a-quick-phenotypic-neurological-scoring-system-for-evaluating-disease

A Quick Phenotypic Neurological Scoring System for Evaluating Disease Progression in the SOD1-G93A Mouse Model of ALS

The SOD1-G93A transgenic mouse is the most widely used animal model of amyotrophic lateral sclerosis (ALS). At ALS TDI we developed a phenotypic screening ...

ALS Therapy Development Institute

The regulation of the glutamatergic projection from the subthalamic nucleus (STN) to the substantia nigra (SN) was investigated using dual-probe microdialysis in the awake behaving rat. Reverse dialysis of the cholinergic receptor agonist carbachol (1 mM) into the STN caused an increase in the extracellular concentrations of glutamate and dopamine in the SN. The increase in glutamate was transient and returned toward basal values despite the continued perfusions of the STN with carbachol. Carbachol-stimulated glutamate release was prolonged by perfusion of the selective D2 dopamine receptor antagonist raclopride (100 microM) into the SN and was attenuated by the perfusion of the selective D2-like receptor agonist quinpirole (10 microM). In contrast, perfusion of the D1 dopamine receptor antagonist SCH-23390 (100 microM) did not alter the carbachol-stimulated glutamate release even though it increased basal glutamate concentrations. Perfusion of the GABAA receptor antagonist bicuculline (10 microM) into the SN prolonged the carbachol-stimulated glutamate release in similar fashion as raclopride. The present findings suggest that somatodendritically released dopamine in the SN regulates glutamate release from subthalamic axon terminals by differentially activating dopamine D2 and D1 receptors. Activation of D2 heteroreceptors, located on STN axon terminals, provides a negative feedback control on stimulated subthalamic glutamate release, while D1 receptor activation preferentially regulates basal glutamate concentrations. The findings of the present study also indicate that GABA exerts an inhibitory control on glutamate release in the SN through GABAA receptors.

Dopaminergic and GABAergic modulation of glutamate release from rat subthalamic nucleus efferents to the substantia nigra.

The therapeutic management of methamphetamine (METH)-induced psychoses often involves treatment with the typical antipsychotic drug and dopamine D2 receptor antagonist haloperidol. We report here that subchronic haloperidol administration after a high-dose regimen of METH produces a heretofore unrecognized toxicity to GABAergic cells, as reflected by GAD67 mRNA expression histochemistry, in the rat substantia nigra pars reticulata (SNr) through an acute and persistent augmentation of glutamate release, NMDA receptor activation, and DNA fragmentation. The dopaminergic cells in the substantia nigra pars compacta were unaffected by METH or haloperidol alone or the combination of METH and haloperidol. These findings suggest that the current therapeutic management of METH-induced psychoses with haloperidol may be contraindicated because of a resultant GABAergic cell death in the SNr, which may predispose some individuals to the development of hyperkinetic movement disorders and seizures.

Haloperidol treatment after high-dose methamphetamine administration is excitotoxic to GABA cells in the substantia nigra pars reticulata.

ALS therapy development has been hindered by the lack of rodent animal models. The discovery of TDP-43, a transcription factor that accumulates in the cytoplasm of motor neurons (MNs) in most cases of ALS, prompted attempts to develop TDP-43-based models of the disease. The current study sought to examine, in extensive detail, the emerging disease phenotype of a transgenic mouse model that overexpresses a mutant human TDP-43 (hTDP-43) gene under mouse prion promoter control. Careful attention was given to ALS-like characteristics to determine the appropriateness of this model for testing therapies for ALS. In light of previous reports that gastrointestinal (GI) dysfunction is responsible for early death in these mice, gut immunohistochemistry (IHC) and longitudinal gut motility assays were used to identify the onset and the progression of these defects. IHC studies revealed that site-specific overexpression of the hTDP-43 transgene in colonic myenteric plexes resulted in progressive neurodegeneration in this region. This change was associated with progressively reduced GI motility, culminating in frank stasis that was primarily responsible for decreasing longevity in these mice. The disease phenotype was gender- and genetic background-dependent, with congenic C57BL/6J male mice exhibiting the most aggressive form of the disease. Spinal cord IHC revealed ubiquitin-positive inclusions, but not TDP-43 aggregates, in the cytoplasm of MNs. Neither gender exhibited compelling ALS-like neuromuscular deficits, irrespective of age. While this model may be useful for studying GI tract neurodegeneration, in its present state it does not display a phenotype suitable for testing ALS therapeutics.

C57BL/6J congenic Prp-TDP43A315T mice develop progressive neurodegeneration in the myenteric plexus of the colon without exhibiting key features of ALS.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that primarily targets the motor system. Although much is known about the effects of ALS on motor neurons and glial cells, little is known about its effect on proprioceptive sensory neurons. This study examines proprioceptive sensory neurons in mice harboring mutations associated with ALS, in SOD1(G93A) and TDP43(A315T) transgenic mice. In both transgenic lines, we found fewer proprioceptive sensory neurons containing fluorescently tagged cholera toxin in their soma five days after injecting this retrograde tracer into the tibialis anterior muscle. We asked whether this is due to neuronal loss or selective degeneration of peripheral nerve endings. We found no difference in the total number and size of proprioceptive sensory neuron soma between symptomatic SOD1(G93A) and control mice. However, analysis of proprioceptive nerve endings in muscles revealed early and significant alterations at Ia/II proprioceptive nerve endings in muscle spindles before the symptomatic phase of the disease. Although these changes occur alongside those at α-motor axons in SOD1(G93A) mice, Ia/II sensory nerve endings degenerate in the absence of obvious alterations in α-motor axons in TDP43(A315T) transgenic mice. We next asked whether proprioceptive nerve endings are similarly affected in the spinal cord and found that nerve endings terminating on α-motor neurons are affected during the symptomatic phase and after peripheral nerve endings begin to degenerate. Overall, we show that Ia/II proprioceptive sensory neurons are affected by ALS-causing mutations, with pathological changes starting at their peripheral nerve endings. J. Comp. Neurol. 523:2477-2494, 2015. © 2015 Wiley Periodicals, Inc.

Degeneration of proprioceptive sensory nerve endings in mice harboring amyotrophic lateral sclerosis-causing mutations.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by loss of motor neurons. The mechanisms leading to motor neuron degeneration in ALS are unclear. However, there is evidence for involvement of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) in ALS, notably in mutant SOD1 mediated models of ALS. Stress induced phosphorylation of the eIF2 alpha subunit by eukaryotic translation initiation factor 2-alpha kinase 3 Perk activates the UPR. Guanabenz is a centrally acting alpha2 adrenergic receptor agonist shown to interact with a regulatory subunit of the protein phosphatase, Pp1/Gadd34, and selectively disrupt the dephosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eif2alpha). Here we demonstrate that guanabenz is protective in fibroblasts expressing G93A mutant SOD1 when they are exposed to tunicamycin mediated ER stress. However, in contrast to other reports, guanabenz treatment accelerated ALS-like disease progression in a strain of mutant SOD1 transgenic ALS mice. This study highlights challenges of pharmacological interventions of cellular stress responses in whole animal models of ALS.

Theo Hatzipetros

ALS Therapy Development Institute

A Quick Phenotypic Neurological Scoring System for Evaluating Disease Progression in the SOD1-G93A Mouse Model of ALS