Nervous system

About: Nervous system is a research topic. Over the lifetime, 16729 publications have been published within this topic receiving 847181 citations.

Toll-like receptor 3 is a potent negative regulator of axonal growth in mammals.

Abstract: Toll is a cell surface receptor with well described roles in the developmental patterning of invertebrates and innate immunity in adult Drosophila. Mammalian toll-like receptors represent a family of Toll orthologs that function in innate immunity by recognizing molecular motifs unique to pathogens or injured tissue. One member in this family of pattern recognition receptors, toll-like receptor 3 (TLR3), recognizes viral double-stranded RNA and host mRNA. We examined the expression and function of TLRs in the nervous system and found that TLR3 is expressed in the mouse central and peripheral nervous systems and is concentrated in the growth cones of neurons. Activation of TLR3 by the synthetic ligand polyinosine:polycytidylic acid (poly I:C) or by mRNA rapidly causes growth cone collapse and irreversibly inhibits neurite extension independent of nuclear factor kappaB. Mice lacking functional TLR3 were resistant to the neurodegenerative effects of poly I:C. Neonatal mice injected with poly I:C were found to have fewer axons exiting dorsal root ganglia and displayed related sensorimotor deficits. No effect of poly I:C was observed in mice lacking functional TLR3. Together, these findings provide evidence that an innate immune pattern recognition receptor functions autonomously in neurons to regulate axonal growth and advances a novel hypothesis that this class of receptors may contribute to injury and limited CNS regeneration.

Insulin and insulin-like growth factor receptors in the nervous system.

Abstract: Insulin and the insulin-like growth factors (I and II) are homologous peptides essential to normal metabolism as well as growth. These peptide hormones are present in the brain, and, based on biosynthetic labeling studies as well as evidence for local gene expression, they are synthesized by nervous tissue as well as being taken up by the brain from the peripheral circulation. Furthermore, the presence of insulin and IGF receptors in the brain, on both neuronal and glial cells, also suggests a role for these peptides in the nervous system. Thus, these ligands affect brain electrical activity, either as neurotransmitters or as neuromodulators, altering the release and re-uptake of other neurotransmitters. The insulin and IGF-I and -II receptors found in the brain exhibit a lower molecular weight than corresponding receptors on peripheral tissues, primarily caused by alterations in glycosylation. Despite these alterations, both brain insulin and IGF-I receptors exhibit tyrosine kinase activity in cell-free systems, as do their peripheral counterparts. Brain insulin and IGF-I receptors are developmentally regulated, with the highest levels appearing in fetal or perinatal life. However, the altered glycosylation of brain receptors does not appear until late in fetal development. The receptors are widely distributed in the brain, but especially enriched in the circumventricular organs, choroid plexus, hypothalamus, cerebellum, and olfactory bulb. These studies on the insulin and IGF receptor in brain, add strong support to the suggestion that insulin and IGFs are important neuroactive substances, regulating growth, development, and metabolism in the brain.