The elevation of plasma beta-endorphin levels in major depression

Endorphins, Sexuality, and Reproduction

Beta-endorphin is secreted from the hypothalamus and pituitary in both mother and newborn. The placenta produces numerous pituitary hormones from the third month of pregnancy, one of which is βE. It has been suggested that βE has a role in the appetitive and precopulatory phase of sexual behavior in animals. An increase in endorphin levels during sexual activity in humans may contribute to attachment and bonding between partners, but contradictory reports in the literature question the association between sexuality and βE levels. The level of βE also increases during pregnancy, rises in early labor, peaks in late labor, and drops in the postpartum period. This fluctuation provides natural analgesia, raises the pain threshold, decreases the sensation of pain, or suppresses pain, and decreases fear levels during labor and birth. Beta-endorphin also protects the fetus from hypoxia during labor and birth and potential neural damage by aiding blood flow to the brain under hypoxic conditions. It has been suggested that a variety of pharmacologic and nonpharmacologic complementary therapies, when used in pregnancy, labor, and birth, activate the opioid receptors in the CNS and alter the sensation of pain during labor and birth, affect the mother-child attachment and affect sexual function. These studies report contradictory results that will be discussed in this chapter.

Biosignature of self-injury behaviors in adolescence: Role of β-endorphin in an acute inpatient unit

Self-injurious behavior (SIB) (either non-suicidal self-injury, NSSI; or suicide attempts, SA) is a common reason for adolescent psychiatric emergency hospitalizations. Altered basal serum β-endorphin (BE) levels have been reported in adults with a history of SIB, but information is lacking in adolescents. We analyzed the psychoclinical profile and serum BE level of 39 adolescents admitted to the acute unit at a hospital in Spain due to SIB. The Mean (SD) serum BE level was high (190.53 ± 74.83). Regarding time sequence, the onset age of NSSI and SA were related (p < 0.001). The older the onset age of NSSI, the shorter the transition between NSSI and the onset of SA behavior (p = 0.05), but this difference does not lead the variation of BE (p = 0.81). Patients diagnosed with depression had lower serum BE levels than adolescents with other diagnoses (p = 0.03). Although adolescents who seem to be addicted to SIB had higher levels of BE, this finding was not statistically significant. The relationship between serum BE levels and SIB in adolescents requires further investigation.

Supplementation with Matured Hop Bitter Acids Improves Cognitive Performance and Mood State in Healthy Older Adults with Subjective Cognitive Decline

BACKGROUND

Prevention of age-related cognitive decline and depression is becoming urgent because of rapid growing aging populations. Effects of vagal nerve activation on brain function by food ingredients are inadequately investigated; matured hop bitter acid (MHBA) administration reportedly improves cognitive function and depression via vagal nerve activation in model mice.

OBJECTIVE

We investigated the effects of MHBA supplementation on cognitive function and mood state in healthy older adults with perceived subjective cognitive decline.

METHODS

Using a randomized double-blind placebo-controlled trial design, 100 subjects (aged 45-69 years) were randomly assigned into placebo (n = 50) and MHBA (n = 50) groups, and received placebo or MHBA capsules daily for 12 weeks.

RESULTS

Symbol Digit Modalities Test (SDMT) score assessing divided attention at week 12 was significantly higher (p = 0.045) and β-endorphin at week 12 was significantly lower (p = 0.043) in the subjects receiving MHBA. Transthyretin in serum, a putative mild cognitive impairment marker, was significantly higher at week 12 in the MHBA group than in the placebo group (p = 0.048). Subgroup analysis classified by the subjective cognitive decline questionnaire revealed that in addition to improved SDMT scores, memory retrieval assessed using the standard verbal paired-associate learning tests and the Ray Verbal Learning Test at week 12 had significantly improved in the subgroup with perceived subjective cognitive decline and without requirement for medical assistance in the MHBA group compared with that in the placebo group.

CONCLUSION

This study suggested that MHBA intake improves cognitive function, attention, and mood state in older adults.

Roles of β-Endorphin in Stress, Behavior, Neuroinflammation, and Brain Energy Metabolism

β-Endorphins are peptides that exert a wide variety of effects throughout the body. Produced through the cleavage pro-opiomelanocortin (POMC), β-endorphins are the primarily agonist of mu opioid receptors, which can be found throughout the body, brain, and cells of the immune system that regulate a diverse set of systems. As an agonist of the body's opioid receptors, β-endorphins are most noted for their potent analgesic effects, but they also have their involvement in reward-centric and homeostasis-restoring behaviors, among other effects. These effects have implicated the peptide in psychiatric and neurodegenerative disorders, making it a research target of interest. This review briefly summarizes the basics of endorphin function, goes over the behaviors and regulatory pathways it governs, and examines the variability of β-endorphin levels observed between normal and disease/disorder affected individuals.

Cholinergic regulation of mood: from basic and clinical studies to emerging therapeutics

Mood disorders are highly prevalent and are the leading cause of disability worldwide. The neurobiological mechanisms underlying depression remain poorly understood, although theories regarding dysfunction within various neurotransmitter systems have been postulated. Over 50 years ago, clinical studies suggested that increases in central acetylcholine could lead to depressed mood. Evidence has continued to accumulate suggesting that the cholinergic system has a important role in mood regulation. In particular, the finding that the antimuscarinic agent, scopolamine, exerts fast-onset and sustained antidepressant effects in depressed humans has led to a renewal of interest in the cholinergic system as an important player in the neurochemistry of major depression and bipolar disorder. Here, we synthesize current knowledge regarding the modulation of mood by the central cholinergic system, drawing upon studies from human postmortem brain, neuroimaging, and drug challenge investigations, as well as animal model studies. First, we describe an illustrative series of early discoveries which suggest a role for acetylcholine in the pathophysiology of mood disorders. Then, we discuss more recent studies conducted in humans and/or animals which have identified roles for both acetylcholinergic muscarinic and nicotinic receptors in different mood states, and as targets for novel therapies.

IL-10 is associated with increased mu-opioid receptor levels in major depressive disorder

Objective:

Activation of the immune-inflammatory response system (IRS) and the compensatory immune-regulatory system (CIRS) and aberrations in endogenous opioids play a role in the pathophysiology of major depressive disorder (MDD). There are no studies which examined the associations between both systems in MDD. The aim of the present study was to examine the relation between β-Endorphin (β-EP), Endomorphin-2, and their mu-opioid receptor (MOR) as well as interleukin (IL)-6 and IL-10, an anti-inflammatory cytokine, in MDD patients.

Method:

The study included 60 depressed drug-free male patients and 30 matched controls. Serum β-EP, Endomorphin-2, MOR, IL-6 and IL-10 levels were measured using ELISA techniques.

Results:

The results revealed a significant increase in serum β-EP, MOR, IL-6 and IL-10 in MDD patients versus healthy controls. MOR levels were strongly associated with IL-10 levels. There were no significant correlations between endogenous opioids and IL-6 and IL-10.

Conclusion:

The results show that MOR levels may function as a possible component of the CIRS whilst there is no evidence that β-EP and EM-2 may modify the IRS. The significant correlation between MOR levels and IL-10 may be explained through central activation of the HPA-axis and increased B-cell numbers expressing MOR as a response to cytokine over-secretion in MDD.

Targeting opioid receptor signaling in depression: do we need selective κ opioid receptor antagonists?

The opioid receptors are a family of G-protein coupled receptors (GPCRs) with close structural homology. The opioid receptors are activated by a variety of endogenous opioid neuropeptides, principally β-endorphin, dynorphins, leu- and met-enkephalins. The clinical potential of targeting opioid receptors has largely focused on the development of analgesics. However, more recent attention has turned to the role of central opioid receptors in the regulation of stress responses, anhedonia and mood. Activation of the κ opioid receptor (KOP) subtype has been shown in both human and rodent studies to produce dysphoric and pro-depressive like effects. This has led to the idea that selective KOP antagonists might have therapeutic potential as antidepressants. Here we review data showing that mixed μ opioid (MOP) and KOP antagonists have antidepressant-like effects in rodent behavioural paradigms and highlight comparable studies in treatment-resistant depressed patients. We propose that developing multifunctional ligands which target multiple opioid receptors open up the potential for fine-tuning hedonic responses mediated by opioids. This alternative approach towards targeting multiple opioid receptors may lead to more effective treatments for depression.

Delta Opioid Receptors and Modulation of Mood and Emotion

Depression is a pervasive and debilitating mental disorder that is inadequately treated by current pharmacotherapies in a majority of patients. Although opioids have long been known to regulate mood states, the use of opioids to treat depression is rarely discussed. This chapter explores the preclinical and clinical evidence supporting the antidepressant-like effects of opioid ligands, and in particular, delta opioid receptor (DOR) agonists. DOR agonists have been shown to produce antidepressant-like effects in a number of animal models. Some DOR agonists also produce convulsions which has limited their clinical utility. However, DOR agonists that generate antidepressant-like effects without convulsions have recently been developed and these drugs are beginning to be evaluated in humans. Work investigating potential mechanisms of action for the antidepressant-like effects of DOR agonists is also explored. Understanding mechanisms that give rise to DOR-mediated behaviors is critical for the development of DOR drugs with improved safety and clinical utility, and future work should be devoted to elucidating these pathways.

Posttraumatic and depressive symptoms in β-endorphin dynamics

A disturbed beta-endorphin system can be a part of the post-traumatic stress disorder (PTSD) and depression allostasis. Study subjects (N=392) included those with PTSD and/or (stress-induced) depression, and healthy controls with and without traumas. The aim of the study was to examine the network of relations centered around plasma beta-endorphin. The network included anxiety (as a personality trait), traumatic events, pain, aggressiveness, depressive symptoms, and three clusters of PTSD symptoms: intrusions, avoidance, and hyperarousal. Beta-endorphin was represented by individual mean from 13 time points (BEmean), reflecting the total amount of the peripherally secreted hormone, and the coefficient of variation (BEvar), calculated as the ratio of standard deviation to the mean, reflecting the hormone׳s dynamics. BEvar correlated with all other variables, BEmean had no correlations. Structural equation modeling (SEM) was used to examine all interrelations (including their directions) of BEvar and the state/trait variables in the context of their entirety. The model revealed that hyperarousal and anxiety were the only direct agents of peripheral beta-endorphin fluctuations, mediating the effects of other variables. Traumatic events and intrusions act on BEvar via hyperarousal, while depressive symptoms, avoidance, and pain act via anxiety. Hyperarousal should be emphasized as the main agent not only because its effect on BEvar is larger than that of anxiety, but also because it increases anxiety itself (via avoidance and pain). All influences on BEvar are positive and they indicate long-term (sensitizing) effects (as opposed to direct stimulation, for example, by acute pain, anger, etc.). Relations apart from beta-endorphin are also discussed.

[The level of beta-endorphin, chronic stress, and depression associated with vestibular pathology]

The objective of the present study was to evaluate the presence and the severity of manifestations of anxiety and depression in the patients presenting with vestibular dysfunction making use of the psychometric scales and taking into consideration variations in the plasma beta-endorphin level as a biochemical marker before and after medicamental and physical rehabilitative treatment. A total of 8 patients presenting with stage I-III Meniere's disease and 8 patients suffering from dyscirculatory encephalopathy concomitant with vestibular ataxic syndrome were available for the observation. We separately analysed the results of examination of two patients with vestibular neuronitis and two others presenting with vestibular migraine. It was shown that the degree of anxiety and depression correlated with the plasma beta-endorphin level whereas its correlation with the severity of vestibular oculomotor and vestibular motor disorders during the inter-bout periods was not documented. It was demonstrated that the plasma beta-endorphin level was many times higher than the normal value of 20 ng/l in the patients with the well apparent vegetative symptoms accompanied by dizziness and the patients suffering from vegetative migraine.

Prenatal beta-endorphin as an early predictor of postpartum depressive symptoms in euthymic women

BACKGROUND

After delivery, many women experience symptoms of postpartum depression (PPD), and early identification of women at risk is therefore important. The opioid peptide beta-endorphin has been implicated in non-puerperal depression but its role in the development of PPD is unknown.

METHODS

Three hundred and seven women with a singleton, full-term (>37.0 weeks' GA) pregnancy were recruited early in pregnancy and followed up into the postpartum period. Blood samples were obtained at 15, 19, 25, 31 and 37 weeks' gestational age (GA) and at 9 weeks postpartum for assessment of beta-endorphin. Depressive symptoms were assessed with the Center for Epidemiological Studies-Depression scale at the last four pregnancy visits and with the Edinburgh Postnatal Depression Scale postpartum.

RESULTS

Among women who were euthymic at 25 weeks' GA, those who proceeded to develop PPD symptoms had higher levels of beta-endorphin throughout pregnancy compared to women without PPD symptoms (all t>2.11, p<.05). At each assessment, women above the cut-off score for beta-endorphin were at more than three-fold risk for PPD symptoms (odds ratios 3.19-4.68) compared to women below the cut-off score.

LIMITATIONS

Self-report of depressive symptoms, no mental health history.

CONCLUSIONS

Beta-endorphin may be a useful early predictor of PPD symptoms in women who do not report depressive symptoms in mid-pregnancy. If replicated, these findings have clinical implications for the identification and treatment of this at-risk group and further suggest that some of the pathways leading to this complex disorder may be specific to subgroups of women.

Histories of major depression and premenstrual dysphoric disorder: Evidence for phenotypic differences

This study examined unique versus shared stress and pain-related phenotypes associated with premenstrual dysphoric disorder (PMDD) and prior major depressive disorder (MDD). Sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA)-axis measures were assessed at rest and during mental stress, as well as sensitivity to cold pressor and tourniquet ischemic pain tasks in four groups of women: (1) non-PMDD with no prior MDD (N=18); (2) non-PMDD with prior MDD (N=9); (3) PMDD with no prior MDD (N=17); (4) PMDD with prior MDD (N=10). PMDD women showed blunted SNS responses to stress compared to non-PMDD women, irrespective of prior MDD; while women with prior MDD showed exaggerated diastolic blood pressure responses to stress versus never depressed women, irrespective of PMDD. However, only in women with histories of MDD did PMDD women have lower cortisol concentrations than non-PMDD women, and only in non-PMDD women was MDD associated with reduced cold pressor pain sensitivity. These results suggest both unique phenotypic differences between women with PMDD and those with a history of MDD, but also indicate that histories of MDD may have special relevance for PMDD.

The role of beta-endorphin in the pathophysiology of major depression

A role for beta-endorphin (beta-END) in the pathophysiology of major depressive disorder (MDD) is suggested by both animal research and studies examining clinical populations. The major etiological theories of depression include brain regions and neural systems that interact with opioid systems and beta-END. Recent preclinical data have demonstrated multiple roles for beta-END in the regulation of complex homeostatic and behavioural processes that are affected during a depressive episode. Additionally, beta-END inputs to regulatory pathways involving feeding behaviours, motivation, and specific types of motor activity have important implications in defining the biological foundations for specific depressive symptoms. Early research linking beta-END to MDD did so in the context of the hypothalamic-pituitary-adrenal (HPA) axis activity, where it was suggested that HPA axis dysregulation may account for depressive symptoms in some individuals. The primary aims of this paper are to use both preclinical and clinical research (a) to critically review data that explores potential roles for beta-END in the pathophysiology of MDD and (b) to highlight gaps in the literature that limit further development of etiological theories of depression and testable hypotheses. In addition to examining methodological and theoretical challenges of past clinical studies, we summarize studies that have investigated basal beta-END levels in MDD and that have used challenge tests to examine beta-END responses to a variety of experimental paradigms. A brief description of the synthesis, location in the CNS and behavioural pharmacology of this neuropeptide is also provided to frame this discussion. Given the lack of clinical improvement observed with currently available antidepressants in a significant proportion of depressed individuals, it is imperative that novel mechanisms be investigated for antidepressant potential. We conclude that the renewed interest in elucidating the role of beta-END in the pathophysiology of MDD must be paralleled by consensus building within the research community around the heterogeneity inherent in mood disorders, standardization of experimental protocols, improved discrimination of POMC products in analytical techniques and consistent attention paid to important confounds like age and gender.

Interaction between serotonin 5-HT1A receptors and beta-endorphins modulates antidepressant response

Interactions between serotonergic and the endogenous opioid systems have been suggested to be involved in the etiopathogenesis of depression and in the mechanism of action of antidepressants. Activation of serotonin 5-HT1A receptors has been shown to increase plasma beta-endorphin (beta-END) levels in animal studies and in healthy humans.

OBJECTIVES

To assess interaction abnormalities between 5-HT1A receptors and the endogenous opioid system in patients with major depression and the possible modulating effect of citalopram.

METHODS

The beta-END response to the 5-HT1A receptor agonist, buspirone (30 mg), was measured in 30 patients with major depression and in 30 age- and sex-matched healthy controls before and after an 8-week treatment with citalopram. Pre-treatment score of the Hamilton Rating Scale for Depression (HRSD) was >or=17. Antidepressant response was defined by a 50% decrease in the HRSD. Pre- and post-treatment maximum peak response (Deltamax) and the area under the curve (AUC) of beta-END response were compared. Three time points were measured (60, 90 and 120 min). We also examined the correlations between the beta-END response and the antidepressant response. Buspirone plasma levels were not measured.

RESULTS

At baseline, beta-END response was similar in patients and controls. After 8 weeks of citalopram treatment depressed patients showed a significant decrease in the beta-END response (Deltamax: p<.001; AUC: p<.001). A significant correlation between the beta-END reduction in the response and the reduction in the HRSD score (r=.656; p<.001) was observed.

CONCLUSIONS

Changes in interaction between 5-HT1A receptor system and the endogenous opioid system may play a role both in the mechanism of action and response to antidepressant drugs.

Stress-evoked opioid release inhibits pain in major depressive disorder

To determine whether stress-evoked release of endogenous opioids might account for hypoalgesia in major depressive disorder (MDD), the mu-opioid antagonist naltrexone (50mg) or placebo was administered double-blind to 24 participants with MDD and to 31 non-depressed controls. Eighty minutes later participants completed a painful foot cold pressor test and, after a 5-min interval, began a 25-min arithmetic task interspersed with painful electric shocks. Ten minutes later participants completed a second cold pressor test. Negative affect was greater in participants with MDD than in non-depressed controls throughout the experiment, and increased significantly in both groups during mental arithmetic. Before the math task, naltrexone unmasked direct linear relationships between severity of depression, negative affect while resting quietly, and cold-induced pain in participants with MDD. In contrast, facilitatory effects of naltrexone on cold- and shock-induced pain were greatest in controls with the lowest depression scores. Naltrexone strengthened the relationship between negative affect and shock-induced pain during the math task, particularly in the depressed group, and heightened anxiety in both groups toward the end of the task. Thus, mu-opioid activity apparently masked a positive association between negative affect and pain in the most distressed participants. These findings suggest that psychological distress inhibits pain via stress-evoked release of opioid peptides in severe cases of MDD. In addition, tonic endogenous opioid neurotransmission could inhibit depressive symptoms and pain in people with low depression scores.

Intracerebroventricular d-Pen2, d-Pen5-enkephalin administration soon after stressor imposition influences behavioral responsivity to a subsequent stressor encounter in CD-1 mice

Endogenous opioid peptide systems diminish stress-induced autonomic nervous system, neuroendocrine (hypothalamic-pituitary-adrenal axis) and behavioral responses, attenuating a collection of physiological symptoms basic to emotional and affective states. Neurogenic stressors may incite specific central changes in opioid peptide availability as well as changes in mu and delta-opioid receptor function. The present investigation evaluated the proactive influence of an intracerebroventricular injection of the opioid receptor agonist D-Pen2, D-Pen5-enkephalin (DPDPE) (0 microg, 0.005 microg, 1.0 microg or 2.5 microg) on locomotor behavior of mice following uncontrollable footshock (Shock) or novel shock chamber exposure (No Shock). It was expected that DPDPE administration following Shock on Day 1 would restore locomotor activity up to 1 week and prevent shock-associated behavior of mice encountering a brief session of footshock 18 days later. Exposure to Shock reduced horizontal locomotor and vertical locomotor (rearing) activity of mice while 2.5 microg DPDPE restored behavior. Eighteen days following Shock and DPDPE challenge, mice were exposed to either an abbreviated session of footshock (Mild Stress) or the shock chamber (Cues). Mice in the No Shock and Shock groups administered 2.5 microg DPDPE on Day 1 did not exhibit any locomotor deficits in response to Mild Stress on Day 18. Mice in the Shock group administered 0.005 microg DPDPE on Day 1, did not exhibit exaggerated rearing deficits following ensuing Mild Stressor encounter relative to mice reexposed to Cues on Day 18. Taken together, these data show that (a) footshock differentially affects rearing and locomotor activity, (b) DPDPE administration increases locomotor activity for up to 1 week following footshock and DPDPE administration, (c) reexposure to Mild Stress affects rearing and locomotor performance differently depending on previous stressor history and DPDPE dose, (d) DPDPE affords long-lasting protection to previously non-stressed mice against the deleterious effects of subsequent mild stress on locomotor activity, while a low dose of DPDE is sufficient to prevent shock-induced sensitization of rearing deficits, 18 days following original stressor and drug presentation. Finally, our investigation demonstrates that DPDPE administration alters the behavioral impact of future stressful encounters and emphasizes the importance of investigating opioid mechanisms in chronic stress disorders.

Psychostimulant withdrawal as an inducing condition in animal models of depression

A large body of evidence indicates that the withdrawal from high doses of psychostimulant drugs in humans induces a transient syndrome, with symptoms that appear isomorphic to those of major depressive disorder. Pharmacological treatment strategies for psychostimulant withdrawal in humans have focused mainly on compounds with antidepressant properties. Animal models of psychostimulant withdrawal have been shown to demonstrate a wide range of deficits, including changes in homeostatic, affective and cognitive behaviors, as well as numerous physiological changes. Many of these behavioral and physiological sequelae parallel specific symptoms of major depressive disorder, and have been reversed by treatment with antidepressant drugs. These combined findings provide strong support for the use of psychostimulant withdrawal as an inducing condition in animal models of depression. In the current review we propound that the psychostimulant withdrawal model displays high levels of predictive and construct validity. Recent progress and limitations in the development of this model, as well as future directions for research, are evaluated and discussed.

Are exercise stress tests appropriate for assessing myocardial ischemia in patients with major depressive disorder?

BACKGROUND

Major depressive disorder (MDD) disproportionately affects patients with coronary artery disease (CAD). Evidence of myocardial ischemia with electrocardiography (ECG) or single-photon-emission-computed-tomography (SPECT) assessments during exercise testing is an important determinant of CAD prognosis. However, many key symptoms of MDD, such as reduced interest in daily activities, lack of energy, and fatigue, may affect exercise performance and the detection of ischemia in patients with MDD. This study evaluated the extent to which MDD and depressive symptomatology moderate exercise test performance and compared the ability of ECG versus SPECT for detecting ischemia in 1367 consecutive patients who underwent exercise testing.

METHODS

All patients underwent a brief, structured psychiatric interview (PRIME-MD) and completed the Beck Depression Inventory (BDI) on the day of their exercise (treadmill) test.

RESULTS

A total of 183 patients (13%) met diagnostic criteria for MDD. Patients with MDD achieved a significantly lower percent of maximal predicted heart rate (%MPHR), exhibited lower peak exercise mets, and spent less time exercising compared with patients without MDD (all P values <.05). BDI scores were also negatively correlated with all 3 indices of exercise performance (all P values <.01). There were no differences in rates of SPECT ischemia in patients with MDD (40%) versus patients without MDD (45%; P =.23); however, rates of ECG ischemia were significantly lower (30%) in patients with MDD than in patients without MDD (48%; P <.0001).

CONCLUSIONS

Results suggest that patients with CAD who have MDD, depressive symptomatology, or both exhibit poor exercise tolerance and performance and that ECG, as compared with SPECT, may not be as reliable in detecting ischemia in patients who are depressed.

Impaired release of beta-endorphin in response to serotonin in a rat model of depression

Involvement of both the serotonergic and the endogenous opioid systems in the onset of depressive behavior has been suggested. Previously we showed that serotonin (5-hydroxytryptamine) facilitates beta-endorphin release in the nucleus accumbens (NAcc). Herein, the microdialysis method was used to assess in vivo the effects of serotonin on beta-endorphin release in a rat model of depressive behavior (the Flinders sensitive line, FSL), before and after antidepressant treatment. The basal extracellular level of beta-endorphin in the NAcc of FSL rats did not differ significantly from that in control rats. However, serotonin-induced beta-endorphin release was impaired in FSL rats. Chronic treatment (18 days) with desipramine or paroxetine did not significantly affect the extracellular levels of beta-endorphin in the NAcc of either the FSL or control rats. However, the chronic antidepressant treatment did normalize the serotonin-induced release of beta-endorphin in FSL rats, as well as their behavioral manifestation of depressive behavior. Our results show that depressive behavior may relate to an impaired effect of serotonin on beta-endorphin release in the NAcc in a rat model of depression, and suggest a possible new mode of action of antidepressant drugs.

The dual control model of male sexual response: a theoretical approach to centrally mediated erectile dysfunction

A theoretical model of dual control of male sexual response is considered, based on the balancing of central excitation and inhibition, with individuals varying in their propensity for both sexual excitation and inhibition of sexual response. A questionnaire method for measuring propensities for sexual excitation and inhibition has been developed (SIS/SES questionnaire), resulting in one excitation factor (SES) and two inhibition factors (SIS1 and SIS2). Evidence for the existence of both inhibitory and excitatory tone is discussed. The first inhibition factor (SIS1) may be related to level of inhibitory tone and is associated with fear of performance failure. The second inhibition factor (SIS2) may be related to external threats (e.g. from within the sexual relationship). The implications for the treatment of centrally mediated erectile dysfunction are discussed, with predictions that high SIS2 individuals will respond to psychological treatment, whereas high SIS1 individuals will respond better to pharmacological methods of treatment.

Central inhibition of sexual response in the male: a theoretical perspective

A theoretical model for central inhibition of sexual response is proposed, postulating individual variability in the propensity for such inhibition. Whereas such inhibition is typically adaptive, individuals with high propensity may be vulnerable to sexual dysfunction, and those with low propensity to high risk sexual behavior. Evidence of the existence and localization of such inhibitory mechanisms from both the animal and human literature is reviewed. Evidence of central neurotransmitters with sexual inhibitory effects is substantial, though in most cases the inhibition is not specific to sexual response or behavior. Recent studies have identified centers in the brain stem and lateral hypothalamus which appear to have specific inhibitory effects on sexual response. A variety of adaptive mechanisms involving inhibition of sexual response are considered, some involving perception of threat, others occurring more directly as consequences of previous sexual activity. These different adaptive functions may well involve different inhibitory mechanisms. This theoretical model opens a new agenda for experimental research into adaptive sexual behavior, both human and animal.

Serotonin-mediated increases in the extracellular levels of beta-endorphin in the arcuate nucleus and nucleus accumbens: a microdialysis study

Although the involvement of both endogenous opioid and serotonergic systems in modulation of pain and emotion was suggested, the neurochemical interaction between these systems in the brain has not previously been studied directly. Herein, the effects of the local application of serotonin (5-HT) and fluoxetine (a 5-HT reuptake inhibitor) on extracellular levels of beta-endorphin in the arcuate nucleus and nucleus accumbens were assessed in freely moving rats using in vivo microdialysis. The mean basal concentrations of beta-endorphin in dialysates obtained from the arcuate nucleus and nucleus accumbens were 259.9 and 143.3 pM, respectively. Specific lesion of the serotonergic system by 5,7-dihydroxytryptamine (5,7-DHT) caused a significant decrease in these dialysate beta-endorphin levels. When 5-HT (0.25-5 microM) was added to the perfusion solution, the levels of beta-endorphin in the dialysate from the arcuate nucleus increased (186-296% of baseline), in a concentration-dependent manner. In the nucleus accumbens, 0.5 and 2 microM 5-HT in the perfusion fluid did not affect the levels of beta-endorphin in the dialysate, whereas 5 and 10 microM 5-HT caused an increase of approximately 190% of baseline. When fluoxetine (250 microM) was present in the perfusing solution, the levels of beta-endorphin in the dialysates from the arcuate nucleus and nucleus accumbens increased two- to threefold. This effect was not obtained in the 5,7-DHT-lesioned rats. Thus, 5-HT, either endogenously or exogenously delivered, appears to facilitate the release of beta-endorphin in the arcuate nucleus and nucleus accumbens. This indication of an interaction between serotonergic and endorphinic systems may be relevant for assessing pain and mood disorder circuits and the mode of action of antidepressant drugs.

Alterations of corticotropin releasing hormone (CRH) and neuropeptide Y (NPY) plasma levels in mood disorder patients with a recent suicide attempt

In order to receive a further understanding of stress-regulation in depressed suicide attempters, peptides that are supposed to be related to the stress system (the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system) were studied in plasma. When compared with healthy controls, cortisol was high (p<0.001) and corticotropin releasing hormone (CRH) and neuropeptide Y (NPY) appeared to be low (p<0.001) in patients who had recently attempted suicide. Patients who had repeatedly attempted suicide had the lowest NPY. A correlation between NPY and cortisol (p<0.05) was found in suicidal patients with depression NOS, whereas beta-endorphins correlated with cortisol (p<0.01) in suicidal patients with major depressive disorder. A postdexamethasone decrease of NPY was noted in the controls but not in the patients. These results suggest stress system alterations in suicidal patients with mood disorders.

Relationship among depression scores, beta-endorphin, and angina pectoris during exercise in patients with coronary artery disease

OBJECTIVES

To determine the relationship between depression scores and (1) anginal indices during exercise including time to onset of angina, duration of angina, and severity of angina and (2) beta-endorphin at rest and in response to exercise.

DESIGN

Prospective clinical trial.

SETTING

Tertiary-care university hospital.

PATIENTS

Fifty-eight patients with documented coronary artery disease and exercise-induced ischemia.

OUTCOME MEASURES

Anginal indices during exercise (time to onset of angina, duration of angina, severity of angina); hemodynamic measures (systolic blood pressure, heart rate, rate pressure product) at rest, at onset of angina and at peak exercise; and plasma beta-endorphin levels at rest and immediately after exercise.

RESULTS

Twenty-two of 58 patients had typical angina and electrocardiographic change indicating myocardial ischemia during exercise. There was a positive correlation between depression scores and duration of angina and a negative correlation between depression scores and time to onset of angina. Among patients with angina during exercise, systolic blood pressure increased to a greater extent in patients with high depression scores. Patients with high depression scores had higher resting beta-endorphin levels.

CONCLUSIONS

Patients with depressed mood had greater perception of anginal pain than nondepressed patients, which cannot be explained by differences in the severity of ischemia. Possible mechanisms include an alteration in beta-endorphin regulation or differences in baroreceptor stimulation.