Humans and other vertebrates depend on a portion of the brain called the hippocampus for learning, memory and their sense of location. Nerve cell structures in the adult hippocampus are sustained by factors whose identities have remained largely mysterious so far.

Now, research by biologists shed light on the subject, potentially pointing the way to a better understanding of how the structure of nerve cells in the adult hippocampus may deteriorate, which can lead to Alzheimer's disease and other neurological disorders.

In a paper in the journal Proceedings of the National Academy of Sciences, scientists report that a protein that has primarily been studied for its role in early animal development also plays a surprising role in maintaining the structure of hippocampal neurons in adult mice.

The team studied a protein called Wnt5a, which belongs to a family of proteins that have been studied primarily for their functions during embryonic development and in nurturing neurons as the young brain forms. Using mice genetically altered to remove Wnt5a from the hippocampus, the team showed that the protein's absence did not affect hippocampus development in young mice, but instead resulted in striking degradation of specific nerve cell structures called dendrites, which resemble clusters of tree branches, in adult mice. These findings suggest that the protein plays an important role in maintaining dendrite structures as the mouse ages.

The team went further by showing that when the Wnt5a protein was reintroduced after the dendrites had started to deteriorate in aged mice, the nerve cell structures were restored - to a degree the scientists did not expect.

The team also tested the ability of mice lacking Wnt5a in the hippocampus to perform learning and memory tasks. Behavior tests were run in a Morris Water Maze designed to show how well mice use spatial cues to navigate in a water pool and how long it takes them to learn to use a hidden platform to escape. They found that mutant mice - those without Wnt5a - were poor learners and had attenuated memory; their performance in behavioral tasks became progressively worse with age.

In the brain, the hippocampus is the seat of short- and long-term memory and governs spatial orientation. Studies have shown that the brains of people with Alzheimer's disease have structural alterations in dendrites, particularly in the hippocampus..

http://releases.jhu.edu/2017/01/18/study-identifies-molecular-signal-for-maintaining-adult-neuron/