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The metabotropic glutamate receptor subtype 8 (mGlu8) is presynaptically located and regulates the release of the transmitter. Dysfunctions of this mechanism are involved in the pathophysiology of different psychiatric disorders. mGlu8 deficient mice have been previously investigated in a range of studies, but the results are contradictory and there are still many open questions. Therefore, we tested mGlu8-deficient animals in different behavioral tasks that are commonly used in neuropsychiatric research. Our results show a robust contextual fear deficit in mGlu8-deficient mice. Furthermore, novel object recognition, chlordiazepoxide-facilitated extinction of operant conditioning and the acoustic startle response were attenuated by mGlu8 deficiency. We found no changes in sensory processing, locomotor activity, prepulse inhibition, phencyclidine-induced changes in locomotion or prepulse inhibition, operant conditioning, conditioned fear to a discrete cue or in animal models of innate fear and post-traumatic stress disorder. We conclude that mGlu8 might be a potential target for disorders with pathophysiological changes in brain areas where mGlu8 modulates glutamate and gamma-amino butyric acid (GABA) transmission. Our data especially point to anxiety disorders involving exaggerated contextual fear, such as generalized anxiety disorders, and to conditions with disturbed declarative memory. [ABSTRACT FROM AUTHOR]

Cognitive flexibility and working memory are important executive functions mediated by the prefrontal cortex and can be impaired by circadian rhythm disturbances such as chronic jet lag (CJL) or shift work. In the present study, we used mice to investigate whether (1) simulated CJL impairs cognitive flexibility, (2) the orexin system is involved in such impairment, and (3) nasal administration of orexin A is able to reverse CJL-induced deficits in cognitive flexibility and working memory. Mice were exposed to either standard light-dark conditions or simulated CJL consisting of series of advance time shifts. Experiment (1) investigated the effects of a mild CJL protocol on cognitive flexibility using the attentional set shifting task. Experiment (2) used a stronger CJL protocol and examined CJL effects on the orexin system utilizing c-Fos and orexin immunohistochemistry. Experiment (3) tested whether nasal orexin application can rescue CJL-induced deficits in cognitive flexibility and working memory, the latter by measuring spontaneous alternation in the Y-maze. The present data show that CJL (1) impairs cognitive flexibility and (2) reduces the activity of orexin neurons in the lateral hypothalamus. (3) Nasal administration of orexin A rescued CJL-induced deficits in working memory and cognitive flexibility. These findings suggest that executive function impairments by circadian rhythm disturbances such as CJL are caused by dysregulation of orexinergic input to the prefrontal cortex. Compensation of decreased orexinergic input by nasal administration of orexin A could be a potential therapy for CJL- or shift work-induced human deficits in executive functions., (© 2024. The Author(s).)

Neurodevelopmental disorders such as autism spectrum disorder (ASD) have a heterogeneous etiology but are largely associated with genetic factors. Robust evidence from recent human genetic studies has linked mutations in the Shank2 gene to idiopathic ASD. Modeling these Shank2 mutations in animal models recapitulates behavioral changes, e.g. impaired social interaction and repetitive behavior of ASD patients. Shank2-deficient mice exhibit NMDA receptor (NMDAR) hypofunction and associated behavioral deficits. Of note, NMDARs are strongly implicated in cognitive flexibility. Their hypofunction, e.g. observed in schizophrenia, or their pharmacological inhibition leads to impaired cognitive flexibility. However, the association between Shank2 mutations and cognitive flexibility is poorly understood. Using Shank2-deficient mice, we explored the role of Shank2 in cognitive flexibility measured by the attentional set shifting task (ASST) and whether ASST performance in Shank2-deficient mice can be modulated by treatment with the partial NMDAR agonist D-cycloserine (DCS). Furthermore, we investigated the effects of Shank2 deficiency, ASST training, and DCS treatment on the expression level of NMDAR signaling hub components in the orbitofrontal cortex (OFC), including NMDAR subunits (GluN2A, GluN2B, GluN2C), phosphoglycerate dehydrogenase and serine racemase. Surprisingly, Shank2 deficiency did not affect ASST performance or alter the expression of the investigated NMDAR signaling hub components. Importantly, however, DCS significantly improved ASST performance, demonstrating that positive NMDAR modulation facilitates cognitive flexibility. Furthermore, DCS increased the expression of GluN2A in the OFC, but not that of other NMDAR signaling hub components. Our findings highlight the potential of DCS as a pharmacological intervention to improve cognitive flexibility impairments downstream of NMDAR modulation and substantiate the key role of NMDAR in cognitive flexibility., Competing Interests: Declaration of competing interest None., (Copyright © 2023. Published by Elsevier Inc.)

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by impaired perceptual processing and social communication, intellectual disabilities, and repetitive behaviors. Interestingly, while not a core symptom, anxiety disorders frequently co-occur in individuals with ASD and deficits in safety learning have been described in patients with anxiety-related disorders. Because genetic factors, such as SHANK deficiency (loss-of-function mutations), have been linked to ASD, the aim of the present study was to investigate whether Shank2 deficiency interferes with associative fear and safety signal learning. To first investigate trait anxiety, male and female Shank2-deficient mice were exposed to a light-dark box test. Mice were then submitted to a combination of contextual fear conditioning and single-cue safety conditioning. The results show that Shank2 deficiency increases trait anxiety but reduces contextual fear learning. In male but not female Shank2-deficient mice, reduced single-cued safety learning was observed. This safety learning deficit was not caused by altered anxiety levels, increased locomotor activity, or reduced contextual fear since these changes were also observed in female Shank2-deficient mice. Concluding, our data indicate that the observed safety learning deficits in Shank2-deficient male mice could contribute to the emotional symptoms observed in ASD and the high comorbidity with anxiety-related disorders., Competing Interests: Declaration of competing interest None., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)