Cortical cells

Wool fibers consist of cells, where battened ovedapping cuticle cells form a protective sheath around cortical cells. In some coarser fibers, a central vacuolated medullary cell type may be present. 

The cortex comprises the main bulk and determines many mechanical properties of wool fibers (see Fig. 1). Cortical cells are long, polyhedral, and... 

Jones, H., Tomos, A.D., Leigh, R.A. Wyn Jones, R.G. (1983). Water relation parameters of epidermal and cortical cells in the primary root of Triticum aestivum L. Planta, 158, 230-6. 

Macklon, A.E.S. (1975). Cortical cell fluxes and transport to the stele in excised root segments of Allium cepa L. I. Potassium, sodium and chloride. Planta, 122, 109-30. 

The spontaneous electrical activity of the brain can be measured by electroencephalography (EEG), a technique that has been widely employed to study neurotoxic effects of chemicals both in humans and in experimental animals. EEG waves represent summated synaptic potentials generated by the pyramidal cells of the cerebral cortex (Misra 1992). These potentials are the responses of cortical cells to rhythmical changes arising from thalamic nuclei. The signals recorded can be separated into frequency bands—faster waves exceeding 13 Hz, and slower ones below 4 Hz. 

During ischaemia, NOS is activated by calcium influx or by cytokines like tumour necrosis factor (TNF) or by lipopolysaccharide (LPS) and NO is produced in excess. It has been proposed that the excitotoxic effect of glutamate, which contributes to ischaemia-induced neuronal damage, is mediated by increased production of NO via a chain of events that includes increases in intracellular calcium (via glutamate activation of NMDA receptors), calcium activation of NOS, production of NO and peroxynitrite, and induction of lipid peroxidation. In fact, N-nitro-L-atginine, a selective inhibitor of NOS, has been shown to prevent glutamate-induced neurotoxicity in cortical cell cultures (Dawson rf /., 1991). 

Figure 11 The different steps of nitrogen metabolism in the extraradical hyphae, ccto-mycorrhizal roots, and roots of the host plant. I, absorption 2, assimilation 3. storage 4. translocation A, extramatrical hyphae B. ectomycorrhizal sheath C, Hartig net D, root cortical cells AA amino. acids.

Active fractions tested for electrophysiological actions on hippocampal and cortical cells mimicked the actions of PCP (Quirion et al. 1984). Iontophoresis of PCP inhibited spontaneous cortical and hippocampal cell firing, as did micropressure ejection of the PCP-like material. Fractions that did not possess PCP-like actions had no effect on spontaneous neuronal activity. 

Other lipophilic weak acids have been shown to alter PD in plant cells. Benzoic and butyric acids (1 PM) rapidly depolarized the PD In oat coleoptile cells at pH 6.0 to about -100 mV (43). Higher concentrations (10 mM) of butyrate produced hyperpolarization. Butyrate also hyperpolarized apical cortical cells of maize roots... 

It has been postulated that CH4 in the gaseous form or dissolved in water enters into root aerenchyma, which forms by degeneration of cortical cells between the exodermis and the vascular bundle, where the dissolved CH4 is gasified and moves by diffusion from the root aerenchyma through the restrictive transition zone into the aerenchyma of the culm and then... 

Eisch, A.J., Marshall, J.F. Methamphetamine neurotoxicity dissociation of striatal dopamine terminal damage from parietal cortical cell body injury. Synapse. 30 433, 1998. 

Hussey, R.S., Mims, C.W. and Westcott, S.W.I. (1992) Ultrastructure of root cortical cells parasitized by the ring nematode Criconemella xenoplax. Protoplasma 167, 55-65. 

Similarly, five closely related melanocortin receptors that respond to various peptides derived from the POMC precursor have been identified (Fig. 18-7) [24]. As expected, the receptor on adrenal cortical cells responds best to ACTH, which normally stimulates adrenal steroidogenesis, and the receptor on melano cytes responds best to aMSH, which causes skin darkening. However, the pattern of melanocortin receptor expression in the brain is not simply explained by the known patterns of peptide expression in the brain or by the known effects of POMC-derived peptides when applied to various brain regions. With this number of peptide receptors, it is obvious that production of final peptide products must be precisely controlled and that different biosynthetic processing pathways can dramatically affect the biological activity observed (Figs 18-5,18-7). 

Zinc is important to the normal functioning of the central nervous system (CNS). At low concentrations, zinc protects mammalian brain neurons by blocking N-methyl-D-aspartate receptor-mediated toxicity. At high concentrations, zinc is a potent, rapidly acting neurotoxicant in the mammalian brain, as judged by zinc-induced neuronal injury of in vitro mature cortical cell cultures (Choi et al. 1988). Increased brain levels of zinc are associated with Pick s disease in certain strains of rodents with inherited epileptic seizures. Intravenous injection of zinc in rats with genetically inherited epilepsy produces seizures a similar response occurs with intracranial injection of zinc in rabbits with inherited audiogenic seizures (Choi et al. 1988). 

Choi, D.W., M. Yokoyama, and J. Koh. 1988. Zinc neurotoxicity in cortical cell culture. Neuroscience 24 67-79. 

Pamavelas, J. G. (1984) Physiological properties of identified neurons, in Functional Properties of Cortical Cells (Jones, E. G. and Peters. A., eds.), Plenum Press, New York, NY, pp. 205-239. 

Damus M, Peterson DA, Enstone DE, Peterson CA. Modifications of cortical cell walls in roots of seedless vascular plants. Bot Acta 1997 110 190-195. 

Amri H, Drieu K, Papadopoulos V. (1997). Ex vivo regulation of adrenal cortical cell steroid and protein synthesis, in response to adrenocorticotropic hormone stimulation, by the Ginkgo biloba extract EGb 761 and isolated ginkgolide B. Endocrinology. 138(12) 5415-26. 

Other Systemic Effects. Endocrine lesions related to 1,2-dibromoethane exposure were reported in the NCI (1978) gavage bioassay. These consisted of adrenal cortical cell degeneration in a small number of exposed male and female Osborne-Mendel rats. The possibility exists that this adrenal change represents a secondary (stress-related) effect rather than a primary effect of 1,2-dibromoethane exposure. 

Figure 6.2 Cross-sections of primary rice roots, (a) Radial section close to tip showing interceUnlar spaces (I), central cylinder (CC), and rhizodermis (RH). (b) and (c) Radial sections of yonnger (39 days) and older (72 days) basal parts showing exodermis (E), schlerenchymatons cylinder (SC), parenchymatons or cortical cells (P) and aerenchyma (AE). (d) and (e) Axial sections of matnre root (72 days) showing break through of lateral roots (Butterbach-Bahl et al., 2000). Reproduced by permission of verlag...

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