Oestrogen made by neurons helps form memories

Oestrogen in the brain is important to keep neurons communicating and making memories, scientists have found.

Neurons in both males and females make oestrogen. Researchers have shown that when they do not, their brains have significantly less dense spines and synapses -- both key communication points for neurons -- in the biggest part of their brain, called the forebrain.

"We think this shows oestrogen has a clear role in synaptic plasticity, how the neurons communicate and in memory," said Darrell Brann, from Augusta University in the US.

The researchers found that mice whose neurons do not make oestrogen have impaired spatial reference memory as well as recognition memory and contextual fear memory -- so they have trouble remembering what's hazardous.

According to the study published in the Journal of Neuroscience, restoring oestrogen levels to the brain area rescues these impaired functions.

It was known that aromatase, the enzyme that converts testosterone to oestrogen, was made in the brain's hippocampus and cerebral cortex in a variety of species that includes humans, Brann said, and that they all can have memory deficits when aromatase is blocked.

Patients who take an aromatase inhibitor for oestrogen-dependent breast cancer also have reported memory problems.

So for these studies in mice, they knocked aromatase out of the forebrain, which includes the hippocampus, which has a role in making long-term memories and spatial memory, and the cerebral cortex, which is important to memory, attention, awareness and thought.

They depleted aromatase only in the excitatory neurons -- called excitatory because they help make some action like a thought happen -- in the forebrain as a way to focus on the role of oestrogen produced by these brain cells.

The bottom line was a 70-80 per cent decrease in aromatase and oestrogen levels in the neurons in these areas of the brain.

The findings implicate neuron-derived oestrogen as a novel neuromodulator, basically a critical messenger one neuron relies on to communicate with others, which is essential to key functions like cognition.