Limits...
All brains are made of this: a fundamental building block of brain matter with matching neuronal and glial masses.

Mota B, Herculano-Houzel S - Front Neuroanat (2014)

Bottom Line: We propose that there is a fundamental building block of brain tissue: the glial mass that accompanies a unit of neuronal mass.We argue that the scaling of this glial mass is a consequence of a universal mechanism whereby numbers of glial cells are added to the neuronal parenchyma during development, irrespective of whether the neurons composing it are large or small, but depending on the average mass of the glial cells being added.We also show how evolutionary variations in neuronal cell mass, glial cell mass and number of neurons suffice to determine the most basic characteristics of brain structures, such as mass, glia/neuron ratio, neuron/glia mass ratio, and cell densities.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Física, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil ; Instituto Nacional de Neurociência Translacional São Paulo, Brazil.

ABSTRACT
How does the size of the glial and neuronal cells that compose brain tissue vary across brain structures and species? Our previous studies indicate that average neuronal size is highly variable, while average glial cell size is more constant. Measuring whole cell sizes in vivo, however, is a daunting task. Here we use chi-square minimization of the relationship between measured neuronal and glial cell densities in the cerebral cortex, cerebellum, and rest of brain in 27 mammalian species to model neuronal and glial cell mass, as well as the neuronal mass fraction of the tissue (the fraction of tissue mass composed by neurons). Our model shows that while average neuronal cell mass varies by over 500-fold across brain structures and species, average glial cell mass varies only 1.4-fold. Neuronal mass fraction varies typically between 0.6 and 0.8 in all structures. Remarkably, we show that two fundamental, universal relationships apply across all brain structures and species: (1) the glia/neuron ratio varies with the total neuronal mass in the tissue (which in turn depends on variations in average neuronal cell mass), and (2) the neuronal mass per glial cell, and with it the neuronal mass fraction and neuron/glia mass ratio, varies with average glial cell mass in the tissue. We propose that there is a fundamental building block of brain tissue: the glial mass that accompanies a unit of neuronal mass. We argue that the scaling of this glial mass is a consequence of a universal mechanism whereby numbers of glial cells are added to the neuronal parenchyma during development, irrespective of whether the neurons composing it are large or small, but depending on the average mass of the glial cells being added. We also show how evolutionary variations in neuronal cell mass, glial cell mass and number of neurons suffice to determine the most basic characteristics of brain structures, such as mass, glia/neuron ratio, neuron/glia mass ratio, and cell densities.

No MeSH data available.


Variation in structure mass as a function of number of neurons and glial cells in the structure. Average brain structure mass for each species is plotted as a function of its total number of neurons (A) and non-neuronal (glial) cells (B). Structure mass is given in picograms. Power functions are plotted separately for cerebral cortex (circles), cerebellum (squares) and rest of brain (triangles) in eulipotyphlans (orange), primates (red) and rodents (green). Power function constants and exponents are listed in Table 1. The two graphs are plotted with identical scales for comparison. Notice that the power functions are overlapping in (B), but not in (A). Data from Herculano-Houzel et al. (2006, 2007, 2011), Azevedo et al. (2009), Sarko et al. (2009), and Gabi et al. (2010).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4228857&req=5

Figure 1: Variation in structure mass as a function of number of neurons and glial cells in the structure. Average brain structure mass for each species is plotted as a function of its total number of neurons (A) and non-neuronal (glial) cells (B). Structure mass is given in picograms. Power functions are plotted separately for cerebral cortex (circles), cerebellum (squares) and rest of brain (triangles) in eulipotyphlans (orange), primates (red) and rodents (green). Power function constants and exponents are listed in Table 1. The two graphs are plotted with identical scales for comparison. Notice that the power functions are overlapping in (B), but not in (A). Data from Herculano-Houzel et al. (2006, 2007, 2011), Azevedo et al. (2009), Sarko et al. (2009), and Gabi et al. (2010).

Mentions: These relationships are illustrated in Figure 1, and all constants and exponents are listed in Table 1. While different neuronal scaling exponents apply to different structures and mammalian orders (Figure 1A), similar glial scaling exponents apply across structures, species, and orders (Figure 1B). Indeed, the comparison of the values of kn, kg, αn, and αg for each structure and mammalian order shows that while αn and kn are highly variable, αg and kg vary little across all cases considered (Table 1), to such an extent that it is visually hard to distinguish between points corresponding to numbers of glial cells of different orders and structures.


All brains are made of this: a fundamental building block of brain matter with matching neuronal and glial masses.

Mota B, Herculano-Houzel S - Front Neuroanat (2014)

Variation in structure mass as a function of number of neurons and glial cells in the structure. Average brain structure mass for each species is plotted as a function of its total number of neurons (A) and non-neuronal (glial) cells (B). Structure mass is given in picograms. Power functions are plotted separately for cerebral cortex (circles), cerebellum (squares) and rest of brain (triangles) in eulipotyphlans (orange), primates (red) and rodents (green). Power function constants and exponents are listed in Table 1. The two graphs are plotted with identical scales for comparison. Notice that the power functions are overlapping in (B), but not in (A). Data from Herculano-Houzel et al. (2006, 2007, 2011), Azevedo et al. (2009), Sarko et al. (2009), and Gabi et al. (2010).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4228857&req=5

Figure 1: Variation in structure mass as a function of number of neurons and glial cells in the structure. Average brain structure mass for each species is plotted as a function of its total number of neurons (A) and non-neuronal (glial) cells (B). Structure mass is given in picograms. Power functions are plotted separately for cerebral cortex (circles), cerebellum (squares) and rest of brain (triangles) in eulipotyphlans (orange), primates (red) and rodents (green). Power function constants and exponents are listed in Table 1. The two graphs are plotted with identical scales for comparison. Notice that the power functions are overlapping in (B), but not in (A). Data from Herculano-Houzel et al. (2006, 2007, 2011), Azevedo et al. (2009), Sarko et al. (2009), and Gabi et al. (2010).
Mentions: These relationships are illustrated in Figure 1, and all constants and exponents are listed in Table 1. While different neuronal scaling exponents apply to different structures and mammalian orders (Figure 1A), similar glial scaling exponents apply across structures, species, and orders (Figure 1B). Indeed, the comparison of the values of kn, kg, αn, and αg for each structure and mammalian order shows that while αn and kn are highly variable, αg and kg vary little across all cases considered (Table 1), to such an extent that it is visually hard to distinguish between points corresponding to numbers of glial cells of different orders and structures.

Bottom Line: We propose that there is a fundamental building block of brain tissue: the glial mass that accompanies a unit of neuronal mass.We argue that the scaling of this glial mass is a consequence of a universal mechanism whereby numbers of glial cells are added to the neuronal parenchyma during development, irrespective of whether the neurons composing it are large or small, but depending on the average mass of the glial cells being added.We also show how evolutionary variations in neuronal cell mass, glial cell mass and number of neurons suffice to determine the most basic characteristics of brain structures, such as mass, glia/neuron ratio, neuron/glia mass ratio, and cell densities.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Física, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil ; Instituto Nacional de Neurociência Translacional São Paulo, Brazil.

ABSTRACT
How does the size of the glial and neuronal cells that compose brain tissue vary across brain structures and species? Our previous studies indicate that average neuronal size is highly variable, while average glial cell size is more constant. Measuring whole cell sizes in vivo, however, is a daunting task. Here we use chi-square minimization of the relationship between measured neuronal and glial cell densities in the cerebral cortex, cerebellum, and rest of brain in 27 mammalian species to model neuronal and glial cell mass, as well as the neuronal mass fraction of the tissue (the fraction of tissue mass composed by neurons). Our model shows that while average neuronal cell mass varies by over 500-fold across brain structures and species, average glial cell mass varies only 1.4-fold. Neuronal mass fraction varies typically between 0.6 and 0.8 in all structures. Remarkably, we show that two fundamental, universal relationships apply across all brain structures and species: (1) the glia/neuron ratio varies with the total neuronal mass in the tissue (which in turn depends on variations in average neuronal cell mass), and (2) the neuronal mass per glial cell, and with it the neuronal mass fraction and neuron/glia mass ratio, varies with average glial cell mass in the tissue. We propose that there is a fundamental building block of brain tissue: the glial mass that accompanies a unit of neuronal mass. We argue that the scaling of this glial mass is a consequence of a universal mechanism whereby numbers of glial cells are added to the neuronal parenchyma during development, irrespective of whether the neurons composing it are large or small, but depending on the average mass of the glial cells being added. We also show how evolutionary variations in neuronal cell mass, glial cell mass and number of neurons suffice to determine the most basic characteristics of brain structures, such as mass, glia/neuron ratio, neuron/glia mass ratio, and cell densities.

No MeSH data available.