Stem cells in adults and embryos

I will continue this time with the topic of neuro-plasticity and I can mention that there are two lines of research which are currently the most studied: on the one hand, it is the idea that postnatal human brain has adult stem cells apparently remain during the adulthood and that they can help rising new neurons, this line of work has opened a door in the field of regenerative medicine because until recently, was believed to be the brain ability to restore its function through neural regeneration was null. 

In this sense some researchers isolated brain live stem cells from human corpses up to five days after the body died. This was possible  keeping frozen the bodies and it was observed that cells obtained from these bodies gave rise to new neurons and glial cells in vitro, so currently, it is believed that the presence of brain stem cells can at least in part, explain the great plasticity and functional improvement seen in patients after cerebral damage, even extensive injury. However, it is not known yet, the specific role and regenerative capacity in response to different congenital and acquired diseases of the central nervous system (Belkind-Gerson and Suárez-Rodriguez, 2004; Aguilar, 2005). 

By this reason, this line of research has focused on studying the fact that under certain conditions, stem cells can be differentiated towards cell type required to regenerate the damaged tissue signals acquired directly on the site of the lesion, since once there is a neural injury, damaged neurons come in contact with the myelin sheath which has released other injured neurons, and since myelin contains several inhibitors, that prevent neurons that have not died to restore their connections, it is not possible even to understand the mechanisms in which it is possible to restore functions (Belkind-Gerson, Suarez-Rodriguez, 2004).

This capacity has generated other kinds of studies searching answers of cell regeneration, which direct their efforts towards the calls stem cells.

 These are embryonic cells, i.e. their destination still has not been decided and will be transformed through a process of differentiation and proliferation in different types of cells. These are very different from any other in the body which can be used to regenerate tissue-specific. The neural stem cells are those which is capable of self-renewal and that can generate other kinds of cells different from them through an asymmetric cell division process, so you are defined by their multipotency. These cells are found in bone marrow and they have been used successfully to generate heart tissue (León Carrión, 2003, Hernandez-Muela, Mules, Mattos, 2004; Shreeve, 2005).

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Certainly this breaks with the dogma that neurons do not grow spontaneously in every part of the adult brains, however, research pioneers began in the decade of the 90s, when researchers in the field of Neurobiology found that mature brains of some mammals were able to generate new neurons.

Of course, biologists believed that this was only possible in young brains, but Elizabeth Gould of the Rockefeller University, showed that new cells grew in adult brains, in particular, it has been found in the hippocampus (part of the limbic system, responsible for learning and memory processes) hundreds of new cells grow every day.

 Since then, many more researchers have shown the cells destined to become neurons travel from the ventricle of the olfactory bulb, especially in a pair of structures responsible for receiving information that olfactory cells in the nose.

Although no one is sure why the olfactory bulb requires so many new neurons.  It can be speculated that this being a necessary structure for learning new information, it is essential to add neurons to create connections between existing neurons and new, thus increasing the brain power to process and store the new information (León Carreón, 2003, Avaria, 2005, Shors, 2009). 

      

While there are other investigations focus on neurogenesis (growth, spontaneous or induced neurons) and the discovery of new neurons out of the hippocampus and the olfactory bulb, these not have systematized their findings, and one of the reasons is that the methods used to prove the existence of neurogenesis is difficult, although recently they have come to detect neural growth in the bone marrow of adults.

Even when neurogenesis depends on the genetic component, the various contributions to this theme in works with other species such as mice have become so clear that different laboratories have tried to make progress with humans. In fact researchers United States and Sweden, showed that this was possible also in humans, though not with as much clarity as in other species (Shors, 2009; Gage, 2007; Avaria, 2005; Leon Carrion, 2003).

In animal studies, it was found that in only a couple of weeks, most of these newly born neurons, died, unless the animal was challenged to learn something. This new learning, which required much effort, especially kept alive those cells. But works have found that neurons are not necessary for all types of learning, because even though they can play a role in the resolution of problems, based on past experience, they are not generated at specific times, since its production is linked mostly with a large number of environmental factors.

 For example it has been observed that alcohol use delays the generation of new cells, while the rate of neurogenesis can be increased by the exercise. This was demonstrated in research with mice, which spent a great time running on a wheel and increased twice the neuronal production compared with mice with a sedentary lifestyle (Shors, 2009).

      

However, even though this discovery takes a turn to the neurobiological research, unanswered questions remain, which do not allow all the application of these findings to identify the effects of learning on the survival of new neurons, for example: what neurotransmitters and receptors, proteins are involved?, and how do they operate these mechanisms?; Why do these new neurons helps learning to integrate neural networks? or Do they only promotes the survival of those that are already connected?; do these neurons contribute to knowledge?.

The goal is that these studies will help to understand degeneration neuronal, but mainly people health, mainly to avoid diseases such as Alzheimer's and Parkinson's, as well as understand the neural processes related to the developmental disorders. 

References: 

 Aguilar, F. (2005) Razones biológicas de la plasticidad cerebral y la restauración neurológica. Revista Plasticidad y Restauración Neurológica. Vol. 4 Num.1. 5-6.

Avaria, M. A. (2005)  Aspectos biológicos del desarrollo psicomotor.  Rev. Ped. Elec. [en línea] Vol 2, N° 1.

Belkind-Gerson, J.  y  Suárez-Rodríguez, R.  (2004) Regeneración cerebral. Realidades, posibilidades y esperanzas. An Med Asoc Med Hosp ABC. 49 (4): 201-207.

Gage, F. (2007) Brain, repairs yourself. In Floyd E, Bloom (2007) The best of the brain from Scientific American: mind, matter, and tomorrow’s brain. Washington DC. Dana Press.

Hernández-Muela, S., Mulas, F. y  Mattos, L. (2004) Plasticidad neuronal funcional Rev Neurol. 38 (Supl 1): S58-S68.

León Carrión, J. (2003) Células madre, genética y neuropsicología. Revista Española de Neuropsicología. 5 (1) 1-13. 

Shors, T. (2009) Saving new brain cells. Scientific American. Vol. 300. num. 3. 41-48.