Reinhard Sohr

A Humanized Version of Foxp2 Affects Cortico-Basal Ganglia Circuits in Mice

It has been proposed that two amino acid substitutions in the transcription factor FOXP2 have been positively selected during human evolution due to effects on aspects of speech and language. Here, we introduce these substitutions into the endogenous Foxp2 gene of mice. Although these mice are generally healthy, they have qualitatively different ultrasonic vocalizations, decreased exploratory behavior and decreased dopamine concentrations in the brain suggesting that the humanized Foxp2 allele affects basal ganglia. In the striatum, a part of the basal ganglia affected in humans with a speech deficit due to a nonfunctional FOXP2 allele, we find that medium spiny neurons have increased dendrite lengths and increased synaptic plasticity. Since mice carrying one nonfunctional Foxp2 allele show opposite effects, this suggests that alterations in cortico-basal ganglia circuits might have been important for the evolution of speech and language in humans.

Growth retardation and altered autonomic control in mice lacking brain serotonin

Serotonin synthesis in mammals is initiated by 2 distinct tryptophan hydroxylases (TPH), TPH1 and TPH2. By genetically ablating TPH2, we created mice (Tph2−/−) that lack serotonin in the central nervous system. Surprisingly, these mice can be born and survive until adulthood. However, depletion of serotonin signaling in the brain leads to growth retardation and 50% lethality in the first 4 weeks of postnatal life. Telemetric monitoring revealed more extended daytime sleep, suppressed respiration, altered body temperature control, and decreased blood pressure (BP) and heart rate (HR) during nighttime in Tph2−/− mice. Moreover, Tph2−/− females, despite being fertile and producing milk, exhibit impaired maternal care leading to poor survival of their pups. These data confirm that the majority of central serotonin is generated by TPH2. TPH2-derived serotonin is involved in the regulation of behavior and autonomic pathways but is not essential for adult life.

Maternal infection leads to abnormal gene regulation and brain atrophy in mouse offspring: implications for genesis of neurodevelopmental disorders.

Prenatal viral infection has been associated with development of schizophrenia and autism. Our laboratory has previously shown that viral infection causes deleterious effects on brain structure and function in mouse offspring following late first trimester (E9) administration of influenza virus. We hypothesized that late second trimester infection (E18) in mice may lead to a different pattern of brain gene expression and structural defects in the developing offspring. C57BL6J mice were infected on E18 with a sublethal dose of human influenza virus or sham-infected using vehicle solution. Male offsping of the infected mice were collected at P0, P14, P35 and P56, their brains removed and prefrontal cortex, hippocampus and cerebellum dissected and flash frozen. Microarray, qRT-PCR, DTI and MRI scanning, western blotting and neurochemical analysis were performed to detect differences in gene expression and brain atrophy. Expression of several genes associated with schizophrenia or autism including Sema3a, Trfr2 and Vldlr were found to be altered as were protein levels of Foxp2. E18 infection of C57BL6J mice with a sublethal dose of human influenza virus led to significant gene alterations in frontal, hippocampal and cerebellar cortices of developing mouse progeny. Brain imaging revealed significant atrophy in several brain areas and white matter thinning in corpus callosum. Finally, neurochemical analysis revealed significantly altered levels of serotonin (P14, P35), 5-Hydroxyindoleacetic acid (P14) and taurine (P35). We propose that maternal infection in mouse provides an heuristic animal model for studying the environmental contributions to genesis of schizophrenia and autism, two important examples of neurodevelopmental disorders.

Prenatal immune activation leads to multiple changes in basal neurotransmitter levels in the adult brain: implications for brain disorders of neurodevelopmental origin such as schizophrenia

Maternal infection during pregnancy enhances the offsprings risk for severe neuropsychiatric disorders in later life, including schizophrenia. Recent attempts to model this association in animals provided further experimental evidence for a causal relationship between in-utero immune challenge and the postnatal emergence of a wide spectrum of behavioural, pharmacological and neuroanatomical dysfunctions implicated in schizophrenia. However, it still remains unknown whether the prenatal infection-induced changes in brain and behavioural functions may be associated with multiple changes at the neurochemical level. Here, we tested this hypothesis in a recently established mouse model of viral-like infection. Pregnant dams on gestation day 9 were exposed to viral mimetic polyriboinosinic-polyribocytidilic acid (PolyI:C, 5 mg/kg i.v.) or vehicle treatment, and basal neurotransmitter levels were then compared in the adult brains of animals born to PolyI:C- or vehicle-treated mothers by high-performance liquid chromatography on post-mortem tissue. We found that prenatal immune activation significantly increased the levels of dopamine and its major metabolites in the lateral globus pallidus and prefrontal cortex, whilst at the same time it decreased serotonin and its metabolite in the hippocampus, nucleus accumbens and lateral globus pallidus. In addition, a specific reduction of the inhibitory amino acid taurine in the hippocampus was noted in prenatally PolyI:C-exposed offspring relative to controls, whereas central glutamate and gamma-aminobutyric acid (GABA) content was largely unaffected by prenatal immune activation. Our results thus confirm that maternal immunological stimulation during early/middle pregnancy is sufficient to induce long-term changes in multiple neurotransmitter levels in the brains of adult offspring. This further supports the possibility that infection-mediated interference with early fetal brain development may predispose the developing organism to the emergence of neurochemical imbalances in adulthood, which may be critically involved in the precipitation of adult behavioural and pharmacological abnormalities after prenatal immune challenge.

AMPA receptor subunit 1 (GluR-A) knockout mice model the glutamate hypothesis of depression

Recent evidence indicates that glutamate homeostasis and neurotransmission are altered in major depressive disorder, but the nature of the disruption and the mechanisms by which it contributes to the syndrome are unclear. Glutamate can act via AMPA, NMDA, or metabotropic receptors. Using targeted mutagenesis, we demonstrate here that mice with deletion of the main AMPA receptor subunit GluR‐A represent a depression model with good face and construct validity, showing behavioral and neurochemical features of depression also postulated for human patients. GluR‐A−/− mice display increased learned helplessness, decreased serotonin and norepinephrine levels, and disturbed glutamate ho‐meostasis with increased glutamate levels and increased NMDA receptor expression. These results correspond well with current concepts regarding the role of AMPA and NMDA receptors in depression, postulating that compounds that augment AMPA receptor signaling or decrease NMDA receptor functions have antidepressant effects. GluR‐A−/− mice represent a model to investigate the pathophysiology underlying the depressive phenotype and to identify changes in neural plasticity and resilience evoked by the genetic alterations in glutamatergic function. Furthermore, GluR‐A−/− mice may be a valuable tool to study biological mechanisms of AMPA receptor modulators and the efficacy of NMDA antagonists in reducing behavioral or biochemical changes that correlate with increased helplessness.—Chourbaji, S., Vogt, M. A., Fumagalli, F., Sohr, R., Frasca, A., Brandwein, C, Hörtnagl, H., Riva, M. A., Sprengel, R., Gass, P. AMPA receptor subunit 1 (GluR‐A) knockout mice model the glutamate hypothesis of depression. FASEB J. 22, 3129–3134 (2008)

Phenotypic differences in behavior, physiology and neurochemistry between rats selected for tameness and for defensive aggression towards humans

To better understand the biology of tameness, i.e. tolerance of human presence and handling, we analyzed two lines of wild-derived rats (Rattus norvegicus) artificially selected for tameness and defensive aggression towards humans. In response to a gloved human hand, tame rats tolerated handling, whereas aggressive rats attacked. Cross-fostering showed that these behavioral differences are not caused by postnatal maternal effects. Tame rats were more active and explorative and exhibited fewer anxiety-related behaviors. They also had smaller adrenal glands, larger spleens and lower levels of serum corticosterone. Blood glucose levels were lower in tame rats, whereas the concentrations of nine amino acids were higher. In the brain, tame rats had lower serotonin and higher taurine levels than aggressive rats. Our findings reinforce the notion that tameness is correlated with differences in stress response and will facilitate future efforts to uncover the genetic basis for animal tameness.

Folate Deficiency Induces Neurodegeneration and Brain Dysfunction in Mice Lacking Uracil DNA Glycosylase

Folate deficiency and resultant increased homocysteine levels have been linked experimentally and epidemiologically with neurodegenerative conditions like stroke and dementia. Moreover, folate deficiency has been implicated in the pathogenesis of psychiatric disorders, most notably depression. We hypothesized that the pathogenic mechanisms include uracil misincorporation and, therefore, analyzed the effects of folate deficiency in mice lacking uracil DNA glycosylase (Ung−/−) versus wild-type controls. Folate depletion increased nuclear mutation rates in Ung−/− embryonic fibroblasts, and conferred death of cultured Ung−/− hippocampal neurons. Feeding animals a folate-deficient diet (FD) for 3 months induced degeneration of CA3 pyramidal neurons in Ung−/− but not Ung+/+ mice along with decreased hippocampal expression of brain-derived neurotrophic factor protein and decreased brain levels of antioxidant glutathione. Furthermore, FD induced cognitive deficits and mood alterations such as anxious and despair-like behaviors that were aggravated in Ung−/− mice. Independent of Ung genotype, FD increased plasma homocysteine levels, altered brain monoamine metabolism, and inhibited adult hippocampal neurogenesis. These results indicate that impaired uracil repair is involved in neurodegeneration and neuropsychiatric dysfunction induced by experimental folate deficiency.

Dopamine and serotonin levels following prenatal viral infection in mouse : Implications for psychiatric disorders such as schizophrenia and autism

Prenatal viral infection has been associated with neurodevelopmental disorders such as schizophrenia and autism. It has previously been demonstrated that viral infection causes deleterious effects on brain structure and function in mouse offspring following late first trimester (E9) and middle-late second trimester (E18) administration of influenza virus. Neurochemical analysis following infection on E18 using this model has revealed significantly altered levels of serotonin, 5-hydroxyindoleacetic acid, and taurine, but not dopamine. In order to monitor these different patterns of monoamine expression in exposed offspring in more detail and to see if there are changes in the dopamine system at another time point, pregnant C57BL6J mice were infected with a sublethal dose of human influenza virus or sham-infected using vehicle solution on E16. Male offspring of the infected mice were collected at P0, P14, and P56, their brains removed and cerebellum dissected and flash frozen. Dopamine and serotonin levels were then measured using HPLC-ED technique. When compared to controls, there was a significant decrease in serotonin levels in the cerebella of offspring of virally exposed mice at P14. No differences in levels of dopamine were observed in exposed and control mice, although there was a significant decrease in dopamine at P14 and P56 when compared to P0. The present study shows that the serotonergic system is disrupted following prenatal viral infection, potentially modelling disruptions that occur in patients with schizophrenia and autism.

High frequency stimulation of the subthalamic nucleus influences striatal dopaminergic metabolism in the naive rat.

High frequency stimulation (HFS) of the subthalamic nucleus (STN) can partially alleviate motor symptoms in patients with Parkinsons disease (PD). However, the mechanism of action of HFS is incompletely understood. We investigated the effect of HFS (130 Hz) and low frequency stimulation (LFS, 20 Hz) of the STN on striatal dopaminergic transmission and metabolism using in vivo microdialysis in anaesthetized and freely moving rats. While LFS had no effect, HFS of the STN produced a delayed, stable and intensity-dependent increase of extracellular dopamine metabolites. Striatal extracellular levels of dopamine and 5-HIAA were not influenced by HFS or LFS in the present experimental paradigm. We conclude that HFS of the STN influences striatal dopaminergic metabolism in naive, nonlesioned rats.

Anxious and Hyperactive Phenotype Following Brief Ischemic Episodes in Mice

BACKGROUND Poststroke emotional and behavioral abnormalities have an impact on outcome but have scarcely been characterized in animal models. We tested whether brief ischemic episodes induce behavioral changes in mice. METHODS 129/Sv mice were subjected to 30-min occlusion of left or right middle cerebral artery (MCAo) followed by reperfusion or sham operation (n = 9 or 10 per group). Eight to ten weeks later, mice were tested for spontaneous locomotor activity, anxiety in the elevated plus maze, and depressive behavior in the modified Porsolt forced swim test. Outcome was correlated to monoamine and amino acid levels and compared with histologic damage at 10 weeks. RESULTS Ischemia was associated with increased activity (right MCAo) and anxiety (left MCAo), but not poststroke depression. Noradrenaline increased by 30%-45% in the ischemic striatum and correlated with locomotor activity (r = .48); dopamine and homovanillinic acid were decreased compared with sham. The lesion was confined to the striatum, and scattered neuronal death was observed in a number of remote brain regions. CONCLUSION Brief ischemic episodes in the mouse induce an anxious, hyperactive but not depressive phenotype that may relate to left versus right hemispheric lesion location, alterations in brain monoamine levels, and selective neurodegeneration.