u-50488 and 17-cyclopropylmethyl-6-7-didehydro-4-5-epoxy-5--guanidinyl-3-14-dihydroxyindolo(2--3--6-7)morphinan

The μ opioid receptor (MOR) and κ opioid receptor (KOR) have been implicated in pair-bond formation and maintenance in socially monogamous species. Utilizing monogamous titi monkeys (Callicebus cupreus), the present study examined the potential role opioids play in modulating the response to separation, a potent challenge to the pair-bond. In Experiment 1, paired male titi monkeys were separated from their pair-mate for 30-min and then received saline, naloxone (1.0mg/kg), morphine (0.25mg/kg), or the KOR agonist, U50,488 (0.01, 0.03, or 0.1mg/kg) in a counter-balanced fashion, immediately prior to a 30-min reunion with their mate. Blood samples were collected immediately prior to and after the reunion. Males receiving morphine approached females less, initiated contact less, and females broke contact with the males less. The increase in cortisol in response to naloxone was greater compared to vehicle, and the increase in cortisol in response to the high dose of U50,488 compared to vehicle approached significance. In Experiment 2, paired males were treated with the KOR antagonist, GNTI (0.1, 0.3, or 1.0mg/kg), or saline 24h prior to a 60-min separation from their mate. Blood samples were collected at the time of injection and immediately before and after separation. Administration of the low dose of GNTI decreased the locomotor component of the separation response compared to vehicle. The present study found that the opioid system is involved in both the affiliative and separation distress components of a pair-bond, and these components are regulated by different opioid receptors.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Female; Guanidines; Hydrocortisone; Male; Morphinans; Morphine; Naloxone; Narcotic Antagonists; Pair Bond; Pitheciidae; Receptors, Opioid, kappa; Social Behavior; Vasopressins

The kappa opioid receptor (KOR) is involved in mediating pruritus; agonists targeting this receptor have been used to treat chronic intractable itch. Conversely, antagonists induce an itch response at the site of injection. As a G protein-coupled receptor (GPCR), the KOR has potential for signaling via G proteins and βarrestins, however, it is not clear which of these pathways are involved in the KOR modulation of itch. In this study asked whether the actions of KOR in pruritus involve βarrestins by using βarrestin2 knockout (βarr2-KO) mice as well as a recently described biased KOR agonist that biases receptor signaling toward G protein pathways over βarrestin2 recruitment. We find that the KOR antagonists nor-binaltorphimine (NorBNI) and 5'-guanidinonaltrindole (5'GNTI) induce acute pruritus in C57BL/6J mice, with reduced effects in KOR-KO mice. βArr2-KO mice display less of a response to KOR antagonist-induced itch compared to wild types, however no genotype differences are observed from chloroquine phosphate (CP)-induced itch, suggesting that the antagonists may utilize a KOR-βarrestin2 dependent mechanism. The KOR agonist U50,488H was equally effective in both WT and βarr2-KO mice in suppressing CP-induced itch. Furthermore, the G protein biased agonist, Isoquinolinone 2.1 was as effective as U50,488H in suppressing the itch response induced by KOR antagonist NorBNI or CP in C57BL/6J mice. Together these data suggest that the antipruritic effects of KOR agonists may not require βarrestins.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Opioid; Animals; Arrestins; beta-Arrestins; Chloroquine; Disease Models, Animal; Dose-Response Relationship, Drug; Guanidines; Isoquinolines; Male; Mice, Inbred C57BL; Mice, Knockout; Morphinans; Motor Activity; Naltrexone; Pruritus; Receptors, Opioid, kappa

We recently demonstrated that endogenous prodynorphin-derived peptides mediate anticonvulsant, antiepileptogenic and neuroprotective effects via kappa opioid receptors (KOP). Here we show acute and delayed neurodegeneration and its pharmacology after local kainic acid injection in prodynorphin knockout and wild-type mice and neuroprotective effect(s) of KOP activation in wild-type mice. Prodynorphin knockout and wild-type mice were injected with kainic acid (3 nmoles in 50 nl saline) into the stratum radiatum of CA1 of the right dorsal hippocampus. Knockout mice displayed significantly more neurodegeneration of pyramidal cells and interneurons than wild-type mice 2 days after treatment. This phenotype could be mimicked in wild-type animals by treatment with the KOP antagonist GNTI and rescued in knockout animals by the KOP agonist U-50488. Minor differences in neurodegeneration remained 3 weeks after treatment, mostly because of higher progressive neurodegeneration in wild-type mice compared with prodynorphin-deficient animals. In wild-type mice progressive neurodegeneration, but not acute neuronal loss, could be mostly blocked by U-50488 treatment. Our data suggest that endogenous prodynorphin-derived peptides sufficiently activate KOP receptors during acute seizures, and importantly in situations of reduced dynorphinergic signaling-like in epilepsy-the exogenous activation of KOP receptors might also have strong neuroprotective effects during excitotoxic events.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; CA1 Region, Hippocampal; Enkephalins; Guanidines; Humans; Interneurons; Kainic Acid; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphinans; Neurodegenerative Diseases; Protein Precursors; Pyramidal Cells; Receptors, Opioid, kappa; Seizures

Stress and anxiety are mainly regulated by amygdala and hypothalamic circuitries involving several neurotransmitter systems and providing physiological responses to peripheral organs via the hypothalamic-pituitary-adrenal axis and other pathways. The role of endogenous opioid peptides in this process is largely unknown. Here we show for the first time that anxiolytic parameters of explorative behavior in mice lacking prodynorphin were increased 2-4-fold in the open field, the elevated plus maze and the light-dark test. Consistent with this, treatment of wild-type mice with selective kappa-opioid receptor antagonists GNTI or norbinaltorphimine showed the same effects. Furthermore, treatment of prodynorphin knockout animals with U-50488H, a selective kappa-opioid receptor agonist, fully reversed their anxiolytic phenotype. These behavioral data are supported by an approximal 30% reduction in corticotropin-releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus and central amygdala and an accompanying 30-40% decrease in corticosterone serum levels in prodynorphin knockout mice. Although stress-induced increases in corticosterone levels were attenuated in prodynorphin knockout mice, they were associated with minor increases in depression-like behavior in the tail suspension and forced swim tests. Taken together, our data suggest a pronounced impact of endogenous prodynorphin-derived peptides on anxiety, but not stress coping ability and that these effects are mediated via kappa-opioid receptors. The delay in the behavioral response to kappa-opioid receptor agonists and antagonist treatment suggests an indirect control level for the action of dynorphin, probably by modulating the expression of CRH or neuropeptide Y, and subsequently influencing behavior.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Amygdala; Animals; Anxiety; Brain Stem; Corticosterone; Corticotropin-Releasing Hormone; Dynorphins; Enkephalins; Exploratory Behavior; Female; Guanidines; Hypothalamus; Male; Maze Learning; Mesencephalon; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphinans; Naltrexone; Neuropeptide Y; Neuropeptides; Protein Precursors; Raphe Nuclei; Receptors, Opioid, kappa; Stress, Psychological

Neuropsychiatric disorders are one of the main challenges of human medicine with epilepsy being one of the most common serious disorders of the brain. Increasing evidence suggest neuropeptides, particularly the opioids, play an important role in epilepsy. However, little is known about the mechanisms of the endogenous opioid system in epileptogenesis and epilepsy. Therefore, we investigated the role of endogenous prodynorphin-derived peptides in epileptogenesis, acute seizure behaviour and epilepsy in prodynorphin-deficient mice. Compared with wild-type littermates, prodynorphin knockout mice displayed a significantly reduced seizure threshold as assessed by tail-vein infusion of the GABA(A) antagonist pentylenetetrazole. This phenotype could be entirely rescued by the kappa receptor-specific agonist U-50488, but not by the mu receptor-specific agonist DAMGO. The delta-specific agonist SNC80 decreased seizure threshold in both genotypes, wild-type and knockout. Pre-treatment with the kappa selective antagonist GNTI completely blocked the rescue effect of U-50488. Consistent with the reduced seizure threshold, prodynorphin knockout mice showed faster seizure onset and a prolonged time of seizure activity after intracisternal injection of kainic acid. Three weeks after local injection of kainic acid into the stratum radiatum CA1 of the dorsal hippocampus, prodynorphin knockout mice displayed an increased extent of granule cell layer dispersion and neuronal loss along the rostrocaudal axis of the ipsi- and partially also of the contralateral hippocampus. In the classical pentylenetetrazole kindling model, dynorphin-deficient mice showed significantly faster kindling progression with six out of eight animals displaying clonic seizures, while none of the nine wild-types exceeded rating 3 (forelimb clonus). Taken together, our data strongly support a critical role for dynorphin in the regulation of hippocampal excitability, indicating an anticonvulsant role of kappa opioid receptors, thereby providing a potential target for antiepileptic drugs.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Benzamides; Cell Count; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Epilepsy, Temporal Lobe; Guanidines; Hippocampus; Kindling, Neurologic; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphinans; Naltrexone; Nerve Degeneration; Piperazines; Protein Precursors; Receptors, Opioid, kappa; Synaptic Transmission; Time Factors

Opioid receptors are divided into three types: kappa, mu, and delta receptors. Receptor-selective antagonists are useful experimental tools for evaluation of opioid receptor-mediated processes. 5'-Guanidinonaltrindole (GNTI) was recently developed as a novel kappa-selective antagonist.. To evaluate the potency, time course, and selectivity of GNTI's opioid antagonist effects in rhesus monkeys in an assay of schedule-controlled responding.. Five rhesus monkeys were trained to respond under a fixed ratio 30 schedule of food reinforcement. The rate-decreasing effects of the kappa agonists U50,488 and U69,593, the mu agonist morphine, and the delta agonist SNC80 were examined alone and after pretreatment with GNTI (0.1 and 1.0 mg/kg i.m.; 1 h to 14 days).. U50,488, U69,593, morphine, and SNC80 dose-dependently decreased response rates in this procedure. GNTI produced a dose- and time-dependent antagonism of the rate-decreasing effects of U50,488. The kappa antagonist effects of GNTI had a slow onset and a long duration of action, and peak antagonist effects were observed after 24 h. A higher dose of 3.2 mg/kg GNTI eliminated responding in one monkey and was not studied further. The antagonist effects of GNTI were kappa selective, because 1.0 mg/kg GNTI also antagonized the effects of U69,593, but not those of morphine or SNC80.. These results suggest that GNTI is a potent and selective kappa antagonist with a slow onset and long duration of action in rhesus monkeys. Relative to the prototype kappa antagonist nor-binaltorphimine, GNTI may have some advantages as a tool for the study of kappa receptor-mediated processes.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Analgesics, Non-Narcotic; Animals; Benzamides; Benzeneacetamides; Conditioning, Operant; Dose-Response Relationship, Drug; Drug Interactions; Female; Guanidines; Macaca mulatta; Male; Morphinans; Morphine; Naltrexone; Narcotic Antagonists; Narcotics; Piperazines; Pyrrolidines; Receptors, Opioid, delta; Receptors, Opioid, kappa; Reinforcement Schedule; Time Factors

Antagonists selective for either kappa- [e.g. nor-binaltorphimine (nor-BNI)] and mu- (e.g. beta-funaltrexamine) opioid receptors have previously been shown to reduce both kappa- and mu-opioid-induced feeding. In the present studies, the anorectic effects of GNTI, a newly synthesized antagonist selective for kappa-opioid receptors, were studied in rats. GNTI (0.032-0.32 nmol; i.c.v.), administered 15 min prior to food access, reduced feeding induced by the kappa-opioid agonist U50,488 (producing a 70% maximal decrease), the mu-opioid agonist DAMGO (90% maximal decrease), and 24 h acute food deprivation (60% maximal decrease). GNTI did not reduce the orexigenic effects of butorphanol, an agonist that binds to both kappa- and mu-opioid receptors, and neuropeptide Y (NPY). Taken together, these results suggest that GNTI is a potent anorectic agent and opioid antagonist in rats. Like nor-BNI, GNTI reduced feeding induced by both kappa- and mu-opioid agonists. However, unlike nor-BNI, GNTI did not alter the orexigenic effects of butorphanol or NPY. Given the selectivity of GNTI and its effectiveness in several of the present experiments, its potency, and its short duration of action compared to nor-BNI, GNTI may serve to be a useful tool to study behavioral effects mediated by kappa-opioid receptors.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Non-Narcotic; Analgesics, Opioid; Animals; Brain; Butorphanol; Drug Interactions; Eating; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Food Deprivation; Guanidines; Male; Morphinans; Naltrexone; Narcotic Antagonists; Narcotics; Neuropeptide Y; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa