CRF1-R Activation of the Dynorphin/Kappa Opioid System in the Mouse Basolateral Amygdala Mediates Anxiety-Like Behavior

Stress is a complex human experience and having both rewarding and aversive motivational properties. The adverse effects of stress are well documented, yet many of underlying mechanisms remain unclear and controversial. Here we report that the anxiogenic properties of stress are encoded by the endogenous opioid peptide dynorphin acting in the basolateral amygdala. Using pharmacological and genetic approaches, we found that the anxiogenic-like effects of Corticotropin Releasing Factor (CRF) were triggered by CRF1-R activation of the dynorphin/kappa opioid receptor (KOR) system. Central CRF administration significantly reduced the percent open-arm time in the elevated plus maze (EPM). The reduction in open-arm time was blocked by pretreatment with the KOR antagonist norbinaltorphimine (norBNI), and was not evident in mice lacking the endogenous KOR ligand dynorphin. The CRF1-R agonist stressin 1 also significantly reduced open-arm time in the EPM, and this decrease was blocked by norBNI. In contrast, the selective CRF2-R agonist urocortin III did not affect open arm time, and mice lacking CRF2-R still showed an increase in anxiety-like behavior in response to CRF injection. However, CRF2-R knockout animals did not develop CRF conditioned place aversion, suggesting that CRF1-R activation may mediate anxiety and CRF2-R may encode aversion. Using a phosphoselective antibody (KORp) to identify sites of dynorphin action, we found that CRF increased KORp-immunoreactivity in the basolateral amygdala (BLA) of wildtype, but not in mice pretreated with the selective CRF1-R antagonist, antalarmin. Consistent with the concept that acute stress or CRF injection-induced anxiety was mediated by dynorphin release in the BLA, local injection of norBNI blocked the stress or CRF-induced increase in anxiety-like behavior; whereas norBNI injection in a nearby thalamic nucleus did not. The intersection of stress-induced CRF and the dynorphin/KOR system in the BLA was surprising, and these results suggest that CRF and dynorphin/KOR systems may coordinate stress-induced anxiety behaviors and aversive behaviors via different mechanisms

Effects of topically applied heterologous serum on reepithelialization rate of superficial chronic corneal epithelial defects in dogs

OBJECTIVE To assess the effects of topical application of undiluted heterologous serum on time to corneal reepithelialization in dogs with superficial chronic corneal epithelial defects (SCCEDs). DESIGN Multicenter, randomized, double-masked, controlled clinical trial. ANIMALS 41 client-owned dogs. PROCEDURES After collection of baseline clinical and historical data, dogs were randomly assigned to receive topically applied undiluted heterologous serum (n = 22) or isotonic saline (0.9% NaCl) solution (19) along with tobramycin and atropine. Epithelial debridement (at all visits) and grid keratotomy (at visits 2, 3, and 4) of SCCEDs were performed. Ophthalmic examination including fluorescein application was performed once weekly for 4 weeks or until corneal reepithelialization. Clinicians and owners were masked to treatment group. RESULTS No differences in baseline data were detected between treatment groups. No difficulties with medication administration, noncompliance, or adverse reactions were noted. All SCCEDs in both groups healed by 4 weeks after treatment began. Median time to reepithelialization (2 weeks) was not significantly different between serum-treated and placebo-treated eyes. Irrespective of treatment group, median time to reepithelialization was not significantly different for Boxers versus non-Boxer breeds. Direct correlations were detected between time to reepithelialization and vascularization score at study entry, vascularization score at time of reepithelialization, and ulcer area at study entry in both groups. Time to reepithelialization was not correlated with age, sex, or duration of signs in either group. CONCLUSIONS AND CLINICAL RELEVANCE Topical application of undiluted heterologous serum was well tolerated by dogs with SCCEDs but, as an adjunct to standard treatment, did not reduce time to corneal reepithelialization

Behavioral Stress May Increase the Rewarding Valence of Cocaine-Associated Cues Through a Dynorphin/κ-Opioid Receptor-Mediated Mechanism without Affecting Associative Learning or Memory Retrieval Mechanisms

Stress exposure increases the risk of addictive drug use in human and animal models of drug addiction by mechanisms that are not completely understood. Mice subjected to repeated forced swim stress (FSS) before cocaine develop significantly greater conditioned place preference (CPP) for the drug-paired chamber than unstressed mice. Analysis of the dose dependency showed that FSS increased both the maximal CPP response and sensitivity to cocaine. To determine whether FSS potentiated CPP by enhancing associative learning mechanisms, mice were conditioned with cocaine in the absence of stress, then challenged after association was complete with the κ-opioid receptor (KOR) agonist U50,488 or repeated FSS, before preference testing. Mice challenged with U50,488 60 min before CPP preference testing expressed significantly greater cocaine–CPP than saline-challenged mice. Potentiation by U50,488 was dose and time dependent and blocked by the KOR antagonist norbinaltorphimine (norBNI). Similarly, mice subjected to repeated FSS before the final preference test expressed significantly greater cocaine–CPP than unstressed controls, and FSS-induced potentiation was blocked by norBNI. Novel object recognition (NOR) performance was not affected by U50,488 given 60 min before assay, but was impaired when given 15 min before NOR assay, suggesting that KOR activation did not potentiate CPP by facilitating memory retrieval or expression. The results from this study show that the potentiation of cocaine–CPP by KOR activation does not result from an enhancement of associative learning mechanisms and that stress may instead enhance the rewarding valence of cocaine-associated cues by a dynorphin-dependent mechanism