Psychopharmacology · 2026
Effects of repeated treatment with opioids that vary in mu opioid receptor efficacy on pain-depressed locomotor behavior in mice.
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Harris Jawaun, Chambers Dana R, Hernandez Delmis E, Jacobson Arthur E, Lutz Joshua A, Rice Kenner C, Sulima Agnieszka, Negus S Stevens
Аннотация
RATIONALE: Mu opioid receptor (MOR) analgesics like morphine have high intrinsic MOR efficacy but produce side effects. Lower efficacy MOR agonists like buprenorphine can produce analgesia with improved safety. We recently described a series of novel phenylmorphan-based MOR agonists with graded MOR efficacies, including several with sub-buprenorphine efficacies, and we described their acute effectiveness in mice to produce (a) antinociception in an assay of pain-related locomotor depression, and (b) improved safety on a range of side effects. Effects of repeated treatment with these compounds have not been examined.
OBJECTIVE: The present objective was to compare effects of repeated treatment with four opioids that ranged from high to low MOR efficacy (morphine> buprenorphine > JL-2-39 > DC-1-76.1).
METHODS: Female and male ICR mice were treated once daily for 7 days with a selected dose of each drug ± intraperitoneal lactic acid (IP acid) as a noxious stimulus and evaluated for vertical and horizontal locomotor activity on Days 1 and 7.
RESULTS: IP acid alone produced sustained, concentration-dependent, and pain-related locomotor depression. When administered as a daily pretreatment to IP acid, all four opioids produced sustained antinociception expressed as significant alleviation of IP acid-induced behavioral depression on Days 1 and 7. However, when these opioids were administered alone, effects were efficacy dependent. Morphine produced locomotor stimulation and sensitization; buprenorphine and JL-2-39 produced locomotor stimulation without sensitization; DC-1-76.1 produced neither stimulation or sensitization.
CONCLUSIONS: These findings support continued consideration of low-efficacy MOR agonists as candidate analgesics that can produce sustained antinociception with reduced side effects during repeated treatment.
OBJECTIVE: The present objective was to compare effects of repeated treatment with four opioids that ranged from high to low MOR efficacy (morphine> buprenorphine > JL-2-39 > DC-1-76.1).
METHODS: Female and male ICR mice were treated once daily for 7 days with a selected dose of each drug ± intraperitoneal lactic acid (IP acid) as a noxious stimulus and evaluated for vertical and horizontal locomotor activity on Days 1 and 7.
RESULTS: IP acid alone produced sustained, concentration-dependent, and pain-related locomotor depression. When administered as a daily pretreatment to IP acid, all four opioids produced sustained antinociception expressed as significant alleviation of IP acid-induced behavioral depression on Days 1 and 7. However, when these opioids were administered alone, effects were efficacy dependent. Morphine produced locomotor stimulation and sensitization; buprenorphine and JL-2-39 produced locomotor stimulation without sensitization; DC-1-76.1 produced neither stimulation or sensitization.
CONCLUSIONS: These findings support continued consideration of low-efficacy MOR agonists as candidate analgesics that can produce sustained antinociception with reduced side effects during repeated treatment.