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Arid1b is a high confidence risk gene for autism spectrum disorder that encodes a subunit of a chromatin remodeling complex expressed in neuronal progenitors. Haploinsufficiency causes a broad range of social, behavioral, and intellectual disability phenotypes, including Coffin-Siris syndrome. Recent work using transgenic mouse models suggests pathology is due to deficits in proliferation, survival, and synaptic development of cortical neurons. However, there is conflicting evidence regarding the relative roles of excitatory projection neurons and inhibitory interneurons in generating abnormal cognitive and behavioral phenotypes. Here, we conditionally knocked out either one or both copies of Arid1b from excitatory projection neuron progenitors and systematically investigated the effects on intrinsic membrane properties, synaptic physiology, social behavior, and seizure susceptibility. We found that disrupting Arid1b expression in excitatory neurons alters their membrane properties, including hyperpolarizing action potential threshold; however, these changes depend on neuronal subtype. Using paired whole-cell recordings, we found increased synaptic connectivity rate between projection neurons. Furthermore, we found reduced strength of excitatory synapses to parvalbumin (PV)-expression inhibitory interneurons. These data suggest an increase in the ratio of excitation to inhibition. However, the strength of inhibitory synapses from PV interneurons to excitatory neurons was enhanced, which may rebalance this ratio. Indeed, Arid1b haploinsufficiency in projection neurons was insufficient to cause social deficits and seizure phenotypes observed in a preclinical germline haploinsufficient mouse model. Our data suggest that while excitatory projection neurons likely contribute to autistic phenotypes, pathology in these cells is not the primary cause.

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Autism spectrum disorder (ASD) presents with diverse cognitive and behavioral abnormalities beginning during early development. Although the neural circuit mechanisms remain unclear, recent work suggests pathology in cortical inhibitory interneurons (INs) plays a crucial role. However, we lack fundamental information regarding changes in the physiology of synapses to and from INs in ASD. Here, we used transgenic mice to conditionally knockout one copy of the high confidence ASD risk gene Arid1b from the progenitors of parvalbumin-expressing fast-spiking (PV-FS) INs and somatostatin-expressing non-fast-spiking (SST-NFS) INs. In brain slices, we performed paired whole-cell recordings between INs and excitatory projection neurons (PNs) to investigate changes in synaptic physiology. In neonates, we found reduced synaptic input to INs but not PNs, with a concomitant reduction in the frequency of spontaneous network events, which are driven by INs in immature circuits. In mature mice, we found a reduction in the number of PV-FS INs in cortical layers 2/3 and 5. However, changes in PV-FS IN synaptic physiology were cortical layer and PN cell-type dependent. In layer 5, synapses from PV-FS INs to subcortical-projecting PNs were weakened. In contrast, in layer 2/3, synapses to and from PV-FS INs and corticocortical-projecting PNs were strengthened, leading to enhanced feedforward inhibition of input from layer 4. Finally, we found a novel synaptic deficit among SST-NFS INs, in which excitatory synapses from layer 2/3 PNs failed to facilitate. Our data highlight that changes in unitary synaptic dynamics among INs in ASD depend on neuronal cell-type.

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Pyramidal cells (PCs) in CA1 hippocampus can be classified by their radial position as deep or superficial and organize into subtype-specific circuits necessary for differential information processing. Specifically, superficial PCs receive fewer inhibitory synapses from parvalbumin (PV)-expressing interneurons than deep PCs, resulting in weaker feedforward inhibition of input from CA3 Schaffer collaterals. Using mice, we investigated mechanisms underlying PC differentiation and the development of this inhibitory circuit motif. We found that expression of the transcriptional regulator SATB2 is biased towards superficial PCs during early postnatal development and necessary to suppress PV+ interneuron synapse formation. In the absence of SATB2, the number of PV+ interneuron synaptic puncta surrounding superficial PCs increases during development to match deep PCs. This results in equivalent inhibitory current strength observed in paired whole-cell recordings, and equivalent feedforward inhibition of Schaffer collateral input. Thus, SATB2 is necessary for superficial PC differentiation and biased feedforward inhibition in CA1.

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INTRODUCTION: The purpose of this study was to determine if pharmacological treatment could increase progenitor cell proliferation in the Sub-ventricular Zone of aged rats. Previous work had shown that increasing progenitor cell proliferation in this region correlated well (R2=0.78; p= 0.0007) with functional recovery in a damaged corpus callosum (white matter tract), suggesting that progenitor cell proliferation results in oligodendrocytes in this region. METHODS: 10 month old male and female Sprague Dawley rats were fed the drugs for 30 days in cookie dough, then immunocytochemistry was performed on coronal brain sections, using Ki67 labeling to determine progenitor cell proliferation. RESULTS: Female rats showed low endogenous (control) progenitor cell proliferation, significantly different from male rats (P<0.0001), at this age. Ascorbic Acid (20 mg/kg, daily for 30 days) increased progenitor cell proliferation overall, but maintained the innate gender difference in stem cell proliferation (P=0.001). Prozac (5 mg/kg, daily for 30 days) increased progenitor cell proliferation for females but decreased stem cell proliferation for males, again showing a gender difference (P<0.0001). Simvastatin (1 mg/kg for 30 days) also increased progenitor cell proliferation in females and decreased progenitor cell proliferation in males, leading to a significant gender difference. DISCUSSION: The three drug combinations (fluoxetine, simvastatin, and ascorbic acid, patent # 9,254,281) led to ~ 4 fold increase in progenitor cell proliferation in females, while male progenitor cell proliferation was highest with 50 mg/kg ascorbic acid. However, the ascorbic acid increase in proliferation appears to be only on the sides of the ventricles, which is not the region that normally gives rise to oligodendrocytes. CONCLUSION: There are innate gender differences in progenitor cell proliferation at the Sub-Ventricular Zone at middle age in rats, possibly due to the loss of estrogen in females. We also see notable gender differences in progenitor cell proliferation in the Sub ventricular Zone in response to common drugs, such as fluoxetine, simvastatin and Vitamin C (ascorbic acid).

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BACKGROUND: Forelimb Asymmetry Test is a simple test of motor function, using exploration behavior of a rat in a novel environment and counting the number of times that a rat touches the wall with either forepaw. Our lab has noticed, however, that there appears to be an increased number of fingertip touches to the wall following a stroke in the impaired forelimb. NEW METHOD: We counted the number of times that the animal either laid its palm flat against the wall of the chamber or touched the wall with only its fingertips, for both the left and right forepaws. We also separated bouts of exploration, so we could clearly determine if fingertip touches normally were associated with a transition from resting state to exploration state. RESULTS AND COMPARISON WITH EXISTING METHODS: Fishers exact test indicated that there were significant differences in the way that the animals touched the wall pre-stroke compared to post-stroke, with more fingertip touches occurring post-stroke. Counting palm touches as normal and fingertip touches as abnormal increases the sensitivity of the Forelimb Asymmetry analysis and gives a good correlation with the contralateral functional deficits determined by Montoya Staircase post-stroke. If we counted every wall touch as normal (palm touches and fingertip touches), we see a loss of sensitivity and a poor correlation with contralateral function as determined by Montoya Staircase. CONCLUSIONS: This refinement of the Forelimb Asymmetry analysis improves correlation with Montoya Staircase contralateral function after stroke.

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