Sexy eyes? Estrogen in the visual system

Neurotransmitters get all the glory as the most interesting molecules in the nervous system. They are responsible for the fast signalling between two neurons; things that are all over in a few milliseconds.

But the nervous system is awash in chemicals, which influence neurons in many ways. Hormones, for instance, influence behaviour by acting on nervous systems.

It’s a little unusual, though, to think of brains making their own hormones. Oh, sure, the pituitary gland sits right next to brains in mammals, but it’s still generally considered an endocrine gland rather than neural tissue.

I was therefore intrigued by a new paper showing that the visual cortex in mice makes estrogen, which is a classic sex hormone, and responds to it. The evidence is quite straightforward for some of the story. Jeong and colleagues used fluorescent labels for messenger RNA for the chemical to show that neurons make it (left column in figure), and another fluorescent label for the messenger RNA of estrogen receptors to show that the neurons were able to detect it (middle and right columns).

The production of the estrogen doesn’t seem to be dependent on, or affected by, by visual experience. Mice raised in the dark had the same density of estrogen-producing neurons in three different areas of the visual cortex. Similarly, there was no change in that density when mice were given different degrees of visual stimulation after being placed temporarily in the dark.

What is this brain-produced estrogen doing to vision? Not clear yet, but there seem to be analogs in other brain regions. Estrogen affects auditory cortex in mice, and can alter the physiology of neurons in the hippocampus. The effects may be subtle, and might not have noticeable perceptual consequences for the mice.

Reference

Jeong J, Tremere L, Burrows K, Majewska A, Pinaud R. 2011. The mouse primary visual cortex is a site of production and sensitivity to estrogens. PLoS ONE 6(5): e20400. DOI: 10.1371/journal.pone.0020400