SOD1G93A Mutant Mice Develop a Neuroinflammation-Independent Dendropathy in Excitatory Neuronal Subsets of the Olfactory Bulb and Retina.

Nonmotor neuron-related pathology is a feature of amyotrophic lateral sclerosis (ALS), both in patients and in animal models. There is emerging evidence that sensory systems (olfaction and vision) are affected in humans. Here, we asked whether such sensory neuropathology is recapitulated in the superoxide dismutase 1 (SOD1G93A) mouse model of ALS. Neuronal vacuolization in olfaction and vision pathways was assessed in tissue sections from presymptomatic and symptomatic disease stages, and compared to wild type. In both, the olfactory bulb and retina, vacuolization started around postnatal day 60, and vacuole sizes increased until disease end-stage. Notably, vacuolization was largely restricted to the external plexiform layer of the olfactory bulb and to the inner plexiform layer of the retina. In both layers, hSOD1-immunoreactive vacuoles localized to dendrites of excitatory neurons. Downstream olfaction and vision pathway fiber tracts and relay stations did not display obvious vacuolization. Finally, on a morphological level, there was no evidence for an activation of astrocytes and microglia in the 2 affected areas. Thus, we identified a new pathology hallmark in SOD1G93A ALS mice: a glutamatergic sensory neuron dendropathy restricted to olfactory bulb mitral cells and retinal ganglionic cells.