Developing nervous system

What are the effects on the developing nervous system after chronic in utero exposure Neurophysiological, neurophar-macol ogical, and neuroanatomi cal studies should be useful. 

This mode of regulation seems appropriate to the ERTs since their cells are already terminally differentiated, and their primary function is to grow and provide a nutrient rich incubator for the undifferentiated neuroblasts and imaginal cells that eventually produce the reproductive adult. The response of these undifferentiated progenitor cells to food withdrawal is quite unlike that of the ERTs. Larval neuroblasts and imaginal disc cells continue to proliferate for many days after a larva is starved, and seem to complete their normal proliferation programs. In this instance the ERTs lose mass, presumably as they transfer stored nutrients to the developing nervous system and the discs. 

Hoffer BJ, Olson L, Palmer MR. 1987. Toxic effects of lead in the developing nervous system Inoculo experimental models. Environ Health Perspect 74 169-175. 

Burek, M. J. and Oppenheim, R. W. Programmed cell death in the developing nervous system. Brain Pathol. 6 427-446, 1991. 

The factors are secreted into the extracellular milieu where they diffuse and then act in a paracrine fashion on other cells (Fig. 27-1). Indeed, there is evidence that this type of paracrine support is necessary to sustain neurons as they extend their processes over long distances in the developing nervous system [2]. An analogous process, autocrine stimulation, occurs when a cell synthesizes and secretes a growth factor to which the cell itself is responsive. In this case, the cell provides its own trophic support. 

The synthesis of TGFp, following injury in the nervous system is consistent with its effects on inflammatory responses in other organ systems. Although this factor is not particularly well studied in the developing nervous system, it has been reported to play an instructive role in specifying cellular phenotype. 

STEM CELLS CONTRIBUTE TO THE DEVELOPING NERVOUS SYSTEM 507... 

A series of International Neurochemical Symposia led to the organization of the International Society for Neurochemistry and subsequently the ASN. The first symposium volume (1954) was titled Biochemistry of the Developing Nervous System and the second volume (1956), contains an historically interesting chapter which begins ... 

Risk is the probability that some harmful event will occur. What is the probability that certain types of cancer will develop in populations exposed to aflatoxin in peanut products or benzene from gasoline What is the likelihood that workers exposed to lead will develop nervous system disorders ... 

Absorption readily absorbed by intestine, food will delay absorption Sensitive individuals fetus (fetal alcohol syndrome - FAS) Toxicity/symptoms developing nervous system very sensitive to low levels of exposure children - lowered IQ, learning and behavioral problems adults — memory loss, inebriation, liver disease, cancer... 

The decline in acceptable childhood blood levels was a function of research and improved control of lead contamination, such as the removal of lead from gasoline. A blood lead level of 10 lg/dl does not represent a safe level, only one where it is prudent to take action to reduce exposure. But it must be noted that a level of 10 (Xg/dl is considered an action level and does not provide any margin of safety for a child s developing nervous system. Currently, there appears to be no safe level of lead exposure for the developing child. 

There is no simple or correct way to examine the causes of neurotoxicity. I have divided them into three overlapping areas neurotransmitter/receptor effects, which are often transient damage to the peripheral nerves, which is often permanent and damage to the developing nervous system, which is almost always permanent. 

In the majority of cases, the cells of the nervous system cannot divide and replace themselves, thus most damage is permanent. The developing nervous system exposed to lead will be damaged for a lifetime. However, peripheral nerves can grow, recovering some of the connections and functionality that results in some sensation and return of movement, usually most noticeable in the arms and legs. 

During the 1960s and 1970s researchers and physicians documented that heavy metals, such as lead and mercury, could seriously harm the developing infant. While high levels of exposure resulted in death or obviously serious consequences, the harmful effects from low levels of exposure remained unexplored. The laboratory I worked in designed and performed studies that ultimately demonstrated that even very low levels of exposure to lead or mercury could harm the developing nervous system. The fundamental issue was not death, but quality of life and the consequences for the individual, particularly sensitive individuals such as children. 

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