The entorhino-hippocampal neurons of pre-symptomatic SOD1(G93A) mice

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.