The control of cell number during central nervous system development in flies and mice

Growth is confined within a size that is normal for each species, revealing that somehow an organism 'knows' when this size has been reached. Within a species, growth is also variable, but despite this, proportion and structure are maintained. Perhaps, the key element in the control of size is the control of cell number. Here we review current knowledge on the mechanisms controlling cell number in the nervous system of vertebrates and flies. During growth, clonal expansion is confined, the number of progeny cells is balanced through the control of cell survival and cell proliferation and excess cells are eliminated by apoptosis. Simultaneously, organ architecture emerges and as neurons become active they also influence growth. The interactive control of cell number provides developmental plasticity to nervous system development. Many findings are common between flies and mice, other aspects have been studied more in one organism than the other and there are also aspects that are unique to either organism. Although cell number control has long been studied in the nervous system, analogous mechanisms are likely to operate during the growth of other organs and organisms.     

Regulation of proliferation during central nervous system development

The retina is one of the best-characterized regions of the central nervous system (CNS) and has served as a model for many of the principles that now form the foundation for CNS development. In the past several years, a number of advances have been made in our understanding of the coordination of proliferation and cell fate specification during retinal development. In this review, we will draw on findings from studies of the retina and highlight similarities and differences in other regions in the CNS, namely the cerebellum and cortex. We will present a framework in which to pose challenges and outstanding questions for future studies on the coordination of proliferation and cell fate specification in the developing CNS.     

Fluctuations of acetylcholinesterase in the mouse spinal cord and in vivo sodium effect during the development of morphine tolerance,dependence, and withdrawal

Tolerance to and physical dependence on morphine were produced and assessed in Swiss inbred albino mice by giving morphine sulphate (s.c.) three times a day for a period of 15 days in an increasing dose of 10 mg/kg every 24 hours. Physical dependence was assessed taking naloxone induced jumping as well as weight loss during normal withdrawal into consideration. The effect of sodium ions in the potency of naloxone in antagonizing morphine's effect was also analyzed. The spinal cord was assayed for acetylcholinesterase employing both biochemical and histochemical parameters. It was found that the amount of the enzyme increased with the development of tolerance but the amount decreased as the animals became physically dependent. However, the values were significantly above the control. Administration of naloxone brought about a sudden and significant fall in the level of the enzyme. Normal withdrawal too was characterized by a weak activity of the enzyme. It has been found that sodium ions can influence naloxone antagonism in an in vivo system.     

Changes in ribonuclease activity during development of the mosquito, Aedes aegypti

In the mosquito Aedes aegypti, quantitative and qualitative changes have been detected in ribonuclease activity during development. Ribonuclease activity is particularly high in extracts from larvae, relative to that in extracts from pupae or adults. Larval extract is enriched for a ribonuclease that is heat-labile, has an alkaline pH optimum, and is extremely sensitive to the divalent cation, manganese. Extract from adult females is enriched for a heat-stable component that has an acidic pH optimum and is more active at 56 than at 30 degrees C. Throughout the vitellogenic cycle, no major changes in ribonuclease activity were detected in fat body extracts.     

Effect of chronic administration of lithium chloride on the development of dopamine receptor sensitivity during morphine withdrawal in rats

The morphine withdrawal syndrome was studied in male Wistar rats. Spontaneous aggressiveness, enhanced apomorphine aggressiveness, lowered pain threshold and decreased dopamine turnover were observed after withdrawal of 10-day treatment with the increasing doses of morphine (30-300 mg/kg). These changes attested to the increased sensitivity of dopamine receptors. Administration of morphine in conjunction with lithium chloride in a dose of 2 mekv/kg prevented the development of dopamine receptor hypersensitivity. Also, this method did not produce the increased spontaneous and apomorphine aggressiveness or the decreased dopamine turnover. Meanwhile the pain threshold remained lowered.     

Formation and specification of neurons during the development of the leech central nervous system

In the leech embryo, neurogenesis takes place within the context of a stereotyped cell lineage. The prospective germ layers are formed during the early cleavage divisions by the reorganization and segregation of circumscribed domains within the cytoplasm of the fertilized egg. The majority of central neurons arise from the ectoderm, and central neuroblasts are distributed throughout both the length and width of each ectodermal hemisegment. Much of the segmental ganglion arises from medial neuroblasts, but there are also lateral ectodermal neuroblasts and mesodermal neuroblasts that migrate into the nascent ganglion from peripheral sites of origin. Some of these migratory cells are committed to neurogenesis prior to reaching their central destination. In addition, the leech embryo exhibits a secondary phase of neurogenesis that is restricted to the two sex segment ganglia. Secondary neurogenesis requires that a mitogenic or trophic signal be conveyed from the peripherally located male sex organ to a particular set of centrally located neuroblasts, apparently via already differentiated central neurons that innervate the sex organ. The differential specification of neuronal phenotypes within the leech central nervous system occurs in multiple steps. Some aspects of a neuron's identity are already specified at the time of its terminal cell division and would seem to involve the lineal inheritance of developmental commitments made by one of the neuron's progenitors. This lineage-based identity can then be modified by interactions between the postmitotic neuron and other neurons or non-neuronal target cells encountered during its terminal differentiation. © 1995 John Wiley & Sons, Inc.     

Cytokines in the central nervous system of mice during chronic relapsing experimental allergic encephalomyelitis

Clinical disease phases of chronic relapsing experimental allergic encephalomyelitis (CREAE) in the Biozzi AB/H mouse model are associated with extensive cellular infiltration of the central nervous system, principally the spinal cord. The activation of these cells is further suggested by the immunocytochemical demonstration of cytokines (migration inhibition factor, interferon-gamma, tumour necrosis factor-alpha, and interleukins 1, 2, and 3) within these infiltrates. The in vitro functions attributed to these cytokines indicate their potential role in cell recruitment, activation, and differentiation of the ongoing immune response which could contribute to the pathogenesis of disease.     

NMDA受体与中枢神经系统发育

中枢神经系统兴奋性氨基酸离子型受体－ＮＭＤＡ受体,是由ＮＭＤＡＲ１和ＮＭＤＡＲ２两个亚单位共同构成的受体通道复合体。ＮＭＤＡ受本激活后可引起神经元细胞对Ｎａ＾＋,Ｋ＾＋和Ｃａ＾２＋通透性增强,产生兴奋性突触后电位,在中枢神经发育的过程中,ＮＭＤＡ受体通过不同亚型的选择性表达,改变自身的结构和功能,进而影响ＮＭＤＡ受体介导的Ｃａ＾２＋内流,调节神经元内Ｃａ＾２＋依赖的第二信使系统,最终实现对中枢神经     

NMDA受体与中枢神经系统的发育

离子型谷氨酸受体分为NMDA型和非NMDA型两类,其中NMDA型受体与中枢神经系统发育关系密切。本文综述了NMDA受体的分子特性及NMDA受体五种亚单位NR1、NR2A、NR2B、NR2C和NR2D在动物出生后脑内的时空表达;NMDA受体亚单位在发育中的作用以及NMDA受体活性的胞内调节机制。     

Effect of methamphetamine on the development of acute morphine tolerance and dependence in mice

The effect of methamphetamine on morphine analgesia (tail-flick assay) was studied in non-tolerant mice and in mice made acutely tolerant to morphine following a single injection of 100 mg/kg morphine. The analgesic potency of morphine was increased in non-tolerant and tolerant mice to the same extent by 3.2 mg/kg methamphetamine (3.3 and 4.4 fold increases, respectively). In contrast, the ED50's for morphine analgesia and naloxone-precipitated jumping in mice pretreated with either 100 mg/kg morphine or both morphine and 3.2 mg/kg methamphetamine were not significantly different, indicating that methamphetamine had no effect on the development of acute morphine tolerance and dependence. Although methamphetamine had no effect on the development of acute tolerance to morphine, 4-day pretreatment with methamphetamine produced cross-tolerance to morphine analgesia. However, cross-tolerance to morphine was not accompanied by enchanced sensitivity to naloxone.     

GABA在中枢神经系统发育的早期阶段具有兴奋作用

在发育早期中枢神经系统γ－氨基丁酸（γ-aminobutyric acid,GABA）主要作为兴奋性神经递质而发挥作用,它可使神经元产生去极化,升高胞内Ca^2 浓度,此时GABA发挥了重要的神经营养性作用,随着兴奋性谷氨酸能系统的发育,通过Cl^-转运体的表达变化,胞内Cl^-浓度降低,从而使GABA由兴奋性转变为抑制性。     

Protein degradation rates in regions of the central nervous system in vivo during development.

The rate of protein degradation was estimated in several regions of rat brain at various ages by subtracting the rate of accumulation of protein from the rate of synthesis. The rate of degradation in cerebral hemisphere, which was 1.3%/h at 2 days of age, declined steadily with age, approaching the synthesis rate is about 30 days of age (0.8%/h). Degradation rates in the pons medulla, mid-brain and spinal cord were of a similar order to that in the cerebral hemisphere. The cerebellum had an exceptionally high rate of degradation in young rats, 1.9%/h at 2 days of age, which complemented its high rates of synthesis and accumulation. The degradation rate in the young was 2-2.5 times the rate in older rats and was approx. 65% of the synthesis rate during the more active phase of growth. The rapid accumulation of protein in the nervous system during the first week post partum was accompanied by high rates of breakdown, and was the result of a relatively small difference between that high rate of degradation and an even higher synthesis rate.