Stress and endogenous opioids: behavioral and circulatory interactions

Hypothalamic Pituitary Adrenal and Autonomic Nervous System Biomarkers of Stress and Tobacco Relapse: Review of the Research

Tobacco smoking is a risk factor for countless diseases, and smoking relapse remains a major public health concern. Subjective reports of stress by smokers are a common theme for relapse, however, the role of objective stress-related biomarkers in predicting tobacco relapse risk has been less studied. The aim of this manuscript was to review existing literature on the connection between biomarkers of stress and smoking relapse. Overall, trends indicate that blunted hypothalamic-pituitary-adrenal (HPA) responses to acute stress, larger reductions in HPA biomarkers during the initial days of abstinence during cessation (compared to pre-cessation levels), and exaggerated autonomic responses to stress predict increased risk of relapse. In addition, successful cessation is followed by changes in stress biomarkers (e.g., reductions in cortisol and heart rate, HR). This review also identifies potential modifiers, such as methodological differences, biological sex, and chronic stress, to account for heterogeneity of findings within and across studies. In addition, we identify gaps in the literature and suggest future research directions focusing on the roles of genetics and gene expression as well as the influence of neurobiological mechanisms on stress and relapse risk. Future clinical implications of this research include identifying reliable indicators of relapse risk and the potential of pharmacotherapeutic treatments to target stress response systems to correct dysregulation and potentially reduce stress-related risk of relapse.

A single session of exercise reduces blood pressure reactivity to stress: a systematic review and meta-analysis

Stressful situations are common in everyday life and disturb homeostasis. So, an exercise session is a strategy to mitigate blood pressure (BP) peaks in response to stress (i.e., BP reactivity), decreasing the cardiovascular risk. This is a systematic review and meta-analysis that aims to verify the effects of a single session of physical exercises on BP reactivity to stress in adults. The searches were performed in digital databases (MEDLINE, LILACS, EMBASE, SPORTDiscus, and PsycInfo) and 29 studies were included, totaling 795 individuals (quantitative analysis: k = 25, n = 659). As for exercise characteristics, 21 of the 29 studies focused on aerobic exercises, and 23 studies focused on low to moderate intensities. As for the stress tests, we have them in the following order from the most to the least frequent: stroop color and word test, cold pressor test, arithmetic test, public speaking, handgrip, trier social stress test, and study task. Favorable metanalytic results (standardized mean differences through random-effects approach) for the exercises were found, with attenuated reactivity in systolic BP (pooled effect size = - 0.38 [- 0.49; - 0.27], representing average reductions of 3.7 ± 3.8 mmHg), diastolic BP (pooled effect size = - 0.51 [- 0.70; - 0.33], representing average reductions of 2.9 ± 3.7 mmHg), and mean BP (pooled effect size = - 0.51 [- 0.72; - 0.31], representing average reductions of 4.1 ± 3.3 mmHg). So, acute physical exercise lowers systolic, diastolic, and mean blood pressure reactivity in response to stressor tasks. However, given the small magnitude of effects, the clinical relevance of this result must be interpreted with caution and be better explored.

Exploring the Association of Hypertension With Risk for Depression: Evidence for Tamed Neurobehavioral Arousal Versus Central Emotional Dysregulation

Depression is an established predictor of adverse cardiovascular disease outcomes. Less is known about cardiovascular risk factors as predictors of depression. In this issue of Psychosomatic Medicine (2018;80:508-514), Patel et al. report data indicating that pre-existing hypertension may be inversely associated with the atypical but not typical form of depression. We highlight here the strengths and limitations of the article and discuss the findings in light of research linking blood pressure and emotion regulation. In general, evidence suggests that higher blood pressure is associated with reduced expression of negative emotions and pain. Two prominent models of interaction have been proposed and supported by epidemiological and experimental research: one assumes that elevations in blood pressure lead to reduced arousal and pain sensitivity through baroreceptor activation and possibly additional afferent mechanisms. Operant conditioning may then result in (chronic) hypertension. The other one posits that impaired emotion processing as indicated by dampened emotion recognition may lead to disinhibition of hypothalamic centers and thereby result in sustained increases in blood pressure. These models are described in context of the current literature and open research questions are formulated.

Stress and Addiction: When a Robust Stress Response Indicates Resiliency

OBJECTIVE

Stress reactivity research has traditionally focused on the idea that exaggerated responses to stress may have adverse effects on health. Accumulating evidence suggests that attenuated responses to stress and delayed recovery may also be problematic.

METHODS

This review focuses on the role of the stress response of the hypothalamic-pituitary-adrenocortical axis, the endogenous opioid system, and the cardiovascular system in hypertension, pain perception, and addictive behaviors. Results from multiple methods of assessment and stress paradigms conducted in our laboratory over the past two decades are integrated with research from other investigators and with existing theories.

RESULTS

Research indicates that exaggerated biological and physiological responses to stress and attenuated pain perception are associated with hypertension and risk for cardiovascular diseases. This research complements work linking reduced stress responses with enhanced pain sensitivity and discomfort. Multiple studies have also demonstrated that an attenuated stress response is linked to exacerbation of withdrawal symptoms and relapse in nicotine addiction. Evidence indicates important moderators (i.e., sex, personality traits, and early life adversity) and hypothalamic-pituitary-adrenocortical- and endogenous opioid system-related mechanisms in the altered response to stress. I integrate these findings in a conceptual model emphasizing that robust stress responses in the context of addiction and relapse should be considered as a marker of resiliency.

CONCLUSIONS

A blunted stress response may indicate long-term physiological dysregulation that could usher harmful consequences for cardiovascular disease, pain perception, and addictive disorders. The impact of dysregulation is influenced by multiple individual and situational factors that should be considered in evaluating the clinical significance of stress response dysregulation.

Do Resting Plasma β-Endorphin Levels Predict Responses to Opioid Analgesics?

OBJECTIVES

Clinically feasible predictors of opioid analgesic responses for use in precision pain medicine protocols are needed. This study evaluated whether resting plasma β-endorphin (BE) levels predicted responses to an opioid analgesic, and whether chronic pain status or sex moderated these effects.

METHODS

Participants included 73 individuals with chronic low back pain (CLBP) and 88 pain-free controls, all using no daily opioid analgesics. Participants attended 2 identical laboratory sessions during which they received either intravenous morphine (0.08 mg/kg) or saline placebo, with blood samples obtained before drug administration to assay resting plasma BE levels. Once peak drug activity was achieved in each session, participants engaged in an ischemic forearm pain task (ISC) and a heat pain task. Morphine analgesic effects were derived reflecting the difference in pain outcomes between placebo and morphine conditions.

RESULTS

In hierarchical regressions, significant Type (CLBP vs. control)×BE interactions (Ps<0.05) were noted for morphine effects on ISC tolerance, ISC intratask pain ratings, and thermal VAS unpleasantness ratings. These interactions derived primarily from associations between higher BE levels and smaller morphine effects restricted to the CLBP subgroup. All other BE-related effects, including sex interactions, for predicting morphine analgesia failed to reach statistical significance.

DISCUSSION

BE was a predictor of morphine analgesia for only 3 out of 9 outcomes examined, with these effects moderated by chronic pain status but not sex. On the whole, results do not suggest that resting plasma BE levels are likely to be a clinically useful predictor of opioid analgesic responses.

Affectionate Touch to Promote Relational, Psychological, and Physical Well-Being in Adulthood: A Theoretical Model and Review of the Research

Throughout the life span, individuals engage in affectionate touch with close others. Touch receipt promotes well-being in infancy, but the impacts of touch in adult close relationships have been largely unexplored. In this article, we propose that affectionate touch receipt promotes relational, psychological, and physical well-being in adulthood, and we present a theoretical mechanistic model to explain why affectionate touch may promote these outcomes. The model includes pathways through which touch could affect well-being by reducing stress and by promoting well-being independent of stress. Specifically, two immediate outcomes of affectionate touch receipt—relational-cognitive changes and neurobiological changes—are described as important mechanisms underlying the effects of affectionate touch on well-being. We also review and evaluate the existing research linking affectionate touch to well-being in adulthood and propose an agenda to advance research in this area. This theoretical perspective provides a foundation for future work on touch in adult close relationships.

The long-term impact of early life pain on adult responses to anxiety and stress: Historical perspectives and empirical evidence

Approximately 1 in 6 infants are born prematurely each year. Typically, these infants spend 25 days in the Neonatal Intensive Care Unit (NICU) where they experience 10-18 painful and inflammatory procedures each day. Remarkably, pre-emptive analgesics and/or anesthesia are administered less than 25% of the time. Unalleviated pain during the perinatal period is associated with permanent decreases in pain sensitivity, blunted cortisol responses and high rates of neuropsychiatric disorders. To date, the mechanism(s) by which these long-term changes in stress and pain behavior occur, and whether such alterations can be prevented by appropriate analgesia at the time of insult, remains unclear. Work in our lab using a rodent model of early life pain suggests that inflammatory pain experienced on the day of birth blunts adult responses to stress- and pain-provoking stimuli, and dysregulates the hypothalamic pituitary adrenal (HPA) axis in part through a permanent upregulation in central endogenous opioid tone. This review focuses on the long-term impact of neonatal inflammatory pain on adult anxiety- and stress-related responses, and underlying neuroanatomical changes in the context of endogenous pain control and the HPA axis. These two systems are in a state of exaggerated developmental plasticity early in postnatal life, and work in concert to respond to noxious or aversive stimuli. We present empirical evidence from animal and clinical studies, and discuss historical perspectives underlying the lack of analgesia/anesthetic use for early life pain in the modern NICU.

Single housing during early adolescence causes time-, area- and peptide-specific alterations in endogenous opioids of rat brain

BACKGROUND AND PURPOSE

A number of experimental procedures require single housing to assess individual behaviour and physiological responses to pharmacological treatments. The endogenous opioids are closely linked to social interaction, especially early in life, and disturbance in the social environment may affect opioid peptides and thereby confound experimental outcome. The aim of the present study was to examine time-dependent effects of single housing on opioid peptides in rats.

EXPERIMENTAL APPROACH

Early adolescent Sprague Dawley rats (post-natal day 22) were subjected to either prolonged (7 days) or short (30 min) single housing. Several brain regions were dissected and immunoreactive levels of Met-enkephalin-Arg(6) Phe(7) (MEAP), dynorphin B and nociception/orphanin FQ, as well as serum corticosterone were measured using RIA.

KEY RESULTS

Prolonged single housing reduced immunoreactive MEAP in hypothalamus, cortical regions, amygdala, substantia nigra and periaqueductal grey. Short single housing resulted in an acute stress response as indicated by high levels of corticosterone, accompanied by elevated immunoreactive nociceptin/orphanin FQ in medial prefrontal cortex, nucleus accumbens and amygdala. Neither short nor prolonged single housing affected dynorphin B.

CONCLUSIONS AND IMPLICATIONS

Disruption in social environmental conditions of rats, through single housing during early adolescence, resulted in time-, area- and peptide-specific alterations in endogenous opioids in the brain. These results provide further evidence for an association between early life social environment and opioids. Furthermore, the results have implications for experimental design; in any pharmacological study involving opioid peptides, it is important to distinguish between effects induced by housing and treatment.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Effects of estrogen and opioid blockade on blood pressure reactivity to stress in postmenopausal women

Estrogen may influence coronary heart disease risk in women through the effects of endogenous opioids on autonomic control of blood pressure. In a randomized, placebo-controlled trial, we examined the combined effects of estrogen and the opioid antagonist, naltrexone, on blood pressure responses to psychological stress in 42 postmenopausal women. After 3 months of estrogen or estrogen plus progestin (hormone replacement therapy; n = 27) or placebo replacement, participants completed a mental arithmetic task after administration of .7 mg/kg oral naltrexone or placebo. Systolic blood pressure (SBP), diastolic blood pressure, mean arterial pressure and heart rate (HR) were measured at rest and during the arithmetic stressor. Stress produced significant increases in circulatory measures regardless of estrogen condition or opioid blockade (p's < .001). Interestingly, there was an estrogen by naltrexone interaction on SBP reactivity scores [F(1,38) = 4.36, p < .05], where women on estrogen with intact opioid receptors showed the largest SBP responses to stress, compared with all other conditions. This is consistent with some studies of premenopausal women, suggesting that estrogens may alter opioid function during stress. The interaction between estrogen and endogenous opioids may explain sex differences in opioid effects on stress reactivity in younger premenopausal women.

Adolescent opiate exposure in the female rat induces subtle alterations in maternal care and transgenerational effects on play behavior

The non-medical use of prescription opiates, such as Vicodin(®) and MSContin(®), has increased dramatically over the past decade. Of particular concern is the rising popularity of these drugs in adolescent female populations. Use during this critical developmental period could have significant long-term consequences for both the female user as well as potential effects on her future offspring. To address this issue, we have begun modeling adolescent opiate exposure in female rats and have observed significant transgenerational effects despite the fact that all drugs are withdrawn several weeks prior to pregnancy. The purpose of the current set of studies was to determine whether adolescent morphine exposure modifies postpartum care. In addition, we also examined juvenile play behavior in both male and female offspring. The choice of the social play paradigm was based on previous findings demonstrating effects of both postpartum care and opioid activity on play behavior. The findings revealed subtle modifications in the maternal behavior of adolescent morphine-exposed females, primarily related to the amount of time females' spend nursing and in non-nursing contact with their young. In addition, male offspring of adolescent morphine-exposed mothers (MOR-F1) demonstrate decreased rough and tumble play behaviors, with no significant differences in general social behaviors (i.e., social grooming and social exploration). Moreover, there was a tendency toward increased rough and tumble play in MOR-F1 females, demonstrating the sex-specific nature of these effects. Given the importance of the postpartum environment on neurodevelopment, it is possible that modifications in maternal-offspring interactions, related to a history of adolescent opiate exposure, plays a role in the observed transgenerational effects. Overall, these studies indicate that the long-term consequences of adolescent opiate exposure can impact both the female and her future offspring.

A review of neuroimaging studies of stressor-evoked blood pressure reactivity: emerging evidence for a brain-body pathway to coronary heart disease risk

An individual's tendency to show exaggerated or otherwise dysregulated cardiovascular reactions to acute stressors has long been associated with increased risk for clinical and preclinical endpoints of coronary heart disease (CHD). However, the 'brain-body' pathways that link stressor-evoked cardiovascular reactions to CHD risk remain uncertain. This review summarizes emerging neuroimaging research indicating that individual differences in stressor-evoked blood pressure reactivity (a particular form of cardiovascular reactivity) are associated with activation patterns in corticolimbic brain areas that are jointly involved in processing stressors and regulating the cardiovascular system. As supported empirically by activation likelihood estimates derived from a meta-analysis, these corticolimbic areas include divisions of the cingulate cortex, insula, and amygdala--as well as networked cortical and subcortical areas involved in mobilizing hemodynamic and metabolic support for stress-related behavioral responding. Contextually, the research reviewed here illustrates how behavioral medicine and health neuroscience methods can be integrated to help characterize the 'brain-body' pathways that mechanistically link stressful experiences with CHD risk.

Mu-opioid and corticotropin-releasing-factor receptors show largely postsynaptic co-expression, and separate presynaptic distributions, in the mouse central amygdala and bed nucleus of the stria terminalis

The anxiolytic effects of opiates active at the mu-opioid receptor (mu-OR) may be ascribed, in part, to suppression of neurons that are responsive to the stress-associated peptide, corticotropin releasing factor (CRF), in the central amygdala (CeA) and bed nucleus of the stria terminalis (BNST). The corticotropin releasing factor receptor (CRFr) and mu-OR are expressed in both the CeA and BNST, but their subcellular relationship to each other is not known in either region. To address this question, we used dual electron microscopic immunolabeling of mu-OR and CRFr in the mouse lateral CeA and anterolateral BNST. Immunolabeling for each receptor was detected in the same as well as in separate somatic, dendritic and axonal profiles of neurons in each region. CRFr had a plasmalemmal or cytoplasmic distribution in many dendrites, including those co-expressing mu-OR. The co-expression of CRFr and mu-OR also was seen near excitatory-type synapses on dendritic spines. In both the CeA and BNST, over 50% of the CRFr-labeled dendritic profiles (dendrites and spines) contained immunoreactivity for the mu-OR. However, less than 25% of the dendritic profiles containing the mu-OR were labeled for CRFr in either region, suggesting that opiate activation of the mu-OR affects many neurons in addition to those responsive to CRF. The dendritic profiles containing CRFr and/or mu-OR received asymmetric, excitatory-type synapses from unlabeled or CRFr-labeled axon terminals. In contrast, the mu-OR was identified in terminals forming symmetric, inhibitory-type synapses. Thus, in both the CeA and BNST, mu-OR and CRFr have strategic locations for mediation of CRF and opioid effects on the postsynaptic excitability of single neurons, and on the respective presynaptic release of excitatory and inhibitory neurotransmitters. The commonalities in the synaptic location of both receptors in the CeA and BNST suggest that this is a fundamental cellular association of relevance to both drug addiction and stress-induced disorders.

Coregulation, Dysregulation, Self-Regulation: An Integrative Analysis and Empirical Agenda for Understanding Adult Attachment, Separation, Loss, and Recovery

An integrative framework is proposed for understanding how multiple biological and psychological systems are regulated in the context of adult attachment relationships, dysregulated by separation and loss experiences, and, potentially, re-regulated through individual recovery efforts. Evidence is reviewed for a coregulatory model of normative attachment, defined as a pattern of interwoven physiology between romantic partners that results from the conditioning of biological reward systems and the emergence of felt security within adult pair bonds. The loss of coregulation can portend a state of biobehavioral dysregulation, ranging from diffuse psychophysiological arousal and disorganization to a full-blown (and highly organized) stress response. The major task for successful recovery is adopting a self-regulatory strategy that attenuates the dysregulating effects of the attachment disruption. Research evidence is reviewed across multiple levels of analysis, and the article concludes with a series of testable research questions on the interconnected nature of attachment, loss, and recovery processes.

Time dependent alterations on tyrosine hydroxylase, opioid and cannabinoid CB1 receptor gene expressions after acute ethanol administration in the rat brain

The aim of this study was to examine the differential regulation after acute ethanol administration on tyrosine hydroxylase, proenkephalin and cannabinoid CB(1) receptor gene expressions in selected areas of the rat brain. Rats received an intragastric administration of 3 g/kg ethanol and were killed by decapitation at 1, 2, 4, 8 and 24 h. The results showed an activation of tyrosine hydroxylase gene expression in the ventral tegmental area and the substantia nigra, increased proenkephalin gene expression in the caudate-putamen, nucleus accumbens core and shell, central and medial amygdala, ventromedial hypothalamic nucleus and the paraventricular hypothalamic nucleus. In contrast, a significant decrease in the cannabinoid CB1 receptor gene expression was found in caudate-putamen, central amygdala and ventromedial hypothalamic nucleus. In conclusion, the results suggest that an acute dose of ethanol induces neuroplastic alterations in proenkephalin, tyrosine hydroxylase and cannabinoid CB1 receptor gene expressions that may contribute to trigger the rewarding effects of ethanol consumption.

Nociceptive flexion reflex thresholds and pain during rest and computer game play in patients with hypertension and individuals at risk for hypertension

Supraspinal pain modulation may explain hypertensive hypoalgesia. We compared nociceptive flexion reflex (NFR) thresholds and pain during rest and computer game play in hypertensives and normotensives (Experiment 1) and normotensives with and without hypertensive parents (Experiment 2). The game was selected to modulate activity in pain pathways. NFR thresholds did not differ between groups during rest or game play. Pain ratings never differed between hypertensives and normotensives, whereas individuals with hypertensive parents reported less pain during the first two NFR assessments, compared to those without. NFR thresholds and pain were reduced by game play compared to rest. The failure of game play to differentially modulate NFR thresholds or associated pain reports between groups argues against enhanced supraspinal modulation of nociception and pain in hypertensives and those at increased risk for hypertension.

Effects of Opioid Blockade with Naltrexone and Distraction on Cold and Ischemic Pain in Hypertension

Essential hypertension is characterised by reduced pain sensitivity. Hypertensive hypoalgesia has been attributed to elevated endogenous opioids and/or increased activation of descending pain modulation systems. A double-blind placebo-controlled design compared the effects of naltrexone and placebo on cold and ischemic pain in unmedicated newly-diagnosed patients with essential hypertension. Patients performed a cold pressor task while resting and while performing a distracting secondary task. They also performed a forearm ischemia task while resting. Although the cold pressor and ischemia tasks elicited significant increases in pain and blood pressure, pain ratings and pressor responses did not differ between naltrexone and placebo. Cold pain was reduced by distraction compared to rest. The finding that opioid blockade with naltrexone did not moderate the pain and pressor responses to cold and ischemia suggests that pain and associated blood pressure responses are not modulated by opioids in hypertension. The finding that the distracting secondary task successfully reduced pain ratings suggests normal supraspinal pain modulation in essential hypertension.

Neuroendocrine and Behavioral Mechanisms Mediating the Relationship between Anger Expression and Cardiovascular Risk: Assessment Considerations and Improvements

The hypothesis that intense anger experience may increase risk for or exacerbate cardiovascular diseases has been under active theoretical and empirical interest for decades. Biopsychological models of disease suggest that persons displaying exaggerated physiological responses to acute emotional or stressful states are at a greater risk to develop cardiovascular disorders. The last two decades have witnessed active work to refine means by which anger expression can be assessed, and laboratory research has produced evidence suggesting that certain expression styles may predict enhanced physiological responses to acute stress. In this paper, we review methodological and definition issues related to the assessment of anger, and we summarize recent improvements on the assessment of anger expression. We also review recent studies addressing the association between anger and cardiovascular diseases, and we present potential neuroendocrine and behavioral mechanisms through which anger expression may increase risk for cardiovascular disease.

Trait anger and blood pressure recovery following acute pain: evidence for opioid-mediated effects

Previous work has suggested that positive associations between trait anger (TRANG) and pain sensitivity are due to dysfunctional endogenous opioid analgesic systems. In this study, we examined whether TRANG is associated with impaired opioid modulation of blood pressure (BP) recovery. A total of 46 pain-free normotensive controls and 69 normotensive chronic low back pain (LBP) sufferers received opioid blockade (8 mg naloxone i.v.) or placebo in randomized, counterbalanced order in separate sessions. During each, participants underwent a 1-min finger pressure pain task followed by an ischemic forearm pain task. Opioid blockade impaired post-pain BP recovery in controls but not LBP participants (ps < .001). In controls, low TRANG was associated with blockade-induced recovery impairments, with no blockade effect in high TRANG participants. In LBP participants, blockade did not alter recovery regardless of TRANG (interaction ps < .05). Results support dysfunctional opioid modulation of BP recovery in healthy high TRANG controls and further suggest chronic pain-related impairments in opioid-mediated cardiovascular recovery.

Adrenocortical and nociceptive responses to opioid blockade in hypertension-prone men and women

OBJECTIVE

Attenuated pain sensitivity and exaggerated adrenocortical stress reactivity have been documented in individuals at high risk for hypertension. The endogenous opioid system may play a role in these response alterations. We compared adrenocortical and nociceptive responses to opioid blockade using naltrexone in hypertension-prone men and women.

METHODS

Ninety-nine participants completed two sessions during which a placebo or 50 mg naltrexone was administered using a double-blind, counterbalanced design. Participants rated their pain and completed the McGill Pain Questionnaire (MPQ) after three assessments of the nociceptive flexion reflex and after assessment of nociceptive pain threshold and tolerance. Saliva samples were obtained throughout the sessions.

RESULTS

Salivary cortisol levels increased after pain assessment after the ingestion of naltrexone, but not after placebo, with the low-risk group exhibiting an earlier peak of cortisol response. Participants reported greater pain ratings and higher MPQ scores in the naltrexone versus placebo condition, and these effects were more pronounced in women. Pain threshold and tolerance were higher among high-risk men relative to low-risk men.

CONCLUSIONS

The results are consistent with the inhibitory effects of the endogenous opioids on cortisol response and suggest an altered response timeline among hypertension-prone individuals. The results demonstrate that hypoalgesia may be a marker of hypertension risk in men but not in women.

Anxiety stress and nociceptive responses in mice

Nociception in laboratory animals appears to be influenced by physical or emotional stressors. Nevertheless, the reported data are not univocal. Discrepancies seem to be caused by some kind of stress model and/or by the timing of stressor application. The aim of the present work is to study the influence of chronic application of a well-controlled and defined anxiety stress paradigm (rotational stress) on the behavioral formalin pain responses in mice maintained in a low-stress environment. The results indicate that emotional chronic stress increases specific pain responses in the late inflammatory phase and, correspondingly, decreases self-grooming. Locomotor activity appears influenced by pain presence only. The hormonal and neural mechanisms that could be involved in the observed nonspecific and specific nociceptive responses to stress are discussed.

Effects of baroreceptor stimulation and opioids on the auditory startle reflex

We examined (a) whether carotid baroreceptor stimulation attenuates the auditory startle response and its modulation by preceding affective pictures, and (b) whether these effects are mediated by endogenous opioids. Seventy-eight young normotensive adults with or without a parental history of hypertension received brief exposures to affective pictures and noise bursts during phasic manipulation of the carotid baroreceptors. In each participant, opioids were blocked by naltrexone in half of the sessions. Baroreceptor stimulation had a strong dampening effect on the startle response. This effect was not influenced by opioid blockade, sex, or parental history of hypertension. No baroreceptor effects were obtained regarding ratings of the affective pictures or startle modulation by the pictures. The baroreceptor stimulation effects seem to be mediated by the basal primary acoustic startle circuit rather than by higher affective circuits.

Anger management style, blood pressure reactivity, and acute pain sensitivity: evidence for "Trait x Situation" models

BACKGROUND

Anger management style is related to acute and chronic pain, but it is not clear whether anger arousal is needed for these associations to emerge or whether physiological mechanisms mediate these links.

PURPOSE

"Trait x Situation" models were examined to determine whether relationships between anger-out and pain and anger-in and pain depended on anger provocation's preceding pain induction and whether pain sensitivity variance explained by anger management style overlapped with variance in harassment-induced blood pressure reactivity.

METHODS

Healthy individuals (N = 53) underwent either mental arithmetic with harassment and then a cold pressor (MA/CP) or vice versa (CP/MA). The Spielberger Anger Expression Inventory assessed anger-out using the Anger-Out subscale (AOS) and anger-in using the Anger-In subscale (AIS).

RESULTS

AOS x Order and AIS x Order interactions for pain tolerance emerged, such that (a) AOS was related negatively to tolerance among MA/CP participants, whereas AOS and tolerance were not related in CP/MA; (b) AIS was related positively to tolerance in MA/CP, whereas AIS was related negatively to tolerance in CP/MA; and (c) tolerance variance accounted for by AOS in MA/CP overlapped substantially with tolerance variance accounted for by diastolic blood pressure reactivity.

CONCLUSIONS

Findings support the notion that anger management style affects pain and are consistent with evidence that deficient endogenous opioid functioning may be one mechanism through which anger-out is linked to both pain sensitivity and cardiovascular stress reactivity, a connection that appears most reliably when anger is provoked.

Beta-endorphin modulates the acute response to a social conflict in male mice but does not play a role in stress-induced changes in sleep

Beta-endorphin is an endogenous opioid peptide that is released during stress and has been associated with many physiological functions. In this experiment beta-endorphin deficient mice were used to study the role of endorphins in the acute physiological and behavioral responses to a social conflict, as well as their role in social stress-induced changes in sleep. Adult male beta-endorphin deficient and wild type mice were subjected to the stress of a 1 h social conflict with an aggressive dominant conspecific. After the conflict, the beta-endorphin deficient mice had higher corticosterone levels but the peak increase in body temperature was not different from that in wild type animals. In fact, body temperature returned to baseline levels faster in the beta-endorphin deficient mice. During their interaction with the aggressive conspecific several of the beta-endorphin deficient mice showed clear signs of counter aggression whereas this was not seen in any of the wild type mice. Overall, the beta-endorphin deficient mice and wild type mice had fairly similar sleep patterns under baseline conditions and also showed similar amounts of NREM sleep, REM sleep and EEG slow-wave energy after the social conflict. In addition, no differences were found in the sleep patterns of mice that showed counter aggression and mice that did not. In conclusion, the results suggest that beta-endorphin modulates the acute endocrine, thermoregulatory and behavioral response to a social conflict but the data do not support a major role for beta-endorphin in the regulation of sleep or social stress-induced alterations in sleep.

Biobehavioral approaches to the treatment of essential hypertension

Despite recent advances in the medical management of hypertension, chronically elevated blood pressure remains a major health problem in the United States, affecting almost 50 million Americans. It is widely recognized that lifestyle factors contribute to the development and maintenance of elevated blood pressure. This article critically reviews current approaches to the nonpharmacological treatment of high blood pressure and highlights outcome studies of exercise, weight loss and dietary modification, and stress management and relaxation therapies. Methodological issues in the assessment and treatment of hypertension are discussed, along with possible mechanisms by which lifestyle modification may reduce elevated blood pressure.

Stressful animal housing conditions and their potential effect on sympathetic neurotransmission in mice

Although the sympathetic nervous system (SNS) plays a major role in mediating the peripheral stress response, due consideration is not usually given to the effects of prolonged stress on the SNS. The present study examined changes in neurotransmission in the SNS after exposure of mice (BALB/c) to stressful housing conditions. Focal extracellular recording of excitatory junction currents (EJCs) was used as a relative measure of neurotransmitter release from different regions of large surface areas of the mouse vas deferens. Mice were either group housed (control), isolation housed (social deprivation), group housed in a room containing rats (rat odor stress), or isolation housed in a room containing rats (concurrent stress). Social deprivation and concurrent stressors induced an increase of 30 and 335% in EJC amplitude, respectively. The success rate of recording EJCs from sets of varicosities in the concurrent stressor group was greater compared with all other groups. The present study has shown that some common animal housing conditions act as stressors and induce significant changes in sympathetic neurotransmission.

Negative affect and sensitization to pain

Pain usually has a strong negative affective component, which is believed to modulate pain perception. After reviewing theories on the link between negative affect and pain, mechanisms are discussed by which negative affect may either increase or inhibit pain. Possible pain-inhibiting mechanisms are endogenous opioid release, blood pressure reactivity, and distraction of attention; possible pain-increasing mechanisms are autonomic and muscular reactivity, misattribution of arousal, hypervigilance to pain, worrying, and avoidance behavior. It is emphasized that each of these mechanisms can be very adaptive in acute pain situations to prevent injury and promote recovery. In chronic pain, however, ongoing physiological arousal and hypervigilance to pain, induced or magnified by negative affect, may cause sensitization to pain. Furthermore, worrying about pain and avoidance of pain-inducing activities may increase negative affect, ypervigilance, and functional disability. It is argued that, in the long run, pain-related negative affect has sensitizing and disabling effects.

Prevention of isolation-induced hypertension by intrahippocampal administration of a nonpeptide kappa-opioid receptor agonist

Previous research in this laboratory showed that hypertension in the spontaneous hypertensive rat (SHR) appears to correlate to insufficient production of hippocampal dynorphins, and that blood pressure could be reduced by intrahippocampal administration of dynorphins and nonpeptide kappa agonists. The purpose of the present study was to investigate whether kappa agonists could prevent the development of hypertension in a different hypertensive model, i.e., the isolated male rat model of hypertension (IHR). Isolation of young male rats for 5-7 days in standard rat cages caused an increase in systolic blood pressure from a mean of 132 to 184 mmHg. The blood pressures of rats grouped 3 per cage remained stable. Rats received the nonpeptide kappa agonist U62, 066E, (Spiradoline, Upjohn), 10 nmoles/0.2 microl or drug vehicle bilaterally into the the hippocampus for 3 days prior to and during isolation or grouping. Animals treated with U62, 066E did not develop hypertension as compared to isolated animals treated with vehicle. The isolation procedure used in these studies appears to induce anxietal stress, as indicated by reduced time spent by the rats in the open arms of the elevated-plus maze. This time is increased by U62, 066E, suggesting that the drug possesses anxiolytic properties and may reduce hypertension in part, by blocking an anxiety/stress component. These data strengthen our previous findings that opioids in the hippocampus may be important in restraining increased blood pressure provoked by environmental stimuli such as isolation.

Dexamethasone modulates hypotension induced by opioids in anaesthetised rats

The effect of dexamethasone on hypotension induced by mu-, kappa- and delta-opioid receptor agonists was investigated in pentobarbital-anaesthetised rats. Morphine (nonselective opioid receptor agonist), DAGO (D-Ala2-N-methyl-[Phe4-Gly5-ol]enkephalin; mu-opioid receptor-selective agonist), U50-488H (trans(+/-)-3,4-dichloro-N-methyl-N-(2[1pyrrolidynyl]cyclohexyl)-benzeneacetamide; kappa-opioid receptor-selective agonist) and deltorphin II (delta-opioid receptor-selective agonist), given intravenously, 5 micromol/kg, induced hypotension in rats. This hypotension was characterised by a fall in mean arterial blood pressure in 1-2 min that recovered in 30 min for morphine and U50-488H and in 5 or 20 min for DAGO and deltorphin II, respectively. Dexamethasone per se at a dose of 7.5 micromol/kg, i.v. did not significantly modify the mean arterial blood pressure of animals. Dexamethasone administration 90 min, but not 30 or 60 min, before the opioid agonists injection, prevented the hypotension induced by morphine or U50-488H, but not that induced by DAGO or deltorphin II. Pretreatment with RU-38486 (mifepristone; 7.5 micromol/kg, i.v.), a glucocorticoid receptor antagonist, 15 min before the steroid, prevented dexamethasone inhibition of hypotension induced by morphine and U50-488H. Furthermore, pretreatment with cycloheximide, a protein synthesis inhibitor (3.5 micromol/kg, i.v.), was also able to abolish the effects of dexamethasone on morphine- and U50-488H-induced hypotension. Results of the present study indicate that dexamethasone inhibited kappa-opioid receptor-mediated hypotension in rats, indicating a further important functional interaction between corticosteroids and the opioid system at kappa receptors. The ability of cycloheximide and RU-38486 to block dexamethasone effects indicates that steroid interference with kappa-opioid receptor-mediated hypotension involves a protein synthesis-dependent mechanism via glucocorticoid receptors.

Role of endogenous opioid system in the regulation of the stress response

Numerous studies and reviews support an important contribution of endogenous opioid peptide systems in the mediation, modulation, and regulation of stress responses including endocrine (hypothalamopituitary-adrenal, HPA axis), autonomic nervous system (ANS axis), and behavioral responses. Although several discrepancies exist, the most consistent finding among such studies using different species and stressors is that opioids not only diminish stress-induced neuroendocrine and autonomic responses, but also stimulate these effector systems in the non-stressed state. A distinctive feature of the analgesic action of opioids is the blunting of the distressing, affective component of pain without dulling the sensation itself. Therefore, opioid peptides may diminish the impact of stress by attenuating an array of physiologic responses including emotional and affective states. The widespread distribution of enkephalin (ENK) throughout the limbic system (including the extended amygdala, cingulate cortex, entorhinal cortex, septum, hippocampus, and the hypothalamus) is consistent with a direct role in the modulation the stress responses. The predictability of stressful events reduces the impact of a wide range of stressors and ENK appears to play an important role in this process. Therefore, ENK and its receptors could represent a major modulatory system in the adaptation of an organism to stress, balancing the response that the stressor places on the central stress system with the potentially detrimental effects that a sustained stress may produce. Chronic neurogenic stressors will induce changes in specific components of the stress-induced ENKergic system, including ENK, delta- and mu-opioid receptors. This review presents evidences for adaptive cellular mechanisms underlying the response of the central stress system when assaulted by repeated psychogenic stress, and the involvement of ENK in these processes.

Expression of mu, kappa, and delta opioid receptor messenger RNA in the human CNS: a 33P in situ hybridization study

The existence of at least three opioid receptor types, referred to as mu, kappa, and delta, is well established. Complementary DNAs corresponding to the pharmacologically defined mu, kappa, and delta opioid receptors have been isolated in various species including man. The expression patterns of opioid receptor transcripts in human brain has not been established with a cellular resolution, in part because of the low apparent abundance of opioid receptor messenger RNAs in human brain. To visualize opioid receptor messenger RNAs we developed a sensitive in situ hybridization histochemistry method using 33P-labelled RNA probes. In the present study we report the regional and cellular expression of mu, kappa, and delta opioid receptor messenger RNAs in selected areas of the human brain. Hybridization of the different opioid receptor probes resulted in distinct labelling patterns. For the mu and kappa opioid receptor probes, the most intense regional signals were observed in striatum, thalamus, hypothalamus, cerebral cortex, cerebellum and certain brainstem areas as well as the spinal cord. The most intense signals for the delta opioid receptor probe were found in cerebral cortex. Expression of opioid receptor transcripts was restricted to subpopulations of neurons within most regions studied demonstrating differences in the cellular expression patterns of mu, kappa, and delta opioid receptor messenger RNAs in numerous brain regions. The messenger RNA distribution patterns for each opioid receptor corresponded in general to the distribution of opioid receptor binding sites as visualized by receptor autoradiography. However, some mismatches, for instance between mu opioid receptor receptor binding and mu opioid receptor messenger RNA expression in the anterior striatum, were observed. A comparison of the distribution patterns of opioid receptor messenger RNAs in the human brain and that reported for the rat suggests a homologous expression pattern in many regions. However, in the human brain, kappa opioid receptor messenger RNA expression was more widely distributed than in rodents. The differential and region specific expression of opioid receptors may help to identify targets for receptor specific compounds in neuronal circuits involved in a variety of physiological functions including pain perception, neuroendocrine regulation, motor control and reward.

Comparison of cardiovascular responses to intra-hippocampal mu, delta and kappa opioid agonists in spontaneously hypertensive rats and isolation-induced hypertensive rats

OBJECTIVE

To investigate the cardiovascular effects of microinjection into the hippocampus of selective mu, delta and kappa opioid receptor agonists in anesthetized spontaneously hypertensive rats, isolation-induced hypertensive rats and their normotensive Wistar-Kyoto and group-housed Sprague-Dawley controls.

METHODS AND RESULTS

The microinjection of a selective kappa agonist, spiradoline mesylate, (+/-)-(5alpha, 7alpha, 8beta)-3,4-dichloro-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro++ +[4.5]dec-8-yl]-benzeneacetamide mesylate) (5 nmol) into the dorsal region of hippocampus, where injection of control saline failed to affect cardiovascular activities, induced centrally mediated decreases in mean blood pressure and heart rate in both hypertensive and normotensive rats. The effects were blocked by prior treatment of the hippocampus with nor-binaltorphimine dihydrochloride, a selective kappa opioid receptor antagonist The hypotensive and bradycardic effects were quantitatively similar between spontaneously hypertensive rats and Wistar-Kyoto rats and between isolated hypertensive rats and normotensive group-housed rats. The sequential administration of increasing doses (5, 10, 50 nmol) of the selective mu agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin and delta agonists [D-Ala2, D-Leu5]-enkephalin or [D-Pen2, D-Pen5]-enkephalin into the same areas of the hippocampus as used for the kappa agonist had no significant effects on mean blood pressure and heart rate in either hypertensive or normotensive rats.

CONCLUSION

The present results extend our previous findings of a hippocampally mediated hypotensive effect of kappa agonists in the spontaneously hypertensive rat to the isolated rat model of hypertension and they establish that mu and delta opioid receptor agonists similarly applied are ineffective. Hippocampal kappa receptors may have a greater role in cardiovascular control than mu and delta receptors.

The role of subtypes of the opioid receptor in the anxiolytic action of chlordiazepoxide

Previous studies have shown that the opiate antagonist naloxone blocks the anxiolytic-like effects of benzodiazepines in several models of anxiety, including the elevated plus-maze. Although naloxone preferentially binds to the mu opioid receptor, its selectivity is rather low. The opioid receptor subtype important for anxiolytic-like actions of benzodiazepines in the plus-maze remains, therefore, unknown. In the present experiments, the ability of antagonists selective for subtypes of the opioid receptor to block the anxiolytic-like effects of chlordiazepoxide in the elevated plus-maze was evaluated in Swiss mice. Chlordiazepoxide, 5 mg/kg, increased the proportion as well as the number of open arms entries without modifying closed arms entries. Lower doses of the benzodiazepine were ineffective. The mu receptor antagonist beta-funaltrexamine, 10 and 20 mg/kg, the delta antagonist naltrindole, 10 mg/kg, and the kappa antagonist nor-binaltorphimine, 2.5 and 5 mg/kg, were then combined with chlordiazepoxide, 5 mg/kg. beta-funaltrexamine, 10 mg/kg, reduced the effects of the benzodiazepine while the dose of 20 mg/kg completely blocked the effects. Nor-binaltorphimine was ineffective at a dose of 2.5 mg/kg, but completely inhibited the actions of chlordiazepoxide when the dose was 5 mg/kg. Naltrindole was ineffective. None of the antagonists affected plus-maze behavior when administered alone. It was concluded that the mu and kappa receptors are important for the anxiolytic-like actions of chlordiazepoxide in the elevated plus maze.

Responses of the nervous system to low frequency stimulation and EEG rhythms: clinical implications

The present paper reviews literature data on the role of the non-specific central nervous system response mechanisms on the therapeutic effects of relatively weak external stimulations used in clinical practice. The factors affecting the stimulation efficiency and increased sensitiveness of living things to extra-low-frequency periodic stimulations (in the range of from less than 1 Hz to tens of Hz) are discussed. Among the factors determining such effects, the non-specific response mechanisms of the nervous system, the resonance phenomena in different organism systems, and the interaction of external stimulation with endogenous rhythmic processes are analyzed. Most attention is given to endogenous rhythms of the electrical brain activity reflected in the EEG rhythms. A high resolution EEG processing approach that is used to reveal the intrinsic oscillators in the individual EEG spectrum is described. Synchronization of sensory stimulation parameters with the frequencies of intrinsic EEG oscillators is supposed to be an appropriate way to enhance the therapeutic effects of various sensory stimulation treatments. Specific methods for utilizing resonance therapy via sensory stimulation with intrinsic EEG frequencies, and for automatic modulation of stimulation parameters by endogenous organism rhythms are delineated; some preliminary results are described.

Endogenous opioids inhibit ambulatory blood pressure during naturally occurring stress

OBJECTIVE

Laboratory experiments suggest that endogenous opioids inhibit blood pressure responses during psychological stress. Moreover, there seem to be considerable individual differences in the efficacy of opioid blood pressure inhibition, and these differences may be involved in the expression of risk for cardiovascular disease. To further evaluate the possible role of opioid mechanisms in cardiovascular control, the present study sought to document the effects of the long-lasting oral opioid antagonist naltrexone (ReVia, DuPont, Wilmington, DE) on ambulatory blood pressure responses during naturally occurring stress.

METHOD

Thirty male volunteers participated in a laboratory stress study using naltrexone followed by ambulatory blood pressure under placebo and during the subsequent 24-hour period. Within-subject analyses were performed on ambulatory blood pressures under placebo and naltrexone conditions.

RESULTS

Laboratory results indicate no significant group effects of naltrexone on blood pressure levels or reactivity. Ambulatory results indicate that during periods of low self-reported stress, no effect of opioid blockade was apparent. In contrast, during periods of high stress, opioid blockade increased ambulatory blood pressure.

CONCLUSIONS

These findings suggest that naltrexone-sensitive opioid mechanisms inhibit ambulatory blood pressure responses during naturally occurring stress.

Elevation of plasma beta-endorphin levels of shy elderly in response to novel laboratory experiences

Heightened psychophysiological reactivity to the novel or unfamiliar is a leading characteristic of sky or behaviorally inhibited individuals. To assess one aspect of the physiological stress response in shyness, the authors compared the morning plasma beta-endorphin levels of 15 extremely sky, healthy elderly individuals with beta-endorphin levels of 15 extremely outgoing persons on three pairs of 2 successive days. The primary finding was that sky participants exhibited significantly higher levels of beta-endorphin on the 1st days of each pair of days, compared with the 2nd days in the laboratory. No main effect for shyness or interaction between shyness and diet on endorphin levels was found. The findings are consistent with a peripheral opioid hyperreactivity to novelty in shy elderly persons. Shyness may constitute a risk factor for panic disorder in younger adults and for nasal allergies and certain cancers in older adults. Experimental design and interpretation of future studies of shy individuals' stress responses may need to consider novelty versus familiarity of the procedures and setting.

Pain perception and cardiovascular responses in men with positive parental history for hypertension

Evidence suggests a reduced pain sensitivity in hypertensive individuals. This study sought to extend this work to normotensive individuals with hypertensive parents. Men with a positive (PH+) or negative (PH-) parental history for hypertension rated their pain every 15 s during a 90-s hand cold pressor test and for 90 s after the cold pressor test. Systolic (SBP) and diastolic (DBP) blood pressures and heart rate were measured throughout. After the cold pressor test, the men recalled their pain using the McGill Pain Questionnaire. PH+ men showed greater SBP and DBP responses to the cold pressor test. Although pain ratings during the cold pressor test did not differ between groups, posttest reported pain receded faster in the PH+ than in the PH- men. The PH+ men also reported less total pain on the McGill. These findings support the hypothesis that risk for hypertension may be associated with attenuated pain responses to nociceptive stimuli.

Psychological coping with acute pain: an examination of the role of endogenous opioid mechanisms

This study examined the relationship among endogenous opioids, Monitoring and Blunting coping styles, and acute pain responses. Fifty-eight male subjects underwent a 1-min pressure pain stimulus during two laboratory sessions. Subjects experienced this pain stimulus once under endogenous opioid blockade with naltrexone and once in a placebo condition. Blunting was found to be negatively correlated with pain ratings, but this relationship was significantly more prominent under opioid blockade. Results for coping behaviors subjects used to manage the experimental pain were generally consistent with the Blunting results, indicating that cognitive coping was related more strongly to decreased pain ratings and cardiovascular stress responsiveness under opioid blockade. Overall, the beneficial effects of Blunting and cognitive coping on pain responses did not depend upon endogenous opioids and, in fact, became stronger when opioid receptors were blocked. The relationship between endogenous opioids and coping appears to be dependent upon situational and stimulus characteristics.

Do endogenous opioids mediate the relationship between blood pressure and pain sensitivity in normotensives?

Elevated resting blood pressure is associated with decreased pain sensitivity in both animals and humans. Recent evidence suggests that this relationship may be mediated by endogenous opioid peptides in hypertensives, but the precise mechanism has not been investigated in normotensives. We examined the effect of opioid receptor blockade with naloxone on the relationship between resting blood pressure and pain sensitivity in normotensive humans. Sixteen young adults were given cold pressor and handgrip challenges after treatment with either naloxone or saline in a placebo-controlled, within-subject design. Multiple regression procedures indicated that resting systolic blood pressure was a significant predictor of cold pain ratings even after the effects of naloxone were statistically controlled. The interaction between systolic blood pressure and opioid blockade was non-significant. These data suggest that the relationship between resting blood pressure and pain sensitivity in normotensive humans is mediated, at least in part, by non-opioid mechanisms.

Coping styles, opioid blockade, and cardiovascular response to stress

We investigated the hypothesis that the effects of Monitoring and Blunting coping styles are mediated in part by endogenous opioids. Mean arterial pressure (MAP) and heart rate (HR) were measured in 39 males before, during, and after a mental arithmetic stressor. Each subject experienced the protocol once under opioid blockade (naltrexone) and once in a placebo condition, in counterbalanced order. Monitoring and Blunting were assessed using the Miller Behavioral Style Scale. High Blunting and high Monitoring were both associated with poorer MAP recovery under opioid blockade than in the placebo condition. Similar effects were noted for Blunting on the measure of HR. These results indicate that the coping styles of Monitoring and Blunting may be associated with enhanced opioid mediation of cardiovascular recovery from stress.