Synaptic mechanisms underlying onset and progression of memory deficits caused by hippocampal and midbrain synucleinopathy.

Cognitive deficits, including working memory, and visuospatial deficits are common and debilitating in Parkinson's disease. α-synucleinopathy in the hippocampus and cortex is considered as the major risk factor. However, little is known about the progression and specific synaptic mechanisms underlying the memory deficits induced by α-synucleinopathy. Here, we tested the hypothesis that pathologic α-Synuclein (α-Syn), initiated in different brain regions, leads to distinct onset and progression of the pathology. We report that overexpression of human α-Syn in the murine mesencephalon leads to late onset memory impairment and sensorimotor deficits accompanied by reduced dopamine D1 expression in the hippocampus. In contrast, human α-Syn overexpression in the hippocampus leads to early memory impairment, altered synaptic transmission and plasticity, and decreased expression of GluA1 AMPA-type glutamate receptors. These findings identify the synaptic mechanisms leading to memory impairment induced by hippocampal α-synucleinopathy and provide functional evidence of the major neuronal networks involved in disease progression.

Chronic adolescent exposure to cannabis in mice leads to sex-biased changes in gene expression networks across brain regions.

During adolescence, frequent and heavy cannabis use can lead to serious adverse health effects and cannabis use disorder (CUD). Rodent models of adolescent exposure to the main psychoactive component of cannabis, delta-9-tetrahydrocannabinol (THC), mimic the behavioral alterations observed in adolescent users. However, the underlying molecular mechanisms remain largely unknown. Here, we treated female and male C57BL6/N mice with high doses of THC during early adolescence and assessed their memory and social behaviors in late adolescence. We then profiled the transcriptome of five brain regions involved in cognitive and addiction-related processes. We applied gene coexpression network analysis and identified gene coexpression modules, termed cognitive modules, that simultaneously correlated with THC treatment and memory traits reduced by THC. The cognitive modules were related to endocannabinoid signaling in the female dorsal medial striatum, inflammation in the female ventral tegmental area, and synaptic transmission in the male nucleus accumbens. Moreover, cross-brain region module-module interaction networks uncovered intra- and inter-region molecular circuitries influenced by THC. Lastly, we identified key driver genes of gene networks associated with THC in mice and genetic susceptibility to CUD in humans. This analysis revealed a common regulatory mechanism linked to CUD vulnerability in the nucleus accumbens of females and males, which shared four key drivers (Hapln4, Kcnc1, Elavl2, Zcchc12). These genes regulate transcriptional subnetworks implicated in addiction processes, synaptic transmission, brain development, and lipid metabolism. Our study provides novel insights into disease mechanisms regulated by adolescent exposure to THC in a sex- and brain region-specific manner.

Reelin deficiency exacerbates cocaine-induced hyperlocomotion by enhancing neuronal activity in the dorsomedial striatum.

The Reln gene encodes for the extracellular glycoprotein Reelin, which regulates several brain functions from development to adulthood, including neuronal migration, dendritic growth and branching and synapse formation and plasticity. Human studies have implicated Reelin signaling in several neurodevelopmental and psychiatric disorders. Mouse studies using the heterozygous Reeler (HR) mice have shown that reduced levels of Reln expression are associated with deficits in learning and memory and increased disinhibition. Although these traits are relevant to substance use disorders, the role of Reelin in cellular and behavioral responses to addictive drugs remains largely unknown. Here, we compared HR mice to wild-type (WT) littermate controls to investigate whether Reelin signaling contributes to the hyperlocomotor and rewarding effects of cocaine. After a single or repeated cocaine injections, HR mice showed enhanced cocaine-induced locomotor activity compared with WT controls. This effect persisted after withdrawal. In contrast, Reelin deficiency did not induce cocaine sensitization, and did not affect the rewarding effects of cocaine measured in the conditioned place preference assay. The elevated cocaine-induced hyperlocomotion in HR mice was associated with increased protein Fos expression in the dorsal medial striatum (DMS) compared with WT. Lastly, we performed an RNA fluorescent in situ hybridization experiment and found that Reln was highly co-expressed with the Drd1 gene, which encodes for the dopamine receptor D1, in the DMS. These findings show that Reelin signaling contributes to the locomotor effects of cocaine and improve our understanding of the neurobiological mechanisms underlying the cellular and behavioral effects of cocaine.

RNA binding protein DDX5 directs tuft cell specification and function to regulate microbial repertoire and disease susceptibility in the intestine.

OBJECTIVE: Tuft cells residing in the intestinal epithelium have diverse functions. In the small intestine, they provide protection against inflammation, combat against helminth and protist infections, and serve as entry portals for enteroviruses. In the colon, they had been implicated in tumourigenesis. Commitment of intestinal progenitor cells to the tuft cell lineage requires Rho GTPase Cell Division Cycle 42 (CDC42), a Rho GTPase that acts downstream of the epidermal growth factor receptor and wingless-related integration site signalling cascades, and the master transcription factor POU class 2 homeobox 3 (POU2F3). This study investigates how this pathway is regulated by the DEAD box containing RNA binding protein DDX5 in vivo. DESIGN: We assessed the role of DDX5 in tuft cell specification and function in control and epithelial cell-specific Ddx5 knockout mice (DDX5ΔIEC) using transcriptomic approaches. RESULTS: DDX5ΔIEC mice harboured a loss of intestinal tuft cell populations, modified microbial repertoire, and altered susceptibilities to ileal inflammation and colonic tumourigenesis. Mechanistically, DDX5 promotes CDC42 protein synthesis through a post-transcriptional mechanism to license tuft cell specification. Importantly, the DDX5-CDC42 axis is parallel but distinct from the known interleukin-13 circuit implicated in tuft cell hyperplasia, and both pathways augment Pou2f3 expression in secretory lineage progenitors. In mature tuft cells, DDX5 not only promotes integrin signalling and microbial responses, it also represses gene programmes involved in membrane transport and lipid metabolism. CONCLUSION: RNA binding protein DDX5 directs tuft cell specification and function to regulate microbial repertoire and disease susceptibility in the intestine.

Reelin deficiency contributes to long-term behavioral abnormalities induced by chronic adolescent exposure to Δ9-tetrahydrocannabinol in mice.

Cannabis use is widespread among adolescents and has been associated with long-term negative outcomes on neurocognitive functions. However, the factors that contribute to the long-term detrimental effects of cannabis use remain poorly understood. Here, we studied how Reelin deficiency influences the behavior of mice exposed to cannabis during adolescence. Reelin is a gene implicated in the development of the brain and of psychiatric disorders. To this aim, heterozygous Reeler (HR) mice, that express reduced level of Reelin, were chronically injected during adolescence with high doses (10 mg/kg) of Δ9-tetrahydrocannabinol (THC), a major psychoactive component of cannabis. Two weeks after the last injection of THC, mice were tested with multiple behavioral assays, including working memory, social interaction, locomotor activity, anxiety-like responses, stress reactivity, and pre-pulse inhibition. Compared to wild-type (WT), HR mice treated with THC showed impaired social behaviors, elevated disinhibitory phenotypes and increased reactivity to aversive situations, in a sex-specific manner. Overall, these findings show that Reelin deficiency influences behavioral abnormalities caused by heavy consumption of THC during adolescence and suggest that elucidating Reelin signaling will improve our understanding of neurobiological mechanisms underlying behavioral traits relevant to the development of psychiatric conditions.

A cell type-specific expression map of NCoR1 and SMRT transcriptional co-repressors in the mouse brain.

The ability to rapidly change gene expression patterns is essential for differentiation, development, and functioning of the brain. Throughout development, or in response to environmental stimuli, gene expression patterns are tightly regulated by the dynamic interplay between transcription activators and repressors. Nuclear receptor corepressor 1 (NCoR1) and silencing mediator for retinoid or thyroid-hormone receptors (SMRT) are the best characterized transcriptional co-repressors from a molecular point of view. They mediate epigenetic silencing of gene expression in a wide range of developmental and homeostatic processes in many tissues, including the brain. For instance, NCoR1 and SMRT regulate neuronal stem cell proliferation and differentiation during brain development and they have been implicated in learning and memory. However, we still have a limited understanding of their regional and cell type-specific expression in the brain. In this study, we used fluorescent immunohistochemistry to map their expression patterns throughout the adult mouse brain. Our findings reveal that NCoR1 and SMRT share an overall neuroanatomical distribution, and are detected in both excitatory and inhibitory neurons. However, we observed striking differences in their cell type-specific expression in glial cells. Specifically, all oligodendrocytes express NCoR1, but only a subset express SMRT. In addition, NCoR1, but not SMRT, was detected in a subset of astrocytes and in the microglia. These novel observations are corroborated by single cell transcriptomics and emphasize how NCoR1 and SMRT may contribute to distinct biological functions, suggesting an exclusive role of NCoR1 in innate immune responses in the brain.

Motor learning and metaplasticity in striatal neurons: relevance for Parkinson's disease.

Nigro-striatal dopamine transmission is central to a wide range of neuronal functions, including skill learning, which is disrupted in several pathologies such as Parkinson's disease. The synaptic plasticity mechanisms, by which initial motor learning is stored for long time periods in striatal neurons, to then be gradually optimized upon subsequent training, remain unexplored. Addressing this issue is crucial to identify the synaptic and molecular mechanisms involved in striatal-dependent learning impairment in Parkinson's disease. In this study, we took advantage of interindividual differences between outbred rodents in reaching plateau performance in the rotarod incremental motor learning protocol, to study striatal synaptic plasticity ex vivo. We then assessed how this process is modulated by dopamine receptors and the dopamine active transporter, and whether it is impaired by overexpression of human α-synuclein in the mesencephalon; the latter is a progressive animal model of Parkinson's disease. We found that the initial acquisition of motor learning induced a dopamine active transporter and D1 receptors mediated long-term potentiation, under a protocol of long-term depression in striatal medium spiny neurons. This effect disappeared in animals reaching performance plateau. Overexpression of human α-synuclein reduced striatal dopamine active transporter levels, impaired motor learning, and prevented the learning-induced long-term potentiation, before the appearance of dopamine neuronal loss. Our findings provide evidence of a reorganization of cellular plasticity within the dorsolateral striatum that is mediated by dopamine receptors and dopamine active transporter during the acquisition of a skill. This newly identified mechanism of cellular memory is a form of metaplasticity that is disrupted in the early stage of synucleinopathies, such as Parkinson's disease, and that might be relevant for other striatal pathologies, such as drug abuse.

Information content of dendritic spines after motor learning.

Dendritic spines, small protrusions emerging from the dendrites of most excitatory synapses in the mammalian brain, are highly dynamic structures and their shape and number is continuously modulated by memory formation and other adaptive changes of the brain. In this study, using a behavioral paradigm of motor learning, we applied the non-linear analysis of dendritic spines to study spine complexity along dendrites of cortical and subcortical neural systems, such as the basal ganglia, that sustain important motor learning processes. We show that, after learning, the spine organization has greater complexity, as indexed by the maximum Lyapunov exponent (LyE). The positive value of the exponent demonstrates that the system is chaotic, while recurrence plots show that the system is not simply composed by random noise, but displays quasi-periodic behavior. The increase in the maximum LyE and in the system entropy after learning was confirmed by the modification of the reconstructed trajectories in phase-space. Our results suggest that the remodeling of spines, as a result of a chaotic and non-random dynamical process along dendrites, may be a general feature associated with the structural plasticity underlying processes such as long-term memory maintenance. Furthermore, this work indicates that the non-linear method is a very useful tool to allow the detection of subtle stimulus-induced changes in dendritic spine dynamics, giving a key contribution to the study of the relationship between structure and function of spines.

Pituitary adenylate cyclase-activating polypeptide (PACAP) in the central nucleus of the amygdala induces anxiety via melanocortin receptors.

RATIONALE: Anxiety disorders are the most common mental disorders in the USA. Characterized by feelings of uncontrollable apprehension, they are accompanied by physical, affective, and behavioral symptoms. The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor PAC1 (PAC1R) are highly expressed in the central nucleus of the amygdala (CeA), and they have gained growing attention for their proposed role in mediating the body's response to stress. OBJECTIVES: The aim of this study was to evaluate the anxiogenic effects of PACAP in the CeA and its effects on the hypothalamic-pituitary-adrenal (HPA) axis. Furthermore, the mechanism of action of PACAP in the CeA was investigated. METHODS: PACAP was microinfused into the CeA of rats, and its effects in the elevated plus maze (EPM), the defensive withdrawal tests, and plasma corticosterone levels were evaluated. The ability of the melanocortin receptor antagonist SHU9119 to block PACAP effect in the EPM was assessed. RESULTS: Intra-CeA PACAP exerted a dose-dependent anxiogenic effect and activated the HPA axis. In contrast, PACAP microinfused into the basolateral nucleus of the amygdala (BlA) had no effect. Finally, the anxiogenic effect of intra-CeA PACAP was prevented by SHU9119. CONCLUSIONS: These data prove an anxiogenic role for the PACAP system of the CeA and reveal that the melanocortin receptor 4 (MC4R) system of CeA mediates these effects. Our data provide insights into this neuropeptide system as a mechanism for modulating the behavioral and endocrine response to stress and suggest that dysregulations of this system may contribute to the pathophysiology of anxiety-related disorders.

Pituitary Adenylate Cyclase-Activating Peptide in the Central Amygdala Causes Anorexia and Body Weight Loss via the Melanocortin and the TrkB Systems.

Growing evidence suggests that the pituitary adenylate cyclase-activating polypeptide (PACAP)/PAC1 receptor system represents one of the main regulators of the behavioral, endocrine, and autonomic responses to stress. Although induction of anorexia is a well-documented effect of PACAP, the central sites underlying this phenomenon are poorly understood. The present studies addressed this question by examining the neuroanatomical, behavioral, and pharmacological mechanisms mediating the anorexia produced by PACAP in the central nucleus of the amygdala (CeA), a limbic structure implicated in the emotional components of ingestive behavior. Male rats were microinfused with PACAP (0-1 µg per rat) into the CeA and home-cage food intake, body weight change, microstructural analysis of food intake, and locomotor activity were assessed. Intra-CeA (but not intra-basolateral amygdala) PACAP dose-dependently induced anorexia and body weight loss without affecting locomotor activity. PACAP-treated rats ate smaller meals of normal duration, revealing that PACAP slowed feeding within meals by decreasing the regularity and maintenance of feeding from pellet-to-pellet; postprandial satiety was unaffected. Intra-CeA PACAP-induced anorexia was blocked by coinfusion of either the melanocortin receptor 3/4 antagonist SHU 9119 or the tyrosine kinase B (TrKB) inhibitor k-252a, but not the CRF receptor antagonist D-Phe-CRF(12-41). These results indicate that the CeA is one of the brain areas through which the PACAP system promotes anorexia and that PACAP preferentially lessens the maintenance of feeding in rats, effects opposite to those of palatable food. We also demonstrate that PACAP in the CeA exerts its anorectic effects via local melanocortin and the TrKB systems, and independently from CRF.