THE NITTY GRITTY of TRANSPLANTATION
So we know that we can use neurons borrowed from animals or from humans to replace missing or damaged neurons. We also know that we can produce neurons from stem cells and transplant those. The big question remains, "What's the surgery like? What is going to happen in the operating room?" The following section will be dedicated to explaining surgical techniques and methods during neuronal transplantation.
Neurons prepared for implantation are generally stored frozen in liquid nitrogen vapors. About 1 hour before implantation, the vials that contain the neurons are thawed and gently washed and centrifuged. The cells are then suspended in a fluid that is similar in composition to the fluid in our bodies at a standard concentration and brought into the operating room. The surgical team then determines how many cells are needed depending on the amount of damage in the brain. A clinical study on the safety and efficacy of this procedure transplanted 2 million cells into a human brain.
Before any surgery begins, the doctors have to map out where the neurons are going to be injected and the path of their instruments. This is done with the use of a stereotaxic apparatus as well as computerized tomography. A stereotaxic apparatus is a tool that has a head holder, and multiple calibrated mechanisms that hold and position electrodes, cannulas, and a whole array of tools that neuroscientists use. First, a stereotactic coordinate frame is applied to the head while the patient is under mild anesthesia. This is a sort of generic blue-print of the layout of the human brain. Scientists use this to estimate where to place an instrument.
Then a computerized tomography (CT) scan is performed for stereotactic targeting. The CT scan provides a pretty detailed image of the brain. Usually, multiple scans from different angles are made to generate a three dimensional picture of the brain. The surgeons then decide on a path for their tools that will be the least obtrusive. A responsible neurosurgeon will spare important structures of the brain. Once this path is determined, a craniostomy is done to get through that thick protective skull. Once there's a hole in the skull, the dura mater surrounding the brain is opened just a tiny bit. It only has to be a small hole to fit a really thin stabilizing probe, which is less than 2mm in diameter. An even skinnier cannula filled with the cell suspension liquid is then inserted in through the stabilizing probe, and a syringe containing the neurons is attached to the cannula. The cells are injected slowly to the site of damage. The cannula and stabilizing probe are then removed from the brain, and the wound is closed. A post-operative CT scan is generally performed to confirm the absence of hemmorhage from the operation.
The hole they make will NOT be this big!!!
It will probably be the size of the lower case "o" in the word "Bone" you see in the photograph.
The methods described above were derived from an experimental procedure on human sufferers of strokes. The same type of methodology could be used in patients with spinal cord damage as well. A really promising find for patients with spinal cord damage is the tendency for hippocampus-derived cells to migrate after transplantation further into the spinal cord. Wu, et al treated rats with spinal cord damage with cells that were generated from hippocampal stem cells. The neurons traveled up to 2mm away from the site of the lesion into the host spinal cord.
The cell therapy procedures that I have just described are only one of the potential uses for neuronal transplantation. Another potential use for the implantation of stem cell-derived neurons are for gene therapy. This type of treatment would employ the use of stem cell-derived neurons as a platform to deliver exogenous proteins into the central nervous system. You can read about the specific diseases in which cell replacement therapy may be used in the next section.