There is increasing evidence that neurotrophins (NTs) are involved in processes of neuronal plasticity besides their well-established actions in regulating the survival, differentiation, and maintenance of functions of specific populations of neurons. Nerve growth factor, brain-derived neurotrophic factor, NT-4/5, and corresponding antibodies dramatically modify the development of the visual cortex. Although the neuronal elements involved have not yet been identified, complementary studies of other systems have demonstrated that NT synthesis is rapidly regulated by neuronal activity and that NTs are released in an activity-dependent manner from neuronal dendrites. These data, together with the observation that NTs enhance transmitter release from neurons that express the corresponding signal-transducing Trk receptors, suggest a role for NTs as selective retrograde messengers that regulate synaptic efficacy.

https://science.sciencemag.org/content/sci/270/5236/593.full.pdf

Neurotrophins and neuronal plasticity.

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the p...

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Biology of Oligodendrocyte and Myelin in the Mammalian Central Nervous System

Trophic factors and neuronal survival

Microglia and inflammation-mediated neurodegeneration: Multiple triggers with a common mechanism

NT-3, BDNF, and NGF in the developing rat nervous system: parallel as well as reciprocal patterns of expression.

In situ hybridization with complementary DNA probes for nerve growth factor (NGF) was used to identify cells containing NGF messenger RNA in rat and mouse brain. The most intense labeling occurred in hippocampus, where hybridizing neurons were found in the dentate gyrus and the pyramidal cell layer. The neuronal identity of NGF mRNA-containing cells was further assessed by a loss of NGF-hybridizing mRNA in hippocampal areas where neurons had been destroyed by kainic acid or colchicine. RNA blot analysis also revealed a considerable decrease in the level of NGF mRNA in rat dentate gyrus after a lesion was produced by colchicine. This lesion also caused a decrease in the level of Thy-1 mRNA and an increase in the level of glial fibrillary acidic protein mRNA. Neuronal death was thus associated with the disappearance of NGF mRNA. These results suggest a synthesis of NGF by neurons in the brain and imply that, in hippocampus, NGF influences NGF-sensitive neurons through neuron-to-neuron interactions.

Expression of the beta-nerve growth factor gene in hippocampal neurons

A cDNA clone encoding rat basic fibroblast growth factor (bFGF) was used as a hybridization probe to determine the level of bFGF mRNA during rat brain development as well as in different adult rat brain regions. In the rat brain, a 3.7kb bFGF mRNA was detected together with lower levels of two minor bFGF mRNA species of 1.8kb and 1.5kb, respectively. The 3.7kb bFGF mRNA was detected in the rat brain already at embryonic day 16, the earliest time point tested. The embryonic brain contained 1.5 to 2 times higher levels of the 3.7kb bFGF mRNA than the adult brain. The amount of the 3.7kb bFGF mRNA in the adult rat brain was approximately 50 times higher than the level of beta-nerve growth factor mRNA in the rat brain. bFGF mRNA was found in all 12 brain regions tested in the adult rat brain with the highest level in colliculi, cerebral cortex, thalamus, and olfactory bulb. The lowest levels were found in pons and medulla oblongata. All three bFGF mRNA species showed the same regional distribution in the brain. In contrast to nerve growth factor mRNA, the level of bFGF mRNA in the neonatal hippocampus was slightly decreased 10 days after a cholinergic denervation by transection of the fimbria-fornix.

Developmental and regional expression of basic fibroblast growth factor mRNA in the rat central nervous system

Substances which regulate expression of nerve growth factor (NGF) were examined in embryonic rat hippocampal cultures containing both neurons and glial cells. Both cell types expressed NGF mRNA when cultivated in vitro. Lipopolysaccharide, an activator of macrophages, elicited a significant increase in NGF mRNA. Interleukin-1 beta evoked a similar increase in NGF mRNA which was accompanied by a rise in NGF protein. The Il-1-induced increase was partially blocked by indomethacin, suggesting that prostaglandins might mediate this effect. Treatment of the cultures directly with prostaglandin E2 resulted in elevated levels of both NGF mRNA and protein. Thus, agents which promote inflammatory activity appear to increase NGF expression. Moreover, a suppressor of inflammation, dexamethasone, decreased NGF expression. Our observations indicate that a variety of immunomodulators regulate NGF expression in the hippocampus.

Regulation of beta-nerve growth factor expression by inflammatory mediators in hippocampal cultures.

A series of polyclonal affinity-purified antibodies against mouse submandibular-gland nerve growth factor (NGF) are described. Using the submandibular gland of the male mouse and indirect immunofluorescence, the specificity and sensitivity of affinity-purified immunoglobulins and various other fractions from the immunized animals have been tested. It will be shown that affinity-purification schemes, including pre-purification of protein A-fractionated immunoglobulins to remove antibodies that bind to unrelated hydrophilic and hydrophobic proteins, significantly enhance the signal-to-noise ratio and specificity of the antibodies. The antibodies effectively detect NGF-like immunoreactivity in both fresh and fixed glandular tissue. Optimal fixation procedures are described. Fluorescence intensities are linearly correlated to log antibody concentration. By use of the best antibody fractions and optimal fixation protocols, the distribution of NGF-like immunoreactivity is described in eight different salivary glands (rat and mouse, male and female, submandibular and sublingual glands). In addition to the well-known large numbers of immunoreactive cells in the submandibular gland of the male mouse, immunoreactive cells were found in the sublingual gland of male mice and in the submandibular and sublingual glands of female mice. One antibody revealed a weak specific fluorescence also in the submandibular gland of the male mouse. In a survey of genital organs of male mice, one antibody revealed fluorescence in the germ cell line. We conclude that several polyclonal affinity-purified antibodies have been characterized that show a strong NGF-dependent binding to the secretory granules of tubular cells in the submandibular gland of male mice. These antibodies should make it possible to locate endogenous and perturbed NGF levels immunocytochemically, e.g., in the peripheral and central nervous system, where NGF concentrations may be several orders of magnitude lower than in the salivary glands.

/pdf/nerve-growth-factor-like-immunoreactivities-in-rodent-5e36ruljek.pdf

Nerve growth factor-like immunoreactivities in rodent salivary glands and testis

We have used antiserum raised against neurofilament (NF) protein and indirect immunofluorescence techniques to visualize neuronal structures in rodent, cat, and cow irides. In the adult rat iris a large population of nerve fibers with a nonautonomic distribution show NF-like immunoreactivity. In whole mounts, smooth fluorescent fibers were seen in a fine-meshed plexus from the sphincter margin to the ciliary processes. Superimposed, a sparse pattern of thick meandering axon bundles were seen. Electroblotting and peroxidase immunochemical staining techniques unequivocally showed the presence of all three NF polypeptides in the adult rat iris.



Adult mouse irides showed a somewhat sparser pattern of NF-positive nerves than that of the rat. Adult guinea pig irides contained irregular NF-positive fibers and few axon bundles. In cryostat-sectioned cat iris numerous irregularly distributed individual fibers were found, whereas in similarly sectioned cow iris thick NF-positive axon bundles were more numerous. By embryonic day 18 numerous sparse NF-positive axons were seen, and the subsequent gradual increase in both axons in bundles and fine-meshed plexuses of individual fibers produced an appearance similar to that in the adult by 6 days of postnatal age. One week after grafting of irides to the anterior eye chamber, most NF-positive nerves had disappeared from the iris grafts. Sympathetic and parasympathetic denervation of the irides did not influence the distribution of the NF-positive iris nerves. Five days after electrothermal lesion of the trigeminal nerve just distal to its ganglion a large proportion of the NF-positive nerves had disappeared from the iris. All perikarya in the parasympathetic ciliary and most perikarya in the superior cervical sympathetic and in the trigeminal sensory ganglion showed NF immunoreactivity.



The present report shows a way to visualize nonautonomic nerve populations in stretch-prepared as well as sectioned irides by immunofluorescence techniques using an antiserum to neurofilament protein.

Christiane Ayer-LeLievre

Papers

Expression of the beta-nerve growth factor gene in hippocampal neurons

Developmental and regional expression of basic fibroblast growth factor mRNA in the rat central nervous system

Regulation of beta-nerve growth factor expression by inflammatory mediators in hippocampal cultures.

Nerve growth factor-like immunoreactivities in rodent salivary glands and testis

Appearance and distribution of neurofilament immunoreactivity in iris nerves.