5 research outputs found
Scaling of inhibitory interneurons in areas V1 and V2 of anthropoid primates as revealed by calcium-binding protein immunohistochemistry
Inhibitory GABAergic interneurons are important for shaping patterns of activity in neocortical networks. We examined the distributions of inhibitory interneuron subtypes in layer II/III of areas V1 and V2 in 18 genera of anthropoid primates including New World monkeys, Old World monkeys, and hominoids (apes and humans). Interneuron subtypes were identified by immunohistochemical staining for calbindin, calretinin, and parvalbumin and densities were quantified using the optical disector method. In both V1 and V2, calbindin-immunoreactive neuron density decreased disproportionately with decreasing total neuronal density. Thus, V1 and V2 of hominoids were occupied by a smaller percentage of calbindin-immunoreactive interneurons compared to monkeys who have greater overall neuronal densities. At the transition from V1 to V2 across all individuals, we found a tendency for increased percentages of calbindin-immunoreactive multipolar cells and calretinin-immunoreactive interneurons. In addition, parvalbumin-immunoreactive cell soma volumes increased from V1 to V2. These findings suggest that modifications of specific aspects of inhibition might be critical to establishing the receptive field properties that distinguish visual areas. Furthermore, these results show that phylogenetic variation exists in the microcircuitry of visual cortex that could have general implications for sensory processing
A volumetric comparison of the insular cortex and its subregions in primates
The neuronal composition of the insula in primates displays a gradient, transitioning from granular neocortex in the posterior-dorsal insula to agranular neocortex in the anterior-ventral insula with an intermediate zone of dysgranularity. Additionally, apes and humans exhibit a distinctive subdomain in the agranular insula, the frontoinsular cortex (FI), defined by the presence of clusters of von Economo neurons (VENs). Studies in humans indicate that the ventral anterior insula, including agranular insular cortex and FI, is involved in social awareness, and that the posterodorsal insula, including granular and dysgranular cortices, produces an internal representation of the body's homeostatic state. We examined the volumes of these cytoarchitectural areas of insular cortex in 30 primate species, including the volume of FI in apes and humans. Results indicate that the whole insula scales hyperallometrically (exponent = 1.13) relative to total brain mass, and the agranular insula (including FI) scales against total brain mass with even greater positive allometry (exponent = 1.23), providing a potential neural basis for enhancement of social cognition in association with increased brain size. The relative volumes of the subdivisions of the insular cortex, after controlling for total brain volume, are not correlated with species typical social group size. Although its size is predicted by primate-wide allometric scaling patterns, we found that the absolute volume of the left and right agranular insula and left FI are among the most differentially expanded of the human cerebral cortex compared to our closest living relative, the chimpanzee
Supplementary Material for: Cellular Scaling Rules for the Brains of Marsupials: Not as “Primitive” as Expected
<p>In the effort to understand the evolution of mammalian brains, we
have found that common relationships between brain structure mass and
numbers of nonneuronal (glial and vascular) cells apply across eutherian
mammals, but brain structure mass scales differently with numbers of
neurons across structures and across primate and nonprimate clades. This
suggests that the ancestral scaling rules for mammalian brains are
those shared by extant nonprimate eutherians - but do these scaling
relationships apply to marsupials, a sister group to eutherians that
diverged early in mammalian evolution? Here we examine the cellular
composition of the brains of 10 species of marsupials. We show that
brain structure mass scales with numbers of nonneuronal cells, and
numbers of cerebellar neurons scale with numbers of cerebral cortical
neurons, comparable to what we have found in eutherians. These shared
scaling relationships are therefore indicative of mechanisms that have
been conserved since the first therians. In contrast, while marsupials
share with nonprimate eutherians the scaling of cerebral cortex mass
with number of neurons, their cerebella have more neurons than
nonprimate eutherian cerebella of a similar mass, and their rest of
brain has fewer neurons than eutherian structures of a similar mass.
Moreover, Australasian marsupials exhibit ratios of neurons in the
cerebral cortex and cerebellum over the rest of the brain, comparable to
artiodactyls and primates. Our results suggest that Australasian
marsupials have diverged from the ancestral Theria neuronal scaling
rules, and support the suggestion that the scaling of average neuronal
cell size with increasing numbers of neurons varies in evolution
independently of the allocation of neurons across structures.</p
Supplementary Material for: Synaptosomal Lactate Dehydrogenase Isoenzyme Composition Is Shifted toward Aerobic Forms in Primate Brain Evolution
With the evolution of a relatively large brain size in haplorhine primates (i.e. tarsiers, monkeys, apes, and humans), there have been associated changes in the molecular machinery that delivers energy to the neocortex. Here we investigated variation in lactate dehydrogenase (LDH) expression and isoenzyme composition of the neocortex and striatum in primates using quantitative Western blotting and isoenzyme analysis of total homogenates and synaptosomal fractions. Analysis of isoform expression revealed that LDH in synaptosomal fractions from both forebrain regions shifted towards a predominance of the heart-type, aerobic isoform LDH-B among haplorhines as compared to strepsirrhines (i.e. lorises and lemurs), while in the total homogenate of the neocortex and striatum there was no significant difference in LDH isoenzyme composition between the primate suborders. The largest increase occurred in synapse-associated LDH-B expression in the neocortex, with an especially remarkable elevation in the ratio of LDH-B/LDH-A in humans. The phylogenetic variation in the ratio of LDH-B/LDH-A was correlated with species-typical brain mass but not the encephalization quotient. A significant LDH-B increase in the subneuronal fraction from haplorhine neocortex and striatum suggests a relatively higher rate of aerobic glycolysis that is linked to synaptosomal mitochondrial metabolism. Our results indicate that there is a differential composition of LDH isoenzymes and metabolism in synaptic terminals that evolved in primates to meet increased energy requirements in association with brain enlargement