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Cellular scaling rules of insectivore brains.

Sarko DK, Catania KC, Leitch DB, Kaas JH, Herculano-Houzel S - Front Neuroanat (2009)

Bottom Line: The olfactory bulbs of insectivores, however, offer a noteworthy exception in that neuronal density increases linearly with increasing structure mass.This implies that the average neuronal cell size decreases with increasing olfactory bulb mass in order to accommodate greater neuronal density, and represents the first documentation of a brain structure gaining neurons at a greater rate than mass.This might allow insectivore brains to concentrate more neurons within the olfactory bulbs without a prohibitively large and metabolically costly increase in structure mass.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Vanderbilt University Nashville, TN, USA.

ABSTRACT
Insectivores represent extremes in mammalian body size and brain size, retaining various "primitive" morphological characteristics, and some species of Insectivora are thought to share similarities with small-bodied ancestral eutherians. This raises the possibility that insectivore brains differ from other taxa, including rodents and primates, in cellular scaling properties. Here we examine the cellular scaling rules for insectivore brains and demonstrate that insectivore scaling rules overlap somewhat with those for rodents and primates such that the insectivore cortex shares scaling rules with rodents (increasing faster in size than in numbers of neurons), but the insectivore cerebellum shares scaling rules with primates (increasing isometrically). Brain structures pooled as "remaining areas" appear to scale similarly across all three mammalian orders with respect to numbers of neurons, and the numbers of non-neurons appear to scale similarly across all brain structures for all three orders. Therefore, common scaling rules exist, to different extents, between insectivore, rodent, and primate brain regions, and it is hypothesized that insectivores represent the common aspects of each order. The olfactory bulbs of insectivores, however, offer a noteworthy exception in that neuronal density increases linearly with increasing structure mass. This implies that the average neuronal cell size decreases with increasing olfactory bulb mass in order to accommodate greater neuronal density, and represents the first documentation of a brain structure gaining neurons at a greater rate than mass. This might allow insectivore brains to concentrate more neurons within the olfactory bulbs without a prohibitively large and metabolically costly increase in structure mass.

No MeSH data available.


Related in: MedlinePlus

Scaling rules in insectivore brains. Graphs of power functions relate (A) brain mass to body mass (p = 0.0024), (B) brain mass to total number of cells in the brain (Nc; p = 0.0015), (C) brain mass to the total number of neurons in the brain (NN; p = 0.0023), and (D) brain mass to total number of non-neurons in the brain (NNN; p = 0.0010). Each point represents the average for a species.
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Figure 2: Scaling rules in insectivore brains. Graphs of power functions relate (A) brain mass to body mass (p = 0.0024), (B) brain mass to total number of cells in the brain (Nc; p = 0.0015), (C) brain mass to the total number of neurons in the brain (NN; p = 0.0023), and (D) brain mass to total number of non-neurons in the brain (NNN; p = 0.0010). Each point represents the average for a species.

Mentions: Across the five insectivore species studied, body mass varies approximately 12-fold, from ≈8 g in the smoky shrew to ≈95 g in eastern moles, whereas brain mass varies by a factor of approximately 6, accompanied by an increase of 5.5 times the total number of cells and 6 times the number of total neurons (Table 1). We found that brain mass (MBR) relates to body mass (MBO) by the power function MBR = 0.046 × MBO0.743 (Figure 2A; p = 0.0024) in accordance with studies of other mammals reporting that brain size increases more slowly than body size (Fox and Wilczynski, 1986; Martin, 1981). As a result, relative brain mass ranged from 2.3% in the smoky shrew to 1.0% in the eastern mole, decreasing with increasing body size (Spearman correlation, p = 0.0455).


Cellular scaling rules of insectivore brains.

Sarko DK, Catania KC, Leitch DB, Kaas JH, Herculano-Houzel S - Front Neuroanat (2009)

Scaling rules in insectivore brains. Graphs of power functions relate (A) brain mass to body mass (p = 0.0024), (B) brain mass to total number of cells in the brain (Nc; p = 0.0015), (C) brain mass to the total number of neurons in the brain (NN; p = 0.0023), and (D) brain mass to total number of non-neurons in the brain (NNN; p = 0.0010). Each point represents the average for a species.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2713736&req=5

Figure 2: Scaling rules in insectivore brains. Graphs of power functions relate (A) brain mass to body mass (p = 0.0024), (B) brain mass to total number of cells in the brain (Nc; p = 0.0015), (C) brain mass to the total number of neurons in the brain (NN; p = 0.0023), and (D) brain mass to total number of non-neurons in the brain (NNN; p = 0.0010). Each point represents the average for a species.
Mentions: Across the five insectivore species studied, body mass varies approximately 12-fold, from ≈8 g in the smoky shrew to ≈95 g in eastern moles, whereas brain mass varies by a factor of approximately 6, accompanied by an increase of 5.5 times the total number of cells and 6 times the number of total neurons (Table 1). We found that brain mass (MBR) relates to body mass (MBO) by the power function MBR = 0.046 × MBO0.743 (Figure 2A; p = 0.0024) in accordance with studies of other mammals reporting that brain size increases more slowly than body size (Fox and Wilczynski, 1986; Martin, 1981). As a result, relative brain mass ranged from 2.3% in the smoky shrew to 1.0% in the eastern mole, decreasing with increasing body size (Spearman correlation, p = 0.0455).

Bottom Line: The olfactory bulbs of insectivores, however, offer a noteworthy exception in that neuronal density increases linearly with increasing structure mass.This implies that the average neuronal cell size decreases with increasing olfactory bulb mass in order to accommodate greater neuronal density, and represents the first documentation of a brain structure gaining neurons at a greater rate than mass.This might allow insectivore brains to concentrate more neurons within the olfactory bulbs without a prohibitively large and metabolically costly increase in structure mass.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Vanderbilt University Nashville, TN, USA.

ABSTRACT
Insectivores represent extremes in mammalian body size and brain size, retaining various "primitive" morphological characteristics, and some species of Insectivora are thought to share similarities with small-bodied ancestral eutherians. This raises the possibility that insectivore brains differ from other taxa, including rodents and primates, in cellular scaling properties. Here we examine the cellular scaling rules for insectivore brains and demonstrate that insectivore scaling rules overlap somewhat with those for rodents and primates such that the insectivore cortex shares scaling rules with rodents (increasing faster in size than in numbers of neurons), but the insectivore cerebellum shares scaling rules with primates (increasing isometrically). Brain structures pooled as "remaining areas" appear to scale similarly across all three mammalian orders with respect to numbers of neurons, and the numbers of non-neurons appear to scale similarly across all brain structures for all three orders. Therefore, common scaling rules exist, to different extents, between insectivore, rodent, and primate brain regions, and it is hypothesized that insectivores represent the common aspects of each order. The olfactory bulbs of insectivores, however, offer a noteworthy exception in that neuronal density increases linearly with increasing structure mass. This implies that the average neuronal cell size decreases with increasing olfactory bulb mass in order to accommodate greater neuronal density, and represents the first documentation of a brain structure gaining neurons at a greater rate than mass. This might allow insectivore brains to concentrate more neurons within the olfactory bulbs without a prohibitively large and metabolically costly increase in structure mass.

No MeSH data available.


Related in: MedlinePlus