Expression of insulin-like growth factor-I (IGF-I) and IGF-II in the avian brain: relationship of in situ hybridization patterns with IGF type 1 receptor expression.

Insulin-like growth factors (IGFs) are expressed in defined spatiotemporal patterns during the development of the mammalian central nervous system (CNS). Since IGF expression in avian species is less well documented, we studied here the expression of IGF-I and IGF-II during chicken CNS development, using in situ hybridization and reverse transcriptase-PCR, and compared the results with the expression of the IGF type 1 receptor (IGF-1R). IGF-II expression started early in embryonic life, shortly after the onset of IGF-1R expression. During organogenesis, IGF-II was strongly expressed in kidney, liver and gut primordia, in contrast with IGF-1R mRNA, which is highly enriched in proliferating neuroepithelia. During the second half of embryonic development, IGF-I and IGF-II had distinct expression patterns, suggesting specific roles for each ligand during brain maturation. IGF-II mRNA was found in numerous brainstem nuclei and in the optic tectum, whereas IGF-I mRNA was found predominantly in telencephalic regions. Both ligands were expressed in the cerebellum, but each by different cell layers. Some brain regions (olfactory bulb and olivo-cerebellar system) did not exhibit the postnatal downregulation typical of extrahepatic IGF-I expression, but continued to express IGF-I into adulthood. Purkinje cells expressed IGF-II in the embryo, but switched to IGF-I expression in the adult. The conservation of embryonic and postnatal IGF expression patterns in the CNS between avians and mammals suggests that the involvement of the IGF system in neurogenesis and differentiation, and possibly in neural plasticity and learning, may have arisen early during tetrapode/vertebrate evolution.

Mild kainate toxicity produces selective motoneuron death with marked activation of CA(2+)-permeable AMPA/kainate receptors.

Motoneuron death could be produced by higher sensitivity to excitoxicity during the development and pathological conditions. We report here that in ventral spinal cord cultures mild kainate exposure (12.5 microM, 20 min or 100 microM, 2.5 min) induced selective cobalt stain of motoneurons, indicating a specific Ca2+ entry through the Ca(2+)-permeable AMPA/kainate receptors. This result was associated with a selective motoneuron death as previously described. In these cultures, motoneuron immunoreactivity for the Ca2+ buffering protein, calretinin was negative. These findings suggest that the selective motoneuron death due to a mild excitotoxic insult could be linked to a marked Ca2+ influx associated with the lack of some Ca2+ buffering proteins.

Changes in IGF-1 receptors in the hippocampus of adult rats after long-term adrenalectomy: receptor autoradiography and in situ hybridization histochemistry.

Alteration of insulin-like growth factor-1 (IGF-1) receptor and its mRNA after long-term adrenalectomy (ADX) was studied in the hippocampus by in vitro receptor autoradiography and in situ hybridization histochemistry, respectively. Significantly, decreased levels of IGF-1 receptor and its mRNA was noted in the dentate and CA1-CA4 regions of the hippocampus of the ADX animals, suggesting that the level and expression of IGF-1 receptors in the hippocampus is influenced by adrenal hormones.

[Two strains of genetically hypertensive rats, LH and SRH, have distinct profiles of postnatal expression of tropoelastin and type III collagen in the aortic wall]. / Deux souches de rats génétiquement hypertendues, LH et SHR, se différencient par leur profil postnatal d'expression de tropoélastine et de collagène de type III dans la paroi aortique.

Experimental pharmacology and studies on hypertension frequently use genetically hypertensive animal models like the SHR or the Lyon hypertensive rat LH. In order to further characterize these two models we measured the expression levels of three major extracellular matrix components in the aortic wall, tropoelastin (TE) and type I and type III collagen, during postnatal development. The type I collagen expression decreases progressively during the first twelve weeks of postnatal development without significant differences between SHR and LH, or their normotensive controls, WKY or LN respectively. No differences were detected either for the expression levels of TE and type III collagen between the hypertensive strains and their respective controls. However, direct comparison of the two hypertensive strains SHR and LH, revealed a specific, strong increase of TE and type III expression for the LH at 5 and 12 weeks (p < 0.001 and 0.005 respectively). The evolution of the ratios of expression levels between the two collagens (type III/type I) on one side and of TE and collagen type I (TE/type I) on the other side were similar for the hypertensive strains and their respective controls, but diverged significantly for LH and SHR animals (up to p < 0.001 depending on the age group). Both indicators, III/I and TE/I, are considerably higher in LH compared to SHR from 5 weeks of postnatal development onwards. Our results indicate that the genes for TE and type I and III collagen are regulated during postnatal development of LH and SHR. It is however not possible at this point to establish a link between mRNA levels and hypertension in these animals. Nevertheless, the ratios III/I and TE/I seem to be good phenotypic markers for the characterisation of LH and SHR strains.

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

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.

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

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.

Class II major histocompatibility complex (MHC) gene expression in the mouse brain is elevated in the autoimmune MRL/Mp-lpr/lpr strain.

Brain levels of Ia mRNA, quantified by RNA blot analysis, were found to be 30-50-fold lower than splenic levels in all autoimmune and normal mouse strains examined except MRL/l, whose brain content of Ia mRNA was comparable to normal splenic levels. Prior perfusion to remove blood cells did not alter the amount of Ia mRNA obtainable from MRL/l brain. Elevation of Ia mRNA in MRL/l as compared to control C3H mice was also found in kidney, liver, and spleen, though not in thymus or lung. Results are discussed in relation to an animal model for central nervous system involvement in systemic lupus erythematosus.

Expression of nerve growth factor receptor mRNA during early development of the chicken embryo: emphasis on cranial ganglia.

In situ hybridization with beta-nerve growth factor receptor (NGF-R) oligonucleotide probes was used to study NGF-R mRNA expression in early chicken embryos. Sections through the region of the visceral arches showed high levels of NGF-R mRNA in mesenchyme of the visceral arches, neural tube and myotomes. Labelling was also seen over E3 primordium of the trigeminal ganglion (V) and in the placodal thickening of the petrosal (IX) and nodose (X) ganglionic primordia. In the E5 embryo, all cranial sensory ganglia (V, VII, VIII, IX, X) expressed NGF-R mRNA although at varying levels with higher levels in the ganglia of the Vth, IXth and Xth cranial nerves than in ganglia of the VIIth and the VIIIth nerves. Within ganglia of the Vth, IXth and Xth cranial nerves, levels of NGF-R mRNA were higher in regions containing placode-derived neurons, than in regions with neural-crest-derived neurons. The placode-derived nodose ganglion (X) expressed NGF-R mRNA at all stages of development. In the E15 embryo and later in development, two thirds of the large neuron-like cells expressed high levels of NGF-R mRNA. Our results show that expression of NGF-R mRNA, in peripheral neurons, is not restricted to cells of neural crest origin. We also show a transient expression of NGF-R mRNA early in development in a wide range of non-neuronal differentiating cells. The high level of NGF-R mRNA in early differentiating tissues suggest that the NGF-R plays a wider role during development than previously anticipated.

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

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.

Nerve growth factor mRNA and protein in the testis and epididymis of mouse and rat.

In situ hybridization using beta-nerve growth factor (NGF) DNA probes was used to demonstrate NGF mRNA in spermatocytes and early spermatids of adult mouse. NGF mRNA-containing cells were also identified in the epithelium of convoluted ducts in mouse corpus epididymidis. Blot-hybridization analysis of RNA prepared from mouse testis and epididymis as well as from rat epididymis confirmed the presence of a 1.3-kilobase (kb) NGF mRNA in these tissues. In the rat testis, however, only a 1.5-kb NGF mRNA was found, corresponding in size to a minor NGF mRNA detected in the rat brain, heart, and epididymis. By using affinity-purified anti-NGF antibodies, NGF-like immunoreactivity was observed in germ cells of rat and mouse testis and in the lumen of epididymis. Extracts of both mouse epididymis and testis stimulated fiber outgrowth in cultured sympathetic ganglia, and the effect was blocked by antibodies to mouse NGF. A two-site enzyme immunoassay showed the presence of 10 and 70 ng of NGF per g of tissue in the mouse testis and epididymis, respectively. Furthermore, RNA blot analysis showed the presence of mRNA for the NGF receptor in mouse testis. These results suggest a nonneurotrophic role for NGF in the male reproductive system, possibly in survival maturation and/or motility of spermatozoa.

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

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.

Substance P-containing sensory nerves in the rat iris. Normal distribution, ontogeny and innervation of intraocular iris grafts.

Trigeminal, substance P-containing nerves have been studied in the stretch-prepared rat iris with immunohistochemical techniques. The normal iris exhibited a slightly irregular plexus of individual fibres in the dilator, intermingled with thin, meandering axon bundles. The sphincter contained more circumferentially oriented fibres. Occasional free nerve endings were present in all parts of the iris; no obvious association with blood vessels was detected. All substance P-positive nerves in the iris disappeared after lesioning the trigeminal nerve. Irides of neonates showed scattered, smooth fibres in a sparse plexus, without visible axon bundles. Over the first two postnatal weeks, the density of innervation developed rapidly, reaching a transiently supranormal level and fluorescence intensity, compared to adulthood. From 3 weeks on, the pattern and density of substance P-containing fibres approached the normal adult appearance. In irides grafted to the anterior eye chamber, the intrinsic substance P nerves degenerated, disappearing completely after 5 days. Reinnervation from the host irides transpired over the next few weeks, approximating normal density after 3 weeks, and organotypic density and distribution from 4 weeks on. No obvious hyperinnervation was encountered after longer postoperative times (3 months). In the host iris, many substance P fibres disappear or exhibit low fluorescence intensity during the first postoperative week, recovering fully during the next 2 weeks. Over longer postoperative periods irregular, moderate hyperinnervation developed with increased numbers of axons in bundles. In conclusion, we show normal distribution and plasticity during ontogeny and maturity of substance P-containing iris nerves in the rat, with a sensitive immunohistochemical technique in iris whole mounts.

Substance P-like immunoreactivity in developing cranial parasympathetic neurons of the rat.

Substance P-like immunoreactivity (SPLI) has been observed in cell bodies of fetal cranial parasympathetic ganglia of rat. It first appears at day 16 of gestation at the same time as in cranial sensory ganglia. From day 17 to 21, SPLI neurons constitute most, if not all, submandibular-sublingual and intralingual ganglia, they form 30-40% of otic and pterygopalatine ganglia and numerous such neurons are found in the myenteric plexus of the esophagus as well as in pharyngeal and buccal walls. The immunoreactive material is thinly granular, and its appearance does not change with prenatal development. The immunoreactivity in cell bodies of parasympathetic ganglia decreases at the end of the gestational period, and cannot be evidenced any more in most cells of normal adult ganglia. However, the corresponding SPLI fibers remain intensely immunoreactive. When grafted to rat irides, which have been chemically depleted of intrinsic SPLI fibers, submandibular, otic and pterygopalatine ganglia from pre- or postnatal rats rapidly produce a large amount of SPLI fibers on the iris mimicking the pattern of sensory innervation. This proves the presence of SPLI neurons in adult parasympathetic ganglia, at least in experimental conditions. This study of fetuses and grafts demonstrates the existence of neurons in SPLI parasympathetic cranial ganglia which has been underestimated or ignored previously as a result of observations on adult ganglia. The very large proportion of SPLI neurons in the ganglia of the salivary gland might be of importance for the interpretation of experimental studies on the control of salivation. The presence of SPLI in all three types of peripheral ganglia, sensory, sympathetic and parasympathetic, raises the question of its functional significance in the different compartments of the peripheral nervous system.

Neurofilament immunoreactivity in developing rat autonomic and sensory ganglia.

Immunoreactivity to neurofilament (NF) antiserum appears early in the development of both the central and peripheral nervous systems of the rat fetus. In 10 somite embryos, positive cell bodies are present in the ventromedial part of anterior rhombencephalic and mesencephalic neural tube. From there the appearance of immunoreactivity spreads cranially to the prosencephalic anlage before closure of the anterior neuropore and caudally following the sequence of neural tube closure. Immunoreactivity increases rapidly in axon bundles of central and peripheral systems, but in immature cell bodies of sensory ganglia the NF material only forms a ring around the nucleus. At 16 days of gestation, some cell bodies are progressively loaded with NF-immunoreactive material as a thick perinuclear network first and then in more excentrically located aggregates. This category of neurons is mainly observed in the distal part of the trigeminal ganglion, in petrous and nodose ganglia and in cervical dorsal root ganglia. In adult ganglia large cell bodies and some small ones present high NF immunoreactivity. In autonomic cell bodies (in superior cervical ganglion and in parasympathetic cranial ganglia) the immunoreactive material only forms a perinuclear ring slowly transformed into a loose perinuciear meshwork at the end of gestation. Intensely reactive nerve fibers are observed in cranial sensory as well as in sympathetic and parasympathetic ganglia and nerves. No positive cell bodies and only a few NF-immunoreactive nerves are observed in the carotid bodies. The NF immunoreactivity is better visualized on sections of fresh frozen material, treated with acetone, than in fixed specimens. These results are compared to previous observations reported for other species and for developing dorsal root ganglia. This immunostaining may be used to detect differentiation of peripheral sensory and autonomic neurons under experimental conditions. The uneven distribution of NF immunoreactivity in sensory neurons from stage 16 days of gestation as specific for precise subpopulations of neurons is discussed.

Ultrastructural and histochemical studies of the rat iris: identified neuronal inputs and supportive glia.

A detailed ultrastructural description was made of the rat iris with special emphasis on nerve fibre populations and their supportive glial cells. The location and identity of different autonomic (sympathetic and parasympathetic) and sensory nerves was further studied by monoamine histofluorescence, acetylcholinesterase histochemistry, immunohistochemistry for substance P and neurofilament, and Linder's silver staining. Schwann cells were defined with immunohistochemical techniques using antiserum to glial fibrillary acidic protein. By correlation of these morphological techniques, the relative proportion of different neuronal inputs and their glial constituents in various parts of the rat iris could be determined. The sympathetic and parasympathetic unmyelinated fibres showed the well-known preferential localization in the posterior part, approaching the smooth muscle cells and chromatophores in the dilator muscle. Larger arterioles in the anterior loose stroma of the iris were in close proximity to sympathetic fibres as indicated by monoamine histofluorescence. Sensory trigeminal nerves were visualized both with Linder's silver staining and neurofilament immunohistochemistry. Large myelinated axon bundles in the anterior part of the iris were clearly seen, and thin unmyelinated fibres were scattered throughout the anterior and posterior parts. Unmyelinated substance P-containing fibres were scattered preferentially in the anterior part of the iris, without close association with blood vessels. Distribution of supportive cells, indicated by means of immunofluorescence with antiserum against glial fibrillary acidic protein, appeared largely similar to that of neurofilament-positive nerve fibres. In the sphincter muscle, cholinesterase-positive nerve fibres were densely packed and adrenergic fibres as well as sensory, neurofilament- and substance P-containing fibres were sparse but distributed throughout the muscle. Accompanying glial cells positive for glial fibrillary acidic protein were also found.

Appearance and distribution of neurofilament immunoreactivity in iris nerves.

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-positives 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.

Development of substance P-immunoreactive neurons in cranial sensory ganglia of the rat.

Substance P-like immunoreactivity has been observed in fetal and adult cranial sensory ganglia. It first appears at day 16 of gestation in sensory neurons of trigeminal, superior-jugular, petrous and nodose ganglia, as well as in the autonomic myenteric plexus, and at day 17 in cervical dorsal root ganglion cells. Substance P immunoreactivity can be visualized much earlier (day 12) in the central nervous system. The ganglionic immunoreactivity subsequently increases during fetal life but drops at birth. The reactive material is first diffuse, then slowly becomes granular, and is mostly concentrated in coarse perinuclear inclusions in adult sensory neurons. Most substance P-positive neurons in trigeminal and superior-jugular ganglia are small, but medium-sized and large positive neurons are also observed in the trigeminal, petrous and nodose ganglia. Our observations give a precise picture of the development of substance P immunoreactivity in sensory neurons and are in general agreement with previous reports on some fetal and adult rat sensory ganglia. They indicate that in the rat, maturation of peripheral substance P-containing sensory neurons is slower than that of central substance P neurons or equivalent sensory neurons in other species. The examination of fetal material allows the observation of numerous immunoreactive sensory neurons which cannot be visualized after birth. We hypothesize a possible different embryonic origin (neural crest or placodal) for small nociceptive and larger substance P-containing neurons in rat cranial sensory ganglia.