A change in the alarm level entails a change in behavioural strategy of mice in stress and a change in analgesia induced by it

The effects of anxiogenic (pentylentetrazole) and anxiolytic (diazepam) agents on and cold swim stress-induced analgesia were investigated in SHR and NMRI male mice. It was shown that behavioral response to acute stress was associated with a change in the pain tolerance threshold. Diazepam increased immobility time and attenuated stress-induced analgesia (SIA). NMRI mice were more responsive to anxiolytic than the SHR mice, but the lattes manifested more dramatic changes when anxiety was pharmacologically enhanced (immobility time was significantly reduced and the SIA exaggerated). Our findings suggest that the main parameters change in reciprocal manner following a pharmacologically altered anxiety, and reveal that differences between two strains of mice are determined by differences in their sensitivity to stress.     

The role of the pituitary in the diurnal variation in tolerance to painful stimuli and brain enkephalin levels

Studies were carried out on hypophysectomized rats and mice in comparison to sham-operated controls in order to assess the role of the pituitary in the diurnal rhythm in sensitivity to pain, the hyperalgesic effect of naloxone and the effect of stress on brain levels of met-enkephalin. There were no significant differences in jump latencies between hypophysectomized and sham-operated control mice. The jump latencies in the p.m. were significantly greater than those in the a.m. for both the sham and the hypophysectomized mice. In both the sham and hypophysectomized mice and rats, naloxone significantly reduced the jump latencies in the p.m. The stress-induced increase in the p.m. of brain met-enkephalin, furthermore, persisted in the hypophysectomized rats. We conclude that the pituitary is not essential for the diurnal variation in responsivity to pain, the hyperalgesic activity of naloxone or the stress-induced increases in brain met-enkephalin.     

Stable fly, Stomoxys calcitrans, mouthpart removal influences stress and anticipatory responses in mice

Abstract Biting fly attack induces a variety of stress and anxiety related changes in the physiology and behaviour of the target animals. Significant reductions in pain, or more appropriately, nociceptive sensitivity (latency of a foot-lifting response to an aversive thermal stimulus), are evident in laboratory mice after a 1 h exposure to stable flies, Stomoxys calcitrans. The role of the various components of biting fly attack in the development of this stress-induced reduction in pain sensitivity (analgesia) is, however, unclear. This study demonstrates that fly-naive mice do not exhibit a stress-induced analgesia when exposed to stable flies whose biting mouthparts have been removed. In contrast, mice that have been previously exposed to intact stable flies exhibit significant analgesia when exposed to flies that are incapable of biting. However, the level of analgesia induced is lower than that elicited by exposure to intact stable flies. Exposure to non-biting house flies, Musca domestica , has no effect on nociceptive sensitivity. It appears that the actual bite of the stable fly is necessary for the induction of analgesia and probably other stress and anxiety associated responses in fly naive mice. However, mice rapidly learn to recognize biting flies and exhibit significant, possibly anticipatory analgesic responses to the mere presence of biting flies.     

Deficiency of antinociception and excessive grooming induced by acute immobilization stress in Per1 mutant mice

Acute stressors induce changes in numerous behavioral parameters through activation of the hypothalamic-pituitary-adrenal (HPA) axis. Several important hormones in paraventricular nucleus of the hypothalamus (PVN) play the roles in these stress-induced reactions. Corticotropin-releasing hormone (CRH), arginine-vasopressin (AVP) and corticosterone are considered as molecular markers for stress-induced grooming behavior. Oxytocin in PVN is an essential modulator for stress-induced antinociception. The clock gene, Per1, has been identified as an effecter response to the acute stresses, but its function in neuroendocrine stress systems remains unclear. In the present study we observed the alterations in grooming and nociceptive behaviors induced by acute immobilization stress in Per1 mutant mice and other genotypes (wild types and Per2 mutant). The results displayed that stress elicited a more robust effect on grooming behavior in Per1 mutant mice than in other genotypes. Subsequently, the obvious stress-induced antinociception was observed in the wild-type and Per2 mutant mice, however, in Per1 mutant, this antinociceptive effects were partially-reversed (mechanical sensitivity), or over-reversed to hyperalgesia (thermal sensitivity). The real-time qPCR results showed that in PVN, there were stress-induced up-regulations of Crh, Avp and c-fos in all of genotypes; moreover, the expression change of Crh in Per1 mutant mice was much larger than in others. Another hormonal gene, Oxt, was up-regulated induced by stress in wild-type and Per2 mutant but not in Per1 mutant. In addition, the stress significantly elevated the serum corticosterone levels without genotype-dependent differences, and accordingly the glucocorticoid receptor gene, Nr3c1, expressed with a similar pattern in PVN of all strains. Taken together, the present study indicated that in acute stress treated Per1 mutant mice, there are abnormal hormonal responses in PVN, correlating with the aberrant performance of stress-induced behaviors. Therefore, our findings suggest a novel functional role of Per1 in neuroendocrine stress system, which further participates in analgesic regulation.     

Sex differences in the effects of neuropeptide FF and IgG from neuropeptide FF on morphine- and stress-induced analgesia.

There is evidence suggesting that the endogenous mammalian octapeptide FLFQPQRFamide (F8Fa or neuropeptide FF, NPFF) has modulatory effects on opioid-mediated analgesia in rodents. There is also substantial evidence for sex differences in opioid analgesia, whereby male rats and mice display greater levels of opioid-mediated analgesia than females. In the present study, determinations were made of the effects of NPFF and IgG from antiserum against NPFF on morphine- and restraint stress-induced opioid analgesia in male and female deer mice. Intracerebroventricular (ICV) administrations of NPFF (0.10-10 micrograms) reduced in a dose-dependent manner morphine- and stress-induced analgesia in both male and female mice, with NPFF having markedly greater antagonistic effects in the male than female mice. Additionally, ICV administrations of NPFF-IgG increased the levels of morphine- and stress-induced analgesia and significantly reduced basal nociceptive sensitivity in male mice, whereas, in female mice, NPFF-IgG had no significant effects on either opioid-mediated analgesia or nociceptive sensitivity. These results indicate that there are sex differences in the modulatory effects of NPFF on opioid-mediated analgesia.     

Long-Term Corticosterone Exposure Decreases Insulin Sensitivity and Induces Depressive-Like Behaviour in the C57BL/6NCrl Mouse

Chronic stress or long-term administration of glucocorticoids disrupts the hypothalamus-pituitary-adrenal system leading to continuous high levels of glucocorticoids and insulin resistance (IR). This pre-diabetic state can eventually develop into type 2 diabetes mellitus and has been associated with a higher risk to develop depressive disorders. The mechanisms underlying the link between chronic stress, IR and depression remains unclear. The present study aimed to establish a stress-depression model in mice to further study the effects of stress-induced changes upon insulin sensitivity and behavioural consequences. A pilot study was conducted to establish the optimal administration route and a pragmatic measurement of IR. Subsequently, 6-month-old C57BL/6NCrl mice were exposed to long-term oral corticosterone treatment via the drinking water. To evaluate insulin sensitivity changes, blood glucose and plasma insulin levels were measured at different time-points throughout treatment and mice were behaviourally assessed in the elevated zero maze (EZM), forced swimming test (FST) and open field test to reveal behavioural changes. Long-term corticosterone treatment increased body weight and decreased insulin sensitivity. The latter was revealed by a higher IR index and increased insulin in the plasma, whereas blood glucose levels remained unchanged. Corticosterone treatment induced longer immobility times in the FST, reflecting depressive-like behaviour. No effects were observed upon anxiety as measured in the EZM. The effect of the higher body weight of the CORT treated animals at time of testing did not influence behaviour in the EZM or FST, as no differences were found in general locomotor activity. Long-term corticosterone treatment via the drinking water reduces insulin sensitivity and induces depressive-like behaviour in the C57BL/6 mouse. This mouse model could thus be used to further explore the underlying mechanisms of chronic stress-induced T2DM and its association with increased prevalence of major depressive disorder on the short-term and other behavioural adaptations on the longer term.     

Seasonal alterations in adrenocortical cell function associated with stress-responsiveness and sex in the eastern fence lizard (Sceloporus undulatus)

We characterized steroidogenic properties of dispersed adrenocortical cells from field-active male and female eastern fence lizards (Sceloporus undulatus) to investigate whether alterations in cell function could, in part, explain seasonal variation in baseline and stress-induced plasma corticosterone (B). Lizards were collected during the breeding and postbreeding seasons and shortly prior to hibernation. Dispersed cells in vitro produced B, aldosterone (ALDO), and progesterone in response to 8-Br-cAMP, 25-(OH)cholesterol, adrenocorticotropin (ACTH; as little as 100 fM), and angiotensin II. Maximal progesterone, B, and ALDO responses to ACTH were roughly 1000%, 500%, and 100% greater than corresponding basal values. Angiotensin II was an effective steroidogenic stimulant but much less so than ACTH. Corticosteroid production exhibited considerable steroid-specific variation among seasons. Maximal ACTH-induced B production was lower in the postbreeding season than at either of the other two measurement points, essentially opposite to the pattern for ALDO. Males and females generally produced B at similar rates, but ALDO and progesterone showed numerous sex differences that usually covaried between the two steroids. Cellular sensitivity to 25-(OH)cholesterol and angiotensin II showed few sex differences or seasonal changes. In contrast, sensitivity to ACTH decreased markedly from the breeding to the postbreeding season in males, corresponding to the decrease in stress-responsiveness, and in both sexes was considerably lower prior to hibernation than during the breeding season. Under some conditions, plasma B may be limited by the production capacity of adrenocortical cells. In summary, seasonal variations in body condition, reproductive activity, and baseline and stress-induced plasma B may be attributed at least in part to alterations in adrenocortical cell steroidogenic function.     

Stress-Induced Allodynia – Evidence of Increased Pain Sensitivity in Healthy Humans and Patients with Chronic Pain after Experimentally Induced Psychosocial Stress

Background

Experimental stress has been shown to have analgesic as well as allodynic effect in animals. Despite the obvious negative influence of stress in clinical pain conditions, stress-induced alteration of pain sensitivity has not been tested in humans so far. Therefore, we tested changes of pain sensitivity using an experimental stressor in ten female healthy subjects and 13 female patients with fibromyalgia.

Methods

Multiple sensory aspects of pain were evaluated in all participants with the help of the quantitative sensory testing protocol before (60 min) and after (10 and 90 min) inducing psychological stress with a standardized psychosocial stress test (“Trier Social Stress Test”).

Results

Both healthy subjects and patients with fibromyalgia showed stress-induced enhancement of pain sensitivity in response to thermal stimuli. However, only patients showed increased sensitivity in response to pressure pain.

Conclusions

Our results provide evidence for stress-induced allodynia/hyperalgesia in humans for the first time and suggest differential underlying mechanisms determining response to stressors in healthy subjects and patients suffering from chronic pain. Possible mechanisms of the interplay of stress and mediating factors (e.g. cytokines, cortisol) on pain sensitivity are mentioned. Future studies should help understand better how stress impacts on chronic pain conditions.     

Sex Differences in Acute Swim Stress-Induced Changes in the Binding of MK-801 to the NMDA Subclass of Glutamate Receptors in Mouse Forebrain

Acute swim stress (3 min at 32°C) in mice produces increases in the binding of MK-801 to the NMDA subclass of glutamate receptors to forebrain membranes prepared from male mice. Scatchard analyses indicate that the observed increases in the binding of MK-801 in membranes from male mice are the result of changes in the affinity and density of low-affinity binding sites and in the density of high-affinity binding sites. In female mice, any changes in the binding of MK-801 appear to be much less pronounced and restricted to the low-affinity binding sites. These results are in contrast to the situation with binding to GABA receptors where acute swim stress increases GABA binding in forebrain membranes much more in female than in male mice. This indicates significant sex differences in the responses of receptors for the major excitatory and inhibitory transmitters to acute swim stress. These rapid changes in MK-801 binding may result from changes in endogenous modulators as appears to be the case in the acute swim stress-induced changes in GABA binding. As with GABA binding, the endogenous modulators are likely to include steroids, the sex differences reflecting differences in modulation by gonadal steroids and the stress-induced changes reflecting differences in modulation by adrenal steroids. Estradiol, progesterone, and corticosterone treatments have been reported by other workers to influence the properties of glutamate receptors.     

Pituitary-adrenal function in female mice with mutation Agouti yellow (A(y))

Agouti protein is a paracrine signaling factor modulating action of ACTH and alpha-MSH. Dominant mutation Ay causes ectopic, ubiquitous expression of Agouti protein in mice. It was shown that Ay mutation increased stress-induced hypothalamo-adrenal activity in male mice. There is a sex difference in the hypothalamo-pituitary-adrenal axis in rodents. The aim of this study was to test effects of ectopic overexpression of Agouti protein on pituitary-adrenal function in female mice. Female mice of C57Bl/6J strain with Ay mutation (Ay/alpha) and with mutation nonagouti (alpha/alpha; lack of Agouti protein) were used. Ay/alpha-females had an increased blood level of corticosterone and ACTH after 10-minute restriction as compared with alpha/alpha-females. The adrenal threshold sensitivity and reaction to exogenous ACTH in vivo suggests that increased corticosterone reaction to emotional stress is caused by increased pituitary stimulation.     

Expression of stress-evoked analgesia, connected with activity of animals in a forced swimming test]

The influence of forced swimming on the development of stress-induced analgesia was studied in 35 SHR mice, 65 NMRI mice, and 23 white outbred male rats. Mice were subjected to swimming conditions (at a temperature of 11 degrees C) for a period of 4 minutes and rats for 6 minutes. Pain thresholds were measured by a footshock. It was shown that behavioral response to acute stress is associated with a change in the pain tolerance threshold: activity of an animal under test conditions positively correlated with stress-induced analgesia. The response to stress and parameters of stress-induced analgesia depend on the genetic factor and age, however, the correlation between the activity during exposure to stress and the extent of stress-induced analgesia conserves in all cases.     

Neurotensin and pain modulation

Neurotensin (NT) can produce a profound analgesia or enhance pain responses, depending on the circumstances. Recent evidence suggests that this may be due to a dose-dependent recruitment of distinct populations of pain modulatory neurons. NT knockout mice display defects in both basal nociceptive responses and stress-induced analgesia. Stress-induced antinociception is absent in these mice and instead stress induces a hyperalgesic response, suggesting that NT plays a key role in the stress-induced suppression of pain. Cold water swim stress results in increased NT mRNA expression in hypothalamic regions known to project to periaqueductal gray, a key region involved in pain modulation. Thus, stress-induced increases in NT signaling in pain modulatory regions may be responsible for the transition from pain facilitation to analgesia. This review focuses on recent advances that have provided insights into the role of NT in pain modulation.     

Mice lacking Ca(v)2.3 (alpha1E) calcium channel exhibit hyperglycemia.

To investigate the functional role of Ca(v)2.3 channel in glucose homeostasis, we performed in vivo glucose tolerance and insulin tolerance tests together with stress-induced glucose release tests using mice deficient in Ca(v)2.3 channel (Ca(v)2.3-/-). The Ca(v)2.3-/- mice were significantly heavier than wild-type mice. In glucose tolerance and insulin tolerance tests, Ca(v)2.3-/- mice showed a significantly higher blood glucose level compared to wild-type mice. However, stress-induced blood glucose changes in Ca(v)2.3-/- mice were similar to those in wild-type mice. These results suggest that Ca(v)2.3 channel plays a role in glucose homeostasis by reducing insulin sensitivity and that Ca(v)2.3-/- mice exhibit symptoms resembling non-insulin-dependent diabetes mellitus.     

Hyperalgesic effect of emotional stress in mice of strains C57BL/6J and CBA/CaLac: Interaction with circadian rhythm-related effects

We studied emotional stress-induced modulations of the pain reaction evoked in mice of strains C57BL/6J and CBA/CaLac by subcutaneous injections of formalin; the measurements were performed at midtimes of a “dark” and a “light” phase of the pre-set fixed circadian rhythm. The magnitude of the pain reaction was estimated indirectly, according to characteristics of locomotion of the animal in a running wheel (the velocity of locomotion and the distance covered were considered values inversely correlating with the intensity of the pain response). We found that the intensity of the pain reaction within both phases of the circadian rhythm increased under the influence of stress, and that there were significant differences between the emotional stress-modulated intensities of the pain response observed in the examined genetic strains of mice. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 466–471, September–December, 2006.     

Naloxone hyperalgesia and stress-induced analgesia in rats

Since past studies concerning the effects of naloxone on nociception have yielded inconclusive findings, the variables of pain test, baseline sensitivity, and stress condition were examined. Within a pure-bred strain of rats, consistent individual differences did not occur. All three measures of pain responsiveness demonstrated hyperalgesic effects of naloxone, but they differed in their capacity to reflect the effects of analgesia produced by continuous or intermittent electrical shock. By some measures, naloxone reversed the stress-induced analgesia due to intermittent shock; it did not influence the analgesia produced by continuous stress. The data support a model of pain inhibition involving both opioid and non-opioid systems and suggest that the hyperalgesic effects of naloxone can sometime gives rise to erroneous conclusions concerning apparent naloxone-reversability of putative analgesic procedures.     

Influence of seasons on circadian rhythm of acid phosphatase and beta-acetyl-glucosaminidase activity in the mouse salivary gland and liver

Influence of seasons on circadian changes in acid phosphatase and beta-acetylglucosaminidase activity was studied in the liver and submandibular gland of sexually mature mice. Seasonal differences in circadian rhythm was found in both examined enzymes in both organs. These changes were independent from each other and each rhythm was differently subjected to seasonal changes. The lowest seasonal influence was observed in acid phosphatase in the salivary gland. Activity of the other enzymes changed in different degrees, having their acrophases at different times of the day and different rhythm intensity. The highest circadian activity changes measured by amplitude and mesor were observed in spring and summer whereas in the autumn and winter their activity had much weaker rhythms or even they disappeared completely. An attempt was made to explain the observed changes by changes in hormonal background and a certain kind of genetic memory pertaining to laboratory animals.     

Analgesic effect of corticotropin-releasing factor administered into midbrain periaqueductal grey matter

Corticotropin-releasing factor (CRF) participates in development of stress-induced analgesia. Midbrain periaqueductal grey matter (MPAG) is one of crucial structures of the brain antinociceptive system. The aim of the study was to investigate effects of the CRF administration into the MPAG on pain sensitivity in alert rats and contribution of opioid mechanisms to these CRF-induced effects. Somatic pain sensitivity was tested by tail flick response latency following thermal stimuli. The opioid antagonist naltrexone administered systemically or centrally into the MPAG was used to study involvement ofopioid mechanisms in the CRF-induced effects. The CRF administration (0.7 microg/rat) into the MPAG caused analgesic effect. The CRF-induced analgesic effects were eliminated by systemic as well as central naltrexone pretreatment. Effect of central naltrexone on the CRF-induced analgesia manifested itself faster as compared with effect of systemic naltrexone. The data obtained suggest that one of central mechanisms of the CRF-induced analgesic effect on somatic pain sensitivity in alert rats may be mediated by the MPAG neurons and provided by involvement of opioid mechanisms.     

Modulation of Behavioral Reactions of Rats with Different Profiles of Motor Asymmetry upon the Action of Hypokinetic Stress

Hypokinetic stress-induced modifications of behavioral reactions recorded under conditions of the open-field test were studied in rats. Animals with different profiles of motor asymmetry demonstrated significant individual typological specificity of behavior. Experimental 9-day-long restriction of mobility caused clearly pronounced changes in behavioral and emotional reactions in the animals; manifestations of such changes depended significantly on motor lateralization.