Long-term adaptation of prefrontal circuits in a mouse model of NMDAR hypofunction.

Pharmacological approaches to induce N-methyl-d-aspartate receptor (NMDAR) hypofunction have been intensively used to understand the aetiology and pathophysiology of schizophrenia. Yet, the precise cellular and molecular mechanisms that relate to brain network dysfunction remain largely unknown. Here, we used a set of complementary approaches to assess the functional network abnormalities present in male mice that underwent a 7-day subchronic phencyclidine (PCP 10 mg/kg, subcutaneously, once daily) treatment. Our data revealed that pharmacological intervention with PCP affected cognitive performance and auditory evoked gamma oscillations in the prefrontal cortex (PFC) mimicking endophenotypes of some schizophrenia patients. We further assessed PFC cellular function and identified altered neuronal intrinsic membrane properties, reduced parvalbumin (PV) immunostaining and diminished inhibition onto L5 PFC pyramidal cells. A decrease in the strength of optogenetically-evoked glutamatergic current at the ventral hippocampus to PFC synapse was also demonstrated, along with a weaker shunt of excitatory transmission by local PFC interneurons. On a macrocircuit level, functional ultrasound measurements indicated compromised functional connectivity within several brain regions particularly involving PFC and frontostriatal circuits. Herein, we reproduced a panel of schizophrenia endophenotypes induced by subchronic PCP application in mice. We further recapitulated electrophysiological signatures associated with schizophrenia and provided an anatomical reference to critical elements in the brain circuitry. Together, our findings contribute to a better understanding of the physiological underpinnings of deficits induced by subchronic NMDAR antagonist regimes and provide a test system for characterization of pharmacological compounds.

Encoding of Environmental Cues in Central Amygdala Neurons during Foraging.

To successfully forage in an environment filled with rewards and threats, animals need to rely on familiar structures of their environment that signal food availability. The central amygdala (CeA) is known to mediate a panoply of consummatory and defensive behaviors, yet how specific activity patterns within CeA subpopulations guide optimal choices is not completely understood. In a paradigm of appetitive conditioning in which mice freely forage for food across a continuum of cues, we found that two major subpopulations of CeA neurons, Somatostatin-positive (CeASst) and protein kinase Cδ-positive (CeAPKCδ) neurons, can assign motivational properties to environmental cues. Although the proportion of food responsive cells was higher within CeASst than CeAPKCδ neurons, only the activities of CeAPKCδ, but not CeASst, neurons were required for learning of contextual food cues. Our findings point to a model in which CeAPKCδ neurons may incorporate stimulus salience together with sensory features of the environment to encode memory of the goal location.SIGNIFICANCE STATEMENT The CeA has a very important role in the formation of memories that associate sensory information with aversive or rewarding representation. Here, we used a conditioned place preference paradigm, where freely moving mice learn to associate external cues with food availability, to investigate the roles of CeA neuron subpopulations. We found that CeASst and CeAPKCδ neurons encoded environmental cues during foraging but only the activities of CeAPKCδ neurons were required for learning of contextual food cues.

The Insula Cortex Contacts Distinct Output Streams of the Central Amygdala.

The emergence of genetic tools has provided new means of mapping functionality in central amygdala (CeA) neuron populations based on their molecular profiles, response properties, and importantly, connectivity patterns. While abundant evidence indicates that neuronal signals arrive in the CeA eliciting both aversive and appetitive behaviors, our understanding of the anatomy of the underlying long-range CeA network remains fragmentary. In this study, we combine viral tracings, electrophysiological, and optogenetic approaches to establish in male mice, a wiring chart between the insula cortex (IC), a major sensory input region of the lateral and capsular part of the CeA (CeL/C), and four principal output streams of this nucleus. We found that retrogradely labeled output neurons occupy discrete and likely strategic locations in the CeL/C, and that they are disproportionally controlled by the IC. We identified a direct line of connection between the IC and the lateral hypothalamus (LH), which engages numerous LH-projecting CeL/C cells whose activity can be strongly upregulated on firing of IC neurons. In comparison, CeL/C neurons projecting to the bed nucleus of the stria terminalis (BNST) are also frequently contacted by incoming IC axons, but the strength of this connection is weak. Our results provide a link between long-range inputs and outputs of the CeA and pave the way to a better understanding of how internal, external, and experience dependent information may impinge on action selection by the CeA.SIGNIFICANCE STATEMENT Our current knowledge of the circuit organization within the central amygdala (CeA), a critical regulator of emotional states, includes independent information about its long-range efferents and afferents. We do not know how incoming sensory information is appraised and routed through the CeA to the different output channels. We address this issue by using three different techniques to investigate how a sensory region, the insula cortex (IC), connects with the motor, physiological and autonomic output centers of the CeA. We uncover a strong connection between the IC and the lateral hypothalamus (LH) with a monosynaptic relay in the CeA and shed new light on the previously described functions of IC and CeA through direct projections to the LH.

Central amygdala circuits modulate food consumption through a positive-valence mechanism.

The complex behaviors underlying reward seeking and consumption are integral to organism survival. The hypothalamus and mesolimbic dopamine system are key mediators of these behaviors, yet regulation of appetitive and consummatory behaviors outside of these regions is poorly understood. The central nucleus of the amygdala (CeA) has been implicated in feeding and reward, but the neurons and circuit mechanisms that positively regulate these behaviors remain unclear. Here, we defined the neuronal mechanisms by which CeA neurons promote food consumption. Using in vivo activity manipulations and Ca2+ imaging in mice, we found that GABAergic serotonin receptor 2a (Htr2a)-expressing CeA neurons modulate food consumption, promote positive reinforcement and are active in vivo during eating. We demonstrated electrophysiologically, anatomically and behaviorally that intra-CeA and long-range circuit mechanisms underlie these behaviors. Finally, we showed that CeAHtr2a neurons receive inputs from feeding-relevant brain regions. Our results illustrate how defined CeA neural circuits positively regulate food consumption.

The composition of EphB2 clusters determines the strength in the cellular repulsion response.

Trans interactions of erythropoietin-producing human hepatocellular (Eph) receptors with their membrane-bound ephrin ligands generate higher-order clusters that can form extended signaling arrays. The functional relevance of the cluster size for repulsive signaling is not understood. We used chemical dimerizers and fluorescence anisotropy to generate and visualize specific EphB2 cluster species in living cells. We find that cell collapse responses are induced by small-sized EphB2 clusters, suggesting that extended EphB2 arrays are dispensable and that EphB2 activation follows an ON-OFF switch with EphB2 dimers being inactive and trimers and tetramers being fully functional. Moreover, the strength of the collapse response is determined by the abundance of multimers over dimers within a cluster population: the more dimers are present, the weaker the response. Finally, we show that the C-terminal modules of EphB2 have negative regulatory effects on ephrin-induced clustering. These results shed new light on the mechanism and regulation of EphB2 activation and provide a model on how Eph signaling translates into graded cellular responses.

The multi-PDZ domain protein-1 (MUPP-1) expression regulates cellular levels of the PALS-1/PATJ polarity complex.

MUPP-1 (multi-PDZ domain protein-1) and PATJ (PALS-1-associated tight junction protein) proteins are closely related scaffold proteins and bind to many common interactors including PALS-1 (protein associated with Lin seven) a member of the Crumbs complex. Our goal is to understand how MUPP-1 and PATJ and their interaction with PALS-1 are regulated in the same cells. We have shown that in MCF10A cells there are at least two different and co-existing complexes, PALS-1/MUPP-1 and PALS-1/PATJ. Surprisingly, MUPP-1 levels inversely correlated with PATJ protein levels by acting on the stabilization of the PATJ/PALS-1 complex. Upon MUPP-1 depletion, the increased amounts of PATJ are in part localized at the migrating front of MCF10A cells and are able to recruit more PAR3 (partition defective 3). All together these data indicate that a precise balance between MUPP-1 and PATJ is achieved in epithelial cells by regulating their association with PALS-1.