Enhanced Social Dominance and Altered Neuronal Excitability in the Prefrontal Cortex of Male KCC2b Mutant Mice.

The K-Cl cotransporter KCC2 is essential in the development of the "GABA switch" that produces a change in neuronal responses to GABA signaling from excitatory to inhibitory early in brain development, and alterations in this progression have previously been hypothesized to play a causal role in autism spectrum disorder (ASD). We investigated the KCC2b (Slc12a5) heterozygous knockout mouse using a battery of rodent behavioral tests relevant to core and comorbid ASD symptoms. Compared to wild-type littermates, KCC2+/- mice were normal in standard measures of locomotor activity, grooming and digging behaviors, and social, vocalization, and anxiety-like behaviors. However, KCC2+/- mice exhibited increased social dominance behaviors and increased amplitude of spontaneous postsynaptic currents in the medial prefrontal cortex (PFC) that were previously implicated in governing social hierarchy and dominance behaviors. Treatment of wild-type mouse brain slices with the KCC2 inhibitor VU0240511 increased the amplitude and frequency of excitatory postsynaptic currents, partially recapitulating the phenotype of KCC2+/- mice. These findings indicate that the activity of KCC2 plays a role in social dominance, in parallel with effects on PFC signaling, further suggesting that KCC2 function has some relevance to social behavior but without the breadth of impact on autism-like behavior suggested by previous studies. Further testing could assess whether KCC2 alters other circuits and whether additional factors such as environmental insults may precipitate autism-related behavioral phenotypes. Autism Research 2019, 12: 732-743. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: A mouse model of altered chloride transporter expression was used to look for a role in behaviors and brain function relevant to autism. There was an imbalance in signaling in the prefrontal cortex, and increased social dominance behavior, although other autism-related behaviors were not changed. These findings indicate that altered chloride transporter function affects prefrontal cortex function and social dominance without a broader impact on autism-like behaviors.

The transcription factor NeuroD2 coordinates synaptic innervation and cell intrinsic properties to control excitability of cortical pyramidal neurons.

KEY POINTS: Synaptic excitation and inhibition must be properly balanced in individual neurons and neuronal networks to allow proper brain function. Disrupting this balance may lead to autism spectral disorders and epilepsy. We show the basic helix-loop-helix transcription factor NeuroD2 promotes inhibitory synaptic drive but also decreases cell-intrinsic neuronal excitability of cortical pyramidal neurons both in vitro and in vivo. We identify two genes potentially downstream of NeuroD2-mediated transcription that regulate these parameters: gastrin-releasing peptide and the small conductance, calcium-activated potassium channel, SK2. Our results reveal an important function for NeuroD2 in balancing synaptic neurotransmission and intrinsic excitability. Our results offer insight into how synaptic innervation and intrinsic excitability are coordinated during cortical development. ABSTRACT: Synaptic excitation and inhibition must be properly balanced in individual neurons and neuronal networks for proper brain function. Disruption of this balance during development may lead to autism spectral disorders and epilepsy. Synaptic excitation is counterbalanced by synaptic inhibition but also by attenuation of cell-intrinsic neuronal excitability. To maintain proper excitation levels during development, neurons must sense activity over time and regulate the expression of genes that control these parameters. While this is a critical process, little is known about the transcription factors involved in coordinating gene expression to control excitatory/inhibitory synaptic balance. We show here that the basic helix-loop-helix transcription factor NeuroD2 promotes inhibitory synaptic drive but also decreases cell-intrinsic neuronal excitability of cortical pyramidal neurons both in vitro and in vivo as shown by ex vivo analysis of a NeuroD2 knockout mouse. Using microarray analysis and comparing wild-type and NeuroD2 knockout cortical networks, we identified two potential gene targets of NeuroD2 that contribute to these processes: gastrin-releasing peptide (GRP) and the small conductance, calcium-activated potassium channel, SK2. We found that the GRP receptor antagonist RC-3059 and the SK2 specific blocker apamin partially reversed the effects of increased NeuroD2 expression on inhibitory synaptic drive and action potential repolarization, respectively. Our results reveal an important function for NeuroD2 in balancing synaptic neurotransmission and intrinsic excitability and offer insight into how these processes are coordinated during cortical development.

Two cellular hypotheses explaining the initiation of ketamine's antidepressant actions: Direct inhibition and disinhibition.

A single, low dose of ketamine evokes antidepressant actions in depressed patients and in patients with treatment-resistant depression (TRD). Unlike classic antidepressants, which regulate monoamine neurotransmitter systems, ketamine is an antagonist of the N-methyl-D-aspartate (NMDA) family of glutamate receptors. The effectiveness of NMDAR antagonists in TRD unveils a new set of targets for therapeutic intervention in major depressive disorder (MDD) and TRD. However, a better understanding of the cellular mechanisms underlying these effects is required for guiding future therapeutic strategies, in order to minimize side effects and prolong duration of efficacy. Here we review the evidence for and against two hypotheses that have been proposed to explain how NMDAR antagonism initiates protein synthesis and increases excitatory synaptic drive in corticolimbic brain regions, either through selective antagonism of inhibitory interneurons and cortical disinhibition, or by direct inhibition of cortical pyramidal neurons. This article is part of the Special Issue entitled 'Synaptopathy--from Biology to Therapy'.

Long pre-mRNA depletion and RNA missplicing contribute to neuronal vulnerability from loss of TDP-43.

We used cross-linking and immunoprecipitation coupled with high-throughput sequencing to identify binding sites in 6,304 genes as the brain RNA targets for TDP-43, an RNA binding protein that, when mutated, causes amyotrophic lateral sclerosis. Massively parallel sequencing and splicing-sensitive junction arrays revealed that levels of 601 mRNAs were changed (including Fus (Tls), progranulin and other transcripts encoding neurodegenerative disease-associated proteins) and 965 altered splicing events were detected (including in sortilin, the receptor for progranulin) following depletion of TDP-43 from mouse adult brain with antisense oligonucleotides. RNAs whose levels were most depleted by reduction in TDP-43 were derived from genes with very long introns and that encode proteins involved in synaptic activity. Lastly, we found that TDP-43 autoregulates its synthesis, in part by directly binding and enhancing splicing of an intron in the 3' untranslated region of its own transcript, thereby triggering nonsense-mediated RNA degradation.

Specific inflammatory cell types and disease severity as predictors of postsurgical outcomes in patients with chronic sinusitis.

Chronic sinusitis is a common condition that is frequently refractory to medical and surgical intervention. It has not been well defined as to which patient subgroups benefit from surgical intervention and which do not. Our purpose is to determine whether the presence of certain inflammatory cell types is predictive of postoperative outcome in sinus surgery for chronic sinusitis. We performed a retrospective chart review of 75 patients who underwent endoscopic sinus surgery or polypectomy between 1994 and 1996. Of these patients, 15 met inclusion criteria for chronic sinusitis, asthma requiring inhaled steroids, and 1 year preoperative and postoperative management by the allergist or otolaryngologist at Northwestern Medical Faculty Foundation. Ten of these 15 patients had a complete set of data allowing immunohistochemical analysis. Sections of sinus tissue obtained at surgery were hematoxylin and eosin stained and evaluated for the presence of lymphocytes, plasma cells, eosinophils, and macrophages. Immunostains for T lymphocytes, B lymphocytes, and macrophages were performed also. The total number of antibiotic courses patients received were enumerated into 6-month blocks for 1 year preoperatively and 1 year postoperatively as markers of disease activity. Postoperatively, four patients improved, three patients worsened, and three patients remained unchanged, as defined by the number of antibiotic courses required 1 year postoperatively compared with 1 year preoperatively. We found no difference in the magnitude or specific type of inflammatory cells present at the time of surgery between the groups. However, when the difference between the preoperative versus postoperative antibiotic courses was compared between patients who improved versus patients who did not improve, the improved group required markedly fewer courses relative to the nonimproved group (p < 0.009). Neither total magnitude of inflammation nor specific inflammatory cell types correlated with surgical outcome in this group. The patients who did not improve postoperatively had a statistically significantly lower number of preoperative antibiotics than the patients who improved. These findings suggest that patients with less severe disease may be less likely to benefit from sinus surgery.

Long-term evaluation of hypersensitivity pneumonitis: a case study follow-up and literature review.

This study reports a 3-year follow-up of a classic presentation of hypersensitivity pneumonitis (HP), originally reported elsewhere, after removal of the causative antigens. The literature is reviewed and this case is compared with outcomes of series previously reported. The patient was reevaluated by clinical, serologic, radiographic, and pulmonary function testing 3 years after removal of her home's contaminated humidifier, cleaning of the home, and administration of a course of prednisone. Repeat serologic measurements revealed positive serum precipitins only for Aspergillus flavus and Phoma herbarum, significantly fewer than her original panel, which revealed precipitating antibodies to her humidifier water and 10 other specific antigens. Pulmonary function tests remained stable. Physical exam revealed bibasilar rales. Computed tomography scan revealed pulmonary fibrosis, bronchiectasis, and honeycombing that was compared with 3 years earlier. Although most of the data obtained on reevaluation suggest remission, radiographic findings have not remitted. Long-term follow-up of parameters of HP disease activity do not always reveal consistent findings. This patient appears to be in a category of HP between the classic subacute and chronic stages.