Effects of Co-Administration of Intrathecal Nociceptin/Orphanin FQ and Opioid Antagonists on Formalin-Induced Pain in Rats

PURPOSE: Nociceptin/orphanin FQ (N/OFQ) as an endogeneous hexadecapeptide is known to exert antinociceptive effects spinally. The aims of this study were to demonstrate the antinociceptive effects of i.t. N/OFQ and to investigate the possible interaction between N/OFQ and endogenous opioid systems using selective opioid receptor antagonists in rat formalin tests. MATERIALS AND METHODS: I.t. N/OFQ was injected in different doses (1-10 nmol) via a lumbar catheter prior to a 50 microL injection of 5% formalin into the right hindpaw of rats. Flinching responses were measured from 0-10 min (phase I, an initial acute state) and 11-60 min (phase II, a prolonged tonic state). To observe which opioid receptors are involved in the anti-nociceptive effect of i.t. N/OFQ in the rat-formalin tests, naltrindole (5-20 nmol), beta-funaltrexamine (1-10 nmol), and norbinaltorphimine (10 nmol), selective delta-, micro- and kappa-opioid receptor antagonists, respectively, were administered intrathecally 5 min after i.t. N/OFQ. RESULTS: I.t. N/OFQ attenuated the formalin-induced flinching responses in a dose-dependent manner in both phases I and II. I.t. administration of naltrindole and beta-funaltrexamine dose-dependently reversed the N/OFQ-induced attenuation of flinching responses in both phases; however, norbinaltorphimine did not. CONCLUSION: I.t. N/OFQ exerted an antinociceptive effect in both phases of the rat-formalin test through the nociceptin opioid peptide receptor. In addition, the results suggested that delta- and micro-opioid receptors, but not kappa-opioid receptors, are involved in the antinociceptive effects of N/OFQ in the spinal cord of rats.

Assessment of differential doses of buprenorphine for long term pharmacotherapy among opiate dependent subjects.

The aim of the present study was to evaluate, two different doses of sublingual buprenorphine (2 mg and 4 mg) among patients on maintenance treatment and to assess the relationship of steady state plasma level with craving. Twenty three male opioid dependent (ICD-10 DCR) subjects, were assigned to double blind randomized controlled trial of 2 and 4 mg/day doses of buprenorphine in an inpatient setting. They were evaluated thrice (2nd, 7th and 14th day) in 2 weeks for withdrawal symptoms (acute and protracted), sedation, euphoria, craving, side effects, global rating of well being and for measurement of plasma levels of buprenorphine. The data showed that there were no significant difference in scores of euphoria and sedation, protracted withdrawal symptoms and side effects, craving and overall well being and plasma level of buprenorphine among the subjects. However, both the groups had significant difference in score on almost all the measurements on final observation in comparison to initial observation. Both 2 mg/day and 4 mg/day dose of buprenorphine were effective in long term pharmacotherapy of opioid dependence without significant difference as compared by different measures used in the study.

Additive Antinociception between Intrathecal Sildenafil and Morphine in the Rat Formalin Test

The possible characteristics of spinal interaction between sildenafil (phosphodiesterase 5 inhibitor) and morphine on formalin-induced nociception in rats was examined. Then the role of the opioid receptor in the effect of sildenafil was further investigated. Catheters were inserted into the intrathecal space of male Sprague-Dawley rats. For induction of pain, 50 microliter of 5% formalin solution was applied to the hindpaw. Isobolographic analysis was used for the evaluation of drug interaction between sildenafil and morphine. Furthermore, naloxone was intrathecally given to verify the involvement of the opioid receptor in the antinociception of sildenafil. Both sildenafil and morphine produced an antinociceptive effect during phase 1 and phase 2 in the formalin test. The isobolographic analysis revealed an additive interaction after intrathecal delivery of the sildenafil-morphine mixture in both phases. Intrathecal naloxone reversed the antinociception of sildenafil in both phases. These results suggest that sildenafil, morphine, and the mixture of the two drugs are effective against acute pain and facilitated pain state at the spinal level. Thus, the spinal combination of sildenafil with morphine may be useful in the management of the same state. Furthermore, the opioid receptor is contributable to the antinocieptive mechanism of sildenafil at the spinal level.

Successful treatment of intrathecal morphine overdose.

A 47-year-old woman was diagnosed with secondary progressive multiple sclerosis, and was treated with intrathecal morphine for chronic pain via a slow-release subcutaneous pump. She accidentally received a 35-ml (510 mg) bolus injection of morphine by this route, which led to status epilepticus. She was treated with continuous intravenous naloxone infusion, and with medication to control hypertension and stop the seizure activity. The outcome was excellent, and the patient returned to her neurological baseline. This report describes the complications and the successful treatment of intrathecal morphine overdose. In order to prevent these serious errors, it is vital that only care providers who are proficient with these devices perform the refilling procedure.

Enkephalinergic involvement in substantia nigra in the modulation of hypothalamically-induced predatory attack behavior.

The present study was carried out in five cats which did not attack the rats spontaneously. Predatory attack on an anaesthetized rat was elicited by electrical stimulation of lateral hypothalamus at a mean current strength of 650 microA. The attack was accompanied by minimal affective display and culminated in neck biting. Microinfusions of DAME (delta-alanine methionine enkephaline) in 500 ng dose in substantia nigra facilitated the predatory attack and there was a significant reduction in the threshold current strength for affective display as well as somatomotor components. Microinfusions of naloxone, an opioid antagonist in 1.0 microg dose when DAME effect was at its peak reversed the facilitatory effects and the threshold returned to the control levels within 10 minutes of naloxone infusion at the same locus. Microinfusions of naloxone alone in similar dosage completely blocked the predatory attack response as indicated by an increase in the threshold current strength for somatomotor as well as affective display components. The somatomotor were completely inhibited and could not be elicited even when the current strength was increased to 1000 microA. Control injections of saline in similar volumes (0.5 microl) failed to produce any response Microinfusions of naloxone in lower dose (250 ng) failed to produce any blocking effect. These findings indicate that hypothalamically elicited predatory attack is facilitated by enkephalinergic mechanisms operating at the midbrain level.

Naltrexona en el tratamiento de la dependencia al alcohol: revisión bibliográfica crítica / Naltrexone in the treatment of alcohol dependence: bibliographic critical review

Se revisa la bibliografía médica existente respecto a las posibles interacciones entre el consumo de alcohol y opioides, los posibles mecanismos de interacción del alcohol con los receptores del sistema opioide, las hipótesis explicativas de como dicho sistema promueve la ingesta de alcohol y los resultados obtenidos en animales de experimentación con el uso de fármacos antagonistas opioides. Se analizan los tres estudios clínicos más importantes que utilizan naltrexona en el tratamiento de la dependencia a alcohol. Dos de ellos sugieren que el fármaco pareciera disminuir la tasa de recaída, en el otro estudio no se encuentran diferencias significativas entre el uso del fármaco y placebo. Se concluye que es necesario continuar y perfeccionar la investigación en este tema, para lo cual se debiera definir y uniformar conceptos tales como recaídas, efectividad de tratamiento e intentar objetivar la ingesta, sus montos, sin depender necesariamente de los autorreportes de los pacientes. Hechas estas precisiones los resultados de la investigación permitirían aclarar la real efectividad de éste y otros fármacos

Studies on the effect of intratesticular administration of opioid peptides, naloxone or N-acetyl beta-endorphin antiserum on some testicular parameters in rats.

Opioid peptides have been localized in a variety of peripheral tissues like placenta, thyroid, pancreas, gastrointestinal tract, in the reproductive tract of male and female and in the testes of rats. Immunoassayable material was detected in extracts of gonads, reproductive tract and accessory reproductive organs. Studies with naloxone have suggested that beta-endorphin may have an important role in steroidogenesis and may have a role in regulating transport of luminal material. In our studies met-enkephalin, beta-endorphin, naloxone or N-acetyl beta-endorphin antiserum were microinjected intra testicularly once on alternate days for one week and autopsied 24 h after the last injection. Intratesticular administration of 25, 50 and 100 micrograms doses of naloxone induced significant decrease in in vitro secretion of testosterone per se, which was significantly greater with 50 micrograms dose than with those of the other two doses. A 25 micrograms dose had no effect on hyaluronidase or acid phosphatase activity while 50 micrograms dose significantly decreased the enzyme activity. One hundred micrograms dose also significantly decreased hyaluronidase activity. Intratesticular injection of 10 micrograms met-enkephalin or 1 microgram beta-endorphin significantly decreased hyaluronidase activity whereas 20 microliters N-acetyl beta-endorphin antiserum increased the specific activity of hyaluronidase. There was no change in the weight of the testes on treatment with the above agents.

Role of midbrain ventro-lateral tegmental area (VTA) enkephalinergic mechanisms in the facilitation of hypothalamically-induced predatory attack behaviour.

Bipolar concentric electrodes were implanted in five cats in extreme lateral regions of hypothalamus. These sites were electrically stimulated using biphasic square wave pulses at a current strength ranging from 300-800 microA to evoke predatory attack on an anaesthetized but live rat. At lower current strength (300 microA) only alertness with pupillary dilatation was produced. Gradual increase in the current strength led to the recruitment of somatic and affective components and a predatory attack was exhibited at a mean current strength of 700 microA. A scoring system allowed the construction of stimulus response curves, which remained fairly constant when repeated over a period of 3-4 weeks. Bilateral microinjections of delta-alanine methoinine enkephaline (DAME) (500 ng in 0.5 microliter saline) in ventrolateral tegmental area (VTA) elevated the mean threshold current strength for affective components while somatomotor components were totally inhibited. The blocking effect of DAME persisted for 1 hour. Microinjections of naloxone (1 microgram) in similar volumes facilitated the response as indicated by a reduction in threshold current strength for somatomotor and affective components. Microinjections of naloxone (1 microgram) in similar volumes facilitated the response as indicated by a reduction in threshold current strength for somatomotor and affective components. Microinjections of naloxone (1 microgram) also reversed the blocking effect of DAME and the thresholds returned to the control level within 10 min while microinjection of normal saline as control had no effect. The excitatory effects of naloxone and inhibitory effects of DAME were statistically significant at P < 0.01 and P < 0.05 respectively with Wilcoxon's signed rank test. The present study indicates that enkephalinergic as well as opioidergic mechanisms operating at the midbrain (VTA) level are involved in the inhibition of predatory attack as elicited from lateral hypothalamus.

Effect of aspartate and glutamate on nociception, catalepsy and core temperature in rats.

Effects of excitatory aminoacids (EAAs) aspartate (ASP) and glutamate (GLU) in a low (50 ng, i.c.) and high dose (20 micrograms, i.c.), were studied on nociception, catalepsy and rectal temperature in albino rats. Both ASP and GLU altered the tail flick reaction time to thermal stimulation in a dose dependent manner, increasing it with low doses and reduced with high doses. Naloxone (10 micrograms, ic) antagonized the anti-nociceptive effect of EAAs while ketamine (10 micrograms, ic)-a NMDA receptor antagonist antagonized the hyperalgesic effect. These EAAs also antagonized catalepsy induced by haloperidol, chlorpromazine, trifluoperazine and morphine. Both ASP and GLU produced a hyperthermic response in all animals, including those in which hypothermia was induced by reserpine. These EAAs produced a comparable central modulatory effects on nociception, catalepsy and core temperature.

Efecto de los antagonistas opiaceos en el choque / Effects of the narcotic antagonists in the shock

I. Administración de naloxona en choque hipovolémico, provocado en una rata. En las distintas variedades de choque se ha documentado experimental y clinicamente la participación de opiáceos endógenos contribuyendo a la hipotensión y a la parálisis de la regulación de la presión arteriual, la cual explica la utilidad de la naloxona en el tratamineto clínico de algunas formas de choque. Aun cuando se ha documentado la efectividad de estos compuestos en variedades ebdotóxicas e hipovolémicas de choque, la utilidad de naloxona tiene inconvenientes relacionados con la capacidad de bloqueo del efecto analgésico de los opiáceos que resulta en hiperalgesía, lo cual ha estimulado a la búsqueda de otros antagonistas parciales que preserven el efecto analgésico de la morfina y el efecto antishock de la naloxona. En este trabajo se presenta evidencia experimental de los efectos de la naloxona en un modelo de shock hipovolémico en rata derpierta, modelo que permitira el estudio de otros compuestos que reúnan las características mencionadas .