Abstract
Rationale: The endocannabinoidome mediators, N-Oleoylglycine (OlGly) and N-Oleoylalanine (OlAla), have been shown to reduce acute naloxone-precipitated morphine withdrawal affective and somatic responses.Objectives: To determine the role and mechanism of action of OlGly and OlAla in withdrawal responses from chronic exposure to opiates in male Sprague-Dawley rats.Methods: Opiate withdrawal was produced: 1) spontaneously 24 h following chronic exposure to escalating doses of morphine over 14 days (Experiments 1 and 2) and steady-state exposure to heroin by minipumps for 12 days (Experiment 3), 2) by naloxone injection during steady-state heroin exposure (Experiment 4), 3) by naloxone injection during operant heroin self-administration (Experiment 5).Results: In Experiment 1, spontaneous morphine withdrawal produced somatic withdrawal reactions. The behavioral withdrawal reactions were accompanied by suppressed endogenous levels of OlGly in the nucleus accumbens, amygdala, and prefrontal cortex, N-Arachidonylglycerol and OlAla in the amygdala, 2-arachidonoylglycerol in the nucleus accumbens, amygdala and interoceptive insular cortex, and by changes in colonic microbiota composition. In Experiment 2, treatment with OlAla, but not OlGly, reduced spontaneous morphine withdrawal responses. In Experiment 3, OlAla attenuated spontaneous steady-state heroin withdrawal responses at both 5 and 20 mg/kg; OlGly only reduced withdrawal responses at the higher dose of 20 mg/kg. Experiment 4 demonstrated that naloxone-precipitated heroin withdrawal from steady-state exposure to heroin (7 mg/kg/day for 12 days) is accompanied by tissue-specific changes in brain or gut endocannabinoidome mediator, including OlGly and OlAla, levels and colonic microbiota composition, and that OlAla (5 mg/kg) attenuated behavioural withdrawal reactions, while also reversing some of the changes in brain and gut endocannabinoidome and gut microbiota induced by naloxone. Experiment 5 demonstrated that although OlAla (5 mg/kg) did not interfere with operant heroin self-administration on its own, it blocked naloxone-precipitated elevation of heroin self-administration behavior.Conclusion: These results suggest that OlAla and OlGly are two endogenous mediators whose brain concentrations respond to chronic opiate treatment and withdrawal concomitantly with changes in colon microbiota composition, and that OlAla may be more effective than OlGly in suppressing chronic opiate withdrawal responses.
Highlights
A new member of the increasing family of endocannabinoid-like mediators, which, together with their receptors and metabolic enzymes, constitute the endocannabinoidome (Di Marzo 2018), N-Oleoylglycine (OlGly) is an endogenous lipoaminoacid produced in the brain following mild trauma and has been shown to reduce the behavioral consequences of this condition (Piscitelli et al, 2020) as well as the abuse-related effects of nicotine addiction in mouse models (Donvito al., 2019)
We have provided here data suggesting for the first time that OlGly and/or OlAla, two endogenous lipid mediators belonging to the family of lipoaminoacids of the expanded endocannabinoid system, or eCBome (Di Marzo 2018): 1) are present in brain areas involved in opiate addiction, and their concentrations, like those of other eCBome mediators, are altered following morphine administration and spontaneous withdrawal, or chronic heroin infusion and naloxone-precipitated heroin withdrawal; and 2) when exogenously administered, counteract some somatic signs of withdrawal from chronic opiate exposure, with OlAla being more effective than OlGly, and inducing effects that were dependent on activation of CB1 and PPARα receptors and accompanied by changes in gut or brain eCBome mediators and gut microbiota composition
As we have shown with acute naloxone precipitated morphine withdrawal (MWD) (Ayoub et al, 2020), the effect of OlAla on naloxone-precipitated withdrawal from chronic heroin was reversed by pretreatment with either the CB1 antagonist, AM251, or the PPARα antagonist, MK886, at doses shown not to affect opiate withdrawal behaviors per se (Rock et al, 2020)
Summary
A new member of the increasing family of endocannabinoid (eCB)-like mediators, which, together with their receptors and metabolic enzymes, constitute the endocannabinoidome (eCBome) (Di Marzo 2018), N-Oleoylglycine (OlGly) is an endogenous lipoaminoacid produced in the brain following mild trauma and has been shown to reduce the behavioral consequences of this condition (Piscitelli et al, 2020) as well as the abuse-related effects of nicotine addiction in mouse models (Donvito al., 2019). Reduced responses produced by acute naloxone-precipitated morphine withdrawal (MWD) in rats as assessed by conditioned place aversion (CPA; Petrie et al, 2019) and somatic withdrawal behaviors (Rock et al, 2020). In rats, OlGly reduces acute naloxone-precipitated MWD somatic responses by PPARα- and CB1 receptor-dependent mechanisms, whereas its effect on affective responses during withdrawal are mediated exclusively by the CB1 receptor, probably via its indirect activation due to FAAH inhibition leading to increased levels of endogenous CB1 agonists
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