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Alkadhi KA. NMDA receptor-independent LTP in mammalian nervous system. Prog Neurobiol 2021; 200:101986. [PMID: 33400965 DOI: 10.1016/j.pneurobio.2020.101986] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 12/16/2020] [Accepted: 12/28/2020] [Indexed: 11/17/2022]
Abstract
Long-term potentiation (LTP) of synaptic transmission is a form of activity-dependent synaptic plasticity that exists at most synapses in the nervous system. In the central nervous system (CNS), LTP has been recorded at numerous synapses and is a prime candidate mechanism associating activity-dependent plasticity with learning and memory. LTP involves long-lasting increase in synaptic strength with various underlying mechanisms. In the CNS, the predominant type of LTP is believed to be dependent on activation of the ionotropic glutamate N-methyl-D-aspartate receptor (NMDAR), which is highly calcium-permeable. However, various forms of NMDAR-independent LTP have been identified in diverse areas of the nervous system. The NMDAR-independent LTP may require activation of glutamate metabotropic receptors (mGluR) or ionotropic receptors other than NMDAR such as nicotinic acetylcholine receptor (α7-nAChR), serotonin 5-HT3 receptor or calcium-permeable AMPA receptor (CP-AMPAR). In this review, NMDAR-independent LTP of various areas of the central and peripheral nervous systems are discussed.
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Affiliation(s)
- Karim A Alkadhi
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX, 77204, USA.
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Alkadhi KA. Long-term potentiation in autonomic ganglia: Potential role in cardiovascular disorders. World J Pharmacol 2016; 5:51-58. [DOI: 10.5497/wjp.v5.i2.51] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2016] [Accepted: 07/13/2016] [Indexed: 02/06/2023] Open
Abstract
Ganglionic long-term potentiation (gLTP) is an activity-dependent, enduring enhancement of ganglionic transmission. This phenomenon may be induced in autonomic ganglia of an organism under certain conditions where repetitive impulses surge from the central nervous system (CNS) to the periphery. Chronic stress, repetitive epileptic seizure or chronic use of CNS stimulants could induce gLTP, which would result in a long lasting heightening of sympathetic tone to the cardiovascular system causing hypertension and disturbed cardiac rhythm that may lead to sudden cardiac death. These conditions are briefly reviewed in this article.
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Jayakar SS, Pugh PC, Dale Z, Starr ER, Cole S, Margiotta JF. PACAP induces plasticity at autonomic synapses by nAChR-dependent NOS1 activation and AKAP-mediated PKA targeting. Mol Cell Neurosci 2014; 63:1-12. [PMID: 25168001 DOI: 10.1016/j.mcn.2014.08.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Revised: 08/06/2014] [Accepted: 08/23/2014] [Indexed: 12/12/2022] Open
Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide found at synapses throughout the central and autonomic nervous system. We previously found that PACAP engages a selective G-protein coupled receptor (PAC1R) on ciliary ganglion neurons to rapidly enhance quantal acetylcholine (ACh) release from presynaptic terminals via neuronal nitric oxide synthase (NOS1) and cyclic AMP/protein kinase A (PKA) dependent processes. Here, we examined how PACAP stimulates NO production and targets resultant outcomes to synapses. Scavenging extracellular NO blocked PACAP-induced plasticity supporting a retrograde (post- to presynaptic) NO action on ACh release. Live-cell imaging revealed that PACAP stimulates NO production by mechanisms requiring NOS1, PKA and Ca(2+) influx. Ca(2+)-permeable nicotinic ACh receptors composed of α7 subunits (α7-nAChRs) are potentiated by PKA-dependent PACAP/PAC1R signaling and were required for PACAP-induced NO production and synaptic plasticity since both outcomes were drastically reduced following their selective inhibition. Co-precipitation experiments showed that NOS1 associates with α7-nAChRs, many of which are perisynaptic, as well as with heteromeric α3*-nAChRs that generate the bulk of synaptic activity. NOS1-nAChR physical association could facilitate NO production at perisynaptic and adjacent postsynaptic sites to enhance focal ACh release from juxtaposed presynaptic terminals. The synaptic outcomes of PACAP/PAC1R signaling are localized by PKA anchoring proteins (AKAPs). PKA regulatory-subunit overlay assays identified five AKAPs in ganglion lysates, including a prominent neuronal subtype. Moreover, PACAP-induced synaptic plasticity was selectively blocked when PKA regulatory-subunit binding to AKAPs was inhibited. Taken together, our findings indicate that PACAP/PAC1R signaling coordinates nAChR, NOS1 and AKAP activities to induce targeted, retrograde plasticity at autonomic synapses. Such coordination has broad relevance for understanding the control of autonomic synapses and consequent visceral functions.
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Affiliation(s)
- Selwyn S Jayakar
- Department of Neurosciences, University of Toledo, College of Medicine and Life Sciences, United States.
| | - Phyllis C Pugh
- Department of Neurosciences, University of Toledo, College of Medicine and Life Sciences, United States.
| | - Zack Dale
- Department of Neurosciences, University of Toledo, College of Medicine and Life Sciences, United States.
| | - Eric R Starr
- Department of Neurosciences, University of Toledo, College of Medicine and Life Sciences, United States.
| | - Samantha Cole
- Department of Neurosciences, University of Toledo, College of Medicine and Life Sciences, United States.
| | - Joseph F Margiotta
- Department of Neurosciences, University of Toledo, College of Medicine and Life Sciences, United States.
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Samson ML, Kajitani K, Robertson GS. Nitric-Oxide Synthase Mediates the Ability of Darbepoetin Alfa to Attenuate Pre-Existing Spatial Working Memory Deficits in Rats Subjected to Transient Global Ischemia. J Pharmacol Exp Ther 2010; 333:437-44. [DOI: 10.1124/jpet.110.165530] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
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Pugh PC, Jayakar SS, Margiotta JF. PACAP/PAC1R signaling modulates acetylcholine release at neuronal nicotinic synapses. Mol Cell Neurosci 2009; 43:244-57. [PMID: 19958833 DOI: 10.1016/j.mcn.2009.11.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Revised: 11/18/2009] [Accepted: 11/19/2009] [Indexed: 12/11/2022] Open
Abstract
Neuropeptides collaborate with conventional neurotransmitters to regulate synaptic output. Pituitary adenylate cyclase-activating polypeptide (PACAP) co-localizes with acetylcholine in presynaptic nerve terminals, is released by stimulation, and enhances nicotinic acetylcholine receptor- (nAChR-) mediated responses. Such findings implicate PACAP in modulating nicotinic neurotransmission, but relevant synaptic mechanisms have not been explored. We show here that PACAP acts via selective high-affinity G-protein coupled receptors (PAC(1)Rs) to enhance transmission at nicotinic synapses on parasympathetic ciliary ganglion (CG) neurons by rapidly and persistently increasing the frequency and amplitude of spontaneous, impulse-dependent nicotinic excitatory postsynaptic currents (sEPSCs). Of the canonical adenylate cyclase (AC) and phospholipase-C (PLC) transduction cascades stimulated by PACAP/PAC(1)R signaling, only AC-generated signals are critical for synaptic modulation since the increases in sEPSC frequency and amplitude were mimicked by 8-Bromo-cAMP, blocked by inhibiting AC or cAMP-dependent protein kinase (PKA), and unaffected by inhibiting PLC. Despite its ability to increase agonist-induced nAChR currents, PACAP failed to influence nAChR-mediated impulse-independent miniature EPSC amplitudes (quantal size). Instead, evoked transmission assays reveal that PACAP/PAC(1)R signaling increased quantal content, indicating that it modulates synaptic function by increasing vesicular ACh release from presynaptic terminals. Lastly, signals generated by the retrograde messenger, nitric oxide- (NO-) are critical for the synaptic modulation since the PACAP-induced increases in spontaneous EPSC frequency, amplitude and quantal content were mimicked by NO donor and absent after inhibiting NO synthase (NOS). These results indicate that PACAP/PAC(1)R activation recruits AC-dependent signaling that stimulates NOS to increase NO production and control presynaptic transmitter output at neuronal nicotinic synapses.
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Affiliation(s)
- Phyllis C Pugh
- University of Toledo College of Medicine, Department of Neurosciences, Toledo, OH 43614-5804, USA
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Alzoubi K, Alkadhi K. Calmodulin and guanylyl cyclase inhibitors block the in vivo expression of gLTP in sympathetic ganglia from chronically stressed rats. Neurosci Res 2009; 63:95-9. [DOI: 10.1016/j.neures.2008.10.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2008] [Revised: 10/08/2008] [Accepted: 10/24/2008] [Indexed: 02/06/2023]
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Alzoubi KH, Aleisa AM, Alkadhi KA. Expression of gLTP in sympathetic ganglia of obese Zucker rats in vivo: molecular evidence. J Mol Neurosci 2008; 35:297-306. [PMID: 18563301 DOI: 10.1007/s12031-008-9110-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Accepted: 05/21/2008] [Indexed: 12/20/2022]
Abstract
Long-term potentiation in sympathetic ganglia (gLTP) is similar to LTP of the hippocampal area CA1 in that its expression involves similar changes in signaling molecules. We have shown previously that the stress-prone, hypertensive obese Zucker rats (OZR) expressed gLTP in sympathetic ganglia and that high blood pressure was reduced by treatment with 5-HT(3) receptor antagonists. In the present study, we present additional electrophysiological evidence for the pre-expression of gLTP in sympathetic ganglia from OZR indicated by failure of repetitive stimulation to express gLTP in isolated superior cervical ganglia (SCG) and inhibition of baseline ganglionic transmission by a 5-HT(3) receptor antagonist. We have also investigated the role of key signaling molecules in the expression of gLTP in the hypertensive OZR. Immunoblot analysis showed a significant increase in the levels of phosphorylated (P-)CaMKII and protein kinase C gamma (PKCgamma) in SCG from OZR. The ratio of P-CaMKII to the total CaMKII was markedly increased in OZR ganglia, suggesting increased phosphorylation of this molecule. Additionally, there was a significant decrease in the levels of calcineurin in ganglia. Furthermore, the neural nitric oxide synthase and hemeoxygenase II, which are essential for the expression of gLTP, were significantly elevated in OZR ganglia. The present findings confirm that ganglia from OZR have expressed gLTP and that synaptic plasticity in sympathetic ganglia may involve a molecular cascade similar to that of LTP of the brain hippocampal area CA1.
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Affiliation(s)
- K H Alzoubi
- Department of Clinical Pharmacy, Faculty of Pharmacy, Jordan University of Science and Technology, Irbid, Jordan
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Expression of gLTP in sympathetic ganglia from stress-hypertensive rats: molecular evidence. J Mol Neurosci 2008; 35:201-9. [PMID: 18386186 DOI: 10.1007/s12031-008-9054-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2007] [Accepted: 02/12/2008] [Indexed: 01/30/2023]
Abstract
We previously reported behavioral and electrophysiological evidence indicating that superior cervical ganglia (SCG) from rats that developed hypertension as a result of chronic psychosocial stress expressed ganglionic long-term potentiation (gLTP) in vivo. In the present study, we present additional supportive evidence by measuring changes in protein levels of essential signaling molecules in ganglia from chronically stressed rats. We compared protein levels of essential, LTP-related signaling molecules in ganglia isolated from chronic stress-hypertensive rats, known to have expressed gLTP, with those of the same molecules in normal ganglia 1h after eliciting gLTP by high frequency stimulation (HFS) in vitro. Immunoblot analysis showed a significant increase in the levels of phosphorylated CaMKII, total CaMKII, nitric oxide synthase (NOS-1), and calmodulin in SCG from both chronically stressed rats and from normal rat ganglia in which gLTP was expressed by HFS in vitro. Additionally, there was a parallel reduction in calcineurin protein levels in ganglia from both groups. The present results confirm that ganglia from stressed rats have expressed gLTP in vivo and that synaptic plasticity in sympathetic ganglia may involve a molecular cascade largely similar to that of LTP in the hippocampal CA1 region.
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Alkadhi K, Alzoubi K. Role of long-term potentiation of sympathetic ganglia (gLTP) in hypertension. Clin Exp Hypertens 2007; 29:267-86. [PMID: 17653963 DOI: 10.1080/10641960701500356] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Ganglionic long-term potentiation (gLTP) is an activity-dependent sustained increase in the synaptic efficacy of the nicotinic pathway that has been demonstrated in autonomic ganglia. Sustained enhancement in ganglionic transmission as in chronic mental stress may affect the activity of autonomic functions, including blood pressure and heart rate. An increase in sympathetic activity associated with psychosocial stress and stress-prone conditions such as obesity and aging could result in in vivo expression of gLTP leading to hypertension of a neural origin. Recent reports indicated that the prevention of the expression of gLTP in animal models of hypertension prevented or reduced high blood pressure. Although stress-induced hypertension normalizes within a few days of stress relief, prolonged mild-moderate hypertension may contribute to atherosclerotic cardiovascular diseases. The relation between hypertension and enhanced ganglionic transmission as a result of in vivo expression of gLTP is discussed in this review.
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Affiliation(s)
- Karim Alkadhi
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas 77204-5515, USA.
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Vitek MP, Brown C, Xu Q, Dawson H, Mitsuda N, Colton CA. Characterization of NO and cytokine production in immune-activated microglia and peritoneal macrophages derived from a mouse model expressing the human NOS2 gene on a mouse NOS2 knockout background. Antioxid Redox Signal 2006; 8:893-901. [PMID: 16771679 DOI: 10.1089/ars.2006.8.893] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Significant differences exist in the production and release of nitric oxide (NO) from human macrophages versus macrophages of mouse origin. Human macrophages have been shown to respond poorly to stimuli that provoke strong inflammatory reactions from mouse macrophages. To address the differences in macrophage function in an animal model, a transgenic mouse was created that contained the entire human NOS2 gene, including the human promoter and all of its exons and introns. The huNOS2 transgenic mouse was then mated to mice lacking a functional NOS2 gene (muNOS2(/) or NOS2 knockout mice) to generate a double transgenic mouse (huNOS2(+/0)/muNOS2(/)) that expresses a functional human NOS2 gene in place of the mouse NOS2 gene. These double transgenic mice were found to express only human NOS2 mRNA and human iNOS proteins in response to immune stimulation. The production and release of nitric oxide from isolated macrophages from the doubly transgenic mouse also more closely paralleled human responses rather than mouse. Peritoneal macrophages from double transgenic mice generated nanomolar levels of nitrite in response to inflammatory stimuli, while peritoneal macrophages from wild-type mice generated micromolar levels of nitrite in response to the same inflammatory stimuli. Similarly, microglia from the huNOS2(+/0)/muNOS2(/) mice accumulated nanomolar levels of nitrite following inflammatory stimulation. Reduced nitrite release persisted in spite of normal responsiveness to inflammatory stimulation as measured by tumor necrosis factor alpha and interleukin-6 production and release. These data suggest that the human-specific release of nanomolar levels of nitrite may largely result from differences between the human and mouse NOS2 genes, which may program different degrees of nitric oxide responses to inflammatory signals in humans than in mice.
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Affiliation(s)
- Michael P Vitek
- Division of Neurology, Duke University Medical Center, Durham North Carolina 27710, USA
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Toda N, Ayajiki K. Phylogenesis of constitutively formed nitric oxide in non-mammals. REVIEWS OF PHYSIOLOGY BIOCHEMISTRY AND PHARMACOLOGY 2006; 157:31-80. [PMID: 17236649 DOI: 10.1007/112_0601] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
It is widely recognized that nitric oxide (NO) in mammalian tissues is produced from L-arginine via catalysis by NO synthase (NOS) isoforms such as neuronal NOS (nNOS) and endothelial NOS (eNOS) that are constitutively expressed mainly in the central and peripheral nervous system and vascular endothelial cells, respectively. This review concentrates only on these constitutive NOS (cNOS) isoforms while excluding information about iNOS, which is induced mainly in macrophages upon stimulation by cytokines and polysaccharides. The NO signaling pathway plays a crucial role in the functional regulation of mammalian tissues and organs. Evidence has also been accumulated for the role of NO in invertebrates and non-mammalian vertebrates. Expression of nNOS in the brain and peripheral nervous system is widely determined by staining with NADPH (reduced nicotinamide adenine dinucleotide phosphate) diaphorase or NOS immunoreactivity, and functional roles of NO formed by nNOS are evidenced in the early phylogenetic stages (invertebrates and fishes). On the other hand, the endothelium mainly produces vasodilating prostanoids rather than NO or does not liberate endothelium-derived relaxing factor (EDRF) (fishes), and the ability of endothelial cells to liberate NO is observed later in phylogenetic stages (amphibians). This review article summarizes various types of interesting information obtained from lower organisms (invertebrates, fishes, amphibians, reptiles, and birds) about the properties and distribution of nNOS and eNOS and also the roles of NO produced by the cNOS as an important intercellular signaling molecule.
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Affiliation(s)
- N Toda
- Toyama Institute for Cardiovascular Pharmacology Research, 7-13, 1-Chome, Azuchi-machi, Chuo-ku, Osaka, Japan.
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Alzoubi KH, Bedawi AS, Aleisa AM, Alkadhi KA. Hypothyroidism impairs long-term potentiation in sympathetic ganglia: electrophysiologic and molecular studies. J Neurosci Res 2005; 78:393-402. [PMID: 15389831 DOI: 10.1002/jnr.20268] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Electrophysiologic and molecular techniques were used to study the effect of adult-onset hypothyroidism on synaptic plasticity in the superior cervical sympathetic ganglion. Ganglia excised from adult thyroidectomized and sham-operated rats were subjected to a brief high-frequency stimulation of the preganglionic nerve to express long-term potentiation (gLTP). Western blotting was carried out to determine the protein levels of key signaling molecules that may be involved in the expression of gLTP. Input/output relationship in ganglia from hypothyroid rats indicated a normal basal synaptic transmission, whereas activity-dependent types of synaptic plasticity, posttetanic potentiation (PTP) and gLTP, were impaired. Immunoblot analysis showed that both calcium/calmodulin kinase II (CaMKII) and phosphorylated CaMKII (P-CaMKII) levels were reduced markedly in hypothyroid rat ganglia compared to those from euthyroid controls. Additionally, protein levels of nitric oxide synthase-1, heme oxygenase-2, calmodulin, protein kinase C (PKC), and calcineurin were also reduced in hypothyroid rat ganglia. The results indicate that abnormally low basal levels of signaling molecules may be responsible for hypothyroidism-induced impairment of gLTP in superior cervical ganglia. In addition, the results indicate that synaptic plasticity in sympathetic ganglia may involve a molecular sequence of events similar to that proposed for LTP in the hippocampus.
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Affiliation(s)
- K H Alzoubi
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX 77204-5515, USA
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Altememi GF, Alkadhi KA. Nitric oxide is required for the maintenance but not initiation of ganglionic long-term potentiation. Neuroscience 1999; 94:897-902. [PMID: 10579581 DOI: 10.1016/s0306-4522(99)00362-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The role of nitric oxide in long-term potentiation of the nicotinic pathway of synaptic transmission in the isolated superior cervical ganglia of rat was studied. Long-term potentiation was induced by a brief tetanizing pulse (tetanus, 20 Hz/20 s) to the preganglionic nerve. The amplitude of the extracellularly recorded postganglionic compound action potential was used as an index of synaptic transmission. Pretreatment with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (10 microM) or L-N(G)-nitro-arginine (10 microM) 30 min before tetanus, inhibited long-term potentiation. The inactive enantiomer of the nitric oxide synthase inhibitor, N(G)-nitro-D-arginine methyl ester (10 microM), failed to inhibit the long-term potentiation when given 30 min before the tetanus. Washout of L-N(G)-nitro-arginine, but not N(G)-nitro-L-arginine methyl ester, resulted in complete recovery of long-term potentiation. The nitric oxide synthase inhibitor had no significant effect on the basal ganglionic neurotransmission or post-tetanic potentiation. Furthermore, established long-term potentiation was blocked by superfusion of ganglia with N(G)-nitro-L-arginine methyl ester 1 h after a tetanus. Pretreatment of ganglia with the nitric oxide donor, sodium nitroprusside (100 microM), or the nitric oxide synthase substrate, L-arginine (1 mM), completely prevented the inhibitory effects of N(G)-nitro-L-arginine methyl ester on the tetanus-induced long-term potentiation. These findings present evidence for a requirement of nitric oxide for the maintenance but not induction of long-term potentiation in rat isolated superior cervical ganglia.
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Affiliation(s)
- G F Altememi
- Department of Pharmacology, College of Pharmacy, University of Houston, TX 77204-5515, USA
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Involvement of cGMP-dependent protein kinase in adrenergic potentiation of transmitter release from the calyx-type presynaptic terminal. J Neurosci 1999. [PMID: 10377340 DOI: 10.1523/jneurosci.19-13-05293.1999] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
I have previously reported that norepinephrine (NE) induces a sustained potentiation of transmitter release in the chick ciliary ganglion through a mechanism pharmacologically distinct from any known adrenergic receptors. Here I report that the adrenergic potentiation of transmitter release was enhanced by a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) and by zaprinast, an inhibitor of cGMP-selective phosphodiesterase. Exogenous application of the membrane-permeable cGMP, 8-bromo-cGMP (8Br-cGMP), potentiated the quantal transmitter release, and after potentiation, the addition of NE was no longer effective. On the other hand, 8Br-cAMP neither potentiated the transmitter release nor occluded the NE-induced potentiation. The NE-induced potentiation was blocked by neither nitric oxide (NO) synthase inhibitor nor NO scavenger. The quantal transmitter release was not potentiated by NO donors, e.g., sodium nitroprusside. The NE-induced potentiation and its enhancement by IBMX was antagonized by two inhibitors of protein kinase G (PKG), Rp isomer of 8-(4-chlorophenylthio) guanosine-3', 5'-cyclic monophosphorothioate and KT5823. As with NE-induced potentiation, the effects of 8Br-cGMP on both the resting intraterminal [Ca2+] ([Ca2+]i) and the action potential-dependent increment of [Ca2+]i (DeltaCa) in the presynaptic terminal were negligible. The reduction of the paired pulse ratio of EPSC is consistent with the notion that the NE- and cGMP-dependent potentiation of transmitter release was attributable mainly to an increase of the exocytotic fusion probability. These results indicate that NE binds to a novel adrenergic receptor that activates guanylyl cyclase and that accumulation of cGMP activates PKG, which may phosphorylate a target protein involved in the exocytosis of synaptic vesicles.
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Yawo H. Involvement of cGMP-dependent protein kinase in adrenergic potentiation of transmitter release from the calyx-type presynaptic terminal. J Neurosci 1999; 19:5293-300. [PMID: 10377340 PMCID: PMC6782301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023] Open
Abstract
I have previously reported that norepinephrine (NE) induces a sustained potentiation of transmitter release in the chick ciliary ganglion through a mechanism pharmacologically distinct from any known adrenergic receptors. Here I report that the adrenergic potentiation of transmitter release was enhanced by a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) and by zaprinast, an inhibitor of cGMP-selective phosphodiesterase. Exogenous application of the membrane-permeable cGMP, 8-bromo-cGMP (8Br-cGMP), potentiated the quantal transmitter release, and after potentiation, the addition of NE was no longer effective. On the other hand, 8Br-cAMP neither potentiated the transmitter release nor occluded the NE-induced potentiation. The NE-induced potentiation was blocked by neither nitric oxide (NO) synthase inhibitor nor NO scavenger. The quantal transmitter release was not potentiated by NO donors, e.g., sodium nitroprusside. The NE-induced potentiation and its enhancement by IBMX was antagonized by two inhibitors of protein kinase G (PKG), Rp isomer of 8-(4-chlorophenylthio) guanosine-3', 5'-cyclic monophosphorothioate and KT5823. As with NE-induced potentiation, the effects of 8Br-cGMP on both the resting intraterminal [Ca2+] ([Ca2+]i) and the action potential-dependent increment of [Ca2+]i (DeltaCa) in the presynaptic terminal were negligible. The reduction of the paired pulse ratio of EPSC is consistent with the notion that the NE- and cGMP-dependent potentiation of transmitter release was attributable mainly to an increase of the exocytotic fusion probability. These results indicate that NE binds to a novel adrenergic receptor that activates guanylyl cyclase and that accumulation of cGMP activates PKG, which may phosphorylate a target protein involved in the exocytosis of synaptic vesicles.
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Affiliation(s)
- H Yawo
- Department of Neurophysiology, Tohoku University School of Medicine, Sendai 980-8575, Japan
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Lengyel I, Olesen LE, Nichol KA, Brain KL, Wang X, Robinson PJ, Bennett MR, Rostas JA. Phosphorylation of proteins in chick ciliary ganglion under conditions that induce long-lasting changes in synaptic transmission: phosphoprotein targets for nitric oxide action. Neuroscience 1999; 90:607-19. [PMID: 10215163 DOI: 10.1016/s0306-4522(98)00452-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Production of nitric oxide and the activation of protein kinases are required for long-term potentiation of synaptic transmission at the giant synapses in chicken ciliary ganglion. In the present study, we investigated the ability of nitric oxide to regulate the phosphorylation of endogenous proteins under conditions that induced long-term potentiation in intact ciliary ganglion and the protein kinases responsible for the phosphorylation of these proteins in lysed ciliary ganglion. Using Calcium Green-1 we showed that the nitric oxide donor sodium nitroprusside did not change the intraterminal Ca2+ dynamics in ciliary ganglion. Two dimensional phosphopeptide analysis of 32Pi-labelled intact ciliary ganglion showed that the sodium nitroprusside (300 microM) increased the phosphorylation of several phosphopeptides (P50a, P50b and P41) derived from proteins at 50,000 and 41,000 mol. wts which we have called nitric oxide-responsive phosphoproteins. A similar stimulation of phosphorylation was achieved by 8-bromo-cyclic AMP (100 microM), which also induced long-term potentiation, but not by phorbol dibutyrate (2 microM) that does not induce long-term potentiation in ciliary ganglion. When subcellular fractions from lysed ciliary ganglion were labelled in vitro by [gamma-32P]ATP in the presence of purified cGMP-dependent, cAMP-dependent or Ca2+-phospholipid-dependent protein kinases, we identified cyclic GMP-dependent protein kinase substrates that gave rise to phosphopeptides co-migrating with P50a, P50b and P41 from 32Pi-labelled intact ciliary ganglion. P50a and P41 were derived from soluble proteins while P50b was derived from a membrane-associated protein. The proteins giving rise to P50a, P50b and P41 were also substrates for cyclic AMP-dependent protein kinase, but not for calcium and phospholipid-dependent protein kinase in vitro, suggesting that nitric oxide-responsive phosphoproteins are convergence points in information processing in vivo and their phosphorylation might represent an important mechanism in nitric oxide-mediated synaptic plasticity in ciliary ganglion.
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Affiliation(s)
- I Lengyel
- The Neuroscience Group, Faculty of Medicine and Health Sciences, University of Newcastle, Callaghan, NSW, Australia
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Lengyel I, Nichol KA, Bennett MR, Heath JW, Little GJ, Rostas JA. Alpha and beta subunits of CaM-kinase II are localized in different neurons in chick ciliary ganglion. Neuroreport 1998; 9:2753-5. [PMID: 9760115 DOI: 10.1097/00001756-199808240-00013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The ciliary ganglion of the chicken contains only two types of neurons. Using monoclonal antibodies against the alpha and the beta subunits of Ca2+/calmodulin-stimulated protein kinase II (CaMPK-II) we found that the alpha-subunit was localized to the choroid neurons while beta subunit was associated with the ciliary neurons. As both neurons receive their inputs from the oculomotor nerve, while their postganglionic axons leave via different nerves, the ciliary ganglion of the chicken is a neuronal system in which the functional differences between alpha and beta CaMPK-II homopolymers in the regulation of synaptic transmission can be investigated.
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Affiliation(s)
- I Lengyel
- The Neuroscience Group, Faculty of Medicine and Health Sciences, University of Newcastle, NSW, Australia
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18
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Schmid HA, Riedel W, Simon E. Role of nitric oxide in temperature regulation. PROGRESS IN BRAIN RESEARCH 1998; 115:87-110. [PMID: 9632931 DOI: 10.1016/s0079-6123(08)62031-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- H A Schmid
- Max-Planck-Institute for Physiological and Clinical Research, William G. Kerckhoff-Institute, Bad Nauheim, Germany.
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19
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Abstract
Nitric oxide (NO) is an unconventional neurotransmitter and neuromodulator molecule that is increasingly found to have important signaling functions in animals from nematodes to mammals. NO signaling mechanisms in the past were identified largely through experiments on mammals, after the discovery of NO's vasodilatory functions. The use of gene knock out mice has been particularly important in revealing the functions of the several isoforms of nitric oxide synthase (NOS), the enzyme that produces NO. Recent studies have revealed rich diversity in NO signaling. In addition to the well-established pathway in which NO activates guanylyl cyclase and cGMP production, redox mechanisms involving protein nitrosylation are important contributors to modulation of neurotransmitter release and reception. NO signaling studies in invertebrates are now generating a wealth of comparative information. Invertebrate NOS isoforms have been identified in insects and molluscs, and the conserved and variable amino acid sequences evaluated. Calcium-calmodulin dependence and cofactor requirements are conserved. NADPH diaphorase studies show that NOS is found in echinoderms, coelenterates, nematodes, annelids, insects, crustaceans and molluscs. Accumulating evidence reveals that NO is used as an orthograde transmitter and cotransmitter, and as a modulator of conventional transmitter release. NO appears to be used in diverse animals for certain neuronal functions, such as chemosensory signaling, learning, and development, suggesting that these NO functions have been conserved during evolution. The discovery of NO's diverse and unconventional signaling functions has stimulated a plethora of enthusiastic investigations into its uses. We can anticipate the discovery of many more interesting and some surprising NO signaling functions.
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Affiliation(s)
- J W Jacklet
- Department of Biological Sciences, University at Albany, SUNY 12222, USA.
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20
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Abstract
The effects of nitric oxide-containing solution and different nitric oxide donors were investigated on spontaneously active neurons using extracellular recording technique in areas of rat spinal cord slices where high levels of nitric oxide synthase are present. In lamina X, 93% of all neurons investigated (n = 84) increased their firing rate and 2% decreased it by superfusion with the nitric oxide donor sodium nitroprusside. In contrast, 49% of all neurons in laminae I and II (n = 90) were inhibited and only 28% were activated. Both effects were due to the postsynaptic action of sodium nitroprusside, because they could still be observed in medium containing 0.3 mM Ca2+ and 9 mM Mg2+, known to block synaptic transmission. Application of 8-bromo-cyclic-GMP caused an excitation of every neuron which was excited by sodium nitroprusside and an inhibition of every cell which was inhibited by sodium nitroprusside (n = 25). This effect was different from the effect of 8-bromo-cyclic-AMP, which mimicked only the excitatory, but not the inhibitory response of sodium nitroprusside. These results provide evidence that nitric oxide in the spinal cord can directly cause an excitation or an inhibition of the electrical activity of spinal neurons. Another, more general conclusion from our results is that the nitric oxide-induced production of cyclic-GMP alone does not allow any prediction about an excitatory or inhibitory effect on the neuronal activity, which has to be determined separately.
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Affiliation(s)
- U Pehl
- Max-Planck-Institut für physiologische und klinische Forschung, W. G. Kerckhoff-Institut, Bad Nauheim, Germany
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21
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Southam E, Charles SL, Garthwaite J. The nitric oxide-cyclic GMP pathway and synaptic plasticity in the rat superior cervical ganglion. Br J Pharmacol 1996; 119:527-32. [PMID: 8894173 PMCID: PMC1915702 DOI: 10.1111/j.1476-5381.1996.tb15703.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. We have investigated the possibility that nitric oxide (NO) and soluble guanylyl cyclase, an enzyme that synthesizes guanosine 3':5'-cyclic monophosphate (cyclic GMP) in response to NO, contributes to plasticity of synaptic transmission in the rat isolated superior cervical ganglion (SCG). 2. Exposure of ganglia to the NO donor, nitroprusside, caused a concentration-dependent accumulation of cyclic GMP which was augmented in the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine. The compound, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylyl cyclase, completely blocked this cyclic GMP response. 3. As assessed by extracellular recording, nitroprusside (100 microM) and another NO donor, S-nitrosoglutathione (30 microM) increased the efficacy of ganglionic synaptic transmission in response to electrical stimulation of the preganglionic nerve, an effect that was reversible and which could be replicated by the cyclic GMP analogue, 8-bromo-cyclic GMP. Ganglionic depolarizations resulting from stimulation of nicotinic receptors with carbachol were not increased by nitroprusside. The potentiating actions of the NO donors on synaptic transmission, but not that of 8-bromo-cyclic GMP, were inhibited by ODQ. 4. Brief tetanic stimulation of the preganglionic nerve resulted in a long-term potentiation (LTP) of synaptic transmission that was unaffected by ODQ, either in the absence or presence of the NO synthase inhibitor, NG-nitro-L-arginine (L-NOARG, 100 microM). A lack of influence of L-NOARG was confirmed in intracellular recordings of LTP of the excitatory postsynaptic potential. Furthermore, under conditions where tetanically-induced LTP was saturated, nitroprusside was still able to potentiate synaptic transmission, as judged from extracellular recording. 5. We conclude that NO is capable of potentiating ganglionic neurotransmission and this effect is mediated through the stimulation of soluble guanylyl cyclase and the accumulation of cyclic GMP. However, this potentiation is distinct from LTP of nicotinic synaptic transmission, in which neither NO nor soluble guanylyl cyclase appear to participate.
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Affiliation(s)
- E Southam
- Neuroscience Research, Wellcome Research Laboratories, Beckenham, Kent
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22
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Mothet JP, Fossier P, Tauc L, Baux G. Opposite actions of nitric oxide on cholinergic synapses: which pathways? Proc Natl Acad Sci U S A 1996; 93:8721-6. [PMID: 8710938 PMCID: PMC38740 DOI: 10.1073/pnas.93.16.8721] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Nitric oxide (NO) produced opposite effects on acetylcholine (ACh) release in identified neuroneuronal Aplysia synapses depending on the excitatory or the inhibitory nature of the synapse. Extracellular application of the NO donor, SIN-1, depressed the inhibitory postsynaptic currents (IPSCs) and enhanced the excitatory postsynaptic currents (EPSCs) evoked by presynaptic action potentials (1/60 Hz). Application of a membrane-permeant cGMP analog mimicked the effect of SIN-1 suggesting the participation of guanylate cyclase in the NO pathway. The guanylate cyclase inhibitor, methylene blue, blocked the NO-induced enhancement of EPSCs but only reduced the inhibition of IPSCs indicating that an additional mechanism participates to the depression of synaptic transmission by NO. Using nicotinamide, an inhibitor of ADP-ribosylation, we found that the NO-induced depression of ACh release on the inhibitory synapse also involves ADP-ribosylation mechanism(s). Furthermore, application of SIN-1 paired with cGMP-dependent protein kinase (cGMP-PK) inhibitors showed that cGMP-PK could play a role in the potentiating but not in the depressing effect of NO on ACh release. Increasing the frequency of stimulation of the presynaptic neuron from 1/60 Hz to 0.25 or 1 Hz potentiated the EPSCs and reduced the IPSCs. In these conditions, the potentiating effect of NO on the excitatory synapse was reduced, whereas its depressing effect on the inhibitory synapse was unaffected. Moreover the frequency-dependent enhancement of ACh release in the excitatory synapse was greatly reduced by the inhibition of NO synthase. Our results indicate that NO may be involved in different ways of modulation of synaptic transmission depending on the type of the synapse including synaptic plasticity.
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Affiliation(s)
- J P Mothet
- Laboratoire de Neurobiologie Cellulaire et Moléculaire, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France
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23
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Mothet JP, Fossier P, Tauc L, Baux G. NO decreases evoked quantal ACh release at a synapse of Aplysia by a mechanism independent of Ca2+ influx and protein kinase G. J Physiol 1996; 493 ( Pt 3):769-84. [PMID: 8799898 PMCID: PMC1159024 DOI: 10.1113/jphysiol.1996.sp021421] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. The exogenous nitric oxide (NO) donor, SIN-1, decreased the postsynaptic response evoked by a presynaptic spike at an identified cholinergic neuro-neuronal synapse in the buccal ganglion of Aplysia californica. 2. The statistical analysis of long duration postsynaptic responses evoked by square depolarizations of the voltage-clamped presynaptic neurone showed that the number of evoked acetylcholine (ACh) quanta released was decreased by SIN-1, pointing to a presynaptic action of the drug. 3. Vitamin E, a scavenger of free radicals, prevented the effects of SIN-1 on ACh release. SIN-1 still decreased ACh release in the presence of superoxide dismutase, whereas haemoglobin suppressed the effects of SIN-1. These results showed that NO is the active compound. 4. 8-Bromoguanosine 3', 5' cyclic monophosphate (8-Br-cGMP) mimicked the inhibitory effect of NO on ACh release suggesting the involvement of a NO-sensitive guanylate cyclase. This was reinforced by the reversibility of the effects of SIN-1 by inhibitors of guanylate cyclase, Methylene Blue, cystamine or LY83583. Methylene Blue partially reduced the inhibitory effect of NO. In addition, in the presence of superoxide dismutase, Methylene Blue blocked and cystamine significantly reduced the NO-induced inhibition of ACh release. 5. In the presence of KT5823 or R-p-8-pCPT-cGMPS, two inhibitors of protein kinase G, the reduction of ACh release by SIN-1 still took place indicating that the effects of NO most probably did not involve protein kinase G-dependent phosphorylation. 6. Presynaptic voltage-dependent Ca2+ (L-, N- and P-types) and K+ (IA and late outward rectifier) currents were unmodified by SIN-1. 7. The modulation of ACh release in opposite ways by L-arginine and N omega-nitro-L-arginine points to the involvement of an endogenous NO synthase-dependent regulation of transmitter release.
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Affiliation(s)
- J P Mothet
- Laboratoire de Neurobiologie Cellulaire et Moléculaire, CNRS, Gif sur Yvette, France
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24
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Rentería RC, Constantine-Paton M. Exogenous nitric oxide causes collapse of retinal ganglion cell axonal growth cones in vitro. JOURNAL OF NEUROBIOLOGY 1996; 29:415-28. [PMID: 8656208 DOI: 10.1002/(sici)1097-4695(199604)29:4<415::aid-neu1>3.0.co;2-b] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
We show that nitric oxide (NO) from applied NO-donating chemicals induces collapse of ganglion cell axonal growth cones extending from explants of tadpole retina in culture. Peroxynitrite, a neurotoxic product of NO and superoxide reaction, did not induce collapse, and oxyhemoglobin, which binds NO, blocked the highly effective collapsing activity of the NO donor S-nitrosocysteine. Membrane-permeable analogs of cyclic guanosine monophosphate had no collapsing activity. Inhibitors of NO synthase did not induce collapse. NO is a potential retrograde messenger through which postsynaptic neurons signal to their inputs to modify synaptic efficacy following NMDA receptor activation. Our results suggest a role for NO as such a messenger during development of the retinotectal projection.
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Affiliation(s)
- R C Rentería
- Interdepartmental Neuroscience Program, Yale University, New Haven, Connecticut 06520-8103, USA
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25
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Brain KL, Bennett MR. Calcium in the nerve terminals of chick ciliary ganglia during facilitation, augmentation and potentiation. J Physiol 1995; 489 ( Pt 3):637-48. [PMID: 8788930 PMCID: PMC1156835 DOI: 10.1113/jphysiol.1995.sp021079] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. The calyciform nerve terminals of chick ciliary ganglia were loaded with the calcium indicators calcium green 1 or fura-2. These were used to determine the change in calcium concentration in the terminal, [Ca2+]t, following short (10 impulses) and long (600 impulses) trains of high-frequency (30 Hz) stimulation. 2. Following a single impulse or a short train, the elevated [Ca2+]t declined along two exponentials with time constants similar to slow (F2) facilitation (0.52 s) and augmentation (4.0 s). After a long train elevated [Ca2+]t declined eventually along a single exponential with the time constant of post-tetanic potentiation (162 s). [Ca2+]t was not elevated through long-term potentiation. 3. Addition of Ba2+ (0.75 mM) to the extracellular solution slowed only the decline of [Ca2+]t associated with augmentation. The addition of the nitric oxide donor sodium nitroprusside did not affect [Ca2+]t following short or long trains. 4. Removal of extracellular calcium (buffered with EGTA) and the blockade of calcium channels with Cd2+ completely prevented the changes in [Ca2+]t. 5. The soma of ciliary ganglion cells were loaded with calcium green and the postganglionic nerves stimulated with a single impulse or a short train of impulses. Following stimuli, the elevated [Ca2+]t declined along a single exponential with a time constant similar to F2 facilitation with no augmentation component evident. 6. The results are discussed in terms of the hypothesis that each impulse in a train gives an equal increment of residual Ca2+ to a compartment for secretion and that Ca2+ is removed from the compartment by three first-order kinetics processes associated with F2 facilitation, augmentation and post-tetanic potentiation.
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Affiliation(s)
- K L Brain
- Department of Physiology F13, University of Sydney, NSW, Australia
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26
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Hakim MA, Hirooka Y, Coleman MJ, Bennett MR, Dampney RA. Evidence for a critical role of nitric oxide in the tonic excitation of rabbit renal sympathetic preganglionic neurones. J Physiol 1995; 482 ( Pt 2):401-7. [PMID: 7714831 PMCID: PMC1157738 DOI: 10.1113/jphysiol.1995.sp020527] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
1. A large proportion of sympathetic preganglionic neurones contain nitric oxide synthase. The purpose of this study was to determine the effects of facilitation and inhibition of nitric oxide synthesis within the lower thoracic spinal cord (which contains the majority of renal preganglionic neurones) on renal sympathetic nerve activity (rSNA). 2. In anaesthetized rabbits, rSNA was recorded before and after intrathecal injection (50 microliters of 0.5 M solution) of either L-arginine, a precursor of nitric oxide, or N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, into the lower thoracic spinal cord. Spinal cord sections were also stained for the presence of NADPH diaphorase, a marker of nitric oxide synthesizing neurones. 3. A high density of NADPH diaphorase-containing neurones was found within the intermediolateral cell column of the lower thoracic spinal cord. 4. Intrathecal injection of L-arginine and L-NAME resulted in a large increase (113 +/- 25%) and decrease (43 +/- 8%), respectively, in rSNA. In contrast, injection of the inactive isomers D-arginine and D-NAME had no significant effect on rSNA. 5. The results indicate that endogenous nitric oxide in the lower thoracic spinal cord (1) has a potent excitatory action on renal sympathetic preganglionic neurones, and (2) helps to maintain the tonic activity of renal sympathetic nerves under resting conditions.
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Affiliation(s)
- M A Hakim
- Department of Physiology, University of Sydney, NSW, Australia
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27
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Bennett MR. Nitric oxide release and long term potentiation at synapses in autonomic ganglia. GENERAL PHARMACOLOGY 1994; 25:1541-51. [PMID: 7721027 DOI: 10.1016/0306-3623(94)90353-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
1. Long-term potentiation (LTP) of synaptic transmission in autonomic ganglia is reviewed, together with the possible role of nitric oxide (NO) in this process. 2. Calcium levels in preganglionic nerve terminals are elevated during at least the induction phase of LTP following a tetanus as well as during LTP induced by transmitter substances acting on the nerve terminals. Of the large number of calcium-dependent processes in the nerve terminal that might affect transmitter release, only calcium-calmodulin has been shown to be important in both the induction and maintenance of LTP. 3. The possibility that there is a decrease in the open time of nerve-terminal potassium channels following a tetanus, leading to an increase in duration of the terminal action potential and hence an increase in calcium influx and transmitter release is considered. There is little evidence for such an effect as yet for preganglionic nerve terminals. 4. Phosphorylation of potassium channels by cAMP-dependent protein kinase can lead to their inactivation with consequent action potential broadening in some systems. Exogenous cAMP enhances synaptic efficacy at preganglionic nerve terminals. Whether this occurs through an inactivation of potassium channels is not known. 5. Nitric oxide (NO) synthase is present in both sympathetic ganglia and the ciliary ganglia. NO increases synaptic efficacy in both ganglia. In at least the case of ciliary ganglion this is due to elevation of quantal secretion. 6. NO can in some conditions increase the terminal action potential duration in ciliary ganglia, probably through decrease in the Ic potassium current. There is evidence that this happens through cGMP modulating cAMP phosphodiesterases, thereby affecting cAMP phosphorylation of the Ic channel. 7. Blocking NO synthase markedly decreases LTP following a tetanus in the ciliary ganglion. The possibility is considered that NO is released from the terminal during a tetanus and through altering cAMP phosphorylation of Ic enhances transmitter release.
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Affiliation(s)
- M R Bennett
- Department of Physiology, University of Sydney, NSW, Australia
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