The nociceptin/orphanin FQ receptor partial agonist sunobinop promotes non-REM sleep in rodents and patients with insomnia.

The potent and partial agonist sunobinop activates the nociceptin/orphanin-FQ peptide receptor and promotes non-REM sleep in rodents and patients with insomnia.

Pharmacological evaluation of NSAID-induced gastropathy as a "Translatable" model of referred visceral hypersensitivity.

AIM: To evaluate whether non-steroidal anti-inflammatory drugs (NSAIDs)-induced gastropathy is a clinically predictive model of referred visceral hypersensitivity. METHODS: Gastric ulcer pain was induced by the oral administration of indomethacin to male, CD1 mice (n = 10/group) and then assessed by measuring referred abdominal hypersensitivity to tactile application. A diverse range of pharmacological mechanisms contributing to the pain were subsequently investigated. These mechanisms included: transient receptor potential (TRP), sodium and acid-sensing ion channels (ASICs) as well as opioid receptors and guanylate cyclase C (GC-C). RESULTS: Results showed that two opioids and a GC-C agonist, morphine, asimadoline and linaclotide, respectively, the TRP antagonists, AMG9810 and HC-030031 and the sodium channel blocker, carbamazepine, elicited a dose- and/or time-dependent attenuation of referred visceral hypersensitivity, while the ASIC blocker, amiloride, was ineffective at all doses tested. CONCLUSION: Together, these findings implicate opioid receptors, GC-C, and sodium and TRP channel activation as possible mechanisms associated with visceral hypersensitivity. More importantly, these findings also validate NSAID-induced gastropathy as a sensitive and clinically predictive mouse model suitable for assessing novel molecules with potential pain-attenuating properties.

A randomized, double-blind, positive-controlled, 3-way cross-over human experimental pain study of a TRPV1 antagonist (V116517) in healthy volunteers and comparison with preclinical profile.

This experimental, translational, experimental pain, single-center, randomized, double-blind, single-dose, 3-treatment, 3-period cross-over proof-of-concept volunteer trial studied the efficacy of a novel TRPV1 antagonist (V116517) on capsaicin- and UV-B-induced hyperalgesia. Heat and pressure pain thresholds, von Frey stimulus-response functions, and neurogenic inflammation were assessed together with safety. Each treatment period was 4 days. The 3 single oral treatments were 300 mg V116517, 400 mg celecoxib (a COX-2 inhibitor), and placebo. The heat pain detection and tolerance thresholds were increased significantly (P < 0.0001) by V116517. Heat pain detection and tolerance thresholds showed significantly less capsaicin hyperalgesia after V116517 (P = 0.004 and P < 0.0001, respectively). Celecoxib reduced UV-B-provoked pressure pain sensitization (P = 0.01). Laser Doppler flowmetry and erythema index after UV-B were significantly (P < 0.0001) reduced by celecoxib. Stimulus-response function in capsaicin-treated areas showed significant differences between both celecoxib and placebo and between V116517 and placebo. The body temperature showed no change, and no side effects were reported for any of the treatments. The TRPV1 antagonists and the COX-2 inhibitor showed different antihyperalgesic profiles indicating different clinical targets. In addition, the preclinical profile of V116517 in rat models of UV-B and capsaicin-induced hypersensitivity was compared with the human experimental data and overall demonstrated an alignment between 2 of the 3 end points tested. The TRPV1 antagonist showed a potent antihyperalgesic action without changing the body temperature but heat analgesia may be a potential safety issue.

Robustness of arterial blood gas analysis for assessment of respiratory safety pharmacology in rats.

Whole body plethysmography using unrestrained animals is a common technique for assessing the respiratory risk of new drugs in safety pharmacology studies in rats. However, wide variations in experimental technique make cross laboratory comparison of data difficult and raise concerns that non-appropriate conditions may mask the deleterious effects of test compounds - in particular with suspected respiratory depressants. Therefore, the objective of this study was to evaluate the robustness of arterial blood gas analysis as an alternative to plethysmography in rats. We sought to do this by assessing the effect of different vehicles and times post-surgical catheterization on blood gas measurements, in addition to determining sensitivity to multiple opioids. Furthermore, we determined intra-lab variability from multiple datasets utilizing morphine and generated within a single lab and lastly, inter-lab variability was measured by comparing datasets generated in two separate labs. Overall, our data show that arterial blood gas analysis is a measure that is both flexible in terms of experimental conditions and highly sensitive to respiratory depressants, two key limitations when using plethysmography. As such, our data strongly advocate the adoption of arterial blood gas analysis as an investigative approach to reliably examine the respiratory depressant effects of opioids.

Pain is a salient "stressor" that is mediated by corticotropin-releasing factor-1 receptors.

Corticotropin-releasing factor (CRF) plays a major role in controlling the body's response to stress. Because painful conditions are inherently stressful, we hypothesize that CRF may act via CRF-1 receptors to contribute to the pain experience. Studies were designed to investigate whether blocking CRF-1 receptors with selective antagonists or reducing their expression with CRF-Saporin, would attenuate ulcer, inflammatory- and neuropathic-like pain. Five experimental designs were undertaken. In experiment 1, ulcer pain was induced in mice following oral administration of indomethacin, while in experiments 2 and 3, inflammatory pain was induced in rats with either carrageenan or FCA, respectively. For these studies, animals were dosed with CP-154,526 (3, 10, 30 mg/kg) and NBI 27914 (1-30 mg/kg) 1 h prior to the assessment of tactile, thermal or mechanical hypersensitivity, respectively. In experiment 4, neuropathic pain was induced. Twenty-one days following spinal nerve ligation (SNL), animals received CRF-Saporin or control. Three weeks later tactile allodynia was assessed. Similarly, in experiment 5, a separate set of rats received CRF-Saporin or control. Twenty-one days later, mechanical hyperalgesia was assessed following intraplantar carrageenan. Results from the antagonist studies showed that CP-154,526 and NBI 27914 either fully or partially reversed the referred ulcer pain with minimal effective doses (MED) equal to 3 and 10 mg/kg, respectively. Similarly, both NBI 27914 and CP-154,526 reversed the thermal and mechanical hypersensitivity elicited by carrageenan and FCA with MEDs

CNS penetration of small molecules following local inflammation, widespread systemic inflammation or direct injury to the nervous system.

AIMS: We sought to investigate effects of local and systemic inflammation on CNS permeability of small molecules and compare these to effects of direct injury to the nervous system. MAIN METHODS: Evans blue was used to determine the integrity of the blood-brain barrier (BBB) following local inflammation, systemic inflammation, injury to the L5 spinal nerve or transient occlusion of the middle cerebral artery. In addition, three compounds having low, medium and high brain permeability (atenolol, morphine and oxycodone, respectively) were used. Following model establishment (4-hr post-carrageenan, 24-hr post-FCA, 2-, 4- and 24-hr post-LPS, 21 days post-nerve injury) compounds were administered and 30 min later the brain, spinal cord and blood removed. The plasma and tissue concentrations of compounds were quantified by LC/MS/MS. KEY FINDINGS: Localized inflammation did not affect Evans blue penetration into the CNS but significantly increased morphine penetration into the spinal cord. Systemic inflammation increased the quantity of Evans blue in the CNS but also decreased the penetration of atenolol, morphine and oxycodone into the brain 4-hr post-insult. Nerve injury had no effect on Evans blue or compound penetration, while middle cerebral artery occlusion resulted in a large but short lived increase in Evans blue penetration into both the cortex and striatum. SIGNIFICANCE: The presence of inflammation may affect the CNS penetration of some compounds but is unlikely to lead to a large non-selective BBB breakdown. As a result, it is appropriate to test for side-effects, and conduct brain pharmacokinetic determinations, in naïve rats.

Assessment of seizure susceptibility in pilocarpine epileptic and nonepileptic Wistar rats and of seizure reinduction with pentylenetetrazole and electroshock models.

PURPOSE: Pentylenetetrazole (PTZ) and maximal electroshock (MES) models are often used to induce seizures in nonepileptic control animals or naive animals. Despite being widely used to screen antiepileptic drugs (AEDs), both models have so far failed to detect potentially useful AEDs for treating drug-resistant epilepsies. Here we investigated whether the acute induction of MES and PTZ seizures in epileptic rats might yield a distinct screening profile for AEDs. METHODS: Status epilepticus (SE) was induced in adult male Wistar rats by intraperitoneal pilocarpine injection (Pilo, 320 mg/kg, i.p.). One month later, controls or naive animals (Cont) that did not develop SE postpilocarpine (N-Epi) and pilocarpine-epileptic rats (Epi) received one of the following: phenobarbital (PB, 40 mg/kg), phenytoin (PHT, 50 mg/kg), or valproic acid (VPA, 400 mg/kg). Thirty min later the animals were challenged with either subcutaneous MES or PTZ (50 mg/kg, s.c.). RESULTS: VPA, PB, and PHT were able to prevent MES in all groups tested (Cont, N-Epi, and Epi groups), whereas for the PTZ model, only the Cont group (naive animals) had seizure control with the same AEDs. In addition, Epi and N-Epi groups when challenged with PTZ exhibited a higher incidence of severe seizures (scores IV-IX) and SE (p < 0.05, Fisher's exact test). CONCLUSIONS: Our findings suggest that the induction of acute seizures with PTZ, but not with MES, in animals pretreated with pilocarpine (regardless of SE induction) might constitute an effective and valuable method to screen AEDs and to study mechanisms involved in pharmacoresistant temporal lobe epilepsy (TLE).

The persistence of a long-term negative affective state following the induction of either acute or chronic pain.

Clinically, pain is a complex phenomenon consisting of both sensory and affective aberrations that can persist indefinitely. Pre-clinically, several animal paradigms have been established that reliably mimic both the acute and chronic aspects of pain pertinent to the human condition; however, the commonly used behavioral models only assess the sensory component of pain elicited by an evoked nociceptive stimulus. Since the affective-motivational component of pain is an important determinant of the overall pain experience in man, we investigated how this aspect may be modeled long-term in rats using novel objects and a modified conditioned place aversion (CPA) paradigm. Findings demonstrate that animals subjected to either neuropathic injury or inflammatory insult display a significant conditioned place aversion to a pain-paired environment that is paralleled by an increased number of hind paw withdrawals and fewer number of novel object interactions during painful conditioning sessions. Moreover, this aversion is maintained for 1 month in the absence of further conditioning. We also determined that a non-analgesic, non-rewarding dose of morphine administered prior to pain-paired conditioning sessions attenuates the pain-induced aversion and its relative persistence in both pain models. Together, these findings underscore the importance of negative affect accompanying painful conditions and its long-term persistence even when the injury or insult has resolved. Lastly, these results suggest how both sensory and affective aberrations associated with neuropathic- and inflammatory-like conditions and the memory of such known to impact quality of life in man may be addressed pre-clinically in rodents.

A role for mu opioid receptors in cocaine-induced activity, sensitization, and reward in the rat.

RATIONALE: Considerable evidence suggests that the endogenous opioid system plays a role in mediating the behavioral effects of psychostimulants. Opioidergic drugs have been shown to have profound effects on cocaine-induced behavioral sensitization and conditioned reward. However, the role specifically of the mu opioid receptor in this regard is unclear as most previous pharmacological studies have used nonselective opioid receptor ligands. OBJECTIVES: The objective of this series of experiments was to elucidate the role of mu opioid receptors in the behavioral effects of cocaine in the rat. MATERIALS AND METHODS: Adult male rats were used to assess the effects of the selective mu opioid receptor antagonist D: -Phe-Cys-Tyr-D: -Trp-Arg-Thr-Pen-Thr (CTAP) on acute hyperactivity, locomotor sensitization, and conditioned place preference induced by cocaine. Intracerebroventricular administration of CTAP, 4 microg, was paired with peripheral injections of cocaine, 10-15 mg/kg. RESULTS: Mu receptor blockade significantly attenuated cocaine-induced hyperactivity, as well as the development of behavioral sensitization. Pretreatment with CTAP also prevented the development of conditioned place preference to cocaine. Administration of CTAP alone had neither effect on locomotor activity nor did it demonstrate aversive or rewarding properties. CONCLUSIONS: These results suggest that activation of mu opioid receptors by endogenous opioids is an important contributor to cocaine-induced hyperactivity and the development of behavioral sensitization and conditioned reward.

Disruption of G(i/o) protein signaling in the nucleus accumbens results in a D1 dopamine receptor-mediated hyperactivity.

Intra-accumbens infusion of pertussis toxin (PTX) results in a progressive and persistent locomotor hyperactivity and sensitizes rats to the locomotor-activating effects of cocaine. The present study further defined the hyperactivity resulting from inactivation of accumbens Gi/Go proteins and tested the hypothesis that PTX-induced hyperactivity is mediated by dopamine D1 receptors. PTX (0.15 microg/side) infused bilaterally into the nucleus accumbens of rats resulted in a progressive increase in locomotor activity that peaked at 218% of preinjection activity levels 15 days after injection and persisted for greater than 5 weeks postinjection. Administration of the D1 receptor antagonist SCH23390 16 and 23 days after PTX injections dose dependently attenuated PTX-induced hyperactivity. D1 receptor blockade did not significantly alter activity in sham-injected animals. These findings support the hypothesis that the hyperactivity resulting from PTX-mediated inactivation of G(i/o) proteins reflects increased nucleus accumbens D1 receptor activation and suggest that striatal D1 receptors are important mediators of activity-related behavior, such as cocaine-induced hyperactivity.

Repeated intracerebroventricular forskolin administration enhances behavioral sensitization to cocaine.

Repeated cocaine exposure produces behavioral sensitization expressed as an increased locomotor response to subsequent drug administration. Chronic cocaine administration also results in increased activity of adenylyl cyclase and cyclic-AMP (cAMP) dependent protein kinase (PKA) in the nucleus accumbens. To investigate the relationship between cocaine-induced behavioral sensitization and cAMP signaling, the present study examined the effect of forskolin, a direct adenylyl cyclase activator, on cocaine-induced hyperlocomotion and behavioral sensitization to cocaine. Rats were given intracerebroventricular (i.c.v.) injections of a water soluble form of forskolin (7DMB-forskolin) or vehicle 10 min prior to intraperitoneal (i.p.) cocaine or saline administration on 7 consecutive days. Acute or chronic forskolin alone had no effect on locomotor activity at the doses tested. On days 1 and 2, the activity of rats that received i.c.v. forskolin paired with cocaine was not significantly different from rats that received i.c.v. injections of vehicle co-administered with cocaine. By the third day of forskolin/cocaine co-administration, rats displayed enhanced cocaine-induced hyperlocomotor activity compared to rats that received cocaine alone, an effect that persisted through day 7. When challenged with cocaine on day 14, animals that had previously received forskolin paired with cocaine on days 1-7 displayed similar locomotor activity to animals that received cocaine only. These results suggest that alterations in adenylyl cyclase activity and/or cAMP levels may underlie the hyperlocomotor response to cocaine and may play a role in behavioral sensitization.

Intra-accumbens pertussis toxin sensitizes rats to the locomotor activating effects of a single cocaine challenge.

Drugs of abuse share common neurochemical signaling substrates, many of which are components of the cAMP cascade. Interestingly, a number of these substrates have been linked to drug-influenced behaviors. This study sought to understand the role of one signaling substrate, inhibitory G-proteins, in a drug-induced phenomenon known as behavioral sensitization. Specifically, we used pertussis toxin (PTX) as a tool to investigate the relationship between cocaine-induced alterations in cAMP signaling and behavior. Vehicle (1 micro l/side) or PTX (0.15 or 0.25 micro g/1 micro l/side) was bilaterally infused into the nucleus accumbens of rats. Locomotor activity was assessed on days 7, 14 and 21 post-infusion. Intra-accumbal PTX produced a dose-dependent increase in locomotor activity. On day 21 following behavioral monitoring for 1 h, rats were acutely challenged with cocaine (15 mg/kg, i.p.) and behavioral data were accumulated for an additional 2 h. Intra-accumbal PTX sensitized rats to the locomotor-activating effects of a single cocaine challenge which was dose-dependent. After behavioral testing, brains were removed and processed for in vitro receptor autoradiography using the D(1) receptor ligand [3H] SCH 23390. No changes in D(1) dopamine receptor binding were observed. These findings suggest a role for inhibitory proteins (G(i)/G(o)) within the nucleus acumbens in locomotor activity and also cocaine-induced behavioral sensitization.

D1 dopamine receptor: a putative neurochemical and behavioral link to cocaine action.

Cocaine is one of the most abused psychostimulants known to man and as such, researchers have been steadfast in their attempts to understand the neurobiological mechanisms responsible for its abuse. Cocaine undoubtedly wreaks havoc on a number of mammalian neuronal neurotransmitter systems, and it is maintained that this dysregulatory effect supports cocaine abuse. Cocaine's mechanism of action has been well described. Cocaine binds differentially to the dopamine, serotonin, and norepinephrine transport proteins and directly prevents the re-uptake of dopamine, serotonin, and norepinephrine into pre-synaptic neurons (Heikkila et al., 1975, Biochem Pharmacol 24(8):847-852; Reith et al., 1986, Biochem Pharmacol 35(7):1123-1129; Ritz et al., 1987, Science 237:1219-1223). Inhibition of re-uptake subsequently elevates the synaptic concentrations of each of these neurotransmitters. In addition to this direct effect, cocaine also produces a number of indirect actions, which alter other neuromodulatory systems (i.e., opioidergic, glutamatergic, and GABAergic systems). Many of these effects are just beginning to be elucidated, but nonetheless contribute to this agent's diverse pharmacological profile. Interestingly, it is the indirect actions of this mellifluous molecule, which mediate most of its sought and unsought effects. The intricacy with which cocaine produces neuronal alterations beyond its direct effects on neurotransmitter re-uptake appear to be most relevant to cocaine abuse, and hence the phenomenon of addiction. In light of cocaine's multifarious effects on numerous neuronal systems, its effect on dopaminergic neurotransmission has attracted the most attention, particularly because of the implicated role of dopamine in brain reward. Pharmacologically, the psychostimulant effects of cocaine appear to be mediated by its ability to enhance dopaminergic activity within the mesocorticolimbic circuit (Roberts et al., 1977, Pharmacol Biochem Behav 6(6):615-620). Additionally, it is the intensity with which cocaine produces alterations in dopaminergic circuitry that have enabled this drug to prevail as one of the most addictive substances known to man. This review will summarize findings relevant to cocaine-induced alterations in dopamine-mediated signal transduction. Specifically, it will concentrate on the D1 dopamine receptor and intracellular signaling mediated by this receptor subtype. It will describe cocaine-induced cellular and behavioral alterations relevant to this pathway and how these changes potentially effect gene transcription and protein expression. This article too will review a common behavioral manifestation associated with repeated cocaine exposure, sensitization, and why the D1 dopamine receptor and its associated signaling pathway have been implicated in this phenomenon. Lastly, this article will discuss how targeting the D1 dopamine receptor and its signaling pathway may offer some insight into understanding cocaine addiction, a somewhat elusive brain disease.