Can hypothalamic neurons regenerate

brain research

Gerd Kempermann

To person

Dr. med., born 1965; Professor for the Genomic Basics of Regeneration at the DFG Research Center for Regenerative Therapies (CRTD) at the TU Dresden, Tatzberg 47 - 49, 01307 Dresden.
Email: [email protected]

Regenerative medicine is a very promising, transdisciplinary approach which, because of the high complexity of the brain, also includes "systems biology" and neurosciences.

introduction

When it was discovered in the early 1990s - to be more precise: rediscovered - that the adult brain can still form new nerve cells, [1] this was often commented on with the sentence that now the dogma that the brain cannot regenerate has finally fallen. [2] A dogma is an authoritarian doctrine, and the authority who supposedly spoke dogmatically here is Santiago Ramón y Cajal, the father (and over-father) of brain research. Cajal had indeed expressed himself pessimistically about the regenerative capacity of the brain and was by no means wrong. [3] Because the great challenge that many neurological and psychiatric diseases present in an aging population lies in the fact that the brain apparently hardly regenerates or not at all. As we shall see, we have reason to be cautiously optimistic today, although Ramón y Cajal's assessment is still true.






What could "regeneration" consist of? Involuntarily one would say: in the restoration of the condition that existed before the illness. If, for example, part of the brain is briefly cut off from the blood and thus the oxygen supply during a stroke, nerve and other brain cells die. Regeneration here means the reconstitution of the lost brain structure and the function it has lost with it. The latter is of course the decisive factor.

This idea of ​​regeneration extrapolates from regeneration, as we know it well from other organs, to the brain: Our skin heals very well if it is not damaged too extensively and deeply. Even a simple broken bone usually heals completely. The blood-forming bone marrow quickly makes up for moderate blood loss and provides immune cells that can cope with infections. And our liver is so regenerative that half can be removed, after which the remaining half grows back to its old size.

But the brain - like the heart and kidneys - is more susceptible to permanent damage. Diseases of these organs tend not to heal spontaneously and become chronic. The brain is a special case because its structure is extremely complex and the range of tasks that the brain has to cope with only allows compensation to a limited extent. If you keep hearing that after damage, another brain region takes over the tasks of the damaged one, that is only partly true. There are astonishing examples of such "plasticity", but ultimately this ability is too limited to provide complete or at least extensive relief in the case of severe damage.

In addition, we are our brains in a very peculiar sense. The brain is the seat of our personality, our self and our individual history. Our self-perception as a subject depends on the brain. It does not matter whether we believe that the one is identical to the other, or at least believe that the subject can be more than just a brain. In any case, it doesn't work without a brain. Even the impairments caused by intoxication and hangovers after a birthday party that has gone out of joint, at which the brain tries to get rid of the symptoms of acute intoxication caught in exuberance, show in their breadth, ranging from misperceptions and memory loss to the proverbial hangover mood, how much we are depend on the proper functioning of our brain.

In the case of neurological and psychiatric illnesses and in particular in the case of injuries to the brain, content is also lost, since the brain is above all a store of enormous amounts of information. "Function" does not only mean working on acute problems, but also constant recourse to experience. The brain not only works reactively to external stimuli, but is constantly active; even (or especially) in sleep. Therefore, reconstitution has limits here. Our memory is considerably more fluid and changeable than the zeros and ones on a computer's hard drive. In contrast to the computer's memory, information in the brain is constantly exchanged with one another. The cerebral cortex is therefore also called the "association cortex". This means that in the case of the brain, structure and function cannot be separated.

Memories are not neatly stored in card index boxes in the brain, but rather reflect "states" of mostly extensive networks of nerve cells that can overlap. Damage does not always have to affect the entire memory and the entire information and function. But they can also erase associations. Even if the reconstruction of structural damage to the brain were possible, many contents and functions would be irretrievably lost with the old structure that has vanished. Because of the functions of the brain that are so central to our ego, the lack of regenerative capacity also means that the organ that could handle the psychological processing of the problem is also affected. Because the brain does not become ill like other organs purely "physically", but to a certain extent, by definition, always also on a "psychological" level.