Obligatory role of B cells and adherent accessory cells in the transfer of a defect in morphine-mediated antinociception in C57BL/6J-bg/bg (beige-J) mice

Efficacy of 3 Buprenorphine Formulations for the Attenuation of Hypersensitivity after Plantar Incision in Immunodeficient NSG Mice

Buprenorphine is perhaps the most prescribed analgesic for management of postoperative pain in mice. Although various buprenorphine formulations are effective in commonly used immunocompetent mouse strains, a knowledge gap exists regarding its efficacy in immunodeficient mice. Here we used a plantar incision to evaluate the efficacy of 3 buprenorphine formulations for attenuating postoperative mechanical and thermal hypersensitivity in the immunodeficient NSG mouse strain. We also characterized the pharmacokinetics of these formulations over a 72-h period. We hypothesized that all 3 buprenorphine formulations evaluated-the standard preparation and 2 extended-release products (Bup-HCl, Bup-ER, and Bup-XR, respectively)-would attenuate postoperative mechanical and thermal hypersensitivity resulting from a plantar incision in NSG mice. Male and female NSG mice (n = 48) were allocated to 4 treatment groups: saline (0.9% NaCl, 5 mL/kg SC once); Bup-HCl (0.1 mg/kg SC, BID for 2 d); Bup-ER (1.0 mg/kg SC once); and Bup-XR (3.25 mg/kg SC once). Mechani- cal and thermal hypersensitivity assessments were conducted 24 h before surgery and at 4, 8, 24, 48, and 72 h afterward. All groups of mice showed mechanical and thermal hypersensitivity within the first 24 h after surgery. Behavioral pain indicators (guarding, toe-touching [intermittent partial weight bearing], licking the incision, vocalizations) were observed in some mice from each group at every postoperative time point. Plasma buprenorphine was measured in a separate group of mice and concentrations surpassed the suggested therapeutic level (1.0 ng/mL) for less than 4 h for Bup-HCl, for at least 24 h for Bup-ER, and for 72 h for Bup-XR. Our results indicate that at the dosages studied, these buprenorphine formulations do not adequately attenuate postoperative mechanical and thermal hypersensitivity in the plantar incisional model in NSG mice. These findings support the need for strain-specific analgesic protocols for mice used in research.

Increased pain sensitivity and decreased opioid analgesia in T-cell-deficient mice and implications for sex differences

The processing of pain in the central nervous system is now known to have an important immune component, including T cells of the adaptive immune system. T cells have been shown to release endogenous opioids, and although it is well known that opioids have effects on T-cell populations, very little attention has been given to the converse: how T cells may affect opioid regulation. We find here that, in addition to displaying significantly increased baseline pain sensitivity across various pain modalities, T-cell-deficient mice (CD-1 nude, Rag1 null mutant, and Cd4 null mutant) exhibit pronounced deficiencies in morphine inhibition of thermal or inflammatory pain. Nude mice are also deficient in endogenous opioid-mediated analgesia, exhibiting no stress-induced analgesia from restraint. The relevant T-cell subpopulation seems to be CD4 T cells because adoptive transfer of them but not CD8 cells into nude mice rescues both the pain and morphine analgesia phenotypes. As previously reported, we also observe a sex difference in CD-1 mice, with females requiring 2- to 3-fold more morphine than males to produce equal analgesia. Nude mice display no sex differences in morphine analgesia, and the sex difference is restored in nude mice of either sex receiving CD4 T cells from CD-1 donor male or female mice. These results suggest that CD4 T cells play an as yet unappreciated role in opioid analgesia and may be a driver of sex differences therein.

Exploring the neuroimmunopharmacology of opioids: an integrative review of mechanisms of central immune signaling and their implications for opioid analgesia

Vastly stimulated by the discovery of opioid receptors in the early 1970s, preclinical and clinical research was directed at the study of stereoselective neuronal actions of opioids, especially those played in their crucial analgesic role. However, during the past decade, a new appreciation of the non-neuronal actions of opioids has emerged from preclinical research, with specific appreciation for the nonclassic and nonstereoselective sites of action. Opioid activity at Toll-like receptors, newly recognized innate immune pattern recognition receptors, adds substantially to this unfolding story. It is now apparent from molecular and rodent data that these newly identified signaling events significantly modify the pharmacodynamics of opioids by eliciting proinflammatory reactivity from glia, the immunocompetent cells of the central nervous system. These central immune signaling events, including the release of cytokines and chemokines and the associated disruption of glutamate homeostasis, cause elevated neuronal excitability, which subsequently decreases opioid analgesic efficacy and leads to heightened pain states. This review will examine the current preclinical literature of opioid-induced central immune signaling mediated by classic and nonclassic opioid receptors. A unification of the preclinical pharmacology, neuroscience, and immunology of opioids now provides new insights into common mechanisms of chronic pain, naive tolerance, analgesic tolerance, opioid-induced hyperalgesia, and allodynia. Novel pharmacological targets for future drug development are discussed in the hope that disease-modifying chronic pain treatments arising from the appreciation of opioid-induced central immune signaling may become practical.

In vitro opioid induced proliferation of peripheral blood immune cells correlates with in vivo cold pressor pain tolerance in humans: a biological marker of pain tolerance

There is substantial evidence for bidirectional communication between the immune system and the central nervous system, as the cells and signalling molecules of the immune system influence many central nervous system functions, for instance nociception. Opioids, such as morphine, produce analgesia and numerous other central and peripheral effects including sedation and euphoria, while their effects on the immune system are wide-ranging. There is considerable interindividual variability in basal nociception and response to opioids, however, the physiological and biological mechanisms underlying this are unclear. Therefore, we investigated the relationship between the immune system and basal nociceptive thresholds, using the proliferative response of isolated peripheral blood mononuclear cells and cold pressor pain tolerance. Here we show that the percent increase in proliferation of peripheral immune cells from 13 healthy subjects incubated with morphine ex vivo is highly correlated with the subjects' tolerance to noxious cold stimuli (Pearson r = 0.92, P < 0.0001). These pilot data provide evidence of a novel objective biological marker of pain tolerance in humans, which also links the immune and opioid systems with basal pain tolerance.

The interaction between IL-1beta and morphine: possible mechanism of the deficiency of morphine-induced analgesia in diabetic mice

It is known that diabetic mice are less sensitive to the analgesic effect of morphine. Some factor(s) derived from mononuclear cells, e.g. interleukin-1beta (IL-1beta), may be responsible for the diminished analgesic effect of morphine in diabetic mice. Therefore, we examined direct effects of IL-1beta, intracerebroventricularly (i.c.v.), on morphine-induced analgesia, subcutaneously (s.c.), in diabetic and control mice by using the tail-flick test. Morphine at doses of 1, 2 and 5 mg/kg (s.c.) produced dose-dependent analgesia in diabetic and control mice but diabetic mice were less sensitive to the analgesic effect of morphine when compared to the controls. IL-1beta at a dose of 0.1 ng/mouse produced analgesia in control mice but not in diabetics, whereas IL-1beta at a dose of 10 ng/mouse produced a hyperalgesic effect both in diabetic and control mice. IL-1beta at a dose of 1 ng/mouse has neither an analgesic nor a hyperalgesic effect in control and diabetic mice. Administration of a neutral (neither analgesic nor hyperalgesic) dose of IL-1beta, 1 ng/mouse (i.c.v.), just prior to administration of morphine (s.c.) abolished the analgesic effect of morphine at doses of 1, 2 and 5 mg/kg in control mice and the analgesic effect of morphine became similar to that in diabetics. The diminished analgesic effect of morphine in diabetes was attenuated further with IL-1beta at a dose of 1 ng/mouse (i.c.v.). These results suggest that the decreased analgesic effect of morphine in diabetes may be related to IL-1beta.

Role of spleen or spleen products in the reduced locomotor-enhancing effect of morphine in diabetic mice

In the present study, we examined the possibility that factor(s) derived from spleen cells are involved in the reduced morphine-induced hyperlocomotion in diabetic mice. The mean total locomotor activity after s.c. administration of morphine (20 mg/kg) in non-diabetic mice was significantly greater than that in diabetic mice. Splenectomized diabetic mice had a significantly higher sensitivity to morphine-induced hyperlocomotion than untreated or sham-operated diabetic mice. However, morphine-induced hyperlocomotion in non-diabetic mice was unaffected by splenectomy or sham-operation. Furthermore, 7 days after adoptive transfer of the supernatant of spleen cell homogenate (SSCH) from diabetic mice (SSCH-D), naive mice that had been injected with SSCH-D showed lower morphine-induced locomotor activity than mice which had been injected with SSCH from non-diabetic mice (SSCH-ND). These results suggest that some factor(s) derived from spleen cells may play an important direct or indirect role in the selective reduction of morphine's locomotor-enhancing effect in diabetic mice.

The combined immunological and antinociceptive defects of beige-J mice: the possible existence of a 'mu-repressin'

A selective non-responsiveness to the analgesic effects of opioid mu receptor-, but not opioid delta receptor-, mediated antinociception in the tail-flick test has been identified in C57BL/6J-bgJ (beige-J) mice. The beige-J mutation is also known to give rise to multiple immunological disorders and immune cell dysfunctions. A link between these apparently disparate manifestations has been examined in a series of studies using, for example, adoptive transfer of spleen cells. The findings appear to have broad implications for the link between the immune and opioid systems.

Effects of in vivo morphine treatment on antibody responses in C57BL/6 bgJ/bgJ (beige) mice

C57BL/6J bgJ/bgJ (beige) mice are less sensitive than other strains to the analgesic effects of morphine, although they have normal numbers of mu receptors. In the present study, beige mice and their normal littermates (beige+) were treated in vivo with morphine or the opioid antagonist, naltrexone and their primary in vitro antibody responses were assessed. Morphine treatment caused splenic atrophy and suppressed the primary in vitro antibody response in beige and beige+ mice. However, these effects were not blocked by naltrexone co-treatment. In these mouse strains, naltrexone decreased spleen size and antibody responses by itself, which may mask its ability to antagonize morphine. In beige mice, placebo pellet implantation suppressed the primary in vitro antibody response. Morphine did not cause a further suppression of the antibody response in beige mice compared to placebo. Because of this anomalous response to placebo treatment, the immunosuppressive effects of morphine on the antibody response/10(7) cells can not be attributed to a specific drug effect in this strain. However, when antibody responses were expressed on a per spleen basis, the overall capacity to respond to antigenic challenge was suppressed by morphine treatment.