Analgesic Effects of 1st Generation Anti-histamines in Mice

Antihistamine promotes electroacupuncture analgesia in healthy human subjects: A pilot study

Background and aim

We have previously reported that histamine H₁ receptor antagonists facilitate electroacupuncture (EA) analgesia in experimental animals. In this pilot study, we sought to determine whether the histamine H₁ receptor antagonist dexchlorpheniramine (DCPA) facilitates EA analgesia in healthy human subjects.

Experimental procedure

Forty healthy subjects aged 20–30 years were randomly allocated to 1 of 4 groups: (1) sham EA at acupoints Zusanli (ST36) and Yanglingquan (GB34) (sham EA; n = 10); (2) EA at ST36 and GB34 (n = 10); (3) EA at ST36 and GB34 plus low-dose DCPA (2 mg, n = 10); (4) EA at ST36 and GB34 plus high-dose DCPA (4 mg, n = 10). Before and after acupuncture treatment, pain thresholds were determined by transcutaneous electrical stimuli on the glabrous skin of the left upper arm.

Results

After the acupuncture session, subjects in the EA plus high-dose DCPA group had a significantly higher pain threshold elevation compared with the other 3 study groups. The change from baseline in pain threshold in the EA plus high-dose DCPA group was significantly greater than the change in pain threshold with EA only, indicating that DCPA 4 mg facilitated EA analgesia.

Conclusion

The results suggest that combining H₁ receptor antagonist treatment with EA appears to relieve pain to a greater extent compared with EA alone. This study is registered with ClinicalTrials.gov (https://clinicaltrials.gov/), number NCT03805035 (https://clinicaltrials.gov/ct2/show/NCT03805035).

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Histamine H₁ receptor antagonist treatment appears to augment the pain-relieving effects of EA in healthy subjects.

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EA increased the pain thresholds in EA treated groups.

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Combination of EA and high-dose of DCPA further increased pain thresholds.

Effects of chemotherapy on operant responding for palatable food in male and female mice

Patients treated with cancer chemotherapeutics frequently report chemotherapy-induced peripheral neuropathy (CIPN), changes in mood (depression and anxiety) and functional impairments. Rodent models of CIPN elicit limited alterations in functional behaviors, which pose challenges in developing preclinical models of chemotherapy-induced behavioral depression. The study examined the consequences of chemotherapy-induced mechanical hypersensitivity (paclitaxel: 32 or 64 mg/kg, cumulative; oxaliplatin: 30 mg/kg, cumulative) on behavioral depression, as measured with operant responding for palatable food during periods of food restriction and ad libitum chow, consumption of noncontingently available palatable food in the presence of ad libitum chow, and voluntary wheel running. The study employed two inbred mouse strains (C57BL/6J and Balb/cJ) and examined potential sex differences. All chemotherapeutic regimens caused profound mechanical hypersensitivity for the duration of the observation periods (up to 7 months), but no treatments changed voluntary wheel running or consumption of noncontingent palatable food. The high dose of paclitaxel temporarily reduced operant responding for palatable food in male C57BL/6J mice undergoing food restriction or maintained on ad libitum chow. However, paclitaxel failed to decrease operant responding for palatable food in free-feeding female C57BL/6J mice or Balb/cJ mice of either sex. Moreover, oxaliplatin did not significantly alter operant responding for palatable food in male or female C57BL/6J mice maintained on ad libitum chow. These findings demonstrate a dissociation between chemotherapy-induced mechanical hypersensitivity and behavioral depression. The transient effects of paclitaxel on operant responding in male C57BL/6J mice may represent a fleeting behavioral correlate of chemotherapy-associated pain-like behaviors.

Synergistic interaction between matrine and paracetamol in the acetic acid writhing test in mice

The purpose of this study was to investigate the analgesic interaction between matrine and paracetamol in an acetic acid-induced writhing model in mice. Fifty percent effective dose (ED₅₀) values of the individual drugs were determined, and the different proportions of matrine and paracetamol were assayed using the isobolographic method. Our study demonstrated that both of matrine and paracetamol dose-dependently inhibited the writhing response evoked by acetic acid, and the ED₅₀ values and their 95% confidence intervals against these tonic pain were 21.10 (17.86-24.92) mg/kg and 61.30 (50.71-74.10) mg/kg for matrine and paracetamol, respectively. At the fixed ratios of 1:1, 1:3 and 3:1, the experimental ED₅₀ values of matrine and paracetamol combinations and their 95% confidence intervals were 10.52 (5.14-21.55) mg/kg, 9.13 (4.46-18.70) mg/kg and 4.98 (4.17-5.95) mg/kg, respectively, their theoretical ED₅₀ values and 95% confidence intervals were 41.20 (36.31-46.74) mg/kg, 51.25 (44.19-59.44) mg/kg and 31.15 (27.25-35.60) mg/kg, and the experimental ED₅₀ values of matrine and paracetamol combination were significantly lower than their calculated theoretical ED₅₀ values (all P < 0.01), as revealed by isobolographic analysis. Furthermore, the experimental regression line was also significantly different from the calculated additive equal-effect line over the range of the tested doses (all P < 0.01). Our results suggest that the combination of matrine with paracetamol exerts analgesic synergistic interactions in a mouse acetic acid-induced writhing model, thereby offering a possible therapeutic alternative for the clinical management of inflammatory pain.

Histamine H1Receptor Antagonists Facilitate Electroacupuncture Analgesia

This study investigated the influence of the histamine H1receptor antagonists, chlorpheniramine (CHL) and pyrilamine, on the analgesic effects of acupuncture in mice. Nociceptive response was evaluated by the acetic acid-induced abdominal writhe test. Electroacupuncture (EA) at bilateral ST36 reduced the manifestations of acetic acid-induced abdominal writhing, whereas needle insertion without electrostimulation had no such effect. Notably, EA treatment was not associated with any analgesic effects in mice pretreated with naloxone. Low doses of CHL (0.6[Formula: see text]mg/kg; p.o.) or pyrilamine (2.5[Formula: see text]mg/kg; i.p.) as monotherapy did not affect acetic acid-induced abdominal writhing. However, when each agent was combined with EA, acetic acid-induced abdominal writhing was reduced by a greater extent when compared with EA alone. Interestingly, the effects of CHL on acupuncture analgesia were not completely reversed by naloxone treatment. Acetic acid induced increases of phospho-p38 expression in spinal cord, as determined by immunofluorescence staining and Western blot analysis. These effects were attenuated by EA at ST36 and by low doses of histamine H1receptor antagonists, alone or in combination. Our findings show that relatively low doses of histamine H1receptor antagonists facilitate EA analgesia via non-opioid receptors. These results suggest a useful strategy for increasing the efficacy of EA analgesia in a clinical situation.