David is a mild-mannered able-bodied person with a very calm and measured way of speaking. You can tell that he also has a wicked sense of humor.
His talk is called Activity and Physical Therapy after Incomplete SCI in the Rat (Aside from me … okay, I like this because it’s about incomplete injuries and I feel frustration because it’s about rats. Ahem, move on, Kate.)
Can you feel it? Can you feel the energy and anticipation and urgency in this room? This isn’t one of those meetings where you keep checking your watch …
What I think is that we’re not — right now — maximizing the remaining function we have.
Rats are sort of rear wheel drive creatures. The brain says go, and the spinal cord figures out how to do it. Rhythm, pattern, and gain are generated by the cord, not by the brain. Movement gets refined over time, through sensory information and through practice. The cord reacts to signals that get generated in real time.
In my lab, we’re looking at SCI as a whole body disease … these days when I write a grant, I begin with the idea that inactivity is toxic. (Ouch, that’s hard to hear in this room. I mean, we know, but … there’s so little we can do about it.)
I study rats. The rat has a dramatic advantage over other models, one of them being that it has a low center of gravity; they don’t get hurt if they fail and fall. What we see is incredible improvement even in rats with only 10% of function. We used to spend forever trying to get more improvement than rats get naturally by being able to move around their cages easily.
So, we decided to try to figure out how to replicate the safe in-cage self-retraining that rats do. We started with rats stepping in 2 inches of water (60% body weight support). They could step instantly. Instantly. It absolutely blew my mind. These animals on the ground would have been dragging their back legs. The body weight support allowed them to step beautifully without a rigorous re-training strategy. (He’s showing a picture of a rat about a week post injury, whose stepping shows clearly that the pattern generating mechanism in the rat is working fine.)
I had a high school student in my lab. They like to save time, right? My student suggested that it might make sense to put 3 or 4 rats into the pool at once instead of one at a time, which improved their in-water stepping. What didn’t happen is that the rats that could walk in water could then walk over ground. Also, if we waited 9 weeks to put the rats in water, the rats couldn’t do it in the water as well.
He’s saying that right after injury, the pattern generator is working. The spontaneous recovery overground in cages suggests that what the rats are retraining is their ability to reload. To carry weight and step.
Courtine in 2009. Full transection, bipedal weight supported training with epidural stimulation and quipazine — that combo worked right after injury, but again, didn’t work a few weeks later.
The spinal cord can respond to a challenge … Starkey 2014 put rats into “condominiums”
In Magnuson’s lab, one thing they showed was that putting rats into wheelchairs made their recovery worse and gave them secondary complications.
I expect that a lot of you have had a stretching protocol .. what we found with the rats is that when we put rats through a version of that kind of protocol, we messed with their ability to recover. This happened even when we did it after the rats had been recovering their walking ability for awhile. Then they figured out that the loss in functions to do with loss of C-fiber
So, stretching is negative, but the damage it causes can be fixed with c-fiber repair.
Anything that’s going on post injury is going to have an impact on the cord. One of the most severe contributions is inactivity.
(Again, we know. Let’s do something about that.)