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Molecular identification of mixed-species pollen samples has a range of applications in various fields of research. To date, such molecular identification has primarily been carried out via amplicon sequencing, but whole-genome shotgun (WGS) sequencing of pollen DNA has potential advantages, including (1) more genetic information per sample and (2) the potential for better quantitative matching. In this study, we tested the performance of WGS sequencing methodology and publicly available reference sequences in identifying species and quantifying their relative abundance in pollen mock communities. Using mock communities previously analyzed with DNA metabarcoding, we sequenced approximately 200Mbp for each sample using Illumina HiSeq and MiSeq. Taxonomic identifications were based on the Kraken k -mer identification method with reference libraries constructed from full-genome and short read archive data from the NCBI database. We found WGS to be a reliable method for taxonomic identification of pollen with near 100% identification of species in mixtures but generating higher rates of false positives (reads not identified to the correct taxon at the required taxonomic level) relative to rbcL and ITS2 amplicon sequencing. For quantification of relative species abundance, WGS data provided a stronger correlation between pollen grain proportion and sequence read proportion, but diverged more from a 1:1 relationship, likely due to the higher rate of false positives. Currently, a limitation of WGS-based pollen identification is the lack of representation of plant diversity in publicly available genome databases. As databases improve and costs drop, we expect that eventually genomics methods will become the methods of choice for species identification and quantification of mixed-species pollen samples., Competing Interests: None declared.sss, (© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

Background: Understanding the mental health consequences of child maltreatment at different life stages is important in accurately quantifying the burden of maltreatment. This study investigated the association between child maltreatment and incident mental disorders in middle and older age as well as the potential mediators and moderators., Methods: This is a retrospective cohort study of 56,082 participants from UK Biobank. Child maltreatment was recalled using the Childhood Trauma Screener. Incident mental disorders, including depressive, anxiety and affective disorders, behavioural syndromes, post-traumatic stress disorder (PTSD), schizophrenia, substance abuse, and dementia, after baseline assessment were ascertained through linkage to primary care records., Findings: There was a dose-response relationship between child maltreatment and mental disorder. Those who experienced three or more maltreatment types had the highest risk of all mental disorders (HR 1.85, 95% CI: 1.67-2.06) followed by those who experienced two (HR 1.48, 95% CI: 1.35-1.63) and then one (HR 1.26, 95% CI: 1.19-2.35). Child maltreatment was most strongly associated with PTSD (HR 1.59, 95% CI: 1.20-2.10 P=0.001). The excess risk was largely unexplained by the included mediators. The association between child maltreatment and all mental disorders were stronger among participants who binge drank (P interaction =0.003) or had few social visits (P interaction =0.003)., Interpretation: The mental health consequence of child maltreatment could last decades, even among those who had no recorded mental disorders in early adulthood. In the absence of strong mediators, prevention of child maltreatment remains the priority., Funding: Wellcome Trust Institutional Strategic Support Fund., Competing Interests: The authors declared no potential conflicts of interest., (© 2021 The Author(s).)

Task-level goals such as maintaining standing balance are achieved through coordinated muscle activity. Consistent and individualized groupings of synchronously activated muscles can be estimated from muscle recordings in terms of motor modules or muscle synergies, independent of their temporal activation. The structure of motor modules can change with motor training, neurological disorders, and rehabilitation, but the central and peripheral mechanisms underlying motor module structure remain unclear. To assess the role of peripheral somatosensory input on motor module structure, we evaluated changes in the structure of motor modules for reactive balance recovery following pyridoxine-induced large-fiber peripheral somatosensory neuropathy in previously collected data in four adult cats. Somatosensory fiber loss, quantified by postmortem histology, varied from mild to severe across cats. Reactive balance recovery was assessed using multidirectional translational support-surface perturbations over days to weeks throughout initial impairment and subsequent recovery of balance ability. Motor modules within each cat were quantified by non-negative matrix factorization and compared in structure over time. All cats exhibited changes in the structure of motor modules for reactive balance recovery after somatosensory loss, providing evidence that somatosensory inputs influence motor module structure. The impact of the somatosensory disturbance on the structure of motor modules in well-trained adult cats indicates that somatosensory mechanisms contribute to motor module structure, and therefore may contribute to some of the pathological changes in motor module structure in neurological disorders. These results further suggest that somatosensory nerves could be targeted during rehabilitation to influence pathological motor modules for rehabilitation. NEW & NOTEWORTHY Stable motor modules for reactive balance recovery in well-trained adult cats were disrupted following pyridoxine-induced peripheral somatosensory neuropathy, suggesting somatosensory inputs contribute to motor module structure. Furthermore, the motor module structure continued to change as the animals regained the ability to maintain standing balance, but the modules generally did not recover pre-pyridoxine patterns. These results suggest changes in somatosensory input and subsequent learning may contribute to changes in motor module structure in pathological conditions.

As phylogenetically controlled experimental designs become increasingly common in ecology, the need arises for a standardized statistical treatment of these datasets. Phylogenetically paired designs circumvent the need for resolved phylogenies and have been used to compare species groups, particularly in the areas of invasion biology and adaptation. Despite the widespread use of this approach, the statistical analysis of paired designs has not been critically evaluated. We propose a mixed model approach that includes random effects for pair and species. These random effects introduce a "two-layer" compound symmetry variance structure that captures both the correlations between observations on related species within a pair as well as the correlations between the repeated measurements within species. We conducted a simulation study to assess the effect of model misspecification on Type I and II error rates. We also provide an illustrative example with data containing taxonomically similar species and several outcome variables of interest. We found that a mixed model with species and pair as random effects performed better in these phylogenetically explicit simulations than two commonly used reference models (no or single random effect) by optimizing Type I error rates and power. The proposed mixed model produces acceptable Type I and II error rates despite the absence of a phylogenetic tree. This design can be generalized to a variety of datasets to analyze repeated measurements in clusters of related subjects/species.

Over the past 500 years, North America has been the site of ongoing mixing of Native Americans, European settlers, and Africans (brought largely by the trans-Atlantic slave trade), shaping the early history of what became the United States. We studied the genetic ancestry of 5,269 self-described African Americans, 8,663 Latinos, and 148,789 European Americans who are 23andMe customers and show that the legacy of these historical interactions is visible in the genetic ancestry of present-day Americans. We document pervasive mixed ancestry and asymmetrical male and female ancestry contributions in all groups studied. We show that regional ancestry differences reflect historical events, such as early Spanish colonization, waves of immigration from many regions of Europe, and forced relocation of Native Americans within the US. This study sheds light on the fine-scale differences in ancestry within and across the United States and informs our understanding of the relationship between racial and ethnic identities and genetic ancestry., (Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.)

Although cats that have been spinalized can also be trained to stand and step with full weight support, directionally appropriate long-latency responses to perturbations are impaired, suggesting that these behaviors are mediated by distinct neural mechanisms. However, it remains unclear whether these responses reflect an attenuated postural response using the appropriate muscular coordination patterns for balance or are due to fundamentally different neural mechanisms such as increased muscular cocontraction or short-latency stretch responses. Here we used muscle synergy analysis on previously collected data to identify whether there are changes in the spatial organization of muscle activity for balance within an animal after spinalization. We hypothesized that the modular organization of muscle activity for balance control is disrupted by spinal cord transection. In each of four animals, muscle synergies were extracted from postural muscle activity both before and after spinalization with nonnegative matrix factorization. Muscle synergy number was reduced after spinalization in three animals and increased in one animal. However, muscle synergy structure was greatly altered after spinalization with reduced direction tuning, suggesting little consistent organization of muscle activity. Furthermore, muscle synergy recruitment was correlated to subsequent force production in the intact but not spinalized condition. Our results demonstrate that the modular structure of sensorimotor feedback responses for balance control is severely disrupted after spinalization, suggesting that the muscle synergies for balance control are not accessible by spinal circuits alone. Moreover, we demonstrate that spinal mechanisms underlying weight support are distinct from brain stem mechanisms underlying directional balance control.

Although a few hundred single nucleotide polymorphisms (SNPs) suffice to infer close familial relationships, high density genome-wide SNP data make possible the inference of more distant relationships such as 2(nd) to 9(th) cousinships. In order to characterize the relationship between genetic similarity and degree of kinship given a timeframe of 100-300 years, we analyzed the sharing of DNA inferred to be identical by descent (IBD) in a subset of individuals from the 23andMe customer database (n = 22,757) and from the Human Genome Diversity Panel (HGDP-CEPH, n = 952). With data from 121 populations, we show that the average amount of DNA shared IBD in most ethnolinguistically-defined populations, for example Native American groups, Finns and Ashkenazi Jews, differs from continentally-defined populations by several orders of magnitude. Via extensive pedigree-based simulations, we determined bounds for predicted degrees of relationship given the amount of genomic IBD sharing in both endogamous and 'unrelated' population samples. Using these bounds as a guide, we detected tens of thousands of 2(nd) to 9(th) degree cousin pairs within a heterogenous set of 5,000 Europeans. The ubiquity of distant relatives, detected via IBD segments, in both ethnolinguistic populations and in large 'unrelated' populations samples has important implications for genetic genealogy, forensics and genotype/phenotype mapping studies.

Africa is inferred to be the continent of origin for all modern human populations, but the details of human prehistory and evolution in Africa remain largely obscure owing to the complex histories of hundreds of distinct populations. We present data for more than 580,000 SNPs for several hunter-gatherer populations: the Hadza and Sandawe of Tanzania, and the ≠Khomani Bushmen of South Africa, including speakers of the nearly extinct N|u language. We find that African hunter-gatherer populations today remain highly differentiated, encompassing major components of variation that are not found in other African populations. Hunter-gatherer populations also tend to have the lowest levels of genome-wide linkage disequilibrium among 27 African populations. We analyzed geographic patterns of linkage disequilibrium and population differentiation, as measured by F(ST), in Africa. The observed patterns are consistent with an origin of modern humans in southern Africa rather than eastern Africa, as is generally assumed. Additionally, genetic variation in African hunter-gatherer populations has been significantly affected by interaction with farmers and herders over the past 5,000 y, through both severe population bottlenecks and sex-biased migration. However, African hunter-gatherer populations continue to maintain the highest levels of genetic diversity in the world.

While the cost and speed of generating genomic data have come down dramatically in recent years, the slow pace of collecting medical data for large cohorts continues to hamper genetic research. Here we evaluate a novel online framework for obtaining large amounts of medical information from a recontactable cohort by assessing our ability to replicate genetic associations using these data. Using web-based questionnaires, we gathered self-reported data on 50 medical phenotypes from a generally unselected cohort of over 20,000 genotyped individuals. Of a list of genetic associations curated by NHGRI, we successfully replicated about 75% of the associations that we expected to (based on the number of cases in our cohort and reported odds ratios, and excluding a set of associations with contradictory published evidence). Altogether we replicated over 180 previously reported associations, including many for type 2 diabetes, prostate cancer, cholesterol levels, and multiple sclerosis. We found significant variation across categories of conditions in the percentage of expected associations that we were able to replicate, which may reflect systematic inflation of the effects in some initial reports, or differences across diseases in the likelihood of misdiagnosis or misreport. We also demonstrated that we could improve replication success by taking advantage of our recontactable cohort, offering more in-depth questions to refine self-reported diagnoses. Our data suggest that online collection of self-reported data from a recontactable cohort may be a viable method for both broad and deep phenotyping in large populations.

Despite the recent rapid growth in genome-wide data, much of human variation remains entirely unexplained. A significant challenge in the pursuit of the genetic basis for variation in common human traits is the efficient, coordinated collection of genotype and phenotype data. We have developed a novel research framework that facilitates the parallel study of a wide assortment of traits within a single cohort. The approach takes advantage of the interactivity of the Web both to gather data and to present genetic information to research participants, while taking care to correct for the population structure inherent to this study design. Here we report initial results from a participant-driven study of 22 traits. Replications of associations (in the genes OCA2, HERC2, SLC45A2, SLC24A4, IRF4, TYR, TYRP1, ASIP, and MC1R) for hair color, eye color, and freckling validate the Web-based, self-reporting paradigm. The identification of novel associations for hair morphology (rs17646946, near TCHH; rs7349332, near WNT10A; and rs1556547, near OFCC1), freckling (rs2153271, in BNC2), the ability to smell the methanethiol produced after eating asparagus (rs4481887, near OR2M7), and photic sneeze reflex (rs10427255, near ZEB2, and rs11856995, near NR2F2) illustrates the power of the approach., Competing Interests: NE, JMM, JYT, LSH, BN, SS, LA, AW, and JM are or have been employed by 23andMe and own stock options in the company. 23andMe co-president AW has provided general guidance, including guidance related to the company's research undertakings and direction. PLoS Genetics' Editor-in-Chief Gregory S. Barsh is a potential consultant to 23andMe and therefore recused himself from the editorial and peer-review process. PLoS co-founder Michael B. Eisen is a member of the 23andMe Scientific Advisory Board.

A recent genomewide screen identified 13 transposable elements that are likely to have been adaptive during or after the spread of Drosophila melanogaster out of Africa. One of these insertions, Bari-Juvenile hormone epoxy hydrolase (Bari-Jheh), was associated with the selective sweep of its flanking neutral variation and with reduction of expression of one of its neighboring genes: Jheh3. Here, we provide further evidence that Bari-Jheh insertion is adaptive. We delimit the extent of the selective sweep and show that Bari-Jheh is the only mutation linked to the sweep. Bari-Jheh also lowers the expression of its other flanking gene, Jheh2. Subtle consequences of Bari-Jheh insertion on life-history traits are consistent with the effects of reduced expression of the Jheh genes. Finally, we analyze molecular evolution of Jheh genes in both the long- and the short-term and conclude that Bari-Jheh appears to be a very rare adaptive event in the history of these genes. We discuss the implications of these findings for the detection and understanding of adaptation.

Transposable elements (TEs) constitute a substantial fraction of the genomes of many species, and it is thus important to understand their population dynamics. The strength of natural selection against TEs is a key parameter in understanding these dynamics. In principle, the strength of selection can be inferred from the frequencies of a sample of TEs. However, complicated demographic histories, such as found in Drosophila melanogaster, could lead to a substantial distortion of the TE frequency distribution compared with that expected for a panmictic, constant-sized population. The current methodology for the estimation of selection intensity acting against TEs does not take into account demographic history and might generate erroneous estimates especially for TE families under weak selection. Here, we develop a flexible maximum likelihood methodology that explicitly accounts both for demographic history and for the ascertainment biases of identifying TEs. We apply this method to the newly generated frequency data of the BS family of non-long terminal repeat retrotransposons in D. melanogaster in concert with two recent models of the demographic history of the species to infer the intensity of selection against this family. We find the estimate to differ substantially compared with a prior estimate that was made assuming a model of constant population size. Further, we find there to be relatively little information about selection intensity present in the derived non-African frequency data and that the ancestral African subpopulation is much more informative in this respect. These findings highlight the importance of accounting for demographic history and bear on study design for the inference of selection coefficients generally.

Much effort and interest have focused on assessing the importance of natural selection, particularly positive natural selection, in shaping the human genome. Although scans for positive selection have identified candidate loci that may be associated with positive selection in humans, such scans do not indicate whether adaptation is frequent in general in humans. Studies based on the reasoning of the MacDonald-Kreitman test, which, in principle, can be used to evaluate the extent of positive selection, suggested that adaptation is detectable in the human genome but that it is less common than in Drosophila or Escherichia coli. Both positive and purifying natural selection at functional sites should affect levels and patterns of polymorphism at linked nonfunctional sites. Here, we search for these effects by analyzing patterns of neutral polymorphism in humans in relation to the rates of recombination, functional density, and functional divergence with chimpanzees. We find that the levels of neutral polymorphism are lower in the regions of lower recombination and in the regions of higher functional density or divergence. These correlations persist after controlling for the variation in GC content, density of simple repeats, selective constraint, mutation rate, and depth of sequencing coverage. We argue that these results are most plausibly explained by the effects of natural selection at functional sites -- either recurrent selective sweeps or background selection -- on the levels of linked neutral polymorphism. Natural selection at both coding and regulatory sites appears to affect linked neutral polymorphism, reducing neutral polymorphism by 6% genome-wide and by 11% in the gene-rich half of the human genome. These findings suggest that the effects of natural selection at linked sites cannot be ignored in the study of neutral human polymorphism., Competing Interests: The authors have declared that no competing interests exist.

Segmental kinematics were investigated in horses during overground locomotion and compared with published reports on humans and other primates to determine the impact of a large neck on rotational mobility (> 20 deg.) and stability (< or = 20 deg.) of the head and trunk. Three adult horses (Equus caballus) performing walks, trots and canters were videotaped in lateral view. Data analysis included locomotor velocity, segmental positions, pitch and linear displacements and velocities, and head displacement frequencies. Equine, human and monkey skulls and cervical spines were measured to estimate eye and vestibular arc length during head pitch displacements. Horses stabilized all three segments in all planes during all three gaits, unlike monkeys and humans who make large head pitch and yaw rotations during walks, and monkeys that make large trunk pitch rotations during gallops. Equine head angular displacements and velocities, with some exceptions during walks, were smaller than in humans and other primates. Nevertheless, owing to greater off-axis distances, orbital and vestibular arc lengths remained larger in horses, with the exception of head-neck axial pitch during trots, in which equine arc lengths were smaller than in running humans. Unlike monkeys and humans, equine head peak-frequency ranges fell within the estimated range in which inertia has a compensatory stabilizing effect. This inertial effect was typically over-ridden, however, by muscular or ligamentous intervention. Thus, equine head pitch was not consistently compensatory, as reported in humans. The equine neck isolated the head from the trunk enabling both segments to provide a spatial reference frame.

Although transposable elements (TEs) are known to be potent sources of mutation, their contribution to the generation of recent adaptive changes has never been systematically assessed. In this work, we conduct a genome-wide screen for adaptive TE insertions in Drosophila melanogaster that have taken place during or after the spread of this species out of Africa. We determine population frequencies of 902 of the 1,572 TEs in Release 3 of the D. melanogaster genome and identify a set of 13 putatively adaptive TEs. These 13 TEs increased in population frequency sharply after the spread out of Africa. We argue that many of these TEs are in fact adaptive by demonstrating that the regions flanking five of these TEs display signatures of partial selective sweeps. Furthermore, we show that eight out of the 13 putatively adaptive elements show population frequency heterogeneity consistent with these elements playing a role in adaptation to temperate climates. We conclude that TEs have contributed considerably to recent adaptive evolution (one TE-induced adaptation every 200-1,250 y). The majority of these adaptive insertions are likely to be involved in regulatory changes. Our results also suggest that TE-induced adaptations arise more often from standing variants than from new mutations. Such a high rate of TE-induced adaptation is inconsistent with the number of fixed TEs in the D. melanogaster genome, and we discuss possible explanations for this discrepancy.

A beneficial mutation that has nearly but not yet fixed in a population produces a characteristic haplotype configuration, called a partial selective sweep. Whether nonadaptive processes might generate similar haplotype configurations has not been extensively explored. Here, we consider 5 population genetic data sets taken from regions flanking high-frequency transposable elements in North American strains of Drosophila melanogaster, each of which appears to be consistent with the expectations of a partial selective sweep. We use coalescent simulations to explore whether incorporation of the species' demographic history, purifying selection against the element, or suppression of recombination caused by the element could generate putatively adaptive haplotype configurations. Whereas most of the data sets would be rejected as nonneutral under the standard neutral null model, only the data set for which there is strong external evidence in support of an adaptive transposition appears to be nonneutral under the more complex null model and in particular when demography is taken into account. High-frequency, derived mutations from a recently bottlenecked population, such as we study here, are of great interest to evolutionary genetics in the context of scans for adaptive events; we discuss the broader implications of our findings in this context.

The effect of recurrent selective sweeps is a spatially heterogeneous reduction in neutral polymorphism throughout the genome. The pattern of reduction depends on the selective advantage and recurrence rate of the sweeps. Because many adaptive substitutions responsible for these sweeps also contribute to nonsynonymous divergence, the spatial distribution of nonsynonymous divergence also reflects the distribution of adaptive substitutions. Thus, the spatial correspondence between neutral polymorphism and nonsynonymous divergence may be especially informative about the process of adaptation. Here we study this correspondence using genomewide polymorphism data from Drosophila simulans and the divergence between D. simulans and D. melanogaster. Focusing on highly recombining portions of the autosomes, at a spatial scale appropriate to the study of selective sweeps, we find that neutral polymorphism is both lower and, as measured by a new statistic Q(S), less homogeneous where nonsynonymous divergence is higher and that the spatial structure of this correlation is best explained by the action of strong recurrent selective sweeps. We introduce a method to infer, from the spatial correspondence between polymorphism and divergence, the rate and selective strength of adaptation. Our results independently confirm a high rate of adaptive substitution (approximately 1/3000 generations) and newly suggest that many adaptations are of surprisingly great selective effect (approximately 1%), reducing the effective population size by approximately 15% even in highly recombining regions of the genome.

Background: Levels of molecular diversity in Drosophila have repeatedly been shown to be higher in ancestral, African populations than in derived, non-African populations. This pattern holds for both coding and noncoding regions for a variety of molecular markers including single nucleotide polymorphisms and microsatellites. Comparisons of X-linked and autosomal diversity have yielded results largely dependent on population of origin., Results: In an attempt to further elucidate patterns of sequence diversity in Drosophila melanogaster, we studied nucleotide variation at putatively nonfunctional X-linked and autosomal loci in sub-Saharan African and North American strains of D. melanogaster. We combine our experimental results with data from previous studies of molecular polymorphism in this species. We confirm that levels of diversity are consistently higher in African versus North American strains. The relative reduction of diversity for X-linked and autosomal loci in the derived, North American strains depends heavily on the studied loci. While the compiled dataset, comprised primarily of regions within or in close proximity to genes, shows a much more severe reduction of diversity on the X chromosome compared to autosomes in derived strains, the dataset consisting of intergenic loci located far from genes shows very similar reductions of diversities for X-linked and autosomal loci in derived strains. In addition, levels of diversity at X-linked and autosomal loci in the presumably ancestral African population are more similar than expected under an assumption of neutrality and equal numbers of breeding males and females., Conclusion: We show that simple demographic scenarios under assumptions of neutral theory cannot explain all of the observed patterns of molecular diversity. We suggest that the simplest model is a population bottleneck that retains an ancestral female-biased sex ratio, coupled with higher rates of positive selection at X-linked loci in close proximity to genes specifically in derived, non-African populations.

Although the balance difficulties accompanying vestibular loss are well known, the underlying cause remains unclear. We examined the role of vestibular inputs in the automatic postural response (APR) to pitch and roll rotations of the support surface in freely standing cats before and in the first week after bilateral labyrinthectomy. Support surface rotations accelerate the body center of mass toward the downhill side. The normal APR consists of inhibition in the extensors of the uphill limbs and excitation in the downhill limbs to decelerate the body and maintain the alignment of the limbs with respect to earth-vertical. After vestibular lesion, cats were unstable during rotation perturbations and actively pushed themselves downhill rather than uphill, using a postural response that was opposite to that seen in the control trials. The extensors of the uphill rather than downhill limbs were activated, whereas those of the downhill limbs were inhibited rather than being excited. We propose that vestibular inputs provide an important reference to earth-vertical, which is critical to computing the appropriate postural response during active orientation to the vertical. In the absence of this vestibular information, subjects orient to the support surface using proprioceptive inputs, which drives the body downhill resulting in instability and falling. This is consistent with current models of sensory integration for computation of body posture and orientation.

We recently showed that four muscle synergies can reproduce multiple muscle activation patterns in cats during postural responses to support surface translations. We now test the robustness of functional muscle synergies, which specify muscle groupings and the active force vectors produced during postural responses under several biomechanically distinct conditions. We aimed to determine whether such synergies represent a generalized control strategy for postural control or if they are merely specific to each postural task. Postural responses to multidirectional translations at different fore-hind paw distances and to multidirectional rotations at the preferred stance distance were analyzed. Five synergies were required to adequately reconstruct responses to translation at the preferred stance distance-four were similar to our previous analysis of translation, whereas the fifth accounted for the newly added background activity during quiet stance. These five control synergies could account for > 80% total variability or r2 > 0.6 of the electromyographic and force tuning curves for all other experimental conditions. Forces were successfully reconstructed but only when they were referenced to a coordinate system that rotated with the limb axis as stance distance changed. Finally, most of the functional muscle synergies were similar across all of the six cats in terms of muscle synergy number, synergy activation patterns, and synergy force vectors. The robustness of synergy organization across perturbation types, postures, and animals suggests that muscle synergies controlling task-variables are a general construct used by the CNS for balance control.

The purpose of this study was to determine the source of postural instability in labyrinthectomized cats during lateral head turns. Cats were trained to maintain the head in a forward orientation and then perform a rapid, large-amplitude head turn to left or right in yaw, while standing freely on a force platform. Head turns were biomechanically complex with the primary movement in the yaw plane accompanied by an ipsilateral ear-down roll and nose-down pitch. Cats used a strategy of pushing off by activating extensors of the contralateral forelimb while using all four limbs to produce a rotational moment of force about the vertical axis. After bilateral labyrinthectomy, the initial components of the head turn and accompanying postural responses were hypermetric, but otherwise similar to those produced before the lesion. However, near the time of peak yaw velocity, the lesioned cats produced an unexpected burst in extensors of the contralateral limbs that thrust the body to the ipsilateral side, leading to falls. This postural error was in the frontal (roll) plane, even though the primary movement was a rotation in the horizontal (yaw) plane. The response error decreased in amplitude with compensation but did not disappear. We conclude that lack of vestibular input results in active destabilization of balance during voluntary head movement. We postulate that the postural imbalance arises from the misperception that the trunk was rolling contralaterally, based on signals from neck proprioceptors in the absence of vestibular inputs.

To study adaptation, it is essential to identify multiple adaptive mutations and to characterize their molecular, phenotypic, selective, and ecological consequences. Here we describe a genomic screen for adaptive insertions of transposable elements in Drosophila. Using a pilot application of this screen, we have identified an adaptive transposable element insertion, which truncates a gene and apparently generates a functional protein in the process. The insertion of this transposable element confers increased resistance to an organophosphate pesticide and has spread in D. melanogaster recently.

Recently developed computational techniques have been used to reduce muscle activation patterns of high complexity to a simple synergy organization and to bring new insights to the long-standing degrees of freedom problem in motor control. We used a nonnegative factorization approach to identify muscle synergies during postural responses in the cat and to examine the functional significance of such synergies for natural behaviors. We hypothesized that the simplification of neural control afforded by muscle synergies must be matched by a similar reduction in degrees of freedom at the biomechanical level. Electromyographic data were recorded from 8-15 hindlimb muscles of cats exposed to 16 directions of support surface translation. Results showed that as few as four synergies could account for >95% of the automatic postural response across all muscles and all directions. Each synergy was activated for a specific set of perturbation directions, and moreover, each was correlated with a unique vector of endpoint force under the limb. We suggest that, within the context of active balance control, postural synergies reflect a neural command signal that specifies endpoint force of a limb.

The force exerted by skeletal muscle is modulated by compliance of tissues to which it is connected. Force of the muscle sarcomere is modulated by compliance of the myofilaments. We tested the hypothesis that myofilament compliance influences Ca2+ regulation of muscle by constructing a computational model of the muscle half sarcomere that includes compliance of the filaments as a variable. The biomechanical model consists of three half-filaments of myosin and 13 thin filaments. Initial spacing of motor domains of myosin on thick filaments and myosin-binding sites on thin filaments was taken to be that measured experimentally in unstrained filaments. Monte-Carlo simulations were used to determine transitions around a three-state cycle for each cross-bridge and between two-states for each thin filament regulatory unit. This multifilament model exhibited less "tuning" of maximum force than an earlier two-filament model. Significantly, both the apparent Ca(2+)-sensitivity and cooperativity of activation of steady-state isometric force were modulated by myofilament compliance. Activation-dependence of the kinetics of tension development was also modulated by filament compliance. Tuning in the full myofilament lattice appears to be more significant at submaximal levels of thin filament activation.

Polymorphisms in microsatellites on the human Y chromosome have been used to estimate important demographic parameters of human history. We compare two coalescent-based statistical methods that give estimates for a number of demographic parameters using the seven Y chromosome polymorphisms in the HGDP-CEPH Cell Line Panel, a collection of samples from 52 worldwide populations. The estimates for the time to the most recent common ancestor vary according to the method used and the assumptions about the prior distributions of model parameters, but are generally consistent with other global Y chromosome studies. We explore the sensitivity of these results to assumptions about the prior distributions and the evolutionary models themselves.

This study sought to identify the sensory signals that encode perturbation direction rapidly enough to shape the directional tuning of the automatic postural response. We compared reactions to 16 directions of pitch and roll rotation and 16 directions of linear translation in the horizontal plane in freely standing cats. Rotations and translations that displaced the center of mass in the same direction relative to the feet evoked similar patterns of muscle activity and active ground-reaction force, suggesting the presence of a single, robust postural strategy for stabilizing the center of mass in both rotation and translation. Therefore we postulated there should be a common sensory input that encodes the direction of the perturbation and leads to the directional tuning of the early electromyographic burst in the postural response. We compared the mechanical changes induced by rotations and translations prior to the active, postural response. The only consistent feature common to the full range of rotation and translation directions was the initial change in ground-reaction force angle. Other variables including joint angles, ground-reaction force magnitudes, center of pressure, and center of mass in space showed opposite or nonsignificant changes for rotation and translation. Change in force angle at the paw reflects the ratio of loading force to slip force, analogous to slips during finger grip tasks. We propose that cutaneous sensors in the foot soles detect change in ground-reaction force angle and provide the critical input underlying the directional tuning of the automatic postural response for balance.

Pyridoxine given in large doses is thought to destroy selectively the large-diameter peripheral sensory nerve fibers, leaving motor fibers intact. This study examined the effects of pyridoxine-induced somatosensory loss on automatic postural responses to sudden displacements of the support surface in the standing cat. Two cats were trained to stand on four force plates mounted on a movable platform. They were given pyridoxine (350 mg/kg, i.p.) on 2 successive days (0 and 1). Electromyographic (EMG) activity was recorded from selected hindlimb muscles during linear ramp-and-hold platform displacements in each of 12 directions at 15 cm/sec. In control trials onset latencies of evoked activity in hindlimb flexor and extensor muscles ranged from 40 to 65 msec after the onset of platform acceleration. After injection the EMG latencies increased over days, becoming two to three times longer than controls by day 7. Excursions of the body center of mass (CoM) in the direction opposite to that of platform translation were significantly greater at day 7 compared with controls, and the time at which the CoM subsequently reversed direction was delayed. Both animals were ataxic from day 2 onward. Histological analysis of cutaneous and muscle nerves in the hindlimb revealed a significant loss of fibers in the group I range. Our results suggest that large afferent fibers are critical for the timing of automatic postural responses to ensure coordinated control of the body CoM and balance after unexpected disturbances of the support surface.

A genomic clone encoding a thiohydroximate S-glucosyltransferase (S-GT) was isolated from Brassica napus by library screening with probes generated by PCR using degenerated primers. Its corresponding cDNA was amplified by rapid amplification of cDNA ends (RACE) PCR and also cloned by cDNA library screening. The genomic clone was 5 896 bp long and contained a 173-bp intron. At least two copies of the S-GT gene were present in B. napus. The full-length cDNA clone was 1.5 kb long and contained an open reading frame encoding a 51-kDa polypeptide. The deduced amino acid sequence shared a significant degree of homology with other glucosyltransferases characterized in other species, including a highly conserved motif within this family of enzymes corresponding to the glucose-binding domain. The recombinant protein was expressed in Escherichia coli, and the enzyme activity was tested by a biochemical assay based on the measure of glucose incorporation. The high thiohydroximate S-GT activity detected from the recombinant protein confirmed that this clone was indeed a S-glucosyltransferase.

The intact cat maintains balance during unexpected disturbances of stance through automatic postural responses that are stereotyped and rapid. The extent to which the chronic spinal cat can maintain balance during stance is unclear, and there have been no quantitative studies that examined this question directly. This study examined whether the isolated lumbosacral cord of the chronic spinal cat can generate automatic postural responses in the hindlimbs during translation of the support surface. Responses to 16 directions of linear translation in the horizontal plane were quantified before and after spinalization at the T(6) level in terms of forces exerted by each paw against the support, motion of the body segments (kinematics), and electromyographic (EMG) activity. After spinalization, the cats were trained on a daily basis to stand on the force platform, and all four cats were able to support their full body weight. The cats usually required assistance for balance or stability in the horizontal plane, which was provided by an experimenter exerting gentle lateral force at the level of the hips. Three of the four animals could maintain independent stance for a brief period (10 s) after the experimenter stabilized them. The fourth cat maintained weight support but always required assistance with balance. Perturbations were delivered during the periods of independent stance in three cats and during assisted stance in the fourth. A response to translation in the spinal cats was observed only in those muscles that were tonically active to maintain stance and never in the flexors. Moreover, latencies were increased and amplitudes of activation were diminished compared with control. Nevertheless, flexors and extensors were recruited easily during behaviors such as paw shake and stepping. It is concluded that centers above the lumbosacral cord are required for the full elaboration of automatic postural responses. Although the spinal cat can achieve good weight support, it cannot maintain balance during stance except for brief periods and within narrow limits. This limited stability is probably achieved through spinal reflex mechanisms and the stiffness characteristics of the tonically active extensors.

Standing is a dynamic task that requires antigravity support of the body mass and active regulation of the position of the body center of mass. This study examined the extent to which the chronic spinal cat can maintain postural orientation during stance and adapt to changes in stance distance (fore-hindpaw separation). Intact cats adapt to changes in stance distance by maintaining a constant horizontal orientation of the trunk and changing orientation of the limbs, while keeping intralimb geometry constant and aligning the ground reaction forces closely with the limb axes. Postural adaptation was compared in four cats before and after spinalization at the T(6) level, in terms of the forces exerted by each paw against the support, body geometry (kinematics) and electromyographic (EMG) activity recorded from chronic, indwelling electrodes, as well as the computed net torques in the fore and hindlimbs. Five fore-hindpaw distances spanning the preferred distance were tested before spinalization, with a total range of 20 cm from the shortest to the longest stance. After spinalization, the cats were trained on a daily basis to stand on the force platform, and all four cats were able to support their full body weight. Three of the four cats could adapt to changes in stance distance, but the range was smaller and biased toward the shorter distances. The fourth cat could stand only at one stance distance, which was 8 cm shorter than the preferred distance before spinalization. All cats shifted their center of pressure closer to the forelimbs after spinalization, but the amount of shift could largely be accounted for by the weight loss in the hindquarters. The three cats that could adapt to changes in stance distance used a similar strategy as the intact cat by constraining the trunk and changing orientation of the limb axes in close relation with the forces exerted by each limb. However, different postures in the fore- and hindlimbs were adopted, particularly at the scapula (more extended) and pelvis (tipped more anteriorly). Other changes from control included a redistribution of net extensor torque across the joints of the forelimb and of the hindlimb. We concluded that the general form of body axis orientation is relatively conserved in the spinal cat, suggesting that the lumbosacral spinal circuitry includes rudimentary set points for hindlimb geometry. Both mechanical and neural elements can contribute toward maintaining body geometry through stiffness regulation and spinal reflexes.

This study examined (1) how changes in head position affect postural orientation variables during stance and (2) whether changes in head position affect the rapid postural response to linear translation of the support surface in the horizontal plane. Cats were trained to stand quietly on a moveable platform and to maintain five different head positions: center, left, right, up, and down. For each head position, stance was perturbed by translating the support surface linearly in 16 different directions in the horizontal plane. Postural equilibrium responses were quantified in terms of the ground reaction forces, kinematics, dynamics (net joint torques), body center of mass, and electromyographic (EMG) responses of selected limb and trunk muscles. A change in head position involved rotation of not only the neck but also the scapulae and anterior trunk. Tonic EMG levels were modulated in several forelimb and scapular muscles but not hindlimb muscles. Finally, large changes in head orientation in both horizontal and vertical planes did not hamper the ability of cats to maintain postural equilibrium during linear translation of the support surface. The trajectory of the body's center of mass was the same, regardless of head position. The main change was observed in joint torques at the forelimbs evoked by the perturbation. Evoked EMG responses of forelimb and scapular muscles were modulated in terms of magnitude but not spatial tuning. Hindlimb responses were unchanged. Thus, the spatial and temporal pattern of the automatic postural response was unchanged and only amplitudes of evoked activity were modulated by head position.

This study examined the configuration of the vertebral column of the cat during independent stance and in various flexed positions. The range of motion in the sagittal plane is similar across most thoracic and lumbar joints, with the exception of a lesser range at the transition region from thoracic-type to lumbar-type vertebrae. The upper thoracic column exhibits most of its range in dorsiflexion and the lower thoracic and lumbar in ventroflexion. Lateral flexion is limited to less than 5 degrees at all segments. The range in torsion is almost 180 degrees and occurs primarily in the midthoracic region, T4-T11. Contrary to the depiction in most atlases, the standing cat exhibits several curvatures, including a mild dorsiflexion in the lower lumbar segments, a marked ventroflexion in the lower thoracic and upper lumbar segments, and a profound dorsiflexion in the upper thoracic (above T9) and cervical segments. The curvatures are not significantly changed by altering stance distance but are affected by head posture. During stance, the top of the scapula lies well above the spines of the thoracic vertebrae, and the glenohumeral joint is just below the bodies of vertebrae T3-T5. Using a simple static model of the vertebral column in the sagittal plane, it was estimated that the bending moment due to gravity is bimodal with a dorsiflexion moment in the lower thoracic and lumbar region and a ventroflexion moment in the upper thoracic and cervical region. Given the bending moments and the position of the scapula during stance, it is proposed that two groups of scapular muscles provide the major antigravity support for the head and anterior trunk. Levator scapulae and serratus ventralis form the lateral group, inserting on the lateral processes of cervical vertebrae and on the ribs. The major and minor rhomboids form the medial group, inserting on the spinous tips of vertebrae from C4 to T4. It is also proposed that the hypaxial muscles, psoas major, minor, and quadratus lumborum could support the lumbar trunk during stance.

This study examined the role of trunk extensor muscles in the thoracic and lumbar regions during postural adjustments in the freely standing cat. The epaxial extensor muscles participate in the rapid postural responses evoked by horizontal translation of the support surface. The muscles segregate into two regional groups separated by a short transition zone, according to the spatial pattern of the electromyographic (EMG) responses. The upper thoracic muscles (T5-9) respond best to posteriorly directed translations, whereas the lumbar muscles (T13 to L7) respond best to anterior translations. The transition group muscles (T10-12) respond to almost all translations. Muscles group according to vertebral level rather than muscle species. The upper thoracic muscles change little in their response with changes in stance distance (fore-hindpaw separation) and may act to stabilize the intervertebral angles of the thoracic curvature. Activity in the lumbar muscles increases along with upward rotation of the pelvis (iliac crest) as stance distance decreases. Lumbar muscles appear to stabilize the pelvis with respect to the lumbar vertebrae (L7-sacral joint). The transition zone muscles display a change in spatial tuning with stance distance, responding to many directions of translation at short distances and focusing to respond best to contralateral translations at the long stance distance.

In summary, adequate control of postural orientation and equilibrium is a prerequisite for virtually all skilled motor acts, even those apparently simple tasks of standing and walking. In the cat, certain aspects of postural orientation appear to be organized at the spinal level. In contrast, postural equilibrium is not achieved by spinal circuits in isolation, but seems to require input from higher centers. The challenge is to identify those higher centers and the means by which they produce appropriate postural reactions for maintaining balance. If, indeed, postural equilibrium is a function of descending systems, then in the future, the amount of recovery of postural equilibrium after injury and/or treatment could provide a quantitative measure of the degree of sparing and/or re-establishment of functional connections between higher centers and the spinal cord.

1. This study examined the relation between electromyographic (EMG) activation and the contact force and joint torques of the left hindlimb during postural equilibrium tasks in the standing cat. It is the appropriate application of force by the limbs against the support surface that allows the animal to control its center of mass and maintain equilibrium. 2. Cats were trained to stand quietly on a moveable force platform. During quiet stance, the cat was perturbed by a platform translation in each of 12 directions evenly spaced in the horizontal plane. EMG activity of mono- and biarticular thigh muscles, three-dimensional ground reaction force under the paw (contact force), and kinematics of the hindlimb segments were recorded Net joint torques were computed using inverse dynamics. The analysis focused on the functional organization of the rapid, automatic postural response in relation to the sagittal plane contact force and joint torques. 3. The muscles of the thigh were subdivided into two functional groups, based on the relationship of the evoked response to the various components of the sagittal plane contact force or joint torques. The first group, consisting of the monoarticular and some biarticular muscles, was correlated with the vertical force component, Fz. The second group, consisting of a separate group of biarticular muscles, was correlated with the difference between knee and hip torque. This torque difference is a function of both sagittal plane force components, Fz and Fy, and is related to contact force direction. 4. It is suggested that this subdivision of muscle activations reflects a neural strategy of parallel control of the two muscle groups in relation to their influence on Fz and Fy. Such a control mechanism could be a strategy for simplifying the control of the multisegmented limb in contact force tasks such as maintaining postural equilibrium.

1. This study examined the role of vestibular afferent information on the postural responses of four cats, evoked by movements of the support surface during stance. Animals were exposed to linear translations of the supporting surface in eight evenly spaced directions in the horizontal plane, before and after bilateral labyrinthectomy. Postural responses were quantified in terms of the ground reaction forces under each paw and the evoked activity in selected muscles. 2. The cats were able to stand on the platform within 1-3 days after labyrinthectomy and were able to maintain balance during all perturbations of stance, even when they stood in total darkness, completely deprived of visual information. After lesion, postural responses were characterized by normal latency and normal spatial and temporal patterning of electromyographic (EMG) response. The pattern of force response showed the force constraint strategy that characterizes postural responses in the intact animal. 3. The only deficit in the postural response after lesion was a hypermetria, or active over-response that caused the animals to overbalance somewhat but did not impair their ability to remain upright. Analysis of the trajectory of the animal's center of mass during the trials indicated that the hypermetria was due to an abnormally large, active response on the part of the animal and could not be attributed to changes in the passive stiffness of the musculoskeletal system. The hypermetria was transient, and response amplitude returned to control levels after the rapid compensation phase of 10-15 days. 4. It is concluded that vestibular information is not essential for triggering the rapid, automatic postural response to translations of the support surface, nor is it necessary for the selection or shaping of the evoked response. Instead, somatosensory information appears to predominate in these postural adjustments. However, vestibular afferent input does influence the scaling of the postural response.

The polymerase chain reaction (PCR) method to randomly amplify polymorphic DNA (RAPD) was used to differentiate between Sarcocystis cruzi DNA and bovine DNA. This assay was also exploited to identify a S. cruzi DNA fragment which may be useful as a probe. Five primers ranging in length from 16 to 20 nucleotides were analyzed for their ability to direct the amplification of either bovine or parasite DNA fragments. Two primers, TGA and TGD, preferentially amplified bovine DNA in a mixture of S. cruzi and bovine DNA. The primers TGB and TGF each directed the amplification of S. cruzi DNA instead of bovine DNA. Assays using TGF and S. cruzi DNA resulted in the production of a unique 0.8 kilobase (kb) DNA fragment. This fragment was not amplified from two other closely related coccidian species, Toxoplasma gondii and Sarcocystis campestris. When the 0.8 kb DNA fragment was purified and used as a DNA probe, it only hybridized with DNA from S. cruzi. The results of this study indicate that this DNA fragment may be developed into a useful DNA probe for S. cruzi, and that the RAPD-PCR method may be successfully exploited for the rapid development of DNA probes for parasites and other organisms.

Four isolates of Sarcocystis neurona from horses with equine protozoal myeloencephalitis and eight species of coccidia from the genera Sarcocystis, Toxoplasma or Eimeria were differentiated using the random amplified polymorphic DNA assay. A single, common, 550-bp DNA fragment was amplified from the DNA of each S. neurona isolate using a 16-nucleotide primer. Crosshybridization analyses among S. neurona isolates showed that DNA fragments had at least partial sequence homology. The primer generated several DNA fragments, including a 550-bp DNA fragment, from S. cruzi, Eimeria falciformis, E. neischulzi, E. ahsata and E. bovis. DNA hybridization analyses indicated no sequence homology between these fragments and the 550-bp DNA fragment generated from S. neurona. The S. neurona 550-bp DNA fragment also did not hybridize with genomic blots of various other coccidia. These results suggest that the S. neurona DNA fragment may be exploited as a species-specific probe for this parasite.

1. A longitudinal study of the control of quiet and perturbed stance was conducted before and for 1 yr after complete spinal transection (T12) in a cat trained to stand on a moveable force platform. 2. With daily training, the spinal cat recovered full weight support and some intermittent control of lateral stability within 1 mo. Within the second month postspinalization, the spinal cat achieved the ability to maintain independent, unassisted stance (no external support or stimulation) for up to 45 s during quiet stance, as well as for 62-97% of the trials of horizontal translations of the support surface. 3. Control of lateral stability in the spinal cat was severely compromised, however, as eventually the spinal cat always lost its balance. Head movements and the tendency for the hindlimbs to initiate stepping movements were more destabilizing than platform translations. 4. Our preliminary results indicate that the recovery of partial lateral stability of the hindquarters in the spinal cat is the product of passive muscle properties and segmental reflexes, which, in isolation can provide only limited balance control in the chronic spinal cat.

1. The purpose of this study was to examine the effect of changing initial stance conditions on the postural response of the cat to horizontal plane translations of the support surface. Cats were trained to stand, unrestrained, on a moveable force platform. The platform was translated linearly in each of 16 directions in the horizontal plane, with a ramp-and-hold displacement. The animal's response was quantified in terms of the forces exerted at the ground. The trajectory of the center of mass (CoM) was computed from the forces. 2. Stance length was varied along the longitudinal (sagittal) axis by adjusting the distance between the forepaw and hindpaw force plates. Translation perturbations of the platform were recorded at stance distances varying from 66 to 110% of the preferred stance distance. 3. Changing stance distance had a significant effect on the amplitude and direction of the active forces exerted by the cat both during quiet stance and during the response to platform translation. At long stance distances, each limb exerted a force outward, along the diagonals during quiet stance. The response to translation was characterized by an invariance in the direction of force exerted against the ground, a strategy that was described previously. At short stance distances, quiet stance forces were more laterally directed. The force constraint strategy was usually not observed for the response to translation. Nevertheless, the cats were equally effective at all stance distances in restoring the position of the center of mass after translation of the support surface. 4. There was no discrete boundary between the presence and absence of the force constraint, suggesting that the strategy for exerting forces against the support surface is characterized by a continuum of response, from a bimodal, or anisotropic distribution of force vectors on the one extreme, to a uniform, or isotropic distribution on the other. Arguments are developed to suggest that the force constraint strategy may be useful in stabilizing the vertebral column during the response to platform translation, to allow linear translation of the CoM rather than bending of the trunk.

The purpose of this study was to examine the effect of prior experience concerning direction of a postural perturbation on the balance response of cats to translations of their support surface. Previous work has shown that, when cats are translated in many directions in the horizontal plane, they respond by exerting active forces with each paw in only two directions, termed the force constraint strategy. This study examined whether the force constraint strategy could be modified based on predictability of the direction of translation and whether this strategy is used by the naive animal with no prior experience of platform translation. Four cats were trained to stand quietly on the force platform using positive reinforcement, and then were implanted with chronically indwelling electrodes for recording electromyographic (EMG) activity. The first experiment concerned the response of the naive cats to their first exposure to platform translation and consisted of translations presented randomly in four different directions in the horizontal plane. The second experiment consisted of two complete sets of 16 directions of translation (15 trials per direction), with the direction of translation randomized in one set and serially ordered in the other, to make the direction of translation unpredictable or predictable, respectively. Forces exerted by the cat, EMG activity, and platform position were recorded during the 1-s trials. The use of the force constraint strategy was independent of prior experience with direction of translation, as was the amplitude of the response.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The electromyographic (EMG) activity of the four neuromuscular compartments in lateral gastrocnemius (LG) of cats was investigated to determine whether these intramuscular subdivisions could be activated differentially during automatic postural corrections. EMG electrodes were surgically implanted into each of the four compartments of left LG-LG1, LG2, LG3, and LGm--in two cats. Electrodes were also implanted into soleus and gluteus medius for comparative purposes. 2. Quiet quadrupedal stance was disturbed first by linearly translating the cats on a movable platform in each of 16 different horizontal directions. Mechanical events during corrections were characterized in terms of the three-dimensional forces exerted by each paw on the platform. EMG and force traces were quantified (area under the curve) and normalized, and tuning curves were constructed that relate muscle response and force change to direction of platform movement. 3. In a second series of trials, translations were presented along one direction only over a series of six velocities ranging from 5 to 16 cm/s. The third series of perturbations, termed the pop-up, consisted of a rapid upward displacement of the support under the left hindlimb only over a series of six amplitudes ranging from 1 to 10 mm. Evoked EMG activity and average change in force were normalized and regressions were computed onto velocity and amplitude, respectively. The slopes of the regressions were compared. 4. EMG tuning curves associated with the multidirectional horizontal translations revealed no differential activity across LG compartments. Similarly, there was no statistical difference among the slopes of the regressions within LG. In contrast, soleus exhibited significantly different slopes from LG for the regressions. Thus it is concluded that LG compartments are not differentially activated during automatic postural responses to perturbations of the support surface.

The reproducibility of the generation of random amplified polymorphic DNA fragments from three commonly used thermal cyclers was determined using identical assay conditions. In all cases, different results were obtained from the three instruments. Variation in the length of the primer (20 nt or 10 nt) did not have any effect on the reproducibility of the assays from the three machines tested. A DNA concentration of 1 ng generated poorly staining DNA fragments whereas concentrations between 10 ng and 100 ng gave similar banding patterns when using the same thermal cycler. Low concentrations of primer (0.05 microM) did not produce any detectable DNA fragments. Increased primer concentrations of 0.25 microM or higher generated intensely staining DNA fragments, and concentrations above 0.5 microM did not improve the clarity of the banding patterns but did direct the synthesis of increasing amounts of very short DNA fragments. Surprisingly, the 20 nt-long primer was able to direct the synthesis of more DNA fragments than a primer of only 10 nt long.

We describe the development of five oligonucleotide probes which target the small sub-unit rRNA of Toxoplasma gondii. These probes bind to different regions within the rRNA and all were effective in producing a detectable signal with as little as 10 ng of total cellular RNA. One probe in particular, TGB, was able to detect as little as 1 ng of RNA and was the most specific. A sixth probe, previously developed for hybridization with Sarcocystis spp., was evaluated for its specificity and was shown to be useful as a multi-species coccidial probe. Four of the five T. gondii-specific probes did not cross-hybridize with RNA from nine related species of coccidia, Escherichia coli, cattle, people, cat or dog. One probe cross-hybridized strongly with RNA of Eimeria ahsata and Isospora suis, but not to RNA of any other coccidia species tested nor bovine, human, feline or canine RNA. The potential of this assay for use in veterinary and human medicine as well as food safety programmes is discussed.

A polymerase chain reaction (PCR) method was developed for the detection of Toxoplasma gondii. A universal- and a T. gondii-specific primer was used to amplify a region of the small subunit ribosomal RNA gene. This approach allows for a theoretical detection limit of 0.01 zoite of T. gondii per sample assayed. Experiments showed that this PCR method could detect 0.1 pg of T. gondii DNA, which represents about one organism. Polymerase chain reaction tests using DNAs of cat, dog, swine, cattle, human, Sarcocystis cruzi, Eimeria ahsata, E. vermiformis, and Escherichia coli indicated no cross-reaction with nucleic acids of hosts, related coccidia, or bacteria. Data on the sensitivity and specificity suggest that this PCR assay could be extremely useful for the diagnosis of toxoplasmosis in human and veterinary medicine, as well as for food safety surveys.

Although vestibular input codes head acceleration, it is not clear whether or not this signal is critical for triggering the initial postural response to a perturbation of stance, and for determining the appropriate direction of response. These experiments were designed to examine the contribution of vestibular inputs to the control of balance in the freely standing cat. Four cats were trained to stand quietly on a moveable force platform. The animal's stance was unexpected perturbed by applying a linear ramp-and-hold translation to the support surface in each of eight different directions in the horizontal plane. The characteristics of quiet stance and the response to the perturbations were quantified in terms of the 3-D ground reaction forces under each paw and the EMG activity in selected muscles. The animals were bilaterally labyrinthectomized, and their responses compared before and after lesion. The cats were able to stand stably on the platform within 2-3 days of the lesion. During quiet stance, there was no change in the distribution of vertical forces under the paws and no increase in sway area. Horizontal plane forces, which were normally outwardly directed on the diagonals, became more laterally directed and transiently larger in amplitude. The level of tonic EMG activity increased in some extensors and flexors, and decreased in others, compared to control. The responses to platform translation were characterized by normal spatial and temporal patterns and latencies of EMG activity. Furthermore, all cats continued to use the force constraint strategy that is characteristic of the intact animal (Macpherson, 1988a). The only clear deficit in performance was a transient hypermetria, characterized by an over-response to the translation. Although the cats over-responded, they were still able to maintain their balance successfully. The moderate changes in quiet stance and in response to perturbation gradually returned to control values over 8-10 days following the lesion. These results suggest that vestibular information is not necessary for triggering appropriate postural responses evoked by support surface translations, nor for selecting the direction of response.

Eimeria species were differentiated by the polymerase chain reaction using random amplified polymorphic DNA. Seven arbitrary primers ranging in length from ten to 20 nucleotides were used with DNA of seven species of eimerian oocysts to generate unique DNA fingerprints. DNA fragments ranging from 200 to 2200 base pairs (bp) were synthesized in the different reactions. Species-specific DNA fragment mobility patterns were observed in most cases. In several assays, multiple DNA fragments were synthesized and, in the majority of assays conducted, the Eimeria species could be easily differentiated. Only six of the 49 assays performed failed to generate DNA fragments.

The potential pathogenicity of Beauveria bassiana was examined by intramuscular injection of high (2 x 10(8)) or low (2 x 10(5)) concentrations of conidia spores, into the left or right quadriceps muscles of CD-1 mice, respectively. The injection sites were monitored over a period of 28 days by both microbiological and histopathological methods. Focal muscle necrosis, edema and inflammation occurred rapidly (within 12 hours) at the high dose application (2 x 10(8)) site, but such lesions were far less severe with the low dose spore application (2 x 10(5)). Fungal spores in the high dose site persisted in normal shape for 2 weeks, after which time they began to degenerate. Almost all spores were cleared from the injection site within the 28-day observation period. Spread to other organs of the body was not observed, except by macrophage transport to regional lymph nodes. At the low dose rate, most spores were cleared within 12 h to 2 d, leaving only mild focal edema and inflammation. Viable fungal colonies could be recovered up to 3 d after injection from the high dose site, but only up to 12 h from the low dose site. It was concluded that B. bassiana does not cause infection, nor multiply, nor survive for more than 3 days when injected intramuscularly into healthy mice.