclude that high-frequency discharge must occur synchronously] in 4-5 CA3 cells for LTP to be induced in a common postsynaptic CA1 cell. Asynchronous pairing of presynaptic action potentials with postsynaptic depolarizing current pulses (preceding each EPSP by 800 ms) depressed both naive and previously potentiated unitary EPSPs. Likewise, homosynaptic LTD of unitary EPSPs was induced when the presynaptic cell was tetanized at 3 Hz for 3 min, regardless of their amplitude (0.3-3.2 mV). Homosynaptic LTD of extracellularly evoked Schaffer collateral EPSPs < 4 mV could be induced if no inhibitory postsynaptic potential was apparent, but was prevented by eliciting a large inhibitory postsynaptic potential or by injection of hyperpolarizing current in the postsynaptic cell. We conclude that cooperative interactions among multiple excitatory inputs are not required for induction of homosynaptic LTD of unitary EPSPs.

Mechanisms underlying the neuropathological consequences of epileptic activity in the rat hippocampus in vitro

Blockage of gamma-aminobutyric acid (GABA)ergic synaptic transmission in mature hippocampal slice cultures for a period of 3 days with convulsants was shown previously to induce chronic epileptiform activity and to mimic many of the degenerative changes observed in the hippocampi of epileptic humans. The cellular mechanisms underlying the induction of this degeneration were examined in the present study by comparing the effects of GABA blockers with the effects produced by the K+ channel blocker tetraethylammonium (2 mM). Both types of convulsant caused a comparable decrease in the number of Nissl-stained pyramidal cells in areas CA1 and CA3. No significant cell loss was induced by tetraethylammonium when epileptiform discharge was reduced by simultaneous exposure of cultures to tetrodotoxin (0.5 microM) or to the anticonvulsants pentobarbital (50 microM) or tiagabine (50 microM). We conclude that this degeneration was mediated by convulsant-induced epileptiform discharge itself. The hypothesis that N-methyl-d-aspartate (NMDA) receptor-mediated excitotoxicity underlies cell death in this model was tested by applying convulsants together with specific antagonists of glutamate receptors. Whereas coapplication of antagonists of both non-NMDA and NMDA receptors strongly reduced the degeneration induced by the convulsants, application of either class of antagonist alone did not. Application of exogenous NMDA produced potent cell death, and this degeneration was blocked by the NMDA receptor antagonist methyl-10,11-dihydro-5-H-dibenzocyclohepten-5,10-imine (MK-801). Convulsants also induced a loss of dendritic spines that could be partially prevented by NMDA or non-NMDA receptor antagonists. We conclude that NMDA receptor activation is not solely responsible for the neuronal pathology resulting as a consequence of epileptiform discharge.

Functional characterization and modulation of feedback inhibitory circuits in area CA3 of rat hippocampal slice cultures

Feedback inhibitory circuits were characterized electrophysiologically in the CA3 region of organotypic rat hippocampal cultures. Pyramidal cells were impaled with sharp microelectrodes and brief depolarizing current pulses were injected intracellularly to elicit single action potentials. An inhibitory postsynaptic potential (IPSP) was observed at fixed latency after the action potential in 27% of impaled cells (n = 131). These IPSPs were fully blocked by bicuculline, indicating that they were mediated solely by gamma-aminobutyric acid type A (GABAA) receptors. They were also blocked by 6-cyano-7-nitro-quinoxaline-2, 3-dione but not D-2-amino-5-phosphonovalerate, indicating that non-N-methyl-D-aspartate receptors were necessary and sufficient for activating interposed GABAergic interneurons. Adenosine (0.1-5 microM) increased the percentage of action potentials that were not followed by IPSPs by reducing the probability of glutamatergic activation of the interneurons. In 18 of 21 experiments adenosine also decreased the mean amplitude of successfully elicited IPSPs, indicating that more than one interneuron participated in the feedback inhibition of those pyramidal cells. In three experiments the non-failure IPSP amplitude was not affected by adenosine, suggesting that only one interneuron participated. Repetitive stimulation at 2-4 Hz decreased the amplitude of non-failure feedback IPSPs and usually increased the number of failures of transmission. These effects were transient and insensitive to the GABAB antagonist CGP 35348. We conclude that both the excitation of interneurons and the release of GABA from interneurons are modulated by repetitive stimulation.

Presynaptic inhibition of calcium-dependent and -independent release elicited with ionomycin, gadolinium, and alpha-latrotoxin in the hippocampus

1. Presynaptic inhibition of synaptic transmission in the hippocampus was investigated by comparing the effects of several agonists on miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs). 2. The Ca2+ ionophore ionomycin increased the frequency of mEPSCs and mIPSCs but did not affect their amplitude. Ionomycin-induced release required extracellular Ca2+ and was prevented by pretreatment with botulinum neurotoxin serotype F, like evoked synaptic transmission. Unlike evoked transmission, however, this increase did not involve activation of voltage-dependent Ca2+ channels because it was insensitive to Cd2+. 3. Both the lanthanide gadolinium and alpha-latrotoxin produced increases in the frequency of mEPSCs and mIPSCs, but their actions were independent of extracellular Ca2+. 4. Adenosine, the gamma-aminobutyric acid-B (GABAB) receptor agonist baclofen, and a mu-opioid receptor agonist strongly reduced the frequency of synaptic currents triggered by all three secretagogues. 5. We conclude that activation of these presynaptic receptors can reduce high frequencies of vesicular glutamate and GABA release by directly impairing transmitter exocytosis. Presynaptic inhibition of gadolinium- and alpha-latrotoxin-induced release indicates that this impairment occurs without changes in intraterminal Ca2+ homeostasis and when vesicle fusion is rendered Ca2+ independent, respectively. 6. The inhibition of ionomycin-induced release provides additional evidence for a direct, neurotransmitter receptor-mediated modulation of the proteins underlying vesicular docking or fusion as an important component of presynaptic inhibition of evoked synaptic transmission.

Paired-pulse facilitation and depression at unitary synapses in rat hippocampus: quantal fluctuation affects subsequent release

1. Excitatory synaptic transmission between pairs of monosynaptically coupled pyramidal cells was examined in rat hippocampal slice cultures. Action potentials were elicited in single CA3 pyramidal cells impaled with microelectrodes and unitary excitatory postsynaptic currents (EPSCs) were recorded in whole-cell voltage-clamped CA1 or CA3 cells. 2. The amplitude of successive unitary EPSCs in response to single action potentials varied. The amplitude of EPSCs was altered by adenosine or changes in the [Mg2+]/[CA2+] ratio. We conclude that single action potentials triggered the release of multiple quanta of glutamate. 3. When two action potentials were elicited in the presynaptic cell, the amplitude of the second EPSC was inversely related to the amplitude of the first. Paired-pulse facilitation (PPF) was observed when the first EPSC was small, i.e. the second EPSC was larger than the first, whereas paired-pulse depression (PPD) was observed when the first EPSC was large. 4. The number of trials displaying PPD was greater when release probability was increased, and smaller when release probability was decreased. 5. PPD was not postsynaptically mediated because it was unaffected by decreasing ionic flux with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or receptor desensitization with aniracetam. 6. PPF was maximal at an interstimulus interval of 70 ms and recovered within 500 ms. Recovery from PPD occurred within 5 s. 7. We propose that multiple release sites are formed by the axon of a CA3 pyramidal cell and a single postsynaptic CA1 or CA3 cell. PPF is observed if the first action potential fails to release transmitter at most release sites. PPD is observed if the first action potential successfully triggers release at most release sites. 8. Our observations of PPF are consistent with the residual calcium hypothesis. We conclude that PPD results from a decrease in quantal content, perhaps due to short-term depletion of readily releasable vesicles.

Multivariate analysis of factors affecting waiting time to heart transplantation

BACKGROUND

The growing clinical success of cardiac transplantation has resulted in a dramatic increase in the number of patients referred and subsequently listed for cardiac transplantation. Paradoxically, in the presence of a limited donor organ pool, such expansion has increased both the waiting time for transplantation and the number of patients dying while on the waiting list.

METHODS

We performed univariate and multivariate analyses of the waiting times of 301 patients listed for transplantation using a Cox proportional hazards model to evaluate the simultaneous effect of multiple variables on the waiting time of heart transplant candidates. Variables considered included age, sex, race, blood type, weight at listing, United Network for Organ Sharing (UNOS) status at listing, UNOS status at transplantation, and proportion of time on the waiting list as UNOS status 1.

RESULTS

The mean waiting time for patients ultimately having transplantation was 170.2 +/- 206.0 days; the median waiting time was 103.5 days. Age, sex, weight, blood type, and percent of time as UNOS status 1 all had a significant impact on waiting time in the univariate analysis. By multivariate analysis, proportion of time as UNOS status 1, lower weight at listing, and blood type AB were all highly associated as predictors of a shorter waiting time. Weight at listing represented a continuous variable whose risk ratio for a shorter waiting time correlated in such a way that the risk of a longer waiting time increased 2.3 per 22.5-kg (50-pound) increase in weight. Blood types A and B, although associated with a shorter waiting time, correlated less strongly than the other three variables.

CONCLUSIONS

Our findings from this multivariate analysis demonstrate that UNOS status, blood type, and weight were the variables that most strongly affected overall waiting time for transplantation. It is our hope to define more accurately a group of patients with both a high likelihood of a long waiting time and a prohibitive risk of death while on the waiting list, who therefore may benefit from surgical alternatives to transplantation.