Cocaine self-administration augments kappa opioid receptor system-mediated inhibition of dopamine activity in the mesolimbic dopamine system

Morphine-Induced Antinociception Is Potentiated and Dopamine Elevations Are Inhibited by the Biased Kappa Opioid Receptor Agonist Triazole 1.1

Traditional analgesic opioid compounds, which act through μ opioid receptors (MORs), engender a high risk for misuse and dependence. κ opioid receptor (KOR) activation, a potential target for pain treatment, produces antinociception without euphoric side effects but results in dysphoria and aversion. Triazole 1.1 is a KOR agonist biased toward G-protein coupled signaling, potentially promoting antinociception without dysphoria. We tested whether triazole 1.1 could provide antinociception and its effects in combination with morphine. We employed a lactic acid abdominal pain model, which induced acute pain behaviors, decreased basal dopamine levels in the nucleus accumbens (NAc), and increased KOR function. We administered several interventions including triazole 1.1 (30 mg/kg) and morphine (12 or 24 mg/kg), individually and in combination. Triazole 1.1 alone reduced the pain behavioral response and changes to KOR function but did not prevent the reduction in basal dopamine levels. Morphine not only dose-dependently prevented behavioral pain responses but also elevated NAc dopamine and did not prevent the pain-induced increase in KOR function. However, combining low-dose morphine with triazole 1.1 prevents behavioral pain responses, changes to NAc dopamine levels, and changes to KOR function. Therefore, we present triazole 1.1 as a dose-sparing pain treatment to be used in combination with a lower dose of morphine, thus reducing the potential for opioid misuse.

The Dynorphin/-Opioid Receptor System at the Interface of Hyperalgesia/Hyperkatifeia and Addiction

Purpose of Review

Drug addiction is characterized by compulsive drug seeking and use, accompanied by negative emotional states (hyperkatifeia) and heightened pain sensitivity (hyperalgesia) during withdrawal. Both hyperalgesia and hyperkatifeia are integral components of substance use disorders, negatively impacting treatment and recovery. The underlying neurobiological mechanisms of hyperalgesia and hyperkatifeia involve alterations of brain reward and stress circuits, including the dynorphin/κ-opioid receptor (KOR) system. The dynorphin/KOR system modulates pain perception, negative affect, and addictive behaviors. Here, we review the preclinical evidence of dynorphin/KOR signaling in opioid withdrawal-induced hyperalgesia and hyperkatifeia.

Recent Findings

In opioid dependence models, pharmacological and genetic interventions of the dynorphin/KOR system attenuate somatic and motivational signs of withdrawal and addictive-like behaviors, highlighting its therapeutic potential. Understanding the intricate interplay between dynorphin/KOR signaling, hyperalgesia, hyperkatifeia, and addiction offers novel insights into treatment strategies for opioid use disorder and other substance use disorders.

Summary

Further research is needed to elucidate precise mechanisms of the sexual dimorphism of dynorphin/KOR signaling and identify targeted interventions to mitigate hyperalgesia and hyperkatifeia and facilitate recovery from addiction.

Endogenous opiates and behavior: 2023

This paper is the forty-sixth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2023 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug and alcohol abuse (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Co-targeting the kappa opioid receptor and dopamine transporter reduces motivation to self-administer cocaine and partially reverses dopamine system dysregulation

Cocaine disrupts dopamine (DA) and kappa opioid receptor (KOR) system activity, with long-term exposure reducing inhibiton of DA uptake by cocaine and increasing KOR system function. Single treatment therapies have not been successful for cocaine use disorder; therefore, this study focuses on a combination therapy targeting the dopamine transporter (DAT) and KOR. Sprague Dawley rats self-administered 5 days of cocaine (1.5 mg/kg/inf, max 40 inf/day, FR1), followed by 14 days on a progressive ratio (PR) schedule (0.19 mg/kg/infusion). Behavioral effects of individual and combined administration of phenmetrazine and nBNI were then examined using PR. Additionally, ex vivo fast scan cyclic voltammetry was then used to assess alterations in DA and KOR system activity in the nucleus accumbens before and after treatments. Chronic administration of phenmetrazine as well as the combination of phenmetrazine and nBNI-but not nBNI alone-significantly reduced PR breakpoints. In addition, the combination of phenmetrazine and nBNI partially reversed cocaine-induced neurodysregulations of the KOR and DA systems, indicating therapeutic benefits of targeting the DA and KOR systems in tandem. These data highlight the potential benefits of the DAT and KOR as dual-cellular targets to reduce motivation to administer cocaine and reverse cocaine-induced alterations of the DA system.