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Jang EY, Lee BH, Yun J, Yang CH, Yoon SS. Effects of the Synthetic Cathinone α-Pyrrolidinobutiothiophenone (α-PBT) on Discriminative Stimulus Effects and Intracranial Self-Stimulation Thresholds in Male Rats. ACS Chem Neurosci 2024; 15:2420-2431. [PMID: 38838000 DOI: 10.1021/acschemneuro.4c00143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2024] Open
Abstract
Recently, the abuse of synthetic cathinones is increasing among young people. α-Pyrrolidinobutiothiophenone (α-PBT), a synthetic cathinone, is a designer drug that is freely traded online with no legal restrictions. Moreover, there is currently no scientific basis for legal regulation. Here, we examined the addictive properties of α-PBT using a drug discrimination (DD) task. We also investigated the role of α-PBT in brain stimulation reward (BSR) using an intracranial self-stimulation (ICSS) paradigm in rats. Initially, the rats were trained to discriminate between cocaine and saline. After the discrimination training criteria were met, we determined the dose-effect curves of cocaine and conducted generalization tests with α-PBT and α-pyrrolidinopentiothiophenone (α-PVT) using a cumulative dosing protocol. In a separate set of studies, we examined the dopaminergic mechanisms underlying the function of α-PBT as an interoceptive stimulus (17.8 mg/kg) by intraperitoneally injecting either the dopamine (DA) D1 antagonist SCH23390 (0.06 and 0.12 mg/kg) or the D2 antagonist eticlopride (0.05 and 0.1 mg/kg) 15 min before DD testing. Brain reward function was measured using an ICSS procedure to examine the effects of α-PBT on ICSS threshold under the frequency-rate procedure. Our results showed that α-PBT functioned as a discriminative cue similar to cocaine in rats. More importantly, SCH23390 abolished the effects of α-PBT as an interoceptive stimulus in a dose-dependent manner in rats trained to press a lever to receive cocaine. Similarly, eticlopride dose-dependently attenuated the effect of α-PBT used as a discriminative cue. Additionally, cumulative α-PBT administration dose-dependently lowered ICSS thresholds compared with those in saline-treated rats. Furthermore, α-PBT-induced potentiation of BSR was abolished by pretreatment with both SCH23390 and eticlopride. Taken together, our results suggest that α-PBT can function as a cocaine-like discriminative cue via the activation of D1 and D2 receptors. α-PBT also appears to influence BSR by reducing the brain reward threshold via changes in D1 and D2 receptors. The present study suggests that α-PBT could have addictive properties through DA D1 and D2 receptors and thus poses a threat to humans.
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Affiliation(s)
- Eun Young Jang
- Department of Advanced Toxicology Research, Korea Institute of Toxicology, Daejeon 34114, Republic of Korea
| | - Bong Hyo Lee
- Department of Acupuncture, Moxibustion and Acupoint, College of Korean Medicine, Daegu Haany University, 136 Sincheondong-ro, Suseong-gu, Daegu 42158, Republic of Korea
| | - Jaesuk Yun
- College of Pharmacy and Medical Research Center, Chungbuk National University, Osongsaengmyeong 1-ro, Osong-eup, Heungdeok-gu, Cheongju, Chungbuk 28160, Republic of Korea
| | - Chae Ha Yang
- Department of Physiology, College of Korean Medicine, Daegu Haany University, 136 Sincheondong-ro, Suseong-gu, Daegu 42158, Republic of Korea
| | - Seong Shoon Yoon
- Department of Physiology, College of Korean Medicine, Daegu Haany University, 136 Sincheondong-ro, Suseong-gu, Daegu 42158, Republic of Korea
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Negus SS, Akbarali HI, Kang M, Lee YK, Marsh SA, Santos EJ, Zhang Y. Role of mu opioid receptor (MOR) agonist efficacy as a determinant of opioid antinociception in a novel assay of pain-depressed behavior in female and male mice. FRONTIERS IN PAIN RESEARCH 2023; 4:1281698. [PMID: 37886350 PMCID: PMC10598607 DOI: 10.3389/fpain.2023.1281698] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Accepted: 09/21/2023] [Indexed: 10/28/2023] Open
Abstract
Introduction Intermediate efficacy mu opioid receptor (MOR) agonists have potential to retain analgesic effectiveness while improving safety, but the optimal MOR efficacy for effective and safe opioid analgesia is unknown. Preclinical assays of pain-depressed behavior can assess effects of opioids and other candidate analgesics on pain-related behavioral depression, which is a common manifestation of clinically relevant pain and target of pain treatment. Accordingly, the present study goal was to validate a novel assay of pain-depressed locomotor behavior in mice and evaluate the role of MOR efficacy as a determinant of opioid analgesic effects and related safety measures. Methods Male and female ICR mice were tested in a locomotor chamber consisting of 2 compartments connected by a doorway that contained a 1-inch-tall barrier. Dependent measures during 15-min behavioral sessions included crosses between compartments (which required vertical activity to surmount the barrier) and total movement counts (which required horizontal activity to break photobeams in each compartment). Results and Discussion Intraperitoneal injection of lactic acid (IP acid) produced a concentration- and time-dependent depression of both endpoints. Optimal blockade of IP acid-induced behavioral depression with minimal motor impairment was achieved with intermediate-efficacy MOR treatments that also produced less gastrointestinal-transit inhibition and respiratory depression than the high-efficacy MOR agonist fentanyl. Sex differences in treatment effects were rare. Overall, these findings validate a novel procedure for evaluating opioids and other candidate analgesic effects on pain-related behavioral depression in mice and support continued research with intermediate-efficacy MOR agonists as a strategy to retain opioid analgesic effectiveness with improved safety.
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Affiliation(s)
- S. Stevens Negus
- Department of Pharmacology & Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, VA, United States
| | - Hamid I. Akbarali
- Department of Pharmacology & Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, VA, United States
| | - Minho Kang
- Department of Pharmacology & Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, VA, United States
| | - Young K. Lee
- Department of Pharmacology & Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, VA, United States
| | - Samuel A. Marsh
- Department of Pharmacology & Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, VA, United States
| | - Edna J. Santos
- Department of Pharmacology & Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, VA, United States
| | - Yan Zhang
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, United States
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Baird TR, Akbarali HI, Dewey WL, Elder H, Kang M, Marsh SA, Peace MR, Poklis JL, Santos EJ, Negus SS. Opioid-like adverse effects of tianeptine in male rats and mice. Psychopharmacology (Berl) 2022; 239:2187-2199. [PMID: 35211768 PMCID: PMC10055856 DOI: 10.1007/s00213-022-06093-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 02/13/2022] [Indexed: 01/22/2023]
Abstract
RATIONALE Tianeptine is a mu-opioid receptor (MOR) agonist with increasing reports of abuse in human populations. Preclinical data regarding the abuse potential and other opioid-like adverse effects of tianeptine at supratherapeutic doses are sparse. OBJECTIVES The present study evaluated tianeptine in a rat model of abuse potential assessment and in mouse models of motor, gastrointestinal, and respiratory adverse effects. METHODS Abuse potential was assessed in adult male Sprague-Dawley rats using an intracranial self-stimulation (ICSS) procedure to determine effects of acute and repeated tianeptine on responding for electrical brain stimulation. Male ICR mice were used to determine the effects of tianeptine in assays of locomotor behavior and gastrointestinal motility. Male Swiss-Webster mice were monitored for respiratory changes using whole-body plethysmography. RESULTS In rats, acute tianeptine produced weak and delayed evidence for abuse-related ICSS facilitation at an intermediate dose (10 mg/kg, IP) and pronounced, naltrexone-preventable ICSS depression at a higher dose (32 mg/kg, IP). Repeated 7-day tianeptine (10 and 32 mg/kg/day, IP) produced no increase in abuse-related ICSS facilitation, only modest tolerance to ICSS depression, and no evidence of physical dependence. In mice, tianeptine produced dose-dependent, naltrexone-preventable locomotor activation. Tianeptine (100 mg/kg, SC) also significantly inhibited gastrointestinal motility and produced naloxone-reversible respiratory depression. CONCLUSIONS Tianeptine presents as a MOR agonist with resistance to tolerance and dependence in our ICSS assay in rats, and it has lower abuse potential by this metric than many commonly abused opioids. Nonetheless, tianeptine produces MOR agonist-like acute adverse effects that include motor impairment, constipation, and respiratory depression.
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Affiliation(s)
- T R Baird
- Integrative Life Sciences Doctoral Program, Virginia Commonwealth University, 1000 West Cary St., Richmond, VA, 23284, USA.,Department of Forensic Science, Virginia Commonwealth University, 1015 Floyd Avenue, Richmond, VA, 23284, USA
| | - H I Akbarali
- Department of Pharmacology & Toxicology, Virginia Commonwealth University, 410 N. 12th St, Richmond, VA, 23298, USA
| | - W L Dewey
- Department of Pharmacology & Toxicology, Virginia Commonwealth University, 410 N. 12th St, Richmond, VA, 23298, USA
| | - H Elder
- Department of Pharmacology & Toxicology, Virginia Commonwealth University, 410 N. 12th St, Richmond, VA, 23298, USA
| | - M Kang
- Department of Pharmacology & Toxicology, Virginia Commonwealth University, 410 N. 12th St, Richmond, VA, 23298, USA
| | - S A Marsh
- Department of Pharmacology & Toxicology, Virginia Commonwealth University, 410 N. 12th St, Richmond, VA, 23298, USA
| | - M R Peace
- Department of Forensic Science, Virginia Commonwealth University, 1015 Floyd Avenue, Richmond, VA, 23284, USA
| | - J L Poklis
- Department of Pharmacology & Toxicology, Virginia Commonwealth University, 410 N. 12th St, Richmond, VA, 23298, USA
| | - E J Santos
- Department of Pharmacology & Toxicology, Virginia Commonwealth University, 410 N. 12th St, Richmond, VA, 23298, USA
| | - S S Negus
- Department of Pharmacology & Toxicology, Virginia Commonwealth University, 410 N. 12th St, Richmond, VA, 23298, USA.
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Moerke MJ, Negus SS, Banks ML. Lack of effect of the nociceptin opioid peptide agonist Ro 64-6198 on pain-depressed behavior and heroin choice in rats. Drug Alcohol Depend 2022; 231:109255. [PMID: 34998256 PMCID: PMC8810604 DOI: 10.1016/j.drugalcdep.2021.109255] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 11/11/2021] [Accepted: 12/01/2021] [Indexed: 02/03/2023]
Abstract
RATIONALE AND OBJECTIVE One objective of the National Institutes of Health Helping to End Addiction Long-term (HEAL) initiative is to accelerate research on safer and more effective medications for both pain and opioid use disorder. Ligands that activate the nociceptin opioid peptide receptor (NOP) constitute one class of candidate drugs for both applications. The present preclinical study determined the effectiveness of the NOP agonist Ro 64-6198 to produce antinociception in a pain-depressed behavior procedure and attenuate opioid self-administration in a heroin-vs-food choice procedure. METHODS In Experiment 1, Adult Sprague-Dawley rats were equipped with microelectrodes and trained to respond for electrical brain stimulation in an intracranial self-stimulation (ICSS) procedure. The potency, time course, and receptor mechanism of effects produced by R0 64-6198 alone (0.32-3.2 mg/kg) on ICSS were examined, followed by evaluation of 0.32-1.0 mg/kg Ro 64-6198 effectiveness to block lactic acid-induced depression of ICSS. In Experiment 2, rats self-administered heroin under a heroin-vs-food choice procedure during a regimen of repeated, daily intraperitoneal administration of vehicle or Ro 64-6198 (1-3.2 mg/kg/day). RESULTS Ro 64-6198 produced dose- and time-dependent ICSS depression that was blocked by the selective NOP antagonist SB612111 but not by naltrexone. Ro 64-6198 failed to block acid-induced depression of ICSS. Repeated Ro 64-6198 pretreatment also failed to attenuate heroin-vs-food choice up to doses that significantly decreased operant behavior. CONCLUSIONS These results do not support the utility of Ro 64-6198 as a stand-alone medication for either acute pain or opioid use disorder.
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Affiliation(s)
- Megan Jo Moerke
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, USA; Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, USA
| | - S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, USA
| | - Matthew L Banks
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, USA.
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Temporal parameters of enhanced opioid reward after initial opioid exposure in rats. Psychopharmacology (Berl) 2021; 238:725-734. [PMID: 33410983 PMCID: PMC7914195 DOI: 10.1007/s00213-020-05725-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Accepted: 11/16/2020] [Indexed: 10/22/2022]
Abstract
RATIONALE Mu opioid receptor agonists are indispensable for the treatment of pain, but clinical use carries the inherent risk of transition from effective treatment to abuse. Abuse potential appears to increase rapidly during periods of initial opioid exposure in humans, and this increase in opioid reward during initial opioid exposure can be modeled in rats using an intracranial self-stimulation (ICSS) procedure. OBJECTIVES The goal of the present study was to examine temporal parameters of this phenomenon. METHODS Adult male Sprague-Dawley rats responded for electrical brain stimulation using a frequency-rate ICSS procedure. In the first experiment, rats received daily morphine injections for 6 days, and morphine effects on ICSS were re-determined 1 day, 1 week, or 1 month after the repeated morphine treatment regimen to evaluate the persistence of enhanced opioid reward. In the second experiment, rats received six repeated morphine injections with different interdose intervals (two per day, one per day, every other day, every fourth day), and morphine effects were re-determined 1 day after the last dose to determine dosing frequencies sufficient to produce enhanced opioid reward. RESULTS Results of the first experiment indicated that enhanced opioid reward was greatest 1 day after the morphine treatment regimen and completely dissipated after 4 weeks. The second experiment indicated that all dosing frequencies tested were sufficient to produce enhanced reward. CONCLUSIONS Taken together, these results suggest that enhancement of opioid reward after initial opioid exposure is relatively transient but can be produced by a range of different dosing frequencies.
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Baird TR, Davies RA, Glennon RA, Peace MR, Negus SS. A Strategy to Prioritize Emerging Drugs of Abuse for Analysis: Abuse Liability Testing Using Intracranial Self-Stimulation (ICSS) in Rats and Validation with α-Pyrrolidinohexanophenone (α-PHP). EMERGING TRENDS IN DRUGS, ADDICTIONS, AND HEALTH 2021; 1:100004. [PMID: 34296204 PMCID: PMC8294200 DOI: 10.1016/j.etdah.2021.100004] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Novel psychoactive substances (NPS) threaten public health and safety while also straining the limited resources of forensic laboratories. To efficiently allocate the finite resources available, we propose a new strategy for prioritizing NPS with abuse liability testing using a preclinical behavioral procedure in rats known as intracranial self-stimulation (ICSS). To validate this assay, the recently-scheduled synthetic cathinone α-PHP was compared to cocaine, a mechanistically similar drug of abuse, as a positive control and saline as a negative control. Male Sprague-Dawley rats (n=6) were implanted with electrodes targeting the medial forebrain bundle and trained to respond by lever-press for electrical brain stimulation. The rats were tested with doses of 0.32, 1.0, and 3.2 mg/kg α-PHP as well as 10 mg/kg of cocaine and saline administered by intraperitoneal injection. Neither saline nor 0.32 mg/kg α-PHP altered ICSS response rates compared to baseline levels of responding; however, doses of 1.0 and 3.2 mg/kg α-PHP and 10 mg/kg cocaine facilitated ICSS responding. This ICSS profile suggests that α-PHP has high abuse potential, with a rapid onset of effects and a long duration of action, and supports the decision to schedule this compound. This study demonstrates the ability of ICSS to distinguish between compounds of low and high potential for abuse. A strategy is proposed here to screen NPS using ICSS and classify emerging drugs into four priority categories for further analysis.
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Affiliation(s)
- Tyson R. Baird
- Integrative Life Sciences Doctoral Program, Virginia Commonwealth University
- Department of Forensic Science, Virginia Commonwealth University
| | - Rachel A. Davies
- Department of Medicinal Chemistry, Virginia Commonwealth University
| | | | | | - S. Stevens Negus
- Department of Pharmacology & Toxicology, Virginia Commonwealth University
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Altarifi AA, Moerke MJ, Alsalem MI, Negus SS. Preclinical assessment of tramadol abuse potential: Effects of acute and repeated tramadol on intracranial self-stimulation in rats. J Psychopharmacol 2020; 34:269881120944153. [PMID: 32842842 DOI: 10.1177/0269881120944153] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Tramadol is a widely used analgesic that activates mu-opioid receptors (MOR) and inhibits serotonin and norepinephrine transporters. This mixed pharmacology may limit both its own abuse potential and its modulation of abuse potential of other MOR agonists. AIMS This study used an intracranial self-stimulation (ICSS) procedure to compare abuse-related effects produced by acute or repeated treatment with tramadol or morphine in rats. Abuse potential in ICSS procedures is indicated by a drug-induced increase (or 'facilitation') of ICSS responding. METHODS Adult male Sprague-Dawley rats were implanted with electrodes targeting the medial forebrain bundle and trained to respond on a lever for pulses of electrical brain stimulation. Tramadol effects were evaluated after acute administration (3.2-32 mg/kg) in the absence or presence of the opioid antagonist naltrexone, the CYP2D6 hepatic-enzyme inhibitor quinine or a combination of both. Additionally, both tramadol and morphine were also tested before and after repeated tramadol (32 mg/kg/day for six days) or repeated morphine (3.2 mg/kg/day for six days). RESULTS Acute tramadol produced primarily ICSS rate-decreasing effects that were antagonised by naltrexone but not by quinine or naltrexone + quinine. Tramadol also produced little or no ICSS facilitation after repeated tramadol or repeated morphine, and repeated tramadol did not enhance ICSS facilitation by morphine. By contrast, morphine-induced ICSS facilitation was enhanced by repeated morphine treatment. CONCLUSIONS These results suggest that tramadol has lower abuse potential than other abused MOR agonists and that repeated tramadol exposure produces relatively little enhancement of abuse potential of other MOR agonists.
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Affiliation(s)
- Ahmad A Altarifi
- Department of Pharmacology, Faculty of Medicine, Jordan University of Science and Technology, Irbid, Jordan
| | - Megan J Moerke
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, USA
| | - Mohammad I Alsalem
- Department of Anatomy and Histology, Faculty of Medicine, The University of Jordan, Amman, Jordan
| | - S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, USA
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Alsalem M, Altarifi A, Haddad M, Aldossary SA, Kalbouneh H, Aldaoud N, Saleh T, El-Salem K. Antinociceptive and Abuse Potential Effects of Cannabinoid/Opioid Combinations in a Chronic Pain Model in Rats. Brain Sci 2019; 9:brainsci9110328. [PMID: 31744226 PMCID: PMC6896179 DOI: 10.3390/brainsci9110328] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 11/04/2019] [Accepted: 11/14/2019] [Indexed: 12/15/2022] Open
Abstract
Chronic pain is a persistent and debilitating health problem. Although the use of analgesics such as opioids is useful in mitigating pain, their prolonged use is associated with unwanted effects including abuse liability. This study assesses the antinociceptive effect of combining subtherapeutic doses of two opioids (morphine or tramadol) with the synthetic cannabinoid CP55940 (2-[(1R,2R,5R)-5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]-5-(2-methyloctan -2-yl)phenol). It also evaluates the associated adverse effects of these drugs and combinations. Adult male rats were injected with intraplantar complete Freund’s adjuvant (CFA) to produce mechanical allodyia. Antinociceptive effect of morphine, tramadol, the synthetic cannabinoid CP55940, or their combinations was evaluated three to nine days post-CFA injections. Intracranial self-stimulation (ICSS) was utilized to evaluate the abuse liability of these drugs or their combinations. All drugs alone produced a dose-dependent antinociceptive effect. Morphine produced minimal effect on ICSS, but both tramadol and CP55940 produced dose-dependent depression of ICSS. Morphine at a dose of 0.32 mg/kg enhanced the antinociceptive effects of CP55940, in that, CP55940 produced antinociception at a lower dose (0.1 mg/kg) when compared to the vehicle. The aforementioned combinations did not change CP55940-induced depression of ICSS. On the other hand, tramadol failed to enhance the antinociceptive effect of CP55940. Our data suggest that combining CP55940 with morphine, but not tramadol, shows a better antinociceptive profile with no additional risk of abuse liability, which represents a potential pain management approach.
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Affiliation(s)
- Mohammad Alsalem
- Faculty of Medicine, The University of Jordan, Amman 11942, Jordan; (H.K.); (N.A.)
- Correspondence:
| | - Ahmad Altarifi
- Faculty of Medicine, Jordan University of Science and Technology, Irbid 22110, Jordan; (A.A.); (K.E.-S.)
| | - Mansour Haddad
- Faculty of Pharmacy, Philadelphia University, Amman 19392, Jordan;
| | - Sara A. Aldossary
- Faculty of Clinical Pharmacy, King Faisal University, Hofuf 31982, Saudi Arabia;
| | - Heba Kalbouneh
- Faculty of Medicine, The University of Jordan, Amman 11942, Jordan; (H.K.); (N.A.)
| | - Nour Aldaoud
- Faculty of Medicine, The University of Jordan, Amman 11942, Jordan; (H.K.); (N.A.)
| | - Tareq Saleh
- Faculty of Medicine, The Hashemite University, Zarqa 13133, Jordan;
| | - Khalid El-Salem
- Faculty of Medicine, Jordan University of Science and Technology, Irbid 22110, Jordan; (A.A.); (K.E.-S.)
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Moerke MJ, Negus SS. Role of agonist efficacy in exposure-induced enhancement of mu opioid reward in rats. Neuropharmacology 2019; 151:180-188. [PMID: 30880123 DOI: 10.1016/j.neuropharm.2019.03.020] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 02/14/2019] [Accepted: 03/13/2019] [Indexed: 10/27/2022]
Abstract
The abuse potential of opioid analgesics in humans appears to increase rapidly during initial regimens of opioid exposure. Previous work using intracranial self-stimulation (ICSS), a preclinical procedure useful for studying rewarding drug effects in drug-naïve animals, has similarly shown that rewarding effects of mu opioid receptor (MOR) agonists increase rapidly in rats during initial regimens of opioid administration. The goal of the present study was to evaluate the role of MOR agonist efficacy as a determinant in eliciting this trajectory of increased rewarding effects during initial opioid exposure in opioid-naïve rats. Separate groups of adult, male Sprague-Dawley rats responded for electrical brain stimulation using a frequency-rate ICSS procedure and received repeated daily treatment with vehicle or one of five MOR agonists that ranged from low to high efficacy (NAQ, nalbuphine, buprenorphine, fentanyl, methadone). Two additional groups were used to evaluate effects of repeated treatment with non-opioids (the cannabinoid CP55940 or the monoamine releaser amphetamine). Morphine was tested after each repeated treatment. In opioid-naïve rats tested before repeated dosing, MOR agonists produced primarily dose- and efficacy-dependent decreases in ICSS. Following repeated treatment, all MOR agonists except NAQ produced tolerance to opioid-induced rate-decreasing effects and enhanced expression of ICSS facilitation (indicative of opioid reward) by both the repeatedly administered drug and morphine. Repeated treatment with CP55940 and amphetamine produced different effects. Collectively, these results provide evidence to suggest that enhanced expression of opioid reward after initial regimens of opioid exposure has a low requirement for MOR agonist efficacy and is pharmacologically selective.
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Affiliation(s)
- Megan J Moerke
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 N 12th Street, Richmond, VA, 23298, USA
| | - S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 N 12th Street, Richmond, VA, 23298, USA.
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Effects of repeated treatment with methcathinone, mephedrone, and fenfluramine on intracranial self-stimulation in rats. Psychopharmacology (Berl) 2019; 236:1057-1066. [PMID: 30232529 PMCID: PMC6424659 DOI: 10.1007/s00213-018-5029-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Accepted: 09/04/2018] [Indexed: 12/29/2022]
Abstract
RATIONALE Synthetic cathinones constitute a class of abused drugs that can act at dopamine, norepinephrine, and serotonin transporters (DAT, NET, and SERT, respectively). Intracranial self-stimulation (ICSS) is a preclinical procedure that can be used to evaluate abuse potential of drugs, and prior studies have indicated that abuse-related ICSS effects of monoamine-transporter substrates, including some synthetic cathinones, are positively correlated with drug selectivity for DAT vs. SERT. Abuse potential of drugs can also be influenced by regimens of repeated drug exposure, but the role of repeated exposure on abuse-related ICSS effects of synthetic cathinones has not been examined. OBJECTIVES This study used ICSS to evaluate effects of repeated treatment with the DAT>SERT substrate methcathinone, the DAT<SERT substrate fenfluramine, and the DAT≈SERT substrate mephedrone. METHODS Male Sprague-Dawley rats were trained in a frequency-rate ICSS procedure, and different groups were used to evaluate effects of methcathinone, mephedrone, and fenfluramine before, during, and after regimens of repeated treatment with the designated drug. RESULTS Before repeated treatment, methcathinone produced dose-dependent and abuse-related ICSS facilitation, fenfluramine produced dose-dependent ICSS depression, and mephedrone produced mixed effects that included both facilitation and depression. Chronic treatment produced no change in effects of methcathinone, but complete tolerance to effects of fenfluramine. For mephedrone, chronic treatment produced partial tolerance to ICSS depression and enhanced expression of ICSS facilitation. CONCLUSIONS Repeated exposure to mixed-action DAT≈SERT substrates such as mephedrone can result in increased abuse potential due to sustained expression of DAT-mediated abuse-related effects and tolerance to SERT-mediated abuse-limiting effects.
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Negus SS, Moerke MJ. Determinants of opioid abuse potential: Insights using intracranial self-stimulation. Peptides 2019; 112:23-31. [PMID: 30391425 PMCID: PMC6342636 DOI: 10.1016/j.peptides.2018.10.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Revised: 10/24/2018] [Accepted: 10/25/2018] [Indexed: 12/14/2022]
Abstract
Intracranial self-stimulation (ICSS) is one procedure that can be used for preclinical abuse potential assessment. In ICSS procedures, subjects with microelectrodes implanted into a brain-reward region are trained to press an operant response lever for pulses of electrical brain stimulation, and drugs are evaluated for their effectiveness to increase or "facilitate" ICSS responding (an abuse-related effect) or to depress ICSS responding (an abuse-limiting effect). ICSS has been used for decades to evaluate determinants of opioid abuse potential, and this article reviews pharmacological and biological determinants of opioid abuse potential as revealed by ICSS studies in rodents. One of the most important observations from ICSS studies is that abused mu opioid receptor (MOR) agonists like morphine often fail to produce abuse-related ICSS facilitation in opioid-naïve subjects, but several days of repeated opioid exposure is sufficient for opioid-induced facilitation to emerge. Future studies with ICSS could help (a) to clarify mechanisms that increase MOR agonist abuse potential during early opioid exposure or during chronic exposure leading to dependence, (b) to evaluate novel opioids either developed as candidate analgesics with reduced abuse potential or identified as designer opioids being synthesized and distributed for illicit use, and (c) to test candidate pharmacotherapies for treatment of opioid abuse in non-dependent and dependent subjects.
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Affiliation(s)
- S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond VA 23298, United States.
| | - Megan J Moerke
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond VA 23298, United States
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Sakloth F, Negus SS. Naltrexone maintenance fails to alter amphetamine effects on intracranial self-stimulation in rats. Exp Clin Psychopharmacol 2018; 26. [PMID: 29528663 PMCID: PMC5897164 DOI: 10.1037/pha0000183] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Pharmacotherapy to treat stimulant use disorders continues to be an unmet medical need. Some evidence supports both the role of opioids in mediating abuse-related amphetamine effects and the potential utility of opioid antagonists as therapeutic candidates for treating amphetamine abuse. This study used intracranial self-stimulation (ICSS) to evaluate effects of exposure to and termination of naltrexone maintenance on rewarding amphetamine effects in an ICSS procedure in rats. Morphine and cocaine were included as positive and negative controls, respectively. Male Sprague-Dawley rats (N = 40) were trained to lever press for electrical brain stimulation to the medial forebrain bundle via an implanted electrode. Rats were then implanted with osmotic pumps delivering naltrexone (0.001 mg/kg/h, SC, 0.01 mg/kg/h, SC, or 0.1 mg/kg/h, SC) or saline for 14 days. Cumulative dose-effect curves were determined for amphetamine (0.032 mg/kg to 0.32 mg/kg), cocaine (1 mg/kg to 10 mg/kg), and morphine (1 mg/kg to 10 mg/kg) during the 2nd week of naltrexone maintenance. Additionally, dose-effect curves for morphine and amphetamine were determined again 24 hr after pump removal. Our results suggest that (a) exposure to and termination of naltrexone maintenance do not affect baseline ICSS responding, (b) naltrexone doses sufficient to antagonize morphine did not alter amphetamine or cocaine effects, and (c) termination of naltrexone treatment produced weak evidence for increased morphine sensitivity but no change in amphetamine effects. Our results do not support naltrexone as a pharmacotherapy for amphetamine and cocaine abuse and also suggest that termination from chronic naltrexone does not increase sensitivity to abuse-related morphine or amphetamine effects in ICSS. (PsycINFO Database Record
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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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Freitas K, Carroll FI, Negus SS. Comparison of effects produced by nicotine and the α4β2-selective agonist 5-I-A-85380 on intracranial self-stimulation in rats. Exp Clin Psychopharmacol 2016; 24:65-75. [PMID: 26461167 PMCID: PMC4821675 DOI: 10.1037/pha0000055] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Intracranial self-stimulation (ICSS) is one type of preclinical procedure for research on pharmacological mechanisms that mediate abuse potential of drugs acting at various targets, including nicotinic acetylcholine receptors (nAChRs). This study compared effects of the nonselective nAChR agonist nicotine (0.032-1.0 mg/kg) and the α4β2-selective nAChR agonist 5-I-A-85380 (0.01-1.0 mg/kg) on ICSS in male Sprague-Dawley rats. Rats were implanted with electrodes targeting the medial forebrain bundle at the level of the lateral hypothalamus and trained to respond under a fixed-ratio 1 schedule for a range of brain stimulation frequencies (158-56 Hz). A broad range of 5-I-A-85380 doses produced an abuse-related increase (or "facilitation") of low ICSS rates maintained by low brain-stimulation frequencies, and this effect was blocked by both the nonselective nAChR antagonist mecamylamine and the selective α4β2 antagonist dihyrdo-β-erythroidine (DHβE). Conversely, nicotine produced weaker ICSS facilitation across a narrower range of doses, and higher nicotine doses decreased high rates of ICSS maintained by high brain-stimulation frequencies. The rate-decreasing effects of a high nicotine dose were blocked by mecamylamine but not DHβE. Chronic nicotine treatment produced selective tolerance to rate-decreasing effects of nicotine but did not alter ICSS rate-increasing effects of nicotine. These results suggest that α4β2 receptors are sufficient to mediate abuse-related rate-increasing effects of nAChR agonists in this ICSS procedure. Conversely, nicotine effects at non-α4β2 nAChRs appear to oppose and limit abuse-related effects mediated by α4β2 receptors, although tolerance can develop to these non-α4β2 effects. Selective α4β2 agonists may have higher abuse potential than nicotine.
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Affiliation(s)
- Kelen Freitas
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond VA, USA
| | - F. Ivy Carroll
- Research Triangle Institute, Research Triangle Park, NC, USA
| | - S. Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond VA, USA
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Wiebelhaus JM, Walentiny DM, Beardsley PM. Effects of Acute and Repeated Administration of Oxycodone and Naloxone-Precipitated Withdrawal on Intracranial Self-Stimulation in Rats. J Pharmacol Exp Ther 2015; 356:43-52. [PMID: 26491062 DOI: 10.1124/jpet.115.228940] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Accepted: 10/20/2015] [Indexed: 01/24/2023] Open
Abstract
Incidence of prescription opioid abuse and overdose, often led by oxycodone, continues to increase, producing twice as many overdose deaths as heroin. Surprisingly, preclinical reports relevant to oxycodone's abuse-related effects are relatively sparse considering its history and patient usage. The goal of this study was to characterize dose- and time-dependent effects of acute and repeated oxycodone administration in a frequency-rate intracranial self-stimulation (ICSS) procedure, an assay often predictive of drug-related reinforcing effects, in male Sprague-Dawley rats. We hypothesized that oxycodone would produce a biphasic profile of rate-increasing and rate-decreasing effects maintained by ICSS similar to μ-opioid receptor agonists. Oxycodone (0.03, 0.3, 1, and 3 mg/kg, s.c.) produced dose- and time-dependent alterations on ICSS, with the predicted biphasic profile of rate-increasing effects at lower stimulation frequencies followed by rate-decreasing effects at higher frequencies. Peak effects were observed between 30 and 60 minutes, which were reversed by naloxone pretreatment (30 minutes). Tolerance to rate-decreasing effects was observed over a 5-day period when rats were treated with 1 mg/kg oxycodone twice a day. Subsequently, the dosing regimen was increased to 3 mg/kg twice a day over 10 days, although further marked tolerance did not develop. When then challenged with 10 mg/kg naloxone, a significant suppression below baseline levels of ICSS-maintained responding occurred indicative of dependence that recovered to baseline within 5 hours. The results of this study provide the first report of acute and chronic effects of oxycodone on responding maintained by ICSS presentation and the use of ICSS-maintained responding to characterize its tolerance and dependence effects.
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Affiliation(s)
- Jason M Wiebelhaus
- Department of Pharmacology and Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, Virginia
| | - D Matthew Walentiny
- Department of Pharmacology and Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, Virginia
| | - Patrick M Beardsley
- Department of Pharmacology and Toxicology, School of Medicine, Virginia Commonwealth University, Richmond, Virginia
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Miller LL, Altarifi AA, Negus SS. Effects of repeated morphine on intracranial self-stimulation in male rats in the absence or presence of a noxious pain stimulus. Exp Clin Psychopharmacol 2015; 23:405-14. [PMID: 26375515 PMCID: PMC4578993 DOI: 10.1037/pha0000042] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Research on opioid analgesics such as morphine suggests that expression of abuse-related effects increases with repeated exposure. Repeated exposure to opioids often occurs clinically in the context of pain management, and a major concern for clinicians is the risk of iatrogenic addiction and dependence in patients receiving opioids for treatment of pain. This study compared abuse-related morphine effects in male rats in an intracranial self-stimulation (ICSS) procedure after repeated treatment either with morphine alone or with morphine in combination with a repeated noxious stimulus (intraperitoneal administration of dilute acid). The study also permitted comparison of morphine potency and effectiveness to block acid-induced depression of ICSS (antinociception) and to produce enhanced facilitation of ICSS (abuse-related effect). There were 3 main findings. First, initial morphine exposure to drug naïve rats did not produce abuse-related ICSS facilitation. Second, repeated daily treatment with 3.2 mg/kg/day morphine for 6 days increased expression of ICSS facilitation. This occurred whether morphine was administered in the absence or presence of the noxious stimulus. Finally, a lower dose of 1.0 mg/kg/day morphine was sufficient to produce antinociception during repeated acid treatment, but this lower dose did not reliably increase abuse-related morphine effects. Taken together, these results suggest that prior morphine exposure can increase abuse liability of subsequent morphine treatments even when that morphine exposure occurs in the context of a pain state. However, it may be possible to relieve pain with relatively low morphine doses that do not produce increases in abuse-related morphine effects.
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Affiliation(s)
- Laurence L. Miller
- Department of Psychological Science, Georgia Regents University, Augusta GA, USA
| | - Ahmad A. Altarifi
- Department of Pharmacology, Jordan University of Science and Technology, Irbid, Jordan
| | - S. Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond VA, USA
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Miller LL, Leitl MD, Banks ML, Blough BE, Negus SS. Effects of the triple monoamine uptake inhibitor amitifadine on pain-related depression of behavior and mesolimbic dopamine release in rats. Pain 2015; 156:175-184. [PMID: 25599313 DOI: 10.1016/j.pain.0000000000000018] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Pain-related depression of behavior and mood is a key therapeutic target in the treatment of pain. Clinical evidence suggests a role for decreased dopamine (DA) signaling in pain-related depression of behavior and mood. Similarly, in rats, intraperitoneal injection of dilute lactic acid (IP acid) serves as a chemical noxious stimulus to produce analgesic-reversible decreases in both (1) extracellular DA levels in nucleus accumbens (NAc) and (2) intracranial self-stimulation (ICSS), an operant behavior reliant on NAc DA. Intraperitonial acid-induced depression of ICSS is blocked by DA transporter (DAT) inhibitors, but clinical viability of selective DAT inhibitors as analgesics is limited by abuse potential. Drugs that produce combined inhibition of both DA and serotonin transporters may retain efficacy to block pain-related behavioral depression with reduced abuse liability. Amitifadine is a "triple uptake inhibitor" that inhibits DAT with approximately 5- to 10-fold weaker potency than it inhibits serotonin and norepinephrine transporters. This study compared amitifadine effects on IP acid-induced depression of NAc DA and ICSS and IP acid-stimulated stretching in male Sprague-Dawley rats. Amitifadine blocked IP acid-induced depression of both NAc DA and ICSS and IP acid-stimulated stretching. In the absence of the noxious stimulus, amitifadine increased NAc levels of both DA and serotonin, and behaviorally, amitifadine produced significant but weak abuse-related ICSS facilitation. Moreover, amitifadine was more potent to block IP acid-induced depression of ICSS than to facilitate control ICSS. These results support consideration of amitifadine and related monoamine uptake inhibitors as candidate analgesics for treatment of pain-related behavioral depression.
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Affiliation(s)
- Laurence L Miller
- Department of Psychological Sciences, Georgia Regents University Augusta, Augusta, GA, USA Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, USA Center for Drug Discovery, Research Triangle Institute International, Research Triangle Park, NC, USA
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Grim TW, Wiebelhaus JM, Negus SS, Lichtman AH, Lichtman AH. Effects of acute and repeated dosing of the synthetic cannabinoid CP55,940 on intracranial self-stimulation in mice. Drug Alcohol Depend 2015; 150:31-7. [PMID: 25772438 PMCID: PMC4601922 DOI: 10.1016/j.drugalcdep.2015.01.022] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 01/19/2015] [Accepted: 01/21/2015] [Indexed: 01/19/2023]
Abstract
BACKGROUND Synthetic cannabinoids have emerged as a significant public health concern. To increase the knowledge of how these molecules interact on brain reward processes, we investigated the effects of CP55,940, a high efficacy synthetic CB1 receptor agonist, in a frequency-rate intracranial self-stimulation (ICSS) procedure. METHODS The impact of acute and repeated administration (seven days) of CP55,940 on operant responding for electrical brain stimulation of the medial forebrain bundle was investigated in C57BL/6J mice. RESULTS CP55,940 attenuated ICSS in a dose-related fashion (ED50 (95% C.L.)=0.15 (0.12-0.18)mg/kg). This effect was blocked by the CB1 receptor antagonist rimonabant. Tolerance developed quickly, though not completely, to the rate-decreasing effects of CP55,940 (0.3mg/kg). Abrupt discontinuation of drug did not alter baseline responding for up to seven days. Moreover, rimonabant (10mg/kg) challenge did not alter ICSS responding in mice treated repeatedly with CP55,940. CONCLUSIONS The finding that CP55,940 reduced ICSS in mice with no evidence of facilitation at any dose is consistent with synthetic cannabinoid effects on ICSS in rats. CP55,940-induced ICSS depression was mediated through a CB1 receptor mechanism. Additionally, tolerance and dependence following repeated CP55,940 administration were dissociable. Thus, CP55,940 does not produce reward-like effects in ICSS under these conditions.
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Affiliation(s)
| | | | | | | | - Aron H Lichtman
- Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, PO Box 980613, Richmond, 23298-0613, VA U.S.A
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Altarifi AA, Yuan Y, Zhang Y, Selley DE, Negus SS. Effects of the novel, selective and low-efficacy mu opioid receptor ligand NAQ on intracranial self-stimulation in rats. Psychopharmacology (Berl) 2015; 232:815-24. [PMID: 25178814 PMCID: PMC4310756 DOI: 10.1007/s00213-014-3719-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Accepted: 08/06/2014] [Indexed: 12/31/2022]
Abstract
RATIONALE Low-efficacy mu opioid receptor agonists may be useful for some clinical indications, but clinically available low-efficacy mu agonists also have low selectivity for mu vs. kappa opioid receptors. NAQ (17-cyclopropylmethyl-3,14ß-dihydroxy-4,5α-epoxy-6α-[(3'-isoquinolyl)acetamido]morphinan) is a novel opioid receptor ligand with low-efficacy at mu receptors and greater mu-receptor selectivity than existing low-efficacy agonists. OBJECTIVES This study examined behavioral effects of NAQ in rats using an intracranial self-stimulation (ICSS) procedure that has been used previously to examine other opioids. NAQ effects were examined before, during, and after chronic morphine treatment, and effects of NAQ were compared to effects of nalbuphine and naltrexone. METHODS Adult male Sprague-Dawley rats were trained to respond for electrical brain stimulation delivered via electrodes implanted in the medial forebrain bundle. A range of brain stimulation frequencies maintained a wide range of baseline ICSS rates. Effects of NAQ (0.32-10 mg/kg), nalbuphine (1.0 mg/kg), and naltrexone (0.1 mg/kg) were determined before morphine treatment and during treatment with 3.2 and 18 mg/kg/day morphine. NAQ effects were also redetermined beginning 2 weeks after termination of morphine treatment. RESULTS NAQ produced weak ICSS facilitation in morphine-naïve rats but more robust ICSS facilitation during and after morphine treatment and also reversed morphine withdrawal-associated depression of ICSS. These effects were similar to effects of nalbuphine. CONCLUSIONS These results agree with the in vitro characterization of NAQ as a low-efficacy mu agonist. Opioid exposure may enhance abuse-related effects of NAQ, but NAQ may also serve as a low-efficacy and relatively safe option for treatment of opioid withdrawal or dependence.
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Affiliation(s)
- Ahmad A. Altarifi
- Faculty of Medicine, Jordan University of Science and Technology, Irbid 22110, Jordan,Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond VA, USA
| | - Yunyun Yuan
- Department of Medicinal Chemistry, Virginia Commonwealth University, Richmond VA, USA
| | - Yan Zhang
- Department of Medicinal Chemistry, Virginia Commonwealth University, Richmond VA, USA
| | - Dana E. Selley
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond VA, USA
| | - S. Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond VA, USA
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Altarifi AA, Negus SS. Differential tolerance to morphine antinociception in assays of pain-stimulated vs. pain-depressed behavior in rats. Eur J Pharmacol 2014; 748:76-82. [PMID: 25530266 DOI: 10.1016/j.ejphar.2014.12.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Revised: 11/28/2014] [Accepted: 12/07/2014] [Indexed: 12/14/2022]
Abstract
In preclinical research on pain and analgesia, noxious stimuli can stimulate expression of some behaviors (e.g. withdrawal reflexes) and depress others (e.g. feeding, locomotion, and positively reinforced operant responding). Tolerance to morphine antinociception is a robust and reliable phenomenon in preclinical assays of pain-stimulated behavior, but development of morphine tolerance in assays of pain-depressed behavior has not been studied. This study compared morphine antinociceptive tolerance in parallel assays of pain-stimulated and pain-depressed behavior in male Sprague-Dawley rats. Intraperitoneal injection of dilute lactic acid served as a noxious stimulus to stimulate a stretching response in one group of rats and to depress operant responding for electrical brain stimulation (intracranial self-stimulation; ICSS) in another group of rats. Antinociception produced by morphine (1.0 mg/kg) was determined after a regimen of chronic treatment with either saline or morphine in separate subgroups of rats in each procedure. In rats receiving chronic saline, acid alone stimulated a stretching response and depressed ICSS, and both acid effects were blocked by 1.0 mg/kg morphine. Rats receiving chronic morphine displayed hyperalgesic responses to the acid noxious stimulus in both procedures. Complete tolerance developed to morphine antinociception in the assay of acid-stimulated stretching, but morphine retained full antinociceptive effectiveness in the assay of acid-depressed ICSS. These results suggest that morphine antinociception in an assay of pain-depressed behavior is relatively resistant to tolerance. More broadly, these results suggest that antinociceptive tolerance can develop at different rates or to different degrees for different measures of antinociception.
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Affiliation(s)
- Ahmad A Altarifi
- Department of Pharmacology, School of Medicine, Faculty of Medicine, Jordan University of Science and Technology, P.O.Box 3030, Irbid 22110, Jordan; Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, USA.
| | - S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, USA
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Altarifi AA, Rice KC, Negus SS. Effects of μ-opioid receptor agonists in assays of acute pain-stimulated and pain-depressed behavior in male rats: role of μ-agonist efficacy and noxious stimulus intensity. J Pharmacol Exp Ther 2014; 352:208-17. [PMID: 25406170 DOI: 10.1124/jpet.114.219873] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Pain is associated with stimulation of some behaviors and depression of others, and μ-opioid receptor agonists are among the most widely used analgesics. This study used parallel assays of pain-stimulated and pain-depressed behavior in male Sprague-Dawley rats to compare antinociception profiles for six μ-agonists that varied in efficacy at μ-opioid receptors (from highest to lowest: methadone, fentanyl, morphine, hydrocodone, buprenorphine, and nalbuphine). Intraperitoneal injection of diluted lactic acid served as an acute noxious stimulus to either stimulate stretching or depress operant responding maintained by electrical stimulation in an intracranial self-stimulation (ICSS). All μ-agonists blocked both stimulation of stretching and depression of ICSS produced by 1.8% lactic acid. The high-efficacy agonists methadone and fentanyl were more potent at blocking acid-induced depression of ICSS than acid-stimulated stretching, whereas lower-efficacy agonists displayed similar potency across assays. All μ-agonists except morphine also facilitated ICSS in the absence of the noxious stimulus at doses similar to those that blocked acid-induced depression of ICSS. The potency of the low-efficacy μ-agonist nalbuphine, but not the high-efficacy μ-agonist methadone, to block acid-induced depression of ICSS was significantly reduced by increasing the intensity of the noxious stimulus to 5.6% acid. These results demonstrate sensitivity of acid-induced depression of ICSS to a range of clinically effective μ-opioid analgesics and reveal distinctions between opioids based on efficacy at the μ-receptor. These results also support the use of parallel assays of pain-stimulated and -depressed behaviors to evaluate analgesic efficacy of candidate drugs.
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Affiliation(s)
- Ahmad A Altarifi
- Department of Pharmacology, School of Medicine, Jordan University of Science and Technology, Irbid, Jordan (A.A.A.); Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (A.A.A., S.S.N.); and Chemical Biology Research Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
| | - Kenner C Rice
- Department of Pharmacology, School of Medicine, Jordan University of Science and Technology, Irbid, Jordan (A.A.A.); Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (A.A.A., S.S.N.); and Chemical Biology Research Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
| | - S Stevens Negus
- Department of Pharmacology, School of Medicine, Jordan University of Science and Technology, Irbid, Jordan (A.A.A.); Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (A.A.A., S.S.N.); and Chemical Biology Research Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
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Hillhouse TM, Porter JH, Negus SS. Comparison of antidepressant-like and abuse-related effects of phencyclidine in rats. Drug Dev Res 2014; 75:479-88. [PMID: 25315690 DOI: 10.1002/ddr.21228] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 08/06/2014] [Indexed: 01/23/2023]
Abstract
Preclinical Research N-methyl-D-aspartate (NMDA) receptor antagonists, such as ketamine, have emerged as novel candidate treatments for major depressive disorder, but abuse potential of these agents is a concern. The NMDA antagonist phencyclidine has known abuse liability but undefined efficacy as an antidepressant. To further evaluate the relationship between antidepressant-like and abuse-related effects of NMDA antagonists, this study evaluated the effects of phencyclidine (1.0-10.0 mg/kg) in male Sprague-Dawley rats responding under two procedures that have been used to assess antidepressant-like effects (differential-reinforcement-of-low-rate [DRL] 72 s schedule of food reinforcement; n = 9) and abuse-related drug effects (intracranial self-stimulation [ICSS]; n = 6). Under the DRL 72 s schedule, phencyclidine (10.0 mg/kg) increased reinforcers and decreased responses without shifting the peak location of the interresponse time (IRT) distribution. Ketamine (10.0 mg/kg) also increased reinforcers and decreased responses, but unlike phencyclidine, it produced a rightward shift in the peak location of the IRT distribution. The 10.0 mg/kg phencyclidine dose that decreased DRL 72 s responding also decreased rates of ICSS for 50 min after its administration; however, abuse-related ICSS facilitation was observed at later times (100-300 min) or after a lower phencyclidine dose (3.2 mg/kg). These results suggest that phencyclidine produces weaker antidepressant-like effects, but stronger abuse-related effects than ketamine in these procedures.
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Affiliation(s)
- Todd M Hillhouse
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, 48109, USA
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Leitl MD, Potter DN, Cheng K, Rice KC, Carlezon WA, Negus SS. Sustained pain-related depression of behavior: effects of intraplantar formalin and complete freund's adjuvant on intracranial self-stimulation (ICSS) and endogenous kappa opioid biomarkers in rats. Mol Pain 2014; 10:62. [PMID: 25245060 PMCID: PMC4180532 DOI: 10.1186/1744-8069-10-62] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 09/10/2014] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND Intraplantar administration of complete Freund's adjuvant (CFA) and formalin are two noxious stimuli commonly used to produce sustained pain-related behaviors in rodents for research on neurobiology and treatment of pain. One clinically relevant manifestation of pain is depression of behavior and mood. This study compared effects of intraplantar CFA and formalin on depression of positively reinforced operant behavior in an assay of intracranial self-stimulation (ICSS) in rats. Effects of CFA and formalin on other physiological and behavioral measures, and opioid effects on formalin-induced depression of ICSS, were also examined. RESULTS There were four main findings. First, consistent with previous studies, both CFA and formalin produced similar paw swelling and mechanical hypersensitivity. Second, CFA produced weak and transient depression of ICSS, whereas formalin produced a more robust and sustained depression of ICSS that lasted at least 14 days. Third, formalin-induced depression of ICSS was reversed by morphine doses that did not significantly alter ICSS in saline-treated rats, suggesting that formalin effects on ICSS can be interpreted as an example of pain-related and analgesic-reversible depression of behavior. Finally, formalin-induced depression of ICSS was not associated with changes in central biomarkers for activation of endogenous kappa opioid systems, which have been implicated in depressive-like states in rodents, nor was it blocked by the kappa antagonist norbinaltorphimine. CONCLUSIONS These results suggest differential efficacy of sustained pain stimuli to depress brain reward function in rats as assessed with ICSS. Formalin-induced depression of ICSS does not appear to engage brain kappa opioid systems.
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Affiliation(s)
- Michael D Leitl
- />Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 N. 12th St., PO Box 980613, Richmond, VA USA
| | - David N Potter
- />Behavioral Genetics Laboratory, McLean Hospital, Harvard Medical School, Belmont, MA USA
| | - Kejun Cheng
- />Chemical Biology Research Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD USA
| | - Kenner C Rice
- />Chemical Biology Research Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD USA
| | - William A Carlezon
- />Behavioral Genetics Laboratory, McLean Hospital, Harvard Medical School, Belmont, MA USA
| | - S Stevens Negus
- />Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 N. 12th St., PO Box 980613, Richmond, VA USA
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Strain differences in the expression of endocannabinoid genes and in cannabinoid receptor binding in the brain of Lewis and Fischer 344 rats. Prog Neuropsychopharmacol Biol Psychiatry 2014; 53:15-22. [PMID: 24607771 DOI: 10.1016/j.pnpbp.2014.02.012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 02/23/2014] [Accepted: 02/26/2014] [Indexed: 01/27/2023]
Abstract
The Lewis (LEW) and Fischer 344 (F344) rat strains have been proposed as a model to study certain genetic influences on drug use. These strains differ in terms of the self-administration of several drugs, and in their expression of various components of the dopaminergic, glutamatergic, GABAergic and endogenous opioid neurotransmitter systems. As the endocannabinoid system is linked to these systems, we investigated whether these two strains exhibit differences in cannabinoid receptor binding and in the expression of cannabinoid-related genes. Quantitative autoradiography of [(3)H]-CP 55,940 binding levels and real-time PCR assays were used. F344 rats displayed higher levels of cannabinoid receptor binding in the lateral globus pallidus and weaker CNR1 gene expression in the prefrontal cortex (PFc) than LEW rats. Moreover, the N-acyl phosphatidylethanolamine-specific phospholipase D/fatty acid amide hydrolase ratio was greater in the PFc and NAcc of F344 rats. Our results suggest that the endocannabinoid system may be a mediator of the individual differences that exist in the susceptibility to the rewarding effects of drugs of abuse.
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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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Hillhouse TM, Porter JH, Negus SS. Dissociable effects of the noncompetitive NMDA receptor antagonists ketamine and MK-801 on intracranial self-stimulation in rats. Psychopharmacology (Berl) 2014; 231:2705-16. [PMID: 24522331 PMCID: PMC4058412 DOI: 10.1007/s00213-014-3451-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Accepted: 12/31/2013] [Indexed: 11/27/2022]
Abstract
RATIONALE The noncompetitive NMDA antagonist ketamine produces rapid antidepressant effects in treatment-resistant patients suffering from major depressive and bipolar disorders. However, abuse liability is a concern. OBJECTIVES This study examined abuse-related effects of ketamine using intracranial self-stimulation (ICSS) in rats. The higher-affinity NMDA antagonist MK-801 and the monoamine reuptake inhibitor cocaine were examined for comparison. METHODS Male Sprague Dawley rats were implanted with electrodes targeting the medial forebrain bundle and trained to respond to brain stimulation under a frequency-rate ICSS procedure. The first experiment compared the potency and time course of ketamine (3.2-10.0 mg/kg) and MK-801 (0.032-0.32 mg/kg). The second experiment examined effects of repeated dosing with ketamine (3.2-20.0 mg/kg/day) and acute cocaine (10.0 mg/kg). RESULTS Following acute administration, ketamine (3.2-10 mg/kg) produced only dose- and time-dependent depressions of ICSS and failed to produce an abuse-related facilitation of ICSS at any dose or pretreatment time. In contrast, MK-801 (0.032-0.32 mg/kg) produced a mixed profile of rate-increasing and rate-decreasing effects; ICSS facilitation was especially prominent at an intermediate dose of 0.18 mg/kg. Repeated dosing with ketamine produced dose-dependent tolerance to the rate-decreasing effects of ketamine (10.0 and 18.0 mg/kg) but failed to unmask expression of ICSS facilitation. Termination of ketamine treatment failed to produce withdrawal-associated decreases in ICSS. As reported previously, 10.0 mg/kg cocaine facilitated ICSS. CONCLUSIONS The dissociable effects of ketamine and MK-801 suggest differences in the pharmacology of these nominally similar NMDA antagonists. Failure of ketamine to facilitate ICSS contrasts with other evidence for the abuse liability of ketamine.
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Affiliation(s)
- Todd M. Hillhouse
- Department of Psychology, Virginia Commonwealth University, PO Box 842018, 806 West Franklin Street, Richmond 23284, VA, USA
| | - Joseph H. Porter
- Department of Psychology, Virginia Commonwealth University, PO Box 842018, 806 West Franklin Street, Richmond 23284, VA, USA
| | - S. Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 North 12th Street, PO Box 980613, Richmond VA 23298, USA
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Abstract
This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).
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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, United States.
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Abuse-related effects of µ-opioid analgesics in an assay of intracranial self-stimulation in rats: modulation by chronic morphine exposure. Behav Pharmacol 2013; 24:459-70. [PMID: 23881045 DOI: 10.1097/fbp.0b013e328364c0bd] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Intracranial self-stimulation (ICSS) is an operant procedure in which responding is maintained by electrical brain stimulation. Stimulation frequency can be varied rapidly to maintain a wide range of baseline response rates, and drugs' effects can be evaluated simultaneously on both low ICSS rates maintained by low stimulation frequencies and high ICSS rates maintained by high stimulation frequencies. ICSS 'facilitation' indicates drug-induced increases in low ICSS rates and is often considered an abuse-related effect, whereas ICSS 'depression' indicates decreases in high ICSS rates and may indicate abuse-limiting effects. This study examined the roles of µ-agonist efficacy and of previous µ-agonist exposure as determinants of µ-agonist effects on ICSS in rats with electrodes implanted into the medial forebrain bundle. The high-efficacy, intermediate-efficacy, and low-efficacy µ agonists methadone, fentanyl, and nalbuphine were tested during escalating regimens of morphine exposure (vehicle, 3.2, and 18 mg/kg/day). During vehicle treatment, methadone and fentanyl primarily depressed ICSS, whereas nalbuphine produced weak facilitation that was not dose dependent. Chronic morphine produced tolerance to ICSS depression and increased expression of ICSS facilitation. These results suggest that µ-agonist exposure increases the expression of abuse-related ICSS facilitation by µ agonists with a broad range of efficacies at µ receptors.
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