Amyotrophic Lateral Sclerosis (ALS) is a fatal disease primarily characterized by degeneration of
the motorneurons. Studies on animal models and ALS patients suggest the involvement of circuits
not directly associated with motor control, such as those of the hippocampus, providing
neurobiological bases for the cognitive impairments affecting a subpopulation of ALS patients.
Also, the entorhino-hippocampal (EH) pathway is damaged in Alzheimer’s disease, a pathology
having some etiopathogenic connections with ALS. Prompted by a lack of information on EH
connections of the SOD1(G93A) mouse, we used a retrograde tract-tracing technique to investigate
the morphology of EH projection neurons in these mice. Animals were anaesthetized and placed on
stereotaxic frame. After opening of the skull and exposing the temporal region, animals received
hippocampal pressure injections of a solution containing a retrograde tracer (10% biotinylated
dextran amine; BDA), coinjected with NMDA, to promote tracer uptake. After 96h, mice were
sacrified. Brains were dissected out and cut into 50 μm thick coronal sections. Selected sections
were processed for immunofluorescence to visualize retrogradely labeled EH neurons. Sections
containing the BDA injection points and the entorhinal cortex were collected. For each selected cell,
optical sections were collected by Leica confocal microscope and imported into ImageJ (NIH) to
perform the data analysis, conducted blind to genotype. Parameters investigated include: number of
EH neurons, lengths of dendrite segments, and density of dendritic spines. The possible anomalies
of EH neurons could provide relevant knowledge for the role of this circuitry as potential cause for
cognitive impairment in ALS patients
