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Translational research in behavioral neuroscience seeks causes and remedies for human mental health problems in animals, following leads imposed by clinical research in psychiatry. This endeavor faces several problems because scientists must read and interpret animal movements to represent human perceptions, mood, and memory processes. Yet, it is still not known how mammalian brains bundle all these processes into a highly compressed motor output in the brain stem and spinal cord, but without that knowledge, translational research remains aimless. Based on some four decades of experience in the field, the article identifies sources of interpretation problems and illustrates typical translational pitfalls. (1) The sensory world of mice is different. Smell, hearing, and tactile whisker sensations dominate in rodents, while visual input is comparatively small. In humans, the relations are reversed. (2) Mouse and human brains are equated inappropriately: the association cortex makes up a large portion of the human neocortex, while it is relatively small in rodents. The predominant associative cortex in rodents is the hippocampus itself, orchestrating chiefly inputs from secondary sensorimotor areas and generating species-typical motor patterns that are not easily reconciled with putative human hippocampal functions. (3) Translational interpretation of studies of memory or emotionality often neglects the ecology of mice, an extremely small species surviving by freezing or flight reactions that do not need much cognitive processing. (4) Further misinterpretations arise from confounding neuronal properties with system properties, and from rigid mechanistic thinking unaware that many experimentally induced changes in the brain do partially reflect unpredictable compensatory plasticity. (5) Based on observing hippocampal lesion effects in mice indoors and outdoors, the article offers a simplistic general model of hippocampal functions in relation to hypothalamic input and output, placing hypothalamus and the supraspinal motor system at the top of a cerebral hierarchy. (6) Many translational problems could be avoided by inclusion of simple species-typical behaviors as end-points comparable to human cognitive or executive processing, and to rely more on artificial intelligence for recognizing patterns not classifiable by traditional psychological concepts. ISSN:1662-5153

Objective Clinical trials targeting β‐amyloid peptides (Aβ) for Alzheimer disease (AD) failed for arguable reasons that include selecting the wrong stages of AD pathophysiology or Aβ being the wrong target. Targeting Aβ to prevent cerebral amyloid angiopathy (CAA) has not been rigorously followed, although the causal role of Aβ for CAA and related hemorrhages is undisputed. CAA occurs with normal aging and to various degrees in AD, where its impact and treatment is confounded by the presence of parenchymal Aβ deposition. Methods APPDutch mice develop CAA in the absence of parenchymal amyloid, mimicking hereditary cerebral hemorrhage with amyloidosis Dutch type (HCHWA‐D). Mice were treated with a β‐site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitor. We used 3‐dimensional ultramicroscopy and immunoassays for visualizing CAA and assessing Aβ in cerebrospinal fluid (CSF) and brain. Results CAA onset in mice was at 22 to 24 months, first in frontal leptomeningeal and superficial cortical vessels followed by vessels penetrating the cortical layers. CSF Aβ increased with aging followed by a decrease of both Aβ40 and Aβ42 upon CAA onset, supporting the idea that combined reduction of CSF Aβ40 and Aβ42 is a specific biomarker for vascular amyloid. BACE1 inhibitor treatment starting at CAA onset and continuing for 4 months revealed a 90% Aβ reduction in CSF and largely prevented CAA progression and associated pathologies. Interpretation This is the first study showing that Aβ reduction at early disease time points largely prevents CAA in the absence of parenchymal amyloid. Our observation provides a preclinical basis for Aβ‐reducing treatments in patients at risk of CAA and in presymptomatic HCHWA‐D., Annals of Neurology, 86 (4), ISSN:0364-5134, ISSN:1531-8249

Neurochemical Research, 34 (4), ISSN:0364-3190, ISSN:1573-6903

The habenular complex linking forebrain and midbrain structures is subdivided into the medial (mHb) and the lateral nuclei (lHb). The mHb is characterized by the expression of specific nicotinic acetylcholine receptor isoforms and the release of acetylcholine to the interpeduncular nucleus (IPN), the sole output region of the mHb. The specific function of this circuit, however, is poorly understood. Here we generated transgenic mice in which mHb cells were selectively ablated postnatally. These lesions led to large reductions in acetylcholine levels within the IPN. The mutant mice exhibited abnormalities in a wide range of behavioral domains. They tended to be hyperactive during the early night period and were maladapted when repeatedly exposed to new environments. Mutant mice also showed a high rate of premature responses in the 5-choice serial reaction time task (5-CSRTT), indicating impulsive and compulsive behavior. Additionally, mice also exhibited delay and effort aversion in a decision-making test, deficits in spatial memory, a subtle increase in anxiety levels, and attenuated sensorimotor gating. IntelliCage studies under social housing conditions confirmed hyperactivity, environmental maladaptation, and impulsive/compulsive behavior, delay discounting, deficits in long-term spatial memory, and reduced flexibility in complex learning paradigms. In 5-CSRTT and adaptation tasks, systemic administration of nicotine slowed down nose-poke reaction and enhanced adaptation in control but not mutant mice. These findings demonstrate that the mHb–IPN pathway plays a crucial role in inhibitory control and cognition-dependent executive functions., Frontiers in Behavioral Neuroscience, 7, ISSN:1662-5153

Gene mutations and gene copy number variants are associated with autism spectrum disorders (ASDs). Affected gene products are often part of signaling networks implicated in synapse formation and/or function leading to alterations in the excitation/inhibition (E/I) balance. Although the network of parvalbumin (PV)-expressing interneurons has gained particular attention in ASD, little is known on PV’s putative role with respect to ASD. Genetic mouse models represent powerful translational tools for studying the role of genetic and neurobiological factors underlying ASD. Here, we report that PV knockout mice (PV−/−) display behavioral phenotypes with relevance to all three core symptoms present in human ASD patients: abnormal reciprocal social interactions, impairments in communication and repetitive and stereotyped patterns of behavior. PV-depleted mice also showed several signs of ASD-associated comorbidities, such as reduced pain sensitivity and startle responses yet increased seizure susceptibility, whereas no evidence for behavioral phenotypes with relevance to anxiety, depression and schizophrenia was obtained. Reduced social interactions and communication were also observed in heterozygous (PV+/−) mice characterized by lower PV expression levels, indicating that merely a decrease in PV levels might be sufficient to elicit core ASD-like deficits. Structural magnetic resonance imaging measurements in PV−/− and PV+/− mice further revealed ASD-associated developmental neuroanatomical changes, including transient cortical hypertrophy and cerebellar hypoplasia. Electrophysiological experiments finally demonstrated that the E/I balance in these mice is altered by modification of both inhibitory and excitatory synaptic transmission. On the basis of the reported changes in PV expression patterns in several, mostly genetic rodent models of ASD, we propose that in these models downregulation of PV might represent one of the points of convergence, thus providing a common link between apparently unrelated ASD-associated synapse structure/function phenotypes., Translational Psychiatry, 5, ISSN:2158-3188

Synaptosomal-associated protein of 25 kDa (SNAP-25) is a protein that participates in the regulation of synaptic vesicle exocytosis through the formation of the soluble NSF attachment protein receptor complex and modulates voltage-gated calcium channels activity. The Snap25 gene has been associated with schizophrenia, attention deficit hyperactivity disorder, and bipolar disorder, and lower levels of SNAP-25 have been described in patients with schizophrenia. We used SNAP-25 heterozygous (SNAP-25+/−) mice to investigate at which extent the reduction of the protein levels affects neuronal network function and mouse behavior. As interactions of genotype with the specific laboratory conditions may impact behavioral results, the study was performed through a multilaboratory study in which behavioral tests were replicated in at least 2 of 3 distinct European laboratories. Reductions of SNAP-25 levels were associated with a moderate hyperactivity, which disappeared in the adult animals, and with impaired associative learning and memory. Electroencephalographic recordings revealed the occurrence of frequent spikes, suggesting a diffuse network hyperexcitability. Consistently, SNAP-25+/− mice displayed higher susceptibility to kainate-induced seizures, paralleled by degeneration of hilar neurons. Notably, both EEG profile and cognitive defects were improved by antiepileptic drugs. These results indicate that reduction of SNAP-25 expression is associated to generation of epileptiform discharges and cognitive dysfunctions, which can be effectively treated by antiepileptic drugs., Cerebral Cortex, 24 (2), ISSN:1047-3211, ISSN:1460-2199

Mutations in OCRL encoding the inositol polyphosphate 5-phosphatase OCRL (Lowe oculocerebrorenal syndrome protein) disrupt phosphoinositide homeostasis along the endolysosomal pathway causing dysfunction of the cells lining the kidney proximal tubule (PT). The dysfunction can be isolated (Dent disease 2) or associated with congenital cataracts, central hypotonia and intellectual disability (Lowe syndrome). The mechanistic understanding of Dent disease 2/Lowe syndrome remains scarce due to limitations of animal models of OCRL deficiency. Here, we investigate the role of OCRL in Dent disease 2/Lowe syndrome by using OcrlY/− mice, where the lethal deletion of the paralogue Inpp5b was rescued by human INPP5B insertion, and primary culture of proximal tubule cells (mPTCs) derived from OcrlY/− kidneys. The OcrlY/− mice show muscular defects with dysfunctional locomotricity and present massive urinary losses of low-molecular-weight proteins and albumin, caused by selective impairment of receptor-mediated endocytosis in PT cells. The latter was due to accumulation of phosphatidylinositol 4,5–bisphosphate PI(4,5)P2 in endolysosomes, driving local hyper-polymerization of F-actin and impairing trafficking of the endocytic LRP2 receptor, as evidenced in OcrlY/− mPTCs. The OCRL deficiency was also associated with a disruption of the lysosomal dynamic and proteolytic activity. Partial convergence of disease-pathways and renal phenotypes observed in OcrlY/− and Clcn5Y/− mice suggest shared mechanisms in Dent diseases 1 and 2. These studies substantiate the first mouse model of Lowe syndrome and give insights into the role of OCRL in cellular trafficking of multiligand receptors. These insights open new avenues for therapeutic interventions in Lowe syndrome and Dent disease., Human Molecular Genetics, 28 (12), ISSN:0964-6906, ISSN:1460-2083

I. SUMMARY During the last decades, incidence of age-related metabolic and degenerative diseases increased steadily in all industrialized countries turning aging issues into the focus of many socioeconomic discussions. Aging is characterized by a progressive loss of physiological integrity due to accumulation of changes, malfunctions and congregating damage to organs and tissue systems. It is challenging to dissect the interconnectedness between the elicitors, their relative contribution to aging, and the influence between different type of damages and compensatory responses provoked by them. Several studies have shown that impaired mitochondrial function is involved in the pathogenesis of aging and age-related neurodegenerative diseases like Parkinson’s disease and Alzheimer’s disease. Several theories exist on how aging and mitochondria depend on and influence each other. Most of them focus on reactive oxygen species (ROS) production, reduced respiration, mitochondrial DNA (mtDNA) mutations and morphological alterations of mitochondria. Next to these aspects, mitochondrial translation came into focus as experiments in yeast have shown that increasing the accuracy of mitochondrial ribosomes extended cellular lifespan. So, could it be that reduced accuracy shortens lifespan? And could this be a potential source for age-related mitochondrial dysfunction and a trigger for premature aging? In this thesis we are focusing on consequences of mitoribosomal mistranslation on the behavioral phenotype of aging mice. Mutations which reduce the translational fidelity of the ribosome have been found to naturally occur in bacteria as well as in yeast. Our collaboration partners in the Böttger lab identified the candidate position in mammalian mitoribosomal proteins homologue to two of these mutations as amino acid substitutions V338Y and G315R in the nuclear encoded mitoribosomal protein MRPS5 (uS5m). This protein is an important building block of the fully assembled mitoribosome and plays a crucial part in fine-tuning the mitoribosomal translational machinery. We studied these two mutations separately in aging female mice to evaluate the effect of mistranslation on aging. Because neurons and muscles are particularly dependent on mitochondrial function and as long-lived cells particularly sensitive to the accumulation of damage, a strong focus was placed on the behavioral screening of the knock-in lines at three ages (9, 14 and 19 months). Behavioral phenotyping included standard behavioral tests of sensorimotor function, emotional behavior, as well as learning and memory. In addition, new approaches based on fully automated behavioral profiling of group-housed mice in their home cage were used. This was complemented by the monitoring of clinical signs of aging, the characterization of mitochondrial function, as well as functional genomic, proteomic and metabolomic analyses in cooperation with the Böttger lab and others. Overall the results from the V338Y mouse line suggest that the mutation increases anxiety and reduces explorative behavior in 9 months old mice, making their behavior similar to that of 19 months old wild-type mice of the same genetic background. Performance in hippocampus-dependent learning tasks strongly depended on the paradigm. In aversive environments e.g. the water maze place navigation task, the performance of V338Y mutants was reduced while in T-maze or IntelliCage experiments with less aversive settings, no decline was observed. By studying the G315R mouse line, no evidence for a phenotypic difference between mutants and wild-types could be found. The only difference was found in the water maze place navigation task where a mild deficit appeared in the probe trial. Later, it was realized that the G315R mutation is not producing a sterical hindrance at the interface of MRPS5 (uS5m) and bS18-2 (mS40) in the mitoribosome as it can be observed in the underlying mutation G104R in E. coli. Therefore, this line was further considered as additional control line for discussing results from the V338Y mouse line. Unfortunately male animals for this study were already too old for regrouping when we started planning the experimental process. As all animals should experience the same tests to avoid possible confounding effects due to prior learnings, we decided to work with only females in the whole study. With a retrospective study on variability in male and female mouse behavior during the water maze place navigation task and the open field test, we could show that including female mice in experiments does not cause a relevant increase of data variability – contrary to the view of many. Therefore, we assume that the results from the V338Y and G315R line are as variable as if only male mice would have been tested. Questions regarding a sex-dependent mutation effect though cannot be answered with our study. The observed cognitive impairment under stress, the anxiety-related behavioral deterioration, and the enhanced metabolic aging in the V338Y line let us conclude that the data presented in this study indicates an association of translational fidelity with aging processes during lifetime. Then again, despite the pivotal role of mitochondria in cellular physiology, the observed behavioral alterations due to mistranslation of mtDNA-encoded proteins can be considered rather little at the organismal level. Further investigations on the behavioral as well as on the cellular level are needed to understand if and how the mitochondrion can adapt and reach for functional complementation to face the consequences of such a fundamental mutation.

In all higher organisms, the experience of pain is associated with an unpleasant feeling. Nevertheless, our ability to perceive pain warns us of harmful threats that originate either from the inside of our body or from the environment. Perceiving pain relies on a well-functioning nociceptive system, which starts with nociceptive fibers conveying noxious inputs from the periphery to the first relay platform in the central nervous system (CNS), namely the spinal dorsal horn. At this site, inputs are modulated and filtered by a network of excitatory and inhibitory interneurons. The final output is relayed via projection neurons to higher cortical areas in the brain where pain becomes a conscious experience. However, in some cases nociception becomes dysfunctional and eventually leads to persistent and chronic pain. Underlying symptoms of chronic pain are allodynia, where innocuous stimuli such as light-touch become painful and hyperalgesia defined as an enhanced sensitivity to noxious stimuli. Studies have shown that reduced GABAergic or glycinergic neurotransmission in the dorsal horn leads to increased nociceptive signaling to the brain. This indicates that a functional inhibitory network in the dorsal horn is important for avoiding uncontrolled transmission of nociceptive stimuli to higher levels of the central nervous system. Several studies in rodent models of neuropathic or inflammatory pain have demonstrated that GABAA receptors containing the α2 subunit (α2-GABAA receptors) in addition to certain glycine receptors play a key role in the inhibitory control of nociceptive signaling at the spinal cord level. In the three experimental studies of this thesis, I used optogenetics and whole-cell patch-clamp recordings to provide a detailed analysis of inhibitory neurotransmission in the spinal dorsal horn of mice. In the first chapter, I focused on a genetic mouse model of diminished GABAergic inhibition at the spinal cord level. The mice used in this study were hoxb8α2-/- mice which lack α2-GABAA receptors in the spinal cord up to the cervical segment C4. Although these mice lacked a GABAA receptor subtype (α2-GABAA receptors) that is critically involved in spinal nociceptive control and although GABAergic inhibitory postsynaptic currents (GABA-IPSCs) recorded from excitatory superficial dorsal horn neurons were reduced, these mice did not show exaggerated pain responses indicating that some compensatory mechanisms were active in these mice. Several potential compensatory mechanisms were investigated. No significant differences were found for the decay kinetics of GABA-IPSCs. No changes were found in the amplitude of glycinergic IPSCs or of membrane currents evoked by extracellular application of GABA. I also did not find significant changes in the amplitudes of sensory afferent evoked excitatory postsynaptic currents (EPSCs), which are known to be under control by presynaptic GABAA receptors. By contrast, I found increased bicuculline-sensitive (GABAergic) tonic membrane currents in hoxb8α2-/- mice. Furthermore, in immunohistochemical experiments, I found a significant increase in serotonin immunoreactivity and in the expression of the serotonin producing enzyme tryptophan hydroxylase (TPH2). Both the increases in tonic GABAergic currents and in serotonergic input to the spinal cord may on a behavioral level compensate for the loss of synaptic GABAergic inhibition and may explain why hoxb8α2-/- mice lack a pronociceptive phenotype. In the second chapter, Part A, I aimed at identifying the origin of inhibitory inputs onto excitatory lamina II (LII) neurons. To this end, I used laser scanning photostimulation (LSPS) in combination with whole-cell patch-clamp recordings in spinal cord slices of BAC transgenic vGAT::ChR2 mice. These mice express the blue light-activated ion channel channelrhodopsin 2 in all inhibitory neurons of the CNS including the spinal cord. About half (46%) of the sites triggering inhibitory input to the recorded neurons were located in the superficial dorsal horn, one third was located in the deep dorsal horn, and 21% were in the white matter. These results indicate that inhibitory input to LII neurons does not only originate from inhibitory neurons of the same lamina but also from deep dorsal horn interneurons and very likely from inhibitory fiber tracts descending from higher CNS areas. This interpretation is consistent with results described in Part B, where I characterized inhibitory neurotransmission in GlyT2::Cre;vGAT::ChR2 mice in which dorsal horn glycinergic neurons were locally ablated by virus-mediated cre-dependent diphtheria toxin expression. In these experiments, I found a reduction of inhibitory neurotransmission to excitatory LII neurons by 55%. Because most of the glycinergic neurons are located in the deep dorsal horn, these results also support a strong contribution of deep dorsal horn neurons to inhibition of neurons and circuits of LII. Taken together, this thesis provides new insights on the organization of inhibitory neurotransmission in the spinal dorsal horn and on potential mechanisms contributing to a compensation of compromised synaptic inhibition in spinal dorsal horn nociceptive circuits.