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Alam MR, Singh S. Neuromodulation in Parkinson's disease targeting opioid and cannabinoid receptors, understanding the role of NLRP3 pathway: a novel therapeutic approach. Inflammopharmacology 2023:10.1007/s10787-023-01259-0. [PMID: 37318694 DOI: 10.1007/s10787-023-01259-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Accepted: 05/26/2023] [Indexed: 06/16/2023]
Abstract
Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta, resulting in motor and non-motor symptoms. Although levodopa is the primary medication for PD, its long-term use is associated with complications such as dyskinesia and drug resistance, necessitating novel therapeutic approaches. Recent research has highlighted the potential of targeting opioid and cannabinoid receptors as innovative strategies for PD treatment. Modulating opioid transmission, particularly through activating µ (MOR) and δ (DOR) receptors while inhibiting κ (KOR) receptors, shows promise in preventing motor complications and reducing L-DOPA-induced dyskinesia. Opioids also possess neuroprotective properties and play a role in neuroprotection and seizure control. Similar to this, endocannabinoid signalling via CB1 and CB2 receptors influences the basal ganglia and may contribute to PD pathophysiology, making it a potential therapeutic target. In addition to opioid and cannabinoid receptor targeting, the NLRP3 pathway, implicated in neuroinflammation and neurodegeneration, emerges as another potential therapeutic avenue for PD. Recent studies suggest that targeting this pathway holds promise as a therapeutic strategy for PD management. This comprehensive review focuses on neuromodulation and novel therapeutic approaches for PD, specifically highlighting the targeting of opioid and cannabinoid receptors and the NLRP3 pathway. A better understanding of these mechanisms has the potential to enhance the quality of life for PD patients.
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Affiliation(s)
- Md Reyaz Alam
- Neuropharmacology Division, Department of Pharmacology, ISF College of Pharmacy, Moga, Punjab, 142001, India
| | - Shamsher Singh
- Neuropharmacology Division, Department of Pharmacology, ISF College of Pharmacy, Moga, Punjab, 142001, India.
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Leyrer-Jackson JM, Hood LE, Olive MF. Sex differences and the lack of effects of chemogenetic manipulation of pro-opiomelanocortin (POMC) neurons on alcohol consumption in male and female mice. Brain Res 2022; 1786:147901. [PMID: 35367433 DOI: 10.1016/j.brainres.2022.147901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 03/02/2022] [Accepted: 03/29/2022] [Indexed: 11/17/2022]
Abstract
The endogenous opioid system has been implicated in the rewarding and reinforcing effects of alcohol. Pro-opiomelanocortin (POMC) neurons located within the arcuate nucleus of the hypothalamus (ArcN) secrete multiple peptides associated with alcohol consumption, including β-endorphin (β-END), α-melanocyte stimulating hormone (α-MSH), and adrenocorticotropic hormone (ACTH). In this study, we utilized chemogenetics to bidirectionally modulate ArcN POMC neurons to determine their role in alcohol and saccharin consumption and regional levels of POMC-derived peptides. Male and female POMC-cre mice were infused with viral vectors designed for cre-dependent expression of either excitatory and inhibitory DREADDs or a control vector into the ArcN. Following recovery, animals were allowed to consume alcohol or saccharin using the drinking-in-the-dark (DID) paradigm of binge-like intake for 4 consecutive days. Prior to the final test session, animals were injected with clozapine-N-oxide (2.5 mg/kg, i.p.) for DREADD activation. Following the last DID session, animals were euthanized and the ArcN, VTA, amygdala and NAc were dissected and assessed for POMC peptide expression utilizing western blotting. We found that female mice consumed more alcohol than males during DID sessions 2-4, and that chemogenetic activation had no effect on alcohol or saccharin consumption in either sex. We found that β-END expression within the ArcN positively correlated with alcohol consumption. Given the molecular and functional heterogeneity of ArcN POMC neurons, future studies are needed to assess the effects of modulation of specific subpopulations of these neurons within the ArcN on consumption of rewarding substances such as alcohol and saccharin.
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Affiliation(s)
| | - Lauren E Hood
- Department of Psychology, Arizona State University, Tempe, AZ 85281, USA
| | - M Foster Olive
- Department of Psychology, Arizona State University, Tempe, AZ 85281, USA
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Hood LE, Nagy EK, Leyrer‐Jackson JM, Olive MF. Ethanol consumption activates a subset of arcuate nucleus pro‐opiomelanocortin (POMC)‐producing neurons: a c‐fos immunohistochemistry study. Physiol Rep 2022; 10:e15231. [PMID: 35312178 PMCID: PMC8935532 DOI: 10.14814/phy2.15231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Revised: 02/21/2022] [Accepted: 02/28/2022] [Indexed: 11/24/2022] Open
Affiliation(s)
- Lauren E. Hood
- Department of Psychology Arizona State University Tempe Arizona 85281 USA
| | - Erin K. Nagy
- Department of Psychology Arizona State University Tempe Arizona 85281 USA
| | | | - M. Foster Olive
- Department of Psychology Arizona State University Tempe Arizona 85281 USA
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Leyrer-Jackson JM, Hood LE, Olive MF. Alcohol consumption preferentially activates a subset of pro-opiomelanocortin (POMC) producing neurons targeting the amygdala. Neuropharmacology 2021; 195:108674. [PMID: 34153315 DOI: 10.1016/j.neuropharm.2021.108674] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 05/26/2021] [Accepted: 06/12/2021] [Indexed: 12/22/2022]
Abstract
BACKGROUND Alcohol abuse is a worldwide public health concern and leads to an estimated 90,000 alcohol-related deaths in the United States annually. Alcohol may promote its euphoric and motivational effects, in part, by activating the endogenous opioid system. Pro-opiomelanocortin (POMC) producing neurons located within the arcuate nucleus (ArcN) of the hypothalamus make up one circuit of the endogenous opioid system, and heavily projects to reward-related brain areas such as the amygdala, nucleus accumbens (NAc) and ventral tegmental area (VTA). POMC producing neurons release β-endorphin and other peptides that target opioid receptors within reward areas to elicit their associated rewarding effects. Here we explore ArcN POMC neuronal activation, as assessed via FosB expression, following alcohol consumption to determine whether activation varied within subsets of ArcN POMC projection neurons targeting different reward-related areas. METHODS Fluorescent retrobeads were used to label ArcN POMC projection neurons targeting the NAc, amygdala and VTA in POMC-cre mice expressing the reporter tdTomato. Animals (n = 57) were then allowed to voluntarily consume alcohol or water using the drinking-in-the-dark (DID) paradigm, and sacrificed for immunohistochemistry to examine FosB expression within ArcN POMC neurons. RESULTS Female mice displayed escalation of alcohol intake across DID sessions, whereas males did not. A greater percent of ArcN POMC neurons target the amygdala over the NAc and VTA, and alcohol consumption preferentially activated ArcN POMC neurons targeting the amygdala over other areas. CONCLUSION These findings highlight a novel aspect alcohol-induced activation of the endogenous opioid system, whereby alcohol activates a specific subpopulation of ArcN POMC producing neurons that project primarily to the amygdala.
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Affiliation(s)
| | - Lauren E Hood
- Department of Psychology, Arizona State University, Tempe, AZ, 85281, USA
| | - M Foster Olive
- Department of Psychology, Arizona State University, Tempe, AZ, 85281, USA
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Nam MH, Han KS, Lee J, Won W, Koh W, Bae JY, Woo J, Kim J, Kwong E, Choi TY, Chun H, Lee SE, Kim SB, Park KD, Choi SY, Bae YC, Lee CJ. Activation of Astrocytic μ-Opioid Receptor Causes Conditioned Place Preference. Cell Rep 2020; 28:1154-1166.e5. [PMID: 31365861 DOI: 10.1016/j.celrep.2019.06.071] [Citation(s) in RCA: 63] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Revised: 05/22/2019] [Accepted: 06/20/2019] [Indexed: 11/19/2022] Open
Abstract
The underlying mechanisms of how positive emotional valence (e.g., pleasure) causes preference of an associated context is poorly understood. Here, we show that activation of astrocytic μ-opioid receptor (MOR) drives conditioned place preference (CPP) by means of specific modulation of astrocytic MOR, an exemplar endogenous Gi protein-coupled receptor (Gi-GPCR), in the CA1 hippocampus. Long-term potentiation (LTP) induced by a subthreshold stimulation with the activation of astrocytic MOR at the Schaffer collateral pathway accounts for the memory acquisition to induce CPP. This astrocytic MOR-mediated LTP induction is dependent on astrocytic glutamate released upon activation of the astrocytic MOR and the consequent activation of the presynaptic mGluR1. The astrocytic MOR-dependent LTP and CPP were recapitulated by a chemogenetic activation of astrocyte-specifically expressed Gi-DREADD hM4Di. Our study reveals that the transduction of inhibitory Gi-signaling into augmented excitatory synaptic transmission through astrocytic glutamate is critical for the acquisition of contextual memory for CPP.
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MESH Headings
- Animals
- Astrocytes/metabolism
- CA1 Region, Hippocampal/metabolism
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Memory
- Mice
- Mice, Knockout
- Receptors, Metabotropic Glutamate/genetics
- Receptors, Metabotropic Glutamate/metabolism
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/metabolism
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Affiliation(s)
- Min-Ho Nam
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea; Department of Science in Korean Medicine, Graduate School, Kyung Hee University, Seoul 02447, Korea
| | - Kyung-Seok Han
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea; Department of Neuroscience, Division of Bio-Medical Science & Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Korea
| | - Jaekwang Lee
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - Woojin Won
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea; KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Korea; Center for Cognition and Sociality, Institute for Basic Science, Daejeon 34126, Korea
| | - Wuhyun Koh
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea; Department of Neuroscience, Division of Bio-Medical Science & Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Korea; Center for Cognition and Sociality, Institute for Basic Science, Daejeon 34126, Korea
| | - Jin Young Bae
- Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 41940, Korea
| | - Junsung Woo
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea; Department of Neuroscience, Division of Bio-Medical Science & Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Korea
| | - Jayoung Kim
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - Elliot Kwong
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - Tae-Yong Choi
- Department of Physiology and Dental Research Institute, Seoul National University School of Dentistry, Seoul 03080, Korea
| | - Heejung Chun
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea; Center for Cognition and Sociality, Institute for Basic Science, Daejeon 34126, Korea
| | - Seung Eun Lee
- Virus Facility, Research Animal Resource Center, KIST, Seoul 02792, Korea
| | - Sang-Bum Kim
- New Drug Development Center, Daegu-Gyeongbuk Medical Innovation Foundation, Daegu 41061, Korea
| | - Ki Duk Park
- Department of Neuroscience, Division of Bio-Medical Science & Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Korea; KHU-KIST Department of Converging Science and Technology, Kyung Hee University, Seoul 02447, Korea; Convergence Research Center for Diagnosis, Treatment and Care System of Dementia, KIST, Seoul 02792, Korea
| | - Se-Young Choi
- Department of Physiology and Dental Research Institute, Seoul National University School of Dentistry, Seoul 03080, Korea
| | - Yong Chul Bae
- Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 41940, Korea.
| | - C Justin Lee
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea; Department of Neuroscience, Division of Bio-Medical Science & Technology, KIST School, Korea University of Science and Technology, Seoul 02792, Korea; Center for Cognition and Sociality, Institute for Basic Science, Daejeon 34126, Korea.
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Ethanol has concentration-dependent effects on hypothalamic POMC neuronal excitability. Alcohol 2020; 86:103-112. [PMID: 32304714 DOI: 10.1016/j.alcohol.2020.04.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 03/31/2020] [Accepted: 04/01/2020] [Indexed: 11/21/2022]
Abstract
Alcohol abuse is a worldwide public health concern, yet the precise molecular targets of alcohol in the brain are still not fully understood. Alcohol may promote its euphoric and motivational effects, in part, by activating the endogenous opioid system. One particular component of this system consists of pro-opiomelanocortin (POMC) -producing neurons in the arcuate nucleus (ArcN) of the hypothalamus, which project to reward-related brain areas. To identify the physiological effects of ethanol on ArcN POMC neurons, we utilized whole cell patch-clamp recordings and bath application of ethanol (5-40 mM) to identify alterations in spontaneous baseline activity, rheobase, spiking characteristics, or intrinsic neuronal properties. We found that 10 mM ethanol increased the number of depolarization-induced spikes in the majority of recorded cells, whereas higher concentrations of ethanol (20-40 mM) decreased the number of spikes. Interestingly, we found that basal firing rates of ArcN POMC neurons may predict physiological responding to ethanol. Rheobase and spontaneous activity, measured by spontaneous excitatory post-synaptic potentials (EPSPs) at rest, were unchanged after exposure to ethanol, regardless of concentration. These results suggest that ethanol has concentration-dependent modulatory effects on ArcN POMC neuronal activity, which may be relevant to treatments for alcohol use disorders that target endogenous opioid systems.
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Fricker LD, Margolis EB, Gomes I, Devi LA. Five Decades of Research on Opioid Peptides: Current Knowledge and Unanswered Questions. Mol Pharmacol 2020; 98:96-108. [PMID: 32487735 DOI: 10.1124/mol.120.119388] [Citation(s) in RCA: 74] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2020] [Accepted: 05/06/2020] [Indexed: 12/20/2022] Open
Abstract
In the mid-1970s, an intense race to identify endogenous substances that activated the same receptors as opiates resulted in the identification of the first endogenous opioid peptides. Since then, >20 peptides with opioid receptor activity have been discovered, all of which are generated from three precursors, proenkephalin, prodynorphin, and proopiomelanocortin, by sequential proteolytic processing by prohormone convertases and carboxypeptidase E. Each of these peptides binds to all three of the opioid receptor types (μ, δ, or κ), albeit with differing affinities. Peptides derived from proenkephalin and prodynorphin are broadly distributed in the brain, and mRNA encoding all three precursors are highly expressed in some peripheral tissues. Various approaches have been used to explore the functions of the opioid peptides in specific behaviors and brain circuits. These methods include directly administering the peptides ex vivo (i.e., to excised tissue) or in vivo (in animals), using antagonists of opioid receptors to infer endogenous peptide activity, and genetic knockout of opioid peptide precursors. Collectively, these studies add to our current understanding of the function of endogenous opioids, especially when similar results are found using different approaches. We briefly review the history of identification of opioid peptides, highlight the major findings, address several myths that are widely accepted but not supported by recent data, and discuss unanswered questions and future directions for research. SIGNIFICANCE STATEMENT: Activation of the opioid receptors by opiates and synthetic drugs leads to central and peripheral biological effects, including analgesia and respiratory depression, but these may not be the primary functions of the endogenous opioid peptides. Instead, the opioid peptides play complex and overlapping roles in a variety of systems, including reward pathways, and an important direction for research is the delineation of the role of individual peptides.
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Affiliation(s)
- Lloyd D Fricker
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York (L.D.F.); Department of Neurology, UCSF Weill Institute for Neurosciences, San Francisco, California (E.B.M.); and Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York (I.G., L.A.D.)
| | - Elyssa B Margolis
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York (L.D.F.); Department of Neurology, UCSF Weill Institute for Neurosciences, San Francisco, California (E.B.M.); and Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York (I.G., L.A.D.)
| | - Ivone Gomes
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York (L.D.F.); Department of Neurology, UCSF Weill Institute for Neurosciences, San Francisco, California (E.B.M.); and Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York (I.G., L.A.D.)
| | - Lakshmi A Devi
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York (L.D.F.); Department of Neurology, UCSF Weill Institute for Neurosciences, San Francisco, California (E.B.M.); and Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York (I.G., L.A.D.)
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Chakravarthy S, Balasubramani PP, Mandali A, Jahanshahi M, Moustafa AA. The many facets of dopamine: Toward an integrative theory of the role of dopamine in managing the body's energy resources. Physiol Behav 2018; 195:128-141. [DOI: 10.1016/j.physbeh.2018.06.032] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 05/07/2018] [Accepted: 06/20/2018] [Indexed: 02/07/2023]
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Vanholder R, Pletinck A, Schepers E, Glorieux G. Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update. Toxins (Basel) 2018; 10:toxins10010033. [PMID: 29316724 PMCID: PMC5793120 DOI: 10.3390/toxins10010033] [Citation(s) in RCA: 200] [Impact Index Per Article: 33.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Revised: 12/21/2017] [Accepted: 12/23/2017] [Indexed: 02/07/2023] Open
Abstract
In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β2-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.
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Affiliation(s)
- Raymond Vanholder
- Nephrology Section, Department of Internal Medicine, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium.
| | - Anneleen Pletinck
- Nephrology Section, Department of Internal Medicine, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium.
| | - Eva Schepers
- Nephrology Section, Department of Internal Medicine, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium.
| | - Griet Glorieux
- Nephrology Section, Department of Internal Medicine, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium.
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‘Naltrexone Blocks Endorphins Released when Dancing in Synchrony’. ADAPTIVE HUMAN BEHAVIOR AND PHYSIOLOGY 2017. [DOI: 10.1007/s40750-017-0067-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Ide S, Takahashi T, Takamatsu Y, Uhl GR, Niki H, Sora I, Ikeda K. Distinct Roles of Opioid and Dopamine Systems in Lateral Hypothalamic Intracranial Self-Stimulation. Int J Neuropsychopharmacol 2016; 20:403-409. [PMID: 28031268 PMCID: PMC5417052 DOI: 10.1093/ijnp/pyw113] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2016] [Accepted: 12/18/2016] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Opioid and dopamine systems play crucial roles in reward. Similarities and differences in the neural mechanisms of reward that are mediated by these 2 systems have remained largely unknown. Thus, in the present study, we investigated the differences in reward function in both µ-opioid receptor knockout mice and dopamine transporter knockout mice, important molecules in the opioid and dopamine systems. METHODS Mice were implanted with electrodes into the right lateral hypothalamus (l hour). Mice were then trained to put their muzzle into the hole in the head-dipping chamber for intracranial electrical stimulation, and the influences of gene knockout were assessed. RESULTS Significant differences are observed between opioid and dopamine systems in reward function. µ-Opioid receptor knockout mice exhibited enhanced intracranial electrical stimulation, which induced dopamine release. They also exhibited greater motility under conditions of "despair" in both the tail suspension test and water wheel test. In contrast, dopamine transporter knockout mice maintained intracranial electrical stimulation responding even when more active efforts were required to obtain the reward. CONCLUSIONS The absence of µ-opioid receptor or dopamine transporter did not lead to the absence of intracranial electrical stimulation responsiveness but rather differentially altered it. The present results in µ-opioid receptor knockout mice are consistent with the suppressive involvement of µ-opioid receptors in both positive incentive motivation associated with intracranial electrical stimulation and negative incentive motivation associated with depressive states. In contrast, the results in dopamine transporter knockout mice are consistent with the involvement of dopamine transporters in positive incentive motivation, especially its persistence. Differences in intracranial electrical stimulation in µ-opioid receptor and dopamine transporter knockout mice underscore the multidimensional nature of reward.
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Affiliation(s)
- Soichiro Ide
- Addictive Substance Project (Drs Ide, Takahashi, Takamatsu, Niki, Sora, and Ikeda), and The Basic Technology Research Center (Dr Takamatsu), Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Branch of Molecular Neurobiology, National Institute on Drug Abuse, Baltimore, Maryland (Dr Uhl); Research Service, New Mexico VA Health Care System, Albuquerque, New Mexico (Dr Uhl); Department of Psychiatry, Kobe University Graduate School of Medicine, Kobe, Japan (Dr Sora)
| | - Takehiro Takahashi
- Addictive Substance Project (Drs Ide, Takahashi, Takamatsu, Niki, Sora, and Ikeda), and The Basic Technology Research Center (Dr Takamatsu), Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Branch of Molecular Neurobiology, National Institute on Drug Abuse, Baltimore, Maryland (Dr Uhl); Research Service, New Mexico VA Health Care System, Albuquerque, New Mexico (Dr Uhl); Department of Psychiatry, Kobe University Graduate School of Medicine, Kobe, Japan (Dr Sora).,Current address (T.T.): Pharmaceutical Research Laboratories, Toray Industries, Inc., 6-10-1 Tebiro, Kamakura 248–8555, Japan
| | - Yukio Takamatsu
- Addictive Substance Project (Drs Ide, Takahashi, Takamatsu, Niki, Sora, and Ikeda), and The Basic Technology Research Center (Dr Takamatsu), Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Branch of Molecular Neurobiology, National Institute on Drug Abuse, Baltimore, Maryland (Dr Uhl); Research Service, New Mexico VA Health Care System, Albuquerque, New Mexico (Dr Uhl); Department of Psychiatry, Kobe University Graduate School of Medicine, Kobe, Japan (Dr Sora)
| | - George R. Uhl
- Addictive Substance Project (Drs Ide, Takahashi, Takamatsu, Niki, Sora, and Ikeda), and The Basic Technology Research Center (Dr Takamatsu), Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Branch of Molecular Neurobiology, National Institute on Drug Abuse, Baltimore, Maryland (Dr Uhl); Research Service, New Mexico VA Health Care System, Albuquerque, New Mexico (Dr Uhl); Department of Psychiatry, Kobe University Graduate School of Medicine, Kobe, Japan (Dr Sora)
| | - Hiroaki Niki
- Addictive Substance Project (Drs Ide, Takahashi, Takamatsu, Niki, Sora, and Ikeda), and The Basic Technology Research Center (Dr Takamatsu), Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Branch of Molecular Neurobiology, National Institute on Drug Abuse, Baltimore, Maryland (Dr Uhl); Research Service, New Mexico VA Health Care System, Albuquerque, New Mexico (Dr Uhl); Department of Psychiatry, Kobe University Graduate School of Medicine, Kobe, Japan (Dr Sora)
| | - Ichiro Sora
- Addictive Substance Project (Drs Ide, Takahashi, Takamatsu, Niki, Sora, and Ikeda), and The Basic Technology Research Center (Dr Takamatsu), Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Branch of Molecular Neurobiology, National Institute on Drug Abuse, Baltimore, Maryland (Dr Uhl); Research Service, New Mexico VA Health Care System, Albuquerque, New Mexico (Dr Uhl); Department of Psychiatry, Kobe University Graduate School of Medicine, Kobe, Japan (Dr Sora)
| | - Kazutaka Ikeda
- Addictive Substance Project (Drs Ide, Takahashi, Takamatsu, Niki, Sora, and Ikeda), and The Basic Technology Research Center (Dr Takamatsu), Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Branch of Molecular Neurobiology, National Institute on Drug Abuse, Baltimore, Maryland (Dr Uhl); Research Service, New Mexico VA Health Care System, Albuquerque, New Mexico (Dr Uhl); Department of Psychiatry, Kobe University Graduate School of Medicine, Kobe, Japan (Dr Sora)
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The Influence of Palatable Diets in Reward System Activation: A Mini Review. Adv Pharmacol Sci 2016; 2016:7238679. [PMID: 27087806 PMCID: PMC4818794 DOI: 10.1155/2016/7238679] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Revised: 02/12/2016] [Accepted: 02/16/2016] [Indexed: 11/29/2022] Open
Abstract
The changes in eating patterns that have occurred in recent decades are an important cause of obesity. Food intake and energy expenditure are controlled by a complex neural system involving the hypothalamic centers and peripheral satiety system (gastrointestinal and pancreatic hormones). Highly palatable and caloric food disrupts appetite regulation; however, palatable foods induce pleasure and reward. The cafeteria diet is such a palatable diet and has been shown consistently to increase body weight and induce hyperplasia in animal obesity models. Moreover, palatable high-fat foods (such as those of the cafeteria diet) can induce addiction-like deficits in brain reward function and are considered to be an important source of motivation that might drive overeating and contribute to the development of obesity. The mechanism of neural adaptation triggered by palatable foods is similar to those that have been reported for nondrug addictions and long-term drug use. Thus, this review attempts to describe the potential mechanisms that might lead to highly palatable diets, such as the cafeteria diet, triggering addiction, or compulsion through the reward system.
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The kappa-opioid receptor antagonist, nor-binaltorphimine (nor-BNI), decreases morphine withdrawal and the consequent conditioned place aversion in rats. Behav Brain Res 2015; 283:16-21. [PMID: 25591478 DOI: 10.1016/j.bbr.2015.01.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Revised: 12/23/2014] [Accepted: 01/06/2015] [Indexed: 01/02/2023]
Abstract
Much data suggest that the binding of dynorphin-like peptides to kappa-opioid receptors (KORs) during the administration of and withdrawal from a variety of addictive drugs is aversive and serves to limit the reinforcing properties of those drugs and to enhance tolerance, withdrawal, and the probability of stress-induced relapse. In this study, we examined the role of KORs in mediating opioid withdrawal and its aversive consequences in rats. We found that selective blockade of KORs by i.p. administration of 20mg/kg nor-binaltorphimine (nor-BNI) 5h prior to naltrexone-precipitated withdrawal in morphine-dependent rats decreased feces excreted during a 30-min withdrawal session. More critically, this injection of nor-BNI decreased the subsequent conditioned place aversion (CPA) for the withdrawal chamber 2 days later. The subsequent finding that administration of nor-BNI 2h following withdrawal did not affect the CPA 2 days later suggested that nor-BNI reduced the CPA in the prior experiment because it reduced the aversive effects of withdrawal, not because it reduced the aversive/anxiogenic effects of the withdrawal chamber at the time of CPA testing. These data indicate that the binding of dynorphin-like peptides to KORs during opioid withdrawal serves to enhance withdrawal and its aversive consequences and suggest that selective KOR antagonists may be useful in reducing these aversive effects and consequent relapse.
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Soyka M. Alcohol use disorders in opioid maintenance therapy: prevalence, clinical correlates and treatment. Eur Addict Res 2015; 21:78-87. [PMID: 25413371 DOI: 10.1159/000363232] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Maintenance therapy with methadone or buprenorphine is an established and first-line treatment for opioid dependence. Clinical studies indicate that about a third of patients in opioid maintenance therapy show increased alcohol consumption and alcohol use disorders. Comorbid alcohol use disorders have been identified as a risk factor for clinical outcome and can cause poor physical and mental health, including liver disorders, noncompliance, social deterioration and increased mortality risk. The effects of opioid maintenance therapy on alcohol consumption are controversial and no clear pattern has emerged. Most studies have not found a change in alcohol use after initiation of maintenance therapy. Methadone and buprenorphine appear to carry little risk of liver toxicity, but further research on this topic is required. Recent data indicate that brief intervention strategies may help reduce alcohol intake, but the existing evidence is still limited. This review discusses further clinical implications of alcohol use disorders in opioid dependence.
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Affiliation(s)
- Michael Soyka
- Department of Psychiatry and Psychotherapy, Ludwig Maximilian University, Munich, Germany; Private Hospital Meiringen, Willigen, Meiringen, Switzerland
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Abstract
Intracranial self-stimulation (ICSS) is a behavioral procedure in which operant responding is maintained by pulses of electrical brain stimulation. In research to study abuse-related drug effects, ICSS relies on electrode placements that target the medial forebrain bundle at the level of the lateral hypothalamus, and experimental sessions manipulate frequency or amplitude of stimulation to engender a wide range of baseline response rates or response probabilities. Under these conditions, drug-induced increases in low rates/probabilities of responding maintained by low frequencies/amplitudes of stimulation are interpreted as an abuse-related effect. Conversely, drug-induced decreases in high rates/probabilities of responding maintained by high frequencies/amplitudes of stimulation can be interpreted as an abuse-limiting effect. Overall abuse potential can be inferred from the relative expression of abuse-related and abuse-limiting effects. The sensitivity and selectivity of ICSS to detect abuse potential of many classes of abused drugs is similar to the sensitivity and selectivity of drug self-administration procedures. Moreover, similar to progressive-ratio drug self-administration procedures, ICSS data can be used to rank the relative abuse potential of different drugs. Strengths of ICSS in comparison with drug self-administration include 1) potential for simultaneous evaluation of both abuse-related and abuse-limiting effects, 2) flexibility for use with various routes of drug administration or drug vehicles, 3) utility for studies in drug-naive subjects as well as in subjects with controlled levels of prior drug exposure, and 4) utility for studies of drug time course. Taken together, these considerations suggest that ICSS can make significant contributions to the practice of abuse potential testing.
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Affiliation(s)
- S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia
| | - Laurence L Miller
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia
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Abstract
To date, few pharmacotherapies have been established for the treatment of alcoholism. There is a plethora of research concerning the involvement of the opioid-endorphin system in mediating the reinforcing effects of alcohol. The opioid antagonist naltrexone has been found to be effective in alcohol treatment. In addition, the mu-opioid antagonist and partial kappa agonist nalmefene was recently approved by the European Medicines Agency for the treatment of alcoholism. The relevant studies followed a harm-reduction, 'as needed' approach and showed a reduction in alcohol consumption with nalmefene 20 mg rather than increased abstinence rates, (which was not the primary goal of the relevant studies). The available literature is reviewed and discussed. Nalmefene appears to be a safe and effective treatment for alcohol dependence.
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Affective consequences and subsequent effects on morphine self-administration of d-ala2-methionine enkephalin. ACTA ACUST UNITED AC 2013. [DOI: 10.3758/bf03332900] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Addictive agents and intracranial stimulation (ICS): Morphine, naloxone, and pressing for amygdaloid ICS. ACTA ACUST UNITED AC 2013. [DOI: 10.3758/bf03329521] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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20
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Naloxone reverses ethanol’s effects on sexual behavior of the female Syrian hamster. ACTA ACUST UNITED AC 2013. [DOI: 10.3758/bf03326997] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Houchi H, Persyn W, Legastelois R, Naassila M. The adenosine A2A receptor agonist CGS 21680 decreases ethanol self-administration in both non-dependent and dependent animals. Addict Biol 2013; 18:812-25. [PMID: 23301633 DOI: 10.1111/adb.12032] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
There is emerging evidence that the adenosinergic system might be involved in drug addiction and alcohol dependence. We have already demonstrated the involvement of A2A receptors (A2AR) in ethanol-related behaviours in mice. Here, we investigated whether the A2AR agonist CGS 21680 can reduce ethanol operant self-administration in both non-dependent and ethanol-dependent Wistar rats. To rule out a potential involvement of the A1R in the effects of CGS 21680, we also tested its effectiveness to reduce ethanol operant self-administration in both heterozygous and homozygous A1R knockout mice. Our results demonstrated that CGS 21680 (0.065, 0.095 and 0.125 mg/kg, i.p.) had a bimodal effect on 10% ethanol operant self-administration in non-dependent rats. The intermediate dose was also effective in reducing 2% sucrose self-administration. Interestingly, the intermediate dose reduced 10% ethanol self-administration in dependent animals more effectively (75% decrease) when compared with non-dependent animals (57% decrease). These results suggest that the A2AR are involved in CGS 21680 effects since the reduction of ethanol self-administration was not dependent upon the presence of A1R in mice. In conclusion, our findings demonstrated the effectiveness of the A2AR agonist CGS 21680 in a preclinical model of alcohol addiction and suggested that the adenosinergic pathway is a promising target to treat alcohol addiction.
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Affiliation(s)
- Hakim Houchi
- Groupe de Recherche sur l'Alcool & les Pharmacodépendances (GRAP); INSERM ERi 24; UFR de Pharmacie; Université de Picardie Jules Verne; France
| | | | - Rémi Legastelois
- Groupe de Recherche sur l'Alcool & les Pharmacodépendances (GRAP); INSERM ERi 24; UFR de Pharmacie; Université de Picardie Jules Verne; France
| | - Mickaël Naassila
- Groupe de Recherche sur l'Alcool & les Pharmacodépendances (GRAP); INSERM ERi 24; UFR de Pharmacie; Université de Picardie Jules Verne; France
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Desai SJ, Upadhya MA, Subhedar NK, Kokare DM. NPY mediates reward activity of morphine, via NPY Y1 receptors, in the nucleus accumbens shell. Behav Brain Res 2013; 247:79-91. [DOI: 10.1016/j.bbr.2013.03.018] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Revised: 03/05/2013] [Accepted: 03/09/2013] [Indexed: 10/27/2022]
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Dunbar RIM, Kaskatis K, MacDonald I, Barra V. Performance of music elevates pain threshold and positive affect: implications for the evolutionary function of music. EVOLUTIONARY PSYCHOLOGY 2012. [PMID: 23089077 DOI: 10.1177/147470491201000403] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
It is well known that music arouses emotional responses. In addition, it has long been thought to play an important role in creating a sense of community, especially in small scale societies. One mechanism by which it might do this is through the endorphin system, and there is evidence to support this claim. Using pain threshold as an assay for CNS endorphin release, we ask whether it is the auditory perception of music that triggers this effect or the active performance of music. We show that singing, dancing and drumming all trigger endorphin release (indexed by an increase in post-activity pain tolerance) in contexts where merely listening to music and low energy musical activities do not. We also confirm that music performance results in elevated positive (but not negative) affect. We conclude that it is the active performance of music that generates the endorphin high, not the music itself. We discuss the implications of this in the context of community bonding mechanisms that commonly involve dance and music-making.
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Affiliation(s)
- R I M Dunbar
- Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, UK.
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Abstract
Naltrexone is an opioid receptor antagonist that has been shown to be effective for maintaining abstinence in alcohol-dependent persons. It is particularly effective in a subset of persons who suffer from high craving, as it reduces craving for alcohol. Family history has been shown to be a predictor of treatment response and, indeed, allelic variation in the mu opioid receptor gene predicts treatment response to naltrexone. The therapeutic effects of naltrexone are mediated by blockade of central mu opioid receptors. The site of action is under investigation but evidence supports a role of mu opioid receptors in the central nucleus of the amygdala, nucleus accumbens, and ventral tegmental area in the therapeutic actions of naltrexone for alcohol dependence. This article reviews the role of the endogenous opioid system in addictive diseases, especially alcoholism and discusses the pharmacological basis for the use of naltrexone in the treatment of alcohol dependence.
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Light and electron-microscopic study of leucine enkephalin immunoreactivity in the cat claustrum. J Mol Histol 2012; 43:641-9. [DOI: 10.1007/s10735-012-9448-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2012] [Accepted: 08/31/2012] [Indexed: 11/29/2022]
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Simon MJ, Garcia R, Puerto A. Concurrent stimulation-induced place preference in lateral hypothalamus and parabrachial complex: Differential effects of naloxone. Behav Brain Res 2011; 225:311-6. [DOI: 10.1016/j.bbr.2011.07.029] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 07/12/2011] [Accepted: 07/17/2011] [Indexed: 12/01/2022]
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Opioid Antagonists May Reverse Endogenous Opiate “Dependence” in the Treatment of Self-Injurious Behavior. Pharmaceuticals (Basel) 2011. [PMCID: PMC4053960 DOI: 10.3390/ph4020366] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Nandhu MS, Naijil G, Smijin S, Jayanarayanan S, Paulose CS. Opioid system functional regulation in neurological disease management. J Neurosci Res 2011; 88:3215-21. [PMID: 20734417 DOI: 10.1002/jnr.22463] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
There is increasing evidence to suggest a role for the opioid system in the control of pathophysiology of neurological disorders (Alzheimer's, Parkinson's, and Huntington's diseases, spinal cord injury, epilepsy, hypoxia, and autism). Resuscitation of the altered expression of the opioid system in various neurological disorders is of therapeutic importance. Such treatment may be beneficial in ameliorating the clinical symptoms of the disorder. This Mini-Review provides a brief update on opioid system regulation in neurological disorders and focuses on the opioids' pharmacological importance.
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Affiliation(s)
- M S Nandhu
- Molecular Neurobiology and Cell Biology Unit, Centre for Neuroscience, Department of Biotechnology, Cochin University of Science and Technology, Cochin, Kerala, India
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Abstract
IMPORTANCE OF THE FIELD Alcohol use and dependence are frequent disorders. Despite numerous established psychosocial approaches, relapse to heavy drinking is common in alcohol-dependent patients after detoxification and relapse prevention remains a significant medical challenge. AREAS COVERED IN THIS REVIEW The opioidergic system plays a crucial role in mediating the rewarding effects of alcohol, in part by modulating dopaminergic neurotransmission in mesolimbic brain areas. This review will discuss the neurochemical basis of alcoholism with respect to the opiodergic system. Nalmefene is an alternate opioid receptor that also targets the kappa opioid receptors and thus offers a different treatment approach. The treatment studies conducted so far are discussed. WHAT THE READER WILL GAIN We present a comprehensive overview of the implication of the opioidergic system in mediating the rewarding effects of alcoholism and the preclinical and clinical studies conducted so far with nalmefene. TAKE HOME MESSAGE Although the number of clinical studies conducted with naltrexone by far exceeds the number conducted with nalmefene, the four studies on nalmefene published so far may indicate a role of this opioid antagonist in the treatment of alcoholism. Results of some ongoing studies on nalmefene will provide additional data on its use for this indication.
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Affiliation(s)
- Michael Soyka
- University of Munich, Psychiatric Hospital, Nussbaumstr. 7, D-80336 Munich, Germany
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The opioid systems – Panacea and nemesis. Biochem Biophys Res Commun 2010; 396:140-2. [DOI: 10.1016/j.bbrc.2010.04.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Accepted: 04/01/2010] [Indexed: 11/18/2022]
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The reward-effort model: An economic framework for examining the mechanism of neuroleptic action. Behav Brain Sci 2010. [DOI: 10.1017/s0140525x0001058x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Dopamine and the limits of behavioral reduction – or why aren't all schizophrenics fat and happy? Behav Brain Sci 2010. [DOI: 10.1017/s0140525x00010451] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Abstract
AbstractNeuroleptic drugs disrupt the learning and performance of operant habits motivated by a variety of positive reinforcers, including food, water, brain stimulation, intravenous opiates, stimulants, and barbiturates. This disruption has been demonstrated in several kinds of experiments with doses that do not significantly limit normal response capacity. With continuous reinforcement neuroleptics gradually cause responding to cease, as in extinction or satiation. This pattern is not due to satiation, however, because it also occurs with nonsatiating reinforcement (such as saccharin or brain stimulation). Repeated tests with neuroleptics result in earlier and earlier response cessation reminiscent of the kind of decreased resistance to extinction caused by repeated tests without the expected reward. Indeed, withholding reward can have the same effect on responding under later neuroleptic treatment as prior experience with neuroleptics themselves; this suggests that there is a transfer of learning (really unlearning) from nonreward to neuroleptic conditions. These tests under continuous reinforcement schedules suggest that neuroleptics blunt the ability of reinforcers to sustain responding at doses which largely spare the ability of the animal to initiate responding. Animals trained under partial reinforcement, however, do not respond as well during neuroleptic testing as animals trained under continuous reinforcement. Thus, neuroleptics can also impair responding (though not response capacity) that is normally sustained by environmental stimuli (and associated expectancies) in the absence of the primary reinforcer. Neuroleptics also blunt the euphoric impact of amphetamine in humans. These data suggest that the most subtle and interesting effect of neuroleptics is a selective attenuation of motivational arousal which is (a) critical for goal-directed behavior, (b) normally induced by reinforcers and associated environmental stimuli, and (c) normally accompanied by the subjective experience of pleasure. Because these drugs are used to treat schizophrenia and because they cause parkinsonian-like side effects, this action has implications for a better understanding of human pathology as well as normal motivational processes.
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