The intercellular communication via nitric oxide and its regulation in coupling of cyclic GMP synthesis upon stimulation of muscarinic cholinergic receptors in rat superior cervical sympathetic ganglia

Hippocampal GABAergic synapses possess the molecular machinery for retrograde nitric oxide signaling

Nitric oxide (NO) plays an important role in synaptic plasticity as a retrograde messenger at glutamatergic synapses. Here we describe that, in hippocampal pyramidal cells, neuronal nitric oxide synthase (nNOS) is also associated with the postsynaptic active zones of GABAergic symmetrical synapses terminating on their somata, dendrites, and axon initial segments in both mice and rats. The NO receptor nitric oxide-sensitive guanylyl cyclase (NOsGC) is present in the brain in two functional subunit compositions: alpha1beta1 and alpha2beta1. The beta1 subunit is expressed in both pyramidal cells and interneurons in the hippocampus. Using immunohistochemistry and in situ hybridization methods, we describe that the alpha1 subunit is detectable only in interneurons, which are always positive for beta1 subunit as well; however, pyramidal cells are labeled only for beta1 and alpha2 subunits. With double-immunofluorescent staining, we also found that most cholecystokinin- and parvalbumin-positive and smaller proportion of the somatostatin- and nNOS-positive interneurons are alpha1 subunit positive. We also found that the alpha1 subunit is present in parvalbumin- and cholecystokinin-positive interneuron terminals that establish synapses on somata, dendrites, or axon initial segments. Our results demonstrate that NOsGC, composed of alpha1beta1 subunits, is selectively expressed in different types of interneurons and is present in their presynaptic GABAergic terminals, in which it may serve as a receptor for NO produced postsynaptically by nNOS in the very same synapse.

Intracellular cGMP may promote Ca2+-dependent and Ca2+-independent release of catecholamines from sympathetic nerve terminals

OBJECTIVE

This study examined the hypothesis that intracellular cGMP stimulates the release of catecholamines from sympathetic nerve terminals (SNTs) in conscious rats.

METHODS

Conscious rats were prepared to determine the effects of intravenously-administered agents on heart rate (HR) and mean arterial blood pressure (MAP).

RESULTS

Bolus intravenous injections of the membrane-permeable cGMP analogue, 8-(4-chlorophenylthio)-cGMP (8-CPT-cGMP), elicited immediate and pronounced increases in HR before any changes in MAP were observed. In contrast, injections of cGMP did not elicit changes in HR or MAP. The 8-CPT-cGMP-induced tachycardia was markedly diminished by (1) the beta(1,2)-adrenoceptor antagonist, propranolol, (2) the ganglion blocking agent, chlorisondamine, and (3) bretylium, which blocks Ca2+-dependent mobilization of vesicular stores of catecholamines from SNTs. 8-CPT-cGMP also elicited minor falls in MAP in propranolol-treated rats but elicited pronounced falls in MAP in rats treated with chlorisondamine, bretylium, or combined administration of bretylium and the muscarinic receptor antagonist, methyl-atropine.

CONCLUSIONS

These findings suggest that (1) intracellular cGMP elicits the release of Ca2+-sensitive and Ca2+-insensitive stores of catecholamines from SNTs in conscious rats, and (2) cGMP-mediated release of catecholamines from SNTs antagonizes cGMP-mediated relaxation of vascular smooth muscle in resistance arteries. Taken together, these findings support the concept that increases in intracellular cGMP levels by atrial natriuretic peptide and endothelium- and cardiac-derived nitric oxide regulate sympathetic control of the heart and the microvasculature of conscious rats via cGMP-dependent release of catecholamines.

Distribution of cGMP in guinea pig autonomic ganglia after stimulation with sodium nitroprusside

Nitric oxide (NO) is an intercellular messenger molecule in the nervous system and exerts its action in many regions by generating cyclic GMP (cGMP) via soluble guanylyl cyclase. In this study, on the male guinea pig, we have analyzed the localization of cGMP in some autonomic ganglia with immunohistochemistry after stimulation with sodium nitroprusside (SNP) as NO donor, and made correlations with the NO synthesizing enzyme NO synthase (NOS), tyrosine hydroxylase (TH) and some neuropeptides. The putative target neurons for NO were examined in the anterior pelvic ganglia (APGs), as well as some pre- and paravertebral sympathetic ganglia. The results show that cGMP-like immunoreactivity (LI) in the APG was in most cases observed in the TH-positive, NOS-negative neuron population after SNP stimulation, whereas the NOS-expressing cholinergic population mostly lacked detectable cGMP-LI. In the pre- and paravertebral ganglia, SNP stimulation increased cGMP levels to a much lesser extent than in the APGs. cGMP was also observed in blood vessels, in the ganglion capsule, and in some cases. possibly in satellite cells. We propose, as one alternative, that there is a functional, intraganglionic regulatory loop between the parasympathetic and sympathetic divisions of the APG, using the NO/cGMP pathway.

Muscarinic receptor activation is a prerequisite for the endogenous release of nitric oxide modulating nicotinic transmission within the coeliac ganglion in the rabbit

The aim of the present study was to investigate whether the activation of muscarinic receptors is a preliminary step to the endogenous release of nitric oxide modulating nicotinic transmission within the prevertebral ganglia. This work has been performed in vitro in isolated rabbit coeliac ganglion. The electrical activity of the ganglionic neurons was recorded using intracellular recording techniques. When a train of pulses of supramaximal intensity was applied to the splanchnic nerves, gradual depression of fast nicotinic transmission occurred: the pulses do not systematically elicit action potentials, but very often elicit excitatory postsynaptic potentials only. The use of pharmacological agents that interfere with the nitric oxide pathway such as L-arginine (precursor of nitric oxide) or 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (nitric oxide scavenger) demonstrated that nitric oxide modulates this depression phenomenon by facilitating or inhibiting the nicotinic transmission of the ganglionic neurons. A nitric oxide donor (diethylamine/nitric oxide complex) induced an inhibition of the nicotinic synaptic transmission. In the presence of the muscarinic receptors antagonist atropine, L-arginine and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide failed to modify the nicotinic transmission of the ganglionic neurons but diethylamine/nitric oxide complex was still able to inhibit it. These results demonstrate that in the coeliac ganglion, the activation of muscarinic cholinergic receptors is a prerequisite for the activation of neuronal nitric oxide synthase in preganglionic fibres. The nitric oxide released then exerts a facilitation or an inhibition of the nicotinic transmission of the ganglionic neurons. Atropine triggered a facilitation of the nicotinic transmission when superfused alone and an inhibition when superfused in the presence of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. These results confirm that muscarinic receptors activate the nitric oxide pathway modulating the nicotinic transmission of the prevertebral neurons. Our results also demonstrate that when the nitric oxide pathway is blocked, activation of muscarinic receptors leads to facilitation of the nicotinic transmission. Our study brings new insights concerning the modulation by nitric oxide and by muscarinic receptors of the synaptic transmission within the prevertebral ganglia.

Nocturnal increase in plasma cGMP levels in humans

The circadian dynamics of responses to cyclic guanosine 3',5'-monophosphate (cGMP) in in vitro experiments and the stimulating effects of the pineal hormone melatonin on cGMP levels both in vitro and in vivo provoked an investigation into the diurnal pattern of occurrence of this second messenger in human plasma and its correlation with plasma melatonin levels. Plasma cGMP levels were measured in 9 normal human subjects who were over 50 years of age. Samples were obtained hourly through a 20-h period (11 a.m. to 7 a.m.) that included the subjects' habitual hours of nocturnal sleep; physical activity was kept to a minimum during the daylight hours. The area under the time-plasma cGMP concentration curve showed a significant increase during the period of nocturnal sleep compared to that observed during the period of daytime wakefulness. The individual temporal pattern of the nocturnal rise in plasma cGMP differed among the subjects; however, the initial increase typically was observed soon after bedtime. No significant correlation was observed between individual nocturnal plasma melatonin levels and cGMP levels.

Real-time patch-cram detection of intracellular cGMP reveals long-term suppression of responses to NO and muscarinic agonists

Cyclic GMP (cGMP) is a crucial intracellular messenger in neuronal, muscle, and endocrine cells. The intracellular concentration of cGMP is regulated by various neurotransmitters, including acetylcholine (ACh) and nitric oxide (NO). While much is known about the biochemical steps leading to cGMP synthesis, little is known about cGMP kinetics in intact cells. Here, we use "patch-cramming," in which an excised, inside-out membrane patch containing cyclic nucleotide-gated ion channels is used as a biosensor, to obtain the first real-time measurements of cGMP in intact cells. Patch-cramming experiments on neuroblastoma cells show that both muscarinic agonists and NO rapidly elevate cGMP. NO elicits cGMP responses repeatedly without decrement, whereas responses to muscarinic agonists exhibit a profound and prolonged desensitization. Remarkably, muscarinic agonists also cause long-term (>30 min) suppression (LTS) of cGMP responses elicited by NO. Biochemical measurements reveal that rat sympathetic neurons also exhibit LTS of cGMP, suggesting that LTS is a widespread mechanism that may contribute to synaptic plasticity.

Coupling of muscarinic cholinergic receptors and cGMP in nocturnal regulation of the suprachiasmatic circadian clock

Acetylcholine has long been implicated in nocturnal phase adjustment of circadian rhythms, yet the subject remains controversial. Although the suprachiasmatic nucleus (SCN), site of the circadian clock, contains no intrinsic cholinergic somata, it receives choline acetyltransferase-immunopositive projections from basal forebrain and mesopontine tegmental nuclei that contribute to sleep and wakefulness. We have demonstrated that the SCN of inbred rats in a hypothalamic brain slice is sensitive to cholinergic phase adjustment via muscarinic receptors (mAChRs) only at night. We used this paradigm to probe the muscarinic signal transduction mechanism and the site(s) gating nocturnal responsiveness. The cholinergic agonist carbachol altered the circadian rhythm of SCN neuronal activity in a pattern closely resembling that for analogs of cGMP; nocturnal gating of clock sensitivity of each is preserved in vitro. Specific inhibitors of guanylyl cyclase (GC) and cGMP-dependent protein kinase (PKG), key elements in the cGMP signal transduction cascade, blocked phase shifts induced by carbachol. Further, carbachol administration to the SCN at night increased cGMP production and PKG activity. The carbachol-induced increase in cGMP was blocked both by atropine, an mAChR antagonist, and by LY83583, a GC inhibitor. We conclude that (1) mAChR regulation of the SCN is mediated via GC-->cGMP-->PKG, (2) nocturnal gating of this pathway is controlled by the circadian clock, and (3) a gating site is positioned downstream from cGMP. This study is among the first to identify a functional context for mAChR-cGMP coupling in the CNS.

Nitric oxide mediates long-term potentiation in rat superior cervical ganglion

Long-term potentiation (LTP) of the nicotinic pathway of the superior cervical ganglion (SCG) is remarkably similar to that of the hippocampus which has been shown to involve nitric oxide (NO). We investigated a similar possible involvement of NO in the LTP of the SCG of the rat. Treatment of ganglia with the NO-synthase inhibitor N(G)-nitro-L-arginine (L-NOARG, 10 microM) blocked LTP at the maintenance phase.

Possible involvement of nitric oxide in carbachol-induced activation of transglutaminase in rat superior cervical sympathetic ganglia

The addition of a muscarinic agonist, carbachol (Carb, 0.1 mM), to a physiological medium markedly increased Ca(2+)-dependent transglutaminase (TG) activity (approximately 10-fold) in isolated rat superior cervical sympathetic ganglia (SCG) following in vitro aerobic incubation for 30 min at 37 degrees C. The Carb-evoked stimulation of ganglionic TG activity was considerably reduced (-51%) in the presence of NG-monomethyl-L-arginine (L-NMMA, 50 microM), a selective inhibitor of nitric oxide (NO) synthase. While the suppressant effect of L-NMMA was completely eliminated by the addition of an excess concentration of L-arginine (0.5 mM), a precursor of NO. These observations imply that Carb-induced TG activation possibly involves NO mediation in SCG tissue. The Carb-induced elevation in ganglionic TG activity was markedly reduced (-84%) at as early as 15 min of incubation in the medium containing hemoglobin (Hb) (20 microM), an agent that scavenges only extracellular NO gas. Thus, it is evident that a large fraction of NO released from inside the neuronal cells to extracellular space could rapidly diffuse back into the same group of cells to induce activation of the tissue TG. Methylene blue (MB), an inhibitor of soluble guanylate cyclase (GC), at 0.5 mM, a concentration which is effective in almost abolishing the Carb-evoked synthesis of cyclic GMP (cGMP), had no effect on ganglionic TG activation induced by Carb. Therefore, an increase in cGMP synthesis mediated by NO might not participate in NO-dependent ganglionic TG activation following the stimulation with Carb.(ABSTRACT TRUNCATED AT 250 WORDS)