Disease-related regressive alterations of forebrain cholinergic system in SOD1 mutant transgenic mice

Transgenic mice carrying the human mutated SOD1 gene with a glycine/alanine substitution at codon 93 (G93A) are a widely used model for the fatal human disease amyotrophic lateral sclerosis (ALS). In these transgenic mice, we carried out a neurochemical study not only restricted to the primarily affected regions, the cervical and lumbar segments of the spinal cord, but also to several other brain regions. At symptomatic (110 and 125 days of age), but not at pre-symptomatic (55 days of age) stages, we found significant decreases in catalytic activity of the cholinergic enzyme, choline acetyltransferase (ChAT) in the hippocampus, olfactory cortex and fronto-parietal cortex. In parallel, we observed a decreased number of basal forebrain cholinergic neurons projecting to these areas. No alterations of the cholinergic markers were noticed in the striatum and the cerebellum. A widespread marker for GABAergic neurons, glutamate decarboxylase (GAD), was unaffected in all the areas examined. Alteration of cholinergic markers in forebrain areas was paralleled by concomitant alterations in the spinal cord and brainstem, as a consequence of progressive apoptotic elimination of cholinergic motor neuron. Gestational supplementation of choline, while able to result in long-term enhancement of cholinergic activity, did not improve transgenic mice lifespan nor counteracted cholinergic impairment in brain regions and spinal cord.