Surgery..

This week I performed my first operation on the mouse inner ear. I'd love to tell you people what it's like but that's hard to do without giving some detailed information about the anatomy of the ear first. This first picture is of a mouse's skull. The hole at which is says external auditory meatus is basically the ear-opening and in the mouse it has a diameter of approximately 1 mm. That's our starting point But to get there we should make a little incision between the mouse's eye and ear and make our way through some muscle and fat tissue. Needless to say that the mouse is at that moment under anesthesia and it won't feel a thing. Once we have our ear-opening free we remove the tympanic membrane (eardrum) and we can see the inner ear. This procedure and everything from that point is done with tiny tools and under a microscope. In the inner ear there are three little bones that are interconnected and are there to transport the oscillation we call sound from the tympanic membrane to the deepest part of the inner ear; the cochlea where the auditory nerve takes the signal to the brain. The three little bones are called malleus (hammer), incus (anvil) and stapes (stirrup). The lower picture shows you the orientation of these bones. The picture is of a human ear, but in the mouse it's very similar (only a lot smaller and other angles). We remove the malleus and incus pretty easy, but the stapes offers a problem. As you can see in the picture it has a triangular shape and right through the middle goes a major arterie. Avoiding bloodloss is already very important since a mouse only has about three mililitres, but with such a (relatively) big arterie we have to be extra careful. So we use a microdrill to drill away a pice of bone to create better acces to the arterie and than we coagulate it (burn it shut). Than we can remove the stapes, if it is not burnt during the coagulation already (remember those bones are a couple of micrometres in size) and we will see the oval window which is the entrance to the inner ear. We then inject a little bit of neurotoxin in the inner ear and plug it off with gelfoam. The mouse gets put back together with about three stitches and the Labyrinthectomy is complete. Won't the animal be deaf on one ear then, you might ask. Well, yes it would be, but more importantly the neurotoxin will destroy the receptor haircells of the vestibular system, so no "balance-information" will be provided by that side of the head. This is an important aspect in our research to unravel the neural circuitry behind balance maintenaince. It would go to far to tell you why, and besides I don't think many of you will truly be interested in that. If you are, I'll be more than happy to explain it to you one day....

Last week we haven't actually let a mouse come out of the anesthesia, because we had to practise the technique first. I'm new to the basic idea of operating an live animals and Vadim who has many years experience in neurosurgery had done these operations on rats and rabbits but it was his first time on a mouse as well. Our conclusion is that it is definately doable, but I should get a little faster. Right now it takes me about 1.5h and that for the best result we should do it within the hour to keep the mouse in shape and under anesthesia. We will try that next week, so we can monitor the recovery of the mouse better.