Motor coordination in mice with hotfoot, Lurcher, and double mutations of the Grid2 gene encoding the delta-2 excitatory amino acid receptor

The ortholog of human ssDNA-binding protein SSBP3 influences neurodevelopment and autism-like behaviors in Drosophila melanogaster

1p32.3 microdeletion/duplication is implicated in many neurodevelopmental disorders-like phenotypes such as developmental delay, intellectual disability, autism, macro/microcephaly, and dysmorphic features. The 1p32.3 chromosomal region harbors several genes critical for development; however, their validation and characterization remain inadequate. One such gene is the single-stranded DNA-binding protein 3 (SSBP3) and its Drosophila melanogaster ortholog is called sequence-specific single-stranded DNA-binding protein (Ssdp). Here, we investigated consequences of Ssdp manipulations on neurodevelopment, gene expression, physiological function, and autism-associated behaviors using Drosophila models. We found that SSBP3 and Ssdp are expressed in excitatory neurons in the brain. Ssdp overexpression caused morphological alterations in Drosophila wing, mechanosensory bristles, and head. Ssdp manipulations also affected the neuropil brain volume and glial cell number in larvae and adult flies. Moreover, Ssdp overexpression led to differential changes in synaptic density in specific brain regions. We observed decreased levels of armadillo in the heads of Ssdp overexpressing flies, as well as a decrease in armadillo and wingless expression in the larval wing discs, implicating the involvement of the canonical Wnt signaling pathway in Ssdp functionality. RNA sequencing revealed perturbation of oxidative stress-related pathways in heads of Ssdp overexpressing flies. Furthermore, Ssdp overexpressing brains showed enhanced reactive oxygen species (ROS), altered neuronal mitochondrial morphology, and up-regulated fission and fusion genes. Flies with elevated levels of Ssdp exhibited heightened anxiety-like behavior, altered decisiveness, defective sensory perception and habituation, abnormal social interaction, and feeding defects, which were phenocopied in the pan-neuronal Ssdp knockdown flies, suggesting that Ssdp is dosage sensitive. Partial rescue of behavioral defects was observed upon normalization of Ssdp levels. Notably, Ssdp knockdown exclusively in adult flies did not produce behavioral and functional defects. Finally, we show that optogenetic manipulation of Ssdp-expressing neurons altered autism-associated behaviors. Collectively, our findings provide evidence that Ssdp, a dosage-sensitive gene in the 1p32.3 chromosomal region, is associated with various anatomical, physiological, and behavioral defects, which may be relevant to neurodevelopmental disorders like autism. Our study proposes SSBP3 as a critical gene in the 1p32.3 microdeletion/duplication genomic region and sheds light on the functional role of Ssdp in neurodevelopmental processes in Drosophila.

The oDGal Mouse: A Novel, Physiologically Relevant Rodent Model of Sporadic Alzheimer's Disease

Sporadic Alzheimer's disease (sAD) represents a serious and growing worldwide economic and healthcare burden. Almost 95% of current AD patients are associated with sAD as opposed to patients presenting with well-characterized genetic mutations that lead to AD predisposition, i.e., familial AD (fAD). Presently, the use of transgenic (Tg) animals overexpressing human versions of these causative fAD genes represents the dominant research model for AD therapeutic development. As significant differences in etiology exist between sAD and fAD, it is perhaps more appropriate to develop novel, more sAD-reminiscent experimental models that would expedite the discovery of effective therapies for the majority of AD patients. Here we present the oDGal mouse model, a novel model of sAD that displays a range of AD-like pathologies as well as multiple cognitive deficits reminiscent of AD symptomology. Hippocampal cognitive impairment and pathology were delayed with N-acetyl-cysteine (NaC) treatment, which strongly suggests that reactive oxygen species (ROS) are the drivers of downstream pathologies such as elevated amyloid beta and hyperphosphorylated tau. These features demonstrate a desired pathophenotype that distinguishes our model from current transgenic rodent AD models. A preclinical model that presents a phenotype of non-genetic AD-like pathologies and cognitive deficits would benefit the sAD field, particularly when translating therapeutics from the preclinical to the clinical phase.

Garlic passion fruit (Passiflora tenuifila Killip): Assessment of eventual acute toxicity, anxiolytic, sedative, and anticonvulsant effects using in vivo assays

Several Passiflora species are known for their sedative and anxiolytic properties. However, the functional properties of Passiflora tenuifila Killip are still unexplored. The objective of this work was to evaluate the phenolic composition and acute toxicity, anxiolytic, sedative, and anticonvulsant effects using in vivo assays. The whole fruit (peel, pulp, and seed) was lyophilized and used for all assays. LC-MS showed 19 phenolic compounds, tentatively identified as flavonoids and phenolic acids. Acute treatment with single doses of up to 2000 mg kg^-1 in Wistar rats showed no signs of mortality or toxicity over 14 days. The assay of functional effects was performed with Swiss mice, four groups, received by gavage, doses of P. tenuifila (200 or 400 mg kg^-1 body weight), water, and diazepam (as negative and positive control), and behavior tests were performed after 60 min of the treatments. The animals treated with P. tenuifila fruit showed a significant decrease in locomotor activity, indicating a sedative and anxiolytic activity. No significant changes were observed in the rotarod apparatus, suggesting that the P. tenuifila fruit did not cause muscle relaxation. The 400 mg kg^-1 dose of P. tenuifila exerted a protective effect against pentylenetetrazole-induced seizures, decreasing the severity and not causing the death of the animals. In conclusion, P. tenuifila showed no acute toxicity and had a promising effect as an anxiolytic agent, hypnotic-sedative and anticonvulsant, which could be related to its composition of flavonoids and phenolic acids.

Deletion of the GluRδ2 Receptor in the Hotfoot Mouse Mutant Causes Granule Cell Loss, Delayed Purkinje Cell Death, and Reductions in Purkinje Cell Dendritic Tree Area

Recent studies have found that in the cerebellum, the δ2 glutamate receptor (GluRδ2) plays a key role in regulating the differentiation of parallel fiber-Purkinje synapses and mediating key physiological functions in the granule cell-Purkinje cell circuit. In the hotfoot mutant or GluRδ2 knockout mice, the absence of GluRδ2 expression results in impaired motor-related tasks, ataxia, and disruption of long-term depression at parallel fiber-Purkinje cell synapses. The goal of this study was to determine the long-term consequences of deletion of GluRδ2 expression in the hotfoot mutant (GluRδ2 ^ho/ho ) on Purkinje and granule cell survival and Purkinje cell dendritic differentiation. Quantitative estimates of Purkinje and granule cell numbers in 3-, 12-, and 20-month-old hotfoot mutants and wild-type controls showed that Purkinje cell numbers are within control values at 3 and 12 months in the hotfoot mutant but reduced by 20 % at 20 months compared with controls. In contrast, the number of granule cells is significantly reduced from 3 months onwards in GluRδ2 ^ho/ho mutant mice compared to wild-type controls. Although the overall structure of Purkinje cell dendrites does not appear to be altered, there is a significant 27 % reduction in the cross-sectional area of Purkinje cell dendritic trees in the 20-month-old GluRδ2 ^ho/ho mutants. The interpretation of the results is that the GluRδ2 receptor plays an important role in the long-term organization of the granule-Purkinje cell circuit through its involvement in the regulation of parallel fiber-Purkinje cell synaptogenesis and in the normal functioning of this critical cerebellar circuit.

Jan Evangelista Purkyně and the cerebellum then and now

The name of Jan Evangelista Purkyně and the cerebellum belong inseparably together. He was the first who saw and described the largest nerve cells in the brain, de facto in the cerebellum. The most distinguished researchers of the nervous system then showed him the highest recognition by naming these neurons as Purkinje cells. Through experiments by J. E. Purkyně and his followers properly functionally was attributed to the cerebellum share in precision of motor skills. Despite ongoing and fruitful research, after a relatively long time, especially in the last two decades, scientists had to constantly replenish and re-evaluate the traditional conception of the cerebellum and formulate a new one. It started in the early 1990s, when it was found that cerebellar cortex contains more neurons than the cerebral cortex. Shortly thereafter it was gradually revealed that such enormous numbers of neural cells are not without an impact on brain functions and that the cerebellum, except its traditional role in the motor skills, also participates in higher nervous activity. These new findings were obtained thanks to the introduction of modern methods of examination into the clinical praxis, and experimental procedures using animal models of cerebellar disorders described below.

Abbreviated exposure to hypoxia is sufficient to induce CNS dysmyelination, modulate spinal motor neuron composition, and impair motor development in neonatal mice

Neonatal white matter injury (nWMI) is an increasingly common cause of cerebral palsy that results predominantly from hypoxic injury to progenitor cells including those of the oligodendrocyte lineage. Existing mouse models of nWMI utilize prolonged periods of hypoxia during the neonatal period, require complex cross-fostering and exhibit poor growth and high mortality rates. Abnormal CNS myelin composition serves as the major explanation for persistent neuro-motor deficits. Here we developed a simplified model of nWMI with low mortality rates and improved growth without cross-fostering. Neonatal mice are exposed to low oxygen from postnatal day (P) 3 to P7, which roughly corresponds to the period of human brain development between gestational weeks 32 and 36. CNS hypomyelination is detectable for 2–3 weeks post injury and strongly correlates with levels of body and brain weight loss. Immediately following hypoxia treatment, cell death was evident in multiple brain regions, most notably in superficial and deep cortical layers as well as the subventricular zone progenitor compartment. PDGFαR, Nkx2.2, and Olig2 positive oligodendrocyte progenitor cell were significantly reduced until postnatal day 27. In addition to CNS dysmyelination we identified a novel pathological marker for adult hypoxic animals that strongly correlates with life-long neuro-motor deficits. Mice reared under hypoxia reveal an abnormal spinal neuron composition with increased small and medium diameter axons and decreased large diameter axons in thoracic lateral and anterior funiculi. Differences were particularly pronounced in white matter motor tracts left and right of the anterior median fissure. Our findings suggest that 4 days of exposure to hypoxia are sufficient to induce experimental nWMI in CD1 mice, thus providing a model to test new therapeutics. Pathological hallmarks of this model include early cell death, decreased OPCs and hypomyelination in early postnatal life, followed by dysmyelination, abnormal spinal neuron composition, and neuro-motor deficits in adulthood.

From mice to men: lessons from mutant ataxic mice

Ataxic mutant mice can be used to represent models of cerebellar degenerative disorders. They serve for investigation of cerebellar function, pathogenesis of degenerative processes as well as of therapeutic approaches. Lurcher, Hot-foot, Purkinje cell degeneration, Nervous, Staggerer, Weaver, Reeler, and Scrambler mouse models and mouse models of SCA1, SCA2, SCA3, SCA6, SCA7, SCA23, DRPLA, Niemann-Pick disease and Friedreich ataxia are reviewed with special regard to cerebellar pathology, pathogenesis, functional changes and possible therapeutic influences, if any. Finally, benefits and limitations of mouse models are discussed.

A homozygous deletion in GRID2 causes a human phenotype with cerebellar ataxia and atrophy

GRID2 is a member of the ionotropic glutamate receptor family of excitatory neurotransmitter receptors. GRID2 encodes the glutamate receptor subunit delta-2, selectively expressed in cerebellar Purkinje cells. The phenotype associated with loss of GRID2 function was described only in mice until now, characterized by different degrees of cerebellar ataxia and usually relatively mild abnormalities of the cerebellum. This work describes for the first time the human phenotype associated with homozygous partial deletion of GRID2 in 3 children in one large consanguineous Turkish family. Homozygous deletion of exons 3 and 4 of GRID2 (94 153 589-94 298 037 bp) in the proband and similarly affected cousins, and heterozygous deletions in parental DNA were shown using Affymetrix® 6.0 single-nucleotide polymorphism array, confirmed by real-time polymerase chain reaction. The phenotype includes nystagmus, hypotonia with marked developmental delay in gross motor skills in early infancy followed by a static encephalopathy course with development of cerebellar ataxia, oculomotor apraxia, and pyramidal tract involvement.

Assessment of Motor Coordination and Balance in Mice Using the Rotarod, Elevated Bridge, and Footprint Tests

In order fully to utilize animal models of disease states, to test experimental therapeutics, and to understand the underlying pathophysiology of neurodegenerative disease, behavioral characterization of the model is essential. Deterioration of normal motor function within a disease state signals the progression of an underlying pathological process, and identifies disease-sensitive time points according to which the onset of therapeutic trials may be scheduled. Deterioration in the performance of motor tasks may also indicate the point when motor deficits begin to compromise our ability to measure other deficits within cognitive and behavioral domains. In acute therapeutic trials, the separation of motor from cognitive or behavioral function may be crucial in determining the functional specificity of the drug effect. If we are to accurately measure motor performance in disease progression or during drug trials, tests of motor function that have been highly optimized with respect to sensitivity must be applied. Since motor coordination and balance are essential to normal motor function, tests that probe these facets are ideal for the purpose. In this chapter, we describe in detail three test protocols that principally measure motor coordination (the rotarod and footprint tests) and balance (the elevated bridge test) in mice. Curr. Protoc. Mouse Biol. 2:37-53 © 2012 by John Wiley & Sons, Inc.

Behavioral phenotyping of mouse models of neurodegeneration

Neurodegenerative disorders, such as amyotrophic lateral sclerosis (ALS), Huntington's (HD), Parkinson's (PD) and Alzheimer's diseases (AD), are characterized by the loss of structure and function of specific neuronal circuitry in the brain. As a result of this loss, behavioral symptoms occur progressively. Understanding the causes of neurodegeneration is fundamental for the development of new therapeutic targets. For this purpose, several animal models of neurodegenerative disorders have been generated and characterized. During the characterization, behavioral science plays a crucial role by identifying specific symptoms in these animal models of human disorders. Later on, it also allows scientists to verify the efficacy of new treatments. This chapter describes some of the standard tests used to assess behavioral symptoms present in mouse models of neurodegenerative disorders. A list of procedures is provided to evaluate motor skills for the study of ALS, HD, and PD models, and to evaluate spatial learning and memory for the study of AD models.

The cerebellum harbors a circadian oscillator involved in food anticipation

The cerebellum participates in motor coordination as well as in numerous cerebral processes, including temporal discrimination. Animals can predict daily timing of food availability, as manifested by food-anticipatory activity under restricted feeding. By studying ex vivo clock gene expression by in situ hybridization and recording in vitro Per1-luciferase bioluminescence, we report that the cerebellum contains a circadian oscillator sensitive to feeding cues (i.e., whose clock gene oscillations are shifted in response to restricted feeding). Food-anticipatory activity was markedly reduced in mice injected intracerebroventricularly with an immunotoxin that depletes Purkinje cells (i.e., OX7-saporin). Mice bearing the hotfoot mutation (i.e., Grid2(ho/ho)) have impaired cerebellar circuitry and mild ataxic phenotype. Grid2(ho/ho) mice fed ad libitum showed regular behavioral rhythms and day-night variations of clock gene expression in the hypothalamus and cerebellum. When challenged with restricted feeding, however, Grid2(ho/ho) mice did not show any food-anticipatory rhythms, nor timed feeding-induced changes in cerebellar clock gene expression. In hypothalamic arcuate and dorsomedial nuclei, however, shifts in Per1 expression in response to restricted feeding were similar in cerebellar mutant and wild-type mice. Furthermore, plasma corticosterone and metabolites before mealtime did not differ between cerebellar mutant and wild-type mice. Together, these data define a role for the cerebellum in the circadian timing network and indicate that the cerebellar oscillator is required for anticipation of mealtime.

Deletion of astrocyte connexins 43 and 30 leads to a dysmyelinating phenotype and hippocampal CA1 vacuolation

Astrocytes are coupled via gap junctions (GJs) comprising connexin 43 (Cx43) (Gja1) and Cx30 (Gjb6), which facilitate intercellular exchange of ions. Astrocyte connexins also form heterotypic GJs with oligodendrocytic somata and lamellae. Loss of oligodendrocyte gap junctions results in oligodendrocyte and myelin pathology. However, whether loss of astrocyte GJs affects oligodendrocytes and myelin is not known. To address this question, mice with astrocyte-targeted deletion of Cx43 and global loss of Cx30 [double knock-out (dKO)] were studied using Western blotting, immunohistochemistry, electron microscopy, and functional assays. Commencing around postnatal day 23 and persisting into old age, we found widespread pathology of white matter tracts comprising vacuolated oligodendrocytes and intramyelinic edema. In contrast, gray matter pathology was restricted to the CA1 region of the hippocampus, and consisted of edematous astrocytes. No differences were observed in synaptic density or total NeuN(+) cells in the hippocampus, or olig2(+) cells in the corpus callosum. However, in dKO mice, fewer CC1-positive mature oligodendrocytes were detected, and Western blotting indicated reduced myelin basic protein. Pathology was not noted in mice expressing a single allele of either Cx43 or Cx30. When compared with single connexin knock-outs, dKO mice were impaired in sensorimotor (rotarod, balance beam assays) and spatial memory tasks (object recognition assays). We conclude that loss of astrocytic GJs can result in white matter pathology that has functional consequences.

The regular and light-dark Suok tests of anxiety and sensorimotor integration: utility for behavioral characterization in laboratory rodents

Animal behavioral models are crucial for neurobiological research, allowing for the thorough investigation of brain pathogenesis to be performed. In both animals and humans, anxiety has long been linked to vestibular disorders. However, although there are many tests of anxiety and vestibular deficits, there are few protocols that address the interplay between these two domains. The Suok test and its light-dark modification presented here appear to be suitable for testing this pathogenetic link in laboratory rodents. This protocol adds a new dimension to previously used tests by assessing animal anxiety and balancing simultaneously, resulting in efficient, high-throughput screens for testing psychotropic drugs, phenotyping genetically modified animals, and modeling clusters of human disorders related to stress/anxiety and balancing.

Behavioural characterisation of the robotic mouse mutant

The ataxic mouse mutant robotic is characterised by progressive adult-onset Purkinje cell loss that occurs in a distinctive region-specific pattern. We report the first behavioural characterisation of this mutant and quantify its performance on tests of motor function, locomotor and exploratory activity over a time course that reflects specific stages of cell loss in the cerebellum. Robotic mutants are significantly impaired on the rotarod and static rod tests of coordination and their performance declined during aging. In addition, gait analysis revealed an increase in the severity of the ataxia displayed by mutants over time. Interestingly, spontaneous alternation testing in a T-maze was not significantly affected in robotic mice, unlike other ataxic mutants with more rapid and extensive cerebellar degeneration; robotic therefore provides an opportunity to investigate the necessity of specific Purkinje cell populations for various behavioural tasks.

Spontaneous and induced mouse mutations with cerebellar dysfunctions: behavior and neurochemistry

Grid2(Lc) (Lurcher), Grid2(ho) (hot-foot), Rora(sg) (staggerer), nr (nervous), Agtpbp1(pcd) (Purkinje cell degeneration), Reln(rl) (reeler), and Girk2(Wv) (Weaver) are spontaneous mutations with cerebellar atrophy, ataxia, and deficits in motor coordination tasks requiring balance and equilibrium. In addition to these signs, the Dst(dt) (dystonia musculorum) spinocerebellar mutant displays dystonic postures and crawling. More recently, transgenic models with human spinocerebellar ataxia mutations and alterations in calcium homeostasis have been shown to exhibit cerebellar anomalies and motor coordination deficits. We describe neurochemical characteristics of these mutants with respect to regional brain metabolism as well as amino acid and biogenic amine concentrations, uptake sites, and receptors.