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.

Sleep/Wake Physiology and Quantitative Electroencephalogram Analysis of the Neuroligin-3 Knockout Rat Model of Autism Spectrum Disorder.

Study Objectives: Neuroligin-3 (NLGN3) is one of the many genes associated with autism spectrum disorder (ASD). Sleep dysfunction is highly prevalent in ASD, but has not been rigorously examined in ASD models. Here, we evaluated sleep/wake physiology and behavioral phenotypes of rats with genetic ablation of Nlgn3. Methods: Male Nlgn3 knockout (KO) and wild-type (WT) rats were assessed using a test battery for ASD-related behaviors and also implanted with telemeters to record the electroencephalogram (EEG), electromyogram, body temperature, and locomotor activity. 24-h EEG recordings were analyzed for sleep/wake states and spectral composition. Results: Nlgn3 KO rats were hyperactive, exhibited excessive chewing behavior, and had impaired prepulse inhibition to an auditory startle stimulus. KO rats also spent less time in non-rapid eye movement (NREM) sleep, more time in rapid eye movement (REM) sleep, exhibited elevated theta power (4-9 Hz) during wakefulness and REM, and elevated delta power (0.5-4 Hz) during NREM. Beta (12-30 Hz) power and gamma (30-50 Hz) power were suppressed across all vigilance states. Conclusions: The sleep disruptions in Nlgn3 KO rats are consistent with observations of sleep disturbances in ASD patients. The EEG provides objective measures of brain function to complement rodent behavioral analyses and therefore may be a useful tool to study ASD.

Cntnap2 Knockout Rats and Mice Exhibit Epileptiform Activity and Abnormal Sleep-Wake Physiology.

Study Objectives: Although recent innovations have enabled modification of the rat genome, it is unclear whether enhanced utility of rodents as human disease models will result. We compared electroencephalogram (EEG) and behavioral phenotypes of rats and mice with homozygous deletion of Cntnap2, a gene associated with cortical dysplasia-focal epilepsy (CDFE) and autism spectrum disorders (ASD). Methods: Male contactin-associated protein-like 2 (Cntnap2) knockout (KO) and wild-type (WT) rats and male Cntnap2 KO and WT mice were implanted with telemeters to record EEG, electromyogram, body temperature, and locomotor activity. Animals were subjected to a test battery for ASD-related behaviors, followed by 24-hr EEG recordings that were analyzed for sleep-wake parameters and subjected to spectral analysis. Results: Cntnap2 KO rats exhibited severe motor seizures, hyperactivity, and increased consolidation of wakefulness and REM sleep. By contrast, Cntnap2 KO mice demonstrated absence seizure-like events, hypoactivity, and wake fragmentation. Although seizures observed in Cntnap2 KO rats were more similar to those in CDFE patients than in KO mice, neither model fully recapitulated the full spectrum of disease symptoms. However, KOs in both species had reduced spectral power in the alpha (9-12 Hz) range during wake, suggesting a conserved EEG biomarker. Conclusions: Deletion of Cntnap2 impacts similar behaviors and EEG measures in rats and mice, but with profound differences in nature and phenotypic severity. These observations highlight the importance of cross-species comparisons to understand conserved gene functions and the limitations of single- species models to provide translational insights relevant to human diseases.

Advancing the discovery of medications for autism spectrum disorder using new technologies to reveal social brain circuitry in rodents.

INTRODUCTION: Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental condition characterized by core differences and impairments in social behavioral functioning. There are no approved medications for improving social cognition and behavior in ASD, and the underlying mechanisms needed to discover safer, more effective medications are unclear. DISCUSSION: In this review, we diagram the basic neurocircuitry governing social behaviors in order to provide a neurobiological framework for the origins of the core social behavioral symptoms of ASD. In addition, we discuss recent technological innovations in research tools that provide unprecedented observation of cellular morphology and activity deep within the intact brain and permit the precise control of discrete brain regions and specific cell types at distinct developmental stages. CONCLUSIONS: The use of new technologies to reveal the neural circuits underlying social behavioral impairments associated with ASD is advancing our understanding of the brain changes underlying ASD and enabling the discovery of novel and effective therapeutic interventions.

Adult-born hippocampal dentate granule cells undergoing maturation modulate learning and memory in the brain.

Adult-born dentate granule cells (DGCs) contribute to learning and memory, yet it remains unknown when adult-born DGCs become involved in the cognitive processes. During neurogenesis, immature DGCs display distinctive physiological characteristics while undergoing morphological maturation before final integration into the neural circuits. The survival and activity of the adult-born DGCs can be influenced by the experience of the animal during a critical period when newborn DGCs are still immature. To assess the temporal importance of adult neurogenesis, we developed a transgenic mouse model that allowed us to transiently reduce the numbers of adult-born DGCs in a temporally regulatable manner. We found that mice with a reduced population of adult-born DGCs at the immature stage were deficient in forming robust, long-term spatial memory and displayed impaired performance in extinction tasks. These results suggest that immature DGCs that undergo maturation make important contributions to learning and memory.

Paradoxical influence of hippocampal neurogenesis on working memory.

To explore the function of adult hippocampal neurogenesis, we ablated cell proliferation by using two independent and complementary methods: (i) a focal hippocampal irradiation and (ii) an inducible and reversible genetic elimination of neural progenitor cells. Previous studies using these methods found a weakening of contextual fear conditioning but no change in spatial reference memory, suggesting a supportive role for neurogenesis in some, but not all, hippocampal-dependent memory tasks. In the present study, we examined hippocampal-dependent and -independent working memory using different radial maze tasks. Surprisingly, ablating neurogenesis caused an improvement of hippocampal-dependent working memory when repetitive information was presented in a single day. These findings suggest that adult-born cells in the dentate gyrus have different, and in some cases, opposite roles in distinct types of memory.

Ablation of hippocampal neurogenesis impairs contextual fear conditioning and synaptic plasticity in the dentate gyrus.

Although hippocampal neurogenesis has been described in many adult mammals, the functional impact of this process on physiology and behavior remains unclear. In the present study, we used two independent methods to ablate hippocampal neurogenesis and found that each procedure caused a limited behavioral deficit and a loss of synaptic plasticity within the dentate gyrus. Specifically, focal X irradiation of the hippocampus or genetic ablation of glial fibrillary acidic protein-positive neural progenitor cells impaired contextual fear conditioning but not cued conditioning. Hippocampal-dependent spatial learning tasks such as the Morris water maze and Y maze were unaffected. These findings show that adult-born neurons make a distinct contribution to some but not all hippocampal functions. In a parallel set of experiments, we show that long-term potentiation elicited in the dentate gyrus in the absence of GABA blockers requires the presence of new neurons, as it is eliminated by each of our ablation procedures. These data show that new hippocampal neurons can be preferentially recruited over mature granule cells in vitro and may provide a framework for how this small cell population can influence behavior.

Substance P antagonists: meet the new drugs, same as the old drugs? Insights from transgenic animal models.

Antidepressants that primarily target the reuptake of monoamines have been highly successful treatments. However, therapies with these drugs still have several drawbacks, namely severe side effects, delays in the onset of action, and a significant percentage of non-responders. Recently, non-peptidic antagonists of the neurokinin 1 receptor, or substance P antagonists, have emerged as a novel class of drugs with antidepressant efficacy that is comparable to current drugs, but a potentially reduced side effect profile. This review summarizes the pre-clinical evidence derived from pharmacological and transgenic animal studies that suggests an important role for the substance P/neurokinin 1 system in anxiety and depression. Also, potential mechanisms by which substance P antagonists may produce their therapeutic effects are discussed.