Single genomic enhancers drive experience-dependent GABAergic plasticity to maintain sensory processing in the adult cortex

Experience-dependent plasticity of synapses modulates information processing in neural circuits and is essential for cognitive functions. The genome, via non-coding enhancers, was proposed to control information processing and circuit plasticity by regulating experience-induced transcription of genes that modulate specific sets of synapses. To test this idea, we analyze here the cellular and circuit functions of the genomic mechanisms that control the experience-induced transcription of Igf1 (insulin-like growth factor 1) in vasoactive intestinal peptide (VIP) interneurons (INs) in the visual cortex of adult mice. We find that two sensory-induced enhancers selectively and cooperatively drive the activity-induced transcription of Igf1 to thereby promote GABAergic inputs onto VIP INs and to homeostatically control the ratio between excitation and inhibition (E/I ratio)-in turn, this restricts neural activity in VIP INs and principal excitatory neurons and maintains spatial frequency tuning. Thus, enhancer-mediated activity-induced transcription maintains sensory processing in the adult cortex via homeostatic modulation of E/I ratio.

Bicuculline restores frequency-dependent hippocampal I/E ratio and circuit function in PGC-1ɑ null mice

Altered inhibition/excitation (I/E) balance contributes to various brain disorders. Dysfunctional GABAergic interneurons enhance or reduce inhibition, resulting in I/E imbalances. Differences in short-term plasticity between excitation and inhibition cause frequency-dependence of the I/E ratio, which can be altered by GABAergic dysfunction. However, it is unknown whether I/E imbalances can be rescued pharmacologically using a single dose when the imbalance magnitude is frequency-dependent. Loss of PGC-1α (peroxisome proliferator activated receptor γ coactivator 1α) causes transcriptional dysregulation in hippocampal GABAergic interneurons. PGC-1α-/- slices have enhanced baseline inhibition onto CA1 pyramidal cells, causing increased I/E ratio and impaired circuit function. High frequency stimulation reduces the I/E ratio and recovers circuit function in PGC-1α-/- slices. Here we tested if using a low dose of bicuculline that can restore baseline I/E ratio can also rescue the frequency-dependent I/E imbalances in these mice. Remarkably, bicuculline did not reduce the I/E ratio below that of wild type during high frequency stimulation. Interestingly, bicuculline enhanced the paired-pulse ratio (PPR) of disynaptic inhibition without changing the monosynaptic inhibition PPR, suggesting that bicuculline modifies interneuron recruitment and not GABA release. Bicuculline improved CA1 output in PGC-1α-/- slices, enhancing EPSP-spike coupling to wild type levels at high and low frequencies. Our results show that it is possible to rescue frequency-dependent I/E imbalances in an animal model of transcriptional dysregulation with a single treatment.

Dynamic interplay between thalamic activity and Cajal-Retzius cells regulates the wiring of cortical layer 1

Cortical wiring relies on guidepost cells and activity-dependent processes that are thought to act sequentially. Here, we show that the construction of layer 1 (L1), a main site of top-down integration, is regulated by crosstalk between transient Cajal-Retzius cells (CRc) and spontaneous activity of the thalamus, a main driver of bottom-up information. While activity was known to regulate CRc migration and elimination, we found that prenatal spontaneous thalamic activity and NMDA receptors selectively control CRc early density, without affecting their demise. CRc density, in turn, regulates the distribution of upper layer interneurons and excitatory synapses, thereby drastically impairing the apical dendrite activity of output pyramidal neurons. In contrast, postnatal sensory-evoked activity had a limited impact on L1 and selectively perturbed basal dendrites synaptogenesis. Collectively, our study highlights a remarkable interplay between thalamic activity and CRc in L1 functional wiring, with major implications for our understanding of cortical development.

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Prenatal thalamic waves of activity regulate CRc density in L1

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Prenatal and postnatal CRc manipulations alter specific interneuron populations

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Postnatal CRc shape L5 apical dendrite structural and functional properties

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Early sensory activity selectively regulates L5 basal dendrite spine formation

Presynaptic GABAB receptor-mediated network excitation in the medial prefrontal cortex of Tsc2+/- mice

The TSC1 and TSC2 tumor suppressor genes control the activity of mechanistic target of rapamycin (mTOR) pathway. Elevated activity of this pathway in Tsc2^+/- mouse model leads to reduction of postsynaptic GABA_B receptor-mediated inhibition and hyperexcitability in the medial prefrontal cortex (mPFC). In this study, we asked whether presynaptic GABA_B receptors (GABA_BRs) can compensate this shift of hyperexcitability. Experiments were performed in brain slices from adolescent wild-type (WT) and Tsc2^+/- mice. Miniature and spontaneous postsynaptic currents (m/sPSCs) were recorded from layer 2/3 pyramidal neurons in mPFC using patch-clamp technique using a Cs⁺-based intrapipette solution. Presynaptic GABA_BRs were activated by baclofen (10 µM) or blocked by CGP55845 (1 µM). Independent on genotype, GABA_BR modulators bidirectionally change miniature excitatory postsynaptic current (mEPSC) frequency by about 10%, indicating presynaptic GABA_BR-mediated effects on glutamatergic transmission are comparable in both genotypes. In contrast, frequencies of both mIPSCs and sIPCSs were suppressed by baclofen stronger in Tsc2^+/- neurons than in WT ones, whereas CGP55845 significantly increased (m/s)IPSC frequencies only in WT cells. Effects of baclofen and CGP55845 on the amplitudes of evoked (e)IPSCs confirmed these observations. These data indicate (1) that GABAergic synapses are inhibited by ambient GABA in WT but not in Tsc2^+/- slices, and (2) that baclofen shifts the E/I ratio, determined as the ratio of (m/s)EPSC frequency to (m/s)IPSC frequency, towards excitation only in Tsc2^+/- cells. This excitatory presynaptic GABA_BR-mediated action has to be taken into account for a possible medication of mental disorders using baclofen.

Optimal Organization of Functional Connectivity Networks for Segregation and Integration With Large-Scale Critical Dynamics in Human Brains

The optimal organization for functional segregation and integration in brain is made evident by the “small-world” feature of functional connectivity (FC) networks and is further supported by the loss of this feature that has been described in many types of brain disease. However, it remains unknown how such optimally organized FC networks arise from the brain's structural constrains. On the other hand, an emerging literature suggests that brain function may be supported by critical neural dynamics, which is believed to facilitate information processing in brain. Though previous investigations have shown that the critical dynamics plays an important role in understanding the relation between whole brain structural connectivity and functional connectivity, it is not clear if the critical dynamics could be responsible for the optimal FC network configuration in human brains. Here, we show that the long-range temporal correlations (LRTCs) in the resting state fMRI blood-oxygen-level-dependent (BOLD) signals are significantly correlated with the topological matrices of the FC brain network. Using structure-dynamics-function modeling approach that incorporates diffusion tensor imaging (DTI) data and simple cellular automata dynamics, we showed that the critical dynamics could optimize the whole brain FC network organization by, e.g., maximizing the clustering coefficient while minimizing the characteristic path length. We also demonstrated with a more detailed excitation-inhibition neuronal network model that loss of local excitation-inhibition (E/I) balance causes failure of critical dynamics, therefore disrupting the optimal FC network organization. The results highlighted the crucial role of the critical dynamics in forming an optimal organization of FC networks in the brain and have potential application to the understanding and modeling of abnormal FC configurations in neuropsychiatric disorders.

Modulation of Coordinated Activity across Cortical Layers by Plasticity of Inhibitory Synapses

In the neocortex, synaptic inhibition shapes all forms of spontaneous and sensory evoked activity. Importantly, inhibitory transmission is highly plastic, but the functional role of inhibitory synaptic plasticity is unknown. In the mouse barrel cortex, activation of layer (L) 2/3 pyramidal neurons (PNs) elicits strong feedforward inhibition (FFI) onto L5 PNs. We find that FFI involving parvalbumin (PV)-expressing cells is strongly potentiated by postsynaptic PN burst firing. FFI plasticity modifies the PN excitation-to-inhibition (E/I) ratio, strongly modulates PN gain, and alters information transfer across cortical layers. Moreover, our LTPi-inducing protocol modifies firing of L5 PNs and alters the temporal association of PN spikes to γ-oscillations both in vitro and in vivo. All of these effects are captured by unbalancing the E/I ratio in a feedforward inhibition circuit model. Altogether, our results indicate that activity-dependent modulation of perisomatic inhibitory strength effectively influences the participation of single principal cortical neurons to cognition-relevant network activity.

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Feedforward inhibition (FFI) of layer 5 pyramidal neurons (PNs) is highly plastic

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Long-term potentiation of FFI modulates spiking activity of layer 5 PNs

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LTPi affects information transfer across cortical layers

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The strength of LTPi determines the phase locking of PN firing to γ-oscillations

Activity labeling in vivo using CaMPARI2 reveals intrinsic and synaptic differences between neurons with high and low firing rate set points

Neocortical pyramidal neurons regulate firing around a stable mean firing rate (FR) that can differ by orders of magnitude between neurons, but the factors that determine where individual neurons sit within this broad FR distribution are not understood. To access low- and high-FR neurons for ex vivo analysis, we used Ca2+- and UV-dependent photoconversion of CaMPARI2 in vivo to permanently label neurons according to mean FR. CaMPARI2 photoconversion was correlated with immediate early gene expression and higher FRs ex vivo and tracked the drop and rebound in ensemble mean FR induced by prolonged monocular deprivation. High-activity L4 pyramidal neurons had greater intrinsic excitability and recurrent excitatory synaptic strength, while E/I ratio, local output strength, and local connection probability were not different. Thus, in L4 pyramidal neurons (considered a single transcriptional cell type), a broad mean FR distribution is achieved through graded differences in both intrinsic and synaptic properties.

Haploinsufficiency of Tsc2 Leads to Hyperexcitability of Medial Prefrontal Cortex via Weakening of Tonic GABAB Receptor-mediated Inhibition

Loss-of-function mutation in one of the tumor suppressor genes TSC1 or TSC2 is associated with several neurological and psychiatric diseases, including autism spectrum disorders (ASDs). As an imbalance between excitatory and inhibitory neurotransmission, E/I ratio is believed to contribute to the development of these disorders, we investigated synaptic transmission during the first postnatal month using the Tsc2+/- mouse model. Electrophysiological recordings were performed in acute brain slices of medial prefrontal cortex. E/I ratio at postnatal day (P) 15-19 is increased in Tsc2+/- mice as compared with wildtype (WT). At P25-30, facilitated GABAergic transmission reduces E/I ratio to the WT level, but weakening of tonic GABAB receptor (GABABR)-mediated inhibition in Tsc2+/- mice leads to hyperexcitability both at single cell and neuronal network level. Short (1 h) preincubation of P25-30 Tsc2+/- slices with baclofen restores the GABABR-mediated inhibition and reduces network excitability. Interestingly, the same treatment at P15-19 leads to weakening of GABABR-mediated inhibition. We hypothesize that a dysfunction of tonic GABABR-mediated inhibition might contribute to the development of ASD symptoms and suggest that GABABR activation within an appropriate time window may be considered as a therapeutic target in ASD.

Subanesthetic ketamine exerts antidepressant-like effects in adult rats exposed to juvenile stress

Juvenile stress, like that caused by childhood maltreatment, is a significant risk factor for psychiatric disorders such as depression later in life. Recently, the antidepressant effect of ketamine, a noncompetitive N-methyl-d-aspartate receptor antagonist, has been widely investigated. However, little is known regarding its efficacy against depressive-like alterations caused by juvenile stress, which is clinically relevant in human depression. In the present study, we evaluated the antidepressant-like effect of ketamine in adult rats that had been subjected to juvenile stress. Depressive-like behavior was assessed using the forced swim test (FST), and electrophysiological and morphological alterations in the layer V pyramidal cells of the prelimbic cortex were examined using whole-cell patch-clamp recordings and subsequent recording-cell specific fluorescence imaging. We demonstrated that ketamine (10 mg/kg) attenuated the increased immobility time caused by juvenile stress in the FST, restored the diminished excitatory postsynaptic currents, and caused atrophic changes in the apical dendritic spines. Ketamine's effects reversing impaired excitatory/inhibitory ratio of postsynaptic currents were also revealed. These results indicated that ketamine could be effective in reversing the depression-like alterations caused by juvenile stress.

Cross-Modal Reinstatement of Thalamocortical Plasticity Accelerates Ocular Dominance Plasticity in Adult Mice

Plasticity of thalamocortical (TC) synapses is robust during early development and becomes limited in the adult brain. We previously reported that a short duration of deafening strengthens TC synapses in the primary visual cortex (V1) of adult mice. Here, we demonstrate that deafening restores NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) of TC synapses onto principal neurons in V1 layer 4 (L4), which is accompanied by an increase in NMDAR function. In contrast, deafening did not recover long-term depression (LTD) at TC synapses. Potentiation of TC synapses by deafening is absent in parvalbumin-positive (PV+) interneurons, resulting in an increase in feedforward excitation to inhibition (E/I) ratio. Furthermore, we found that a brief duration of deafening adult mice recovers rapid ocular dominance plasticity (ODP) mainly by accelerating potentiation of the open-eye responses. Our results suggest that cross-modal sensory deprivation promotes adult cortical plasticity by specifically recovering TC-LTP and increasing the E/I ratio.

Plasticity of thalamocortical (TC) synapses is limited in adults. Rodríguez et al. demonstrate that a brief period of deafening adults recovers LTP at TC synapses in visual cortex and accelerates ocular dominance plasticity. These results suggest that cross-modal sensory deprivation may be an effective way to promote adult cortical plasticity.

Loss of Synapse Repressor MDGA1 Enhances Perisomatic Inhibition, Confers Resistance to Network Excitation, and Impairs Cognitive Function

Synaptopathies contributing to neurodevelopmental disorders are linked to mutations in synaptic organizing molecules, including postsynaptic neuroligins, presynaptic neurexins, and MDGAs, which regulate their interaction. The role of MDGA1 in suppressing inhibitory versus excitatory synapses is controversial based on in vitro studies. We show that genetic deletion of MDGA1 in vivo elevates hippocampal CA1 inhibitory, but not excitatory, synapse density and transmission. Furthermore, MDGA1 is selectively expressed by pyramidal neurons and regulates perisomatic, but not distal dendritic, inhibitory synapses. Mdga1^-/- hippocampal networks demonstrate muted responses to neural excitation, and Mdga1^-/- mice are resistant to induced seizures. Mdga1^-/- mice further demonstrate compromised hippocampal long-term potentiation, consistent with observed deficits in spatial and context-dependent learning and memory. These results suggest that mutations in MDGA1 may contribute to cognitive deficits through altered synaptic transmission and plasticity by loss of suppression of inhibitory synapse development in a subcellular domain- and cell-type-selective manner.

Pupillary autonomic dysfunction in patients with ANCA-associated vasculitis

OBJECTIVE

To assess autonomic function by infrared dynamic pupillometry in patients with ANCA-vasculitis (AAV) in correlation to autonomic symptoms, disease specific clinical parameters and cardiovascular reflex tests.

METHODS

Patients with AAV and healthy controls underwent pupillometry at rest and after sympathetic stimulation (cold pressor test). Three parasympathetic parameters (amplitude, relative amplitude, maximum constriction velocity) and one sympathetic parameter (late dilatation velocity) were assessed. Results were correlated with clinical parameters, symptoms of autonomic dysfunction (COMPASS31 questionnaire), heart rate variability during deep breathing test and blood pressure response to pain.

RESULTS

23 patients and 18 age-matched controls were enrolled. Patients had a smaller amplitude (1.44 vs. 1.70 mm; p = 0.009) and a slower constriction velocity (4.15 vs. 4.71 mm/s; p = 0.028) at baseline and after sympathetic stimulation (1.47 vs. 1.81 mm, p = 0.001; 4.38 vs. 5.19 mm/s, p = 0.006, respectively). Relative amplitude was significantly smaller in patients after sympathetic stimulation (28.6 vs. 32.5%; p = 0.043), but not at baseline. There was no difference in sympathetic pupillary response between the groups. In patients, parasympathetic pupil response was correlated negatively with age and positively with parasympathetic cardiac response. After adjusting for age, no significant correlation was observed with clinical parameters. However, there was a trend towards a negative correlation with disease duration, vasculitis damage index and CRP.

CONCLUSION

Patients with AAV exhibit parasympathetic pupillary autonomic dysfunction. Although correlations were weak and not significant, pupillary autonomic dysfunction is rather linked to chronic damage than to active inflammation or symptoms of autonomic dysfunction.

Interneuron Transcriptional Dysregulation Causes Frequency-Dependent Alterations in the Balance of Inhibition and Excitation in Hippocampus

Circuit dysfunction in complex brain disorders such as schizophrenia and autism is caused by imbalances between inhibitory and excitatory synaptic transmission (I/E). Short-term plasticity differentially alters responses from excitatory and inhibitory synapses, causing the I/E ratio to change as a function of frequency. However, little is known about I/E ratio dynamics in complex brain disorders. Transcriptional dysregulation in interneurons, particularly parvalbumin interneurons, is a consistent pathophysiological feature of schizophrenia. Peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α) is a transcriptional coactivator that in hippocampus is highly concentrated in inhibitory interneurons and regulates parvalbumin transcription. Here, we used PGC-1α(-/-) mice to investigate effects of interneuron transcriptional dysregulation on the dynamics of the I/E ratio at the synaptic and circuit level in hippocampus. We find that loss of PGC-1α increases the I/E ratio onto CA1 pyramidal cells in response to Schaffer collateral stimulation in slices from young adult mice. The underlying mechanism is enhanced basal inhibition, including increased inhibition from parvalbumin interneurons. This decreases the spread of activation in CA1 and dramatically limits pyramidal cell spiking, reducing hippocampal output. The I/E ratio and CA1 output are partially restored by paired-pulse stimulation at short intervals, indicating frequency-dependent effects. However, circuit dysfunction persists, indicated by alterations in kainate-induced gamma oscillations and impaired nest building. Together, these results show that transcriptional dysregulation in hippocampal interneurons causes frequency-dependent alterations in I/E ratio and circuit function, suggesting that PGC-1α deficiency in psychiatric and neurological disorders contributes to disease by causing functionally relevant alterations in I/E balance.

SIGNIFICANCE STATEMENT

Alteration in the inhibitory and excitatory synaptic transmission (I/E) balance is a fundamental principle underlying the circuit dysfunction observed in many neuropsychiatric and neurodevelopmental disorders. The I/E ratio is dynamic, continuously changing because of synaptic short-term plasticity. We show here that transcriptional dysregulation in interneurons, particularly parvalbumin interneurons, causes frequency-dependent alterations in the I/E ratio and in circuit function in hippocampus. Peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α-deficient) mice have enhanced inhibition in CA1, the opposite of what is seen in cortex. This study fills an important gap in current understanding of how changes in inhibition in complex brain disorders affect I/E dynamics, leading to region-specific circuit dysfunction and behavioral impairment. This study also provides a conceptual framework for analyzing the effects of short-term plasticity on the I/E balance in disease models.

Long-lasting changes in neural networks to compensate for altered nicotinic input

The nervous system must balance excitatory and inhibitory input to constrain network activity levels within a proper dynamic range. This is a demanding requirement during development, when networks form and throughout adulthood as networks respond to constantly changing environments. Defects in the ability to sustain a proper balance of excitatory and inhibitory activity are characteristic of numerous neurological disorders such as schizophrenia, Alzheimer's disease, and autism. A variety of homeostatic mechanisms appear to be critical for balancing excitatory and inhibitory activity in a network. These are operative at the level of individual neurons, regulating their excitability by adjusting the numbers and types of ion channels, and at the level of synaptic connections, determining the relative numbers of excitatory versus inhibitory connections a neuron receives. Nicotinic cholinergic signaling is well positioned to contribute at both levels because it appears early in development, extends across much of the nervous system, and modulates transmission at many kinds of synapses. Further, it is known to influence the ratio of excitatory-to-inhibitory synapses formed on neurons during development. GABAergic inhibitory neurons are likely to be key for maintaining network homeostasis (limiting excitatory output), and nicotinic signaling is known to prominently regulate the activity of several GABAergic neuronal subtypes. But how nicotinic signaling achieves this and how networks may compensate for the loss of such input are important questions remaining unanswered. These issues are reviewed.

Shank3-mutant mice lacking exon 9 show altered excitation/inhibition balance, enhanced rearing, and spatial memory deficit

Shank3 is a postsynaptic scaffolding protein implicated in synapse development and autism spectrum disorders. The Shank3 gene is known to produce diverse splice variants whose functions have not been fully explored. In the present study, we generated mice lacking Shank3 exon 9 (Shank3 (Δ9) mice), and thus missing five out of 10 known Shank3 splice variants containing the N-terminal ankyrin repeat region, including the longest splice variant, Shank3a. Our X-gal staining results revealed that Shank3 proteins encoded by exon 9-containing splice variants are abundant in upper cortical layers, striatum, hippocampus, and thalamus, but not in the olfactory bulb or cerebellum, despite the significant Shank3 mRNA levels in these regions. The hippocampal CA1 region of Shank3 (Δ9) mice exhibited reduced excitatory transmission at Schaffer collateral synapses and increased frequency of spontaneous inhibitory synaptic events in pyramidal neurons. In contrast, prelimbic layer 2/3 pyramidal neurons in the medial prefrontal cortex displayed decreased frequency of spontaneous inhibitory synaptic events, indicating alterations in the ratio of excitation/inhibition (E/I ratio) in the Shank3 (Δ9) brain. These mice displayed a mild increase in rearing in a novel environment and mildly impaired spatial memory, but showed normal social interaction and repetitive behavior. These results suggest that ankyrin repeat-containing Shank3 splice variants are important for E/I balance, rearing behavior, and spatial memory.

Impaired activity-dependent neural circuit assembly and refinement in autism spectrum disorder genetic models

Early-use activity during circuit-specific critical periods refines brain circuitry by the coupled processes of eliminating inappropriate synapses and strengthening maintained synapses. We theorize these activity-dependent (A-D) developmental processes are specifically impaired in autism spectrum disorders (ASDs). ASD genetic models in both mouse and Drosophila have pioneered our insights into normal A-D neural circuit assembly and consolidation, and how these developmental mechanisms go awry in specific genetic conditions. The monogenic fragile X syndrome (FXS), a common cause of heritable ASD and intellectual disability, has been particularly well linked to defects in A-D critical period processes. The fragile X mental retardation protein (FMRP) is positively activity-regulated in expression and function, in turn regulates excitability and activity in a negative feedback loop, and appears to be required for the A-D remodeling of synaptic connectivity during early-use critical periods. The Drosophila FXS model has been shown to functionally conserve the roles of human FMRP in synaptogenesis, and has been centrally important in generating our current mechanistic understanding of the FXS disease state. Recent advances in Drosophila optogenetics, transgenic calcium reporters, highly-targeted transgenic drivers for individually-identified neurons, and a vastly improved connectome of the brain are now being combined to provide unparalleled opportunities to both manipulate and monitor A-D processes during critical period brain development in defined neural circuits. The field is now poised to exploit this new Drosophila transgenic toolbox for the systematic dissection of A-D mechanisms in normal versus ASD brain development, particularly utilizing the well-established Drosophila FXS disease model.

Cardiac autonomic function and insulin resistance for the development of hypertension: a six-year epidemiological follow-up study

BACKGROUND AND AIMS

To explore the impact of cardiac autonomic function (CAF) and insulin resistance (IR) on incident hypertension.

METHODS AND RESULTS

In 1996, 1638 subjects finished baseline examination, which included anthropometry, blood pressures, CAF, blood biochemistry, plasma insulin, urine examination and electrocardiogram. CAF included standard deviation of normal-to-normal intervals or RR intervals (SDNN), low- and high-frequency power spectrum (LF and HF), and LF/HF ratio at supine for 5 min, the RR interval changes during lying-to-standing maneuver, and the ratio between the longest RR interval during expiration and the shortest RR interval during inspiration (E/I ratio). We used homeostasis model assessment to define beta cell function (HOMA-B) and insulin resistance (HOMA-IR). In total, 992 non-hypertensive participants completed the follow-up assessment in 2003 and 959 participants were included for the final analysis. Incident hypertension was determined by blood pressure status at follow-up. In unadjusted model, both square root of HOMA-IR (OR:3.37, 95%CI: 2.10-6.64) and HOMA-B (OR:0.996, 95%CI: 0.992-0.999) were related to incident hypertension. In multivariate model, square root of HOMA-IR (OR:1.97, 95%CI: 1.05-3.70), but not HOMA-B, was associated with incident hypertension. After further adjustment for baseline CAF, the positive relationship between the square root of HOMA-IR and incident hypertension disappeared. In contrast, LF/HF ratio (OR:1.18, 95%CI: 1.01-1.37), HF power (OR:0.98, 95%CI: 0.96-0.999), and E/I ratio (OR:0.71, 95%CI: 0.54-0.95) were each independently associated with incident hypertension after further adjustment for HOMA measures.

CONCLUSION

Sympathovagal imbalance with an apparently decreased parasympathetic tone is an important predictor of incident hypertension independent of IR.

Genetic controls balancing excitatory and inhibitory synaptogenesis in neurodevelopmental disorder models

Proper brain function requires stringent balance of excitatory and inhibitory synapse formation during neural circuit assembly. Mutation of genes that normally sculpt and maintain this balance results in severe dysfunction, causing neurodevelopmental disorders including autism, epilepsy and Rett syndrome. Such mutations may result in defective architectural structuring of synaptic connections, molecular assembly of synapses and/or functional synaptogenesis. The affected genes often encode synaptic components directly, but also include regulators that secondarily mediate the synthesis or assembly of synaptic proteins. The prime example is Fragile X syndrome (FXS), the leading heritable cause of both intellectual disability and autism spectrum disorders. FXS results from loss of mRNA-binding FMRP, which regulates synaptic transcript trafficking, stability and translation in activity-dependent synaptogenesis and plasticity mechanisms. Genetic models of FXS exhibit striking excitatory and inhibitory synapse imbalance, associated with impaired cognitive and social interaction behaviors. Downstream of translation control, a number of specific synaptic proteins regulate excitatory versus inhibitory synaptogenesis, independently or combinatorially, and loss of these proteins is also linked to disrupted neurodevelopment. The current effort is to define the cascade of events linking transcription, translation and the role of specific synaptic proteins in the maintenance of excitatory versus inhibitory synapses during neural circuit formation. This focus includes mechanisms that fine-tune excitation and inhibition during the refinement of functional synaptic circuits, and later modulate this balance throughout life. The use of powerful new genetic models has begun to shed light on the mechanistic bases of excitation/inhibition imbalance for a range of neurodevelopmental disease states.