{"id":{"repo_id":"vcu","oai_identifier":"oai:scholarscompass.vcu.edu:etd-1517"},"canonical_url":"https://search.dev.ndltd.org/etd/vcu/oai:scholarscompass.vcu.edu:etd-1517","repository":{"repo_id":"vcu","name":"Virginia Commonwealth University","base_url":"https://scholarscompass.vcu.edu/do/oai/"},"display":{"title":"EFFECTS OF MU OPIOID RECEPTOR AGONISTS ON INTRACRANIAL SELF-STIMULATION IN THE ABSENCE AND PRESENCE OF “PAIN” IN RATS","abstract":"Pain is a significant health problem. Mu opioid receptor agonists are used clinically as analgesics, but their use is constrained by high abuse liability. Intracranial self-stimulation (ICSS) is a preclinical behavioral procedure that has been used to assess abuse potential of opioids, and drug-induced facilitation of ICSS is interpreted as an abuse-related effect. ICSS can also be used as a behavioral baseline to detect affective dimensions of pain. Specifically, pain-related depression of ICSS can model pain-related depression of behavior and mood, and drug-induced blockade of pain-related ICSS depression can serve as a measure of affective analgesia. This dissertation used mu agonists that vary in efficacy at the mu receptor (methadone> fentanyl> morphine> hydrocodone> buprenorphine> nalbuphine) and compared their effects on ICSS in the absence (phase one) or presence (phase 2) of pain. Adult male Sprague-Dawley rats were equipped with intracranial electrodes targeting the medial forebrain bundle and trained to lever press for brain stimulation. Different frequencies of stimulation maintained a frequency-dependent increase in ICSS rates, and permitted detection of both rate-increasing and rate-decreasing treatment effects. During phase 1, medium- and high-efficacy mu agonists produced initial rate-decreasing effects, followed by abuse-related rate-increasing effects at later time points. Repeated morphine administration produced tolerance to its own rate-decreasing effects, cross-tolerance to rate-decreasing effects of other mu agonists, and enhanced expression of rate-increasing effects. Low efficacy mu agonists only produced rate-increasing effects, which were enhanced after repeated morphine. These results suggest that previous opioid exposure increases expression of abuse-related facilitation of ICSS by mu agonists regardless of efficacy. During phase 2, intraperitoneal administration of lactic acid (1.8%) served as a noxious stimulus to depress ICSS. All mu agonists blocked acid-induced depression of ICSS at doses similar to those that facilitated ICSS in the absence of pain. A higher intensity noxious stimulus (5.6 % acid) produced further depression of ICSS and reduced the antinociceptive potency of both methadone and nalbuphine. Morphine antinociception was resistant to tolerance in the assay of acid-depressed ICSS. Overall, these results provide a basis for comparing determinants of abuse-related opioid effects in the absence of pain with their affective analgesic effects in the presence of pain.","abstract_html":"Pain is a significant health problem. Mu opioid receptor agonists are used clinically as analgesics, but their use is constrained by high abuse liability. Intracranial self-stimulation (ICSS) is a preclinical behavioral procedure that has been used to assess abuse potential of opioids, and drug-induced facilitation of ICSS is interpreted as an abuse-related effect. ICSS can also be used as a behavioral baseline to detect affective dimensions of pain. Specifically, pain-related depression of ICSS can model pain-related depression of behavior and mood, and drug-induced blockade of pain-related ICSS depression can serve as a measure of affective analgesia. This dissertation used mu agonists that vary in efficacy at the mu receptor (methadone> fentanyl> morphine> hydrocodone> buprenorphine> nalbuphine) and compared their effects on ICSS in the absence (phase one) or presence (phase 2) of pain. Adult male Sprague-Dawley rats were equipped with intracranial electrodes targeting the medial forebrain bundle and trained to lever press for brain stimulation. Different frequencies of stimulation maintained a frequency-dependent increase in ICSS rates, and permitted detection of both rate-increasing and rate-decreasing treatment effects. During phase 1, medium- and high-efficacy mu agonists produced initial rate-decreasing effects, followed by abuse-related rate-increasing effects at later time points. Repeated morphine administration produced tolerance to its own rate-decreasing effects, cross-tolerance to rate-decreasing effects of other mu agonists, and enhanced expression of rate-increasing effects. Low efficacy mu agonists only produced rate-increasing effects, which were enhanced after repeated morphine. These results suggest that previous opioid exposure increases expression of abuse-related facilitation of ICSS by mu agonists regardless of efficacy. During phase 2, intraperitoneal administration of lactic acid (1.8%) served as a noxious stimulus to depress ICSS. All mu agonists blocked acid-induced depression of ICSS at doses similar to those that facilitated ICSS in the absence of pain. A higher intensity noxious stimulus (5.6 % acid) produced further depression of ICSS and reduced the antinociceptive potency of both methadone and nalbuphine. Morphine antinociception was resistant to tolerance in the assay of acid-depressed ICSS. Overall, these results provide a basis for comparing determinants of abuse-related opioid effects in the absence of pain with their affective analgesic effects in the presence of pain.","abstract_has_math":false,"creators":["Altarifi, Ahmad"],"institution":null,"degree_name":"Doctor of Philosophy","degree_level":"Dissertation","degree_discipline":"Pharmacology & Toxicology","degree_department":null,"school":null,"contributors":["S. Stevens Negus"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2013,"date_issued":"2013-05-02T07:00:00Z","date_published":"2013-05-02T07:00:00Z","updated_at":"2026-07-24T05:54:02Z","subjects":["opioids","intracranial self-stimulation","pain","opioid efficacy","opioid abuse","opioid dependence","mu receptor","chronic morphine","rats","Medical Pharmacology","Medical Sciences","Medicine and Health Sciences"],"languages":[],"rights":["© The Author"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://scholarscompass.vcu.edu/etd/518"],"render_values":[{"text":"https://scholarscompass.vcu.edu/etd/518","href":"https://scholarscompass.vcu.edu/etd/518","code":true}]}]},"links":{"outbound_url":"https://doi.org/10.25772/0TXZ-XX93","outbound_label":"DOI","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["S. 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Mu opioid receptor agonists are used clinically as analgesics, but their use is constrained by high abuse liability. Intracranial self-stimulation (ICSS) is a preclinical behavioral procedure that has been used to assess abuse potential of opioids, and drug-induced facilitation of ICSS is interpreted as an abuse-related effect. ICSS can also be used as a behavioral baseline to detect affective dimensions of pain. Specifically, pain-related depression of ICSS can model pain-related depression of behavior and mood, and drug-induced blockade of pain-related ICSS depression can serve as a measure of affective analgesia. This dissertation used mu agonists that vary in efficacy at the mu receptor (methadone> fentanyl> morphine> hydrocodone> buprenorphine> nalbuphine) and compared their effects on ICSS in the absence (phase one) or presence (phase 2) of pain. Adult male Sprague-Dawley rats were equipped with intracranial electrodes targeting the medial forebrain bundle and trained to lever press for brain stimulation. Different frequencies of stimulation maintained a frequency-dependent increase in ICSS rates, and permitted detection of both rate-increasing and rate-decreasing treatment effects. During phase 1, medium- and high-efficacy mu agonists produced initial rate-decreasing effects, followed by abuse-related rate-increasing effects at later time points. Repeated morphine administration produced tolerance to its own rate-decreasing effects, cross-tolerance to rate-decreasing effects of other mu agonists, and enhanced expression of rate-increasing effects. Low efficacy mu agonists only produced rate-increasing effects, which were enhanced after repeated morphine. These results suggest that previous opioid exposure increases expression of abuse-related facilitation of ICSS by mu agonists regardless of efficacy. During phase 2, intraperitoneal administration of lactic acid (1.8%) served as a noxious stimulus to depress ICSS. All mu agonists blocked acid-induced depression of ICSS at doses similar to those that facilitated ICSS in the absence of pain. A higher intensity noxious stimulus (5.6 % acid) produced further depression of ICSS and reduced the antinociceptive potency of both methadone and nalbuphine. Morphine antinociception was resistant to tolerance in the assay of acid-depressed ICSS. Overall, these results provide a basis for comparing determinants of abuse-related opioid effects in the absence of pain with their affective analgesic effects in the presence of pain."]},{"key":"dc:title","label":"Title","values":["EFFECTS OF MU OPIOID RECEPTOR AGONISTS ON INTRACRANIAL SELF-STIMULATION IN THE ABSENCE AND PRESENCE OF “PAIN” IN RATS"]}]}],"canonical_facts":{"dc:contributor":["S. Stevens Negus"],"dc:creator":["Altarifi, Ahmad"],"dc:date.available":["2018-06-03T07:00:00Z"],"dc:description.abstract":["Pain is a significant health problem. Mu opioid receptor agonists are used clinically as analgesics, but their use is constrained by high abuse liability. Intracranial self-stimulation (ICSS) is a preclinical behavioral procedure that has been used to assess abuse potential of opioids, and drug-induced facilitation of ICSS is interpreted as an abuse-related effect. ICSS can also be used as a behavioral baseline to detect affective dimensions of pain. Specifically, pain-related depression of ICSS can model pain-related depression of behavior and mood, and drug-induced blockade of pain-related ICSS depression can serve as a measure of affective analgesia. This dissertation used mu agonists that vary in efficacy at the mu receptor (methadone> fentanyl> morphine> hydrocodone> buprenorphine> nalbuphine) and compared their effects on ICSS in the absence (phase one) or presence (phase 2) of pain. Adult male Sprague-Dawley rats were equipped with intracranial electrodes targeting the medial forebrain bundle and trained to lever press for brain stimulation. Different frequencies of stimulation maintained a frequency-dependent increase in ICSS rates, and permitted detection of both rate-increasing and rate-decreasing treatment effects. During phase 1, medium- and high-efficacy mu agonists produced initial rate-decreasing effects, followed by abuse-related rate-increasing effects at later time points. Repeated morphine administration produced tolerance to its own rate-decreasing effects, cross-tolerance to rate-decreasing effects of other mu agonists, and enhanced expression of rate-increasing effects. Low efficacy mu agonists only produced rate-increasing effects, which were enhanced after repeated morphine. These results suggest that previous opioid exposure increases expression of abuse-related facilitation of ICSS by mu agonists regardless of efficacy. During phase 2, intraperitoneal administration of lactic acid (1.8%) served as a noxious stimulus to depress ICSS. All mu agonists blocked acid-induced depression of ICSS at doses similar to those that facilitated ICSS in the absence of pain. A higher intensity noxious stimulus (5.6 % acid) produced further depression of ICSS and reduced the antinociceptive potency of both methadone and nalbuphine. Morphine antinociception was resistant to tolerance in the assay of acid-depressed ICSS. Overall, these results provide a basis for comparing determinants of abuse-related opioid effects in the absence of pain with their affective analgesic effects in the presence of pain."],"dc:identifier":["https://doi.org/10.25772/0TXZ-XX93","https://scholarscompass.vcu.edu/etd/518"],"dc:rights":["© The Author"],"dc:subject":["opioids","intracranial self-stimulation","pain","opioid efficacy","opioid abuse","opioid dependence","mu receptor","chronic morphine","rats","Medical Pharmacology","Medical Sciences","Medicine and Health Sciences"],"dc:title":["EFFECTS OF MU OPIOID RECEPTOR AGONISTS ON INTRACRANIAL SELF-STIMULATION IN THE ABSENCE AND PRESENCE OF “PAIN” IN RATS"],"thesis:degree_discipline":["Pharmacology & Toxicology"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy"]},"updated_at":"2026-07-24T05:54:02Z"}