Injection Of Morphine In Rats Research Articles

Systemic Morphine but Not Local Administration Shows Preventive Anti-Inflammatory Effect in a Rat Model of Capsaicin-Induced Paw Edema

Peripheral opioids and analogues have demonstrated their efficacy in controlling inflammatory response and hyperalgesia. However, it is not yet clear whether the effect on edematogenic response is determined by the action at peripheral level or by systemic opioid receptors. Methods: In this study we investigated the effects of subcutaneous, intraplantar and intraperitoneal morphine injection in rats with acute capsaicin-induced hind paw inflammation. The experiment was conducted on 50 male Sprague-Dawley rats randomly divided into 5 groups of equal numerosity. Group 1 was control group; group 2 was treated with 5 mg/kg morphine by intraperitoneal injection; group 3 with 5 mg/kg morphine injected in the back subcutaneously; group 4 and group 5 were treated respectively with 0.05 mg/kg and 0.1 mg/kg morphine locally injected in the paw before induction of neurogenic edema. Neurogenic edema was induced by the administration of 50 mcg capsaicin in 50 mcl saline in the paw. The edema was measured using a calibrated plethysmometer.

The ventilatory depressant actions but not the antinociceptive effects of morphine are blunted in rats receiving intravenous infusion of L-cysteine ethyl ester

This study demonstrates that intravenous infusion of the cell-penetrant thiol ester, L-cysteine ethyl ester (L-CYSee), to adult male Sprague-Dawley rats elicited (a) minor alterations in frequency of breathing, expiratory time, tidal volume, minute ventilation, or expiratory drive but pronounced changes in inspiratory time, end-inspiratory and expiratory pauses, peak inspiratory and expiratory flows, EF50, relaxation time, apneic pause, inspiratory drive and non-eupneic breathing index, (b) minimal changes in arterial blood-gas (ABG) chemistry (pH, pCO2, pO2, SO2) and Alveolar-arterial (A-a) gradient (index of alveolar gas exchange), and (c) minimal changes in antinociception (tail-flick latency). Subsequent injection of morphine (10 mg/kg, IV) elicited markedly smaller effects on the above parameters, ABG chemistry, and A-a gradient in rats receiving L-CYSee, whereas morphine antinociception was not impaired. Infusions of L-cysteine or L-serine ethyl ester (oxygen rather than sulfur moiety), did not affect morphine actions on ABG chemistry or A-a gradient. L-CYSee (250 μmol/kg, IV) injection elicited dramatic changes in ventilatory parameters given 15 min after injection of morphine in rats receiving L-CYSee. Our findings suggest that (a) L-CYSee acts in neurons that drive ventilation, (b) L-CYSee reversal of the adverse actions of morphine on ventilation, ABG chemistry and A-a gradient may be via modulation of intracellular signaling pathways activated by morphine rather than by direct antagonism of opioid receptors since morphine antinociception was not diminished by L-CYSee, and (c) the thiol moiety of L-CYSee is vital to efficacy, (d) intracellular conversion of L-CYSee to an S-nitrosylated form may be part of its mechanism of action.

Mu-opioid receptors in septum mediate the development of behavioural sensitization to a single morphine exposure in male rats.

Behavioural sensitization (BS) is characterized by enhanced psychomotor responses to a dose of substance of abuse after prior repeated exposure. We previously reported that BS can be induced by a single injection of morphine in rats, whereas septal nuclei are specifically involved in the development phase of BS. Here, we demonstrated that intra-LS or intra-MS microinjections also incubated BS to a systemic morphine injection in a cross-sensitization fashion, whereas inactivation of either subdivision of septal nuclei (LS: lateral septum; MS: medial septum) can negate this ability of morphine. Then, non-selective (naloxone) and selective (μ-, δ- and κ-)opioid receptor antagonists were directly delivered into LS or MS, respectively, ahead of a morphine microinjection, whereas only μ-opioid receptors in both LS and MS play indispensable roles in mediating the BS development. Finally, there was a pronounced elevation in the levels of the monoamines (i.e. dopamine, homovanillic acid, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid) in the septum, 8h after a morphine injection detected with a HPLC-ECD method, suggesting that dopaminergi and serotoninergic systems are implicated in the BS formation. Our studies demonstrated that septal nuclei critically participate in the BS development. Essentially, μ- instead of δ- or κ-opioid receptors in LS and MS mediate sensitization to opiates.

Possible mechanism and potential application of anti-opioid effect of diazepam-binding inhibitor

AimsOur previous study has demonstrated that porcine diazepam-binding inhibitor (pDBI) and its active fragments, pDBI-16 and pDBI-19, have inhibition effect on morphine analgesia in mice. The present study aimed to investigate the underlying mechanism and potential application of this anti-opioid effect. Materials and methodsEffect of DBI on morphine analgesia was examined by the tail electric stimulation vocalization test. Complementary peptides and antiserum were used to further confirm the effect of DBI in morphine tolerance and dependence. Pharmacological and microinjection methods were used to investigate the underlying mechanism. Key findingsFirstly, pDBI administered either intracerebroventricularly or intravenously dose-dependently inhibited morphine analgesia, while blocking DBI-16 or DBI-19 by the complementary peptides for DBI-16 (CP-DBI-16) or DBI-19 (CP-DBI-19) potentiated it in mice. Secondly, explicit immunoexpression of DBI in the lateral habenular (LHb) was observed in naive rats, and intra-LHb injection of pDBI dose-dependently abolished analgesic effect produced by intra-periaqueductal gray (PAG) injection of morphine in rats. Thirdly, pretreatment with N-Methyl-d-Aspartate receptor (NMDAR) antagonist MK-801 or nitric oxide (NO) synthase inhibitor L-NAME abolished the inhibition effect of pDBI, pDBI-16 or pDBI-19 on morphine analgesia in mice. Finally, antiserum against DBI dose-dependently reversed analgesic tolerance induced by increasing doses of morphine twice daily for 13 days in mice, while CP-DBI-16 or CP-DBI-19 significantly inhibited naloxone-precipitated morphine withdrawal jumping in mice. SignificanceTaken together, our results demonstrated that NMDAR/NO signaling and LHb-PAG pathway are crucially involved in the anti-opioid effect of DBI, which could provide a potential biological target for opioid tolerance and dependence.

Effects of l-tetrahydropalmatine on conditioned place preference and expression of dopamine in the striatum of morphine dependent rats

Objective To observe effects of conditioned place preference(CPP) of morphine dependent rats, variation of dopamine neurotransmitter and its receptor 2 of the striatum in rats suffered from l-tetrahydropalmatine(l-THP). Methods The CPP model was established by morphine injection in rats with a increasing dose for 10 days, with the initial dose of 10 mg·kg-1 and the final dose of 100 mg·kg-1, 10 mg·kg-1 was increased each day, thus 100 mg·kg-1 was injected by day 10. Treatments with administration of l-THP(3.76, 1.88 and 0.94 mg/kg) were performed respectively for 6 days, and the effects of CPP for psychological dependence in these rats were observed. Striatum samples were taken out and their variable contents of dopamine neurotransmitter and its receptor 2 in striatum were detected by high performance liquid chromatography and immunohistochemisty, respectively. Results Compared with the NS treatment group, the time of animals treated with l-THP(3.76 and 1.88 mg/kg) staying in drug-paired compartment were reduced(354±58, 373±79) (P<0.01); the raised of variation contents of dopamine neurotransmitter were reduced in striatum from those rats(5.49±1.95, 6.11±1.05), while the expression level of dopamine receptor 2 was increased(0.08±0.02, 0.07±0.03)(P<0.01 or P<0.05). Conclusion Reversing dopamine neurotransmitter and its receptor 2 in striatum of morphine dependent rats may be one of the possible mechanisms that l-THP effectively inhibit the effects of morphine CPP. Key words: l-tetrahydropalmatine; Morphine; Psychological dependence; Dopamine system

Septal nuclei critically mediate the development of behavioral sensitization to a single morphine injection in rats

Behavioral sensitization to a single morphine injection is a unique model to study the neuroanatomical substrates of long-lasting behavioral plasticity associated with opioid reward and abuse. Earlier observations have demonstrated that septal nuclei are critically involved in the processes of reward, learning and memory. In the present study, we investigated the effects of septal nuclei lesions on behavioral sensitization to a single morphine injection, morphine induced conditioned place preference and antinociception in rats. Behavioral sensitization was established by a single injection of 3–30mg/kg morphine in rats. Bilateral electrical lesions of septal nuclei were carried out 7days before morphine pretreatment. Acute morphine injection induced hyperactivity in the non-surgery control, sham surgery and septal nuclei-lesioned rats. Seven days later, the challenge injection with 3mg/kg morphine induced significant behavioral sensitization in rats with no surgery and sham surgery, but failed to induce behavioral sensitization in septal nuclei-lesioned rats. When the septal nuclei ablation was carried out after acute morphine pretreatment, the expression of behavioral sensitization was unaffected and not different among rats. In addition, septal nuclei lesions did not impact the rewarding and antinociceptive effects of 10mg/kg morphine when the rats were tested in a conditioned place preference test and tail-flick test, respectively. Collectively, these results suggest that septal nuclei may be selectively involved in the initiation of behavioral sensitization to morphine, which is separable from the effects of morphine for exerting its rewarding and antinociceptive effects.

A Single Dose of Intrathecal Morphine in Rats Induces Long-Lasting Hyperalgesia: The Protective Effect of Prior Administration of Ketamine

An active pronociceptive process involving N-methyl-D-aspartate (NMDA) receptor activation is initiated by opioid administration, leading to opioid-induced pain sensitivity. Experimental observations in rats have reported reduction of baseline nociceptive threshold after prolonged spinal opioid administration. In this study we sought to determine whether a single dose of intrathecal morphine can induce hyperalgesia in uninjured rats and to assess the effects of pretreatment with the NMDA-antagonist ketamine on nociceptive thresholds. Sensitivity to nociceptive stimuli (paw pressure test) was assessed for several days after an acute intrathecal injection of morphine (5 microg and 10 microg) in male Sprague-Dawley rats. The effects of subcutaneously administered NMDA-receptor antagonist ketamine (10 mg/kg) before intrathecally administered morphine were also evaluated. A single intrathecal injection of morphine led to a biphasic effect on nociception; early analgesia associated with an increase in the nociceptive threshold lasting 3-5 h was followed by delayed hyperalgesia associated with a decrease in the nociceptive threshold lasting 1-2 days. Subcutaneous ketamine did not significantly modify the early analgesic component but almost completely prevented the delayed decrease in nociceptive threshold after intrathecal administration of morphine. A single intrathecal injection of morphine in rats produces a delayed and sustained hyperalgesia linked to the development of opioid-induced pain sensitivity.

Does chronic nociceptive stimulation alter the development of morphine tolerance?

Conflicting results exist concerning the issues of whether chronic nociceptive stimulation (a) increases or decreases the effectiveness of morphine analgesia, and (b) facilitates or inhibits the development of narcotic tolerance. We carried out a series of experiments with appropriate controls in order to examine these two issues and their possible relationship. In experiment 1, rats received complete Freund's adjuvant (CFA), a chronic nociceptor, injected into a single hind paw or anesthesia without injection, together with morphine or placebo pellets in a 2 × 2 study design. The data indicate that the presence of the chronic nociceptive stimulus significantly facilitated the development of tolerance to morphine analgesia as measured using tail-flick latency (TFL) testing. Experiment 2 was designed to compare the analgetic effectiveness of an acute injection of morphine in rats experiencing chronic nociceptive stimulation and in controls. CFA was injected in the right hindpaw, and nine days later TFLs were tested after morphine doses of 1 and 2 mg/kg s.c. The data obtained showed that chronic nociceptive stimulation significantly reduced the effectiveness of morphine at the 1 mg/kg dose. However, baseline TFLs appeared to be shorter in rats treated with CFA, suggesting that the decrease in morphine effectiveness could be due to a general increase in pain sensitivity. Therefore, a third experiment was performed, using a less intense thermal stimulus to prolong baseline TFLs and accentuate any potential differences. Sixteen rats either received CFA or served as controls. TFLs were then measured at baseline and one hour after a 0.5 mg/kg dose of morphine. TFLs were significantly shorter in CFA injected animals at both times, suggesting that hyperalgesia had developed and that the observed decrease in morphine effectiveness could be due to an increase in pain sensitivity. We suggest that the primary effect is a facilitation of pain responsiveness in animals exposed to chronic nociceptors, and that experimental variables can lead to an apparent increase or decrease in the rate of development of tolerance to morphine. These results and their relation to previous findings are discussed.

Spinal 5-HT or NA uptake inhibition potentiates supraspinal morphine antinociception in rats.

Spinal injection of the specific uptake inhibitor of 5-hydroxytryptamine (5-HT), citalopram, or of noradrenaline (NA), desipramine, potentiated the antinociception following intracerebroventricular injection of morphine in rats tested on the hot plate. Combined spinal injection of citalopram and desipramine caused a synergistic potentiation. The unselective and less potent inhibitor of both 5-HT and NA uptake, amitriptyline, did not cause potentiation. The results support the suggested involvement of both 5-HT and NA pathways in supraspinal morphine antinociception.

Alleviation of narcotic withdrawal syndrome by conditional stimuli.

We systematically paired auditory, olfactory, and social stimuli with each injection of morphine in rats. We found that, when morphine was kept constant at a low dose, the external stimuli acquired the property of a conditional stimulus (CS) to cause hyperthermia which was antagonized by naloxone. In rats in which morphine doses were regularly increased to cause morphine dependence, the CS presented during withdrawal, caused reduction in withdrawal signs (wet shakes, hypothermia, aggression) and produced hyperglycemia as well as elevation of striatal homovanillic acid. CS-induced alleviation of withdrawal hypothermia was blocked by mecamylamine, phenoxybenzamine, haloperidol, benztropine or naloxone but not by cyproheptadine or propranolol.