Anja Ronnenberg

Reduced social interaction and ultrasonic communication in a mouse model of monogenic heritable autism.

Autism spectrum conditions (ASCs) are heritable conditions characterized by impaired reciprocal social interactions, deficits in language acquisition, and repetitive and restricted behaviors and interests. In addition to more complex genetic susceptibilities, even mutation of a single gene can lead to ASC. Several such monogenic heritable ASC forms are caused by loss-of-function mutations in genes encoding regulators of synapse function in neurons, including NLGN4. We report that mice with a loss-of-function mutation in the murine NLGN4 ortholog Nlgn4, which encodes the synaptic cell adhesion protein Neuroligin-4, exhibit highly selective deficits in reciprocal social interactions and communication that are reminiscent of ASCs in humans. Our findings indicate that a protein network that regulates the maturation and function of synapses in the brain is at the core of a major ASC susceptibility pathway, and establish Neuroligin-4-deficient mice as genetic models for the exploration of the complex neurobiological disorders in ASCs.

Neuroligin-3-deficient mice: model of a monogenic heritable form of autism with an olfactory deficit.

Autism spectrum disorder (ASD) is a frequent neurodevelopmental disorder characterized by variable clinical severity. Core symptoms are qualitatively impaired communication and social behavior, highly restricted interests and repetitive behaviors. Although recent work on genetic mutations in ASD has shed light on the pathophysiology of the disease, classifying it essentially as a synaptopathy, no treatments are available to date. To develop and test novel ASD treatment approaches, validated and informative animal models are required. Of particular interest, in this context are loss‐of‐function mutations in the postsynaptic cell adhesion protein neuroligin‐4 and point mutations in its homologue neuroligin‐3 (NL‐3) that were found to cause certain forms of monogenic heritable ASD in humans. Here, we show that NL‐3‐deficient mice display a behavioral phenotype reminiscent of the lead symptoms of ASD: reduced ultrasound vocalization and a lack of social novelty preference. The latter may be related to an olfactory deficiency observed in the NL‐3 mutants. Interestingly, such olfactory phenotype is also present in a subgroup of human ASD patients. Tests for learning and memory showed no gross abnormalities in NL‐3 mutants. Also, no alterations were found in time spent in social interaction, prepulse inhibition, seizure propensity and sucrose preference. As often seen in adult ASD patients, total brain volume of NL‐3 mutant mice was slightly reduced as assessed by magnetic resonance imaging (MRI). Our findings show that the NL‐3 knockout mouse represents a useful animal model for understanding pathophysiological events in monogenic heritable ASD and for developing novel treatment strategies in this devastating human disorder.

Erythropoietin enhances hippocampal long-term potentiation and memory

BackgroundErythropoietin (EPO) improves cognition of human subjects in the clinical setting by as yet unknown mechanisms. We developed a mouse model of robust cognitive improvement by EPO to obtain the first clues of how EPO influences cognition, and how it may act on hippocampal neurons to modulate plasticity.ResultsWe show here that a 3-week treatment of young mice with EPO enhances long-term potentiation (LTP), a cellular correlate of learning processes in the CA1 region of the hippocampus. This treatment concomitantly alters short-term synaptic plasticity and synaptic transmission, shifting the balance of excitatory and inhibitory activity. These effects are accompanied by an improvement of hippocampus dependent memory, persisting for 3 weeks after termination of EPO injections, and are independent of changes in hematocrit. Networks of EPO-treated primary hippocampal neurons develop lower overall spiking activity but enhanced bursting in discrete neuronal assemblies. At the level of developing single neurons, EPO treatment reduces the typical increase in excitatory synaptic transmission without changing the number of synaptic boutons, consistent with prolonged functional silencing of synapses.ConclusionWe conclude that EPO improves hippocampus dependent memory by modulating plasticity, synaptic connectivity and activity of memory-related neuronal networks. These mechanisms of action of EPO have to be further exploited for treating neuropsychiatric diseases.

A myelin gene causative of a catatonia-depression syndrome upon aging

Severe mental illnesses have been linked to white matter abnormalities, documented by postmortem studies. However, cause and effect have remained difficult to distinguish. CNP (2′,3′‐cyclic nucleotide 3′‐phosphodiesterase) is among the oligodendrocyte/myelin‐associated genes most robustly reduced on mRNA and protein level in brains of schizophrenic, bipolar or major depressive patients. This suggests that CNP reduction might be critical for a more general disease process and not restricted to a single diagnostic category. We show here that reduced expression of CNP is the primary cause of a distinct behavioural phenotype, seen only upon aging as an additional ‘pro‐inflammatory hit’. This phenotype is strikingly similar in Cnp heterozygous mice and patients with mental disease carrying the AA genotype at CNP SNP rs2070106. The characteristic features in both species with their partial CNP ‘loss‐of‐function’ genotype are best described as ‘catatonia‐depression’ syndrome. As a consequence of perturbed CNP expression, mice show secondary low‐grade inflammation/neurodegeneration. Analogously, in man, diffusion tensor imaging points to axonal loss in the frontal corpus callosum. To conclude, subtle white matter abnormalities inducing neurodegenerative changes can cause/amplify psychiatric diseases.

Heart rate dynamics and behavioral responses during acute emotional challenge in corticotropin-releasing factor receptor 1-deficient and corticotropin-releasing factor-overexpressing mice

The role of corticotropin-releasing factor in autonomic regulation of heart rate, heart rate variability and behavior responses was investigated in two genetic mouse models: corticotropin-releasing factor receptor 1-deficient mice, and corticotropin-releasing factor-transgenic mice overexpressing corticotropin-releasing factor. Heart rate was recorded by radio-telemetry during novelty exposure and auditory fear conditioning. Locomotor activity and freezing served as behavioral indices. Locomotor activity and heart rate were invariably increased in response to novelty exposure in both corticotropin-releasing factor receptor 1-deficient mice and littermate wild-type controls. The heart rate responses during retention of conditioned auditory fear and the exponential relationship between heart rate and heart rate variability were unaffected by genotype. Moreover, conditioned fear responses inferred from multiple behavioral measures including freezing did not differ between corticotropin-releasing factor receptor 1-deficient and corticotropin-releasing factor receptor 1 wild-type control mice. Corticotropin-releasing factor-transgenic mice exhibited markedly reduced locomotor activity during novelty exposure when compared with littermate wild-type controls. Baseline and novelty-driven heart rate was slightly elevated in corticotropin-releasing factor-transgenic mice, whereas the novelty-induced increase of heart rate was not different between genotypes. In contrast, corticotropin-releasing factor-transgenic mice did not display a heart rate response indicative of conditioned auditory fear. It is concluded that corticotropin-releasing factor receptor 1-deficiency does not affect heart rate adjustment and behavioral responses to acute fearful stimuli. The resiliency of behavioral and cardiovascular patterns elevation argues against the involvement of corticotropin-releasing factor receptor 1 in acute emotional regulation on these two functional levels despite an absent corticosterone elevation in corticotropin-releasing factor receptor 1-deficient mice. It is hypothesized that the lack of a conditioned heart rate response in corticotropin-releasing factor-transgenic mice is attributable to an impairment of cognitive function. The results are compared with those of corticotropin-releasing factor receptor 2-deficient mice, and the role of the corticotropin-releasing factor system in cardiovascular regulation is discussed.

Genetic markers of a Munc13 protein family member, BAIAP3, are gender specifically associated with anxiety and benzodiazepine abuse in mice and humans.

Anxiety disorders and substance abuse, including benzodiazepine use disorder, frequently occur together. Unfortunately, treatment of anxiety disorders still includes benzodiazepines, and patients with an existing comorbid benzodiazepine use disorder or a genetic susceptibility for benzodiazepine use disorder may be at risk of adverse treatment outcomes. The identification of genetic predictors for anxiety disorders, and especially for benzodiazepine use disorder, could aid the selection of the best treatment option and improve clinical outcomes. The brain-specific angiogenesis inhibitor I-associated protein 3 (Baiap3) is a member of the mammalian uncoordinated 13 (Munc13) protein family of synaptic regulators of neurotransmitter exocytosis, with a striking expression pattern in amygdalae, hypothalamus and periaqueductal gray. Deletion of Baiap3 in mice leads to enhanced seizure propensity and increased anxiety, with the latter being more pronounced in female than in male animals. We hypothesized that genetic variation in human BAIAP3 may also be associated with anxiety. By using a phenotype-based genetic association study, we identified two human BAIAP3 single-nucleotide polymorphism risk genotypes (AA for rs2235632, TT for rs1132358) that show a significant association with anxiety in women and, surprisingly, with benzodiazepine abuse in men. Returning to mice, we found that male, but not female, Baiap3 knockout (KO) mice develop tolerance to diazepam more quickly than control animals. Analysis of cultured Baiap3 KO hypothalamus slices revealed an increase in basal network activity and an altered response to diazepam withdrawal. Thus, Baiap3/BAIAP3 is gender specifically associated with anxiety and benzodiazepine use disorder, and the analysis of Baiap3/BAIAP3-related functions may help elucidate mechanisms underlying the development of both disorders.

Dissociation of temporal dynamics of heart rate and blood pressure responses elicited by conditioned fear but not acoustic startle

Fear-inducing stimuli were hypothesized to elicit fast heart rate (HR) responses but slow mean arterial blood pressure (MAP) responses and thus were studied in auditory fear conditioning and acoustic startle at high temporal resolution in freely moving mice and rats. Fear-induced instantaneous acceleration of HR reaching maximum physiological values and subsequent recovery to baseline were observed. The MAP response consisted of an immediate, mild, and transient increase followed by a sluggish, profound elevation and slow recovery. HR and MAP responses served as reliable indicators of conditioned fear in mice with dissociated temporal dynamics. Unconditioned auditory stimuli, including acoustic startle stimuli, elicited only fast, mild, and transient MAP and HR elevations in mice and rats, reflecting arousal and attention under these experimental conditions.

Gpm6b deficiency impairs sensorimotor gating and modulates the behavioral response to a 5-HT2A/C receptor agonist.

The neuronal tetraspan proteins, M6A (Gpm6a) and M6B (Gpm6b), belong to the family of proteolipids that are widely expressed in the brain. We recently reported Gpm6a deficiency as a monogenetic cause of claustrophobia in mice. Its homolog proteolipid, Gpm6b, is ubiquitously expressed in neurons and oligodendrocytes. Gpm6b is involved in neuronal differentiation and myelination. It interacts with the N-terminal domain of the serotonin transporter (SERT) and decreases cell-surface expression of SERT. In the present study, we employed Gpm6b null mutant mice (Gpm6b(-/-)) to search for behavioral functions of Gpm6b. We studied male and female Gpm6b(-/-) mice and their wild-type (WT, Gpm6b(+/+)) littermates in an extensive behavioral test battery. Additionally, we investigated whether Gpm6b(-/-) mice exhibit changes in the behavioral response to a 5-HT2A/C receptor agonist. We found that Gpm6b(-/-) mice display completely normal sensory and motor functions, cognition, as well as social and emotionality-like (anxiety, depression) behaviors. On top of this inconspicuous behavioral profile, Gpm6b(-/-) mice of both genders exhibit a selective impairment in prepulse inhibition of the acoustic startle response. Furthermore, in contrast to WT mice that show the typical locomotion suppression and increase in grooming activity after intraperitoneal administration of DOI [(±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride], Gpm6b(-/-) mice demonstrate a blunted behavioral response to this 5-HT2A/C receptor agonist. To conclude, Gpm6b deficiency impairs sensorimotor gating and modulates the behavioral response to a serotonergic challenge.

Ablation of BAF170 in Developing and Postnatal Dentate Gyrus Affects Neural Stem Cell Proliferation, Differentiation, and Learning

The BAF chromatin remodeling complex plays an essential role in brain development. However its function in postnatal neurogenesis in hippocampus is still unknown. Here, we show that in postnatal dentate gyrus (DG), the BAF170 subunit of the complex is expressed in radial glial-like (RGL) progenitors and in cell types involved in subsequent steps of adult neurogenesis including mature astrocytes. Conditional deletion of BAF170 during cortical late neurogenesis as well as during adult brain neurogenesis depletes the pool of RGL cells in DG, and promotes terminal astrocyte differentiation. These derangements are accompanied by distinct behavioral deficits, as reflected by an impaired accuracy of place responding in the Morris water maze test, during both hidden platform as well as reversal learning. Inducible deletion of BAF170 in DG during adult brain neurogenesis resulted in mild spatial learning deficits, having a more pronounced effect on spatial learning during the reversal test. These findings demonstrate involvement of BAF170-dependent chromatin remodeling in hippocampal neurogenesis and cognition and suggest a specific role of adult neurogenesis in DG in adaptive behavior.

Hypersocial behavior and biological redundancy in mice with reduced expression of PSD95 or PSD93

ABSTRACT The postsynaptic density proteins 95 (PSD95) and 93 (PSD93) belong to a family of scaffolding proteins, the membrane‐associated guanylate kinases (MAGUKs), which are highly enriched in synapses and responsible for organizing the numerous protein complexes required for synaptic development and plasticity. Genetic studies have associated MAGUKs with diseases like autism and schizophrenia, but knockout mice show severe, complex defects with difficult‐to‐interpret behavioral abnormalities due to major motor dysfunction which is atypical for psychiatric phenotypes. Therefore, rather than studying loss‐of‐function mutants, we comprehensively investigated the behavioral consequences of reduced PSD95 expression, using heterozygous PSD95 knockout mice (PSD95+/−). Specifically, we asked whether heterozygous PSD95 deficient mice would exhibit alterations in the processing of social stimuli and social behavior. Additionally, we investigated whether PSD95 and PSD93 would reveal any indication of functional or biological redundancy. Therefore, homozygous and heterozygous PSD93 deficient mice were examined in a similar behavioral battery as PSD95 mutants. We found robust hypersocial behavior in the dyadic interaction test in both PSD95+/− males and females. Additionally, male PSD95+/− mice exhibited higher levels of aggression and territoriality, while female PSD95+/− mice showed increased vocalization upon exposure to an anesthetized female mouse. Both male and female PSD95+/− mice revealed mild hypoactivity in the open field but no obvious motor deficit. Regarding PSD93 mutants, homozygous (but not heterozygous) knockout mice displayed prominent hypersocial behavior comparable to that observed in PSD95+/− mice, despite a more severe motor phenotype, which precluded several behavioral tests or their interpretation. Considering that PSD95 and PSD93 reduction provoke strikingly similar behavioral consequences, we explored a potential substitution effect and found increased PSD93 protein expression in hippocampal synaptic enrichment preparations of PSD95+/− mice. These data suggest that both PSD95 and PSD93 are involved in processing of social stimuli and control of social behavior. This important role may be partly assured by functional/behavioral and biological/biochemical redundancy.