Differential Structure of Hippocampal CA1 Pyramidal Neurons in the Human and Mouse.

Pyramidal neurons are the most common cell type and are considered the main output neuron in most mammalian forebrain structures. In terms of function, differences in the structure of the dendrites of these neurons appear to be crucial in determining how neurons integrate information. To further shed light on the structure of the human pyramidal neurons we investigated the geometry of pyramidal cells in the human and mouse CA1 region-one of the most evolutionary conserved archicortical regions, which is critically involved in the formation, consolidation, and retrieval of memory. We aimed to assess to what extent neurons corresponding to a homologous region in different species have parallel morphologies. Over 100 intracellularly injected and 3D-reconstructed cells across both species revealed that dendritic and axonal morphologies of human cells are not only larger but also have structural differences, when compared to mouse. The results show that human CA1 pyramidal cells are not a stretched version of mouse CA1 cells. These results indicate that there are some morphological parameters of the pyramidal cells that are conserved, whereas others are species-specific.

Metabolomic Study of Hibernating Syrian Hamster Brains: In Search of Neuroprotective Agents.

Syrian hamsters undergo a reversible hyperphosphorylation of protein τ during hibernation, providing a unique natural model that may unveil the physiological mechanisms behind this critical process involved in the development of Alzheimer's disease and other tauopathies. The hibernation cycle of these animals fluctuates between a pair of stages: 3-4 days of torpor bouts interspersed with periods of euthermia called arousals that last several hours. In this study, we investigated for the first time the metabolic changes in brain tissue during hibernation. A total of 337 metabolites showed statistically significant differences during hibernation. Based on these metabolites, several pathways were found to be significantly regulated and, therefore, play a key role in the regulation of hibernation processes. The increase in the levels of ceramides containing more than 20 C atoms was found in torpor animals, reflecting a higher activity of CerS2 during hibernation, linked to neurofibrillary tangle generation and structural changes in the Golgi apparatus. Our results open up the debate about the possible significance of some metabolites during hibernation, which may possibly be related to τ phosphorylation and dephosphorylation events. In general, this study may provide insights into novel neuroprotective agents because the alterations described throughout the hibernation process are reversible.

Evaluation of the Safety and Efficacy of the Therapeutic Potential of Adipose-Derived Stem Cells Injected in the Cerebral Ischemic Penumbra.

INTRODUCTION: Stroke represents an attractive target for cell therapy. Although different types of cells have been employed in animal models with variable results, the human adipose-derived stem cells (hASCs) have demonstrated favorable characteristics in the treatment of diseases with inflammatory substrate, but experience in their intracerebral administration is lacking. The purpose of this study is to evaluate the effect and safety of the intracerebral application of hASCs in a stroke model. METHODS: A first group of Athymic Nude mice after stroke received a stereotactic injection of hASCs at a concentration of 4 × 104/µL at the penumbra area, a second group without stroke received the same cell concentration, and a third group had only stroke and no cells. After 7, 15, and 30 days, the animals underwent fluorodeoxyglucose-positron emission tomography and magnetic resonance imaging; subsequently, they were sacrificed for histological evaluation (HuNu, GFAP, IBA-1, Ki67, DCX) of the penumbra area and ipsilateral subventricular zone (iSVZ). RESULTS: The in vitro studies found no alterations in the molecular karyotype, clonogenic capacity, and expression of 62 kDa transcription factor and telomerase. Animals implanted with cells showed no adverse events. The implanted cells showed no evidence of proliferation or differentiation. However, there was an increase of capillaries, less astrocytes and microglia, and increased bromodeoxyuridine and doublecortin-positive cells in the iSVZ and in the vicinity of ischemic injury. CONCLUSIONS: These results suggest that hASCs in the implanted dose modulate inflammation, promote endogenous neurogenesis, and do not proliferate or migrate in the brain. These data confirm the safety of cell therapy with hASCs.

Changes in tau phosphorylation in hibernating rodents.

Tau is a cytoskeletal protein present mainly in the neurons of vertebrates. By comparing the sequence of tau molecule among different vertebrates, it was found that the variability of the N-terminal sequence in tau protein is higher than that of the C-terminal region. The N-terminal region is involved mainly in the binding of tau to cellular membranes, whereas the C-terminal region of the tau molecule contains the microtubule-binding sites. We have compared the sequence of Syrian hamster tau with the sequences of other hibernating and nonhibernating rodents and investigated how differences in the N-terminal region of tau could affect the phosphorylation level and tau binding to cell membranes. We also describe a change, in tau phosphorylation, on a casein kinase 1 (ck1)-dependent site that is found only in hibernating rodents. This ck1 site seems to play an important role in the regulation of tau binding to membranes.

Pyramidal cell axon initial segment in Alzheimer´s disease.

The axon initial segment (AIS) is a region of the neuron that is critical for action potential generation as well as for the regulation of neural activity. This specialized structure-characterized by the expression of different types of ion channels as well as adhesion, scaffolding and cytoskeleton proteins-is subjected to morpho-functional plastic changes in length and position upon variations in neural activity or in pathological conditions. In the present study, using immunocytochemistry with the AT8 antibody (phospho-tau S202/T205) and 3D confocal microscopy reconstruction techniques in brain tissue from Alzheimer's disease patients, we found that around half of the cortical pyramidal neurons with hyperphosphorylated tau showed changes in AIS length and position in comparison with AT8-negative neurons from the same cortical layers. We observed a wide variety of AIS alterations in neurons with hyperphosphorylated tau, although the most common changes were a proximal shift or a lengthening of the AISs. Similar results were found in neocortical tissue from non-demented cases with neurons containing hyperphosphorylated tau. These findings support the notion that the accumulation of phospho-tau is associated with structural alterations of the AIS that are likely to have an impact on normal neuronal activity, which might contribute to neuronal dysfunction in AD.

Hypothalamic orexinergic neuron changes during the hibernation of the Syrian hamster.

Hibernation in small mammals is a highly regulated process with periods of torpor involving drops in body temperature and metabolic rate, as well as a general decrease in neural activity, all of which proceed alongside complex brain adaptive changes that appear to protect the brain from extreme hypoxia and low temperatures. All these changes are rapidly reversed, with no apparent brain damage occurring, during the short periods of arousal, interspersed during torpor-characterized by transitory and partial rewarming and activity, including sleep activation, and feeding in some species. The orexins are neuropeptides synthesized in hypothalamic neurons that project to multiple brain regions and are known to participate in the regulation of a variety of processes including feeding behavior, the sleep-wake cycle, and autonomic functions such as brown adipose tissue thermogenesis. Using multiple immunohistochemical techniques and quantitative analysis, we have characterized the orexinergic system in the brain of the Syrian hamster-a facultative hibernator. Our results revealed that orexinergic neurons in this species consisted of a neuronal population restricted to the lateral hypothalamic area, whereas orexinergic fibers distribute throughout the rostrocaudal extent of the brain, particularly innervating catecholaminergic and serotonergic neuronal populations. We characterized the changes of orexinergic cells in the different phases of hibernation based on the intensity of immunostaining for the neuronal activity marker C-Fos and orexin A (OXA). During torpor, we found an increase in C-Fos immunostaining intensity in orexinergic neurons, accompanied by a decrease in OXA immunostaining. These changes were accompanied by a volume reduction and a fragmentation of the Golgi apparatus (GA) as well as a decrease in the colocalization of OXA and the GA marker GM-130. Importantly, during arousal, C-Fos and OXA expression in orexinergic neurons was highest and the structural appearance and the volume of the GA along with the colocalization of OXA/GM-130 reverted to euthermic levels. We discuss the involvement of orexinergic cells in the regulation of mammalian hibernation and, in particular, the possibility that the high activation of orexinergic cells during the arousal stage guides the rewarming as well as the feeding and sleep behaviors characteristic of this phase.

Effect of Phosphorylated Tau on Cortical Pyramidal Neuron Morphology during Hibernation.

The dendritic spines of pyramidal cells are the main postsynaptic target of excitatory glutamatergic synapses. Morphological alterations have been described in hippocampal dendritic spines during hibernation-a state of inactivity and metabolic depression that occurs via a transient neuronal tau hyperphosphorylation. Here, we have used the hibernating Syrian hamster to investigate the effect of hyperphosphorylated tau regarding neocortical neuronal structure. In particular, we examined layer Va pyramidal neurons. Our results indicate that hibernation does not promote significant changes in dendritic spine density. However, tau hyperphosphorylated neurons show a decrease in complexity, an increase in the tortuosity of the apical dendrites, and an increase in the diameter of the basal dendrites. Tau protein hyperphosphorylation and aggregation have been associated with loss or alterations of dendritic spines in neurodegenerative diseases, such as Alzheimer's disease (AD). Our results may shed light on the correlation between tau hyperphosphorylation and the neuropathological processes in AD. Moreover, we observed changes in the length and area of the apical and basal dendritic spines during hibernation regardless of tau hyperphosphorylation. The morphological changes observed here also suggest region specificity, opening up debate about a possible relationship with the differential brain activity registered in these regions in previous studies.

The Golgi Apparatus of Neocortical Glial Cells During Hibernation in the Syrian Hamster.

Hibernating mammals undergo torpor periods characterized by a general decrease in body temperature, metabolic rate, and brain activity accompanied by complex adaptive brain changes that appear to protect the brain from extreme conditions of hypoxia and low temperatures. These processes are accompanied by morphological and neurochemical changes in the brain including those in cortical neurons such as the fragmentation and reduction of the Golgi apparatus (GA), which both reverse a few hours after arousal from the torpor state. In the present study, we characterized - by immunofluorescence and confocal microscopy - the GA of cortical astrocytes, oligodendrocytes, and microglial cells in the Syrian hamster, which is a facultative hibernator. We also show that after artificial induction of hibernation, in addition to neurons, the GA of glia in the Syrian hamster undergoes important structural changes, as well as modifications in the intensity of immunostaining and distribution patterns of Golgi structural proteins at different stages of the hibernation cycle.

Phospho-Tau Changes in the Human CA1 During Alzheimer's Disease Progression.

Despite extensive studies regarding tau phosphorylation progression in both human Alzheimer's disease cases and animal models, the molecular and structural changes responsible for neurofibrillary tangle development are still not well understood. Here, by using the antibodies AT100 (recognizes tau protein phosphorylated at Thr212 and Ser214 in the proline-rich region) and pS396 (recognizes tau protein phosphorylated at serine residue 396 in the C-terminal region), we examined phospho-tau immunostaining in neurons from the hippocampal CA1 region of 21 human cases with tau pathology ranging from Braak stage I to VI. Our results indicate that the AT100/pS396 ratio decreases in CA1 in accordance with the severity of the disease, along with its colocalization. We therefore propose the AT100/pS396 ratio as a new tool to analyze the tau pathology progression. Our findings also suggest a conformational modification in tau protein that may cause the disappearance of the AT100 epitope in the late stages of tau pathology, which may play a role in the toxic tangle aggregation. Thus, this study provides new insights underlying the stages for the formation of neurofibrillary tangles in Alzheimer's disease.

Biohybrids of scaffolding hyaluronic acid biomaterials plus adipose stem cells home local neural stem and endothelial cells: Implications for reconstruction of brain lesions after stroke.

Endogenous neurogenesis in stroke is insufficient to replace the lost brain tissue, largely due to the lack of a proper biological structure to let new cells dwell in the damaged area. We hypothesized that scaffolds made of hyaluronic acid (HA) biomaterials (BM) could provide a suitable environment to home not only new neurons, but also vessels, glia and neurofilaments. Further, the addition of exogenous cells, such as adipose stem cells (ASC) could increase this effect. Athymic mice were randomly assigned to a one of four group: stroke alone, stroke and implantation of BM, stroke and implantation of BM with ASC, and sham operated animals. Stroke model consisted of middle cerebral artery thrombosis with FeCl3 . After 30 days, animals underwent magnetic resonance imaging (MRI) and were sacrificed. Proliferation and neurogenesis increased at the subventricular zone ipsilateral to the ventricle and neuroblasts, glial, and endothelial cells forming capillaries were seen inside the BM. Those effects increased when ASC were added, while there was less inflammatory reaction. Three-dimensional scaffolds made of HA are able to home newly formed neurons, glia, and endothelial cells permitting the growth neurofilaments inside them. The addition of ASC increase these effects and decrease the inflammatory reaction to the implant. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1598-1606, 2019.