Embryonic Development and Postnatal Changes in Free d-Aspartate and d-Serine in the Human Prefrontal Cortex

Abstract: We have analyzed free chiral amino acids (aspartate and serine) in the human frontal cortex at different ontogenic stages (from 14 weeks of gestation to 101 years of age) by HPLC with fluorometric detection after derivatization with N-tert -butyl-oxycarbonyl- l -cysteine and o -phthaldialdehyde. Exceptionally high levels of free d -aspartate and d -serine were demonstrated in the fetal cortex at gestational week 14. The ratios of d -aspartate and of d -serine to the total corresponding amino acids were also high, at 0.63 and 0.27, respectively. The concentration of d -aspartate dramatically decreased to a trace level by gestational week 41 and then remained very low during all postnatal stages. In contrast, the frontal tip contained persistently high levels of d -serine throughout embryonic and postnatal life, whereas the d -amino acid content in adolescents and aged individuals was about half of that in the fetuses. Because d -aspartate and d -serine are known to have selective actions at the NMDA-type excitatory amino acid receptor, the present data suggest that these d -amino acids might play a pivotal role in cerebral development and functions that are related to the NMDA receptor.     

Influence of liposome charge and composition on their interaction with human blood serum proteins

The roles of sulfhydryl and disulfide groups in the specific binding of synthetic cannabinoid CP-55,940 to the cannabinoid receptor in membrane preparations from the rat cerebral cortex have been examined. Various sulfhydryl blocking reagents including p-chloromercuribenzoic acid (p-CMB), N-ethylmaleimide (NEM), o-iodosobenzoic acid (o-ISB), and methyl methanethiosulfonate (MMTS) inhibited the specific binding of [³H]CP-55,940 to the cannabinoid receptor in a dose-dependent manner. About 80–95% inhibition was obtained at a 0.1 mM concentration of these reagents. Scatchard analysis of saturation experiments indicates that most of these sulfhydryl modifying reagents reduce both the binding affinity (K_d) and capacity (B_max). On the other hand, DL-dithiothreitol (DTT), a disulfide reducing agent, also irreversibly inhibited the specific binding of [³H]CP-55,940 to the receptor and about 50% inhibition was obtained at a 5 mM concentration. Furthermore, 5mM DTT was abelt to dissociate 50% of the bound ligand from the ligand-receptor complex. The marked inhibition of [³H]CP-55,940 binding by sulfhydryl reagents suggests that at least one free sulfhydryl group is essential to the binding of the ligand to the receptor. In addition, the inhibition of the binding by DTT implies that besides free sulfhydryl group(s), the integrity of a disulfide bridge is also important for [³H]CP-55,940 binding to the cannabinoid receptor.     

恒河猴、懒猴和树鼩的短时空间记忆功能与前额叶背侧部进化水平的相关性(英文)

本文研究探讨了进化地位不同的三种动物的短时空间记忆功能及其与前额叶背侧部进化水平的相关性。结果表明,在延缓反应作业中,经1000次训练后,7只恒河猴对空间位置的记忆时间平均为7.7±3.2min,懒猴为3.8±0.44min,而树鼩即使在延缓时间几乎为零秒的延缓反应中,其正确反应率也未达到90％标准。一种延缓时间仅测试一个单元,即不经训练的实验表明,恒河猴在延缓期为“0”—5min的各测试单元中,正确反应率稳定在80％以上;懒猴在延缓时间为“0”—4min的各测试单元中,平均正确反应率与恒河猴无明显差异,而当延缓时间增加到5min时,在延缓反应作业中取得的成绩显著下降;树鼩在延缓时间为1—5min的作业中取得的正确反应率在70％以下。3种动物在视觉辨别学习作业中却无明显差异。形态学研究表明,灵长类大脑前额叶的面积和结构的复杂性在进化过程中逐渐增大,如恒河猴大脑前额叶的表面积占大脑半球表面积的11.5％(Brodmann,1929),其内颗粒层发达,背侧部明显凸起,主沟区发达;懒猴的前额叶表面积占其大脑半球表面积的8.3％,背侧部凸起不显著,主沟未形成,额极内颗粒层分化明显,背侧部的内颗粒层较内侧部的发达程度差(Sanides,1967);树鼩的前额叶表面积占7.5％,额极的内颗粒层分化不明显,为非颗粒化区,此区之后为颗粒区     

Regional differences in glutaminase activation by phosphate and calcium in rat brain: Impairment in aged rats and implications for regional glutaminase isozymes

Regional regulation of glutaminase by phosphate and calcium was examined in the temporal cortex (TCX), striatum (STR) and hippocampus (HIPP) from adult and aged male F344 rats. Phosphate-dependent glutaminase activity in adult rats was significantly lower (35–43%) in the HIPP (100 and 150 mM) and STR (150 mM) compared to PAG activity in the TCX. Phosphate activation in aged rats was 50–60% lower in the HIPP at concentrations greater than 25 mM compared to the aged TCX or STR. PAG activity in the TCX and STR was unaffected by age, but was significantly reduced (30–50%) in the HIPP from aged rats at phosphate concentrations of 25 mM and greater when compared to adult rats. In adult rats at concentrations of CaCl₂ above 1 mM, PAG activity was significantly lower (60–75%) in the STR and HIPP when compared to the TCX. In aged rats, PAG activity (1 mM CaCl₂) in the HIPP was significantly less (50%) than STR PAG activity in aged rats. Diminished PAG activity was seen only in the TCX (2.5 mM; 32%), and the HIPP (0.5 mM; 25% and 1 mM; 38%) at higher calcium concentrations compared to adult. Phosphate-independent calcium activation of PAG occurred in the HIPP but not in either the TCX or the STR. Addition of phosphate resulted in a synergistic activation of PAG in the STR and TCX, but not in the HIPP. These findings suggest that PAG is regionally regulated by phosphate and calcium, and this regulation is impaired in aged rats. These data also support the hypothesis that isozymes of PAG exist with different regulatory properties.Abbreviation PAG Phosphate-activated glutaminase - L-glutamine amidohydrolase EC 3.5.1.2 - TCX temporal cortex - STR striatum - HIPP hippocampus - F344 Fischer-344 rat     

Effects of DSP-4 on monoamine and monoamine metabolite levels and on beta adrenoceptor binding kinetics in rat brain at different times after administration

Effects of DSP-4 on noradrenaline (NA), 3-methoxy-4-hydroxyphenyl glycol (MHPG), serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels and on beta adrenoceptor binding kinetics (Bmax and K_D) in rat hippocampus, cortex and hypothalamus were studied between 24 hours and 14 days after systemic administration. Beta adrenoceptor numbers in hippocampus and cortex, but not in hypothalamus, were significantly increased after DSP-4. No significant changes in K_D values were observed in hypothalamus, but significant increases in this parameter were measured in hippocampus and cortex. NA and MHPG levels were significantly decreased in all three brain regions, but MHPG/NA ratios were increased in hippocampus, decreased in cortex and unchanged in hypothalamus. Very prominent increases in 5-HIAA levels were observed in all three brain regions, but only at one day after DSP-4. The greatest increases in 5-HIAA levels occurred in the hippocampus, but this effect of DPS-4 appeared to be slightly diminished by pre-treatment with fluoxetine. In cortex and hippocampus 5-HT levels were slightly, but significantly decreased after DSP-4.     

Aspects of early postnatal development of cortical neurons that proceed independently of normally present extrinsic influences

To examine the contribution of local versus extrinsic influences on postnatal development of cortical neurons, we compared the maturation of deep (infragranular) layer neurons in isolated slices of neocortex grown in organotypic culture to a similar population of neurons developing in vivo. All slice cultures were prepared from sensorimotor cortices of newborn mice (P0) and neurons in these cultures were examined at daily intervals during the first 9 days in vitro (DIV). The maturational state of neurons developing in vivo over this same time period was assessed in acute slices prepared from animals of equivalent postnatal age, P1–P9. Electrophysiological recordings were obtained from neurons in both cultured and acute slices, using Lucifer yellow filled whole-cell recording electrodes, enabling subsequent morphometric analysis of the labeled cells. We report significant changes in both cellular morphology and electrical membrane properties of these deep layer cortical neurons during the frist week in culture. Morphological maturation over this time period was characterized by a two- to three-fold increase in cell body size and total process length, and an increase in dendritic complexity. In this same population of cells a three-fold decrease in input resistance and changes in the action potential waveform, including a two-fold decrease in the AP duration, also occur. The degree of morphological and electrophysiological differentiation of individual neurons was highly correlated across developmental ages, suggesting that the maturational state of a cell is reflected in both cellular morphology and intrinsic membrane properties. A remarkably similar pattern of neuronal maturation was observed in neurons in layers V, VI/SP examined in acute slices prepared from animals between P1–P9. Because our culture system preserves many aspects of the local cortical environment while eliminating normal extrinsic influences (including thalamic, brainstem, and callosal connections), our findings argue that this early phase of neuronal differentiation, including the rate and extent of dendritic growth and development of AP waveform, results from instructive and/or permissive local influences, and appears to proceed independently of the many normally present extrinsic factors. © 1993 John Wiley & Sons, Inc.     

Iron Regulation in the Developing Rat Brain: Effect of In Utero Ethanol Exposure

Abstract: Fetal alcohol syndrome produces defects that parallel abnormalities associated with early iron deficiency. Hence, we examined the effects of prenatal exposure to ethanol on iron, transferrin, and ferritin concentrations. The subjects were the offspring of pregnant rats fed an ethanol-containing diet (Et), pair-fed an isocaloric control diet (Ct), or fed chow and water. The amounts of iron, transferrin, and ferritin were assessed in three CNS regions (cerebral cortex, subcortical forebrain, and brain-stem). In all three segments of the control rats, iron, transferrin, and ferritin levels decreased during the first 2 postnatal weeks, reached a minimum during week 3, and then rose to adult levels. This pattern was delayed by ethanol treatment, e.g., the minimal concentrations in iron, transferrin, and ferritin in the Et-treated rats were achieved later (3 days, 7 days, and 2 weeks, respectively) than they were in the Ct-treated rats. Ethanol-induced alterations in iron homeostasis persisted into adulthood; iron concentration was reduced, transferrin concentration was unaffected, and ferritin concentration was increased. The net result was that the timely delivery and bioavailability of iron were compromised by ethanol exposure. The defects in iron regulation are permanent and may underlie ethanol-induced abnormalities in iron-dependent growth processes such as myelination.