Abdallah Salem

Role of endogenous adenosine in the expression of opiate withdrawal in rats

Samples of extracellular fluid from striatum and nucleus accumbens of anaesthetised rats undergoing opiate withdrawal were collected using microdialysis and then analysed for adenosine and its metabolites using high performance liquid chromatography (HPLC) and ultraviolet (UV) detection. Although the amount of adenosine present in the dialysate from either brain region was below the limit of detection by 90 min after probe placement, the metabolites could still be detected. Samples of dialysates collected from the nucleus accumbens contained significantly higher concentrations of hypoxanthine and inosine following naloxone challenge. The data are compatible with the hypothesis that endogenous adenosine might be involved in the expression of the opiate abstinence syndrome.

Model of methadone-induced hyperalgesia in rats and effect of memantine.

Methadone used for opioid dependence therapy is associated with increased pain sensitivity. This study aimed to investigate whether methadone administration lowers nociceptive threshold in adult male Sprague-Dawley (SD) rats, and if this threshold could be altered by the NMDA receptor antagonist memantine. Rats were implanted with osmotic pumps delivering 1mg/kg/day methadone (n=6), or saline placebo (n=6) (0.51 microl/h). A separate cohort of rats received either methadone 1mg/kg/day (n=8) or methadone 1mg/kg/day with 20mg/kg/day memantine (n=8). Nociception was measured by the Hargreaves paw withdrawal test. Baseline nociception was measured on day 0 prior to osmotic pump implantation and was measured daily for the following 21 days. Osmotic pumps were removed following nociceptive testing on day 14. Methadone only treated rats had a mean paw withdrawal latency significantly lower than the corresponding values for saline on days 8, 9, 10, 11, 12, 14, and 17 (P<0.05). At all other time points the mean paw withdrawal latency was not significantly different from saline (P>0.05). Paw withdrawal latency of rats treated with methadone co-administered with memantine did not differ significantly compared to methadone only (P>0.05). This demonstrates that methadone induces hyperalgesia in the SD rat yet this hyperalgesia resolves following discontinuation of methadone administration. Furthermore, memantine does not alter the development of methadone-induced hyperalgesia.

POTENTIATION OF 3,4-METHYLENEDIOXYMETHAMPHETAMINE-INDUCED 5-HT RELEASE IN THE RAT SUBSTANTIA NIGRA BY CLORGYLINE, A MONOAMINE OXIDASE A INHIBITOR

1 It is well established that the commonly used recreational drugs 3,4‐methylenedioxymethamphetamine (MDMA, ‘ecstasy’) and para‐methoxyamphetamine (PMA) facilitate the release and prevent the reuptake of 5‐hydroxytryptamine (5‐HT, serotonin). Although these drugs have similar potencies for their abilities to increase the release and inhibit the re‐uptake of 5‐HT, PMA has greater potency as an inhibitor of monoamine oxidase (MAO)‐A. 2 The present study compared the abilities of PMA and MDMA to increase extracellular 5‐HT concentrations in animals with functional MAO‐A and when MAO‐A activity was inhibited by clorgyline. 3 Samples of extracellular fluid from rat substantia nigra were collected using microdialysis and then analysed for 5‐HT and 5‐hydroxyindol acetic acid (5‐HIAA) by high‐performance liquid chromatography coupled with electrochemical detection. The 5‐HT‐mediated effects on body temperature and behaviour were also recorded. Rats were pretreated with saline or 10 mg/kg, i.p., clorgyline and, 24 h later, injected with 10 mg/kg MDMA, PMA or saline. 4 Both MDMA and PMA produced significant increases in extracellular 5‐HT concentrations (482 ± 83 and 726 ± 287%, respectively; P < 0.05). Rats treated with PMA and MDMA displayed significantly increased 5‐HT‐related behavours (P < 0.05). Furthermore, only MDMA was capable of producing additional significant increases in 5‐HT concentrations (1033 ± 131%; P < 0.01) when coadministered with clorgyline. 5 The results of the present study suggest that PMA and MDMA are similar in their abilities to increase extracellular 5‐HT levels in animals with functional MAO‐A activity. However, coadministration of these substituted amphetamines with an MAO‐A inhibitor causes significant potentiation in the ability to increase extracellular levels of 5‐HT for MDMA, but not PMA.

Increased effects of 3,4-methylenedioxymethamphetamine (ecstasy) in a rat model of depression

3,4‐Methylenedioxymethamphetamine (MDMA, ecstasy) is associated with increases in core body temperature (TC) and depressive mood states in users. Flinders Sensitive Line (FSL) rats represent a rat model of depression originally bred from Sprague‐Dawley (SD) rats. They are more sensitive to both muscarinic and serotonergic agonists and have altered thermoregulatory responses to various drugs. To examine the link between MDMA and depression, eight FSL and eight SD rats were administered saline and 5 and 7.5 mg/kg MDMA. Immediately following administration, rats were confined to an area with an ambient temperature (TA) of 30 ± 1°C for 30 minutes before being allowed access to a thermal gradient for four hours. The brains were removed one week after final dose of MDMA and concentrations of serotonin and dopamine were measured. Treatment with MDMA at both doses led to a higher TC in the FSL rats than the SD rats at high TA (P < 0.01). Fatalities due to hyperthermia occurred in the FSL rats after both doses, whereas all but one of the SD rats recovered well. Heart rate was also much higher after MDMA in the FSL rats throughout the experiments. The FSL rats showed significant decreases in all transmitters measured (P < 0.05). These differences between strains were not accounted for by altered blood or brain concentrations of MDMA. The results indicate that the FSL rats may be more susceptible to developing MDMA‐induced hyperthermia and possible damage to the brain. These findings may be of importance to human users of MDMA who also have depression.

Portable optical fiber probe for in vivo brain temperature measurements

This work reports on the development of an optical fiber based probe for in vivo measurements of brain temperature. By utilizing a thin layer of rare-earth doped tellurite glass on the tip of a conventional silica optical fiber a robust probe, suitable for long-term in vivo measurements of temperature can be fabricated. This probe can be interrogated using a portable optical measurement setup, allowing for measurements to be performed outside of standard optical laboratories.

Absorption of morphine from a slow-release emulsion used to induce morphine dependence in rats.

This study was performed to measure absorption of morphine from the injection site following treatment of rats with slow-release emulsions formulated with morphine hydrochloride and morphine base. Samples of emulsion were collected from the injection site of halothane anesthetized animals at 24 and 48 h following emulsion treatment and concentrations of morphine remaining in the emulsion were analyzed using high-performance liquid chromatography (HPLC). In another group of morphine-treated rats, at times equivalent to collecting samples of emulsion, the intensity of naloxone-precipitated withdrawal behaviors was monitored. Both morphine base- and hydrochloride-containing emulsions induced a high degree of physical dependence in animals treated over 48 h. Release of morphine from emulsions containing morphine base was slower than that from the hydrochloride formulations. In the 24-h morphine base-treated animals, approximately 45% was absorbed from the injection site as opposed to 99% in the 24-h morphine hydrochloride-treated animals. These results suggest that morphine base containing emulsions provide a more sustained exposure to the opioid.

A study on seasonal variation in the development of morphine dependence in rats.

The possibility that naloxone-precipitated opiate withdrawal behaviors varied qualitatively over the course of the year was investigated. The experiments were carried out at monthly intervals over a 2-year period using rats treated with a morphine-containing slow-release emulsion. The results obtained from these experiments were equivocal, neither providing support for seasonal variance in the expression of the opiate abstinence syndrome, nor showing a complete lack of time-related differences. Although some behavioral signs of opiate abstinence showed seasonally related alterations in frequency over one of the years, this was not consistent from one year to another. It was therefore concluded that no significant relationship between the severity of the abstinence syndrome and the time of the year in which the experiment carried out could be demonstrated.

A portable optical fiber probe for in vivo brain temperature measurements

We report on the development of an optical fiber based probe for in vivo measurements of brain temperature. By using a thin layer of rare-earth doped tellurite glass on the tip of a silica optical fiber a durable probe, suitable for long-term in vivo measurements of temperature can be fabricated. The probe can be interrogated using a portable optical measurement setup, allowing for measurements to be performed outside of standard optical laboratories as no alignment of components is required. This setup is deployed to a medical research laboratory to show preliminary results on the use of these optical fibers for in vivo pre-clinical measurements of brain temperature.

3,4-Methylenedioxymethamphetamine (MDMA) Induced Hyperthermia- The Role of Pro-Inflammatory Cytokines

Project Background The main MDMA-induced adverse effect is disruption of normal thermoregulation leading to life threatening hyperthermia which is exacerbated by high ambient temperature and linked to chronic neurotoxicity. Although the focus of the majority of research on MDMAinduced loss of thermoregulation has been on brain serotonergic and dopaminergic systems, results obtained from our recent studies suggest an association between microglial activation and MDMA-induced hyperthermia. We have demonstrated that pretreatment with minocycline, an antibiotic with glial attenuating properties, can significantly reduce the severity of MDMA-induced hyperthermia in rats. We have also demonstrated that minocycline’s ability to inhibit MDMA induced hyperthermia is time-dependent process and you need up to three days pre-treatment with minocycline to achieve maximum effects.

Attenuating Glial Activation with Minocycline Reduces the Hyperthermic Response to 3, 4-Methylenedioxymethamphetamine (MDMA) In the Rat

Hyperthermia is a key clinical outcome from recreational use of MDMA and is the leading cause of MDMA related hospital admissions as well as being linked to enhanced neurotoxicity [1, 2]. Animal models of ischemia which also display hyperthermia have shown an inflammatory process mediated by microglia and the release of the proinflammatory cytokine interleukin 1(IL-1 ) play a role in hyperthermicreactions [3]. Previous studies showed that microglia is prominently activated and IL-1 levels increased following MDMA administration [4], lending support to the hypothesis microglia play a role in MDMA induced hyperthermia. Minocycline is a tetracycline antibiotic with powerful anti-inflammatory properties, thought to be a result of its ability to attenuate glial activation [5]. This study examined whether preventing microglial activation through the administration of minocycline could limit or prevent the hyperthermia induced by MDMA.