Locomotion analysis is now widely used across many animal species to understand the motor defects in disease, functional recovery following neural injury, and the effectiveness of various treatments. More recently, rodent locomotion analysis has become an increasingly popular method in a diverse range of research. Speed is an inseparable aspect of locomotion that is still not fully understood, and its effects are often not properly incorporated while analyzing data. In this hybrid manuscript, we accomplish three things: (1) review the interaction between speed and locomotion variables in rodent studies, (2) comprehensively analyze the relationship between speed and 162 locomotion variables in a group of 16 wild-type mice using the CatWalk gait analysis system, and (3) develop and test a statistical method in which locomotion variables are analyzed and reported in the context of speed. Notable results include the following: (1) over 90% of variables, reported by CatWalk, were dependent on speed with an average R2 value of 0.624, (2) most variables were related to speed in a nonlinear manner, (3) current methods of controlling for speed are insufficient, and (4) the linear mixed model is an appropriate and effective statistical method for locomotion analyses that is inclusive of speed-dependent relationships. Given the pervasive dependency of locomotion variables on speed, we maintain that valid conclusions from locomotion analyses cannot be made unless they are analyzed and reported within the context of speed.

The target disconnection theory of amyotrophic lateral sclerosis (ALS) pathogenesis suggests disease onset is initiated by a peripheral pathological event resulting in neuromuscular junction loss and motoneuron (MN) degeneration. Pre-symptomatic mSOD1G93A mouse facial MN (FMN) are more susceptible to axotomy-induced cell death than wild-type (WT) FMN, which suggests additional CNS pathology. We have previously determined that the mSOD1 molecular response to facial nerve axotomy is phenotypically regenerative and indistinguishable from WT, whereas the surrounding microenvironment shows significant dysregulation in the mSOD1 facial nucleus. To elucidate the mechanisms underlying the enhanced mSOD1 FMN loss after axotomy, we superimposed the facial nerve axotomy model on pre-symptomatic mSOD1 mice and investigated gene expression for death receptor pathways after target disconnection by axotomy vs. disease progression. We determined that the TNFR1 death receptor pathway is involved in axotomy-induced FMN death in WT, and partially responsible for the mSOD1 FMN death. In contrast, an inherent mSOD1 CNS pathology resulted in a suppressed glial reaction and an upregulation in the Fas death pathway after target disconnection. We propose that the dysregulated mSOD1 glia fail to provide support to injured MN, leading to Fas-induced FMN death. Finally, we demonstrated that during disease progression, the mSOD1 facial nucleus displays target disconnection-induced gene expression changes that mirror those induced by axotomy. This validates the use of axotomy as an investigative tool in understanding the role of peripheral target disconnection in the pathogenesis of ALS.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving motoneuron (MN) axonal withdrawal and cell death. Previously, we established that facial MN (FMN) survival levels in the SOD1G93A transgenic mouse model of ALS are reduced and nerve regeneration is delayed, similar to immunodeficient RAG2-/- mice, after facial nerve axotomy. The objective of this study was to examine the functionality of SOD1G93A splenic microenvironment, focusing on CD4+ T cells, with regard to defects in immune-mediated neuroprotection of injured MN. We utilized the RAG2-/- and SOD1G93A mouse models, along with the facial nerve axotomy paradigm and a variety of cellular adoptive transfers, to assess immune-mediated neuroprotection of FMN survival levels. We determined that adoptively transferred SOD1G93A unfractionated splenocytes into RAG2-/- mice were unable to support FMN survival after axotomy, but that adoptive transfer of isolated SOD1G93A CD4+ T cells could. Although WT unfractionated splenocytes adoptively transferred into SOD1G93A mice were able to maintain FMN survival levels, WT CD4+ T cells alone could not. Importantly, these results suggest that SOD1G93A CD4+ T cells retain neuroprotective functionality when removed from a dysfunctional SOD1G93A peripheral splenic microenvironment. These results also indicate that the SOD1G93A central nervous system microenvironment is able to re-activate CD4+ T cells for immune-mediated neuroprotection when a permissive peripheral microenvironment exists. We hypothesize that dysfunctional SOD1G93A peripheral splenic microenvironment may compromise neuroprotective CD4+ T cell activation and/or differentiation, which, in turn, results in impaired immune-mediated neuroprotection for MN survival after peripheral axotomy in SOD1G93A mice.