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Mechanisms of seasonal changes of brain size in Sorex shrews (Dehnel’s effect) remain largely unknown. Hypothesis postulating changes of brain cell numbers has been recently rejected (Bartkowska et al. 2008). Other possible mechanisms are reorganisation of the neuropil and change in the composition of brain tissue (e.g. dehydration). Shrews were captured in the spring, summer and autumn. Some shrews collected in the autumn wintered in captivity. Volumes of selected forebrain structures were measured stereologically on Nissl stained series of sections. Largest oscillations were found in the volume of cortex and basal ganglia. Lack of correlation between the rate of neurogenesis and the volume of hippocampus confi rms previous fi ndings. Relative quantity of myelin was determined by densitometry of sections stained with the method of Gallyas. Volumes of neocortex and hippocampus that are myelinised to a similar degree change differently, while volumes of striatum and neocortex, differing in myelin density, reduce their volumes similarly in the winter. Moreover, the overall ratio of forebrain volume to myelin quantity did not change throughout life. This implies that general dehydration may be excluded as a signifi - cant reason of brain size alterations and that different mechanisms are engaged in various brain structures. The comparison of analysed structures in terms of connectivity and water permeability by measuring levels of synaptophysin and aquaporin 4 was attempted.
Neurotrophins belonging to the class of growth factors and including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4/5 (NT-4/5) are widely recognized as essential factors in the developing central nervous system (CNS). Neurotrophins are synthesized as precursor forms (proneurotrophins). Mature forms of neurotrophins exert their effect by binding to specific tyrosine kinases receptors (TrkA, TrkB and TrkC) as well as via the p75 receptor, a member of the tumor necrosis factor receptor superfamily while proneurotrophins interact with the receptor p75 or co-receptor complex of p75 and sortilin, that is a Vps10p domain-containing transmembrane protein. Expression of neurotrophins corresponds with the onset of neurogenesis in developing mammalian species. BDNF is low in early embryonic stages of development, while NT-3 highly expresses in the developing CNS. Expression of neurotrophins receptors mainly overlaps at early development. Data concerning early distribution of neurotrophins and their receptors in the nervous system and results in mice with targeted disruptions of neurotrophin or receptor genes show that neurotrophins and their receptors play distinct roles in control and regulation of the most crucial developmental processes such as proliferation, migration, differentiation, survival, apoptosis and synaptic plasticity.
Neurotrophins are important regulators of neuronal function in the developing and adult brain. We studied expression of TrkB receptors in the postnatally (P) developing brain of the opossum (Monodelphis domestica). The Western blot analysis showed presence of the full-length catalytical isoform of TrkB and three truncated kinase-lacking isoforms in the opossum brain. Expression of the fulllength TrkB receptor was present in the newborn opossum, whereas truncated forms of TrkB receptors were almost undetectable at this period. The level of the full-length TrkB protein gradually increased with a developing opossum brain, reaching maximum at P12–20. The highest levels of expression of the full-length TrkB correspond to the time of cortical layers generation. The level of truncated TrkB rapidly increased at P20 and started to dominate since P35 (when opossums open eyes). Immunohistochemical staining for TrkB receptors showed that the majority of labeled neurons were placed in the olfactory bulb, cerebral cortex, hippocampus, thalamus, hypothalamus, cerebellum and various brainstem structures. Interestingly, TrkB receptors were predominantly expressed in neurons. Lack of TrkB receptors in glial cells, especially astrocytes and oligodendrocytes, provides the evidence that TrkB receptors can play functionally different role in marsupials than in eutherians. Supported by the NSC grant No 2011/01/B/NZ4/01575.
INTRODUCTION: The grey short-tailed opossum, Monodelphis domestica is a laboratory animal useful in developmental research due to its slow and mostly postnatal growth. Little is known about marsupials brain development. AIM(S): The aim of the study was to investigate cerebellum development in the Monodelphis opossum. METHOD(S): We performed Nissl staining on the brain sectionsfrom opossumsin different age to see the overall pattern of cerebellum development. To find out when progenitor cells are present in this structure, we performed bromodeoxyuridine (BrdU) intraperitoneal injections in different time points. Phenotype of proliferating cells wasidentified by double immunofluorescence staining for a neuronal marker, NeuN or an astrocyte marker, GFAP and BrdU. RESULTS: We found that in the newborn Monodelphis opossum cerebellum is not yet morphologically formed. Immunostainig of BrdU-positive cells showed that Purkinje cells were generated between postnatal day (P) 1–5, whereas the highest rate of granule cells generation occurred between P11–P40. Double immunostaining revealed that the majority of BrdU-positive cells in the opossum cerebellum generated from P11 to P50 was neurons, as they showed colocalization with NeuN immunoreactivity. CONCLUSIONS: Our study shows that cerebellum development in the opossum is longer and more extended in time than in rodents. FINANCIAL SUPPORT: The work was supported by the National Science Center grant 2015/17/B/NZ4/02410.
INTRODUCTION: All mammals have the six-layered brain neocortex and neurons of upper layers (III/II) forming interhemispheric connections link the two cerebral hemispheres. In marsupials the interhemispheric connections of the neocortex pass via the anterior commissure, ed to show dramatically reduced number of actively proliferating cells in SGZ, however, molecular and cellular mechanisms of proliferation deficiency in the SVZ still need to be characterized. AIM(S): In our study, we investigated the role of cyclin D2 in SVZ neural progenitors proliferation activity, migration of neuroblasts and their differentiation to olfactory bulb interneurons. METHOD(S): In order to assess in details proliferation activity, wildtype (WT) and cyclin D2-knockout (cD2-KO) mice were injected with EdU, a thymidine analogue, and analyzed together with endogenous proliferation marker Ki67, enabling quantification of cells at different cell cycle stages. RESULTS: We observed a significant reduction in the number of EdU(+) and/or Ki67(+) progenitors along anterior-posterior and dorsal-ventral axis of the SVZ. We also revealed differences in expression of transcription factors between cD2-WT and cD2-KO mice, bearing in mind SVZ mosaic organization and that certain SVZ domains produce certain subpopulations of interneurons. CONCLUSIONS: Understanding of the mechanisms governing adult neurogenesis at the cellular and molecular level may lead towards cell-based therapies in neurodegenerative diseases or after brain injuries. FINANCIAL SUPPORT: Supported by the National Science Center (NCN) grant no UMO-2012/07/B/ NZ4/01733 and partially by the National Center for Research and Development (NCBiR) grant Strategmed Regennova (235077/9/ NCBR/2014).
We studied consequences of maternal immune response on the course of pregnancy and the behavior of adult offspring. Mice in late gestation (day 16-17) were injected with lipopolysaccharide (LPS). Treatment of pregnant mice with high doses of LPS resulted in fetal resorption or stillbirths. Pregnant mice treated with low doses (100 or 300 ^g/kg) of LPS gave birth to normal numbers of pups. However, behavior of the offspring was altered. Adult offspring of dams injected at a dose of 300 ^g/kg of LPS traveled longer distances in the open field and spent more time in the central part of the arena, than mice in the control group. Female mice of this group spent more time in open arms of the elevated plus maze, in comparison to female control mice. Results of the Morris water maze test showed impairment of spatial learning and memory in male offspring born to LPS-injected dams. Furthermore, in the nest building test adult mice born from LPS challenged pregnancies constructed worse quality nests, which points to the presence of hippocampal dysfunction. These findings indicate that maternal bacterial infections during pregnancy may alter offspring behavior in adult life.
INTRODUCTION: Adult hippocampal neurogenesis occurs in many mammalian species, including the laboratory opossum (Monodelphis domestica). Newborn neurons in the dentate gyrus (DG) of the hippocampal formation are involved in learning and spatial memory.The rate of neurogenesis decreases with aging, which was suggested as the cause of the deterioration of cognitive functions. AIM(S): The aim of the study was to examine association between adult neurogenesis in the DG and spatial memory in young and aged opossums METHOD(S): To understand whether new neurons contribute to learning and memory, we performed experiments on young and aged laboratory opossums using the Morris water maze test in which animals learn to locate the hidden platform. After behavioral test, sections from opossum brains were immunostained with doublecortin – a marker of newly born neurons – to investigate the rate of adult neurogenesis in the DG. RESULTS: In the group of young opossums, the time required to find the hidden platform was already significantly lower on the third day of training (vs. day 1, p<0.005), while in aged opossums a significant difference was observed on the fourth day of training (vs. day 1, p<0.02). The level of neurogenesis in the DG of the hippocampal formation was lower in the aged opossums than in the young animals. CONCLUSIONS: However, even the low number of newly formed neurons in the DG of aged opossums are likely to be involved in the formation of spatial memory. FINANCIAL SUPPORT: This research was supported by the National Science Centre Poland, grant number 2015/17/B/NZ4/02410.
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