Oscillating gradient diffusion kurtosis imaging of normal and injured mouse brains

Recent advances in diffusion MRI employ multiple diffusion encoding schemes with varying diffusion direction, weighting, and diffusion time to investigate specific microstructural properties in biological tissues. In this study, we examined time‐dependent diffusion kurtosis contrast in adult mouse brains and in neonatal mouse brains after hypoxic–ischemic (HI) injury. In vivo diffusion kurtosis maps were acquired with a short diffusion time using an oscillating gradient spin echo (OGSE) sequence at 100 Hz and with a relatively long diffusion time (20 ms) using a pulsed gradient spin echo (PGSE) sequence. In the adult mouse brain, we found that the cortex and hippocampus showed larger differences between OGSE kurtosis and PGSE kurtosis than major white matter tracts. In neonatal mouse brains with unilateral HI injury, the OGSE kurtosis map overall provided stronger edema contrast than the PGSE kurtosis map, and the differences between OGSE and PGSE kurtosis measurements in the edema region reflected heterogeneity of injury. This is the first in vivo study that has demonstrated multi‐direction OGSE kurtosis contrasts in the mouse brain. Comparing PGSE and OGSE kurtosis measures may provide additional information on microstructural changes after ischemic stroke.     

Metaplastic Regulation of the Median Raphe Nucleus via Serotonin 5-HT1A Receptor on Hippocampal Synaptic Plasticity Is Associated With Gender-Specific Emotional Expression in Rats

Gender differences in psychiatric disorders are considered to be associated with the serotonergic (5-HTergic) system; however the underlying mechanisms have not been clearly elucidated. In this study, possible involvement of the median raphe nucleus (MRN)-hippocampus 5-HTergic system in gender-specific emotional regulation was investigated, focusing on synaptic plasticity in rats. A behavioral study using a contextual fear conditioning (CFC) paradigm showed that the females exhibited low anxiety-like behavior. Extracellular 5-HT levels in the hippocampus were increased by CFC only in the males. Long-term potentiation (LTP) in the hippocampal CA1 field was suppressed after CFC in the males, which was mimicked by the synaptic response to MRN electrical stimulation. In the MRN, 5-HT immunoreactive cells significantly increased in the females compared with those in the males. Pretreatment with the 5-HT_1A receptor agonists tandospirone (10 mg/kg, i.p.) and 8-OH DPAT (3 mg/kg, i.p.) significantly suppressed LTP induction in the males. Synaptic responses to CFC and 5-HT_1A receptor interventions were not observed in the females. These results suggest that the metaplastic 5-HTergic mechanism via 5-HT_1A receptors in the MRN-hippocampus pathway is a key component for gender-specific emotional regulation and may be a cause of psychiatric disorders associated with vulnerability or resistance to emotional stress.     

Hippocampal Volumes in Juvenile Neuronal Ceroid Lipofuscinosis: A Longitudinal Magnetic Resonance Imaging Study

BackgroundJuvenile neuronal ceroid lipofuscinosis is an inherited, autosomal recessive, progressive, neurodegenerative disorder of childhood. It belongs to the lysosomal storage diseases, which manifest with loss of vision, seizures, and loss of cognitive and motor functions, and lead to premature death. Imaging studies have shown cerebral and cerebellar atrophy, yet no previous studies evaluating particularly hippocampal atrophy have been published. This study evaluates the hippocampal volumes in adolescent juvenile neuronal ceroid lipofuscinosis patients in a controlled 5-year follow-up magnetic resonance imaging study.MethodsHippocampal volumes of eight patients (three female, five male) and 10 healthy age- and sex-matched control subjects were measured from two repeated magnetic resonance imaging examinations. Three male patients did not have controls and were excluded from the statistics. In the patient group, the first examination was performed at the mean age of 12.2 years and the second examination at the mean age of 17.3 years. In the control group, the mean ages at the time of examinations were 12.5 years and 19.3 years.ResultsProgressive hippocampal atrophy was found in the patient group. The mean total hippocampal volume decreased by 0.85 cm³ during the 5-year follow-up in the patient group, which corresponds to a 3.3% annual rate of volume loss. The whole brain volume decreased by 2.9% per year. The observed annual rate of hippocampal atrophy also exceeded the previously reported 2.4% annual loss of total gray matter volume in juvenile neuronal ceroid lipofuscinosis patients.ConclusionsThese data suggest that progressive hippocampal atrophy is one of the characteristic features of brain atrophy in juvenile neuronal ceroid lipofuscinosis in adolescence.     

Susceptibility to interference and intrusion errors in consequence of the dominant hemisphere’s hippocampal infarct: A case report

We present a case of a man with an ischemic lesion of the left hippocampus. Detailed neuropsychological assessment revealed susceptibility to retroactive interference and a tendency to make intrusion errors in addition to mild deficits in the verbal memory processes. Although retroactive interference and intrusion errors are normally considered to be the manifestations of frontal lobe dysfunctions, the idea of susceptibility to interference has recently begun to emerge in the literature, as an explanation of medial temporal lobe amnesia. Our data support this new theory, suggesting that one role of the hippocampus is to decrease the interference during the learning processes.     

mBDNF/Akt/CREB和proBDNF/RhoA信号传导失衡在丙泊酚致新生鼠认知功能障碍的作用

目的探讨m BDNF/Akt/CREB和pro BDNF/Rho A信号传导失衡在丙泊酚致新生鼠认知功能障碍的作用。方法新生7 d大鼠随机分为6组(每组n=12):C组连续7 d腹腔注射0.9%氯化钠溶液;P1组注射0.9%氯化钠溶液6d后,第7天注射丙泊酚;P2组连续7 d注射丙泊酚;T、K及D组连续7 d注射丙泊酚后,第7天再分别注射TATPep5、K252a与DMSO。各组随机抽取6只大鼠进行血糖血气的监测,其余大鼠喂养至第25天进行Morris水迷宫实验,测试空间学习记忆能力。取海马组织,通过Western blot检测m BDNF/Akt/CREB及pro BDNF/Rho A信号通路的表达。结果与C组比较,P1组与P2组大鼠幼年期逃逸潜伏期延长,空间探索时间缩短(P0.05),且P2组改变更为显著。与D组比较,K组大鼠幼年期逃逸潜伏期延长,空间探索时间缩短(P0.05);T组大鼠幼年期逃逸潜伏期缩短,空间探索时间延长(P0.05)。与C组比较,P1组与P2组海马m BDNF/Akt/CREB表达下调(P0.05),且P2组下调更为显著;P1组与P2组海马pro BDNF/Rho A表达上调(P0.05),且P2组上调更为显著。与D组比较,K组海马Akt/CREB下调(P0.05),T组海马Rho A下调(P0.05)。结论丙泊酚导致新生大鼠幼年期学习记忆功能障碍与m BDNF/Akt/CREB抗凋亡信号通路抑制,pro BDNF/Rho A促凋亡信号通路增强有关。     

Heterogeneity of Age-Related Neural Hyperactivity along the CA3 Transverse Axis

Age-related memory deficits are correlated with neural hyperactivity in the CA3 region of the hippocampus. Abnormal CA3 hyperactivity in aged rats has been proposed to contribute to an imbalance between pattern separation and pattern completion, resulting in overly rigid representations. Recent evidence of functional heterogeneity along the CA3 transverse axis suggests that proximal CA3 supports pattern separation while distal CA3 supports pattern completion. It is not known whether age-related CA3 hyperactivity is uniformly represented along the CA3 transverse axis. We examined the firing rates of CA3 neurons from young and aged, male, Long–Evans rats along the CA3 transverse axis. Consistent with prior studies, young CA3 cells showed an increasing gradient in mean firing rate from proximal to distal CA3. However, aged CA3 cells showed an opposite, decreasing trend, in that CA3 cells in aged rats were hyperactive in proximal CA3, but possibly hypoactive in distal CA3, compared with young (Y) rats. We suggest that, in combination with altered inputs from the entorhinal cortex and dentate gyrus (DG), the proximal CA3 region of aged rats may switch from its normal function that reflects the pattern separation output of the DG and instead performs a computation that reflects an abnormal bias toward pattern completion. In parallel, distal CA3 of aged rats may create weaker attractor basins that promote abnormal, bistable representations under certain conditions.SIGNIFICANCE STATEMENT Prior work suggested that age-related CA3 hyperactivity enhances pattern completion, resulting in rigid representations. Implicit in prior studies is the notion that hyperactivity is present throughout a functionally homogeneous CA3 network. However, more recent work has demonstrated functional heterogeneity along the CA3 transverse axis, in that proximal CA3 is involved in pattern separation and distal CA3 is involved in pattern completion. Here, we show that age-related hyperactivity is present only in proximal CA3, with potential hypoactivity in distal CA3. This result provides new insight in the role of CA3 in age-related memory impairments, suggesting that the rigid representations in aging result primarily from dysfunction of computational circuits involving the dentate gyrus (DG) and proximal CA3.     

Protein Content and Methyl Donors in Maternal Diet Interact to Influence the Proliferation Rate and Cell Fate of Neural Stem Cells in Rat Hippocampus

Maternal diet during pregnancy and early postnatal life influences the setting up of normal physiological functions in the offspring. Epigenetic mechanisms regulate cell differentiation during embryonic development and may mediate gene/environment interactions. We showed here that high methyl donors associated with normal protein content in maternal diet increased the in vitro proliferation rate of neural stem/progenitor cells isolated from rat E19 fetuses. Gene expression on whole hippocampi at weaning confirmed this effect as evidenced by the higher expression of the Nestin and Igf2 genes, suggesting a higher amount of undifferentiated precursor cells. Additionally, protein restriction reduced the expression of the insulin receptor gene, which is essential to the action of IGFII. Inhibition of DNA methylation in neural stem/progenitor cells in vitro increased the expression of the astrocyte-specific Gfap gene and decreased the expression of the neuron-specific Dcx gene, suggesting an impact on cell differentiation. Our data suggest a complex interaction between methyl donors and protein content in maternal diet that influence the expression of major growth factors and their receptors and therefore impact the proliferation and differentiation capacities of neural stem cells, either through external hormone signals or internal genomic regulation.