Gait performance of adolescent mice assessed by the CatWalk XT depends on age, strain and sex and correlates with speed and body weight

Loss of Elp1 in cerebellar granule cell progenitors models ataxia phenotype of Familial Dysautonomia

Familial Dysautonomia (FD) is an autosomal recessive disorder caused by a splice site mutation in the gene ELP1, which disproportionally affects neurons. While classically characterized by deficits in sensory and autonomic neurons, neuronal defects in the central nervous system have also been described. Although ELP1 expression remains high in the normal developing and adult cerebellum, its role in cerebellar development is unknown. To explore the role of Elp1 in the cerebellum, we knocked out Elp1 in cerebellar granule cell progenitors (GCPs) and examined the outcome on animal behavior and cellular composition. We found that GCP-specific conditional knockout of Elp1 (Elp1cKO) resulted in ataxia by 8 weeks of age. Cellular characterization showed that the animals had smaller cerebella with fewer granule cells. This defect was already apparent as early as 7 days after birth, when Elp1cKO animals also had fewer mitotic GCPs and shorter Purkinje dendrites. Through molecular characterization, we found that loss of Elp1 was associated with an increase in apoptotic cell death and cell stress pathways in GCPs. Our study demonstrates the importance of ELP1 in the developing cerebellum, and suggests that loss of Elp1 in the GC lineage may also play a role in the progressive ataxia phenotypes of FD patients.

Non-motor symptoms associated with progressive loss of dopaminergic neurons in a mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by three main motor symptoms: bradykinesia, rigidity and tremor. PD is also associated with diverse non-motor symptoms that may develop in parallel or precede motor dysfunctions, ranging from autonomic system dysfunctions and impaired sensory perception to cognitive deficits and depression. Here, we examine the role of the progressive loss of dopaminergic transmission in behaviors related to the non-motor symptoms of PD in a mouse model of the disease (the TIF-IADATCreERT2 strain). We found that in the period from 5 to 12 weeks after the induction of a gradual loss of dopaminergic neurons, mild motor symptoms became detectable, including changes in the distance between paws while standing as well as the swing speed and step sequence. Male mutant mice showed no apparent changes in olfactory acuity, no anhedonia-like behaviors, and normal learning in an instrumental task; however, a pronounced increase in the number of operant responses performed was noted. Similarly, female mice with progressive dopaminergic neuron degeneration showed normal learning in the probabilistic reversal learning task and no loss of sweet-taste preference, but again, a robustly higher number of choices were performed in the task. In both males and females, the higher number of instrumental responses did not affect the accuracy or the fraction of rewarded responses. Taken together, these data reveal discrete, dopamine-dependent non-motor symptoms that emerge in the early stages of dopaminergic neuron degeneration.

Coordination function index: A novel indicator for assessing hindlimb locomotor recovery in spinal cord injury rats based on catwalk gait parameters

In preclinical studies of spinal cord injury (SCI), behavioral assessments are crucial for evaluating treatment effectiveness. Commonly used methods include Basso, Beattie, Bresnahan (BBB) score and the Louisville swim scale (LSS), relying on subjective observations. The CatWalk automated gait analysis system is also widely used in SCI studies, providing extensive gait parameters from footprints. However, these parameters are often used independently or combined simply without utilizing the vast amount of data provided by CatWalk. Therefore, it is necessary to develop a novel approach encompassing multiple CatWalk parameters for a comprehensive and objective assessment of locomotor function. In this work, we screened 208 CatWalk XT gait parameters and identified 38 suitable for assessing hindlimb motor function recovery in a rat thoracic contusion SCI model. Exploratory factor analysis was used to reveal structural relationships among these parameters. Weighted scores for Coordination effectively differentiated hindlimb motor function levels, termed as the Coordinated Function Index (CFI). CFI showed high reliability, exhibiting high correlations with BBB scores, LSS, and T2WI lesion area. Finally, we simplified CFI based on factor loadings and correlation analysis, obtaining a streamlined version with reliable assessment efficacy. In conclusion, we developed a systematic assessment indicator utilizing multiple CatWalk parameters to objectively evaluate hindlimb motor function recovery in rats after thoracic contusion SCI.

[Effects of α1-antitrypsin on motor function in mice with immature brain white matter injury]

OBJECTIVES

To investigate the effects of α1-antitrypsin (AAT) on motor function in adult mice with immature brain white matter injury.

METHODS

Five-day-old C57BL/6J mice were randomly assigned to the sham surgery group (n=27), hypoxia-ischemia (HI) + saline group (n=27), and HI+AAT group (n=27). The HI white matter injury mouse model was established using HI methods. The HI+AAT group received intraperitoneal injections of AAT (50 mg/kg) 24 hours before HI, immediately after HI, and 72 hours after HI; the HI+saline group received intraperitoneal injections of the same volume of saline at the corresponding time points. Brain T2-weighted magnetic resonance imaging scans were performed at 7 and 55 days after modeling. At 2 months of age, adult mice were evaluated for static, dynamic, and coordination parameters using the Catwalk gait analysis system.

RESULTS

Compared to the sham surgery group, mice with HI injury showed high signal intensity on brain T2-weighted magnetic resonance imaging at 7 days after modeling, indicating significant white matter injury. The white matter injury persisted at 55 days after modeling. In comparison to the sham surgery group, the HI+saline group exhibited decreased paw print area, maximum contact area, average pressure, maximum pressure, paw print width, average velocity, body velocity, stride length, swing speed, percentage of gait pattern AA, and percentage of inter-limb coordination (left hind paw → left front paw) (P<0.05). The HI+saline group showed increased inter-paw distance, percentage of gait pattern AB, and percentage of phase lag (left front paw → left hind paw) compared to the sham surgery group (P<0.05). In comparison to the HI+saline group, the HI+AAT group showed increased average velocity, body velocity, stride length, and swing speed (right front paw) (P<0.05).

CONCLUSIONS

The mice with immature brain white matter injury may exhibit significant motor dysfunction in adulthood, while the use of AAT can improve some aspects of their motor function.

The mechanosensitive ion channel ASIC2 mediates both proprioceptive sensing and spinal alignment

By translating mechanical forces into molecular signals, proprioceptive neurons provide the CNS with information on muscle length and tension, which is necessary to control posture and movement. However, the identities of the molecular players that mediate proprioceptive sensing are largely unknown. Here, we confirm the expression of the mechanosensitive ion channel ASIC2 in proprioceptive sensory neurons. By combining in vivo proprioception-related functional tests with ex vivo electrophysiological analyses of muscle spindles, we showed that mice lacking Asic2 display impairments in muscle spindle responses to stretch and motor coordination tasks. Finally, analysis of skeletons of Asic2 loss-of-function mice revealed a specific effect on spinal alignment. Overall, we identify ASIC2 as a key component in proprioceptive sensing and a regulator of spine alignment.

Behavioral Analysis of NMDAR Function in Rodents: Tests of Long-Term Spatial Memory

NMDAR-dependent forms of synaptic plasticity in brain regions like the hippocampus are widely believed to provide the neural substrate for long-term associative memory formation. However, the experimental data are equivocal at best and may suggest a more nuanced role for NMDARs and synaptic plasticity in memory. Much of the experimental data available comes from studies in genetically modified mice in which NMDAR subunits have been deleted or mutated in order to disrupt NMDAR function. Behavioral assessment of long-term memory in these mice has involved tests like the Morris watermaze and the radial arm maze. Here we describe these behavioral tests and some of the different testing protocols that can be used to assess memory performance. We discuss the importance of distinguishing selective effects on learning and memory processes from nonspecific effects on sensorimotor or motivational aspects of performance.

High-throughput gait acquisition system for freely moving mice

Normal and pathological locomotion can be discriminated by analyzing an animal's gait on a linear walkway. This step is labor intensive and introduces experimental bias due to the handling involved while placing and removing the animal between trials. We designed a system consisting of a runway embedded within a larger arena, which can be traversed ad libitum by unsupervised, freely moving mice, triggering the recording of short clips of locomotor activity. Multiple body parts were tracked using DeepLabCut and fed to an analysis pipeline (GaitGrapher) to extract gait metrics. We compared the results from unsupervised against the standard experimenter-supervised approach and found that gait parameters analyzed via the new approach were similar to a previously validated approach (Visual Gait Lab). These data show the utility of incorporating an unsupervised, automated, approach for collecting kinematic data for gait analysis.NEW & NOTEWORTHY The acquisition and analysis of walkway data is a time-consuming task. Here, we provide an unmonitored approach for collecting gait metrics that reduces the handling and stress of mice and saves time. A detailed pipeline is outlined that provides for the collection and analysis of data using an integrated suite of tools.

Intermediate gray matter interneurons in the lumbar spinal cord play a critical and necessary role in coordinated locomotion

Locomotion is a complex task involving excitatory and inhibitory circuitry in spinal gray matter. While genetic knockouts examine the function of individual spinal interneuron (SpIN) subtypes, the phenotype of combined SpIN loss remains to be explored. We modified a kainic acid lesion to damage intermediate gray matter (laminae V-VIII) in the lumbar spinal enlargement (spinal L2-L4) in female rats. A thorough, tailored behavioral evaluation revealed deficits in gross hindlimb function, skilled walking, coordination, balance and gait two weeks post-injury. Using a Random Forest algorithm, we combined these behavioral assessments into a highly predictive binary classification system that strongly correlated with structural deficits in the rostro-caudal axis. Machine-learning quantification confirmed interneuronal damage to laminae V-VIII in spinal L2-L4 correlates with hindlimb dysfunction. White matter alterations and lower motoneuron loss were not observed with this KA lesion. Animals did not regain lost sensorimotor function three months after injury, indicating that natural recovery mechanisms of the spinal cord cannot compensate for loss of laminae V-VIII neurons. As gray matter damage accounts for neurological/walking dysfunction in instances of spinal cord injury affecting the cervical or lumbar enlargement, this research lays the groundwork for new neuroregenerative therapies to replace these lost neuronal pools vital to sensorimotor function.

Degeneration of muscle spindles in a murine model of Pompe disease

Pompe disease is a debilitating medical condition caused by a functional deficiency of lysosomal acid alpha-glucosidase (GAA). In addition to muscle weakness, people living with Pompe disease experience motor coordination deficits including an instable gait and posture. We reasoned that an impaired muscle spindle function might contribute to these deficiencies and therefore analyzed proprioception as well as muscle spindle structure and function in 4- and 8-month-old Gaa-/- mice. Gait analyses showed a reduced inter-limb and inter-paw coordination in Gaa-/- mice. Electrophysiological analyses of single-unit muscle spindle proprioceptive afferents revealed an impaired sensitivity of the dynamic and static component of the stretch response. Finally, a progressive degeneration of the sensory neuron and of the intrafusal fibers was detectable in Gaa-/- mice. We observed an increased abundance and size of lysosomes, a fragmentation of the inner and outer connective tissue capsule and a buildup of autophagic vacuoles in muscle spindles from 8-month-old Gaa-/- mice, indicating lysosomal defects and an impaired autophagocytosis. These results demonstrate a structural and functional degeneration of muscle spindles and an altered motor coordination in Gaa-/- mice. Similar changes could contribute to the impaired motor coordination in patients living with Pompe disease.

Clicker Training Mice for Improved Compliance in the Catwalk Test

The CatWalk test relies on the run of mice across the platform to measure a constant speed with low variation. Mice usually require a stimulus to walk to the end of the catwalk. However, such stimuli are usually aversive and can impair welfare. Positive reinforcement training of laboratory animals is a thriving tool for refinement and contributes to meeting the demands instituted by Directive 2010/63/EU. We have already demonstrated the positive effects of clicker training. In this study, we trained male and female mice to complete the CatWalk protocol while assessing the effects of training on their well-being (Open Filed and Elevated Plus Maze). In the CatWalk test, we observed that clicker training improved the running speed of the mice. In addition, clicker training reduced the number of runs required by mice, which was more pronounced in males. Clicker training lowered anxiety-like behaviors in our mice, especially in females, where a significant difference was observed between trained and untrained ones. Based on our findings, we hypothesize that clicker training is an effective tool to motivate mice and increase performance on the CatWalk test without potentially impairing their welfare (e.g., by puffing them).

Sexual Dimorphism in Lesion Size and Sensorimotor Responses Following Spinal Cord Injury

Spinal cord injury (SCI) is a devastating disorder, which impacts the lives of millions of people worldwide with no clinically standardized treatment. Both pro-recovery and anti-recovery factors contribute to the overall outcome after the initial SCI. Sex is emerging as an important variable, which can affect recovery post-SCI. Contusion SCI at T10 was generated in male and female rats. Open-field Basso, Beattie, Bresnahan (BBB) behavioral test, Von Frey test, and CatWalk gate analysis were performed. Histological analysis was performed at the 45-day post-SCI end point. Male/female differences in sensorimotor function recovery, lesion size, and the recruitment of immune cells to the lesion area were measured. A group of males with less severe injuries was included to compare the outcomes for severity. Our results show that both sexes with the same injury level plateaued at a similar final score for locomotor function. Males in the less severe injury group recovered faster and plateaued at a higher BBB score compared to the more severe injury group. Von Frey tests show faster recovery of sensory function in females compared to both male groups. All three groups exhibited reduced mechanical response thresholds after SCI. The lesion area was significantly larger in the male group with severe injury than in females, as well as in males of less severe injury. No significant differences in immune cell recruitment were identified when comparing the three groups. The faster sensorimotor recovery and significantly smaller lesion area in females potentially indicate that neuroprotection against the secondary injury is a likely reason for sex-dependent differences in functional outcomes after SCI.