Effects of treadmill exercise on methadone withdrawal-induced locomotor sensitization and the ventral pallidum and ventral tegmental area BDNF levels in morphine withdrawn rats receiving methadone maintenance treatment

Brain-derived neurotrophic factor levels in morphine-addicted rodents under different exercise protocols: a systematic review and meta-analysis

OBJECTIVES

Exercise might restore morphine-induced behavioural and molecular changes, but related evidence is inconsistent. We conducted a systematic review and meta-analysis of animal studies to elucidate the contribution of brain-derived neurotrophic factor (BDNF) to exercise effects on morphine addiction.

METHODS

We searched papers published until May 25, 2024, in databases, manually searched related references, screened eligible studies, and extracted relevant data. The risk of bias was assessed using the SYstematic Review Centre for Laboratory animal Experimentation (SYRCLE)'s risk bias tool. Subsequently, we summarised study characteristics, reported risks of bias, and conducted a meta-analysis. Subgroup and sensitivity analyses were also conducted.

RESULTS

The meta-analysis showed that exercise increased BDNF levels in morphine-addicted male animals, regardless of the exercise type and intensity. Under morphine addiction, voluntary exercise (running wheel) affected BDNF levels in males, whilst forced exercise (treadmill exercise) did not. Furthermore, different exercise intensities did not affect BDNF levels in males. The sensitivity analysis determined that the results were robust.

CONCLUSIONS

Exercise increased BDNF levels in male but not in female animals. BDNF level changes might be related to the type of exercise but not its intensity. Therefore, BDNF might serve as a biomarker for the effects of different exercise types.

Impact of high-access exercise prior to and during early adolescence on later vulnerability to opioid use and relapse in male rats

Middle- and high-school athletes participating in certain team sports are at greater risk of opioid misuse and addiction than those who do not. While this risk is thought to be due to increased access to opioids, in this study we explored the possibility that the sensitizing effects of discontinued high-intensity exercise may also contribute. Specifically, using male rat models with fentanyl, we tested the hypothesis that high-access exercise (24 h/day access to a running wheel) during pre/early adolescence (two weeks, postnatal-day 24-37) would enhance vulnerability to opioid use and relapse during late adolescence/adulthood. Rats with a history of high-access exercise showed stronger fentanyl-associated lever discrimination during acquisition, greater motivation to obtain infusions of fentanyl following acquisition, and had an enhanced sensitivity to the reinstating effects of fentanyl-associated cues following extended (24 h/day), intermittent-access self-administration and protracted abstinence (14 days) compared to sedentary controls. In contrast, sedentary rats had greater overall responding (active- and inactive-lever) during acquisition and greater non-specific (inactive-lever) responding during extended-access self-administration. Molecular markers associated with opioid seeking/relapse were also differentially expressed in the nucleus accumbens core of rats with versus without a history of high-access exercise following relapse testing (e.g., Bdnf-IV and Drd2 expression). Together, these findings demonstrate that high-access exercise prior to and throughout early-adolescence enhances vulnerability to the reinforcing and cue-induced reinstating effects of opioids during later adolescence/adulthood. Thus, it is possible that the discontinuation of high intensity exercise contributes to the enhanced vulnerability observed in middle- and high-school athletes.

Enriched Environment Ameliorates Cognitive Deficits and Locomotor Sensitization in Morphine-Withdrawn Rats Receiving Methadone Maintenance Treatment

OBJECTIVE

This study was designed to examine whether enriched environments (EE) would attenuate object recognition and spatial learning and memory deficits and locomotor sensitization induced by methadone maintenance treatment (MMT) in morphine-withdrawn rats.

METHODS

Male Wistar rats (170 ± 10 g) were injected with bi-daily doses (10 mg/kg, 12-h intervals) of morphine for 14 days. Rats receiving MMT were reared in the standard environment (SE) or EE during 30 days of morphine withdrawal. Then, the rats were tested for object recognition (the object recognition memory test, ORMT) and spatial learning and memory (the water maze) and then challenged with morphine (1 mg/kg, i.p.) and evaluated for locomotor activity (open-field box).

RESULTS

The results revealed that the dependent/saline/EE (D/Sal/EE) and D/methadone/EE (D/Meth/EE) rats exhibited significant preference for the new object (p = 0.006 and p = 0.049), spent more time in the target zone (p = 0.045 and p = 0.005) on the water maze, and displayed a lower level of distance traveled (p = 0.002 and p = 0.0001) compared to their control groups reared in SE.

CONCLUSIONS

We conclude that exposure to EE could ameliorate the object recognition and spatial memory deficits and also decrease locomotor sensitivity in morphine-withdrawn rats receiving MMT. Thus, EE may be beneficial in the treatment of addiction during MMT.

Saffron (Crocus sativus L.) stigma reduces symptoms of morphine-induced dependence and spontaneous withdrawal in rats

Background: Chronic morphine induces physical and psychological dependence signs. Saffron (Crocus sativus L.) stigma has been shown to have anxiolytic, antidepressant, and antinociceptive properties and to alleviate naloxone-precipitated withdrawal signs.Objectives: Therefore, this study was designed to examine the effects of saffron aqueous extract on the severity of physical-psychological dependence, voluntary morphine consumption, and the cerebrospinal fluid (CSF) serotonin levels following locomotor sensitization in morphine-dependent rats and in rats undergoing morphine withdrawal.Materials: Adult male rats were treated with morphine (10 mg/kg, sc twice daily) for 10 days. Rats received saffron extract (60 mg/kg, ip) daily, during the induction of morphine dependence and/or withdrawal. Then, rats were tested for spontaneous withdrawal signs, anxiety using the elevated plus-maze, depression using sucrose preference test, and voluntary morphine consumption using a two-bottle choice paradigm, and then challenged with morphine (1 mg/kg, ip) to evaluate of locomotor sensitization and CSF serotonin levels.Results: The results showed saffron extract during induction of morphine dependence decreased the severity of withdrawal signs (P = .05), while it had no effect on anxiety and depression-like behaviors. Saffron extract during morphine withdrawal exhibited an increase in the percentage (or ratio) of open/total arm entries (P = .017), higher levels of sucrose preference (P = .0001), a lower morphine preference ratio (P = .02) and also, a decrease in locomotor activity (P = .004) and an increase in the CSF serotonin levels (P = .041) in rats challenged to morphine.Conclusions: Saffron extract may exert a protective effect against morphine-induced behavioral sensitization in rats, probably through increasing serotonin levels.

BDNF receptor antagonism during the induction of morphine dependence exacerbates the severity of physical dependence and ameliorates psychological dependence in rats

This study examined the effects of systemic administration of the TrkB receptor antagonist (ANA-12) during induction of morphine dependence on the severity of physical and psychological dependence and the cerebrospinal fluid (CSF) BDNF levels in morphine-dependent and withdrawn rats. Rats became morphine-dependent by increasing daily doses of morphine for 7 days, along with ANA-12 injection. Then, rats were tested for the severity of physical dependence on morphine (spontaneous withdrawal signs), anxiety-like (the elevated plus maze), depressive-like (sucrose preference test) behaviors after spontaneous morphine withdrawal. Also, the CSF BDNF levels were assessed 2 h after the last dose of morphine and day 13 after morphine withdrawal in morphine-dependent and withdrawn rats. We found that the morphine withdrawal signs were significantly higher in morphine dependent rats receiving ANA-12 on days of 5-7 after morphine withdrawal, also ANA-12 exacerbated overall dependence severity. While, the percentage of time spent in the open arms and sucrose preference were higher in morphine-dependent rats receiving ANA-12 than morphine-dependent rats receiving saline. Also, the ANA-12 injection decreased the CSF BDNF levels following morphine dependence, while increased it after morphine withdrawal. We conclude that the ANA-12 exacerbated the severity of physical morphine dependence but attenuated the anxiety/depressive-like behaviors in morphine-dependent and withdrawn rats. Also, ANA-12 injection was able to reverse the changes in the CSF BDNF levels. Therefore, ANA-12 is not more likely to complete treatment for opiate addiction.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 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 (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).