Caterina Aurilio

The antinociceptive effect of tramadol in the formalin test is mediated by the serotonergic component

The aim of this study was to investigate the neurotransmissions involved in the antinociceptive effect of tramadol in the formalin test, which is an animal model of acute and tonic pain. A subcutaneous injection of formalin produces a biphasic nociceptive response: phase 1 (0-10 min-acute pain) and phase 2 (21-60 min-tonic pain). Nociceptive activity is reduced greatly during the 10 min between these two phases. We measured in mice the effects of (+/-)-tramadol, and of (+)- and (-)-tramadol administered before the induction of pain by formalin, in the presence and absence of drugs that act on the opioidergic, serotonergic and noradrenergic systems (naloxone, ketanserin, fluoxetine, maprotiline). With respect to animals treated with formalin alone, (+/-)-tramadol and its enantiomers significantly reduced the duration of nociceptive behaviours (lifting, licking, favouring, shaking, and flinching of the formalin-treated paw) during phase 2. This effect was prevented by the 5-HT(2) receptor antagonist ketanserin, but not by naloxone which, on the contrary, was able to prevent the antinociceptive effect of morphine. Naloxone and ketanserin did not affect the duration of nociceptive behaviour in animals not treated with tramadol. Fluoxetine (a selective 5-hydroxytryptamine (5-HT) reuptake inhibitor), but not maprotiline (a selective norepinephrine reuptake inhibitor), potentiated the antinociceptive effect of (+/-)-tramadol. In conclusion, we demonstrate that the serotonergic pathway is responsible for the antinociceptive effect of tramadol in phase 2 of the formalin test, and that this effect is mediated by 5-HT(2) receptors.

Neurobiology of pain

The neurobiology of pain had a notable interest in research focused on the study of neuronal plasticity development, nociceptors, molecular identity, signaling mechanism, ionic channels involved in the generation, modulation and propagation of action potential in all type of excitable cells. All the findings open the possibility for developing new therapeutic treatment. Nociceptive/inflammatory pain and neuropathic pain represent two different kinds of persistent chronic pain. We have reviewed the different mechanism suggested for the maintenance of pain, like descending nociceptive mechanism and their changes after tissue damage, including suppression and facilitation of defence behavior during pain. The role of these changes in inducing NMDA and AMPA receptors gene expression, after prolonged inflammation is emphasized by several authors. Furthermore, a relation between a persistent pain and amygdale has been shown. Molecular biology is the new frontier in the study of neurobiology of pain. Since the entire genome has been studied, we will able to find new genes involved in specific condition such as pain, because an altered gene expression can regulate neuronal activity after inflammation or tissue damage. J. Cell. Physiol. 209: 8–12, 2006.

Endocrine consequences of opioid therapy

Gonadal hormones are known to be affected by morphine and other opioids. In this paper, we summarize data collected in recent years which clearly indicate that the opioid-induced effects on steroid hormones depend on the opioid used and in some cases on the sex of the subject. Indeed morphine is able to reduce hormones like testosterone and cortisol in both male and female subjects in just a few hours, probably acting directly on peripheral glands. These depressant effects of morphine on hormones are also present in the treatment of surgical pain and are quickly reversible once opioid administration is suspended. Similar actions were also found to occur in experimental animals and in vitro in glial cells, further confirming the morphine-induced reduction of testosterone cell content. Testosterone and its metabolites are well known substances involved in the development and maintenance of the brain and all body structures. Thus when treating pain with opioids, their effects on hypothalamo-pituitary-gonadal and hypothalamo-pituitary-adrenal-related hormones must be considered and, where possible, hormone replacement therapy should be started.

Trigeminal pain transmission requires reactive oxygen species production

Three experiments were conducted in order to investigate the possible involvement of the reactive oxygen species in the nociception within the subnucleus caudalis of the spinal trigeminal nucleus (Vc). In the first experiment the extracellular level of hydrogen peroxide was evaluated by microdialysis in the Vc of two groups of six rats before and after a formalin (group 1) or saline solution (group 2) injection into the upper lip. In the second experiment the formalin test was conducted in three groups of 6 rats after a microinjection of 2-methoxyestradiol (2-ME, a superoxide-dismutase inhibitor; group 1) or N-acetylcysteine (NAC, an oxygen intermediate scavenger; group 2) or saline solution (group 3) into the Vc. In the third experiment an histochemical assay for superoxide dismutase activity was performed on two groups of 4 rats each 2 h after a formalin (group 1) or saline solution (group 2) injection into the upper lip. The results showed that (1) the level of hydrogen peroxide increases into the Vc during facial pain (134% of baseline); (2) the inhibition of superoxide dismutase or the removal of oxygen intermediate within the Vc decreases the sensibility to facial pain stimuli; and (3) persistent facial pain stimuli decrease the superoxide activity into the Vc (90% of counter-lateral). These data indicate that reactive oxygen species are produced in the Vc during persistent facial pain and are necessary for the transmission of pain.

Antinociceptive effect in mice of intraperitoneal N-methyl-d-aspartate receptor antagonists in the formalin test

Although the antinociceptive effect of NMDA antagonists in the formalin test is well recognised, these compounds can induce adverse motor effects. The aim of this study was to identify the systemic doses of NMDA antagonists that induce analgesia without causing side effects. Male Swiss mice (30–40 g) received a subcutaneous (sc) injection of 1.25% formalin () in the dorsal surface of the right hind‐paw and, 15 min before or after formalin, an ip injection of one of the following NMDA receptor antagonists: MK 801 (0.01, 0.025, and 0.05 mg/kg), memantine (0.1, 0.5, and 1 mg/kg), ketamine (0.125, 0.25, and 0.5 mg/kg), dextromethorphan (5, 10, and 20 mg/kg), and CGP 37849 (4, 6, and 8 mg/kg). Pain‐related behaviour (licking, lifting, favouring, shaking, and flinching of the treated paw) was recorded at 5‐min intervals for 60 min. The NMDA receptor antagonists significantly (p<0.01) and dose‐dependently reduced, versus controls, nociceptive activity during the second phase of the formalin test (from the 20th to the 60th min): at the highest doses, 97.6±0.1% with MK 801; 90.4±0.2% with memantine; 74.7±0.3% with ketamine; 92.8±0.4% with dextromethorphan; and 80.7±0.3% with CGP 37849, without affecting coordination. The rank order potency of antinociceptive activity of NMDA antagonists was: . The NMDA antagonists administered after formalin (during the analgesic interval) did not affect the late phase of the formalin test. In conclusion, systemic administration of NMDA receptor antagonists decreases the nociception observed during the late phase of the formalin test.

Synthesis of SiO2 and CaO rich calcium silicate systems via sol-gel process: Bioactivity, biocompatibility, and drug delivery tests

Silica and calcium silicate amorphous materials, mixed with sodium ampicillin, a broad-spectrum antibiotic, have been synthesized by sol-gel method. The amorphous nature of the gels was ascertained by X-ray diffraction analysis. The bioactivity of the synthesized materials has been put into evidence by the appearance of a crystal of hydroxyapatite on the surface of the samples soaked in a fluid simulating the composition of the human blood plasma, as detected through FTIR measurements and SEM micrographs. The present work refers to a series of in-vitro biocompatibility tests, which has been performed on silicate and CaO rich calcium silicate gel-glasses, to study the cell behavior when seeded on 1 cm(2) material fragments, introduced into an in-vitro culture system. 3T3 cell lines have been used and the viability has been evaluated by WST-8 test. The composition of the adopted glasses can be expressed by the following general formula: x CaO• (1 - x) SiO2 with x = 0.00; 0.30; 0.40; 0.50; 0.60. Subsequently, release kinetics in a simulate body fluid (SBF) has been investigated. The amount of sodium ampicillin released has been detected by UV-Vis spectroscopy. The release kinetics has appeared to occur in more than one stage. All data have shown that those materials could be used as drug delivery bioactive systems.

Control of post-thoracotomy pain by transcutaneous electrical nerve stimulation: effect on serum cytokine levels, visual analogue scale, pulmonary function and medication

OBJECTIVES Transcutaneous electrical nerve stimulation (TENS) has been used to control post-thoracotomy pain with contrasting results. We aimed to assess the efficacy of TENS on post-thoracotomy pain in relation of four criterion measurements as: (i) cytokines; (ii) pain; (iii) respiratory function and (iv) intake of narcotic medication. METHODS Between January 2008 and October 2010, 58 patients underwent standard posterolateral thoracotomy for resectable lung cancer. Fifty patients were enrolled in the present study and randomized in two groups: TENS group (25 patients) who received postoperatively TENS for 5 days and placebo group (25 patients) without TENS. In both groups (i) serum cytokines (IL-6, IL-10, TNF-α) were measured by ELISA before surgery and at 6, 12, 24, 48, 72, 96 and 120 postoperative hours (POHs); (ii) at the same POHs, the pain score was measured using visual analogue scale (VAS) ranging from 0 to 10 levels; (iii) respiratory function (FEV 1% and FVC % of predicted value) were valuated on 72, 96 and 120 POHs; (iv) the total intake of narcotic medication given during postoperative period of 5 days was recorded. Repeated measures of analysis of variance assess the difference between two study groups. A value of P < 0.05 was considered statistically significant. RESULTS Of the 50 patients enrolled, two patients of TENS group and two patients of the placebo group were lost to follow-up. (i) Serum IL-6 (P = 0.001), IL-10 (P = 0.001) and TNF-α (P = 0.001) levels in TENS group were significantly lower than in the control group; (ii) VAS score in TENS group was significantly lower than in the control group (P < 0.001); (iii) recovery of FEV 1 (P = 0.02) and of FVC (P = 0.02) was statistically better in the TENS group than in control group; (iv) morphine requirement was lower in the TENS group with respect to placebo TENS (P = 0.004). After 48 POHs, no patient required supplementary dose of morphine. TENS group compared with placebo-group presented a significant reduction of non-opioid consumption (P = 0.002). CONCLUSIONS TENS is a valuable strategy to alleviate post-thoracotomy pain with reduction of cytokine production and of analgesic consumption, and with positive effects on pulmonary ventilation function.

Ionic channels and neuropathic pain: Phisiopatology and applications

Neuropathic pain is defined by the International Association for Pain research as a pain associated to a primary lesion or a dysfunction of the central or peripheral system. Over the past few years the causes of the neuropathic pain were not known and there were not good treatments for it, now we have a better knowledge of the physiopathological aspects and there is a wider diffusion of the research for target aimed therapies. The physiologic genesis of nervous messages occurs exclusively in skin sensorial endings or in nerve tissues as a consequence of an adequate sensorial stimulus and depends on the quick variations of the electric potential difference at the endings of ionic membranes. These variations of even 500 V a second are possible because of the presence of ionic channels. In neuropathic pain impulses can be originated even from ectopic sites. Ectopic discharges originated in a peripheral neuropathic system have an important role in the early stage of neuropathic pain development in two different ways. First they give an excess of spontaneous and evoked electric impulses to the central nervous system, causing a primitive neuropathic pain signal; then the ectopic activity develops and maintains the central sensitisation process. All this amplifies the afferent signals deriving from residual efferents that go on innerving cutaneous areas damaged and partly disnerved, causing tactile allodynie. Sodium channels are the greatest responsible for electrogenesis, that is the basis of the action potential generation and its propagation. Action potential begins after a depolarization such that it could cause a membrane transitory modification, turning prevalently permeable to Na+ more than to K+ as during a release phase. Neuropathy generates a local accumulation of sodium channels, with a consequent increase of density. This remodel seems to be the basis of neuro hyperexecitably. Calcium channels have also an important role in cell working. Intracellular calcium increase contributes to depolarization processes, through kinase and determines the phosphorylation of membrane proteins that can make powerful the efficacy of the channels themselves. In the future new diagnostic opportunities of physiopathologist mechanism leading to neuropathic pain will allow treatments aimed at specific molecular changes of ionic channels. J. Cell. Physiol. 215: 8–14, 2008.

Buprenorphine in long-term control of chronic pain in cancer patients.

The aim of this randomized open-label prospective study was to evaluate the analgesic activity of buprenorphine in a transdermal formulation for cancer chronic pain control versus sustained-release morphine, in all cases combined with oral tramadol. A transdermal system with 35 microg/h buprenorphine was applied to the first group of patients (BT); the second group received 60 mg/day of sustained-release morphine (MT). In both groups oral tramadol was administered to a maximum of 200 mg daily, in case of need. The administration of transdermal buprenorphine versus morphine resulted in significant differences in the physical pain (P = 0.01), mental health (P = 0.03) and vitality (P = 0.001). These data indicated that the BT group showed an improvement of pain and a positive effect on the quality life.

Estradiol and testosterone differently affect visceral pain-related behavioural responses in male and female rats

In the study of pain, the presence of sex differences is well known, with female subjects being more affected in a number of chronic painful conditions; however, the underlying mechanisms and the involvement of gonadal hormones, are still controversial. This study evaluated visceral pain in a validated rat model of artificial calculosis and the effects of estradiol and testosterone administration. Adult male and female rats were divided into groups and treated with one of the substances or Oil (vehicle) for 5 days, starting 2 days before surgery, with half receiving an artificial calculosis (Stone) and half only a sham (Sham) procedure. The animals’ behaviour (ureteral crises, frequency and duration) were recorded for 72 h; estradiol and testosterone plasma levels were determined in all groups at the end of the observation period. After surgery, only Stone rats showed ureteral pain crises, with a significant sex difference in the Oil‐treated groups in which the number and duration of crises were higher in females than in males. This difference was not present in the estradiol‐treated groups in which ureteral crises were decreased only in females while testosterone treatment had no effect in either sex. Estradiol and testosterone plasma levels were affected by treatments in both sexes. These results confirm that, also in this model of visceral pain, females experience more pain than males; moreover, they show that supraphysiological levels of estradiol, but not of testosterone, are analgesic only in females. A dose and sex‐dependent efficacy of gonadal hormones is suggested and discussed.