Effect of the number of vortices on the torque scaling in Taylor-Couette flow

Torque measurements in Taylor-Couette flow, with large radius ratio and large aspect ratio, over a range of velocities up to a Reynolds number of 24 000 are presented. Following a specific procedure, nine states with distinct number of vortices along the axis were found and the aspect ratio of the vortices were measured. The relationship between the speed and the torque for a given number of vortices is reported. In the turbulent Taylor vortex flow regime, at relatively high Reynolds number, a change in behaviour is observed corresponding to intersections of the torque-speed curves for different states. Before each intersection, the torque for a state with larger number of vortices is higher. After each intersection, the torque for a state with larger number of vortices is lower. The exponent, from the scaling laws of the torque, always depends on the aspect ratio of the vortices. When the Reynolds number is rescaled using the mean aspect ratio of the vortices, only a partial collapse of the exponent data is found.Comment: 11 pages, 6 figure

How age, sex and genotype shape the stress response

Exposure to chronic stress is a leading pre-disposing factor for several neuropsychiatric disorders as it often leads to maladaptive responses. The response to stressful events is heterogeneous, underpinning a wide spectrum of distinct changes amongst stress-exposed individuals'. Several factors can underlie a different perception to stressors and the setting of distinct coping strategies that will lead to individual differences on the susceptibility/resistance to stress. Beyond the factors related to the stressor itself, such as intensity, duration or predictability, there are factors intrinsic to the individuals that are relevant to shape the stress response, such as age, sex and genetics. In this review, we examine the contribution of such intrinsic factors to the modulation of the stress response based on experimental rodent models of response to stress and discuss to what extent that knowledge can be potentially translated to humans.FEDER through the Operational Programme Competitiveness Factors - COMPETE and National Funds through FCT - Foundation for Science and Technology under the project POCI-01-0145-FEDER-007038; and by the project NORTE-01-0145-FEDER-000013, supported by Norte Portugal Regional Operational Programme (NORTE, 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). We acknowledge the Portuguese Foundation for Science and Technology (FCT) for providing a post-doctoral fellowship to SR (SFRH/BPD/72710/2010), a doctoral fellowship to SM (SFRH/BD/69311/2010) and a fellowship to AN (ANR/NEU-OSD/0258/2012)info:eu-repo/semantics/publishedVersio

High-starch diets alter equine faecal microbiota and increase behavioural reactivity

Gut microbiota have been associated with health, disease and behaviour in several species and are an important link in gut-brain axis communication. Diet plays a key role in affecting the composition of gut microbiota. In horses, high-starch diets alter the hindgut microbiota. High-starch diets are also associated with increased behavioural reactivity in horses. These changes in microbiota and behaviour may be associated. This study compares the faecal microbiota and behaviour of 10 naïve ponies. A cross-over design was used with experimental groups fed high-starch (HS) or high-fibre (HF) diets. Results showed that ponies were more reactive and less settled when being fed the HS diet compared to the HF diet. Irrespective of diet, the bacterial profile was dominated by two main phyla, Firmicutes, closely followed by Bacteroidetes. However, at lower taxonomic levels multivariate analysis of 16S rRNA gene sequencing data showed diet affected faecal microbial community structure. The abundance of 85 OTUs differed significantly related to diet. Correlative relationships exist between dietary induced alterations to faecal microbiota and behaviour. Results demonstrate a clear link between diet, faecal microbial community composition and behaviour. Dietary induced alterations to gut microbiota play a role in affecting the behaviour of the host

5-hydroxyoxindole, an indole metabolite, is present at high concentrations in brain

International audience5-Hydroxyoxindole has been identified as a urinary metabolite of indole, which is produced from tryptophane via the tryptophanase activity of gut bacteria. We have demonstrated recently that 5-hydroxyoxindole is an endogenous compound in blood and tissues of mammals, including humans. To date, 5-hydroxyoxindole's role is unknown. The aim of this study was to compare 5-hydroxyoxindole levels in plasma and cerebrospinal fluid (CSF) during day-night and seasonal changes, as a common approach to pilot physiological characterization of any compound. Simultaneous blood and CSF sampling was performed in the ewe, because its size allows collection in quantities suitable for 5hydroxyoxindole assay (HPLC-ED) in awake animals, without obvious physiological or behavioral disturbance. 5-Hydroxyoxindole concentration was quite stable in plasma (2-6 nM range), whereas, in CSF, it displayed marked day-night and photoperiodic variations (4-116 nM range). 5-Hydroxyoxindole levels in CSF were twofold higher at night than during the day and at least one order of magnitude higher during the long compared with the short photoperiod. These day/night and photoperiodic variations persisted after pinealectomy, indicating that 5-hydroxyoxindole rhythms in CSF are independent of melatonin formation. In conclusion, high levels of 5-hydroxyoxindole in the CSF during long photoperiod and its daily modulation suggest physiological involvement of 5-hydroxyoxindole in rhythmic adjustments in the brain, independently of the pineal gland

Receptors for interleukin-1 in the central nervous and neuroendocrine systems. Role in infection and stress.

International audienceThe functional interactions between the Immune (IS) and the Central Nervous Systems (CNS) are clearly indicated by the fact these systems are sharing mediators and receptors. Interleukins and more specifically Interleukin-1 (IL-1) have been shown to be powerful regulators of both system activity which suggested IL-1 receptors in the CNS. IL-1 receptors, similar to type I lymphocyte receptors, have been characterized in murine nervous structures (dentate gyrus of the hippocampus and frontal cortex), in vascular structures (vessels, choroid plexus) and in a neuroendocrine structure (anterior pituitary). Stimulation of the immune system and of IL-1 synthesis by bacterial product (intra peritoneal injection of LPS) induced a marked decrease of IL-1 receptor levels in the CNS. Under the same conditions pituitary receptors were unaffected indicating the autonomy of brain functioning. This decrease is in relation with an increase in local IL-1 synthesis as indicated by the increase of IL-1 mRNA in the brain tissue. During viral infection (rabies virus) very similar results are observed. Brain receptors are decreasing in the brain at day 4 post infection while IL-1 concentration is increasing in the brain tissue. Pituitary receptors are not modified during the evolution of the disease. Stress and glucocorticoid treatment are strong inhibitors of immune functions by inhibiting IL-1 synthesis. Neither treatment modified brain receptors suggesting that IL-1 synthesis is not modulated by glucocorticoids in the CNS as in the immune system. However an increase in pituitary receptor level was observed in both cases.(ABSTRACT TRUNCATED AT 250 WORDS

Absence of the gut microbiota enhances anxiety-like behavior and neuroendocrine response to acute stress in rats

Background and aims: Establishment of the gut microbiota is one of the most important events in early life and emerging evidence indicates that the gut microbiota influences several aspects of brain functioning, including reactivity to stress. To better understand how the gut microbiota contributes to a vulnerability to the stress-related psychiatric disorders, we investigated the relationship between the gut microbiota, anxiety-like behavior and HPA axis activity in stress-sensitive rodents. We also analyzed the monoamine neurotransmitters in the brain upper structures involved in the regulation of stress and anxiety. Methods: Germfree (GF) and specific pathogen free (SPF) F344 male rats were first subjected to neurological tests to rule out sensorimotor impairments as confounding factors. Then, we examined the behavior responses of rats to social interaction and open-field tests. Serum corticosterone concentrations, CRF mRNA expression levels in the hypothalamus, glucocorticoid receptor (GR) mRNA expression levels in the hippocampus, and monoamine concentrations in the frontal cortex, hippocampus and striatum were compared in rats that were either exposed to the open-field stress or not. Results: GF rats spent less time sniffing an unknown partner than SPF rats in the social interaction test, and displayed a lower number of visits to the aversive central area, and an increase in latency time, time spent in the corners and number of defecations in the open-field test. In response to the open-field stress, serum corticosterone concentrations were 2.8-fold higher in GF than in SPF rats. Compared to that of SPF rats, GF rats showed elevated CRF mRNA expression in the hypothalamus and reduced GR mRNA expression in the hippocampus. GF rats also had a lower dopaminergic turnover rate in the frontal cortex, hippocampus and striatum than SPF rats. Conclusions: In stress-sensitive F344 rats, absence of the gut microbiota exacerbates the neuroendocrine and behavioral responses to acute stress and the results coexist with alterations of the dopaminergic turnover rate in brain upper structures that are known to regulate reactivity to stress and anxiety-like behavior. (C) 2014 Elsevier Ltd. All rights reserved

Prolactin receptors in the rat hypothalamus: autoradiographic localization and characterization

A precise mapping of prolactin (PRL) receptors in the rat brain has been achieved. Localization of binding sites for both 125I-human growth hormone (125I-hGH) and 125I-monoclonal anti-PRL receptor (125I-U5) was studied by in vitro autoradiography on brain sections in female rats (n = 7). The analysis of autoradiograms generated from 12 adjacent sections at 11 different brain levels (bregma 0.2 to -4.8 mm) revealed 9 distinctive localizations for 125I-hGH binding sites: preoptic suprachiasmatic nucleus, medial preoptic area, periventricular, supraoptic, paraventricular, arcuate and vetromedial nuclei and also the median eminence and the infundibulum. Specificity for PRL binding was assessed by competition experiment of 125I-hGH with unlabeled hGH and ovine PRL. Binding sites were similarly localized by 125I-U5 indicating the presence of PRL receptors moiety. The quantitative analysis with 0.6 nM 125I-hGH demonstrated maximal densities in the preoptic suprachiasmatic and arcuate nuclei and minimal densities in the median eminence and the infundibulum. Due to ample antero-posterior variations no significant changes were observed during the estrous cycle. Saturation analysis of binding in the arcuate nucleus indicated a single class of high affinity (Kd from 0.9 to 2.2 nM) receptors (Bmax from 34 to 44 fmol/mg of proteins). The present data provide the hypothalamic cartography of PRL receptors in the female rat brain and support all the physiological evidence for the existence of a direct action of PRL in the hypothalamus

Rat interleukin-1 beta binding sites in rat hypothalamus and pituitary gland.

International audienceIn this study, radiolabeled recombinant rat interleukin-1 beta (r125I-IL-1 beta) was used to localize and characterize IL-1 beta binding in rat hypothalamus and pituitary gland by quantitative autoradiography. The ability of this ligand to bind to type I IL-1 receptor was first tested on murine lymphoma cells (EL-4). In the rat-tissue sections, high densities of specific r125I-IL-1 beta binding sites were localized in the anterior as well as the posterior pituitary and in the choroid plexus. A fine labeling was observed in meninges and third ventricle walls while no binding was detected in the hypothalamic nuclei. Saturation experiments, in the anterior and posterior pituitary, revealed one specific binding site with an affinity constant (Kd) of 0.5 nM. Competition experiments were achieved using either rat IL-1 beta (rIL-1 beta) or human IL-1s (hIL-1 alpha, hIL-1 beta and IL-1 receptor antagonist: hIL-1a). Affinity constants (Ki) were drastically different according to the ligand used, while Ki values were found similar in anterior and posterior pituitary. Competition with rIL-1 beta revealed one binding affinity (Ki of 0.1 nM range). In contrast, competition with hIL-1 beta revealed two binding affinities: a high (Ki: 0.1 pM range) and a low one (Ki: 1 nM range). Competition with hIL-1ra was obtained for high concentrations only (Ki: 10-100 nM range), whereas human IL-1 alpha (hIL-1 alpha) was unable to compete at 1-100 nM.(ABSTRACT TRUNCATED AT 250 WORDS