Search results for "opioid"
showing 10 items of 320 documents
Long-lasting rewarding effects of morphine induced by drug primings.
2005
To evaluate the persistence of the rewarding effects of morphine, the acquisition, maintenance, extinction and reinstatement of a conditioned place preference (CPP) was assessed in OF1 mice. In Experiment 1, the persistence of morphine-induced CPP was evaluated weekly. Mice showed CPP after four sessions of conditioning with 5, 10, 20 and 40 mg/kg of morphine, which lasted 0, 1, 2 and 4 weeks, respectively. In Experiment 2, after four sessions of conditioning with 40 mg/kg of morphine, the effects of four schedules of extinction differing in the time interval (2, 4, 6 or 8 weeks) between sessions were evaluated. CPP was no longer evident after 8 weeks for the groups examined each 2 or 8 wee…
Regional differences in mu-opioid receptor-dependent modulation of basal dopamine transmission in rat striatum
2016
Abstract The nigrostriatal dopamine system is implicated in the regulation of reward and motor activity. Dopamine (DA) release in dorsal striatum (DS) is controlled by the firing rate of DA neurons in substantia nigra pars compacta. However, influences at terminal level, such as those involving activation of mu opioid receptors (MORs), can play a key role in determining DA levels in striatum. Nonetheless, published data also suggest that the effect of opioid drugs on DA levels may differ depending on the DS subregion analyzed. In this study, in vivo microdialysis in rats was used to explore this regional dependence. Changes in basal DA levels induced by local retrodialysis application of DA…
The effects of morphine on the temporal structure of Wistar rat behavioral response to pain in hot-plate
2016
Rationale: The largest amount of researches on the hot-plate test was carried out using quantitative assessments. However, the evaluation of the relationships among the different elements that compose the behavioral response to pain requires different approaches. Although previous studies have provided clear information on the behavioral structure of the response, no data are available on its temporal structure. Objectives: The objective of this study was to investigate the temporal structure of the behavioral response to pain in Wistar rat tested in hot-plate and how this structure was influenced by morphine-induced analgesia. Methods: The behavior of four groups of subjects tested in hot-…
Spontaneous Cingulate High-Current Spikes Signal Normal and Pathological Pain States
2019
Prominent 7–12 Hz oscillations in frontal cortical networks in rats have been reported. However, the mechanism of generation and the physiological function of this brain rhythm have not yet been clarified. Multichannel extracellular field potentials of the ACC were recorded and analyzed using the current source density method in halothane-anesthetized rats. Spontaneous high-current spikes (HCSs) were localized in the deep part of layer II/III and upper part of layer V of the ACC. The frequency of HCSs in the ACC was 7–12 Hz, with an amplitude of 6.5 ± 0.76 mV/mm(2) and duration of 55.24 ± 2.43 ms. The power density significantly decreased (84.56 ± 6.93%, p < 0.05, t test) after pinching the…
7-Nitroindazole blocks conditioned place preference but not hyperactivity induced by morphine.
2003
The effects of 7-nitroindazole (7-NI), a neural nitric oxide synthase (nNOS) inhibitor, on spontaneous locomotor activity, morphine-induced hyperactivity, acquisition of place conditioning and morphine-induced conditioned place preference (CPP) were evaluated in male mice. In experiment 1, animals treated with 7-NI (25, 50 and 100 mg/kg), morphine (40 mg/kg) or morphine (40 mg/kg) plus 7-NI (25, 50 or 100 mg/kg) were placed in an actimeter for 3 h. In experiment 2, animals treated with the same drugs and doses were conditioned following an unbiased procedure. 7-NI did not affect the spontaneous locomotor activity or hyperactivity induced by morphine. However, the moderate and high doses of …
Shell/core differences in mu- and delta-opioid receptor modulation of dopamine efflux in nucleus accumbens
2008
The mu- and delta-opioid receptors located at the terminal level in nucleus accumbens are involved in the opiate modulation of dopamine release in this brain area. However, recent studies suggest that the effects of opioid drugs on the core subregion of nucleus accumbens may completely differ from those observed in the shell. We used in vivo microdialysis to simultaneously apply selective mu- and delta-opioid receptor agonists and to measure extracellular levels of dopamine in three subregions of the accumbens, namely shell, core, and the transition zone between them. The regional analysis of these subregions of the accumbens demonstrated that basal levels of dopamine and its metabolites we…
The use of low doses of a sublingual fentanyl formulation for breakthrough pain in patients receiving low doses of opioids
2017
Objective: The aim of this study was to prospectively assess the efficacy and safety of low doses of sublingual fentanyl (SLF) for the treatment of breakthrough pain (BTP) in cancer patients in patients who were receiving low opioid doses for background analgesia. Methods: A sample of cancer patients presenting BTP episodes and receiving stable low doses of opioids for background pain (less than 60 mg of oral morphine equivalents) was selected to assess the efficacy and safety of low doses of SLF (67 μg). For each patient, data from four consecutive episodes were collected. For each episode, changes in pain intensity and adverse effects when pain got severe (T0), and 5, 10, and 15 min a…
Switching from morphine to methadone to improve analgesia and tolerability in cancer patients: A prospective study
2001
PURPOSE: To evaluate the clinical benefits of switching from morphine to oral methadone in patients who experience poor analgesia or adverse effects from morphine. PATIENTS AND METHODS: Fifty-two consecutive cancer patients receiving oral morphine but with uncontrolled pain and/or moderate to severe opioid adverse effects were switched to oral methadone administered every 8 hours using different dose ratios. Intensity of pain and adverse effects were assessed daily, and the symptom distress score (DS) was calculated before and after switching. RESULTS: Data were analyzed for 50 patients. Switching was considered effective in 80% of the patients; results were achieved in an average of 3.65 …
Amitriptyline in neuropathic cancer pain in patients on morphine therapy: A randomized placebo-controlled, double-blind crossover study
2002
Aims and Background Amitriptyline is the most common analgesic adjuvant used in cancer patients with neuropathic pain, even though no specific studies have demonstrated a benefit. A randomized placebo-controlled, double-blind crossover study was designed to evidence the effects of amitriptyline in patients with neuropathic cancer pain. Methods Sixteen advanced cancer patients with neuropathic pain on systemic morphine therapy, no longer receiving oncologic treatment, presenting moderate pain (about 4 or more, but less than 7, on a numerical scale of 0-10) in the last week, and given a stable morphine dose in the last 2 days were admitted to the study. During the first week of study, patient…
Does pain intensity predict a poor opioid response in cancer patients?
2011
Abstract Aim The aim of this study was to test the hypothesis that initial pain intensity is not a predictive factor of poor opioid response in advanced cancer patients, as suggested by a recent work. Methods A secondary analysis of one-hundred-sixty-seven patients referred for treatment of cancer-related pain was conducted. Pain intensity at admission was recorded and patients were divided in three categories of pain intensity: mild, moderate and severe. Patients were offered a treatment with opioid dose titration, according to department policy. Data regarding opioid doses and pain intensity were collected after dose titration was completed. Four levels of opioid response were considered:…