Effects of co-administration of 2-arachidonylglycerol (2-AG) and a selective µ-opioid receptor agonist into the nucleus accumbens on high-fat feeding behaviors in the rat

The Endocannabinoid System and Eating Behaviours: a Review of the Current State of the Evidence

PURPOSE OF THE REVIEW

The endocannabinoid system (ENS) has emerged as an important factor in food intake and may have implications for nutrition research. The objective of the current report is to summarise the available evidence on the ENS and eating behaviour from both animal and human studies.

RECENT FINDINGS

The literature reviewed demonstrates a clear link between the ENS and eating behaviours. Overall, studies indicate that 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA) via cannabinoid receptor-1 (CNR1) binding may stimulate hunger and food intake while oleylethanolamide (OEA) may inhibit hunger. Mechanisms of these associations are not yet well understood, although the evidence suggests that there may be interactions with other physiological systems to consider. Most studies have been conducted in animal models, with few human studies available. Additional research is warranted among human populations into the ENS and eating behaviour. Evaluation of relationships between variation in ENS genes and dietary outcomes is an important area for investigation.

Polyunsaturated fatty acids and endocannabinoids in health and disease

Polyunsaturated fatty acids (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA, and eicosapentaenoic acid, EPA) or of omega-6 (arachidonic acid, ARA) synthesized from membrane phospholipids and used as a precursor for endocannabinoids (ECs). They mediate significant effects in the fine-tune adjustment of body homeostasis. Phyto- and synthetic cannabinoids also rule the daily life of billions worldwide, as they are involved in obesity, depression and drug addiction. Consequently, there is growing interest to reveal novel active compounds in this field. Cloning of cannabinoid receptors in the 90s and the identification of the endogenous mediators arachidonylethanolamide (anandamide, AEA) and 2-arachidonyglycerol (2-AG), led to the characterization of the endocannabinoid system (ECS), together with their metabolizing enzymes and membrane transporters. Today, the ECS is known to be involved in diverse functions such as appetite control, food intake, energy balance, neuroprotection, neurodegenerative diseases, stroke, mood disorders, emesis, modulation of pain, inflammatory responses, as well as in cancer therapy. Western diet as well as restriction of micronutrients and fatty acids, such as DHA, could be related to altered production of pro-inflammatory mediators (e.g. eicosanoids) and ECs, contributing to the progression of cardiovascular diseases, diabetes, obesity, depression or impairing conditions, such as Alzheimer' s disease. Here we review how diets based in PUFAs might be linked to ECS and to the maintenance of central and peripheral metabolism, brain plasticity, memory and learning, blood flow, and genesis of neural cells.

2-Arachidonoylglycerol as a possible treatment for anorexia nervosa in animal model in mice

We have investigated the effects of 0.001mg/kg 2-arachidonoylglycerol (2-AG) administered in combination with compounds present in the body alongside 2-AG like 2-palmitoylglycerol and 2-linoleylglycerol (also termed "entourage"), on cognitive function,food intake, and neurotransmitter levels in the hippocampus and hypothalamus of mice under diet restriction. Young female Sabra mice were treated with vehicle, 2-AG, 2-AG+entourage, 2-AG+entourage+5-(4-Chlorophenyl)-1-(2,4-dichloro-phenyl)- 4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide (SR141716A, a CB₁ antagonist) and SR141716A. The mice were fed for 2.5h a day for 14days. Cognitive function was evaluated by the eight arm maze test, and neurotransmitter (norepinephrine, dopamine, L-DOPA and serotonin) levels were measured in the hippocampus and hypothalamus by high-performance liquid chromatography-electrochemical detection. Food intake was increased by 2-AG and, to an even greater extent, by 2-AG+entourage. SR141716A reversed the effect of 2-AG+entourage. The administration of 2-AG+entourage improved cognitive function compared to the vehicle mice, and this improvement was blocked by SR141716A. 2-AG+entourage-treated mice showed an increase in norepinephrine (NE), dopamine and L-DOPA levels in the hippocampus. SR141716A normalized NE and L-DOPA levels. There were no significant changes in hypothalamic neurotransmitter levels. The use of very low doses of the endocannabinoid 2-AG+entourage can improve cognitive function by elevating norepinephrine and L-DOPA levels in the hippocampus, without cannabinomimetic side effects. These findings may have implications for cognitive enhancement in anorexia nervosa.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Pseudoginsenoside-F11 inhibits methamphetamine-induced behaviors by regulating dopaminergic and GABAergic neurons in the nucleus accumbens

RATIONALE

Although dependence to methamphetamine (METH) is associated with serious psychiatric symptoms and is a global health and social problem, no effective therapeutic approaches have been identified. Pseudoginsenoside-F11 (PF11) is an ocotillol-type saponin that is isolated from Panax quinquefolius (American ginseng) and was shown to have neuroprotective effects to promote learning and memory and to antagonize the pharmacological effects of morphine. Furthermore, PF11 also shows protective effects against METH-induced neurotoxicity in mice. However, the effects of PF11 on METH-induced preference and dopamine (DA) release have not been defined.

OBJECTIVES

We investigated the effects of PF11 administration on METH-induced hyperlocomotion and conditioned place preference (CPP) in mice. Subsequently, extracellular DA and gamma-aminobutyric acid (GABA) levels were determined in the nucleus accumbens (NAc) of mice after co-administration of PF11 and METH using in vivo microdialysis analyses. Moreover, the effects of PF11 administration on the μ-opioid neuronal responses, DAMGO (μ-opioid receptor agonist; [D-Ala(2), N-MePhe(4), Gly-ol]-enkephalin)-induced hyperlocomotion and accumbal extracellular DA increase were investigated to elucidate how PF11 inhibits METH-induced dependence by dopaminergic neuronal hyperfunction.

RESULTS

Co-administration of PF11 and METH for 6 days attenuated METH-induced locomotor sensitization compared with treatment with METH alone. In the CPP test, PF11 administration also inhibited METH-induced place preference. In vivo microdialysis analyses indicated that co-administration of PF11 and METH for 7 days prevented METH-induced extracellular DA increase in the NAc and repeated PF11 administration with or without METH for 7 days increased extracellular GABA levels in the NAc, whereas single administration of PF11 did not. Furthermore, DAMGO-induced hyperlocomotion and accumbal extracellular DA increase were significantly inhibited by acute PF11 administration.

CONCLUSIONS

The present data suggest that PF11 inhibits METH-induced hyperlocomotion, preference, and accumbal extracellular DA increase by regulating GABAergic neurons and μ-opioid receptors.