Laila Brito Torres

Cellular Scaling Rules for the Brains of an Extended Number of Primate Species

What are the rules relating the size of the brain and its structures to the number of cells that compose them and their average sizes? We have shown previously that the cerebral cortex, cerebellum and the remaining brain structures increase in size as a linear function of their numbers of neurons and non-neuronal cells across 6 species of primates. Here we describe that the cellular composition of the same brain structures of 5 other primate species, as well as humans, conform to the scaling rules identified previously, and that the updated power functions for the extended sample are similar to those determined earlier. Accounting for phylogenetic relatedness in the combined dataset does not affect the scaling slopes that apply to the cerebral cortex and cerebellum, but alters the slope for the remaining brain structures to a value that is similar to that observed in rodents, which raises the possibility that the neuronal scaling rules for these structures are shared among rodents and primates. The conformity of the new set of primate species to the previous rules strongly suggests that the cellular scaling rules we have identified apply to primates in general, including humans, and not only to particular subgroups of primate species. In contrast, the allometric rules relating body and brain size are highly sensitive to the particular species sampled, suggesting that brain size is neither determined by body size nor together with it, but is rather only loosely correlated with body size.

Updated Neuronal Scaling Rules for the Brains of Glires (Rodents/Lagomorphs)

Brain size scales as different functions of its number of neurons across mammalian orders such as rodents, primates, and insectivores. In rodents, we have previously shown that, across a sample of 6 species, from mouse to capybara, the cerebral cortex, cerebellum and the remaining brain structures increase in size faster than they gain neurons, with an accompanying decrease in neuronal density in these structures [Herculano-Houzel et al.: Proc Natl Acad Sci USA 2006;103:12138–12143]. Important remaining questions are whether such neuronal scaling rules within an order apply equally to all pertaining species, and whether they extend to closely related taxa. Here, we examine whether 4 other species of Rodentia, as well as the closely related rabbit (Lagomorpha), conform to the scaling rules identified previously for rodents. We report the updated neuronal scaling rules obtained for the average values of each species in a way that is directly comparable to the scaling rules that apply to primates [Gabi et al.: Brain Behav Evol 2010;76:32–44], and examine whether the scaling relationships are affected when phylogenetic relatedness in the dataset is accounted for. We have found that the brains of the spiny rat, squirrel, prairie dog and rabbit conform to the neuronal scaling rules that apply to the previous sample of rodents. The conformity to the previous rules of the new set of species, which includes the rabbit, suggests that the cellular scaling rules we have identified apply to rodents in general, and probably to Glires as a whole (rodents/lagomorphs), with one notable exception: the naked mole-rat brain is apparently an outlier, with only about half of the neurons expected from its brain size in its cerebral cortex and cerebellum.

No relative expansion of the number of prefrontal neurons in primate and human evolution

Significance Human brain evolution is often considered synonymous with cortical expansion, in particular of the prefrontal cortex, a cortical region required for our remarkable cognitive abilities such as personality expression, planning, and decision making. In this study, we show that the expansion of numbers of cortical neurons in human and nonhuman primate evolution occurred in a similar manner across the cortex, without an increase in the relative number of neurons in the prefrontal region, and without a relative increase in the number of cells in the prefrontal white matter. One thing that distinguishes the human brain from other primate brains is thus not the relative size of its prefrontal cortex but its absolute number of neurons. Human evolution is widely thought to have involved a particular expansion of prefrontal cortex. This popular notion has recently been challenged, although controversies remain. Here we show that the prefrontal region of both human and nonhuman primates holds about 8% of cortical neurons, with no clear difference across humans and other primates in the distribution of cortical neurons or white matter cells along the anteroposterior axis. Further, we find that the volumes of human prefrontal gray and white matter match the expected volumes for the number of neurons in the gray matter and for the number of other cells in the white matter compared with other primate species. These results indicate that prefrontal cortical expansion in human evolution happened along the same allometric trajectory as for other primate species, without modification of the distribution of neurons across its surface or of the volume of the underlying white matter. We thus propose that the most distinctive feature of the human prefrontal cortex is its absolute number of neurons, not its relative volume.

Contamination of mesenchymal stem-cells with fibroblasts accelerates neurodegeneration in an experimental model of Parkinson's disease.

Pre-clinical studies have supported the use of mesenchymal stem cells (MSC) to treat highly prevalent neurodegenerative diseases such as Parkinson’s disease (PD) but preliminary trials have reported controversial results. In a rat model of PD induced by MPTP neurotoxin, we first observed a significant bilateral preservation of dopaminergic neurons in the substantia nigra and prevention of motor deficits typically observed in PD such as hypokinesia, catalepsy, and bradykinesia, following intracerebral administration of human umbilical cord-derived MSC (UC-MSC) early after MPTP injury. However, surprisingly, administration of fibroblasts, mesenchymal cells without stem cell properties, as a xenotransplantation control was highly detrimental, causing significant neurodegeneration and motor dysfunction independently of MPTP. This observation prompted us to further investigate the consequences of transplanting a MSC preparation contaminated with fibroblasts, a plausible circumstance in cell therapy since both cell types display similar immunophenotype and can be manipulated in vitro under the same conditions. Here we show for the first time, using the same experimental model and protocol, that transplantation of UC-MSC induced potent neuroprotection in the brain resulting in clinical benefit. However, co-transplantation of UC-MSC with fibroblasts reverted therapeutic efficacy and caused opposite damaging effects, significantly exacerbating neurodegeneration and motor deficits in MPTP-exposed rats. Besides providing a rationale for testing UC-MSC transplantation in early phases of PD aiming at delaying disease progression, our pre-clinical study suggests that fibroblasts may be common cell contaminants affecting purity of MSC preparations and clinical outcome in stem cell therapy protocols, which might also explain discrepant clinical results.

Neuroprotective effect of pyruvate and oxaloacetate during pilocarpine induced status epilepticus in rats

Recent research data have shown that systemic administration of pyruvate and oxaloacetate causes an increased brain-to-blood glutamate efflux. Since increased release of glutamate during epileptic seizures can lead to excitotoxicity and neuronal cell death, we tested the hypothesis that glutamate scavenging mediated by pyruvate and oxaloacetate systemic administration could have a neuroprotective effect in rats subjected to status epilepticus (SE). SE was induced by a single dose of pilocarpine (350mg/kgi.p.). Thirty minutes after SE onset, a single dose of pyruvate (250mg/kgi.p.), oxaloacetate (1.4mg/kgi.p.), or both substances was administrated. Acute neuronal loss in hippocampal regions CA1 and hilus was quantitatively determined five hours after SE onset, using the optical fractionator method for stereological cell counting. Apoptotic cascade in the hippocampus was also investigated seven days after SE using caspase-1 and -3 activity assays. SE-induced neuronal loss in CA1 was completely prevented in rats treated with pyruvate plus oxaloacetate. The SE-induced caspase-1 activation was significantly reduced when rats were treated with oxaloacetate or pyruvate plus oxaloacetate. The treatment with pyruvate and oxaloacetate caused a neuroprotective effect in rats subjected to pilocarpine-induced SE.

Distinctive hippocampal CA2 subfield of the Amazon rodent Proechimys.

Previous data of our laboratory have shown that the Amazonian rodents Proechimys do not present spontaneous seizures in different models of epilepsy, suggesting endogenous inhibitory mechanisms. Here, we describe a remarkably different Proechimys cytoarchitecture organization of the hippocampal cornu Ammonis 2 (CA2) subfield. We identified a very distinctive Proechimys CA2 sector exhibiting disorganized cell presentation of the pyramidal layer and atypical dispersion of the pyramidal-like cells to the stratum oriens, strongly contrasting to the densely packed CA2 cells in the Wistar rats. Studies showed that CA2 is the only cornu ammonis (CA) subfield resistant to the extensive pyramidal neural loss in mesial temporal lobe epilepsy (MTLE) associated to hippocampal sclerosis. Thus, in order to investigate this region, we used Nissl and Timm staining, stereological approach to count neurons and immunohistochemistry to neuronal nuclei (NeuN), parvalbumin (PV), calbindin (CB) and calretinin (CR). We did not notice statistically significant differences in the total number of neurons of the CA2 region between Proechimys and Wistar. However, Proechimys rodents presented higher CA2 volume than Wistar rats. Furthermore, no significant difference in the optical density of parvalbumin-immunoreactivity was found between subject groups. On the other hand, Proechimys presented significant higher density of calbindin and calretinin-immunoreactivity when compared to Wistar rats. In this context, this unique CA2 subfield seen in Proechimys opens up a new set of possibilities to explore the contribution of CA2 neurons in normal and pathological brain circuits.

Hippocampal expression and distribution of CB1 receptors in the Amazonian rodent Proechimys: An animal model of resistance to epilepsy

Proechimys, a rodent living in the Amazon region, has shown resistance to developing chronic epilepsy when submitted to different experimental models. Recently, many studies have attributed a potent anticonvulsant action to cannabinoid receptor CB1. This study investigated the distribution and expression of the CB1 receptor in the hippocampal formation of Proechimys using immunohistochemistry and Western blotting techniques. Results were compared with values obtained from adult Wistar rats. The immunoreactivity for CB1 was evident throughout the Ammons horn and in the hilar region of both animal species. However, the distribution of these receptors was higher in the stratum lucidum of CA3 and in the hilar region of Proechimys. In addition, higher expression of CB1 receptors was observed in the Proechimys hippocampus. These data could explain, at least partially, the natural resistance of this animal species to developing spontaneous seizures following epileptogenic precipitating events.

The use of new world primates for biomedical research: an overview of the last four decades

Animal experimentation contributes significantly to the progression of science. Nonhuman primates play a particularly important role in biomedical research not only because of their anatomical, physiological, biochemical, and behavioral similarities with humans but also because of their close phylogenetic affinities. In order to investigate the use of New World primates (NWP) in biomedical research over the last four decades (1966–2005), we performed a quantitative study of the literature listed in bibliographic databases from the Health Sciences. The survey was performed for each genus of NWP that has been bred in the National Center of Primates in Brazil. The number of articles published was determined for each genus and sorted according to the country from which the studies originated and the general scientific field. The data obtained suggests that Brazil is a leader in generating knowledge with NWP models for translational medicine. Am. J. Primatol. 72:1055–1061, 2010.

Seizures during pregnancy modify the development of hippocampal interneurons of the offspring

We investigated the effect of epileptic seizures during pregnancy on hippocampal expression of calcium-binding proteins in the offspring. Female Wistar rats were submitted to the pilocarpine model and mated during the chronic period. Seizure frequency was monitored over the entire pregnancy. Pups were perfused at postnatal days 6 and 13, and the brains processed for Nissl staining and immunohistochemistry for NeuN, calbindin, calretinin, and parvalbumin. Number of stained cells in the hippocampus was estimated through stereological methods. Our results showed a decrease in epileptic seizure frequency during pregnancy. No differences were observed in NeuN-positive, CR-positive cells, and Nissl-stained hippocampal neurons between the groups. However, there was a significant decrease in calbindin-positive cells (P=0.005) and a significant increase in parvalbumin-positive cells (P=0.02) in the experimental group when compared with the control group. These results suggest that seizures during pregnancy affect the development of specific hippocampal interneurons of the offspring.

Epilepsy-induced electrocardiographic alterations following cardiac ischemia and reperfusion in rats

The present study evaluated electrocardiographic alterations in rats with epilepsy submitted to an acute myocardial infarction (AMI) model induced by cardiac ischemia and reperfusion. Rats were randomly divided into two groups: control (n=12) and epilepsy (n=14). It was found that rats with epilepsy presented a significant reduction in atrioventricular block incidence following the ischemia and reperfusion procedure. In addition, significant alterations were observed in electrocardiogram intervals during the stabilization, ischemia, and reperfusion periods of rats with epilepsy compared to control rats. It was noted that rats with epilepsy presented a significant increase in the QRS interval during the stabilization period in relation to control rats (P<0.01). During the ischemia period, there was an increase in the QRS interval (P<0.05) and a reduction in the P wave and QT intervals (P<0.05 for both) in rats with epilepsy compared to control rats. During the reperfusion period, a significant reduction in the QT interval (P<0.01) was verified in the epilepsy group in relation to the control group. Our results indicate that rats submitted to an epilepsy model induced by pilocarpine presented electrical conductivity alterations of cardiac tissue, mainly during an AMI episode.