Comparison Between the Effects of Botulinum Toxin-Induced Paralysis and Denervation on Molecular Forms of Acetylcholinesterase in Muscles

Abstract: Velocity sedimentation analysis of acetylcholinesterase (AChE) molecular forms in the fast extensor digitorum longus muscle and in the slow soleus muscle of the rat was carried out on days 4, 8, and 14 after induction of muscle paralysis by botulinum toxin type A (BoTx). The results were compared with those observed after muscle denervation. In addition, the ability of BoTx-paralyzed muscles to resynthesize AChE was studied after irreversible inhibition of the preexistent enzyme by diisopropyl phosphorofluoridate. Major differences were observed between the effects of BoTx treatment and nerve section on AChE in the junctional region of the muscles. A precipitous drop in content of the asymmetric A12 AChE form was observed after denervation, whereas its decrease was much slower and less extensive in the BoTx-paralyzed muscles. Recovery of junctional AChE and of its A12 form after irreversible inhibition of the preexistent AChE in BoTx-paralyzed muscles was nevertheless very slow. It seems that a greater part of the junctional A12 AChE form pertains to a fraction with a very slow turnover that is rapidly degraded after denervation but not after BoTx-produced muscle paralysis. The postdenervation decrease in content of junctional A12 AChE is therefore not primarily due to muscle inactivity. The extrajunctional molecular forms of AChE seem to be regulated mostly by muscle activity because they undergo virtually identical changes both after denervation and BoTx paralysis. The differences observed in this respect between the fast and slow muscles after their inactivation must be intrinsic to muscles.     

QUANTITATIVE GENETICS OF RESPONSE TO COMPETITORS IN NEMOPHILA MENZIESII: A GREENHOUSE STUDY

To determine the potential for adaptation to a local biotic environment, we examined the magnitude and nature of genetic variation in response to neighboring plants within a natural population of the native California annual, Nemophila menziesii. A total of 22 plants from a natural population were crossed in three reciprocal factorials. The progeny were grown in a greenhouse in nine treatments that varied in conspecific density and in the density of a naturally co-occurring grass species, Bromus diandrus. Increasing the density of each species significantly reduced individual survival, fruit number, and dry weight. Among survivors, we found small to moderate heritability of dry weight within treatments. Additive genetic correlations (r_A) of dry weight between competitive regimes were generally large and positive. In no case were they significantly different from 1, as expected under the null hypothesis that the relative performance of the genotypes under consideration is the same in all environments. On the basis of these results, we cannot conclude that the structure of genetic covariation within this population would promote genetic differentiation in response to locally varying conditions of density of these two species. Aspects of the experiment that may have compromised our ability to detect r_A differing from 1 are discussed.     

REACTION NORMS OF MORPHOLOGICAL AND LIFE-HISTORY TRAITS TO LIGHT AVAILABILITY IN IMPATIENS CAPENSIS

For plants, light availability is an important environmental factor that varies both within and between populations. Although the existence of sun and shade “ecotypes” is controversial, it is often assumed that trade-offs may exist between performance in sun and in shade. This study therefore investigated variation in reaction norms to light availability within and between two neighboring natural populations of the annual Impatiens capensis, one in full sun and the other in a forest understory. Seedlings were collected randomly from both populations and grown to maturity in a greenhouse under two light conditions: full light and 18% of full light. Selfed full-sib seed families were collected from plants from both populations grown in both parental light environments. To characterize family reaction norms, seedlings from each family were divided into the same two light treatments and individuals were scored for a variety of morphological and life-history traits. The maternal light environment had little impact on progeny reaction norms. However, the two study populations differed both qualitatively and quantitatively in plastic response to light availability (indicated by significant population x environment interactions in mixed-model ANCOVA). Much of this difference was attributable to population differences in light sensitivity of axillary meristem allocation patterns, which produced concurrent differences in reaction norms for a suite of developmentally linked traits. Within each population, different sets of traits displayed significant variation in plasticity (indicated by significant family x environment interactions). Thus, the genetic potential for evolutionary response to selection in heterogeneous light environments may differ dramatically between neighboring plant populations. Between-environment genetic correlations were largely positive in the woods population and positive or nonsignificant in the sun population; there was no evidence for performance trade-offs across environments or sun or shade “specialist” genotypes within either population. There was little evidence that population differences represented adaptive differentiation for sun or shade; rather, the results suggested the hypothesis of differential selection on patterns of meristem allocation caused by population differences in timing of mortality and intensity of competition.     

Normalization of electromyogram in the neck-shoulder region

Linear and curvilinear electromyogram (EMG) normalization methods were compared among ten healthy men during a simulated work cycle demanding attention and static holding of the arm (Solitaire test). Maximal voluntary contractions (MVC) and gradually increasing contractions up to 70% of MVC were used for normalization in different arm postures. The test contractions studied included inward and outward rotations, abduction, shoulder elevation, and flexion in different arm positions. The shoulder load moment was calculated for the flexion tests using a simple two-dimensional model. The effect of arm posture on the EMG versus shoulder load moment relationship was studied on the following muscles: supraspinatus, infraspinatus, trapezius (three parts), deltoid (two parts) and pectoralis major. All muscles participated in the MVC tests performed, and its was not possible to suggest a single recommended test for each muscle. Differences in normalized EMG median values ranging up to 30% of MVC were found between linear and curvilinear normalization methods. Short-term repeatability of normalization based on a contraction with gradually increasing force was good. Arm posture affected the relationships between shoulder load moment and EMG activity of all muscles studied. Arm posture did not, however, have a significant effect on the estimated amplitude probability distribution functions during the simulated work task. Therefore, at least for the tasks studied, the principle of normalizing in the middle position of the range of movement was deemed acceptable.     

Shoulder muscle load and muscle fatigue among industrial sewing-machine operators

Physiological responses to physical work were assessed for 29 female industrial sewing-machine operators during an 8-h working day under ordinary working conditions. During sewing-machine work, the average (left and right) static load in the trapezius muscle was 9% of the maximal electromyogram (EMG) amplitude (% EMG_max), while the average mean load was 15% EMG_max, and the average peak load was 23% EMG_max. The static load level was unrelated to the muscle strength of the sewing-machine operators, which for the group as a whole was within the normal range. The load levels remained unchanged during the working day, while changes in the EMG mean power frequency and zero crossing frequency rate occurred, both indicating the development of muscle fatigue in left and right trapezius muscle during the working day. In line with this, the rating of perceived exertion in the shoulder and neck region increased during. the working day. Dividing the group of sewing-machine operators into two groups, those with the highest frequency and those with the lowest frequency of shoulder/neck troubles showed that the former group had significantly lower muscle strength, despite the fact that no differences in the surface EMG during sewing were found between the two groups. It was concluded that industrial sewing-machine work involves a pattern of shoulder muscle activity which induces fatiguing processes in the shoulder and neck regions. Furthermore, since the static shoulder muscle load was independent of muscle strength, factors other than working posture may be of significance for the static shoulder muscle load.     

Polarized distribution of γ interferon-stimulated MHC antigens and transferrin receptors in a clonal cell line isolated from Fisher rat thyroid (FRT cells)

Summary The fine structure of single identified muscle fibers and their nerve terminals in the limb closer muscle of the shore crab Eriphia spinifrons was examined, using a previous classification based on histochemical evidence which recognizes a slow (Type-I) fiber and three fast (Type-II, Type-III, Type-IV) fibers. All four fiber types have a fine structure characteristic of crustacean slow muscle, with 10–12 thin filaments surrounding each thick filament and sarcomere lengths of 6–13 m. Type-IV fibers have sarcomere lengths of 6 m while the other three types have substantially longer sarcomeres (10–13 m). Structural features of nerve terminals revealed excitatory innervation in all four fiber types but inhibitory innervation in Type-I, Type-II, and Type-III fibers only. Thus fibers with longer sarcomeres receive the inhibitor axon but those with shorter sarcomeres do not. Amongst the former, synaptic contact from an inhibitory nerve terminal onto an excitatory one, denoting presynaptic inhibition, was seen in Type-I and Type-II fibers but not in Type-III and Type-IV fibers. Inhibitory innervation of the walking leg closer muscle is therefore highly differentiated: some fibers lack inhibitory nerve terminals, some possess postsynaptic inhibition, and some possess both postsynaptic and presynaptic inhibition.     

Interactive effects of rising temperatures and urbanisation on birds across different climate zones: A mechanistic perspective

Climate change and urbanisation are among the most pervasive and rapidly growing threats to biodiversity worldwide. However, their impacts are usually considered in isolation, and interactions are rarely examined. Predicting species' responses to the combined effects of climate change and urbanisation, therefore, represents a pressing challenge in global change biology. Birds are important model taxa for exploring the impacts of both climate change and urbanisation, and their behaviour and physiology have been well studied in urban and non-urban systems. This understanding should allow interactive effects of rising temperatures and urbanisation to be inferred, yet considerations of these interactions are almost entirely lacking from empirical research. Here, we synthesise our current understanding of the potential mechanisms that could affect how species respond to the combined effects of rising temperatures and urbanisation, with a focus on avian taxa. We discuss potential interactive effects to motivate future in-depth research on this critically important, yet overlooked, aspect of global change biology. Increased temperatures are a pronounced consequence of both urbanisation (through the urban heat island effect) and climate change. The biological impact of this warming in urban and non-urban systems will likely differ in magnitude and direction when interacting with other factors that typically vary between these habitats, such as resource availability (e.g. water, food and microsites) and pollution levels. Furthermore, the nature of such interactions may differ for cities situated in different climate types, for example, tropical, arid, temperate, continental and polar. Within this article, we highlight the potential for interactive effects of climate and urban drivers on the mechanistic responses of birds, identify knowledge gaps and propose promising future research avenues. A deeper understanding of the behavioural and physiological mechanisms mediating species' responses to urbanisation and rising temperatures will provide novel insights into ecology and evolution under global change and may help better predict future population responses.     

A data-driven framework to model the organism–environment system

Organisms modify their development and function in response to the environment. At the same time, the environment is modified by the activities of the organism. Despite the ubiquity of such dynamical interactions in nature, it remains challenging to develop models that accurately represent them, and that can be fitted using data. These features are desirable when modeling phenomena such as phenotypic plasticity, to generate quantitative predictions of how the system will respond to environmental signals of different magnitude or at different times, for example, during ontogeny. Here, we explain a modeling framework that represents the organism and environment as a single coupled dynamical system in terms of inputs and outputs. Inputs are external signals, and outputs are measurements of the system in time. The framework uses time-series data of inputs and outputs to fit a nonlinear black-box model that allows to predict how the system will respond to novel input signals. The framework has three key properties: it captures the dynamical nature of the organism–environment system, it can be fitted with data, and it can be applied without detailed knowledge of the system. We study phenotypic plasticity using in silico experiments and demonstrate that the framework predicts the response to novel environmental signals. The framework allows us to model plasticity as a dynamical property that changes in time during ontogeny, reflecting the well-known fact that organisms are more or less plastic at different developmental stages.