GABAB Receptor Agonist R-Baclofen Reverses Altered Auditory Reactivity and Filtering in the Cntnap2 Knock-Out Rat

Altered sensory information processing, and auditory processing, in particular, is a common impairment in individuals with autism spectrum disorder (ASD). One prominent hypothesis for the etiology of ASD is an imbalance between neuronal excitation and inhibition. The selective GABAB receptor agonist R-Baclofen has been shown previously to improve social deficits and repetitive behaviors in several mouse models for neurodevelopmental disorders including ASD, and its formulation Arbaclofen has been shown to ameliorate social avoidance symptoms in some individuals with ASD. The present study investigated whether R-Baclofen can remediate ASD-related altered sensory processing reliant on excitation/inhibition imbalance in the auditory brainstem. To assess a possible excitation/inhibition imbalance in the startle-mediating brainstem underlying ASD-like auditory-evoked behaviors, we detected and quantified brain amino acid levels in the nucleus reticularis pontis caudalis (PnC) of rats with a homozygous loss-of-function mutation in the ASD-linked gene Contactin-associated protein-like 2 (Cntnap2) and their wildtype (WT) littermates using Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI MS). Abnormal behavioral read-outs of brainstem auditory signaling in Cntnap2 KO rats were accompanied by increased levels of GABA, glutamate, and glutamine in the PnC. We then compared the effect of R-Baclofen on behavioral read-outs of brainstem auditory signaling in Cntnap2 KO and WT rats. Auditory reactivity, sensory filtering, and sensorimotor gating were tested in form of acoustic startle response input-output functions, short-term habituation, and prepulse inhibition before and after acute administration of R-Baclofen (0.75, 1.5, and 3 mg/kg). Systemic R-Baclofen treatment improved disruptions in sensory filtering in Cntnap2 KO rats and suppressed exaggerated auditory startle responses, in particular to moderately loud sounds. Lower ASR thresholds in Cntnap2 KO rats were increased in a dose-dependent fashion, with the two higher doses bringing thresholds close to controls, whereas shorter ASR peak latencies at the threshold were further exacerbated. Impaired prepulse inhibition increased across various acoustic prepulse conditions after administration of R-Baclofen in Cntnap2 KO rats, whereas R-Baclofen did not affect prepulse inhibition in WT rats. Our findings suggest that GABAB receptor agonists may be useful for pharmacologically targeting multiple aspects of sensory processing disruptions involving neuronal excitation/inhibition imbalances in ASD

Characterizing maternal isolation-induced ultrasonic vocalizations in a gene-environment interaction rat model for autism.

Deficits in social communication and language development belong to the earliest diagnostic criteria of autism spectrum disorders. Of the many risk factors for autism spectrum disorder, the contactin-associated protein-like 2 gene, CNTNAP2, is thought to be important for language development. The present study used a rat model to investigate the potential compounding effects of autism spectrum disorder risk gene mutation and environmental challenges, including breeding conditions or maternal immune activation during pregnancy, on early vocal communication in the offspring. Maternal isolation-induced ultrasonic vocalizations from Cntnap2 wildtype and knockout rats at selected postnatal days were analyzed for their acoustic, temporal and syntax characteristics. Cntnap2 knockout pups from heterozygous breeding showed normal numbers and largely similar temporal structures of ultrasonic vocalizations to wildtype controls, whereas both parameters were affected in homozygously bred knockouts. Homozygous breeding further exacerbated altered pitch and transitioning between call types found in Cntnap2 knockout pups from heterozygous breeding. In contrast, the effect of maternal immune activation on the offspring\u27s vocal communication was confined to call type syntax, but left ultrasonic vocalization acoustic and temporal organization intact. Our results support the double-hit hypothesis of autism spectrum disorder risk gene-environment interactions and emphasize that complex features of vocal communication are a useful tool for identifying early autistic-like features in rodent models

Loss of auditory sensitivity from inner hair cell synaptopathy can be centrally compensated in the young but not old brain

AbstractA dramatic shift in societal demographics will lead to rapid growth in the number of older people with hearing deficits. Poorer performance in suprathreshold speech understanding and temporal processing with age has been previously linked with progressing inner hair cell (IHC) synaptopathy that precedes age-dependent elevation of auditory thresholds. We compared central sound responsiveness after acoustic trauma in young, middle-aged, and older rats. We demonstrate that IHC synaptopathy progresses from middle age onward and hearing threshold becomes elevated from old age onward. Interestingly, middle-aged animals could centrally compensate for the loss of auditory fiber activity through an increase in late auditory brainstem responses (late auditory brainstem response wave) linked to shortening of central response latencies. In contrast, old animals failed to restore central responsiveness, which correlated with reduced temporal resolution in responding to amplitude changes. These findings may suggest that cochlear IHC synaptopathy with age does not necessarily induce temporal auditory coding deficits, as long as the capacity to generate neuronal gain maintains normal sound-induced central amplitudes

Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications

This work was supported by a restricted research grant of Bayer AG

What we can learn from a genetic rodent model about autism

Autism spectrum disorders (ASD) are complex neurodevelopmental disorders that are caused by genetic and/or environmental impacts, often probably by the interaction of both. They are characterised by deficits in social communication and interaction and by restricted and repetitive behaviours and interests from early childhood on, causing significant impairment. While it is clear that no animal model captures the full complexity of ASD in humans, genetic models are extremely useful for studying specific symptoms associated with ASD and the underlying cellular and molecular mechanisms. In this review we summarize the behavioral paradigms used in rodents to model ASD symptoms as they are listed in the DSM-5. We then review existing genetic rodent models with disruptions in ASD candidate genes, and we map their phenotypes onto these behavioural paradigms. The goal of this review is to give a comprehensive overview on how ASD symptoms can be studied in animal models and to give guidance for which animal models are appropriate to study specific symptom clusters

Age-dependent auditory processing deficits after cochlear synaptopathy depend on auditory nerve latency and the ability of the brain to recruit ltp/bdnf

© 2020 by the authors.Age-related decoupling of auditory nerve fibers from hair cells (cochlear synaptopathy) has been linked to temporal processing deficits and impaired speech recognition performance. The link between both is elusive. We have previously demonstrated that cochlear synaptopathy, if centrally compensated through enhanced input/output function (neural gain), can prevent age-dependent temporal discrimination loss. It was also found that central neural gain after acoustic trauma was linked to hippocampal long-term potentiation (LTP) and upregulation of brain-derived neurotrophic factor (BDNF). Using middle-aged and old BDNF-live-exon-visualization (BLEV) reporter mice we analyzed the specific recruitment of LTP and the activity-dependent usage of Bdnf exon-IV and -VI promoters relative to cochlear synaptopathy and central (temporal) processing. For both groups, specimens with higher or lower ability to centrally compensate diminished auditory nerve activity were found. Strikingly, low compensating mouse groups differed from high compensators by prolonged auditory nerve latency. Moreover, low compensators exhibited attenuated responses to amplitude-modulated tones, and a reduction of hippocampal LTP and Bdnf transcript levels in comparison to high compensators. These results suggest that latency of auditory nerve processing, recruitment of hippocampal LTP, and Bdnf transcription, are key factors for age-dependent auditory processing deficits, rather than cochlear synaptopathy or aging per se.We acknowledge grants from the Deutsche Forschungsgemeinschaft FOR 2060 project RU 713/3-2 (W.S., L.R., D.M.), Projektnummer 335549539/GRK 2381 (P.M.), SPP 1608 RU 316/12-1 (L.R.), and KN 316/12-1 (M.M, M.K.), Siegmund Kiener Stiftung (D.S.) and BFU2016-76580-P (T.S)

Loss of Cntnap2 in the Rat Causes Autism-Related Alterations in Social Interactions, Stereotypic Behavior, and Sensory Processing

Autism spectrum disorder (ASD) is characterized by social interaction and communication impairments, as well as restrictive/repetitive patterns of behavior, interests or activities, which can coexist with intellectual disability and altered sensory processing. To study the mechanisms underlying these core features of ASD, preclinical research has developed animal models with manipulations in ASD-linked genes, such as CNTNAP2. In order to fully interpret the findings from mechanistic studies, the extent to which these models display behaviors consistent with ASD must be determined. Toward that goal, we conducted an investigation of the consequences of a functional loss of Cntnap2 on ASD-related behaviors by comparing the performance of rats with a homozygous or heterozygous knockout of Cntnap2 to their wildtype littermates across a comprehensive test battery. Cntnap2−/− rats showed deficits in sociability and social novelty, and they displayed repetitive circling and hyperlocomotion. Moreover, Cntnap2−/− rats demonstrated exaggerated acoustic startle responses, increased avoidance to sounds of moderate intensity, and a lack of rapid audiovisual temporal recalibration; indicating changes in sensory processing at both the pre-attentive and perceptual levels. Notably, sensory behaviors requiring learned associations did not reveal genotypic differences, whereas tasks relying on automatic/implicit behaviors did. Ultimately, because these collective alterations in social, stereotypic, and sensory behaviors are phenotypically similar to those reported in individuals with ASD, our results establish the Cntnap2 knockout rat model as an effective platform to study not only the molecular and cellular mechanisms associated with ASD, but also the complex relationship between altered sensory processing and other core ASD-related behaviors. Lay Summary: Autism spectrum disorder (ASD) is characterized by social interaction differences, and restrictive/repetitive patterns of behavior. We studied the behavioral alterations caused by the loss of an autism-linked gene, Cntnap2, in the rat to determine how mutations in this gene contribute to autism-related behaviors. We show the loss of Cntnap2 leads to changes in social, stereotypic, and sensory behaviors, indicating this rat model can be used to better understand the brain changes underlying ASD. Autism Res 2020, 13: 1698–1717. © 2020 International Society for Autism Research and Wiley Periodicals LLC

Central Compensation of Cochlear Synaptopathy is not Dependent on Age, but on LTP/BDNF Recruitment

Trabajo presentado en el 44th Annual MidWinter Meeting, celebrado en modalidad virtual del 20 al 24 de febrero de 2022.[Background]: Age-related loss of synaptic contacts between inner hair cells and auditory-nerve fibers (cochlear synaptopathy) has been linked to temporal processing deficits and impaired speech-in-noise recognition. In individual cases age-dependent temporal discrimination loss may be attenuated due to central compensation mechanism (neural gain). We hypothesize that cochlear synaptopathy, central neural gain and the ability for fast auditory temporal processing are connected to changes in hippocampal long-term potentiation (LTP) and brain-derived neurotrophic factor (BDNF) expression independent of the age. [Methods]: Here, we investigated middle-aged and old BDNF-live-exon-visualization (BLEV) reporter mice and analyzed auditory brainstem responses, auditory steady state responses and hippocampal field excitatory postsynaptic potentials. [Results]: In both, middle-aged and old groups, animals with lower or higher ability to centrally compensate reduced auditory nerve activity were found. The low compensators exhibited attenuated responses to amplitudemodulated tones and a reduction of hippocampal LTP and Bdnf transcript levels in comparison to high compensators. [Conclusions]: These results suggest that not the age itself but rather the diminished capacity for central compensation and LTP/BDNF recruitment play a key role in age-related loss of central auditory function caused by cochlear synaptopathy

Age-Dependent Auditory Processing Deficits after Cochlear Synaptopathy Depend on Auditory Nerve Latency and the Ability of the Brain to Recruit LTP/BDNF

© 2020 by the authors.Age-related decoupling of auditory nerve fibers from hair cells (cochlear synaptopathy) has been linked to temporal processing deficits and impaired speech recognition performance. The link between both is elusive. We have previously demonstrated that cochlear synaptopathy, if centrally compensated through enhanced input/output function (neural gain), can prevent age-dependent temporal discrimination loss. It was also found that central neural gain after acoustic trauma was linked to hippocampal long-term potentiation (LTP) and upregulation of brain-derived neurotrophic factor (BDNF). Using middle-aged and old BDNF-live-exon-visualization (BLEV) reporter mice we analyzed the specific recruitment of LTP and the activity-dependent usage of Bdnf exon-IV and -VI promoters relative to cochlear synaptopathy and central (temporal) processing. For both groups, specimens with higher or lower ability to centrally compensate diminished auditory nerve activity were found. Strikingly, low compensating mouse groups differed from high compensators by prolonged auditory nerve latency. Moreover, low compensators exhibited attenuated responses to amplitude-modulated tones, and a reduction of hippocampal LTP and Bdnf transcript levels in comparison to high compensators. These results suggest that latency of auditory nerve processing, recruitment of hippocampal LTP, and Bdnf transcription, are key factors for age-dependent auditory processing deficits, rather than cochlear synaptopathy or aging per se.We acknowledge grants from the Deutsche Forschungsgemeinschaft FOR 2060 project RU 713/3-2 (W.S., L.R., D.M.), Projektnummer 335549539/GRK 2381 (P.M.), SPP 1608 RU 316/12-1 (L.R.), and KN 316/12-1 (M.M, M.K.), Siegmund Kiener Stiftung (D.S.) and BFU2016-76580-P (T.S)