Age-dependent extinction and the neutral theory of biodiversity

Red Queen (RQ) theory states that adaptation does not protect species from extinction because their competitors are continually adapting alongside them. RQ was founded on the apparent independence of extinction risk and fossil taxon age, but analytical developments have since demonstrated that age-dependent extinction is widespread, usually most intense among young species. Here, we develop ecological neutral theory as a general framework for modeling fossil species survivorship under incomplete sampling. We show that it provides an excellent fit to a high-resolution dataset of species durations for Paleozoic zooplankton and more broadly can account for age-dependent extinction seen throughout the fossil record. Unlike widely used alternative models, the neutral model has parameters with biological meaning, thereby generating testable hypotheses on changes in ancient ecosystems. The success of this approach suggests reinterpretations of mass extinctions and of scaling in eco-evolutionary systems. Intense extinction among young species does not necessarily refute RQ or require a special explanation but can instead be parsimoniously explained by neutral dynamics operating across species regardless of age.

Measurement theory and paleobiology

Measurement theory, a branch of applied mathematics, offers guiding principles for extracting meaning from empirical observations and is applicable to any science involving measurements. Measurement theory is highly relevant in paleobiology because statistical approaches assuming ratio-scaled variables are commonly used on data belonging to nominal and ordinal scale types. We provide an informal introduction to representational measurement theory and argue for its importance in robust scientific inquiry. Although measurement theory is widely applicable in paleobiology research, we use the study of disparity to illustrate measurement theoretical challenges in the quantitative study of the fossil record. Respecting the inherent properties of different measurements enables meaningful inferences about evolutionary and ecological processes from paleontological data.

Motor learning without physical practice: The effects of combined action observation and motor imagery practice on cup-stacking speed

In this study we explored training effects for combined action observation and motor imagery (AO + MI) instructions on a complex cup-stacking task, without physical practice. Using a Graeco-Latin Square design, we randomly assigned twenty-six participants into four groups. This counterbalanced the within-participant factor of practice condition (AO + MI, AO, MI, Control) across four cup-stacking tasks, which varied in their complexity. On each of the three consecutive practice days participants experienced twenty trials under each of the three mental practice conditions. On each trial, a first-person perspective video depicted bilateral cup-stacking performed by an experienced model. During AO, participants passively observed this action, responding only to occasional colour cues. For AO + MI, participants imagined performing the observed action and synchronised their concurrent MI with the display. For MI, a sequence of pictures cued imagery of each stage of the task. Analyses revealed a significant main effect of practice condition both at the 'surprise' post-test (Day 3) and at the one-week retention test. At both time points movement execution times were significantly shorter for AO + MI compared with AO, MI and the Control. Execution times were also shorter overall at the retention compared with the post-test. These results demonstrate that a complex novel motor task can be acquired without physical training. Practitioners can therefore use AO + MI practice to supplement physical practice and optimise skill learning.

Absolute abundance and preservation rate of Tyrannosaurus rex

Although much can be deduced from fossils alone, estimating abundance and preservation rates of extinct species requires data from living species. Here, we use the relationship between population density and body mass among living species combined with our substantial knowledge of Tyrannosaurus rex to calculate population variables and preservation rates for postjuvenile T. rex We estimate that its abundance at any one time was ~20,000 individuals, that it persisted for ~127,000 generations, and that the total number of T. rex that ever lived was ~2.5 billion individuals, with a fossil recovery rate of 1 per ~80 million individuals or 1 per 16,000 individuals where its fossils are most abundant. The uncertainties in these values span more than two orders of magnitude, largely because of the variance in the density-body mass relationship rather than variance in the paleobiological input variables.

Predicting responses to inhibitory synaptic input in substantia nigra pars reticulata neurons

The changes in firing probability produced by a synaptic input are usually visualized using the poststimulus time histogram (PSTH). It would be useful if postsynaptic firing patterns could be predicted from patterns of afferent synaptic activation, but attempts to predict the PSTH from synaptic potential waveforms using reasoning based on voltage trajectory and spike threshold have not been successful, especially for inhibitory inputs. We measured PSTHs for substantia nigra pars reticulata (SNr) neurons inhibited by optogenetic stimulation of striato-nigral inputs or by matching artificial inhibitory conductances applied by dynamic clamp. The PSTH was predicted by a model based on each SNr cell's phase-resetting curve (PRC). Optogenetic activation of striato-nigral input or artificial synaptic inhibition produced a PSTH consisting of an initial depression of firing followed by oscillatory increases and decreases repeating at the SNr cell's baseline firing rate. The phase resetting model produced PSTHs closely resembling the cell data, including the primary pause in firing and the oscillation. Key features of the PSTH, including the onset rate and duration of the initial inhibitory phase, and the subsequent increase in firing probability could be explained from the characteristic shape of the SNr cell's PRC. The rate of damping of the late oscillation was explained by the influence of asynchronous phase perturbations producing firing rate jitter and wander. Our results demonstrate the utility of phase-resetting models as a general method for predicting firing in spontaneously active neurons and their value in interpretation of the striato-nigral PSTH. NEW & NOTEWORTHY The coupling of patterned presynaptic input to sequences of postsynaptic firing is a Gordian knot, complicated by the multidimensionality of neuronal state and the diversity of potential initial states. Even so, it is fundamental for even the simplest understanding of network dynamics. We show that a simple phase-resetting model constructed from experimental measurements can explain and predict the sequence of spike rate changes following synaptic inhibition of an oscillating basal ganglia output neuron.

Long-term effects of very low-carbohydrate and high-carbohydrate weight-loss diets on psychological health in obese adults with type 2 diabetes: randomized controlled trial

BACKGROUND/OBJECTIVE

Very low-carbohydrate, high-fat (LC) diets are used for type 2 diabetes (T2DM) management, but their effects on psychological health remain largely unknown. This study examined the long-term effects of an LC diet on psychological health.

METHODS

One hundred and fifteen obese adults [age: 58.5 ± 7.1 years; body mass index: 34.6 ± 4.3 kg m(-2) ; HbA1c : 7.3 ± 1.1%] with T2DM were randomized to consume either an energy-restricted (~6 to 7 MJ), planned isocaloric LC or high-carbohydrate, low-fat (HC) diet, combined with a supervised exercise programme (3 days week(-1) ) for 1 year. Body weight, psychological mood state and well-being [Profile of Mood States (POMS), Beck Depression Inventory (BDI) and Spielberger State Anxiety Inventory (SAI)] and diabetes-specific emotional distress [Problem Areas in Diabetes (PAID) Questionnaire] and quality of life [QoL Diabetes-39 (D-39)] were assessed.

RESULTS

Overall weight loss was 9.5 ± 0.5 kg (mean ± SE), with no difference between groups (P = 0.91 time × diet). Significant improvements occurred in BDI, POMS (total mood disturbance and the six subscales of anger-hostility, confusion-bewilderment, depression-dejection, fatigue-inertia, vigour-activity and tension-anxiety), PAID (total score) and the D-39 dimensions of diabetes control, anxiety and worry, sexual functioning and energy and mobility, P < 0.05 time. SAI and the D-39 dimension of social burden remained unchanged (P ≥ 0.08 time). Diet composition had no effect on the responses for the outcomes assessed (P ≥ 0.22 time × diet).

CONCLUSION

In obese adults with T2DM, both diets achieved substantial weight loss and comparable improvements in QoL, mood state and affect. These results suggest that either an LC or HC diet within a lifestyle modification programme that includes exercise training improves psychological well-being.

The ionic mechanism of membrane potential oscillations and membrane resonance in striatal LTS interneurons

Striatal low-threshold spiking (LTS) interneurons spontaneously transition to a depolarized, oscillating state similar to that seen after sodium channels are blocked. In the depolarized state, whether spontaneous or induced by sodium channel blockade, the neurons express a 3- to 7-Hz oscillation and membrane impedance resonance in the same frequency range. The membrane potential oscillation and membrane resonance are expressed in the same voltage range (greater than -40 mV). We identified and recorded from LTS interneurons in striatal slices from a mouse that expressed green fluorescent protein under the control of the neuropeptide Y promoter. The membrane potential oscillation depended on voltage-gated calcium channels. Antagonism of L-type calcium currents (Ca_V1) reduced the amplitude of the oscillation, whereas blockade of N-type calcium currents (Ca_V2.2) reduced the frequency. Both calcium sources activate a calcium-activated chloride current (CaCC), the blockade of which abolished the oscillation. The blocking of any of these three channels abolished the membrane resonance. Immunohistochemical staining indicated anoctamin 2 (ANO2), and not ANO1, as the CaCC source. Biophysical modeling showed that Ca_V1, Ca_V2.2, and ANO2 are sufficient to generate a membrane potential oscillation and membrane resonance, similar to that in LTS interneurons. LTS interneurons exhibit a membrane potential oscillation and membrane resonance that are both generated by Ca_V1 and Ca_V2.2 activating ANO2. They can spontaneously enter a state in which the membrane potential oscillation dominates the physiological properties of the neuron.

The relationship between sun protection policies and practices in schools with primary-age students: the role of school demographics, policy comprehensiveness and SunSmart membership

Schools can implement evidence-based sun protection policies that guide practices to help protect children from harmful sun exposure. This national study assessed the relationship between the existence and comprehensiveness of written policies and the comprehensiveness of sun protection practices. The impact of school demographics on the strength of the relationship was also examined, as was the possibility that 'SunSmart' membership would have an additional impact on practices, beyond having any formal policy. In 2011-12, staff members of 1573 schools catering to primary-age students completed a self-administered survey about sun protection policies and practices (response rate of 57%). Results showed that schools with a written policy had more comprehensive practices than schools without a written policy. The relationship between having a written policy and sun protection practices was stronger for remote schools compared with metropolitan and regional schools, and for schools catering to both primary and secondary students compared with primary students only. In addition, policy comprehensiveness was associated with practice comprehensiveness, and SunSmart membership was indirectly related to practice comprehensiveness via policy comprehensiveness. These results indicate that written policies relate to practice comprehensiveness, but the strength of the association can vary according to the characteristics of the organization.

Active decorrelation in the basal ganglia

The cytoarchitecturally-homogeneous appearance of the globus pallidus, subthalamic nucleus and substantia nigra has long been said to imply a high degree of afferent convergence and sharing of inputs by nearby neurons. Moreover, axon collaterals of neurons in the external segment of the globus pallidus and the substantia nigra pars reticulata arborize locally and make inhibitory synapses on other cells of the same type. These features suggest that the connectivity of the basal ganglia may impose spike-time correlations among the cells, and it has been puzzling that experimental studies have failed to demonstrate such correlations. One possible solution arises from studies of firing patterns in basal ganglia cells, which reveal that they are nearly all pacemaker cells. Their high rate of firing does not depend on synaptic excitation, but they fire irregularly because a dense barrage of synaptic inputs normally perturbs the timing of their autonomous activity. Theoretical and computational studies show that the responses of repetitively-firing neurons to shared input or mutual synaptic coupling often defy classical intuitions about temporal synaptic integration. The patterns of spike-timing among such neurons depend on the ionic mechanism of pacemaking, the level of background uncorrelated cellular and synaptic noise, and the firing rates of the neurons, as well as the properties of their synaptic connections. Application of these concepts to the basal ganglia circuitry suggests that the connectivity and physiology of these nuclei may be configured to prevent the establishment of permanent spike-timing relationships between neurons. The development of highly synchronous oscillatory patterns of activity in Parkinson's disease may result from the loss of pacemaking by some basal ganglia neurons, and accompanying breakdown of the mechanisms responsible for active decorrelation.

Detection of bursts and pauses in spike trains

Midbrain dopaminergic neurons in vivo exhibit a wide range of firing patterns. They normally fire constantly at a low rate, and speed up, firing a phasic burst when reward exceeds prediction, or pause when an expected reward does not occur. Therefore, the detection of bursts and pauses from spike train data is a critical problem when studying the role of phasic dopamine (DA) in reward related learning, and other DA dependent behaviors. However, few statistical methods have been developed that can identify bursts and pauses simultaneously. We propose a new statistical method, the Robust Gaussian Surprise (RGS) method, which performs an exhaustive search of bursts and pauses in spike trains simultaneously. We found that the RGS method is adaptable to various patterns of spike trains recorded in vivo, and is not influenced by baseline firing rate, making it applicable to all in vivo spike trains where baseline firing rates vary over time. We compare the performance of the RGS method to other methods of detecting bursts, such as the Poisson Surprise (PS), Rank Surprise (RS), and Template methods. Analysis of data using the RGS method reveals potential mechanisms underlying how bursts and pauses are controlled in DA neurons.

Biophysical properties of salmonid alphaviruses: influence of temperature and pH on virus survival

A series of laboratory studies were undertaken to investigate the survival of salmonid alphaviruses (SAV) under a range of conditions relevant to waste disposal, persistence and spread in the field, and to laboratory studies and testing. SAV was found to be rapidly inactivated in the presence of high levels of organic matter at 60 degrees C at pH 7.2 and at pH 4 and pH 12 at 4 degrees C, suggesting that composting, ensiling and alkaline hydrolysis would all be effective at inactivating virus in fish waste. Testing was conducted under sterile conditions at 4, 10, 15 and 20 degrees C in sea water, half-strength sea water and fresh (hard) water, both in the absence and the presence of added organic matter. Virus survival was shown to be inversely related to temperature, and to be reduced by the presence of organic matter. Calculated half lives (t(1/2)) under these conditions ranged from 61.0 to 1.5 days. Testing in non-sterile sea water resulted in reduced t(1/2) values. The half life of SAV in serum was also found to be inversely related to temperature, emphasizing the need for rapid shipment of samples at 4 degrees C to laboratories for virus isolation studies.

Susceptibility of salmonid alphavirus to a range of chemical disinfectants

A range of commercially available disinfectants were tested for efficacy against salmonid alphavirus under a range of different conditions including variations in concentration, temperature, contact time, water type and presence or absence of organic matter. Testing was based on the protocol defined in the draft European Standard prEN 14675, for which the effective standard is a 4 log(10) reduction in viral titre. All disinfectants were found to be effective under at least some of the conditions tested. However, the presence of organic matter in particular was shown to be detrimental in some cases, either through rendering some disinfectants ineffective, or by production of a visible inhomogeneity.

The lactose repressor system: paradigms for regulation, allosteric behavior and protein folding

In 1961, Jacob and Monod proposed the operon model for gene regulation based on metabolism of lactose in Escherichia coli. This proposal was followed by an explication of allosteric behavior by Monod and colleagues. The operon model rationally depicted how genetic mechanisms can control metabolic events in response to environmental stimuli via coordinated transcription of a set of genes with related function (e.g. metabolism of lactose). The allosteric response found in the lactose repressor and many other proteins has been extended to a variety of cellular signaling pathways in all organisms. These two models have shaped our view of modern molecular biology and captivated the attention of a surprisingly broad range of scientists. More recently, the lactose repressor monomer was used as a model system for experimental and theoretical explorations of protein folding mechanisms. Thus, the lac system continues to advance our molecular understanding of genetic control and the relationship between sequence, structure and function.

Vanishing white matter disease in a child presenting with ataxia

Vanishing white matter disease is a recently described leukoencephalopathy that is characterized by chronic and episodic neurological deterioration. These episodes often follow periods of fever or minor head trauma. It frequently presents in childhood with problems of ataxia and tremor. Five genes have been identified for the disease, EIF2B1-5, which encode the five subunits of translation initiation factor eIF2B. Mutations in each of the genes may independently cause the disease. The defect in eIF2B results in abnormalities in translation and its regulation, leading to abnormalities in protein synthesis and its regulation. Magnetic resonance imaging of the brain reveals extensive cerebral white matter abnormalities with evidence of white matter rarefaction and cystic degeneration, which has been confirmed pathologically. We report the first confirmed Australasian patient.

Dendritic synchrony and transient dynamics in a coupled oscillator model of the dopaminergic neuron

Transient increases in spontaneous firing rate of mesencephalic dopaminergic neurons have been suggested to act as a reward prediction error signal. A mechanism previously proposed involves subthreshold calcium-dependent oscillations in all parts of the neuron. In that mechanism, the natural frequency of oscillation varies with diameter of cell processes, so there is a wide variation of natural frequencies on the cell, but strong voltage coupling enforces a single frequency of oscillation under resting conditions. In previous work, mathematical analysis of a simpler system of oscillators showed that the chain of oscillators could produce transient dynamics in which the frequency of the coupled system increased temporarily, as seen in a biophysical model of the dopaminergic neuron. The transient dynamics was shown to be consequence of a slow drift along an invariant subset of phase space, with rate of drift given by a Lyapunov function. In this paper, we show that the same mathematical structure exists for the full biophysical model, giving physiological meaning to the slow drift and the Lyapunov function, which is shown to describe differences in intracellular calcium concentration in different parts of the cell. The duration of transients was long, being comparable to the time constant of calcium disposition. These results indicate that brief changes in input to the dopaminergic neuron can produce long lasting firing rate transients whose form is determined by intrinsic cell properties.

Five year review of the Rotaglide total knee arthroplasty

In this study we present the outcome for patients with the Rotaglide mobile meniscal knee prosthesis implanted for osteoarthritis. All patients reviewed had this prosthesis implanted as a primary total knee Arthroplasty in Crosshouse Hospital. The minimum follow-up period was 5 years (range 5-8.2). Patients were assessed clinically by the junior author (C.W.) and results were standardised using the Hospital for Specialist Surgery (HSS) knee score. Standard radiographs were taken in antero-posterior and lateral planes to assess for loosening using the Knee Society roentgenographic system. Case notes were then examined for evidence of peri and post-operative problems. Sixty-seven patients (71 knees) were reviewed. Ninety-four percent of patients had an excellent clinical outcome with HSS scores of 85 or more. Two knees were revised, one for meniscal fracture and one for meniscal dislocation. Both of these failures were early in our series and in a total of 312 knees to date there have been no other meniscal failures. No knees were revised for aseptic loosening and there have been no deep infections. We feel this prosthesis offers a safe and effective treatment for osteoarthritis with a good clinical outcome at 5 years with a low level of complications.

Physiology and morphology of intratelencephalically projecting corticostriatal-type neurons in pigeons as revealed by intracellular recording and cell filling

Much of the Wulst and dorsal ventricular ridge (DVR) in birds, which together make up the part of the avian telencephalon functionally resembling mammalian cerebral cortex, projects to the striatum. Those connections arise from neurons projecting additionally to the brainstem as well as from neurons projecting only within the telencephalon. As part of an effort to further characterize corticostriatal-type projection neurons in birds, we recorded intracellularly from neurons of the outer DVR, identified neurons projecting to the striatum by antidromic stimulation from the ipsilateral rostromedial striatum or subsequently by their axonal projection, characterized these neurons physiologically and then filled them with biocytin. As neurons in the outer DVR only project within telencephalon, neurons within it projecting to the striatum are of the intratelencephalically projecting (IT) type. Our studies suggest that: (1) the membrane potentials of avian IT-type neurons fluctuate between two preferred subthreshold values, and action potentials occur only in the 'up' state, (2) avian IT-type neurons show a time-dependent inward rectification in response to hyperpolarization and regular firing in response to constant current injection, (3) the conduction velocity of avian IT-type neurons is slow (about 0.2 m/s), (4) avian IT-type neurons possess radially disposed densely spiny dendrites but no apical dendrite, (5) avian IT-type neurons have local and distant collateral projections within the DVR, and (6) individual avian IT-type neurons give rise to an extensive terminal field within the striatum. Aside from the shape of their dendritic tree, IT-type neurons in birds closely resemble IT-type corticostriatal neurons in mammals in these various aspects, although it is presently uncertain whether this neuron type has been inherited in common by birds and mammals from stem amniotes.

Regulation of the timing and pattern of action potential generation in rat subthalamic neurons in vitro by GABA-A IPSPs

The regulation of activity in the subthalamic nucleus (STN) by GABAergic inhibition from the reciprocally connected globus pallidus (GP) plays an important role in normal movement and disorders of movement. To determine the precise manner in which GABAergic synaptic input, acting at A-type receptors, influences the firing of STN neurons, we recorded the response of STN neurons to GABA-A inhibitory postsynaptic potentials (IPSPs) that were evoked by supramaximal electrical stimulation of the internal capsule using the perforated-patch technique in slices at 37 degrees C. The mean equilibrium potential of the GABA-A IPSP (EGABA-A IPSP) was -79.4 +/- 7.0 mV. Single IPSPs disrupted the spontaneous oscillation that underlies rhythmic single-spike firing in STN neurons. As the magnitude of IPSPs increased, the effectiveness of prolonging the interspike interval was related more strongly to the phase of the oscillation at which the IPSP was evoked. Thus the largest IPSPs tended to reset the oscillatory cycle, whereas the smallest IPSPs tended to produce relatively phase-independent delays in firing. Multiple IPSPs were evoked at various frequencies and over different periods and their impact was studied on STN neurons held at different levels of polarization. Multiple IPSPs reduced and/or prevented action potential generation and/or produced sufficient hyperpolarization to activate a rebound depolarization, which generated a single spike or restored rhythmic spiking and/or generated a burst of activity. The pattern of IPSPs and the level of polarization of STN neurons were critical in determining the nature of the response. The duration of bursts varied from 20 ms to several hundred milliseconds, depending on the intrinsic rebound properties of the postsynaptic neuron. These data demonstrate that inhibitory input from the GP can produce a range of firing patterns in STN neurons, depending on the number and frequencies of IPSPs and the membrane properties and voltage of the postsynaptic neuron.

Corticostriatal combinatorics: the implications of corticostriatal axonal arborizations

The complete striatal axonal arborizations of 16 juxtacellularly stained cortical pyramidal cells were analyzed. Corticostriatal neurons were located in the medial agranular or anterior cingulate cortex of rats. All axons were of the extended type and formed synaptic contacts in both the striosomal and matrix compartments as determined by counterstaining for the mu-opiate receptor. Six axonal arborizations were from collaterals of brain stem-projecting cells and the other 10 from bilaterally projecting cells with no brain stem projections. The distribution of synaptic boutons along the axons were convolved with the average dendritic tree volume of spiny projection neurons to obtain an axonal innervation volume and innervation density map for each axon. Innervation volumes varied widely, with single axons occupying between 0.4 and 14.2% of the striatum (average = 4%). The total number of boutons formed by individual axons ranged from 25 to 2,900 (average = 879). Within the innervation volume, the density of innervation was extremely sparse but inhomogeneous. The pattern of innervation resembled matrisomes, as defined by bulk labeling and functional mapping experiments, superimposed on a low background innervation. Using this sample as representative of all corticostriatal axons, the total number of corticostriatal neurons was estimated to be 17 million, about 10 times the number of striatal projection neurons.

Utilisation of bone allograft by orthopaedic surgeons in Scotland

The use of bone allograft in orthopaedic surgery has been predicted to increase, particularly in joint revision surgery. This has led to a potential problem with supply. Questionnaires were distributed to all 146 Consultant Orthopaedic surgeons working in Scotland in 2000. They were asked to indicate their current usage of bone and tissue allograft, any problems encountered with supply and if alternatives to allograft, such as processed bone, might be used. The questions asked were very similar to those asked in a previous study in 1995 to enable comparisons to be made. Replies were received from 125 Consultants (87%) of whom 93 reported using bone allograft. Forty-one consultants (46%) predicted an increase in their requirement for bone allograft, and 23 (26%) felt they could currently use more bone if this was available. Sixty percent of surgeons would consider using processed bone as an alternative. In comparison with figures from 1995, an increasing number of surgeons are prepared to use processed bone as an alternative to fresh frozen allograft.

Plasma glutamine and ammonia concentrations in ornithine carbamoyltransferase deficiency and citrullinaemia

A retrospective review of the plasma ammonia and glutamine concentrations during the long-term management of 7 patients with ornithine carbamoyltransferase (OCT) deficiency and three with citrullinaemia is presented. The relationship between the plasma concentrations of ammonia and glutamine is not a simple linear one and there are significant differences between the two disorders. Patients with citrullinaemia tend to have higher plasma ammonia concentrations for a given plasma glutamine concentration compared to those with OCT deficiency. The possible reasons for these differences and the implications for management are discussed.

Streptococcus pneumoniae PstS production is phosphate responsive and enhanced during growth in the murine peritoneal cavity

Differential display-PCR (DDPCR) was used to identify a Streptococcus pneumoniae gene with enhanced transcription during growth in the murine peritoneal cavity. Northern dot blot analysis and comparative densitometry confirmed a 1.8-fold increase in expression of the encoded sequence following murine peritoneal culture (MPC) versus laboratory culture or control culture (CC). Sequencing and basic local alignment search tool analysis identified the DDPCR fragment as pstS, the phosphate-binding protein of a high-affinity phosphate uptake system. PCR amplification of the complete pstS gene followed by restriction analysis and sequencing suggests a high level of conservation between strains and serotypes. Quantitative immunodot blotting using antiserum to recombinant PstS (rPstS) demonstrated an approximately twofold increase in PstS production during MPC from that during CCs, a finding consistent with the low levels of phosphate observed in the peritoneum. Moreover, immunodot blot and Northern analysis demonstrated phosphate-dependent production of PstS in six of seven strains examined. These results identify pstS expression as responsive to the MPC environment and extracellular phosphate concentrations. Presently, it remains unclear if phosphate concentrations in vivo contribute to the regulation of pstS. Finally, polyclonal antiserum to rPstS did not inhibit growth of the pneumococcus in vitro, suggesting that antibodies do not block phosphate uptake; moreover, vaccination of mice with rPstS did not protect against intraperitoneal challenge as assessed by the 50% lethal dose.

Light and electron microscopic study of corticorubral synapses in adult cat: evidence for extensive synaptic remodeling during postnatal development

Spine-like dendritic protrusions (SLDPs) emanating from developing dendrites have been proposed to play an important role in early synaptogenesis. We previously analyzed synaptic termination sites on soma-dendritic membrane of newborn cats and found that corticorubral (CR) axons form synapses preferentially on SLDPs (Saito et al., 1997). In the present study, we examined CR synapses in adult cats to elucidate the maturation process of CR synapses in relation to SLDPs. Electron microscopic observation of serial thin sections of Phaseolus vulgaris-leucoagglutinin-labeled axons revealed that approximately 60% of CR terminals in adult cats formed synapses on dendritic spines. We also found that CR axons terminate on dendritic spines originating from the intermediate or distal dendrites of rubrospinal cells (more than 200 microm apart from the soma), in contrast to kittens in which CR fibers terminate on SLDPs originating from the proximal dendrites (less than 100 microm apart from the soma) of rubrospinal cells (Saito et al. [1997] J. Neurosci. 17:8792-8803). These results suggest that CR synapses undergo remarkable remodeling after initial termination on SLDP during postnatal development.

An evaluation of methods for calculating mean sediment quality guideline quotients as indicators of contamination and acute toxicity to amphipods by chemical mixtures

Mean sediment quality guideline quotients (mean SQGQs) were developed to represent the presence of chemical mixtures in sediments and are derived by normalizing a suite of chemicals to their respective numerical sediment quality guidelines (SQGs). Mean SQGQs incorporate the number of SQGs exceeded and the degree to which they are exceeded and are used for comparison with observed biological effects in the laboratory or field. The current research makes it clear, however, that the number and type of SQGs used in the derivation of these mean quotients can influence the ability of mean SQGQ values to correctly predict acute toxicity to marine amphipods in laboratory toxicity tests. To determine the optimal predictive ability of mean SQGQs, a total of 18 different chemical combinations were developed and compared. The ability of each set of mean SQGQs to correctly predict the presence and absence of acute toxicity to amphipods was determined using three independent databases (n = 605, 2753, 226). Calculated mean SQGQ values for all chemical combinations ranged from 0.002 to 100. The mean SQGQ that was most predictive of acute toxicity to amphipods is calculated as SQGQ1 = ((sigma ([cadmium]/4.21 )([copper]/270)([lead]/ 12.18)([silver]/1.77)([zinc]/ 410)([total chlordane]/6)([dieldrin]/8)([total PAHoc]/1,800)([total PCB]/400))/9). Both the incidence and magnitude of acute toxicity to amphipods increased with increasing SQGQI values. To provide better comparability between regions and national surveys, SQGQ1 is recommended to serve as the standard method for combination of chemicals and respective SQGs when calculating mean SQGQs.

Yeast artificial chromosome targeting technology: an approach for the deletion of genes in the C57BL/6 mouse

An approach is described to modify yeast artificial chromosomes (YACs) with cassettes that can be easily excised for embryonic stem (ES) cell gene targeting experiments. YAC targeting technology (YTT) uses the WIBR/MIT-820 C57BL/6-mapped YAC library derived from the C57BL/6 mouse as the starting point for Internet- or PCR-based clone isolation, although in principle any YAC system can be used. Homologous recombination is initially performed in yeast using cassettes that function in Saccharomyces cerevisiae, Escherichia coli, and ES cells, followed by cloning or conversion of the targeted locus into a plasmid. The completed targeting vector can be transfected into C57BL/6 ES cells and clones selected with G418 followed by injection into Balb/c blastocysts. YTT increases the speed of targeting vector construction and obviates the need for extensive backcrossing to the C57BL/6 background.

Suicidal ideation and help-negation: Not just hopelessness or prior help

Few distressed young people seek professional psychological help and little is known about what sources of help young people seek for different problems. In suicidal youth, the process of help-negation may exacerbate poor help-seeking. Three hundred and two undergraduate university students completed a questionnaire measuring suicidal ideation, hopelessness, prior help-seeking experience, and help-seeking intentions. Participants indicated they would seek help from different sources of help for different types of problems, but friends consistently were rated as the most likely source of help. Help-negation was suggested by higher levels of suicidal ideation being associated with lower help-seeking intentions. However, the negative suicidal ideation/help-seeking-intentions relationship was not explained by hopelessness or prior help-seeking. Help-negation appears to involve more than just negative expectations regarding the future. The discussion proposes social problem-solving orientation as one of a number of potential explanatory variables.

A SURF1 gene mutation presenting as isolated leukodystrophy

Mitochondrial respiratory chain defects are increasingly recognized in patients with leukodystrophy. We report the first case of leukodystrophy with systemic cytochrome oxidase deficiency caused by a loss of function mutation in the SURF1 gene in a 2-year-old girl presenting with failure to thrive, global neurodevelopmental regression, and lactic acidosis. Although all previously reported mutations in the SURF1 gene have been found in patients with cytochrome oxidase (COX)-deficient Leigh syndrome, the phenotype associated with SURF1 protein deficiency should be extended to include leukodystrophy.

Evaluation and use of sediment toxicity reference sites for statistical comparisons in regional assessments

Sediment reference sites were used to establish toxicity standards against which to compare results from sites investigated in San Francisco Bay (California, USA) monitoring programs. The reference sites were selected on the basis of low concentrations of anthropogenic chemicals, distance from active contaminant sources, location in representative hydrographic areas of the Bay, and physical features characteristic of depositional areas (e.g., fine grain size and medium total organic carbon [TOC]). Five field-replicated sites in San Francisco Bay were evaluated over three seasons. Samples from each site were tested with nine toxicity test protocols and were analyzed for sediment grain size and concentrations of trace metals, trace organics, ammonia, hydrogen sulfide, and TOC. The candidate sites were found to have relatively low concentrations of measured chemicals and generally exhibited low toxicity. Toxicity data from the reference sites were then used to calculate numerical tolerance limits to be used as threshold values to determine which test sites had significantly higher toxicity than reference sites. Tolerance limits are presented for four standard test protocols, including solid-phase sediment tests with the amphipods Ampelisca abdita and Eohaustorius estuarius and sea urchin Strongylocentrotus purpuratus embryo/larval development tests in pore water and at the sediment-water interface (SWI). Tolerance limits delineating the lowest 10th percentile (0.10 quantile) of the reference site data distribution were 71% of the control response for Ampelisca, 70% for Eohaustorius, 94% for sea urchin embryos in pore water, and 87% for sea urchins embryos exposed at the SWI. The tolerance limits are discussed in terms of the critical values governing their calculation and the management implications arising from their use in determining elevated toxicity relative to reference conditions.

A large-scale categorization of sites in San Francisco Bay, USA, based on the sediment quality triad, toxicity identification evaluations, and gradient studies

Sediment quality was assessed in San Francisco Bay, California, USA, using a two-tiered approach in which 111 sites were initially screened for sediment toxicity. Sites exhibiting toxicity were then resampled and analyzed for chemical contamination, recurrent toxicity, and, in some cases, benthic community impacts. Resulting data were compared with newly derived threshold values for each of the metrics in a triad-based weight-of-evidence evaluation. Sediment toxicity test results were compared with tolerance limits derived from reference site data, benthic community data were compared with threshold values for a relative benthic index based on the presence and abundance of pollution-tolerant and -sensitive taxa, and concentrations of chemicals and chemical mixtures were compared with sediment quality guideline-based thresholds. A total of 57 sites exceeded threshold values for at least one metric, and each site was categorized based on triad inferences. Nine sites were found to exhibit recurrent sediment toxicity associated with elevated contaminant concentrations, conditions that met program criteria for regulatory attention. Benthic community impacts were also observed at three of these sites, providing triad evidence of pollution-induced degradation. Multi- and univariate correlations indicated that chemical mixtures, heavy metals, chlordanes, and other organic compounds were associated with measured biological impacts in the Bay. Toxicity identification evaluations indicated that metals were responsible for pore-water toxicity to sea urchin larvae at two sites. Gradient studies indicated that the toxicity tests and benthic community metrics employed in the study predictably tracked concentrations of chemical mixtures in Bay sediments.

Sediment quality in Los Angeles Harbor, USA: a triad assessment

Sediment quality in the Los Angeles and Long Beach Harbor area of southern California, USA, was assessed from 1992 to 1997 as part of the California State Water Resources Control Board's Bay Protection and Toxic Cleanup Program and the National Oceanic and Atmospheric Administration's National Status and Trends Program. The assessment strategy relied on application of various components of the sediment quality triad, combined with bioaccumulation measures, in a weight-of-evidence approach to sediment quality investigations. Results of bulk-phase chemical measurements, solid-phase amphipod toxicity tests, pore-water toxicity tests with invertebrate embryos, benthic community analyses (presented as a relative benthic index), and bioaccumulation measures indicated that inner harbor areas of this system are polluted by high concentrations of a mixture of sediment-associated contaminants and that this pollution is highly correlated with toxicity in laboratory experiments and degradation of benthic community structure. While 29% of sediment samples from this system were toxic to amphipods (Rhepoxynius abronius or Eohaustorius estuarius), 79% were toxic to abalone embryos (Haliotis rufescens) exposed to 100% pore-water concentrations. Statistical analyses indicated that amphipod survival in laboratory toxicity tests was significantly correlated with the number of crustacean species and the total number of species measured in the benthos at these stations. Triad measures were incorporated into a decision matrix designed to classify stations based on degree of sediment pollution, toxicity, benthic community degradation, and, where applicable, tissue concentrations in laboratory-exposed bivalves and feral fish.

Statistical significance of sediment toxicity test results: threshold values derived by the detectable significance approach

A number of methods have been employed to determine the statistical significance of sediment toxicity test results. To allow consistency among comparisons, regardless of among-replicate variability, a protocol-specific approach has been used that considers protocol performance over a large number of comparisons. Ninetieth-percentile minimum significant difference (MSD) values were calculated to determine a critical threshold for statistically significant sample toxicity. Significant toxicity threshold values (as a percentage of laboratory control values) are presented for six species and nine endpoints based on data from as many as 720 stations. These threshold values are useful for interpreting sediment toxicity data from large studies and in eliminating cases where statistical significance is assigned in individual cases because among-replicate variability is small.

Genome-wide location and function of DNA binding proteins

Understanding how DNA binding proteins control global gene expression and chromosomal maintenance requires knowledge of the chromosomal locations at which these proteins function in vivo. We developed a microarray method that reveals the genome-wide location of DNA-bound proteins and used this method to monitor binding of gene-specific transcription activators in yeast. A combination of location and expression profiles was used to identify genes whose expression is directly controlled by Gal4 and Ste12 as cells respond to changes in carbon source and mating pheromone, respectively. The results identify pathways that are coordinately regulated by each of the two activators and reveal previously unknown functions for Gal4 and Ste12. Genome-wide location analysis will facilitate investigation of gene regulatory networks, gene function, and genome maintenance.

Mitochondrial DNA point mutation T9176C in Leigh syndrome

Leigh syndrome is a progressive neurodegenerative disease frequently associated with mitochondrial abnormalities. The mitochondrial DNA T9176C mutation in the adenosine triphosphatase 6 gene has recently been described as a cause of Leigh syndrome. Leukocyte DNA from 59 children with Leigh syndrome was screened for the T9176C mutation by conventional polymerase chain reaction methods. Two unrelated patients were found to be homoplasmic for this mutation in blood. Both patients had similar clinical and biochemical features. They had first presented acutely at 3 and 5 years, respectively, with ataxia and slurred speech. Magnetic resonance imaging changes were consistent with Leigh syndrome, and the cerebrospinal fluid lactate was elevated. They have both had relatively stable disease since the time of diagnosis. The mother of one of the children had presented at age 29 years with sudden onset of ataxia, headache, and blurred vision. She was heteroplasmic for the T9176C mutation. The T1976C is an important cause of Leigh syndrome especially in the subgroup of patients with more stable disease and normal respiratory chain enzyme analysis.

Marfanoid habitus, dysmorphic features, and web neck

Bilateral pneumothoraces and aortic dilatation developed in a 25-year-old white man with marfanoid habitus, dysmorphic features, web neck, and intellectual impairment. He had physical features suggestive of Shprintzen-Goldberg syndrome. We review the common characteristics of Marfan and Shprintzen-Goldberg syndromes and compare them with our case. Physicians should beware of potential cardiovascular abnormalities in patients with marfanoid habitus and dysmorphic features.

Intrinsic membrane properties underlying spontaneous tonic firing in neostriatal cholinergic interneurons

Neostriatal cholinergic interneurons produce spontaneous tonic firing in the absence of synaptic input. Perforated patch recording and whole-cell recording combined with calcium imaging were used in vitro to identify the intrinsic membrane properties underlying endogenous excitability. Spontaneous firing was driven by the combined action of a sodium current and the hyperpolarization-activated cation current (I(h)), which together ensured that there was no zero current point in the subthreshold voltage range. Blockade of sodium channels or I(h) established a stable subthreshold resting membrane potential. A tetrodotoxin-sensitive region of negative slope conductance was observed between approximately -60 mV and threshold (approximately -50 mV) and the h-current was activated at all subthreshold voltages. Calcium imaging experiments revealed that there was minimal calcium influx at subthreshold membrane potentials but that action potentials produced elevations of calcium in both the soma and dendrites. Spike-triggered calcium entry shaped the falling phase of the action potential waveform and activated calcium-dependent potassium channels. Blockade of big-conductance channels caused spike broadening. Application of apamin, which blocks small-conductance channels, abolished the slow spike afterhyperpolarization (AHP) and caused a transition to burst firing. In the absence of synaptic input, a range of tonic firing patterns are observed, suggesting that the characteristic spike sequences described for tonically active cholinergic neurons (TANs) recorded in vivo are intrinsic in origin. The pivotal role of the AHP in regulating spike patterning indicates that burst firing of TANs in vivo could arise from direct or indirect modulation of the AHP without requiring phasic synaptic input.

Phenylalanine supplementation improves the phenylalanine profile in tyrosinaemia

Tyrosinaemia types I and II are caused by enzyme deficiencies in the tyrosine catabolism pathway. Successful treatment is possible with the novel enzyme inhibitor NTBC in tyrosinaemia type I and with dietary tyrosine and phenylalanine restriction in both conditions. This is achieved with a low natural protein intake and a supplementary amino acid formula that is phenylalanine- and tyrosine-free. Patients on this regimen had been noted, periodically, to have very low plasma phenylalanine concentrations (<20 micromol/L). The tyrosine and phenylalanine profiles in six patients were measured. Five of the six patients had very low concentrations of phenylalanine during the later half of the day. The response to phenylalanine supplementation was assessed and supplementing the diet with phenylalanine 30-40 mg/kg per day resulted in normal concentrations throughout the day. Possible complications of hypophenylalaninaemia and potential preventive treatment strategies are discussed. Further studies are needed to investigate the longer-term clinical and biochemical consequences of phenylalanine supplementation.

Coupled oscillator model of the dopaminergic neuron of the substantia nigra

Calcium imaging using fura-2 and whole cell recording revealed the effective location of the oscillator mechanism on dopaminergic neurons of the substantia nigra, pars compacta, in slices from rats aged 15-20 days. As previously reported, dopaminergic neurons fired in a slow rhythmic single spiking pattern. The underlying membrane potential oscillation survived blockade of sodium currents with TTX and was enhanced by blockade of voltage-sensitive potassium currents with TEA. Calcium levels increased during the subthreshold depolarizing phase of the membrane potential oscillation and peaked at the onset of the hyperpolarizing phase as expected if the pacemaker potential were due to a low-threshold calcium current and the hyperpolarizing phase to calcium-dependent potassium current. Calcium oscillations were synchronous in the dendrites and soma and were greater in the dendrites than in the soma. Average calcium levels in the dendrites overshot steady-state levels and decayed over the course of seconds after the oscillation was resumed after having been halted by hyperpolarizing currents. Average calcium levels in the soma increased slowly, taking many cycles to achieve steady state. Voltage clamp with calcium imaging revealed the voltage dependence of the somatic calcium current without the artifacts of incomplete spatial voltage control. This showed that the calcium current had little or no inactivation and was half-maximal at -40 to -30 mV. The time constant of calcium removal was measured by the return of calcium to resting levels and depended on diameter. The calcium sensitivity of the calcium-dependent potassium current was estimated by plotting the slow tail current against calcium concentration during the decay of calcium to resting levels at -60 mV. A single compartment model of the dopaminergic neuron consisting of a noninactivating low-threshold calcium current, a calcium-dependent potassium current, and a small leak current reproduced most features of the membrane potential oscillations. The same currents much more accurately reproduced the calcium transients when distributed uniformly along a tapering cable in a multicompartment model. This model represented the dopaminergic neuron as a set of electrically coupled oscillators with different natural frequencies. Each frequency was determined by the surface area to volume ratio of the compartment. This model could account for additional features of the dopaminergic neurons seen in slices, such as slow adaptation of oscillation frequency and may produce irregular firing under different coupling conditions.

Equilibrium potential of GABA(A) current and implications for rebound burst firing in rat subthalamic neurons in vitro

Reciprocally connected glutamatergic subthalamic and GABAergic globus pallidus neurons have recently been proposed to act as a generator of low-frequency oscillatory activity in Parkinson's disease. To determine whether GABA(A) receptor-mediated synaptic potentials could theoretically generate rebound burst firing in subthalamic neurons, a feature that is central to the proposed oscillatory mechanism, we determined the equilibrium potential of GABA(A) current (E(GABA(A))) and the degree of hyperpolarization required for rebound firing using perforated-patch recording. In the majority of neurons that fired rebounds, E(GABA(A)) was equal to or more hyperpolarized than the hyperpolarization required for rebound burst firing. These data suggest that synchronous activity of pallidal inputs could underlie rhythmic bursting activity of subthalamic neurons in Parkinson's disease.

Parental preparation of children for routine physical examinations

Preparation of the child and parents/caretakers for health care events is expected to decrease a child's anxiety and uncooperative behaviors. The purpose of this study was to ascertain the methods of preparation (discussion, reading, play, other) and levels of discussion used by parents in readying their preschool and school-age children for six selected events during routine physical examinations. A phone survey was conducted to all parents of children, ages 2 to 12 years, who visited an academic nursing center or public school for a routine physical examination (n = 132). The events are "listen to heart," "look in ears," "take temperature," "feel the stomach," "look at the throat," and "give a shot." The most common method of preparation parents used was discussion that consisted largely of procedural information rather than a reciprocal dialogue with the child. Preschool children were told what the health care provider would do and what they should do during the physical examination more often than school-age children.

Mechanisms underlying spontaneous oscillation and rhythmic firing in rat subthalamic neurons

Subthalamic neurons drive basal ganglia output neurons in resting animals and relay cortical and thalamic activity to the same output neurons during movement. The first objective of this study was to determine the mechanisms underlying the spontaneous activity of subthalamic neurons in vitro and to gain insight into their resting discharge in vivo. The second objective was to determine the response of subthalamic neurons to depolarizing current injection and how intrinsic properties may shape their response to cortical and thalamic inputs during movement. Cell-attached and whole-cell recordings were made from subthalamic neurons in brain slices prepared from 3- to 4-week-old rats. The slow, rhythmic discharge of subthalamic neurons was resistant to blockade of excitatory synaptic transmission indicating that intrinsic currents underlie their spontaneous discharge. A persistent sodium current was the source of current during the depolarizing phase of the oscillation. A powerful afterhyperpolarization following each action potential was sufficient to terminate the depolarization. A long duration component of the spike afterhyperpolarization determined the period of the oscillation and was generated by an apamin-sensitive calcium-activated potassium current. Calcium entry responsible for that current was associated with action potentials. Subthalamic neurons exhibited a sigmoidal frequency-current relationship with the steeper portion starting at approximately 30-40 Hz. This property makes subthalamic neurons more sensitive to input at high firing rates associated with movement than at low rates associated with rest. We propose that the subthreshold persistent sodium current overcomes calcium activated potassium current which accumulates during high frequency firing and underlies the enhanced sensitivity to current >30 Hz.

Spontaneous activity of neostriatal cholinergic interneurons in vitro

Neostriatal cholinergic interneurons fire irregularly but tonically in vivo. The summation of relatively few depolarizing potentials and their temporal sequence are thought to underlie spike triggering and the irregularity of action potential timing, respectively. In these experiments we used whole-cell, cell-attached, and extracellular recording techniques to investigate the role of spontaneous synaptic inputs in the generation and patterning of action potentials in cholinergic interneurons in vitro. Cholinergic cells were spontaneously active in vitro at 25 +/- 1 degrees C during whole-cell recording from 2 to 3 week postnatal slices and at 35 +/- 2 degrees C during cell-attached and extracellular recording from 3 to 4 week postnatal slices. A range of firing frequencies and patterns was observed including regular, irregular, and burst firing. Blockade of AMPA and NMDA receptors altered neither the firing rate nor the pattern, and accordingly, voltage-clamp data revealed a very low incidence of spontaneous EPSCs. GABAA receptor antagonists were also ineffective in altering the spiking frequency or pattern owing to minimal inhibitory input in vitro. Functional excitatory and inhibitory inputs to cholinergic cells were disclosed after application of 4-aminopyridine (100 microM), indicating that these synapses are present but not active in vitro. Blockade of D1 or D2 dopamine receptors or muscarinic receptors also failed to influence tonic activity in cholinergic cells. Together these data indicate that cholinergic interneurons are endogenously active and generate action potentials in the absence of any synaptic input. Interspike interval histograms and autocorrelograms generated from unit recordings of cholinergic cells in vitro were indistinguishable from those of tonically active neurons recorded in vivo. Irregular spiking is therefore embedded in the mechanism responsible for endogenous activity.

The rise and fall of the Aldabran giant tortoise population

At the end of the 19th century, after prolonged and extensive harvesting, indigenous giant tortoises had been eliminated from all islands in the Indian Ocean, except Aldabra atoll, where only a few survived. With greatly reduced levels of exploitation during the 20th century, the population recovered to a revised estimated total of 129,000 in 1973-1974, when the first sample census was conducted. A repeat census in 1997 revealed a highly significant reduction in numbers over the past 24 years to an estimated total of 100,000. The great majority of tortoises are still found at relatively high density in south-eastern Grande Terre, where the number of animals has declined by more than one-third. In contrast, low-density subpopulations on Malabar and Picard have almost doubled in size, but they represent less than 5% of the total population. Corroborative evidence for the crash in the Grande Terre subpopulation comes from two independent observations: a significant increase in tortoise mortality; and a significant decline in tortoise counts on long-term population monitoring transects. These population changes are attributed to natural population regulatory mechanisms, exacerbated by low rainfall years in the period 1980-1997, including two consecutive years of below average rainfall in 1995-1996 and 1996-1997.