Related Experiment Video
Updated: Aug 15, 2026
07:23
Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
The influence of p-chlorophenylalanine on different morphine effects
Drug and Alcohol Dependence
|May 1, 1980
Summary
p-Chlorophenylalanine (p-CPA) depletes brain serotonin (5-HT) and affects morphine
Area of Science:
- Neuroscience
- Pharmacology
- Biochemistry
Background:
- Serotonin (5-HT) is a key neurotransmitter influencing various physiological processes.
- The interaction between serotonin and opioid pathways, particularly morphine, is complex and not fully understood.
- p-Chlorophenylalanine (p-CPA) is a pharmacological tool used to deplete brain serotonin levels.
Purpose of the Study:
- To investigate the role of brain serotonin (5-HT) in morphine's effects, including analgesia, toxicity, hypothermia, and behavioral responses.
- To examine how p-Chlorophenylalanine (p-CPA) treatment influences morphine's actions and the development of physical dependence.
- To explore potential alternative mechanisms of morphine-induced hypothermia in serotonin-deficient states.
Main Methods:
- Administration of p-Chlorophenylalanine (p-CPA) to reduce brain 5-HT levels in mice.
- Assessment of morphine's effects on analgesia, toxicity, hypothermia, and running behavior.
- Evaluation of naloxone-precipitated withdrawal reactions and physical dependence development.
Main Results:
- p-CPA significantly reduced brain 5-HT without affecting dopamine or norepinephrine.
- Morphine analgesia and toxicity were not altered by p-CPA.
- p-CPA diminished morphine-induced running behavior but did not affect the development of physical dependence.
- While acute morphine hypothermia was unaffected, chronic p-CPA treatment altered the dose-response curve for morphine hypothermia, suggesting alternative mechanisms.
Conclusions:
- Brain serotonin (5-HT) plays a role in modulating morphine-induced running behavior and certain aspects of hypothermia.
- Serotonin depletion does not appear to influence morphine analgesia, toxicity, or the development of physical dependence.
- These findings highlight the complex interplay between serotonin and opioid systems in mediating the diverse effects of morphine.
Related Concept Videos
01:16Adrenergic Agonists: Chemistry and Structure-Activity Relationship
Adrenergic agonists' structure-activity relationship (SAR) determines their selectivity and efficacy. These agonists comprise a phenylethylamine moiety with an aromatic ring and an ethylamine side chain.
Aromatic ring substitutions: Substituting the aromatic ring with –OH groups at positions 3 and 4 yields catecholamines (e.g., epinephrine), which have a high affinity for adrenoceptors. Hydrogen bonding between –OH groups and receptors enhances adrenergic activity.
Separation of the aromatic...
Aromatic ring substitutions: Substituting the aromatic ring with –OH groups at positions 3 and 4 yields catecholamines (e.g., epinephrine), which have a high affinity for adrenoceptors. Hydrogen bonding between –OH groups and receptors enhances adrenergic activity.
Separation of the aromatic...
01:29Drugs Affecting Neurotransmitter Synthesis
Drugs affecting neurotransmitter synthesis can impact the adrenergic neuron and the synthesis of neurotransmitters. For example, α-methyltyrosine and carbidopa target specific enzymes involved in catecholamine synthesis. α-methyltyrosine inhibits the enzyme tyrosine hydroxylase, which converts tyrosine into dopamine. By blocking this enzyme, α-methyltyrosine reduces dopamine production and other catecholamines. Carbidopa, on the other hand, inhibits the enzyme dopa decarboxylase, which converts...
01:22Opioid Receptors: Overview
Opioid receptors, including the mu (μ, MOR), delta (δ, DOR), and kappa (κ, KOR) types, belong to the rhodopsin family of G protein-coupled receptors. These receptors are located throughout the central and peripheral nervous systems and in non-neuronal tissues such as macrophages and astrocytes. Opioid receptor ligands can be categorized into agonists or antagonists. Highly selective agonists include [d-Ala2, MePhe4, Gly(ol)5]-enkephalin or DAMGO for MOR, [D-Pen2, D-Pen5]-enkephalin or DPDPE for...
01:25Analgesia and Pain Management
Pain is critical to various clinical pathologies, provoking an urgent need for effective management. Pain, whether acute or chronic, is a complex neurochemical process. Its alleviation depends on the type, with nonopioid analgesics effective for mild to moderate pain, such as musculoskeletal or inflammatory pain, while neuropathic pain responds best to anticonvulsants, tricyclic antidepressants, or serotonin/norepinephrine reuptake inhibitors. For severe acute or chronic pain, opioids may be...
01:20Opioid Analgesics: Morphine and Other Natural Cogeners
Opioids are a class of drugs that mimic endogenous opioid peptides and act on opioid receptors, and help in pain relief. These compounds are classified as natural, synthetic, or semi-synthetic. Natural opioids, like morphine, codeine, and thebaine, are derived from the opium poppy plant (Papaver somniferum or Papaver album) and are termed opiates. Synthetic opioids are artificial, while semi-synthetic opioids combine natural and synthetic compounds. Morphine, a prototypical opioid, possesses a...
01:15Opioid Analgesics: Synthetic and Semisynthetic Opioids
Synthetic and semisynthetic opioids are pivotal in pain management and tackling opioid addiction. Semisynthetic opioids, including morphinans (morphine derivatives), oxycodone, oxymorphone, hydrocodone, and hydromorphone, have improved pharmacokinetic profiles compared to morphine. Additionally, heroin and 6-MAM (6-Monoacetylmorphine) show better CNS penetration than morphine due to heightened lipid solubility. Hydromorphone, a potent opioid, undergoes hepatic metabolism to form the active...