Sensory and motor development in mice: genes, environment and their interactions

No significant sex differences in incidence or phenotype for the SMNΔ7 mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive disease that affects 1 out of every 6,000-10,000 individuals at birth, making it the leading genetic cause of infant mortality. In recent years, reports of sex differences in SMA patients have become noticeable. The SMNΔ7 mouse model is commonly used to investigate pathologies and treatments in SMA. However, studies on sex as a contributing biological variable are few and dated. Here, we rigorously investigated the effect of sex on a series of characteristics in SMA mice of the SMNΔ7 model. Incidence and lifespan of 23 mouse litters were tracked and phenotypic assessments were performed at 2-day intervals starting at postnatal day 6 for every pup until the death of the SMA pup(s) in each litter. Brain weights were also collected post-mortem. We found that male and female SMA incidence does not differ significantly, survival periods are the same across sexes, and there was no phenotypic difference between male and female SMA pups, other than for females exhibiting lesser body weights at early ages. Overall, this study ensures that sex is not a biological variable that contributes to the incidence ratio or disease severity in the SMNΔ7 mouse model.

A transient developmental increase in prefrontal activity alters network maturation and causes cognitive dysfunction in adult mice

Disturbed neuronal activity in neuropsychiatric pathologies emerges during development and might cause multifold neuronal dysfunction by interfering with apoptosis, dendritic growth, and synapse formation. However, how altered electrical activity early in life affects neuronal function and behavior in adults is unknown. Here, we address this question by transiently increasing the coordinated activity of layer 2/3 pyramidal neurons in the medial prefrontal cortex of neonatal mice and monitoring long-term functional and behavioral consequences. We show that increased activity during early development causes premature maturation of pyramidal neurons and affects interneuronal density. Consequently, altered inhibitory feedback by fast-spiking interneurons and excitation/inhibition imbalance in prefrontal circuits of young adults result in weaker evoked synchronization of gamma frequency. These structural and functional changes ultimately lead to poorer mnemonic and social abilities. Thus, prefrontal activity during early development actively controls the cognitive performance of adults and might be critical for cognitive symptoms in neuropsychiatric diseases.

Measuring Preweaning Sensorial and Motor Development in the Mouse

The immaturity at birth and the slowness of ontogenic processes in mice provide the opportunity to measure rates of development. We describe here 18 measures covering the sensorial and motor onset from birth to weaning. The measures are non-invasive, making a follow-up strategy possible. The first basic protocol indicates how to produce mice with known conceptional or chronological age, as the control of the age is a prerequisite to compare rates of development in groups of mice. The second basic protocol describes a set of methods for identifying the pups during a follow-up study. A third basic protocol describes testing newborn mice for the appearance of sensorial and motor abilities in a follow-up design. Taken together, the three protocols make possible the validation of potential murine models of interest for understanding human developmental disorders. © 2018 by John Wiley & Sons, Inc.

Pathophysiological and behavioral deficits in developing mice following rotational acceleration-deceleration traumatic brain injury

Abusive head trauma (AHT) is the leading cause of death from trauma in infants and young children. An AHT animal model was developed on 12-day-old mice subjected to 90° head extension-flexion sagittal shaking repeated 30, 60, 80 and 100 times. The mortality and time until return of consciousness were dependent on the number of repeats and severity of the injury. Following 60 episodes of repeated head shakings, the pups demonstrated apnea and/or bradycardia immediately after injury. Acute oxygen desaturation was observed by pulse oximetry during respiratory and cardiac suppression. The cerebral blood perfusion was assessed by laser speckle contrast analysis (LASCA) using a PeriCam PSI system. There was a severe reduction in cerebral blood perfusion immediately after the trauma that did not significantly improve within 24 h. The injured mice began to experience reversible sensorimotor function at 9 days postinjury (dpi), which had completely recovered at 28 dpi. However, cognitive deficits and anxiety-like behavior remained. Subdural/subarachnoid hemorrhage, damage to the brain-blood barrier and parenchymal edema were found in all pups subjected to 60 insults. Proinflammatory response and reactive gliosis were upregulated at 3 dpi. Degenerated neurons were found in the cerebral cortex and olfactory tubercles at 30 dpi. This mouse model of repetitive brain injury by rotational head acceleration-deceleration partially mimics the major pathophysiological and behavioral events that occur in children with AHT. The resultant hypoxia/ischemia suggests a potential mechanism underlying the secondary rotational acceleration-deceleration-induced brain injury in developing mice.

Neurobehavioral Alterations in a Genetic Murine Model of Feingold Syndrome 2

Feingold syndrome (FS) is an autosomal dominant disorder characterized by microcephaly, short stature, digital anomalies, esophageal/duodenal atresia, facial dysmorphism, and various learning disabilities. Heterozygous deletion of the miR-17-92 cluster is responsible for a subset of FS (Feingold syndrome type 2, FS2), and the developmental abnormalities that characterize this disorder are partially recapitulated in mice that harbor a heterozygous deletion of this cluster (miR-17-92∆/+ mice). Although Feingold patients develop a wide array of learning disabilities, no scientific description of learning/cognitive disabilities, intellectual deficiency, and brain alterations have been described in humans and animal models of FS2. The aim of this study was to draw a behavioral profile, during development and in adulthood, of miR-17-92∆/+ mice, a genetic mouse model of FS2. Moreover, dopamine, norepinephrine and serotonin tissue levels in the medial prefrontal cortex (mpFC), and Hippocampus (Hip) of miR-17-92∆/+ mice were analyzed.Our data showed decreased body growth and reduced vocalization during development. Moreover, selective deficits in spatial ability, social novelty recognition and memory span were evident in adult miR-17-92∆/+ mice compared with healthy controls (WT). Finally, we found altered dopamine as well as serotonin tissue levels, in the mpFC and Hip, respectively, of miR-17-92∆/+ in comparison with WT mice, thus suggesting a possible link between cognitive deficits and altered brain neurotransmission.

Lifetime development of behavioural phenotype in the house mouse (Mus musculus)

With each trajectory taken during the ontogeny of an individual, the number of optional behavioural phenotypes that can be expressed across its life span is reduced. The initial range of phenotypic plasticity is largely determined by the genetic material/composition of the gametes whereas interacting with the given environment shapes individuals to adapt to/cope with specific demands. In mammalian species, the phenotype is shaped as the foetus grows, depending on the environment in the uterus, which in turn depends on the outer environment the mother experiences during pregnancy. After birth, a complex interaction between innate constitution and environmental conditions shapes individual lifetime trajectories, bringing about a wide range of diversity among individual subjects.

In laboratory mice inbreeding has been systematically induced in order to reduce the genetic variability between experimental subjects. In addition, within most laboratories conducting behavioural phenotyping with mice, breeding and housing conditions are highly standardised. Despite such standardisation efforts a considerable amount of variability persists in the behaviour of mice. There is good evidence that phenotypic variation is not merely random but might involve individual specific behavioural patterns consistent over time. In order to understand the mechanisms and the possible adaptive value of the maintenance of individuality we review the emergence of behavioural phenotypes over the course of the life of (laboratory) mice. We present a literature review summarizing developmental stages of behavioural development of mice along with three illustrative case studies. We conclude that the accumulation of environmental differences and experiences lead to a “mouse individuality” that becomes increasingly stable over the lifetime.

Evaluation of animal models of neurobehavioral disorders

Animal models play a central role in all areas of biomedical research. The process of animal model building, development and evaluation has rarely been addressed systematically, despite the long history of using animal models in the investigation of neuropsychiatric disorders and behavioral dysfunctions. An iterative, multi-stage trajectory for developing animal models and assessing their quality is proposed. The process starts with defining the purpose(s) of the model, preferentially based on hypotheses about brain-behavior relationships. Then, the model is developed and tested. The evaluation of the model takes scientific and ethical criteria into consideration.Model development requires a multidisciplinary approach. Preclinical and clinical experts should establish a set of scientific criteria, which a model must meet. The scientific evaluation consists of assessing the replicability/reliability, predictive, construct and external validity/generalizability, and relevance of the model. We emphasize the role of (systematic and extended) replications in the course of the validation process. One may apply a multiple-tiered 'replication battery' to estimate the reliability/replicability, validity, and generalizability of result.Compromised welfare is inherent in many deficiency models in animals. Unfortunately, 'animal welfare' is a vaguely defined concept, making it difficult to establish exact evaluation criteria. Weighing the animal's welfare and considerations as to whether action is indicated to reduce the discomfort must accompany the scientific evaluation at any stage of the model building and evaluation process. Animal model building should be discontinued if the model does not meet the preset scientific criteria, or when animal welfare is severely compromised. The application of the evaluation procedure is exemplified using the rat with neonatal hippocampal lesion as a proposed model of schizophrenia.In a manner congruent to that for improving animal models, guided by the procedure expounded upon in this paper, the developmental and evaluation procedure itself may be improved by careful definition of the purpose(s) of a model and by defining better evaluation criteria, based on the proposed use of the model.

Morphological correlates of emotional and cognitive behaviour: insights from studies on inbred and outbred rodent strains and their crosses

Every study in rodents is also a behavioural genetic study even if only a single strain is used. Outbred strains are genetically heterogeneous populations with a high intrastrain variation, whereas inbred strains are based on the multiplication of a unique individual. The aim of the present review is to summarize findings on brain regions involved in three major components of rodent behaviour, locomotion, anxiety-related behaviour and cognition, by paying particular attention to the genetic context, genetic models used and interstrain comparisons. Recent trends correlating gene expression in inbred strains with behavioural data in databases, morpho-behavioural-haplotype analyses and problems arising from large-scale multivariate analyses are discussed. Morpho-behavioural correlations in multiple strains are presented, including correlations with projection neurons, interneurons and fibre systems in the striatum, midbrain, amygdala, medial septum and hippocampus, by relating them to relevant transmitter systems. In addition, brain areas differentially activated in different strains are described (hippocampus, prefrontal cortex, nucleus accumbens, locus ceruleus). Direct interstrain comparisons indicate that strain differences in behavioural variables and neuronal markers are much more common than usually thought. The choice of the appropriate genetic model can therefore contribute to an interpretation of positive results in a wider context, and help to avoid misleading interpretations of negative results.

Abnormal motor phenotype in the SMNDelta7 mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a recessive motor neuron disease that affects motor neurons in the anterior horn of the spinal cord. SMA results from the reduction of SMN (survival motor neuron) protein. Even though SMN is ubiquitously expressed, motor neurons are more sensitive to the reduction in SMN than other cell types. We have previously generated mouse models of SMA with varying degrees of clinical severity. So as to more clearly understand the pathogenesis of motor neuron degeneration in SMA, we have characterized the phenotype of the SMNDelta7 SMA mouse which normally lives for 13.6+/-0.7 days. These mice are smaller than their non-SMA littermates and begin to lose body mass at 10.4+/-0.4 days. SMNDelta7 SMA mice exhibit impaired responses to surface righting, negative geotaxis and cliff aversion but not to tactile stimulation. Spontaneous motor activity and grip strength are also significantly impaired in SMNDelta7 SMA mice. In summary, we have demonstrated an impairment of neonatal motor responses in SMNDelta7 SMA mice. This phenotype characterization could be used to assess the effectiveness of potential therapies for SMA.

Genetics of behavioural domains across the neuropsychiatric spectrum; of mice and men

Family and twin studies have revealed that genetic factors play a major role in psychiatric disorders, however, attempts to find susceptibility genes for these complex disorders have been largely unsuccessful. Therefore, new research strategies are required to tackle the complex interactions of genes, developmental, and environmental events. Here, we will address a behavioural domain concept that focuses on the genetics of behavioural domains relevant to both animal behaviour and across human psychiatric disorders. We believe that interspecies trait genetics rather than complex syndrome genetics will optimize genotype-phenotype relationships for psychiatric disorders and facilitate the identification of biological substrates underlying these disorders.

Early motor development is abnormal in complexin 1 knockout mice

Complexin I expression is dysregulated in a number of neurological diseases including schizophrenia and depression. Adult complexin 1 knockout (Cplx1(-/-)) mice are severely ataxic and show deficits in exploration and emotional reactivity. Here, we evaluated early behavioural development of Cplx1(-/-) mice. Cplx1(-/-) mice showed marked abnormalities. They develop ataxia by post-natal day 7 (P7), and by P21 show marked deficits in tasks requiring postural skills and complex movement. These deficits are consistent with abnormalities in sensory and motor development found in infants that develop schizophrenia in later life. A role for complexin I depletion should be considered in diseases where deficits in early sensory and motor development exist, such as autism and schizophrenia.

Pre-weaning sensorial and motor development in mice transpolygenic for the critical region of trisomy 21

Trisomy 21 occurs every 1/800 births and is the most frequent genetic cause of mental retardation. Children with trisomy 21 show delayed sensorial and motor development as well as cognitive disorders. We selected a mouse model of trisomy 21 (TRS21): transgenic mice carrying extra copies of a HSA21 region corresponding to the D21S17-ETS2 region (previously referred to as "Down syndrome critical region 1"). Sensorial and motor development was measured in these partially transgenic mice, from birth to weaning. The four HSA21 regions contributed unequally to sensorial and motor development delay. The more centromeric region (230E8) modified 4 of the development indicators plus the size of the effect, indicated by partial eta(2)(eta(p)(2), reached a median value of 14.5%. The neighboring 141G6 region contributed to 5 developmental differences (eta(p)(2) median value 14%). The most telomeric region (285E6) only modified one development indicator. An extra copy of an HSA21 fragment (referred to here as the 152F7 region) induced modifications to 14 of the 18 indicators measured with a eta(2) median value reaching 20%. The results indicate a noticeable contribution of the 152F7 region to sensorial and motor development. The contribution of this region to cognitive functioning and its neurobiological basis has been already reported. This set of result suggests the location in the D21S17-ETS2 region of several genes playing crucial role in cognitive and developmental impairment observed in TRS21.

Behavioral seizure correlates in animal models of epilepsy: a road map for assay selection, data interpretation, and the search for causal mechanisms

A broad spectrum of learning/memory, social interaction, and affective behavioral measures serve as functional correlates for neurobiological changes in seizure-prone animals as well as in epileptic clinical populations. The utility of such measures is demonstrated by their ability to distinguish anomalous characteristics in developing organisms predisposed to seizure onset, as well as to discriminate prior seizure history in organisms with established pathology. For instance, typical findings that generalize across species suggest that seizure-experienced organisms exhibit a variety of deficits in cognitive function as well as inappropriate social neglect and aggression. Behavioral testing batteries have also proven useful in assessing neural mechanisms for seizure induction, subcortical neural circuits, and neuropeptide modulators, for example, as well as in identifying neural pathology resulting from prior seizure activity. However, the wanton application of behavioral tests can also produce false positives in the identification of seizure-related disorders unless alternative performance and motivational hypotheses are discounted effectively. Accordingly, the present review attempts to provide the reader interested in behavioral phenotyping and characterization of seizure-prone rats and mice with a roadmap for rational selection, implementation, and interpretation of data from behavior assays while highlighting potential successes and pitfalls inherent in employing functional correlates of brain activity using animal models of epilepsy.

Olfactory classical conditioning in newborn mice

Determining the behavioural phenotype of genetically altered mice is a valuable approach for elucidating the function of genes and their role in cognitive disorders. Methods for phenotyping newborn mice are scarce and generally confined to sensorimotor reflexes. Here, we describe a simple method for assessing associative abilities in newborn mice. We used a two-odour-choice classical conditioning paradigm in mice from the day of birth (post-natal age 0, P0) to P6. Acquisition required 20 trials: 10 trials during which the pups were placed over the conditioned stimulus (CS+) odour (lemon or peppermint) for 30s and simultaneously stroked gently with a paintbrush and 10 trials during which the pups were placed over the other odour (CS-) for 30s, without stroking. Then, the pups were subjected to five odour-preference trials to test for conditioning. This sequence of five trials was repeated after 5 and 24h to assess retention of the conditioned odour preference. During the immediate post-acquisition sequence, the pups spent significantly more time over the CS+ than over the CS- (p<0.0001). No extinction of the conditioned preference was observed during this test. No preference was observed after 5 or 24h, indicating that the conditioned response was promptly lost. Conditioning was effective as soon as P0-P1. Thus, conditioning may emerge in newborn mice sooner than previously reported. This paradigm is well suited to phenotyping of large samples of genetically altered mice and may shed light on the role for genes in paediatric cognitive impairments.

Comparisons between C57BL/6J and A/J mice in motor activity and coordination, hole-poking, and spatial learning

The C57BL/6J (B6) inbred mouse strain was compared to the A/J inbred strain for motor activity in an open-field, exploration of a hole-board, motor coordination in the coat-hanger test, and spatial learning in the Morris water maze. B6 mice displayed a higher number of segment crossings in the open-field and of hole-poking responses than A/J mice. The performance of B6 mice was superior to that of A/J mice not only in the submerged but also in the visible platform version of the Morris water maze. By contrast to their hypoactivity, the A/J strain had shorter movement times in the coat-hanger test, indicating faster motor speed, although the groups did not differ in latencies before falling. These results indicate that recombinant inbred or congenic strains derived from B6 and A/J mice offer considerable potential for discerning the genetic basis of several behavioral phenotypes.