Nitric oxide as neurotransmitter and neuromodulator Under supervision of : Dr. Bothaina Fouad

By : Hala Aly Hafez

Course : 1701802

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Nitric oxide as neurotransmitter and neuromodulator

Abstract

Nitric oxide (NO), is a neurotransmitter and neuromodulator, was

discovered as an endothelium-derived relaxing factor more than two decades

ago. Since then, it has been shown to participate in many pathways. NO has

been described as a key mediator of different pathways in the central and

peripheral nervous system in both healthy and diseased processes.

Introduction

Nitric oxide (NO), a ubiquitous gaseous cellular messenger, plays

significant roles in a variety of neurobiological processes. Several functions of

this regulatory molecule have been identified in the nervous system, in the

process of endothelium-dependent vasodilatation, in neurotransmission, and in

host-defense mechanisms. The discovery that NO functions as a signalling

molecule in the nervous system had radically changed the concept of neural

communication. Indeed, the adoption of the term nitrergic for nerves whose

transmitter function depends on the release of NO or for transmission

mechanisms brought about by NO (Moncada et al., 1997) emphasizes the

specific characteristics of this mediator. The physical properties of NO prevent

its storage in lipid-lined vesicles and metabolism by hydrolytic degradatory

enzymes. Therefore, unlike established neurotransmitters, NO is synthesized on

demand and is neither stored in synaptic vesicles nor released by exocytosis, but

simply diffuses from nerve terminals. The distance of this NO diffusion (40 ±

300 mm in diameter) implies that structures in the vicinity of the producing cell,

both neuronal and non-neuronal, are influenced following its release. This

suggests that, as well as acting as a neurotransmitter, NO has a neuromodulatory

role (J Garthwaite et al., 1995). In addition, it diffuses into rather than binds

with protein receptors on adjacent cells, and most of its known actions are the

consequence of interplay with intracellular targets that would usually be

regarded as secondary messengers. The activity of conventional

neurotransmitters is terminated either by re-uptake mechanisms or enzymatic

degradation while inactivation of NO follows reaction with a substrate. There

are multiple points at which biological control can be exerted over the

production and activity of conventional neurotransmitters. However, control of

the synthesis of NO is the key to regulating its activity (Džoljić et al., 2015).

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Several studies have demonstrated that NO, a freely diffusible gaseous

compound, has an important role in a variety of neurobiological processes

(Džoljić et al., 2015). Numerous functions of this regulatory molecule have

been identified in the CNS, in the process of endothelium-dependent

vasodilatation, in neurotransmission, and in host-defense mechanisms. NO is

produced from the oxidation of the terminal guanidine nitrogen of the amino

acid arginine. This reaction is catalyzed by the NADPH-dependent enzyme,

nitric oxide synthase (NOS). After its formation, NO diffuses outside the cell.

NO derived from eNOS maintains the CNS microcirculation by inhibiting

platelet aggregation and leukocyte adhesion and migration. NO derived from

nNOS is an important neurotransmitter related to neuronal plasticity, memory

formation, regulation of CNS blood flow, and neurotransmitter release (Toda et

al., 2003).

Nitric oxide synthesis

Much is known about the mechanism of NO synthesis from biochemical

studies of the purified NO synthase (NOS) enzymes. They are complex proteins

found constitutively in two isoforms, neuronal (nNOS) and endothelial (eNOS).

The third, inducible, type (iNOS) is rarely present normally but can be

expressed in numerous cell types (prototypically in macrophages, mainly in

microglia in the CNS) when subjected to immunological challenge. All three

isoforms generate NO from L-arginine but have distinct functional and

structural features. iNOS is usually linked with pathological situations (Stuehr

et al., 2004).

The three isoforms of nitric oxide synthase differ in their activity patterns

and expression in different cells. Neuronal nitric oxide synthase (nNOS) is

localized in synaptic spines, astrocytes, and the loose connective tissue

surrounding blood vessels in the brain; eNOS is present in both cerebral

vascular endothelial cells and motor neurons; and iNOS is induced in astrocytes

and microglia under pathological conditions. During physiological processes,

NO produced by eNOS/nNOS, respectively, controls blood flow activation, and

act as a messenger during long-term potentiation (LTP). However, under

pathological conditions, eNOS appears to be impaired, leading to a reduction in

blood flow and, consequently, low oxygen/metabolites delivery, efflux of

toxicological agents from the brain tissue and disturbance in the blood brain

barrier (BBB). The NO produced by iNOS in glial cells and nNOS, which

triggers the NMDA- excitotoxic pathway, combines with superoxide anion and

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results in peroxynitrite synthesis, a potent free radical that contributes to tissue

damage in the brain. Because these enzymes may have different sites of

expression and activation, they have a pivotal role in the divergent functions of

NO (Reis et al., 2017). All NOS isoforms have phosphorylation sites for

different protein kinases, including protein kinase A, B, and C, and calcium-

calmodulin kinase. NOS enzymes are very important for the maintenance of

physiological mechanisms within an organism, and the genetic ablation of NOS

in mice has been informative for establishing the functional roles of NOS-

generated NO in different systems (Cossenza et al., 2014).

Neurotransmission by Nitric oxide

Depending on the circuit, NO may be produced pre- or postsynaptically.

In many brain areas, the prototypic coupling with postsynaptic NMDA

receptors appears to apply. In others, NO may derive from presynaptic axon

terminals, much as it does in peripheral nitrergic nerves. In these nerves, the

stimulus for NO synthesis is usually the action potential-dependent opening of

presynaptic N-type and ⁄ or other Ca2+ channels, with the resulting NO

affecting smooth muscle relaxation (Toda et al., 2005).

Nitric oxide inactivation

It is often stated that NO does not need a specialised inactivation

mechanism because it is disposed of by virtue of its natural reactivity. However,

at the low nanomolar concentrations and below that are likely to be

physiological, NO is remarkably unreactive. Reaction with O2, for example, is

obvious at micromolar NO concentrations but negligible at low nanomolar

concentrations. Reaction with superoxide ions, giving peroxynitrite, is

extremely rapid but, over the presumed physiological NO concentration range,

superoxide dismutase is greatly in excess of NO so that superoxide ions are

removed too quickly to allow reaction with NO. Low NO concentrations will,

however, react avidly with lipid peroxyl radicals in a beneficial process that

stops lipid peroxidation. In physiological conditions, one pathway for NO

degradation will be through reaction with haemoglobin in circulating

erythrocytes, forming nitrate and methaemoglobin (John Garthwaite, 2008).

The main roles of nitric oxide in the brain

Nitric oxide binds to guanylyl cyclase, the cyclic guanosine-

monophosphate (cGMP)-producing enzyme which is a soluble NO receptor, and

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through cGMP-mediated signaling cascades it expresses its modulating effects

either as a post- or a pre-synaptic retrograde messenger. As a retrograde

neurotransmitter, NO activates the cGMP-dependent protein kinase G (PKG)

pathway which phosphorylates synaptophysin, essential for fusion of glutamate

(Glu)-containing granules with the membrane of presynaptic nerve endings.

This potentiates and facilitates Glu-ergic neurotransmission, thus making NO

the neuromodulator of excitatory neurotransmission (Wang et al., 2005). NO

also acts on inhibitory gamma-aminobutyric acid (GABA)-ergic synaptic

transmission. Recent studies have demonstrated its actions, through cGMP-

dependent pathways, on ion channels and ion exchangers with directly

modulating effects on membrane excitability (Yamamoto et al., 2015).

Furthermore, other study had shown that NO signaling modulates synaptic

inhibition in the superior paraolivary nucleus via cGMP-dependent suppression

of a potassium/chloride co-transporter. Although, through this effect at post-

synaptic level, NO acts as a reducer of strength of inhibition, this in turn enables

fine tuning of information processing (Yassin et al., 2014).

Soon after its identification as an endothelium-derived relaxing factor and

neuromodulator, NO emerged as a possible mediator of neurovascular coupling.

Neurovascular coupling is an active mechanism through which vessel diameter

is enlarged in response to increasing metabolic demands imposed by neuronal

activity; it is of vital importance in preserving the structural and functional

integrity of the brain. NO, due to its peculiar properties – it is a potent

vasodilator, released during enhanced neuronal activity resulting from Glu-ergic

activation – is well suited to mediate the coupling between neuronal activity and

cerebral blood flow (Girouard et al., 2006).

Nitric oxide has been linked to the release of other neurotransmitters and

the effects which they produce, in particular acetylcholine, noradrenaline

dopamine, glutamate, g-aminobutyric acid (GABA), serotonin, adenosin

triphosphate (ATP), bombesin, carbon monoxide, opioids and endothelin. The

mechanisms responsible for these interactions are still not fully understood, but

direct S-nitrosylation of receptors, activation of cyclic GMP-dependent protein

phosphorylation cascades, regulation of neuronal energy dynamics and a

modulating effect on transporters are potentially involved. In addition, a

presynaptic modulation of NO release through the activation of a2-

adrenoceptors, nicotinic receptors, purinergic receptors etc. has also been

proposed. Finally, it has been suggested that NO modulates gene transcription

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and translation in neurones and glia (Peunova et al., 1995). However, these

effects would seem to be indirect since there is little evidence of the existence of

DNA elements within the promotor regions of eukaryotic cells that respond

directly to NO (Morris, 1995).

Effects of centrally released nitric oxide

Modulation of synaptic plasticity

Nitric oxide has been proposed as the retrograde messenger which co-

ordinates the enhancement of both pre- and post-synaptic mechanisms involved

in two forms of synaptic plasticity; namely long-term potentiation (LTP) and

long-term depression (LTD). LTP is a property of many central excitatory

synapses characterized by a prolonged enhancement of synaptic transmission, or

an activity-dependent increase in synaptic strength, lasting from hours to weeks

or even longer. The process by which LTP is induced is not completely clear,

but it involves glutamate acting on amino-3-hydroxy-5-methylisooxazole-4-

propionic acid (AMPA) or NMDA-receptors. This activates a series of events in

which Ca2+/calmodulin-dependent protein kinase II, NOS and protein tyrosine

kinases are implicated. LTP is thought to be a synaptic correlate of learning and

memory, and is most pronounced in higher brain centres involved in cognitive

functions, particularly in the cerebral cortex and hippocampus. Guanylate

cyclase seems to be the main effector of NO in the induction of LTP (Figure 1)

(Reis et al., 2017), however, ADP-ribosylation and activation of calmodulin-

dependent kinases have also been implicated. LTD is characterized by a long

lasting depression of parallel fibre synapses, which follows repeated excitation

of the climbing fibres of Purkinje cells. The reduction in synaptic strength

appears to result from a diminished sensitization of postsynaptic AMPA

receptors which is mediated by activation of protein kinases C and G and of the

NO-cyclic GMP signalling pathway. LTD can be observed in higher regions of

the brain, although it has been particularly well studied in the cerebellum where

it has been proposed as a model for the learning of motor movements (Hölscher,

1997).

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Figure 1. NO act as an unconventional neurotransmitter that is not stored in

synaptic vesicles and not released upon membrane depolarization; it

releases as soon it is synthesized and does not bind to any receptors, but

diffuses from one neuron to another. NO stimulate soluble guanylyl-

cyclase to form the second messenger molecule, cyclic guanosine

monophosphate (cGMP) either as a post or a presynaptic messenger.

PKG, protein kinase G; ERK, extracellular signal regulated kinases; LTP,

long-term potentiation (Reis et al., 2017).

Involvement in central and peripheral functions

Nitric oxide has complex influences on brain development, memory

formation and behaviour through regulation of synaptic plasticity. Inhibition of

NO synthesis produces amnesia, disrupts spatial learning and olfactory memory,

blunts behavioural performance during task acquisition and decreases locomotor

activity in habituation tasks. NO has also been implicated in neuronal targeting

and brain development, visual processing, discriminative learning, food and

drinking behaviour, thermoregulation, opiate tolerance and withdrawal,

circadian rhythm, sleep and respiratory pattern generation. Likewise,

behavioural responses mediated by oxytocinergic and ser- otoninergic pathways

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are thought to involve NO generation or stimulation of central nitrergic

neurones (Cossenza et al., 2014).

There is evidence implicating central NO in the regulation of blood

pressure, heart rate, stimulated renal sympathetic nerve activity, gastric acid

secretion and motility and motor disruption associated with alcohol abuse.

Likewise, NO in the CNS appears to be involved in reflexes leading to a

diminished sympathetic output to the periphery and the modulation of various

neuroendocrine responses, including the production of oxytocin, luteinizing

hormone-releasing hormone, osmoregulator peptide corticotropin-releasing

hormone and adrenocorticotrophic hormone (Cossenza et al., 2014).

Neuronal damage and protection

The neuronal damage that accompanies cerebral ischaemia involves an

excessive release of glutamate and a subsequent activation of NMDA receptors

that, if maintained for a sufficient period of time, induces a massive influx of

Ca2+ into the postsynaptic neurone which, in turn, triggers the activation of

nNOS and overproduction of NO. In contrast, NO produced by activation of

eNOS, and even NMDA receptors, plays a protective role in brain ischaemia by

maintaining regional cerebral blood flow. The first indications that NO could

mediate neurotoxic effects came with the discovery that inhibition of NOS

attenuates glutamate toxicity in primary neuronal cultures from the rat cerebral

cortex and induces neuroprotection in animal models of stroke (Nowicki et al.,

1991).

The interactions and signalling mechanisms involved in these NO-related

effects are complex. Vascular protection is linked to cyclic GMP-mediated

mechanisms. In addition, s-nitrosylation of glutathione by NO has been

implicated in the antioxidative neuronal defence system, while NO is thought to

scavenge reactive oxygen species and partially offset ischaemia induced

oxidative damage. Likewise NO could be directly neuroprotective by interacting

with a specific site of the NMDA-receptor channel, resulting in a decreased

binding of glutamate or a diminished flow of Ca2+ through the channel after

activation (Džoljić et al., 2015).

Generation of peroxynitrite seems to be the leading cytotoxic mediator in

glutamate-induced damage. Damage caused to DNA by NO and peroxynitrite

appears to be an important neurotoxic mechanism. This is due to the subsequent

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activation of the nuclear repair enzyme polyADP-ribose synthase which is

capable of triggering massive energy depletion resulting in cellular death if the

DNA damage is severe. In addition, inhibition of mitochondrial respiratory

chain enzymes exacerbates the depletion of neuronal energy stores. High local

concentrations of NO may also reduce cellular viability by nitrosylating several

enzymes, including phosphokinases C and glyceraldehyde-3-phosphate

dehydrogenase, or by interacting with the iron present in haem or non- haem

complexes associated with enzymes such as cytochrome P450 or aconitases

(Moncada et al., 2002).

Role in central disorders

Nitric oxide is also an important mediator under pathological conditions.

For instance, in brain ischemia-reperfusion injury, NO formation is initially

increased and has a protective function by inducing collateral perfusion as a

result of its powerful stimulatory effect on vasodilatation and angiogenesis. NO

donors induce neuroprotective effects. NO can exist in distinct

oxidation/reduction states and present dual biological actions as either a

neuroprotective or a neurotoxic molecule. Under physiological conditions,

nNOS produces hydrogen peroxide (H2O2) and superoxide (O2 •−) in addition

to NO (Costa et al., 2016).

There is growing evidence to support a role for NO in the aetiology of

neurologic conditions, including autoimmune and chronic neurodegenerative

diseases. Concentrations of NO present in inflamed tissue cause reversible

conduction block in normal, demyelinated and early remyelinated axons. Thus,

diseases such as multiple sclerosis and Guillain-Barre syndrome, characterized

by widespread loss of myelin, may see their neuronal symptoms exacerbated via

the release of NO that accompanies the severe inflammation in the central and

peripheral nervous system occurring in these conditions. NO may also be

important in secondary neuronal cell death following trauma. In the spinal cord,

nNOS expression precedes the death of motorneurones, which follows avulsion

of spinal nerve roots, and pre-treatment with nNOS inhibitors substantially

increases the number of surviving neurones. NOS neurones are resistant to

NMDA and NO neurotoxicity although the protective mechanism responsible is

still not fully known. Likewise, the excessive release of both glutamate and NO,

coupled with mitochondrial dysfunction and oxidative stress, has been

implicated in a number of neurodegenerative diseases. This highlights a

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potential therapeutic role for specific NOS inhibitors in their pharmacological

control (Hobbs et al., 1999).

The gaseous signaling molecule NO has a variety of cellular functions,

including neurotransmission, regulation of blood‐vessel tone, and immunity.

Under pathological conditions, free radicals may deplete NO produced by

eNOS through the formation of ONOO − , thus decreasing the vascular

bioavailability of NO, which results in BBB dysfunction. This ultimately results

in endothelial damage, edema development, and hypoxia. Furthermore, the NO

produced by iNOS in glial cells or by nNOS under excitotoxic process can form

with free radicals (particularly O2−) ONOO− and produce several deleterious

effects on tissue, such as through tyrosine nitration and cysteine oxidation in

various proteins. These free radicals can further decompose into highly toxic‐

free radicals, such as NO2 • and •OH (Figure 2) (Reis et al., 2017).

The influence of peripheral systemic inflammatory conditions on the

expression of central NOS isoforms is still controversial, however,

overproduction of NO by iNOS is known to play a pathological role in acute

inflammatory disorders of the CNS. There are increased levels of NO

production in viral and bacterial infections such as meningitis, and a role for NO

has been clearly indicated in the disruption of the blood-brain barrier during

inflammatory conditions (Esplugues, 2002).

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Figure 2. Different steps in the NO signaling cascade under

physiological/pathological conditions in the brain. During long‐ term

potentiation, NOS1 or neuronal NOS (nNOS) catalyze the NO synthesis

after the activation of the NMDA receptor by Ca2+. Under excitotoxic

conditions, excessive Ca2+ leads to nNOS hyperactivity, whereas

excessive NO production can combine with superoxide to form

peroxynitrite, which is responsible for tissue damage due to several

biological effects, including blockage of the eNOS pathway and BBB

impairment. NO is synthesized following the transcriptional expression of

a Ca2+‐independent NOS2 or iNOS isoform in glial cells (astrocytes

and microglia) after cytokine exposure, thereby contributing to

neuroinflammation and tissue damage in the brain. Intracellular Ca2+

activates NOS3 or eNOS to release NO from brain microvessels. This NO

binds to soluble guanylyl‐cyclase (sGC) receptors, which triggers a

cGMP‐dependent pathway and interacts with its downstream mediators

of the physiological regulation of vasodilation and vascular resistance,

platelet adhesion and aggregation, leukocyte‐ endothelial interaction,

and BBB integrity maintenance (Reis et al., 2017).

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Nitric oxide has been implicated as a potential mediator of microglia-

dependent primary demyelination, a hallmark of multiple sclerosis, and iNOS

induction has been noted in the brains of patients with this autoimmune disease.

NO may also be involved in the pathogenesis of sporadic amyotrophic lateral

sclerosis and that of AIDS dementia. In the latter condition, neurotoxicity

induced by certain HIV coat proteins is partially mediated by activation of

NOS, whereas HIV patients who develop severe dementia exhibit a substantial

increase in cortical iNOS (Esplugues, 2002).

Nitric oxide in the peripheral nervous system

It is now well established that NO has a leading role as an inhibitory

neurotransmitter of peripheral non-adrenergic, non-cholinergic (NANC) nerves.

Peripheral nitrergic nerves have a widespread distribution, and are particularly

important in that they produce relaxation of smooth muscle in the

gastrointestinal, respiratory, vascular and urogenital systems. It is generally

assumed that free NO is the transmitter substance released by nitrergic nerves.

However, several controversial experimental observations have pointed to the

possibility of obtaining a closely related redox product from NO, and also

suggest that the inhibitory nitrergic transmitter is a NO-releasing molecule

(Barbier et al., 1992; Lefebvre, 1995).

Effects of peripherally released nitric oxide

Gastrointestinal system

In the gastrointestinal tract the majority of NOS positive fibres are

intrinsic, with smooth muscle cells containing sCG next to axon varicosities

containing NOS. This neuronally produced NO is implicated in many

physiological and pathophysiological reflexes in which changes in

gastrointestinal muscle relaxation are noted. Dysfunction of the inhibitory

NANC nerves in the lower oesophageal sphincter results in the motility

disorder, achalasia, and is probably involved in oesophageal spasms and related

primary motor disorders in the oesophageal body (Barrachina et al., 2001;

Calatayud et al., 2001).

Pulmonary system

The density of extrinsic NOS-containing fibres increases progressively

from the top of the trachea to the primary bronchi, and then diminishes as the

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bronchial diameter decreases. Nitrergic nerves are believed to represent the

main nervous bronchodilator pathway in humans, and dysfunction of this

system may be implicated in the increased tone and hyper-responsiveness

observed in asthma. Furthermore, inhalation of NO has become an important

therapeutic tool in the treatment of diseases such as acute respiratory distress

syndrome, hypoxic respiratory failure, high pulmonary artery pressure, lung

transplantation, sickle cell disease and specifically paediatric conditions such as

neonatal pulmonary hypertension (Weinberger et al., 1999).

Vascular system

Neuronal NOS is found in the perivascular nerves of various blood

vessels and appears to constitute an alternative regional control mechanism for

blood flow, independent of eNOS. This neuronally produced NO seems to be

particularly relevant in the regulation of cerebral blood flow. High levels of

nNOS are present in vasodilator nerves in cerebral blood vessels, although, in

most cases, nNOS is co-localized with different vasoactive neurotransmitters. In

the brain, activity-dependent activation of nNOS is associated with a local

increase in blood blow, and this response is prevented by inhibitors of NOS

(Toda et al., 2003).

Urogenital system

Neuronal NOS is most prominent in the para-sympathetic postganglionic

innervation of the urethra. Like-wise, stimulation of bladder afferent nerves

leads to the release of NO and chronic irritation of the bladder augments nNOS

expression in dorsal root ganglion cells. Finally, bladder hyperactivity provoked

by intravesical irritants can be moderated by inhibition of NO synthesis, thus

suggesting a role for spinal cord NO in the micturition reflex pathway (Sciarra

et al., 2000).

Recent years have seen a major focus on the pharmacological modulation

of the NO released by the endothelium and nitrergic nerves and which is

involved in penile erection. nNOS neurones innervate the corpus cavernosum

and blood vessels of the penis and nerve stimulation leads to erection, which

involves sGC stimulation and is blocked by NOS inhibitors. Nitrergic neurones

are also implicated in the effects of sexual hormones. For instance, nNOS levels

in the penis decrease substantially after castration but return to normal levels

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following testosterone replacement. Levels of nNOS diminish with age, and this

decrease correlates with impaired erectile responses (Sciarra et al., 2000).

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REFERENCES

Barbier, A. J., & Lefebvre, R. A. (1992). Effect of LY 83583 on relaxation

induced by non-adrenergic non-cholinergic nerve stimulation and

exogenous nitric oxide in the rat gastric fundus. European journal of

pharmacology, 219(2), 331-334.

Barrachina, M., Panes, J., & Esplugues, J. (2001). Role of nitric oxide in

gastrointestinal inflammatory and ulcerative diseases: perspective for

drugs development. Current pharmaceutical design, 7(1), 31-48.

Calatayud, S., Barrachina, D., & Esplugues, J. V. (2001). Nitric oxide: relation

to integrity, injury, and healing of the gastric mucosa. Microscopy

research and technique, 53(5), 325-335.

Cossenza, M., Socodato, R., Portugal, C. C., Domith, I. C., Gladulich, L. F.,

Encarnação, T. G., . . . Paes-de-Carvalho, R. (2014). Nitric oxide in the

nervous system: biochemical, developmental, and neurobiological aspects

Vitamins & Hormones (Vol. 96, pp. 79-125): Elsevier.

Costa, E. D., Rezende, B. A., Cortes, S. F., & Lemos, V. S. (2016). Neuronal

nitric oxide synthase in vascular physiology and diseases. Frontiers in

physiology, 7, 206.

Džoljić, E., Grbatinić, I., & Kostić, V. (2015). Why is nitric oxide important for

our brain? Functional neurology, 30(3), 159-163.

doi:10.11138/fneur/2015.30.3.159

Esplugues, J. V. (2002). NO as a signalling molecule in the nervous system.

British journal of pharmacology, 135(5), 1079-1095.

Garthwaite, J. (2008). Concepts of neural nitric oxide‐mediated transmission.

European Journal of Neuroscience, 27(11), 2783-2802.

Garthwaite, J., & Boulton, C. (1995). Nitric oxide signaling in the central

nervous system. Annual review of physiology, 57(1), 683-706.

Girouard, H., & Iadecola, C. (2006). Neurovascular coupling in the normal

brain and in hypertension, stroke, and Alzheimer disease. Journal of

applied physiology, 100(1), 328-335.

Hobbs, A. J., Higgs, A., & Moncada, S. (1999). Inhibition of nitric oxide

synthase as a potential therapeutic target. Annual review of pharmacology

and toxicology, 39(1), 191-220.

06

Hölscher, C. (1997). Nitric oxide, the enigmatic neuronal messenger: its role in

synaptic plasticity. Trends in neurosciences, 20(7), 298-303.

Lefebvre, R. A. (1995). Nitric oxide in the peripheral nervous system. Annals of

medicine, 27(3), 379-388.

Moncada, S., & Erusalimsky, J. D. (2002). Does nitric oxide modulate

mitochondrial energy generation and apoptosis? Nature Reviews

Molecular Cell Biology, 3(3), 214-220.

Moncada, S., Higgs, A., & Furchgott, R. (1997). XIV. International union of

pharmacology nomenclature in nitric oxide research. Pharmacological

reviews, 49(2), 137-142.

Morris, B. J. (1995). Stimulation of immediate early gene expression in striatal

neurons by nitric oxide. Journal of Biological Chemistry, 270(42), 24740-

24744.

Nowicki, J., Duval, D., Poignet, H., & Scatton, B. (1991). Nitric oxide mediates

neuronal death after focal cerebral ischemia in the mouse. European

journal of pharmacology, 204(3), 339-340.

Peunova, N., & Enikolopov, G. (1995). Nitric oxide triggers a switch to growth

arrest during differentiation of neuronal cells. Nature, 375(6526), 68-73.

Reis, P. A., de Albuquerque, C. F. G., Gutierrez, T., Silva, A. R., & de Castro

Faria Neto, H. (2017). Role of nitric oxide synthase in the function of the

central nervous system under normal and infectious conditions. Nitric

Oxide Synthase–Simple Enzyme-Complex Roles. London: InTech, 55-70.

Sciarra, A., Voria, G., Gentile, V., Pastore, A., Di, C. C., Loreto, A., & Di, F. S.

(2000). Role of nitric oxide in the urogenital system: physiology and

pathology. Minerva urologica e nefrologica= The Italian journal of

urology and nephrology, 52(4), 201-206.

Stuehr, D. J., Santolini, J., Wang, Z.-Q., Wei, C.-C., & Adak, S. (2004). Update

on mechanism and catalytic regulation in the NO synthases. Journal of

Biological Chemistry, 279(35), 36167-36170.

Toda, N., & Herman, A. G. (2005). Gastrointestinal function regulation by

nitrergic efferent nerves. Pharmacological reviews, 57(3), 315-338.

Toda, N., & Okamura, T. (2003). The pharmacology of nitric oxide in the

peripheral nervous system of blood vessels. Pharmacological reviews,

55(2), 271-324.

07

Wang, H.-G., Lu, F.-M., Jin, I., Udo, H., Kandel, E. R., De Vente, J., . . .

Antonova, I. (2005). Presynaptic and postsynaptic roles of NO, cGK, and

RhoA in long-lasting potentiation and aggregation of synaptic proteins.

Neuron, 45(3), 389-403.

Weinberger, B., Heck, D. E., Laskin, D. L., & Laskin, J. D. (1999). Nitric oxide

in the lung: therapeutic and cellular mechanisms of action. Pharmacology

& therapeutics, 84(3), 401-411.

Yamamoto, K., Takei, H., Koyanagi, Y., Koshikawa, N., & Kobayashi, M.

(2015). Presynaptic cell type-dependent regulation of GABAergic

synaptic transmission by nitric oxide in rat insular cortex. Neuroscience,

284, 65-77.

Yassin, L., Radtke-Schuller, S., Asraf, H., Grothe, B., Hershfinkel, M.,

Forsythe, I. D., & Kopp-Scheinpflug, C. (2014). Nitric oxide signaling

modulates synaptic inhibition in the superior paraolivary nucleus (SPN)

via cGMP-dependent suppression of KCC2. Frontiers in neural circuits,

8, 65.