Age- and sex-related changes in the severity of physical and psychological dependence in morphine-dependent rats

Diurnal sex differences in morphine withdrawal revealed by continuous assessment of voluntary home cage wheel running in the rat

Animal studies modeling recreational opioid use show more severe withdrawal symptoms in male compared to female rats, whereas our study modeling opioid use for pain showed a greater withdrawal-induced decrease in wheel running in female rats. The objective of this experiment was to determine whether sex differences in spontaneous morphine withdrawal are caused by differences in assessment method (i.e., wheel running vs. somatic symptoms). Twice daily injections of morphine (5 - 20 mg/kg, s.c.) for 5 days produced a dose and time dependent decrease in wheel running that was greater in male compared to female rats. Termination of morphine administration resulted in an overall decrease in running and a decrease in the amount of running during the dark phase of the light cycle from 95 % to approximately 75 %. In male rats, this decrease in the percent of dark running was caused by a large decrease in dark phase running, whereas female rats had a slightly higher increase in light phase running. Withdrawal also reduced maximal running speed and caused a decrease in body weight that was larger in male than female rats. Withdrawal symptoms were greatest on the day following the last morphine injection, but persisted for all 3 days of assessment. Morphine withdrawal produced a greater decrease in dark phase wheel running and body weight in male rats and a greater increase in light phase running in female rats. Voluntary home cage wheel running provides a continuous measure of opioid withdrawal that is consistent with other measures of opioid withdrawal.

Differential effects of acute and prolonged morphine withdrawal on motivational and goal-directed control over reward-seeking behaviour

Opioid addiction is a relapsing disorder marked by uncontrolled drug use and reduced interest in normally rewarding activities. The current study investigated the impact of spontaneous withdrawal from chronic morphine exposure on emotional, motivational and cognitive processes involved in regulating the pursuit and consumption of food rewards in male rats. In Experiment 1, rats experiencing acute morphine withdrawal lost weight and displayed somatic signs of drug dependence. However, hedonically driven sucrose consumption was significantly elevated, suggesting intact and potentially heightened reward processing. In Experiment 2, rats undergoing acute morphine withdrawal displayed reduced motivation when performing an effortful response for palatable food reward. Subsequent reward devaluation testing revealed that acute withdrawal disrupted their ability to exert flexible goal-directed control over reward seeking. Specifically, morphine-withdrawn rats were impaired in using current reward value to select actions both when relying on prior action-outcome learning and when given direct feedback about the consequences of their actions. In Experiment 3, rats tested after prolonged morphine withdrawal displayed heightened rather than diminished motivation for food rewards and retained their ability to engage in flexible goal-directed action selection. However, brief re-exposure to morphine was sufficient to impair motivation and disrupt goal-directed action selection, though in this case, rats were only impaired in using reward value to select actions in the presence of morphine-paired context cues and in the absence of response-contingent feedback. We suggest that these opioid-withdrawal induced deficits in motivation and goal-directed control may contribute to addiction by interfering with the pursuit of adaptive alternatives to drug use.

Sucrose preference test: A systematic review of protocols for the assessment of anhedonia in rodents

Anhedonia is described as a decreased ability to experience rewarding and enjoyable activities, a core symptom of major depressive disorder. The sucrose preference test (SPT) is a widely used and reliable behavioural test to assess anhedonia in rodents, based on a two-bottle choice paradigm. To date, different protocols are in use, inducing variability between researchers and hampering comparisons between studies. We performed a systematic review of the SPT protocols used in 2021 to identify the parameters in which they differ and their potential impact. We searched a total of four databases (PubMed, Scopus, Web of Science and Science Direct), from 1st January 2021 to 31st December 2021, and screened a total of 1066 articles. After screening by title and abstract, a total of 415 articles were included in this review. We extracted and analysed the different procedures used, the type of sweet solution and the habituation, deprivation, and testing protocols. The overall quality of the studies was considered very good, however, SPT protocols were extremely variable between studies with a total of 65 different habituation protocols and 104 combinations of food/water deprivation and preference testing duration. As the SPT is one of the most used tests to assess anhedonia in rodents, this work raises awareness of the great variability in SPT protocols being currently used. Furthermore, we call for standardization in the protocol used, and overall improvement of data reporting of methodologies and results, to increase the consistency between studies and allow a better comparison of results between different labs.

Differential effects of acute and prolonged morphine withdrawal on motivational and goal-directed control over reward-seeking behavior

Opioid addiction is a relapsing disorder marked by uncontrolled drug use and reduced interest in normally rewarding activities. The current study investigated the impact of spontaneous withdrawal from chronic morphine exposure on emotional, motivational, and cognitive processes involved in regulating the pursuit and consumption of natural food rewards in male rats. In Experiment 1, rats experiencing acute morphine withdrawal lost weight and displayed somatic signs of drug dependence. However, hedonically-driven sucrose consumption was significantly elevated, suggesting intact and potentially heightened emotional reward processing. In Experiment 2, rats undergoing acute morphine withdrawal displayed reduced motivation when performing an effortful response for palatable food reward. Subsequent reward devaluation testing revealed that acute withdrawal also disrupted their ability to exert flexible goal-directed control over their reward-seeking behavior. Specifically, morphine-withdrawn rats displayed insensitivity to reward devaluation both when relying on prior action-outcome learning and when given direct feedback about the consequences of their actions. In Experiment 3, rats tested after prolonged morphine withdrawal displayed heightened rather than diminished motivation for food rewards and retained their ability to engage in flexible goal-directed action selection. However, brief re-exposure to morphine was sufficient to impair motivation and disrupt goal-directed action selection, though in this case insensitivity to reward devaluation was only observed in the presence of morphine-paired context cues and in the absence of response-contingent feedback. We suggest that these opioid-withdrawal induced deficits in motivation and goal-directed control may contribute to addiction by interfering with the pursuit of adaptive alternatives to drug use.

Endomorphin analog ZH853 shows low reward, tolerance, and affective-motivational signs of withdrawal, while inhibiting opioid withdrawal and seeking

Currently available μ-opioid receptor agonist pharmacotherapies for opioid use disorder possess adverse effects limiting their use and, despite treatment, rates of relapse remain high. We previously showed that endomorphin analog ZH853 had no effect in rodent models that predict abuse liability in humans. Here we extended these findings by examining dependence liability and reinforcing properties in female rats and male rats with previous opioid exposure. The potential use of ZH853 in managing opioid use disorder was evaluated by examining its effect on opioid-seeking behavior and withdrawal. We found that ZH853 did not induce locomotor activation in male and female mice and was not self-administered by female rats. Relative to morphine, ZH853 led to similar somatic signs of withdrawal, but low affective-motivational signs of withdrawal, and absent changes in ventral tegmental area K(+)-Cl(-) co-transporter expression associated with reward dysregulation. The low abuse liability of ZH853 was further supported in oxycodone self-administering male rats, where ZH853 substitution extinguished opioid-seeking behavior. ZH853 priming also did not reinstate morphine conditioned place preference. Lastly, ZH853 inhibited oxycodone-seeking behavior during relapse after forced abstinence and decreased the expression of morphine withdrawal. These findings suggest the potential use of ZH853 as a safer opioid medication for long-term treatment of pain and opioid use disorder.

Effects of treadmill exercise and chronic stress on anxiety-like behavior, neuronal activity, and oxidative stress in basolateral amygdala in morphine-treated rats

The basolateral amygdala (BLA), which is sensitive to stress, is necessary for reward-seeking behavior and addiction. Regular exercise can produce various positive effects by affecting the BLA. Therefore, we aimed to investigate the effects of chronic stress and treadmill running (TR) on anxiety-like behavior, neuronal activity, lipid peroxidation (measured by malondialdehyde (MDA) levels, a marker for oxidative stress), and total thiol in BLA, in morphine-treated rats. Male Wistar rats were restricted in restraint stress and/or ran on the treadmill and treated with morphine (5 mg/kg) for 21 days. Anxiety-like behavior was evaluated using an elevated plus maze (EPM) and open field tests (OFTs), on day 22. On day 23, neuronal activity in BLA was assessed via single-unit recording. Finally, MDA and total thiol were assessed in BLA. Our results showed that chronic administration of morphine (5 mg/kg) did not affect anxiety-like behavior. However, the morphine-treated rats, subjected to chronic stress and exercise, showed fewer anxiety-like behaviors. Morphine increased BLA's MDA levels but it was prevented by TR. Glutamatergic and GABAergic basal neuronal activities were low in morphine-treated rats but after acute morphine application, there was a significant decrease in GABAergic neuronal activities in the morphine-exercise-stress (Mor-Exe-St) group. The results of this study showed that in morphine-treated rats, stress and exercise or their combination could have either co-directional or opposite effects to the chronic effects of morphine. These results indicate the existence of common pathways similar to endogenous opioids.

Involvement of GABAA receptors of lateral habenula in the acquisition and expression phases of morphine-induced place preference in male rats

The lateral habenula (LHb) is a critical brain structure involved in the aversive response to drug abuse. It has been determined that the gamma-aminobutyric acid (GABA)-ergic system plays the main role in morphine dependency. The role of GABA type A receptors (GABAARs) in LHb on morphine-induced conditioned place preference (CPP) remains unknown. In this study, the effect of bilateral intra-LHb microinjection of GABAAR agonist and antagonist on the acquisition and expression phases of CPP, utilizing a 5-day CPP paradigm in male rats, was evaluated. Subcutaneous administration of different doses of morphine caused a dose-dependent CPP. Intra-LHb microinjection of the GABAAR agonist, muscimol, in combination with morphine (5 mg/kg; subcutaneously) enhanced CPP scores in the acquisition phase of morphine CPP, whereas the GABAAR antagonist, bicuculline, significantly reduced the conditioning scores in the acquisition phase. Furthermore, pretreatment with a high dose of bicuculline reversed the additive effect of muscimol during the acquisition phase, yet the low dose of antagonist had no significant effect on agonist-induced CPP scores. On the other hand, muscimol (3 µg/rat) significantly increased CPP scores in the expression phase but bicuculline did not induce a significant effect on CPP scores. Bicuculline and muscimol microinjections did not affect locomotor activity in the testing sessions. Our results confirm that GABAARs in LHb play an active role in morphine reward. In addition, microinjections of bicuculline/muscimol may alter the morphine response through the GABAergic system.

Sex differences in the impact of pain, morphine administration and morphine withdrawal on quality of life in rats

The disruptive effects of pain on quality of life are greater in men than in women, but the disruptive effects of opioid administration and withdrawal tend to be greater in women. These sex differences in pain, acute opioid effects, and opioid withdrawal tend to be opposite to sex differences reported in laboratory rats. We hypothesized that sex differences in humans and rats would more closely align if animal research measured quality of life as opposed to traditional evoked behaviors of pain (e.g., nociceptive reflexes) and opioid withdrawal (e.g., wet dog shakes). The present study assessed quality of life in adult female and male rats by measuring voluntary wheel running in the rat's home cage. Hindpaw inflammation induced by administration of Complete Freund's Adjuvant (CFA) into the right hindpaw caused a greater depression of wheel running in male compared to female rats. Twice daily injections of high morphine doses (5-20 mg/kg) and the subsequent morphine withdrawal caused a greater depression of wheel running in female compared to male rats. These sex differences are consistent with human data that shows the impact of pain on quality of life is greater in men than women, but the negative effects of opioid administration and withdrawal are greater in women. The present data indicate that the clinical significance of animal research would be enhanced by shifting the endpoint from pain and opioid evoked behaviors to measures of quality of life such as voluntary wheel running.

Trends and Disparities in Quality of Life Among Older Adults From 1998 to 2018 in China: A National Observational Study

Objective

To investigate 20-year trends and disparities in quality of life among older adults in China from 1998 to 2018.

Methods

Our study was based on eight representative nationwide health surveys among older adults conducted in China from 1998 to 2018. Quality of life data were obtained from 91,993 individuals aged 65 years or above. All surveys included identical indicators of self-reported quality of life, demographic factors, socioeconomic status, lifestyle habits, and health status. The trends in the standardized prevalence of poor quality of life from 1998 to 2018 were examined by locally weighted scatterplot smoothing regression (LOWESS) analysis. We assessed the prevalence of poor quality of life and its related factors by logistic regression models after adjusting for potential confounders.

Results

The prevalence of poor quality of life was 38.2% (95% CI: 37.9–38.5%). The trends of poor quality of life showed an inverted “U” shape, that the prevalence increased from 27.8% in 1998 to 43.6% in 2008, and then decreased from 39.2% in 2011 to 32.1% in 2018. Disparities in the prevalence of poor quality of life were exacerbating among participants with low or moderate household income per capita and participants with high household income per capita from 1998 to 2018. After controlling potential confounders, living in rural areas, aged below 80 years, unmarried, living alone, low household income, current smoker, poor dietary diversity, never participating in organized social activities, with chronic diseases, functional disability, poor self-reported health, and unhealthy psychological status were risk factors related with poor quality of life in the multivariate model (all p < 0.05).

Conclusion

During the past two decades, poor quality of life in Chinese older adults showed an inverted “U” trend from 1998 to 2018 that the prevalence of poor quality of life peaked in 2008 and declined since China's deepening health system reform in 2009. However, disparities in the poor quality of life were exacerbating among participants with different socioeconomic statuses. Strengthening the health system is of great importance in improving the quality of life. More efforts are needed to reduce the disparities in the quality of life among the population at the different socioeconomic levels.

High-fat diet attenuates morphine withdrawal effects on sensory-evoked locus coeruleus norepinephrine neural activity in male obese rats

Objective: These experiments sought to characterize the effects of obesity propensity and obesogenic diet on locus coeruleus (LC) norepinephrine (NE) activity and determine the effects of obesity on LC neural responses to morphine withdrawal.Methods: In vivo single-unit LC electrophysiological activity was measured in obese prone (OP) and obese resistant (OR) male SD rats following high-fat (HFD: 45% fat) or low-fat (LFD; 10% fat) feeding. A separate cohort of LFD and HFD rats underwent in vivo LC recording on day 3 of spontaneous morphine withdrawal following an escalation dose paradigm (5-15 mg/kg; SQ twice daily).Results: OP (LFD: 34 cells/7 rats; HFD: 32 cells/6 rats) had higher spontaneous and tonic activity, and lower sensory-evoked activity compared with OR (LFD: 31 cells/6 rats; HFD: 41 cells/7 rats). Interacting effect of diet x strain status was observed on signal-to-noise ratio with OR-LFD having higher ratio than OP-LFD and OP-HFD. Morphine treatment decreased body weights. Withdrawal increased sensory-evoked rate in LFD (morphine; 20 cells/10 rats; saline 24 cells/6 rats) but not HFD (saline: 22 cells/7 rats; morphine: 21 cells/5 rats) rats. In a separate group of age-matched SD rats, a similar weight loss (5-7%) in response to the morphine did not alter sensory-evoked rate but decreased signal-to-noise ratio (Control: 22 cells/8 rats; Weight-matched: 23 cells/8 rats).Discussion: Taken together, our findings suggest that obesity and diet alter the sensory-evoked LC-NE neural responses, which could have implication for emotional stress and opioid-withdrawal behaviors.

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.

Bulleyaconitine A Inhibits Morphine-Induced Withdrawal Symptoms, Conditioned Place Preference, and Locomotor Sensitization Via Microglial Dynorphin A Expression

Bulleyaconitine A (BAA), a C19-diterpenoid alkaloid, has been prescribed as a nonnarcotic analgesic to treat chronic pain over four decades in China. The present study investigated its inhibition in morphine-induced withdrawal symptoms, conditioned place preference (CPP) and locomotor sensitization, and then explored the underlying mechanisms of actions. Multiple daily injections of morphine but not BAA up to 300 μg/kg/day into mice evoked naloxone-induced withdrawal symptoms (i.e., shakes, jumps, genital licks, fecal excretion and body weight loss), CPP expression, and locomotor sensitization. Single subcutaneous BAA injection (30–300 μg/kg) dose-dependently and completely attenuated morphine-induced withdrawal symptoms, with ED₅₀ values of 74.4 and 105.8 μg/kg in shakes and body weight loss, respectively. Subcutaneous BAA (300 μg/kg) also totally alleviated morphine-induced CPP acquisition and expression and locomotor sensitization. Furthermore, subcutaneous BAA injection also specifically stimulated dynorphin A expression in microglia but not astrocytes or neurons in nucleus accumbens (NAc) and hippocampal, measured for gene and protein expression and double immunofluorescence staining. In addition, subcutaneous BAA-inhibited morphine-induced withdrawal symptoms and CPP expression were totally blocked by the microglial metabolic inhibitor minocycline, dynorphin A antiserum, or specific KOR antagonist GNTI, given intracerebroventricularly. These results, for the first time, illustrate that BAA attenuates morphine-induced withdrawal symptoms, CPP expression, and locomotor sensitization by stimulation of microglial dynorphin A expression in the brain, suggesting that BAA may be a potential candidate for treatment of opioids-induced physical dependence and addiction.

Swimming exercise during morphine abstinence in parents-to-be attenuated morphine-induced conditioned place preference and locomotor sensitization only in male rat offspring

This study was designed to examine the effects of swimming exercise during morphine abstinence in parents-to-be before mating on morphine-induced conditioned place preference (CPP) and locomotor sensitization in the pubertal male and female rat offspring. Male and female Wistar rats were injected with bi-daily doses (10 mg/kg, 12 h intervals) of morphine for 14 days. The exercising rats exposed to a regular swimming exercise (45 min/d, five days per a week) during 30 days of morphine abstinence before mating. Then, the pubertal male and female rat offspring were tested for morphine-induced CPP and locomotor sensitization (using the open field). The results showed that the pubertal male offspring of the morphine-abstinent parents-to-be exhibited an increase in CPP to morphine and locomotor activity after morphine challenge than the offspring from the control group. While, swimming exercise in morphine-abstinent parents-to-be decreased CPP score and locomotor activity in the pubertal male offspring than control offspring. Thus, exposure to swimming exercise in morphine-abstinent parents-to-be before mating may exert a protective effect against morphine-induced reward and locomotor sensitization in their pubertal offspring which may prevent the vulnerability of the first generation to drug abuse following opiate-addicted parents before mating.

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.

Use of home cage wheel running to assess the behavioural effects of administering a mu/delta opioid receptor heterodimer antagonist for spontaneous morphine withdrawal in the rat

Opioid abuse is a major health problem. The objective of the present study was to evaluate the potentially disruptive side effects and therapeutic potential of a novel antagonist (D24M) of the mu-/delta-opioid receptor (MOR/DOR) heterodimer in male rats. Administration of high doses of D24M (1 & 10 nmol) into the lateral ventricle did not disrupt home cage wheel running. Repeated twice daily administration of increasing doses of morphine (5-20 mg/kg) over 5 days depressed wheel running and induced antinociceptive tolerance measured with the hot plate test. Administration of D24M had no effect on morphine tolerance, but tended to prolong morphine antinociception in non-tolerant rats. Spontaneous morphine withdrawal was evident as a decrease in body weight, a reduction in wheel running and an increase in sleep during the normally active dark phase of the circadian cycle, and an increase in wheel running and wakefulness in the normally inactive light phase. Administration of D24M during the dark phase on the third day of withdrawal had no effect on wheel running. These data provide additional evidence for the clinical relevance of home cage wheel running as a method to assess spontaneous opioid withdrawal in rats. These data also demonstrate that blocking the MOR/DOR heterodimer does not produce disruptive side effects or block the antinociceptive effects of morphine. Although administration of D24M had no effect on morphine withdrawal, additional studies are needed to evaluate withdrawal to continuous morphine administration and other opioids in rats with persistent pain.