Neurotrophic molecules

Skeletal muscle extract and nerve growth factor have developmentally regulated survival promoting effects on distinct populations of mammalian sensory neurons

Neurotrophic factors appear to be relevant to the therapy of degenerative diseases as well as neural regeneration. In this respect, we have investigated the neurotrophic effects of skeletal muscle extract on DRG neuron survival by examining the survival and neurite outgrowth promoting activity of factor(s) present in skeletal muscle extracts (SME) on dissociated cultures of embryonic or early postnatal mouse dorsal root ganglion (DRG) sensory neurons. The numbers of surviving neurons resulting from SME addition increased continuously from embryonic day 13 (15%) to birth (55%), then decreased up to 7 days after hatching (0%). Preliminary characterization of the factor(s) present in SME suggests that the active molecule is a protein different from the known neurotrophic factors NGF, BDNF, NT3, CNTF, and bFGF, and that its neurotrophic effect is not mediated by direct interaction with the substratum.

Axonal regeneration is associated with glial migration: comparison between the injured optic nerves of fish and rats

The central nervous systems of mammals and fish differ significantly in their ability to regenerate. Central nervous system axons in the fish readily regenerate after injury, while in mammals they begin to elongate but their growth is aborted at the site of injury, an area previously shown to contain no glial cells. In the present study we compared the ability of glial cells to migrate and thus to repopulate the injured area in fish and rats, and used light and electron microscopy in an attempt to correlate such migration with the ability of axons to traverse this area. One week after the optic nerve was crushed, both axonal and glial responses to injury were similar in fish and rat. In both species glial cells were absent in the injured area (indicated by the disappearance of glial fibrillary acidic protein and vimentin immunoreactive cells from the site of injury in rat and fish, respectively), while at the same time axonal growth, indicated by expression of the growth-associated protein GAP-43, was restricted to the proximal part of the nerve. In fish, 2 weeks after the crush, GAP-43 staining (i.e., growing axons) was seen at the site of injury, in association with migrating vimentin-positive glial cells. One week later the site of injury in the fish optic nerve was repopulated by vimentin-positive glial cells, and GAP-43-positive axons had already traversed the site of injury and reached the distal part of the nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y-producing neurons of the arcuate nucleus regenerate axons after surgical deafferentation of the mediobasal hypothalamus

Dorsolateral and ventomedial surgical deafferentiation of the hypothalamus were used to study the capacity of different types of neuropeptide Y-containing axons afferent to the dorsal hypothalamus to regenerate through surgical lesions. The kinetics of the postlesional responses of transected neuropeptide Y-axons was studied on 30-40 microns thick vibratome sections, either (i) by light or electron microscopy after peroxidase immunostaining for neuropeptide Y or (ii) by confocal microscopy after double fluorescence immunostaining for neuropeptide Y and for glial fibrillary acidic protein. The dorsolateral cut was found to sever 2 main pathways containing neuropeptide Y axons located, respectively, below the bed nucleus of the stria terminalis and in the perifornical region. In both regions transected fibers were found to abut onto the surgical lesion, but even 45 days after the lesion, they were very rarely observed to penetrate into the astroglial scar forming along the lesion. The ventromedial cut was found to sever numerous neuropeptide axons that originate in the underlying arcuate nucleus. Seven to 15 days after the lesion neuropeptide Y fibers located below this type of cut presented a dramatic increase in both their numerical density and their immunostaining intensity. With increasing post-surgery times, an increased number of neuropeptide Y fibers was observed to penetrate and to cross the lesional scar formed by densely packed astrocytic processes. Electron microscope observations further demonstrated that 45 days after the lesion, numerous neuropeptide Y-immunoreactive axonal profiles were included in the scar matrix, which appeared to be mainly composed of closely interdigitating astrocytic processes containing dense bundles of filaments. These data indicate that, in contrast to other neuropeptide Y neurons innervating the dorsal hypothalamus, neuropeptide Y neurons of the arcuate nucleus regenerate axons through the astroglial scar produced by a surgical lesion placed in the ventromedial hypothalamus.

Zeta (zeta), the opioid growth factor receptor: identification and characterization of binding subunits

The zeta (zeta) opioid receptor mediates the activity of the opioid growth factor, [Met5]-enkephalin, a peptide that regulates developmental events in a variety of normal and tumorigenic tissues and cells, including the nervous system. To identify the binding subunit(s) of the zeta receptor, protein blots of rat cerebellar proteins from 6-day-old animals were separated by sodium dodecyl sulfate 10% polyacrylamide gel electrophoresis (SDS-PAGE) and electrophoretically transferred onto nitrocellulose. Ligand blotting of these blots with 1.5 nM [125I]-[Met5]-enkephalin revealed four binding polypeptides of 32, 30, 17, and 16 kDa. Binding occurred at concentrations relevant to the Kd of the receptor, was blocked by cold ligand and opioid antagonists, and exhibited a stereospecific response. No binding was recorded in the adult rat cerebellum. Subcellular fractionation studies using ligand blotting and receptor-binding analysis indicated that these binding subunits were associated with the nucleus. Two-dimensional protein analysis using non-equilibrium pH gradient electrophoresis (NEPHGE) SDS-PAGE of 6-day-old cerebellum and ligand blotting showed that the 32-, 30-, 17-, and 16-kDa subunits have basic isoelectric points. Two-dimensional chymotryptic peptide mapping showed a strong homology between the 32- and 30-kDa subunits, but not with the 17- and 16-kDa polypeptides. The 17- and 16-kDa subunits had only a partial homology to each other. These results are consistent with the biology, biochemistry, and pharmacology of the zeta receptor, and are the first to identify and characterize the binding polypeptides of an opioid receptor that has important growth-related properties.

Migrated fetal astrocytes modulate nerve growth factor expression in host nucleus gracilis of the medulla after grafting in third cervical hindlimb dorsal columns of the spinal cord

Nerve growth factor (NGF) immunoreactivity in the nucleus gracilis of the medulla was quantitated for 90 days after aspiration of the C3 spinal hindlimb dorsal columns of 36 adult rats. Half the lesioned animals were a lesion-only group. The remaining lesioned animals received an immediate graft of two 1.0-mm pieces of 14 day gestation fetal rat cervical spinal cord (prelabeled with Phaseolus vulgaris leucoagglutinin) into the aspiration pocket (graft group). There were 3 normal controls. Groups of animals were analyzed at 7, 14, 21, 30, 60, and 90 days. At 90 days, NGF immunoreactivity was significantly elevated in the nucleus gracilis of lesion-only animals. This increase in NGF immunoreactivity was augmented in glial end-feet surrounding neurons and was also observed in the cytoplasm of astrocytes and some neurons. Previous experiments have shown that the cluster neurons of the nucleus gracilis undergo atrophy at this time with a concomitant decrease in hindlimb placement. NGF immunoreactivity (90 days) in grafted animals, however, was significantly less than in lesion-only animals (P < 0.05) but remained significantly elevated above control animals (P < 0.05). Unlike in lesion-only animals, there were no NGF positive neurons in the nucleus gracilis of grafted animals. Previous experiments have shown that astrocytes from fetal spinal cord grafts migrate to the nucleus gracilis, maintain cluster neuron cell size, and improve hindlimb placement at 90 days. The present data indicate that modulation of detrimental increases in NGF appeared to be a mechanism by which migrated fetal astrocytes can be used as a system for cell therapy.

Developmental expression of the platelet-derived growth factor alpha-receptor gene in mammalian central nervous system

We recently reported that the platelet-derived growth factor (PDGF) A-chain gene is highly expressed in neurons of embryonic and adult mouse central nervous system and suggested that its secretion by neurons may support development and maintenance of glia. We have now analyzed the levels and sites of expression of the cognate PDGF alpha-receptor gene in brain and spinal cord of embryonic and adult mice by in situ hybridization. The predominant cell populations in both gray and white matter expressing transcripts of the PDGF alpha-receptor gene are glial cells or their precursors. Transcripts consistently were not detected in neurons. Expression of the PDGF alpha-receptor gene was first observed at embryonic day 15, increased through postnatal day 14, and fell to lower levels in adults. Expression of the alpha-receptor gene corresponds in temporal sequence to the developmental period of glial migration and proliferation and to the expression of PDGF A by neurons. The results indicate that glia but not neurons have the potential to respond to PDGF A and suggest that neurons influence glial cell development through paracrine regulation.

Cylindroma expresses immunohistochemical markers linking it to eccrine coil

Nerve growth factor, S-100 protein, CD44, and CD34 have unique expressions in or surrounding eccrine coil but are not found in eccrine duct or apocrine gland. We studied 15 cases of cutaneous cylindroma to see if these antigens are found in this neoplasm. All were found in cylindroma to varying degrees. These results link the histogenesis of cylindroma to the eccrine coil. A unique feature of cylindroma is the large number of prominent dendritic cells most likely representing Langerhans cells that permeate the tumor aggregates.

Local protective effects of nerve growth factor-secreting fibroblasts against excitotoxic lesions in the rat striatum

Neurotrophic factors, such as nerve growth factor (NGF), in addition to their role in neuronal development, have protective effects on neuronal survival. Intracerebral implantation of cells genetically altered to secrete high levels of NGF is also found to promote neuronal survival in experimental lesioning models of the brain. The range of activity for such biological delivery systems has not yet been well described either spatially or temporally. Therefore, the authors chose to study the local and distant protective effects of an NGF-secreting rat fibroblast cell line implanted in an excitotoxic lesion model of Huntington's disease. They found that preimplantation of NGF-secreting fibroblasts placed within the corpus callosum reduced the maximum cross-sectional area of a subsequent excitotoxic lesion in the ipsilateral striatum by 80% when compared to the effects of a non-NGF-secreting fibroblast graft, and by 83% when compared to excitotoxic lesions in ungrafted animals (p < 0.003). However, NGF-secreting cells placed in the contralateral corpus callosum failed to affect striatal lesion size significantly when compared to contralateral or ipsilateral non-NGF-secreting cell implants. Of note, fibroblasts were clearly visible within the graft site at 7 and 18 days after implantation; however, few cells within the grafts stained positively for NGF peptide or for the messenger ribonucleic acid (mRNA) encoding the transfected NGF gene-construct at either time point. These results show that biological delivery systems for NGF appear to have a profound but local effect on neuronal excitotoxicity, which will necessitate careful neurosurgical placement for maximum effect. Furthermore, the ability of this genetically altered cell line to synthesize NGF mRNA and peptide appears to decrease spontaneously in vivo, a characteristic that will need to be addressed before this method of biological delivery can be utilized as a treatment for chronic degenerative diseases.

NGF receptor (p75)-immunoreactivity in the developing primate basal ganglia

The distribution of the p75 nerve growth factor receptor (NGFr) was determined within the developing human basal ganglia in specimens between weeks 16 through 40 of gestation, 5 years of age, and adulthood. Although NGFr-immunoreactive neurons were rarely seen in the caudate nucleus, a few such neurons were seen in the putamen between prenatal weeks 16 and 26 of development. At 26 and 40 weeks of gestation, the putamen also displayed NGFr-immunoreactive fibers of putative basal forebrain origin. Some of these fibers coursed through the putamen en route to the cortex while others appeared to remain within the putamen. The external segment of the globus pallidus contained dense collections of NGFr-immunoreactive neurons between 16 and 26 weeks of gestation, whereas the internal segment was devoid of immunoreactive perikarya. A few NGFr-immunoreactive neurons were observed within the globus pallidus at embryonic week 40. The expression of NGFr-immunoreactive neurons within the external segment of the globus pallidus was paralleled by a dense granular NGFr-immunoreactive terminal-like staining pattern within the subthalamic nucleus. This staining pattern was most intense at midgestation (weeks 21-26) and was not observed at 40 weeks of gestation or in adulthood. Interestingly, a similar NGFr-immunoreactive terminal-like pattern was also observed within the monkey subthalamic nucleus at embryonic day 120. These data indicate that NGF receptor mediated mechanisms may underlie developmental processes within the primate basal ganglia. The absence of NGFr-immunoreactive neurons within the caudate nucleus, and the paucity of such neurons in the putamen, suggests that NGF receptors play a limited role in primate neostriatal development. Alternatively, developmental events mediated through NGF receptors may occur prior to embryonic week 16. Furthermore, an NGFr/trophic interaction appears to underlie the development of the pallidal-subthalamic nucleus pathway.

Modulation of HOX2 gene expression following differentiation of neuronal cell lines

The expression of the genes in the human HOX2 locus has been studied during differentiation of two human neuroblastoma (SH-SY5Y and Kelly), a human glioblastoma (251-MG), and the murine F9 embryonal carcinoma cell lines. Cells were differentiated with retinoic acid (RA), or with RA together with dibutyral cyclic AMP (db-cAMP) and nerve growth factor (NGF) in order to assess the changes in the expression patterns of these homeobox genes during neuronal differentiation. We show that the genes of the HOX2 locus are expressed in a complex transcription pattern that varies with cell type. The two uninduced neuroblastoma cell lines show a similar pattern of expression for a number of HOX2 genes although the levels of expression are different for individual cell lines. The embryonal carcinoma cell line F9 expresses low levels of several HOX2 genes which is restricted to the 5' region of the HOX2 cluster. The glioblastoma cell line, 251-MG expresses almost all of the genes of the HOX2 locus. Differentiation of these cells modulates the expression of the HOX2 genes in a manner that is dependent upon the cell type as well as the differentiation factor. Differentiation affects both the level of HOX2 gene expression and the distribution of transcript sizes. In conclusion, our analysis reveals a complex pattern of expression for the genes of the HOX2 locus in neuronal and glial cells and suggests that the cell-specific expression of these genes may be correlated with the phenotypic differences that are observed between different neuronal and glial cell populations within the nervous system.

Brain-derived neurotrophic factor rescues spinal motor neurons from axotomy-induced cell death

Current ideas about the dependence of neurons on target-derived growth factors were formulated on the basis of experiments involving neurons with projections to the periphery. Nerve growth factor (NGF) and recently identified members of the NGF family of neuronal growth factors, known as neurotrophins, are thought to regulate survival of sympathetic and certain populations of sensory ganglion cells during development. Far less is known about factors that regulate the survival of spinal and cranial motor neurons, which also project to peripheral targets. NGF has not been shown to influence motor neuron survival, and whether the newly identified neurotrophins promote motor neuron survival is unknown. We show here that brain-derived neurotrophic factor (BDNF) is retrogradely transported by motor neurons in neonatal rats and that local application of BDNF to transected sciatic nerve prevents the massive death of motor neurons that normally follows axotomy in the neonatal period. These results show that BDNF has survival-promoting effects on motor neurons in vivo and suggest that BDNF may influence motor neuron survival during development.

Expression of the HBNF (heparin-binding neurite-promoting factor) gene in the brain of fetal, neonatal and adult rat: an in situ hybridization study

HBNF (heparin-binding neurite-promoting factor) and MK (midkine) are members of a newly recognized family of proteins, the expression of which is developmentally regulated. These proteins are expressed highest during fetal development in many tissues but they seem to be rather restricted to the brain in adult animals. Gene expression for these proteins is inducible by retinoic acid in embryonal carcinoma cell lines. They induce neurite outgrowth in cultured neurons, and they are characterized by high sequence conservation between species. While the function(s) of these proteins are unknown, available evidence suggests possible roles in the development and the maintenance of neural tissues. This in situ hybridization study investigates the temporal and spatial expression pattern of the HBNF gene in the brain of developing rats. The HBNF gene is highly expressed in the neuroepithelium and the ependyma from fetal day 15 on. Although most ependymal structures express the gene strongly, a few restricted areas of the ependyma do not express HBNF (ventral part of the fourth ventricle, subcommissural organ). In the brain parenchyma, HBNF is expressed in the thalamo-hippocampal area from fetal day 15 and in the cerebral cortex from fetal day 16, with high expression occurring in the superficial layers of the cortex. The nature of the cells expressing the gene, while difficult to ascertain, is probably glial for the most part. However, certain neurons (in limited areas of the brain parenchyma) and most pial cells (in the meninges), also express the gene. HBNF gene expression decreases sharply a few days after birth. HBNF mRNA is also detectable at fetal days 15 and 16 in the face fetal mesenchyma. In the adult rat brain, the expression of the HBNF gene appears to be restricted to neurons of the hippocampus and of the olfactory bulb and to the superficial layers of the cortex. The structurally related MK gene, though not extensively studied here, shows an entirely different temporal and spatial expression pattern. MK gene is weakly expressed during ontogeny in most brain areas, and in the adult animal, MK mRNA is present only in the choroid plexus. The intense and widely distributed expression of the HBNF gene in several cell populations in the fetus, the progressive spatial and quantitative restriction of HBNF gene expression with brain differentiation, as well as the properties of the protein suggest important and diverse functions for HBNF in cellular interactions and cell differentiation in the developing brain, that must act temporally and spatially by ways distinct from its MK companion molecule.

Changes in neurotrophin responsiveness during the development of cerebellar granule neurons

Neurotrophins and their receptors are widespread in the developing and mature CNS. Identifying the differentiation state of neurotrophin-responsive cells provides a basis for understanding the developmental functions of these factors. Studies using dissociated and organotypic cultures of rat cerebellum demonstrated that the neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) affect developing granule cells at distinct stages in differentiation. While early granule neurons in the external germinal layer responded to BDNF, more mature granule cells responded to NT-3. BDNF, but not NT-3, enhanced survival of granule cells in cultures of embryonic cerebella. Thus, BDNF and NT-3 have distinct sequential functions that are likely to be critical in the development of the cerebellum. BDNF may promote the initial commitment, while NT-3 may direct the subsequent maturation of granule cells.

Developmental expression of brain derived neurotrophic factor mRNA by neurons of fetal and adult monkey prefrontal cortex

In situ hybridization histochemistry with labeled cRNA probes complementary to monkey brain derived neurotrophic factor (BDNF) mRNAs has been used to study the cellular localization and expression of this neurotrophin in the prefrontal cerebral cortex of fetal and adult monkeys. Expression could not be detected in prefrontal cortex before the 121st fetal day. Thereafter, in fetal life and in adulthood BDNF mRNA could be detected primarily in large, putative pyramidal cells of layers III and VI throughout the prefrontal cortex. The temporal course and cellular localization of BDNF expression suggests its association with the development and stabilization of specific connections in regions of cortex that display marked functional plasticity.

Ontogeny of zeta (zeta), the opioid growth factor receptor, in the rat brain

Opioid growth factor (OGF), [Met5]enkephalin, serves as an inhibitory influence on the developing nervous system and is especially targeted to cell proliferative events. OGF interacts with the zeta (zeta) opioid receptor to perform its function. Using [3H]-[Met5]enkephalin, the ontogeny of the zeta receptor in the whole brain and cerebellum of rats was explored. Specific and saturable binding was recorded at the earliest time sampled, prenatal day 15 (E15). In the whole brain, binding capacity (Bmax) was two-fold greater at E15 than at E18 and E20. The quantity of zeta receptor appeared to increase in the first postnatal week, reaching a maximum on postnatal day 8. Binding decreased the remainder of the 2nd week and between postnatal days 15 and 25 binding was no longer recorded. In the cerebellum, binding capacity increased from E20 to the 2nd postnatal week, reaching a maximum on postnatal days 8-10. The Bmax of the zeta receptor decreased precipitously on postnatal day 11, being 5.4-fold lower than on postnatal day 10. Between postnatal days 21 and 30, no binding was observed. The binding affinities of the whole brain and cerebellum were 2.3 and 2.7 nM, respectively, and no differences between ages could be detected. Continuous opioid receptor blockade from birth to postnatal day 6 increased body weight, the Bmax of the zeta receptor in the whole brain and cerebellum (but not the Kd), and increased the number of layers of germinal cells in the cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical characterization of programmed cell death in NGF-deprived sympathetic neurons

Young sympathetic neurons die when deprived of nerve growth factor (NGF). Under such circumstances, cell death is appropriate to the developing nervous system and requires RNA and protein synthesis. We have hypothesized the existence of an endogenous death program within neurons that is suppressed by trophic factors. The extent and timing of required changes in the synthetic events that comprise the death program are unknown. In an effort to characterize the biochemical events that mediate the death program further, we performed several experiments on embryonic rat sympathetic neurons in vitro. The death program was blocked with cycloheximide when total protein synthesis was inhibited > or = 80%. When protein synthesis was inhibited within 22 +/- 4 h of NGF deprivation, death was prevented in half the neurons. Hence, we define the commitment point for protein synthesis to be 22 +/- 4 h. Analogously, the commitment point for RNA synthesis was 26 +/- 4 h and that for NGF rescue, 24 +/- 4 h. We tested the ability of a wide variety of chemicals to interfere with the death program. Most compounds tested were unable to prevent neuronal death. Some treatments, however, did save NGF-deprived neurons and were subsequently characterized. These included ultraviolet light and agents that raise intracellular concentrations of cAMP. Finally, we looked for the neuronal expression in vitro and in vivo of genes that have been associated with programmed death in other cell types, including TRPM-2/SGP-2, polyubiquitin, TGF beta-1, c-fos, and c-myc. None of these genes showed significant activation associated with neuronal death.

Sensory nerves impair sympathetic reinnervation and recovery of smooth muscle function

Neuronal populations projecting to a common target may compete for neurotrophic substances. To determine if competition impairs target reinnervation, we examined the effect of capsaicin-induced sensory denervation on sympathetic nerve ingrowth to the sympathectomized rat superior tarsal smooth muscle. In tarsal muscles with intact sympathetic innervation, capsaicin injection on Day 2 reduced numbers of perimuscular CGRP-ir sensory nerves by 68% at 3-4 months; however, it did not alter dopamine-beta-hydroxylase-ir nerve density, response to nerve stimulation, or tarsal muscle adrenoceptor-mediated contraction. Tarsal muscles denervated by ipsilateral superior cervical ganglionectomy on Postnatal Day 4 were partially reinnervated by fibers from the contralateral ganglion, as noted in previous studies. Sensory denervation by capsaicin improved sympathetic reinnervation, as evidenced by a 174% increase in numbers of DBH-ir nerves and a 62% increase in neurally mediated smooth muscle contraction evoked by electrical stimulation of the contralateral pathway relative to reinnervated muscles of vehicle-injected rats; smooth muscle function was also influenced, as indicated by a decrease toward normal in adrenoceptor sensitivity. Tarsal muscles denervated at 30 days were not reinnervated in either vehicle-injected or capsaicin-treated rats, indicating that sensory denervation does not extend the developmental window during which contralateral reinnervation can occur. Both the vehicle-injected and capsaicin-treated preparations with sustained juvenile sympathectomy showed sensory hyperinnervation as adults; thus, a chronic reduction in competition from sympathetics is a sufficiently powerful stimulus to overcome the decreased nerve density induced by neonatal capsaicin treatment. We conclude that sensory nerves limit the extent of sympathetic reinnervation and functional recovery that can occur following neonatal sympathetic denervation.

Time course of dorsal root axon regeneration into transplants of fetal spinal cord: I. A light microscopic study

Cut dorsal root axons regenerate into intraspinal transplants of fetal spinal cord and establish synaptic connections there. The aims of the present study were to describe the progression of dorsal root growth within the transplants and the maturation of transplant morphology and to determine whether the regenerated dorsal root axons persist within the transplants or eventually withdraw. Embryonic (E) day 14 spinal cord was grafted into the lumbar enlargement of adult Sprague-Dawley rats, and the L4 or L5 dorsal root was cut and juxtaposed to the transplants. The morphology of the transplants was examined from 1 day to over 1 year after surgery, and the regenerated dorsal roots were labeled with immunohistochemical methods to study the subset that contains calcitonin gene-related peptide (CGRP). Embryonic spinal cord transplants survived and grew within the host spinal cord in over 90% of the animals. Transplant volume increased and the morphology of the transplants matured over the first 12 weeks and then did not change for 48-60 weeks. During the first week the transplants were composed of dissociated neurons, glia, and hematogenous cells with considerable extracellular space between them. Subsequently, the grafted neurons became densely aggregated, and non-neuronal elements such as inflammatory cells and myelin debris disappeared. CGRP-immunoreactive dorsal roots began to regenerate into the transplants within 24 hours, formed dense bundles by 4 days, and were still present at 60 weeks, the longest survival period examined. Myelination of axons within transplants began at 2 weeks. Quantitative analysis showed that the area of the transplants occupied by CGRP-labeled axons and the distribution area of the labeled axons within the transplants increased until 12 weeks and persisted unchanged for over 48 weeks. These results indicate that regenerated dorsal root axons are permanently maintained within transplants of embryonic spinal cord and suggest that the transplants can contribute to the permanent restoration of damaged intraspinal neural circuits.

Nerve growth factor receptor-immunoreactive neurons within the developing human cortex

A monoclonal antibody recognizing the p75 receptor for nerve growth factor (NGF) was used to assess the immunohistochemical expression of NGF receptors within the developing human neo-, limbic, and paralimbic cortices as well as the hippocampal complex. Between embryonic weeks 16 and 26, a transient population of neurons located within the upper and lower subplate zones of the neo-, limbic, and paralimbic cortices expressed the receptor for NGF. In contrast, NGF receptor-immunoreactive neurons were only observed in the upper subplate zone of the entorhinal cortex at embryonic week 40 (term), a staining pattern not observed in a 5-year-old specimen. The expression of NGF receptor-immunoreactive neurons within the upper subplate zone between embryonic weeks 16 and 40 was characterized by a dense band of immunoreactive neurons and neuropil. These neurons were bipolar with basal and apically directed neurites. NGF receptor-immunoreactive neurons were also scattered throughout the lower subplate zone and underlying white matter between embryonic weeks 19 and 26. These neurons were multipolar, with less apically directed neurites. NGF receptor-immunoreactive subplate neurons displayed a topographic distribution with the heaviest concentration found within limbic and paralimbic cortices as well as association neocortex. In contrast, light to moderate NGF receptor-immunoreactivity was seen in sensory-motor cortex. Within the hippocampal complex, only a few lightly stained NGF receptor-immunoreactive neurons were seen within the fimbria, hilar region of the dentate gyrus, and subiculum. The expression of NGF receptor-immunoreactivity increased within the subplate zone of the pre- and parasubiculum culminating in intense entorhinal cortex staining. As the entorhinal cortex merged with the developing inferior temporal association cortex, there was a marked reduction in staining intensity. In contrast to those in the subplate zone, neurons within the germinal zone and cortical plate were NGF receptor immunonegative at all times examined. The presence of NGF receptors in the subplate zone suggests that neurotrophins such as NGF play an important role in the transient viability of these neurons as well as in the guidance of cortical afferent inputs into topographically organized regions of the cerebral cortex.

The pharmacological potential of neurotrophins: a perspective

Until recently nerve growth factor (NGF) was the only widely characterized neurotrophic factor which had been shown both in vitro and in vivo to be essential for the survival of selected populations of neurons during development and to be important for maintenance of the differentiated phenotype of mature neurons. The recent cloning of new members of the NGF family, namely brain-derived neurotrophic factor neurotrophin-3 (NT-3), NT-4 and NT-5, has greatly expanded our knowledge of the structural properties and neurotrophic activities of these proteins. Elucidation of their developmental and topographical expression and associated receptors in both the central nervous system and peripheral nervous system is proceeding at a brisk pace, leading to proposals for a potential pharmacological use of these proteins. This possibility will ultimately rely upon a more complete understanding of the roles of these trophic factors in human nervous system physiology and pathology.

Insulin-like growth factor-I counteracts bFGF-induced survival of nitric oxide synthase (NOS)-positive spinal cord neurons after target-lesion in vivo

We have used nitric oxide synthase (NOS) histochemistry as a perikaryal viability marker to trace the retrograde reaction of spinal cord intermediolateral (IML) sympathoadrenal projection (SAP)-neurons to target-removal, i.e., selective adrenomedullectomy and local administration of either insulin-like growth factor-I (IGF-I), basic fibroblast growth factor (bFGF) or a combination of both. Counting of NOS-positive preganglionic spinal cord neurons 4 weeks post surgery indicated that more than 80% of stained neurons were lost from the IML-cell column. This percentage loss corresponds to the numerical loss of NOS-stained SAP-neurons labeled retrogradely with Fast-blue prior to adrenomedullectomy. Basic FGF-supplementation at the site of lesion resulted in maintenance of the majority of NOS-positive IML-neurons, a finding confirmed by the survival rate of Fast-blue prelabeled SAP-neurons. Thus, besides maintenance of the structural integrity of SAP-neurons, bFGF prevents loss of intracellular NOS-activity which may reflect unaltered cell metabolism (and function) of these neurons following target-removal in vivo. By contrast, IGF-I failed to alter the rate of disappearance of NOS-staining and labeling index of neurons within the IML-cell column postlesion, suggesting that IGF-I is not neurotrophic for SAP-neurons by itself. Combined treatment with both factors resulted in a more widespread loss of NOS-stained and Fast-blue-prelabeled SAP-neurons than registered after bFGF-only treatment. No co-trophic effect of bFGF and IGF-I was evident; rather, the pronounced bFGF-induced rescuing effect was significantly suppressed by exogenous IGF-I in vivo, supporting the idea that this or another molecule induced by the treatment enhances rather than prevents retrograde degeneration and neuronal death within the adult lesioned IML-adrenal pathway.

Developmental regulation of parasympathetic nerve density by sympathetic innervation in the tarsal smooth muscle of the rat

The developmental influence of sympathetic innervation on parasympathetic nerve density was investigated in the tarsal smooth muscle of the rat. Specificity of acetylcholinesterase staining as a marker for parasympathetic innervation was first determined by acute selective denervations. Excision of the ipsilateral superior cervical ganglion caused a 39% reduction in the density of acetylcholinesterase-positive nerves seven days later, indicating that sympathetic nerves contribute to cholinesterase-positive tarsal muscle innervation. Excision of the pterygopalatine ganglion concurrent with superior cervical ganglionectomy caused a virtually complete disappearance of acetylcholinesterase-positive innervation within seven days, indicating that non-sympathetic cholinesterase-positive fibers derive from the pterygopalatine ganglion and are presumed to be parasympathetic. Analysis of the control population indicated that parasympathetic nerve density did not vary significantly between males and females, between the superior and inferior muscles, or in rats studied at four and 12 months of age. The influence of sympathetic innervation on parasympathetic nerve density during postnatal development was examined by conducting surgical sympathectomies on postnatal day 5 and quantifying acetylcholinesterase-positive nerve density at four months of age. Neonatal sympathectomy caused a 46% reduction in cholinesterase-positive nerve density beyond that which occurred in acutely sympathectomized adult controls. It is concluded that sympathetic innervation is required for developing parasympathetic nerves to attain their normal density within the rat tarsal muscle. This finding is consistent with the idea that sympathetic nerves can exert positive effects on parasympathetic nerve outgrowth during development.

Serotonergic fibres degenerating in the aging rat brain or sprouting from grafted fetal neurons are not affected by the neurotrophic ACTH analogue Org 2766

The effects of chronic treatment with the purported neurotrophic factor ACTH(4-9) analogue Org 2766 were studied on age-related degeneration of serotonergic fibres and on gliosis in the rat hippocampus and caudate putamen complex. In addition, the potential growth-promoting effects of Org 2766 were investigated on fetal serotonergic cells implanted in a previously denervated hippocampus of young adult rats. Chronic treatment of rats from the age of 11 months to 17-18 months did not affect the incidence of aberrant serotonergic fibres in the caudate-putamen complex or the fibres densities in the hippocampus or the caudate-putamen complex. Gliosis was unaffected by Org 2766 treatment as indicated by increased number and staining intensity of glial fibrillary acidic protein-immunoreactive cell bodies in both brain areas. Grafting of fetal raphe cells in young adult rats caused a time-dependent reinnervation of the previously denervated hippocampus. The reinnervation was not affected by treatment of the rats with Org 2766 for 4 weeks following implantation.

Modifications of motoneuron development following transplantation of thoracic spinal cord to the lumbar region in the chick embryo: evidence for target-derived signals that regulate differentiation

In order to examine the role of target cells in the development of spinal motoneurons, the neural tube from thoracic segments was transplanted to the lumbar region on embryonic day (E) 2, and allowed to innervate hindlimb muscles in the chick embryo. When examined at later stages of development, the proportion of white and gray matter in the thoracic transplant was altered to resemble normal lumbar cord. Many thoracic motoneurons were able to survive up to posthatching stages following transplantation. The branching and arborization of dendrites of thoracic motoneurons innervating hindlimb muscles, as well as motoneuron (soma) size, were also increased to an extent approximating that seen in normal lumbar motoneurons. In support of previous studies using a similar transplant model, we have also found that the peripheral (intramuscular) branching pattern of thoracic motoneuron axons innervating hindlimb muscles was similar to that of normal lumbar motoneurons. Axon size and the degree of myelination of transplanted thoracic motoneuron axons were also increased so that these parameters more closely resembled axons of normal lumbar than normal thoracic spinal motoneurons. Virtually all of the changes in motoneuron properties noted above were observed irrespective of whether or not the transplanted spinal cord had developed in anatomical continuity with the host rostral cord. Accordingly, it is unlikely that the changes in the development of transplanted thoracic motoneurons reported here are induced either entirely, or in part, by signals derived from the host central nervous system. Rather, these changes appear to be mediated by interactions between the transplanted motoneurons and the hindlimb. We favor the notion that retrograde trophic signals derived from the hindlimb act to modulate the development of innervating motoneurons. Whether this signal involves a diffusible trophic agent released from target cells, or acts by some other mechanism is presently unknown.

Modulation of sprouting in organ culture after axotomy of an identified molluscan neuron

We examined a variety of factors that might modulate the initiation of neurite outgrowth in an attempt to identify means by which its initiation might be accelerated. We examined this initiation from an identified molluscan neuron, Helisoma trivolvis buccal neuron B5 after axotomy, and determined whether the site of injury, temperature, ion channel blockers, pH, the second messenger cAMP, and protein synthesis affect the initiation of neurite outgrowth. Neurite outgrowth was assayed from axotomized neurons by filling the neurons intracellularly with Lucifer Yellow and examining the percentage of axons that extended (sprouted) new process after 9 or 24 h in organ culture. About one-third (31%) of axotomized neurons sprouted from the site of injury after 9 h (n = 22), and 88% (n = 20) sprouted after 24 h in saline at 22 degrees-24 degrees C when the injury was located 800 microns from the soma. Elevating the temperature to 32 degrees C or moving the lesion site to 400 or 1500 microns from the soma did not significantly alter the incidence of sprouting. Blocking sodium channels with tetrodotoxin [TTX (2 x 10(-5) M)] did not significantly reduce the incidence of sprouting, whereas the sodium channel agonist, veratridine (10(-5) M) did. The calcium channel blocker lanthanum (10(-6)-10(-4) M), stimulated neurite outgrowth; however, the organic calcium channel blocker verapamil (10(-3)-10(-5) M), and the calcium ionophore A23187 (10(-5) M), had no effect on sprouting. Exposure of neurons to the potassium channel blocker tetraethylammonium [TEA (20 mM)], elevation of intracellular pH with NH4Cl (5 mM), or treatment with the adenylate cyclase activator forskolin (10(-5) M) reduced the incidence of sprouting, whereas dideoxy-forskolin (10(-5) M) had no effect. Inhibition of protein synthesis with anisomycin (2 x 10(-4) to 2 x 10(-6) M) did not significantly suppress sprouting 24 h after axotomy. Both D and L isomers of glutamate (300 microM) stimulated sprouting. The present results suggest that the initiation of sprouting is regulated locally at or near the site of injury, and that blocking specific ion channels may either inhibit or enhance the initiation of neurite outgrowth.

Cytoskeletal events underlying dendrite formation by cultured pigment cells

In contrast to neurite outgrowth, pigment cell dendrite formation is relatively unstudied. Keratinocyte-conditioned medium (KCM) induces a striking dendricity in human melanocytes and B16 melanoma cells that is detectable within 30 min, maximal in 24-48 hr, and quantifiable by computerized image analysis. Cytochalasin B (CB), known to disrupt actin microfilaments, completely blocks dendrite formation if added to cultures before or with KCM. This effect is rapidly reversible, and dendrites appear within 1 hr after refeeding with KCM alone. In contrast, CB treatment fails to disrupt existing dendrites previously induced by KCM. Agents known to cause microtubule disassembly (colchicine, nocodazole, or vinblastine) do not inhibit dendrite formation if added before or with KCM. In contrast, these agents disrupt established dendrites. Inhibition of protein synthesis with cycloheximide or actinomycin D completely blocks dendrite formation, but if cultures are provided fresh KCM lacking protein synthesis inhibitors, dendrites reappear within 24 hr. Actin microfilaments visualized with a monoclonal antibody or rhodamine-phalloidin are poorly organized in untreated cells, but form numerous fibers localized along dendrites in KCM-treated cells. Microtubules visualized with a monoclonal anti-tubulin antibody are localized in the center of dendrites. These cytoskeletal changes occur without altering beta actin or beta tubulin mRNA levels. Taken together, these data implicate actin microfilaments in dendrite outgrowth, but not in maintenance, and conversely microtubules in dendrite maintenance but not in formation. These keratinocyte-induced changes involving beta actin and beta tubulin polymerization appear to require both new protein synthesis and post-translational regulation. The observed similarities between melanocytes and other neural crest-derived cells suggest that cutaneous pigment cells might serve as an alternative model for studies of neurite outgrowth.

The neurotrophins BDNF, NT-3, and NGF display distinct patterns of retrograde axonal transport in peripheral and central neurons

The pattern of retrograde axonal transport of the target-derived neurotrophic molecule, nerve growth factor (NGF), correlates with its trophic actions in adult neurons. We have determined that the NGF-related neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), are also retrogradely transported by distinct populations of peripheral and central nervous system neurons in the adult. All three 125I-labeled neurotrophins are retrogradely transported to sites previously shown to contain neurotrophin-responsive neurons as assessed in vitro, such as dorsal root ganglion and basal forebrain neurons. The patterns of transport also indicate the existence of neuronal populations that selectively transport NT-3 and/or BDNF, but not NGF, such as spinal cord motor neurons, neurons in the entorhinal cortex, thalamus, and neurons within the hippocampus itself. Our observations suggest that neurotrophins are transported by overlapping as well as distinct populations of neurons when injected into a given target field. Retrograde transport may thus be predictive of neuronal types selectively responsive to either BDNF or NT-3 in the adult, as first demonstrated for NGF.

Mammalian neurotrophin-4: structure, chromosomal localization, tissue distribution, and receptor specificity

Nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 (NT-3) are the three members of the neurotrophin family known to exist in mammals. Recently, a fourth neurotrophin (designated neurotrophin-4 or NT-4), which shares all of the features found in the mammalian neurotrophins, has been identified in Xenopus and viper. We used sequences specific to the Xenopus/viper NT-4 to isolate a neurotrophin from both human and rat genomic DNA that appears to represent the mammalian counterpart of Xenopus/viper NT-4. Human NT-4 as well as a human NT-4 pseudogene colocalize to chromosome 19 band q13.3. Mammalian NT-4 has many unusual features compared to the previously identified neurotrophins and is less conserved evolutionarily than the other neurotrophins. However, mammalian NT-4 displays bioactivity and trk receptor specificity similar to that of Xenopus NT-4.

Expression of nerve growth factor in vivo from a defective herpes simplex virus 1 vector prevents effects of axotomy on sympathetic ganglia

Sympathetic neurons in the superior cervical ganglion (SCG) of adult rats depend on target-derived nerve growth factor (NGF) for maintenance of tyrosine hydroxylase (TH) levels and the noradrenergic neurotransmitter system. Axotomy of a SCG results in NGF deprivation, causing a decline in TH activity; continuous local application of NGF can prevent this decline in TH activity. We now report that injection of a defective herpes simplex virus 1 vector that expresses NGF (pHSVngf) into a SCG can prevent the decline in TH activity that follows axotomy. SCG of adult rats were injected with either pHSVngf virus or pNFlac virus, which expresses Escherichia coli beta-galactosidase. Analysis of RNA from pHSVngf-infected SCG indicated that the NGF gene was efficiently transcribed and processed. Furthermore, 4 days after pHSVngf injection animals underwent axotomy of the virus-injected SCG. After another 10 days, animals were sacrificed and both the injected-axotomized and contralateral control ganglia were assayed for TH activity. Axotomy of SCG injected with pNFlac virus produced a 50% decline in TH activity relative to control ganglia (P = 0.02). In contrast, SCG injected with pHSVngf virus did not show a decline in TH activity following axotomy; instead, these ganglia manifested an 18% increase in TH levels relative to control ganglia. These data demonstrate that herpes simplex virus 1 vectors can be used to modify neuronal physiology in vivo; specifically, expression of a critical gene product by neural cells that do not normally produce it has potential applications for gene therapy.

Binding of neurotrophin-3 to its neuronal receptors and interactions with nerve growth factor and brain-derived neurotrophic factor

Neurotrophin-3 (NT-3) has low-affinity (Kd = 8 x 10(-10) M), as well as high-affinity receptors (Kd = 1.8 x 10(-11) M) on embryonic chick sensory neurons, the latter in surprisingly high numbers. Like the structurally related proteins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), NT-3 also binds to the low-affinity NGF receptor, a molecule that we suggest to designate low-affinity neurotrophin receptor (LANR). NT-3 dissociates from the LANR much more rapidly than BDNF, and more slowly than NGF. The binding of labelled NT-3 to the LANR can be reduced by half using a concentration of BDNF corresponding to the Kd of BDNF to the LANR. In contrast, the binding of NT-3 to its high-affinity neuronal receptors can only be prevented by BDNF or NGF when used at concentrations several thousand-fold higher than those corresponding to their Kd to their high-affinity neuronal receptors. Thus, specific high-affinity NT-3 receptors exist on sensory neurons that can readily discriminate between three structurally related ligands. These findings, including the remarkable property of the LANR to bind three related ligands with similar affinity, but different rate constants, are discussed.

Release of neurite outgrowth promoting factors by Helisoma central ganglia depends on neural activity

Identified buccal neurons B5 and B19 from the mollusc, Helisoma trivolvis, were plated into cell culture in order to assay for neurite outgrowth promoting factors released from central ring ganglia. The release and attachment of neurite promoting factors to the substratum of poly-lysine coated dishes could be inhibited by blocking spontaneous bioelectric activity in central ring ganglia used to condition the medium and dishes. Bioelectric activity within neurons in central ring ganglia was assayed by intracellular recording and found to be inhibited by exposure to the sodium channel blocker, tetrodotoxin (TTX; 2 x 10(-5) M), or CoCl2 (10 mM). Neither of these agents appeared to be toxic over a three day period since activity within neurons in central ring ganglia was restored following superfusion with saline. To examine the effect of blocking neural activity on the ability of central ring ganglia to release neurite outgrowth promoting factors, we compared the percentage of neurons that extended processes under 5 different conditions: (1) dishes containing conditioned medium and substrate attached growth factors (Super SAM); (2) dishes with substrate attached growth factors only and defined medium (SAM); (3) dishes containing substrate attached growth factors prepared in the presence of TTX; or (4) CoCl2; and (5) dishes containing unconditioned defined medium. The percentage of neurons extending processes under the 5 conditions were: (1) 71% (n = 32); (2) 51% (n = 33); (3) 14% (n = 37); (4) 15% (n = 47); (5) 0% (n = 40), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in nerve growth factor receptor-like immunoreactivity in the spinal cord after ventral funiculus lesion in adult cats

Spinal motoneurons have a capability to regenerate CNS-type axons after intramedullary lesions in the adult cat. Regrowing axons have been traced through CNS-type scar tissue in the ventral funiculus of the spinal cord and into adjacent ventral root fascicles. This scar tissue, which appears to support and sustain regenerating axons, has been shown to have a persistent defect in the blood-brain barrier. It has been suggested that the blood-brain barrier may play a vital role in CNS regeneration by regulating the access of blood-borne trophic factors to the lesion area. In the present study, the binding of antibodies to the human nerve growth factor receptor in the cat spinal cord was examined with immunohistochemical methods 2 days to 8 weeks after a ventral funiculus lesion. The results show that, while no neurons in the ventral horn of the control material contained nerve growth factor receptor-like immunoreactivity as revealed by fluorescence microscopy, affected motoneurons expressed nerve growth factor receptor after ventral funiculus lesion. Nerve growth factor receptor-like immunoreactivity associated to both capillaries and interstitium was present in the scar tissue. Electron microscopic examination of sections labelled with the immunogold-silver method showed that perivascular nerve growth factor receptor-like immunoreactivity was located exclusively to non-pericytic perivascular cells. These cells were abundant in the expanded capillary perivascular spaces adjacent to the traumatic lesion. Similar cells, with or without relation to blood vessels, were observed in the scar tissue and in the pia mater. In a separate set of specimens it was observed that a ventral funiculus lesion combined with ventral root avulsion, which removes denervated PNS tissue, resulted in an expression of nerve growth factor receptor-like immunoreactivity which was similar to the one observed after ventral funiculus lesion only. The results of the present study show that affected motoneurons and cells in the scar tissue express nerve growth factor receptor after ventral funiculus lesion which implies that neurotrophic factors related to nerve growth factor may be of importance for the regenerative response.

GM1 ganglioside enhances cholinergic parameters in the brain of senescent rats

GM1 ganglioside and nerve growth factor both promote the recovery of injured central cholinergic neurons in young animals. Brain cholinergic activity declines with aging and nerve growth factor has been shown to correct cholinergic deficits in senescent animals. We have administered GM1, to young (three months old) or senescent (22-24 months old) rats and evaluated acetylcholine and choline content, choline acetyltransferase and acetylcholinesterase activity as well as choline uptake in striatum, hippocampus and frontal cortex. For some studies, nerve growth factor was administered alone or together with GM1. Our results indicate that cholinergic neurochemical parameters are decreased in some brain areas of senescent animals and that both GM1 and nerve growth factor can enhance their recovery.

Gene sequences of chicken BDNF and NT-3

The respective amino acid sequences of mature brain-derived neurotrophic factor (BDNF) and of mature neurotrophin-3 (NT-3) are identical among mammals, making these among the structurally conserved factors known. Here we show that only a single conservative amino acid substitution distinguishes the chicken mature NT-3 protein from its mammalian counterpart. Chicken mature BDNF shows slightly more variation, differing from mammalian BDNF at several positions. We also note the presence of amino acid sequence motifs in the precursor protein sequences of chicken BDNF and NT-3 that are universally conserved among all known mammalian neurotrophin precursors and have been demonstrated to play a crucial role in promoting correct processing of the pro-proteins.

An opioid growth factor regulates the replication of microorganisms

An opioid growth factor (OGF), [Met5]-enkephalin, interacts with the zeta (zeta) opioid receptor to modulate development of eukaryotes. We have found that [Met5]-enkephalin, an endogenous opioid peptide serves to inhibit the growth of S. aureus. This effect on growth involves cell proliferative events and is under tonic control, since potent opioid antagonists accelerate cell replication. Both the OGF and zeta opioid receptor were associated with these microorganisms. Other opioid receptors (mu, delta and kappa) were not detected. OGF also controlled the growth of other bacteria: P. aeruginosa and S. marcesans. These results indicate that OGF and its receptor, known to be important in the regulation of mammalian development, also function in the growth of simple unicellular organisms. We suggest that the endogenous opioid system related to growth originated billions of years ago.

Enhancement of motor nerve regeneration by nerve growth factor

The sciatic nerves of adult Wistar rats were severed bilaterally. Each nerve was sutured into a silicone tube used as a conduit, leaving a 5 mm gap in length between the nerve ends. Nerve growth factor in a saline solution vehicle was injected into the silicone chamber on the right side and normal saline solution (control) on the left. Six weeks after surgery, electrophysiological studies were performed. The motor nerve conduction velocities (MNCV) were significantly increased in the NGF-treated nerves. In one rat, the MNCV on the NGF-treated side was 66.6 m/s, in the range of normal nerves. There was no significant difference between the two sides in the amplitudes of evoked muscle action potentials. There are apparently no reports on the effect of NGF on motor neuron regeneration in vitro. In this study, NGF was found to enhance motor nerve regeneration.

Ciliary neurotrophic factor and its receptor complex

Ciliary neurotrophic factor (CNTF), originally identified for its ability to promote survival of neurons of the ciliary ganglion, is now known to have additional survival and differentiative actions on cells of the nervous system. CNTF is, however, unrelated in structure to the nerve growth factor family of neurotrophic factors. Instead, CNTF is distantly related to, and in fact shares receptor components with, a number of hemopoietic cytokines. This review focuses on the biological actions of CNTF, the shared and unique features of the CNTF receptor complex and signaling pathways, and the distribution of CNTF and its receptor during development, in the adult and in response to injury.

Molecular mechanisms for generation of neural diversity and specificity: roles of polypeptide factors in development of postmitotic neurons

Development of postmitotic neurons is influenced by two groups of polypeptide factors. Neurotrophic factors promote neuronal survival both in vivo and in vitro. Neuronal differentiation factors influence transmitter phenotypes without affecting neuronal survival. The list of neurotrophic factors is increasing partly because certain growth factors and cytokines have been shown to possess neurotrophic activities and also because new neurotrophic factors including new members of the nerve growth factor (NGF) family have been identified at the molecular level. In vitro assays using recombinant neurotrophic factors and distributions of their mRNAs and proteins have indicated that members of a neurotrophic gene family may play sequential and complementary roles during development and in the adult nervous system. Most of the receptors for neurotrophic factors contain tyrosine kinase domains, suggesting the importance of tyrosine phosphorylation and subsequent signal transduction for their effects. Molecules such as LIF (leukemia inhibitory factor) and CNTF (ciliary neurotrophic factor) have been identified as neuronal differentiation factors in vitro. At the moment, however, it remains to be determined whether or not the receptors for a group of neuronal differentiation factors constitute a gene family or contain domains of kinase or phosphatase activity. Synergetic combinations of neurotrophic and neuronal differentiation factors as well as their receptors may contribute to the generation of neural specificity and diversity.

Medical therapy in spinal muscular atrophy: a realistic expectation?

The hereditary spinal muscular atrophies (SMA) type I-III belong to those diseases for which even the thought of medical therapy seems forbidden. Two neurotrophic factors are, however, now known to exert a markedly stimulating effect on survival of motor neurons in vivo! In principle such factors may become available by recombinant DNA techniques for experiments in animal models of SMA and if these experiments are successful for clinical trials in man. Medical therapy in SMA should aim primarily at patients early in the rapidly progressive phase of their disease, before massive loss of motoneuron has taken place.

Isolated hepatic granulomas from mice infected with Schistosoma mansoni contain nerve growth factor

Nerve growth factor (NGF) is a neurotrophic factor essential for the development and maintenance of specific neuronal cell populations. In addition, NGF has biological effects on inflammatory cells. The aim of this study was to determine whether NGF is present in chronic inflammation, using isolated hepatic granulomas from mice infected with Schistosoma mansoni as the model. The schistosome granuloma is a complex T-cell-mediated immune response to the egg. Intact granulomas were isolated from the livers of infected mice and examined for the presence of NGF. In homogenized granuloma samples, radioimmunoassay and immunoblotting analyses detected an immunoreactive NGF that had the same molecular mass as that of purified murine NGF (13 kDa). Isolated granulomas cultured in vitro released soluble factor(s) with NGF-like neurite-promoting activity in a rat pheochromocytoma (PC12) bioassay. This activity was partially inhibited by a blocking anti-NGF antibody. There were two potential sources of this NGF-like neurite-promoting activity, either the schistosome egg or the host inflammatory response. Since neither isolated eggs nor soluble egg antigen had neurite-promoting activity, the inflammation was the source of this activity. The inability of the anti-NGF antibody to inhibit completely the granuloma-induced neurite outgrowth in the bioassay signifies that NGF is not the only neurotrophic factor present in these granulomas. The presence of NGF within the granulomas may indicate that NGF has a role in the granulomatous response.

Induction of proliferating cell nuclear antigen (PCNA)-immunoreactive cells in goldfish retina following intravitreal injection with 6-hydroxydopamine

1. The dopaminergic neurotoxin, 6-hydroxydopamine (6-OHDA), was injected intravitreally into the eyes of juvenile (5- to 6-cm) goldfish. 2. Proliferation of rod neuroblasts caused by 6-OHDA (2 micrograms in 2 microliters saline) was detected in retinal wholemounts by immunofluorescence for proliferating cell nuclear antigen (PCNA) 3, 7, 14, 20, or 30 days after injection. 3. The injected dose of 6-OHDA was sufficient to cause permanent loss of dopaminergic interplexiform and serotonergic amacrine cells in the injected eye but not in the contralateral control eye. 4. 6-OHDA increased the density (mm-2) of PCNA-ir cells in the outer nuclear layer (ONL) of the injected eye to 2.65 times the initial density 20-30 days after injection, and it increased the density of PCNA-ir cells in the ONL of the contralateral, untreated eye, equally but after a delay of less than or equal to 7 days with respect to the injected eye. 5. 6-OHDA also increased the density of PCNA-ir cells in the inner nuclear layer (INL) to greater than 20 times the initial density 7 days after injection, followed by a rapid decline almost to control levels by 14 days after injection. 6. The sequence of responses to 6-OHDA, with PCNA-ir cells first scattered in the ONL and then clustered in the INL, suggests that neuroblasts from the ONL migrate to the INL to compensate for toxin-induced cell loss. 7. Double staining for 5-bromodeoxyuridine (BrUdR; a thymidine analogue) and PCNA, carried out on 7 days after intravitreal injection with 6-OHDA, showed that 77% of all PCNA-ir cells in the outer nuclear layer had been in S phase during the previous 24 hr. 8. Immunoreactivity for PCNA was found to be a valid marker for rod neuroblasts which have entered S phase within 1-2 days before sampling and was shown to be especially convenient for investigating the distribution of proliferating cells in whole mounts. 9. In controls injected unilaterally with saline or saline plus 1% dimethyl sulfoxide (DMSO), the differences in densities of PCNA-ir rod precursor nuclei 2-30 days after injection vs. day 0 (uninjected) were statistically insignificant in both injected and uninjected eyes (Negishi et al., 1991). Therefore the local effect of injecting 6-OHDA was due to 6-OHDA itself, not to mechanical damage or nonspecific actions of foreign substances.(ABSTRACT TRUNCATED AT 400 WORDS)

Herpes simplex virus latency in the nervous system--a new model

Permissive herpes simplex virus (HSV) infection in tissue culture results in host cell destruction. Latent HSV infection in vivo occurs in neurons of peripheral sensory ganglia (PSG) and it therefore can not take place in neurons in which the virus has completed a lytic replication cycle similar to that present in vitro. Our hypothesis, based on experimental data and observations in humans, suggests that establishment of latent infection and reactivation of HSV-1 does not involve neuronal cell loss. Latency is established in neurons in which the virus does not replicate and is determined, in part, by the tissue levels of a herpes transactivating protein (Vmw65) that is a component of the viral tegument. We also suggest that reactivation of latent infection does not involve destruction of neurons and is due to replication of virus at the peripheral mucocutaneous tissues to where virus or viral DNA have been transported from the nervous tissue. Alternatively, reactivation is initiated in the PSG using a replication cycle which does not involve irreversible damage to neurons. This model explains the lack of damage to neurons which continue to serve as permanent reservoirs of latent virus for the entire life of the host.

NGF and bFGF protect rat hippocampal and human cortical neurons against hypoglycemic damage by stabilizing calcium homeostasis

NGF and bFGF have recently been shown to have biological activity in central neurons, but their normal functions and mechanisms of action are unknown. Since central neurons are particularly vulnerable to hypoglycemia that occurs with ischemia or insulin overdose, we tested the hypothesis that growth factors can protect neurons against hypoglycemic damage. NGF and bFGF each prevented glucose deprivation-induced neuronal damage in human cerebral cortical and rat hippocampal cell cultures (EGF was ineffective). Protection was afforded when the growth factors were administered before (NGF and bFGF) or up to 12 hr following (NGF) the onset of hypoglycemia. Direct measurements of intracellular calcium levels and manipulations of calcium influx demonstrated that sustained elevations in intracellular calcium levels mediated the hypoglycemic damage. NGF and bFGF each prevented the hypoglycemia-induced elevations of intracellular calcium. These findings indicate that growth factors can stabilize neuronal calcium homeostasis in central neurons and thereby protect them against environmental insults.

Administration or deprivation of nerve growth factor during development permanently alters neuronal geometry

We investigated whether the administration or deprivation of a neuronal growth factor during development can permanently alter the dendritic architecture of sensitive neurons. Nerve growth factor (NGF) or NGF antiserum treatment in the first 2-3 postnatal weeks markedly affected the survival, size, and dendritic arborization of mouse sympathetic ganglion cells acutely. Six months after the completion of treatment, the number of surviving neurons, cell body size, and higher order dendritic branching had changed considerably from their values at 3 weeks, suggesting that these parameters remain malleable throughout postnatal life. However, the number of primary dendrites, a fundamental determinant of organization within sympathetic ganglia, was permanently altered by the neonatal treatment protocol. The idea emerging from this study is that NGF influences the elaboration of primary dendrites by sympathetic ganglion cells only during a critical developmental period. In maturity, NGF acts as a "maintenance" factor necessary for normal neuronal function and survival, but neurons lose the capacity to respond with wholesale rearrangements of dendritic architecture.

Receptor-mediated retrograde transport in CNS neurons after intraventricular administration of NGF and growth factors

Radiolabel tracer techniques were used to follow the distribution of nerve growth factor (NGF) and other neuromodulatory factors after intraventricular injection. Autoradiography showed that shortly after intraventricular injection of radio-iodinated NGF (125I-NGF), substantial amounts of radioactivity had penetrated the ventricular wall surfaces; this binding was transient and nonspecific. The 125I-NGF was progressively cleared from the central nervous system (CNS), presumably via the flow of cerebrospinal fluid (CSF) into the blood. A relatively small proportion of the injected 125I-NGF was taken up by NGF receptor-positive neurons in the CNS. Retrograde accumulation of radiolabel was observed within the basal forebrain cholinergic neurons at 5 hours after intraventricular injection. Labeling intensity was maximal at 18 hours and much reduced by 30 hours. This labeling was blocked by co-injection of an excess of unlabeled NGF. Specific and saturable retrograde labeling was also observed within other NGF receptor-bearing neurons, including the prepositus hypoglossal nucleus and the raphe obscurus nucleus. When epidermal growth factor (EGF), transforming growth factor-beta 1 (TGF-beta 1), platelet-derived growth factor-AA (PDGF-AA), PDGF-BB, leukemia inhibitory factor (LIF), insulin-like growth factor-I (IGF-I), or IGF-II was radiolabeled and injected intraventricularly, specific labeling of neurons was observed for 125I-IGF-II and 125I-LIF within separate subpopulations of the dorsal and medial raphe. No retrograde accumulation within neurons was observed for EGF, TGF-beta 1, PDGF-AA, PDGF-BB, or IGF-I. This study describes an in vivo method for identifying putative neuromodulatory factors and their responsive neurons.

Fibroblast growth factor receptor-bearing neurons in the CNS: identification by receptor-mediated retrograde transport

Neurons that internalize and retrogradely accumulate acidic (aFGF) or basic (bFGF) fibroblast growth factor were identified by autoradiography after injections of 125 I-aFGF or 125I-bFGF into the adult rat central nervous system (CNS). Neuronal cell bodies within the lateral hypothalamus, pedunculpontine tegmental nucleus, laterodorsal tegmental nucleus, and the paracentral dorsal tegmental nucleus accumulated 125I-aFGF. Neurons in the hippocampus, subiculum, the centrolateral, paracentral, central medial, and parafascicular thalamic nuclei, the supramammillary nucleus, and substantia nigra compacta accumulated 125I-bFGF. The pattern of neuronal labeling with 125I-bFGF in adult rats was similar to that observed in newborn guinea pigs. No 125I-FGF labeling was observed in nerve growth factor (NGF) receptor-bearing neurons, including the basal forebrain cholinergic neurons. Time-course studies indicate that 125I-FGF was internalized at the terminals and retrogradely transported to the neuronal cell bodies. Neurons were retrogradely labeled either by injection of 125I-bFGF into the lateral ventricle or by injection into innervated target tissues. Co-injection of a 250-fold excess of unlabeled FGF with the 125I-FGF abolished the neuronal labeling. Co-injection of wheat germ agglutinin (WGA), which nonspecifically blocks binding of 125I-bFGF to its receptor, also prevented neuronal labeling. These studies demonstrate that specific neuronal populations within the CNS express functional receptors for aFGF and/or bFGF; in these neurons, aFGF and/or bFGF bind specifically to these receptors, are internalized and retrogradely transported to the neuronal soma in a manner analogous to NGF. The data indicate that FGF can provide trophic support to CNS neurons by both direct and indirect mechanisms.