Spinal neurophysiologic correlates of the analgesic actions of intravesical dimethyl sulfoxide and capsaicin in the rat

Estrogen can abolish oxytocin-induced spinal anti-hyperalgesia

Our previous study verified a sex difference of anti-hyperalgesia in rats and anti-allodynia in mice induced by intrathecal oxytocin (OT). In the model of intraplantar carrageenan-induced inflammatory hyperalgesia, intrathecal OT injection induced a substantial anti-hyperalgesia in male rats even at a low dose (0.125 nmol). In contrast, female rats only responded to an extremely high dose (1.25 nmol). This sex difference concurs with a lower expression of OT receptors and higher expression of insulin-regulated aminopeptidase (IRAP; OT degrading enzyme) in the spinal cords of female rats. In this study, we further determined the role of female hormones in this sex difference by using ovariectomized rats. Our results show that a low dose of intrathecal OT caused a significant anti-hyperalgesia effect in ovariectomized female rats, similar to that seen in male rats. Ovariectomy did not cause any change of paw edema except at the late stage of convalescence when compared with the sham-operated group. Ovariectomy-induced faster recovery from edema but did not affect the severity of hyperalgesia. Moreover, there was a similar amount of IRAP expression in ovariectomized and sham rats. When estradiol (E2) was given together with OT, OT-induced anti-hyperalgesia was abolished at the developmental stage of hyperalgesia in ovariectomized rats. These results show an inhibitory role of female hormones generated from ovaries (mainly estrogen) in the sex difference of anti-hyperalgesia induced by OT. This study suggests the feasibility of a novel OT-based remedy to treat hyperalgesia in men and in menopausal women no receiving hormonal supplements.

Unsuitable use of DMSO for assessing behavioral endpoints in aquatic model species

Dimethyl sulfoxide (DMSO) is a universally used aprotic solvent with the ability to permeate biological membranes and thus is commonly used to achieve appropriate biological availability of hydrophobic toxicants. While DMSO as a carrier medium has a reportedly low toxicity and is routinely employed in ecotoxicology, very little is known about its effect on dynamic behavioral parameters. This study presents a comparative analysis of the lethal and behavioral effects of exposures to DMSO concentrations of 0.1-10% on several test species such as: neonates of the freshwater crustacean Daphnia magna, nauplii of the marine crustacean Artemia franciscana, the marine crustacean Allorchestes compressa, embryos and larvae of the freshwater fish Danio rerio. The results demonstrated that DMSO did not cause statistically significant mortality even at concentrations close to 1% but induced clear and significant behavioral abnormalities in response to sublethal concentrations on all test species. These included hypoactivity syndrome in A. franciscana, A. compressa, D. magna and zebrafish larvae while a slight time-dependent hyperactivity response was observed in zebrafish embryos. For the majority of test species, behavioral changes such as moving distance, acceleration and burst movement were often observed during the first hours of exposure. These results indicate that caution should be exercised when using DMSO as a carrier solvent in experiments assessing behavioral endpoints.

Effects of dimethylsulfoxide on behavior and antioxidant enzymes response of planarian Dugesia japonica

In this study, the toxicity, behavioral and antioxidant activity effects of dimethylsulfoxide (DMSO) on planarian Dugesia japonica were investigated. The results showed that the mortality was directly proportional to the DMSO concentration, and planarian locomotor velocity decreased as the concentration of DMSO increased. The recovery of the motility for planarians pre-exposed to DMSO was found to be time- and dose-dependent, and only those pre-exposed to 0.1-3% DMSO resulted in full recovery. The antioxidant enzymes of planarians in response to long-term DMSO stress was also altered in a time- and dose-dependent manner. Planarians revealed more tolerance to DMSO toxicity at low DMSO (0.1%) level in short- and long-term DMSO stress, in which an efficient antioxidant system was involved and the motility was not affected.

Dimethyl sulphoxide relaxes rabbit detrusor muscle by decreasing the Ca2+ sensitivity of the contractile apparatus

BACKGROUND AND PURPOSE

The intravesical administration of dimethyl sulphoxide (DMSO) is used to alleviate the symptoms of interstitial cystitis. We investigated the relaxant effect of DMSO and its underlying mechanism in the detrusor muscle.

EXPERIMENTAL APPROACH

The effects of DMSO on contraction, on Ca2+ sensitivity of myofilaments, and on myosin light chain (MLC) phosphorylation were investigated in both intact and alpha-toxin-permeabilized strips of rabbit detrusor muscle.

KEY RESULTS

In fura-PE3-loaded strips, DMSO (>1%) induced a significant relaxation during sustained contractions induced by 60 mM K+-depolarization or 10 microM carbachol, while having no effect on the [Ca2+](i) level. DMSO decreased the level of MLC phosphorylation during the contractions induced by 60 mM K+ and 10 microM carbachol. DMSO also inhibited both the contraction and MLC phosphorylation induced by calyculin-A in intact strips. In the alpha-toxin-permeabilized preparations, DMSO relaxed the Ca2+-induced contraction and also inhibited the tension development induced by a stepwise increment of Ca2+ concentrations. Such a relaxant effect of DMSO was enhanced in the presence of phosphate.

CONCLUSIONS AND IMPLICATIONS

DMSO relaxes rabbit detrusor muscle by decreasing the Ca2+ sensitivity of myofilaments. Inhibition of the kinase activities involved in myosin phosphorylation may play a major role in DMSO-induced Ca2+ desensitization. Inhibition of the cross-bridge cycling at the step of phosphate release may also contribute to the relaxant effect of DMSO. Such relaxant effects of DMSO could be linked to the therapeutic effect of DMSO in interstitial cystitis.

Toxicity and behavioral effects of dimethylsulfoxide in planaria

In this work, we describe aspects of the toxicity and behavioral effects of dimethylsulfoxide (DMSO) in planaria. Planarian worms have traditionally been a favored animal model in developmental biology. More recently, this organism is being recognized as an animal model in neuropharmacology research. DMSO is often used in cell and tissue culture as a cryoprotectant agent and is also commonly used to enhance the solubility of hydrophobic drugs in aqueous solutions. This compound can elicit various physiological effects in both vertebrates and invertebrates. Many drugs and drug candidates are hydrophobic, needing solvents like DMSO to be able to reach their physiological targets. As planaria becomes increasingly popular in neuropharmacology research, a description of the DMSO effects in this organism is essential. We found that DMSO is toxic to planarians at concentrations above 5% (705 mM), with an LD(50) of 10% (1.4M) at exposure times above 5 min. At sub-toxic concentrations, DMSO decreases planarian exploratory behavior in a concentration-dependent manner. This reduction in locomotor behavior is reversible and preincubation-independent. DMSO at a concentration of 0.1% (14.1 mM), which is usually enough to solubilize hydrophobic substances in aqueous solutions, did not display any toxic or behavioral effects in planaria. Therefore, in this animal model, DMSO concentrations above 0.1% should be avoided in order to be able to reliably observe any behavioral or toxic effects of hydrophobic drugs.

Characterization of chronic constriction of the saphenous nerve, a model of neuropathic pain in mice showing rapid molecular and electrophysiological changes

Neuropathic pain is one of the most inextricable problems encountered in clinics, because few facts are known about its etiology. Nerve injury often leads to allodynia and hyperalgesia, which are symptoms of neuropathic pain. The aim of this study was to understand some molecular and electrophysiological mechanisms of neuropathic pain after chronic constriction of the saphenous nerve (CCS) in mice. After surgery, CCS mice displayed significant allodynia and hyperalgesia, which were sensitive to acute systemic injection of morphine (4 mg/kg), gabapentin (50 mg/kg), amitriptyline (10 mg/kg), and the cannabinoid agonist WIN 55,212-2 (5 mg/kg). These behavioral changes were accompanied after surgery by an increase of c-Fos expression and by an overexpression of mu-opioid and cannabinoid CB1 and CB2 receptors in the spinal cord and the dorsal hind paw skin. In combination with the skin-nerve preparation, this model showed a decrease in functional receptive fields downstream to the injury and the apparition of A-fiber ectopic discharges. In conclusion, CCS injury induced behavioral, molecular, and electrophysiological rearrangements that might help us in better understanding the peripheral mechanisms of neuropathic pain. This model takes advantage of the possible use in the future of genetically modified mice and of an exclusively sensory nerve for a comprehensive study of peripheral mechanisms of neuropathic pain.