LAURA FOX: Hello, my name is Laura Fox, and I'm a junior here at Cornell University in the College of Arts and Sciences, and I'm a concentrator in neurology here, neuro bio and behavior the major is called. And I work for Chrstian Linster on mice and memory in the olfactory bulb.
In our work with the olfactory bulb of Mice, we have learned over time that females, particularly ones that are doped up on estrogen, have a better ability to remember something they have smelled 30 or even 60 minutes later than male mice do. Male mice are terrible at remembering what they have smelled. And so, we are wondering if that is a function of the estrogen in the body of the female. Does estrogen help the mice remember odors better? And so, what I do is I'm testing to see if we can do a sex reversal on the mice. And by giving the boys an injection of estrogen, allow them to remember as well as the females do so the time of investigation of the tea balls, I'll show you in a minute, is not statistically different. And if that's true, we will know that estrogen has an activational effect in memory in the olfactory bulb.
What we do with the mice is we have a couple different groups of mice that we work with and we give some of the estrogen, some of them not, but we take a lot of their gonads out so their bodies don't have the ability to mess with our system, per se. We control them pretty well. And these girls here are implanted with estrogen pellets that are very, very small and their time released. And what they do is they cause the level of estrogen in the mouse to be set at a level we want to test. And then we do learning and memory trials on them with smells because we work at the olfactory bulb.
We take tea balls like these, and we put little scented pieces of paper in them. And we use investigation time of the tea ball with the smell in it to gauge how well the mouse remembers. A mouse will investigate something a lot and smell it quite a bit if it doesn't know what it is or if it's a novel odor. A mouse, however, that has smelled the odor before is not going to be as interested and will probably wander off to do something else. So investigation time is a very accurate measure of whether or not they remember the scent.
OK. So the first thing we're going to do is we're going to take the lids off their cages so we can actually give them the tea ball-- excuse me, sweetie-- without distractions. Get off your house. Thank you. We give them lots of little toys to play with normally, but now that we have to test them we have to take everything that is interesting out of their cage so the only thing they can pay attention to is the tea ball. And I'm going to test two of them at a time here today. Give me your little house. There we go. And so what we do for an odor trial is we start out with a tea ball and then we start with a little piece of paper that we can put an odor on.
And the odor usually is a carbon based thing. And it's at a concentration where mice can smell it, but not so strong it's offensive to them. OK, so we'll put that in there. Close up the tea ball so she can't eat the paper. And then we're going to put it in her cage. And now we're going to time how long she smells it. So she hasn't seen it yet. Come on. There it is, OK. And so what I'm doing is I'm pressing this button every time, essentially, she takes a breath. That's why my thumb is moving so quickly. What we'd love to get an accurate measure of is exactly how long the odor is coming into her nose and touching her olfactory bulb.
She's very interested in this. Now she's climbing on the tea ball. We don't count that as odor investigation. Now the toy is novel. OK. So it looks like she's done. So now what I'm going to do is take the tea ball out of her cage and start the timer. And this timer gives her an inter trial period of about five minutes. And that allows her to have time to think about the odor and not forget it necessarily, but it's not short enough that she can store it in short term memory. She's going to have to think about it somewhere else.
This research is important because estrogen has been shown to increase spine density on the dendrites of neurons. And this can help with memory. And in older women, sometimes post menopause, there can be dementia, there can be other problems that involve memory loss. And this research can help us learn yet another piece of the puzzle if possibly hormone replacement therapy could be an assistive thing for memory loss in postmenopausal women.
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Mice are very sensitive to foreign odors and female mice more so than males. Could it be the estrogen level, typically higher in females than males, that causes this increased odor memory?
Laura Fox, an undergraduate working in Christianne Linster's Laboratory aims to find out by manipulating the estrogen levels in mice and then testing their olfactory memory.