NO decreases evoked quantal ACh release at a synapse of Aplysia by a mechanism independent of Ca2+ influx and protein kinase G.

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-I 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 Ca2P (L-, N-and P-types) and K+ (IA and late outward rectifier) currents were unmodified by SIN-1i.7. The modulation of ACh release in opposite ways by L-arginine and N-nitro-L-arginine points to the involvement of an endogenous NO synthase-dependent regulation of transmitter release.

Opposite actions of nitric oxide on cholinergic synapses: which pathways?

“…This observation agrees with data showing that ADPribosyltransferase is a potential target for NO action in hippocampal long-term potentiation (58). Nevertheless, this ADP-ribosylation cannot affect the N-and P-type Ca2+ channels that are involved in ACh release at this synapse (12) because the presynaptic Ca2+ current remains unchanged by NO as we reported elsewhere (32).…”

Ryanodine-, IP3- and NAADP-dependent calcium stores control acetylcholine release

“…The good voltage control of the terminal was also ascertained by experiments in which the blockade of K + channels did not affect the amplitude of the LDIPSCs [39].…”

“…The postsynaptic response induced this way, referred to as the long-duration-induced postsynaptic current (LDIPSC), was used to calculate the mean amplitude and the mean decay time of the evoked miniature postsynaptic currents (MPSCs), which sum to build up the LDIPSC (for a detailed description of the method see [5,39]). The number of MPSCs evoked by a presynaptic depolarization (which corresponds exactly to the number of released ACh quanta) was then calculated using the equation: number of quanta = (mean amplitude of the LDIPSC × duration of the LDIPSC)/(calculated mean amplitude of the MPSC × mean decay time of the MPSC).…”

Distribution of NO-Induced cGMP-Like Immunoreactive Neurones in the Abdominal Nervous System of the Crayfish, Procambarus clarkii

“…Sensory neurones innervating the hind gut in the terminal abdominal ganglion were strongly stained by anti-cGMP immunohistochemistry, suggesting that NO-cGMP signalling regulates hind gut systems, while no mechanosensory afferents that innervate mechanoreceptors on the tailfan or chordotonal organ showed detectable immunoreactivity. NO has been known to mediate procerebral oscillations by modifying patterns of neuronal activity through cholinergic neuro-neuronal synapses in molluscs, (Gelperin, 1994, Mothet et al, 1996. NO-induced cGMP immunoreactive sensory neurones that innervate hind gut would possibly regulate hind gut muscle or anus movements (Muramoto, 1985) by changing efficacy of transmitter release onto hind gut system.…”

“…NO is also thought to act as a neuromodulator in several species of invertebrate animals (Elphick et al ., 1993). In molluscs, NO mediates procerebral oscillations by modifying patterns of neuronal activity (Gelperin, 1994), while it modulates the synaptic efficacy of cholinergic neuro-neuronal synapses (Mothet et al ., 1996). This NO-cGMP signalling is involved in feeding behaviour (Sadamoto et al ., 1998;Kobayashi et al ., 2000a).…”