Evaluation the effects of dextromethorphan and midazolam on morphine induced tolerance and dependence in mice

Repeated central administration of selegiline attenuated morphine physical dependence in rat

BACKGROUND

Long-term exposure to opiates induces physical dependence; however, the neurobiological mechanisms of this phenomenon are not completely clear. The purpose of this study was to evaluate the effects of systemic and intracerebroventricular (icv) administration of selegiline (a selective inhibitor of monoamine oxidase B) on the morphine withdrawal syndrome in rats.

METHODS

To this aim, adult male Sprague Dawley rats were selected randomly, and then growing doses of morphine were administered subcutaneously at an interval of 12 h for nine days with the intention of inducing dependency. Nine days after, only the morning dose of morphine was administered, followed by systemic or central injection of saline or selegiline. Later, naloxone was injected after 30 min and withdrawal signs recorded for a period of 60 min.

RESULTS

Results showed failure of systemic administration of selegiline in changing the withdrawal symptoms; nevertheless, icv injection attenuated the withdrawal signs significantly.

CONCLUSION

In conclusion we found that central administration of selegiline attenuated morphine withdrawal symptoms.

A new pharmacological role for donepezil: attenuation of morphine-induced tolerance and apoptosis in rat central nervous system

BACKGROUND

Tolerance to the analgesic effect of opioids is a pharmacological phenomenon that occurs after their prolonged administration. It has been shown that morphine-induced tolerance is associated with apoptosis in the central nervous system and neuroprotective agents which prevented apoptosis signaling could attenuate tolerance to the analgesic effects. On the other hand donepezil, an acetylcholinesterase inhibitor, has been reported to have neuroprotective effects. Therefore in this study, the effect of systemic administration of donepezil on morphine-induced tolerance and apoptosis in the rat cerebral cortex and lumbar spinal cord was evaluated. Various groups of rats received morphine (ip) and different doses of donepezil (0, 0.5, 1, 1.5 mg/kg/day). Nociception was assessed using tail flick apparatus. Tail flick latency was recorded when the rat shook its tail. For apoptosis assay other groups of rats received the above treatment and apoptosis was evaluated by in situ terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) method.

RESULTS

The results showed that administration of donepezil (0.5, 1, 1.5 mg/kg, ip) delayed the morphine tolerance for 9, 12 and 17 days, respectively. Furthermore pretreatment injection of donepezil attenuated the number of apoptotic cells in the cerebral cortex and lumbar spinal cord compared to the control group.

CONCLUSION

In conclusion, we found that systemic administration of donepezil attenuated morphine-induced tolerance and apoptosis in the rat cerebral cortex and lumbar spinal cord.

Midazolam in rabbits terminates dysrhythmias caused by intracerebroventricular ropivacaine

The current study was designed to investigate the mechanisms by which ropivacaine may act within the central nervous system (CNS) to produce cardiotoxicity. Eighty New Zealand rabbits were divided into four groups randomly. In Group 1, 20 rabbits received intracerebroventricular (icv) saline, and then received icv ropivacaine 30 min later. In Group 2, 20 rabbits received icv ropivacaine. Whenever dysrhythmias continued for more than 5 min, 0.1 ml saline was administered into the left cerebral ventricle. Ten minutes later, 0.1 ml midazolam was given into the left lateral ventricle. In Group 3, 20 rabbits received icv ropivacaine, and once the dysrhythmias developed, the inspired isoflurane concentration was increased from 0.75% to 1.50%. In Group 4, 20 animals received an intravenous (iv) phenylephrine infusion until dysrhythmias occurred. In Group 1, the rabbits did not develop dysrhythmias in response to icv saline, whereas dysrhythmias did develop in these animals after icv ropivacaine. In Group 2, icv saline had no effect on the dysrhythmias; however, icv midazolam terminated cardiac dysrhythmias. In Group 3, an increase in the concentration of the inspired isoflurane had no effect on dysrhythmias. In Group 4, icv midazolam had no effect on dysrhythmias in response to iv phenylephrine. Ropivacaine administered directly into the CNS is capable of producing cardiac dysrhythmias; midazolam terminated dysrhythmias presumably by potentiation of γ-aminobutyric acid (GABA) receptor activity. Our results suggest that ropivacaine produces some of its cardiotoxicity not only by the direct cardiotoxicity of the drug, but also by the CNS effects of ropivacaine.

Effects of a Rhodiola rosea L. extract on acquisition and expression of morphine tolerance and dependence in mice

This study investigated the effect of Rhodiola rosea L. extract on acquisition and expression of morphine tolerance and dependence in mice. Therefore animals were injected with repeated administration of morphine (10 mg/kg, subcutaneous) twice daily for five or six days, in order to make them tolerant or dependent. Rhodiola rosea L. extract (0, 10, 15 and 20 mg/kg) was administered by the intragastric route 60 min prior to each morphine injection (for acquisition) or prior the last injection of morphine or naloxone on test day (for tolerance or dependence expression, respectively). Morphine tolerance was evaluated by testing its analgesic effect in the tail flick test at the 1st and 5th days. Morphine dependence was evaluated by counting the number of withdrawal signs (jumping, rearing, forepaw tremor, teeth chatter) after naloxone injection (5 mg/kg; intraperitoneal) on the test day (day 6). Results showed that Rhodiola rosea L. extract significantly reduced the expression of morphine tolerance, while it was ineffective in modulating its acquisition. Conversely, Rhodiola rosea L. extract significantly and dose-dependently attenuated both development and expression of morphine dependence after chronic or acute administration. These data suggest that Rhodiola rosea L. may have human therapeutic potential for treatment of opioid addiction.

Endogenous opiates and behavior: 2008

This paper is the 31st consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2008 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Central administration of minocycline and riluzole prevents morphine-induced tolerance in rats

BACKGROUND

Long-term exposure to opiates induces tolerance to the analgesic effect. The neurobiological mechanism of this phenomenon is not completely clear. In this study, we evaluated the effects of central administration of minocycline (a tetracycline derivative) and riluzole (an antiglutamatergic drug) on morphine-induced tolerance in rats.

METHODS

Groups of rats received daily morphine (10 mg/kg, IP) in combination with saline (10 microL/rat, intracerebroventricular [ICV]) or 1% Tween 80 (10 microL/rat, ICV) or minocycline (60, 120, and 240 microg/10 microL per rat, ICV) or riluzole (20, 40, 80 microg/10 microL per rat, ICV). Nociception was assessed using hotplate apparatus (55 degrees C +/- 0.5 degrees C). Hotplate latency was recorded when the rat licked its hindpaw. Baseline latencies were determined once per day for each rat, then morphine (10 mg/kg) was injected. After 20 min, the above-mentioned drugs were administered and postdrug latency was measured 10 min after the injection of drugs or vehicles.

RESULTS

Results showed that ICV administration of minocycline and riluzole delayed morphine-induced tolerance. Morphine tolerance was complete after 8 days in the control groups but was complete in the groups treated with minocycline (120 microg/10 microL per rat) and riluzole (80 microg/10 microL per rat) on the 13th day. In addition, our results showed that minocycline and riluzole increased the total analgesic effect of morphine (area under the curve of the percentage of maximal possible effect values).

CONCLUSION

The effects of minocycline on nitric oxide and the glutamatergic system and the effect of riluzole on the glutamate system are potentially important mechanisms in delaying morphine-induced tolerance.

Development of morphine induced tolerance and withdrawal symptoms is attenuated by lamotrigine and magnesium sulfate in mice

The goal of this study was to evaluate the effects of lamotrigine and magnesium sulfate on morphine induced tolerance and withdrawal symptoms in mice. Different groups of mice were received morphine (30 mg kg(-1), s.c.) or morphine (30 mg kg(-1), s.c.)+lamotrigine (10, 20, 30 or 40 mg kg(-1), i.p.) or morphine (30 mg kg(-1), s.c.) + magnesium sulfate (20, 40 or 60 mg kg(-1), i.p.) or morphine (30 mg kg(-1), s.c.) + [lamotrigine (10 mg kg(-1), i.p.) + magnesium sulfate (20mg kg(-1), i.p.)] daily for 4 days. Tolerance was assessed using hot plate after administration of a test dose of morphine (9 mg kg(-1), i.p.) on fifth day. Withdrawal zsymptoms (Jumping and Rearing) were assessed by administration of naloxone (5 mg kg(-1), i.p.) 2 h after the last dose of morphine in fourth day. It was found that administration of lamotrigine or magnesium sulfate or their combination decreased the morphine induced tolerance and withdrawal symptoms. From these results it is concluded that lamotrigine and magnesium sulfate alone or in combination could prevent the development of morphine tolerance and withdrawal symptoms. Glutamate release inhibitory effect of lamotrigine and its possible mechanism and property of magnesium, blocking the N-Methyl-D-Aspartate (NMDA) receptor calcium channel, is probably its mechanism on preventing morphine induced tolerance and dependence.