Activation of G-protein-coupled receptors (GPCRs) results in a variety of cellular responses, such as binding to the same receptor of different ligands that activate distinct downstream cascades. Additional signaling complexity is achieved when two or more receptors are integrated into one signaling unit. Lateral receptor interactions can allosterically modulate the receptor response to a ligand, which creates a mechanism for tissue-specific fine tuning, depending on the cellular receptor coexpression pattern. GPCR homomers or heteromers have been explored widely for GPCR classes A and C but to lesser extent for class B. In the present study, we used bioluminescence resonance energy transfer (BRET) techniques, calcium flux measurements, and microscopy to study receptor interactions within the glucagon receptor family. We found basal BRET interactions for some of the receptor combinations tested that decreased upon ligand binding. A BRET increase was observed exclusively for the gastric inhibitory peptide (GIP) receptor and the glucagon-like peptide 1 (GLP-1) receptor upon binding of GLP-1 that could be reversed with GIP addition. The interactions of GLP-1 receptor and GIP receptor were characterized with BRET donor saturation studies, shift experiments, and tests of glucagon-like ligands. The heteromer displayed specific pharmacological characteristics with respect to GLP-1-induced ␤-arrestin recruitment and calcium flux, which suggests a form of allosteric regulation between the receptors. This study provides the first example of ligand-induced heteromer formation in GPCR class B. In the body, the receptors are functionally related and coexpressed in the same cells. The physiological evidence for this heteromerization remains to be determined.

In various mental disorders, dysfunction of the prefrontal cortex contributes to cognitive deficits. Here we studied how the claustrum (CLA), a nucleus sharing reciprocal connections with the cortex, may participate in these cognitive impairments. We show that specific ensembles of CLA and of medial prefrontal cortex (mPFC) neurons are activated during a task requiring cognitive control such as attentional set-shifting, i.e. the ability to shift attention towards newly relevant stimulus-reward associations while disengaging from irrelevant ones. CLA neurons exert a direct excitatory input on mPFC pyramidal cells, and chemogenetic inhibition of CLA neurons suppresses the formation of specific mPFC assemblies during attentional set-shifting. Furthermore, impairing the recruitment of specific CLA assemblies through opto/chemogenetic manipulations prevents attentional set-shifting. In conclusion, we propose that the CLA controls the reorganization of mPFC ensembles to enable attentional set-shifting, emphasizing a potential role of the CLA-mPFC network in attentional dysfunctions.

Schizophrenia is a severely debilitating neurodevelopmental disorder. Establishing a causal link between circuit dysfunction and particular behavioral traits that are relevant to schizophrenia is crucial to shed new light on the mechanisms underlying the pathology. We studied an animal model of the human 22q11 deletion syndrome, the mutation that represents the highest genetic risk of developing schizophrenia. We observed a desynchronization of hippocampal neuronal assemblies that resulted from parvalbumin interneuron hypoexcitability. Rescuing parvalbumin interneuron excitability with pharmacological or chemogenetic approaches was sufficient to restore wild-type-like CA1 network dynamics and hippocampal-dependent behavior during adulthood. In conclusion, our data provide insights into the network dysfunction underlying schizophrenia and highlight the use of reverse engineering to restore physiological and behavioral phenotypes in an animal model of neurodevelopmental disorder.

Schizophrenia is a severely debilitating neurodevelopmental disorder. Establishing a causal link between circuit dysfunction and particular behavioural traits relevant to schizophrenia is crucial to shed new light on the mechanisms underlying the pathology. Here we studied an animal model of the 22q11 deletion syndrome, which is the highest genetic risk to develop the pathology. We report a desynchronization of hippocampal neuronal assemblies that resulted from parvalbumin interneuron hypoexcitability. Rescuing parvalbumin interneuron excitability with pharmacological or chemogenetic approaches is sufficient to restore wild type-like network dynamics and behaviour during adulthood. In conclusion, our data provide mechanistic insights underlying network dysfunction relevant to schizophrenia and demonstrate the potential of reverse engineering in fostering new therapeutic strategies to alleviate the burden of neurodevelopmental disorders.not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/151795 doi: bioRxiv preprint first posted online 3 Main textAlterations of network dynamics have been proposed to be instrumental in schizophrenia [1][2][3] . A specific population of inhibitory neurons, the parvalbumin interneurons (PVIs), plays a key role in regulating network dynamics 4-7 and may be involved in the pathology [8][9][10][11] . Although specific manipulations of PVI can reproduce behavioural phenotypes relevant to schizophrenia in rodents 12,13 , it remains unclear whether PVI dysfunction is causally linked to network dysfunction and pathological behaviour associated with schizophrenia. More importantly, it is not known whether manipulating PVI could restore altered physiology.Among various genetic alterations, the specific deletion of ~30 genes on chromosome 22 that leads to the 22q11 deletion syndrome (22q11DS), is the highest identified genetic risk to develop schizophrenia 14,15 . We used a genetically engineered mouse bearing a hemizygous deletion on chromosome 16, termed Lgdel/+, which replicates the chromosomal alteration of the human 22q11DS 16 . In the CA1 area of the hippocampus, mouse models of 22q11DS differ from wild-type (WT) animals regarding their structural [17][18][19] and electrophysiological properties 20 , and their functional connectivity with distant brain areas 3 . We first tested whether those differences were accompanied by intrinsic differences in network dynamics. Neural activity was monitored in hippocampal slices using the genetically encoded calcium indicator GCaMP6s expressed by CA1 neurons following adeno-associated viral (AAV) vector transfection (Fig. 1a,b). Network dynamics were induced by bath application of carbachol (50 µM), which triggered spontaneous calcium activity in individual neurons of wild type (WT) mice 21,22 (Fig. 1c,d). Likewise, individual CA1neurons of Lgdel/+ mice exhibited spontaneous calcium activity during the duration ...

The consolidation and recall of episodic memories rely on distributed cortical activity. The claustrum, a subcortical structure reciprocally connected to most of the cortex, may facilitate inter-areal communication necessary for these processes. We report here that the functional inhibition of claustral projection neurons affects directional interactions and the coordination of oscillatory neuronal patterns in the fronto-parietal network. Moreover, the inhibition of these neurons has a detrimental effect on concurrent oscillatory events relevant to the consolidation of contextual fear memory. Last, we demonstrate that biasing the directional flow of information between the latter two cortical areas enhances the retrieval of a remote contextual memory. We propose that the claustrum orchestrates inter-areal cortical interactions relevant to contextual memory processes by affecting the latency of neuronal responses.One-Sentence SummaryThe claustrum coordinates inter-areal cortical activity.