In Situ Hybridization: Effects of NFT on Selected mRNA

What are the neurobiological deficits that account for the cognitive declines of Alzheimer’s disease (AD)? An answer to this question would give important insights into the pathophysiological mechanisms of the disease, potential treatment strategies and perhaps elucidate the etiology of the disease. The history of answers to this question has been one of shifting emphasis and waxing and waning of competing theories over the years. The early description of Alzheimer’s disease by Alois Alzheimer (1907) described what are now known as senile plaques (SP) and neurofibrillary tangles (NFT) in the brain of the patient, thereby making the implicit assumption that these lesions were responsible for the symptomatology of the disease. Many hypotheses since then have been based on these early descriptions of the disease, as well as its frequent confirmation over the years. Previous studies from several laboratories have shown that one of the pathologies of AD that correlates best with the dementia of the disease is loss of synapses. This is particularly appealing since the synapse constitutes the structure by which the brain transmits, processes and stores information. The work proposed here is aimed at testing the hypothesis that it is neurons that contain NFT that may be largely responsible for the loss of synapses in AD. Thus, this proposal is aimed at contributing to our understanding of the mechanisms by which NFT relate to dementia. Understanding these mechanisms could lead to the development of ways to interrupt them and effectively treat the dementia of AD. We propose here to determine whether neurons containing neurofibrillary tangles may be responsible for the loss of synapses in AD, while their neighboring non-tangle bearing neurons remain functional. We propose to do this by using in situ hybridization to examine message levels for proteins related to the synapse in NFT bearing and adjacent NFT-free neurons in AD (and control) brain. The synapse- and growth cone associated protein messages we will examine are synaptophysin, GAP-43, and actin.

We will extend our studies to investigating neurons believed to in various disease states. We will approach this in two ways 1) we will examine messages for proteins reflecting a stress response by the neuron since they may be among the early events in the progression from a normal neuron to a neuron containing NFT and losing synaptic connections, and 2) using double immunocytochemistry we will use antibodies that will enable us to screen neurons that are undergoing the presumed intermediate events of the disease. We believe that the studies proposed here will contribute to our understanding of the pathological cascade by which NFTs relate to axon proliferation, synapse formation and dementia. An understanding of the mechanisms of this cascade will lead to effective, rational treatment of Alzheimer’s disease.