Enriched environment and exercise effects on parvalbumin expression and distribution in the hippocampal formation of developing rats.

Several models of environmental enrichment and physical exercise have been used to explore the experience effects on brain functions and plasticity, mainly in adult animals. In order to examine the early influence of these stimuli on developing brain, the present study used calcium-binding protein parvalbumin as neuroplastic marker in the hippocampal formation of male Wistar rats subjected to environmental enrichment or physical exercise from postnatal days 21 to 60 (P21-P60). In our study, no significant difference in hippocampal expression and distribution of parvalbumin was found between enriched and control rats. However, a significant increase in parvalbumin protein expression as well as in the number of neurons stained with parvalbumin was observed in the hippocampal formation of rats submitted to daily treadmill exercise when compared to the control rats. The hippocampal region with the highest number of parvalbumin neurons in exercised rats was Cornus of Amon 2 e 3 (CA2/CA3). These findings indicate that developing brain may be differentially sensitive to environmental stimulation models. Specifically, our results show that hippocampal expression and distribution of parvalbumin in developing rats may be more influenced by exercise than by enriched environment. The mechanisms are not yet known.

Early exercise induces long-lasting morphological changes in cortical and hippocampal neurons throughout of a sedentary period of rats.

Life experiences at early ages, such as physical activity in childhood and adolescence, can result in long-lasting brain effects able to reduce future risk of brain disorders and to enhance lifelong brain functions. However, how early physical exercise promotes these effects remains unclear. A possible hypothesis is that physical exercise increases the expression of neurotrophic factors and stimulates neuronal growth, resulting in a neural reserve to be used at later ages. Basing our study on this hypothesis, we evaluated the absolute number and morphology of neuronal cells, as well as the expression of growth, proliferation and survival proteins (BDNF, Akt, mTOR, p70S6K, ERK and CREB) in the cerebral cortex and hippocampal formation throughout of a sedentary period of rats who were physically active during youth. To do this, male Wistar rats were submitted to an aerobic exercise protocol from the 21st to the 60th postnatal days (P21-P60), and evaluated at 0 (P60), 30 (P90) and 60 (P120) days after the last exercise session. Results showed that juvenile exercise increased, and maintained elevated, the number of cortical and hippocampal neuronal cells and dendritic arborization, when evaluated at the above post-exercise ages. Hippocampal BDNF levels and cortical mTOR expression were found to be increased at P60, but were restored to control levels at P90 and P120. Overall, these findings indicate that, despite the short-term effects on growth and survival proteins, early exercise induces long-lasting morphological changes in cortical and hippocampal neurons even during a sedentary period of rats.

Altered Gene Expression of Thyroid Hormone Transporters and Deiodinases in iPS MeCP2-Knockout Cells-Derived Neurons.

MeCP2 is an X-linked gene; its mutation causes Rett Syndrome (RTT), a severe neurodevelopmental disability that affects mainly girls. Acting as a transcription factor, the MeCP2 protein is able to regulate several hormone-related genes, such as the thyroid hormones (TH), which are known to play an important role in the development of the central nervous system (CNS). Although only a few studies have associated RTT and TH, TH deficit can lead to neurological deregulation by triggering functional deficiencies during adulthood. Here, we used human-induced pluripotent stem cell (iPSC) to generate MeCP2-knockout neuronal progenitor cells and adult neurons. Using this cellular model, we then investigated the expression of genes associated with TH homeostasis, such as the TH transporters (LAT1, LAT2, MCT8, MCT10, and OATP4A1) and deiodinases (DIO1, 2, and 3). Then, we treated the neural cells with THs and analyzed the expression of several genes related to neurodevelopment and functional maintenance. Our results showed that several TH-related genes, such as deiodinases, are altered in RTT samples when compared to WT cells. Moreover, the treatment of the neural cells with THs increased the amount of MAP2 and synapsin-1 expression in RTT cells. Our work provided evidences that TH homeostasis is compromised in RTT-derived neural cells, which could be an important factor to contribute to the imbalance in the neurodevelopmental phenotype presented in this syndrome and can lead us to better understand other neurodevelopmental diseases.

Cerebal overinhibition could be the basis for the high prevalence of epilepsy in persons with Down syndrome.

Down syndrome (DS) is the most common cause of genetic intellectual disability, and the trisomy 21 is associated with more than 80 clinical traits, including higher risk for epilepsy. Several hypotheses have been put forward to explain the mechanisms underlying increased seizure susceptibility in DS: inherent structural brain abnormalities, abnormal cortical lamination, disruption of normal dendritic morphology, and underdeveloped synaptic profiles. A deficiency or loss of GABA inhibition is hypothesized to be one of the main alterations related to the epileptogenic process. Paradoxically, enhanced GABA inhibition has also been reported to promote seizures. One major functional abnormality observed in the brains of individuals and mouse models with DS appears to be an imbalance between excitatory and inhibitory neurotransmission, with excessive inhibitory brain function. This review discusses the GABAergic system in the human DS brain and the possible implication of the GABAergic network circuit in the epileptogenic process in individuals where the pathogenetic basis for epilepsy is unknown.

Parvalbumin expression and distribution in the hippocampal formation of Cebus apella.

New World primates play an important role in biomedical research. However, the literature still lacks information on many structural features of the brain in these species, particularly structures of the hippocampal formation that are related to long-term memory storage. This study was designed to provide information, for the first time, about the distribution and number of neurons expressing parvalbumin-immunoreactivity (PV-I) in the subregions of the hippocampal formation in Cebus apella, a New World primate species commonly used in biomedical research. Our results revealed that for several morphometric variables, PV-I cells differ significantly among the subregions CA1, CA2, CA3, and the hilus. Based upon our findings and those of other studies, we hypothesize that the proportional increase from monkeys to humans in PV-I cell density within CA1 is a factor contributing to the evolution of increased memory formation and storage.

Evolutionary history of the PER3 variable number of tandem repeats (VNTR): idiosyncratic aspect of primate molecular circadian clock.

The PER3 gene is one of the clock genes, which function in the core mammalian molecular circadian system. A variable number of tandem repeats (VNTR) locus in the 18th exon of this gene has been strongly associated to circadian rhythm phenotypes and sleep organization in humans, but it has not been identified in other mammals except primates. To better understand the evolution and the placement of the PER3 VNTR in a phylogenetical context, the present study enlarges the investigation about the presence and the structure of this variable region in a large sample of primate species and other mammals. The analysis of the results has revealed that the PER3 VNTR occurs exclusively in simiiforme primates and that the number of copies of the primitive unit ranges from 2 to 11 across different primate species. Two transposable elements surrounding the 18th exon of PER3 were found in primates with published genome sequences, including the tarsiiforme Tarsius syrichta, which lacks the VNTR. These results suggest that this VNTR may have evolved in a common ancestor of the simiiforme branch and that the evolutionary copy number differentiation of this VNTR may be associated with primate simiiformes sleep and circadian phenotype patterns.

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.

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.

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.

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 Ammon's 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.