Abstract:
BACKGROUND: Hyperlocomotion induced by psychotomimetic agents is considered a proxy for positive psychotic-like symptoms and is used in antipsychotic drug screenings with rodents. Cannabinoids are psychotomimetic drugs in humans, and low doses of cannabinoid CB(1) receptor (CB1R) agonists induce hyperlocomotion in rodents. However, the cellular and molecular mechanisms underlying this effect remain unexplored so far. METHODS: We used a combination of pharmacological and genetic manipulations in cultured cells and adult male mouse models, together with an intracellular signaling detection method. Our multidisciplinary approach included locomotor activity (n = 10-12 mice/group), alphaLISA technology (n = 4-12 mice/group), transfection of the beta-arrestin 1 protein in STHdh (Q7/Q7) cells (n = 4-6/group) and a viral strategy in transgenic lines to selectively block GSK-3beta (glycogen synthase kinase-3beta) phosphorylation (n = 8-10 mice/group). We also used fluorescence in situ hybridization, real-time quantitative and droplet digital polymerase chain reaction, and tandem mass spectrometry. RESULTS: We showed that the hyperlocomotion induced by a low dose (0.3 mg/kg) of cannabinoid Delta(9)-tetrahydrocannabinol depends on the activation of plasma membrane CB1R located on dopamine D(2) receptor-positive striatopallidal projecting neurons. This activation regulates the beta-arrestin 1/Akt/GSK-3beta signaling pathway, which is required for the hyperlocomotor effect. The signaling-specific CB1R inhibitors, pregnenolone and its clinically developed analog, AEF0117, prevent GSK-3beta-dependent psychomotor stimulation induced by THC. CONCLUSIONS: This work highlights an intracellular mechanism of CB1R expressed by a selective key neuronal pathway mediating the psychotomimetic effect of THC and, by extension, low-dose cannabis consumption. This discovery will likely aid the development of unprecedented therapeutic modalities for the treatment of psychotic conditions.

Abstract:
Many brain disorders involve mitochondrial alterations, but owing to the lack of suitable tools, the causal role of mitochondrial dysfunction in pathophysiological processes is difficult to establish. Heterotrimeric guanine nucleotide-binding (G) proteins are key regulators of cell functions, and they can be found within mitochondria. Therefore, we reasoned that the activation of stimulatory mitochondrial G proteins (G(s)) could rapidly promote the activity of the organelle and possibly compensate for bioenergetic dysfunction. Here, we show that a mitochondria-targeted recombinant designer receptor exclusively activated by designer drugs (mitoDREADD-G(s)) can acutely trigger intramitochondrial signaling to increase mitochondrial membrane potential and oxygen consumption. In vivo activation of mitoDREADD-G(s) abolished memory alterations in cannabinoid-treated mice and in two mouse models of Alzheimer's disease and frontotemporal dementia. Thus, mitoDREADD-G(s) enables the establishment of causal relationships between mitochondria and biological or disease-related processes and represents an innovative potential therapeutic approach for disorders associated with mitochondrial impairment.

Abstract:
The Nucleus Accumbens (NAc) is a critical brain region for the effects of psychostimulant drugs. Type-1 cannabinoid receptors (CB(1)), the main elements of the endocannabinoid system (ECS) in the brain, participate in these effects and modulate synaptic functions in the NAc. Besides their neuronal expression, CB(1) receptors are also present in astrocytes, where they contribute to the regulation of synaptic plasticity and behavior. However, the impact of astroglial CB(1) receptors on synaptic plasticity in the NAc and on psychostimulant-induced synaptic and behavioral effects is currently unknown. This study shows that the psychostimulant amphetamine impairs a form of astroglial CB(1) receptor-dependent synaptic plasticity in the NAc of male, but not female mice. Consistently, locomotor effects of amphetamine require astroglial CB(1) receptors in male, but not female mice. These results, by revealing unforeseen mechanisms underlying sex-dependent effects of amphetamine, pave the way to a better understanding of the diverse impact of psychostimulants in women and men.

Abstract:
Repeated exposure to psychostimulants, such as amphetamine, causes a long-lasting enhancement in the behavioral responses to the drug, called behavioral sensitization.(1) This phenomenon involves several neuronal systems and brain areas, among which the dorsal striatum plays a key role.(2) The endocannabinoid system (ECS) has been proposed to participate in this effect, but the neuronal basis of this interaction has not been investigated.(3) In the CNS, the ECS exerts its functions mainly acting through the cannabinoid type-1 (CB(1)) receptor, which is highly expressed at terminals of striatal medium spiny neurons (MSNs) belonging to both the direct and indirect pathways.(4) In this study, we show that, although striatal CB(1) receptors are not involved in the acute response to amphetamine, the behavioral sensitization and related synaptic changes require the activation of CB(1) receptors specifically located at striatopallidal MSNs (indirect pathway). These results highlight a new mechanism of psychostimulant sensitization, a phenomenon that plays a key role in the health-threatening effects of these drugs.

Abstract:
Recent advances in neuroscience have positioned brain circuits as key units in controlling behavior, implying that their positive or negative modulation necessarily leads to specific behavioral outcomes. However, emerging evidence suggests that the activation or inhibition of specific brain circuits can actually produce multimodal behavioral outcomes. This study shows that activation of a receptor at different subcellular locations in the same neuronal circuit can determine distinct behaviors. Pharmacological activation of type 1 cannabinoid (CB1) receptors in the striatonigral circuit elicits both antinociception and catalepsy in mice. The decrease in nociception depends on the activation of plasma membrane-residing CB1 receptors (pmCB1), leading to the inhibition of cytosolic PKA activity and substance P release. By contrast, mitochondrial-associated CB1 receptors (mtCB1) located at the same terminals mediate cannabinoid-induced catalepsy through the decrease in intra-mitochondrial PKA-dependent cellular respiration and synaptic transmission. Thus, subcellular-specific CB1 receptor signaling within striatonigral circuits determines multimodal control of behavior.

Abstract:
The recreational and medical use of cannabis is largely increasing worldwide. Cannabis use, however, can cause adverse side effects, so conducting innovative studies aimed to understand and potentially reduce cannabis-evoked harms is important. Previous research conducted on cultured neural cells had supported that CNR1/CB1R (cannabinoid receptor 1), the main molecular target of cannabis, affects macroautophagy/autophagy. However, it was not known whether CNR1 controls autophagy in the brain in vivo, and, eventually, what the functional consequences of a potential CNR1-autophagy connection could be. We have now found that Delta(9)-tetrahydrocannabinol (THC), the major intoxicating constituent of cannabis, impairs autophagy in the mouse striatum. Administration of autophagy activators (specifically, the rapalog temsirolimus and the disaccharide trehalose) rescues THC-induced autophagy inhibition and motor dyscoordination. The combination of various genetic strategies in vivo supports the idea that CNR1 molecules located on neurons belonging to the direct (striatonigral) pathway are required for the autophagy- and motor-impairing activity of THC. By identifying autophagy as a mechanistic link between THC and motor performance, our findings may open a new conceptual view on how cannabis acts in the brain.

Abstract:
The use of cannabis is rapidly expanding worldwide. Thus, innovative studies aimed to identify, understand and potentially reduce cannabis-evoked harms are warranted. Here, we found that Delta(9)-tetrahydrocannabinol, the psychoactive ingredient of cannabis, disrupts autophagy selectively in the striatum, a brain area that controls motor behavior, both in vitro and in vivo. Boosting autophagy, either pharmacologically (with temsirolimus) or by dietary intervention (with trehalose), rescued the Delta(9)-tetrahydrocannabinol-induced impairment of motor coordination in mice. The combination of conditional knockout mouse models and viral vector-mediated autophagy-modulating strategies in vivo showed that cannabinoid CB1 receptors located on neurons belonging to the direct (striatonigral) pathway are required for the motor-impairing activity of Delta(9)-tetrahydrocannabinol by inhibiting local autophagy. Taken together, these findings identify inhibition of autophagy as an unprecedented mechanistic link between cannabinoids and motor performance, and suggest that activators of autophagy might be considered as potential therapeutic tools to treat specific cannabinoid-evoked behavioral alterations.