Colchicine differentially induces the expressions of nitric oxide synthases in central and peripheral catecholaminergic neurons

nNOS immunoreactivity co-localizes with GABAergic and cholinergic neurons, and associates with β-endorphinergic and met-enkephalinergic opioidergic fibers in rostral ventromedial medulla and A5 of the mouse

The present study examined the co-expression of neuronal nitric oxide synthase (nNOS) in the rostral ventromedial medulla (RVM) and A5 regions of the mouse brainstem within several neurochemical populations involved in nociceptive modulation. Double immunohistochemical methods showed that nNOS+ neurons do not co-localize with serotonergic neurons within any of these regions. Within the RVM, the nuclei raphe magnus and gigantocellularis contain a population of nNOS+/GAD67+ neurons, and within the paragigantocellularis lateralis, there is a smaller population of nNOS+/CHAT+ neurons. Further, nNOS+ neurons overlap the region of expression of β-endorphinergic and met-enkephalinergic fibers within the RVM. No co-labeling was found within the A5 for any of these populations. These findings suggest that pain-modulatory serotonergic neurons within the brainstem do not directly produce nitric oxide (NO). Rather, NO-producing neurons within the RVM belong to GABAergic and cholinergic cell populations, and are in a position to modulate or be modulated by local opioidergic neurons.

Primary culture of glial cells from mouse sympathetic cervical ganglion: a valuable tool for studying glial cell biology

Central nervous system glial cells as astrocytes and microglia have been investigated in vitro and many intracellular pathways have been clarified upon various stimuli. Peripheral glial cells, however, are not as deeply investigated in vitro despite its importance role in inflammatory and neurodegenerative diseases. Based on our previous experience of culturing neuronal cells, our objective was to standardize and morphologically characterize a primary culture of mouse superior cervical ganglion glial cells in order to obtain a useful tool to study peripheral glial cell biology. Superior cervical ganglia from neonatal C57BL6 mice were enzymatically and mechanically dissociated and cells were plated on diluted Matrigel coated wells in a final concentration of 10,000cells/well. Five to 8 days post plating, glial cell cultures were fixed for morphological and immunocytochemical characterization. Glial cells showed a flat and irregular shape, two or three long cytoplasm processes, and round, oval or long shaped nuclei, with regular outline. Cell proliferation and mitosis were detected both qualitative and quantitatively. Glial cells were able to maintain their phenotype in our culture model including immunoreactivity against glial cell marker GFAP. This is the first description of immunocytochemical characterization of mouse sympathetic cervical ganglion glial cells in primary culture. This work discusses the uses and limitations of our model as a tool to study many aspects of peripheral glial cell biology.

Mollaret meningitis may be caused by reactivation of latent cerebral toxoplasmosis

Mollaret meningitis (MM) occurs mainly in females and is characterized by recurrent episodes of headache, transient neurological abnormalities, and the cerebrospinal fluid containing mononuclear cells. HSV-2 was usually identified as the causative agent. Recently, we found that recurrent headaches in non-HIV-infected subjects were due to acquired cerebral toxoplasmosis (CT). The aim of the study was therefore to focus on molecular pathomechanisms that may lead to reactivation of latent CT and manifest as MM. Literature data cited in this work were selected to illustrate that various factors may affect latent CNS Toxoplasma gondii infection/inflammation intensity and/or host defense mechanisms, i.e., the production of NO, cytokines, tryptophan degradation by indoleamine 2,3-dioxygenase, mechanisms mediated by an IFN-gamma responsive gene family, limiting the availability of intracellular iron to T. gondii, and production of reactive oxygen/nitrogen species, finally inducing choroid plexitis and/or vasculitis. Examples of triggers revealing MM and accompanying disturbances of IFN-gamma-mediated immune responses that control HSV-2 and T. gondii include: female predominance (female mice are more susceptible to T. gondii infection than males); HSV-2 infection (increased IFN-gamma, IL-12); metaraminol (increased plasma catecholamine levels, changes in cytokine expression favoring T(H)2 cells responses); probably cholesterol contained in debris from ruptured epidermoid cysts (decreased NO; increased TNF-alpha, IL-6, IL-8). These irregularities induced by the triggers may be responsible for reactivation of latent CT and development of MM. Thus, subjects with MM should have test(s) for T. gondii infection performed obligatorily.

Peptide 19 in the rat superior cervical ganglion

Peptide 19 is a 7.6 kDa polypeptide which can bind to calmodulin and inhibit calcium-calmodulin signaling. In this study, peptide 19-immunoreactivity was examined in the rat superior cervical ganglion. In the ganglion, 54.8% of postganglionic sympathetic neuron profiles were immunoreactive for peptide 19. These neuron profiles were small- to medium-sized and measured 87-845 microm(2) (mean+/-SD = 343+/-111 microm(2)). Double immunofluorescence method revealed that 99.9% of peptide 19-containing neurons had neuropeptide Y in the superior cervical ganglion. Retrograde neuronal tracing and immunohistochemical studies also demonstrated that peptide 19 was common in postganglionic sympathetic neurons which innervated the facial skin and masseter but not the submandibular gland; 55.6% and 75.2% of cutaneous and muscular neuron profiles, respectively, contained peptide 19. Only 9.8% of glandular neurons were immunoreactive for peptide 19. These findings indicate that the content of peptide 19 in superior cervical ganglion neurons depends on their cell sizes and peripheral projections. On the other hand, colchicine injection into the superior cervical ganglion decreased the number of peptide 19-positive neurons (30.7%) compared to saline injection (53.3%). In contrast, the treatment induced nicotine adenine dinucleotide phosphate diaphorase activity in 12.7% of postganglionic sympathetic neurons. Double stain demonstrated that 56.3% of nicotine adenine dinucleotide phosphate diaphorase-positive neurons co-expressed peptide 19. These findings indicate that colchicine treatment causes decrease of peptide 19 expression and increase of nitric oxide synthase activity.

Increased density of neurons containing NADPH diaphorase and nitric oxide synthase in the cerebral cortex of patients with HIV-1 infection and drug abuse

To determine whether nitrogen monoxide (nitric oxide; NO) synthase (NOS) and NADPH diaphorase (NDP) co-containing cerebrocortical neurons (NOSN) neurons are affected in patients infected with human immunodeficiency virus type 1 (HIV-1) with and without associated intake of drugs of abuse, we examined the temporal neocortex of 24 individuals: 12 HIV-1 positive (including 3 drug users, 9 non-drug users) and 12 HIV-1 negative (including 6 drug users, and 6 non-drug users). Histochemical labeling for NDP-an enzymatic domain co-expressed in the NOS enzyme-was employed to visualize NOSN. Drug abuse and HIV-1 infection cause independently an increase in NOSN density, but combined they result in up to a 38-fold increase in NOSN density, suggesting that the combination of these factors induces NOS expression powerfully in neurons that normally do not synthesize NDP/NOS. This is associated with an increase in the proportion of NOSN displaying dystrophic changes, indicating that NOSN undergo massive degeneration in association with NOS synthesis induction. The increase in density of NOSN in HIV-1 infected drug abusers may be among the important sources of NO mediating cerebrocortical dysfunction, and the degeneration of NOS-containing local circuit neurons in patients with HIV-1 infection or drug abuse may underlie in part their neuropsychiatric manifestations.

Distribution of NADPH-diaphorase and expression of nNOS, N-methyl-D-aspartate receptor (NMDAR1) and non-NMDA glutamate receptor (GlutR2) genes in the neurons of the hippocampus after domoic acid-induced lesions in adult rats

Neuronal degeneration followed by detection of nitric oxide (NO)-producing neurons of the hippocampus was investigated at 4 h, 16 h, 24 h, 2 days, 5 days, and 14 days after administration of domoic acid (DA), in the present study. Histopathological analysis (Nissl staining) displayed dark-stained degenerating neurons in the hippocampus at 24 h to 14 days after DA administration, with degeneration most severe at 5-14 days. NADPH-d-positive neurons were observed in different subfields of the hippocampus in control rats and DA treated rats at 4-24 h. Complete loss of NADPH-d-positive neurons in the CA1 and CA3 subfields and also in the hilus of dentate gyrus (DG) was observed at 5 days and 14 days after the administration of DA. In contrast, at 4-24 h, neuronal nitric oxide synthase (nNOS)-immunoreactive cells were absent from the hippocampal subfields in control and DA-treated animals but were observed at 5 days and 14 days after DA administration. N-methyl-D-aspartate receptor (NMDAR1) immunoreactivity was increased in the hippocampal neurons at 5 days after DA administration and double immunofluorescence demonstrated its coexpression with induced nNOS expression. No significant change could be observed in the immunoreactivity of non-NMDA receptor (GlutR2) as compared with the controls, while occasional immunoreactive neurons were colocalized with induced nNOS expression. Reverse transcription-polymerase chain reaction analysis showed the upregulated expression of nNOS and downregulated expression of NMDAR1 at 5 days after the administration of DA. Although nNOS mRNA expression was rapidly induced at 5 days after DA administration, in situ hybridization analysis revealed complete loss of nNOS mRNA expression in the region of neuronal degeneration in the hippocampus at 24 h and 5 days after DA administration. The present study has shown that NADPH-d and nNOS express differentially in the neurons of the hippocampus in DA-induced neurotoxicity. It is speculated that induction of nNOS and glutamate receptor genes in the neurons of the hippocampus in response to DA-induced neurotoxicity could have contributed to the neuronal degeneration.

Regulation of the nitric oxide synthase-nitric oxide-cGMP pathway in rat mesenteric endothelial cells

Most of the available data on the nitric oxide (NO) pathway in the vasculature is derived from studies performed with cells isolated from conduit arteries. We investigated the expression and regulation of components of the NO synthase (NOS)-NO-cGMP pathway in endothelial cells from the mesenteric vascular bed. Basally, or in response to bradykinin, cultured mesenteric endothelial cells (MEC) do not release NO and do not express endothelial NOS protein. MEC treated with cytokines, but not untreated cells, express inducible NOS (iNOS) mRNA and protein, increase nitrite release, and stimulate cGMP accumulation in reporter smooth muscle cells. Pretreatment of MEC with genistein abolished the cytokine-induced iNOS expression. On the other hand, exposure of MEC to the microtubule depolymerizing agent colchicine did not affect the cytokine-induced increase in nitrite formation and iNOS protein expression, whereas it inhibited the induction of iNOS in smooth muscle cells. Collectively, our findings demonstrate that MEC do not express endothelial NOS but respond to inflammatory stimuli by expressing iNOS, a process that is blocked by tyrosine kinase inhibition but not by microtubule depolymerization.

Upregulation of iNOS expression and phosphorylation of eIF-2alpha are paralleled by suppression of protein synthesis in rat hypothalamus in a closed head trauma model

When the inducible form of nitric oxide synthase (iNOS) is expressed after challenge to the nervous system, it results in abnormally high concentrations of nitric oxide (NO). Under such conditions, NO could phosphorylate the eukaryotic translation initiation factor (eIF)-2alpha, thus suppressing protein synthesis in neurons that play a role in endocrine and autonomic functions. Using the Marmarou model of traumatic brain injury (TBI), we observed a rapid increase (at 4 h after TBI) of iNOS mRNA in magno- and parvocellular supraoptic and paraventricular neurons, declining gradually by approximately 30% at 24 h and by approximately 80% at 48 h. Western analysis indicated a trend towards increased iNOS protein synthesis at 4 h, which peaked at 8 h, and tended to decrease at the later time points. At the same time points, we detected immunocytochemically the phosphorylated form of eIF-2alpha (eIF-2alpha[P]) as cytoplasmic and more often as nuclear labeling. The incidence of double-labeled [iNOS and eIF-2alpha(P)] neuronal profiles, particularly at 24 h and 48 h after TBI, was high. De novo protein synthesis assessed quantitatively after infusion of 35S methionine/cysteine was reduced by approximately 20% at 4 h, remained depressed at 24 h, and did not return to control levels up to 48 h following the trauma. The results suggest that iNOS may trigger phosphorylation of eIF-2alpha, which in turn interferes with protein synthesis at the translational (ribosomal complex) and transcriptional (chromatin) levels. The depression in protein synthesis may include downregulation of iNOS itself, which could be an autoregulatory inhibitory feedback mechanism for NO synthesis. Excessive amounts of NO may also participate in dysfunction of hypothalamic circuits that underlie endocrine and autonomic alterations following TBI.

Nitric oxide metabolites, nitrates and nitrites in the cerebrospinal fluid in children with west syndrome

Nitric oxide (NO) has been implicated in the mediation of the neuronal excitotoxic cascade. In order to estimate brain NO production, cerebrospinal fluid (CSF) levels of NO metabolites, nitrates and nitrites (NN(x)) were measured in 31 children with west syndrome (WS) and in 12 controls. There was no age-related change in the NN(x) levels during the first year of life. The mean of the NN(x) levels was significantly higher in patients with WS than in controls (8.43 vs. 5.27 microM; P=0.01). Analysis of the etiological subgroups showed that the patients with a symptomatic etiology of WS had significantly higher NN(x) levels than controls (P<0.005) or than the patients with a cryptogenic etiology. The cryptogenic cases, in turn, did not differ from the controls (P=0.48). Levels of NN(x) were also significantly higher in children with focal brain abnormalities (infarction, atrophy or previous infection) than in those with other abnormalities or with normal neuroradiological findings (P<0.005). No correlation was found between the NN(x) levels and the duration of the symptoms, while paired samples obtained from eight children with WS showed that the NN(x) levels rose significantly (P=0.02) within the first 40 days of symptoms. The levels of NN(x) did not correlate with the CSF levels of neuronal growth factor or with the later decline in mental performance. This study demonstrates that the production of NO can be measured in human epileptic conditions and supports the idea gained from experimental studies that NO is involved in the pathophysiology of epilepsy. However, normal levels of NN(x) in patients with cryptogenic infantile spasms suggest that an increase in NO production be due to the concomitant neuronal damage rather than seizure activity per se. The findings suggest that there are no age-related changes in the NN(x) levels during the first year of life, and that children with symptomatic WS have elevated levels of NN(x), which rise during the first 40 days of symptoms. Although the NN(x) levels cannot be used to estimate the duration of symptoms or to predict the prognosis of mental development, they may support the differentiation of symptomatic from cryptogenic etiologies of WS.

Expression and function of inducible nitric oxide synthase in neurons

Enzymatically derived nitric oxide (NO) has been implicated in numerous physiological and pathological processes in the brain. Whereas during development NO participates in developmental and maturation processes, excess NO production in the adult in response to inflammation, injury, or trauma participates in both cell death and repair. The expression and activity of the inducible isoform of NO synthase (iNOS) play a pivotal role in sustained and elevated NO release. Recent evidence suggests that neurons can respond to proinflammatory stimuli and take part in brain inflammation. Neuronal iNOS expression has been described in different experimental settings, including cytokine stimulation of neuronal cell lines and primary neurons in vitro as well as in animal models of stroke and neurodegeneration. This article outlines different conditions leading to iNOS gene transcription and expression in neurons and neuronal cells and highlights the potential impact on human brain inflammation and neurodegeneration.

Nitric oxide synthase immunoreactivity in the rat hippocampus after status epilepticus induced by perforant pathway stimulation

Nitric oxide has recently been implicated in mediation of neuronal excitotoxicity and damage. This study aimed at elucidating the changes in the expression of neuronal isoform of nitric oxide synthase (nNOS) in the hippocampus after status epilepticus induced by perforant pathway stimulation. nNOS-immunoreactivity (nNOS-ir) and neuronal damage, assessed by silver staining, were evaluated separately in different hippocampal subfields 2 weeks after induction of status epilepticus. Perforant pathway stimulation resulted in an increase in the number of nNOS-immunoreactive neurons in the stratum radiatum of the CA1 and CA3 subfields of the hippocampus proper, and the hilus of the dentate gyrus. The morphology and distribution of the nNOS-ir neurons resembled that of interneurons. No correlation of the number of nNOS-ir neurons to the neuronal damage score was observed. Our results suggest that status epilepticus provokes a de novo expression of nNOS protein, and the nNOS expressing neurons may be selectively resistant to epileptic brain injury.

Differential effects of colchicine on the induction of nitric oxide synthase in neurons containing progesterone receptors of the guinea pig hypothalamus

Using nicotinamide-adenine-dinucleotide-phosphate-diaphorase (NADPHd) histochemistry, we analyzed the effects of an intracerebroventricular injection of colchicine on the activity of neuronal nitric oxide synthase in the hypothalamic nuclei of intact and ovariectomized estradiol-primed guinea pigs. We also examined the effects of colchicine on the immunocytochemical colocalization of nitric oxide synthase with the progesterone receptor in the ventrolateral nucleus, a key region in the control of sexual behavior. Treatment with colchicine resulted in a significant increase in the number of NADPHd-positive neurons in the ventrolateral nucleus in intact as well as in ovariectomized estradiol-primed animals, whereas in the other hypothalamic regions analyzed (preoptic area, paraventricular nucleus and posterior arcuate nucleus), the enzymatic activity remained unchanged. Quantitative analysis showed a significantly greater number of NADPHd-positive cells in the medial and the posterior aspects of the ventrolateral nucleus of colchicine-treated guinea pigs compared to the control group. In the caudal subdivision of this nucleus, colchicine induced nitric oxide synthase in the target cells for progesterone. These results suggest that neuronal nitric oxide synthase activity in the hypothalamus is affected by colchicine in a region-specific manner and especially in the ventrolateral nucleus, which is involved in progesterone-facilitated lordosis.

Exogenous administration of L-arginine protects cholinergic neurons from colchicine neurotoxicity

The effect of L-arginine administration on susceptibility/resistance of NO-producing neurons was investigated in non-ischemic neurodegenerative conditions. ChAT mRNA level was measured by in situ hybridization in the basal forebrain after i.c.v. colchicine administration. Colchicine induced down-regulation of ChAT mRNA level followed by degeneration of cholinergic neurons. L-Arginine treatment increased ChAT mRNA level and prevented/delayed ChAT mRNA decrease by colchicine. These data suggest that L-arginine treatment may protect cholinergic neurons from colchicine-induced degeneration.

Inducible expression of tryptophan hydroxylase without serotonin synthesis in hypothalamic dopaminergic neurons

In the present study we have further studied the previous findings that rat hypothalamic dopaminergic neuronal cell groups may express tryptophan hydroxylase (TpH), the serotonin synthesizing enzyme, without a detectable serotonin synthesis. Chemical and mechanical neuronal injuries, namely colchicine treatment and axonal transection, respectively, were performed, and distributions of neurons exhibiting immunoreactivity for TpH and/or tyrosine hydroxylase (TH), the dopamine synthesizing enzyme, were analyzed throughout the hypothalamic periventricular and arcuate nuclei. After colchicine treatment there was a statistically significant 87% (P = 0,01) increase in the number of TpH expressing neurons, while TH expression remained essentially similar. Axonal transection resulted also in a statistically significant 131% (P < 0,01) increase in the number of TpH expressing neurons, while TH expression was not significantly altered. All TpH expression coexisted with TH expression, and the induction of TpH expression by neuronal injuries occurred evenly throughout the rostrocaudal length of the territory studied. A possible serotonin synthesis by TpH was examined by giving drugs that increase brain serotonin synthesis, but no immunohistochemically detectable serotonin synthesis could be found in any of the TpH expressing neurons. Finally the possibility was studied that the relative shortage of the cofactor tetrahydrobiopterin would limit serotonin synthesis. However, an administration of tetrahydrobiopterin did not result in detectable serotonin synthesis in these neurons. Taken together these results suggest that dopaminergic neurons in the hypothalamic periventricular and arcuate nuclei are able to express TpH, this expression is induced after neuronal injury, and this induction occurs similarly throughout the territories studied. TpH expression occurs independently of TH expression, and the newly expressed TpH appears not to synthesize serotonin, regardless of pharmacological pretreatments. Thus, our findings (i) support the idea that neurons may possess inducible expression of nonfunctional transmitter-synthesizing enzymes, in this case TpH, and (ii) suggest that expression of an enzyme synthesizing a certain transmitter may not necessarily imply the corresponding transmitter phenotype.