Transgenic Brain Cell Transplants: Rat Brain or Mouse Brain?

Researchers in Bangalore destroyed neurons in the subiculum (inferior hippocampus) of 48 adult rats. Half the 48 rats were then given fluorescent protein-tagged transplants of hippocampal cells from neonatal mice, the other half were kept as controls. 

Two months later, the scientists measured how well both the transplant and non-transplant rats learned and remembered, using two well-established maze tests of spatial learning. The rats given cell transplants had recovered completely: On both mazes, they performed as well as those rats which had not had their subiculums damaged. The rats without transplants did not recover: They had many problems learning their way through the mazes.


After studying behavior, the scientists examined what happened in the brain. Under the microscope, it appeared that the transplanted cells had settled mainly in a sub-area of the hippocampus called the dentate gyrus. There, the transplants appeared to promote the secretion of two types of growth factors, namely brain-derived neurotrophic factor and fibroblast growth factor, which boost the growth and survival of the cells that give rise to neurons. In the hippocampi of rats with cell transplants, the expression of brain-derived growth factor went up threefold.


It is significant that transplants can provide more neural growth factors in the hippocampus, because the formation of new neurons there may be critical for cognitive function. _ScienceDaily

One can easily imagine storing cultures of immature neurons for just that purpose -- to replace damaged neurons in more mature animals.   There is good reason to hope that damage from many types of brain trauma, tumour, infection, and neurodegeneration will be reversed by timely transplatation of tissue-banked immature neural cells.

But the transgenic nature of the experiment is also intriguing.  The transplanted rat brains contained functioning rat neurons and functioning mouse neurons.  Imagine expanding the experiment step by step, adding more and more mouse neurons to replace rat neurons that had been destroyed.  At what point does the rat begin thinking and acting more like a mouse?

Or consider the use of neonatal monkey neurons transplanted to damaged area of brain in adult humans.   As one transplants into larger and larger volumes of damaged tissue, when does the adult human begin behaving like a monkey -- perhaps a juvenile monkey?

No, I am not attempting to explain the behaviour of the current US Congress, or the delegates to the Copenhagen climate conference.   The neural transplant therapies I describe reside in the future.  But as a thought experiment, it does call up images "The Island of Dr. Moreau."  Brain cells from different animal sources might very well lead to different behaviours by human recipients.

Realistically, induced pluripotent cells from the patient herself, would more likely be used in such therapies of the future.  Signs are encouraging that many types of damage, disease, and degeneration can be at least partially reversed.  We may well be on the verge of a cascading biosingularity.  Stay tuned.