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Effects of ketogenic diet and ketone monoester supplement on acute alcohol withdrawal symptoms in male mice. Psychopharmacology (Berl) 2021; 238:833-844. [PMID: 33410985 PMCID: PMC7914216 DOI: 10.1007/s00213-020-05735-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Accepted: 11/24/2020] [Indexed: 12/25/2022]
Abstract
RATIONALE After alcohol ingestion, the brain partly switches from consumption of glucose to consumption of the alcohol metabolite acetate. In heavy drinkers, the switch persists after abrupt abstinence, leading to the hypothesis that the resting brain may be "starved" when acetate levels suddenly drop during abstinence, despite normal blood glucose, contributing to withdrawal symptoms. We hypothesized that ketone bodies, like acetate, could act as alternative fuels in the brain and alleviate withdrawal symptoms. OBJECTIVES We previously reported that a ketogenic diet during alcohol exposure reduced acute withdrawal symptoms in rats. Here, our goals were to test whether (1) we could reproduce our findings, in mice and with longer alcohol exposure; (2) ketone bodies alone are sufficient to reduce withdrawal symptoms (clarifying mechanism); (3) introduction of ketogenic diets at abstinence (a clinically more practical implementation) would also be effective. METHODS Male C57BL/6NTac mice had intermittent alcohol exposure for 3 weeks using liquid diet. Somatic alcohol withdrawal symptoms were measured as handling-induced convulsions; anxiety-like behavior was measured using the light-dark transition test. We tested a ketogenic diet, and a ketone monoester supplement with a regular carbohydrate-containing diet. RESULTS The regular diet with ketone monoester was sufficient to reduce handling-induced convulsions and anxiety-like behaviors in early withdrawal. Only the ketone monoester reduced handling-induced convulsions when given during abstinence, consistent with faster elevation of blood ketones, relative to ketogenic diet. CONCLUSIONS These findings support the potential utility of therapeutic ketosis as an adjunctive treatment in early detoxification in alcohol-dependent patients seeking to become abstinent. TRIAL REGISTRATION clinicaltrials.gov NCT03878225, NCT03255031.
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Koob GF. Drug Addiction: Hyperkatifeia/Negative Reinforcement as a Framework for Medications Development. Pharmacol Rev 2021; 73:163-201. [PMID: 33318153 PMCID: PMC7770492 DOI: 10.1124/pharmrev.120.000083] [Citation(s) in RCA: 145] [Impact Index Per Article: 48.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Compulsive drug seeking that is associated with addiction is hypothesized to follow a heuristic framework that involves three stages (binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation) and three domains of dysfunction (incentive salience/pathologic habits, negative emotional states, and executive function, respectively) via changes in the basal ganglia, extended amygdala/habenula, and frontal cortex, respectively. This review focuses on neurochemical/neurocircuitry dysregulations that contribute to hyperkatifeia, defined as a greater intensity of negative emotional/motivational signs and symptoms during withdrawal from drugs of abuse in the withdrawal/negative affect stage of the addiction cycle. Hyperkatifeia provides an additional source of motivation for compulsive drug seeking via negative reinforcement. Negative reinforcement reflects an increase in the probability of a response to remove an aversive stimulus or drug seeking to remove hyperkatifeia that is augmented by genetic/epigenetic vulnerability, environmental trauma, and psychiatric comorbidity. Neurobiological targets for hyperkatifeia in addiction involve neurocircuitry of the extended amygdala and its connections via within-system neuroadaptations in dopamine, enkephalin/endorphin opioid peptide, and γ-aminobutyric acid/glutamate systems and between-system neuroadaptations in prostress corticotropin-releasing factor, norepinephrine, glucocorticoid, dynorphin, hypocretin, and neuroimmune systems and antistress neuropeptide Y, nociceptin, endocannabinoid, and oxytocin systems. Such neurochemical/neurocircuitry dysregulations are hypothesized to mediate a negative hedonic set point that gradually gains allostatic load and shifts from a homeostatic hedonic state to an allostatic hedonic state. Based on preclinical studies and translational studies to date, medications and behavioral therapies that reset brain stress, antistress, and emotional pain systems and return them to homeostasis would be promising new targets for medication development. SIGNIFICANCE STATEMENT: The focus of this review is on neurochemical/neurocircuitry dysregulations that contribute to hyperkatifeia, defined as a greater intensity of negative emotional/motivational signs and symptoms during withdrawal from drugs of abuse in the withdrawal/negative affect stage of the drug addiction cycle and a driving force for negative reinforcement in addiction. Medications and behavioral therapies that reverse hyperkatifeia by resetting brain stress, antistress, and emotional pain systems and returning them to homeostasis would be promising new targets for medication development.
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Affiliation(s)
- George F Koob
- National Institute on Alcohol Abuse and Alcoholism and National Institute on Drug Abuse, National Institutes of Health, Bethesda, Maryland
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3
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Serum Oxytocin Level Among Male Patients With Opioid Dependence and Its Relation to Craving. ADDICTIVE DISORDERS & THEIR TREATMENT 2020. [DOI: 10.1097/adt.0000000000000231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Brown CH, Ludwig M, Tasker JG, Stern JE. Somato-dendritic vasopressin and oxytocin secretion in endocrine and autonomic regulation. J Neuroendocrinol 2020; 32:e12856. [PMID: 32406599 PMCID: PMC9134751 DOI: 10.1111/jne.12856] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 03/29/2020] [Accepted: 04/11/2020] [Indexed: 12/29/2022]
Abstract
Somato-dendritic secretion was first demonstrated over 30 years ago. However, although its existence has become widely accepted, the function of somato-dendritic secretion is still not completely understood. Hypothalamic magnocellular neurosecretory cells were among the first neuronal phenotypes in which somato-dendritic secretion was demonstrated and are among the neurones for which the functions of somato-dendritic secretion are best characterised. These neurones secrete the neuropeptides, vasopressin and oxytocin, in an orthograde manner from their axons in the posterior pituitary gland into the blood circulation to regulate body fluid balance and reproductive physiology. Retrograde somato-dendritic secretion of vasopressin and oxytocin modulates the activity of the neurones from which they are secreted, as well as the activity of neighbouring populations of neurones, to provide intra- and inter-population signals that coordinate the endocrine and autonomic responses for the control of peripheral physiology. Somato-dendritic vasopressin and oxytocin have also been proposed to act as hormone-like signals in the brain. There is some evidence that somato-dendritic secretion from magnocellular neurosecretory cells modulates the activity of neurones beyond their local environment where there are no vasopressin- or oxytocin-containing axons but, to date, there is no conclusive evidence for, or against, hormone-like signalling throughout the brain, although it is difficult to imagine that the levels of vasopressin found throughout the brain could be underpinned by release from relatively sparse axon terminal fields. The generation of data to resolve this issue remains a priority for the field.
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Affiliation(s)
- Colin H. Brown
- Department of Physiology, Brain Health Research Centre, Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand
| | - Mike Ludwig
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK
- Department of Immunology, Centre for Neuroendocrinology, University of Pretoria, Pretoria, South Africa
| | - Jeffrey G. Tasker
- Department of Cell and Molecular Biology, Brain Institute, Tulane University, New Orleans, LA, USA
| | - Javier E. Stern
- Neuroscience Institute, Georgia State University, Atlanta, GA, USA
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Altered Signaling in the Descending Pain-modulatory System after Short-Term Infusion of the μ-Opioid Agonist Remifentanil. J Neurosci 2018; 38:2454-2470. [PMID: 29440535 DOI: 10.1523/jneurosci.2496-17.2018] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 01/17/2018] [Accepted: 01/22/2018] [Indexed: 12/24/2022] Open
Abstract
μ-Opioid receptor agonists are widely used within the contemporary treatment of pain, but abrupt opioid suspension, even after short-term infusion, can paradoxically increase the sensitivity to noxious stimuli, a phenomenon that has been, for example, reported after application of the fast-acting μ-opioid receptor agonist remifentanil. To investigate the mechanisms underlying the effects of discontinuation of remifentanil application on pain processing in the human CNS, we analyzed neuronal responses to thermal stimuli before and after a short-term infusion of remifentanil (30 min 0.1 μg/kg body weight/min) compared with control in the brain, brainstem, and spinal cord in drug-naive male volunteers using fMRI. Subsequent to remifentanil suspension, we observed reduced heat pain thresholds and increased neuronal responses in pain-encoding as well as in key regions of the descending pain-modulatory system, such as the periaqueductal gray matter, the nucleus cuneiformis, and the rostral ventromedial medulla. Moreover, the spinal pain-related multivoxel activity pattern showed an opioid-specific change after drug suspension. Importantly, remifentanil suspension increased the functional coupling between the nucleus cuneiformis and the rostral anterior cingulate cortex, and the coupling strength between the rostral anterior cingulate cortex and the nucleus cuneiformis correlated negatively with the individual pain threshold after opioid suspension. These findings demonstrate that, already subsequent to a short-term infusion of the μ-opioid receptor agonist remifentanil, signaling in the descending pain-modulatory system is fundamentally altered and that these changes are directly related to the behavioral sensitivity to pain.SIGNIFICANCE STATEMENT Opioids are widely used in modern medicine, but, in addition to their known side effects, it is increasingly recognized that opioids can also increase sensitivity to pain subsequent to their use. Using the fast-acting μ-opioid receptor agonist remifentanil and fMRI in healthy male volunteers, this study demonstrates how signaling changes occur along the entire descending pain-modulatory pathway after opioid discontinuation and how these alterations are closely linked to increased behavioral pain sensitivity. Particularly by revealing modified responses in pain-modulatory brainstem regions that have been previously demonstrated to be causally involved in acute opioid withdrawal effects in rodents, the data provide a plausible neuronal mechanism by which the increased sensitivity to pain after opioid suspension is mediated in humans.
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Augustine RA, Seymour AJ, Campbell RE, Grattan DR, Brown CH. Integrative neuro-humoral regulation of oxytocin neuron activity in pregnancy and lactation. J Neuroendocrinol 2018; 30. [PMID: 29323764 DOI: 10.1111/jne.12569] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Accepted: 01/07/2018] [Indexed: 02/02/2023]
Abstract
Oxytocin is required for normal birth and lactation. Oxytocin is synthesised by hypothalamic supraoptic and paraventricular nuclei neurons and is released into the circulation from the posterior pituitary gland. Under basal conditions, circulating oxytocin levels are relatively constant but during birth and lactation, pulsatile oxytocin release triggers rhythmic contraction of the uterus during birth and milk ejection during suckling. Oxytocin levels are principally determined by the pattern of action potential firing that is, in turn, determined by the interplay between the intrinsic properties of the oxytocin neurons, regulation of their excitability by surrounding glia as well as by synaptic drive from their afferent inputs. During birth and suckling, oxytocin neurons fire high-frequency bursts of action potentials that are coordinated across the population of neurons and these bursts underpin the pulsatile secretion of oxytocin required for normal birth and lactation. Neuroglial regulation of oxytocin neurons changes during pregnancy to favour burst firing. However, these changes still require afferent input activity to drive activity. While it has long been known that noradrenergic inputs to oxytocin neurons are activated during birth and lactation, the involvement of other afferent inputs is less clear. Here, we provide a brief overview of the current understanding of the mechanisms that regulate oxytocin neuron activity during pregnancy and lactation, and focus on recent evidence from our laboratory identifying an input that increases kisspeptin production to excite oxytocin neurons in late pregnancy. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Rachael A Augustine
- Department of Physiology Brain Health Research Centre, Centre for Neuroendocrinology
| | - Alexander J Seymour
- Department of Physiology Brain Health Research Centre, Centre for Neuroendocrinology
| | - Rebecca E Campbell
- Department of Physiology Brain Health Research Centre, Centre for Neuroendocrinology
| | - David R Grattan
- Department of Anatomy, University of Otago, Dunedin, New Zealand
| | - Colin H Brown
- Department of Physiology Brain Health Research Centre, Centre for Neuroendocrinology
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Nikolaou K, Kapoukranidou D, Ndungu S, Floros G, Kovatsi L. Severity of Withdrawal Symptoms, Plasma Oxytocin Levels, and Treatment Outcome in Heroin Users Undergoing Acute Withdrawal. J Psychoactive Drugs 2017; 49:233-241. [PMID: 28443705 DOI: 10.1080/02791072.2017.1312644] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Pre-clinical studies show that, following chronic opioid exposure, oxytocin neurons exhibit over-excitation upon withdrawal, causing an increase in oxytocin brain and plasma levels. Relevant clinical data on humans are scarce. This study investigates the opioid withdrawal stress effect on oxytocin plasma levels in humans. We evaluated 57 male chronic heroin users in a residential detoxification program. We determined plasma oxytocin levels by ELISA and measured the stress effects of withdrawal using the COWS scale for opioid withdrawal, the VAS scale for craving, and the Hamilton scales for anxiety and depression on the second day of admission. Out of the 57 patients enrolled in the study, 27 completed the 21-day program, while the remaining 30 dropped out prior to completion. Plasma oxytocin levels were significantly higher in those individuals who dropped out than in those who completed the program. Participants who dropped out at some stage scored higher in the COWS, VAS-Craving, and Hamilton-anxiety scales, indicating a higher stress and explaining the higher oxytocin levels. In addition, plasma oxytocin levels correlated positively with the scores achieved in the COWS and Hamilton-anxiety scales. Higher withdrawal stress levels are associated with higher plasma oxytocin levels and early treatment discharge.
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Affiliation(s)
- Kakia Nikolaou
- a Consultant Psychiatrist, Head of the Addictions Department IANOS , Papanikolaou General Hospital of Thessaloniki-Psychiatric Hospital of Thessaloniki , Thessaloniki , Greece
| | - Dorothea Kapoukranidou
- b Associate Professor, Department of Physiology, School of Medicine , Aristotle University of Thessaloniki , Thessaloniki , Greece
| | - Samuel Ndungu
- c Emeritus Professor, Laboratory of Forensic Medicine and Toxicology, School of Medicine , Aristotle University of Thessaloniki , Thessaloniki , Greece
| | - Georgios Floros
- d Scientific Associate, Second Department of Psychiatry, School of Medicine , Aristotle University of Thessaloniki , Thessaloniki , Greece
| | - Leda Kovatsi
- e Assistant Professor, Laboratory of Forensic Medicine and Toxicology, School of Medicine , Aristotle University of Thessaloniki , Thessaloniki , Greece
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Augustine RA, Ladyman SR, Bouwer GT, Alyousif Y, Sapsford TJ, Scott V, Kokay IC, Grattan DR, Brown CH. Prolactin regulation of oxytocin neurone activity in pregnancy and lactation. J Physiol 2017; 595:3591-3605. [PMID: 28211122 DOI: 10.1113/jp273712] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Accepted: 01/30/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS During lactation, prolactin promotes milk synthesis and oxytocin stimulates milk ejection. In virgin rats, prolactin inhibits the activity of oxytocin-secreting neurones. We found that prolactin inhibition of oxytocin neurone activity is lost in lactation, and that some oxytocin neurones were excited by prolactin in lactating rats. The change in prolactin regulation of oxytocin neurone activity was not associated with a change in activation of intracellular signalling pathways known to couple to prolactin receptors. The change in prolactin regulation of oxytocin neurone activity in lactation might allow coordinated activation of both populations of neurones when required for successful lactation. ABSTRACT Secretion of prolactin for milk synthesis and oxytocin for milk secretion is required for successful lactation. In virgin rats, prolactin inhibits oxytocin neurones but this effect would be counterproductive during lactation when secretion of both hormones is required for synthesis and delivery of milk to the newborn. Hence, we determined the effects of intracerebroventricular (i.c.v.) prolactin on oxytocin neurones in urethane-anaesthetised virgin, pregnant and lactating rats. Prolactin (2 μg) consistently inhibited oxytocin neurones in virgin and pregnant rats (by 1.9 ± 0.4 and 1.8 ± 0.5 spikes s-1 , respectively), but not in lactating rats; indeed, prolactin excited six of 27 oxytocin neurones by >1 spike s-1 in lactating rats but excited none in virgin or pregnant rats (χ22 = 7.2, P = 0.03). Vasopressin neurones were unaffected by prolactin (2 μg) in virgin rats but were inhibited by 1.1 ± 0.2 spikes s-1 in lactating rats. Immunohistochemistry showed that i.c.v. prolactin increased oxytocin expression in virgin and lactating rats and increased signal transducer and activator of transcription 5 phosphorylation to a similar extent in oxytocin neurones of virgin and lactating rats. Western blotting showed that i.c.v. prolactin did not affect phosphorylation of extracellular regulated kinase 1 or 2, or of Akt in the supraoptic or paraventricular nuclei of virgin or lactating rats. Hence, prolactin inhibition of oxytocin neurones is lost in lactation, which might allow concurrent elevation of prolactin secretion from the pituitary gland and activation of oxytocin neurones for synthesis and delivery of milk to the newborn.
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Affiliation(s)
- Rachael A Augustine
- Brain Health Research Centre, University of Otago, Dunedin, New Zealand.,Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Sharon R Ladyman
- Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Anatomy, University of Otago, Dunedin, New Zealand
| | - Gregory T Bouwer
- Brain Health Research Centre, University of Otago, Dunedin, New Zealand.,Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Yousif Alyousif
- Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Tony J Sapsford
- Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Anatomy, University of Otago, Dunedin, New Zealand
| | - Victoria Scott
- Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Ilona C Kokay
- Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Anatomy, University of Otago, Dunedin, New Zealand
| | - David R Grattan
- Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Anatomy, University of Otago, Dunedin, New Zealand
| | - Colin H Brown
- Brain Health Research Centre, University of Otago, Dunedin, New Zealand.,Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.,Department of Physiology, University of Otago, Dunedin, New Zealand
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Kim JS, Brown CH, Anderson GM. Anti-opioid Effects of RFRP-3 on Magnocellular Neuron Activity in Morphine-naïve and Morphine-treated Female Rats. Endocrinology 2016; 157:4003-4011. [PMID: 27533886 DOI: 10.1210/en.2016-1374] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Neuropeptide FF receptors (NPFFR1 and NPFFR2) have been proposed to possess anti-opioid properties, and be involved in the development of opiate tolerance and dependence. However, there is no evidence to date supporting such opioid effects at the cellular level in vivo. Using in vivo electrophysiological recordings from vasopressin and oxytocin neurons in the supraoptic nucleus, we aimed to determine the effects of NPFFRs on opiate inhibition, tolerance, and dependence at a cellular level. Both vasopressin and oxytocin neurons are acutely inhibited by opioids and develop opiate tolerance. Oxytocin neurons also develop cellular opiate dependence and undergo withdrawal hyperexcitation upon cessation of opiate administration. Here, the classical μ-opioid receptor agonist, morphine robustly inhibited the spontaneous firing rate of vasopressin and oxytocin neurons, and this inhibition was attenuated by pretreatment with the NPFFR1 agonist, RFamide-related peptide-3. In rats infused with morphine for 6 d, vasopressin neurons were unresponsive to morphine, indicating the development of cellular tolerance, but pretreatment with the NPFFR antagonist, GJ14, restored acute morphine inhibition. In morphine-infused rats, RFamide related peptide-3 did not induce withdrawal excitation in oxytocin neurons and GJ14 did not reverse naloxone-precipitated withdrawal excitation. This is the first evidence of anti-opioid effects of the NPFFR system at a cellular level in vivo. Our results suggest that the anti-opioid properties of the NPFFR system reduce morphine sensitivity during tolerance but that it is not involved in dependence.
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Affiliation(s)
- Joon S Kim
- Centre for Neuroendocrinology and Departments of Anatomy (J.S.K., G.M.A.) and Physiology (C.H.B.), University of Otago, Dunedin 9054, New Zealand
| | - Colin H Brown
- Centre for Neuroendocrinology and Departments of Anatomy (J.S.K., G.M.A.) and Physiology (C.H.B.), University of Otago, Dunedin 9054, New Zealand
| | - Greg M Anderson
- Centre for Neuroendocrinology and Departments of Anatomy (J.S.K., G.M.A.) and Physiology (C.H.B.), University of Otago, Dunedin 9054, New Zealand
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Moaddab M, Hyland BI, Brown CH. Oxytocin excites nucleus accumbens shell neurons in vivo. Mol Cell Neurosci 2015; 68:323-30. [DOI: 10.1016/j.mcn.2015.08.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Revised: 08/12/2015] [Accepted: 08/24/2015] [Indexed: 01/20/2023] Open
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11
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Proft J, Weiss N. G protein regulation of neuronal calcium channels: back to the future. Mol Pharmacol 2014; 87:890-906. [PMID: 25549669 DOI: 10.1124/mol.114.096008] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Accepted: 12/30/2014] [Indexed: 11/22/2022] Open
Abstract
Neuronal voltage-gated calcium channels have evolved as one of the most important players for calcium entry into presynaptic endings responsible for the release of neurotransmitters. In turn, and to fine-tune synaptic activity and neuronal communication, numerous neurotransmitters exert a potent negative feedback over the calcium signal provided by G protein-coupled receptors. This regulation pathway of physiologic importance is also extensively exploited for therapeutic purposes, for instance in the treatment of neuropathic pain by morphine and other μ-opioid receptor agonists. However, despite more than three decades of intensive research, important questions remain unsolved regarding the molecular and cellular mechanisms of direct G protein inhibition of voltage-gated calcium channels. In this study, we revisit this particular regulation and explore new considerations.
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Affiliation(s)
- Juliane Proft
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Norbert Weiss
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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12
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Brunton PJ, Russell JA, Hirst JJ. Allopregnanolone in the brain: protecting pregnancy and birth outcomes. Prog Neurobiol 2014; 113:106-36. [PMID: 24012715 DOI: 10.1016/j.pneurobio.2013.08.005] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Revised: 08/12/2013] [Accepted: 08/25/2013] [Indexed: 01/09/2023]
Abstract
A successful pregnancy requires multiple adaptations in the mother's brain that serve to optimise foetal growth and development, protect the foetus from adverse prenatal programming and prevent premature delivery of the young. Pregnancy hormones induce, organise and maintain many of these adaptations. Steroid hormones play a critical role and of particular importance is the progesterone metabolite and neurosteroid, allopregnanolone. Allopregnanolone is produced in increasing amounts during pregnancy both in the periphery and in the maternal and foetal brain. This review critically examines a role for allopregnanolone in both the maternal and foetal brain during pregnancy and development in protecting pregnancy and birth outcomes, with particular emphasis on its role in relation to stress exposure at this time. Late pregnancy is associated with suppressed stress responses. Thus, we begin by considering what is known about the central mechanisms in the maternal brain, induced by allopregnanolone, that protect the foetus(es) from exposure to harmful levels of maternal glucocorticoids as a result of stress during pregnancy. Next we discuss the central mechanisms that prevent premature secretion of oxytocin and consider a role for allopregnanolone in minimising the risk of preterm birth. Allopregnanolone also plays a key role in the foetal brain, where it promotes development and is neuroprotective. Hence we review the evidence about disruption to neurosteroid production in pregnancy, through prenatal stress or other insults, and the immediate and long-term adverse consequences for the offspring. Finally we address whether progesterone or allopregnanolone treatment can rescue some of these deficits in the offspring.
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Affiliation(s)
- Paula J Brunton
- Division of Neurobiology, The Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Scotland, UK.
| | - John A Russell
- Centre for Integrative Physiology, School of Biomedical Sciences, University of Edinburgh, Scotland, UK
| | - Jonathan J Hirst
- Mothers and Babies Research Centre, School of Biomedical Sciences, University of Newcastle, Newcastle, N.S.W., Australia
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13
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Sarnyai Z, Kovács GL. Oxytocin in learning and addiction: From early discoveries to the present. Pharmacol Biochem Behav 2013; 119:3-9. [PMID: 24280016 DOI: 10.1016/j.pbb.2013.11.019] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 11/15/2013] [Indexed: 01/15/2023]
Abstract
Oxytocin (OXT) has a plethora of effects on brain function. This review provides a historical overview of the development of research on OXT and drug addiction. By focusing on research that has emerged from our laboratories, we describe how early discoveries of the influence of OXT on learning and memory processes and the emerging conceptualization of addiction as 'pathological learning' have contributed to the demonstration that OXT effectively attenuates long-term neuroadaptation related to opiate and psychostimulant addiction. Through integrating earlier evidence with recent discoveries of the social/affiliative role of OXT, we propose that OXT may interfere with reward and addiction by influencing neurobiological processes involved in stress, learning and memory and social/affiliative behavior.
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Affiliation(s)
- Zoltán Sarnyai
- Discipline of Physiology and Pharmacology, Faculty of Medicine, Health and Molecular Sciences, James Cook University, Townsville, QLD, Australia.
| | - Gábor L Kovács
- Department of Laboratory Medicine, University of Pécs, Pécs, Hungary
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14
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Brown CH, Bains JS, Ludwig M, Stern JE. Physiological regulation of magnocellular neurosecretory cell activity: integration of intrinsic, local and afferent mechanisms. J Neuroendocrinol 2013; 25:678-710. [PMID: 23701531 PMCID: PMC3852704 DOI: 10.1111/jne.12051] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2013] [Revised: 05/08/2013] [Accepted: 05/20/2013] [Indexed: 01/12/2023]
Abstract
The hypothalamic supraoptic and paraventricular nuclei contain magnocellular neurosecretory cells (MNCs) that project to the posterior pituitary gland where they secrete either oxytocin or vasopressin (the antidiuretic hormone) into the circulation. Oxytocin is important for delivery at birth and is essential for milk ejection during suckling. Vasopressin primarily promotes water reabsorption in the kidney to maintain body fluid balance, but also increases vasoconstriction. The profile of oxytocin and vasopressin secretion is principally determined by the pattern of action potentials initiated at the cell bodies. Although it has long been known that the activity of MNCs depends upon afferent inputs that relay information on reproductive, osmotic and cardiovascular status, it has recently become clear that activity depends critically on local regulation by glial cells, as well as intrinsic regulation by the MNCs themselves. Here, we provide an overview of recent advances in our understanding of how intrinsic and local extrinsic mechanisms integrate with afferent inputs to generate appropriate physiological regulation of oxytocin and vasopressin MNC activity.
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Affiliation(s)
- C H Brown
- Department of Physiology and Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.
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Apamin increases post-spike excitability of supraoptic nucleus neurons in anaesthetized morphine-naïve rats and morphine-dependent rats: consequences for morphine withdrawal excitation. Exp Brain Res 2011; 212:517-28. [DOI: 10.1007/s00221-011-2759-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Accepted: 05/31/2011] [Indexed: 12/14/2022]
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16
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Ruan M, Russell JA, Brown CH. Acute morphine administration and withdrawal from chronic morphine increase afterdepolarization amplitude in rat supraoptic nucleus neurons in hypothalamic explants. Neuropharmacology 2011; 61:789-97. [PMID: 21645529 DOI: 10.1016/j.neuropharm.2011.05.025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Revised: 05/03/2011] [Accepted: 05/18/2011] [Indexed: 11/18/2022]
Abstract
Supraoptic nucleus (SON) neurons secrete either oxytocin or vasopressin into the bloodstream from their axon terminals in the posterior pituitary gland. SON neurons are powerfully inhibited by the classical μ-opioid receptor agonist, morphine. Oxytocin neurons develop morphine dependence when chronically exposed to this opiate, and undergo robust withdrawal excitation when morphine is subsequently acutely antagonized by naloxone. Morphine withdrawal excitation is evident as an increased firing rate and is associated with an increased post-spike excitability that is consistent with the expression of an enhanced post-spike afterdepolarization (ADP) during withdrawal. Here, we used sharp electrode recording from SON neurons in hypothalamic explants from morphine naïve and morphine treated rats to determine the effects of morphine on the ADP, and to test the hypothesis that morphine withdrawal increases ADP amplitude in SON neurons. Acute morphine administration (0.05-5.0 μM) caused a dose-dependent hyperpolarization of SON neurons that was reversed by concomitant administration of 10 μM naloxone, or by washout of morphine; counter-intuitively, acute exposure to 5 μM morphine increased ADP amplitude by 78 ± 11% (mean ± SEM). Naloxone-precipitated morphine withdrawal did not alter baseline membrane potential in SON neurons from morphine treated rats, but increased ADP amplitude by 48 ± 11%; this represents a hyper-activation of ADPs because the basal amplitude of the ADP was similar in SON neurons recorded from explants prepared from morphine naïve and morphine treated rats. Hence, an enhanced ADP might contribute to morphine withdrawal excitation of oxytocin neurons.
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Affiliation(s)
- Ming Ruan
- Centre for Neuroendocrinology and Department of Physiology, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand.
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17
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Dopamine and oxytocin interactions underlying behaviors: potential contributions to behavioral disorders. CNS Neurosci Ther 2010; 16:e92-123. [PMID: 20557568 DOI: 10.1111/j.1755-5949.2010.00154.x] [Citation(s) in RCA: 233] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Dopamine is an important neuromodulator that exerts widespread effects on the central nervous system (CNS) function. Disruption in dopaminergic neurotransmission can have profound effects on mood and behavior and as such is known to be implicated in various neuropsychiatric behavioral disorders including autism and depression. The subsequent effects on other neurocircuitries due to dysregulated dopamine function have yet to be fully explored. Due to the marked social deficits observed in psychiatric patients, the neuropeptide, oxytocin is emerging as one particular neural substrate that may be influenced by the altered dopamine levels subserving neuropathologic-related behavioral diseases. Oxytocin has a substantial role in social attachment, affiliation and sexual behavior. More recently, it has emerged that disturbances in peripheral and central oxytocin levels have been detected in some patients with dopamine-dependent disorders. Thus, oxytocin is proposed to be a key neural substrate that interacts with central dopamine systems. In addition to psychosocial improvement, oxytocin has recently been implicated in mediating mesolimbic dopamine pathways during drug addiction and withdrawal. This bi-directional role of dopamine has also been implicated during some components of sexual behavior. This review will discuss evidence for the existence dopamine/oxytocin positive interaction in social behavioral paradigms and associated disorders such as sexual dysfunction, autism, addiction, anorexia/bulimia, and depression. Preliminary findings suggest that whilst further rigorous testing has to be conducted to establish a dopamine/oxytocin link in human disorders, animal models seem to indicate the existence of broad and integrated brain circuits where dopamine and oxytocin interactions at least in part mediate socio-affiliative behaviors. A profound disruption to these pathways is likely to underpin associated behavioral disorders. Central oxytocin pathways may serve as a potential therapeutic target to improve mood and socio-affiliative behaviors in patients with profound social deficits and/or drug addiction.
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18
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Mitra A, Gosnell BA, Schiöth HB, Grace MK, Klockars A, Olszewski PK, Levine AS. Chronic sugar intake dampens feeding-related activity of neurons synthesizing a satiety mediator, oxytocin. Peptides 2010; 31:1346-52. [PMID: 20399242 PMCID: PMC3175817 DOI: 10.1016/j.peptides.2010.04.005] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Revised: 04/06/2010] [Accepted: 04/07/2010] [Indexed: 01/08/2023]
Abstract
Increased tone of orexigens mediating reward occurs upon repeated consumption of sweet foods. Interestingly, some of these reward orexigens, such as opioids, diminish activity of neurons synthesizing oxytocin, a nonapeptide that promotes satiety and feeding termination. It is not known, however, whether consumption-related activity of the central oxytocin system is modified under chronic sugar feeding reward itself. Therefore, we examined how chronic consumption of a rewarding high-sucrose (HS) vs. bland cornstarch (CS) diet affected the activity of oxytocin cells in the hypothalamus at the time of meal termination. Schedule-fed (2h/day) rats received either a HS or CS powdered diet for 20 days. On the 21st day, they were given the same or the opposite diet, and food was removed after the main consummatory activity was completed. Animals were perfused 60 min after feeding termination and brains were immunostained for oxytocin and the marker of neuronal activity, c-Fos. The percentage of c-Fos-positive oxytocin cells in the hypothalamic paraventricular nucleus was significantly lower in rats chronically exposed to the HS than to the CS diet, regardless of which diet they received on the final day. A similar pattern was observed in the supraoptic nucleus. We conclude that the chronic rather than acute sucrose intake reduces activity of the anorexigenic oxytocin system. These findings indicate that chronic consumption of sugar blunts activity of pathways that mediate satiety. We speculate that a reduction in central satiety signaling precipitated by regular intake of foods high in sugar may lead to generalized overeating.
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Affiliation(s)
- Anaya Mitra
- Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Ave., St. Paul, MN 55108, USA.
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19
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Slattery DA, Neumann ID. Oxytocin and Major Depressive Disorder: Experimental and Clinical Evidence for Links to Aetiology and Possible Treatment. Pharmaceuticals (Basel) 2010; 3:702-724. [PMID: 27713275 PMCID: PMC4033976 DOI: 10.3390/ph3030702] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2010] [Revised: 02/24/2010] [Accepted: 03/05/2010] [Indexed: 11/16/2022] Open
Abstract
Affective disorders represent the most common psychiatric diseases, with substantial co-morbidity existing between major depressive disorders (MDD) and anxiety disorders. The lack of truly novel acting compounds has led to non-monoaminergic based research and hypotheses in recent years. The large number of brain neuropeptides, characterized by discrete synthesis sites and multiple receptors, represent likely research candidates for novel therapeutic targets. The present review summarises the available preclinical and human evidence regarding the neuropeptide, oxytocin, and its implications in the aetiology and treatment of MDD. While the evidence is not conclusive at present additional studies are warranted to determine whether OXT may be of therapeutic benefit in subsets of MDD patients such as those with comorbid anxiety symptoms and low levels of social attachment.
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Affiliation(s)
- David A Slattery
- Department of Behavioural and Molecular Neuroendocrinology, University of Regensburg, Universitätsstr 31, Regensburg D-93053, Germany.
| | - Inga D Neumann
- Department of Behavioural and Molecular Neuroendocrinology, University of Regensburg, Universitätsstr 31, Regensburg D-93053, Germany
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20
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Drdla R, Gassner M, Gingl E, Sandkühler J. Induction of synaptic long-term potentiation after opioid withdrawal. Science 2009; 325:207-10. [PMID: 19590003 DOI: 10.1126/science.1171759] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
mu-Opioid receptor (MOR) agonists represent the gold standard for the treatment of severe pain but may paradoxically also enhance pain sensitivity, that is, lead to opioid-induced hyperalgesia (OIH). We show that abrupt withdrawal from MOR agonists induces long-term potentiation (LTP) at the first synapse in pain pathways. Induction of opioid withdrawal LTP requires postsynaptic activation of heterotrimeric guanine nucleotide-binding proteins and N-methyl-d-aspartate receptors and a rise of postsynaptic calcium concentrations. In contrast, the acute depression by opioids is induced presynaptically at these synapses. Withdrawal LTP can be prevented by tapered withdrawal and shares pharmacology and signal transduction pathways with OIH. These findings provide a previously unrecognized target to selectively combat pro-nociceptive effects of opioids without compromising opioid analgesia.
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Affiliation(s)
- Ruth Drdla
- Department of Neurophysiology, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria
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21
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McGregor IS, Callaghan PD, Hunt GE. From ultrasocial to antisocial: a role for oxytocin in the acute reinforcing effects and long-term adverse consequences of drug use? Br J Pharmacol 2008; 154:358-68. [PMID: 18475254 DOI: 10.1038/bjp.2008.132] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Addictive drugs can profoundly affect social behaviour both acutely and in the long-term. Effects range from the artificial sociability imbued by various intoxicating agents to the depressed and socially withdrawn state frequently observed in chronic drug users. Understanding such effects is of great potential significance in addiction neurobiology. In this review we focus on the 'social neuropeptide' oxytocin and its possible role in acute and long-term effects of commonly used drugs. Oxytocin regulates social affiliation and social recognition in many species and modulates anxiety, mood and aggression. Recent evidence suggests that popular party drugs such as MDMA and gamma-hydroxybutyrate (GHB) may preferentially activate brain oxytocin systems to produce their characteristic prosocial and prosexual effects. Oxytocin interacts with the mesolimbic dopamine system to facilitate sexual and social behaviour, and this oxytocin-dopamine interaction may also influence the acquisition and expression of drug-seeking behaviour. An increasing body of evidence from animal models suggests that even brief exposure to drugs such as MDMA, cannabinoids, methamphetamine and phencyclidine can cause long lasting deficits in social behaviour. We discuss preliminary evidence that these adverse effects may reflect long-term neuroadaptations in brain oxytocin systems. Laboratory studies and preliminary clinical studies also indicate that raising brain oxytocin levels may ameliorate acute drug withdrawal symptoms. It is concluded that oxytocin may play an important, yet largely unexplored, role in drug addiction. Greater understanding of this role may ultimately lead to novel therapeutics for addiction that can improve mood and facilitate the recovery of persons with drug use disorders.
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Affiliation(s)
- I S McGregor
- School of Psychology, University of Sydney, Sydney, Australia.
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22
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Nunez C, Földes A, Laorden ML, Milanes MV, Kovács KJ. Activation of stress‐related hypothalamic neuropeptide gene expression during morphine withdrawal. J Neurochem 2007; 101:1060-71. [PMID: 17286593 DOI: 10.1111/j.1471-4159.2006.04421.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Morphine withdrawal results in serious affective and somatic symptoms including activation of the hypothalamo-pituitary-adrenocortical (HPA) axis. To reveal secretory, activational and transcriptional changes in the hypothalamus of morphine-dependent rats during naloxone precipitated opioid withdrawal, we measured corticosterone secretion, c-Fos induction and heteronuclear (hn)RNA levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in naïve and morphine dependent animals injected with saline or 5 mg/kg naloxone. Naloxone precipitated morphine withdrawal resulted in a significant increase in corticosterone secretion and induction of neuronal activation in the hypothalamic paraventricular nucleus (PVH) 2 h after challenge. Using probes complementary to intronic sequences of genes encoding neuropeptides in parvocellular neurosecretory neurons of the PVH, we found robust increases in CRH and AVP hnRNAs in morphine dependent rats during naloxone precipitated withdrawal. Naïve rats and animals that were implanted with morphine pellets for 8 days did not display significant up-regulation of ongoing neuropeptide expression in the parvocellular compartment of the PVH. In addition to hypophyseotropic neurons, naloxone precipitated withdrawal resulted in a marked activation in autonomic-related projection neurons in PVH and in the magnocellular neurons in the PVH and supraoptic nuclei. These activations however were not associated with induction of CRH or AVP hnRNAs.
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Affiliation(s)
- Cristina Nunez
- Department of Pharmacology, University of Murcia, Murcia, Spain
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23
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Wang D, Schreurs BG. Characteristics of IA currents in adult rabbit cerebellar Purkinje cells. Brain Res 2006; 1096:85-96. [PMID: 16716270 DOI: 10.1016/j.brainres.2006.04.048] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Revised: 04/07/2006] [Accepted: 04/10/2006] [Indexed: 10/24/2022]
Abstract
Classical conditioning the rabbit nictitating membrane involves changes in synaptic and intrinsic membrane properties of cerebellar Purkinje cell dendrites, and a 4-aminopyridine (4-AP)-sensitive potassium channel underlies these membrane properties. We characterized I(A) currents in adult, rabbit Purkinje cells to determine whether I(A) is the target channel involved in learning. Whole-cell recordings of Purkinje cell somas and dendrites revealed a fast activating and inactivating current with half maximal activation at -27.08 +/- 3.48 mV and -25.51 +/- 1.15 mV in somas and dendrites, respectively; half maximal inactivation at -58.91 +/- 2.34 mV and -49.90 +/- 2.58 mV; and a recovery time constant of 22.81 +/- 1.92 ms and 16.60 +/- 4.26 ms. Outside-out patch recordings from cerebellar Purkinje cell somas confirmed these 4-AP-sensitive currents with half maximal activation at -13.85 +/- 1.17 mV and half maximal inactivation at -55.07 +/- 5.54 mV. More importantly, there was an overlap of activation and incomplete inactivation at potentials from -60 to -40 mV, suggesting a "window" current that was responsible for subthreshold variations of membrane potential and might underlie conditioning-specific increases in Purkinje cell excitability. The potassium current was inhibited by 4-AP and by Heteropodatoxin, a specific blocker of Kv4.2 and Kv4.3 channels, but not by Stromatoxin, a blocker of Kv4.2 channels. Mouse monoclonal antibody labeling identified both Kv4.3 and Kv4.2 subunits in the granule cell layer but only Kv4.3 subunits in the molecular layer. This is the first demonstration of A-type currents in adult, rabbit Purkinje cells that may play a role in regulating membrane potential and firing frequency and comprise the target channel mediating conditioning-specific changes of excitability in rabbit Purkinje cell dendrites.
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Affiliation(s)
- Desheng Wang
- Department of Physiology and Pharmacology and Blanchette Rockefeller Neurosciences Institute, West Virginia University School of Medicine, Morgantown, 26506, USA.
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24
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Abstract
This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, NY 11367, USA.
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25
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Brown CH, Stern JE, Jackson KLM, Bull PM, Leng G, Russell JA. Morphine withdrawal increases intrinsic excitability of oxytocin neurons in morphine-dependent rats. Eur J Neurosci 2005; 21:501-12. [PMID: 15673449 DOI: 10.1111/j.1460-9568.2005.03885.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
To determine whether intrinsic mechanisms drive supraoptic nucleus oxytocin neuron excitation during morphine withdrawal, we calculated the probability of action potential (spike) firing with time after each spike for oxytocin neurons in morphine-naive and morphine-dependent rats in vivo and measured changes in intrinsic membrane properties in vitro. The opioid receptor antagonist, naloxone, increased oxytocin neuron post-spike excitability in morphine-dependent rats; this increase was greater for short interspike intervals (<0.1 s). Naloxone had similar, but smaller (P=0.04), effects in oxytocin neurons in morphine-naive rats. The increased post-spike excitability for short interspike intervals was specific to naloxone, because osmotic stimulation increased excitability without potentiating excitability at short interspike intervals. By contrast to oxytocin neurons, neither morphine dependence nor morphine withdrawal increased post-spike excitability in neighbouring vasopressin neurons. To determine whether increased post-spike excitability in oxytocin neurons during morphine withdrawal reflected altered intrinsic membrane properties, we measured the in vitro effects of naloxone on transient outward rectification (TOR) and after-hyperpolarization (AHP), properties mediated by K+ channels and that affect supraoptic nucleus neuron post-spike excitability. Naloxone reduced the TOR and AHP (by 20% and 60%, respectively) in supraoptic nucleus neurons from morphine-dependent, but not morphine-naive, rats. In vivo, spike frequency adaptation (caused by activity-dependent AHP activation) was reduced by naloxone (from 27% to 3%) in vasopressin neurons in morphine-dependent, but not morphine-naive, rats. Thus, multiple K+ channel inhibition increases post-spike excitability for short interspike intervals, contributing to the increased firing of oxytocin neurons during morphine withdrawal.
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Affiliation(s)
- Colin H Brown
- School of Biomedical and Clinical Laboratory Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK.
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26
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Russell JA, Ueta Y. Neuropeptide hormones and stress. Stress 2004; 7:73-4. [PMID: 15512849 DOI: 10.1080/10253890410001733526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
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