Regulation of nerve growth factor synthesis in mouse submaxillary glands by testosterone

The Crosstalk between Nerves and Cancer-A Poorly Understood Phenomenon and New Possibilities

INTRODUCTION

Crosstalk occurs between nerve and cancer cells. These interactions are important for cancer homeostasis and metabolism. Nerve cells influence the tumor microenvironment (TME) and participate in metastasis through neurogenesis, neural extension, and axonogenesis. We summarized the past and current literature on the interaction between nerves and cancer, with a special focus on pancreatic ductal adenocarcinoma (PDAC), prostate cancer (PCa), and the role of the nerve growth factor (NGF) in cancer.

MATERIALS/METHODS

We reviewed PubMed and Google Scholar for the relevant literature on the relationship between nerves, neurotrophins, and cancer in general and specifically for both PCa and PDAC.

RESULTS

The NGF helped sustain cancer cell proliferation and evade immune defense. It is a neuropeptide involved in neurogenic inflammation through the activation of several cells of the immune system by several proinflammatory cytokines. Both PCa and PDAC employ different strategies to evade immune defense. The prostate is richly innervated by both the sympathetic and parasympathetic nerves, which helps in both growth control and homeostasis. Newly formed autonomic nerve fibers grow into cancer cells and contribute to cancer initiation and progression through the activation of β-adrenergic and muscarinic cholinergic signaling. Surgical or chemical sympathectomy prevents the development of prostate cancer. Beta-blockers have a high therapeutic potential for cancer, although current clinical data have been contradictory. With a better understanding of the beta-receptors, one could identify specific receptors that could have an effect on prostate cancer development or act as therapeutic agents.

CONCLUSION

The bidirectional crosstalk between the nervous system and cancer cells has emerged as a crucial regulator of cancer and its microenvironment. Denervation has been shown to be promising in vitro and in animal models. Additionally, there is a potential relationship between cancer and psychosocial biology through neurotransmitters and neurotrophins.

Sex-dependent Regeneration Patterns in Mouse Submandibular Glands

Our previous studies indicated that YIGSR-A99 peptides chemically conjugated to fibrin hydrogel (FH) and applied to wounded submandibular gland (SMG) in vivo, formed new organized salivary tissue, whereas wounded SMG treated with FH alone or in the absence of a scaffold showed disorganized collagen formation and poor tissue healing. While these studies indicated that damaged SMG grow and differentiate when treated with FH containing L1 peptide, they were performed only in female mice. However, there is a well-established sexual dimorphism present in mouse SMG (e.g., males develop well-differentiated granular convoluted tubules, but these structures are poorly developed in females) and little is known about how these sex differences influence wound healing events. Therefore, the goal of this study was to conduct comparative analyses of regeneration patterns in male and female mice using L_1p-FH in a wounded SMG mouse model. Particularly, we focused on sex-dependent wound healing events such as macrophage polarization, vascularization, tissue organization, and collagen deposition, and how these events affect salivary gland functioning.

The role of neurotrophic factors conjugated to iron oxide nanoparticles in peripheral nerve regeneration: in vitro studies

Local delivery of neurotrophic factors is a pillar of neural repair strategies in the peripheral nervous system. The main disadvantage of the free growth factors is their short half-life of few minutes. In order to prolong their activity, we have conjugated to iron oxide nanoparticles three neurotrophic factors: nerve growth factor (βNGF), glial cell-derived neurotrophic factor (GDNF), and basic fibroblast growth factor (FGF-2). Comparative stability studies of free versus conjugated factors revealed that the conjugated neurotrophic factors were significantly more stable in tissue cultures and in medium at 37°C. The biological effects of free versus conjugated neurotrophic factors were examined on organotypic dorsal root ganglion (DRG) cultures performed in NVR-Gel, composed mainly of hyaluronic acid and laminin. Results revealed that the conjugated neurotrophic factors enhanced early nerve fiber sprouting compared to the corresponding free factors. The most meaningful result was that conjugated-GDNF, accelerated the onset and progression of myelin significantly earlier than the free GDNF and the other free and conjugated factors. This is probably due to the beneficial and long-acting effect that the stabilized conjugated-GDNF had on neurons and Schwann cells. These conclusive results make NVR-Gel enriched with conjugated-GDNF, a desirable scaffold for the reconstruction of severed peripheral nerve.

Nerve growth factor promoter activity revealed in mice expressing enhanced green fluorescent protein

Nerve growth factor (NGF) and its precursor proNGF are perhaps the best described growth factors of the mammalian nervous system. There remains, however, a paucity of information regarding the precise cellular sites of proNGF/NGF synthesis. Here we report the generation of transgenic mice in which the NGF promoter controls the ectopic synthesis of enhanced green fluorescent protein (EGFP). These transgenic mice provide an unprecedented resolution of both neural cells (e.g., neocortical and hippocampal neurons) and non-neural cells (e.g., renal interstitial cells and thymic reticular cells) that display NGF promoter activity from postnatal development to adulthood. Moreover, the transgene is inducible by injury. At 2 days after sciatic nerve ligation, a robust population of EGFP-positive cells is seen in the proximal nerve stump. These transgenic mice offer novel insights into the cellular sites of NGF promoter activity and can be used as models for investigating the regulation of proNGF/NGF expression after injury.

Nerve growth factor

In contrast to all other molecules which are labelled 'growth factor', NGF is not a mitogen. It is a neurotrophic molecule essential for the development and maintenance of function of specific populations of peripheral and possibly also central neurons. The availability of NGF in large quantities from exocrine glands (e.g. male mouse submandibular gland), where NGF does not play a neurotrophic role, has allowed the purification of NGF, the production of specific antibodies, the determination of its amino acid sequence and finally the molecular cloning of NGF leading to the elucidation of its precursor structure and its genomic organization. Comparison of the biological activities and the immunological properties of NGF isolated from different sources demonstrated that the active centre of the molecule has been highly conserved during evolution, whereas other parts of the molecule determining immunological properties have undergone considerable changes. After a survey of the essential biological actions of NGF, this paper concentrates on two actual questions of NGF research, namely the regulation of NGF synthesis in the target tissues of NGF-responsive neurons, and the molecular mechanism(s) of action of NGF on these neurons.

Neurotrophins in clinical diagnostics: pathophysiology and laboratory investigation

There is now growing evidence that a number of multifunctional signaling molecules, originally discovered as signal molecules in specific cells, exert their effects in various other tissue compartments. Neurotrophins, a class of homologues growth factors initially discovered to promote neuronal growth and survival, display such a dual activity and contribute to the development of a variety of non-neuronal tissues. Nowadays, several examples of essential non-neuronal functions played by neurotrophins and of variations of neurotrophin expression that accompany these processes can be presented. As will be shown, neurotrophins are found in many body tissues produced by a variety of non-neuronal cell types such as immune cells, adipocytes, endothelia, epithelia, fibroblasts, keratinocytes and endocrine cells. Assuming a general role as growth and survival factors, changes in neurotrophin expression may reflect physiological or pathological processes, such as activation, proliferation or repair followed by injury in the tissues. Neurotrophins were also present in the systemic blood circulation and variations in blood concentrations indicate vascular as well as peripheral production. In this review, we will discuss changes in local and systemic neurotrophin concentrations as well as their known pathophysiological relationship in various inflammatory and non-inflammatory disorders. Beside the nervous system, these will include diseases of the airways, skin and joints as well as systemic autoimmune diseases. Furthermore, new aspects of neurotrophin actions in maintenance of body energy balance and in reproductive endocrinology will be presented.

Leukemia inhibitory factor receptor signaling negatively modulates nerve growth factor-induced neurite outgrowth in PC12 cells and sympathetic neurons

Nerve growth factor (NGF) is required for the development of sympathetic neurons and subsets of sensory neurons. Our current knowledge on the molecular mechanisms underlying the biological functions of NGF is in part based on the studies with PC12 rat pheochromocytoma cells, which differentiate into sympathetic neuron-like cells upon NGF treatment. Here we report that the expression of leukemia inhibitory factor receptor (LIFR), one of the signaling molecules shared by several neuropoietic cytokines of the interleukin-6 family, is specifically up-regulated in PC12 cells following treatment with NGF. Attenuation of LIFR signaling through stable transfection of antisense- or dominant negative-LIFR constructs enhances NGF-induced neurite extension in PC12 cells. On the contrary, overexpression of LIFR retards the growth of neurites. More importantly, whereas NGF-induced Rac1 activity is enhanced in antisense-LIFR and dominant negative-LIFR expressing PC12 cells, it is reduced in LIFR expressing PC12 cells. Following combined treatment with NGF and ciliary neurotrophic factor, sympathetic neurons exhibit attenuated neurite growth and branching. On the other hand, in sympathetic neurons lacking LIFR, neurite growth and branching is enhanced when compared with wild type controls. Taken together, our findings demonstrate that LIFR expression can be specifically induced by NGF and, besides its known function in cell survival and phenotype development, activated LIFR signaling can exert negative regulatory effects on neurite extension and branching of sympathetic neurons.

Sex-related variations in serum nerve growth factor concentration in humans

A role of nerve growth factor (NGF) in the neuro-endocrine-immune interactions has been recently suggested by the presence of NGF and its receptors in cells of the immune and endocrine systems. The improvement in the comprehension of the role played by NGF in humans is linked to the availability of a sensitive and reliable method to quantify NGF concentrations in body fluids and tissues. As a consequence of different methods used, normal levels of human serum NGF reported in the literature show wide differences. The present results indicate that ELISA appears very sensitive (detection limit 1.4pg/ml) and allows the discrimination of subtle variations of serum NGF concentrations. ELISA performed in serum obtained from men indicated that NGF concentration was 40.8+/-10.8pg/ml, whereas women showed significantly lower levels that were influenced by the menstrual cycle. In particular, the mean value of this neurotrophin during the follicular phase was 8.2+/-1.4pg/ml; the luteal phase, in turn, showed levels up to 14.4+/-2.9pg/ml. The difference of serum NGF concentrations between the follicular and luteal phase in each woman was statistically significant. Differences in NGF concentrations between men and women (in both phases of the menstrual cycles) were also statistically significant. In conclusion, a possible role of sex steroids as modulators of NGF secretion in humans is strongly supported by the present paper. However, mechanisms underlying this phenomenon are still unknown. The evidence indicating physiological sex hormone-related variations in NGF levels would be of interest in view of the possible use of circulating NGF modifications as a laboratory biomarker in different diseases.

Early days of the nerve growth factor proteins

Adult male mouse submaxillary glands served as the preferred starting material for the isolation of the nerve growth factor (NGF) proteins in most of the isolation studies done. Two types of NGF proteins were isolated from extracts of the gland, a high-molecular-weight 7S NGF complex and a low-molecular-weight protein variously called NGF, betaNGF, or 2.5S NGF. The latter, which mediated all known biological functions of NGF, were closely related forms of a basic NGF dimer in which the N and C termini of two monomers (chains) were modified by proteolytic enzymes to different extents with no effect on biological activity. The betaNGF dimer showed a novel protein structure in which the two chains interacted non-covalently over a wide surface. Correspondingly, the betaNGF dimer was found to be unusually stable and the form through which NGFs actions were mediated at physiological concentrations. The betaNGF dimer was one of three subunits in 7S NGF; the other two were the gamma subunit, an arginine esteropeptidase or kallikrein, and the alpha subunit, an inactive kallikrein. Two zinc ions were also present in the complex and contributed greatly to its stability. There was much debate about whether 7S NGF was a specific protein complex of interacting subunits and, if so, what functions it might play in the biology of NGF. Observations of the inhibition of the enzyme activity of the gamma subunit and of the biological activity of betaNGF in 7S NGF were important in determining that 7S NGF was a naturally occurring complex and the sole source of NGF in the gland extract or in saliva. Specific interactions between the active site of the gamma subunit and the C-terminal arginine residues of the NGF chains, confirmed in the three-dimensional structure of 7S NGF, suggested a role for the gamma subunit in pro-NGF processing during the assembly of 7S NGF. In spite of the detailed knowledge of 7S NGF structure, no information on the role of this complex in the neurobiology of NGF has emerged. With the exception of the submaxillary gland of an African rodent, no other source of NGF has been convincingly shown to synthesize the alpha and gamma subunits, and they may well be irrelevant to NGFs actions.

Psychosocial vs. "physical" stress situations in rodents and humans: role of neurotrophins

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are well-studied polypeptide growth factors involved in the development and maintenance of specific peripheral and central populations of neuronal cells. In addition to its role as a neurotrophic agent, NGF controls very complex functions in vertebrate physiology. A variety of cells outside the nervous system are in fact able to synthesize NGF including epithelial cells, fibroblasts, lymphocytes, and macrophages. NGF target cells have been identified in the nervous, immune, and endocrine systems, suggesting that NGF may operate through multiple paths to ultimately regulate physiological homeostasis and behavioral coping. We used a mouse model of social stress to demonstrate that NGF levels increase both in plasma and in the hypothalamus following intermale aggressive interactions. The investigation has been extended to other species, including humans, to show that labour, lactation, and the anticipation of the first jump with a parachute also result in increased NGF plasma levels and in changes in the distribution of NGF receptors on lymphocytes. BDNF activation is caused by both physical and social stress events. The aim of this review is to (1) outline the current understanding of the roles of NGF and BDNF in stress-related physiological changes in vertebrates, in particular for physical vs. psychological stressors, which may activate both similar and different neurobiological pathways, and (2) summarize recent efforts to derive pharmacological strategies from the increasing body of BDNF and NGF neurobehavioral data.

Unusual autonomic ganglia: connections, chemistry, and plasticity of pelvic ganglia

The pelvic ganglia provide the majority of the autonomic nerve supply to reproductive organs, urinary bladder, and lower bowel. Of all autonomic ganglia, they are probably the least understood because in many species their anatomy is particularly complex. Furthermore, they are unusual autonomic ganglia in many ways, including their connections, structure, chemistry, and hormone sensitivity. This review will compare and contrast the normal structure and function of pelvic ganglia with other types of autonomic ganglia (sympathetic, parasympathetic, and enteric). Two aspects of plasticity in the pelvic pathways will also be discussed. First, the influence of gonadal steroids on the maturation and maintenance of pelvic reflex circuits will be considered. Second, the consequences of nerve injury will be discussed, particularly in the context of the pelvic ganglia receiving distributed spinal inputs. The review demonstrates that in many ways the pelvic ganglia differ substantially from other autonomic ganglia. Pelvic ganglia may also provide a useful system in which to study many fundamental neurobiological questions of broader relevance.

Melatonin increases nerve growth factor in mouse submandibular gland

The effect of melatonin administration on nerve growth factor (NGF) was studied in the submandibular glands of adult Swiss male mice. Melatonin injection, at 1 microg daily for 30 days, resulted in an increase in the NGF content as detected by immunohistochemistry. The submandibular gland weight and the area of the granular convoluted tubules, which contained NGF, were also increased significantly. These effects were not observed when the dose of melatonin was increased to 10 and 50 microg daily. None of the melatonin treatments used influenced the weights or histology of the testes or seminal vesicles of the mice. The results suggest that melatonin, at physiological concentrations, directly regulates NGF synthesis in the mouse submandibular gland.

Plasticity in adult and ageing sympathetic neurons

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

NGF regulatory role in stress and coping of rodents and humans

Nerve growth factor (NGF) is a polypeptide growth factor which exerts trophic and differentiative effects on specific peripheral and central populations of neurons. Recent data showing that various cellular types of the endocrine and immune systems are able to synthesize and release NGF have suggested that this neurotrophic factor may also play an important role in vertebrate physiologic homeostasis. Previous studies using a mouse model of aggressive behavior have shown that NGF levels increase in both plasma and the CNS following intermale agonistic encounters. More recently, we have extended this research area to include other species: in particular, humans. The data now available indicate that labour and lactation, or the occurrence of a stressful event such as the very first jump with a parachute causes in NGF plasma levels as well as changes in the distribution of NGF receptors on lymphocytes. This review aimed to outline the current understanding of NGF role in vertebrates in stress-related events.

Update of the NGF saga

Nerve growth factor (NGF), initially characterized for its survival and differentiating actions on embryonic sensory and sympathetic neurons, is now known to display a greatly extended spectrum of biological functions. NGF exerts a profound modulatory role on sensory nociceptive nerve physiology during adulthood which appears to correlate with hyperalgesic phenomena occurring in tissue inflammation. Other newly detected NGF-responsive cells belong to the hematopoietic-immune and neuroendocrine systems. In particular, mast cells and NGF both appear to be involved in neuroimmune interactions and tissue inflammation, with NGF acting as a general "alert" molecule capable of recruiting and priming both local tissue and systemic defense processes following stressful events. NGF can thus be viewed as a multifactorial mediator modulating neuroimmune-endocrine functions of vital importance to the regulation of homeostatic interactions, with potential involvement in pathological processes deriving from dysregulation of either local or systemic homeostatic balances.

Flutamide-induced testicular undescent in the rat is associated with alterations in genitofemoral nerve morphology

Androgen regulation of testicular descent is an established fact. However, the mechanisms by which androgens assert their influence is unknown. One of the leading hypotheses regarding androgenic control of testicular descent is based upon the assumption that testosterone regulates the development of the sexually dimorphic genitofemoral nucleus and nerve (GFN). To investigate whether or not alterations in the genitofemoral nerve are indeed androgen dependent and associated with testicular undescent, we administered flutamide in a time-specific manner to pregnant Sprague-Dawley rats. The GFN of ten animals with unilateral intra-abdominal testicular undescent was compared with the contralateral GFN associated with the descended testicle. Digital microscopic evaluations found that the GFN associated with testicular undescent did express altered morphologic abnormalities. Specifically, the GFN associated with the cryptorchid testicle had significant reductions in the neural diameter (.0169 +/- .0024 mm.2 versus .0275 +/- .0079 mm.2; p < .01), the number of large myelinated fibers per mm.2 (8.4 +/- 3.3 versus 18.8 +/- 5; p < .001) and the number of small myelinated nerve fibers per mm.2 (632 +/- 87.4 versus 1090.7 +/- 104.3; p < .001). These data suggest that testicular undescent in the rat is associated with morphologic alterations in the ipsilateral genitofemoral nerve. The exact mechanism of how these alterations are related to cryptorchidism remains to be elucidated.

The granular convoluted tubule (GCT) cell of rodent submandibular glands

The granular convoluted tubule (GCT) is a segment of the duct system of all rodents, situated between the striated and intercalated ducts. It has the peculiar property of synthesizing a large variety of biologically active polypeptides whose role in saliva remains unknown. The literature on the fine structure of GCT cells is critically reviewed. Some recent developments on endocrine regulation of the structure and contents of rodent GCT cells are summarized, with emphasis on EGF, NGF, renin, and kallikrein proteases. A survey of the distribution of GCT cells in several vertebrate families is presented.

Molecular aspects of the regulation of tyrosine hydroxylase by testosterone

Previous studies have demonstrated that the sympathetic hypogastric ganglia (HG) are dependent upon the continued presence of testosterone for normal development and maintenance of tyrosine hydroxylase (TH) activity. The regulation of TH by testosterone has been examined further to determine whether the reduction in TH activity following castration is associated with changes in levels of TH protein and mRNA. TH protein was measured by immunotitration of HG homogenates using a TH-specific antibody, and TH-specific mRNA was detected by hybridization of dot blots of total RNA isolated from HG with a cDNA probe coding for TH. The results show that tyrosine hydroxylase activity, protein and mRNA are coordinately reduced in a graded fashion at 1, 2 and 4 weeks following castration. Testosterone replacement therapy immediately following castration prevents the decrease in TH levels. The results indicate that gonadal steroids regulate the biosynthesis of TH in the HG. Testosterone may control TH either directly by interacting with neurons of the HG, or indirectly by altering levels of trophic factors in the target tissues.

Induction of NGF by isoproterenol, 4-methylcatechol and serum occurs by three distinct mechanisms

Evidence is provided that isoproterenol, 4-methylcatechol and serum induce NGF by three separate mechanisms. Isoproterenol and 4-methylcatechol induced NGF and NGF mRNA in mouse fibroblast L929 cells in either the presence or absence of serum. Propranolol prevented NGF induction by isoproterenol, but not by 4-methylcatechol or serum. All possible combinations of these inducers resulted in additive increases in the levels of NGF and NGF mRNA.

Effects of estrogen and fimbria/fornix transection on p75NGFR and ChAT expression in the medial septum and diagonal band of Broca

NGF receptor-expressing cells located in the basal forebrain have recently been shown to contain estrogen (E) receptors (Toran-Allerand and MacLusky. 1989. Soc. Neurosci. Abstr. 15: 954). In the present study, we have examined the effects of E-treatment on p75NGFR and choline acetyltransferase (ChAT) expression by neurons in the medial septum (MS) and the vertical (VDB) and horizontal (HDB) limbs of the diagonal band of Broca using immunocytochemical and in situ hybridization techniques. First, since E-treatment has been shown to affect neuronal survival and to stimulate synaptic reorganization and growth within various regions of the brain, we hypothesized that E-treatment might attenuate the loss of p75NGFR immunoreactivity (IR) which occurs in the MS and VDB following transection of the fimbria/fornix. Contrary to our hypothesis, E-treatment did not attenuate the effects of fimbria/fornix transection. In fact, E-treatment alone produced a significant decrease in the number of p75NGFR-IR cells detected in the MS. Subsequent experiments confirmed that chronic E-treatment produces a down-regulation of both p75NGFR-IR and p75NGFR mRNA in the MS and VDB. In the MS, estrogen appeared to affect a subpopulation of p75NGFR-expressing neurons which were also affected by fimbria/fornix transection since the effects of these two treatments were not additive. In addition, effects of E-treatment on p75NGFR-IR were sex-specific (observed in females but not in males) and were reversible in the MS after 2 weeks, but not after 4 weeks (allowing 2 weeks recovery), of E-treatment. A time-course analysis revealed that effects of E-treatment on p75NGFR-IR were not observed until after 16 days (MS) or 30 days (VDB) of E-treatment and were preceded by a significant and transient increase in ChAT expression in both the MS and VDB. The data are consistent with the possibility that continuous, long-term exposure to gonadal steroids may contribute to a loss of p75NGFR-expressing neurons with age. In addition, the data suggest that p75NGFR expression may play a role in regulating the functioning of specific basal forebrain cholinergic neurons. Different mechanisms by which E-treatment might influence ChAT and p75NGFR expression in brain are discussed.

Thyroid hormone and androgen regulation of nerve growth factor gene expression in the mouse submandibular gland

The nerve growth factor (NGF) content of the mouse submandibular gland (SMG) is under hormonal control and is modulated by both thyroid hormones (TH) and androgens. The sexual dimorphism of the gland is well documented. In the adult male mouse, the SMG contains 10 times more NGF compared to the female. Conversely, castration of male mice reduces the SMG NGF levels to those found in control females. In order to determine the locus at which androgens and TH exert their effect on NGF gene expression in the SMG, steady-state NGF mRNA levels were determined. Daily treatment of adult female mice with TH for 1 week increased NGF mRNA levels 6-fold. Androgen treatment produced a 20-fold increase in SMG NGF mRNA, which was comparable to levels detected in the control adult male SMG. The effect of TH on NGF mRNA levels was time-dependent and coincided with the increase in NGF protein concentrations. At 48 h after a single TH injection, NGF mRNA levels (measured in SMG total RNA) increased 2-4-fold, while heteronuclear (hn) RNA levels were increased 1.5-2-fold. The NGF gene transcription rate was determined by run-on assay following TH treatment. A small but significant 2-fold induction by TH of NGF gene transcription was found at 24-48 h. Cytoplasmic RNA prepared from the same SMGs used in the run-on experiments was tested by S1 nuclease protection; NGF cytoplasmic RNA was increased 7-fold in the SMGs of females treated with TH 48 h previously. These results demonstrate that the effect of TH on NGF gene expression is due in part to an induction of NGF gene transcription. The discrepancies observed between transcription rate and mRNA levels suggest that the major effect of TH is at the post-transcriptional level, possibly mRNA stabilization. The time required to observe an induction of TH on NGF gene transcription is suggestive of an indirect effect, possibly through the induction by TH of another protein which in turn activates the NGF gene.

Hyperalgesia induced in the rat by the amino-terminal octapeptide of nerve growth factor

Nerve growth factor (NGF) in the mouse submandibular gland undergoes cleavage of its amino-terminal octapeptide when salivation is induced by epinephrine. The significance of this event is uncertain; cleaved NGF demonstrates bioactivity and no function has been attributed to the octapeptide produced (NGF-OP; Ser-Ser-Thr-His-Pro-Val-Phe-His). Enzyme inhibition studies indicating structural relatedness of NGF-OP and bradykinin (BK) prompted us to determine whether NGF-OP would elicit BK-like actions. We found that like BK, NGF-OP induced a decrease in mechanical nociceptive threshold (i.e., produced hyperalgesia) in the hairy skin of the rat. This effect was dose-dependent and sequence-specific; like BK it was attenuated by sympathectomy and indomethacin pretreatment. However, NGF-OP actions appeared to be distinct from those for BK in that tissue injury was required for NGF-OP to induce hyperalgesia. Furthermore, we found no evidence that NGF-OP bound to or activated BK receptors. Our data indicate that NGF-OP is a distinct mediator of hyperalgesia. We suggest that NGF-OP alters pain threshold in the injured target regions of NGF-responsive neurons.

Purification and tissue distribution of rat epidermal growth factor

1. Two forms of rat epidermal growth factor, EGF-I and EGF-II, were purified to homogeneity from male rat submandibular glands. 2. The mol. wts of EGF-I and -II were estimated to be 5200 and 5400, respectively, both of them having an apparent biological activity. 3. The antiserum against EGF-II strongly cross-reacted with EGF-I; however, it did so only slightly with mouse or human EGF. 4. EGF was detected by radioimmunoassay in various tissues of male and female rats, and the concentrations of rat EGF in the submandibular gland, parotid gland, sublingual gland, and liver were significantly higher in the male than in the female.

Structure and biosynthesis of nerve growth factor

Most of our knowledge about NGF comes from extensive study of the mouse submaxillary gland protein. NGF from this source is isolated as a high molecular weight complex consisting of beta-NGF and two subunits, alpha and gamma, belonging to the kallikrein family of serine proteases. There are few other tissues where NGF is found in sufficient quantities for protein purification and study, although new molecular biological techniques have accelerated the study of NGFs from a variety of species and tissues. Mouse submaxillary gland NGF is synthesized as a large precursor that is cleaved at both N- and C-terminals to produce mature NGF. This biologically active molecule can be further cleaved by submaxillary gland proteases. The roles of the alpha and gamma subunits in the processing of the beta-NGF precursor, the modulation of the biological activity of beta-NGF, and the protection of mature beta-NGF from degradation have been well studied in the mouse. However, the apparent lack of alpha and gamma subunits in most other tissues and species and the existence of a large family of murine kallikreins, many of which are expressed in the submaxillary gland, challenge the relevance of murine high molecular weight NGF as a proper model for NGF biosynthesis and regulation. It is important therefore to identify and characterize other NGF complexes and to study their subunit interactions, biosynthesis, processing, and regulation. This review points out a number of other species and tissues in which the study of NGF has just begun. At this time, there exist many more questions than answers regarding the presence and the functions of NGF processing and regulatory proteins. By studying NGF in other species and tissues and comparing the processing and regulation of NGF from several sources, we will discover the unifying concepts governing the expression of NGF biological activity.

Reduction of nerve growth factor level in the brain of genetically ataxic mice (weaver, reeler)

By a highly sensitive enzyme immunoassay we measured the level of nerve growth factor (NGF) in the cerebellum and cerebrum of the neurologically mutant mice, weaver, reeler and Purkinje cell degeneration (PCD). A significant decrease in NGF level was observed in both cerebellum and cerebrum of weaver and reeler mutants of either sex. However, there was no such difference between normals and mutants in the case of the PCD mice. These results show that weaver and reeler mice have abnormalities of NGF synthesis and/or degradation not only in the cerebellum but also in the cerebrum.

The impact of sexual dimorphism on neuron numbers in the superior cervical ganglion of the rat

Other workers have reported a sexual dimorphism in the number of neurons that project from the rat superior cervical ganglion (SCG) via the internal carotid nerve (ICN). We have re-examined this situation by comparing ganglionic neuron numbers as well as the number of neurons labelled retrogradely from the iris and the pineal gland, in age-matched adult male and female rats. No significant dimorphism was seen in total cell numbers or in the cell populations supplying iris or pineal gland, although there was a trend towards more neurons in male animals. From evaluation of our results and the published data, we suggest that the variation in absolute numbers of neurons counted in the SCG is so wide, within genders, that any impact of gender differences on cell numbers is of little significance.

Cell-specific and developmental regulation of a nerve growth factor-human growth hormone fusion gene in transgenic mice

We recently showed that a nerve growth factor-human growth hormone (NGF-hGH) fusion gene containing the promoter and 750 bp of 5' flanking region is transcriptionally active in the NGF-secreting L929 mouse fibroblast cell line. For the present experiments, we extended the 5' flank by 5 kb and constructed transgenic mice. These mice began to secrete hGH into saliva at puberty. hGH was detected immunocytochemically in the granulated convoluted tubular cells of the submandibular gland (SMG). SMG levels of hGH mRNA were 10-fold higher in adult males than in females. hGH mRNA was very abundant in SMG, moderately abundant in heart, brain, and kidney, rare in skin and adrenal gland, and undetectable in lung, liver, and spleen. Thus, the NGF-hGH gene reflects NGF gene expression. We conclude that basal NGF gene transcription is regulated by sequences in the cloned NGF gene fragment.

The NGF and kallikrein genes of mouse, the African rat Mastomys natalensis and man: their distribution and mode of expression in the salivary gland

The kallikrein genes and their expression in the salivary glands of mouse, the African rat Mastomys natalensis and human were compared. The Mastomys kallikrein genes comprise a family of genes similar to those of mouse. Androgen markedly enhances transcription of glandular nerve growth factor (NGF) and kallikrein in both male and female Mastomys suggesting the presence of testosterone regulated kallikrein genes for growth factor precursor-processing in both sexes. In contrast, although a kallikrein transcript was detected in human salivary glands of the same size as the mouse or Mastomys transcript no difference in the amount of transcript was seen in adult male or female. The absence of kallikrein genes regulated by testosterone and of NGF transcripts in the human implies that there is no human equivalent of the mouse salivary 7S NGF complex.

Developmental changes of nerve growth factor levels in sympathetic ganglia and their target organs

The predominant source of nerve growth factor (NGF) used by mature sympathetic neurons originates in their target organs (Heumann, R., Korsching, S., Scott, J., and Thoenen, H. (1984), EMBO J. 3, 3183-3189; Korsching, S., and Thoenen, H. (1985), J. Neurosci. 5, 1058-1061). We have determined the NGF content of two sympathetically innervated mouse organs, submandibular gland and heart ventricle, and of sympathetic ganglia from mouse and rat between embryonic Day 12 (E12) and adulthood. NGF levels were measured by a two-site enzyme immunassay (Korsching, S., and Thoenen, H. (1983), Proc. Natl. Acad. Sci. USA 80, 3513-3516). In heart ventricle and submandibular gland, NGF first became detectable around the time of initial innervation by sympathetic neurons (E12 and E13, respectively) and increased respectively 14- and 7-fold in the following 2 days, to reach adult levels already at E14 for heart ventricle (1.4 +/- 0.2 ng NGF/g wet wt). NGF in the superior cervical ganglion (SCG) was first detected at the same time as in its target organ, the submandibular gland. NGF content in the SCG then increased 6-fold during the next 2 days and continued to increase until the end of the third postnatal week, when adult levels were reached. Although the levels of NGF in the adult mouse submandibular gland are sexually dimorphic and six orders of magnitude higher than those in other sympathetic target organs, no sex difference in the NGF content was found in either developing submandibular gland or SCG until the end of the third postnatal week. Moreover, the steep NGF increase observed in the male submandibular gland after postnatal Day 18 (250-fold within the following 3 days and up to the 55,000-fold in the next 7 days) was not reflected in a corresponding increase in the NGF content of the male SCG. These data indicate that, in accordance with earlier findings (see Levi-Montalcini, R., and Angeletti, P. U. (1968), Physiol. Rev. 48, 534-569), SCG neurons do not have access to the large amounts of NGF synthesized during and after adolescence in the mouse submandibular gland. Our results support the concept that initial fiber outgrowth of sympathetic neurons is neither dependent on NGF nor mediated by it. The time course of NGF levels in the SCG is consistent with the concept that sympathetic neurons are provided with NGF by means of retrograde axonal transport from the innervated organs already early in development.

De novo synthesis of NGF subunits in S-180 mouse sarcoma cell line

It is an accepted hypothesis that the nerve growth factor protein (NGF) plays an important role in the development of vertebrate sympathetic and sensory ganglia and has effects on some central neurons. The best known NGF species is that isolated from mouse submaxillary gland, MSG-NGF. MSG-NGF can be isolated as a subunit containing protein, 7S-NGF, made up of three dissimilar subunits called alpha-, beta-, and gamma-NGF. Beta-NGF is the biologically active subunit and its synthesis in vivo and in vitro has been demonstrated. Less is known about the synthesis of the alpha- and gamma-NGF or the assembly of the subunits into the 7S complex. In order to develop a clonal model system for the study of NGF synthesis, processing and secretion, affinity chromatography techniques were applied to cell extracts of S180 mouse sarcoma, a cell line known to synthesize NGF. After incubating S180 cells in 35S-Methionine, cell extracts were exposed to antibody directed against alpha-NGF, gamma-NGF or beta-NGF covalently bound to Sepharose beads in order to elute and characterize the desired NGF subunits. Parallel experiments using immunoabsorbed [35S]Methionine-beta-NGF were carried out in the presence or absence of excess NGF, in order to demonstrate the specificity of this procedure. Affinity chromatography with a substrate analogue to arginine ester bound to Sepharose beads was also used to isolate de novo synthesized gamma-NGF.(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve growth factor modulates tubulin transcript levels in pheochromocytoma PC12 cells

We report that nerve growth factor (NGF) can elevate tubulin transcript levels in cultured rat pheochromocytoma PC12 cells in a manner which correlates with its capacity to enhance neurite formation. The elevation is due, at least in part, to transcript stabilization. We have previously shown that insulin and its homologs can similarly enhance neurite outgrowth and tubulin mRNA levels in human neuroblastoma cells. Insulin by itself can neither induce neurite formation nor increase tubulin transcript levels in PC12 cells. However, both responses are potentiated in cells treated with the combination of insulin and NGF. The results together support the generalization that tubulin transcript levels are specifically elevated whenever neurite elongation is initiated by polypeptide neuritogenic factors.

Altered sympathetic-salivary gland development: delayed response to postnatal castration

These studies defined the normal and hormonally altered development of activity for tyrosine hydroxylase (T-OH), the rate-limiting enzyme in catecholamine biosynthesis (Levitt et al., 1965), and choline acetyltransferase activity (CAT) in the male rat superior cervical ganglion (SCG). Additionally, salivary gland weight was monitored. Two distinct developmental plateaus for postsynaptic T-OH activity exist. The first plateau represents the prepubertal level, which is significantly lower than the second postpubertal plateau. In contrast, presynaptic CAT activity displayed only a single plateau, commencing at approximately 45 days of age. The effects of postnatal castration (at 10 or 11 days of age) on the submandibular gland and T-OH activity were delayed until after puberty. No change in T-OH activity was seen at two and four post-operative weeks between control and castrated animals; however, T-OH activity was significantly less in castrated animals at 12 and 16 post-operative weeks. Testosterone replacement reversed the effect of castration on T-OH activity. Conversely, CAT activity in the SCG was unchanged by postnatal castration for at least 16 post-operative weeks, the longest time point studied. The failure of castrated animals to display the normal developmental increase in T-OH activity following puberty was comparable with the effect of castration on the development of submandibular salivary gland weight. These results suggest that in postpubertal male rats, development of T-OH activity in the superior cervical ganglion is influenced by testosterone. The parallel effects of castration on submandibular gland weight imply that testosterone regulates T-OH activity via an indirect mechanism. In contrast to noradrenergic enzyme activity and target tissue size, the ontogeny of presynaptic CAT activity appears to be insensitive to testosterone levels.

Sex differences in nerve growth factor levels in superior cervical ganglia and pineals

The current studies were undertaken to determine whether males or neonatally testosterone-treated rats of either gender have elevated endogenous levels of NGF in the SCG and one of its targets, the pineal gland. The ages studied were 5 days postnatal, which is at the peak of normal neuron death in the SCG but before a significant gender difference is present; 15 days, when normal neuron death is largely complete and males have more SCG neurons than females; and 30 days, when target innervation has matured. At 5 days, while neuron death is occurring, but before there is a significant gender difference in neuron number in the SCG, pineal glands and SCGs of males had higher NGF content than those of females. The increased NGF in the ganglia of males at the time that these neurons are undergoing neuron death may play a role in the development of the sex difference in SCG neuron numbers. At 15 days, females had more NGF in their pineal glands and SCGs than did males, even though males have significantly more SCG neurons at this age than do females. This gender difference in the developmental course of NGF content could promote the survival of different populations of neurons in males and females. By 30 days, SCG and pineal NGF content of males was almost twice that of females. This is consistent with the presence of more neurons in the SCGs of males at this age. Both the pineal gland and the SCG showed a loss of approximately 80% content of NGF during the first postnatal month(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve growth factor (NGF) in serum: evaluation of serum NGF levels with a sensitive bioassay employing embryonic sensory neurons

Considerable controversy surrounds the question of whether or not nerve growth factor (NGF) or a related nerve growth-promoting factor is present in serum. Recently, supporting its role as a local neuronotrophic factor, the presence of NGF in glial cells and its production in target tissues of NGF-responsive neurons were demonstrated [Rush: Nature 312:364-367, 1984; Heumann, Korsching, Scott, Thoenen: EMBOJ 3:3183-3189, 1984; Shelton and Reichardt: Proc Natl Acad Sci USA 81:7952-7955, 1984]. At the same time, the concept that NGF may play a role as a humoral factor has been questioned, since careful analyses of serum with specific and sensitive radioimmunoassays [Suda, Barde, Thoenen: Proc Natl Acad Sci USA 75:4042-4046, 1978; Korsching and Thoenen; Proc Natl Acad Sci USA 80:3513-3516, 1983; Furukawa, Kamo, Furukawa, Akazawa, Satoyoshi, Itoh, Hayashi: J Neurochem 40:734-744, 1983] as well as bioassays [Skaper and Varon: Exp Neurol 76:655-665, 1982] have not confirmed earlier reports [Levi-Montalcini and Booker; Proc Natl Acad Sci USA 46:373-391, 1960; Banks, Banthorpe, Charlwood, Pearce, Vernon: Nature 246:503-504, 1973; Hendry: Biochem J 128:1265-1272, 1972] on NGF's representation in serum. In this study serum from mouse, rat, and man was analyzed with an in vitro bioassay system which employs sensory neurons from chicken embyro dorsal root ganglia and which allows the measurement of NGF concentrations as low as 0.8 pM. It was found that sera from all these species contained neuronotrophic activity (S-NGF). The target cell spectrum as well as characteristic parameters of the neuronal growth response of S-NGF and of NGF were identical. S-NGF of mouse serum was completely inhibitable by polyclonal and monoclonal antibodies to mouse submandibular gland beta NGF. On polyacrylamide isoelectric focussing gels mouse and human S-NGF could be recovered from the same position as NGF as well as from the region where alpha 2-macroglobulin and serum albumin focused. In newborn and adult male and female mice basal S-NGF levels were equivalent to 10-50 pM NGF. A fraction of the serum samples of male mice showed elevated S-NGF levels. The incidence of high S-NGF levels was more frequent in NMRI and C57BL/6 males than in BALB/c males. Following sialectomy of male mice only basal S-NGF levels were observed up to 5 weeks after the operation. This indicates that although the submandibular gland may contribute to S-NGF levels in serum under certain conditions that appeared to be stress related, it cannot be the only source of S-NGF.

Uptake and transepithelial transport of nerve growth factor in suckling rat ileum

Nerve growth factor (NGF) is necessary for the development of sympathetic and some sensory neurons. Milk may be a source of NGF for suckling young, but sites of intestinal absorption of the protein have not been identified. To determine whether NGF is transported across the absorptive epithelium of suckling rat ileum, we assessed binding, uptake, and transport of 125I-NGF by light microscopy and EM autoradiography. Blood and tissue extracts were analyzed by biochemical and immunological methods to determine whether NGF was taken up structurally intact. NGF binding sites were identified on microvilli and apical invaginations of ileal absorptive cells in vitro. Injected into ileal loops in vivo, NGF radioactivity retained by fixation was evident after 20 min in apical regions of absorptive cells, in endocytic tubules (which mediate the uptake of membrane-bound ligands), in vesicles (which mediate nonspecific endocytosis), and in the supranuclear lysosomal vacuole. At 1 and 2 h, radiolabel in these compartments increased and silver grains were evident at the basal cell surface, and in cells, matrix, and vessels of the lamina propria. In blood and liver, radiolabeled molecules that were immunologically and electrophoretically indistinguishable from NGF and that co-eluted with NGF on gel filtration columns were detected, confirming that some NGF was transported across the epithelium structurally intact. Thus, absorptive cells of suckling rat ileum can take up NGF by both receptor-mediated and nonspecific endocytosis, and direct NGF either to the lysosome for degradation, or into a transepithelial transport pathway.

Dexamethasone rapidly reduces the expression of the beta-NGF gene in mouse L-929 cells

Mouse L-929 cells were treated with dexamethasone, and the cellular levels of beta-NGF mRNA were estimated by hybridization of the RNAs with a beta-NGF cDNA probe. The results revealed that the glucocorticoid decreased specifically, in a dose-dependent manner, the pool of beta-NGF transcripts. After 4 h, L-929 cells cultured with 10(-7) M dexamethasone contained one-fifth as much beta-NGF mRNA as untreated control cells, and as little as one-tenth as much when the glucocorticoid concentration was 10(-6) M. The effect of the hormone became maximal after 8 h of treatment. Amounts of beta-NGF secreted by the cells during 24 h were measured with a two-site enzyme immunoassay. They also appeared reduced in cultures exposed to the glucocorticoid. These data indicate that dexamethasone controls negatively the expression of the beta-NGF gene in L-929 cells at some pre-translational level.

Multiple sites of regulation of mouse renin expression in ontogeny

How local renin expression is regulated in many tissues has yet to be defined. In the present studies the ontogeny of renin in submandibular gland (SMG) and kidney of CD-1 mice was examined in order to determine whether renal and extrarenal renin are similarly expressed. In males, submandibular gland (SMG) renin and renin secretory rate increase at puberty as androgen rises. The ratio of secreted forms (1-chain renin cf. 2-chain) seen on Western blots shows predominance of 1-chain prior to puberty and 2-chain thereafter. This androgen influence on renin processing and secretion was supported by reversion to prepubertal patterns with castration of adult males and by conversion to male pattern in androgen treated females which otherwise have low renin levels. In contrast, renal renin remains unchanged throughout development. The influence of ontogeny on renal and SMG renin mRNA was examined by Northern analysis using renin cDNA: SMG renin mRNA increases from near zero to high levels at puberty while renal renin mRNA level is high throughout. Taken together, these data suggest that SMG renin is influenced by androgens, whereas renal renin is not. Apparent differences in tissue renin regulation may have important implications for local function of this enzyme.

Insulin, insulin-like growth factor II, and nerve growth factor effects on tubulin mRNA levels and neurite formation

We have previously shown that insulin and the insulin-like growth factors share some important neurotrophic properties with nerve growth factor (NGF), including the capacity to enhance neurite formation. In this study, we have examined the effects of these neuritogenic agents on the expression of genes coding for important cytoskeletal proteins of axons and dendrites. Insulin specifically and coordinately increased the levels of alpha- and beta-tubulin mRNAs in human neuroblastoma SH-SY5Y cells. The dose-response curves for these increases were very similar to that for enhancement of neurite formation. Tubulin transcripts reached a transient maximum in approximately 1 day, suggesting that higher levels are important during initiation of neurites and that high levels are not required to sustain neurites once formed. Insulin-like growth factor II shared with insulin the capacity to substantially increase tubulin mRNA levels. NGF had but a small effect. Complementary mechanisms for these neurotrophic agents are suggested, because other studies show NGF and insulin can synergistically potentiate neurite formation. None of the factors altered the levels of actin mRNA. Thus, neurite formation does not seem to require a coordinate increase in actin and tubulin transcripts in SH-SY5Y cells.

Serum and thyroid hormones T3 and T4 regulate nerve growth factor mRNA levels in mouse L cells

Mouse L cells synthesize and secrete a neurotrophic factor related to the beta subunit of the submaxillary gland nerve growth factor (NGF) of male mice. Use of a cDNA probe which encodes the beta-NGF mRNA demonstrated that L cells produce a transcript identical in size to that of the submaxillary gland. Moreover, target sites of restriction enzymes EcoRI, PstI and BamHI were not significantly rearranged in the beta-NGF gene locus of these cells. The abundance of the beta-NGF transcript was found to depend on culture conditions. Removal of serum depressed the cellular content of polyadenylated RNA by a factor of 1.7, and decreased specifically the pool of beta-NGF transcript by an additional factor of 4. The presence of 10(-7) M testosterone in the serum-free medium did not modify the level of beta-NGF mRNA, while addition of 10(-7) M T3 (or T4) increased this level by a factor of 1.5. These data provide the first evidence that the beta-NGF mRNA of L cells is subjected to regulation, but in a way apparently different from that described for the submaxillary gland.

Neurite formation modulated by nerve growth factor, insulin, and tumor promoter receptors

Until recently, nerve growth factor could be considered the only neurotrophic factor with an established physiological role. We discuss the emerging evidence indicating that the insulinlike factors may constitute a family of related neurotrophic proteins, and the observations suggesting that the receptor for the phorbol ester tumor promoters is closely associated with neuronal differentiation. The emphasis of the discussion is placed on neurite formation under multiple modulation by insulinlike factors, nerve growth factor, and tumor promoter receptors in sensory, sympathetic and human neuroblastoma cells.

Effects of insulin, insulin-like growth factor-II and nerve growth factor on neurite outgrowth in cultured human neuroblastoma cells

The identification of biologically important and chemically well-defined substances that can promote axon and dendrite formation would improve present understanding of the development of the nervous system. Physiological concentrations of insulin and insulin-like growth factor-II (IGF-II) reversibly enhanced neurite outgrowth (NTO) in human neuroblastoma SH-SY5Y cells cultured in media with and without serum. Nerve growth factor (NGF), in contrast, did not enhance NTO in serum-free media. Furthermore, anti-NGF antiserum inhibited NGF but not insulin-enhanced NTO. Insulin increased [3H]leucine and [3H]uridine uptake. These increases, together with increased NTO, were inhibited by cycloheximide and actinomycin D, respectively. The inhibition of NTO by cycloheximide was reversible. Human neuroblastoma cell lines that were responsive by NTO to NGF were also responsive to insulin, with the exception of line CHP-270. Moreover, cell lines unresponsive by NTO to NGF, and to tumor promoters, were uniformly unresponsive to insulin. These findings suggest that there are common defects in distal sites, because specific NGF and tumor promotor receptors are present in these lines. Insulin increased [3H]thymidine uptake in SH-SY5Y and CHP-100 cells. However, the enhancement of NTO by insulin and IGF-II in SH-SY5Y cells was independent of the cellular proliferation rate. Our results, together with the observations of others, suggest that insulin and IGF-II may modulate NTO in the nervous system.

Insulin and insulin-like growth factor II permit nerve growth factor binding and the neurite formation response in cultured human neuroblastoma cells

In serum-free medium, SH-SY5Y human neuroblastoma cells specifically and reversibly lost the capacity to bind 125I-labeled nerve growth factor (NGF) to the high-affinity sites (slow sites) and to respond by neurite outgrowth, unless physiological concentrations of insulin or insulin-like growth factor II were present. In serum-containing medium, anti-insulin antiserum decreased the neurite formation response to NGF, and insulin supplementation increased the number of available NGF slow sites. The low-affinity NGF fast sites are absent from SH-SY5Y cells and did not emerge on treatment with insulin. Insulin potentiated the induction of neurites by NGF in rat pheochromocytoma PC12 cells also. These results implicate a wider role for insulin and its homologs in the nervous system.

Hyperplasia in the spinal sensory system of the frog. II. Central and peripheral connectivity patterns

Central and peripheral connectivity patterns of hyperplastic dorsal root ganglia (DRGs) in Rana pipiens are examined in order to determine the relative roles of peripheral and central contacts in the production of DRG hyperplasias. The hyperplasias are produced in the intact hindlimb DRGs after the removal in tadpoles and young postmetamorphic frogs of neighboring DRGs (Davis and Constantine-Paton, '83). The peripheral target zones of the hyperplastic DRGs, determined by physiological recordings of sensory receptive fields, are found to undergo a significant degree of expansion relative to controls. Peripheral expansion is most pronounced in caudalmost DRG 10, and this effect occurs in experimental animals operated during larval and postmetamorphic stages. Further, anatomical labelling of peripheral sensory fibers coursing to the hindlimb reveals that the hyperplastic DRG 10 actually contains additional fibers projecting to the denervated regions. The central projection of the hyperplastic DRG 10 does not show corresponding increases in longitudinal arborization after the application of horseradish peroxidase to the appropriate dorsal roots. These observations are made on some of the same experimental animals in which peripheral fields are shown to have vastly expanded. We conclude that the peripheral processes of the hyperplastic DRGs are less rigidly specified than the central terminations, and that it is the periphery which plays the primary role in controlling the cell numbers increases. A second aim of this investigation is to identify whether sexually dimorphic connectivity patterns in normal frogs explain the production of DRG 10 hyperplasias exclusively in male experimental animals (Davis and Constantine-Paton, '83). We apply the same techniques used in our connectivity studies of hyperplastic DRGs to the investigation of connectivity patterns of DRG 10s in normal males and females. No sex-dependent differences in peripheral and central connectivity are found. Thus, since normal male and female frogs possess an equivalent amount of target space for DRG 10, the unique production of hyperplasias in male experimental animals cannot be explained solely on the basis of connectivity. We speculate on what other factors may be involved.

Human beta-nerve growth factor gene sequence highly homologous to that of mouse

Nerve growth factor (NGF) is thought to have a profound effect on the development and maintenance of sympathetic and embryonic sensory neurones (see refs 1-3 for review). NGF activity isolated from the male mouse submaxillary gland (MSG) consists of three types of subunits, alpha, beta and gamma, which specifically interact to form a 7S, approximately 130,000-molecular weight (Mr) complex. The 7S complex contains two identical 118-amino acid beta-chains, which are solely responsible for the nerve growth-stimulating activity of NGF. While NGF is found in almost all vertebrates, most research has focused on murine NGF, as the mouse male submaxillary gland contains higher levels of this polypeptide than other tissues. Even so, beta-NGF comprises only approximately 0.1% of the protein in this small gland, which has made the study of this polypeptide difficult. The amino acid sequence of the mouse NGF beta-chain has been determined and some information has been obtained regarding the size of a mouse precursor molecule, pro-beta-NGF, but little was known about the structure and relatedness of beta-NGF from other vertebrates. Here we describe the isolation of mouse beta-NGF complementary DNA (cDNA) and present its nucleotide sequence, which predicts a prepro-beta-NGF molecule of Mr 27,000 (27K) and a pro-beta-NGF molecule of Mr 25K. We have used the mouse beta-NGF cDNA clone to isolate the human beta-NGF gene, the coding regions of which are highly homologous to the mouse prepro-beta-NGF nucleotide and amino acid sequences.

Neonatal testosterone treatment increases neuron and synapse numbers in male rat superior cervical ganglion

Neonatal treatment with gonadal steroids has been reported to alter morphological as well as functional development in various regions of the brain and spinal cord. Among the observed alterations are changes in numbers of neurons and in the organization and numbers of synapses. These regions have been found to be sexually dimorphic, and the dimorphism dependent upon gender differences in circulating levels of gonadal steroids. Neonatal treatment with testosterone has been shown to produce an increase in the number of neurons in the superior cervical sympathetic ganglion in female rats. The present studies were designed to investigate the possibility of a normally occurring sexual dimorphism in the SCG of the rat, and to characterize the effect of neonatal treatment with testosterone on neurons and synapses in the male rat. We report a sexual dimorphism in the number of neurons but not in the number of preganglionic axons or ganglionic synapses. In addition, neonatal administration of testosterone propionate results in a 40% increase in the number of superior cervical ganglion neurons in treated male rats over the control male number at 15 and 30 days of age. The testosterone propionate treatment results in a 66% increase in the number of synapses in male superior cervical ganglia, without a concomitant increase in the number of preganglionic axons.

Nerve growth factor effects and receptors in cultured human neuroblastoma cell lines

We studied the effects of nerve growth factor (NGF) to determine whether neuroblastoma (NB) cells share the pattern of altered response to growth regulatory factors shown by various malignant transformed cells. NGF induces neurite outgrowth, arrests growth, and enhances survival in normal neurons and in the rat pheochromocytoma, a tumor cell closely related to NB. With respect to neurite outgrowth, lines SK-N-SH, SH-SY5Y, LA-N-5, and CHP-126 were sensitive, IMR-32 was resistant, and SH-EP1, SK-N-MC, MC-IXC, CHP-100, and CHP-134 were unresponsive. Conditioned media from unresponsive cells did not inhibit response in sensitive cells. Unexpectedly, NGF neither reduced the growth rate nor enhanced survival in any NB cell line. Conditioned medium from all NB cell lines enhanced 125I-NGF binding in embryonic sensory cells. Regulation of growth rate and neurite outgrowth, then, are separable. A fundamental defect in NB may be the acquisition of a capacity for growth and survival independent of NGF. 125I-NGF was bound to both Fast and Slow receptors in MC-IXC cells, but only to Slow receptors in NGF-responsive SH-SY5Y and LA-N-5 cells, showing Fast receptors are not required for neurite outgrowth. Independence from NGF-regulated growth and survival is unexplainable by an absence of NGF receptors.

Molecular cloning of a mouse submaxillary gland renin cDNA fragment

The mRNA encoding mouse renin has been partially purified from total poly(A)-containing RNA of submaxillary glands of male Swiss mice. Corresponding cDNAs were cloned in the Pst I site of pBR322. Recombinants have been characterized by differential screening and hybrid-arrested translation. The DNA of clone pRn3-5 has been used to study the expression of renin mRNA in the submaxillary gland and in the kidney of different mouse strains. The renin mRNA from submaxillary gland and kidney have the same length (1600 nucleotides) and appear to be the products of the same gene. In vitro translation of mRNAs and RNA blotting experiments have shown that renin mRNA sequences are accumulated in the submaxillary gland of males of AKR and Swiss strains but not in the gland of male BALB/c.