Synaptic alterations in the l geniculate bodies in Alzheimer's disease

What is it about?

The neuronal loss and the alteration of the synapses in the medial geniculate bodies and the inferior colliculi may be involved in the impairment of communication and symbolic sound perception, which is noticed even in the early stages of Alzheimer’s disease. Objectives. Alzheimer’s disease (AD) is a neurodegenerative disorder, causing a progressive decline of intellectual faculties, gradual impairment of behavior and social performance, impairment of communication and speech eloquence, and various neurological manifestations. We attempted to figure out the synaptic alterations in the medial geniculate bodies and the inferior colliculi in 12 early cases of Alzheimer’s disease, who fulfilled the clinical, and laboratory diagnostic criteria of Alzheimer’s disease. Subjects and methods. For the histological study we applied routine neuropathological techniques as well as Bodian staining and rapid Golgi method. We proceeded to electron microscopy for the ultrastructural study of synapses and dendritic spines. Results. The morphological and morphometric analysis revealed substantial neuronal loss and synaptic alterations in the medial geniculate bodies as well as in inferior colliculi. Dendritic spines of the polyhedral and elongated cells of the medial geniculate bodies were decreased in number. Mitochondrial alterations and fragmentation of Golgi apparatus were seen in 15% of the neurons of the medial geniculate bodies and in 5% of the neurons of the inferior colliculi. Senile plaques and neurofibrillary tangles were not seen in either the medial geniculate bodies or the inferior colliculi.

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Why is it important?

It is important to emphasize that even in early cases of Alzheimer’s disease Golgi staining and electron microscopy revealed pathological alterations of the dendritic spines and marked decrease of spine density in subcortical areas of the auditory pathway, such as the medial geniculate bodies and the inferior colliculi. In previous studies Alzheimer’s pathology has been described in the primary auditory area , in the medial geniculate bodies, and in the inferior colliculi, as well as the auditory association cortices Neuron from the medial geniculate bodies of a patient aged 58 years who suffered from Alzheimer’s disease. although tau pathology has also been described in subcortical argyrophilic degenerations. In addition, we have described neuronal loss and synaptic alterations in the acoustic cortex in brains of patients who suffered from Alzheimer’s disease according to Golgi staining and electron microscopy [6]. In all of the cases, the alterations of the mitochondria in the soma and the dendritic spines in the majority of neurons of the acoustic cortex and the subcortical centers of the auditory pathway plead in favor of the oxidative damage, even in early cases of Alzheimer’s disease, since there is an intimate and early association between oxidative stress and mitochondrial abnormalities . Synaptic pathology in Alzheimer’s disease is the main cause of the cognitive decline, which is the clinical hallmark of the dementias. It is important that the synaptic pathology in the medial geniculate bodies is independent from tau pathology, since no neurofibrillary tangles were seen in our early cases of Alzheimer’s disease. The study of the synaptic alterations in the acoustic cortex, as well as in the medial geniculate bodies and the inferior colliculi in early cases of Alzheimer’s disease, may contribute to a further understanding of the speech deficits and the impairment of communication and symbolic sound perception, which is noticed even in the early stages of Alzheimer’s disease.

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