Ultra-low dose (+)-naloxone restores the thermal threshold of morphine tolerant rats

Naloxone could limit morphine hypersensitivity: Considering the molecular mechanisms

BACKGROUND

Naloxone has been used as an opioid antagonist to prevent multiple adverse side effects of opioid-like tolerance and hyperalgesia. This study has investigated naloxone combined with morphine to limit pain hypersensitivity. In addition, the expression of brain-derived neurotrophic factor (BDNF) and K⁺ Cl^- cotransporter2 (KCC2) were also studied.

METHODS

Forty-eight adult male Wistar rats (180-220 g) were divided into eight groups, with six rats in each group. Rats were divided into two tolerance and hyperalgesia groups; the sham group, the morphine group, the treatment group (naloxone along with morphine), and the sham group (naloxone along with saline) for eight consecutive days. Tail-flick test was performed on days 1, 5, and 8, and the plantar test on days 1 and 10. On days 8 and 10, the lumbar segments of the spinal cord were collected, and BDNF and KCC2 expression were analyzed using western blotting and immunohistochemistry, respectively.

RESULTS

Results showed that tolerance and hyperalgesia developed following eight days of repeated morphine injection. BDNF expression significantly increased, but KCC2 was downregulated. Co-administration of naloxone and morphine decreased tolerance and hyperalgesia by decreasing BDNF and increasing KCC2 expression, respectively.

CONCLUSION

This study suggests that BDNF and KCC2 may be candidate molecules for decreased morphine tolerance and hyperalgesia.

Melatonin regulation of transcription in the reversal of morphine tolerance: Microarray analysis of differential gene expression

Tolerance and associated hyperalgesia induced by long‑term morphine administration substantially restrict the clinical use of morphine in pain treatment. Melatonin, a neurohormone released by the pineal gland, has been demonstrated to attenuate anti‑nociceptive morphine tolerance. The present study investigates differentially expressed genes in the process of morphine tolerance and altered gene expression subsequent to melatonin treatment in chronic morphine‑infused ratspinal cords. Morphine tolerance was induced in male Wistar rats by intrathecal morphine infusion (the MO group). Melatonin (the MOMa group) was administered to overcome the effects derived by morphine. The mRNA collected from L5‑S3 of the spinal cord was extracted and analysed by rat expression microarray. Principal component analysis and clustering analysis revealed that the overall gene profiles were different in morphine and melatonin treatments. Subsequent to Gene Ontology analysis, the biological processes of differentially expressed genes of MO and MOMa compared with the control group were constructed. Furthermore, a panel of genes exclusively expressed following melatonin treatment and another panel of genes with inverse expression between the MO and MOMa group were also established. Subsequent to PANTHER pathway analysis, a group of genes with inverse expression following melatonin administrated compared with morphine alone were identified. The expression levels of genes of interest were also confirmed using a reverse transcription‑quantitative polymerase chain reaction. The gene panel that was constructed suggests a potential signaling pathway in morphine tolerance development and is valuable for investigating the mechanism of morphine tolerance and the regulatory gene profiles of melatonin treatment. These results may contribute to the discovery of potential drug targets in morphine tolerance treatments in the future.

Melatonin and their analogs as a potential use in the management of Neuropathic pain

Melatonin (N-acetyl-5-methoxytryptamine), secreted by the pineal gland is known to perform multiple functions including, antioxidant, anti-hypertensive, anti-cancerous, immunomodulatory, sedative and tranquilizing functions. Melatonin is also known to be involved in the regulation of body mass index, control the gastrointestinal system and play an important role in cardioprotection, thermoregulation, and reproduction. Recently, several studies have reported the efficacy of Melatonin in treating various pain syndromes. The current paper reviews the studies on Melatonin and its analogs, particularly in Neuropathic pain. Here, we first briefly summarized research in preclinical studies showing the possible mechanisms through which Melatonin and its analogs induce analgesia in Neuropathic pain. Second, we reviewed research indicating the role of Melatonin in attenuating analgesic tolerance. Finally, we discussed the recent studies that reported novel Melatonin agonists, which were proven to be effective in treating Neuropathic pain.

(+)-Naloxone inhibits morphine-induced chemotaxis via prevention of heat shock protein 90 cleavage in microglia

BACKGROUND/PURPOSE

Microglia have a crucial role in maintaining neuronal homeostasis in the central nervous system. Immune factors released from microglia have important roles in nociceptive signal transduction. Activation of microglia seems to be a shared mechanism in pathological pain and morphine tolerance because pharmacological attenuation of microglia activation provides satisfactory management in both situations.

METHODS

In the present study, we investigated the effect of 1nM (+)-naloxone, which is not an opioid receptor antagonist, on morphine-induced activation of microglia EOC13.31 cells.

RESULTS

Our results showed that 1μM morphine enhanced microglia activation and migration, decreased α-tubulin acetylation, and induced heat shock protein 90 (HSP90) fragmentation and histone deacetylase 6 (HDAC6) expression. Morphine-induced α-tubulin deacetylation and HSP90 fragmentation were HDAC6-dependent. Pretreatment with (+)-naloxone (1nM) inhibited morphine-evoked microglia activation and chemotaxis and prevented α-tubulin deacetylation and HSP90 fragmentation by inhibiting HDAC6 expression.

CONCLUSION

Based on the findings of the present study, we suggest that (+)-naloxone inhibits morphine-induced microglia activation by regulating HDAC6-dependent α-tubulin deacetylation and HSP90 fragmentation.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.