Project description:Empathy is crucial for our social lives, and its disruption is a prominent characteristic of various psychiatric conditions. However, the specific genes and neurobiological mechanisms underlying empathy deficits remain elusive. By combining forward genetic mapping with transcriptome analysis, we discovered that the Arnt2 gene encoding a basic-helix-loop-helix (bHLH)-PAS transcription factor is a key driver of significant alteration in observational fear, a basic form of affective empathy. Selective deletion of Arnt2 in somatostatin (SST)-expressing inhibitory neurons resulted in reduced excitability of pyramidal cells, an increase in spontaneous firing, and alteration in in vivo Ca2+ dynamics in SST neurons in the anterior cingulate cortex (ACC), leading to deficits in observational fear and affective state discrimination. Together, our findings provide the first direct evidence that ARNT2 regulates emotion recognition and affect sharing through its functional actions in the cortical inhibitory circuit and highlight the neural substrates underlying social affective dysfunctions in psychiatric disorders.
Project description:Total RNA-sequencing of FACs isolated nucleus accumbens somatostatin interneuron nuclei Somatostatin interneuron loss in multiple cortical brain regions has been observed postmortem in humans with several neuropsychiatric disorders and their loss is proposed to underlie some common pathological changes in circuit function across numerous syndromes. However, somatostatin interneurons in the nucleus accumbens (NAc), a key brain reward region, remain poorly understood due to the fact that these cells account for <1% of NAc neurons. Here, we used Flouresence activated cell sorting to isolate nuclei of somatostatin-expressing interneurons in the Nucleus Accumbens from individual SST-TLG498 reporter mice that express membrane bound EGFP-F specifically in somatostatin-expressing neurons. We then performed cell-type specific Total RNA-sequencing to characterize the entire transcriptome of NAc somatostatin interneurons after repeated exposure (7 days) to either saline or cocaine. We identified a wide variety of coding and non-coding transcripts that were expressed at high levels and were differentially expressed between saline and cocaine treated mice. Repeated cocaine administration induces transcriptome-wide changes in gene expression within NAc somatostatin interneurons, with particular regulation of transcripts related to neural plasticity. Our results identify alterations in NAc induced by cocaine in a sparse population of somatostatin interneurons, and illustrate the value of studying brain diseases using cell type-specific whole transcriptome RNA-sequencing to identify novel neurpathophysiology.
Project description:People with schizophrenia show hyperactivity in the ventral hippocampus (vHipp) and we have previously demonstrated distinct behavioral roles for vHipp cell populations. Here, we test the hypothesis that parvalbumin (PV) and somatostatin (SST) interneurons differentially innervate and regulate hippocampal pyramidal neurons based on their projection target. First, we use eGRASP to show that PV-positive interneurons form a similar number of synaptic connections with pyramidal cells regardless of their projection target while SST-positive interneurons preferentially target nucleus accumbens (NAc) projections. To determine if these anatomical differences result in functional changes, we used in vivo opto-electrophysiology to show that SST cells also preferentially regulate the activity of NAc-projecting cells. These results suggest vHipp interneurons differentially regulate that vHipp neurons that project to the medial prefrontal cortex (mPFC) and NAc. Characterization of these cell populations may provide potential molecular targets for the treatment schizophrenia and other psychiatric disorders associated with vHipp dysfunction.
Project description:Somatostatin interneurons are the earliest born population of inhibitory cells. They are crucial to support normal brain development and function; however, the mechanisms underlying their integration into nascent cortical circuitry are not well understood. In this study, we begin by demonstrating that the maturation of somatostatin interneurons is activity dependent. We then investigated the relationship between activity, alternative splicing and synapse formation within this population. Specifically, we discovered that the Nova family of RNA-binding proteins are activity-dependent and are essential for the maturation of somatostatin interneurons, as well as their afferent and efferent connectivity. Moreover, in somatostatin interneurons, Nova2 preferentially mediates the alternative splicing of genes required for axonal formation and synaptic function. Hence, our work demonstrates that the Nova family of proteins are centrally involved in coupling developmental neuronal activity to cortical circuit formation.
Project description:The mammalian cerebral cortex contains an extraordinary diversity of cell types that emerge through the implementation of different developmental programs. Delineating when and how cellular diversification occurs is particularly challenging for cortical inhibitory neurons, as they represent a relatively small proportion of all cortical cells, migrate tangentially from their embryonic origin to the cerebral cortex, and have a protracted development. Here we combine single-cell RNA sequencing and spatial transcriptomics to characterize the emergence of neuronal diversity among somatostatin-expressing (SST+) cells, the most diverse subclass of inhibitory neurons in the mouse cerebral cortex. We found that SST+ inhibitory neurons segregate during embryonic stages into long-range projection (LRP) neurons and two types of interneurons, Martinotti cells and non-Martinotti cells, following distinct developmental trajectories. Two main subtypes of LRP neurons and several subtypes of interneurons are readily distinguishable in the embryo, although interneuron diversity is further refined during early postanal life. Our results suggest that the timing for cellular diversification is unique for different subtypes of SST+ neurons and particularly divergent for LRP neurons and interneurons. Thus, the diversification of SST+ inhibitory neurons involves a temporal cascade of unique molecular programs driving their divergent developmental trajectories.
Project description:Theories stipulate that memories are encoded within networks of cortical projection neurons. Conversely, GABAergic interneurons are thought to function primarily to inhibit projection neurons and thereby impose network gain control, an important but purely modulatory role. Here we show in male mice that associative fear learning potentiates synaptic transmission and cue-specific activity of medial prefrontal cortex somatostatin (SST) interneurons and that activation of these cells controls both memory encoding and expression. Furthermore, the synaptic organization of SST and parvalbumin interneurons provides a potential circuit basis for SST interneuron-evoked disinhibition of medial prefrontal cortex output neurons and recruitment of remote brain regions associated with defensive behavior. These data suggest that, rather than constrain mnemonic processing, potentiation of SST interneuron activity represents an important causal mechanism for conditioned fear.