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

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) are blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupts the behavioral effects of ketamine. Ketamine treatment rapidly increases levels of β-endorphin and the expression of the μ-opioid receptor gene (Oprm1) in the mPFC, and the expression of gene that encodes proopiomelanocortin, the precursor of β-endorphin, in the hypothalamus, in vivo. Finally, neutralization of β-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolishes both behavioral and molecular effects. Together, these findings indicate that presence of β-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

The endogenous opioid system in the medial prefrontal cortex mediates ketamine's antidepressant-like actions

Recent studies have implicated the endogenous opioid system in the antidepressant actions of ketamine, but the underlying mechanisms remain unclear. We used a combination of pharmacological, behavioral, and molecular approaches in rats to test the contribution of the prefrontal endogenous opioid system to the antidepressant-like effects of a single dose of ketamine. Both the behavioral actions of ketamine and their molecular correlates in the medial prefrontal cortex (mPFC) were blocked by acute systemic administration of naltrexone, a competitive opioid receptor antagonist. Naltrexone delivered directly into the mPFC similarly disrupted the behavioral effects of ketamine. Ketamine treatment rapidly increased levels of β-endorphin and the expression of the μ-opioid receptor gene (Oprm1) in the mPFC, and the expression of the gene that encodes proopiomelanocortin, the precursor of β-endorphin, in the hypothalamus, in vivo. Finally, neutralization of β-endorphin in the mPFC using a specific antibody prior to ketamine treatment abolished both behavioral and molecular effects. Together, these findings indicate that presence of β-endorphin and activation of opioid receptors in the mPFC are required for the antidepressant-like actions of ketamine.

Attenuated serotonin transporter association between dorsal raphe and ventral striatum in major depression

Suffering from anhedonia, patients with major depressive disorder (MDD) exhibit alterations in several parts of the serotonergic neurotransmitter system, which are in turn involved in reward processing. However, previous investigations of the serotonin transporter (SERT) focused on regional differences with varying results depending on the clinical syndrome. Here, we aimed to describe the serotonergic system of MDD patients on a network level by evaluating SERT associations across brain regions. Twenty medication free patients with major depression and 20 healthy controls underwent positron emission tomography using the radioligand [(11) C]DASB. SERT binding potentials (BPND ) were quantified voxel-wise with the multilinear reference tissue model 2. In addition, SERT BPND was extracted from the dorsal raphe nucleus (DRN) as an indicator of midbrain serotonergic neurotransmission. Whole-brain linear regression analysis was applied to evaluate the association of DRN SERT bindings to those in projection areas, which was followed by ANCOVA to assess differences in interregional relationships between patients and controls. Although both groups showed widespread positive correlations, group differences were restricted to decreased SERT associations between the DRN and the ventral striatum (right and left respectively: t=5.85, P<0.05 corrected and t=5.07, P<0.1 corrected) when comparing MDD patients (R(2)=0.11 and 0.24) to healthy subjects (R(2)=0.72 and 0.66, P<0.01 and 0.05 corrected). Adjusting for age and sex did not change these findings. This study indicates a disturbed regulation between key regions involved in reward processing via the SERT. Our interregional approach highlights the importance of evaluating pathophysiological alterations on a network level to gain complementary information in addition to regional investigations.

Opioids and anxiety

The opioid system plays a crucial role in the neural modulation of anxiety. The involvement of opioid ligands and receptors in physiological and dysfunctional forms of anxiety is supported by findings from a wide range of preclinical and clinical studies, including clinical trials, experimental research, and neuroimaging, genetic, and epidemiological data. In this review we provide a summary of studies from a variety of research disciplines to elucidate the role of the opioid system in the neurobiology of anxiety. First, we report data from preclinical studies using animal models to examine the modulatory role of central opioid system on defensive responses conducive to fear and anxiety. Second, we summarize the human literature providing evidence that clinical and experimental human studies are consistent with preclinical models. The implication of these data is that activation of the opioid system leads to anxiolytic responses both in healthy subjects and in patients suffering from anxiety disorders. The role of opioids in suppressing anxiety may serve as an adaptive mechanism, collocated in the general framework of opioid neurotransmission blunting acute negative and distressing affective responses.

Monoaminergic Antidepressants in the Relief of Pain: Potential Therapeutic Utility of Triple Reuptake Inhibitors (TRIs)

Over 75% of depressed patients suffer from painful symptoms predicting a greater severity and a less favorable outcome of depression. Imaging, anatomical and functional studies have demonstrated the existence of common brain structures, neuronal pathways and neurotransmitters in depression and pain. In particular, the ascending serotonergic and noradrenergic pathways originating from the raphe nuclei and the locus coeruleus; respectively, send projections to the limbic system. Such pathways control many of the psychological functions that are disturbed in depression and in the perception of pain. On the other hand, the descending pathways, from monoaminergic nuclei to the spinal cord, are specifically implicated in the inhibition of nociception providing rationale for the use of serotonin (5-HT) and/or norepinephrine (NE) reuptake inhibitors (SSRIs, NRIs, SNRIs), in the relief of pain. Compelling evidence suggests that dopamine (DA) is also involved in the pathophysiology and treatment of depression. Indeed, recent insights have demonstrated a central role for DA in analgesia through an action at both the spinal and suprasinal levels including brain regions such as the periaqueductal grey (PAG), the thalamus, the basal ganglia and the limbic system. In this context, dopaminergic antidepressants (i.e., containing dopaminergic activity), such as bupropion, nomifensine and more recently triple reuptake inhibitors (TRIs), might represent new promising therapeutic tools in the treatment of painful symptoms with depression. Nevertheless, whether the addition of the dopaminergic component produces more robust effects than single- or dual-acting agents, has yet to be demonstrated. This article reviews the main pathways regulating pain transmission in relation with the monoaminergic systems. It then focuses on the current knowledge regarding the in vivo pharmacological properties and mechanism of action of monoaminergic antidepressants including SSRIs, NRIs, SNRIs and TRIs. Finally, a synthesis of the preclinical studies supporting the efficacy of these antidepressants in analgesia is also addressed in order to highlight the relative contribution of 5-HT, NE and DA to nociception.

Neurochemistry of the nucleus accumbens and its relevance to depression and antidepressant action in rodents

There is accumulating evidence that the nucleus accumbens (NAc) plays an important role in the pathophysiology of depression. Given that clinical depression is marked by anhedonia (diminished interest or pleasure), dysfunction of the brain reward pathway has been suggested as contributing to the pathophysiology of depression.Since the NAc is the center of reward and learning, it is hypothesized that anhedonia might be produced by hampering the function of the NAc. Indeed, it has been reported that stress, drug exposure and drug withdrawal, all of which produce a depressive-phenotype, alter various functions within the NAc, leading to inhibited dopaminergic activity in the NAc.In this review, we describe various factors as possible candidates within the NAc for the initiation of depressive symptoms. First, we discuss the roles of several neurotransmitters and neuropeptides in the functioning of the NAc, including dopamine, glutamate, gamma-aminobutyric acid (GABA), acetylcholine, serotonin, dynorphin, enkephaline, brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), melanin-concentrating hormone (MCH) and cocaine- and amphetamine-regulated transcript (CART). Second, based on previous studies, we propose hypothetical relationships among these substances and the shell and core subregions of the NAc.

Reward and the serotonergic system

Anhedonia, as a failure to experience rewarding stimuli, is a key characteristic of many psychiatric disorders including depression and schizophrenia. Investigations on the neurobiological correlates of reward and hedonia/anhedonia have been a growing subject of research demonstrating several neuromodulators to mediate different aspects of reward processing. Whereas the majority of research on reward mainly focused on the dopamine and opioid systems, a serotonergic mechanism has been neglected. However, recent promising results strengthen the pivotal role of serotonin in reward processing. Evidence includes electrophysical and pharmacological as well as genetic and imaging studies. Primate research using single-unit recording of neurons within the dorsal raphe nucleus argues for a serotonergic mediation of reward value, whereas studies using intracranial self-stimulation point to an important contribution of serotonin in modulating motivational aspects of rewarding brain stimulation. Pharmacological studies using agonists and antagonists of serotonergic receptor subtypes and approaches investigating an increase or decrease of the extracellular level of serotonin offer strong evidence for a serotonergic mediation, ranging from aversion to pleasure. This review provides an argument for serotonin as a fundamental mediator of emotional, motivational and cognitive aspects of reward representation, which makes it possibly as important as dopamine for reward processing.

Effects of acute ethanol on beta-endorphin release in the nucleus accumbens of selectively bred lines of alcohol-preferring AA and alcohol-avoiding ANA rats

RATIONALE

The selectively bred lines of alcohol-preferring alko alcohol (AA) and alcohol-avoiding alko nonalcohol (ANA) rats have been used to demonstrate differences in relevant neurotransmitters which could account for their difference in alcohol consumption. Studies have demonstrated differences in distinct components of the endogenous opioid system in various brain regions associated with the process of reinforcement between the AA and ANA lines of rats.

OBJECTIVES

The goal of this current study was to investigate the hypotheses that the AA and ANA rats will show differences in the release of beta-endorphin at the level of nucleus accumbens (NAC) and in locomotor activity in response to acute systemic administration of ethanol.

MATERIALS AND METHODS

AA and ANA rats were unilaterally implanted with a guide cannula to aim microdialysis probes at the level of NAC. Intraperitoneal injections of 0.0, 1.5, 2.0, and 2.5 g ethanol/kg body weight were administered. Dialysate samples were collected at 30-min intervals prior to and following the injection. Radioimmunoassay specific for beta-endorphin was used to determine the dialysate beta-endorphin content.

RESULTS

The 2.5-g/kg ethanol dose induced a transient increase in extracellular beta-endorphin at the level of NAC of AA but not of ANA rats. The 2.5-g/kg ethanol dose also attenuated locomotor activity in the AA but not in the ANA rats.

CONCLUSIONS

The lack of an increase in the beta-endorphin concentration in the NAC of ANA rats in response to ethanol may partially account for their lower alcohol consumption and lower alcohol-induced attenuation of locomotor activity compared to AA rats.

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.

Modulation of MDMA-induced behavioral and transcriptional effects by the delta opioid antagonist naltrindole in mice

The delta opioid system is involved in the behavioral effects of various drugs of abuse. However, only a few studies have focused on the possible interactions between the opioid system and the effects of 3,4-methylenedioxymethamphetamine (MDMA). In order to examine the possible role of the delta opioid system in MDMA-induced behaviors in mice, locomotor activity and conditioned place preference (CPP) were investigated in the presence of naltrindole (NTI), a selective delta opioid antagonist. Moreover, the consequences of acute and chronic MDMA administration on pro-enkephalin (Penk) and pro-opiomelanocortin (Pomc) gene expression were assessed by real-time quantitative polymerase chain reaction (QPCR). The results showed that, after acute MDMA administration (9 mg/kg; i.p.), NTI (5 mg/kg, s.c.) was able to totally block MDMA-induced hyperlocomotion. Penk gene expression was not modulated by acute MDMA, but a decrease of Pomc gene expression was observed, which was not antagonized by NTI. Administration of the antagonist prevented the acquisition of MDMA-induced CPP, suggesting an implication of the delta opioid receptors in this behavior. Following chronic MDMA treatment, only the level of Pomc was modulated. The observed increase was totally blocked by NTI pre-treatment. All these results confirm the interactions between the delta opioid system (receptors and peptides) and the effects of MDMA.

Evidence for the involvement of the opioid system in the antidepressant-like effect of folic acid in the mouse forced swimming test

The opioid system has been implicated in major depression and in the mechanism of action of antidepressants. This study investigated the involvement of the opioid system in the antidepressant-like effect of the water-soluble B-vitamin folic acid in the forced swimming test (FST). The effect of folic acid (10 nmol/site, i.c.v.) was prevented by the pretreatment of mice with naloxone (1 mg/kg, i.p., a nonselective opioid receptor antagonist), naltrindole (3 mg/kg, i.p., a selective delta-opioid receptor antagonist), naloxonazine (10 mg/kg, i.p., a selective mu(1)-opioid receptor antagonist, 24 h before), but not with naloxone methiodide (1 mg/kg, s.c., a peripherally acting opioid receptor antagonist). In addition, a sub-effective dose of folic acid (1 nmol/site, i.c.v.) produced a synergistic antidepressant-like effect in the FST with a sub-effective dose of morphine (1 mg/kg, s.c.). A further approach was designed to investigate the possible relationship between the opioid system and NMDA receptors in the mechanism of action of folic acid in the FST. Pretreatment of the animals with naloxone (1 mg/kg, i.p.) prevented the synergistic antidepressant-like effect of folic acid (1 nmol/site, i.c.v.) and MK-801 (0.001 mg/kg, i.p., a non-competitive NMDA receptor antagonist). Together the results firstly indicate that the anti-immobility effect of folic acid in the FST is mediated by an interaction with the opioid system (mu(1) and delta), likely dependent on the inhibition of NMDA receptors elicited by folic acid.

Heterologous expression of the invertebrate FMRFamide-gated sodium channel as a mechanism to selectively activate mammalian neurons

Considerable effort has been directed toward the development of methods to selectively activate specific subtypes of neurons. Focus has been placed on the heterologous expression of proteins that are capable of exciting neurons in which they are expressed. Here we describe the heterologous expression of the invertebrate FMRFamide (H-phenylalanine-methionine-arginine-phenylalanine-NH2) -gated sodium channel from Helix aspersa (HaFaNaC) in hippocampal slice cultures. HaFaNaC was co-expressed with a fluorescent protein (green fluorescent protein (GFP), red fluorescent protein from Discosoma sp (dsRed) or mutated form of red fluorescent protein from Discosoma sp (tdTomato)) in CA3 pyramidal neurons of rat hippocampal slice cultures using single cell electroporation. Pressure application of the agonist FMRFamide to HaFaNaC-expressing neuronal somata produced large prolonged depolarizations and bursts of action potentials (APs). FMRFamide responses were inhibited by amiloride (100 microM). In contrast, pressure application of FMRFamide to the axons of neurons expressing HaFaNaC produced no response. Fusion of GFP to the N-terminus of HaFaNaC showed that GFP-HaFaNaC was absent from axons. Bath application of FMRFamide produced persistent AP firing in HaFaNaC-expressing neurons. This FMRFamide-induced increase in the frequency of APs was dose-dependent. The concentrations of FMRFamide required to activate HaFaNaC-expressing neurons were below that required to activate the homologous acid sensing ion channel normally found in mammalian neurons. Furthermore, the mammalian neuropeptides neuropeptide FF and RFamide-related peptide-1, which have amidated RF C-termini, did not affect HaFaNaC-expressing neurons. Antagonists of NPFF receptors (BIBP3226) also had no effect on HaFaNaC. Therefore, we suggest that heterologous-expression of HaFaNaC in mammalian neurons could be a useful method to selectively and persistently excite specific subtypes of neurons in intact nervous tissue.

Dopamine-2 receptors in the arcuate nucleus modulate cocaine-seeking behavior

Beta-endorphin is an endogenous opioid peptide, implicated in the behavioral effects of drugs of abuse. It is synthesized in the arcuate nucleus and secreted into the nucleus accumbens. In the present study, we examined the interaction between arcuate nucleus dopaminergic cells and accumbal beta-endorphin, during cocaine exposure. Using microdialysis, we found that blockade of arcuate dopamine-2 receptors with a selective antagonist significantly attenuated cocaine-induced increases of beta-endorphin levels in the nucleus accumbens. Moreover, rats chronically exposed to cocaine using the self-administration paradigm displayed extinction-like behavior following blockade of dopamine-2 receptors. These findings indicate that dopaminergic neurons in the arcuate nucleus may induce the secretion of beta-endorphin in the nucleus accumbens, and that they are implicated in the cocaine reward pathway.

Smoking modulation of mu-opioid and dopamine D2 receptor-mediated neurotransmission in humans

This is a pilot examination of the hypothesis that some of the effects of smoking cigarettes in humans are mediated through nicotine activation of opioid and dopamine (DA) neurotransmission. Neuroimaging was performed using positron emission tomography and the radiotracers [11C]carfentanil and [11C]raclopride, labeling mu-opioid and DA D2 receptors, respectively. Six healthy male smokers were abstinent overnight. After radiotracer administration, subjects smoked two denicotinized cigarettes, followed 45 min later by two average nicotine cigarettes. Dynamic data were acquired over 90 min, and transformed into parametric maps of receptor availability in vivo (binding potential, BP), corresponding to low and high nicotine smoking periods and analyzed on a voxel-by-voxel basis using SPM'99 and correction for multiple comparisons. Significant activation of mu-opioid receptor-mediated neurotransmission from denicotinized to average nicotine conditions was observed in the right anterior cingulate cortex. DA D2 neurotransmission was activated in the ventral basal ganglia, correlating with Fagerström scale nicotine dependence scores. Lower mu-opioid receptor BP was also detected during the denicotinized smoking condition in the smoker group, compared to baseline scans in non-smokers, in the cingulate cortex, thalamus, ventral basal ganglia, and amygdala. These reductions were reversed during the average nicotine condition in the thalamus, ventral basal ganglia and amygdala. These data point to both the feasibility of simultaneously examining opioid and DA neurotransmission responses to smoking in humans, as well as to the need to examine non-nicotine aspects of smoking to more fully understand the behavioral effects of this drug.

Sympathetic nervous system and neurotransmitters: their possible role in neuroimmunomodulation of multiple sclerosis and some other autoimmune diseases

Multiple sclerosis is still a disease without a cure. Although intensive research efforts have led to the development of drugs that modify the activity of the disease, most of them have various side effects and are expensive. At the same time it is becoming apparent that some remedies usually used to treat somatic and psychic disorders also have immunomodulating properties, and may help manage multiple sclerosis and other autoimmune diseases. We describe here the role of the sympathetic nervous system in the neuro-immune interaction in multiple sclerosis and other immune diseases with increased cellular immunity as well as neurochemical disturbances that take place in these disorders.

Pronociceptive and antinociceptive effects of estradiol through endogenous opioid neurotransmission in women

Prominent interindividual and sex-dependent differences have been described in responses to sustained pain and other stressful stimuli. Variations in mu-opioid receptor-mediated endogenous opioid neurotransmission may underlie some of these processes. We examined both baseline mu-opioid receptor levels and the activation of this neurotransmitter system during sustained pain using positron emission tomography in a sample of young healthy men and women. Women were studied twice, during low and high estrogen states. The high-estrogen state was associated with regional increases in baseline mu-opioid receptor availability in vivo and a greater activation of endogenous opioid neurotransmission during the pain stressor. The latter did not differ from that obtained in males. During the low estrogen condition, however, significant reductions in endogenous opioid tone were observed at the level of thalamus, nucleus accumbens, and amygdala, which were associated with hyperalgesic responses. Estrogen-associated variations in the activity of mu-opioid neurotransmission correlated with individual ratings of the sensory and affective perceptions of the pain and the subsequent recall of that experience. These data demonstrate a significant role of estrogen in modulating endogenous opioid neurotransmission and associated psychophysical responses to a pain stressor in humans.

Evidence for the involvement of the opioid system in the agmatine antidepressant-like effect in the forced swimming test

This study investigated the involvement of the opioid system in the antidepressant-like effect of agmatine in the mouse forced swimming test (FST). The antidepressant-like effects of agmatine (10 mg/kg, i.p.), as well as those of fluoxetine (32 mg/kg, i.p, a selective serotonin reuptake inhibitor, SSRI) or morphine (5 mg/kg, s.c., a nonselective opioid receptor agonist) in the FST was completely blocked by pretreatment of mice with naloxone (1 mg/kg, i.p., a nonselective opioid receptor antagonist). Pretreatment of mice with naltrindole (3 mg/kg, i.p., a selective delta-opioid receptor antagonist), clocinnamox (1 mg/kg, i.p., an irreversible mu-opioid receptor antagonist), but not with 2-(3,4-dichlorophenyl)-N-methyl-N-[(1S)-1-(3-isothiocyanatophenyl)-2-(1-pyrrolidinyl)ethyl]acetamide (DIPPA; 1 mg/kg, i.p., a selective kappa-opioid receptor antagonist) completely blocked the anti-immobility effect of agmatine (10 mg/kg, i.p.) in the FST. These results firstly demonstrate that the antidepressant-like effects of agmatine in the FST seem to be mediated, at least in part, by an interaction with the opioid system, that involves an activation of delta- and mu-opioid receptors.

5-HT2A-mu opioid receptor mechanisms in the hypothalamus mediate interleukin-1beta fever in rats

Direct administration of interleukin-1beta (IL-1beta) into the lateral cerebral ventricle of rat brain, in addition to inducing febrile responses, upregulated the immunoreactivity of tryptophan hydroxylase in the preoptic anterior hypothalamus. The fever induced by IL-1beta was significantly attenuated by pretreatment with intracerebroventricular injection of 5-HT2A receptor antagonists including cyproheptadine, ketanserin, or mianserin. In addition, the IL-1beta-induced fever was mimicked by intracerebroventricular administration of a 5-HT2A receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-amionpropane (DOI). The DOI-induced (present results) or IL-1beta-induced (previous results) fever was further attenuated by pretreatment with an intracerebroventricular dose of mu-opioid receptor antagonists (e.g., buprenorphine or cyclic d-phe-cys-Try-d-Arg-Thr-pen-Thr-NH2) or 5-HT receptor antagonists (e.g., ketanserin or cyproheptadine). These findings suggest that a 5-HT2A-mu opioid receptor mechanism in the hypothalamus may mediate the IL-1beta fever.

Suicidal ideation in outpatients with chronic musculoskeletal pain: an exploratory study of the role of sleep onset insomnia and pain intensity

OBJECTIVES

Sleep disturbance, depression, and heightened risk of suicide are among the most clinically significant sequelae of chronic pain. While sleep disturbance is associated with suicidality in patients with major depression and is a significant independent predictor of completed suicide in psychiatric patients, it is not known whether sleep disturbance is associated with suicidal behavior in chronic pain. This exploratory study evaluates the importance of insomnia in discriminating suicidal ideation in chronic pain relative to depression severity and other pain-related factors.

METHODS

Fifty-one outpatients with non-cancer chronic pain were recruited. Subjects completed a pain and sleep survey, the Pittsburgh Sleep Quality Index, the Beck Depression Inventory, and the Multidimensional Pain Inventory. Subjects were classified as "suicidal ideators" or "non-ideators" based on their responses to BDI-Item 9 (Suicide). Bivariate analyses and multivariate discriminant function analyses were conducted.

RESULTS

Twenty-four percent reported suicidal ideation (without intent). Suicidal ideators endorsed higher levels of: sleep onset insomnia, pain intensity, medication usage, pain-related interference, affective distress, and depressive symptoms (P < 0.03). These 6 variables were entered into stepwise discriminant function analyses. Two variables predicted group membership: Sleep Onset Insomnia Severity and Pain Intensity, respectively. The discriminant function correctly classified 84.3% of the cases (P < 0.0001).

DISCUSSION

Chronic pain patients who self-reported severe and frequent initial insomnia with concomitant daytime dysfunction and high pain intensity were more likely to report passive suicidal ideation, independent from the effects of depression severity. Future research aimed at determining whether sleep disturbance is a modifiable risk factor for suicidal ideation in chronic pain is warranted.

Nucleus accumbens beta-endorphin levels are not elevated by brain stimulation reward but do increase with extinction

Beta-endorphin is an endogenous opioid peptide implicated in reward processes, but the brain sites directly involved in its putative role in reward have not been identified. Here we used in vivo microdialysis in rats to study the effect of a potent reinforcer, lateral hypothalamus self-stimulation (LHSS), on the extracellular levels of beta-endorphin in the nucleus accumbens (NAS). The NAS is involved in the reinforcing effects of natural and artificial rewards, has high density of opioid receptors and is innervated by arcuate nucleus beta-endorphin neurons. LHSS had no effect on extracellular levels of beta-endorphin in the NAS. Surprisingly, extinction of the self-stimulation behaviour induced a rapid increase in NAS beta-endorphin levels. In a subsequent experiment in rats previously trained to self-administer heroin for 10 days, beta-endorphin levels also were increased during a test for extinction of the heroin-reinforced behaviour. Finally, the increase in extracellular beta-endorphin levels in the NAS was also observed during exposure to an aversive stimulus, intermittent footshock (20 min). These results indicate a possible role for increased levels of NAS beta-endorphin in the organism's adaptive response to stress and frustration.

Effect of experimenter-delivered and self-administered cocaine on extracellular beta-endorphin levels in the nucleus accumbens

Beta-endorphin is an endogenous opioid peptide that has been hypothesized to be involved in the behavioral effects of drugs of abuse including psychostimulants. Using microdialysis, we studied the effect of cocaine on extracellular levels of beta-endorphin in the nucleus accumbens, a brain region involved in the reinforcing effects of psychostimulant drugs. Experimenter-delivered cocaine (2 mg/kg, i.v.) increased extracellular beta-endorphin immunoreactive levels in the nucleus accumbens, an effect attenuated by 6-hydroxy-dopamine lesions or systemic administration of the D1-like receptor antagonist, SCH-23390 (0.25 mg/kg, i.p.). The effect of cocaine on beta-endorphin release in the nucleus accumbens was mimicked by a local perfusion of dopamine (5 microm) and was blocked by coadministration of SCH-23390 (10 microm). Self-administered cocaine (1 mg/kg/infusion, i.v.) also increased extracellular beta-endorphin levels in the nucleus accumbens. In addition, using functional magnetic resonance imaging, we found that cocaine (1 mg/kg, i.v.) increases regional brain activity in the nucleus accumbens and arcuate nucleus. We demonstrate an increase in beta-endorphin release in the nucleus accumbens following experimenter-delivered and self-administered cocaine mediated by the local dopaminergic system. These findings suggest that activation of the beta-endorphin neurons within the arcuate nucleus-nucleus accumbens pathway may be important in the neurobiological mechanisms underlying the behavioral effects of cocaine.

Pyrogens Enhance β-Endorphin Release in Hypothalamus and Trigger Fever That Can Be Attenuated by Buprenorphine

At first, we investigated whether both beta-endorphin release level in the hypothalamus and body temperature can be altered after intracerebroventricular (i.c.v.) injection of either lipopolysaccharide (LPS), interleukin-1beta (IL-1beta), or prostaglandin E(2) (PGE(2)) in rats. It was found that in the rat, i.c.v. administration of either LPS (0.5 microg in 10 microl), IL-1beta (10 ng in 10 microl), or PGE(2) (200 ng in 10 microl), in addition to producing fever, upregulated the immunoreactivity of beta-endorphin in the preoptic anterior hypothalamus of rat brain. Secondarily, we assessed whether the fever induced by either LPS, IL-1beta, or PGE(2) can be altered by pretreatment with buprenorphine (an opioid receptor antagonist). The results revealed that i.c.v. administration of buprenorphine (1 - 10 microg in 10 microl) alone had an insignificant effect on the body temperature. However, the fever induced by i.c.v. injection of either LPS, IL-1beta, or PGE(2) was significantly attenuated by pretreatment with i.c.v. injection of buprenorphine 1 h before the pyrogen injection in rats. The results suggest that pyrogens enhance beta-endorphin release in the hypothalamus and trigger fever which can be attenuated by buprenorphine, an opioid receptor antagonist.

Effects of chronic antidepressants and electroconvulsive shock on serotonergic neurotransmission in the rat hypothalamus

The hypothalamus may play a critical role in the pathophysiology and treatment of depression. There are two main lines of evidence for this: firstly, many of its functions correspond to those altered in depression; and secondly, many hypothalamic functions are regulated by the serotonergic system, which is a common target of antidepressant treatments. In keeping with observations from other laboratories, we have found that chronic antidepressants and electroconvulsive shock increase serotonergic neurotransmission in the rat hypothalamus by inducing desensitization of presynaptic autoreceptors. We have also found that chronic hypercorticosolemia, which constitutes a model of depression, has an opposite effect. We postulate that presynaptic autoregulation of serotonergic neurotransmission in the hypothalamus may play a critical role in the pathophysiology and treatment of depression.

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.

Assessment and management of pain in neonates

Neonates are capable of experiencing pain from birth onwards. An impressive body of neuroanatomical, neurochemical and biobehavioural evidence, which has accumulated over the past 2 decades, supports this capability. This evidence mandates health professionals to attend to the prevention, elimination, or at the very least, control of pain for infants. This mandate is essential since pain is known to have both immediate and long term effects, especially if pain is untreated and is severe, prolonged or frequently experienced. Therefore, pain must be assessed frequently, not only to measure location, intensity and duration but also to determine the effectiveness of interventions implemented to control pain. An impressive array of measures for assessing acute pain in infants exists which incorporates valid pain indicators in this population. However, there is a need to develop new measures to assess chronic pain conditions and pain in infants in acute situations.

The role of the brain reward system in depression

The goal of this review is to familiarize the reader about the potential involvement of the brain reward system (BRS) in symptoms of Major Depressive Disorder (MDD). The authors introduce a novel approach to study the pathophysiology of MDD that includes pharmacological probing of BRS pathways (e.g. d-amphetamine, hydromorphone) together with an elicited and measurable behavioral component (e.g. pleasant effects, increased energy, altered cognition). To this date, the major focus of MDD pathophysiology studies has been to characterize biological differences between healthy subjects and depressed patients such as alteration in the monoaminergic and endocrine systems. The relative importance of the various biological changes has not been elucidated, that is, linking these with specific behavioral manifestations in MDD have rarely been attempted. One core symptom of MDD is a decreased experience of pleasure or interest in previously enjoyed activities (i.e. anhedonia) such as work or hobbies, and is accompanied by decreased motivation or drive. The BRS consists of the neural pathways involved in eliciting rewarding experiences in animals and humans. The hypothesis is that altered BRS function may be an underlying brain mechanism of the loss of pleasure/interest experienced in MDD, and will be manifested through an altered response to a BRS probe. The authors have examined BRS function in MDD by introducing a pharmacological probe (i.e. d-amphetamine/d-amph). Amphetamine is defined as a probe due to its ability to release dopamine within major components of the BRS (i.e. the mesocorticolimbic dopamine system.) In addition to the objective pharmacological effects (e.g. altered heart rate), BRS probes like d-amph elicit reliable and measurable behavior, that is, the hedonic effects. A review of the neurobiology of MDD, the BRS, the rationale for implicating the BRS in depressive symptoms, and preliminary data, are presented in this article.

Endogenous opiates: 1999

This paper is the twenty-second installment of the annual review of research concerning the opiate system. It summarizes papers published during 1999 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunologic responses.