Daniela Jezova

Repeated stress-induced activation of corticotropin-releasing factor neurons enhances vasopressin stores and colocalization with corticotropin-releasing factor in the median eminence of rats.

Stress-induced release of corticotropin-releasing factor (CRF) and vasopressin (AVP) was studied in rats by measuring the decline of CRF and AVP stores in the median eminence after blockade of fast axonal transport with colchicine (5 micrograms per rat intracisternally). Quantitative immunocytochemistry was used to detect changes in CRFi and AVPi in the external zone of the median eminence (ZEME) selectively. Immobilization stress induced a fast ACTH response to 1,000-2,000 pg/ml which was associated with a fall in both CRFi and AVPi of 34% during the first 30 min. This is followed by different time courses of further AVPi and CRFi depletion. In addition, we investigated the effect of repeated daily stress exposure on CRFi and AVPi in the ZEM 1 day after stress exposure. Repeated daily immobilization for 9 or 16 subsequent days did not affect the CRFi stores in the ZEME, but increased the AVPi stores to 161 +/- 13% and 218 +/- 11% respectively. Quantitative analysis of electron microphotographs of repeatedly handled rats showed a mean density of CRF positive profiles in the ZEME of 45.5 +/- 2.5 per 500 microns 2 of which 25% also stained for pro-AVP-derived peptides. After 9 subsequent days of immobilization the total density of CRF-positive profiles remained unchanged, but the fraction of CRF swellings that also stained for pro-AVP-derived peptides increased approximately 2-fold. We conclude that (1) the secretion of AVPi and CRFi from the ZEME are independently controlled, indicating differential activation of AVP containing and AVP deficient CRF neurons during acute immobilization, and (2) repeated stress leads to plastic changes in hypothalamic CRF neurons resulting in increased AVP stores and colocalization in CRF nerve terminals.

Effect of environmental enrichment on stress related systems in rats

The aim of this study was to test whether environmental enrichment alters the status and responsiveness of pituitary‐adrenocortical and sympathetic‐adrenomedullary hormones in rats. Previous studies have shown that rats kept in an enriched environment differ from those kept in standard cages in dendritic branching, synaptogenesis, memory function, emotionality and behaviour. In male Wistar rats kept in an enriched environment for 40 days, we studied basal concentrations of hormones, endocrine responses to 5‐HT1A challenge and responsiveness and adaptation to repeated handling. Environmental enrichment consisted of large plexiglass cages with 10 rats per cage, which contained variety of objects exchanged three times a week. Rats kept in this enriched environment had higher resting plasma concentrations of corticosterone, larger adrenals and increased corticosterone release to buspirone challenge compared to controls. Lower adrenocorticotropic hormone, corticosterone and adrenaline responses to handling were noticed in rats kept in an enriched environment. Exposure to repeated handling led to a more rapid extinction of corticosterone responses in rats kept in an enriched environment. Thus, environmental enrichment leads to pronounced changes in neuroendocrine regulation, including larger adrenals and increased adrenocortical function, which are so far considered to be indication of chronic stress.

Stress-induced changes in messenger RNA levels of N-methyl-d-aspartate and AMPA receptor subunits in selected regions of the rat hippocampus and hypothalamus

The postsynaptic AMPA/kainate and N-methyl-D-aspartate-selective glutamate receptors are formed by several different subunits and the overall subunit composition of the receptor appears to determine its physiological and pharmacological properties. Although glutamatergic mechanisms have been implicated in various forms of hippocampal stress responses, the impact of stress on glutamate receptor subunit composition has not yet been elucidated. We have used cell-by-cell quantitative in situ hybridization to assess stress-induced changes in transcript levels of N-methyl-D-aspartate and AMPA receptor subunit genes in subdivisions of the rat hippocampus and hypothalamus that are implicated in the stress response. We found that 24 h after a single immobilization stress there was a significant increase in the cellular level of NR1 subunit messenger RNA (about 35-45% above control values) in hippocampal CA3 and CA1 pyramidal cells as well as in neurons of the hypothalamic supraoptic and paraventricular nuclei. Moreover, in the CA3 area we have detected a concomitant increase (50% above controls) in the level of NR2B subunit messenger RNA, while the expression of NR2A subunit gene did not change after stress. Stress induced a selective decrease in the level of AMPA receptor subunit glutamate receptor A messenger RNA in neurons of both the CA3 and CA1 areas (18 and 24%, respectively, below control values). These results suggest that the regulation of specific subunit messenger RNAs of the N-methyl-D-aspartate and AMPA receptors may be involved in altered hippocampal and hypothalamic responsiveness to glutamate and thus could play a critical role in stress-induced changes in their function.

Repeated stress enhances vasopressin synthesis in corticotropin releasing factor neurons in the paraventricular nucleus

The effect of repeated stress on corticotropin-releasing factor (CRF) and vasopressin (AVP) synthesis in parvocellular neurons of the paraventricular nucleus (PVN) was studied by means of double label immunocytochemistry. Once daily immobilization of male rats for 16 days leads to a 75% increase in the number of CRF immunoreactive neurons, but a 5-fold elevation in the number of AVP containing CRF cell bodies. These results demonstrate that repeated stress activates AVP synthesis in CRF neurons.

Vasopressin and Oxytocin in Stress

Though oxytocin and vasopressin are similar in structure and are produced in the same brain regions, they show specific responses under stress conditions. In humans, increases in peripheral blood vasopressin appear to be a consistent finding during many acute stress situations, while in rats, vasopressin secretion is unresponsive to several stimuli known to induce ACTH and catecholamine release. Even decreases in vasopressin levels during stress were described. In accordance with others, we observed enhanced vasopressin release in response to stress stimuli with an osmotic component such as hypertonic saline injection but also during exposure of rats to a warm environment. Immobilization stress which fails to induce vasopressin release was reported to increase hypothalamic vasopressin mRNA and plasma vasopressin levels in chronically adreno-demedullated rats. Unlike vasopressin, oxytocin may be considered a typical stress hormone responding to osmotic as well as other stress stimuli. We found that acute exposure of rats to immobilization stress resulted in an increase in oxytocin mRNA level. In addition, we have shown that magnocellular neurons of the paraventricular nucleus, but not the supraoptic nucleus, are essential for oxytocin release during immobilization stress. The release of posterior pituitary hormones represents an important component of the stress response.

The blood–spinal cord barrier: Morphology and Clinical Implications

The blood–spinal cord barrier (BSCB) is the functional equivalent of the blood–brain barrier (BBB) in the sense of providing a specialized microenvironment for the cellular constituents of the spinal cord. Even if intuitively the BSCB could be considered as the morphological extension of the BBB into the spinal cord, evidence suggests that this is not so. The BSCB shares the same principal building blocks with the BBB; nevertheless, it seems that morphological and functional differences may exist between them. Dysfunction of the BSCB plays a fundamental role in the etiology or progression of several pathological conditions of the spinal cord, such as spinal cord injury, amyotrophic lateral sclerosis, and radiation‐induced myelopathy. This review summarizes current knowledge of the morphology of the BSCB, the methodology of studying the BSCB, and the potential role of BSCB dysfunction in selected disorders of the spinal cord, and finally summarizes therapeutic approaches to the BSCB. Ann Neurol 2011;

Brain angiotensin II modulates sympathoadrenal and hypothalamic pituitary adrenocortical activation during stress.

Angiotensin II (Ang II) type‐1 (AT1) receptors are present in areas of the brain controlling autonomic nervous activity and the hypothalamic‐pituitary‐adrenal (HPA) axis, including CRH cells in the hypothalamic paraventricular nucleus (PVN). To determine whether brain AT1 receptors are involved in the activation of the HPA axis and sympathetic system during stress, we studied the effects of acute immobilization stress on plasma catecholamines, ACTH and corticosterone, and mRNA levels of CRH and CRH receptors (CRH‐R) in the PVN in rats under central AT1 receptor blockade by the selective antagonist, Losartan. While basal levels of epinephrine, norepinephrine and dopamine in plasma were unaffected 30 min after icv injection of Losartan (10 μg), the increases after 5 and 20 min stress were blunted in Losartan treated rats (P<0.05 for norepinephrine, and P<0.01 for epinephrine and dopamine, vs controls). Basal or stress‐stimulated plasma ACTH and corticosterone levels were unaffected by icv Losartan treatment. Using in situ hybridization studies, basal levels of CRH mRNA and CRH‐R mRNA in the PVN were unchanged after icv Losartan. While Losartan had no effect on the increases in CRH‐R mRNA levels 2 or 3 h after 1 h immobilization, it prevented the increases in CRH mRNA. The blunted plasma catecholamine responses after central AT1 receptor blockade indicate that endogenous Ang II in the brain is required for sympathoadrenal activation during immobilization stress. While Ang II appears not to be involved in the acute secretory response of the HPA axis, it may play a role in regulating CRH expression in the PVN.

Activity of the hypothalamic pituitary adrenal axis and sympathoadrenal system during food and water deprivation in the rat

It has been previously shown that chronic water deprivation or hypertonic saline intake, osmotic stress models with concomitant decrease in food intake, decrease hypothalamic CRH mRNA levels and ACTH responses to acute stimulation. To determine the contribution of food restriction to the effects of osmotic stimulation, the function of the hypothalamic pituitary adrenal axis was analyzed in rats subjected to food deprivation, water deprivation or their combination for 60 h. In all three groups, basal levels of plasma corticosterone were increased, while ACTH and catecholamines were unchanged. Basal plasma vasopressin levels were normal in food deprived rats, but significantly increased in water deprived and simultaneously food and water deprived rats. In contrast to the 25% reduction of plasma ACTH responses to 30 min immobilization by water deprivation, food deprivation had no inhibitory effect and prevented the decreased ACTH responsiveness caused by water deprivation. In control rats, plasma corticosterone levels increased 22.5-fold 30 min after immobilization, and this response was significantly potentiated in the water deprived, food deprived and combined food and water deprived groups. The elevation in plasma catecholamines in response to acute immobilization was also enhanced in both water deprived and food deprived rats. In situ hybridization studies showed a 35% increase in VP mRNA levels in the PVN after water deprivation, whereas food deprivation caused a slight decrease and prevented the stimulatory effect of water deprivation. CRH mRNA in the PVN was reduced by 27% after food deprivation and by 67% after water deprivation, but simultaneous food and water deprivation caused a significantly smaller reduction similar to that in food deprivation alone.(ABSTRACT TRUNCATED AT 250 WORDS)

High trait anxiety in healthy subjects is associated with low neuroendocrine activity during psychosocial stress.

Altered stress responsiveness has been repeatedly related to mood and anxiety disorders. In a traditional view, a reduction of the stress response has been thought favorable. The goal of the present study was to verify the hypothesis that high anxiety is accompanied by enhanced hormone release during stress. Healthy subjects at the upper (anxious, n = 15) and lower (non-anxious, n = 12) limits of the normal range of a trait anxiety scale (State trait anxiety inventory) were exposed to psychosocial stress procedure based on public speech. Hormone levels, cardiovascular activation and skin conductance were measured. Exposure to psychosocial stress was associated with significant increases of all parameters measured. During the stress procedure, subjects with high trait anxiety exhibited lower levels of hormones of the hypothalamo-pituitary-adrenocortical axis, namely ACTH and cortisol in plasma, as well as cortisol in saliva. Similarly, the stress-induced activation of epinephrine, norepinephrine and prolactin secretion was significantly lower in anxious subjects in comparison with that in non-anxious subjects. Thus, in contrast to the traditional view, high anxiousness was not associated with exaggerated stress response. Our findings suggest that high trait anxiety may be associated with an inability to respond with adequate hormone release to acute stress stimuli.

Effect of Repeated Lipopolysaccharide Administration on Tissue Cytokine Expression and Hypothalamic‐Pituitary‐Adrenal Axis Activity in Rats

The effects of chronic immune challenge on cytokine expression and hypothalamic‐pituitary‐adrenal axis (HPA) axis responses to stress were studied in Wistar rats after administration of increasing doses of lipopolysaccharide (LPS). Repeated LPS (R‐LPS) decreased body weight and increased adrenal weight and pituitary pro‐opiomelanocortin mRNA levels. LPS injection increased plasma adrenocorticotropic hormone (ACTH) and corticosterone but the effect was attenuated in R‐LPS. Plasma corticosterone but not ACTH responses to restraint were also reduced in R‐LPS. Basal and restraint‐stimulated corticotropin releasing hormone (CRH) mRNA levels were lower in R‐LPS, but responses to a new LPS injection were similar to controls. In contrast, type 1 CRH receptor (CRH‐R1) mRNA responses to both LPS and restraint were blunted in R‐LPS. Vasopressin mRNA levels in parvocellular neurones were higher in R‐LPS, and increased further after restraint but not after a new LPS injection. Glucocorticoid receptor (GR) levels in the paraventricular nucleus (PVN) increased after a single LPS or R‐LPS (24 h after the last injection) but declined after a new injection in R‐LPS. Interleukin (IL)‐1β and IL‐6 mRNAs increased in the pituitary, spleen and circumventricular organs after single or R‐LPS, suggesting that cytokines may contribute to the activation of the HPA axis though pathways from the circumventricular organs as well as paracrine effects in the pituitary. The data show that (i) adaptation of the HPA axis during repeated LPS injection involves increases in vasopressin : CRH expression ratios in parvocellular neurones; (ii) that hypothalamic CRH and vasopressin responses to acute stimulation are independent of CRH‐R1 expression in the PVN; and (iii) there is a dissociation between pituitary and adrenal responses to acute stress suggesting a decrease of adrenal sensitivity to ACTH.