Interneuron-Targeted Disruption of SYNGAP1 Alters Sensory Representations in the Neocortex and Impairs Sensory Learning

SYNGAP1 haploinsufficiency in humans leads to severe neurodevelopmental disorders characterized by intellectual disability, autism, epilepsy, and sensory processing deficits. However, the circuit mechanisms underlying these disorders are not well understood. In mice, a decrease of SynGAP levels results in cognitive deficits by interfering with the development of excitatory glutamatergic connections. Recent evidence suggests that SynGAP also plays a crucial role in the development and function of GABAergic inhibitory interneurons. Nevertheless, it remains uncertain whether and to what extent the expression of SYNGAP1 in inhibitory interneurons contributes to cortical circuit function and related behaviors. The activity of cortical neurons has not been measured simultaneously with behavior. To address these gaps, we recorded from layer 2/3 neurons in the primary whisker somatosensory cortex (wS1) of mice while they learned to perform a whisker tactile detection task. Our results demonstrate that mice with interneuron-specific SYNGAP1 haploinsufficiency exhibit learning deficits characterized by heightened behavioral responses in the absence of relevant sensory input and premature responses to unrelated sensory stimuli not associated with reward acquisition. These behavioral deficits are accompanied by specific circuit abnormalities within wS1. Interneuron-specific SYNGAP1 haploinsufficiency increases detrimental neuronal correlations directly related to task performance and enhances responses to irrelevant sensory stimuli unrelated to the reward acquisition. In summary, our findings indicate that a reduction of SynGAP in inhibitory interneurons impairs sensory representation in the primary sensory cortex by disrupting neuronal correlations, which likely contributes to the observed cognitive deficits in mice with pan-neuronal SYNGAP1 haploinsufficiency.SIGNIFICANCE STATEMENT SYNGAP1 haploinsufficiency leads to severe neurodevelopmental disorders. The exact nature of neural circuit dysfunction caused by SYNGAP1 haploinsufficiency remains poorly understood. SynGAP plays a critical role in the function of GABAergic inhibitory interneurons as well as glutamatergic pyramidal neurons in the neocortex. Whether and how decreasing SYNGAP1 level in inhibitory interneurons disrupts a behaviorally relevant circuit remains unclear. We measure neural activity and behavior in mice learning a perceptual task. Mice with interneuron-targeted disruption of SYNGAP1 display increased detrimental neuronal correlations and elevated responses to irrelevant sensory inputs, which are related to impaired task performance. These results show that cortical interneuron dysfunction contributes to sensory deficits in SYNGAP1 haploinsufficiency with important implications for identifying therapeutic targets.

Delay tactics for action in the cortex

How the brain computes with sensory input to execute a delayed motor response remains elusive. In this issue of Neuron, Esmaeili et al. (2021) reveal a key cortical circuit that underlies sensorimotor transformation to execute a delayed motor output following a specific sensory input.

Spectral hallmark of auditory-tactile interactions in the mouse somatosensory cortex

To synthesize a coherent representation of the external world, the brain must integrate inputs across different types of stimuli. Yet the mechanistic basis of this computation at the level of neuronal populations remains obscure. Here, we investigate tactile-auditory integration using two-photon Ca2+ imaging in the mouse primary (S1) and secondary (S2) somatosensory cortices. Pairing sound with whisker stimulation modulates tactile responses in both S1 and S2, with the most prominent modulation being robust inhibition in S2. The degree of inhibition depends on tactile stimulation frequency, with lower frequency responses the most severely attenuated. Alongside these neurons, we identify sound-selective neurons in S2 whose responses are inhibited by high tactile frequencies. These results are consistent with a hypothesized local mutually-inhibitory S2 circuit that spectrally selects tactile versus auditory inputs. Our findings enrich mechanistic understanding of multisensory integration and suggest a key role for S2 in combining auditory and tactile information.

The Interplay Between Cortical State and Perceptual Learning: A Focused Review

Measurements of population activity in alert animals have demonstrated that the intrinsic response state of the cortex has profound effects on the neuronal representation of sensory inputs, raising the possibility that cortical state could influence the behavioral performance in perceptual learning (PL). PL is a process by which sensory experience leads to gradual and semi-permanent improvements in perceptual judgment, and it is generally agreed that these improvements are modulated by sensory cortical areas. Although the precise neural mechanisms underlying the improved perceptual judgment remain unclear, cortical state has been shown to impact the behavioral outcome of PL. We discuss several ways in which cortical state might influence PL based on the recent evidence for state-dependent modulation of sensory encoding. Conversely, training in a certain perceptual task feeds back to modulate cortical state, suggesting a bi-directional relationship between cortical state and behavioral outcomes of PL. We highlight the recent studies that shed light on the mechanism of the interplay between cortical state and PL.

Organization of orientation-specific whisker deflection responses in layer 2/3 of mouse somatosensory cortex

The rodent whisker-barrel system is characterized by its patterned somatotopic mapping between the sensory periphery and multiple regions of the brain. While somatotopy in the whisker system is established, we know far less about how preferences for stimulus orientation or other features are organized. Mouse somatosensation is an increasingly popular model for circuit-based dissection of perceptual decision making and learning, yet our understanding of how stimulus feature representations are organized in the cortex is incomplete. Here, we used in vivo two-photon calcium imaging to monitor activity of populations of layer (L) 2/3 neurons in the mouse primary somatosensory cortex during deflections of a single whisker in two orthogonal orientations (azimuthal or elevational). We split the population response to whisker deflections into an orientation-specific component and a non-specific component that reflected overall excitability in response to deflection of a single whisker. Orientation-specific responses were organized in a locally heterogeneous and spatially distributed manner. Correlations in the stimulus-independent trial-to-trial variability of pairs of neurons were higher among neurons that preferred the same orientation. These correlations depended on similarity in both orientation-specific and non-specific components of responses to single-whisker deflections. Our results shed light on L2/3 organization in mouse somatosensory cortex, and lay a foundation for dissecting circuit mechanisms of perceptual learning and decision-making during orientation discrimination tasks.

Sensory and decision-related activity propagate in a cortical feedback loop during touch perception

The brain transforms physical sensory stimuli into meaningful perceptions. In animals making choices about sensory stimuli, neuronal activity in successive cortical stages reflects a progression from sensation to decision. Feedforward and feedback pathways connecting cortical areas are critical for this transformation. However, the computational functions of these pathways are poorly understood because pathway-specific activity has rarely been monitored during a perceptual task. Using cellular-resolution, pathway-specific imaging, we measured neuronal activity across primary (S1) and secondary (S2) somatosensory cortices of mice performing a tactile detection task. S1 encoded the stimulus better than S2, while S2 activity more strongly reflected perceptual choice. S1 neurons projecting to S2 fed forward activity that predicted choice. Activity encoding touch and choice propagated in an S1-S2 loop along feedforward and feedback axons. Our results suggest that sensory inputs converge into a perceptual outcome as feedforward computations are reinforced in a feedback loop.

Abstract 2649: Human adipose tissue-derived mesenchymal stem cells can target brain tumor initiating cells

Abstract

The discovery of neural stem cells offers paradigm shift in brain tumor research. In neuro-oncology, the biology of neural stem cells has been pursued in two ways: as cancer stem cells to understand the origin and maintenance of brain tumors and as a potential cell-based vehicle for gene therapy. In addition to neural stem cells, mesenchymal stem cells (MSCs) have been reported to possess tumor-tropic migratory capacities. However, there is scanty data on migratory capacity of MSC toward brain tumor initiating cells (BTICs). This study focuses on investigating the ability of human adipose tissue derived MSCs (hAT-MSCs) to target BTICs and their cross-talk in the microenvironment.

BTICs were isolated from three different kinds of brain tumors (medulloblastoma, atypical teratoid/rhabdoid tumor (ATRT), glioblastoma). The migration capacities of hAT-MSCs toward BTICs were examined both in vitro transwell assay and in vivo bioluminescence imaging analysis. To investigate the crosstalk between hAT-MSCs and BTICs, various cytokines were analyzed. Using co-culture system of hAT-MSCs and BTICs, we analyzed the mRNA expression patterns of cytokine receptors (CCR2, CCR4, CCR5, CCR7, CCR9, CCR10, XCR1, CXCR1, IL-8R, CXCR4, CX3CR1, IL1R1, IL6R, MET, PDGFRB, KDR, CD44, IFNAR1 and TEK) by qRT-PCR and protein level of their ligand in co-cultured media by Bio-Plex human cytokine ELISA.

We confirmed the migratory capacity of t hAT-MSCs toward BTICs in vitro and BTICs-derived xenograft brain tumors in vivo live imaging. mRNA expression of receptors (CCR4, CCR5, CCR10, XCR1, CXCR1, IL-8R, CXCR4, PDGFRB, KDR, CD44, IFNAR1 and TEK) increased two- to eighteen-fold higher levels. The cytokine analysis revealed that the ligand levels of hAT-MSCs (medulloblastoma: VEGF, IL6, IL8, CCL3, CCL2 and TEK; ATRT: VEGF, CCL3 and TEK; glioblastoma: CCL2, PDGF, TEK and IGF1) and the ligand levels BTICs (medulloblastoma: CCL5 and CXCL4; ATRT: IL-8 and CXCL4; glioblastoma: CXCL4 and IGF1) were elevated in the co-cultured media.

Our findings demonstrated that hAT-MSCs can target BTICs. Cross-talk between hAT-MSCs cytokine receptor and BTICs ligand (medulloblastoma: CCR5/CCL5 and CXCR4/CXCL4; ATRT: IL-8R/IL-8 and CXCR4/CXCL4; glioblastoma: CXCR4/CXCL4 and IGF1R/IGF1) play cardinal role in this process.

Citation Format: Seung Ah Choi, Kyu-Chang Wang, Ji Hoon Phi, Ji Yeoun Lee, Jung Won Choi, Hyung Ah Kim, Se Hee Kim, Yong Hwy Kim, Sung Eun Kwon, Young-Hoon Kim, Seung-Ki Kim. Human adipose tissue-derived mesenchymal stem cells can target brain tumor initiating cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2649. doi:10.1158/1538-7445.AM2013-2649

Ipsilateral neglect in a patient following a unilateral frontal lesion

Using a crossed-response task, it has been demonstrated that as a patient with unilateral frontal lesion recovers from visual inattention, he or she may inappropriately saccade to contralateral stimuli (visual grasp). We report a patient with a right frontal lesion who showed a similar phenomenon on sequential line bisection tasks. On day 1, he showed left-sided neglect on line bisections that enhanced with sequential trials. On day 5, he exhibited right-sided neglect (ipsilateral neglect) on line bisection tasks that also enhanced with repeated trials.

Retrosplenial cortex: possible role in habituation of the orienting response

A patient with a unilateral lesion that included the retrosplenial area had a propensity to attend to contralateral stimuli. To determine whether the retrosplenial-area lesion was inducing this defect, unilateral retrosplenial lesions were produced in rats by surgical aspiration. Animals were assessed preoperatively and postoperatively for orientation and habituation to bilateral simultaneous stimulation in 3 sensory modalities: visual, tactile, and auditory. At each session, the orientation test was terminated upon completion of 5 trials per modality, and the habituation test ended after 4 consecutive response failures or upon completion of 15 trials per modality. Postoperatively, contralateral orientation was not significantly different from ipsilateral orientation, suggesting that there was no neglect. However, there was a significant delay in habituation to contralateral stimulation in postoperative weeks 2 and 3-5. Our results suggest that rats with retrosplenial area lesions have normal orientation but fail to habituate to contralateral stimuli.