Early start of progressive motor deficits in Line 61 α-synuclein transgenic mice.

BACKGROUND: Synucleinopathies such as Parkinson's disease or multiple system atrophy are characterized by Lewy bodies in distinct brain areas. These aggregates are mainly formed by α-synuclein inclusions, a protein crucial for synaptic functions in the healthy brain. Transgenic animal models of synucleinopathies are frequently based on over-expression of human wild type or mutated α-synuclein under the regulatory control of different promoters. A promising model is the Line 61 α-synuclein transgenic mouse that expresses the transgene under control of the Thy-1 promoter. RESULTS: Here, we show an extended characterization of this mouse model over age. To this end, we analyzed animals for the progression of human and mouse protein expression levels in different brain areas as well as motor and memory deficits. Our results show, that Line 61 mice exhibited an age dependent increase of α-synuclein protein levels in the hippocampus but not the striatum. While murine α-synuclein was also increased with age, it was lower expressed in Line 61 mice than in non-transgenic littermates. At the age of 9 months animals exhibited increased neuroinflammation. Furthermore, we found that Line 61 mice showed severe motor deficits as early as 1 month of age as assessed by the wire hanging and nest building tests. At later ages, initial motor deficits were validated with the RotaRod, pasta gnawing and beam walk tests. At 8 months of age animals exhibited emotional memory deficits as validated with the contextual fear conditioning test. CONCLUSION: In summary, our results strengthen and further expand our knowledge about the Line 61 mouse model, emphasizing this mouse model as a valuable in vivo tool to test new compounds directed against synucleinopathies.

Elevated levels of soluble total and hyperphosphorylated tau result in early behavioral deficits and distinct changes in brain pathology in a new tau transgenic mouse model.

Tauopathies, characterized by hyperphosphorylation and aggregation of tau protein, include frontotemporal dementias and Alzheimer's disease. To explore disease mechanisms and investigate potential treatments, we generated a transgenic (tg) mouse line overexpressing human tau441 with V337M and R406W mutations. Biochemical characterization of these TMHT (Thy-1 mutated human tau) mice showed a significant increase in human transgene expression relative to endogenous murine tau by Western blot and multi-array immunosorbent assay. Only soluble total tau and phosphorylated tau (ptau at residue Thr(181), Ser(199), Thr(231) and Thr(235)), but not insoluble total tau and ptau were increased. Application of the Phospho-Tau SRM assay revealed that phosphorylation at Ser(396) and Ser(404) in soluble tau in the presence of the R406W mutation was at baseline levels in the cortex of TMHT mice compared to non-tg littermates. Histological analyses showed a progressive increase in human tau protein in the amygdala over age, while hippocampal tau levels remained constant from 2 months onwards. Behavioral testing of TMHT mice in the Morris water maze revealed a distinct progressive spatial learning impairment starting already at 5 months of age. Furthermore, we showed that the TMHT mice have early olfactory deficits. These impairments are unbiased by any motor disturbance or lack of motivation. Our results prove that combination of the V337M and R406W mutations of tau accelerates human tau phosphorylation and induces tau pathology as well as cognitive deficits, making this model a suitable tool for basic research on tau as well as in vivo drug testing.

SEN1500, a novel oral amyloid-ß aggregation inhibitor, attenuates brain pathology in a mouse model of Alzheimer's disease.

INTRODUCTION: Amyloid-ß (Aß) aggregation is thought to be a major pathogenic event underlying the neuropathology of Alzheimer's disease (AD). The development of new drugs inhibiting the Aß aggregation process is, therefore, important. SEN1500, an orally bioavailable and CNS-penetrant Aß aggregation inhibitor, has previously been shown to reduce spatial learning and memory deficits in an APP transgenic mouse model. To verify that the pharmacological properties of SEN1500 are not unique to this model, we investigated brain Aß pathology, neuroinflammation, as well as memory in a different mouse model of AD expressing the human amyloid precursor protein with Swedish and London mutations (APPSL). MATERIALS & METHODS: APPSL transgenic mice and non-transgenic littermates were treated with SEN1500 via food pellets from three months of age for four months. At the end of the treatment, animals were tested for memory deficits using the contextual fear conditioning test and brain tissue was analyzed for soluble and insoluble amyloid-ß1-38, -40, -42, ß-amyloid plaques, ß-sheet plaque cores, as well as for astrocytosis and activated microglia. RESULTS: SEN1500 treatment lowered insoluble Aß levels and ß-amyloid plaque load in the brain compared with control-treated APPSL mice. Activated microglia were significantly reduced in the cortex but not the hippocampus of SEN1500-treated APPSL mice. Memory deficits of APPSL mice could not be rescued by SEN1500. DISCUSSION: SEN1500 is not only able to reduce Aß pathology and activated microglia but also to improve learning and memory as previously shown, making SEN1500 a potential candidate for human AD treatment. This Aß aggregation inhibitor could be a promising therapeutic agent for the disease-modifying treatment of AD.

Epigenetic factors differentially influence postnatal maturation of serotonin (5-HT) innervation in cerebral cortex of gerbils: interaction of rearing conditions and early methamphetamine challenge.

The effects of disjunctive environmental deprivation combined with a single methamphetamine (MA) challenge on postnatal maturation of the serotonin (5-HT) innervation pattern in cerebral cortex of gerbils were studied. Gerbils were assigned to either enriched (ER) or impoverished (IR) environmental rearing conditions. On postnatal day 110, 5-HT was immunostained. The 5-HT innervation pattern of the brain was qualitatively evaluated and provided in graphic form. The densities of 5-HT fibres were quantified in areas of prefrontal, insular, frontal, parietal, and entorhinal cortices of the right hemisphere using digital image analysis. The early MA challenge led to an overshoot of the fibre density in medial and orbital prefrontal cortex and entorhinal cortex of ER animals. IR animals mostly resisted MA effects except of a restraint of the innervation of the insular cortex. In comparison to enriched rearing, restricted rearing caused overshoot maturation of 5-HT innervation in insular and entorhinal cortices. The present data provide evidence for a region-specific postnatal vulnerability of the maturing 5-HT innervation, namely in association cortices. In contrast, both sensory and motor cortices showed no significant changes at all. The results are discussed in context with previously presented findings of alterations of the cortical dopamine innervation depending on both epigenetic factors. In conclusion, both experimental variables together give new insight into raphe-cortical plasticity that may contribute to a better understanding of the role of 5-HT fibre systems in structural maturation of the cortex. Postnatal environment may be involved in individual vulnerability of a variety of mental disorders during adolescence and aging.

Alteration in the GABAergic network of the prefrontal cortex in a potential animal model of psychosis.

The GABAergic input on cortical pyramidal cells has an important influence on the firing activity of the cortex and thus in regulating the behavioural outcome. The aim of the current study was to investigate the long-term neuroplastic adaptation of the GABAergic innervation pattern after an early severe systemic impact. Therefore 40 Mongolian gerbils (Meriones unguiculatus) were either reared under impoverished (IR) or enriched rearing conditions (ER) and received a single early (+)-methamphetamine (MA) challenge (50 mg/kg i.p.) or saline on postnatal day 14. The density of perisomatic immunoreactive GABAergic terminals surrounding layers III and V pyramidal neurons was quantified as well as the overall GABAergic fibre density in layers I/II and V of the medial prefrontal cortex (mPFC) of young adult animals (90 days). We found that IR in combination with an early MA administration led to a significant decrease in GABAergic bouton densities while the overall GABAergic fibre density increased in all investigated layers. The results indicate a shift in inhibition from somatic to dendritic innervation of pyramidal neurons in this potential animal model of psychosis. We conclude that IR combined with early MA trigger changes in the postnatal maturation of the prefrontal cortical GABAergic triggers innervation, which may interfere with proper signal processing within the prefrontal neural network.

The maturation of the acetylcholine system in the dentate gyrus of gerbils (Meriones unguiculatus) is affected by epigenetic factors.

The current study investigated the influence of impoverished rearing (IR) conditions and a single early methamphetamine challenge (MA; 50 mg/kg i.p.) on day 14 on the postnatal maturation of acetylcholinesterase-positive (AChE+) fibres in the hippocampal dentate gyrus (DG) of gerbils (Meriones unguiculatus). The layer-specific densities of histochemically stained AChE+ fibres were quantified in two planes of the left and right DG in young adults (day 90). Compared to enriched reared (ER) animals, the AChE+ fibre densities turned out to be higher in both the septal and the temporal plane of both hemispheres in saline treated IR and MA treated ER gerbils. The temporal plane was slightly more affected than the septal plane. In IR animals, MA treatment selectively diminished the AChE+ fibre densities in the subgranular layer of both left and right temporal DG. In conclusion, the maturation of AChE+ fibres is vulnerable to both rearing conditions and early MA challenge. The results correlate with our previous studies on the dentate cell proliferation rates and the serotonergic innervation, two parameters which are similarly affected by the experimental design. Thus, disturbances of the ACh system may impair the hippocampal plasticity and hippocampus-related cognitive and emotional function.

An early methamphetamine challenge suppresses the maturation of dopamine fibres in the nucleus accumbens of gerbils: on the significance of rearing conditions.

The effect of a single early methamphetamine (MA) challenge on postnatal maturation of the nucleus accumbens (NAC) was studied. Therefore, male gerbils received a single dose of MA (50 mg/kg, i.p.) on postnatal day 14. At the age of postnatal day 90, dopamine fibres were stained immunocytochemically and innervation density was determined in several test fields along the rostrocaudal extent of both core and shell of the NAC. Since we already know that the differential environment can alter ontogeny of dopamine innervation in the prefrontal cortex of gerbils, in the present study we investigated whether probable drug effects may be influenced by rearing conditions. For that purpose, animals were bred and reared either isolated in standard laboratory cages or grouped in an object-filled environment. The results showed that a single early MA challenge significantly alters maturation of dopamine fibre innervation in both subregions of the NAC. In seminaturally reared gerbils the drug challenge caused dopamine fibre densities which were about 54% below those of saline-treated controls in both the shell and core. However, in animals from restricted rearing this MA-induced effect was more pronounced in the core (-43%) but not significant in the shell (-14%). In conclusion, an early MA challenge caused a significant restraint of adult dopamine fibre density developing in the NAC postnatally. Additionally, rearing conditions significantly interfered with drug-induced alterations in maturation of dopaminergic innervation pattern of the NAC. The present results are discussed with recent findings on MA-induced impairment of prefrontal dopamine innervation and further reactive morphogenetic effects caused by the drug. In this respect, functional interactions between the prefrontal cortex and NAC are specifically considered.

Differential influence of rearing conditions and methamphetamine on serotonin fibre maturation in the dentate gyrus of gerbils (Meriones unguiculatus).

Environmental experience and drugs are two parameters that affect the maturation of neurotransmitter systems. The influence of impoverished rearing (IR) versus enriched rearing (ER) was compared in conjunction with postnatal methamphetamine (MA) treatment. The densities of immunostained 5-HT fibres were quantified in septal and temporal regions of the hippocampal dentate gyrus (DG) in young adult gerbils. In the IR group, 5-HT fibre densities were significantly increased in the molecular, granular and polymorphic layers of the DG in the temporal plane. After postnatal MA treatment, the 5-HT fibre density in the ER group reached a level equivalent to that of the IR group in nearly all respects. Under IR conditions, the pharmacological intervention significantly increased the maturation of fibre densities in septal layers only in the right hemisphere with no significant alterations in the left hemisphere and in temporal regions of either hemisphere. According to our previous studies on hippocampal neurogenesis, adaptations of 5-HT fibre densities partly proved to be positively correlated to cell proliferation rates for each of the specific conditions. Thus, the induced MA sensitivity, caused by pharmacological intervention at day 14, was manifested as direct interaction of 5-HT fibre maturation and cell proliferation in dependence of environmental factors. Both IR and MA together give us a better understanding of raphe-hippocampal plasticity and offer new perspectives for pharmacological studies on the 5-HT participation in mental disorders.

Developmentally induced imbalance of dopaminergic fibre densities in limbic brain regions of gerbils ( Meriones unguiculatus).

It is well established that epigenetic factors influence the maturation of neurotransmitter systems. Social isolation as well as an early intervention with methamphetamine (MA) lead to a diminished maturation of dopaminergic (DA) fibres in cortical and striatal areas in the brain of Mongolian gerbils. The aim of this study was to prove whether isolated rearing (IR) and the application of a single dose of MA on postnatal day 14 affect the maturation of DA fibres in caudal limbic areas. Therefore the DA fibre densities were quantified in the dorsolateral and ventrolateral entorhinal cortex (EC), the ventral subiculum (SUB) and in three amygdala nuclei - the basolateral (BLA), the lateral (LA) and the central (CA) nucleus. Our results showed that IR and an early MA application led to an increase of DA fibre densities in various caudal limbic areas. Whereas the BLA was affected by both IR and MA, the LA and the medial left CA were only influenced by MA in IR animals. The DA fibre surplus in the ventrolateral EC was significant in MA treated ER and IR animals in the left and right hemisphere, respectively. The SUB and the dorsolateral EC remained unaffected by both epigenetic factors. Altogether, the BLA seems to be the area which responds most sensitively to IR and MA. Previous studies in our laboratory showed a suppressive maturation of DA fibres in the prefrontal cortex (PFC) and nucleus accumbens (NAC) induced by the same set of epigenetic factors. Thus, due to the close functional connection between the PFC and limbic areas, it could be assumed that the suppressive maturation of prefrontal DA fibres implicates an enhancement of DA innervation densities in caudal limbic areas. Imbalances in the morphology and physiology of the different DA projections are suggested here to be crucial in the aetiology of schizophrenia.

Differential environment alters ontogeny of dopamine innervation of the orbital prefrontal cortex in gerbils.

In the present study, the influence of postnatal environmental conditions on the structural ontogeny of the orbital prefrontal cortex of adult gerbils (Meriones unguiculatus) was examined. The animals were bred and reared either isolated in standard laboratory cages or grouped in an object-filled environment. At the age of postnatal day 90, dopamine fibers were stained immunocytochemically and innervation density was determined in the orbital prefrontal cortex. By comparison, restricted rearing produced a restraint of the subsequent maturation of orbital prefrontal dopamine innervation, leading to adult fiber densities that were approximately 38% below those in seminaturally reared gerbils. Results are discussed in terms of activity-dependent postnatal maturation of the cortex and adaptive neuroplasticity with regard to previously published data concerning diminished dopamine innervation in the medial prefrontal cortex (Winterfeld et al. [1998]