SHANK3 Downregulation in the Ventral Tegmental Area Accelerates the Extinction of Contextual Associations Induced by Juvenile Non-familiar Conspecific Interaction

Haploinsufficiency of the SHANK3 gene, encoding for a scaffolding protein located in the postsynaptic density of glutamatergic synapse, has been linked to forms of autism spectrum disorders (ASDs). It has been shown that SHANK3 controls the maturation of social reward circuits in the ventral tegmental area (VTA). Whether the impairments in associative learning observed in ASD relate to SHANK3 insufficiency restricted to the reward system is still an open question. Here, we first characterize a social-conditioned place preference (CPP) paradigm based on the direct and free interaction with a juvenile and non-familiar conspecific. In both group- and single-housed C57Bl6/j late adolescence male mice, this CPP protocol promotes the formation of social-induced contextual associations that undergo extinction. Interestingly, the downregulation of Shank3 expression in the VTA altered the habituation to a non-familiar conspecific during conditioning and accelerated the extinction of social-induced conditioned responses. Thus, inspired by the literature on drugs of abuse-induced contextual learning, we propose that acquisition and extinction of CPP might be used as behavioral assays to assess social-induced contextual association and “social-seeking” dysfunctions in animal models of psychiatric disorders

Continuous representations of speed by striatal medium spiny neurons

The striatum is critical for controlling motor output. However, it remains unclear how striatal output neurons encode and facilitate movement. A prominent theory suggests that striatal units encode movements in bursts of activity near specific events, such as the start or end of actions. These bursts are theorized to gate or permit specific motor actions, thereby encoding and facilitating complex sequences of actions. An alternative theory has suggested that striatal neurons encode continuous changes in sensory or motor information with graded changes in firing rate. Supporting this theory, many striatal neurons exhibit such graded changes without bursting near specific actions. Here, we evaluated these two theories in the same recordings of mice (both male and female). We recorded single-unit and multiunit activity from the dorsomedial striatum of mice as they spontaneously explored an arena. We observed both types of encoding, although continuous encoding was more prevalent than bursting near movement initiation or termination. The majority of recorded units did not exhibit positive linear relationships with speed but instead exhibited nonlinear relationships that peaked at a range of locomotor speeds. Bulk calcium recordings of identified direct and indirect pathway neurons revealed similar speed tuning profiles, indicating that the heterogeneity in response profiles was not due to this genetic distinction. We conclude that continuous encoding of speed is a central component of movement encoding in the striatum

SHANK3 controls maturation of social reward circuits in the VTA.

Haploinsufficiency of SHANK3, encoding the synapse scaffolding protein SHANK3, leads to a highly penetrant form of autism spectrum disorder. How SHANK3 insufficiency affects specific neural circuits and how this is related to specific symptoms remains elusive. Here we used shRNA to model Shank3 insufficiency in the ventral tegmental area of mice. We identified dopamine (DA) and GABA cell-type-specific changes in excitatory synapse transmission that converge to reduce DA neuron activity and generate behavioral deficits, including impaired social preference. Administration of a positive allosteric modulator of the type 1 metabotropic glutamate receptors mGluR1 during the first postnatal week restored DA neuron excitatory synapse transmission and partially rescued the social preference defects, while optogenetic DA neuron stimulation was sufficient to enhance social preference. Collectively, these data reveal the contribution of impaired ventral tegmental area function to social behaviors and identify mGluR1 modulation during postnatal development as a potential treatment strategy

SHANK3 controls maturation of social reward circuits in the VTA

L'haploinsuffisance de SHANK3, codant la protéine d'échafaudage synaptique SHANK3, conduit à une forme hautement pénétrante des Désordres du Spectre Autistique (ASD). La manière dont l'insuffisance de SHANK3 affecte des circuits neuronaux spécifiques pour générer des symptômes liés à l'ASD demeure obscure. Nous avons utilisé ici un shRNA pour modéliser l'insuffisance de Shank3 au sein de l'Aire Tegmentale Ventrale (VTA). Nous avons identifié des changements spécifiques liés au type cellulaire, Dopaminergique (DA) et GABAergique, dans la transmission synaptique excitatrice, qui convergent pour réduire l'activité des neurones DA et générer des comportements liés à l'ASD, comprenant une détérioration de la préférence sociale. L'administration d'un modulateur allostérique positif des récepteurs métabotropiques au glutamate de type 1 (mGluR1) pendant la première semaine post-natale, a permis de restaurer la transmission excitatrice synaptique des neurones DA et les déficits liés à la préférence sociale, tandis que la stimulation optogénétique des neurones DA a été suffisante pour améliorer cette préférence. Conjointement, ces données révèlent la contribution d'une détérioration du fonctionnement de la VTA aux symptômes liés à l'ASD, et permettent d'identifier la modulation de mGluR1, durant le développement post-natal, comme potentielle stratégie de traitement

VTA DA neuron excitatory synapses in Shank3 Δex4-9 mouse line

Several mutations within SHANK3 gene have been identified in Autism Spectrum Disorder patients and several studies have now started to show that those mutations could impact different brain circuits leading to the heterogeneity of the disease. Here we show that, compared to a mouse model lacking SHANK3 proline-rich containing isoforms, in a mouse model lacking SHANK3 ANK(yrin)-domain containing isoforms, the excitatory synaptic transmission within the Ventral Tegmental Area is not affected. We discuss about the possibility that different domains of SHANK3 are involved in regulating the synapses in a circuit-specific manner resulting in different behavioral and synaptic phenotypes

Corticostriatal deficits underlying cognitive impairments induced by fetal exposure to alcohol

The term Fetal Alcohol Spectrum Disorder (FASD) includes a group of diseases caused by fetal exposure to alcohol (FAE). FASD patients display heterogenous socio-emotional and cognitive deficits, particularly in the domain of executive function, which share symptoms with other neuropsychiatric disorders. Despite the availability of several preclinical models, the developmental brain defects causally linked to behavioral deficits induced by FAE remain poorly understood. Here, we first review the FAE-induced synaptic and circuit impairments in mesocorticolimbic areas involved in social and motor behaviors. Then, we consider the effects of FAE on cortical excitation/inhibition balance and its impact on both corticostriatal pathway function and cognitive abilities. In particular, we propose three non-mutually exclusive circuit models of corticostriatal dysfunctions to account for some of the FAE-induced cognitive deficits. One model posits that associative-sensorimotor imbalance causes hyper goal-directed behavior and a second model implies that alteration of prefrontal-striatal behavioral suppression circuits results in the loss of behavioral inhibition. A third model suggests that local striatal circuit deficits affect striatal neuronal ensemble function to impair action selection and performance. Finally, we discuss how pre-clinical approaches suggest potential rescue strategies for neuronal circuit defects in FASD patients

Ventral tegmental area subcircuits process rewarding and aversive experiences

The ventral tegmental area is a heterogeneous brain structure that plays a central role in rewarding and aversive experience processing. Studies suggest that several subpopulations within the ventral tegmental area form subcircuits that are differentially involved in rewarding and aversive experiences and that could be individually affected in several neuropsychiatric disorders. Here, we focus on the recent advances concerning the functional description of the three major neuronal subpopulations, in terms of neurotransmitter release, their input and output structures, and their role in controlling specific behavioral outcomes. Several subpopulations within the Ventral Tegmental Area form subcircuits that are differentially involved in rewarding and aversive experiences and that could be individually affected in several neuropsychiatric disorders. We focus on the recent advances concerning the functional description of the three major neuronal subpopulations, their input and output structures, and their role in controlling specific behavioral outcomes. This article is part of a mini review series: "Synaptic Function and Dysfunction in Brain Diseases"

Orbitofrontal-striatal potentiation underlies cocaine-induced hyperactivity

Psychomotor stimulants increase dopamine levels in the striatum and promote locomotion but their effects on striatal pathways in vivo remain unclear. The authors show that cocaine increases the activity of direct and indirect pathway striatal neurons of awake mice via the orbitofrontal cortex

Postnatal ethanol exposure impairs social behavior and operant extinction in the adult female mouse offspring

Fetal Alcohol Spectrum Disorder (FASD) comprises a group of neurodevelopmental deficits caused by alcohol exposure during pregnancy. Clinical studies suggest that while the male progeny experiences serious neurodevelopmental defects, female patients have more severe cognitive, social, and affective symptoms. Other than sex, dose, frequency, and timing of exposure determine the neurobehavioral outcomes in young and adult progeny. In this regard, human studies indicate that some individuals relapse during late-term gestational periods. In mice, this interval corresponds to the first 10 days after birth (postnatal, P0-P10). In our model of postnatal ethanol exposure (PEEP0-P10), we tested whether adult female and male offspring show deficits in sociability, anxiety-like, reward consumption, and action-outcome associations. We report that female PEEP0-P10 offspring have mild social impairments and altered extinction of operant responding in the absence of anxiety-like traits and reward consumption defects. None of these deficits were detected in the male PEEP0-P10 offspring. Our data provide novel information on sex-specific neurobehavioral outcomes of postnatal ethanol exposure in female adult offspring

Role of VTA dopamine neurons and neuroligin 3 in sociability traits related to nonfamiliar conspecific interaction

Atypical habituation and aberrant exploration of novel stimuli have been related to the severity of autism spectrum disorders (ASDs), but the underlying neuronal circuits are unknown. Here we show that chemogenetic inhibition of dopamine (DA) neurons of the ventral tegmental area (VTA) attenuates exploration toward nonfamiliar conspecifics and interferes with the reinforcing properties of nonfamiliar conspecific interaction in mice. Exploration of nonfamiliar stimuli is associated with the insertion of GluA2-lacking AMPA receptors at excitatory synapses on VTA DA neurons. These synaptic adaptations persist upon repeated exposure to social stimuli and sustain conspecific interaction. Global or VTA DA neuron-specific loss of the ASD-associated synaptic adhesion molecule neuroligin 3 alters the behavioral response toward nonfamiliar conspecifics and the reinforcing properties of conspecific interaction. These behavioral deficits are accompanied by an aberrant expression of AMPA receptors and an occlusion of synaptic plasticity. Altogether, these findings link impaired exploration of nonfamiliar conspecifics to VTA DA neuron dysfunction in mice