Effects Of Nicotine On The Expression Of Neural Cell Adhesion Molecules During The Development Of Brain

Nicotine is the main alkaloid in tobacco and the toxic granule component in the mainstream smoke. The main approaches of pregnant women to nicotine are active smoking and passive smoking. Nicotine is lipid soluble, so it can quickly enter cells from plasm, freely pass the placent, and accumulate in the body of fetus. It is widely accepted now that the exposure of pregnant women to nicotine has many harmful effects on the development of fetus. According to statistical studies, China is the biggest smoking country with about 300 million smokers now, so pregnant women in our country have many opportunities to expose in tabacco smoke which inevitably hampers the improvment of population constitution. Thus, it is of important practical significance to elucidate the mechanisms of nicotine' s effects on the development of the nervous system and to lay the theoretic foundation for clinical substitutive therapy and popularization of health care knowledge during pregnancy.Reports say nicotine can enhance the activity of the acetylcholine ( Ach) system which prematurely forces cells out of proliferation and into differentiation and thus breaks the brain cells' concordant of proliferation and differentiation; abnormally high activity of the acetylcholine system also can stimulate the expressions of some genes, such as P53 c -fos,which induces apoptosis and delayed loss of cells; nicotine can also effect the neurotransmitter systems of Cate-cholamine and Serotonin by enhancing the synthesization release and catabolism of Dopamine ( DA ) Noradrenaline ( NE) and 5 - Hydroxide Tryptamine ( 5 -HT) , which may be related to the neurotic -psychiatric syndrome.But now, the mechanisms of nicotine's effects on the development of the nervous system have not been thoroughly elucidated yet. For example, people found that nicotine can inhibit the axon elongation of neurons in chick ciliaryganglion and of PC 12 cells; It was also observed that the dendritic lengths of cholinoceptive neurons in the developing chick tectum were shorter than con-trals' , and the same was observed in other brain regions and also in cultured tectum cells; Slotkin et al. found that in the brain of rats intrauterinely exposed to nicotine, the thickness of cell layers in CA3 and Dentate Gyms region of hippocampus were reduced, the number of middle sized pyramidal cells in the primary somatosensory cortex was also reduced with smaller nonpyramidal cells increased, and glia cells increased in all the regions observed. These results suggest that, nicotine not only interferes with cell proliferation and differentiation but also has postmitotic effects on the development of brain, such as the elongation of neurites cell migration and recognition etc. However, the mechanisms of such effects have not been fully reported.Neural cell adhesion molecule ( NCAM) belongs to the cell adhension molecule immunoglobulin superfamily. In the central nervous system ( CNS) , NCAM mainly exists in isoforms of 180 140 and 120 KD, the three isoforms come from one gene with different splicing after transduction. The main post -translational modification of NCAM is glycosylation and polysialic acid ( PSA) -NCAM has been well studied. The main effect of PSA - NCAM is to reduce adhesiveness between cells and facilitate cell migration and the remodeling of synapse.NCAM has wide effects during the development of CNS. It can mediate cell - cell and cell - matrx interaction by homology binding and heterology binding separately. NCAM takes part in cell migration differentiation recognition, modifies axon growth direction and bundling, participates in cell signal transduction and synapse remodeling study and memory etc. For example, NCAM mediates the formalin of cell stratification of retina and cerebellum and the migration of neural crest cells etc. Furthermore, studies in vivo and in vitro show that any interference with NCAM' s function and/or expression will induce morphological changes.According to the above results, can we suppose that the effects of nicotine on the deve...