Central histaminergic involvement during stress in rats.

Effects of some drugs modulating central histaminergic (HA) transmission were evaluated on restraint stress (RS)-induced gastric ulcerogenesis, plasma corticosterone and immune responses in rats. RS for (i) 6 hr or (ii) 24 hr at room temperature, and (iii) 3 hr at 4 degrees C (CRS) all induced gastric mucosal erosions and elevated plasma corticosterone levels, the effects with the latter two RS procedures being most consistent. Pretreatment of rats with neuronal HA depletor, alpha-FMH (100 mg/kg, ip) attenuated both ulcer severity and corticosterone response, during both 24 hr RS and CRS. Similar effects were also seen with the mast cell degranulator, C-48/80 (10 micrograms/kg, i.c.v.) treatment. Further, the H1-blocker, pheniramine (25 mg/kg, ip) but not the centrally acting H2-blocker, zolantidine (5 mg/kg, ip) produced clearcut attenuations in both stress markers, during the experimental stressors. In rats immunized in SRBC, 24 hr RS (and not CRS) significantly prevented the humoral immune responses to the antigen. alpha-FMH, C 48/80 and pheniramine but not zolantidine, reversed this response during 24 hr RS. The results indicate a central HA ergic involvement in the visceral, endocrinal and immune responses during RS and suggest the probable role of both neuronal as well as extraneuronal (mast cell) HA and activation of H1-receptors in the mediation of these effects.     

Contribution of the antioxidative property of astaxanthin to its protective effect on the promotion of cancer metastasis in mice treated with restraint stress

We investigated the effects of astaxanthin on the antitumor effector activity of natural killer (NK) cells suppressed by stress in mice in order to define the immunological significance of astaxanthin (ASX) when combined with restraint stress treatment. When the mice were treated with restraint stress alone, the total number of spleen cells, and the level NK cell activity per spleen were reduced to a nadir on day 3. The stress also caused a significant increase in the lipid peroxidation of liver tissue. ASX (100 mg/kg/day, p.o., 4 days) improved the immunological dysfunction induced by restraint stress. On the other hand, metastatic nodules were observed in the livers of syngenic DBA/2 mice on day 12 after inoculation of P815 mastocytoma cells. Hepatic metastasis was promoted further by restraint stress when applied on day 3 before the inoculation of P815. Daily oral administration of ASX (1 mg/kg/day, p.o., 14 days) markedly attenuated the promotion of hepatic metastasis induced by restraint stress. These results suggested that astaxanthin improves antitumor immune responses by inhibiting of lipid peroxidation induced by stress.     

Possible prostaglandin-dopamine interactions during experimental gastric ulcer formation

The effects of dopamine (DA) agonists and antagonists were investigated on indomethacin--and restraint stress (6 hr at RT)--induced gastric ulcer formation in rats. The DA-agonists, apomorphine and bromocryptine (both at 5 mg/kg) significantly attenuated the frequency and severity of gastric mucosal lesions in both experimental models. The DA-antagonist, haloperidol (0.05 and 1.0 mg/kg) aggravated the gastric ulcerogenesis of both indomethacin and stress, the effects with the lower dose being statistically significant. Haloperidol (0.05 mg/kg) also prevented the cytoprotective effects of apomorphine on indomethacin-ulcers. The atypical DA-antagonist, sulpiride (10 and 50 mg/kg), however, showed differential dose- and model-specific effects. Whereas, the lower dose attenuated indomethacin-ulcers, the higher dose (50 mg/kg) tended to aggravate this phenomenon. The trend of results were reversed in the restraint stress model. Indomethacin (1 mg/kg) aggravated stress-ulcers, an effect which was also appreciably neutralised by apomorphine (5 mg/kg) pretreatment. These results are discussed in light of possible prostaglandin-DA interactions during such experimental gastric pathology.     

Prevention by diazepam of adverse effects of maternal restraint stress on postnatal development and learning in the rat.

Rats on days 12--14 of pregnancy were treated with restraint stress alone (9h daily), restraint stress plus diazepam (1 mg/kg, twice daily), diazepam alone, or left as untreated controls. Postnatal development and behaviour was assessed on a wide-ranging battery of tests. Offspring of mothers subjected to restraint stress alone were significantly retarded on a number of developmental measures including growth, ear-opening, cliff avoidance response, auditory startle response and mid-air righting reflex. When adult these offspring also showed significantly impaired learning ability in a swimming maze. However, the rate of development and learning ability in the restraint plus diazepam or diazepam alone groups was comparable to or slightly advanced of that in untreated controls. It is concluded that concurrent administration of a low dose of the tranquiliser diazepam during restraint stress prevents the adverse postnatal effects of maternal restraint stress.     

Focus: The Science of Stress: The Impact of Maternal Antioxidants on Prenatal Stress Effects on Offspring Neurobiology and Behavior

Prenatal stress is a neuropsychiatric risk factor, and effects may be mediated by prenatal oxidative stress. Cell types in the brain sensitive to oxidative stress—cortical microglia and cortical and hippocampal interneurons—may be altered by oxidative stress generated during prenatal stress and may be neurobiological substrates for altered behavior. Our objective was to determine the critical nature of oxidative stress in prenatal stress effects by manipulating prenatal antioxidants. CD1 mouse dams underwent restraint embryonic day 12 to 18 three times daily or no stress and received intraperitoneal injections before each stress period of vehicle, N-acetylcysteine (200 mg/kg daily), or astaxanthin (30 mg/kg before first daily stress, 10 mg/kg before second/third stresses). Adult male and female offspring behavior, microglia, and interneurons were assessed. Results supported the hypothesis that prenatal stress-induced oxidative stress affects microglia; microglia ramification increased after prenatal stress, and both antioxidants prevented these effects. In addition, N-acetylcysteine or astaxanthin was effective in preventing distinct male and female interneuron changes; decreased female medial frontal cortical parvalbumin interneurons was prevented by either antioxidant; increased male medial frontal cortical parvalbumin interneurons was prevented by N-acetylcysteine and decreased male hippocampal GAD67GFP+ cells prevented by astaxanthin. Prenatal stress-induced increased anxiety-like behavior and decreased sociability were not prevented by prenatal antioxidants. Sensorimotor gating deficits in males was partially prevented by prenatal astaxanthin. This study demonstrates the importance of oxidative stress for persistent impacts on offspring cortical microglia and interneurons, but did not link these changes with anxiety-like, social, and sensorimotor gating behaviors.     

The selective glucocorticoid receptor antagonist CORT 108297 decreases neuroendocrine stress responses and immobility in the forced swim test

Pre-clinical and clinical studies have employed treatment with glucocorticoid receptor (GR) antagonists in an attempt to limit the deleterious behavioral and physiological effects of excess glucocorticoids. Here, we examined the effects of GR antagonists on neuroendocrine and behavioral stress responses, using two compounds: mifepristone, a GR antagonist that is also a progesterone receptor antagonist, and CORT 108297, a specific GR antagonist lacking anti-progestin activity. Given its well-documented impact on neuroendocrine and behavioral stress responses, imipramine (tricyclic antidepressant) served as a positive control. Male rats were treated for five days with mifepristone (10 mg/kg), CORT 108297 (30 mg/kg and 60 mg/kg), imipramine (10 mg/kg) or vehicle and exposed to forced swim test (FST) or restraint stress. Relative to vehicle, imipramine potently suppressed adrenocorticotropin hormone (ACTH) responses to FST and restraint exposure. Imipramine also decreased immobility in the FST, consistent with antidepressant actions. Both doses of CORT 108297 potently suppressed peak corticosterone responses to FST and restraint stress. However, only the higher dose of CORT 108297 (60 mg/kg) significantly decreased immobility in the FST. In contrast, mifepristone induced protracted secretion of corticosterone in response to both stressors, and modestly decreased immobility in the FST. Taken together, the data indicate distinct effects of each compound on neuroendocrine stress responses and also highlight dissociation between corticosterone responses and immobility in the FST. Within the context of the present study, our data suggest that CORT 108297 may be an attractive alternative for mitigating neuroendocrine and behavioral states associated with excess glucocorticoid secretion.     

Interactions of caffeine and restraint stress during pregnancy in mice

The maternal and developmental toxicity of combined exposure to restraint stress and caffeine was assessed in mice. On gestational Days 0-18, three groups of plug-positive females (n = 13-15) were given by gavage caffeine at 30, 60, and 120 mg/kg/day. Three additional groups received the same caffeine doses and were restrained for 2 hr/day. Control groups included restrained and unrestrained plug-positive mice not exposed to caffeine. All animals in the group concurrently exposed to 120 mg/kg/day of caffeine and restraint died during the experimental period. In the remaining groups, cesarean sections were performed on Day 18 of gestation, and the fetuses were weighed and examined for external, internal, and skeletal malformations and variations. Although maternal and embryo/fetal toxicity were observed at all caffeine doses, the adverse maternal and developmental effects were significantly enhanced in the groups concurrently exposed to caffeine and restraint. It was especially remarkable at 60 and 120 mg/kg/day. The results of this study suggest that maternal and developmental toxic effects might occur if high amounts of caffeine were consumed by women under a notable stress during pregnancy.     

Influence of maternal stress on uranium-induced developmental toxicity in rats

It has been demonstrated that uranium is an embryo/fetal toxicant when given orally or subcutaneously to pregnant mice. On the other hand, maternal stress has been shown to enhance the developmental toxicity of a number of metals. In this study, maternal toxicity and developmental effects of a concurrent exposure to uranyl acetate dihydrate (UAD) and restraint stress were evaluated in rats. Four groups of pregnant animals were given subcutaneous injections of UAD at 0.415 and 0.830 mg/kg/day on Days 6 to 15 of gestation. Animals in two of these groups were also subjected to restraint for 2 hr/day during the same gestational days. Control groups included restrained and unrestrained pregnant rats not exposed to UAD. Cesarean sections were performed on gestation Day 20, and the fetuses were weighed and examined for malformations and variations. Maternal toxicity and embryotoxicity were noted at 0.830 mg/kg/day of UAD, while fetotoxicity was evidenced at 0.415 and 0.830 mg/kg/day of UAD by significant reductions in fetal body weight and increases in the total number of skeletally affected fetuses. No teratogenic effects were noted in any group. Maternal restraint enhanced uranium-induced embryo/fetal toxicity only at 0.830 mg/kg/day, a dose that was also significantly toxic to the dams. As in previous studies with other metals, maternal stress enhances uranium-induced developmental toxicity at uranium doses that are highly toxic to the dams; however, at doses that are less acutely toxic the role of maternal stress would not be significant.     

An allosteric modulator of metabotropic glutamate receptors (mGluR₂), (+)-TFMPIP, inhibits restraint stress-induced phasic glutamate release in rat prefrontal cortex

The potential anxiolytic effects of a novel positive allosteric modulator (PAM) of the metabotropic glutamate receptor subgroup 2 (mGluR?) were investigated using a self-referencing recording technique with enzyme-based microelectrode arrays (MEAs) that reliably measures tonic and phasic changes in extracellular glutamate levels in awake rats. Studies involved glutamate measures in the rat prefrontal cortex during subcutaneous injections of the following: vehicle, a mGluR?/? agonist, LY354740 (10?mg/kg), or a mGluR? PAM, 1-Methyl-2-((cis-(R,R)-3-methyl-4-(4-trifluoromethoxy-2-fluoro)phenyl)piperidin-1-yl)methyl)-1H-imidazo[4,5-b]pyridine ((+)-TFMPIP; 1.0 or 17.8?mg/kg). Studies assessed changes in tonic glutamate levels and the glutamatergic responses to a 5-min restraint stress. Subcutaneous injection of (+)-TFMPIP at a dose of 1.0?mg/kg (day 3: -7.1?±?15.1 net AUC; day 5: -24.8?±?24.9 net AUC) and 17.8?mg/kg (day 3: -46.5?±?33.0 net AUC; day 5: 34.6?±?36.8 net AUC) significantly attenuated the stress-evoked glutamate release compared to vehicle controls (day 3: 134.7?±?50.6 net AUC; day 5: 286.6?±?104.5 net?AUC), whereas the mGluR?/? agonist LY354740 had no effect. None of the compounds significantly affected resting glutamate levels, which we have recently shown to be extensively derived from neurons. Taken together, these data support that systemic administration of (+)-TFMPIP produces phasic rather than tonic release of glutamate that may play a major role in the effects of stress on glutamate neuronal systems in the prefrontal cortex.     

Repeated handling, restraint, or chronic crowding impair the hypothalamic-pituitary-adrenocortical response to acute restraint stress.

The purpose of the present study was to assess whether, and to what extent prior handling, restraint or social crowding stress during 3-10 days affects the hypothalamic-pituitary-adrenocortical (HPA) response to an acute short-lasting restraint stress. Also the effect of a feedback inhibitory mechanism of corticosterone in the impairment of HPA axis by these stressors was investigated. Male Wistar rats were pretreated with handling 1 min/day for 3-10 days, restraint 2 times daily for 3-7 days and crowding stress for 7 days before exposure to acute restraint stress in metal tubes for 10 min. Some group of rats received exogenous s.c. corticosterone either once 25 mg/kg or 2 times daily 10 mg/kg for 3-10 days before restraint stress. After the last restraint the rats were decapitated and their trunk blood was collected for the measurement of plasma ACTH and serum corticosterone levels. Handling for 3-7 days, restraint for 3-7 days, and crowding for 7 days and a single pretreatment with corticosterone--all significantly and to a similar extent inhibited the restraint stress-induced increase in ACTH and corticosterone secretion. Chronic pretreatment with corticosterone blunted the restraint stress-induced increase in HPA axis activity. These results indicate that repeated short-lasting stress induced by handling, restraint, or crowding potently attenuates the acute restraint stress-induced stimulatory action of the HPA axis. They also indicate adaptive action of moderate stress on the HPA axis response to acute stress. The results also suggest that a short-lasting hypersecretion of corticosterone during psychological stress may induce a prolonged feedback inhibition of the HPA axis activity. The attenuation of HPA axis response by prior handling has also obvious methodological implications.     

Differential effects of naloxone on basal and stress-induced release of ACTH and prolactin in the male rat

The effect of i.v. injection of various doses of naloxone (NAL) on plasma adrenocorticotropin (ACTH) and prolactin (Prl) in conscious animals bearing an indwelling intrajugular catheter was assessed. The effects were evaluated in animals which were left undisturbed and in others subjected to either restraint or ether stress. The results revealed that the dose of 3 mg/kg of NAL significantly reduced basal Prl levels, whereas a dose of 6 mg/kg of NAL was required to block completely either ether or restraint stress-induced release of Prl. The behavior of ACTH contrasted with that of Prl. There was no effect whatsoever of the 3 mg/kg dose of NAL on either resting or stress-induced ACTH levels, whereas a 6 mg/kg or 12 mg/kg dose of NAL elevated resting ACTH levels and only partially attenuated the further elevation induced by stress in these animals. The results clearly indicate a NAL sensitive step in the control of resting and stress-induced Prl release but indicate that the control of resting and stress-induced release of ACTH is different in that the predominantly millimicron receptor blocker, NAL, can elevate ACTH at high doses and can only partially block the response to stress. In contrast to Prl where opioid peptide control is solely stimulatory, this control of ACTH secretion appears to have both stimulatory and inhibitory features.     

Long-lasting, sex- and age-specific effects of social stressors on corticosterone responses to restraint and on locomotor responses to psychostimulants in rats

Many neural systems are undergoing marked development over adolescence, which may heighten an animal's vulnerability to stressors. One consequence may be altered sensitivity to drugs of abuse. We previously reported that social stressors in adolescence increased behavioral sensitization to nicotine in adulthood in female, but not male, rats. Here we examined whether social stressors in adolescence alter the functioning of the hypothalamic-pituitary-adrenal (HPA) axis by examining corticosterone release in response to restraint in adulthood. To further assess effects of social stressors on behavioral sensitivity to psychostimulants, we examined locomotor activity in response to nicotine and to amphetamine. In a second set of experiments, we investigated whether the same procedure of social stressors administered in adulthood produces effects similar to that observed when administered in adolescence. Rats underwent daily 1 h isolation followed by pairing with a new cage mate on either postnatal days 33-48 (pubertal stress: PS) or days 65-80 (adult stress: AS). Three weeks later rats tested for either: (a) corticosterone levels were measured in response to restraint, or (b) locomotor sensitization to nicotine (0.25 mg/kg; 5 days) followed by an amphetamine challenge (0.5 mg/kg) 24 h later. Effects of social stressors were evident only in females. PS females had increased locomotor activity to amphetamine compared to controls, and AS females had increased corticosterone release compared to controls. No effect of the social stressors was found in males at either age except for reduced weight gain during the stress procedure. Thus, females are more susceptible to the enduring effects of these moderate social stressors than are males. However, in terms of behavioral sensitivity to drugs of abuse, females may be more susceptible to stressors during adolescence than adulthood, although the reverse appears to be true for HPA function.     

Cardiac lipase: effect of ethanol and stress

The effect of ethanol (0, 0.5, 3.0 g/kg) and restraint stress on cardiac neutral (NL) and lipoprotein (LPL) lipase was studied. Although ethanol (3.0 g/kg) or stress decreased NL and increased LPL, ethanol pretreatment significantly attenuated stress induced changes in both enzymes. These results support previous research on the protective effects of ethanol and may be one mechanism through which ethanol may alter susceptibility to certain forms of heart disease.     

Effects of oolong tea on metabolism of plasma fat in mice under restraint stress

We investigated the effects of oolong tea on the basic metabolism of plasma lipids in mice under restraint stress. When a lipid emulsion (Intralipid 20%; a lipid emulsion containing 20% soybean oil) was injected intravenously into mice, the restraint stress prolonged the half-life (T 1/2) of elimination for plasma triglyceride (TG) from 28.7 to 55.5 min. The elimination rate per minute was 48.2% in stressed mice with the rate in starved control mice as 100%. Therefore, TG metabolism was disrupted by the stress, and the use of TG as an energy source decreased. We found that the metabolism of lipids significantly response to the restrained stress in the present study. Plasma TG was 515.9 +/- 29.9mg/dl 35min after Intralipid administration in control stressed mice, 478.7 +/- 26.7 mg/dl in the stressed group given caffeine 100 mg/kg of body weight, and 418.3 +/- 18.4 mg/dl in the stressed group given 1,000 mg/kg oolong tea, an improvement by 7.2% and 18.9%, respectively, with the value for the untreated control group. The intake of oolong tea alleviated the stress-induced decrease in the rate of blood lipid metabolism; this effect may have arisen from some non-specific stress-relieving property of the tea or from acceleration of lipid metabolism by properties of polyphenols, etc. in tea. Oolong tea had anti-stress effects on plasma TG metabolism, and the effects did not depend on caffeine.     

Interactions in developmental toxicology: combined action of restraint stress, caffeine, and aspirin in pregnant mice

BACKGROUND: Stress can result in an increased use of substances such as caffeine and aspirin. The effect of maternal stress on concurrent exposure to caffeine and aspirin on prenatal development was assessed in mice. METHODS: On gestational day 9, mice were assigned to three treatment groups orally exposed to caffeine (30 mg/kg), aspirin (250 mg/kg), or a combination of caffeine (30 mg/kg) and aspirin (250 mg/kg). Three additional groups of pregnant animals received similar caffeine and aspirin doses and were immediately subjected to restraint for 14 hr. Control groups included unrestrained and restrained pregnant mice not exposed to caffeine or aspirin. All dams were euthanized on gestational day 18. Live fetuses were evaluated for sex, body weight, and external, internal, and skeletal malformations and variations. RESULTS: A single oral dose of caffeine or aspirin did not cause significant maternal toxicity. However, coadministration of these drugs with restraint produced some adverse maternal effects (i.e., reduction in maternal weight gain and food consumption on gestational days 9-11). In relation to embryo/fetal toxicity, the incidence of some skeletal defects was significantly increased after exposure to caffeine, aspirin, or maternal restraint, and their binary and ternary combinations. CONCLUSIONS: Although caffeine and aspirin were given in a single dose in this study, the results suggest that prenatal stress could slightly exacerbate the maternal and developmental toxicity of the combination of these drugs in mice.     

Naloxone exerts a dose-dependent gastric cytoprotective effect

Previous work has shown that naloxone inhibits the ulcerogenic effects of indomethacin and stress, although the site, mechanism or dose are unknown. We investigated whether naloxone possessed gastric cytoprotective properties, generating a dose-response curve existed for both intragastric (IG) and intravenous (IV) administration. One hundred and two rats were subjected to a four hour period of restraint, with the last two hours at 4 degrees C. Naloxone was given hourly during restraint at doses of 0 (Control), 1, 5, 10, 20 mg/kg. After sacrifice, the residual gastric volume, and pH were measured and the number of mucosal lesions scored. The cytoprotection offered by naloxone was different from control (p = 0.0001), with the intravenous route having a greater effect (p = 0.038). While this protective effect did not correlate with changes in gastric acidity, it correlated with the dose of naloxone.     

In vivo stimulation of sympathetic nervous system modulates osteoblastic activity in mouse calvaria

Previously, we demonstrated that epinephrine induced the expression of interleukin (IL)-6 mRNA via beta-adrenoceptors in cultured human osteoblastic cells. IL-6 is well known to modulate bone metabolism by regulating the development and function of osteoclasts and osteoblasts. Recently, restraint stress and intracerebroventricular injection of lipopolysaccharide (LPS) have been reported to induce the expression of IL-6 mRNA in peripheral organs in mice in which expression is mediated by the activation of the sympathetic nervous system. To prove the physiological role of sympathetic nerves in bone metabolism in vivo, we examined by RT-PCR analysis the effects of restraint stress and intracerebroventricular injection of LPS on IL-6 mRNA expression in mouse calvaria. The expression of IL-6 mRNA in mouse calvaria was stimulated by either restraint stress (30 min) or intracerebroventricular injection of LPS (50 ng/mouse, 60 min). The treatment of mice with the neurotoxin 6-hydroxydopamine (6-OHDA, 100 mg x kg-1 x day-1 ip for 3 days) inhibited LPS (icv)-induced expression of IL-6 mRNA in their calvaria. The expression of IL-6 mRNA induced by the restraint stress was not influenced by 6-OHDA, which destroys noradrenergic nerve terminals. Furthermore, pretreatment with a beta-blocker, propranolol (15 or 25 mg/kg ip), inhibited both stress- and LPS-induced increases in the level of IL-6 mRNA, but pretreatment with an alpha-blocker, phentolamine (5 mg/kg sc), did not inhibit them in mouse calvaria. In addition, treatment of calvaria with isoprenaline or norepinephrine increased IL-6 synthesis in the organ culture system. These results indicate that in vivo adrenergic stimulation modulates the osteoblastic activity in mouse calvaria via noradrenergic nerve terminals.     

Involvement of nitric oxide (NO) in the regulation of stress susceptibility and adaptation in rats

The present study evaluated the regulatory role of nitric oxide (NO) in stress susceptibility and adaptation in rats. Acute restraint stress (RS x1) reduced the number of entries and time spent in the open arms in the elevated plus maze (EPM) test and raised plasma corticosterone levels. RS (x1)-induced neurobehavioral suppression and raised corticosterone levels were attenuated by pretreatment with the NO precursor, L-arginine (500 and 1000 mg/kg)and unaffected or further aggravated by NO synthase inhibitor, L-NAME or 7-nitroindazole (10 and 50 mg/kg). Biochemical assay of plasma and brain homogenates showed that these RS - induced behavioral and neuroendocrinal changes were associated with lowered levels of plasma and brain total nitrates/nitrites (NOx). L-Arginine attenuated the RS-induced suppression of NOx levels in plasma and brain, whereas, the NO synthase inhibitors tended to produce reverse effects. In the experiments involving repeated stress i.e. RS (x5), exposure resulted in attenuation/reversal of (a) neurobehavioral suppression in the EPM test and (b) lowered brain NOx, that was seen after RS (x1). The RS (x5)-induced changes in EPM parameters and brain Nox were further potentiated after L-arginine pretreatment, whereas, the NO synthase inhibitors were less effective. Rats were screened as high and low emotional in the open-field test, and high emotional rats showed greater(a) behavioral suppression in the EPM, (b) corticosterone responses (c) brain NOx suppression, and (d) cold-restraint stress (CRS) induced gastric mucosal lesions as compared to their low emotional counterparts. L-Arginine pretreatment was more effective in modulating the above RS induced stress responses/markers in the high emotional group of rats. Our data suggest that NO plays a differential role during exposure to acute and repeated stress situations, and that the relationship between stress and emotionality status may be under the regulatory influence of NO.     

Contribution of infralimbic cortex in the cardiovascular response to acute stress

The infralimbic region of the medial prefrontal cortex (IL) modulates autonomic and neuroendocrine function via projections to subcortical structures involved in the response to stress. We evaluated the contribution of the IL to the cardiovascular response evoked by acute stress. Under anesthesia (80 mg/kg ketamine-11.5 mg/kg xylazine), rats were implanted with telemetry probes or arterial lines for recording heart rate and blood pressure. Guide cannulas were implanted to target the IL for microinjection of muscimol (100 pmol/100 nl), N-methyl-d-aspartate (NMDA) (6 pmol/100 nl), or vehicle (100 nl). Microinjection of muscimol, an agonist of GABA(A) receptors, into the IL had no effect on stress-evoked cardiovascular and thermogenic changes in any of the paradigms evaluated (cage switch, restraint plus air-jet noise, or air-jet stress). However, microinjection of the excitatory amino acid NMDA into the IL attenuated the pressor and tachycardic response to air-jet stress. Pretreatment with the selective NMDA antagonist dl-2-amino-5-phosphonopentanoic acid (AP-5, 100 pmol/100 nl) blocked the effect of NMDA on the cardiovascular response to air-jet stress. We conclude that 1) the IL region is not tonically involved in cardiovascular or thermogenic control during stress or under baseline conditions, and 2) activation of NMDA receptors in the IL can suppress the cardiovascular response to acute stress exposure.     

Duodenal calcium transporter mRNA expression in stressed male rats treated with diazepam, fluoxetine, reboxetine, or venlafaxine

Chronic stress has been reported to decrease bone density and intestinal calcium absorption, but its underlying mechanism remains elusive. Since long-term exposure to glucocorticoids, major stress hormones from adrenal gland, is known to downregulate the mRNA expression of intestinal calcium transporter TRPV6, the present study aimed to demonstrate whether decreases in mRNA expressions of duodenal calcium transporter genes were observed in male rats subjected to restraint stress for 4?weeks. The results from quantitative real-time PCR showed that restraint stress significantly downregulated the mRNA expressions of apical calcium channels (TRPV6 and Ca(v)1.3), cytoplasmic calcium-binding protein (calbindin-D(9k)), and basolateral calcium pump (PMCA(1b)), but not the expression of TRPV5 or NCX1. The mRNA expressions of paracellular genes, ZO-1, occludin, and claudin-3, were not altered by restraint stress. Since several antidepressant or anxiolytic drugs effectively alleviate stress-induced depressive and anxiety symptoms, we further hypothesized that these drugs may also enhance calcium transporter gene expression in stressed rats. As expected, 4-week daily administration of 10?mg/kg fluoxetine, 10?mg/kg reboxetine, or 10?mg/kg venlafaxine differentially increased calcium transporter mRNA expression in stressed rats, whereas 2?mg/kg diazepam had no such effect. It could, therefore, be concluded that 4-week restraint stress downregulated some important calcium transporter mRNA expression in the duodenal epithelial cells of male rats, which could be prevented by oral administration of fluoxetine, reboxetine, and venlafaxine. The present findings may be applied to help alleviate the stress-induced bone loss and osteoporosis by restoring intestinal calcium absorption to provide calcium for bone formation.