A role for the parafascicular thalamic nucleus in the development of morphine dependence and withdrawal

Dezocine Alleviates Morphine-Induced Dependence in Rats

BACKGROUND

Opioid dependence is a major public health issue without optimal therapeutics. This study investigates the potential therapeutic effect of dezocine, a nonaddictive opioid, in opioid dependence in rat models.

METHODS

Dezocine was administered intraperitoneally to a morphine-dependent rat model to investigate its effect on withdrawal and conditioned place preference (CPP). Effect of dezocine on morphine withdrawal syndrome and CPP was analyzed using 2-way analysis of variance (ANOVA) followed by Tukey's post hoc test. Buprenorphine and vehicle solution containing 20% (v/v) dimethyl sulfoxide were used for positive and negative control, respectively. The astrocytes activation in nucleus accumbens was assessed by immunofluorescence assay of glial fibrillary acidic protein. Effect of dezocine and buprenorphine on the internalization of κ opioid receptor (KOR) was investigated using Neuro2A expressing KOR fused to red fluorescent protein tdTomato (KOR-tdT). Buprenorphine and dezocine were screened against 44 G-protein-coupled receptors, ion channels, and transporter proteins using radioligand-binding assay to compare the molecular targets.

RESULTS

The mean withdrawal score was reduced in rats treated with 1.25 mg·kg dezocine compared to vehicle-treated control animals starting from the day 1 (mean difference: 7.8; 95% confidence interval [CI], 6.35-9.25; P < .0001 by 2-way ANOVA). Significance was observed at all treatment days, including day 7 (mean difference: 2.13; 95% CI, 0.68-3.58; P < .001 by 2-way ANOVA). Furthermore, dezocine inhibited the reinstatement of morphine-induced CPP (mean difference: 314; 95% CI, 197.9-430.1; P < .0001 by 2-way ANOVA) compared to the control group. Chronic morphine administration induced astrocytes activation in nucleus accumbens, which was attenuated by dezocine. Dezocine blocked the agonist-induced KOR internalization in vitro, 1 of the mechanisms involved in the downstream signaling and development of opioid dependence. Dezocine had affinity to norepinephrine and serotonin transporters and sigma-1 receptor, whereas buprenorphine showed no activity against these targets.

CONCLUSIONS

Dezocine could potentially be used to alleviate opioid dependence. Due to the unique molecular target profile different from buprenorphine, it might have important value in studying the mechanisms of morphine dependence and developing novel therapeutic approaches.

An Engineered Endomorphin-2 Gene for Morphine Withdrawal Syndrome

An optimal therapeutics to manage opioid withdrawal syndrome is desired for opioid addiction treatment. Down-regulation of endogenous endomorphin-2 (EM2) level in the central nervous system after continuous morphine exposure was observed, which suggested that increase of EM2 could be an alternative novel method for opioid dependence. As a short peptide, the short half-life of EM2 limits its clinical usage through conventional administration. In the present study, we engineered an EM2 gene using a signal peptide of mouse growth factor for an out-secretory expression of EM2 and an adenovirus as a vector, which ultimately sustained the release of EM-2. After administration of the adenovirus in central nervous system, a sustained increase of EM2 level in the cerebral spinal fluid (CSF) was observed along with a reduction of morphine withdrawal syndrome. These findings suggest that the engineered EM2 gene delivered to the central nervous system could be a novel therapeutics for withdrawal syndrome in opioid dependent subjects.

Suppression of acute morphine withdrawal syndrome by adenovirus-mediated β-endorphin in rats

BACKGROUND

Endogenous β-endorphin (β-EP) in the central nervous system (CNS) is decreased upon opioid addiction. The current study examined whether exogenous β-EP, delivered using an adenoviral vector into the CNS could attenuate morphine withdrawal syndrome in rats.

METHODS

The model of opioid-dependent rats was set up by receiving subcutaneous injection of morphine using an escalating regimen for 6days (5, 10, 20, 40, 50, 60mg/kg, three times/day). The adenovirus mediated β-EP gene was constructed based on our previous work. The ilea of opioid-dependent rats were isolated and treated with the supernatant of Ad-NEP. The basic and naloxone-induced (4μm/l) contractions of dependent ilea were recorded. The Ad-NEP was injected into the left lateral ventricle of the addition rats. The expression of the β-EP gene was verified by radioimmunoassay of the cerebrospinal fluid (CSF) and immunocytochemistry for β-EP. Withdrawal syndrome was evaluated after intraperitoneal injection of naloxone.

RESULTS

The contractions of dependent ilea were attenuated with supernatant containing β-EP expressed by Ad-NEP. Injection of the Ad-NEP resulted in significant increases in β-EP level in the CSF and β-EP-positive neurons. Rats receiving adenovirus carrying the β-EP gene had significantly less severe withdrawal symptoms upon naloxone challenge.

CONCLUSIONS

Exogenous β-EP mediated by adenovirus could attenuate withdrawal syndrome in morphine-dependent rats.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).