The Role of Histone Acetylation in Mesenchymal Stem Cell Differentiation / 전남의대학술지

The mechanism and action concerning epigenetic modifications, especially that of histone modifications, are not fully understood. However, it is clear that histone modifications play an essential role in several biological processes that are involved in cell proliferation and differentiation. In this article, we focused on how histone acetylation may result in differentiation into mesenchymal stem cells as well as histone acetylation function. Moreover, histone acetylation followed by the action of histone deacetylase inhibitors, which can result in the differentiation of stem cells into other types of cells such as adipocytes, chondrocytes, osteocytes, neurons, and other lineages, were also reviewed.

Atoh1 as a Coordinator of Sensory Hair Cell Development and Regeneration in the Cochlea / 전남의대학술지

Cochlear sensory hair cells (HCs) are crucial for hearing as mechanoreceptors of the auditory systems. Clarification of transcriptional regulation for the cochlear sensory HC development is crucial for the improvement of cell replacement therapies for hearing loss. Transcription factor Atoh1 is the key player during HC development and regeneration. In this review, we will focus on Atoh1 and its related signaling pathways (Notch, fibroblast growth factor, and Wnt/β-catenin signaling) involved in the development of cochlear sensory HCs. We will also discuss the potential applicability of these signals for the induction of HC regeneration.

Atoh1 as a Coordinator of Sensory Hair Cell Development and Regeneration in the Cochlea / 전남의대학술지

Cochlear sensory hair cells (HCs) are crucial for hearing as mechanoreceptors of the auditory systems. Clarification of transcriptional regulation for the cochlear sensory HC development is crucial for the improvement of cell replacement therapies for hearing loss. Transcription factor Atoh1 is the key player during HC development and regeneration. In this review, we will focus on Atoh1 and its related signaling pathways (Notch, fibroblast growth factor, and Wnt/β-catenin signaling) involved in the development of cochlear sensory HCs. We will also discuss the potential applicability of these signals for the induction of HC regeneration.

Neural-Induced Human Mesenchymal Stem Cells Promote Cochlear Cell Regeneration in Deaf Guinea Pigs

OBJECTIVES: In mammals, cochlear hair cell loss is irreversible and may result in a permanent sensorineural hearing loss. Secondary to this hair cell loss, a progressive loss of spiral ganglion neurons (SGNs) is presented. In this study, we have investigated the effects of neural-induced human mesenchymal stem cells (NI-hMSCs) from human bone marrow on sensory neuronal regeneration from neomycin treated deafened guinea pig cochleae. METHODS: HMSCs were isolated from the bone marrow which was obtained from the mastoid process during mastoidectomy for ear surgery. Following neural induction with basic fibroblast growth factor and forskolin, we studied the several neural marker and performed electrophysiological analysis. NI-hMSCs were transplanted into the neomycin treated deafened guinea pig cochlea. Engraftment of NI-hMSCs was evaluated immunohistologically at 8 weeks after transplantation. RESULTS: Following neural differentiation, hMSCs expressed high levels of neural markers, ionic channel markers, which are important in neural function, and tetrodotoxin-sensitive voltage-dependent sodium currents. After transplantation into the scala tympani of damaged cochlea, NI-hMSCs-injected animals exhibited a significant increase in the number of SGNs compared to Hanks balanced salt solution-injected animals. Transplanted NI-hMSCs were found within the perilymphatic space, the organ of Corti, along the cochlear nerve fibers, and in the spiral ganglion. Furthermore, the grafted NI-hMSCs migrated into the spiral ganglion where they expressed the neuron-specific marker, NeuN. CONCLUSION: The results show the potential of NI-hMSCs to give rise to replace the lost cochlear cells in hearing loss mammals.

Pituitary Adenylate Cyclase-activating Polypeptide Inhibits Pacemaker Activity of Colonic Interstitial Cells of Cajal

This study aimed to investigate the effect of pituitary adenylate cyclase-activating peptide (PACAP) on the pacemaker activity of interstitial cells of Cajal (ICC) in mouse colon and to identify the underlying mechanisms of PACAP action. Spontaneous pacemaker activity of colonic ICC and the effects of PACAP were studied using electrophysiological recordings. Exogenously applied PACAP induced hyperpolarization of the cell membrane and inhibited pacemaker frequency in a dose-dependent manner (from 0.1 nM to 100 nM). To investigate cyclic AMP (cAMP) involvement in the effects of PACAP on ICC, SQ-22536 (an inhibitor of adenylate cyclase) and cell-permeable 8-bromo-cAMP were used. SQ-22536 decreased the frequency of pacemaker potentials, and cell-permeable 8-bromo-cAMP increased the frequency of pacemaker potentials. The effects of SQ-22536 on pacemaker potential frequency and membrane hyperpolarization were rescued by co-treatment with glibenclamide (an ATP-sensitive K+ channel blocker). However, neither N(G)-nitro-L-arginine methyl ester (L-NAME, a competitive inhibitor of NO synthase) nor 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) had any effect on PACAP-induced activity. In conclusion, this study describes the effects of PACAP on ICC in the mouse colon. PACAP inhibited the pacemaker activity of ICC by acting through ATP-sensitive K+ channels. These results provide evidence of a physiological role for PACAP in regulating gastrointestinal (GI) motility through the modulation of ICC activity.

The Protective Effect of Epigallocatechin-3-Gallate Against Gentamicin Vestibular Ototoxicity in Type I Vestibular Hair Cell of Guinea Pig / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Gentamicin (GM) is well known for its vestibulotoxicity. There have been many reports about vestibulotoxicity, however, its mechanism is still unclear. So far, it is known that GM affects the voltage-dependent K+ current and nitric oxide (NO) production. Epigallocatechin-3-gallate (EGCG) is the major component of green tea and is known to have anti-oxidative and anti-toxic effect. This study was undertaken to investigate the protective effect of EGCG against gentamicin on vestibular hair cell (VHC). MATERIALS AND METHOD: White guinea pigs (200-250 g) were rapidly decapitated and the temporal bones were immediately removed. Under a dissecting microscope, the crista ampullaris was obtained. The dissociated VHCs were transferred into a recording chamber mounted onto an inverted microscope. Whole-cell membrane currents and potentials were recorded using standard patch-clamp techniques. In addition, measurements of NO production were obtained using the NO-sensitive dye, 4,5-diamino-fluorescein diacetate (DAF-2DA). RESULTS: Type I VHCs Voltage-dependent K+ current was activated from low depolarizing stimulation. As the stimulation increased, higher current was detected. Voltage-dependent K+ current in type I VHCs was decreased when GM (200 microM) was administrated and GM effects of K+ current inhibition was significantly blocked by EGCG. Extracellular GM-induced an increase in DAF-2DA fluorescence, which thus indicates NO production in VHCs. Also, the GMinduced NO production was inhibited by EGCG. CONCLUSION: GM inhibits voltage-dependent K+ current by releasing NO in isolated type I VHCs. EGCG blocks this inhibitory effects, suggesting a protective role on GM vestibulotoxicity.

Spontaneous Electrical Activity of Cultured Interstitial Cells of Cajal from Mouse Urinary Bladder

Interstitial cells of Cajal (ICCs) from the urinary bladder regulate detrusor smooth muscle activities. We cultured ICCs from the urinary bladder of mice and performed patch clamp and intracellular Ca2+ ([Ca2+]i) imaging to investigate whether cultured ICCs can be a valuable tool for cellular functional studies. The cultured ICCs displayed two types of spontaneous electrical activities which are similar to those recorded in intact bladder tissues. Spontaneous electrical activities of cultured ICCs were nifedipine-sensitive. Carbachol and ATP, both excitatory neurotransmitters in the urinary bladder, depolarized the membrane and increased the frequency of spike potentials. Carbachol increased [Ca2+]i oscillations and basal Ca2+ levels, which were blocked by atropine. These results suggest that cultured ICCs from the urinary bladder retain rhythmic phenotypes similar to the spontaneous electrical activities recorded from the intact urinary bladder. Therefore, we suggest that cultured ICCs from the urinary bladder may be useful for cellular and molecular studies of ICCs.

Transplantation of Neural Differentiated Human Mesenchymal Stem Cells into the Cochlea of an Auditory-neuropathy Guinea Pig Model

The aim of this study was to determine the effects of transplanted neural differentiated human mesenchymal stem cells (hMSCs) in a guinea pig model of auditory neuropathy. In this study, hMSCs were pretreated with a neural-induction protocol and transplanted into the scala tympani of the guinea pig cochlea 7 days after ouabain injury. A control model was made by injection of Hanks balanced salt solution alone into the scala tympani of the guinea pig cochlea 7 days after ouabain injury. We established the auditory neuropathy guinea pig model using 1 mM ouabain application to the round window niche. After application of ouabain to the round window niche, degeneration of most spiral ganglion neurons (SGNs) without the loss of hair cells within the organ of Corti and increasing the auditory brain responses (ABR) threshold were found. After transplantation of neural differentiated hMSCs, the number of SGNs was increased, and some of the SGNs expressed immunoreactivity with human nuclear antibody under confocal laser scanning microscopy. ABR results showed mild hearing recovery after transplantation. Based on an auditory neuropathy animal model, these findings suggest that it may be possible to replace degenerated SGNs by grafting stem cells into the scala tympani.

Effects of Cyclic Nucleotide-Gated Channels in Vestibular Nuclear Neurons / 전남의대학술지

This study was designed to investigate the effects an 8-Br-cGMP on the neuronal activity of rat vestibular nuclear cells. Sprague-Dawley rats aged 14 to 16 days were decapitated under ether anesthesia. After treatment with pronase and thermolysin, the dissociated vestibular nuclear cells were transferred into a chamber on an inverted microscope. Spontaneous action potentials and potassium currents were recorded by standard patch-clamp techniques under current and voltage-clamp modes. Twelve vestibular nuclear cells revealed excitatory responses to 1-5 microM of 8-Br-cGMP, and 3 neurons did not respond to 8-Br-cGMP. Whole potassium currents of vestibular nuclear cells were decreased by 8-Br-cGMP (n=12). After calcium-dependent potassium currents were blocked by tetraethylammonium, the potassium currents were not decreased by 8-Br-cGMP. These experimental results suggest that 8-Br-cGMP changes the neuronal activity of vestibular nuclear cells by blocking the calcium-dependent potassium currents that underlie the afterhyperpolarization.

Effects of Epigallocatechin-3-Gallate on the Expression of TGF-beta1, PKC alpha/betaII, and NF-kappaB in High-Glucose-Stimulated Glomerular Epithelial Cells / 전남의대학술지

Epigallocatechin-3-gallate (EGCG) is the most potent antioxidant polyphenol in green tea. In the present study, we investigated whether EGCG plays a role in the expression of transforming growth factor-beta1 (TGF-beta1), protein kinase C (PKC) alpha/betaII, and nuclear factor-kappaB (NF-kappaB) in glomerular epithelial cells (GECs) against high-glucose injury. Treatment with high glucose (30 mM) increased reactive oxygen species (ROS)/lipid peroxidation (LPO) and decreased glutathione (GSH) in GECs. Pretreatment with 100 microM EGCG attenuated the increase in ROS/LPO and restored the levels of GSH, whereas ROS, LPO, and GSH levels were not affected by treatment with 30 mM mannitol as an osmotic control. Interestingly, high-glucose treatment affected 3 separate signal transduction pathways in GECs. It increased the expression of TGF-beta1, PKC alpha/betaII, and NF-kappaB in GECs, respectively. EGCG (1, 10, 100 microM) pretreatment significantly decreased the expression of TGF-beta1 induced by high glucose in a dose-dependent manner. In addition, EGCG (100 microM) inhibited the phosphorylation of PKC alpha/betaII caused by glucose at 30 mM. Moreover, EGCG (1, 10, 100 microM) pretreatment significantly decreased the transcriptional activity of NF-kappaB induced by high glucose in a dose-dependent manner. These data suggest that EGCG could be a useful factor in modulating the injury to GECs caused by high glucose.

Effects of Sphingosine-1-Phosphate on Neural Differentiation and Neurite Outgrowth in Neuroblastoma Cells / 전남의대학술지

Sphingosine-1-phosphate (S1P) is emerging as a new class of second messenger involved in cellular proliferation, differentiation, and apoptosis and is implicated in diverse physiological functions. Despite many studies on the biological functions of S1P, however, little is known about its role in neuronal differentiation. By use of reverse transcription-polymerase chain reaction and immunostaining, this study aimed to explore whether S1P can differentiate neuroblastoma cells into neural cells. After incubation with 1 uM or 10 uM S1P, the number of neurite-bearing cells increased. Furthermore, the neuroblastoma cells revealed immunoreactivity for neural-specific markers such as GAP43, NFH, and SYP by immunostaining. The expression of NFH, MAP2, SYP, NeuroD1, and SYT mRNA, which is specific for neurons, was increased as shown by RT-PCR studies. The results of this study suggest that that S1P can induce neuronal differentiation and may be a good candidate for the treatment of neurodegenerative diseases.

Effects of Sphingosine-1-Phosphate on Neural Differentiation and Neurite Outgrowth in Neuroblastoma Cells / 전남의대학술지

Sphingosine-1-phosphate (S1P) is emerging as a new class of second messenger involved in cellular proliferation, differentiation, and apoptosis and is implicated in diverse physiological functions. Despite many studies on the biological functions of S1P, however, little is known about its role in neuronal differentiation. By use of reverse transcription-polymerase chain reaction and immunostaining, this study aimed to explore whether S1P can differentiate neuroblastoma cells into neural cells. After incubation with 1 uM or 10 uM S1P, the number of neurite-bearing cells increased. Furthermore, the neuroblastoma cells revealed immunoreactivity for neural-specific markers such as GAP43, NFH, and SYP by immunostaining. The expression of NFH, MAP2, SYP, NeuroD1, and SYT mRNA, which is specific for neurons, was increased as shown by RT-PCR studies. The results of this study suggest that that S1P can induce neuronal differentiation and may be a good candidate for the treatment of neurodegenerative diseases.

Effects of Cyclic Nucleotide-Gated Channels in Vestibular Nuclear Neurons / 전남의대학술지

This study was designed to investigate the effects an 8-Br-cGMP on the neuronal activity of rat vestibular nuclear cells. Sprague-Dawley rats aged 14 to 16 days were decapitated under ether anesthesia. After treatment with pronase and thermolysin, the dissociated vestibular nuclear cells were transferred into a chamber on an inverted microscope. Spontaneous action potentials and potassium currents were recorded by standard patch-clamp techniques under current and voltage-clamp modes. Twelve vestibular nuclear cells revealed excitatory responses to 1-5 microM of 8-Br-cGMP, and 3 neurons did not respond to 8-Br-cGMP. Whole potassium currents of vestibular nuclear cells were decreased by 8-Br-cGMP (n=12). After calcium-dependent potassium currents were blocked by tetraethylammonium, the potassium currents were not decreased by 8-Br-cGMP. These experimental results suggest that 8-Br-cGMP changes the neuronal activity of vestibular nuclear cells by blocking the calcium-dependent potassium currents that underlie the afterhyperpolarization.

Effects of Epigallocatechin-3-Gallate on the Expression of TGF-beta1, PKC alpha/betaII, and NF-kappaB in High-Glucose-Stimulated Glomerular Epithelial Cells / 전남의대학술지

Epigallocatechin-3-gallate (EGCG) is the most potent antioxidant polyphenol in green tea. In the present study, we investigated whether EGCG plays a role in the expression of transforming growth factor-beta1 (TGF-beta1), protein kinase C (PKC) alpha/betaII, and nuclear factor-kappaB (NF-kappaB) in glomerular epithelial cells (GECs) against high-glucose injury. Treatment with high glucose (30 mM) increased reactive oxygen species (ROS)/lipid peroxidation (LPO) and decreased glutathione (GSH) in GECs. Pretreatment with 100 microM EGCG attenuated the increase in ROS/LPO and restored the levels of GSH, whereas ROS, LPO, and GSH levels were not affected by treatment with 30 mM mannitol as an osmotic control. Interestingly, high-glucose treatment affected 3 separate signal transduction pathways in GECs. It increased the expression of TGF-beta1, PKC alpha/betaII, and NF-kappaB in GECs, respectively. EGCG (1, 10, 100 microM) pretreatment significantly decreased the expression of TGF-beta1 induced by high glucose in a dose-dependent manner. In addition, EGCG (100 microM) inhibited the phosphorylation of PKC alpha/betaII caused by glucose at 30 mM. Moreover, EGCG (1, 10, 100 microM) pretreatment significantly decreased the transcriptional activity of NF-kappaB induced by high glucose in a dose-dependent manner. These data suggest that EGCG could be a useful factor in modulating the injury to GECs caused by high glucose.

Neurotoxicity Screening in a Multipotent Neural Stem Cell Line Established from the Mouse Brain

Neural stem cells (NSCs) have mainly been applied to neurodegeneration in some medically intractable neurologic diseases. In this study, we established a novel NSC line and investigated the cytotoxic responses of NSCs to exogenous neurotoxicants, glutamates and reactive oxygen species (ROS). A multipotent NSC line, B2A1 cells, was established from long-term primary cultures of oligodendrocyte-enriched cells from an adult BALB/c mouse brain. B2A1 cells could be differentiated into neuronal, astrocytic and oligodendroglial lineages. The cells also expressed genotypic mRNA messages for both neural progenitor cells and differentiated neuronoglial cells. B2A1 cells treated with hydrogen peroxide and L-buthionine-(S,R)-sulfoximine underwent 30-40% cell death, while B2A1 cells treated with glutamate and kainate showed 25-35% cell death. Cytopathologic changes consisting of swollen cell bodies, loss of cytoplasmic processes, and nuclear chromatin disintegration, developed after exposure to both ROS and excitotoxic chemicals. These results suggest that B2A1 cells may be useful in the study of NSC biology and may constitute an effective neurotoxicity screening system for ROS and excitotoxic chemicals.

Effect of Platelet Rich Plasma on Facial Nerve Regeneration in Acute Nerve Injury Model / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The object of this study was to evaluate the effect of platelet rich plasma (PRP) on facial nerve regeneration from an axotomy injury in the guinea pig model. MATERIALS AND METHOD: Experiments involved the transection and repair of right facial nerve. The right facial nerve of 14 albino guinea pigs were completely transected and immediately sutured, followed by fibrin glue only (control group) or fibrin glue +PRP (PRP group). Western blot assay was used to detect neurotrophic factors secreted by PRP. Nerve regeneration was assessed by motor function, electrophysiology, and histology studies. RESULTS: High levels of neurotrophin-3, angiopoietin-1, glial cell line derived neurotrophic factors, nerve growth factors and brain derived neurotrophic factors were demonstrated in PRP. Motor function recovery, compound motor action potentials, and axon count showed significant improvement in guinea pig treated with PRP. CONCLUSION: There was an improved functional outcome with the use of PRP in comparison with control. The increased nerve regeneration found in this study may be due to the neurotrophic factors secreted by PRP.

Tracking of Neural Stem Cells in Rats with Intracerebral Hemorrhage by the Use of 3T MRI

OBJECTIVE: To access the feasibility of clinically available 3T MRI to detect the migration of labeled neural stem cells (NSCs) in intracerebral hemorrhage (ICH) in a rat model. MATERIALS AND METHODS: The ethics committee of our institution approved this study. ICH was induced by the injection of collagenase type IV into the right striatum of ten Sprague-Dawley rats. Human NSCs conjugated with Feridex (super-paramagnetic iron oxide: SPIO) were transplanted into the left striatum one week after ICH induction. MRI was performed on a 3T scanner during the first, second, third, fourth, and sixth weeks post-transplantation. MRI was obtained using coronal T2- and T2*-weighted sequences. Two rats were sacrificed every week after in vivo MRI in order to analyze the histological findings. RESULTS: ICH in the right striatum was detected by MRI one and two weeks after transplantation without migration of the NSCs. There was no migration of the NSCs as seen on the histological findings one week after transplantation. The histological findings two weeks after transplantation showed a small number of NSCs along the corpus callosum. On MRI three weeks after transplantation, there was a hypointense line along the corpus callosum and decreased signal intensity in the right periventricular region. Histological findings three weeks after transplantation confirmed the presence of the hypointense line representing SPIO-labeled NSCs. MRI four and six weeks after transplantation showed a hypointense spot in the right periventricular region. The histological findings four and six weeks after transplantation showed the presence of prominent NSCs in the right periventricular region. CONCLUSION: 3T MRI can detect the migration of NSCs in rats with ICH along the corpus callosum. Therefore, 3T MRI could be feasible for detecting the migration of NSCs in the clinical setting of stem cell therapy.

Neural Differentiation of Mesenchymal Stem Cells from Bone Marrow of Human Mastoid Process / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Reports of neural differentiation of mesenchymal stem cells suggest the possibility that these cells may serve as a source for stem cell-based regenerative medicine to treat neurological disorders. The purpose of this study was to generate neural cells by differentiation of bone marrow-derived mesenchymal stem cells that isolated from human mastoid process. MATERIALS AND METHOD: Human mesenchymal stem cells (hMSCs) isolated from human mastoid process bone marrow during mastoidectomy for chronic otitis media surgery were characterized using fluorescence-activated cell sorter. Induction of neural differentiation from hMSCs was performed using mitogenic factors (basic fibroblast growth factor, epidermal growth factor, forskolin, isobutylmethylxanthine), and the characterization of differentiated hMSCs was performed using immunohistochemistry, RT-PCR and whole cell patch clamp technique. RESULTS: hMSCs from bone marrow of mastoid process were isolated and cultured. Differentiated cells from hMSCs expressed mRNA transcripts for neuron specific markers, TUJ1 and neurofilament proteins (NF-L, NF-M) as determined by RT-PCR, and neuron specific markers, suhc as NeuN, TUJ1, microtubule-associated protein-2 (MAP2) and glial fibrillary acidic protein by immunohistochemistry. These cells showed voltagedependent sodium currents that was blocked by tetrodotoxin. CONCLUSION: hMSCs, which were isolated from human mastoid process bone marrow, were one of the good sources for stem cell-based regenerative medicine to treat neurological disorders.

Protein Kinase C-mediated Neuroprotective Action of (-)-epigallocatechin-3-gallate against Abeta1-42-induced Apoptotic Cell Death in SH-SY5Y Neuroblastoma Cells

The neurotoxicity of amyloid beta (Abeta) is associated with an increased production of reactive oxygen species and apoptosis, and it has been implicated in the development of Alzheimer's disease. While (-)-epigallocatechin-3-gallate (EGCG) suppresses Abeta-induced apoptosis, the mechanisms underlying this process have yet to be completely clarified. This study was designed to investigate whether EGCG plays a neuroprotective role by activating cell survival system such as protein kinase C (PKC), extracellular-signal-related kinase (ERK), c-Jun N-terminal kinase (JNK), and anti-apoptotic and pro-apoptotic genes in SH-SY5Y human neuroblastoma cells. One microM Abeta1-42 decreased cell viability, which was correlated with increased DNA fragmentation evidenced by DAPI staining. Pre-treatment of SH-SY5Y neuroblastoma cells with EGCG (1microM) significantly attenuated Abeta1-42-induced cytotoxicity. Potential cell signaling candidates involved in this neuroprotective effects were further examined. EGCG restored the reduced PKC, ERK, and JNK activities caused by Abeta1-42 toxicity. In addition, gene expression analysis revealed that EGCG prevented both the Abeta1-42-induced expression of a pro-apoptotic gene mRNA, Bad and Bax, and the decrease of an anti-apoptotic gene mRNA, Bcl-2 and Bcl-xl. These results suggest that the neuroprotective mechanism of EGCG against Abeta1-42-induced apoptotic cell death includes stimulation of PKC, ERK, and JNK, and modulation of cell survival and death genes.

Effects of S-nitroso-N-acetylpenicillamine on the Neuronal Excitability of the Medial Vestibular Nuclear Neuron

BACKGROUND: The medial vestibular nucleus is the largest one among the vestibular nuclei and known to play important roles not only in normal vestibular information processing but also in vestibular compensation. Glutamate is known to have a key role in vestibular compensation via long term potentiation and depression. But the action of nitric oxide related with glutamate is poorly studied. This experiment was designed to explore the effects of nitric oxide on the neuronal activity of a rat medial vestibular nuclear neuron using a nitric oxide enhancing drug, S-nitroso-N-acetylpenicillamine (SNAP). METHODS: Experiments were carried out on Sprague-Dawley rats aged 14 to 17 days. Neurons of MVN were obtained via enzymatic dissociation of a microtomized rat brainstem. Whole-cell membrane potentials were recorded at room temperature by using standard patch-clamp techniques. Action potentials were obtained after administration of SNAP. Changes of potassium currents were recorded using SNAP and ODQ (1H-[1, 2, 4] oxadiazolo [4, 3-a] quinozalin-1-one), an inhibitor of guanylyl cyclase. RESULTS: The mean spike frequency of action potentials was increased by adding SNAP. The mean amplitude of afterhyperpolarization was decreased by adding SNAP. The mean potassium current of medial vestibular nuclear neurons was decreased by SNAP. ODQ inhibited the SNAP-induced potassium currents. CONCLUSIONS: These results suggest that nitric oxide increases the neuronal activity of rat medial vestibular nuclear neurons by inhibiting potassium currents via a cGMP dependent mechanism.