Nitric oxide signaling in ctenophores

Nitrate as Warden of Nitric Oxide Homeostasis in Mammals

Homeostasis is the self-regulating processes in cells and organisms designed to maintain stability of the internal environment while adjusting to external changes. To achieve this dynamic stability, internal conditions oscillate within tightly regulated physiological tolerance limits. In mammals, maintaining nitric oxide (NO) availability appears crucial to sustain relatively constant blood flow into all organs and tissues. We hypothesize that NO homeostasis is one of the most important vital processes for warm-blooded animals. It is impossible to conserve the stability of most other vital substances, such as O2, CO2, blood sugar, pH, and temperature, to name just few, without well-functioning tissue perfusion. NO in mammals is generated either from L-arginine by nitric oxide synthases (NOSs) or by the reduction of nitrate (NO3-) to nitrite (NO2-) and NO by several proteins. Here we first discuss the organization of these two NO metabolic pathways, emphasizing that both pathways "cross" and "funnel" unused NO into the overall nitrate-nitrite-NO pathway. This pathway is cyclic, which gives nitrate a unique place in metabolism and predisposes it as a reservoir for NO. Then, we discuss the role of NO homeostasis that, by maintaining organ and tissue perfusion, supports and preserves constancy of other blood-delivered substances. This "governing" role of NO makes even clearer that the existence of NO storage and precursor molecules is necessary, to avoid NO shortages in cases of the precursor's or storage molecule's temporary unavailability, to ensure uninterrupted tissue access to NO. We propose that the skeletomuscular system and skin act as nitrate reservoirs assuring NO bioavailability at various external and internal conditions.

Centella asiatica improves sleep quality and quantity in aged mice

Age-related sleep disruption is common in older adults. Not only does the total amount of time spent in sleep decline, but the number of arousals during sleep increases with age. As sleep is important for both memory consolidation and to prevent neurodegenerative pathology, this decline in sleep and/or sleep consolidation may underlie age-related cognitive decline and dementias. Furthermore, treatment of sleep disruption can improve quality of life. However, few interventions have successfully reversed age-related sleep decline. Extracts from the plant Centella asiatica have demonstrated neuroprotective effects in human, rodent, and fly models of aging and neurodegenerative diseases, and is a promising intervention for dementias, yet little is known about how these extracts affect sleep patterns. Here, we administered Centella asiatica water extract ( CAW) dosed or control chow to male and female C57BL6/J mice aged 18 months. Effects on sleep composition were determined using electrodes that recorded EEG and EMG signals. We found that CAW dosed chow (1000 mg/kg/day) increased REM sleep time in aged male mice and decreased the number of arousals during sleep observed in aged females, compared to age- and sex-matched controls. We conclude that CAW administered in food has a moderate, sex-dependent effect on sleep quantity and quality.

Statement of Significance

Sleep declines with age and may underline age-related cognitive changes. However, few interventions have successfully reversed age-related sleep and cognitive decline. This study found that botanical extract from the plant Centella asiatica increased total REM sleep time in aged male mice, and decreased sleep fragmentation in aged female mice, compared to age- and sex-matched controls. Whether these moderate, sex-dependent effect sizes on sleep in aged mice are impactful enough to affect cognition, quality of life, and/or neurodegenerative pathology could be explored in future studies.

Improving Tracking of Selective Attention in Hearing Aid Users: The Role of Noise Reduction and Nonlinearity Compensation

Hearing impairment (HI) disrupts social interaction by hindering the ability to follow conversations in noisy environments. While hearing aids (HAs) with noise reduction (NR) partially address this, the "cocktail-party problem" persists, where individuals struggle to attend to specific voices amidst background noise. This study investigated how NR and an advanced signal processing method for compensating for nonlinearities in Electroencephalography (EEG) signals can improve neural speech processing in HI listeners. Participants wore HAs with NR, either activated or deactivated, while focusing on target speech amidst competing masker speech and background noise. Analysis focused on temporal response functions to assess neural tracking of relevant target and masker speech. Results revealed enhanced neural responses (N1 and P2) to target speech, particularly in frontal and central scalp regions, when NR was activated. Additionally, a novel method compensated for nonlinearities in EEG data, leading to improved signal-to-noise ratio (SNR) and potentially revealing more precise neural tracking of relevant speech. This effect was most prominent in the left-frontal scalp region. Importantly, NR activation significantly improved the effectiveness of this method, leading to stronger responses and reduced variance in EEG data and potentially revealing more precise neural tracking of relevant speech. This study provides valuable insights into the neural mechanisms underlying NR benefits and introduces a promising EEG analysis approach sensitive to NR effects, paving the way for potential improvements in HAs.

Making Neurobots and Chimerical Ctenophores

Making living machines using biological materials (cells, tissues, and organs) is one of the challenges in developmental biology and modern biomedicine. Constraints in regeneration potential and immune self-defense mechanisms limit the progress in the field. Here, we present unanticipated features related to self-recognition and ancestral neuro-immune architectures of new emerging reference species - ctenophores or comb jellies. These are descendants of the earliest survival metazoan lineage with unique tissues, organs and independent origins of major animal traits such as neurons, muscles, mesoderm, and through-gut. Thus, ctenophores convergently evolved complex organization, compared to bilaterians. Nevertheless, their neural and immune systems are likely functionally coupled, enabling designs and experimental construction of hybrid neural systems and even entire animals. This report illustrates impressive opportunities to build both chimeric animals and neurobots using ctenophores as models for bioengineering. The obtained neurobots and chimeric animals from three ctenophore species (Bolinopsis, Mnemiopsis, and Pleurobrachia) were able to be autonomous and survive for days. In sum, the unification of biodiversity, cell biology, and neuroscience opens unprecedented opportunities for experimental synthetic biology.

No Evidence of Musical Training Influencing the Cortical Contribution to the Speech-Frequency-Following Response and Its Modulation through Selective Attention

Musicians can have better abilities to understand speech in adverse condition such as background noise than non-musicians. However, the neural mechanisms behind such enhanced behavioral performances remain largely unclear. Studies have found that the subcortical frequency-following response to the fundamental frequency of speech and its higher harmonics (speech-FFR) may be involved since it is larger in people with musical training than in those without. Recent research has shown that the speech-FFR consists of a cortical contribution in addition to the subcortical sources. Both the subcortical and the cortical contribution are modulated by selective attention to one of two competing speakers. However, it is unknown whether the strength of the cortical contribution to the speech-FFR, or its attention modulation, is influenced by musical training. Here we investigate these issues through magnetoencephalographic (MEG) recordings of 52 subjects (18 musicians, 25 non-musicians, and 9 neutral participants) listening to two competing male speakers while selectively attending one of them. The speech-in-noise comprehension abilities of the participants were not assessed. We find that musicians and non-musicians display comparable cortical speech-FFRs and additionally exhibit similar subject-to-subject variability in the response. Furthermore, we also do not observe a difference in the modulation of the neural response through selective attention between musicians and non-musicians. Moreover, when assessing whether the cortical speech-FFRs are influenced by particular aspects of musical training, no significant effects emerged. Taken together, we did not find any effect of musical training on the cortical speech-FFR.

Neuropeptide Modulation Enables Biphasic Internetwork Coordination via a Dual-Network Neuron

Linked rhythmic behaviors, such as respiration/locomotion or swallowing/chewing, often require coordination for proper function. Despite its prevalence, the cellular mechanisms controlling coordination of the underlying neural networks remain undetermined in most systems. We use the stomatogastric nervous system of the crab Cancer borealis to investigate mechanisms of internetwork coordination, due to its small, well-characterized feeding-related networks (gastric mill [chewing, ∼0.1 Hz]; pyloric [filtering food, ∼1 Hz]). Here, we investigate coordination between these networks during the Gly1-SIFamide neuropeptide modulatory state. Gly1-SIFamide activates a unique triphasic gastric mill rhythm in which the typically pyloric-only LPG neuron generates dual pyloric-plus gastric mill-timed oscillations. Additionally, the pyloric rhythm exhibits shorter cycles during gastric mill rhythm-timed LPG bursts, and longer cycles during IC, or IC plus LG gastric mill neuron bursts. Photoinactivation revealed that LPG is necessary to shorten pyloric cycle period, likely through its rectified electrical coupling to pyloric pacemaker neurons. Hyperpolarizing current injections demonstrated that although LG bursting enables IC bursts, only gastric mill rhythm bursts in IC are necessary to prolong the pyloric cycle period. Surprisingly, LPG photoinactivation also eliminated prolonged pyloric cycles, without changing IC firing frequency or gastric mill burst duration, suggesting that pyloric cycles are prolonged via IC synaptic inhibition of LPG, which indirectly slows the pyloric pacemakers via electrical coupling. Thus, the same dual-network neuron directly conveys excitation from its endogenous bursting and indirectly funnels synaptic inhibition to enable one network to alternately decrease and increase the cycle period of a related network.

Brief History of Placozoa

Placozoans are morphologically the simplest free-living animals. They represent a unique window of opportunities to understand both the origin of the animal organization and the rules of life for the system and synthetic biology of the future. However, despite more than 100 years of their investigations, we know little about their organization, natural habitats, and life strategies. Here, we introduce this unique animal phylum and highlight some directions vital to broadening the frontiers of the biomedical sciences. In particular, understanding the genomic bases of placozoan biodiversity, cell identity, connectivity, reproduction, and cellular bases of behavior are critical hot spots for future studies.

Brief History of Ctenophora

Ctenophores are the descendants of the earliest surviving lineage of ancestral metazoans, predating the branch leading to sponges (Ctenophore-first phylogeny). Emerging genomic, ultrastructural, cellular, and systemic data indicate that virtually every aspect of ctenophore biology as well as ctenophore development are remarkably different from what is described in representatives of other 32 animal phyla. The outcome of this reconstruction is that most system-level components associated with the ctenophore organization result from convergent evolution. In other words, the ctenophore lineage independently evolved as high animal complexities with the astonishing diversity of cell types and structures as bilaterians and cnidarians. Specifically, neurons, synapses, muscles, mesoderm, through gut, sensory, and integrative systems evolved independently in Ctenophora. Rapid parallel evolution of complex traits is associated with a broad spectrum of unique ctenophore-specific molecular innovations, including alternative toolkits for making an animal. However, the systematic studies of ctenophores are in their infancy, and deciphering their remarkable morphological and functional diversity is one of the hot topics in biological research, with many anticipated surprises.

Neuronal gene expression in two generations of the marine parasitic worm, Cryptocotyle lingua

Trematodes, or flukes, undergo intricate anatomical and behavioral transformations during their life cycle, yet the functional changes in their nervous system remain poorly understood. We investigated the molecular basis of nervous system function in Cryptocotyle lingua, a species of relevance for fisheries. Transcriptomic analysis revealed a streamlined molecular toolkit with the absence of key signaling pathways and ion channels. Notably, we observed the loss of nitric oxide synthase across the Platyhelminthes. Furthermore, we identified upregulated neuronal genes in dispersal larvae, including those involved in aminergic pathways, synaptic vesicle trafficking, TRPA channels, and surprisingly nitric oxide receptors. Using neuronal markers and in situ hybridization, we hypothesized their functional relevance to larval adaptations and host-finding strategies. Additionally, employing a behavior quantification toolkit, we assessed cercaria motility, facilitating further investigations into the behavior and physiology of parasitic flatworms. This study enhances our understanding of trematode neurobiology and provides insights for targeted antiparasitic strategies.

Chemical cognition: chemoconnectomics and convergent evolution of integrative systems in animals

Neurons underpin cognition in animals. However, the roots of animal cognition are elusive from both mechanistic and evolutionary standpoints. Two conceptual frameworks both highlight and promise to address these challenges. First, we discuss evidence that animal neural and other integrative systems evolved more than once (convergent evolution) within basal metazoan lineages, giving us unique experiments by Nature for future studies. The most remarkable examples are neural systems in ctenophores and neuroid-like systems in placozoans and sponges. Second, in addition to classical synaptic wiring, a chemical connectome mediated by hundreds of signal molecules operates in tandem with neurons and is the most information-rich source of emerging properties and adaptability. The major gap-dynamic, multifunctional chemical micro-environments in nervous systems-is not understood well. Thus, novel tools and information are needed to establish mechanistic links between orchestrated, yet cell-specific, volume transmission and behaviors. Uniting what we call chemoconnectomics and analyses of the cellular bases of behavior in basal metazoan lineages arguably would form the foundation for deciphering the origins and early evolution of elementary cognition and intelligence.

Ecological role of bioluminescence of Black sea ctenophores

Bioluminescence, which is a manifestation of the vital activity of an organism in the form of electromagnetic radiation in the visible area of the spectrum, is a highly important ecological and optical factor of the marine environment. Until recently, it was believed that microplankton - bacteria and dinoflagellates - exceptionally contribute to the formation of the bioluminescence field in the Black Sea, as well as in other regions of the World Ocean. However, the ctenophores Mnemiopsis leidyi A. Agassiz, 1865, and Beroe ovata Mayer, 1912, which invaded the Black Sea in the 1980s-1990s, are also luminous organisms whose bioluminescence intensity is millions of times greater than that of most microplankton representatives. It is known that the characteristics of bioluminescence can reveal the state of the organism and, consequently, the state of the environment. At present, there is a fairly large number of works devoted to the physiology and ecology of the Black Sea ctenophores. In recent studies, the variability of light emission parameters of ctenophores following their functional state was revealed. Intensity and duration of light emission as parameters of the ctenophore bioluminescent signal as well as the influence of various abiotic and anthropogenic environmental factors on the ctenophore luminescence have been studied. However, the significance of bioluminescence for the living activity of ctenophores remains unclear. In connection with the above, it is extremely important to assess the ecological role of the bioluminescence of the Black Sea ctenophores.

Recording cilia activity in ctenophores: effects of nitric oxide and low molecular weight transmitters

Cilia are the major effectors in Ctenophores, but very little is known about their transmitter control and integration. Here, we present a simple protocol to monitor and quantify cilia activity and provide evidence for polysynaptic control of cilia coordination in ctenophores. We also screened the effects of several classical bilaterian neurotransmitters (acetylcholine, dopamine, L-DOPA, serotonin, octopamine, histamine, gamma-aminobutyric acid (GABA), L-aspartate, L-glutamate, glycine), neuropeptide (FMRFamide), and nitric oxide (NO) on cilia beating in Pleurobrachia bachei and Bolinopsis infundibulum. NO and FMRFamide produced noticeable inhibitory effects on cilia activity, whereas other tested transmitters were ineffective. These findings further suggest that ctenophore-specific neuropeptides could be major candidates for signal molecules controlling cilia activity in representatives of this early-branching metazoan lineage.

Nitric oxide suppresses cilia activity in ctenophores

Cilia are the major effectors in Ctenophores, but very little is known about their transmitter control and integration. Here, we present a simple protocol to monitor and quantify cilia activity in semi-intact preparations and provide evidence for polysynaptic control of cilia coordination in ctenophores. Next, we screen the effects of several classical bilaterian neurotransmitters (acetylcholine, dopamine, L-DOPA, serotonin, octopamine, histamine, gamma-aminobutyric acid (GABA), L-aspartate, L-glutamate, glycine), neuropeptides (FMRFamide), and nitric oxide (NO) on cilia beating in Pleurobrachia bachei and Bolinopsis infundibulum . Only NO inhibited cilia beating, whereas other tested transmitters were ineffective. These findings further suggest that ctenophore-specific neuropeptides could be major candidate signaling molecules controlling cilia activity in representatives of this early-branching metazoan lineage.