The perception of work stressors is related to reduced parasympathetic activity

Purpose  

The aim was to examine the perception of work stressors in relation to ambulatory measures of heart rate variability (HRV).     

The relationship between pain-related fear and lumbar flexion during natural recovery from low back pain

Pain-related fear has been associated with avoidance behavior and increased risk for chronic low back pain; however, few studies have examined how pain-related fear relates specifically to motion of the spine following an acute episode of back pain. Thirty-six participants with a recent episode of low back pain were recruited from the general population using a combination of fliers and radio advertisements. To explore the natural recovery from low back pain we recruited individuals who were not seeking medical care. Participants performed a forward bending task at 3, 6, and 12 weeks following onset of low back pain. Three-dimensional joint motions of the spine and hip were recorded using an electromagnetic tracking device. Initial assessments of low back pain and pain-related fear were then correlated with joint excursions observed during each forward bending. Lumbar motion was inversely related to pain-related fear, but not low back pain, at all three testing sessions. In contrast, hip motion was inversely related to pain at all three testing sessions but was not related to fear. These findings suggest that pain-related fear results in avoidance behavior that specifically limits or restricts motion of the lumbar spine.     

Evaluation of different tests based on observations for external model evaluation of population analyses

To evaluate by simulation the statistical properties of normalized prediction distribution errors (NPDE), prediction discrepancies (pd), standardized prediction errors (SPE), numerical predictive check (NPC) and decorrelated NPC (NPC_dec) for the external evaluation of a population pharmacokinetic analysis, and to illustrate the use of NPDE for the evaluation of covariate models. We assume that a model M_B has been built using a building dataset B, and that a separate validation dataset, V is available. Our null hypothesis H₀ is that the data in V can be described by M_B. We use several methods to test this hypothesis: NPDE, pd, SPE, NPC and NPC_dec. First, we evaluated by simulation the type I error under H₀ of different tests applied to the four methods. We also propose and evaluate a single global test combining normality, mean and variance tests applied to NPDE, pd and SPE. We perform tests on NPC and NPC_dec, after a decorrelation. M_B was a one compartment model with first order absorption (without covariate), previously developed from two phase II and one phase III studies of the antidiabetic drug, gliclazide. We simulated 500 external datasets according to the design of a phase III study. Second, we investigated the application of NPDE to covariate models. We propose two approaches: the first approach uses correlation tests or mean comparisons to test the relationship between NPDE and covariates; the second evaluates NPDE split by category for discrete covariates or quantiles for continuous covariates. We generated several validation datasets under H₀ and under alternative assumptions with a model without covariate, with one continuous covariate (weight), or one categorical covariate (sex). We calculated the powers of the different tests using simulations, where the covariates of the phase III study were used. The simulations under H₀ show a high type I error for the different tests applied to SPE and an increased type I error for pd. The different tests present a type I error close to 5% for the global test appied to NPDE. We find a type I error higher than 5% for the test applied to classical NPC but this test becomes close to 5% for NPC_dec. For covariate models, when model and validation dataset are consistent, type I error of the tests are close to 5% for both effects. When validation datasets and models are not consistent, the tests detect the correlation between NPDE and the covariate. We recommend to use NPDE over SPE for external model evaluation, since they do not depend on an approximation of the model and have good statistical properties. NPDE represent a better approach than NPC, since in order to perform tests on NPC, a decorrelation step must be applied before. NPDE, in this illustration, is also a good tool to evaluate model with or without covariates.     

Endocrine,neural and pharmacological aspects of sexual satiety in male rats

Sexual satiety is the inhibition of masculine mating behavior produced by copulation itself. This inhibition is manifested in different ways depending upon the species, the time and the amount of sexual behavior prior to sexual satiety. Pharmacological studies indicate that monoaminergic and opioidergic compounds modify this phenomenon in the rat and other species, possibly via a final dopaminergic pathway involving sexual motivation. Reduced androgen receptor expression and/or increased estrogen receptor alpha expression in specific brain areas are associated with the inhibition of mating behavior that characterizes rat sexual satiety. Androgen receptor over-expression in the same and other brain areas coincides with a partial recovery of rat male copulatory behavior after sexual satiety. The lateral septum, medial amygdala and medial preoptic area may participate in the neuroendocrine regulation of sexual satiety, based on changes in the expression of c-Fos, androgen receptor and estrogen receptor alpha in these cerebral regions. These data suggest that changes in steroid receptors, possibly triggered by modifications in neurotransmitters, underlie at least partly the inhibition of copulatory behavior characteristic of rat sexual satiety.