Dopamine modulating agents alter individual subdomains of motivation-related behavior assessed by touchscreen procedures.

Development of novel treatments for motivational deficits experienced by individuals with schizophrenia and major depressive disorder requires procedures that reliably assess effort-related behavior in pre-clinical models. High-throughput touchscreen-based testing, that parallels the computerized assessment of human patients, offers a platform for the establishment of tasks with high level of translational validity. Considerable efforts have been made to validate the touchscreen version of tasks that measure the degree of effort an animal is willing to invest for a reward, such as progressive ratio task. While motivational studies primarily focus on reporting alterations of a breakpoint, touchscreen assessment allows to collect multiple measures, especially if additional tasks would be adapted to the touchscreen environment. Classifying these measures to distinct behavioral subdomains is necessary for an evaluation of pre-clinical models. Here we apply data-driven classification techniques to identify behavioral clusters from dataset obtained in progressive ratio task and a novel effort-related choice task that we established and validated in the touchscreen boxes. Moreover, we measure the effect of pharmacological manipulations of the level of dopamine, a key regulator of reward- and effort-related processing, on individual behavioral subdomains that describe effort-related activity, non-specific activity, locomotion, and effort-related choice. Our approach expands the touchscreen-based assessment of pre-clinical models of motivational symptoms, identifies the most relevant behavioral measures in assessing the degree of reward-driven effort and contributes to the understanding of the role of dopamine in mediating distinct aspects of effort-related motivation.

Altered theta and beta oscillatory synchrony in a genetic mouse model of pathological anxiety.

While the neural circuits mediating normal, adaptive defensive behaviors have been extensively studied, substantially less is currently known about the network mechanisms by which aberrant, pathological anxiety is encoded in the brain. Here we investigate in mice how deletion of Neuroligin-2 (Nlgn2), an inhibitory synapse-specific adhesion protein that has been associated with pathological anxiety and other psychiatric disorders, alters the communication between key brain regions involved in mediating defensive behaviors. To this end, we performed multi-site simultaneous local field potential (LFP) recordings from the basolateral amygdala (BLA), centromedial amygdala (CeM), bed nucleus of the stria terminalis (BNST), prefrontal cortex (mPFC) and ventral hippocampus (vHPC) in an open field paradigm. We found that LFP power in the vHPC was profoundly increased and was accompanied by an abnormal modulation of the synchrony of theta frequency oscillations particularly in the vHPC-mPFC-BLA circuit. Moreover, deletion of Nlgn2 increased beta and gamma frequency synchrony across the network, and this increase was associated with increased center avoidance. Local deletion of Nlgn2 in the vHPC and BLA revealed that they encode distinct aspects of this avoidance phenotype, with vHPC linked to immobility and BLA linked to a reduction in exploratory activity. Together, our data demonstrate that alterations in long-range functional connectivity link synaptic inhibition to abnormal defensive behaviors, and that both exaggerated activation of normal defensive circuits and recruitment of fundamentally distinct mechanisms contribute to this phenotype. Nlgn2 knockout mice therefore represent a highly relevant model to study the role of inhibitory synaptic transmission in the circuits underlying anxiety disorders.

IgSF9b regulates anxiety behaviors through effects on centromedial amygdala inhibitory synapses.

Abnormalities in synaptic inhibition play a critical role in psychiatric disorders, and accordingly, it is essential to understand the molecular mechanisms linking components of the inhibitory postsynapse to psychiatrically relevant neural circuits and behaviors. Here we study the role of IgSF9b, an adhesion protein that has been associated with affective disorders, in the amygdala anxiety circuitry. We show that deletion of IgSF9b normalizes anxiety-related behaviors and neural processing in mice lacking the synapse organizer Neuroligin-2 (Nlgn2), which was proposed to complex with IgSF9b. This normalization occurs through differential effects of Nlgn2 and IgSF9b at inhibitory synapses in the basal and centromedial amygdala (CeM), respectively. Moreover, deletion of IgSF9b in the CeM of adult Nlgn2 knockout mice has a prominent anxiolytic effect. Our data place IgSF9b as a key regulator of inhibition in the amygdala and indicate that IgSF9b-expressing synapses in the CeM may represent a target for anxiolytic therapies.

Auditory midbrain coding of statistical learning that results from discontinuous sensory stimulation.

Detecting regular patterns in the environment, a process known as statistical learning, is essential for survival. Neuronal adaptation is a key mechanism in the detection of patterns that are continuously repeated across short (seconds to minutes) temporal windows. Here, we found in mice that a subcortical structure in the auditory midbrain was sensitive to patterns that were repeated discontinuously, in a temporally sparse manner, across windows of minutes to hours. Using a combination of behavioral, electrophysiological, and molecular approaches, we found changes in neuronal response gain that varied in mechanism with the degree of sound predictability and resulted in changes in frequency coding. Analysis of population activity (structural tuning) revealed an increase in frequency classification accuracy in the context of increased overlap in responses across frequencies. The increase in accuracy and overlap was paralleled at the behavioral level in an increase in generalization in the absence of diminished discrimination. Gain modulation was accompanied by changes in gene and protein expression, indicative of long-term plasticity. Physiological changes were largely independent of corticofugal feedback, and no changes were seen in upstream cochlear nucleus responses, suggesting a key role of the auditory midbrain in sensory gating. Subsequent behavior demonstrated learning of predictable and random patterns and their importance in auditory conditioning. Using longer timescales than previously explored, the combined data show that the auditory midbrain codes statistical learning of temporally sparse patterns, a process that is critical for the detection of relevant stimuli in the constant soundscape that the animal navigates through.

Inhibition in the amygdala anxiety circuitry.

Inhibitory neurotransmission plays a key role in anxiety disorders, as evidenced by the anxiolytic effect of the benzodiazepine class of γ-aminobutyric acid (GABA) receptor agonists and the recent discovery of anxiety-associated variants in the molecular components of inhibitory synapses. Accordingly, substantial interest has focused on understanding how inhibitory neurons and synapses contribute to the circuitry underlying adaptive and pathological anxiety behaviors. A key element of the anxiety circuitry is the amygdala, which integrates information from cortical and thalamic sensory inputs to generate fear and anxiety-related behavioral outputs. Information processing within the amygdala is heavily dependent on inhibitory control, although the specific mechanisms by which amygdala GABAergic neurons and synapses regulate anxiety-related behaviors are only beginning to be uncovered. Here, we summarize the current state of knowledge and highlight open questions regarding the role of inhibition in the amygdala anxiety circuitry. We discuss the inhibitory neuron subtypes that contribute to the processing of anxiety information in the basolateral and central amygdala, as well as the molecular determinants, such as GABA receptors and synapse organizer proteins, that shape inhibitory synaptic transmission within the anxiety circuitry. Finally, we conclude with an overview of current and future approaches for converting this knowledge into successful treatment strategies for anxiety disorders.

Neuroligin 2 deletion alters inhibitory synapse function and anxiety-associated neuronal activation in the amygdala.

Neuroligin 2 (Nlgn2) is a synaptic adhesion protein that plays a central role in the maturation and function of inhibitory synapses. Nlgn2 mutations have been associated with psychiatric disorders such as schizophrenia, and in mice, deletion of Nlgn2 results in a pronounced anxiety phenotype. To date, however, the molecular and cellular mechanisms linking Nlgn2 deletion to psychiatric phenotypes remain completely unknown. The aim of this study was therefore to define the role of Nlgn2 in anxiety-related neural circuits. To this end, we used a combination of behavioral, immunohistochemical, and electrophysiological approaches in Nlgn2 knockout (KO) mice to expand the behavioral characterization of these mice and to assess the functional consequences of Nlgn2 deletion in the amygdala. Moreover, we investigated the differential activation of anxiety-related circuits in Nlgn2 KO mice using a cFOS activation assay following exposure to an anxiogenic stimulus. We found that Nlgn2 is present at the majority of inhibitory synapses in the basal amygdala, where its deletion affects postsynaptic structures specifically at perisomatic sites and leads to impaired inhibitory synaptic transmission. Following exposure to an anxiogenic environment, Nlgn2 KO mice show a robust anxiety phenotype as well as exacerbated induction of cFOS expression specifically in CaMKII-positive projection neurons, but not in parvalbumin- or somatostatin-positive interneurons. Our data indicate that Nlgn2 deletion predominantly affects inhibitory synapses onto projection neurons in basal amygdala, resulting in decreased inhibitory drive onto these neurons and leading to their excessive activation under anxiogenic conditions. This article is part of the Special Issue entitled 'Synaptopathy--from Biology to Therapy'.