The neurotrophins BDNF, NT-3 and -4, but not NGF, TGF-beta 1 and GDNF, increase the number of NADPH-diaphorase-reactive neurons in rat spinal cord cultures

Potential of brain mast cells for therapeutic application in the immune response to bacterial and viral infections

A wide range of microorganisms can infect the central nervous system (CNS). The immune response of the CNS provides limited protection against microbes penetrating the blood-brain barrier. This results in a neurological deficit and sometimes leads to high morbidity and mortality rates despite advanced therapies. For the last two decades, different studies have expanded our understanding of the molecular basis of human neuroinfectious diseases, especially concerning the contributions of mast cell interactions with other central nervous system compartments. Brain mast cells are multifunctional cells derived from the bone marrow and reside in the brain. Their proximity to blood vessels, their role as "first responders" their unique receptors systems and their ability to rapidly release pathogen responsive mediators enable them to exert a crucial defensive role in the host-defense system. This review describes key biological and physiological functions of mast cells, concerning their ability to recognize pathogens via various receptor systems, followed by a coordinated and selective mediator release upon specific interactions with pathogenic stimulating factors. The goal of this review is to direct attention to the possibilities for therapeutic applications of mast cells against bacterial and viral related infections. We also focus on opportunities for future research activating mast cells via adjuvants.

Enriched environment ameliorates memory impairments in rats after postsurgery sleep deprivation

Postsurgery sleep deprivation is a common complication that severely deteriorates the quality of life of patients. Here we aim to investigate the effects and mechanism of enriched environment in ameliorating sleep deprivation and memory impairments. Hernia repair surgery was performed on rats to induce sleep deprivation. Enriched environment (EE) was used to treat rats with sleep deprivation, and open field and Y-maze tests were performed to compare behavioral parameters of sleep deprivation rats with or without EE treatments to those of normal rats. To understand the mechanism, neurotrophic and growth factors including BDNF, NGF, NT-3 and GDNF were analyzed using enzyme-linked immunosorbent assay (ELISA). AMPAR subunits, including GluA1-A3, and GABA_A receptor α1 subunit expression in hippocampus tissues were assessed using western blot. EE restored normal levels of anxiety index and freezing behavior in open field test and level of alternation in Y-maze test, suggesting the reduction of anxiolytic effects and spatial memory impairment induced by sleep deprivation. EE increased BDNF levels and reduced NT-3 levels in sleep deprivation rats. GluA1/GluA2 ratio was increased by EE. GABA_A receptor α1 subunit expression was decreased by EE. EE is effective in ameliorating the detrimental effects of sleep deprivation in spatial memory impairment, and restoring normal levels of neurotrophic factors, which are potentially mediated by attenuating the changes in AMPAR subunit expression and reducing GABA_A receptor α1 subunit expression. These data provide supporting evidences for the use of EE to treat adverse outcomes of sleep deprivation induced by surgery.

Subregional differences in astrocytes underlie selective neurodegeneration or protection in Parkinson's disease models in culture

Parkinson's disease (PD) is characterized by the selective degeneration of dopamine (DA) neurons of the substantia nigra pars compacta (SN), while the neighboring ventral tegmental area (VTA) is relatively spared. The mechanisms underlying this selectivity are not fully understood. Here, we demonstrate a vital role for subregional astrocytes in the protection of VTA DA neurons. We found that elimination of astrocytes in vitro exposes a novel vulnerability of presumably protected VTA DA neurons to the PD mimetic toxin MPP⁺ , as well as exacerbation of SN DA neuron vulnerability. Conversely, VTA astrocytes protected both VTA and SN DA neurons from MPP⁺ toxicity in a dose dependent manner, and this protection was mediated via a secreted molecule. RNAseq analysis of isolated VTA and SN astrocytes demonstrated a vast array of transcriptional differences between these two closely related populations demonstrating regional heterogeneity of midbrain astrocytes. We found that GDF15, a member of the TGFβ superfamily which is expressed 230-fold higher in VTA astrocytes than SN, recapitulates neuroprotection of both rat midbrain and iPSC-derived DA neurons, whereas its knockdown conversely diminished this effect. Neuroprotection was likely mediated through the GRFAL receptor expressed on DA neurons. Together; these results suggest that subregional differences in astrocytes underlie the selective degeneration or protection of DA neurons in PD.

Nitric oxide-cGMP signaling regulates axonal elongation during optic nerve regeneration in the goldfish in vitro and in vivo

Nitric oxide (NO) signaling results in both neurotoxic and neuroprotective effects in CNS and PNS neurons, respectively, after nerve lesioning. We investigated the role of NO signaling on optic nerve regeneration in the goldfish (Carassius auratus). NADPH diaphorase staining revealed that nitric oxide synthase (NOS) activity was up-regulated primarily in the retinal ganglion cells (RGCs) 5-40 days after axotomy. Levels of neuronal NOS (nNOS) mRNA and protein also increased in the RGCs alone during this period. This period (5-40 days) overlapped with the process of axonal elongation during regeneration of the goldfish optic nerve. Therefore, we evaluated the effect of NO signaling molecules upon neurite outgrowth from adult goldfish axotomized RGCs in culture. NO donors and dibutyryl cGMP increased neurite outgrowth dose-dependently. In contrast, a nNOS inhibitor and small interfering RNA, specific for the nNOS gene, suppressed neurite outgrowth from the injured RGCs. Intra-ocular dibutyryl cGMP promoted the axonal regeneration from injured RGCs in vivo. None of these molecules had an effect on cell death/survival in this culture system. This is the first report showing that NO-cGMP signaling pathway through nNOS activation is involved in neuroregeneration in fish CNS neurons after nerve lesioning.

Nitric oxide has dual opposite roles during early and late phases of apoptosis in cerebellar granule neurons

The involvement and the role of nitric oxide (NO) as a signaling molecule in the course of neuronal apoptosis, whether unique or modulated during the progression of the apoptotic program, has been investigated in a cellular system consisting of cerebellar granule cells (CGCs) where apoptosis can be induced by lowering extracellular potassium. Several parameters involved in NO signaling pathway, such as NO production, neuronal nitric oxide synthase (nNOS) expression, and cyclic GMP (cGMP) production were examined in the presence or absence of different inhibitors. We provide evidence that nitric oxide has dual and opposite effects depending on time after induction of apoptosis. In an early phase, up to 3 h of apoptosis, nitric oxide supports survival of CGCs through a cGMP-dependent mechanism. After 3 h, nNOS expression and activity decreased resulting in shut down of NO and cGMP production. Residual NO then contributes to the apoptotic process by reacting with rising superoxide anions leading to peroxynitrite production and protein inactivation. We conclude that whilst NO over-production protects neurons from death in the early phase of neuronal damage, its subsequent reduction may contribute to neuronal degeneration and ultimate cell death.

Creatine and neurotrophin-4/5 promote survival of nitric oxide synthase-expressing interneurons in striatal cultures

Nitric oxide (NO) mediates a variety of physiological functions in the central nervous system and acts as an important developmental regulator. Striatal interneurons expressing neuronal nitric oxide synthase (nNOS) have been described to be relatively spared from the progressive cell loss in Huntington's disease (HD). We have recently shown that creatine, which supports the phosphagen energy system, induces the differentiation of GABAergic cells in cultured striatal tissue. Moreover, neurotrophin-4/5 (NT-4/5) has been found to promote the survival and differentiation of cultured striatal neurons. In the present study, we assessed the effects of creatine and NT-4/5 on nNOS-immunoreactive (-ir) neurons of E14 rat ganglionic eminences grown for 1 week in culture. Chronic administration of creatine [5mM], NT-4/5 [10ng/ml], or a combination of both factors significantly increased numbers of nNOS-ir neurons. NT-4/5 exposure also robustly increased levels of nNOS protein. Interestingly, only NT-4/5 and combined treatment significantly increased general viability but no effects were seen for creatine supplementation alone. In addition, NT-4/5 and combined treatment resulted in a significant larger soma size and number of primary neurites of nNOS-ir neurons while creatine administration alone exerted no effects. Double-immunolabeling studies revealed that all nNOS-ir cells co-localized with GABA. In summary, our findings suggest that creatine and NT-4/5 affect differentiation and/or survival of striatal nNOS-ir GABAergic interneurons. These findings provide novel insights into the biology of developing striatal neurons and highlight the potential of both creatine and NT-4/5 as therapeutics for HD.

Nitric oxide synthesis inhibition increases proliferation of neural precursors isolated from the postnatal mouse subventricular zone

The subventricular zone (SVZ) of rodents retains the capacity to generate new neurons throughout the entire life of the animal. Neural progenitors of the SVZ survive and proliferate in vitro in the presence of epidermal growth factor (EGF). Nitric oxide (NO) has been shown to participate in neural tissue formation during development and to have antiproliferative actions, mediated in part by inhibition of the EGF receptor. Based on these findings, we have investigated the possible effects of endogenously produced and exogenously added NO on SVZ cell proliferation and differentiation. Explants were obtained from postnatal mouse SVZ and cultured in the presence of EGF. Cells migrated out of the explants and proliferated in culture, as assessed by bromodeoxyuridine (BrdU) incorporation. After 72 h in vitro, the colonies formed around the explants were constituted by cells of neuronal or glial lineages, as well as undifferentiated progenitors. Immunoreactivity for the neuronal isoform of NO synthase was observed in neuronal cells with long varicose processes. Cultures treated with the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) showed an increase in the percentage of BrdU-immunoreactive cells, whereas treatment with the NO donor diethylenetriamine-nitric oxide adduct (DETA-NO) led to a decrease in cell proliferation, without affecting apoptosis. The differentiation pattern was also altered by L-NAME treatment resulting in an enlargement of the neuronal population. The results suggest that endogenous NO may contribute to postnatal neurogenesis by modulating the proliferation and fate of SVZ progenitor cells.

Effects of nerve graft on nitric oxide synthase, NAD(P)H oxidase, and antioxidant enzymes in chronic spinal cord injury

Oxidative stress and nitrosative stress play important roles in the pathogenesis of secondary spinal cord injury. Recently, we demonstrated that peripheral nerve grafts (PNG) with acidic fibroblast growth factor (aFGF) partially restore hind limb locomotion in adult rats with completely transected spinal cords. This study investigated the protein abundances of the superoxide (O2*)-generating enzyme nicotinamide adenine dinucleotide (phosphate) oxidase (NAD(P)H oxidase; gp91phox subunit), nitric oxide synthases (NOS), antioxidant enzymes, superoxide dismutases (Cu Zn SOD, Mn SOD), catalase, and glutathione peroxidase (GPX) as well as nitrotyrosine in the spinal cord tissue 4 months after spinal cord transection in rats with and without PNG and aFGF. The protein abundances of the gp91phox subunit of NAD(P)H oxidase, Mn SOD, catalase, GPX, eNOS, and nitrotyrosine were significantly upregulated, whereas Cu Zn SOD and nNOS were unchanged in the injury group compared to the sham controls. The nerve graft with aFGF treated group showed significantly better hind limb locomotion recovery than the injury group. Although the protein abundances of gp91phox, nitrotyrosine, and Cu Zn SOD were similar in the treated group (nerve graft with aFGF) compared to the injury group, Mn SOD, GPX, catalase, and eNOS protein abundances were significantly higher, whereas nNOS was markedly lower in the treated group. We conclude that the combination of nerve graft and aFGF enhances the local antioxidant defense system after spinal cord transection in rats.

Changes of NADPH-diaphorase reactivity in lumbar spinal cord of short-term streptozotocin induced diabetic rats

Diabetes is an endocrine and metabolic disorder often associated with erectile dysfunction and peripheral neuropathy. Among other factors, penile erection is induced by activation of nitric oxide synthase (NOS). Hypothalamic paraventricular nuclei neurons produce NO and project to spinal cord areas implicated in penile reflexes. These nuclei have shown an increase of NOS in streptozotocin-induced diabetic rats. NOS-containing neurons are identical to the populations of neurons selectively stained for NADPH-diaphorase activity. Using this technique, we have evaluated changes of NOS in the lumbar spinal cord of diabetic rats with or without insulin treatment. Positive staining was found in motoneurons, dorsal horn neurons (layer II), neurons surrounding the ependimus (layer X) and neurons at the intermediolateral cell column (ILCC). Diabetic animals showed significant decrease in reactive area and increase of the histochemical reaction in motoneurons from the sexual dimorphic nuclei and in neurons of the ILCC. A marked decrease of the number of reactive neurons was also observed in layer II. Morphologic alterations were observed in neurons of layer X as an increase in the percentage of multipolar neurons and a decrease in the number and length of secondary processes. The alterations observed in these animals were absent in the insulin treated diabetic animals. These results show the plasticity of lumbar spinal cord neurons, suggesting a direct participation of NO synthesis in the physiopathology of the erection dysfunction in diabetes.

Neuroprotection and nerve grafts in the treatment of neurogenic erectile dysfunction

PURPOSE

The rationale for protecting the nerve supply of the penis derives mainly from the fact that neurological injury or disease states involving this organ commonly result in erectile dysfunction. Novel directions in the management of neurogenic erectile dysfunction that pertain specifically to sustaining penile neuronal function are described.

MATERIALS AND METHODS

The review constitutes a summary of neuroprotective strategies for penile erection that are under investigation at the basic science level or have been brought to clinical practice. The basic exercise consisted primarily of a literature search using the National Library of Medicine PubMed Services, with references made to such keywords as nerve grafts, nerve growth factors, neuroprotection and nerve regeneration.

RESULTS

Primary advances in this field have centered on repairing structural defects and restoring the functional integrity of the cavernous nerves of the penis. In the former autologous nerve conduits, such as sural nerve grafts, have been explored and used prominently in the context of radical prostatectomy. In the latter diverse neurotrophic treatments have been investigated, with progress mostly limited to animal models of cavernous nerve injury. Basic concepts and ongoing developments in the neurobiology of axonal regeneration were identified as being applicable to this area of neurourology.

CONCLUSIONS

Because neurogenic origins represent a leading categorical cause of erectile dysfunction, the importance of developing and applying treatment approaches to alleviate neuropathic effects on the erectile tissue of the penis is certain. Medical and surgical innovations for preserving and reconstituting the functional nerve supply of the penis offer great promise in the management of erectile dysfunction.

The role of NADPH oxidase, neuronal nitric oxide synthase and poly(ADP ribose) polymerase in oxidative neuronal death induced in cortical cultures by brain-derived neurotrophic factor and neurotrophin-4/5

Certain neurotrophins promote or induce oxidative neuronal death in cortical cultures. However, the effector mechanisms mediating this phenomenon have not been delineated. In this study, we investigated the possibility that NADPH oxidase and nitric oxide synthase (NOS) function as such effectors. Western blot analysis showed that treatment with brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-4/5 increased the levels of NADPH oxidase subunits. Moreover, neurotrophin treatment resulted in membrane translocation of p67phox, a characteristic feature of NADPH oxidase activation. Administration of the specific NADPH oxidase inhibitor, 4-(2-aminoethyl)benzenesulfonylfluoride (AEBSF), attenuated increases in oxygen free radicals thereby suggesting that NADPH oxidase contributes to the oxidative stress induced by neurotrophins. Furthermore, neuronal death induced by BDNF or NT-4/5 was significantly attenuated by AEBSF. Treatment with BDNF has previously been shown to induce neuronal NOS (nNOS). Our data indicated that inhibitors of nNOS attenuated neuronal death induced by BDNF or NT-4/5, consistent with an active role of nNOS in the mediation of neurotrophin neurotoxicity. As in other models of oxidative cell death, BDNF-induced neuronal death was accompanied by poly(ADP ribose) polymerase (PARP) activation. AEBSF or N-nitro-l-arginine (NNA) reduced BDNF-mediated PARP activation. PARP and poly(ADP ribose) glycohydrolase (PARG) are actively involved in mediating neurotrophin neurotoxicity since inhibitors of PARP and PARG significantly reduced levels of cell death. These results suggest that NADPH oxidase and nNOS contribute to increased oxidative stress, subsequent activation of PARP/PARG, and neuronal death induced by prolonged neurotrophin exposure.

A possible role for BDNF, NT-4 and TrkB in the spinal cord and muscle of rat subjected to mechanical overload, bupivacaine injection and axotomy

Neurotrophins play a crucial role in the regulation of survival and the maintenance of specific functions for various populations of neurons. Neurotrophin-4 (NT-4) is most abundant in skeletal muscle, and is thought to promote sciatic nerve sprouting, inhibit agrin-induced acetylcholine receptor (AChR) clustering, evoke postsynaptic potentiation and induce mitochondrial proliferation. Using Western blot analysis, immunoprecipitation and immunohistochemistry, we investigated the distribution of NT-4 in slow- and fast-type muscles. We also tested the adaptive response of this protein in the mechanically overloaded muscle, in the regenerating muscle following bupivacaine injection and in the denervated muscle. Additionally, we investigated whether TrkB phosphorylation in the spinal cord and in the sciatic nerve occurs through the interaction with BDNF or NT-4 when the innervating muscle is damaged. Markedly more NT-4 was expressed in fast-type muscles compared with the slow types. TrkB protein was more frequently observed around the edge of myofibers (neuromuscular junction) of the soleus muscle compared with the gastrocnemius muscle. TrkB tyrosine phosphorylation occurred in the spinal cord but not in the sciatic nerve 24 h after bupivacaine injection of the innervating muscle. At the same time, the amount of TrkB co-precipitating with BDNF was markedly increased in the spinal cord. A rapid activation of TrkB (1-8 h) was also observed in the spinal cord after axotomy,while the amount of TrkB co-precipitating with NT-4 was markedly lower after axotomy. These results indicate that NT-4 is preferentially distributed in fast-type muscles. Furthermore, by interacting with BDNF and NT-4, the TrkB in the spinal cord may be important for the survival of motoneurons and outgrowth of injured peripheral axons following muscle damage.

Role of brain-derived neurotrophic factor in wobbler mouse motor neuron disease

Brain-derived neurotrophic factor (BDNF) is neuroprotective for motoneurons undergoing degeneration, including those in natural motor neuron disease (MND) in wobbler mice. To assess the role of BDNF in this model of MND, endogenous BDNF immunoreactivity was analyzed by semiquantitative video-image analysis. Affected cervical spinal cord motoneurons had significantly greater BDNF immunoreactivity compared to motoneurons of healthy littermates (P = 0.01) and affected lumbar spinal cord motoneurons (P = 0.008 at age 4 weeks; P = 0.005 at age 8 weeks). Neuronal nitric oxide synthase (n-NOS) immunocytochemistry revealed increased immunoreactivity in the affected cervical spinal cord motoneurons. Exogenous BDNF treatment partially inhibited the increased NOS activity, as quantitatively measured by nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry. The mean number of NADPH-d(+) motoneurons in the cervical anterior horn decreased from 3.5 +/- 1.2 to 1.5 +/- 1.2 (P = 0.002). The increase in endogenous BDNF immunoreactivity in the affected spinal cord may be compensatory in diseased motoneurons, yet it appears to still be inadequate because exogenous BDNF treatment is required to suppress increased NOS activity in degenerating motoneurons. Our study indicates that BDNF is important in halting nitric oxide (NO)-mediated motor neuron degeneration, which has potential implications for the treatment of neurodegenerative disorders.

Nerve growth factor induces light adaptive cellular and synaptic plasticity in the outer retina of fish

Recent evidence suggests that neurotrophins can be involved in short-term synaptic plasticity in parts of the central nervous system. In the present study, the possible role of nerve growth factor (NGF) in inducing morphologic (cellular and subcellular) changes in the outer retina of carp was assessed. The effects of NGF on cone photomechanical movements (PMMs) and horizontal cell (HC) spinule formation were measured. NGF-induced cone contraction and formation of HC spinules in the dark-adapted retina were consistent with its role in light adaptation. These effects were dose dependent in the range of 5--250 nM. Because cone contraction and HC spinule formation have previously been shown to be controlled by dopamine (DA), nitric oxide (NO), or both, the possibility that the effects of NGF could be occurring by means of release of DA and/or NO was tested. Haloperidol (HAL), a nonspecific DA receptor blocker, or 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide potassium (cPTIO), a NO scavenger, was applied in combination with NGF to dark-adapted eyecups. The results showed that both HAL and cPTIO significantly blocked the effects of NGF on cone PMMs and HC spinule formation. In conclusion, (1) NGF represents a novel light-adaptive signalling mechanism in the outer retina of fish; and (2) NGF-induced cone contraction and HC spinule formation in the retina together with our previous observation would suggest that the effects of NGF may be mediated through NO by means of DA.

Effects of brain-derived neurotrophic factor and neurotrophin-3 on expression of mRNAs encoding c-Fos, neuropeptides and glutamic acid decarboxylase in cultured spinal neurons

There is growing evidence suggesting that neurotrophins have modulating effects on the pain signaling system at spinal levels. In order to determine whether neurotransmitter expression is modulated in response to the elevation of neurotrophins, the changes in c-fos, neuropeptide and glutamic acid decarboxylase (GAD) mRNAs expression was evaluated after BDNF or NT-3 was applied to cultured spinal neurons. Reverse transcription polymerase chain reaction analysis revealed that BDNF induced a significant increase in the expression of preprodynorphin (pDYN), preproenkephalin (pENK), neuropeptide Y (NPY) and GAD mRNAs. In contrast, the pENK, not the pDYN, NPY and GAD, mRNA levels increased after the treatment of NT-3. Both BDNF and NT-3 produced a rapid increase in c-fos mRNA. These results suggest that BDNF and NT-3 have differential neuronal effects on the synthesis of spinal cord neurotransmitters that are involved in the modulation of nociceptive information.

Early BDNF, NT-3, and NT-4 signaling events

Much more is known about nerve growth factor (NGF) signaling than that initiated by brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or NT-4. We sought to study early BDNF, NT-3, and NT-4 signaling events. Using TrkB-expressing cells, we found that BDNF and NT-4 individually induced tyrosine phosphorylation of TrkB in a dose-dependent fashion. At maximally effective concentrations, BDNF or NT-4 induced robust TrkB tyrosine phosphorylation at 5 min; this progressively declined at 15, 30, and 60 min. Using immunoprecipitation, PI3-kinase and tyrosine phosphorylated PLC-gamma1 and SHC were shown to be associated with tyrosine phosphorylated TrkB in response to both BDNF and NT-4. BDNF and NT-4 induced similar intensities of phosphorylation of TrkB and signaling intermediates at equivalent doses. NT-3 treatment of TrkC-expressing cells induced very similar patterns for induction of TrkC tyrosine phosphorylation and recruitment of signaling intermediates. BDNF, NT-3, and NT-4 caused rapid tyrosine phosphorylation of ERK and SNT. These data suggest that the earliest signaling events for BDNF, NT-3, and NT-4 are very similar to those for NGF.

Peripheral nerve graft and neurotrophic factors enhance neuronal survival and expression of nitric oxide synthase in Clarke's nucleus after hemisection of the spinal cord in adult rat

The present study examined the effects of peripheral nerve (PN) graft and neurotrophic factors on the expression of nitric oxide synthase (NOS) and the survival of Clarke's nucleus (CN) neurons at the first lumbar spinal segment (L1) 15 days after hemisection of the spinal cord at T11. Normal intact CN neurons did not express NOS. Forty-one percent of the ipsilateral CN neurons survived after hemisection at T11, and 48% of the surviving neurons expressed NOS. Transplantation of PN graft at the lesion site promoted the survival of CN neurons to 71% and increased the expression of NOS to 70%. Continuous infusion of brain-derived neurotrophic factor, ciliary neurotrophic factor, and neurotrophic-3, but not glial cell-derived neurotrophic factor, at the lesion site enhanced the survival of CN neurons to about 65%. Among the surviving neurons about 70% were NOS-positive. These results indicated that transplantation of autologous PN graft or continuous infusion of neurotrophic factors could enhance the survival of axotomized CN neurons. In addition, the survival-promoting function of the neurotrophic agents was coincided with the upregulation of the expression of NOS. However, whether the upregulation of NOS expression in injured CN neurons is related to the rescue function or is a side effect of the neurotrophic factors is not clear and needed further investigation.

Additive effect of NOS inhibitor and neurotrophic factors on the survival of injured Clarke's neurons

The present study examined the effect of treatment with the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) together with peripheral nerve (PN) graft or brain-derived neurotrophic factor (BDNF) on the survival of CN neurons at the L1 level of the spinal cord following hemisection at T11. In control animals 41% of CN neurons survived 15 days after the hemisection, and 48% of these expressed NOS. Treatment with either PN graft implantation or continuous infusion of BDNF increased the survival rate of CN neurons to 70%; 70% of these expressed NOS. Combined L-NAME and PN graft or L-NAME and BDNF improved the rescue rate up to 94%, but only approximately 33% expressed NOS. Our results suggest that the expression of NOS might adversely influence the neuroprotective function of neurotrophic factors on injured CN neurons in the spinal cord.

Effects of brain-derived neurotrophic factor on the development of NADPH-diaphorase/nitric oxide synthase-positive amacrine cells in the rodent retina

Amacrine neurons expressing nitric oxide synthase (NOS) contain brain-derived neurotrophic factor (BDNF) receptors and respond to exogenous BDNF [Klöcker, N., Cellerino, A. & Bähr, M. (1998) J. Neurosci., 18, 1038-1046]. We analysed the effects of BDNF on the development of neurons which express NOS in the mouse and rat retina. Rat pups received a total of three intraocular injections of BDNF at intervals of 48 h, starting at postnatal day 16 (P16), and were killed at P22. The retinas were stained for NADPH-diaphorase, a histological marker of NOS. NOS-expressing neurons were found in both the inner nuclear layer (INL) and the ganglion cell layer (GCL). Two classes of NOS-expressing neurons, type I and type II, had already been distinguished in the INL [Koistinaho, J. & Sagar, S.M. (1995) In Osborne, N.N. & Chader, G.J. (eds), Progress in Retinal and Eye Research, Vol. 15. Oxford University Press, pp. 69-87] and a third one in the GCL. Up-regulation of NADPH-diaphorase activity was observed after BDNF treatment. The number of type I neurons remained stable, whereas the number of type II neurons and NOS-positive neurons in the GCL increased significantly (P < 0.001). Type I and type II neurons were significantly larger in BDNF-treated retinas. Double-labelling experiments revealed that BDNF induces NADPH-diaphorase in dopaminergic neurons and amacrine cells displaced to the GCL, but not in retinal ganglion cells. In mice homozygous for a null mutation of the bdnf gene, the intensity of NADPH-diaphorase labelling in both somata and processes was reduced, but the number of labelled neurons was not dramatically reduced. These findings indicate that BDNF regulates the neurotransmitter phenotype of NOS-expressing amacrine neurons under physiological conditions, but is not required for their survival.

Brain derived neurotrophic factor and insulin like growth factor-1 attenuate upregulation of nitric oxide synthase and cell injury following trauma to the spinal cord. An immunohistochemical study in the rat

The possibility that brain derived neurotrophic factor (BDNF) and insulin like growth factor-1 (IGF) induced neuroprotection is influenced by mechanisms involving nitric oxide was examined in a rat model of focal spinal cord injury. BDNF or IGF-I (0.1 microgram/10 microliters in phosphate buffer saline) was applied topically 30 min before injury on the exposed spinal cord followed by repeated doses of growth factors immediately before and 30 min after injury. Thereafter application of BDNF or IGF was carried out at every 1 h interval until sacrifice. Five hours after injury, the tissue pieces from the T9 segment were processed for nNOS immunostaining, edema and cell injury. Untreated injured rats showed a profound upregulation of nNOS which was most pronounced in the nerve cells of the ipsilateral side. A marked increase in the blood-spinal cord barrier (BSCB) permeability to 125I-albumin, water content and cell injury in these perifocal segments was also found. Pretreatment with BDNF and IGF significantly reduced the upregulation of nNOS in the spinal cord. This effect of the growth factors was most pronounced in the contralateral side. Rats treated with these neurotrophic factors showed much less signs of BSCB damage, edema and cell injury. These results suggest that BDNF and IGF pretreatment is neuroprotective in spinal cord injury and that these neurotrophic factors have the capacity to down regulate nNOS expression following trauma to the spinal cord. Our data provide new experimental evidences which suggest that BDNF and IGF may exert their potential neuroprotective effects probably via regulation of NOS activity.

Regulation of the transmitter phenotype of rostral and caudal groups of cultured serotonergic raphe neurons

We have studied the regulation of survival and serotonergic markers by neurotrophins and several trophically active cytokines in neurons cultured from the embryonic rat raphe region under defined conditions. At embryonic day 14, saturating concentrations of brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4 and basic fibroblast growth factor elicited a two- to 2.5-fold increase in numbers of tryptophan hydroxylase- and serotonin-immunoreactive neurons over a four-day culture period. Transforming growth factor beta-1 and glial cell line-derived neurotrophic factor were less potent, while fibroblast growth factor-5 was only marginally effective. Distinct responses to different factors were noted depending on embryonic age and regional origin of serotonergic neurons. Thus, brain-derived neurotrophic factor augmented numbers of tryptophan hydroxylase-positive neurons at embryonic day 16 by a factor of seven, but only 1.5- to two-fold when cultures were established from day 13 or 14 embryos. In cultures of rostral serotonergic groups (B4-B9), numbers of tryptophan hydroxylase-positive neurons decreased in the absence of factors, whereas numbers of tryptophan hydroxylase-immunoreactive neurons in cultures from caudal serotonergic groups (B1-B3) increased during a 12-day culture period. There was no evidence that serotonergic neurons undergo apoptosis (as visualized by terminal deoxynucleotidyl transferase dUTP nick end labeling) or proliferate (as visualized by 5-bromodeoxyuridine incorporation) in culture. Numbers of serotonergic neurons also increased when cultures were treated with a brief 24-h pulse of brain-derived neurotrophic factor, supporting the notion that changes in numbers of serotonergic neurons reflected alterations of phenotype rather than cell death or proliferation. The ability of cells to specifically take up the serotonin analog 5,7-dihydroxytryptamine was also up-regulated by brain-derived neurotrophic factor in both rostral and caudal raphe cultures. Lability of the serotonergic phenotype was further suggested by the observation that ciliary neurotrophic factor fully prevented the brain-derived neurotrophic factor-mediated increase in tryptophan hydroxylase-positive neurons. The effect of ciliary neurotrophic factor was dependent on the presence of astrocytes. We conclude that serotonergic neurons show spatially and temporally distinct responses to neurotrophic factors, which seem to have a profound influence of the transmitter phenotype rather than on survival.

GDNF induces the calretinin phenotype in cultures of embryonic striatal neurons

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-beta (TGF-beta) superfamily, is a potent neurotrophic factor for several neuron populations in the central and peripheral nervous system. Members of the neurotrophin, neurokine, and TGF-beta families of growth factors can affect neurons beyond their capacity to promote survival. They can play instructive roles including the determination of a particular transmitter phenotype. Here, we show that GDNF enhances the number of calretinin (CaR)-positive neurons in serum-free cultures of striatal cells isolated from embryonic rats. The effect is dose-dependent, can be elicited with concentrations as low as 0.1 ng/ml, and is not accompanied by increased incorporation of 5-bromo-2'-desoxyuridine and appearance of glial fibrillary acidic protein-positive cells. Similar, but weaker effects can be elicited by brain-derived neurotrophic factor, neurotrophin-3 and -4, fibroblast growth factor-2. Ciliary neurotrophic factor, nerve growth factor, and TGF-beta 1 do not affect striatal CaR expression. GDNF can augment CaR-positive cells at any time point and with a minimal exposure of 18 hr, suggesting induction of the phenotype rather than increased survival. By reverse transcription polymerase chain reaction (RT-PCR), we show that GDNF is expressed in the E16 striatum and in cultures derived from this tissue. GDNF also protected striatal CaR-positive neurons against glutamate toxicity. We conclude that striatal GDNF, in addition to its retrograde trophic role for nigrostriatal dopaminergic neurons, may also act locally within the striatum (e.g., by inducing the CaR phenotype and protecting these cells against toxic insult).

Nerve growth factors and the control of neurotransmitter phenotype selection in the mammalian central nervous system

Determination of neurotransmitter phenotype in the peripheral nervous system (PNS) has been intensively characterized. However, relatively little is known about the underlying molecular and biochemical events involved in determination of transmitter phenotype in the central nervous system (CNS). It has been well established that nerve growth factors regulate cell growth and differentiation. They are increasingly recognized as playing an important role in many decision-making steps during development. Published data suggest that neurotransmitter phenotype is determined largely by exogenous stimuli, such as nerve growth factors--acidic/basic fibroblast growth factor, epidermal growth factor, neurotrophins, etc., working in concert with the genetic programmes. They exert potent effects independently or synergistically with other molecules by acting either on neural precursor cells or differentiated neuronal cells. However, the process of transmitter phenotype determination in the CNS is only beginning to be understood, with more uncharacterized substances, with considerable potency in this respect being reported and in need of isolation and further study. These studies will bring great advances in our existing knowledge of brain development and have potential value for the development of new treatments for neurodegenerative diseases.

Decreased neuronal nitric oxide synthase-immunoreactivity and NADPH-diaphorase activity in rat pterygopalatine ganglion parasympathetic neurons and cerebrovascular innervation following long-term sympathectomy

Neural control of tissue perfusion is mediated predominantly by sympathetic vasoconstrictor and, in some tissues, parasympathetic vasodilator systems. The objective of this study was to determine if changes occur within parasympathetic vasodilator neurons supplying cranial vessels after sympathectomy. Cranial sympathetic innervation was excised unilaterally, and 6 weeks later pterygopalatine ganglion neurons were evaluated for expression of neuronal nitric oxide synthase immunoreactivity (NOS-ir) and NADPH-diaphorase activity. Relative to the unoperated side, the number of parasympathetic neurons staining densely either for NOS or for NADPH-diaphorase decreased by 37% and 47%, respectively, whereas unstained somata increased by 51% and 48%. Internal carotid artery NOS-ir innervation density was reduced by 35%. These findings are consistent with a down-regulation of nitrergic properties in some cranial parasympathetic neurons after sympathectomy.

Nerve growth factor inhibits the expression of nitric oxide synthase in neurones in dissociated cultures of rat dorsal root ganglia

In dissociated cultures of DRG derived from 15-day-old rats the numbers of neurones expressing immunocytochemically detectable quantities of the neuronal isoform of nitric oxide synthase (nNOS) was determined and the effects of different culture media examined. The availability of NGF in the cultures was found to be a critical determinant of nNOS expression. In a serum-rich media (SRM) supplemented with NGF, 24% of the neurones expressed nNOS compared with 72% in the absence of added NGF and the presence of an antibody to NGF (t-test, P < 0.0001). Cultures grown in a defined media (DM) developed poorly and many neurones died, these cultures also showed poor growth of other cell types. Immunostaining for NGF revealed that some of the non-neuronal cells produce NGF and that this would be predicted to contribute to the survival of the neurones. In cultures in which neurones were dying most of the surviving neurones expressed nNOS suggesting it may have a survival promoting function.

Differential susceptibility to neurotoxicity mediated by neurotrophins and neuronal nitric oxide synthase

NMDA neurotoxicity, which is mediated, in part, by formation of nitric oxide (NO) via activation of neuronal NO synthase (nNOS), is modulated by neurotrophins. nNOS expression in rat and mouse primary neuronal cultures grown on a glial feeder layer is significantly less than that of neurons grown on a polyornithine (Poly-O) matrix. Neurotrophins markedly increase the number of nNOS neurons, nNOS protein, and NOS catalytic activity and enhance NMDA neurotoxicity via NO-dependent mechanisms when neurons are grown on glial feeder layers. In contrast, when rat or mouse primary cortical neurons are grown on a Poly-O matrix, neurotrophins have no influence on nNOS neuronal number or NOS catalytic activity and reduce NMDA neurotoxicity. Primary neuronal cultures from mice lacking nNOS grown on a glial feeder layer fail to respond to neurotrophin-mediated enhancement of neurotoxicity. Together, these results indicate that nNOS expression and NMDA NO-mediated neurotoxicity are dependent, in part, on the culture paradigm, and neurotrophins regulate the susceptibility to NMDA neurotoxicity via modulation of nNOS. Furthermore, these results support the idea that NMDA neurotoxicity in culture is critically dependent on the developmental state of the neurons being assessed and suggest that, when cortical neurons are cultured on a glial feeder layer, they do not reach nearly as mature a phenotype as when grown on a Poly-O matrix.

A chromaffin cell-derived protein induces the NADPH-diaphorase phenotype in cultured rat spinal cord neurons

We have recently demonstrated that neurotrophins induce reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase activity in cultured spinal cord neurons. One prominent neuron population of the spinal cord expressing NADPH-diaphorase activity in vivo are preganglionic sympathetic neurons, including those innervating the adrenal medulla. These neurons receive trophic support from their target. We have shown previously that chromaffin cells contain as yet unidentified neurotrophic molecules, which may include releasable factors relevant for the survival and differentiation of developing preganglionic sympathetic neurons. We have studied the influence of proteins derived from bovine chromaffin cells and released by nicotine on NADPH-diaphorase expression in spinal cord cultures established from 16-day-old rat embryos. At this embryonic age, NADPH-diaphorase activity becomes apparent in the spinal cord and predominantly expressed in sympathetic nuclei. Similar to brain-derived neurotrophic factor and neurotrophin-4, a heat- and trypsin-sensitive component from chromaffin cells contained in granule preparations up-regulated the number of NADPH-diaphorase-positive neurons in spinal cord cultures. Combined application of this activity and neurotrophin-4 resulted in an additive effect, indicating that the effect of the chromaffin cell-derived active component is not mediated by one of the trk B ligands. This was confirmed by co-treatment studies with the trk-signalling pathway inhibitor K252b, which did not inhibit the effect of the chromaffin cell-derived protein(s). Further studies revealed that NADPH-diaphorase reactivity is inducible in spinal cord neurons at any time point throughout the entire culture period of six days, suggesting de novo induction of the enzyme rather than a survival-promoting effect of the activity from chromaffin cells. Culture supernatants from nicotine-stimulated bovine chromaffin cells induced NADPH-diaphorase-positive neurons at the same magnitude as the material obtained from chromaffin granule preparations. Our data suggest that chromaffin cell-derived proteins are capable of up-regulating NADPH-diaphorase activity or to induce de novo this transmitter phenotype in neuron populations of the spinal cord, which may include preganglionic sympathetic neurons.