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Bodnar RJ. Endogenous opioid modulation of food intake and body weight: Implications for opioid influences upon motivation and addiction. Peptides 2019; 116:42-62. [PMID: 31047940 DOI: 10.1016/j.peptides.2019.04.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 03/04/2019] [Accepted: 04/08/2019] [Indexed: 12/12/2022]
Abstract
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.
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology, Queens College, City University of New York, United States; Psychology Doctoral Program and CUNY Neuroscience Collaborative, The Graduate Center of the City University of New York, United States.
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O'Dell LE, Nazarian A. Enhanced vulnerability to tobacco use in persons with diabetes: A behavioral and neurobiological framework. Prog Neuropsychopharmacol Biol Psychiatry 2016; 65:288-96. [PMID: 26092247 DOI: 10.1016/j.pnpbp.2015.06.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Revised: 05/15/2015] [Accepted: 06/08/2015] [Indexed: 11/18/2022]
Abstract
Tobacco use significantly magnifies the negative health complications associated with diabetes. Although tobacco use is strongly discouraged in persons with diabetes, clinical evidence suggests that they often continue to smoke and have more difficulty quitting despite serious contraindications. Here, we suggest that a potential reason for enhanced vulnerability to tobacco use in persons with diabetes is greater rewarding effects of nicotine. This review summarizes pre-clinical evidence indicating that the rewarding effects of nicotine are enhanced in rodent models of type 1 and type 2 diabetes. We also provide a framework of neurobiological mechanisms that are posited to promote tobacco use in persons with diabetes. This framework suggests that diabetes induces a disruption in insulin signaling that leads to a suppression of dopamine systems in the mesolimbic reward pathway. Lastly, we consider the clinical implications of enhanced rewarding effects of nicotine that may promote tobacco use in persons with diabetes. The clinical efficacy of smoking cessation medications that enhance dopamine are important to consider, given that persons with diabetes may display disrupted dopaminergic mechanisms. Future work is needed to better understand the complex interaction of dopamine and insulin in order to develop better smoking cessation medications for persons with diabetes.
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Affiliation(s)
- Laura E O'Dell
- Department of Psychology, University of Texas at El Paso, 500 West University Avenue, El Paso, TX 79968, USA
| | - Arbi Nazarian
- Department of Pharmaceutical Sciences, Western University of Health Sciences, 309 East Second Street, Pomona, CA 91766, USA.
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O'Dell LE, Natividad LA, Pipkin JA, Roman F, Torres I, Jurado J, Torres OV, Friedman TC, Tenayuca JM, Nazarian A. Enhanced nicotine self-administration and suppressed dopaminergic systems in a rat model of diabetes. Addict Biol 2014; 19:1006-19. [PMID: 23834715 DOI: 10.1111/adb.12074] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Patients with diabetes display a heightened propensity to use tobacco; however, it is unclear whether they experience enhanced rewarding effects of nicotine. Thus, this study examined the reinforcing effects of nicotine in a rodent model of diabetes involving administration of streptozotocin (STZ), a drug that is toxic to pancreatic insulin-producing cells. The first study compared STZ- and vehicle-treated rats that had 23-hour access to intravenous self-administration (IVSA) of nicotine or saline and concomitant access to food and water. In order to examine the contribution of dopamine to our behavioral effects, dopamine transporter (DAT), D1 and D2 receptor levels were compared in the nucleus accumbens (NAc) following 10 days of nicotine or saline IVSA. Dopamine levels in the NAc were also compared following nicotine administration. Lastly, nicotine metabolism and dose-dependent effects of nicotine IVSA were assessed. The results revealed that STZ-treated rats displayed enhanced nicotine intake and a robust increase in food and water intake relative to controls. Protein analysis revealed an increase in DAT and a decrease in D1 receptor levels in the NAc of STZ- versus vehicle-treated rats regardless of IVSA condition. STZ-treated rats also displayed suppressed NAc dopamine levels during baseline and in response to nicotine. STZ treatment did not alter our assessment of nicotine metabolism. Furthermore, STZ treatment increased nicotine IVSA in a dose-dependent manner. Our findings suggest that STZ-treatment increased the rewarding effects of nicotine. This suggests that strong reinforcing effects of nicotine may contribute to greater tobacco use in patients with diabetes.
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Affiliation(s)
- Laura E. O'Dell
- Department of Psychology; University of Texas at El Paso; El Paso TX USA
| | - Luis A. Natividad
- Department of Psychology; University of Texas at El Paso; El Paso TX USA
| | - Joseph A. Pipkin
- Department of Psychology; University of Texas at El Paso; El Paso TX USA
| | - Francisco Roman
- Department of Psychology; University of Texas at El Paso; El Paso TX USA
| | - Ivan Torres
- Department of Psychology; University of Texas at El Paso; El Paso TX USA
| | - Jesus Jurado
- Department of Psychology; University of Texas at El Paso; El Paso TX USA
| | - Oscar V. Torres
- Department of Psychology; University of Texas at El Paso; El Paso TX USA
| | - Theodore C. Friedman
- Division of Endocrinology, Molecular Medicine and Metabolism; Department of Internal Medicine; Charles Drew University of Medicine and Sciences-UCLA School of Medicine; Los Angeles CA USA
| | - John M. Tenayuca
- Department of Pharmaceutical Sciences; Western University of Health Sciences; Pomona CA USA
| | - Arbi Nazarian
- Department of Pharmaceutical Sciences; Western University of Health Sciences; Pomona CA USA
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Figlewicz DP, Sipols AJ. Energy regulatory signals and food reward. Pharmacol Biochem Behav 2010; 97:15-24. [PMID: 20230849 PMCID: PMC2897918 DOI: 10.1016/j.pbb.2010.03.002] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 02/26/2010] [Accepted: 03/09/2010] [Indexed: 12/23/2022]
Abstract
The hormones insulin, leptin, and ghrelin have been demonstrated to act in the central nervous system (CNS) as regulators of energy homeostasis, acting at medial hypothalamic sites. Here, we summarize research demonstrating that, in addition to direct homeostatic actions at the hypothalamus, CNS circuitry that subserves reward and is also a direct and indirect target for the action of these endocrine regulators of energy homeostasis. Specifically, insulin and leptin can decrease food reward behaviors and modulate the function of neurotransmitter systems and neural circuitry that mediate food reward, the midbrain dopamine (DA) and opioidergic pathways. Ghrelin can increase food reward behaviors, and support midbrain DA neuronal function. We summarize discussion of behavioral, systems, and cellular evidence in support of the contributions of reward circuitry to the homeostatic roles of these hormones in the CNS. The understanding of neuroendocrine modulation of food reward, as well as food reward modulation by diet and obesity, may point to new directions for therapeutic approaches to overeating or eating disorders.
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Affiliation(s)
- Dianne P Figlewicz
- Metabolism/Endocrinology, VA Puget Sound Health Care System, Seattle Division, Seattle, WA 98108, USA.
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Abstract
The hormones insulin, leptin, and ghrelin have been demonstrated to act in the central nervous system (CNS) as regulators of energy homeostasis, acting at medial hypothalamic sites. Here, we summarize research demonstrating that, in addition to direct homeostatic actions at the hypothalamus, CNS circuitry that subserves reward and is also a direct and indirect target for the action of these endocrine regulators of energy homeostasis. Specifically, insulin and leptin can decrease food reward behaviors and modulate the function of neurotransmitter systems and neural circuitry that mediate food reward, the midbrain dopamine (DA) and opioidergic pathways. Ghrelin can increase food reward behaviors, and support midbrain DA neuronal function. We summarize discussion of behavioral, systems, and cellular evidence in support of the contributions of reward circuitry to the homeostatic roles of these hormones in the CNS. The understanding of neuroendocrine modulation of food reward, as well as food reward modulation by diet and obesity, may point to new directions for therapeutic approaches to overeating or eating disorders.
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Vuong C, Van Uum SHM, O'Dell LE, Lutfy K, Friedman TC. The effects of opioids and opioid analogs on animal and human endocrine systems. Endocr Rev 2010; 31:98-132. [PMID: 19903933 PMCID: PMC2852206 DOI: 10.1210/er.2009-0009] [Citation(s) in RCA: 345] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Accepted: 10/02/2009] [Indexed: 02/07/2023]
Abstract
Opioid abuse has increased in the last decade, primarily as a result of increased access to prescription opioids. Physicians are also increasingly administering opioid analgesics for noncancer chronic pain. Thus, knowledge of the long-term consequences of opioid use/abuse has important implications for fully evaluating the clinical usefulness of opioid medications. Many studies have examined the effect of opioids on the endocrine system; however, a systematic review of the endocrine actions of opioids in both humans and animals has, to our knowledge, not been published since 1984. Thus, we reviewed the literature on the effect of opioids on the endocrine system. We included both acute and chronic effects of opioids, with the majority of the studies done on the acute effects although chronic effects are more physiologically relevant. In humans and laboratory animals, opioids generally increase GH and prolactin and decrease LH, testosterone, estradiol, and oxytocin. In humans, opioids increase TSH, whereas in rodents, TSH is decreased. In both rodents and humans, the reports of effects of opioids on arginine vasopressin and ACTH are conflicting. Opioids act preferentially at different receptor sites leading to stimulatory or inhibitory effects on hormone release. Increasing opioid abuse primarily leads to hypogonadism but may also affect the secretion of other pituitary hormones. The potential consequences of hypogonadism include decreased libido and erectile dysfunction in men, oligomenorrhea or amenorrhea in women, and bone loss or infertility in both sexes. Opioids may increase or decrease food intake, depending on the type of opioid and the duration of action. Additionally, opioids may act through the sympathetic nervous system to cause hyperglycemia and impaired insulin secretion. In this review, recent information regarding endocrine disorders among opioid abusers is presented.
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Affiliation(s)
- Cassidy Vuong
- Division of Endocrinology, Charles Drew University of Medicine & Sciences, 1731 East 120th Street, Los Angeles, California 90059, USA
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Hadjimarkou MM, Abbadie C, Kasselman LJ, Pan YX, Pasternak GW, Bodnar RJ. Changes in mouse mu opioid receptor Exon 7/8-like immunoreactivity following food restriction and food deprivation in rats. Synapse 2009; 63:585-97. [PMID: 19301417 DOI: 10.1002/syn.20639] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Opioid agonists and antagonists respectively increase and decrease food intake. That selective mu opioid antagonists are more effective than antisense probes directed against the mu opioid receptor (MOR-1) gene in reducing deprivation-induced feeding suggests a role for isoforms. Both food restriction and deprivation alter protein and mRNA levels of opioid peptides and receptors. Antisera directed against Exon 4 of the MOR-1-like immunoreactivity (LI) (Exon 4) clone or directed against mouse Exons 7/8 (mE7/8-LI) revealed high levels of immunoreactivity in brain nuclei related to feeding behavior. Therefore, the present study assessed MOR-1LI and mE7/8-LI in hypothalamic and extrahypothalamic sites in rats exposed to ad libitum feeding, food restriction (2, 7, 14 days), or food deprivation (24, 48 h). MOR-1-LI displayed robust reactivity, but was insensitive to food restriction or deprivation. mE7/8-LI, both in terms of cell counts and relative optical density, was significantly and selectively increased in the dorsal and ventral parvocellular subdivisions of the hypothalamic paraventricular nucleus in food-restricted (14 days) rats, but all other restriction or deprivation regimens were ineffective in other hypothalamic nuclei. In contrast, significant and site-specific decreases in relative optical density in the rostral part of the nucleus tractus solitarius (NTS) were observed in food-restricted (2, 7 days) or food-deprived (24, 48 h) animals, but these regimens were ineffective in the other extrahypothalamic sites. This study indicates the sensitivity of this mE7/8-LI probe in the hypothalamic parvocellular paraventricular nucleus and rostral NTS to food restriction and deprivation in rats.
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Affiliation(s)
- Maria M Hadjimarkou
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, New York 11367, USA
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Nozaki C, Saitoh A, Kamei J. Characterization of the antinociceptive effects of oxycodone in diabetic mice. Eur J Pharmacol 2006; 535:145-51. [PMID: 16533506 DOI: 10.1016/j.ejphar.2006.02.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Revised: 02/03/2006] [Accepted: 02/06/2006] [Indexed: 11/21/2022]
Abstract
We investigated the antinociceptive efficacy of systemic and centrally injected oxycodone on thermal hyperalgesia in streptozotocin-induced diabetic mice. The antinociceptive response was assessed by recording the latency in the tail-flick test using the radiant heat from a 50-W projection bulb on the tail. The tail-flick latency in diabetic mice was significantly shorter than that in non-diabetic mice. Oral (p.o.) and i.t., but not i.c.v., administration of oxycodone prolonged the tail-flick latency in diabetic mice to a level that was considerably longer than the baseline latency in non-diabetic mice. However, morphine did not significantly inhibit the tail-flick response in diabetic mice. The antinociceptive effect of either p.o. or i.t. oxycodone in non-diabetic mice, but not in diabetic mice, was antagonized by pretreatment with a selective mu-opioid receptor antagonist, beta-funaltrexamine. In non-diabetic mice, pretreatment with a selective kappa-opioid receptor antagonist, nor-binaltorphimine, had no effect on the peak antinociceptive effect of either p.o. or i.t. oxycodone at 30 min after administration, however, it slightly but significantly reduced oxycodone-induced antinociception at 60 and 90 min after administration. On the other hand, pretreatment with nor-binaltorphimine practically abolished the antinociceptive effects of both p.o.- and i.t.-administered oxycodone in diabetic mice. Naltrindole, a selective delta-opioid receptor antagonist, had no effects on the antinociceptive effect of oxycodone in either non-diabetic or diabetic mice. These results suggest that the antinociceptive effects of oxycodone may be mediated by spinal kappa-opioid receptors in diabetic mice, whereas it may interact primarily with supraspinal and spinal mu-opioid receptors in non-diabetic mice.
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MESH Headings
- Analgesics, Opioid/administration & dosage
- Analgesics, Opioid/pharmacokinetics
- Analgesics, Opioid/pharmacology
- Animals
- Area Under Curve
- Diabetes Mellitus, Experimental/chemically induced
- Diabetes Mellitus, Experimental/metabolism
- Diabetes Mellitus, Experimental/physiopathology
- Injections, Intraventricular
- Injections, Spinal
- Injections, Subcutaneous
- Mice
- Mice, Inbred ICR
- Naltrexone/administration & dosage
- Naltrexone/analogs & derivatives
- Naltrexone/pharmacokinetics
- Naltrexone/pharmacology
- Narcotic Antagonists/administration & dosage
- Narcotic Antagonists/pharmacokinetics
- Narcotic Antagonists/pharmacology
- Oxycodone/administration & dosage
- Oxycodone/pharmacokinetics
- Oxycodone/pharmacology
- Pain/physiopathology
- Pain/prevention & control
- Pain Measurement/methods
- Streptozocin
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Affiliation(s)
- Chihiro Nozaki
- Department of Pathophysiology and Therapeutics, School of Pharmacy and Pharmaceutical Sciences, Hoshi University, 4-41, Shinagawa-ku, Tokyo 142-8501, Japan
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Bodnar RJ. Endogenous opioids and feeding behavior: a 30-year historical perspective. Peptides 2004; 25:697-725. [PMID: 15165728 DOI: 10.1016/j.peptides.2004.01.006] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2004] [Revised: 01/15/2004] [Accepted: 01/16/2004] [Indexed: 11/25/2022]
Abstract
This invited review, based on the receipt of the Third Gayle A. Olson and Richard D. Olson Prize for the publication of the outstanding behavioral article published in the journal Peptides in 2002, examines the 30-year historical perspective of the role of the endogenous opioid system in feeding behavior. The review focuses on the advances that this field has made over the past 30 years as a result of the timely discoveries that were made concerning this important neuropeptide system, and how these discoveries were quickly applied to the analysis of feeding behavior and attendant homeostatic processes. The discoveries of the opioid receptors and opioid peptides, and the establishment of their relevance to feeding behavior were pivotal in studies performed in the 1970s. The 1980s were characterized by the establishment of opioid receptor subtype agonists and antagonists and their relevance to the modulation of feeding behavior as well as by the use of general opioid antagonists in demonstrating the wide array of ingestive situations and paradigms involving the endogenous opioid system. The more recent work from the 1990s to the present, utilizes the advantages created by the cloning of the opioid receptor genes, the development of knockout and knockdown techniques, the systematic utilization of a systems neuroscience approach, and establishment of the reciprocity of how manipulations of opioid peptides and receptors affect feeding behavior with how feeding states affect levels of opioid peptides and receptors. The role of G-protein effector systems in opioid-mediated feeding responses, which was the subject of the prize-winning article, is then reviewed.
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Subprogram, Queens College, City University of New York, 65-30 Kissena Blvd., Flushing, NY 11367, USA.
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Hadjimarkou MM, Khaimova E, Pan YX, Rossi GC, Pasternak GW, Bodnar RJ. Feeding induced by food deprivation is differentially reduced by opioid receptor antisense oligodeoxynucleotide probes in rats. Brain Res 2003; 987:223-32. [PMID: 14499967 DOI: 10.1016/s0006-8993(03)03342-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The increases in food intake following 24 h of food deprivation are reduced by systemic and central administration of general opioid antagonists. The use of selective opioid antagonists revealed that mu-selective antagonists were more effective than kappa-selective antagonists in reducing deprivation-induced intake, whereas delta-selective antagonists were minimally effective. Antisense oligodeoxynucleotide (AS ODN) probes directed against different exons of the mu (MOP), delta (DOP), kappa (KOP) and nociceptin (NOP) opioid peptide receptor genes have been able to differentially alter feeding responses elicited by glucoprivation, lipoprivation and by different opioid peptides and receptor agonists. The present study examined whether lateral ventricular administration of AS ODN probes directed against different exons of the MOP, DOP, KOP or NOP opioid receptor genes altered food intake and body weight changes following 24 h of food deprivation in rats. Deprivation-induced feeding was significantly and maximally reduced by an AS ODN probe directed against exon 2, but not exons 1 or 3 of the KOP gene. This response was also significantly though modestly reduced by AS ODN probes directed against exons 2, 3 or 4 of the MOP gene, exon 1 of the DOP gene, or exon 1 of the NOP gene. Recovery of body weight following postdeprivation food reintroduction was significantly reduced by AS ODN probes directed against either exons 2, 3 or 4 of the MOP gene, exons 1 or 2 of the DOP gene, or exons 1, 2 or 3 of the KOP gene. The parallel patterns in the magnitude of alterations in deprivation-induced feeding by delta antagonists and DOP AS ODN probes on one hand, and by kappa antagonists and KOP AS ODN probes on the other, provide converging and complementary evidence for their relative involvement in this response. The modest reductions by MOP AS ODN probes relative to the more potent reductions induced by mu-selective antagonists suggest that the mu receptor-mediated actions upon deprivation-induced feeding may involve recently-identified splice variants or isoforms of the MOP gene.
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Affiliation(s)
- M M Hadjimarkou
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, 65-30 Kissena Blvd., Flushing, NY 11367, USA
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Carr KD, Kim G, Cabeza de Vaca S. Hypoinsulinemia may mediate the lowering of self-stimulation thresholds by food restriction and streptozotocin-induced diabetes. Brain Res 2000; 863:160-8. [PMID: 10773204 DOI: 10.1016/s0006-8993(00)02143-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
7 days beyond cessation of insulin treatment) elevation of threshold in ad libitum fed rats and, more transiently, reversed the threshold-lowering effect of food restriction. Acute insulin treatment (3 mU, 15 min prior) also elevated threshold in food-restricted rats. These results are consistent with the hypothesis that insulin modulates sensitivity of a brain reward system and that hypoinsulinemia may be the common factor in food restriction and diabetes that accounts for the enhancement of perifornical LHSS.
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Affiliation(s)
- K D Carr
- Millhauser Laboratories, Department of Psychiatry, New York University, School of Medicine, 550 First Avenue, New York, NY, USA.
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Park TH, Carr KD. Neuroanatomical patterns of fos-like immunoreactivity induced by a palatable meal and meal-paired environment in saline- and naltrexone-treated rats. Brain Res 1998; 805:169-80. [PMID: 9733960 DOI: 10.1016/s0006-8993(98)00719-7] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Opioid antagonists block the positive hedonic response to food taste and are potent inhibitors of palatability-driven feeding. However, the specific brain regions within which opioid peptide secretion contributes to the maintenance of palatability-driven feeding have not been clearly established. In the present study, c-Fos immunohistochemistry was used to identify regions rostral to the hindbrain that display cellular activation in response to a palatable meal and the meal-paired environment. Further, it was determined whether any of the cellular responses could be prevented by pretreating animals with naltrexone. Twenty brain regions known to be involved in gustation, appetite and reward functions were examined. Ingestion of the palatable meal (3.0 g of 30% shortening, 20% sucrose and 50% powdered Purina rat chow) increased Fos-like immunoreactivity (FLI) in lateral hypothalamus (LH), ventral tegmentum (VTA) and medial preoptic area (MPOA), and decreased FLI in the habenula (Hab). The meal-paired environment increased FLI in the VTA and nucleus accumbens shell (NAC shell). Naltrexone (1.0 mg/kg, i.p.) did not block consumption of the small meal but did prevent all of the distinctive increases in FLI induced by the meal and meal-paired environment. Since naltrexone, alone, increased FLI in VTA, NAC shell, central amygdala (ceA) and laterodorsal bed nucleus of the stria terminalis (BSTLD), the blunting of ingestion reward by naltrexone may result from direct or transsynaptic activating effects on opponent neuronal activity within this highly interconnected set of structures that mediate and modulate reward.
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Affiliation(s)
- T H Park
- Millhauser Laboratories, Department of Psychiatry, New York University, Medical Center, 550 First Avenue, New York, NY 10016, USA
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Malcangio M, Tomlinson DR. A pharmacologic analysis of mechanical hyperalgesia in streptozotocin/diabetic rats. Pain 1998; 76:151-7. [PMID: 9696468 DOI: 10.1016/s0304-3959(98)00037-2] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
This study used streptozotocin (STZ; 50 mg/kg i.p.) diabetic rats and monitored weekly thermal and mechanical nociceptive thresholds for 8 weeks diabetes. Rats developed mechanical hyperalgesia as soon as 2 weeks after STZ injection. Thermal nociceptive threshold was not altered up to 8 weeks after STZ injection. Four week-diabetic rat mechanical hyperalgesia showed reduced sensitivity to the antinociceptive effect of morphine (5-20 mg/kg i.p.). Furthermore, a reduced sensitivity to the antinociceptive effect of the GABA(B) agonist, (+/-)baclofen, was observed. A dose as high as 16 mg/kg i.p. of (+/-)baclofen was necessary to reverse 4 week-diabetic rat hyperalgesia, whereas in control rats the highest antinociceptive dose devoid of muscle-relaxant effect was 4 mg/kg i.p. The non-peptide antagonist for the substance P, neurokinin, (NK1) receptor, RP 67580 (3-9 mg/kg i.p.) was not effective in reversing the mechanical hyperalgesia associated with 4 week-diabetes. A six day-treatment with an antagonist for the N-methyl-D-aspartate (NMDA) receptor for glutamate, (+)MK-801 (0.1 mg/kg i.p. twice a day), gradually but completely reversed 4 week-diabetes-induced mechanical hyperalgesia. These data suggest that diabetes-induced hyperalgesia may be the consequence of increased activity of primary afferent fibres leading to an increased excitatory tone within the spinal cord. An increased release of glutamate and activation of the NMDA receptor, would maintain the hyperalgesic state. Reduced activity of both opioidergic and GABA(B)ergic inhibitory systems, might exacerbate the increased excitation thus contributing to the ongoing pain. It is suggested that NMDA receptor antagonists may constitute an alternative therapy for diabetic neuropathic pain.
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Affiliation(s)
- M Malcangio
- Department of Pharmacology, St. Bartholomew's and the Royal London School of Medicine and Dentistry, Queen Mary and Westfield College, UK.
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