Florence Noble

Deletion of the background potassium channel TREK-1 results in a depression-resistant phenotype

Depression is a devastating illness with a lifetime prevalence of up to 20%. The neurotransmitter serotonin or 5-hydroxytryptamine (5-HT) is involved in the pathophysiology of depression and in the effects of antidepressant treatments. However, molecular alterations that underlie the pathology or treatment of depression are still poorly understood. The TREK-1 protein is a background K+ channel regulated by various neurotransmitters including 5-HT. In mice, the deletion of its gene (Kcnk2, also called TREK-1) led to animals with an increased efficacy of 5-HT neurotransmission and a resistance to depression in five different models and a substantially reduced elevation of corticosterone levels under stress. TREK-1–deficient (Kcnk2−/−) mice showed behavior similar to that of naive animals treated with classical antidepressants such as fluoxetine. Our results indicate that alterations in the functioning, regulation or both of the TREK-1 channel may alter mood, and that this particular K+ channel may be a potential target for new antidepressants.

New treatments for cocaine dependence: a focused review.

Cocaine, already a significant drug problem in North and South America, has become a more prominent part of the European drug scene. Cocaine dependence has major somatic, psychological, psychiatric, socio-economic, and legal implications. No specific effective pharmacological treatment exists for cocaine dependence. Recent advances in neurobiology have identified various neuronal mechanisms implicated in cocaine addiction and suggested several promising pharmacological approaches. Data were obtained from Medline, EMBASE, and PsycINFO searches of English-language articles published between 1985 and June 2007 using the key words: cocaine, addiction, cocaine dependence, clinical trials, pharmacotherapy(ies) singly and in combination. Large well-controlled studies with appropriate statistical methods were preferred. Pharmacological agents such as GABA agents (topiramate, tiagabine, baclofen and vigabatrin) and agonist replacement agents (modafinil, disulfiram, methylphenidate) seem to be the most promising in treatment of cocaine dependence. The results from trials of first- and second-generation neuroleptics are largely negative. Aripiprazole, a partial dopaminergic agonist that may modulate the serotonergic system, shows some promise. Preliminary results of human studies with anti-cocaine vaccine, N-acetylcysteine, and ondansetron, are promising, as are several compounds in preclinical development. While no medication has received regulatory approval for the treatment of cocaine dependence, several medications marketed for other indications have shown efficacy in clinical trials. An anti-cocaine vaccine and several compounds in preclinical development have also shown promise. Findings from early clinical trials must be confirmed in larger, less selective patient populations.

CCK-B receptor: chemistry, molecular biology, biochemistry and pharmacology

Cholecystokinin (CCK) is a peptide originally discovered in the gastrointestinal tract but also found in high density in the mammalian brain. The C-terminal sulphated octapeptide fragment of cholecystokinin (CCK8) constitutes one of the major neuropeptides in the brain; CCK8 has been shown to be involved in numerous physiological functions such as feeding behavior, central respiratory control and cardiovascular tonus, vigilance states, memory processes, nociception, emotional and motivational responses. CCK8 interacts with nanomolar affinities with two different receptors designated CCK-A and CCK-B. The functional role of CCK and its binding sites in the brain and periphery has been investigated thanks to the development of potent and selective CCK receptor antagonists and agonists. In this review, the strategies followed to design these probes, and their use to study the anatomy of CCK pathways, the neurochemical and pharmacological properties of this peptide and the clinical perspectives offered by manipulation of the CCK system will be reported. The physiological and pathological implication of CCK-B receptor will be confirmed in CCK-B receptor deficient mice obtained by gene targeting (Nagata el al., 1996. Proc. Natl. Acad. Sci. USA 93, 11825-11830). Moreover, CCK receptor gene structure, deletion and mutagenesis experiments, and signal transduction mechanisms will be discussed.

Δ9-tetrahydrocannabinol releases and facilitates the effects of endogenous enkephalins: reduction in morphine withdrawal syndrome without change in rewarding effect

Recent studies have suggested that cannabinoids might initiate the consumption of other highly addictive substances, such as opiates. In this work, we show that acute administration of Δ9‐tetrahydrocannabinol in mice facilitates the antinociceptive and antidepressant‐like responses elicited by the endogenous enkephalins protected from their degradation by RB 101, a complete inhibitor of enkephalin catabolism. This emphasizes the existence of a physiological interaction between endogenous opioid and cannabinoid systems. Accordingly, Δ9‐tetrahydrocannabinol increased the release of Met‐enkephalin‐like material in the nucleus accumbens of awake and freely moving rats measured by microdialysis. In addition, this cannabinoid agonist displaced the in vivo[3H]diprenorphine binding to opioid receptors in total mouse brain. The repetitive pretreatment during 3 weeks of Δ9‐tetrahydrocannabinol in mice treated chronically with morphine significantly reduces the naloxone‐induced withdrawal syndrome. However, this repetitive administration of Δ9‐tetrahydrocannabinol did not modify or even decrease the rewarding responses produced by morphine in the place preference paradigm. Taken together, these behavioural and biochemical results demonstrate the existence of a direct link between endogenous opioid and cannabinoid systems. However, chronic use of high doses of cannabinoids does not seem to potentiate the psychic dependence to opioids.

Importance of ERK activation in behavioral and biochemical effects induced by MDMA in mice.

Little is known about the cellular effects induced by 3,4‐methylenedioxymethamphetamine (MDMA, ecstasy), although changes in gene expression have been observed following treatments with other psychostimulants. Thus, the aim of this study was to investigate in mice, the relationships between the ras‐dependent protein kinase ERK and MDMA‐induced reinforcement using the conditioned place preference (CPP) and locomotor activity measurements. This was completed using real‐time quantitative PCR method by a study of immediate early‐genes (IEGs) transcription known to be involved in neuronal plasticity. A significant CPP was observed after repeated MDMA treatment in CD‐1 mice at a dose of 9 mg kg−1 i.p. but not at 3 and 6 mg kg−1. This rewarding effect was abolished by the selective inhibitor of ERK activation, SL327 (50 mg kg−1; i.p.). Similar results were obtained on MDMA‐induced locomotor activity, clearly suggesting a role of ERK pathway in these behavioral responses. Following acute i.p. injection, MDMA induced a strong c‐fos transcription in brain structures, such as caudate putamen, nucleus accumbens and hippocampus, whereas egr‐1 and egr‐3 transcripts were only increased in the caudate putamen. MDMA‐induced IEGs transcription was selectively suppressed by SL327 in the caudate putamen, suggesting a role for other signaling pathways in regulation of IEGs transcription in the other brain structures. In agreement with these results, MDMA‐induced c‐fos protein expression was blocked by SL327 in the caudate putamen. This study confirms and extends to mice the reported role of ERK pathway in the development of addiction‐like properties of MDMA. This could facilitate studies about the molecular mechanism of this process by using mutant mice.

Nociceptin/Orphanin FQ Metabolism: Role of Aminopeptidase and Endopeptidase 24.15

Abstract: The endogenous opioid receptor‐like1 (ORL1) ligand, nociceptin/orphanin FQ (FGGFTGARKSARKLANQ), a heptadecapeptide structurally resembling dynorphin A, has recently been identified. The wide distribution of ORL1 mRNA and nociceptin/orphanin FQ precursor in the CNS, particularly in the limbic system regions and in several areas known to be involved in pain perception, suggests that nociceptin/orphanin FQ is potentially endowed with various central functions. In general, activation and/or inactivation of regulatory peptides occur through the action of cell surface peptidases. The physiological mechanisms under which nociceptin/orphanin FQ is metabolized should lead to a better understanding of its physiological functions. Mouse brain cortical slices were incubated in medium containing the heptadecapeptide in the presence or in the absence of peptidase inhibitors. The critical sites of enzymatic cleavage are Phe1‐Gly2, Ala7‐Arg8, Ala11‐Arg12, and Arg12‐Lys13 bonds. The major role played by metallopeptidases was confirmed by the complete protection of metabolism in the presence of EDTA. Aminopeptidase N and endopeptidase 24.15 are the two main enzymes involved in nociceptin/orphanin FQ metabolism, whereas endopeptidase 24.11 (involved in enkephalin [YGGFM(L)] catabolism) does not appear critically involved in nociceptin/orphanin FQ metabolism. The physiological relevance of aminopeptidase N and endopeptidase 24.15 in the heptadecapeptide metabolism remains to be determined.

Reduction of opioid dependence by the CB1 antagonist SR141716A in mice: evaluation of the interest in pharmacotherapy of opioid addiction

Several compounds, mainly opioid agonists such as methadone, are currently used for long term medication of heroin addicts. Nevertheless, these maintenance treatments have the disadvantage to induce a dependence to another opiate. As interactions between opioid and cannabinoid systems have been demonstrated, the ability of the CB1 antagonist, SR141716A to reduce morphine‐induced addiction was investigated. The effects of SR141716A on the rewarding responses of morphine were evaluated in the place conditioning paradigm. No significant conditioned preference or aversion were observed after repeated treatment with the CB1 antagonist alone. However, SR141716A was able to antagonize the acquisition of morphine‐induced conditioned place preference. SR141716A was co‐administered with morphine for 5 days, and the withdrawal syndrome was precipitated by naloxone administration. A reduction in the incidence of two main signs of abstinence: wet dog shakes and jumping was observed while the other were not significantly modified. In contrast, an acute injection of the CB1 antagonist just before naloxone administration was unable to modify the incidence of the behavioural manifestations of the withdrawal, suggesting that only chronic blockade of CB1 receptors is able to reduce morphine‐induced physical dependence. Several biochemical mechanisms could explain the reduction of opioid dependence by CB1 antagonists. Whatever the hypotheses, this study supports the reported interaction between the endogenous cannabinoid and opioid systems, and suggests that SR 141716A warrants further investigations for a possible use in opioid addiction.

Modulation of opioid antinociception by CCK at the supraspinal level : Evidence of regulatory mechanisms between CCK and enkephalin systems in the control of pain

1 Much evidence in the literature supports the idea that cholecystokinin (CCK) interacts with opioids in pain mechanisms. In this work, we have investigated the supraspinal interactions between enkephalins and CCK, using the hot plate test in mice. 2 Intracerebroventricular (i.c.v.) administration of BDNL (a mixed CCKA/CCKB agonist) induced dose‐dependent antinociceptive responses on both paw lick and jump responses. In contrast, using the same test, the i.c.v. injection of BC 264 (a selective CCKB agonist) induced a hyperalgesic effect, which was restricted to paw licking and occurred only at a high dose of 2.5 nmol. 3 In addition, i.c.v. administration of BDNL potentiated the antinociceptive effects of the mixed inhibitor of enkephalin degrading enzymes, RB 101 and of the μ‐agonist, DAMGO, while BC 264 reduced these effects. 4 Furthermore, at a dose where it interacts selectively with δ‐opioid receptors, the opioid agonist BUBU reversed the hyperalgesic responses of BC 264 (2.5 nmol) but was unable to modify the effects induced by BDNL. 5 Taken together, these results suggest the existence of regulatory mechanisms between CCK and enkephalin systems in the control of pain. These regulatory loops could enhance the antinociceptive effects of morphine allowing the opiate doses used to be reduced and thus, possibly, the side‐effects to be minimized.

Blockade of Acute Microglial Activation by Minocycline Promotes Neuroprotection and Reduces Locomotor Hyperactivity after Closed Head Injury in Mice: A Twelve-Week Follow-Up Study

Traumatic brain injury (TBI) causes a wide spectrum of consequences, such as microglial activation, cerebral inflammation, and focal and diffuse brain injury, as well as functional impairment. In this study we aimed to investigate the effects of acute treatment with minocycline as an inhibitor of microglial activation on cerebral focal and diffuse lesions, and on the spontaneous locomotor activity following TBI. The weight-drop model was used to induce TBI in mice. Microglial activation and diffuse axonal injury (DAI) were detected by immunohistochemistry using CD11b and ss-amyloid precursor protein (ss-APP) immunolabeling, respectively. Focal injury was determined by the measurement of the brain lesion volume. Horizontal and vertical locomotor activities were measured for up to 12 weeks post-injury by an automated actimeter. Minocycline or vehicle were administered three times post-insult, at 5 min (90 mg/kg i.p.), 3 h, and 9 h post-TBI (45 mg/kg i.p.). Minocycline treatment attenuated microglial activation by 59% and reduced brain lesion volume by 58%, yet it did not affect DAI at 24 h post-TBI. More interestingly, minocycline significantly decreased TBI-induced locomotor hyperactivity at 48 h post-TBI, and its effect lasted for up to 8 weeks. Taken together, the results indicate that microglial activation appears to play an important role in the development of TBI-induced focal injury and the subsequent locomotor hyperactivity, and its short-term inhibition provides long-lasting functional recovery after TBI. These findings emphasize the fact that minocycline could be a promising new therapeutic strategy for head-injured patients.

Physiological control of emotion-related behaviors by endogenous enkephalins involves essentially the delta opioid receptors.

The endogenous pentapeptide enkephalins bind to the mu and delta opioid receptors, with a slightly higher affinity for the latter. It remains a controversy regarding the respective physiological role of mu and delta opioid receptors in the control of emotion and motivation. One of the difficulties to investigate this problem is the low tonic extracellular release of enkephalins in various brain structures. To overcome this problem the synaptic levels of these pentapeptides were enhanced by inhibition of enzymes involved in their catabolism with the selective inhibitor H3N-CH(CH2-CH2-S-CH3)-CH2-S-S-CH2-CH(CH2phi)-CONH-CH(CH2phi)-COOCH2phi (RB101). This compound was shown to increase the extracellular levels and lifetime of endogenous enkephalins. Similar responses were obtained in wild-type and mu opioid receptor knockout mice following RB 101 administration in behavioral tests measuring locomotor activity, anxiety (elevated O-maze), and motivation (forced swim test and conditioned suppression of motility). In contrast, RB 101 led to antinociceptive responses only in wild-type animals using hot plate and tail immersion tests. These results clearly demonstrate the critical role of delta opioid receptors activated by the endogenous opioid peptides, in the physiological control of emotion- and motivation-related behaviors. In contrast, antinociceptive modulation, at least with respect to thermal nociceptive stimuli, involves enkephalin-activated mu opioid receptors. These findings could open new perspectives in the treatment of mood disorders using either inhibitors of enkephalin catabolism or delta opioid agonists.