The endocannabinoid transport inhibitor AM404 differentially modulates recognition memory in rats depending on environmental aversiveness

Cannabinoid compounds may influence both emotional and cognitive processes depending on the level of environmental aversiveness at the time of drug administration. However, the mechanisms responsible for these responses remain to be elucidated. The present experiments investigated the effects induced by the endocannabinoid transport inhibitor AM404 (0.5–5 mg/kg, i.p.) on both emotional and cognitive performances of rats tested in a Spatial Open Field task and subjected to different experimental settings, named High Arousal (HA) and Low Arousal (LA) conditions. The two different experimental conditions influenced emotional reactivity independently of drug administration. Indeed, vehicle-treated rats exposed to the LA condition spent more time in the center of the arena than vehicle-treated rats exposed to the HA context. Conversely, the different arousal conditions did not affect the cognitive performances of vehicle-treated animals such as the capability to discriminate a spatial displacement of the objects or an object substitution. AM404 administration did not alter locomotor activity or emotional behavior of animals exposed to both environmental conditions. Interestingly, AM404 administration influenced the cognitive parameters depending on the level of emotional arousal: it impaired the capability of rats exposed to the HA condition to recognize a novel object while it did not induce any impairing effect in rats exposed to the LA condition. These findings suggest that drugs enhancing endocannabinoid signaling induce different effects on recognition memory performance depending on the level of emotional arousal induced by the environmental conditions

Distinct, dosage-sensitive requirements for the autism-associated factor CHD8 during cortical development

Background: CHD8 haploinsufficiency causes autism and macrocephaly with high penetrance in the human population. Chd8 heterozygous mice exhibit relatively subtle brain overgrowth and little gene expression changes in the embryonic neocortex. The purpose of this study was to generate new, sub-haploinsufficient Chd8 mouse models to allow us to identify and study the functions of CHD8 during embryonic cortical development. Methods: To examine the possibility that certain phenotypes may only appear at sub-heterozygous Chd8 levels in the mouse, we created an allelic series of Chd8-deficient mice to reduce CHD8 protein levels to approximately 35% (mild hypomorph), 10% (severe hypomorph) and 0% (neural-specific conditional knockout) of wildtype levels. We used RNA sequencing to compare transcriptional dysregulation, structural MRI and brain weight to investigate effects on brain size, and cell proliferation, differentiation and apoptosis markers in immunostaining assays to quantify changes in neural progenitor fate. Results: Mild Chd8 hypomorphs displayed significant postnatal lethality, with surviving animals exhibiting more pronounced brain hyperplasia than heterozygotes. Over 2000 genes were dysregulated in mild hypomorphs, including autism-associated neurodevelopmental and cell cycle genes. We identify increased proliferation of non-ventricular zone TBR2+ intermediate progenitors as one potential cause of brain hyperplasia in these mutants. Severe Chd8 hypomorphs displayed even greater transcriptional dysregulation, including evidence for p53 pathway upregulation. In contrast to mild hypomorphs, these mice displayed reduced brain size and increased apoptosis in the embryonic neocortex. Homozygous, conditional deletion of Chd8 in early neuronal progenitors resulted in pronounced brain hypoplasia, partly caused by p53 target gene derepression and apoptosis in the embryonic neocortex. Limitations Our findings identify an important role for the autism-associated factor CHD8 in controlling the proliferation of intermediate progenitors in the mouse neocortex. We propose that CHD8 has a similar function in human brain development, but studies on human cells are required to confirm this. Because many of our mouse mutants with reduced CHD8 function die shortly after birth, it is not possible to fully determine to what extent reduced CHD8 function results in autism-associated behaviours in mice. Conclusions: Together, these findings identify important, dosage-sensitive functions for CHD8 in p53 pathway repression, neurodevelopmental gene expression and neural progenitor fate in the embryonic neocortex. We conclude that brain development is acutely sensitive to reduced CHD8 expression and that the varying sensitivities of different progenitor populations and cellular processes to CHD8 dosage result in non-linear effects on gene transcription and brain growth. Shaun Hurley, Conor Mohan and Philipp Suetterlin have contributed equally to this work

Haploinsufficiency of the autism-associated Shank3 gene leads to deficits in synaptic function, social interaction, and social communication

<p>Abstract</p> <p>Background</p> <p>SHANK3 is a protein in the core of the postsynaptic density (PSD) and has a critical role in recruiting many key functional elements to the PSD and to the synapse, including components of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionic acid (AMPA), metabotropic glutamate (mGlu) and <it>N</it>-methyl-D-aspartic acid (NMDA) glutamate receptors, as well as cytoskeletal elements. Loss of a functional copy of the <it>SHANK3 </it>gene leads to the neurobehavioral manifestations of 22q13 deletion syndrome and/or to autism spectrum disorders. The goal of this study was to examine the effects of haploinsufficiency of full-length <it>Shank3 </it>in mice, focusing on synaptic development, transmission and plasticity, as well as on social behaviors, as a model for understanding <it>SHANK3 </it>haploinsufficiency in humans.</p> <p>Methods</p> <p>We used mice with a targeted disruption of <it>Shank3 </it>in which exons coding for the ankyrin repeat domain were deleted and expression of full-length Shank3 was disrupted. We studied synaptic transmission and plasticity by multiple methods, including patch-clamp whole cell recording, two-photon time-lapse imaging and extracellular recordings of field excitatory postsynaptic potentials. We also studied the density of GluR1-immunoreactive puncta in the CA1 stratum radiatum and carried out assessments of social behaviors.</p> <p>Results</p> <p>In <it>Shank3 </it>heterozygous mice, there was reduced amplitude of miniature excitatory postsynaptic currents from hippocampal CA1 pyramidal neurons and the input-output (I/O) relationship at Schaffer collateral-CA1 synapses in acute hippocampal slices was significantly depressed; both of these findings indicate a reduction in basal neurotransmission. Studies with specific inhibitors demonstrated that the decrease in basal transmission reflected reduced AMPA receptor-mediated transmission. This was further supported by the observation of reduced numbers of GluR1-immunoreactive puncta in the stratum radiatum. Long-term potentiation (LTP), induced either with θ-burst pairing (TBP) or high-frequency stimulation, was impaired in <it>Shank3 </it>heterozygous mice, with no significant change in long-term depression (LTD). In concordance with the LTP results, persistent expansion of spines was observed in control mice after TBP-induced LTP; however, only transient spine expansion was observed in <it>Shank3 </it>heterozygous mice. Male <it>Shank3 </it>heterozygotes displayed less social sniffing and emitted fewer ultrasonic vocalizations during interactions with estrus female mice, as compared to wild-type littermate controls.</p> <p>Conclusions</p> <p>We documented specific deficits in synaptic function and plasticity, along with reduced reciprocal social interactions in <it>Shank3 </it>heterozygous mice. Our results are consistent with altered synaptic development and function in <it>Shank3 </it>haploinsufficiency, highlighting the importance of Shank3 in synaptic function and supporting a link between deficits in synapse function and neurodevelopmental disorders. The reduced glutamatergic transmission that we observed in the <it>Shank3 </it>heterozygous mice represents an interesting therapeutic target in <it>Shank3</it>-haploinsufficiency syndromes.</p

Neuroimaging Evidence of Major Morpho-Anatomical and Functional Abnormalities in the BTBR T+TF/J Mouse Model of Autism

BTBR T+tf/J (BTBR) mice display prominent behavioural deficits analogous to the defining symptoms of autism, a feature that has prompted a widespread use of the model in preclinical autism research. Because neuro-behavioural traits are described with respect to reference populations, multiple investigators have examined and described the behaviour of BTBR mice against that exhibited by C57BL/6J (B6), a mouse line characterised by high sociability and low self-grooming. In an attempt to probe the translational relevance of this comparison for autism research, we used Magnetic Resonance Imaging (MRI) to map in both strain multiple morpho-anatomical and functional neuroimaging readouts that have been extensively used in patient populations. Diffusion tensor tractography confirmed previous reports of callosal agenesis and lack of hippocampal commissure in BTBR mice, and revealed a concomitant rostro-caudal reorganisation of major cortical white matter bundles. Intact inter-hemispheric tracts were found in the anterior commissure, ventro-medial thalamus, and in a strain-specific white matter formation located above the third ventricle. BTBR also exhibited decreased fronto-cortical, occipital and thalamic gray matter volume and widespread reductions in cortical thickness with respect to control B6 mice. Foci of increased gray matter volume and thickness were observed in the medial prefrontal and insular cortex. Mapping of resting-state brain activity using cerebral blood volume weighted fMRI revealed reduced cortico-thalamic function together with foci of increased activity in the hypothalamus and dorsal hippocampus of BTBR mice. Collectively, our results show pronounced functional and structural abnormalities in the brain of BTBR mice with respect to control B6 mice. The large and widespread white and gray matter abnormalities observed do not appear to be representative of the neuroanatomical alterations typically observed in autistic patients. The presence of reduced fronto-cortical metabolism is of potential translational relevance, as this feature recapitulates previously-reported clinical observations

Ultrasonic vocalization in rats self-administering heroin and cocaine in different settings: evidence of substance-specific interactions between drug and setting

Rationale Clinical and preclinical evidence indicates that the setting of drug use affects drug reward in a substance-specific manner. Heroin and cocaine co-abusers, for example, indicated distinct settings for the two drugs: heroin being used preferentially at home and cocaine preferentially outside the home. Similar results were obtained in rats that were given the opportunity to self-administer intravenously both heroin and cocaine. Objectives The goal of the present study was to investigate the possibility that the positive affective state induced by cocaine is enhanced when the drug is taken at home relative to a non-home environment, and vice versa for heroin. Methods To test this hypothesis, we trained male rats to self-administer both heroin and cocaine on alternate days and simultaneously recorded the emission of ultrasonic vocalizations (USVs), as it has been reported that rats emit 50-kHz USVs when exposed to rewarding stimuli, suggesting that these USVs reflect positive affective states. Results We found that Non-Resident rats emitted more 50-kHz USVs when they self-administered cocaine than when self-administered heroin whereas Resident rats emitted more 50-kHz USVs when self-administering heroin than when self-administering cocaine. Differences in USVs in Non-Resident rats were more pronounced during the first self-administration (SA) session, when the SA chambers were completely novel to them. In contrast, the differences in USVs in Resident rats were more pronounced during the last SA sessions. Conclusion These findings indicate that the setting of drug taking exerts a substance-specific influence on the ability of drugs to induce positive affective states

Substance-specific influences of setting on drug reward: an ultrasonic vocalization study in rats self-administering heroin and cocaine.

Clinical and preclinical evidence indicate that the setting of drug use affects drug reward in a substance-specific manner (Caprioli et al. 2009; Badiani and Spagnolo 2013). When heroin and cocaine co-abusers, for example, report on the circumstances of drug use, they indicate distinct settings for the two drugs: heroin being used preferentially at home and cocaine preferentially outside the home (Caprioli et al. 2009; Badiani and Spagnolo 2013). Similar results were obtained in rats given the choice between these two drugs (Caprioli et al. 2007, 2008, 2009). Rats that live in the self-administration (SA) chambers (Resident rats) tend in fact to prefer heroin to cocaine, whereas rats that are transferred to the SA chambers only for the test sessions (Non-Resident rats) tend to prefer cocaine to heroin. The goal of this study was to investigate whether the affective value of cocaine and heroin changes as a function of the setting. It has been shown that rats emit ultrasonic vocalizations (USVs) in the range of 50-kHz when exposed to rewarding stimuli, whereas they emit 22-kHz USVs in the presence of aversive stimuli, suggesting that 50-kHz USVs reflect positive affective states (Burgdorf et al. 2000, 2001, 2008). In the present study, we recorded USVs in rats undergoing cocaine and heroin SA on alternate days. We found that Non-Resident rats emit more 50-kHz USVs when self-administering cocaine than when self-administering heroin. In contrast, Resident rats emit more 50-kHz USVs when self-administering heroin than when self-administering cocaine. These findings indicate that the setting of drug taking exert a substance-specific influence on the ability of drugs to induce a positive affective state

Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in <i>Chd8</i> Haploinsufficient Mice

Truncating CHD8 mutations are amongst the highest confidence risk factors for autism spectrum disorder (ASD) identified to date. Here, we report that Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli. Whereas gene expression in the neocortex is only mildly affected at midgestation, over 600 genes are differentially expressed in the early postnatal neocortex. Genes involved in cell adhesion and axon guidance are particularly prominent amongst the downregulated transcripts. Resting-state functional MRI identified increased synchronized activity in cortico-hippocampal and auditory-parietal networks in Chd8 heterozygous mutant mice, implicating altered connectivity as a potential mechanism underlying the behavioral phenotypes. Together, these data suggest that altered brain growth and diminished expression of important neurodevelopmental genes that regulate long-range brain wiring are followed by distinctive anomalies in functional brain connectivity in Chd8+/- mice. Human imaging studies have reported altered functional connectivity in ASD patients, with long-range under-connectivity seemingly more frequent. Our data suggest that CHD8 haploinsufficiency represents a specific subtype of ASD where neuropsychiatric symptoms are underpinned by long-range over-connectivity