Neurexin-3 defines synapse- and sex-dependent diversity of GABAergic inhibition in ventral subiculum
Ontology highlight
ABSTRACT: Ventral subiculum (vSUB) is integral to the regulation of stress and reward, however the intrinsic connectivity and synaptic properties of the inhibitory microcircuit are poorly understood. Neurexin-3 (Nrxn3) is highly expressed in hippocampal inhibitory neurons, but its function at inhibitory synapses has remained elusive. Using slice electrophysiology, imaging, and single-cell RNA sequencing, we identify multiple roles for Nrxn3 at GABAergic parvalbumin (PV) interneuron synapses made onto vSUB regular spiking (RS) and burst spiking (BS) principal neurons. Surprisingly, we found that intrinsic connectivity of vSUB and synaptic function of Nrxn3 in vSUB are sexually dimorphic. We reveal that vSUB PVs make preferential contact with RS neurons in males, but BS neurons in females. Furthermore, we determined that despite comparable Nrxn3 isoform expression in male and female PV neurons, Nrxn3 maintains synapse density at PV-RS synapses in males, but suppresses presynaptic release at the same synapses in females.
Project description:Neuronal activity is regulated in a narrow permissive band for the proper operation of biological neural networks. Changes in synaptic connectivities and network processes during key cognitive activity such as learning might disturb this balance, eliciting compensatory mechanisms to maintain network function1–3. In the neocortex, excitatory pyramidal cells and inhibitory interneurons exhibit robust forms of stabilising plasticity. However, while neuronal plasticity has been thoroughly studied in pyramidal cells4–8, comparatively little is known about how interneurons adapt to ongoing changes in their activity. Here we uncover critical cellular and molecular mechanisms underlying homeostatic regulation of parvalbumin-expressing (PV+) interneurons activity in mouse neocortex. We found that changes in the activity of PV+ interneurons drive cell-autonomous, bi-directional compensatory adjustments of the number and strength of inhibitory synapses received by these cells, specifically from other PV+ interneurons. High-throughput profiling of ribosome-associated mRNAs revealed that increasing the activity of PV+ interneurons leads to the cell-autonomous upregulation of Vgf, a gene encoding multiple neuropeptides. Functional experiments conclusively point towards the role VGF in mediating activity-dependent scaling of inhibitory synapses in PV+ interneurons. Our findings reveal an instructive role for VGF in regulating the connectivity among PV+ interneurons in the adult neocortex.
Project description:Sensitization of spinal nociceptive circuits plays a cardinal role in neuropathic pain. This sensitization depends on new gene expression that is primarily regulated via transcriptional and translational control mechanisms. The relative roles of these mechanisms in regulating gene expression in the clinically relevant chronic phase of neuropathic pain are not well understood. Here, we show that changes in gene expression in the spinal cord during the chronic phase of neuropathic pain are substantially regulated at the translational level. Downregulating spinal translation at the chronic phase alleviated pain hypersensitivity. Cell-type-specific profiling revealed that spinal inhibitory neurons exhibited greater changes in translation after peripheral nerve injury compared to excitatory neurons. Notably, increasing translation selectively in all inhibitory neurons or parvalbumin-positive (PV + ) interneurons, but not excitatory neurons, promoted mechanical pain hypersensitivity. Furthermore, increasing translation in PV + neurons decreased their intrinsic excitability and spiking activity, whereas reducing translation in spinal PV + neurons prevented the nerve injury-induced decrease in excitability. Thus, translational control mechanisms in the spinal cord, primarily in inhibitory neurons, play a critical role in mediating neuropathic pain hypersensitivity.
Project description:Loh KH, Stawski PS, Draycott AS, Udeshi ND, Lehrman EK, Wilton DK, Svinkina T, Deerinck TJ, Ellisman MH, Stevens B, Carr SA, Ting AY. Cell 2016 Excitatory synapses are connections between neurons that promote the propagation of action potentials while inhibitory synapses repress them. Normal brain function relies on the careful balance of these antagonistic connections, which occur via molecularly distinct synaptic clefts. Understanding how this is
achieved relies on knowledge of their protein compositions, yet the clefts remain uncharacterized because they cannot be isolated biochemically. Here, we mapped the proteomes of two of the most common excitatory and inhibitory synaptic clefts in living neurons, using a spatially restricted enzymatic tagging strategy. These proteomes reveal dozens of novel synaptic candidates, and assign numerous known synaptic proteins to a specific cleft type. The molecular differentiation of each cleft allowed us to identify Mdga2 as a specificity factor regulating the presynaptic neurotransmitter recruiting activity of Neuroligin-2 at inhibitory synapses.
Project description:Mutations in the X-linked solute carrier family 6-member (Slc6a8) gene, encoding the protein responsible for cellular creatine (Cr) uptake, cause Creatine Transporter Deficiency (CTD), an X-linked neurometabolic disorder presenting with cognitive dysfunction, autistic-like features, and epilepsy. The pathological determinants of CTD are still poorly understood and this lack of knowledge might hinder the development of therapeutic strategies. Here, we show that Cr deficiency perturbs gene expression in excitatory neurons, inhibitory cells and oligodendrocytes, inducing a remodeling of circuit excitability and synaptic wiring, while no effects are present in astrocytes and endothelial cells. We also describe specific alterations of high-energy demanding, Parvalbumin-expressing (PV+) interneurons, exhibiting a reduction in cellular and synaptic density, and a hypofunctional phenotype, affecting initiation, kinetics and frequency of action potentials. Mice lacking Slc6a8 only in PV+ neurons recapitulate numerous CTD features, such as cognitive deterioration, impaired cortical processing and hyperexcitability of brain circuits, demonstrating that Cr deficit in PV+ cells is sufficient to determine the CTD neurological endophenotype. Moreover, a pharmacological treatment targeted to restore the efficiency of PV+ synapses induces a significant improvement of cortical activity in Slc6a8 knock-out animals. Altogether, these data establish that Slc6a8 is critical for the normal function of PV+ interneurons and that a subtle dysfunction of these cells is critical for the disease pathogenesis, suggesting a novel therapeutic venue for CTD.
Project description:Microglia, the resident immune cells of the brain, have emerged as crucial regulators of synaptic refinement and therefore wiring precision. However, whether the remodeling of distinct synapses during development is mediated by specialized microglia is unknown. Here, using in vivo two-photon imaging, we show that GABA-receptive microglia selectively interact with inhibitory synapses during a critical window of mouse postnatal development. GABA initiates a transcriptional synapse remodeling program within these specialized microglia, which in turn sculpt inhibitory connectivity without impacting excitatory synapses. Ablation of GABAB receptors within microglia impairs this process and leads to stereotyped repetitive behavior and hyperactivity. These findings demonstrate that distinct microglia differentially engage with specific synapse types during development.
Project description:Activity in the healthy brain relies on a concerted interplay of excitation (E) and inhibition (I) via balanced synaptic communication between glutamatergic and GABAergic neurons. A growing number of studies imply that disruption of this E/I balance is a commonality in many brain disorders; however, obtaining mechanistic insight into these disruptions, with translational value for the patient, has typically been hampered by methodological limitations. Cadherin-13 (CDH13) has been associated with autism and attention-deficit/hyperactivity disorder. CDH13 localizes at inhibitory presynapses, specifically of parvalbumin (PV) and somatostatin (SST) expressing GABAergic neurons. However, the mechanism by which CDH13 regulates the function of inhibitory synapses in human neurons remains unknown. Starting from humaninduced pluripotent stem cells, we established a robust method to generate a homogenous population of SST and MEF2C (PV-precursor marker protein) expressing GABAergic neurons (iGABA) in vitro, and co-cultured these with glutamatergic neurons at defined E/I ratios on micro-electrode arrays. We identified functional network parameters that are most reliably affected by GABAergic modulation as such, and through alterations of E/I balance by reduced expression of CDH13 in iGABAs. We found that CDH13 deficiency in iGABAs decreased E/I balance by means of increased inhibition. Moreover, CDH13 interacts with Integrin-β1 and Integrin-β3, which play opposite roles in the regulation of inhibitory synaptic strength via this interaction. Taken together, this model allows for standardized investigation of the E/I balance in a human neuronal background and can be deployed to dissect the cell-type-specific contribution of disease genes to the E/I balance.
Project description:Mutations in the solute carrier family 6-member 8 (Slc6a8) gene, encoding the protein responsible for cellular creatine (Cr) uptake, cause Creatine Transporter Deficiency (CTD), an X-linked neurometabolic disorder presenting with intellectual disability, autistic-like features, and epilepsy. The pathological determinants of CTD are still poorly understood, hindering the development of therapies. In this study, we generated an extensive transcriptomic profile of CTD showing that Cr deficiency causes perturbations of gene expression in excitatory neurons, inhibitory cells, and oligodendrocytes which result in remodeling of circuit excitability and synaptic wiring. We also identified specific alterations of parvalbumin-expressing (PV+) interneurons, exhibiting a reduction in cellular and synaptic density, and a hypofunctional electrophysiological phenotype. Mice lacking Slc6a8 only in PV+ interneurons recapitulated numerous CTD features, including cognitive deterioration, impaired cortical processing and hyperexcitability of brain circuits, demonstrating that Cr deficit in PV+ interneurons is sufficient to determine the neurological phenotype of CTD. Moreover, a pharmacological treatment targeted to restore the efficiency of PV+ synapses significantly improved cortical activity in Slc6a8 knock-out animals. Altogether, these data demonstrate that Slc6a8 is critical for the normal function of PV+ interneurons and that impairment of these cells is central in the disease pathogenesis, suggesting a novel therapeutic venue for CTD.
Project description:Synapses are fundamental organizers of precise signal propagation between neurons. Maintaining synapse assemblies require interactions between pre- and post- synaptic proteins, notably cell adhesion molecules (CAMs). It has been proposed that the function of Neuroligins (Nlgn1 - 4), postsynaptic CAMs, relies on the formation of trans-synaptic complexes with Neurexins (Nrxs), presynaptic CAMs. Nlgn3 is a unique Nlgn isoform that localizes at both excitatory and inhibitory synapses. However, Nlgn3 function mediated through Nrx interaction is mostly unknown. Here, we find for the first time that Nlgn3 localizes at postsynaptic sites apposing vesicular glutamate transporter 3 (VGT3)-expressing inhibitory terminals. Overexpression and knockdown approaches indicate that Nlgn3 regulates VGT3-positive inhibitory interneuron-mediated synaptic transmission. Fluorescent in situ hybridization and single-cell RNA sequencing studies revealed that αNrxn1 and βNrxn3 are VGT3 interneuron-specific Nrxn isoforms and the expression levels of Nrxn splice isoforms are highly diverse in VGT3 interneurons, respectively. Most importantly, postsynaptic Nlgn3 requires presynaptic αNrx1+AS4 expressed in VGT3-positive interneurons to regulate inhibitory synaptic transmission. Our results strongly suggest that specific Nlgn-Nrx interaction generate distinct functional properties at synapses.
Project description:We optimized Voltage-Seq which combines, all-optical physiology, spatial mapping, on-site classification, and RNA-transcriptomics to robustly increase the throughput of synaptic connectivity testing and targeted molecular classification of postsynaptic neurons. Single-cell RNA-sequencing was performed on spatial- and voltage-recorded neurons in the mouse PAG. Uniform Manifold Approximation and Projection (UMAP) clustered cells as excitatory or inhibitory, and further differential expression analyses highlighted putative marker genes of GABAergic neurons. These sequencing results were in agreement with in-situ hybridization (ISH) and neuronal activity recordings.
Project description:Injury of descending motor tracts remodels cortical circuitry and leads to enhanced neuronal excitability, thus influencing recovery following injury. The neuron-specific contributions remain unclear due to the complex cellular composition and connectivity of the CNS. We developed a microfluidics-based in vitro model system to examine intrinsic synaptic remodeling following axon damage. We found that distal axotomy of cultured rat pyramidal neurons caused dendritic spine loss at synapses onto the injured neurons followed by a persistent retrograde enhancement in presynaptic excitability over days. These in vitro results mirrored hyper-activity of directly injured corticospinal neurons in hindlimb motor cortex layer Vb following spinal cord contusion. In vitro axotomy-induced hyper-excitability coincided with elimination of inhibitory presynaptic terminals, including those formed onto dendritic spines. We identified netrin-1 as downregulated following axotomy and exogenous netrin-1 applied 2 days after injury normalized spine density, presynaptic excitability, and the fraction of inhibitory inputs onto injured neurons. These findings demonstrate a novel model system for studying the response of pyramidal circuitry to axotomy and provide new insights of neuron-specific mechanisms that contribute to synaptic remodeling.