Opioids in the hypothalamus control dopamine and acetylcholine levels in the nucleus accumbens

Low-dose nalmefene pretreatment reduces etomidate-induced myoclonus: A randomized, double-blind controlled trial

BACKGROUND

This study compared the effectiveness of nalmefene and fentanyl in reducing the incidence and severity of etomidate-induced myoclonus.

METHODS

One hundred fifty patients were randomized to receive 0.25ug/kg of nalmefene, 1ug/kg of fentanyl, or the same volume of normal saline 3 minutes prior to etomidate-induced anesthesia. The primary observational indexes were the severity level and incidence of etomidate-induced myoclonus, and the secondary observational index included blood pressure, heart rate, and the incidence of adverse effects from anesthesia induction to resuscitation, such as cough, chest wall rigidity, dizziness, nausea, pain after awakening, and intraoperative awareness.

RESULTS

The incidence of myoclonus was significantly lower in the nalmefene group (8.0%) than in the fentanyl group (32.0%) (P = .003) and in the normal saline group (72.0%) (P = .000). The severity level of myoclonus in the nalmefene group was significantly lower than the fentanyl group (P = .001) and normal saline group (P = .000). Meanwhile, the incidences of cough and chest wall rigidity during anesthesia induction were significantly lower in the nalmefene group compared with the fentanyl group (P = .003, P = .027). There were no statistically significant differences in heart rate and mean arterial pressure among the 3 gruops (P > .05). There was no difference in the incidence of adverse effects among the 3 groups during recovery from anesthesia (P > .05).

CONCLUSION

Intravenous injection of 0.25ug/kg of nalmefene 3 minutes prior to etomidate is more effective in preventing etomidate-induced myoclonus during general anesthesia than 1ug/kg of fentanyl.

Bispectral Index (BIS) Monitoring and Postoperative Delirium in Elderly Patients Undergoing Surgery: A Systematic Review and Meta-Analysis With Trial Sequential Analysis

OBJECTIVE

To examine the effect of bispectral index (BIS)-guided anesthesia on the incidence of postoperative delirium (POD) in elderly patients undergoing surgery.

DESIGN

A systematic review, meta-analysis, and trial sequential analysis (TSA).

SETTING

In the operating room, postoperative anesthesia care units (PACU), and ward.

PARTICIPANTS

Elderly patients (>60 years old) undergoing surgery.

INTERVENTIONS

The EMBASE, MEDLINE, and CENTRAL databases were searched systematically from their inception until December 2020 for randomized controlled trials comparing BIS and usual care or blinded BIS.

MEASUREMENTS AND MAIN RESULTS

Ten trials (N = 3,891) were included for quantitative meta-analysis. In comparison to the control group, there was no significant difference in the incidence of POD in elderly patients randomized to BIS-guided anesthesia (odds ratio [OR] 0.71, 95% CI 0.47-1.08, I² = 76%, p = 0.11, level of evidence = very low, TSA = inconclusive). The authors' review demonstrated that elderly patients with BIS-guided anesthesia were significantly associated with a lower incidence of postoperative cognitive dysfunction (POCD) (OR 0.64, 95% CI 0.46-0.88, p = 0.006), extubation time (mean difference [MD] -3.38 minutes, 95% CI -4.38 to -2.39, p < 0.00001), time to eye opening (MD -2.17 minutes, 95% CI -4.21 to -0.14, p = 0.04), and time to discharge from the PACU (MD -10.77 minutes, 95% CI -11.31 to - 10.23, p < 0.00001).

CONCLUSION

The authors' meta-analysis demonstrated that BIS-guided anesthesia was not associated with a reduced incidence of POD, but it was associated with a reduced incidence of POCD and improved recovery parameters.

Delirium in Palliative Care

Simple Summary

Delirium is a generalized cerebral dysfunction that occurs frequently near the end of life. In palliative care, delirium is frequently a sign of impending death; it is distressing for patients, families, and caregivers; and the goals of management, assessment, and treatment are controversial. We provide an update on these topics mainly focusing on patients with cancer.

Abstract

Delirium, a widespread neuropsychiatric disorder in patients with terminal diseases, is associated with increased morbidity and mortality, profoundly impacting patients, their families, and caregivers. Although frequently missed, the effective recognition of delirium demands attention and commitment. Reversibility is frequently not achievable. Non-pharmacological and pharmacological interventions are commonly used but largely unproven. Palliative sedation, although controversial, should be considered for refractory delirium. Psychological assistance should be available to patients and their families at all times.

Mesolimbic opioid-dopamine interaction is disrupted in obesity but recovered by weight loss following bariatric surgery

Obesity is a growing burden to health and the economy worldwide. Obesity is associated with central µ-opioid receptor (MOR) downregulation and disruption of the interaction between MOR and dopamine D₂ receptor (D₂R) system in the ventral striatum. Weight loss recovers MOR function, but it remains unknown whether it also recovers aberrant opioid-dopamine interaction. Here we addressed this issue by studying 20 healthy non-obese and 25 morbidly obese women (mean BMI 41) eligible for bariatric surgery. Brain MOR and D₂R availability were measured using positron emission tomography (PET) with [¹¹C]carfentanil and [¹¹C]raclopride, respectively. Either Roux-en-Y gastric bypass or sleeve gastrectomy was performed on obese subjects according to standard clinical treatment. 21 obese subjects participated in the postoperative PET scanning six months after bariatric surgery. In the control subjects, MOR and D₂R availabilities were associated in the ventral striatum (r = .62) and dorsal caudate (r = .61). Preoperatively, the obese subjects had disrupted association in the ventral striatum (r = .12) but the unaltered association in dorsal caudate (r = .43). The association between MOR and D₂R availabilities in the ventral striatum was recovered (r = .62) among obese subjects following the surgery-induced weight loss. Bariatric surgery and concomitant weight loss recover the interaction between MOR and D₂R in the ventral striatum in the morbidly obese. Consequently, the dysfunctional opioid-dopamine interaction in the ventral striatum is likely associated with an obese phenotype and may mediate excessive energy uptake. Striatal opioid-dopamine interaction provides a feasible target for pharmacological and behavioral interventions for treating obesity.

Taste association capabilities differ in high- and low-yawning rats versus outbred Sprague-Dawley rats after prolonged sugar consumption

Yawning is a stereotypical behavior pattern commonly associated with other behaviors such as grooming, sleepiness, and arousal. Several differences in behavioral and neurochemical characteristics have been described in high-yawning (HY) and low-yawning (LY) sublines from Sprague-Dawley (SD) rats that support they had changes in the neural mechanism between sublines. Differences in behavior and neurochemistry observed in yawning sublines could also overlap in processes needed during taste learning, particularly during conditioned taste aversion (CTA) and its latent inhibition. Therefore, the aim of this study was to analyze taste memory differences, after familiarization to novel or highly sweet stimuli, between yawning sublines and compare them with outbred SD rats. First, we evaluated changes in appetitive response during long-term sugar consumption for 14 days. Then, we evaluated the latent inhibition of CTA strength induced by this long pre-exposure, and we also measured aversive memory extinction rate. The results showed that SD rats and the two sublines developed similar CTA for novel sugar and significantly stronger appetitive memory after long-term sugar exposure. However, after 14 days of sugar exposure, HY and LY sublines were unable to develop latent inhibition of CTA after two acquisition trials and had a slower aversive memory extinction rate than outbreed rats. Thus, the inability of the HY and LY sublines to develop latent inhibition of CTA after long-term sugar exposure could be related to the time/context processes involved in long-term appetitive re-learning, and in the strong inbreeding that characterizes the behavioral traits of these sublines, suggesting that inbreeding affects associative learning, particularly after long-term exposure to sweet stimuli which reflects high familiarization.

Roux-en-Y gastric bypass in rat reduces mu-opioid receptor levels in brain regions associated with stress and energy regulation

Roux-en-Y gastric bypass surgery (RYGB) is the most common and effective weight loss procedure for severe obesity. However, a significant increase in addictive behaviors and new-onset substance use disorder (SUD) are sometimes observed post-surgery. The endogenous opioid system is known to play a major role in motivated behavior and reward, as well as the abuse of substances, including alcohol, tobacco, opioids and highly palatable foods. Here, we examined the effects of RYGB on mu-opioid receptor levels in the brain. Male Sprague-Dawley rats were assigned to one of four groups: standard diet with sham surgery (control), ad libitum high-energy high-fat (HF) diet with sham surgery, calorie restricted HF diet with sham surgery (Sham-FR), or HF diet with RYGB surgery. Control and HF groups were fed their respective diets for 8 weeks, with surgery performed on the eighth week. After 9 weeks on their respective diets post-surgery, animals were sacrificed for mu-opioid receptor autoradiography using the [³H] [D-Ala2,N-Me-Phe4-Gly5-ol]- enkephalin (DAMGO) ligand. Rats with RYGB showed reduced DAMGO binding in the central amygdala compared to sham-operated HF diet controls, and in the hypothalamus compared to high-fat fed Sham-FR. Diet alone did not change [³H] DAMGO binding in any region. These findings show that RYGB surgery, independent of diet or caloric restriction, decreases mu opioid signaling in specific regions important for stress and energy regulation. Thus, RYGB surgery may lead to greater stress sensitivity via downregulated mu opioid signaling in the central amygdala, which may contribute to the observed increased risk in some subjects for addictive behavior.

Endogenous opioid modulation of food intake and body weight: Implications for opioid influences upon motivation and addiction

This review is part of a special issue dedicated to Opioid addiction, and examines the influential role of opioid peptides, opioid receptors and opiate drugs in mediating food intake and body weight control in rodents. This review postulates that opioid mediation of food intake was an example of "positive addictive" properties that provide motivational drives to maintain opioid-seeking behavior and that are not subject to the "negative addictive" properties associated with tolerance, dependence and withdrawal. Data demonstrate that opiate and opioid peptide agonists stimulate food intake through homeostatic activation of sensory, metabolic and energy-related In contrast, general, and particularly mu-selective, opioid receptor antagonists typically block these homeostatically-driven ingestive behaviors. Intake of palatable and hedonic food stimuli is inhibited by general, and particularly mu-selective, opioid receptor antagonists. The selectivity of specific opioid agonists to elicit food intake was confirmed through the use of opioid receptor antagonists and molecular knockdown (antisense) techniques incapacitating specific exons of opioid receptor genes. Further extensive evidence demonstrated that homeostatic and hedonic ingestive situations correspondingly altered the levels and expression of opioid peptides and opioid receptors. Opioid mediation of food intake was controlled by a distributed brain network intimately related to both the appetitive-consummatory sites implicated in food intake as well as sites intimately involved in reward and reinforcement. This emergent system appears to sustain the "positive addictive" properties providing motivational drives to maintain opioid-seeking behavior.

Childhood Fructoholism and Fructoholic Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is an emerging entity, becoming the most prevalent pediatric chronic liver disease. Its broad spectrum of histological findings, comorbidities, and complications, including cirrhosis and liver failure, can occur in childhood, emphasizing the severity of pediatric NAFLD. Current lifestyle and diet modifications have been linked to the increasing prevalence of NAFLD, including the rise of fructose consumption, a monosaccharide present in foods that contain added sugar, such as sugar‐sweetened beverages. Excessive fructose consumption is believed to cause addiction like alcohol and other drugs. As such, the new term “fructoholism” refers to the consumption of a substance (fructose) that can cause psychological and physical damage and become a major public health concern, highlighting the seriousness of the excessive consumption of fructose in the pediatric age. Hepatic fructose metabolization leads to hepatic steatosis and progression to fibrosis through mechanisms comparable to alcoholic liver disease, hence the term “fructoholic liver disease.” Conclusion: The importance of implementing reliable global strategies, such as education campaigns to promote healthy diet, increasing taxes on foods that contain added sugars, subsidies to promote accessibility to fruit and vegetables, and strict food industry regulation to reduce sugar intake in children and adolescents, cannot be overemphasized.

The high efficacy of muscarinic M4 receptor in D1 medium spiny neurons reverses striatal hyperdopaminergia

The opposing action of dopamine and acetylcholine has long been known to play an important role in basal ganglia physiology. However, the quantitative analysis of dopamine and acetylcholine signal interaction has been difficult to perform in the native context because the striatum comprises mainly two subtypes of medium-sized spiny neurons (MSNs) on which these neuromodulators exert different actions. We used biosensor imaging in live brain slices of dorsomedial striatum to monitor changes in intracellular cAMP at the level of individual MSNs. We observed that the muscarinic agonist oxotremorine decreases cAMP selectively in the MSN subpopulation that also expresses D₁ dopamine receptors, an action mediated by the M₄ muscarinic receptor. This receptor has a high efficacy on cAMP signaling and can shut down the positive cAMP response induced by dopamine, at acetylcholine concentrations which are consistent with physiological levels. This supports our prediction based on theoretical modeling that acetylcholine could exert a tonic inhibition on striatal cAMP signaling, thus supporting the possibility that a pause in acetylcholine release is required for phasic dopamine to transduce a cAMP signal in D1 MSNs. In vivo experiments with acetylcholinesterase inhibitors donepezil and tacrine, as well as with the positive allosteric modulators of M₄ receptor VU0152100 and VU0010010 show that this effect is sufficient to reverse the increased locomotor activity of DAT-knockout mice. This suggests that M₄ receptors could be a novel therapeutic target to treat hyperactivity disorders.

Sugar Addiction: From Evolution to Revolution

The obesity epidemic has been widely publicized in the media worldwide. Investigators at all levels have been looking for factors that have contributed to the development of this epidemic. Two major theories have been proposed: (1) sedentary lifestyle and (2) variety and ease of inexpensive palatable foods. In the present review, we analyze how nutrients like sugar that are often used to make foods more appealing could also lead to habituation and even in some cases addiction thereby uniquely contributing to the obesity epidemic. We review the evolutionary aspects of feeding and how they have shaped the human brain to function in "survival mode" signaling to "eat as much as you can while you can." This leads to our present understanding of how the dopaminergic system is involved in reward and its functions in hedonistic rewards, like eating of highly palatable foods, and drug addiction. We also review how other neurotransmitters, like acetylcholine, interact in the satiation processes to counteract the dopamine system. Lastly, we analyze the important question of whether there is sufficient empirical evidence of sugar addiction, discussed within the broader context of food addiction.

The Effects of Perinatal Oxycodone Exposure on Behavioral Outcome in a Rodent Model

Opiate addiction is now a major public health problem. Perinatal insults and exposure to opiates such as morphine in utero are well known to affect development of the hypothalamic-pituitary-adrenal axis of the offspring adversely and are associated with a higher risk of developing neurobehavioral problems. Oxycodone is now one of the most frequently abused pain killers during pregnancy; however, limited data are available regarding whether and how perinatal oxycodone exposure (POE) alters neurobehavioral outcomes of the offspring. We demonstrated that exposure to 0.5 mg/kg/day oxycodone in utero was associated with hyperactivity in adult rats in an open field. No significant effects of POE were detected on isolation-induced ultrasonic vocalizations in the early postnatal period or on learning and memory in the water maze in adult offspring. Our findings are consistent with hyperactivity problems identified in children exposed to opiates in utero.

Activation of mu-opioid receptors in the ventral pallidum decreases the negative hedonic evaluation of a conditioned aversive taste in rats

Conditioned taste aversion (CTA) causes a shift in the hedonic evaluation of a conditioned stimulus (CS) from positive to negative, and reduces the CS intake. Mu-opioid receptors (MORs) in the ventral pallidum (VP) are known to be involved in the hedonic evaluation of positive rewarding stimuli; however, their involvement in evaluation of a negative aversive stimulus is still unclear. To explore the neural mechanisms of the negative hedonic evaluation of the CS in CTA, we examined the effects of the activation of VP MORs on the behavioral responses of rats to a CS. Rats implanted with guide cannulae into the bilateral VP received a pairing of 5mM saccharin solution as a CS with an intraperitoneal injection of 0.15M lithium chloride as an unconditioned stimulus. On the test day, after microinjections of MOR agonist [D-Ala², N-MePhe⁴, Gly-ol]-enkephalin (DAMGO) into the VP, we observed the behavioral responses to the intraorally infused CS solution. The DAMGO injections caused a larger number of ingestive taste reactivity responses to the CS solution. We also measured the consumption of the CS solution in a separate group of rats, using a single-bottle test. The DAMGO injected rats drank a higher volume of the CS solution than the saline injected rats. These results indicate that the activation of MORs in the VP results in the attenuation of aversion to the CS solution, thereby inducing the larger CS intake. Therefore, it is likely that VP MORs are involved in not only positive but also negative hedonic evaluation.

Prenatal fat exposure and hypothalamic PPAR β/δ: Possible relationship to increased neurogenesis of orexigenic peptide neurons

Gestational exposure to a fat-rich diet, while elevating maternal circulating fatty acids, increases in the offspring's hypothalamus and amygdala the proliferation and density of neurons that express neuropeptides known to stimulate consummatory behavior. To understand the relationship between these phenomena, this study examined in the brain of postnatal offspring (day 15) the effect of prenatal fat exposure on the transcription factor, peroxisome proliferator-activated receptor (PPAR) β/δ, which is sensitive to fatty acids, and the relationship of PPAR β/δ to the orexigenic neuropeptides, orexin, melanin-concentrating hormone, and enkephalin. Prenatal exposure to a fat-rich diet compared to low-fat chow increased the density of cells immunoreactive for PPAR β/δ in the hypothalamic paraventricular nucleus (PVN), perifornical lateral hypothalamus (PFLH), and central nucleus of the amygdala (CeA), but not the hypothalamic arcuate nucleus or basolateral amygdaloid nucleus. It also increased co-labeling of PPAR β/δ with the cell proliferation marker, BrdU, or neuronal marker, NeuN, and the triple labeling of PPAR β/δ with BrdU plus NeuN, indicating an increase in proliferation and density of new PPAR β/δ neurons. Prenatal fat exposure stimulated the double-labeling of PPAR β/δ with orexin or melanin-concentrating hormone in the PFLH and enkephalin in the PVN and CeA and also triple-labeling of PPAR β/δ with BrdU and these neuropeptides, indicating that dietary fat increases the genesis of PPAR β/δ neurons that produce these peptides. These findings demonstrate a close anatomical relationship between PPAR β/δ and the increased proliferation and density of peptide-expressing neurons in the hypothalamus and amygdala of fat-exposed offspring.

Hypothalamic neuropeptide signaling in alcohol addiction

The hypothalamus is now known to regulate alcohol intake in addition to its established role in food intake, in part through neuromodulatory neurochemicals termed neuropeptides. Certain orexigenic neuropeptides act in the hypothalamus to promote alcohol drinking, although they affect different aspects of the drinking response. These neuropeptides, which include galanin, the endogenous opioid enkephalin, and orexin/hypocretin, appear to stimulate alcohol intake not only through mechanisms that promote food intake but also by enhancing reward and reinforcement from alcohol. Moreover, these neuropeptides participate in a positive feedback relationship with alcohol, whereby they are upregulated by alcohol intake to promote even further consumption. They contrast with other orexigenic neuropeptides, such as melanin-concentrating hormone and neuropeptide Y, which promote alcohol intake under limited circumstances, are not consistently stimulated by alcohol, and do not enhance reward. They also contrast with neuropeptides that can be anorexigenic, including the endogenous opioid dynorphin, corticotropin-releasing factor, and melanocortins, which act in the hypothalamus to inhibit alcohol drinking as well as reward and therefore counter the ingestive drive promoted by orexigenic neuropeptides. Thus, while multiple hypothalamic neuropeptides may work together to regulate different aspects of the alcohol drinking response, excessive signaling from orexigenic neuropeptides or inadequate signaling from anorexigenic neuropeptides can therefore allow alcohol drinking to become dysregulated.

Sensing Positive versus Negative Reward Signals through Adenylyl Cyclase-Coupled GPCRs in Direct and Indirect Pathway Striatal Medium Spiny Neurons

Transient changes in striatal dopamine (DA) concentration are considered to encode a reward prediction error (RPE) in reinforcement learning tasks. Often, a phasic DA change occurs concomitantly with a dip in striatal acetylcholine (ACh), whereas other neuromodulators, such as adenosine (Adn), change slowly. There are abundant adenylyl cyclase (AC) coupled GPCRs for these neuromodulators in striatal medium spiny neurons (MSNs), which play important roles in plasticity. However, little is known about the interaction between these neuromodulators via GPCRs. The interaction between these transient neuromodulator changes and the effect on cAMP/PKA signaling via Golf- and Gi/o-coupled GPCR are studied here using quantitative kinetic modeling. The simulations suggest that, under basal conditions, cAMP/PKA signaling could be significantly inhibited in D1R+ MSNs via ACh/M4R/Gi/o and an ACh dip is required to gate a subset of D1R/Golf-dependent PKA activation. Furthermore, the interaction between ACh dip and DA peak, via D1R and M4R, is synergistic. In a similar fashion, PKA signaling in D2+ MSNs is under basal inhibition via D2R/Gi/o and a DA dip leads to a PKA increase by disinhibiting A2aR/Golf, but D2+ MSNs could also respond to the DA peak via other intracellular pathways. This study highlights the similarity between the two types of MSNs in terms of high basal AC inhibition by Gi/o and the importance of interactions between Gi/o and Golf signaling, but at the same time predicts differences between them with regard to the sign of RPE responsible for PKA activation.

SIGNIFICANCE STATEMENT

Dopamine transients are considered to carry reward-related signal in reinforcement learning. An increase in dopamine concentration is associated with an unexpected reward or salient stimuli, whereas a decrease is produced by omission of an expected reward. Often dopamine transients are accompanied by other neuromodulatory signals, such as acetylcholine and adenosine. We highlight the importance of interaction between acetylcholine, dopamine, and adenosine signals via adenylyl-cyclase coupled GPCRs in shaping the dopamine-dependent cAMP/PKA signaling in striatal neurons. Specifically, a dopamine peak and an acetylcholine dip must interact, via D1 and M4 receptor, and a dopamine dip must interact with adenosine tone, via D2 and A2a receptor, in direct and indirect pathway neurons, respectively, to have any significant downstream PKA activation.

Endogenous opioids and feeding behavior: A decade of further progress (2004-2014). A Festschrift to Dr. Abba Kastin

Functional elucidation of the endogenous opioid system temporally paralleled the creation and growth of the journal, Peptides, under the leadership of its founding editor, Dr. Abba Kastin. He was prescient in publishing annual and uninterrupted reviews on Endogenous Opiates and Behavior that served as a microcosm for the journal under his stewardship. This author published a 2004 review, "Endogenous opioids and feeding behavior: a thirty-year historical perspective", summarizing research in this field between 1974 and 2003. The present review "closes the circle" by reviewing the last 10 years (2004-2014) of research examining the role of endogenous opioids and feeding behavior. The review summarizes effects upon ingestive behavior following administration of opioid receptor agonists, in opioid receptor knockout animals, following administration of general opioid receptor antagonists, following administration of selective mu, delta, kappa and ORL-1 receptor antagonists, and evaluating opioid peptide and opioid receptor changes in different food intake models.

Polydrug abuse by intravenous use of heroin and tropicamide-containing eyedrops

BACKGROUND

Drug abuse is rarely limited to a single substance; polydrug use is the norm rather than the exception. In many cases, the misuse of potentially psychoactive substances can lead to serious intoxications and results in addictive behavior.

CASE DESCRIPTION

A 22-year-old heroin-addicted woman presented in our clinic reporting a 2-year history of intravenous injection of an eyedrop solution containing 1% tropicamide, an antimuscarinic agent. She reported injecting tropicamide because it attenuated symptoms and signs of opiate withdrawal and it also has hallucinogenic and euphorigenic effects. Despite the large amounts (up to 1.5 g), the rapidity of injection, and the long-term use, tropicamide was relatively well tolerated, without life-threatening consequences.An outpatient detoxification program was performed without any sign or symptom caused by discontinuing tropicamide.

CONCLUSIONS

The present case claims a role for pharmacological interactions, in addition to rewarding effects, in influencing drug association in polyabuse pattern. Moreover, this case underlines the need for physicians to be aware of the potential emergence of tropicamide as a drug of misuse, to prevent further harm.

Pharmacological challenge with naloxone and cue exposure in alcohol dependence: results of a randomized, double-blind placebo-controlled trial

OBJECTIVES

Animal and clinical studies implicated opioid dysfunction in the pathogenesis of alcohol abuse and dependence. The π-opioid antagonist naltrexone reduces craving, eventually modulated by hypothalamic-pituitary-adrenal axis. Altered cortisol response to opioid receptor blockade not only in alcohol dependent persons, but also in persons with a family history of alcohol dependency was reported.

METHODS

Twenty patients with alcohol dependence who had undergone detoxification were recruited. Naloxone (3.2 mg/70 kg body weight) having a very similar receptor profile to naltrexone and placebo were administered in cross-over fashion on two separate days 48 h apart. Mood and craving was assessed with well-established instruments (Alcohol Craving Questionnaire (ACQ), Profile of Mood Scale (POMS)). Both patients and raters were blind to all treatments. Twelve patients were first treated with naloxone, eight were first treated with placebo.

RESULTS

No significant differences were found between the placebo and naloxone groups according to ACQ and POMS. Cortisol levels were significantly higher in naloxone group.

CONCLUSIONS

We could not replicate the result, that blocking of the endogenous opioid system leads to reduced craving in alcohol-dependent individuals, while increase of cortisol after naloxone challenge is the expected biological effect of opioid receptor blockade on the hypothalamic-pituitary-adrenal (HPA) axis.

Neural and behavioral effects of a novel mu opioid receptor antagonist in binge-eating obese people

BACKGROUND

Binge eating is associated with obesity and has been conceptualized as "food addiction." However, this view has received only inconsistent support in humans, and limited evidence relates key neurocircuitry to the disorder. Moreover, relatively few studies have used pharmacologic functional magnetic resonance imaging to probe the underlying basis of altered eating behaviors.

METHODS

In a double-blind, placebo-controlled, parallel group study, we explored the effects of a potent mu-opioid receptor antagonist, GSK1521498, in obese individuals with moderate binge eating. Subjects were tested during a baseline placebo run-in period and retested after 28-days of drug (n = 21) or placebo (n = 21) treatment. Using functional magnetic resonance imaging and behavioral measures, we determined the drug's effects on brain responses to food images and, separately, on motivation to expend energy to view comparable images.

RESULTS

Compared with placebo, GSK1521498 was associated with a significant reduction in pallidum/putamen responses to pictures of high-calorie food and a reduction in motivation to view images of high-calorie food. Intriguingly, although motivational responding was reduced, subjective liking for the same images actually increased following drug treatment.

CONCLUSIONS

Stimulus-specific putamen/pallidal responses in obese people with binge eating are sensitive to altered mu-opioid function. This neuromodulation was accompanied by reductions in motivational responding, as measured by grip force, although subjective liking responses to the same stimuli actually increased. As well as providing evidence for a link between the opioid system and food-related behavior in binge-eating obese individuals, these results support a dissociation across measures of motivation and liking associated with food-related stimuli in these individuals.

Effects of naltrexone on food intake and body weight gain in olanzapine-treated rats

Blockade of opioidergic neurotransmission contributes to reduction in body weight. However, how such blockade affects body weight gain (BWG) attributed to second generation antipsychotic agents (SGAs) has not yet been established. Here we examined the effects of an opioid receptor antagonist, naltrexone (NTX), on food intake and BWG associated with an SGA, olanzapine (OL). Four groups of Wistar Han IGS rats were treated for 28 days with either OL (2 mg/kg twice daily, intraperitoneal (IP)), a combination of OL (2 mg/kg twice daily, IP) + extended-release NTX (50 mg/kg, one-time, intramuscular (IM)), extended-release NTX (50 mg/kg, one-time, IM) or vehicle and their food intake and body weight were measured daily for the first nine days and every other day thereafter. Food intake and BWG that were increased by OL were decreased by the added NTX while NTX alone had no significant effects on food intake or on BWG. Plasma leptin concentrations were significantly elevated in the three groups receiving pharmacological agents, but did not differ among each other, suggesting that changes in leptin secretion and/or clearance alone would not explain the food intake and the body weight findings. Our results extend prior reports on anorexigenic effects of opioid antagonists by demonstrating that such effects may generalize to food intake increases and BWG arising in the context of OL pharmacotherapy.

A high-fat meal, or intraperitoneal administration of a fat emulsion, increases extracellular dopamine in the nucleus accumbens

Evidence links dopamine (DA) in the nucleus accumbens (NAc) shell to the ingestion of palatable diets. Less is known, however, about the specific relation of DA to dietary fat and circulating triglycerides (TG), which are stimulated by fat intake and promote overeating. The present experiments tested in Sprague-Dawley rats whether extracellular levels of NAc DA increase in response to acute access to fat-rich food or peripheral injection of a fat emulsion and, if so, whether this is related to caloric intake or elevated circulating lipids. When rats consumed more calories of a high-fat meal compared with a low-fat meal, there was a significant increase in extracellular accumbens DA (155% vs. 119%). Systemic injection of a fat emulsion, which like a high-fat diet raises circulating TG but eliminates the factor of taste and allows for the control of caloric intake, also significantly increased extracellular levels of DA (127%) compared to an equicaloric glucose solution (70%) and saline (85%). Together, this suggests that a rise in circulating TG may contribute to the stimulatory effect of a high-fat diet on NAc DA.

The Impact of Maternal High-Fat Diet Consumption on Neural Development and Behavior of Offspring

Maternal diet and metabolic state are important factors in determining the environment experienced during perinatal development. Epidemiological studies and evidence from animal models provide evidence that a mother's diet and metabolic condition are important in programming the neural circuitry that regulates behavior, resulting in a persistent impact on the offspring's behavior. Potential mechanisms by which maternal diet and metabolic profile influence the perinatal environment include placental dysfunction and increases in circulating factors such as inflammatory cytokines, nutrients (glucose and fatty acids) and hormones (insulin and leptin). Maternal obesity and high-fat diet (HFD) consumption exposure during development have been observed to increase the risk of developing serious mental health and behavioral disorders including anxiety, depression, attention deficit hyperactivity disorder and autism spectrum disorder. The increased risk of developing these behavioral disorders is postulated to be due to perturbations in the development of neural pathways that regulate behavior, including the serotonergic, dopaminergic and melanocortinergic systems. It is critical to examine the influence that a mother's nutrition and metabolic profile have on the developing offspring considering the current and alarmingly high prevalence of obesity and HFD consumption in pregnant women.

Endogenous opiates and behavior: 2010

This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

Similarities in hypothalamic and mesocorticolimbic circuits regulating the overconsumption of food and alcohol

Historically, studies of food intake regulation started with the hypothalamus and gradually expanded to mesocorticolimbic regions, while studies of drug use began with mesocorticolimbic regions and now include the hypothalamus. As research on ingestive behavior has progressed, it has uncovered more and more similarities between the regulation of palatable food and drug intake. It has also identified specific neurochemicals involved in palatable food and drug intake. Hypothalamic orexigenic neurochemicals specifically involved in controlling fat ingestion, including galanin, enkephalin, orexin and melanin-concentrating hormone, show positive feedback with this macronutrient, with these peptides both increasing fat intake and being further stimulated by its intake. This positive relationship offers some explanation for why foods high in fat are so often overconsumed. Research in Bart Hoebel's laboratory in conjunction with our own has shown that consumption of ethanol, a drug of abuse that also contains calories, is similarly driven by these neurochemical systems involved in fat intake, consistent with evidence closely relating fat and ethanol consumption. Both fat and ethanol intake are also regulated by dopamine and acetylcholine acting in mesocorticolimbic nuclei. This close relationship of fat and ethanol is likely driven in part by circulating lipids, which are increased by fat and ethanol intake, known to increase expression and levels of the neurochemicals, and found to promote further intake of fat and ethanol. Compellingly, recent studies suggest that these systems may already be dysregulated in animals prone to consuming excess fat or ethanol, even before they have ever been exposed to these substances. Further understanding of these systems involved in consummatory behavior will allow researchers to develop effective therapies for the treatment of overeating as well as drug abuse.

Neurobiology of aversive states

Hoebel and colleagues are often known as students of reward and how it is coded in the CNS. This article, however, attempts to focus on the significant advances by Hoebel and others in dissecting out behavioral components of distinct aversive states and in understanding the neurobiology of aversion and the link between aversive states and addictive behaviors. Reward and aversion are not necessarily dichotomous and may reflect an affective continuum contingent upon environmental conditions. Descriptive and mechanistic studies pioneered by Bart Hoebel have demonstrated that the shift in the reward-aversion spectrum may be, in part, a result of changes in central dopamine/acetylcholine ratio, particularly in the nucleus accumbens. The path to aversion appears to include a specific neurochemical signature: reduced dopamine release and increased acetylcholine release in "reward centers" of the brain. Opioid receptors may have a neuromodulatory role on both of these neurotransmitters.

The μ opioid receptor is not involved in ethanol-stimulated dopamine release in the ventral striatum of C57BL/6J mice

BACKGROUND

The mu opioid receptor (MOR) has previously been found to regulate ethanol-stimulated dopamine release under some, but not all, conditions. A difference in ethanol-evoked dopamine release between male and female mixed background C57BL/6J-129SvEv mice led to questions about its ubiquitous role in these effects of ethanol. Using congenic C57BL/6J MOR knockout (KO) mice and C57BL/6J mice pretreated with an irreversible MOR antagonist, we investigated the function of this receptor in ethanol-stimulated dopamine release.

METHODS

Microdialysis was used to monitor dopamine release and ethanol clearance in MOR -/-, +/+, and +/- . male and female mice after intraperitoneal (i.p.) injections of 1.0, 2.0, and 3.0 g/kg ethanol (or saline). We also measured the increase in dopamine release after 5 mg/kg morphine (i.p.) in male and female MOR+/+ and -/- mice. In a separate experiment, male C57BL/6J mice were pretreated with either the irreversible MOR antagonist beta funaltrexamine (BFNA) or vehicle, and dopamine levels were monitored after administration of 2 g/kg ethanol or 5 mg/kg morphine.

RESULTS

Although ethanol-stimulated dopamine release at all the 3 doses of alcohol tested, there were no differences between MOR+/+, -/-, and +/- mice in these effects. Female mice had a more prolonged effect compared to males at the 1 g/kg dose. Administration of 2 g/kg ethanol also caused a similar increase in dopamine levels in both saline-pretreated and BFNA-pretreated mice. Five mg/kg morphine caused a significant increase in dopamine levels in MOR+/+ mice but not in MOR-/- mice and in saline-pretreated mice but not in BFNA-pretreated mice. Intraperitoneal saline injections had a significant, albeit small and transient, effect on dopamine release when given in a volume equivalent to the ethanol doses, but not in a volume equivalent to the 5 mg/kg morphine dose. Ethanol pharmacokinetics were similar in all genotypes and both sexes at each dose and in both pretreatment groups.

CONCLUSIONS

MOR is not involved in ethanol-stimulated dopamine release in the ventral striatum of C57BL/6J mice.

The missing p in psychiatric training: why it is important to teach pain to psychiatrists

CONTEXT

Pain problems are exceedingly prevalent among psychiatric patients. Moreover, clinical impressions and neurobiological research suggest that physical and psychological aspects of pain are closely related entities. Nonetheless, remarkably few pain-related themes are currently included in psychiatric residency training.

OBJECTIVES

To provide clinical and scientific rationale for psychiatric-training enrichment with basic tenets of pain medicine and to raise the awareness and sensitivity of physicians, scientists, and educators to this important yet unmet clinical and public health need.

RESULTS

We present 3 lines of translational research evidence, extracted from a comprehensive literature review, in support of our objectives. First, the neuroanatomical and functional overlap between pain and emotion/reward/motivation brain circuitry suggests integration and mutual modulation of these systems. Second, psychiatric disorders are commonly associated with alterations in pain processing, whereas chronic pain may impair emotional and neurocognitive functioning. Third, given its stressful nature, pain may serve as a functional probe for unraveling pathophysiological mechanisms inherent in psychiatric morbidity.

CONCLUSIONS

Pain training in psychiatry will contribute to deeper and more sophisticated insight into both pain syndromes and general psychiatric morbidity regardless of patients' pain status. Furthermore, it will ease the artificial boundaries separating psychiatric and medical formulations of brain disorders, thus fostering cross-fertilizing interactions among specialists in various disciplines entrusted with the care of patients experiencing pain.

Maternal high-fat diet alters methylation and gene expression of dopamine and opioid-related genes

Maternal obesity during pregnancy increases the risk of obesity in the offspring. Obesity, arising from an imbalance of energy intake and expenditure, can be driven by the ingestion of palatable [high fat (HF), high sugar], energy-dense foods. Dopamine and opioid circuitry are neural substrates associated with reward that can affect animals' preference for palatable foods. Using a mouse model, the long-term effect of maternal consumption of a HF diet on dopamine and opioid gene expression within the mesocorticolimbic reward circuitry and hypothalamus of the offspring was investigated. Mice from dams fed a HF diet during pregnancy and lactation showed an increased preference for sucrose and fat. Gene expression, measured using quantitative real-time PCR, revealed a significant approximately 3- to 10-fold up-regulation of dopamine reuptake transporter (DAT) in the ventral tegmental area, nucleus accumbens, and prefrontal cortex and a down-regulation of DAT in the hypothalamus. Additionally, expression of both μ-opioid receptor (MOR) and preproenkephalin (PENK) was increased in nucleus accumbens, prefrontal cortex, and hypothalamus of mice from dams that consumed the HF diet. Epigenetic mechanisms have been associated with long-term programming of gene expression after various in utero insults. We observed global and gene-specific (DAT, MOR, and PENK) promoter DNA hypomethylation in the brains of offspring from dams that consumed the HF diet. These data demonstrate that maternal consumption of a HF diet can change the offsprings' epigenetic marks (DNA hypomethylation) in association with long-term alterations in gene expression (dopamine and opioids) and behavior (preference for palatable foods).

New approaches to the pharmacological treatment of obesity: can they break through the efficacy barrier?

In this review we assess the range of centrally active anorectics that are either in human clinical trials, or are likely to be so in the near future. We describe their weight loss efficacy, mode of action at both pharmacological and behavioural levels, where understood, together with the range of side effects that might be expected in clinical use. We have however evaluated these compounds against the considerably more rigorous criteria that are now being used by the Federal Drugs Agency and European Medicines Agency to decide approvals and market withdrawals. Several trends are evident. Recent advances in the understanding of energy balance control have resulted in the exploitation of a number of new targets, some of which have yielded promising data in clinical trials for weight loss. A second major trend is derived from the hypothesis that improved weight loss efficacy over current therapy is most likely to emerge from treatments targeting multiple mechanisms of energy balance control. This reasoning has led to the development of a number of new treatments for obesity where multiple mechanisms are targeted, either by a single molecule, such as tesofensine, or through drug combinations such as qnexa, contrave, empatic, and pramlintide+metreleptin. Many of these approaches also utilise advances in formulation technology to widen safety margins. Finally, the practicality of peptide therapies for obesity has become better validated in recent studies and this may allow more rapid exploitation of novel targets, rather than awaiting the development of orally available small molecules. We conclude that novel, more efficacious and better tolerated treatments for obesity may become available in the near future.

Galanin and consummatory behavior: special relationship with dietary fat, alcohol and circulating lipids

Galanin (GAL) plays an integral role in consummatory behavior. In particular, hypothalamic GAL has a positive, reciprocal relationship with dietary fat and alcohol. In this relationship, GAL increases the consumption of fat or alcohol which, in turn, stimulates the expression of GAL, ultimately leading to overconsumption. Through actions in the amygdala, this relationship may become especially important in stress-induced food or drug intake. These effects of GAL in promoting overconsumption may involve various neurotransmitters, with GAL facilitating intake by stimulating norepinephrine and dopamine and reducing satiety by decreasing serotonin and acetylcholine. In addition, GAL in the hypothalamus stimulates the opioid, enkephalin, throughout the brain, which also promotes overconsumption. The relationship between GAL, fat, and alcohol may involve triglycerides, circulating lipids that are released by fat or alcohol and that correlate positively with hypothalamic GAL expression. In females, levels of endogenous GAL also fluctuate across the reproductive cycle, driven by a rise in the ovarian steroids, estrogen, and progesterone. They peak during the proestrous phase and also at puberty, simultaneous to a sharp increase in preference for fat to meet energy demands. Prenatal exposure to a high-fat diet also enhances hypothalamic expression of GAL into adulthood because of an increase in neurogenesis and proliferation of GAL-expressing neurons in this region. This organizational change may reflect the role of GAL in neuronal development, including neurite growth in adulthood, cell survival in aging, and cell stability in the disease state. By responding positively to fat and alcohol and guiding further neuronal development, GAL potentiates a long-term propensity to overconsume fat and alcohol.

Hypothalamic injection of non-opioid peptides increases gene expression of the opioid enkephalin in hypothalamic and mesolimbic nuclei: Possible mechanism underlying their behavioral effects

The peptides galanin (GAL) and orexin (OX) share common features with the opioid enkephalin (ENK) in their relationship to ingestive behavior, stimulating consumption of a fat-rich diet and ethanol when injected into the hypothalamus. Since receptors for GAL and OX are dense in areas where ENK-expressing neurons are concentrated, these non-opioid peptides may exert their effects, in part, through the stimulation of endogenous ENK. This study was conducted to determine whether injection of GAL or OX affects the expression of ENK in hypothalamic and mesolimbic nuclei involved in consummatory behavior. Rats were injected with GAL (1 microg), OX-A (1 microg), or saline vehicle just dorsal to the hypothalamic paraventricular nucleus (PVN). They were sacrificed 1h later for analysis of ENK mRNA levels in the PVN, ventral tegmental area (VTA), central nucleus of the amygdala (CeA), and nucleus accumbens (NAc). Both GAL and OX had similar effects, significantly increasing ENK mRNA expression in each of these areas, except for the NAc. This enhanced ENK expression in the PVN, VTA and CeA was demonstrated with real-time quantitative polymerase chain reaction and confirmed in separate groups using radiolabeled and digoxigenin-labeled in situ hybridization. These findings demonstrate that the non-opioid peptides, GAL or OX, which have similar effects on consummatory behavior, are also similar in their effect on endogenous ENK. In light of published findings showing an opioid antagonist to block GAL- and OX-induced feeding, these results provide additional evidence that ENK is involved in mediating the common behavioral effects of these peptides.