Abstract:
To survive, animals must constantly balance the need to obtain food with the need to avoid danger. Feeding is essential, yet perceived danger shifts priority toward safety and transiently suppresses food intake, even when organisms are hungry. Hypothalamic pro-opiomelanocortin (POMC) neurons align metabolic outputs with energy demands and control feeding. However, the role of POMC neurons in determining the trade-off between feeding and threat responses remains unclear. Here, fasted mice are exposed to a fear-conditioning paradigm to examine how POMC neurons influence the choice between feeding and defensive behaviors. Behavioral analyses combined with chemogenetic, neuroanatomical, and molecular approaches show that activation of POMC neurons suppresses feeding during a learned threat and it is associated with corticotropin releasing hormone (CRH) neuron-dependent activation of the hypothalamic-pituitary-adrenal (HPA) axis. These effects require cannabinoid type 1 receptor (CB1R) signaling in POMC neurons, uncovering a POMC-CB1R pathway that tunes behavioral flexibility under a perceived threat. Collectively, the data identify POMC neurons as key integrators of metabolic and stress signals that bias decision making between feeding and threat-avoidance behaviors.

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:
The insular cortex, or insula, is a large brain region involved in the detection of thirst and the regulation of water intake. However, our understanding of the topographical, circuit, and molecular mechanisms for controlling water intake within the insula remains parcellated. We found that type-1 cannabinoid (CB(1)) receptors in the insular cortex cells participate in the regulation of water intake and deconstructed the circuit mechanisms of this control. Topographically, we revealed that the activity of excitatory neurons in both the anterior insula (aIC) and posterior insula (pIC) increases in response to water intake, yet only the specific removal of CB(1) receptors in the pIC decreases water intake. Interestingly, we found that CB(1) receptors are highly expressed in insula projections to the basolateral amygdala (BLA), while undetectable in the neighboring central part of the amygdala. Thus, we recorded the neurons of the aIC or pIC targeting the BLA (aIC-BLA and pIC-BLA) and found that they decreased their activity upon water drinking. Additionally, chemogenetic activation of pIC-BLA projection neurons decreased water intake. Finally, we uncovered CB(1)-dependent short-term synaptic plasticity (depolarization-induced suppression of excitation [DSE]) selectively in pIC-BLA, compared with aIC-BLA synapses. Altogether, our results support a model where CB(1) receptor signaling promotes water intake by inhibiting the pIC-BLA pathway, thereby contributing to the fine top-down control of thirst responses.

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:
The unfolded protein response (UPR), which comprises three branches: PERK, ATF6alpha, and IRE1, is a major mechanism for maintaining cellular proteostasis. Many studies show that the UPR is a major player in regulating neuron viability and function in various neurodegenerative diseases; however, its role in neurodegeneration is highly controversial. Moreover, while evidence suggests activation of the UPR in neurons under normal conditions, deficiency of individual branches of the UPR has no major effect on brain neurons in animals. It remains unclear whether or how the UPR participates in regulating neuronal proteostasis under normal and disease conditions. To determine the physiological role of the UPR in neurons, we generated mice with double deletion of PERK and ATF6alpha in neurons. We found that inactivation of PERK and ATF6alpha in neurons caused lysosomal dysfunction (as evidenced by decreased expression of the V0a1 subunit of v-ATPase and decreased activation of cathepsin D), impairment of autophagic flux (as evidenced by increased ratio of LC3-II/LC3-I and increased p62 level), and accumulation of p-tau and Abeta42 in the hippocampus, and led to impairment of spatial memory, impairment of hippocampal LTP, and hippocampal degeneration in adult mice. These results suggest that the UPR is required for maintaining neuronal proteostasis (particularly tau and Abeta homeostasis) and the viability and function of neurons in the hippocampus of adult mice.

Abstract:

Abstract:
alpha-Synuclein is a major component of Lewy bodies (LB) and Lewy neurites (LN) appearing in the postmortem brain of Parkinson's disease (PD) and other alpha-synucleinopathies. While most studies of alpha-synucleinopathies have focused on neuronal and synaptic alterations as well as dysfunctions of the astrocytic homeostatic roles, whether the bidirectional astrocyte-neuronal communication is affected in these diseases remains unknown. We have investigated whether the astrocyte Ca(2+) excitability and the glutamatergic gliotransmission underlying astrocyte-neuronal signaling are altered in several transgenic mouse models related to alpha-synucleinopathies, i.e., mice expressing high and low levels of the human A53T mutant alpha-synuclein (G2-3 and H5 mice, respectively) globally or selectively in neurons (iSyn mice), mice expressing human wildtype alpha-synuclein (I2-2 mice), and mice expressing A30P mutant alpha-synuclein (O2 mice). Combining astrocytic Ca(2+) imaging and neuronal electrophysiological recordings in hippocampal slices of these mice, we have found that compared to non-transgenic mice, astrocytes in G2-3 mice at different ages (1-6 months) displayed a Ca(2+) hyperexcitability that was independent of neurotransmitter receptor activation, suggesting that the expression of alpha-synuclein mutant A53T altered the intrinsic properties of astrocytes. Similar dysregulation of the astrocyte Ca(2+) signal was present in H5 mice, but not in I2-2 and O2 mice, indicating alpha-synuclein mutant-specific effects. Moreover, astrocyte Ca(2+) hyperexcitability was absent in mice expressing the alpha-synuclein mutant A53T selectively in neurons, indicating that the effects on astrocytes were cell-autonomous. Consistent with these effects, glutamatergic gliotransmission was enhanced in G2-3 and H5 mice, but was unaffected in I2-2, O2 and iSyn mice. These results indicate a cell-autonomous effect of pathogenic A53T expression in astrocytes that may contribute to the altered neuronal and synaptic function observed in alpha-synucleinopathies.

Abstract:

Abstract:
Nitric oxide (NO) is a fascinating signalling molecule implicated in a plethora of biological functions, especially at the synaptic level. Exploring neurotransmission in the hippocampus could be instrumental in the individuation of putative targets for nitric-oxide mediated neuromodulation, especially in terms of the potential repercussions on fundamental processes i.e. synaptic plasticity and excitability-related phenomena. Among these targets, endovanilloid signalling constitutes an object of study since Transient Receptors Vanilloid type 1 (TRPV1) channels possess a NO-sensitive gate modulating its activation. Also, NO has been referred to as a mediator for numerous endocannabinoid effects. Notwithstanding, the linkage between TRPV1 and NO systems in neuromodulation still remains elusive. To this end, we aim at investigating the involvement of TRPV1 in nitric oxide-mediated influence on hippocampal processes. Electrophysiological whole-cell recordings in CA1 pyramidal neurons were applied to evaluate excitatory neurotransmission in rat brain slices. Indeed, miniature excitatory postsynaptic currents (mEPSCs) were analysed upon pharmacological manipulation of TRPV1 and NO signalling pathways. In detail, only the administration of the specific TRPV1 exogenous agonist - capsaicin - reduced the frequency and amplitude of mEPSC similarly to the inhibitor of neuronal nitric oxide synthase (nNOS), 7-nitroindazole (7NI). In contrast, capsazepine, TRPV1 antagonist, does not influence excitatory transmission. The combined TRPV1 activation and nNOS blockade confirm the presence of a putative common mechanism. When we administered the endovanilloid-endocannabinoid ligand, i.e. anandamide, we unveiled a potentiation of neurotransmission that was selectively reverted by 7NI. Our data suggest that nitric oxide influences TRPV1 hippocampal signalling since these channels are not constitutively active, but can be 'on-demand' activated to modulate excitation in CA1 pyramidal neurons, and that this effect is linked to nitric oxide production.

Abstract:
Intracellular calcium signaling underlies the astroglial control of synaptic transmission and plasticity. Mitochondria-endoplasmic reticulum contacts (MERCs) are key determinants of calcium dynamics, but their functional impact on astroglial regulation of brain information processing is unexplored. We found that the activation of astrocyte mitochondrial-associated type-1 cannabinoid (mtCB(1)) receptors determines MERC-dependent intracellular calcium signaling and synaptic integration. The stimulation of mtCB(1) receptors promotes calcium transfer from the endoplasmic reticulum to mitochondria through a specific molecular cascade, involving the mitochondrial calcium uniporter (MCU). Physiologically, mtCB(1)-dependent mitochondrial calcium uptake determines the dynamics of cytosolic calcium events in astrocytes upon endocannabinoid mobilization. Accordingly, electrophysiological recordings in hippocampal slices showed that conditional genetic exclusion of mtCB(1) receptors or dominant-negative MCU expression in astrocytes blocks lateral synaptic potentiation, through which astrocytes integrate the activity of distant synapses. Altogether, these data reveal an endocannabinoid link between astroglial MERCs and the regulation of brain network functions.