Contribution of α2A-adrenoceptor subtype to effect of dexmedetomidine and xylazine on spinal synaptic transmission of mice

Dexmedetomidine Ameliorates Postoperative Cognitive Dysfunction via the MicroRNA-381-Mediated EGR1/p53 Axis

Postoperative cognitive dysfunction (POCD; cognitive change associated with anesthesia and surgery) is one of the most serious long-term postoperative complications that occur in elderly patients. Dexmedetomidine (DEX) has been shown to be beneficial for improving outcomes of postoperative cognitive function. However, the exact mechanism underlying this role requires is yet to be found. The present study aims to determine the pathways involved in the protective effects of DEX against POCD in C57BL/6 J aged mice. DEX was administered after POCD modeling in C57BL/6 J aged mice. The cognitive function was evaluated after DEX treatment using novel object recognition, open field, and Y-maze tests. We also assessed its effects on neuron apoptosis and production of TNF-α and IL-1β in mouse brain tissues as well as expression levels of DNA damage-related proteins p53, p21, and γH2AX. Interactions between early growth response 1 (EGR1) and p53, microRNA (miR)-381, and EGR1 were identified by ChIP and luciferase reporter assays, and gain- and loss-of-function experiments were performed to confirm the involvement of their interaction in POCD. DEX administration attenuated hippocampal neuron apoptosis, neuroinflammation, DNA damage, and cognitive impairment in aged mice. miR-381 targeted EGR1 and disrupted its interaction with p53, leading to a decline in hippocampal neuron apoptosis, DNA damage, neuroinflammation, and cognitive impairment. Furthermore, DEX administration resulted in the enhancement of miR-381 expression and the subsequent inhibition of EGR1/p53 to protect against cognitive impairment in aged mice. Overall, these results indicate that DEX may have a potential neuroprotective effect against POCD via the miR-381/EGR1/p53 signaling, shedding light on the mechanisms involved in neuroprotection in POCD.

The α2A -adrenoceptor subtype plays a key role in the analgesic and sedative effects of xylazine

Xylazine, the classical α₂ -adrenoceptor (α₂ -AR) agonist, is still used as an analgesic and sedative in veterinary medicine, despite its low potency and affinity for α₂ -ARs. Previous pharmacological studies suggested that the α_2A -AR subtype plays a role in mediating the clinical effects of xylazine; however, these studies were hampered by the poor subtype-selectivity of the antagonists used and a lack of knowledge of their bioavailability in vivo. Here, we attempted to elucidate the role of the α_2A -AR subtype in mediating the clinical effects of xylazine by comparing the analgesic and sedative effects of this drug in wild-type mice with those in α_2A -AR functional knockout mice using the hot-plate and open field tests, respectively. Hippocampal noradrenaline turnover in both mice was also measured to evaluate the contribution of α_2A -AR subtype to the inhibitory effect of xylazine on presynaptic noradrenaline release. In wild-type mice, xylazine (10 or 30 mg/kg) increased the hot-plate latency. Furthermore, xylazine (3 or 10 mg/kg) inhibited the open field locomotor activity and decreased hippocampal noradrenaline turnover. By contrast, all of these effects were abolished in α_2A -AR functional knockout mice. These results indicate that the α_2A -AR subtype is mainly responsible for the clinical effects of xylazine.

Dexmedetomidine as Adjuvant to Lower Doses of Intrathecal Bupivacaine for Lower Limb Orthopedic Surgeries

BACKGROUND

Dexmedetomidine, an α₂ adrenergic agonist, has been found to be a useful adjuvant to local anesthetics. It has been found to produce satisfactory block with lower doses of spinal bupivacaine.

AIM

The aim of this study is to compare the difference in spinal block characteristics and hemodynamic effects of 7, 8, and 9 mg hyperbaric bupivacaine combined with 5 μg dexmedetomidine and to find out the optimum dose that would provide satisfactory block and hemodynamic stability for lower limb orthopedic surgeries.

SETTINGS AND STUDY DESIGN

This was a prospective, observational study.

MATERIALS AND METHODS

Ninety patients undergoing lower limb orthopedic surgeries were allocated to three groups of thirty each. Group A received 7 mg, Group B 8 mg and Group C 9 mg 0.5% hyperbaric bupivacaine along with dexmedetomidine 5 μg. The spinal block characteristics, hemodynamic stability, and side effects were compared.

STATISTICAL ANALYSIS

The quantitative variables were compared using ANOVA test and the qualitative variables using Chi-square test.

RESULTS

All three groups had satisfactory anesthesia and analgesia. The onset of analgesia was slower and peak sensory level lower in Group A. The onset of motor block, time to attain peak sensory levels, duration of analgesia, maximum pain scores, and requirement of rescue analgesics were comparable among groups. Duration of motor block and time of regression of sensory level were more in Group C. Hemodynamics and sedation scores were comparable.

CONCLUSION

Dexmedetomidine with lower doses of bupivacaine produces satisfactory anesthesia without hemodynamic instability. A dose of 7 mg bupivacaine with 5 μg dexmedetomidine may be sufficient for orthopedic surgeries.