Comparative study of dezocine, pentazocine and tapentadol on antinociception and physical dependence

Physical compatibility and chemical stability of dezocine and ramosetron in 0.9% sodium chloride injection for patient-controlled analgesia administration

As an antiemetic, 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist (ramosetron) is generally administered to prevent and treat postoperative nausea and vomiting induced by intravenous dezocine for patient-controlled analgesia. To date, the physicochemical stability of dezocine-ramosetron admixtures has not been assessed. The primary objective of this study was to evaluate the physicochemical stability of a combination of dezocine and ramosetron in 0.9% sodium chloride (normal saline [NS]) injections. Dezocine-ramosetron admixtures were prepared and stored in glass bottles and polyvinyl chloride (PVC) bags refrigerated at 4°C or stored at ambient temperatures (25°C) for up to 14 days. Initial concentrations were 5.0 mg/100 mL for dezocine and 0.3 mg/100 mL for ramosetron used as the diluents. Stability parameters (drug concentrations and pH values) were determined using high-performance liquid chromatography and pH measurements, respectively. Compatibility (cloudiness, discoloration, and precipitation) was assessed visually. After 14 days at 4 °C or 25 °C, the concentration losses of dezocine and ramosetron were both < 4%. Furthermore, there were no significant changes in color, turbidity, or pH values were observed in any of the batches. The results indicated that mixtures of dezocine and ramosetron in NS injections were continuously physically and chemically stable for 14 days in glass bottles or PVC bags stored at 4 °C or 25 °C.

Characterized profiles of gut microbiota in morphine abstinence-induced depressive-like behavior

Morphine is the most widely used analgesic for pain management worldwide. Abstinence of morphine could lead to neuropsychiatric symptoms, including depression. Gut microbiota is believed to contribute to the development of depression. However, the characteristics and potential role of gut microbiota in morphine abstinence-induced depression remain unclear. In the present study, we first established morphine abstinence-induced depressive behavior in mice. After dividing the mice into depressive and non-depressive groups, the gut microbiota of the mice was detected by 16S rRNA gene sequencing. The difference in the diversities and abundance of the gut microbiota were analyzed between groups. Then, the representative microbial markers that could distinguish each group were identified. In addition, gene function prediction of the operational taxonomic units (OTUs) with differential abundance between the depressive and non-depressive groups after morphine abstinence was conducted. Our results suggested that four weeks of abstinence from morphine did not change the richness of the gut microbiota. However, morphine abstinence influenced the gut microbial composition. Several specific genera of gut microbiota were identified as markers for each group. Interestingly, gene function prediction found that the fatty acid metabolism pathway was enriched in the OUTs in the depressive group compared with the non-depressive group after morphine abstinence. Our data suggested that gut microbiota dysbiosis was associated with morphine abstinence-induced depressive behavior, possibly by implicating the fatty acid metabolism pathway.

Activation of locus coeruleus-spinal cord noradrenergic neurons alleviates neuropathic pain in mice via reducing neuroinflammation from astrocytes and microglia in spinal dorsal horn

Background

The noradrenergic neurons of locus coeruleus (LC) project to the spinal dorsal horn (SDH), and release norepinephrine (NE) to inhibit pain transmission. However, its effect on pathological pain and the cellular mechanism in the SDH remains unclear. This study aimed to explore the analgesic effects and the anti-neuroinflammation mechanism of LC-spinal cord noradrenergic pathway (LC:SC) in neuropathic pain (NP) mice with sciatic chronic constriction injury.

Methods

The Designer Receptors Exclusively Activated by Designer Drugs (DREADD) was used to selectively activate LC:SC. Noradrenergic neuron-specific retro–adeno-associated virus was injected to the spinal cord. Pain threshold, LC and wide dynamic range (WDR) neuron firing, neuroinflammation (microglia and astrocyte activation, cytokine expression), and α2AR expression in SDH were evaluated.

Results

Activation of LC:SC with DREADD increased the mechanical and thermal nociceptive thresholds and reduced the WDR neuron firing. LC:SC activation (daily, 7 days) downregulated TNF-α and IL-1β expression, upregulated IL-4 and IL-10 expression in SDH, and inhibited microglia and astrocytes activation in NP mice. Immunofluorescence double staining confirmed that LC:SC activation decreased the expression of cytokines in microglia of the SDH. In addition, the effects of LC:SC activation could be reversed by intrathecal injection of yohimbine. Immunofluorescence of SDH showed that NE receptor α2B-AR was highly expressed in microglia in CCI mice.

Conclusion

These findings indicate that selective activation of LC:SC alleviates NP in mice by increasing the release of NE and reducing neuroinflammation of astrocytes and microglia in SDH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02489-9.