The mammalian brain is one of the organs with the highest energy demands, and mitochondria are key determinants of its functions. Here we show that the type-1 cannabinoid receptor (CB(1)) is present at the membranes of mouse neuronal mitochondria (mtCB(1)), where it directly controls cellular respiration and energy production. Through activation of mtCB(1) receptors, exogenous cannabinoids and in situ endocannabinoids decreased cyclic AMP concentration, protein kinase A activity, complex I enzymatic activity and respiration in neuronal mitochondria. In addition, intracellular CB(1) receptors and mitochondrial mechanisms contributed to endocannabinoid-dependent depolarization-induced suppression of inhibition in the hippocampus. Thus, mtCB(1) receptors directly modulate neuronal energy metabolism, revealing a new mechanism of action of G protein-coupled receptor signaling in the brain.

Cellular activity in the brain depends on the high energetic support provided by mitochondria, the cell organelles which use energy sources to generate ATP. Acute cannabinoid intoxication induces amnesia in humans and animals, and the activation of type-1 cannabinoid receptors present at brain mitochondria membranes (mtCB) can directly alter mitochondrial energetic activity. Although the pathological impact of chronic mitochondrial dysfunctions in the brain is well established, the involvement of acute modulation of mitochondrial activity in high brain functions, including learning and memory, is unknown. Here, we show that acute cannabinoid-induced memory impairment in mice requires activation of hippocampal mtCB receptors. Genetic exclusion of CB receptors from hippocampal mitochondria prevents cannabinoid-induced reduction of mitochondrial mobility, synaptic transmission and memory formation. mtCB receptors signal through intra-mitochondrial Gα protein activation and consequent inhibition of soluble-adenylyl cyclase (sAC). The resulting inhibition of protein kinase A (PKA)-dependent phosphorylation of specific subunits of the mitochondrial electron transport system eventually leads to decreased cellular respiration. Hippocampal inhibition of sAC activity or manipulation of intra-mitochondrial PKA signalling or phosphorylation of the Complex I subunit NDUFS2 inhibit bioenergetic and amnesic effects of cannabinoids. Thus, the G protein-coupled mtCB receptors regulate memory processes via modulation of mitochondrial energy metabolism. By directly linking mitochondrial activity to memory formation, these data reveal that bioenergetic processes are primary acute regulators of cognitive functions.

Comment in Sensory systems: the hungry sense. [Nat Rev Neurosci. 2014] Inhaling: endocannabinoids and food intake. [Nat Neurosci. 2014]International audienceHunger arouses sensory perception, eventually leading to an increase in food intake, but the underlying mechanisms remain poorly understood. We found that cannabinoid type-1 (CB1) receptors promote food intake in fasted mice by increasing odor detection. CB1 receptors were abundantly expressed on axon terminals of centrifugal cortical glutamatergic neurons that project to inhibitory granule cells of the main olfactory bulb (MOB). Local pharmacological and genetic manipulations revealed that endocannabinoids and exogenous cannabinoids increased odor detection and food intake in fasted mice by decreasing excitatory drive from olfactory cortex areas to the MOB. Consistently, cannabinoid agonists dampened in vivo optogenetically stimulated excitatory transmission in the same circuit. Our data indicate that cortical feedback projections to the MOB crucially regulate food intake via CB1 receptor signaling, linking the feeling of hunger to stronger odor processing. Thus, CB1 receptor-dependent control of cortical feedback projections in olfactory circuits couples internal states to perception and behavior

Bidirectional communication between neurons and astrocytes shapes synaptic plasticity and behavior. D-serine is a necessary co-agonist of synaptic N-methyl-D-aspartate receptors (NMDARs), but the physiological factors regulating its impact on memory processes are scantly known. We show that astroglial CB receptors are key determinants of object recognition memory by determining the availability of D-serine at hippocampal synapses. Mutant mice lacking CB receptors from astroglial cells (GFAP-CB-KO) displayed impaired object recognition memory and decreased in vivo and in vitro long-term potentiation (LTP) at CA3-CA1 hippocampal synapses. Activation of CB receptors increased intracellular astroglial Ca levels and extracellular levels of D-serine in hippocampal slices. Accordingly, GFAP-CB-KO displayed lower occupancy of the co-agonist binding site of synaptic hippocampal NMDARs. Finally, elevation of D-serine levels fully rescued LTP and memory impairments of GFAP-CB-KO mice. These data reveal a novel mechanism of in vivo astroglial control of memory and synaptic plasticity via the D-serine-dependent control of NMDARs.

The CB 1 cannabinoid receptor, the main molecular target of endocannabinoids and cannabis active components, is the most abundant G protein-coupled receptor in the mammalian brain. Of note, CB 1 receptors are expressed at the synapses of two opposing (i.e., GABAergic/inhibitory and glutamatergic/excitatory) neuronal populations, so the activation of one and/or another receptor population may conceivably evoke different effects. Despite the widely reported neuroprotective activity of the CB 1 receptor in animal models, the precise pathophysiological relevance of those two CB 1 receptor pools in neurodegenerative processes is unknown. Here, we first induced excitotoxic damage in the mouse brain by (i) administering quinolinic acid to conditional mutant animals lacking CB 1 receptors selectively in GABAergic or glutamatergic neurons, and (ii) manipulating corticostriatal glutamatergic projections remotely with a designer receptor exclusively activated by designer drug pharmacogenetic approach. We next examined the alterations that occur in the R6/2 mouse, a well-established model of Huntington disease, upon (i) fully knocking out CB 1 receptors, and (ii) deleting CB 1 receptors selectively in corticostriatal glutamatergic or striatal GABAergic neurons. The data unequivocally identify the restricted population of CB 1 receptors located on glutamatergic terminals as an indispensable player in the neuroprotective activity of (endo)cannabinoids, therefore suggesting that this precise receptor pool constitutes a promising target for neuroprotective therapeutic strategies. neuroprotection | neuromodulation | excitotoxicity E ndocannabinoids are a family of neuron-communication messengers that act by engaging CB 1 cannabinoid receptors, which are also targeted by Δ 9 -tetrahydrocannabinol (THC), the main bioactive component of cannabis. Endocannabinoid signaling serves as a pivotal feedback mechanism to prevent excessive presynaptic activity, thereby tuning the functionality and plasticity of many synapses (1, 2). The CB 1 receptor is the most abundant G protein-coupled receptor in the brain, and is highly expressed in GABAergic terminals of the forebrain (particularly in cholecystokinin-positive and parvalbumin-negative interneurons) (3), where it inhibits GABA release. Functional CB 1 receptors reside as well on terminals of glutamatergic neurons in several brain regions, where they inhibit glutamate release (4). In concert with this well-established neuromodulatory function, the CB 1 receptor protects neurons in many different animal models of acute brain damage and chronic neurodegeneration, which, during recent years, has raised hope about the possible clinical use of cannabinoids as neuroprotective drugs, especially in still unexplored conditions such as Alzheimer's disease, Huntington disease (HD), amyotrophic lateral sclerosis, and stroke (5-7). However, the assessment of the physiological relevance and therapeutic potential of the CB 1 receptor in neurological diseases is hampered, at least in part, by the lack o...

Background and purpose: Evidence indicates that the endocannabinoid, 2-arachidonoylglycerol (2-AG), increases food intake when injected into the nucleus accumbens shell (NAcS), thereby potentially activating hypothalamic nuclei involved in food intake regulation. We aimed to evaluate potential orexigenic effects of the endocannabinoid anandamide and of AA5HT, a fatty acid amide hydrolase (FAAH) inhibitor, and OMDM-1, an inhibitor of anandamide uptake, injected in the NAcS, as well as the effect of these treatments on activation of hypothalamic nuclei. Experimental approach: Drugs were given into the NAcS of rats and food intake quantified during the next 4 h. In other groups, after the same treatments the brains were processed for c-Fos immunohistochemistry with focus on hypothalamic nuclei. Additional groups were used to quantify endocannabinoid levels in the nucleus accumbens and the hypothalamus after AA5HT and OMDM-1 intra-NAcS injections. Key results. Our results indicate that the above treatments stimulate food intake during 4 h post-injection. They also increase c-Fos immunoreactivity in hypothalamic nuclei. The CB 1 antagonist, AM251, blocked these effects. Finally, we found elevated levels of 2-AG, but not anandamide, after intra-NAcS injections of AA5HT. Conclusions and implications: These data support the involvement of the endocannabinoid system in feeding behavior at the level of the NAcS and hypothalamus. In addition, this is the first experimental demonstration that the pharmacological inhibition of endocannabinoid inactivation in the NAcS stimulates food intake, suggesting that the endocannabinoid degrading proteins can be a target for treating eating disorders.

Complex interactions between periphery and the brain regulate food intake in mammals. Cannabinoid type-1 (CB 1 ) receptor antagonists are potent hypophagic agents, but the sites where this acute action is exerted and the underlying mechanisms are not fully elucidated. To dissect the mechanisms underlying the hypophagic effect of CB 1 receptor blockade, we combined the acute injection of the CB 1 receptor antagonist rimonabant with the use of conditional CB 1 -knockout mice, as well as with pharmacological modulation of different central and peripheral circuits. Fasting/refeeding experiments revealed that CB 1 receptor signaling in many specific brain neurons is dispensable for the acute hypophagic effects of rimonabant. CB 1 receptor antagonist-induced hypophagia was fully abolished by peripheral blockade of β-adrenergic transmission, suggesting that this effect is mediated by increased activity of the sympathetic nervous system. Consistently, we found that rimonabant increases gastrointestinal metabolism via increased peripheral β-adrenergic receptor signaling in peripheral organs, including the gastrointestinal tract. Blockade of both visceral afferents and glutamatergic transmission in the nucleus tractus solitarii abolished rimonabant-induced hypophagia. Importantly, these mechanisms were specifically triggered by lipid-deprivation, revealing a nutrientspecific component acutely regulated by CB 1 receptor blockade. Finally, peripheral blockade of sympathetic neurotransmission also blunted central effects of CB 1 receptor blockade, such as fear responses and anxiety-like behaviors. These data demonstrate that, independently of their site of origin, important effects of CB 1 receptor blockade are expressed via activation of peripheral sympathetic activity. Thus, CB 1 receptors modulate bidirectional circuits between the periphery and the brain to regulate feeding and other behaviors.fear and anxiety | sympathetic system

To maximize their chances of survival, animals need to rapidly and efficiently respond to aversive situations. These responses can be classified as active or passive and depend on the specific nature of threats, but also on individual fear coping styles. In this study, we show that the control of excitatory and inhibitory brain neurons by type-1 cannabinoid (CB 1 ) receptors is a key determinant of fear coping strategies in mice. In classical fear conditioning, a switch between initially predominant passive fear responses (freezing) and active behaviors (escape attempts and risk assessment) develops over time. Constitutive genetic deletion of CB 1 receptors in CB 1 Ϫ/Ϫ mice disrupted this pattern by favoring passive responses. This phenotype can be ascribed to endocannabinoid control of excitatory neurons, because it was reproduced in conditional mutant mice lacking CB 1 receptors from cortical glutamatergic neurons. CB 1 receptor deletion from GABAergic brain neurons led to the opposite phenotype, characterized by the predominance of active coping. The CB 1 receptor agonist ⌬ 9 -tetrahydrocannabinol exerted a biphasic control of fear coping strategies, with lower and higher doses favoring active and passive responses, respectively. Finally, viral re-expression of CB 1 receptors in the amygdala of CB 1 Ϫ/Ϫ mice restored the normal switch between the two coping strategies. These data strongly suggest that CB 1 receptor signaling bimodally controls the spontaneous adoption of active or passive coping strategies in individuals. This primary function of the endocannabinoid system in shaping individual behavioral traits should be considered when studying the mechanisms of physiological and pathological fear.