Enhanced corticosterone concentrations and attenuated Fos expression in the medial amygdala of female oxytocin knockout mice exposed to psychogenic stress

Centrally released oxytocin (OT) is believed to attenuate the response of the hypothalamic-pituitary-adrenal (HPA) axis to psychogenic stress. To test this hypothesis, we measured plasma corticosterone concentrations and Fos-immunoreactive protein in the paraventricular nucleus of the hypothalamus (PVN) and limbic brain areas of female wild-type and OT knockout mice that were exposed to a shaker platform, a predominantly psychogenic stress. Plasma corticosterone concentrations after shaker stress were higher in female OT knockout mice than wild-type mice. Genotypic differences in the corticosterone response after shaker stress persisted across all stages of the estrous cycle and when mice were conditioned to repeated shaker stress. Shaker stress activated Fos in OT-positive neurons of wild-type mice and corticotropin-releasing hormone-positive, but not vasopressin-positive, neurons within the PVN of wild-type and OT knockout mice. Fos expression was also increased after shaker stress in the bed nucleus of the stria terminalis, medial and central nuclei of the amygdala, medial preoptic area, and the paraventricular nucleus of the thalamus of wild-type and OT knockout mice. However, Fos expression in the medial amygdala was significantly lower in female OT knockout mice than wild-type mice. Our findings indicate heightened stress-induced corticosterone release in female OT knockout mice. Therefore, the results suggest that OT pathways play a role in attenuating the HPA axis response to psychogenic stress in female mice.     

Molecular identification and physiological characterization of a novel monosaccharide transporter from Arabidopsis involved in vacuolar sugar transport

The tonoplast monosaccharide transporter (TMT) family comprises three isoforms in Arabidopsis thaliana, and TMT-green fluorescent protein fusion proteins are targeted to the vacuolar membrane. TMT promoter-beta-glucuronidase plants revealed that the TONOPLAST MONOSACCHARIDE TRANSPORTER1 (TMT1) and TMT2 genes exhibit a tissue- and cell type-specific expression pattern, whereas TMT3 is only weakly expressed. TMT1 and TMT2 expression is induced by drought, salt, and cold treatments and by sugar. During cold adaptation, tmt knockout lines accumulated less glucose and fructose compared with wild-type plants, whereas no differences were observed for sucrose. Cold adaptation of wild-type plants substantially promoted glucose uptake into isolated leaf mesophyll vacuoles. Glucose uptake into isolated vacuoles was inhibited by NH(4)(+), fructose, and phlorizin, indicating that transport is energy-dependent and that both glucose and fructose were taken up by the same carrier. Glucose import into vacuoles from two cold-induced tmt1 knockout lines or from triple knockout plants was substantially lower than into corresponding wild-type vacuoles. Monosaccharide feeding into leaf discs revealed the strongest response to sugar in tmt1 knockout lines compared with wild-type plants, suggesting that TMT1 is required for cytosolic glucose homeostasis. Our results indicate that TMT1 is involved in vacuolar monosaccharide transport and plays a major role during stress responses.     

The absence of the SOD1 gene causes abnormal monoaminergic neurotransmission and motivational impairment-like behavior in mice

Copper/zinc superoxide dismutase (SOD1), a primary anti-oxidative enzyme, protects cells against oxidative stress. We report herein on a comparison of behavioral and neurobiological changes between SOD1 knockout (KO) and wild-type mice, in an attempt to assess the role of SOD1 in brain functions. SOD1 KO mice exhibited impaired motivational behavior in both shuttle-box learning and three-chamber social interaction tests. High levels of dopamine transporter protein and an acceleration of serotonin turnover were also detected in the cerebrums of the SOD1 KO mice. These findings suggest that SOD1 deficiency disturbs monoaminergic neurotransmission leading to a decrease in motivational behavior.     

The diagnostic role of glycosaminoglycans in pleural effusions: A pilot study

Background

While modulation of the serotonin transporter (5HTT) has shown to be a risk factor for pulmonary arterial hypertension for almost 40 years, there is a lack of in vivo data about the broad molecular effects of pulmonary inhibition of 5HTT. Previous studies have suggested effects on inflammation, proliferation, and vasoconstriction. The goal of this study was to determine which of these were supported by alterations in gene expression in serotonin transporter knockout mice.

Methods

Eight week old normoxic mice with a 5-HTT knock-out (5HTT-/-) and their heterozygote(5HTT+/-) or wild-type(5HTT+/+) littermates had right ventricular systolic pressure(RVSP) assessed, lungs collected for RNA, pooled, and used in duplicate in Affymetrix array analysis. Representative genes were confirmed by quantitative RT-PCR and western blot.

Results

RVSP was normal in all groups. Only 124 genes were reliably changed between 5HTT-/- and 5HTT+/+ mice. More than half of these were either involved in inflammatory response or muscle function and organization; in addition, some matrix, heme oxygenase, developmental, and energy metabolism genes showed altered expression. Quantitative RT-PCR for examples from each major group confirmed changes seen by array, with an intermediate level in 5HTT +/- mice.

Conclusion

These results for the first time show the in vivo effects of 5HTT knockout in lungs, and show that many of the downstream mechanisms suggested by cell culture and ex vivo experiments are also operational in vivo. This suggests that the effect of 5HTT on pulmonary vascular function arises from its impact on several systems, including vasoreactivity, proliferation, and immune function.     

Epidemiology and clinical presentation of stress-related peptic damage and chronic peptic ulcer

Stress is often considered a risk factor for upper gastrointestinal tract disease, as any acute threat to homeostasis evokes an adaptive or allostatic response. Various types of stress may play a role in the onset and modulation of acute or chronic peptic ulcer disease. When upper endoscopy is employed, stress-related acute mucosal damage is found to develop shortly after admission to an intensive care unit in 60 to 100 percent of patients. However, the epidemiology of chronic peptic damage has not been accurately described by type of stressor, and any association is controversial. The incidence of chronic peptic ulcer disease is falling; the proportion of chronic peptic ulcers that are Helicobacter pylori negative appears to be between 5% and 20%, and some have suggested that stress or other psychological factors may play a role here. Therefore, our objective is to provide an overview of the epidemiology and clinical presentation of stress-related peptic damage, in order to shed insights into the current understanding of the pathophysiology and treatment.     

Stress and arousal

The hypocretins (also know as orexins) are two neuropeptides now commonly described as critical components for maintaining and regulating the stability of arousal. Several lines of evidence have raised the hypothesis that hypocretin-producing neurons are part of the circuitries that mediate the hypothalamic response to acute stress. New data indicate that the corticotrophin-releasing factor (CRF) peptidergic system directly innervates hypocretin-expressing neurons. CRF depolarizes hypocretin neurons, and this effect is blocked by a CRF-R1 antagonist. Furthermore, activation of hypocretinergic neurons by stress is impaired in CRF-R1 knockout mice. These data suggest that CRF-R1 receptor mediates the stress-induced activation of the hypocretinergic system. A significant amount of evidence also indicates that hypocretin cells connect reciprocally to the CRF system. We propose that upon stressor stimuli, CRF activates the hypocretin system, which relays these signals to brain stem nuclei involved in the modulation of arousal as well as to the extended amygdala, a structure involved in the negative motivational state that drives addiction.     

Serotonergic genes modulate amygdala activity in major depression

Serotonergic genes have been implicated in the pathogenesis of depression probably via their influence on neural activity during emotion processing. This study used an imaging genomics approach to investigate amygdala activity in major depression as a function of common functional polymorphisms in the serotonin transporter gene (5-HTTLPR) and the serotonin receptor 1A gene (5-HT(1A)-1019C/G). In 27 medicated patients with major depression, amygdala responses to happy, sad and angry faces were assessed using functional magnetic resonance imaging at 3 Tesla. Patients were genotyped for the 5-HT(1A)-1019C/G and the 5-HTTLPR polymorphism, including the newly described 5-HTT-rs25531 single nucleotide polymorphism. Risk allele carriers for either gene showed significantly increased bilateral amygdala activation in response to emotional stimuli, implicating an additive effect of both genotypes. Our data suggest that the genetic susceptibility for major depression might be transported via dysfunctional neural activity in brain regions critical for emotion processing.     

Predator stress induces behavioral inhibition and amygdala somatostatin receptor 2 gene expression

Psychological stressors precipitate and maintain stress-induced psychopathology, and it is likely that altered amygdala function underlies some of the deleterious effects of psychological stress. To understand the mechanisms underlying the linkage between the response to psychological stressors and maladaptive or psychopathological responses, we have focused on amygdala responsivity in animal models employing species-specific psychological stressors. In the present study, we characterized the effects of a 15-min exposure to a natural predator, the ferret, on rat behavior and the expression of the somatostatin family of genes in the amygdala. We examined the somatostatin family of genes because substantial evidence shows that central somatostatin systems are altered in various neuropsychiatric illnesses. We report that rats respond to acute ferret exposure with a significant increase in fearful and anxious behaviors that is accompanied by robust amygdala activation and an increase in somatostatin receptor 2 (sst2) messenger RNA expression within the amygdala and anterior cingulate cortex. These studies are the first to show stress-induced changes in amygdala sst2 expression and may represent one mechanism by which psychological stress is linked to adaptive and maladaptive behavioral responses.     

Stress-induced extracellular Hsp72 is a functionally significant danger signal to the immune system

Extracellular heat-shock proteins (eHsp) such as those belonging to the 70-kDa family of Hsp (eg, Hsp72) have been hypothesized to act as a "danger signal" to immune cells, promote immune responses, and improve host defense. The current study tested this hypothesis. Adult male F344 rats were exposed to an acute laboratory stressor (100, 5-second, 1.6-mA inescapable tail shocks) and challenged with Escherichia coli. The number of colony-forming units (CFU) of bacteria at the site of injection, the levels of eHsp72, the immune response to eHsp72 and E. coli-derived lipopolysaccharide (LPS), and the amount of time required to recover from in vivo bacterial challenge were measured. CFUs were reduced 2, 4, and 6 hours after injection of E. coli in rats exposed to stress. Rats exposed to stress had elevated eHsp72 that was elevated rapidly (25 minutes) and remained elevated in the circulation and at the inflammatory site (2 hours after stressor termination). Both stressor exposure and eHsp72 administration in the absence of stress resulted in a facilitated pattern of recovery after bacterial inflammation induced by subcutaneous E. coli injection. Rats exposed to acute restraint (100 minutes) did not demonstrate elevated circulating eHsp72 or a facilitated pattern of recovery after bacterial challenge. In vitro stimulation of rat splenocytes and macrophages with eHsp72 elevated nitric oxide (NO), tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta, and IL-6, and this effect was specific to eHsp72 because it was not diminished by polymyxin B and was reduced by earlier heat-denature treatment. Stimulation of cells with eHsp72 combined with LPS resulted in a greater NO and cytokine response than that observed after stimulation with eHsp72 or LPS alone. In vivo, at the inflammatory site, the bacterial-induced NO response was potentiated by stress, and NO inhibition (L-NIO) reduced the stress-induced facilitation but had no effect on the control kinetics of bacterial inflammation recovery. Thus, these results lend support to the hypothesis that intense stressor exposure increases eHsp72, which acts as a danger signal to potentiate the NO response to bacterial challenge and facilitate recovery from bacterial inflammation.     

Postnatal handling reverses social anxiety in serotonin receptor 1A knockout mice

Mice lacking the serotonin receptor 1A (Htr1a knockout, Htr1a ^KO ) show increased innate and conditioned anxiety. This phenotype depends on functional receptor activity during the third through fifth weeks of life and thus appears to be the result of long-term changes in brain function as a consequence of an early deficit in serotonin signaling. To evaluate whether this phenotype can be influenced by early environmental factors, we subjected Htr1a knockout mice to postnatal handling, a procedure known to reduce anxiety-like behavior and stress responses in adulthood. Offspring of heterozygous Htr1a knockout mice were separated from their mother and exposed 15 min each day from postnatal day 1 (PD1) to PD14 to clean bedding. Control animals were left undisturbed. Maternal behavior was observed during the first 13 days of life. Adult male offspring were tested in the open field, social approach and resident–intruder tests and assessed for corticosterone response to restraint stress. Knockout mice showed increased anxiety in the open field and in the social approach test as well as an enhanced corticosterone response to stress. However, while no effect of postnatal handling was seen in wild-type mice, handling reduced anxiety-like behavior in the social interaction test and the corticosterone response to stress in knockout mice. These findings extend the anxiety phenotype of Htr1a ^KO mice to include social anxiety and demonstrate that this phenotype can be moderated by early environmental factors.     

Serotonin transporter deficiency in rats contributes to impaired object memory

Serotonin is well known for its role in affection, but less known for its role in cognition. The serotonin transporter (SERT) has an essential role in serotonergic neurotransmission as it determines the magnitude and duration of the serotonin signal in the synaptic cleft. There is evidence to suggest that homozygous SERT knockout rats (SERT^−/−), as well as humans with the short SERT allele, show stronger cognitive effects than wild-type control rats (SERT^+/+) and humans with the long SERT allele after acute tryptophan depletion. In rats, SERT genotype is known to affect brain serotonin levels, with SERT^−/− rats having lower intracellular basal serotonin levels than wild-type rats in several brain areas. In the present study, it was investigated whether SERT genotype affects memory performance in an object recognition task with different inter-trial intervals. SERT^−/−, heterozygous SERT knockout (SERT^+/−) and SERT^+/+ rats were tested in an object recognition test applying an inter-trial interval of 2, 4 and 8 h. SERT^−/− and SERT^+/− rats showed impaired object memory with an 8 h inter-trial interval, whereas SERT^+/+ rats showed intact object memory with this inter-trial interval. Although brain serotonin levels cannot fully explain the SERT genotype effect on object memory in rats, these results do indicate that serotonin is an important player in object memory in rats, and that lower intracellular serotonin levels lead to enhanced memory loss. Given its resemblance with the human SERT-linked polymorphic region and propensity to develop depression-like symptoms, our findings may contribute to further understanding of mechanisms underlying cognitive deficits in depression.