Neural tissues

DOPA in the bloodstream can be taken up into neural tissue and into tissue devoid of tyrosine hydroxylase, thus bypassing the rate-limiting enzymatic synthetic step (35). Uptake of DOPA by the brain is the basis of the therapeutic effect of DOPA in the treatment of Parkinson s disease (a... 

Vision is vital for human activities, and eyes are very sensitive to a number of toxic insults induced by chemical compounds. The most serious outcome is permanent eye damage which may be so severe as to cause loss of vision. The eye consists of the cornea and conjunctiva, the choroid, the iris, and the ciliary body. It also contains the retina, which is of neural origin, and the optic nerve. The retina contains photoreceptors, a highly specific light-sensitive type of neural tissue. The eye also contains the lens and a small cerebrospinal fluid system, the aqueous humor system, that is important for the maintenance of the steady state of hydration of the lens and thus the transparency of the eye. 

AMPK can also be activated by a Ca2+-mediated pathway involving phosphorylation at Thr-172 by the Ca2+/calmodulin-dependent protein kinase, CaMKK 3. CaMKKa and CaMKK 3 were discovered as the upstream kinase for the calmodulin-dependent protein kinases-1 and -IV they both activate AMPK in a Ca2+/ calmodulin-dependent manner in cell-free assays, although CaMKK 3 appears to much more active against AMPK in intact cells. Expression of CaMKKa and CaMKK(3 primarily occurs in neural tissues, but CaMKKp is also expressed in some other cell types. Thus, the Ca2+-mediated pathway for AMPK activation has now been shown to occur in response to depolarization in rat neuronal tissue, in response to thrombin (acting via a Gq-coupled receptor) in endothelial cells, and in response to activation of the T cell receptor in T cells. 

C) (6) Transplant appropriate neural tissue into the striatum... 

Biogenic amines are decarboxylated derivatives of tyrosine and tryptophan that are found in animals from simple invertebrates to mammals. These compounds are found in neural tissue, where they function as neurotransmitters, and in non-neural tissues, where they have a variety of functions. The enzymes involved in biogenic amine synthesis and many receptors for these compounds have been isolated from both invertebrate and vertebrate sources. In all cases, the individual proteins that effect biogenic amine metabolism and function show striking similarity between species, indicating that these are ancient and well-conserved pathways. 

Vertebrates also show expression of AADC in both neural and non-neural tissues. AADC has been purified from kidney (Christenson et al., 1972), liver (Ando-Yamamoto et al., 1987), adrenal medulla (Albert et al., 1987), and pheochromocytoma (Coge et al., 1989 Ichinose et al., 1989). In the adrenal medulla dopamine is further processed into epinephrine and norepinephrine, which are released from the chromaffin cells during stress to increase heart rate and blood pressure. There are no detectable monoamines in the liver and kidney, and the function of AADC in these tissues is unknown. AADC activity has also been... 

In Drosophila the two tissue-specific mRNAs are generated by alternative splicing of a single primary transcript (Fig. 9). In vertebrates the two tissue specific AADC transcripts are generated from two alternative promoters (Fig. 11) (Albert et al., 1992 Ichinose et al., 1992 Thai et al., 1993). In neural tissue transcription initiates from exon Nl, whereas in non-neural tissue transcription initiates from exon LI. This produces two distinct primary transcripts that are then spliced from the first exon (LI or Nl) to exon 2 to generate two tissue-specific mRNAs. Translation initiates within exon 2, such that the same AADC protein product is synthesized from both AADC mRNAs. 

Finally, the preganglionic neuron may travel to the adrenal medulla and synapse directly with this glandular tissue. The cells of the adrenal medulla have the same embryonic origin as neural tissue and, in fact, function as modified postganglionic neurons. Instead of the release of neurotransmitter directly at the synapse with an effector tissue, the secretory products of the adrenal medulla are picked up by the blood and travel throughout the body to all of the effector tissues of the sympathetic system. 

The ability of the anesthetic agent to function is related to the partial pressure of the drug in the brain. Two major factors dictate the concentration of anesthetic agent in the neural tissue (1) the pressure gradients from lung alveoli to the brain (i.e., inhaled gas —> alveoli — bloodstream —> brain) and (2) the lipid solubility of the drug that enables it to pass between the blood-brain barrier to the central nervous system. 

Implantable microelectronic devices for neural prosthesis require stimulation electrodes to have minimal electrochemical damage to tissue or nerve from chronic stimulation. Since most electrochemical reactions at the stimulation electrode surface alter the hydrogen ion concentration, one can expect a stimulus-induced pH shift [17]. When translated into a biological environment, these pH shifts could potentially have detrimental effects on the surrounding neural tissue and implant function. Measuring depth and spatial profiles of pH changes is important for the development of neural prostheses and safe stimulation protocols. 

Biomedical research continues to broaden our understanding of the molecular mechanisms underlining both health and disease. Research undertaken since the 1950s has pinpointed a host of proteins produced naturally in the body that have obvious therapeutic applications. Examples include the interferons and interleukins (which regulate the immune response), growth factors, such as erythropoietin (EPO which stimulates red blood cell production), and neurotrophic factors (which regulate the development and maintenance of neural tissue). 

Lecuon, E., Luquin, S., Avila, J., Garcia-Segura, L. M. and Martin-Vasallo, P. Expression of the beta 1 and beta2(AMOG) subunits of the Na,K-ATPase in neural tissues cellular and developmental distribution patterns. Brain Res. Bull. 40 167-174,1996. 

Diadenosine polyphosphates are found in the synaptic granules of some nerves, can activate some P2 receptors and are degraded in the extracellular space. In neural tissues the activity of ectodiadenosine polyphosphatases is lower than ecto-ATP-diphosphohydrolase. Hence, the diadenosine polyphosphates have a longer half-life in the extracellular space than does ATP. 

TABLE 20-1 Examples of ligand-activated phosphoinositide hydrolysis in neural tissues... 

At least three distinct forms of the IP3-R have been identified, and these share an overall amino acid homology of 60-80%. Type I predominates in the cerebellum and has been most extensively studied. It is the largest of the 3 forms of the receptor and, unlike type II and III receptors, the gene possesses a 120 nucleotide insert. Type II IP3-Rs are found mainly in non-neural tissues, whereas type III receptors occur in both neural and non-neural tissues. In response to chronic activation, IP3-Rs are degraded via the ubiquitin-proteasome pathway [14] (see also Ch. 2). 

Fisher, S. K., Novak, J. E. and Agranoff, B. W. Inositol and higher inositol phosphates in neural tissues homeostasis, metabolism and functional significance. J. Neurochem. 82 736-754, 2002. 

Different classes of myosin are important for neuronal function. Myosins are remarkably diverse in structure and function. To date, 15 subfamilies of myosin have been defined by sequence homologies [41]. The brain is an abundant source of nonmuscle myosins and one of the earliest studied. Despite their abundance and variety, the roles of myosins in neural tissues have only recently begun to be defined [40]. 

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