Increased beta-endorphin and dynorphin concentrations in discrete hypothalamic regions of genetically obese (ob/ob) mice

Decreased Analgesic Requirements in Super Morbidly Versus Morbidly Obese Patients Undergoing Laparoscopic Sleeve Gastrectomy

Background

Scarce data exists about analgesic requirements in super morbidly obese (SMO) patients who underwent sleeve gastrectomy. We attempted to investigate analgesic requirements for SMO, when compared with morbidly obese (MO) individuals who underwent sleeve gastrectomy and its impact on postoperative outcome.

Methods

We studied 279 consecutive patients (183 MO, 96 SMO) who underwent bariatric surgery. Data analysis included perioperative anaesthetic management, analgesic consumptions, opioids side effects, and ICU admission.

Results

The SMO group showed higher patients with asthma, epilepsy, obstructive sleep apnoea (OSA), and ASA III percentages (P = 0.014, P = 0.016, P ˂ 0.001, and P ˂ 0.001, respectively). There were no significant differences in the total morphine consumption intraoperatively, or after 24 h. However, reduced consumption of intraoperative fentanyl and morphine in SMO when calculated per total body weight (TBW) (P = 0.004 and P = 0.001, respectively). At PACU, tramadol consumption per TBW and lean body mass (LBM) were significantly reduced in SMO (P = 0.001 and P = 0.025, respectively). Paracetamol consumption was significantly reduced in the SMO group (P = 0.04). They showed higher comorbidities (P ˂ 0.001), longer anaesthesia time (P = 0.033), and greater ICU admissions (P ˂ 0.001). Vomiting was higher in the MO group (P = 0.004). Both groups showed comparable pain scores (P = 0.558) and PACU stay time (P = 0.060).

Conclusions

Super morbidly obese patients required fewer opioids and analgesics perioperatively. They exhibited higher comorbidities with greater anaesthesia time and ICU admissions. PACU stay time and pain scores were comparable.

High-fat diet and type 2 diabetes induced disruption of the oestrous cycle and alteration of hormonal profiles, but did not affect subpopulations of KNDy neurones in female rats

Apart from the primary metabolic symptoms of obesity and/or diabetes, there are numerous secondary problems, including disruptions of the reproductive system. The KNDy neurones, which express kisspeptin, neurokinin B and dynorphin A and are located in the arcuate nucleus of the hypothalamus (ARC), are important regulators of reproduction. Their functions are highly influenced by metabolic and hormonal status. We have previously shown that, in male rats with experimentally-induced diabetes type 2 (but not with high-fat diet-induced obesity), there are alterations in the number of these cells. In the present study, we hypothesised that a high-fat diet (HFD) and/or diabetes type 2 (DM2) in female rats affect the oestrous cycle, hormonal profiles and the number of kisspeptin-immunoreactive, neurokinin B-immunoreactive and/or dynorphin A-immunoreactive neurones in the ARC. Rats were assigned to one of three groups: a control group fed a regular chow diet, a high-fat diet group (HFD) and a diabetic group (DM2), with both of the latter two groups receiving a high calorie diet (50% of energy from lard). The third group was additionally treated with streptozotocin to induce DM2. Their oestrous cycles was monitored and their metabolic and hormonal status were assessed. We found that HFD and DM2 female rats, despite having significant alterations in their metabolic and hormonal profiles, as well as disruptions of the oestrous cycle, showed no changes in the number of the kisspeptin-immunoreactive, neurokinin B-immunoreactive and/or dynorphin A-immunoreactive neurones in the ARC. However, slight differences in the rostrocaudal distribution of these neurones among groups were reported. In conclusion, the data from the present study, together with our previously published results in males, indicate sex differences in the response of KNDy neurones to DM2 but not to HFD conditions.

Kisspeptin and Metabolism: The Brain and Beyond

Apart from the well-established role of kisspeptin (Kp) in the regulation of reproductive functions, recent data described its action in the control of metabolism. Of particular interest for the review is the population of Kp neurons localized in the arcuate nucleus (ARC) of the hypothalamus, the site of the brain where reproductive and metabolic cross talk occurs. However, within the hypothalamus Kp does not work alone, but rather interacts with other neuropeptides, e.g., neurokinin B, dynorphin A, proopiomelanocortin, the cocaine- and amphetamine-regulated transcript, agouti-related peptide, and neuropeptide Y. Beyond the brain, Kp is expressed in peripheral tissues involved in metabolic functions. In this review, we will mainly focus on the local action of this peptide in peripheral organs such as the pancreas, liver, and the adipose tissue. We will concentrate on dysregulation of the Kp system in cases of metabolic imbalance, e.g., obesity and diabetes. Importantly, these patients besides metabolic health problems often suffer from disruptions of the reproductive system, manifested by abnormalities in menstrual cycles, premature child birth, miscarriages in women, decreased testosterone levels and spermatogenesis in men, hypogonadism, and infertility. We will review the evidence from animal models and clinical data indicating that Kp could serve as a promising agent with clinical applications in regulation of reproductive problems in individuals with obesity and diabetes. Finally, emerging data indicate a role of Kp in regulation of insulin secretion, potentially leading to development of further therapeutic uses of this peptide to treat metabolic problems in patients with these lifestyle diseases.

Effects of Orchidectomy and Testosterone Replacement on Numbers of Kisspeptin-, Neurokinin B-, and Dynorphin A-Immunoreactive Neurones in the Arcuate Nucleus of the Hypothalamus in Obese and Diabetic Rats

Neurones expressing kisspeptin, neurokinin B and dynorphin A, located in the arcuate nucleus of the hypothalamus (ARC), are important regulators of reproduction. Their functions depend on metabolic and hormonal status. We hypothesised that male rats with high-fat diet-induced obesity (DIO) and/or streptozotocin-induced diabetes mellitus type 1 (DM1) and type 2 (DM2) will have alterations in numbers of immunoreactive (-IR) cells: kisspeptin-IR and/or neurokinin B-IR and dynorphin A-IR neurones in the ARC in the sham condition. In addition, orchidectomy alone (ORX) and with testosterone treatment (ORX+T) will unmask possible deficits in the response of these neurones in DIO, and/or DM1 and DM2 rats. Rats were assigned to four groups: a control (C) and one diabetic group (DM1) were fed a regular chow diet, whereas the obese group (DIO) and the other diabetic group (DM2) were fed a high-fat diet. To induce diabetes, streptozotocin was injected. After 6 weeks, each group was divided into three subgroups: ORX, ORX+T and sham. After another 2 weeks, metabolic and hormonal profiles were assessed and immunocytochemistry was performed. We found that: (1) under sham conditions: (i) DM1 and DM2 animals had higher numbers of kisspeptin-IR cells than controls and (ii) DM2 rats had increased numbers of neurokinin B-IR and dynorphin A-IR cells compared to C animals; (2) ORX and ORX+T treatments unmasked deficits of the studied neurones in DM1 and DM2 but not in DIO animals; and (3) DIO, DM1 and DM2 rats had altered metabolic and hormonal profiles, in particular decreased levels of testosterone. We concluded that alterations in numbers of kisspeptin-IR and neurokinin B-IR neurones in the ARC and their response to ORX and ORX+T may account for disruptions of metabolic and reproductive functions in diabetic but not in obese rats.

Direct inhibition of arcuate proopiomelanocortin neurons: a potential mechanism for the orexigenic actions of dynorphin

Dynorphin, an endogenous ligand of kappa (κ) opioid receptors, has multiple roles in the brain, and plays a positive role in energy balance and food intake. However, the mechanism for this is unclear. With immunocytochemistry, we find that axonal dynorphin immunoreactivity in the arcuate nucleus is strong, and that a large number of dynorphin-immunoreactive boutons terminate on or near anorexigenic proopiomelanocortin (POMC) cells. Here we provide evidence from whole-cell patch-clamp recording that dynorphin-A (Dyn-A) directly and dose-dependently inhibits arcuate nucleus POMC neurons. Dyn-A inhibition was eliminated by the opioid receptor antagonist nor-BNI, but not by the μ receptor antagonist CTAP. The inhibitory effect was mimicked by the (κ)2 receptor agonist GR89696, but not by the 1 receptor agonist U69593. No presynaptic effect of (κ)2 agonists was found. These results suggest that Dyn-A inhibits POMC neurons through activation of the (κ)2 opioid receptor. In whole-cell voltage clamp, Dyn-A opened G-protein-coupled inwardly rectifying potassium (GIRK)-like channels on POMC neurons. Dynorphin attenuated glutamate and GABA neurotransmission to POMC neurons. In contrast to the strong inhibition of POMC neurons by Dyn-A, we found a weaker direct inhibitory effect of Dyn-A on arcuate nucleus neuropeptide Y (NPY) neurons mediated by both 1 and (κ)2 receptors. Taken together, these results indicate a direct inhibitory effect of Dyn-A on POMC neurons through activation of the (κ)2 opioid receptor and GIRK channels. A number of orexigenic hypothalamic neurons release dynorphin along with other neuropeptides. The inhibition of anorexigenic POMC neurons may be one mechanism underlying the orexigenic actions of dynorphin.

Role of the arcuate nucleus of the hypothalamus in regulation of body weight during energy deficit

Acute or long-term energy deficit in lean or obese rodents or humans stimulates food intake or appetite and reduces metabolic rate or energy expenditure. These changes contribute to weight regain in post-obese animals and humans. Some studies show that the reduction in metabolic rate with energy deficit in overweight people is transient. Energy restriction has been shown in some but not all studies to reduce physical activity, and this may represent an additional energy-conserving adaptation. Energy restriction up-regulates expression of the orexigenic neuropeptide Y, agouti related peptide and opioids and down-regulates that of the anorexigenic alpha-melanocyte stimulating hormone or its precursor pro-opioomelanocortin and the co-expressed cocaine and amphetamine-regulated transcript in the arcuate nucleus of the hypothalamus. Recapitulating these hypothalamic changes in sated animals mimics the effects of energy deficit, namely increased food intake, reduced physical activity and reduced metabolic rate, suggesting that these energy-conserving adaptations are at least partially mediated by the hypothalamus.

Serotonin 5-HT2C receptor-independent expression of hypothalamic NOR1, a novel modulator of food intake and energy balance, in mice

NOR1, Nur77 and Nurr1 are orphan nuclear receptors and members of the NR4A subfamily. Here, we report that the expression of hypothalamic NOR1 was remarkably decreased in mildly obese beta-endorphin-deficient mice and obese db/db mice with the leptin receptor mutation, compared with age-matched wild-type mice, whereas there were no genotypic differences in the expression of hypothalamic Nur77 or Nurr1 in these animals. The injection of NOR1 siRNA oligonucleotide into the third cerebral ventricle significantly suppressed food intake and body weight in mice. On the other hand, the decreases in hypothalamic NOR1 expression were not found in non-obese 5-HT2C receptor-deficient mice. Moreover, systemic administration of m-chlorophenylpiperazine (mCPP), a 5-HT2C/1B receptor agonist, had no effect on hypothalamic NOR1 expression, while suppressing food intake in beta-endorphin-deficient mice. These findings suggest that 5-HT2C receptor-independent proopiomelanocortin-derived peptides regulate the expression of hypothalamic NOR1, which is a novel modulator of feeding behavior and energy balance.

Dynorphin knockout reduces fat mass and increases weight loss during fasting in mice

Endogenous opioids, particularly dynorphins, have been implicated in regulation of energy balance, but it is not known how they mediate this in vivo. We investigated energy homeostasis in dynorphin knockout mice (Dyn(-/-) mice) and probed the interactions between dynorphins and the neuropeptide Y (NPY) system. Dyn(-/-) mice were no different from wild types with regards to body weight and basal and fasting-induced food intake, but fecal output was increased, suggesting decreased nutrient absorption, and they had significantly less white fat and lost more weight during a 24-h fast. The neuroendocrine and thermal responses to fasting were at least as pronounced in Dyn(-/-) as in wild types, and there was no stimulatory effect of dynorphin knockout on 24-h energy expenditure (kilocalories of heat produced) or physical activity. However, Dyn(-/-) mice showed increased circulating concentrations of 3,4-dihydroxyphenlacetic acid and 3,4-dihydroxyphenylglycol, suggesting increased activity of the sympathetic nervous system. The respiratory exchange ratio of male but not female Dyn(-/-) mice was reduced, demonstrating increased fat oxidation. Interestingly, expression of the orexigenic acting NPY in the hypothalamic arcuate nucleus was reduced in Dyn(-/-) mice. However, fasting-induced increases in pre-prodynorphin expression in the arcuate nucleus, the paraventricular nucleus, and the ventromedial hypothalamus but not the lateral hypothalamus were abolished by deletion of Y(1) but not Y(2) receptors. Therefore, ablation of dynorphins results in increases in fatty acid oxidation in male mice, reductions in adiposity, and increased weight loss during fasting, possibly via increases in sympathetic activity, decreases in intestinal nutrient absorption, and interactions with the NPYergic system.

Distribution of prodynorphin mRNA and its interaction with the NPY system in the mouse brain

Using radioactive in situ hybridisation, the distribution of prodynorphin mRNA in the brains of C57Bl/6 mice was systemically investigated, and double-labelling in situ hybridisation was used to determine the extent to which neuropeptide Y (NPY) and prodynorphin mRNAs were co-expressed. Our results demonstrate that prodynorphin mRNA expression in the mouse brain is localised at specific subregions of the olfactory bulb, cortex, hippocampus, amygdala, basal ganglia, thalamus, hypothalamus, mesencephalon and myelencephalon. Among the regions displaying the most intense labelling were the olfactory tubercle, lateral septum (LS), caudate putamen (Cpu), central amygdaloid nucleus (Ce), paraventricular hypothalamic nucleus (PVN), supraoptic nucleus (SO), lateral hypothalamic area (LHA), ventromedial hypothalamic nucleus (VMH), lateral reticular nucleus (LRt) and solitary tract nucleus (NTS). In the arcuate nucleus of the hypothalamus (Arc), double-labelling in situ hybridisation revealed that prodynorphin expressing neurons also contained NPY mRNA, with a co-localisation rate of approximately 88% in the lateral part of the Arc, and 79% in the dorsal part of the Arc, respectively, suggesting potential overlapping functions of these two neurotransmitters in feeding type behaviour.

Distribution of preprodynorphin mRNA and dynorphin-a immunoreactivity in the sheep preoptic area and hypothalamus

Endogenous opioid peptides (EOP) are important modulators in a variety of neuroendocrine systems, including those mediating reproduction, energy balance, lactation, and stress. Recent work in the ewe has implicated the EOP, dynorphin (DYN), in the inhibitory effects of progesterone on pulsatile gonadotropin releasing hormone secretion. Although DYN is involved in a number of hypothalamic functions in the sheep, little is known regarding the localization of preprodynorphin (PPD) expression and its major product DYN A (1-17). In this study, we determined the distribution of PPD mRNA and DYN A-containing cell bodies in the brains of ovary-intact, luteal ewes. To detect PPD mRNA, an ovine PPD mRNA was subcloned by reverse transcription-polymerase chain reaction from sheep hypothalamus and used to create a (35)S-labeled riboprobe for in situ hybridization. Neurons that expressed PPD mRNA and DYN A immunoreactivity were widely distributed in the ovine preoptic area and hypothalamus. PPD mRNA-expressing cells were seen in the supraoptic nucleus, paraventricular nucleus, preoptic area, anterior hypothalamus area, bed nucleus of the stria terminalis, ventromedial nucleus (VMN), dorsomedial nucleus of the hypothalamus, and the arcuate nucleus. All of these regions also contained DYN A-positive cell bodies except for the VMN, raising the possibility that PPD is preferentially processed into other peptide products in the VMN. In summary, based on the expression of both mRNA and peptide, DYN cells are located in a number of key hypothalamic regions involved in the neuroendocrine control of homeostasis in sheep.

Intraventricular insulin decreases kappa opioid-mediated sucrose intake in rats

The hormone insulin acts in the central nervous system (CNS) as a regulator of body adiposity and food intake. Recent work from our laboratory has provided evidence that one way by which insulin may decrease food intake is by decreasing the rewarding properties of food. Evidence from others suggests that endogenous opioids may mediate the palatable properties of foods, and insulin may decrease nonfood-related reward via interaction with some CNS kappa opioid systems. In the present study we examined the ability of insulin to interact with exogenous or endogenous kappa opioids to modulate feeding of palatable sucrose pellets by nondeprived rats. Insulin (5 mU intracerebroventricular (i.c.v.), t=-3h) completely reversed the ability of the exogenous kappa agonist U50,488 (26 microg, i.c.v., t=-15 min) to stimulate 90-min sucrose feeding (211+/-32% reduced to 125+/-23% of 90-min baseline intake). Further, i.c.v. insulin (5 mU, t=-3h) interacted with a subthreshold dose of the kappa receptor antagonist norbinaltorphimine (5 microg, i.c.v., t=-15 min) to decrease the 90-min sucrose intake baseline (77+/-11% versus 109+/-10% of 90 min baseline intake, insulin/norbinaltorphimine versus norbinaltorphimine). Together these studies provide new evidence that insulin in the CNS may decrease the action of CNS kappa opioid system(s) that mediate palatable feeding.

Orexins/hypocretins in the ob/ob mouse: hypothalamic gene expression, peptide content and metabolic effects

Orexins (forms A and B) belong to a new family of peptides that, as neuropeptide Y (NPY), stimulate food intake when centrally injected. The ob/ob mouse is a well-characterized model of hyperphagia and obesity associated with strong metabolic disturbances and a central dysregulation of peptides involved in the control of feeding. In the present report, we investigated the hypocretin (Hcrt)/orexin (OX) peptide pathway in lean and ob/ob mice. Prepro-Hcrt/OX mRNA expression, measured by in situ hybridization was restricted to the lateral hypothalamus area. It was significantly decreased in ob/ob mice (-18%; p<0.01). When estimated by real time RT-PCR in the whole hypothalamus, this decrease amounted to 65% (p<0.001). Hcrt-1/OX-A peptide concentrations, measured by RIA in microdissected hypothalamic nuclei were high in the lateral hypothalamus (LH) and lower in the arcuate (ARC) and paraventricular nuclei (PVN). In ob/ob mice, OX-A levels were significantly lower than in lean mice in the LH (-34%; p<0.02) and in the PVN (-72%; p<0.005). Acute intracerebroventricular injection of Hcrt-1/OX-A (1-10 nmol) stimulated feeding in lean, but not in ob/ob mice, whereas Hcrt-2/OX-B (1-10 nmol) had the opposite effect. Acute third ventricle (i3vt) injections of Hcrt/OX peptides in ob/ob mice transiently increased their metabolic rate and stimulated lipid substrate utilization. These findings provide direct evidence that Hcrt/OX peptides are down-regulated in the hypothalamus of ob/ob mice, contrary to the NPY system. The present data argues that Hcrt/OX peptides are not primarily responsible for the metabolic syndrome of the ob/ob mice. The diminution in the OX tone might participate in a counterregulatory system necessary to limit the adverse effects of NPY on food intake and body weight.

Neuropeptides and obesity

This review focuses on the expression, content, and release of neuropeptides and on their role in the development of obesity in animal models with single-gene mutations. The balance between neuropeptides that contribute to the control of feeding behavior is profoundly and variously altered in these models, supporting the concept of the existence of several types of obesity. The hypothalamic neuropeptide Y (NPY) and the pro-opiomelanocortin (POMC) systems are the networks most studied in relation to energy intake. Both receive information about the nutritional status and the level of energy storage through insulin and leptin signaling mediated by specific receptors located on POMC and NPY neurons present predominantly in the arcuate nucleus (ARC). When leptin signaling is defective, through a defect in either the receptor (Zucker fa/fa rat, cp/cp rat, and db/db mouse) or in the peptide itself (ob/ob mouse), the NPY system is upregulated as shown by mRNA overexpression and increased peptide release, whereas the content and/or release of some inhibitory peptides (neurotensin, cholecystokinin) are diminished. For the POMC system, there is a complex interaction between the tonic inhibition of food intake exerted by alpha-melanocyte-stimulating hormone (alpha-MSH) and the Agouti-related protein at the level of the type 4 melanocortin receptor. The latter peptide is coexpressed with NPY in the ARC. Corticotropin-releasing factor (CRF) is the link between food intake and environmental factors. It not only inhibits food intake and prevents weight gain, likely through hypothalamic effects, but also activates the hypothalamo-pituitary axis and therefore contributes to energy storage in adipose tissue. The factors that prod the CRF system toward the hypothalamic or hypothalamo-pituitary axis system remain to be more clearly defined (comodulators, connections between limbic system and ARC, cellular location, and type of receptors, etc. ). The pathways used by all of these neuromodulators include numerous brain areas, but some interest has returned to the classic ones such as the ventromedial and lateral hypothalamic areas because of the recent discovery of some peptides (orexins and melanin-concentrating hormone for the lateral hypothalamus) and receptors (CRF type 2 in the ventromedial hypothalamus). All of these pathways are redundant and function in a coordinated manner and sometimes by the novel expression of a peptide in an unusual area. The importance of such a phenomenon in obesity remains to be determined. Even if single-gene mutations are exceptions in human obesity, the study of genetic animal models of obesity has greatly contributed to the understanding of the regulation of feeding behavior and will allow researchers to develop new drug treatments for obesity that have to be associated with drastic changes in lifestyle (feeding, work habits, and physical activity) for a complete efficiency.

Differential effects of melanocortin peptides on ingestive behaviour in rats: evidence against the involvement of MC(3) receptor in the regulation of food intake

The pro-opiomelanocortin-derived peptides decrease food intake possibly via MC4 receptor. In this study we compared the effects of alpha-melanocyte-stimulating hormone (MSH), beta-MSH and gamma(1)-MSH (0.2, 1.0 and 5.0 microg, i.c.v.) on food intake. alpha-MSH and beta-MSH inhibited spontaneous food intake in a dose dependent manner, whereas the gamma(1)-MSH did not. alpha-MSH and beta-MSH but not gamma(1)-MSH (all 5.0 microg, i.c.v.) inhibited fasting-induced food intake about 50%. None of the three peptides inhibited fluid consumption in water-deprived (24 h) rats. It is suggested that MC(3) receptor, activated selectively by gamma(1)-MSH, is not involved in the regulation of food intake.

Hypothalamic beta-endorphin concentrations are decreased in animals models of autoimmune disease

Complex interactions between the neuroendocrine and the immune systems are present in autoimmune diseases. The central opioid peptide beta-endorphin (BE) has been shown to modulate peripheral immune responses in normal animals. In the present study we analyze the hypothalamic concentrations of this peptide in two models of spontaneous autoimmune disease, the MRL [corrected] lpr/lpr mouse, that develops a lupus-like autoimmune disease, and the obese strain (OS) chickens afflicted with spontaneous autoimmune thyroiditis. In both instances, hypothalamic concentrations of BE are significantly lower than normal controls. In MRL [corrected] lpr/lpr mice, BE is already lower at 1 month of age, when no clinical sign of the disease is yet present. Similarly, low levels of BE are observed in OS chickens before the onset of thyroiditis, i.e., already at the embryonic stage. Moreover, a further decrease of BE is observed in OS chickens in correspondence with the first signs of thyroid mononuclear infiltration. Considering the immunosuppressive effects exerted by central BE, these results are suggestive of the fact that in autoimmune disease prone animals the low hypothalamic concentrations may be one of several factors predisposing for the development of autoimmune disease.

Diet-induced enhancement of naloxone sensitivity is independent of changes in body weight

Intake of palatable solutions can enhance the anorectic potency of opioid antagonists. This experiment examined the relative contributions of orosensory experience and body weight gain to the enhanced anorectic potency of naloxone (0.125, 0.25, 0.5, and 1.0 mg/kg i.p.). Four groups of male hooded Lister rats (Charles River) were maintained on separate feeding regimes for 3 months. S-ADLIB rats were nondeprived with free access to lab chow and 20% (w/v) sucrose solution. S-RESTRICT rats received limited sucrose (50 ml/day) and chow (15 g/day) access, yoking their body weights to ADLIB rats receiving free access to lab chow only. RESTRICT rats received approx. 15 g of chow/day to maintain their body weights at 90% of the ADLIB rats. Fifteen-minute sucrose intake tests revealed marked differences between naloxone sensitivity of chronic sucrose drinkers and sucrose-naive groups. Intakes of S-ADLIB and S-RESTRICT were suppressed at all doses (max suppression >60%). In comparison to animals given sucrose, ADLIB and RESTRICT animals were significantly less sensitive (maximum suppression = 35%). Naloxone potency was independent of body weight differences. The data demonstrate that overconsumption of palatable ingesta, and not diet-induced weight gain, is sufficient to enhance antagonist potency. The study confirms that orosensory stimulation can induce plasticity in opioid systems, supporting an important role for opioids in intake regulation and general reward processes.

Food cravings, endogenous opioid peptides, and food intake: a review

Extensive research indicates a strong relationship between endogenous opioid peptides (EOPs) and food intake. In the present paper, we propose that food cravings act as an intervening variable in this opioid-ingestion link. Specifically, we argue that altered EOP activity may elicit food cravings which in turn may influence food consumption. Correlational support for this opioidergic theory of food cravings is provided by examining various clinical conditions (e.g. pregnancy, menstruation, bulimia, stress, depression) which are associated with altered EOP levels, intensified food cravings, and increased food intake.

Effects of streptozotocin-induced diabetes on prodynorphin-derived peptides in rat brain regions

Pharmacological studies suggest that diabetes produces changes in the brain opioid system, affecting several behavioral functions including analgesia, feeding and self-stimulation. Previous investigations of opioid receptor binding have failed to explain the unusual opioid pharmacology of the diabetic animal. In the present study, the effects of streptozotocin-induced diabetes on levels of three immunoreactive (ir)-prodynorphin-derived peptides, ir-dynorphin A1-17 (A1-17), ir-dynorphin A1-8 (A1-8) and ir-dynorphin B1-13 (B1-13), were determined in eleven brain regions known to be involved in appetite, taste and reward. Diabetes was found to increase levels of A1-17 in the ventromedial and dorsomedial hypothalamic nuclei (+60% and +25%, respectively) and levels of A1-8 in the dorsomedial and lateral hypothalamus (+45% and +35%, respectively). The possible significance of these results is discussed in relation to (i) diabetic hyperphagia, (ii) medial hypothalamic transduction of circulating insulin levels, and (iii) the potentiation of reward by metabolic need states.

Central administration of beta-endorphin increases food intake in goldfish: pretreatment with the opioid antagonist naloxone

The effect of intraperitoneal or intracerebroventricular beta-endorphin administration on food intake has been studied in satiated goldfish. Food intake was evaluated at different time intervals after injections, 0-2, 2-8 and 0-8 h. The 0.1 and 1 micrograms doses of beta-endorphin intracerebroventricularly administered induced an increase in food intake during the first 2 h postinjection, while no modifications on feeding were observed in the next 6 h. These same doses of beta-endorphin used increased cumulative food intake at 8 h postinjection. In contrast, intraperitoneal injection of 1 micrograms of beta-endorphin did not modify food intake in any of the studied time intervals. Naloxone, an opioid antagonist, attenuated the beta-endorphin-induced feeding increase. These results suggest that opioids may play a role in modulation of feeding central regulation, acting via opioid receptors in goldfish.

Effects of chronic food restriction on prodynorphin-derived peptides in rat brain regions

Chronic food restriction produces a variety of physiological and behavioral adaptations including a potentiation of the reinforcing effect of food, drugs and lateral hypothalamic electrical stimulation. Previous work in this laboratory has revealed that the lowering of self-stimulation threshold by food restriction is reduced by mu- and kappa-selective opioid antagonists. In the present study, the effect of chronic food restriction on levels of three prodynorphin-derived peptides, namely dynorphin A1-17 (A1-17), dynorphin A1-8 (A1-8) and dynorphin B1-13 (B1-13) were measured in eleven brain regions known to be involved in appetite, taste and reward. Food restriction increased levels of A1-17 in dorsal medial (+19.6%), ventral medial (+24.2%) and medial preoptic (+82.9%) hypothalamic areas. Levels of A1-17 decreased in the central nucleus of the amygdala (-35.1%). Food restriction increased levels of A1-8 in nucleus accumbens (+34.4%), bed nucleus of the stria terminalis (+24.5%) and lateral hypothalamus (+41.9%). Food restriction had no effect on levels of B1-13. A1-17 is highly kappa-preferring and the brain regions in which levels increased all have a high ratio of kappa: mu and delta receptors. A1-8 is less discriminating among opioid receptor types and the brain regions in which levels increased have a low ratio of kappa: mu and delta receptors. The present results suggest that food restriction alters posttranslational processing within the dynorphin A domain of the prodynorphin precursor, possibly leading to a change in the balance between kappa and non-kappa opioid receptor stimulation in specific brain regions.

Equine pituitary adenoma: a functional and morphological study

Clinico-pathological correlations in horses with pituitary adenomas are poorly understood. This paper describes the functional and morphological features of five cases of equine pituitary adenoma and of a case of multinodular pituitary hyperplasia. New findings reported include immunoreactivity for beta-lipotropin (beta-LPH), beta-melanocyte-stimulating hormone (beta-MSH), gamma 3-MSH, prolactin (PRL), and follicle-stimulating hormone (FSH) in neoplastic cells of the pituitary adenoma; and, in the multinodular hyperplasia, beta-LPH, beta-endorphin (beta-END), alpha-MSH, beta-MSH, gamma 3-MSH and FSH immunoreactivity. It is suggested that the equine pituitary syndrome does not correspond to human Cushing's disease, as generally accepted, but is related to the overproduction of several pro-opiomelanocortin (POMC)-derived peptides by the cells of the tumour or hyperplastic nodules.

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on plasma and tissue beta-endorphin-like immunoreactivity in the most TCDD-susceptible and the most TCDD-resistant rat strain

The salient sign of acutely lethal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) intoxication in rats is hypophagia along with a prominent body weight loss. Endogenous opioid peptides have been implicated as modulators of food intake. In the present study, female rats of both the most TCDD-susceptible (Long-Evans [L-E]; LD50 9.8 micrograms/kg) and the most TCDD-resistant strain (Han/Wistar [H/W]; LD50 > 7200 micrograms/kg) were exposed to a single dose of 50 micrograms/kg TCDD ip. This treatment is usually lethal within 1-6 weeks to all L-E rats and nonlethal to all H/W rats. The animals were killed at 1, 4 or 10 days after the treatment. beta-Endorphin-like immunoreactivity (beta-END-LI) was determined by a validated RIA method in the hypothalamus, pituitary, pancreas, duodenum and plasma. TCDD decreased plasma beta-END-LI concentration by 24-37% at every time point of measurement in L-E rats alone. By contrast, feed-restricted controls exhibited an increase of similar magnitude on day 4. Pancreatic beta-END-LI was also elevated in feed-restricted controls at that time point as compared with either the ad libitum control or TCDD group. TCDD appeared to shrink the pituitary gland in both strains by day 4. Pituitary weight was similarly lowered in TCDD-treated rats and feed-restricted controls at the last time point and this reduction was reflected in pituitary beta-END-LI content. Thus, TCDD affects selectively plasma beta-END-LI levels and this impact correlates with its lethality in these strains.

Endogenous opiates: 1991

This paper is the fourteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1991 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.