Postsynaptic alpha-2 adrenergic receptors are critical for the antidepressant-like effects of desipramine on behavior

The antidepressant desipramine inhibits the reuptake of norepinephrine (NE), leading to activation of both pre- and postsynaptic adrenergic receptors, including alpha-1, alpha-2, beta-1, and beta-2 subtypes. However, it is not clear which adrenergic receptors are involved in mediating its antidepressant effects. Treatment of mice with desipramine (20 mg/kg, i.p.) produced an antidepressant-like effect, as evidenced by decreased immobility in the forced-swim test; this was antagonized by pretreatment with the alpha-2 adrenergic antagonist idazoxan (0.1-2.5 mg/kg, i.p.). Similarly, idazoxan, administered peripherally (0.5-2.5 mg/kg, i.p.) or centrally (1-10 microg, i.c.v.), antagonized the antidepressant-like effect of desipramine in rats responding under a differential-reinforcement-of-low-rate (DRL) 72-s schedule, ie, decreased response rate and increased reinforcement rate. By contrast, pretreatment with the beta-adrenergic antagonists propranolol and CGP-12177 or the alpha-1 adrenergic antagonist prazosin did not alter the antidepressant-like effect of desipramine on DRL behavior. The lack of involvement of beta-adrenergic receptors in mediating the behavioral effects of desipramine was confirmed using knockout lines. In the forced-swim test, the desipramine-induced decrease in immobility was not altered in mice deficient in beta-1, beta-2, or both beta-1 and beta-2 adrenergic receptors. In addition, desipramine (3-30 mg/kg) produced an antidepressant-like effect on behavior under a DRL 36-s schedule in mice deficient in both beta-1 and beta-2 adrenergic receptors. As antagonism of presynaptic alpha-2 adrenergic receptors facilitates NE release, which potentiates the effects of desipramine, the present results suggest that postsynaptic alpha-2 adrenergic receptors play an important role in its antidepressant effects.

Dexmedetomidine for cancer pain: mechanisms and opioid-sparing effects

BACKGROUND AND OBJECTIVE

Cancer pain treatment faces challenges such as ineffective pain management, high-dose opioid use, and insufficient analgesia. Dexmedetomidine (DEX), a novel α2 receptor agonist, is a potential adjuvant analgesic. Its analgesic mechanism involves central coeruleus cell hyperpolarization, activation of peripheral, spinal cord, and spinal α2 receptors, and regulation of cellular signaling pathways and inflammatory factors. DEX reduces harmful neurotransmitter production and pain signal transmission and enhances opioid analgesia while decreasing opioid use and tolerance. This review introduces the main mechanisms of DEX and its potential for treating complex and refractory cancer pain.

METHODS

We conducted literature searches using the terms "dexmedetomidine," "cancer pain," "opioid sparing," "analgesic mechanism," and their combinations in PubMed, Embase, Cochrane Library, and Web of Science. We systematically retrieved research articles, reviews, and editorials published in English up to mid-December 2024. All identified publications were reviewed, and their key references were cross-checked to ensure a comprehensive and high-quality review.

KEY CONTENT AND FINDINGS

Preclinical and clinical studies have demonstrated the advantages and potential of DEX in cancer pain management. DEX has intrinsic analgesic properties and can significantly relieve cancer pain by interacting with opioids, thereby delaying the development of opioid tolerance. It is particularly suitable for patients with refractory cancer pain and provides effective treatment whether used as an analgesic or an anesthetic adjuvant.

CONCLUSIONS

DEX is a promising adjuvant for cancer pain management, utilizing multi-mechanism analgesia and opioid-sparing effects to address unmet needs in refractory cases. Preclinical and clinical studies highlight efficacy heterogeneity across different cancer types and limited long-term safety data. High-quality, multicenter randomized controlled trials are needed to determine the optimal dose, refine dosing regimens, and verify results across diverse populations. Until further evidence is available, DEX should be considered a valuable adjunct in individualized, multimodal analgesic strategies, with careful monitoring of hemodynamic parameters and central nervous system adverse events.