Evaluation of the emotional phenotype and serotonergic neurotransmission of fatty acid amide hydrolase-deficient mice

By enhancing brain anandamide tone, inhibitors of fatty acid amide hydrolase (FAAH) induce anxiolytic-like effects in rodents and enhance brain serotonergic transmission. Mice lacking the faah gene (FAAH(-/-)) show higher anandamide levels. However, their emotional phenotype is still debated and their brain serotonergic tone remained unexplored. In this study, we tested FAAH(-/-) mice in the social interaction and the open field tests performed under different lighting conditions (dim and bright) since variations of the experimental context were proposed to explain opposite findings. Moreover, by microdialysis performed under dim light, we analyzed their serotonergic transmission in frontal cortex (FC) and ventral hippocampus (vHIPP). In both light conditions, FAAH(-/-) mice showed reduced emotionality, compared to wt controls, as suggested by the increased rearing and reduced thigmotaxis displayed in the open field and by the longer time spent in social interaction. Basal serotonergic tone was higher in the FC of mutant mice as compared to control mice, while no difference was observed in the vHIPP. K(+)-induced depolarization produced similar increases of serotonin in both areas of both genotypes. An acute treatment with the CB1 antagonist rimonabant completely abolished the emotional phenotype of FAAH(-/-) mice and prevented the K(+)-stimulated release of serotonin in their FC and vHIPP, without producing any effect in wt mice. Our results support the role of FAAH in the regulation of emotional reactivity and suggest that anandamide-mediated hyperactivation of CB1 is responsible for the emotional phenotype of FAAH(-/-) mice and for their enhanced serotonergic tone

Novel codrugs with GABAergic activity for dopamine delivery in the brain

This study investigates the use of codrugs of the GABAergic agent 2-phenyl-imidazo[1,2-a]pyridinacetamide and dopamine (DA) or ethyl ester L-Dopa (LD) as a strategy to deliver DA and simultaneously activate GABA-receptors in the brain. For this purpose, both DA and LD ethyl ester were linked by carbamate bond to imidazo[1,2-a]pyridine acetamide moieties to yield two DA- and two LD-imidazopyridine derivatives. These compounds were evaluated in vitro to assess their stability, binding affinities and cell membrane transport, and in vivo to assess their bio-availability via microdialysis studies. The two DA derivatives were adequately stable in buffered solution, but underwent cleavage in diluted human serum. By contrast, the LD derivatives were unstable in buffered solution. Receptor binding studies showed that the DA-imidazopyridine carbamates had binding affinity for benzodiazepine receptors in the nanomolar range. Brain microdialysis experiments indicated that intraperitoneal administration of the DA derivatives sustained DA levels in rat striatum over a 4-h period. These results suggest that DA-imidazopyridine carbamates are new DA codrugs with potential application for DA replacement therapy

Monoaminergic Changes in Locus Coeruleus and Dorsal Raphe Nucleus Following Noradrenaline Depletion

The goal of our study was to assess the monoaminergic changes in locus coeruleus (LC) and dorsal raphe nucleus (DRN) following noradrenaline (NA) depletion. Seven days after a single N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) intraperitoneal administration in mice, we observed a decrease of NA in both the LC and DRN, as well as in prefrontal cortex (PFC) and hippocampus (HIPP). Moreover, an increase of serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) was detected at LC level, while no change was found in DRN. DSP-4 also caused a significant decrease of dopamine (DA) tissue content in HIPP and DRN, without affecting the LC and the PFC. A decrease of DA metabolite, homovanillic acid (HVA), was found in the DRN of NA-depleted mice. These results highlight that the neurotoxic action of DSP-4 is not restricted to LC terminal projections but also involves NA depletion at the cell body level, where it is paralleled by adaptive changes in both serotonergic and dopaminergic systems

Monoaminergic changes in locus coeruleus and dorsal raphe nucleus following noradrenaline depletion

The goal of our study was to assess the monoaminergic changes in locus coeruleus (LC) and dorsal raphe nucleus (DRN) following noradrenaline (NA) depletion. Seven days after a single N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) intraperitoneal administration in mice, we observed a decrease of NA in both the LC and DRN, as well as in prefrontal cortex (PFC) and hippocampus (HIPP). Moreover, an increase of serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) was detected at LC level, while no change was found in DRN. DSP-4 also caused a significant decrease of dopamine (DA) tissue content in HIPP and DRN, without affecting the LC and the PFC. A decrease of DA metabolite, homovanillic acid (HVA), was found in the DRN of NA-depleted mice. These results highlight that the neurotoxic action of DSP-4 is not restricted to LC terminal projections but also involves NA depletion at the cell body level, where it is paralleled by adaptive changes in both serotonergic and dopaminergic systems

Evaluation of the emotional phenotype and serotonergic neurotransmission of fatty acid amide hydrolase-deficient mice.

RationaleBy enhancing brain anandamide tone, inhibitors of fatty acid amide hydrolase (FAAH) induce anxiolytic-like effects in rodents and enhance brain serotonergic transmission. Mice lacking the faah gene (FAAH(-/-)) show higher anandamide levels. However, their emotional phenotype is still debated and their brain serotonergic tone remained unexplored.Objectives and methodsIn this study, we tested FAAH(-/-) mice in the social interaction and the open field tests performed under different lighting conditions (dim and bright) since variations of the experimental context were proposed to explain opposite findings. Moreover, by microdialysis performed under dim light, we analyzed their serotonergic transmission in frontal cortex (FC) and ventral hippocampus (vHIPP).ResultsIn both light conditions, FAAH(-/-) mice showed reduced emotionality, compared to wt controls, as suggested by the increased rearing and reduced thigmotaxis displayed in the open field and by the longer time spent in social interaction. Basal serotonergic tone was higher in the FC of mutant mice as compared to control mice, while no difference was observed in the vHIPP. K(+)-induced depolarization produced similar increases of serotonin in both areas of both genotypes. An acute treatment with the CB1 antagonist rimonabant completely abolished the emotional phenotype of FAAH(-/-) mice and prevented the K(+)-stimulated release of serotonin in their FC and vHIPP, without producing any effect in wt mice.ConclusionsOur results support the role of FAAH in the regulation of emotional reactivity and suggest that anandamide-mediated hyperactivation of CB1 is responsible for the emotional phenotype of FAAH(-/-) mice and for their enhanced serotonergic tone

The Fat-Induced Satiety Factor Oleoylethanolamide Suppresses Feeding through Central Release of Oxytocin

Oleoylethanolamide (OEA) is a biologically active lipid amide that is released by small-intestinal enterocytes during the absorption of dietary fat and inhibits feeding by engaging the nuclear receptor, peroxisome proliferator-activated receptor-alpha (PPAR-alpha). Previous studies have shown that the anorexic effects of systemically administered OEA require the activation of sensory afferents of the vagus nerve. The central circuits involved in mediating OEA-induced hypophagia remain unknown. In the present study, we report the results of in situ hybridization and immunohistochemistry experiments in rats and mice, which show that systemic injections of OEA (5-10 mg kg(-1), intraperitoneal) enhance expression of the neuropeptide oxytocin in magnocellular neurons of the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. No such effect is observed with other hypothalamic neuropeptides, including vasopressin, thyrotropin-releasing hormone and pro-opiomelanocortin. The increase in oxytocin expression elicited by OEA was absent in mutant PPAR-alpha-null mice. Pharmacological blockade of oxytocin receptors in the brain by intracerebroventricular infusion of the selective oxytocin antagonist, L-368,899, prevented the anorexic effects of OEA. The results suggest that OEA suppresses feeding by activating central oxytocin transmission