The septo-hippocampal pathway in patients suffering from senile dementia of Alzheimer's type. Evidence for neuronal plasticity?

In 7 cases of senile dementia of Alzheimer's type (SDAT) and in 7 age-matched controls, nerve cells of the medial septal nuclei (area CH1) and of the vertical limb of the diagonal band of Broca (area CH2) of the right hemisphere were counted in Cresyl-fast-violet-stained serial sections. The granular cells of the ipsilateral fascia dentata were Golgi-stained and dendritic spine density was quantified in 10-micron segments. There was a significant loss of neurons in areas CH1 and CH2 in SDAT cases compared to controls. The spine density of the granular cell dendrites was significantly reduced in the distal parts of the dendrites. In the most proximal part, where cholinergic septal fibers form synapses, the spine density was not significantly different between the two groups. We assume that collateral sprouting of undamaged inputs occurs maintaining a constant number of spines in the proximal segments despite the loss of source neurons within CH1 and CH2.