March 9, 2013

Astrocytes: a key "wiring" element behind human intelligence

Recent experiments with mice have shown that those with transplanted human glial cells known as astrocytes perform much better in learning and memory tests afterwards.

Xiaoning Han et al., Forebrain Engraftment by Human Glial Progenitor Cells Enhances Synaptic Plasticity and Learning in Adult Mice. Stem Cell 2013. Pay per viewLINK [doi:10.1016/j.stem.2012.12.015]

See the news article at Science Daily for details. 

One wonders if they gave mice some sort of humanity and the many ethical questions behind this experiment, of course. But what got me wondering after that is do chimpanzees have the same kind of astrocytes as we do?

And the answer seems to be yes but no.

Nancy A. Oberheim et al., Uniquely Hominid Features of Adult Human Astrocytes. The Journal of Neuroscience 2009. Freely accessibleLINK [doi:10.1523/​JNEUROSCI.4707-08.2009]

Chimpanzees and humans share a type of astrocytes not found in our monkey or rodent relatives but the density and complexity of these particular glial cells in humans is much greater than in chimpanzees.

Fig 2 (legend)
One of the most striking features distinguishing humans and chimpanzee from other lower primate and rodent astrocytes was the presence of a previously undescribed pool of morphologically distinct GFAP+ cells residing in layers 5–6, characterized by long fibers with prominent varicosities (Fig. 2A). (...) In our analysis of primate tissue, we were able to locate a small number of varicose projection astrocytes within layers 5 or 6 of the chimpanzee cortex (Fig. 2A, inset). These cells differed from those seen in human in that they were smaller and less complex, with fewer main GFAP+ processes.

This is not the only difference, another subgroup, the interlaminar astrocytes also shows differences:

In addition to being more numerous than their chimpanzee counterparts, the morphology of interlaminar astrocytes is subtly different in humans. Human interlaminar astrocytes have small spheroid cell bodies and several short processes that contribute to the pial glial limitains, creating a thick network of GFAP fibers not seen in the primate.

A third category, the protoplasmatic astrocytes, is also different:

... the average diameter of protoplasmic cortical astrocytes in the chimpanzee brain was 81.7 ± 1.9 μm (n = 36), which is significantly smaller than human astrocytes, but significantly larger than protoplasmic astrocytes in mouse brain...

So what about cetaceans, which include some of the non-human animals most famed for their intellectual capabilities? The brain structure seems different, so maybe not as easy to compare as with our closest relatives, also cetaceans do not seem so well researched. But we know (source) that at least that the proportion of glial cells in bottlenose dolphin forebrains is almost double than that of humans:

Glial cells outnumber neurons by at least 6 to 1 but the ratio differs in different parts of the nervous system. The ratio can be 100 glials to 1 neuron along nerves in the white matter tracts in the brain; in the frontal cortex the ratio is 4 to 1. Interestingly, whales and dolphins have 7 glials for every neuron in their gigantic forebrains. (Fields, R. Douglas, PhD. The Other Brain. P P 24. NY:Simon & Schuster, 2009.)

1 comment:

  1. Hello: May be you would be interested to know:
    -Colombo J.A. Interlaminar astroglial cell processes in the cerebral cortex of adult
    primates: further characterization.
    Glial Contributions to Behavior, pp. 117-118, 1995.
    -Colombo J.A. Interlaminar Astroglial Processes in the Cerebral Cortex of Adult
    Monkeys but not of Adult Rats.
    Acta Anatomica 155:57-62,1996.
    Glia 19: 161- 170, 1997.
    -Colombo J.A., S.Lipina, A.Yáñez, V.Puissant. Postnatal development of interlaminar
    astroglial processes in the cerebral cortex of primates.
    International Journal of Developmental Neuroscience 15: 823-833, 1997.
    -Colombo J.A., A.Yáñez, S.Lipina. Interlaminar astroglial processes in the cerebral
    cortex of non human primates: response to injury.
    J.Brain Research (J.fur Hirnforfschung) 38: 425-564, 1997.
    -Colombo J.A., W.Hartig, S.Lipina, N.Bons. Astroglial interlaminar processes in the
    cerebral cortex of prosimians and Old World monkeys.
    Anat.Embryol. 197:369-376, 1998.
    -Colombo J.A., M..Napp. Cerebrospinal fluid from L-dopa -treated Parkinson’s disease patients is dystrophic for various neural cell types ex vivo: effects of astroglia.
    Experimental Neurology 154: 452-463, 1998.
    -Colombo J.A., A.Schleicher, K.Zilles. Patterned distribution of immunoreactive
    astroglial processes in the striate (V1) cortex of New World monkeys.
    Glia 25:85-92, 1999.
    -Colombo J.A., A.Yáñez, S.Lipina. Disruption of immunoreactive glial fibrillary acidic
    protein patterns in the Cebus apella striate cortex following loss of visual input.
    J. of Brain Research (Journal fur Hirnforschung) 39: 447-451, 1999.
    -Gayol S., T. Pannicke, A. Reichenbach, J.A. Colombo. Cell-cell coupling in cultures of striatal and cortical astrocytes of the monkey.
    J. of Brain Research (Journal fur Hirnforschung) 39: 471-477, 1999.
    -Colombo J.A., E.Fuchs, W.Härtig, L.R.Marotte, V.Puissant. “Rodent - like” and
    “primate-like” types of astroglial architecture in the adult cerebral cortex of mammals.
    A comparative study.
    Anatomy and Embryology 201: 111-120, 2000.
    - Colombo J.A.- Comentarios a propósito del cerebro de Albert Einstein. Medicina 60 (4):530-532, 2000.
    -Colombo J.A., M.I.Napp, A.Yáñez, H.Reisin. Tissue printing of astroglial interlaminar processes from human and non human primate cerebral cortex.
    Brain Research Bulletin 55: 561-565, 2001.
    -Colombo J.A. A columnar - supporting mode of astroglial architecture in the cerebral
    cortex of adult primates?
    Neurobiology 9: 1-16, 2001.
    -Lipina S., J.A.Colombo . Dissociated functional recovery in parkinsonian monkeys
    following transplantation of astroglial cells.
    Brain Research 911: 176-180, 2001.
    -Reisin, H., J.A. Colombo. Astroglial interlaminar processes in human
    cerebral cortex: variations in cytoskeletal profiles.
    Brain Research 937: 51-57, 2002.
    -Colombo J.A., B. Quinn, V. Puissant . Disruption of astroglial interlaminar
    processes in Alzheimer’s Disease.
    Brain Research Bulletin 58: 235-242, 2002.
    -Reisin H.D., J.A.Colombo. Considerations on the astroglial architecture and the
    columnar organization of the cerebral cortex.
    Cellular and Molecular Neurobiology 22: 633-644, 2002.
    -Reisin H.D., J.A.Colombo. Long term disruption of glial interlaminar processes
    following transection of the dorsal spinal cord in adult monkeys.
    Brain Research 1000:179-182, 2003.
    -Colombo J.A., H.D. Reisin. Interlaminar astroglia of the cerebral cortex, a marker of
    the primate brain.
    Brain Research 1006:126-131, 2004.
    -Colombo Jorge A., Sherwood Chet, Hof Patrick. Interlaminar astroglial processes
    in the cerebral cortex of great apes.
    Anatomy and Embryology 429: 391-394, 2004.
    -Colombo J.A., H.D. Reisin, M.Jones, C.Bentham. Development of human
    interlaminar astroglial processes in the cerebral cortex of control and Down’s
    Syndrome cases.
    Experimental Neurology 193: 207-217, 2005.

    My best.
    Jorge A. Colombo MD, PhD
    Buenos Aires


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