Climbing Fibres as a Source of Nitric Oxide in the Cerebellum

Two pathways of cyclic GMP production through glutamate receptor-mediated nitric oxide synthesis

The selective agonists for the metabotropic glutamate receptor and the ionotropic non-N-methyl-D-aspartate (NMDA) glutamate receptor, (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD) and (R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), respectively, increased the cyclic GMP (cGMP) content in cerebellar slices prepared from adult rats. The ACPD-induced rise in cGMP level was blocked by compounds known to antagonize metabotropic glutamate receptors, such as DL-2-amino-3-phosphonopropionic acid and L-2-amino-4-phosphonobutyric acid, but not by ionotropic glutamate receptor antagonists, D-2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), whereas the AMPA-induced rise in cGMP level was suppressed by CNQX. Both rises in cGMP level involved nitric oxide synthase (NOS), because NG-methyl-L-arginine (NMLA), an inhibitor of NOS, blocked both cGMP level rises, and excess L-arginine reversed the effect of NMLA. After lithium chloride treatment, which could exhaust phosphatidylinositol phosphates, ACPD no longer increased cGMP levels, whereas AMPA was still effective. In a calcium-free medium, ACPD still induced a rise in cGMP level, whereas AMPA did not. When the molecular layer was isolated to determine the cGMP content separately from that in the rest of the cerebellar cortex, it was found that ACPD raised the cGMP level mainly in the molecular layer, whereas AMPA raised it in both sections.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel neuronal messenger molecule in brain: the free radical, nitric oxide

Understanding of the organization and function of a newly identified neuronal messenger molecule, nitric oxide, has progressed rapidly. Nitric oxide synthase has been purified and molecularly cloned from brain. Its localization is exclusively neuronal and endothelial. The catalytic activity of nitric oxide synthase accounts for the NADPH diaphorase staining of neurons that are uniquely resistant to toxic insults and neurodegenerative disorders. Nitric oxide has diverse functions. In platelets it inhibits their aggregation, in macrophages it mediates cytotoxicity, and in blood vessels it acts as a vasodilator. In the nervous system nitric oxide may be the retrograde transmitter in long-term potentiation. It is the "neurotransmitter" of cerebral vasodilator nerves and the inhibitory "neurotransmitter" of the motor neurons of the intestines. Nitric oxide in situations of excessive production may function as a neurotoxin, suggesting a role for nitric oxide in neurodegenerative disorders.

Delayed increase of extracellular arginine, the nitric oxide precursor, following electrical white matter stimulation in rat cerebellar slices

Amino acid levels were measured in perfusates from biplanar slices of rat cerebellum installed in a Krebs-filled three-compartment chamber. The two lateral compartments housed the white matter and a section containing parallel fibres respectively. The central compartment housed cortical structures, including the Purkinje cell and granule cell bodies. This arrangement allows selective electrical stimulation of the parallel fibre or mossy fibre pathways, recording of the evoked responses to such stimulation and collection of the perfusion medium passing through the central chamber for amino acid analysis using high-pressure liquid chromatography (HPLC). Both, 2-Hz and 5-Hz stimulation of white matter caused a delayed increase in arginine levels in the perfusate. Since L-arginine is the physiological precursor of nitric oxide, a neuronal messenger in the brain, the data suggest that physiological stimuli can result in the release of this precursor, possibly to supply the nitric oxide synthase.

NMDA-induced release of nitric oxide potentiates aspartate overflow from cerebellar slices

We report that stimulation of neonatal rat cerebellar slices with N-methyl-D-aspartate (NMDA) release nitric oxide (NO) and also increased the release of aspartate. Inhibition of NMDA receptors with the specific antagonist, 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) prevented the NMDA-induced release of both NO and aspartate. Similar results were obtained with the inhibitor of NO synthase, NG-nitroargine (NG-ARG). The NO scavenger, haemoglobin prevented the release of aspartate. Under calcium-free conditions NMDA-induced aspartate release was abolished and NO release significantly reduced. These results indicate that NO has a physiological role in the release of aspartate.

Sources and targets of nitric oxide in rat cerebellum

Nitric oxide (NO) mediates cell-cell signalling in the brain and stimulates cyclic GMP (cGMP) production in target cells. We have used NADPH-diaphorase (reduced nicotinamide adenine dinucleotide phosphate-diaphorase) histochemistry to identify NO-producing neurones and cGMP immunohistochemistry to locate the targets of NO in rat cerebellum. NADPH-diaphorase staining was prominent in granule cells and in the molecular layer. cGMP immunostaining in cerebellar slices stimulated with the NO donors, nitroprusside and SIN-1, was found in granule cells, glomeruli, fibres, Bergmann glia and in other astrocytes. The results provide visible evidence that NO mediates neuron-neuron and neuron-glia communication.

Neurons that say NO

Thirty years ago, Thomas and Pearse discovered what they termed 'solitary active cells'--neurons containing an unusually high nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) activity that could be detected histochemically. Although these neurons were considered as something special, an appropriate mechanism to account for their outstanding metabolism was not provided until the recent identification of neuronal NADPH-diaphorase as nitric oxide synthase. This simple histochemical method now allows the precise anatomical localization of the neurons generating the exotic messenger molecule nitric oxide. This article reviews the functional implications that arise from our new knowledge of the anatomy of the nitric oxide signal transduction pathway in the nervous system. The widespread distribution of this system indicates that for those interested in cellular communication nitric oxide is a gas to study.

The role of nitric oxide in hippocampal long-term potentiation

Long-term potentiation is a long-lasting, use-dependent increase in the strength of synaptic connections. We investigated the role of nitric oxide (NO) in determining the duration of potentiation induced by high frequency stimulation of afferents in the CA1 region of the rat hippocampus. The calcium/calmodulin-dependent production of NO can be initiated by activation of excitatory amino acid receptors and results in increased levels of cGMP in target cells. Here we report that only a relatively short-term potentiation can be induced in the presence of nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor. The effects of L-NAME on the duration of potentiation are partially reversed by coadministration of L-arginine, a precursor of neuronal NO, and by dibutyryl cGMP. Hemoglobin, which binds extracellular NO, also shortens the duration of stimulus-induced potentiation. The results suggest a role for NO in the maintenance of activity-dependent synaptic enhancements, possibly via the generation of cGMP.

Comparative effects of some nitric oxide donors on cyclic GMP levels in rat cerebellar slices

In the central nervous system, glutamate receptor activation and other stimuli can lead to the cellular production of nitric oxide (NO), an activator of the cyclic GMP-synthesising enzyme, soluble guanylate cyclase. Four 'nitrovasodilators' which yield NO were tested for their ability to elevate cGMP levels in rat cerebellar slices. Nitroprusside (NP), SIN-1, S-nitroso-N-penicillamine (SNAP) and hydroxylamine all caused very large (up to 300-fold) increments. Their threshold concentrations were between 1 and 30 microM. SNAP was the most potent (EC50 approximately 50 microM) followed by hydroxylamine (200 microM) and SIN-1 (1 mM), the latter compound having the highest efficacy. No maximal response to NP was evident at concentrations up to 10 mM. Slices could be challenged a second time with NP (300 microM) with no evidence of a change in sensitivity. The NO-donors are likely to be valuable for studying the functions of NO in brain tissue; however, the concentrations of NP, SNAP and SIN-1 required to elevate cGMP in the slices are orders of magnitude higher than those needed to stimulate guanylate cyclase activity in broken cell preparations, suggesting that rapid inactivation of NO takes place in the intact tissue.