Nitric oxide as a multimodal brain transmitter

The Unexpected Role of the Endothelial Nitric Oxide Synthase at the Neurovascular Unit: Beyond the Regulation of Cerebral Blood Flow

Nitric oxide (NO) is a highly versatile gasotransmitter that has first been shown to regulate cardiovascular function and then to exert tight control over a much broader range of processes, including neurotransmitter release, neuronal excitability, and synaptic plasticity. Endothelial NO synthase (eNOS) is usually far from the mind of synaptic neurophysiologists, who have focused most of their attention on neuronal NO synthase (nNOS) as the primary source of NO at the neurovascular unit (NVU). Nevertheless, the available evidence suggests that eNOS could also contribute to generating the burst of NO that, serving as volume intercellular messenger, is produced in response to neuronal activity in the brain parenchyma. Herein, we review the role of eNOS in both the regulation of cerebral blood flow and of synaptic plasticity and discuss the mechanisms by which cerebrovascular endothelial cells may transduce synaptic inputs into a NO signal. We further suggest that eNOS could play a critical role in vascular-to-neuronal communication by integrating signals converging onto cerebrovascular endothelial cells from both the streaming blood and active neurons.

Synapse-specific structural plasticity that protects and refines local circuits during LTP and LTD

Synapses form trillions of connections in the brain. Long-term potentiation (LTP) and long-term depression (LTD) are cellular mechanisms vital for learning that modify the strength and structure of synapses. Three-dimensional reconstruction from serial section electron microscopy reveals three distinct pre- to post-synaptic arrangements: strong active zones (AZs) with tightly docked vesicles, weak AZs with loose or non-docked vesicles, and nascent zones (NZs) with a postsynaptic density but no presynaptic vesicles. Importantly, LTP can be temporarily saturated preventing further increases in synaptic strength. At the onset of LTP, vesicles are recruited to NZs, converting them to AZs. During recovery of LTP from saturation (1-4 h), new NZs form, especially on spines where AZs are most enlarged by LTP. Sentinel spines contain smooth endoplasmic reticulum (SER), have the largest synapses and form clusters with smaller spines lacking SER after LTP recovers. We propose a model whereby NZ plasticity provides synapse-specific AZ expansion during LTP and loss of weak AZs that drive synapse shrinkage during LTD. Spine clusters become functionally engaged during LTP or disassembled during LTD. Saturation of LTP or LTD probably acts to protect recently formed memories from ongoing plasticity and may account for the advantage of spaced over massed learning. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Hydrogen Sulfide (H2S)/Polysulfides (H2Sn) Signalling and TRPA1 Channels Modification on Sulfur Metabolism

Hydrogen sulfide (H2S) and polysulfides (H2Sn, n ≥ 2) produced by enzymes play a role as signalling molecules regulating neurotransmission, vascular tone, cytoprotection, inflammation, oxygen sensing, and energy formation. H2Sn, which have additional sulfur atoms to H2S, and other S-sulfurated molecules such as cysteine persulfide and S-sulfurated cysteine residues of proteins, are produced by enzymes including 3-mercaptopyruvate sulfurtransferase (3MST). H2Sn are also generated by the chemical interaction of H2S with NO, or to a lesser extent with H2O2. S-sulfuration (S-sulfhydration) has been proposed as a mode of action of H2S and H2Sn to regulate the activity of target molecules. Recently, we found that H2S/H2S2 regulate the release of neurotransmitters, such as GABA, glutamate, and D-serine, a co-agonist of N-methyl-D-aspartate (NMDA) receptors. H2S facilitates the induction of hippocampal long-term potentiation, a synaptic model of memory formation, by enhancing the activity of NMDA receptors, while H2S2 achieves this by activating transient receptor potential ankyrin 1 (TRPA1) channels in astrocytes, potentially leading to the activation of nearby neurons. The recent findings show the other aspects of TRPA1 channels-that is, the regulation of the levels of sulfur-containing molecules and their metabolizing enzymes. Disturbance of the signalling by H2S/H2Sn has been demonstrated to be involved in various diseases, including cognitive and psychiatric diseases. The physiological and pathophysiological roles of these molecules will be discussed.

Postnatal development of the enteric neurons expressing neuronal nitric oxide synthase

Neurons, expressing neuronal nitric oxide synthase (nNOS) in the enteric ganglia are inhibitory motor neurons or interneurons. The aim of the study was to identify the percentage, cross-sectional area of nNOS-immunoreactive (IR) neurons and their colocalization with choline acetyltransferase (ChAT), vasoactive intestinal polypeptide (VIP), and neuropeptide Y in the intramural ganglia of the myenteric (MP) and submucous plexus (SP) of the small intestine (SI) and large intestine (LI) of rats of different age groups using immunohistochemical methods. In the intramural ganglia of the MP, the largest percentage of nNOS-IR neurons was detected in newborn rats in the LI (81 ± 0.9%) and SI (48 ± 4.1%). Subsequently, it decreased in ontogenesis up to 60 days of life (26 ± 0.9% LI, 29 ± 3.2% SI), and did not change until senescence. In the SP, abundant nNOS-IR neurons were also detected in newborns (82 ± 7.0% SI, 85 ± 3.2% LI), while their percentage decreased significantly in the next 20 days. Furthermore, a very small number of nNOS-IR neurons was detected in 30-day- and 2-month-old animals, but they again appeared in large numbers in aged rats. In the MP, the highest percentage of nNOS+/ChAT+ neurons was in 1-day-old, 10-day-old, and 2-year-old rats. In the SP, the largest number of nNOS-IR neurons colocalized ChAT regardless of age. In the MP of all rats, many nNOS-IR neurons colocalized VIP, and the maximal percentage of nNOS+/VIP+ neurons was found in 2-year-old rats, minimal-in newborns. In conclusion, nNOS expression in neurons of the gut is decreased in early postnatal ontogenesis and subsequently increased in aged rats.

Enzyme-derived deer velvet extract activate the immune response in cyclophosphamide-induced immunosuppressive mice

Deer velvet (DV) is an oriental traditional medicine used to treat various diseases. The present study examined the effect of flavourzyme-derived DV extract (YC-1101) on macrophages and an immunosuppressed mouse model. YC-1101 induced activation of macrophages as measured by nitric oxide production, cell proliferation, and cytokine release via concentration-dependent phosphorylation of c-Jun N-terminal kinase, extracellular signal-regulated kinase, and AKT, and nuclear translocation of p65 in macrophages. In addition, oral YC-1101 administration significantly increased splenocyte proliferation and natural killer cell activity in the immunosuppressed mouse model. Moreover, the levels of immune-related cytokines such as tumor necrotic factor-α, interferon-γ, and interleukin-2 were significantly increased by YC-1101 treatment comparable to the control group. Thus, these results suggest that YC-1101 is an efficient natural ingredient that has an immune-enhancing effect, and it might be a potential functional food for improving immunity.

Contextual fear expression engages a complex set of interactions between ventromedial prefrontal cortex cholinergic, glutamatergic, nitrergic and cannabinergic signaling

Rats re-exposed to an environment previously associated with the onset of shocks evoke a set of conditioned defensive responses in preparation to an eventual flight or fight reaction. Ventromedial prefrontal cortex (vmPFC) is mutually important for controlling the behavioral/physiological consequences of stress exposure and the one's ability to satisfactorily undergo spatial navigation. While cholinergic, cannabinergic and glutamatergic/nitrergic neurotransmissions within the vmPFC are shown as important for modulating both behavioral and autonomic defensive responses, there is a gap on how these systems would interact to ultimately coordinate such conditioned reactions. Then, males Wistar rats had guide cannulas bilaterally implanted to allow drugs to be administered in vmPFC 10 min before their re-exposure to the conditioning chamber where three shocks were delivered at the intensity of 0.85 mA for 2 s two days ago. A femoral catheter was implanted for cardiovascular recordings the day before fear retrieval test. It was found that the increment of freezing behavior and autonomic responses induced by vmPFC infusion of neostigmine (acetylcholinesterase inhibitor) were prevented by prior infusion of a transient receptor potential vanilloid type 1 (TRPV1) antagonist, N-methyl-d-aspartate receptor antagonist, neuronal nitric oxide synthase inhibitor, nitric oxide scavenger and soluble guanylate cyclase inhibitor. A type 3 muscarinic receptor antagonist was unable to prevent the boosting in conditioned responses triggered by a TRPV1 agonist and a cannabinoid receptors type 1 antagonist. Altogether, our results suggest that expression of contextual conditioned responses involves a complex set of signaling steps comprising different but complementary neurotransmitter pathways.

The Chemical Biology of NO that Regulates Oncogenic Signaling and Metabolism: NOS2 and Its Role in Inflammatory Disease

Nitric oxide (NO) and the enzyme that synthesizes it, nitric oxide synthase 2 (NOS2), have emerged as key players in inflammation and cancer. Expression of NOS2 in tumors has been correlated both with positive outcomes and with poor prognoses. The chemistry of NO is the major determinate to the biological outcome and the concentration of NO, which can range over five orders of magnitude, is critical in determining which pathways are activated. It is the activation of specific oncogenic and immunological mechanisms that shape the outcome. The kinetics of specific reactions determine the mechanisms of action. In this review, the relevant reactions of NO and related species are discussed with respect to these oncogenic and immunological signals.

Carbon Monoxide and Nitric Oxide as Examples of the Youngest Class of Transmitters

The year 2021 is the 100th anniversary of the confirmation of the neurotransmission phenomenon by Otto Loewi. Over the course of the hundred years, about 100 neurotransmitters belonging to many chemical groups have been discovered. In order to celebrate the 100th anniversary of the confirmation of neurotransmitters, we present an overview of the first two endogenous gaseous transmitters i.e., nitric oxide, and carbon monoxide, which are often termed as gasotransmitters.

Nitric oxide and dopamine metabolism converge via mitochondrial dysfunction in the mechanisms of neurodegeneration in Parkinson's disease

The molecular mechanisms underlying the degeneration and neuronal death associated with Parkinson's disease (PD) are not clearly understood. Several pathways and models have been explored in an overwhelming number of studies. Overall, from these studies, mitochondrial dysfunction and nitroxidative stress have emerged as major contributors to degeneration of dopaminergic neurons in PD. In addition, an excessive or inappropriate production of nitric oxide (^•NO) and an abnormal metabolism of dopamine have been independently implicated in both processes. However, the participation of ^•NO in reactions with dopamine relevant to neurotoxicity strongly suggests that dopamine or its metabolites may be potential targets for ^•NO, affecting the physiological chemistry of both, ^•NO and dopamine. In this short review, we provide a critical and integrative appraisal of the nitric oxide-dopamine pathway we have previously suggested and that might be operative in PD. This pathway emphasizes a connection between abnormal dopamine and ^•NO metabolism, which may potentially converge in an integrated mechanism with toxic cellular outcomes. In particular, it encompasses the synergistic interaction of ^•NO with 3,4-dihydroxyphenylacetic acid (DOPAC), a major dopamine metabolite, leading to dopaminergic cell death via mechanisms that involve mitochondrial dysfunction, gluthathione depletion and nitroxidative stress.

The Function and Regulation of Zinc in the Brain

Nearly sixty years ago Fredrich Timm developed a histochemical technique that revealed a rich reserve of free zinc in distinct regions of the brain. Subsequent electron microscopy studies in Timm- stained brain tissue found that this "labile" pool of cellular zinc was highly concentrated at synaptic boutons, hinting a possible role for the metal in synaptic transmission. Although evidence for activity-dependent synaptic release of zinc would not be reported for another twenty years, these initial findings spurred decades of research into zinc's role in neuronal function and revealed a diverse array of signaling cascades triggered or regulated by the metal. Here, we delve into our current understanding of the many roles zinc plays in the brain, from influencing neurotransmission and sensory processing, to activating both pro-survival and pro-death neuronal signaling pathways. Moreover, we detail the many mechanisms that tightly regulate cellular zinc levels, including metal binding proteins and a large array of zinc transporters.