The role of hypothalamo-hypophyseal-adrenocortical system hormones in controlling pain sensitivity

Pain prevalence, intensity, and association with neuropsychiatric symptoms of dementia in immigrant and non-immigrant aged care residents in Australia

Pain recognition for culturally diverse people is complex as pain experience is subjective and influenced by cultural background. We compared the prevalence, intensity, and association of pain with neuropsychiatric symptoms (NPS) between immigrants and non-immigrants living with dementia in residential aged care homes (RACHs) who were referred to two Dementia Support Australia programs. Immigrant status was defined by the documented country of birth. Pain and NPS were assessed using PainChek® and the Neuropsychiatric Inventory, respectively. Subgroup analyses were also completed for English-speaking and non-English-speaking immigrants. A total of 17,637 referrals [immigrants, n = 6340; non-immigrants, n = 11,297] from 2792 RACHs were included. There were no significant differences for the prevalence of pain across all groups. Immigrants were slightly more likely to have moderate pain or severe pain than non-immigrants. Non-English-speaking immigrants had 0.5 points higher total pain scores on average (Cohen's d = 0.10 [0.05, 0.15], p < 0.001) than non-immigrants. Total pain score had a significant effect on total NPS severity scores in all groups. While pain prevalence is similar across groups, higher pain intensities are more common among immigrants living with dementia. Increased care staff awareness, education, and training about the potential effect of culture on pain expression is needed.

Pre-Test Manipulation by Intraperitoneal Saline Injection with or without Isoflurane Pre-Treatment Does Not Influence the Outcome of Social Test in Male Mice

Preclinical studies on rodents should follow the 3R principle minimising the suffering of the animals. To do so, some researchers use inhalation anaesthetic induction even before intraperitoneal injection. However, several studies suggested that both interventions might influence the behaviour of the animals. We aimed to test whether intraperitoneal injection alone or in combination with isoflurane anaesthesia is a preferable treatment method 30 min before a social test. Male C57BL/6 mice were studied using a behavioural test battery comparing three groups (one control group and intraperitoneal saline-treated groups with or without short isoflurane inhalation). Our results confirmed that both interventions had no profound influence on the conventionally measured parameters of social tests (interest in sociability, social discrimination memory, social interaction as well as resident–intruder test) and were not acutely stressful (measured by similar ACTH levels between the groups) not even after repeated administration (similar body weight gain during the one-week observation period). Taking into consideration the possible long-term harmful effect of isoflurane inhalation, we recommend using intraperitoneal injection without it as saline injection did not violate the 3R principle inducing only mild stress.

Psychosocial Stress-Induced Analgesia: An Examination of Effects on Heat Pain Threshold and Tolerance and of Neuroendocrine Mediation

Stress-induced analgesia (SIA) is an adaptive response of reduced nociception following demanding acute internal and external stressors. Although a psychobiological understanding of this phenomenon is of importance for stress-related psychiatric and pain conditions, comparably little is known about the psychobiological mechanisms of SIA in humans. The aim of this study was to investigate the effects of acute psychosocial stress on heat pain perception and its possible neuroendocrine mediation by salivary cortisol levels and α-amylase activity in healthy men. Employing an intra-individual assessment of heat pain parameters, acute psychosocial stress did not influence heat pain threshold but significantly, albeit slightly, increased heat pain tolerance. Using linear mixed-model analysis, this effect of psychosocial stress on heat pain tolerance was not mediated by increases of salivary cortisol and state anxiety levels or by the activity of α-amylase. These results show that while psychosocial stress is selectively analgesic for heat pain tolerance, this observed effect is not mediated by stress-induced increases of salivary cortisol and α-amylase activity, as proxies of both the hypothalamus-pituitary-adrenal axis and the autonomic nervous system activation.

Physiological Indices of Stress Prior to and Following Total Knee Arthroplasty Predict the Occurrence of Severe Post-Operative Pain

OBJECTIVE

The severe pain and disability associated with osteoarthritis often motivate individuals to undergo arthroplastic surgery. However, a significant number of surgical patients continue to experience pain following surgery. Prior research has implicated both the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system (SNS) in the sensitization of pain receptors and chronic pain conditions. This study uses a prospective, observational, cohort design to examine whether physiological stress responses before and after surgery could predict post-operative pain severity.

SUBJECTS

Participants included 110 patients undergoing total knee arthroplasty.

METHODS

Physiological indices of stress included the measurement of catecholamine and cortisol levels in 15-hour urine samples collected prior to and 1 month following surgery, as well as in-hospital heart rate and blood pressure (before and after surgery), which were abstracted from medical records. Patients completed the pain subscale of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [Bellamy et al., J Orthop Rheumatol 1: , 95 (1988)] 2.5 weeks prior to surgery and at a 3-month follow-up.

RESULTS

Contrary to expectations, lower stress hormone levels at baseline were related to more severe post-operative pain. Data at later time points, however, supported our hypothesis: cardiovascular tone shortly before surgery and urinary levels of epinephrine 1 month following surgery were positively related to pain severity 3 months later.

CONCLUSION

Results suggest that the occurrence of post-operative pain can be predicted on the basis of stress physiology prior to and following arthroplastic surgery.

Effects of Acupuncture, RU-486 on the Hypothalamic-Pituitary-Adrenal Axis in Chronically Stressed Adult Male Rats

We have recently reported that pretreatment with electroacupuncture (EA) at stomach meridian point 36 (St36) prevents the chronic cold-stress increase in the hypothalamus-pituitary-adrenal axis (HPA), an action that may be under central control. Given that treatment for stress-related symptoms usually begins after onset of the stress responses, the objectives of the present study were to determine the efficacy of EA St36 on HPA hormones when EA St36 is given after stress was initiated, if the results are long lasting, and if blocking the glucocorticoid receptor (GR) using RU-486 had the same effects as EA St36. Adult male rats were placed in 4 groups of animals, 3 of which were exposed to cold and 1 of which was a nontreatment control group. After exposure to the cold stress, 2 groups were treated with either EA St36 or sham-EA, repeated over 10 days. The increase in ACTH and corticosterone observed in stress-only rats was prevented in EA St36 animals, and the effects remained intact 4 days after withdrawal of EA but continuation of cold stress. When the GR was blocked with RU-486, the efficacy of EA St36 remained unchanged. GR blockade did significantly elevate ACTH, which is not seen with EA St36, suggesting that EA St36 does act centrally. The elevated HPA hormones in stress-only rats were associated with a significant increase in depressive and anxious behavior; this was not observed in the stressed EA St36 animals. The results indicate that EA specifically at St36 vs sham-EA is effective in treating chronic poststress exposure.

Effects of injection of anti-corticotropin release hormone serum in the lateral ventricles and electroacupuncture analgesia on pain threshold in rats with adjuvant arthritis

Rat models of adjuvant arthritis were established, and anti-corticotropin release hormone serum injection in the lateral ventricles and electroacupuncture at right Jiaji (EX-B2) were performed. The pain threshold was decreased at 45 and 60 minutes after injection of the anti-corticotropin release hormone serum. Electroacupuncture at Jiaji can resist this effect. Immunohistochemical staining results showed that the expression of corticotropin release hormone in the hypothalamic paraventricular nucleus was greater in the electroacupuncture + anti-corticotropin release hormone serum group compared with the anti-corticotropin release hormone serum group. The expression of corticotropin release hormone was correlated with the pain threshold. The effect of endogenous corticotropin release hormone in pain modulation can be obstructed by anti-corticotropin release hormone serum. The analgesia of electroacupuncture can partially resist the depressed pain threshold caused by injection of anti-corticotropin release hormone serum. The analgesic effect of electroacupuncture is associated with the corticotropin release hormone content in the hypothalamus.

The psyche and gastric functions

Although the idea that gastric problems are in some way related to mental activity dates back to the beginning of the last century, until now it has received scant attention by physiologists, general practitioners and gastroenterologists. The major breakthrough in understanding the interactions between the central nervous system and the gut was the discovery of the enteric nervous system (ENS) in the 19th century. ENS (also called 'little brain') plays a crucial role in the regulation of the physiological gut functions. Furthermore, the identification of corticotropin-releasing factor (CRF) and the development of specific CRF receptor antagonists have permitted to characterize the neurochemical basis of the stress response. The neurobiological response to stress in mammals involves three key mechanisms: (1) stress is perceived and processed by higher brain centers; (2) the brain mounts a neuroendocrine response by way of the hypothalamic-pituitary-adrenal axis (HPA) and the autonomic nervous system (ANS), and (3) the brain triggers feedback mechanisms by HPA and ANS stimulation to restore homeostasis. Various stressors such as anger, fear, painful stimuli, as well as life or social learning experiences affect both the individual's physiologic and gastric function, revealing a two-way interaction between brain and stomach. There is overwhelming experimental and clinical evidence that stress influences gastric function, thereby outlining the pathogenesis of gastric diseases such as functional dyspepsia, gastroesophageal reflux disease and peptic ulcer disease. A better understanding of the role of pathological stressors in the modulation of disease activity may have important pathogenetic and therapeutic implications.

Analgesic effects of the non-nitrogen-containing bisphosphonates etidronate and clodronate, independent of anti-resorptive effects on bone

Nitrogen-containing bisphosphonates (NBPs) have greater anti-bone-resorptive effects than non-nitrogen-containing bisphosphonates (non-NBPs). Hence, NBPs are the current first-choice drug for osteoporosis. However, NBPs carry a risk of osteonecrosis of jaws. Some animal and human studies suggest that non-NBPs may have anti-bone-resorptive effect-independent analgesic effects, but there has been no detailed comparison between NBPs and non-NBPs. Here, we compared the analgesic effects of several non-NBPs and NBPs, using (a) writhing responses induced in mice by intraperitoneal injection of 1% acetic acid, (b) acetic acid-induced neuronal expression of c-Fos, (c) acetic acid-induced elevation of blood corticosterone, and (d) hindpaw-licking/biting responses induced by intraplantar injection of capsaicin. Among the NBPs and non-NBPs tested, only etidronate and clodronate displayed clear analgesic effects, with various routes of administration (including the oral one) being effective. However, they were ineffective when intraperitoneally injected simultaneously with acetic acid. Intracerebroventricular administration of etidronate or clodronate, but not of minodronate (an NBP), was also effective. The effective doses of etidronate and clodronate were much lower in writhing-high-responder strains of mice. Etidronate and clodronate reduced acetic acid-induced c-Fos expression in the brain and spinal cord, and also the acetic acid-induced corticosterone increase in the blood. Etidronate and clodronate each displayed an analgesic effect in the capsaicin test. Etidronate and clodronate displayed their analgesic effects at doses lower than those inducing anti-bone-resorptive effects. These results suggest that etidronate and clodronate exert potent, anti-bone-resorptive effect-independent analgesic effects, possibly via an interaction with neurons, and that they warrant reappraisal as safe drugs for osteoporosis.

Quality of life in nonfunctioning pituitary macroadenoma patients before and after surgical treatment

BACKGROUND

Nonfunctioning pituitary macroadenoma (NFMA) is a benign neoplasm that causes visual function disturbances and headaches and can be treated by transsphenoidal surgery (TSS). It is unclear how quality of life (QOL) changes with surgery and which QOL factors are affected by treatment.

METHODS

The aim is to assess the temporal transition of QOL in NFMA patients undergoing TSS and to identify influential factors. The QOL of NFMA patients who underwent endoscopic TSS was investigated with the short-form 36 (SF-36) health survey questionnaire, general health questionnaire 30 (GHQ30), and numerical rating scale (NRS) of pain at the following three time points: immediately before, 1 month after, and 6 months after surgery.

RESULTS

Twenty-four of 30 patients had visual deterioration. The SF-36 baseline value of visual function-impaired NFMA patients was lower than that of the normal population. SF-36 results showed that physical summary scores decreased at 1 month after the operation, but recovered up to the normal population level by 6 months. Mental summary scores generally increased at 1 month after surgery and remained stable until 6 months later. The GHQ30 results were similar to the SF-36 mental summary scores. The strongest factor related to the QOL was visual function. The amount of pain and the necessity of hormonal replacement were also influencing factors.

CONCLUSIONS

The QOL of NFMA patients is affected both physically and mentally by surgical treatment and symptoms. This QOL assessment is important for planning treatment strategies.

Ethnic differences in pain and pain management

Considerable evidence demonstrates substantial ethnic disparities in the prevalence, treatment, progression and outcomes of pain-related conditions. Elucidating the mechanisms underlying these group differences is of crucial importance in reducing and eliminating disparities in the pain experience. Over recent years, accumulating evidence has identified a variety of processes, from neurophysiological factors to structural elements of the healthcare system, that may contribute to shaping individual differences in pain. For example, the experience of pain differentially activates stress-related physiological responses across various ethnic groups, members of different ethnic groups appear to use differing coping strategies in managing pain complaints, providers' treatment decisions vary as a function of patient ethnicity and pharmacies in predominantly minority neighborhoods are far less likely to stock potent analgesics. These diverse factors, and others may all play a role in facilitating elevated levels of pain-related suffering among individuals from ethnic minority backgrounds. Here, we present a brief, nonexhaustive review of the recent literature and potential physiological and sociocultural mechanisms underlying these ethnic group disparities in pain outcomes.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Corticosterone does not change open elevated plus maze-induced antinociception in mice

It has been demonstrated that the exposure of rodents to the standard elevated plus-maze (sEPM: 2 open and 2 enclosed arms) elicits defensive behavioral reactions and antinociception and also activates the hypothalamo-pituitary-adrenal (HPA) axis. We have recently reported that EPM-induced antinociception is particularly observed when rats and mice are exposed to a totally open EPM (oEPM: 4 open arms). Given that the oEPM seems to be a more aversive situation than the sEPM, we hypothesized that oEPM exposure would induce higher plasma levels of corticosterone than sEPM exposure in mice. In this study, we investigated the influence of exposure to eEPM (enclosed EPM: 4 enclosed arms), sEPM or oEPM on plasma corticosterone levels in mice, with or without prior nociceptive stimulation (2.5% formalin injection into the right hind paw). We also tested whether the nociceptive response in the formalin test and oEPM-induced antinociception are altered by adrenalectomy. Results showed that oEPM-exposed mice spent less time licking the injected paw than sEPM- and eEPM-exposed animals. All three types of EPM exposure increased plasma corticosterone when compared to the basal group, but sEPM- and oEPM-exposed mice showed higher corticosterone levels than eEPM-exposed mice. Prior nociceptive stimulation (formalin injection) did not enhance the plasma corticosterone response induced by the three types of EPM exposure. Indeed, formalin injection appeared to provoke a ceiling effect on plasma corticosterone concentration. Furthermore, neither the nociceptive response in the formalin test nor oEPM-induced antinociception was changed by adrenalectomy. Present results suggest that oEPM antinociception does not depend on corticosterone release in mice.

Stress-related alterations of visceral sensation: animal models for irritable bowel syndrome study

Stressors of different psychological, physical or immune origin play a critical role in the pathophysiology of irritable bowel syndrome participating in symptoms onset, clinical presentation as well as treatment outcome. Experimental stress models applying a variety of acute and chronic exteroceptive or interoceptive stressors have been developed to target different periods throughout the lifespan of animals to assess the vulnerability, the trigger and perpetuating factors determining stress influence on visceral sensitivity and interactions within the brain-gut axis. Recent evidence points towards adequate construct and face validity of experimental models developed with respect to animals' age, sex, strain differences and specific methodological aspects such as non-invasive monitoring of visceromotor response to colorectal distension as being essential in successful identification and evaluation of novel therapeutic targets aimed at reducing stress-related alterations in visceral sensitivity. Underlying mechanisms of stress-induced modulation of visceral pain involve a combination of peripheral, spinal and supraspinal sensitization based on the nature of the stressors and dysregulation of descending pathways that modulate nociceptive transmission or stress-related analgesic response.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Central CRH administration changes formalin pain responses in male and female rats

Corticotropin-releasing hormone (CRH) is suggested to be involved in the regulation of pain. To better evaluate the CRH-mediated behavioral alterations in the formalin inflammatory pain test, we administered CRH or the CRH receptor antagonist α-helical CRH(9-41) (ahCRH) intracerebroventricularly to male and female rats and compared the effects with those of saline control. Nociceptive stimulation was carried out through a subcutaneous injection of dilute formalin (50μL, 10%) in the plantar surface of the hind paw. In both sexes, formalin-induced responses, recorded for 60min, were affected by CRH but not by ahCRH treatment. Paw flexing duration was decreased in both sexes during the formalin interphase period in the CRH-treated group compared to saline control groups; however, licking of the injected paw was markedly increased by the same treatment at other time periods. Treatments induced only a few changes in spontaneous non-pain behaviors, which do not account for the effects on pain response. In conclusion, these data demonstrate the ability of CRH to affect the behavioral responses to an inflammatory nociceptive stimulus, and that the effects can be in opposite directions depending on the behavioral response considered.

Increased basal mechanical pain sensitivity but decreased perceptual wind-up in a human model of relative hypocortisolism

Clinical data have accumulated showing that relative hypocortisolism, which may be regarded as a neuroendocrinological correlate of chronic stress, may be a characteristic of some functional pain syndromes. However, it has not been clarified yet whether deregulations of the hypothalamus-pituitary-adrenal (HPA) axis may directly alter pain perception and thus be causally involved in the pathophysiology of these disorders. To test this hypothesis, we performed a randomized placebo-controlled crossover trial in N=20 healthy drug-free volunteers (median age 24yrs) and analyzed the effects of metyrapone-induced hypocortisolism on quantitatively assessed basal mechanical pain sensitivity (1.5-13m/s impact stimuli), perceptual wind-up (9m/s impact stimuli at 1Hz) and temporal summation of pain elicited by inter-digital web pinching (IWP; 10N pressure stimuli for 2min). Experimentally induced hypocortisolism significantly decreased pain detection thresholds and augmented temporal summation of IWP-induced pain (p<.05). The latter effect was dependent on the relative reduction in cortisol levels, and seemed to rely on a potentiated sensitization and not merely on the observed changes in basal pain sensitivity. Perceptual wind-up by contrast was reduced when cortisol synthesis was blocked (p<.05). This result is reminiscent of findings from animal studies showing a reversal of NMDA receptor activation by glucocorticoid receptor antagonists in neuropathic pain models. Our results speak in favor of a potential causal role of HPA axis alterations in pain chronicity.

Involvement of NTS2 receptors in stress-induced analgesia

Stress activates multiple neural systems that suppress pain sensation. This adaptive phenomenon referred as stress-induced analgesia (SIA) is mediated by the activation of endogenous pain inhibitory systems. Both opioid and non-opioid forms of SIA have been elicited in rodents according to stressor parameters and duration. There is accumulating evidence that the endogenous neurotensin (NT) system plays an important role in SIA. Especially, NT-deficient mice were shown to exhibit reduced SIA following water avoidance or restraint stress. Since central NT produces naloxone-insensitive analgesic effects by acting on spinal and supraspinal NTS2 receptors, we hypothesized that NT might mediate non-opioid SIA through NTS2 activation. Here, we evaluated the influence of an opioid-independent severe stress produced by a cold-water swim for 3 min at 15 degrees C on rodent offspring's pain perception. Our results demonstrated that mice lacking NTS2 exhibit significantly reduced SIA following cold-water swim stress. Indeed, NTS2 knockout mice submitted to both acute (plantar test) and tonic (formalin test) pain stimuli show a greater sensitivity to pain in comparison to wild-type littermates. Accordingly, pretreatment with the NT receptor antagonist SR142948A results in a hyperalgesic response to stress induced by cold-water swim. Endogenous NT regulates hypothalamic-pituitary-adrenal axis activity in stress condition by increasing corticosterone plasma levels. Accordingly, the plasma levels of corticosterone measured by radioimmunoassay are significantly reduced in non-stressed and stressed NTS2-deficient mice in comparison with wild-type mice. To further investigate the site of action of NT in mediating SIA, we microinjected NTS2 agonists in lumbar spinal cord and quantified post-stress sensitivity to pain in rats using the plantar test. Exogenously administered NTS2 analogs, JMV-431, beta-lactotensin and NT69L markedly enhance the magnitude and duration of stress antinociception in both 25- and 60-day-old rats. In sum, by using genetic and pharmacological approaches, we demonstrated here that NTS2 receptors mediate non-opioid SIA. Our results also revealed that the release of endogenous NT in response to stress requires the presence of NTS2 to stimulate corticotropin-releasing factor (CRF)-induced elevation of plasma corticosterone, and that NTS2 receptors localized at the lumbar spinal cord participate to the disinhibition of descending pain control pathways. Therefore, these data highlight the significance of NTS2 as a novel target for the treatment of pain and stress-related disorders.