β1‐integrin restricts astrocytic differentiation of adult hippocampal neural stem cells

Integrins are transmembrane receptors that mediate cell‐extracellular matrix and cell–cell interactions. The β1‐integrin subunit is highly expressed by embryonic neural stem cells (NSCs) and is critical for NSC maintenance in the developing nervous system, but its role in the adult hippocampal niche remains unexplored. We show that β1‐integrin expression in the adult mouse dentate gyrus (DG) is localized to radial NSCs and early progenitors, but is lost in more mature progeny. Although NSCs in the hippocampal subgranular zone (SGZ) normally only infrequently differentiate into astrocytes, deletion of β1‐integrin significantly enhanced astrocyte differentiation. Ablation of β1‐integrin also led to reduced neurogenesis as well as depletion of the radial NSC population. Activation of integrin‐linked kinase (ILK) in cultured adult NSCs from β1‐integrin knockout mice reduced astrocyte differentiation, suggesting that at least some of the inhibitory effects of β1‐integrin on astrocytic differentiation are mediated through ILK. In addition, β1‐integrin conditional knockout also resulted in extensive cellular disorganization of the SGZ as well as non‐neurogenic regions of the DG. The effects of β1‐integrin ablation on DG structure and astrogliogenesis show sex‐specific differences, with the effects following a substantially slower time‐course in males. β1‐integrin thus plays a dual role in maintaining the adult hippocampal NSC population by supporting the structural integrity of the NSC niche and by inhibiting astrocytic lineage commitment. GLIA 2016;64:1235–1251     

Induction of nitric oxide synthase activity in human astrocytes by interleukin-1β and interferon-γ

Nitric oxide (NO) is a short-lived, diffusible molecule that has a variety of biological activities including vasorelaxation, neurotransmission, and cytotoxicity. In the central nervous system, a constitutive form of nitric oxide synthase (NOS) has been localized in a subset of neurons and in endothelial cells. In addition, both constitutive and LPS-inducible NOS has been demonstrated in rat astrocytes and microglia in vitro. In this report, we present evidence for the production of NO, as measured by the production of nitrite, in highly enriched human fetal astrocyte cultures stimulated with IL-1β. The production of nitrite paralleled the induction of NADPH diaphorase enzyme activity in the perikarya of the majority of stimulated astrocytes. The IL-1β-induced nitrite production by astrocytes was markedly enhanced when cells were co-stimulated with IFN-γ or TNF-α (IFN-γ > TNF-α); LPS had no effect used as a single agent or in combination with other cytokines. N^GMMA and N^G-nitro-arginine, competitive inhibitors of NOS, diminished the accumulation of nitrite, but calmodulin antagonists (trifluoperazine, W-5 and W-7) had little or no inhibitory effect. Human fetal microglia, in contrast to astrocytes, failed to secrete significant amounts of nitrite in response to various stimuli. The results demonstrate the presence of an inducible form of NOS in human fetal astrocytes; human microglia, in turn, may control astrocyte NO production by providing IL-1β as an activating signal.     

Injury‐induced neural stem/progenitor cells in post‐stroke human cerebral cortex

Increasing evidence points to accelerated neurogenesis after stroke, and support of such endogenous neurogenesis has been shown to improve stroke outcome in experimental animal models. The present study analyses post‐stroke cerebral cortex after cardiogenic embolism in autoptic human brain. Induction of nestin‐ and musashi‐1‐positive cells, potential neural stem/progenitor cells, was observed at the site of ischemic lesions from day 1 after stroke. These two cell populations were present at distinct locations and displayed different temporal profiles of marker expression. However, no surviving differentiated mature neural cells were observed by 90 days after stroke in the previously ischemic region. Consistent with recent reports of neurogenesis in the cerebral cortex after induction of stroke in rodent models, the present current data indicate the presence of a regional regenerative response in human cerebral cortex. Furthermore, observations underline the potential importance of supporting survival and differentiation of endogenous neural stem/progenitor cells in post‐stroke human brain.     

Role of Oestrogen Receptors on the Modulation of NADPH‐Diaphorase‐Positive Cell Number in Supraoptic and Paraventricular Nuclei of Ovariectomised Female Rats

Modulation of the nitric oxide producing system (demonstrated via the NADPH‐diaphorase histochemical reaction) by oestradiol has been established in several structures of the rat brain. The present study aimed to explore the possible regulation of NADPH‐diaphorase activity by oestradiol in neurones of the supraoptic (SON) and paraventricular (PVN) nuclei and the role of oestrogen receptors (ERα and ERβ) in this regulation. Adult ovariectomised rats were divided into six groups and injected either with vehicle or a single dose of oestradiol, a selective ERα agonist‐PPT [4,4′,4″‐(4‐propyl‐[1H]‐pyrazole‐1,3,5‐triyl)trisphenol], a selective ERβ agonist‐DPN [2,3‐bis(4‐hydroxyphenyl)‐propionitrile], a selective ERα antagonist‐MPP [1,3‐bis(4‐hydroxyphenyl)‐4‐methyl‐5‐[4‐(2‐piperidinylethoxy)phenol]‐1H‐pyrazole dihydrochloride] or a selective ERβ antagonist‐PHTPP (4‐[2‐phenyl‐5,7‐bis(trifluoromethyl)pyrazolo[1,5‐a]pyrimidin‐3‐yl]phenol). The number of NADPH‐diaphorase positive elements in the SON and the PVN was modulated by both ERs but, depending on the nucleus, ERα and ERβ ligands induced different effects. These results suggest that the regulation of nitrergic system by ERs may play a role in the control of oestrogen‐dependent physiological mechanisms regulated by the SON and the PVN.     

黄芪多糖对2型糖尿病患者外周血内皮祖细胞PI3K/Akt/eNOS信号通路的影响

背景：前期研究证实黄芪通过P38MAPK通路促进内皮祖细胞增殖,其影响是否通过PI3K/Akt/eNOS途径实现？ 目的：观察黄芪多糖对2型糖尿病患者外周血内皮祖细胞蛋白激酶B、内皮型一氧化氮合酶表达的影响。 方法：采用密度梯度离心法获取糖尿病患者外周血单个核细胞,培养7 d后鉴定内皮祖细胞。观察0,50,200,800,3 200,6 400 mg/L黄芪多糖分别干预6,12,24,48 h对内皮祖细胞影响的量效和时效关系;用黄芪多糖及黄芪多糖与PI3K抑制剂LY294002联合干预糖尿病患者内皮祖细胞,Western blot检测磷酸化Akt及磷酸化内皮型一氧化氮合酶的表达水平。以未进行任何处理健康人内皮祖细胞作为对照组。 结果与结论：糖尿病患者内皮祖细胞的增殖能力较对照组明显下降(P < 0.05)。黄芪多糖显著增加糖尿病患者内皮祖细胞的增殖能力,当黄芪多糖在200~800 mg/L质量浓度范围,干预6~24 h可呈时间及剂量依赖性增强内皮祖细胞的增殖能力(P < 0.01),并呈剂量依赖性升高内皮祖细胞磷酸化Akt及磷酸化内皮型一氧化氮合酶的表达(P < 0.05);PI3K抑制剂LY294002能阻断黄芪多糖诱导的Akt、内皮型一氧化氮合酶的磷酸化(P < 0.05)。说明黄芪多糖通过激活PI3K/Akt/eNOS信号通路促进内皮祖细胞增殖和向内皮细胞的分化。     

Identification of cells expressing somatostatin receptor 2 in the gastrointestinal tract of Sstr2 knockout/lacZ knockin mice

Somatostatin is found in neurons and endocrine cells in the gastrointestinal tract. The actions of somatostatin are mediated by a family of G-protein-coupled receptors that compose five subtypes (SSTR1-5), each of which is encoded by a separate gene. lacZ "knockin" mice, in which the reporter gene lacZ was engineered into the genomic locus of Sstr2 by gene targeting, were used to examine the expression pattern of Sstr2 and identify potential targets for neurally released and hormonal somatostatin in the gastrointestinal tract. In the body of the stomach, a large proportion of epithelial cells and subpopulations of myenteric neurons expressed Sstr2. Double- or triple-labeling with antisera to H(+)K(+)ATPase (to identify parietal cells) and/or histidine decarboxylase (to identify enterochromaffin-like [ECL] cells) combined with beta-galactosidase staining revealed that both parietal cells and ECL cells expressed Sstr2, and these two cell types accounted for almost all of the Sstr2-expressing epithelial cells. Somatostatin inhibits gastric acid secretion. The presence of SSTR2 on both parietal and ECL cells suggests that somatostatin acting on SSTR2 may reduce acid secretion by both acting directly on parietal cells and by reducing histamine release from ECL cells. In the small and large intestine, subpopulations of neurons in the myenteric and submucosal plexuses expressed Sstr2, and many of the Sstr2-expressing myenteric neurons also showed SSTR2(a) immunostaining. Most of Sstr2-expressing neurons in the myenteric plexus showed nitric oxide synthase (NOS) immunoreactivity. Previous studies have shown that NOS neurons are descending interneurons and anally projecting, inhibitory motor neurons. Thus, somatostatin acting at SSTR2 receptors on NOS neurons might modulate descending relaxation.     

Involvement of the nitric oxide/protein kinase G pathway in polychlorinated biphenyl-induced cell death in SH-SY 5Y neuroblastoma cells

Polychlorinated biphenyls (PCB) are persistent environmental contaminants whose chronic exposure can affect nervous system development and function. The cellular and molecular mechanisms underlying neuronal damage are not yet clear. In the present study, we investigated whether nitric oxide (NO) could be involved in aroclor 1254 (A1254; a PCB mixture)-induced cytotoxicity in SH-SY5Y human neuroblastoma cells. Prolonged exposure (24 hr) to A1254 (10-100 microg/ml) caused a dose-dependent reduction of cell viability that was attenuated in the presence of a calcium entry blocker, gadolinum (Gd(3+)) at 10 microM, a concentration able to block voltage-sensitive calcium channels. In addition, A1254 caused an increase of cytosolic calcium that was dependent on extracellular calcium, as measured by fura-2 videomicroscopy. A1254-induced calcium rise may stimulate NO production through an activation of neuronal NOS (nNOS). Indeed, the concomitant addition of the selective nNOS inhibitor N(omega)-propyl-L-arginine (NPLA) and A1254 prevented cell injury, suggesting that NO production plays a major role in A1254-evoked cell injury. Furthermore, the exposure (14 hr) to A1254 (30 microg/ml) produced an up-regulation of the expression of beta isoform of nNOS. This up-regulation was calcium dependent and was accompanied by an enhancement of NO production as demonstrated by an increase of nitrite formation. Moreover, A1254-induced cell injury was prevented when KT 5823, a selective cGMP/PKG inhibitor, was added concomitantly to 30 microg/ml A1254. These results suggest that PCB-induced cell death in neuroblastoma cells is mediated by an activation of the cGMP/PKG pathway triggered by NO production.     

Increased PKA and PKC activities accompany neuronal differentiation of NT2/D1 cells

After retinoic acid treatment, a large percentage of cells of the human embryonal carcinoma cell line NT2/D1 differentiate into neuronal cells. We demonstrate here that the differentiated cells, but not the undifferentiated cells, contain high levels of neurofilament mRNA. We have also measured mRNA, protein, and activity levels of two kinases, cAMP-dependent protein kinase (PKA) and protein kinase C (PKC), in order to explore the role of protein kinases in the establishment of the differentiated state. RNA levels for the catalytic (C alpha and C beta) subunits of PKA increased after differentiation. Total PKA activity levels increased 7-fold in the differentiated cells. Parallel with this, a rise in the level of catalytic subunit protein occurred. A 12-fold induction of Type 2 (beta) PKC mRNA levels was observed after neuronal differentiation. Increases in PKC activity and in Type 2 (beta) and Type 3 (alpha) PKC protein levels also accompanied differentiation. These changes in PKA- and PKC-specific RNA levels and enzyme activity may be necessary for production and maintenance of the differentiated state in these cells.     

Synthesis and regulation of apolipoprotein E during the differentiation of human neuronal precursor NT2/D1 cells into postmitotic neurons

Recently, we showed expression of apolipoprotein E (apoE) in human neuronal-type cells such as neuroblastoma SK N SH-SY 5Y cells. In this model, a negative effect of neuronal differentiation on apoE synthesis was suspected. To check this hypothesis, we studied the regulation of apoE in human postmitotic neurons. The presence of apoE was investigated in undifferentiated human teratocarcinoma NT2/D1 (NT2) cells and during their differentiation into postmitotic hNT neurons induced by retinoic acid (RA) treatment. Before differentiation, apoE protein and mRNA were detected in NT2 cells by Western blotting and RT-PCR experiments. Immunofluorescence study showed that apoE was present in all cells. For longer times of RA treatment (3 weeks), the apoE labeling became heterogeneous: only some cells were immunopositive and among them were some differentiating cells in which apoE was located in both cellular body and neuritic process. Interestingly, terminally differentiated hNT cells no longer expressed apoE. These results demonstrate that neuronal precursor and differentiating cells were able to synthesize apoE while the fully neuronal differentiation exerted a negative effect on apoE neuronal expression. Our results are compatible with a weak expression of apoE in neurons of adult brains.     

Expression of Notch-1 receptor and its ligands Jagged-1 and Delta-1 in amoeboid microglia in postnatal rat brain and murine BV-2 cells

Notch-1 receptor signaling pathway is involved in neuronal and glial differentiation. Its involvement in microglial functions, however, has remained elusive. This study reports the localization of Notch-1 receptor immunoreactivity in the amoeboid microglial cells (AMC) in the postnatal rat brain. By immunofluorescence, Notch-1 receptor was colocalized with its ligands, Jagged-1 and Delta-1, in the AMC in the corpus callosum and subventricular zone. Notch-1 immunopositive cells were confirmed to be microglia labeled by OX42 and lectin. Immunoexpression of Notch-1 receptor was progressively reduced with age. Western blot analysis showed that Notch-1 protein level in the corpus callosum in which the AMC were heavily populated was concomitantly decreased. In postnatal rats challenged with lipopolysaccharide (LPS), Notch-1 receptor immunofluorescence in AMC was noticeably enhanced. Furthermore, Notch-1 protein level in the corpus callosum was increased as revealed by Western blotting analysis. In primary microglial culture treated with LPS, mRNA expression of Notch-1 and its ligand Jagged-1 was upregulated but that of Delta-1 was reduced. The expression pattern of Notch-1 and its ligands was confirmed in murine BV-2 cells. Furthermore, Notch-1 neutralization with its antibody reduced its protein expression. More importantly, neutralization of Notch-1 concomitantly suppressed the mRNA expression of IL-6, IL-1, M-CSF, and iNOS; TNF-alpha, mRNA expression, however, was enhanced. Western blot confirmed the changes of protein level of the above except for IL-6, which remained relatively unaltered. It is concluded that Notch-1 signaling in the AMC and LPS-activated microglia/BV-2 cells modulates the expression of proinflammatory cytokines and nitric oxide.     

Postnatal age governs the extent of differentiation of hippocampal CA1 and CA3 subfield neural stem/progenitor cells into neurons and oligodendrocytes

While neural stem/progenitor cells (NSCs) in the dentate gyrus of the hippocampus have been extensively characterized, the behavior of NSCs in the CA1 and CA3 subfields of the hippocampus is mostly unclear. Therefore, we compared the in vitro behavior of NSCs expanded from the micro-dissected CA1 and CA3 subfields of postnatal day (PND) 4 and 12 Fischer 344 rats. A small fraction (∼1%) of dissociated cells from CA1 and CA3 subfields of both PND 4 and 12 hippocampi formed neurospheres in the presence of EGF and FGF-2. A vast majority of neurosphere cells expressed NSC markers such as nestin, Sox-2 and Musashi-1. Differentiation assays revealed the ability of these NSCs to give rise to neurons, astrocytes, and oligodendrocytes. Interestingly, the overall neuronal differentiation of NSCs from both subfields decreased with age (23–28% at PND4 to 5–10% at PND12) but the extent of oligodendrocyte differentiation from NSCs increased with age (24–32% at PND 4 to 45–55% at PND 12). Differentiation of NSCs into astrocytes was however unchanged (40–48%). Furthermore, NSCs from both subfields gave rise to GABA-ergic neurons including subclasses expressing markers such as calbindin, calretinin, neuropeptide Y and parvalbumin. However, the fraction of neurons that expressed GABA decreased between PND4 (59–67%) and PND 12 (25–38%). Additional analyses revealed the presence of proliferating NSC-like cells (i.e. cells expressing Ki-67 and Sox-2) in different strata of hippocampal CA1 and CA3 subfields of both PND4 and PND 12 animals. Thus, multipotent NSCs persist in both CA1 and CA3 subfields of the hippocampus in the postnatal period. Such NSCs also retain their ability to give rise to both GABA-ergic and non-GABA-ergic neurons. However, their overall neurogenic potential declines considerably in the early postnatal period.     

Synergistic induction of cyclin D1 in oligodendrocyte progenitor cells by IGF-I and FGF-2 requires differential stimulation of multiple signaling pathways

D-type cyclins are direct targets of extracellular signals and critical regulators of G(1) progression. Our previous data demonstrated that IGF-I and FGF-2 synergize to enhance cyclin D1 expression, cyclin E/cdk2 complex activation, and S-phase entry in OP cells. Here, we provide a mechanistic explanation for how two growth factor signaling pathways converge on a major cell cycle regulator. IGF-I and FGF-2 differentially activate signaling pathways to coordinately promote cyclin D1 expression. We show that the p44/p42 MAPK signaling pathway is essential for FGF-2 induction of cyclin D1 mRNA. In contrast, blocking the PI3-Kinase pathway results in loss of IGF-I/FGF-2 synergistic induction of cyclin D1 protein levels. Moreover, the presence of IGF-I significantly enhances nuclear localization of cyclin D1, which also requires PI3K signaling. GSK-3beta, a downstream target of the PI3K/Akt pathway, is phosphorylated in the presence of IGF-I in OPs. Consistent with a known role for GSK-3beta in cyclin D1 degradation, we show that proteasome inhibition in OPs exposed to FGF-2 increased cyclin D1 levels, equivalent to levels seen in IGF-I/FGF-2 treated cells. Thus, we provide a model for cyclin D1 coordinate regulation where FGF-2 stimulation of the MAPK pathway promotes cyclin D1 mRNA expression while IGF-I activation of the PI3K pathway inhibits proteasome degradation of cyclin D1 and enhances nuclear localization of cyclin D1.     

β-Amyloid protein-dependent nitric oxide production from microglial cells and neurotoxicity

β-Amyloid protein (Aβ) is the major component of the senile plaques in Alzheimer's disease (AD), and microglial cells have been shown to be closely associated with these plaques. However, the roles of Aβ and microglial cells in pathogenesis of AD remain unclear. Incubation of rat microglial cells with Aβ(1–40) caused a significant increase in nitrite, a stable metabolite of nitric oxide (NO), in culture media, while there was no detectable increase in nitrite in astrocyte-rich glial cells or cortical neurons after incubation with Aβ(1–40). Nitrite production by microglial cells was also induced by Aβ(1–42), but not Aβ(25–35). An inhibitor of NO synthase, N^G-monomethyl-l-arginine (NMMA), as well as dexamethasone and actinomycin D, dose-dependently inhibited this nitrite production. Among the various cytokines investigated such as interleukin-1, interleukin-6, tumor necrosis factor- and interferon-γ (IFN-γ), only IFN-γ markedly enhanced Aβ-dependent nitrite production. Cultured cortical neurons were injured by microglial cells stimulated with Aβ in a dose-dependent manner in the presence of IFN-γ. Neurotoxicity caused by the Aβ plus IFN-γ-stimulated microglial cells was significantly attenuated by NMMA. Thus, although further investigations into the effect of Aβ on human microglial cells are needed, it is likely that Aβ-induced NO production by microglial cells is one mechanism of the neuronal death in AD.     

Cyclin D1 is required for proliferation of olig2‐expressing progenitor cells in the injured cerebral cortex

Little is known about the molecular mechanisms driving proliferation of glial cells after an insult to the central nervous system (CNS). To test the hypothesis that the G1 regulator cyclin D1 is critical for injury‐induced cell division of glial cells, we applied an injury model that causes brain damage within a well‐defined region. For this, we injected the neurotoxin ibotenic acid into the prefrontal cortex of adult mice, which leads to a local nerve cell loss but does not affect the survival of glial cells. Here, we show that cyclin D1 immunoreativity increases drastically after neurotoxin injection. We find that the cyclin D1‐immunopositive (cyclin D1+) cell population within the lesioned area consists to a large extent of Olig2+ oligodendrocyte progenitor cells. Analysis of cyclin D1‐deficient mice demonstrates that the proliferation rate of Olig2+ cells diminishes upon loss of cyclin D1. Further, we show that cyclin‐dependent kinase (cdk) 4, but not cdk6 or cdk2, is essential for driving cell division of Olig2‐expressing cells in our injury model. These data suggest that distinct cell cycle proteins regulate proliferation of Olig2+ progenitor cells following a CNS insult.     

Analysis of the expression and function of BRINP family genes during neuronal differentiation in mouse embryonic stem cell‐derived neural stem cells

We previously identified a novel family of genes, BRINP1, 2, and 3, that are predominantly and widely expressed in both the central nervous system (CNS) and peripheral nervous system (PNS). In the present study, we analyzed the expression pattern of three BRINP genes during differentiation of mouse embryonic stem (ES) cell‐derived neural stem cells (NSCs) and their effects on the cell‐cycle regulation of NSCs. While there was no significant expression of any BRINP‐mRNA expressed in mouse ES cells, BRINP 1 and 2‐mRNAs was expressed at high levels in the ES cell‐derived neural stem cells. Upon differentiation into neuronal cells in the presence of retinoic acid and BDNF, all three types of BRINP‐mRNA were induced with a similar time course peaking at day three of treatment. Upon differentiation into astroglial cells in the presence of serum, BRINP1‐mRNA was slightly up‐regulated, while BRINP2‐ and BRINP3‐mRNAs were almost abolished in the astrocytes. While 69.2, 26.1, and 7.7% of cells in a population of NSCs in the exponentially growing phase were in the G1, S and G2 phases, respectively, over‐expression of any one of the three BRINP genes completely abolished cells in the G2 phase and significantly reduced the cells in S phase to 11.8–13.8%. Based on these results, the physiological roles of induced BRINP genes in the cell‐cycle suppression of terminally differentiated post‐mitotic neurons are discussed. © 2009 Wiley‐Liss, Inc.     

A common polymorphism in the 3′-UTR of the NOS1 gene was associated with completed suicides in Japanese male population

Background

Suicidal behavior has been widely accepted as familial. Its transmission cannot be explained by the transmission of psychiatric disorder alone and seems to be partly explained by the transmission of impulsive–aggressive behavior. Studies in laboratory animal have shown that mice lacking NOS1 manifest significant aggressive behavior. Further, several polymorphisms of neuronal nitric oxide synthase (NOS1) gene have been reported to be associated with impulsivity, aggression and suicide attempts. To further clarify the possible involvement of NOS1 with suicide, we carried out an association study of NOS1 gene polymorphisms with completed suicide.

Methods

We examined 7 single nucleotide polymorphisms (SNPs) of the NOS1 gene which were previously studied in several neuropsychiatric disorders (rs2682826, rs6490121, rs3782206, rs561712, rs3782219, rs3782221, and rs41279104), in age and gender matched 287 healthy control subjects and 284 completed suicides using the TaqMan probe assays.

Results

We found that both the genotypic distribution and the allelic frequencies of rs2682826 SNP were significantly different between the completed suicide and control groups (P = 0.0007 and 0.0005, respectively). The odd ratio for the minor allele of the SNP was 0.653 (95% CI 0.513–0.832). The significance was remained even after correction for multiple testing. Gender-based analysis showed that the significances were appeared in males only.

Conclusion

Our study raises a possibility that a genetic variation of NOS1 may be implicated in the pathophysiology of suicide in Japanese population, especially in males. Further studies on more NOS1 genetic variants are needed to confirm our observations.     

Immuno-electron microscopic localization of the α1 and β1-subunits of soluble guanylyl cyclase in the guinea pig organ of Corti

Guanylyl cyclases (GC) catalyze the formation of the intracellular signal molecule cyclic GMP from GTP. For some years it has been known that the heme-containing soluble guanylyl cyclase (sGC) is stimulated by NO and NO-containing compounds. The sGC enzyme consists of two subunits (α₁ and β₁). In the present study, the α₁ and β₁-subunits were identified in the guinea pig cochlea at the electron microscopic level using a post-embedding immuno-labeling procedure. Ultrathin sections of LR White embedded specimens were incubated with various concentrations of two rabbit polyclonal antibodies to the α₁- and β₁-subunit, respectively. The immunoreactivity was visualized by a gold-labeled secondary antibody in an energy-filtering transmission electron microscope (EFTEM). Marked immunoreactivity for both antibodies was found in the inner and outer hair cells, with numerous gold particles at the border of the cuticular plates, associated with the cell nuclei or attached to electron-dense parts of the cytoplasm. In the pillar cells and apical Deiters cells, soluble guanylyl cyclase immunoreactivity was located at the rim of the cuticular plates and between the microtubuli bundles. Together with the recently identified nitric oxide synthase isoforms [Eur. Arch. Otorhinolaryngol. 254 (1997) 396; Eur. Arch. Otorhinolaryngol. 255 (1998) 483], the soluble guanylyl cyclase may be involved in signalling processes in the organ of Corti.