Opioids represent effective drugs for the relief of pain yet chronic

Opioids represent effective drugs for the relief of pain yet chronic opioid use often leads to CH5132799 a state of increased sensitivity to pain that is exacerbated during withdrawal. systemic administration of the CRF1 receptor antagonist MPZP (20 mg/kg) alleviated withdrawal-induced mechanical hypersensitivity. In contrast several functional adrenergic system antagonists (clonidine prazosin propranolol) failed to alter mechanical hypersensitivity in this state. We then decided the effects of chronic MPZP or clonidine treatment on extended access heroin self-administration and found that MPZP but not clonidine attenuated escalation of heroin intake whereas both drugs alleviated chronic dependence-associated hyperalgesia. These findings suggest that an early potentiation of CH5132799 CRF signaling occurs following opioid exposure that begins to drive both opioid-induced hyperalgesia and eventually intake escalation. and were approved by the Institutional Animal Care and Use Committee of The Scripps Research Institute. Mechanical Sensitivity Testing This test was conducted as previously reported (Edwards et al. 2012 Up to eight rats were placed in individual plastic compartments (26 × 11 × 20 cm) with stainless steel mesh floors for 30 minutes until the rats’ grooming and exploratory behaviors ceased. To assess the presence of mechanical hypersensitivity the mid-plantar area of each hind paw was perpendicularly stimulated with calibrated nylon von Frey filaments (Weinstein-Semmes algesiometer forces) for 5 seconds using the up-down method starting with the 28.84 g force. A brisk withdrawal of the paw (often followed by a sustained retraction and/or licking possibly indicative of supraspinal business) is considered a positive response but paw withdrawals due to locomotion or weight shifting were not counted. For quantitative assessment the 50% probability withdrawal threshold or paw withdrawal threshold (PWT) was calculated as previously described (Chaplan et al. 1994 Baseline mechanical nociceptive thresholds were similar to those reported for the ages CH5132799 of rats employed in this study (Ririe and Eisenach 2006 Paw withdrawal thresholds were measured 10-12 h following the previous heroin self-administration session (i.e. just prior to subsequent sessions). For the prophylactic drug regimen study (eight-hour self-administration sessions) this corresponded to approximately 18-20 h after the final prophylactic drug treatment. Drugs Heroin (3 6 was provided by the National Institute on Drug Abuse and was dissolved in 0.9% sterile saline and injected subcutaneously (SC). Clonidine hydrochloride (presynaptic alpha-2-adrenoceptor agonist) was purchased from Sigma-Aldrich and dissolved in 0.9% saline and injected SC in a CH5132799 volume of 1 ml/kg body weight. Prazosin hydrochloride (alpha-1-adrenoceptor antagonist) and propranolol hydrochloride were Rabbit polyclonal to ARPM1. purchased from Sigma-Aldrich and dissolved in 0.9% saline and injected intraperitoneally (IP) in a volume of 1 ml/kg body weight. The CRF 1 receptor antagonist MPZP was prepared for systemic administration as described (Richardson et al. 2008 Animals were administered MPZP in a volume of 2 ml/kg 20% HBC (hydroxypropyl-beta-cyclodextrin SC). For the chronic prophylactic administration studies the vehicle-treated rats were given repeated SC injections of 2 ml 20% HBC vehicle/kg body weight. Acute Heroin Dependence Model Acute opioid dependence models are designed to reveal early behavioral neuroadaptations associated with the initiation and progression of dependence symptomatology (Azar et al. 2003 Liu and Schulteis 2004 Schulteis et al. 1999 Zhang and Schulteis 2008 To model acute heroin dependence animals were injected (SC) daily with 1.25 mg/kg heroin. This dose was previously shown to induce mechanical hyperalgesia during heroin withdrawal (Laulin et al. 1998 that progressively increases after repeated intermittent heroin injections (Celerier et al. 2001 Control animals received repeated injections of saline on comparative schedules. Heroin Self-Administration The surgery and self-administration procedures have CH5132799 been reported in detail previously (Vendruscolo et al. 2011 Briefly rats were anesthetized with isoflurane (2%) and chronic intravenous catheters were placed in the jugular vein. Rats were allowed to recover for 7 days before behavioral testing. Rats were trained to lever press for heroin (60 μg/kg/infusion) 1.