Repeated and long-term administration of opioids is definitely often accompanied from the initiation of opioid-induced analgesic tolerance and hyperalgesia in chronic pain patients. neuropathic pain conditions remains elusive. MIRA-1 We here observed the effect of intrathecal infusion of rapamycin a specific mTORC1 inhibitor on morphine-induced tolerance MIRA-1 and hyperalgesia inside a neuropathic pain model in rats induced from the fifth lumbar spinal nerve ligation (SNL). Continuous intrathecal infusion of morphine for one week starting on day time 8 post-SNL led to morphine tolerance shown by morphine-induced reduction in maximal possible analgesic effect (MPAE) to tail warmth stimuli and ipsilateral paw withdrawal threshold (PWT) to mechanical stimuli in SNL rats. Such reduction was attenuated by co-infusion of rapamycin. Co-infusion of rapamycin also clogged morphine tolerance shown by attenuation of morphine-induced reduction in MPAE in sham rats and Rabbit Polyclonal to Bcl-6. morphine-induced hyperalgesia shown by the reverse of morphine-induced MIRA-1 reduction in PWT on both sides of sham rats and on the contralateral part of SNL rats. The results suggest that mTORC1 inhibitors could serve as encouraging medications for use as adjuvants with opioids in medical neuropathic pain management. on a 12 h light/12 h dark cycle. Animals were exposed to habituation for 2 days prior to use. Behavioral tests were completed in a blinded manner. Every effort was made to minimize the amount of animals used and their suffering. Surgical procedures and drug infusion Rats underwent a revised unilateral L5 spinal nerve ligation (SNL) MIRA-1 as previously explained (12 13 14 In brief: after the animals were anesthetized by isoflurane the remaining L6 transverse process was eliminated to expose the L4 and L5 spinal nerves. After isolation of the remaining L5 spinal nerve a tight ligature was made with 3-0 silk and the nerve was transected distal to this ligature. In sham-operated rats the remaining L5 spinal nerve was isolated but remained undamaged with no ligature or transection. Rats underwent intrathecal catheter implantation for drug delivery in the same manner as explained previously (15). In brief: while under isoflurane-induced anesthesia a laminectomy of the L5 vertebra was performed and the dura was slice. At the level of the L4/5 spinal cord a polyethylene-10 catheter was put into the subarachnoid space. Following catheter implantation animals underwent 7 days of recovery prior to SNL or sham surgery. A mini-osmotic pump (Alzet Cupertino CA USA) connected to the intrathecal catheter was utilized for continuous infusion of drug at a rate of 1 1 μl/h. Rats were divided into five organizations for drug delivery: saline plus vehicle (10% DMSO in saline) saline plus rapamycin (a selective inhibitor of mTORC1 1 /h Sigma) morphine (15 μg/h West-Ward Eatontown NJ) plus rapamycin morphine plus ascomycin (1 μg /h Sigma) or morphine plus vehicle. Beginning 8 days after SNL or Sham surgery continuous intrathecal infusion was carried out for 24 hours each day for 7 days from day time 8 to day time 14. Given that ascomycin (an analogue of rapamycin) does not inhibit mTORC1 activity (16 17 we used ascomycin to confirm the MIRA-1 specificity of the action of rapamycin on mTORC1. Rats with neurological deficits were excluded from the study. The location of the intrathecal catheter was confirmed after completion of the experiments. Behavioral screening Tail flick screening was carried out as explained previously (9). In brief tail flick latency to noxious warmth was measured on day time 7 (the day before continuous intrathecal morphine injection) and days 8 10 12 and 14 (during continuous morphine injection) using an Analgesic Meter (Model 33B Tail Flick Analgesia Meter IITC Existence Science Woodland Hills CA USA). The cut-off time was 10 s. Three tests were conducted for each rat with an interval of 1 1 min. Morphine’s maximal possible analgesic effect (MPAE) was identified using the following equation: MPAE = [(posttreatment ? pretreatment)/(10 – pretreatment)] × 100%. Mechanical paw withdrawal thresholds (PWTs) were identified MIRA-1 using the up-down method following a previously explained process (13 14 Mechanical paw withdrawal thresholds were measured 1 day before SNL and on days 7 8 10 12 and 14 during continuous morphine injection. In brief each rat was placed in an individual Plexiglas chamber on an elevated mesh display. Von Frey hairs in log increments of.