Zn-Templated synthesis of substituted (2,6-diimine)pyridine proligands and evaluation of their iron complexes as anolytes for flow battery applications.

Pseudo-octahedral iron complexes supported by tridentate N^N^N-binding, redox 'non-innocent' diiminepyridine (DIP) ligands exhibit multiple reversible ligand-based reductions that suggest the potential application of these complexes as anolytes in redox flow batteries (RFBs). When bearing aryl groups at the imine nitrogens, substitution at the 4-position can be used to tune these redox potentials and impact other properties relevant to RFB applications, such as solubility and stability over extended cycling. DIP ligands bearing electron-withdrawing groups (EWGs) in this position, however, can be challenging to isolate via typical condensation routes involving para-substituted anilines and 2,6-diacetylpyridine. In this work, we demonstrate a high-yielding Zn-templated synthesis of DIP ligands bearing strong EWGs. The synthesis and electrochemical characterization of iron(ii) complexes of these ligands is also described, along with properties relevant to their potential application as RFB anolytes.

Tris(1-methyl-imidazol-2-yl)phosphane Complexes of Pnictogen, Tetrel, and Triel Cations.

cations gallium indium nitrogen ligands pnictogens tetrelThe synthesis and characterization of salts with the generic formula [P(Im)3 M][OTf]x (Im=1-methyl-imidazol-2-yl; M=P, As or Sb and x=3; M=Ge or Sn and x=2) are reported. In all cases, the cations adopt a cage structure with two chemically and energetically distinct apical lone pairs. In contrast, complexes of gallium and indium engage two P(Im)3 ligands resulting in a distorted octahedral geometry for the triel center in compounds of the generic formula [{P(Im)3 }2 M][OTf]3 (M=Ga or In). An assessment of the acidity and basicity of the new compounds is presented.

A subset of ipRGCs regulates both maturation of the circadian clock and segregation of retinogeniculate projections in mice.

The visual system consists of two major subsystems, image-forming circuits that drive conscious vision and non-image-forming circuits for behaviors such as circadian photoentrainment. While historically considered non-overlapping, recent evidence has uncovered crosstalk between these subsystems. Here, we investigated shared developmental mechanisms. We revealed an unprecedented role for light in the maturation of the circadian clock and discovered that intrinsically photosensitive retinal ganglion cells (ipRGCs) are critical for this refinement process. In addition, ipRGCs regulate retinal waves independent of light, and developmental ablation of a subset of ipRGCs disrupts eye-specific segregation of retinogeniculate projections. Specifically, a subset of ipRGCs, comprising ~200 cells and which project intraretinally and to circadian centers in the brain, are sufficient to mediate both of these developmental processes. Thus, this subset of ipRGCs constitute a shared node in the neural networks that mediate light-dependent maturation of the circadian clock and light-independent refinement of retinogeniculate projections.

Cationic 2,2'-bipyridine complexes of germanium(ii) and tin(ii).

We present the first systematic study of 2,2'-bipyridine complexes of E(ii) cationic acceptors (E = Ge, Sn). The complexes were comprehensively characterized by spectroscopic and crystallographic methods to yield complexes of ECl1+ and E2+. Computational DFT methods were also employed to survey the bonding in the cations, along with an examination of their molecular orbitals (MOs).

Respiratory Network Stability and Modulatory Response to Substance P Require Nalcn.

Respiration is a rhythmic activity as well as one that requires responsiveness to internal and external circumstances; both the rhythm and neuromodulatory responses of breathing are controlled by brainstem neurons in the preBötzinger complex (preBötC) and the retrotrapezoid nucleus (RTN), but the specific ion channels essential to these activities remain to be identified. Because deficiency of sodium leak channel, non-selective (Nalcn) causes lethal apnea in humans and mice, we investigated Nalcn function in these neuronal groups. We found that one-third of mice lacking Nalcn in excitatory preBötC neurons died soon after birth; surviving mice developed apneas in adulthood. Interestingly, in both preBötC and RTN neurons, the Nalcn current influences the resting membrane potential, contributes to maintenance of stable network activity, and mediates modulatory responses to the neuropeptide substance P. These findings reveal Nalcn's specific role in both rhythmic stability and responsiveness to neuropeptides within the respiratory network.

Barrington's nucleus: Neuroanatomic landscape of the mouse "pontine micturition center".

Barrington's nucleus (Bar) is thought to contain neurons that trigger voiding and thereby function as the "pontine micturition center." Lacking detailed information on this region in mice, we examined gene and protein markers to characterize Bar and the neurons surrounding it. Like rats and cats, mice have an ovoid core of medium-sized Bar neurons located medial to the locus coeruleus (LC). Bar neurons express a GFP reporter for Vglut2, develop from a Math1/Atoh1 lineage, and exhibit immunoreactivity for NeuN. Many neurons in and around this core cluster express a reporter for corticotrophin-releasing hormone (BarCRH ). Axons from BarCRH neurons project to the lumbosacral spinal cord and ramify extensively in two regions: the dorsal gray commissural and intermediolateral nuclei. BarCRH neurons have unexpectedly long dendrites, which may receive synaptic input from the cerebral cortex and other brain regions beyond the core afferents identified previously. Finally, at least five populations of neurons surround Bar: rostral-dorsomedial cholinergic neurons in the laterodorsal tegmental nucleus; lateral noradrenergic neurons in the LC; medial GABAergic neurons in the pontine central gray; ventromedial, small GABAergic neurons that express FoxP2; and dorsolateral glutamatergic neurons that express FoxP2 in the pLC and form a wedge dividing Bar from the dorsal LC. We discuss the implications of this new information for interpreting existing data and future experiments targeting BarCRH neurons and their synaptic afferents to study micturition and other pelvic functions.

The neural control of respiration in lampreys.

This review focuses on past and recent findings that have contributed to characterize the neural networks controlling respiration in the lamprey, a basal vertebrate. As in other vertebrates, respiration in lampreys is generated centrally in the brainstem. It is characterized by the presence of a fast and a slow respiratory rhythm. The anatomical and the basic physiological properties of the neural networks underlying the generation of the fast rhythm have been more thoroughly investigated; less is known about the generation of the slow respiratory rhythm. Comparative aspects with respiratory generators in other vertebrates as well as the mechanisms of modulation of respiration in association with locomotion are discussed.

Testing the evolutionary conservation of vocal motoneurons in vertebrates.

Medullary motoneurons drive vocalization in many vertebrate lineages including fish, amphibians, birds, and mammals. The developmental history of vocal motoneuron populations in each of these lineages remains largely unknown. The highly conserved transcription factor Paired-like Homeobox 2b (Phox2b) is presumed to be expressed in all vertebrate hindbrain branchial motoneurons, including laryngeal motoneurons essential for vocalization in humans. We used immunohistochemistry and in situ hybridization to examine Phox2b protein and mRNA expression in caudal hindbrain and rostral spinal cord motoneuron populations in seven species across five chordate classes. Phox2b was present in motoneurons dedicated to sound production in mice and frogs (bullfrog, African clawed frog), but not those in bird (zebra finch) or bony fish (midshipman, channel catfish). Overall, the pattern of caudal medullary motoneuron Phox2b expression was conserved across vertebrates and similar to expression in sea lamprey. These observations suggest that motoneurons dedicated to sound production in vertebrates are not derived from a single developmentally or evolutionarily conserved progenitor pool.

2-Phosphino-1,3-diphosphonium ions.

A series of 2-phosphino-1,3-diphosphonium trifluoromethanesulfonate salts has been prepared and comprehensively characterized. The compounds represent rare examples of salts containing triphosphorus dications and establish important structural and spectroscopic parameters and trends for catenated phosphorus chains.

Absence of mutations in HCRT, HCRTR1 and HCRTR2 in patients with ROHHAD.

BACKGROUND AND OBJECTIVES: Rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) is a rare pediatric disease of unknown cause. Here, in response to a recent case report describing a ROHHAD patient who suffered from secondary narcolepsy confirmed by an absence of hypocretin-1 in the cerebrospinal fluid, we consider whether the ROHHAD phenotype is owing to one or more mutations in genes specific to hypocretin protein signalling. METHODS: DNA samples from 16 ROHHAD patients were analyzed using a combination of next-generation and Sanger sequencing to identify exonic sequence variations in three genes: HCRT, HCRTR1, and HCRTR2. RESULTS: No rare or novel mutations were identified in the exons of HCRT, HCRTR1, or HCRTR2 genes in a set of 16 ROHHAD patients. CONCLUSIONS: ROHHAD is highly unlikely to be caused by mutations in the exons of the genes for hypocretin and its two receptors.

Diving into the mammalian swamp of respiratory rhythm generation with the bullfrog.

All vertebrates produce some form of respiratory rhythm, whether to pump water over gills or ventilate lungs. Yet despite the critical importance of ventilation for survival, the architecture of the respiratory central pattern generator has not been resolved. In frogs and mammals, there is increasing evidence for multiple burst-generating regions in the ventral respiratory group. These regions work together to produce the respiratory rhythm. However, each region appears to be pivotally important to a different phase of the motor act. Regions also exhibit differing rhythmogenic capabilities when isolated and have different CO2 sensitivity and pharmacological profiles. Interestingly, in both frogs and rats the regions with the most robust rhythmogenic capabilities when isolated are located in rhombomeres 7/8. In addition, rhombomeres 4/5 in both clades are critical for controlling phases of the motor pattern most strongly modulated by CO2 (expiration in mammals, and recruitment of lung bursts in frogs). These key signatures may indicate that these cell clusters arose in a common ancestor at least 400 million years ago.

Dbx1 precursor cells are a source of inspiratory XII premotoneurons.

All behaviors require coordinated activation of motoneurons from central command and premotor networks. The genetic identities of premotoneurons providing behaviorally relevant excitation to any pool of respiratory motoneurons remain unknown. Recently, we established in vitro that Dbx1-derived pre-Bötzinger complex neurons are critical for rhythm generation and that a subpopulation serves a premotor function (Wang et al., 2014). Here, we further show that a subpopulation of Dbx1-derived intermediate reticular (IRt) neurons are rhythmically active during inspiration and project to the hypoglossal (XII) nucleus that contains motoneurons important for maintaining airway patency. Laser ablation of Dbx1 IRt neurons, 57% of which are glutamatergic, decreased ipsilateral inspiratory motor output without affecting frequency. We conclude that a subset of Dbx1 IRt neurons is a source of premotor excitatory drive, contributing to the inspiratory behavior of XII motoneurons, as well as a key component of the airway control network whose dysfunction contributes to sleep apnea.

Rapid-Onset Obesity with Hypothalamic Dysfunction, Hypoventilation, and Autonomic Dysregulation (ROHHAD): exome sequencing of trios, monozygotic twins and tumours.

BACKGROUND: Rapid-onset Obesity with Hypothalamic Dysfunction, Hypoventilation, and Autonomic Dysregulation (ROHHAD) is thought to be a genetic disease caused by de novo mutations, though causative mutations have yet to be identified. We searched for de novo coding mutations among a carefully-diagnosed and clinically homogeneous cohort of 35 ROHHAD patients. METHODS: We sequenced the exomes of seven ROHHAD trios, plus tumours from four of these patients and the unaffected monozygotic (MZ) twin of one (discovery cohort), to identify constitutional and somatic de novo sequence variants. We further analyzed this exome data to search for candidate genes under autosomal dominant and recessive models, and to identify structural variations. Candidate genes were tested by exome or Sanger sequencing in a replication cohort of 28 ROHHAD singletons. RESULTS: The analysis of the trio-based exomes found 13 de novo variants. However, no two patients had de novo variants in the same gene, and additional patient exomes and mutation analysis in the replication cohort did not provide strong genetic evidence to implicate any of these sequence variants in ROHHAD. Somatic comparisons revealed no coding differences between any blood and tumour samples, or between the two discordant MZ twins. Neither autosomal dominant nor recessive analysis yielded candidate genes for ROHHAD, and we did not identify any potentially causative structural variations. CONCLUSIONS: Clinical exome sequencing is highly unlikely to be a useful diagnostic test in patients with true ROHHAD. As ROHHAD has a high risk for fatality if not properly managed, it remains imperative to expand the search for non-exomic genetic risk factors, as well as to investigate other possible mechanisms of disease. In so doing, we will be able to confirm objectively the ROHHAD diagnosis and to contribute to our understanding of obesity, respiratory control, hypothalamic function, and autonomic regulation.

Dysregulation of locus coeruleus development in congenital central hypoventilation syndrome.

Human congenital central hypoventilation syndrome (CCHS), resulting from mutations in transcription factor PHOX2B, manifests with impaired responses to hypoxemia and hypercapnia especially during sleep. To identify brainstem structures developmentally affected in CCHS, we analyzed two postmortem neonatal-lethal cases with confirmed polyalanine repeat expansion (PARM) or Non-PARM (PHOX2B∆8) mutation of PHOX2B. Both human cases showed neuronal losses within the locus coeruleus (LC), which is important for central noradrenergic signaling. Using a conditionally active transgenic mouse model of the PHOX2B∆8 mutation, we found that early embryonic expression (

Diverse reactivity of the cyclo-diphosphinophosphonium cation [(PtBu)3Me]⁺: parallels with epoxides and new catena-phosphorus frameworks.

The cyclo-diphosphinophosphonium salt [(PtBu)3Me][OTf] (2) has been shown to be highly reactive toward Lewis bases, exhibiting diverse reactivity with phosphines, 4-(dimethylamino)pyridine (dmap) and chlorophosphines, providing approaches to new open-chain and cyclic catena-phosphorus frameworks. Reaction of 2 with R3P (R = Me or nPr) or dmap led to the ring-opened adducts [R3P-PtBu-PtBu-P(Me)tBu][OTf] (R = Me (4a), nPr (4b)) and [(dmap)-PtBu-PtBu-P(Me)tBu][OTf] (6), respectively. The complicated (31)P{(1)H} NMR spectra of the three compounds were simulated, evidencing the presence of two diastereomeric forms of 4a, and single diastereomers of 4b and 6. This ring-opening reactivity of the cation in 2 parallels the reactivity of isolobal epoxides with nucleophiles under acidic conditions. Compound 2 was also shown to react with a 2:1 mixture of Me2PCl and TMSOTf to form the unexpected cyclo-diphosphino-1,2-diphosphonium salt [(Me2P)2(PtBu)2][OTf]2 (8), which is postulated to result from two consecutive ring-opening and ring-closing steps. In contrast, reaction with MePCl2 furnished [(MeP)(PtBu)2(P(Me)tBu)][OTf] (9), consistent with insertion of a "MeP" moiety into the cationic phosphorus framework of 2. The importance of ring strain on the reactivity of the cation in 2 was illustrated by comparative studies of the corresponding cyclo-tetraphosphorus cation in [(PtBu)4Me][OTf] (10), which exhibits no reactivity under analogous conditions.

Testing the role of preBötzinger Complex somatostatin neurons in respiratory and vocal behaviors.

Identifying neurons essential for the generation of breathing and related behaviors such as vocalisation is an important question for human health. The targeted loss of preBötzinger Complex (preBötC) glutamatergic neurons, including those that express high levels of somatostatin protein (SST neurons), eliminates normal breathing in adult rats. Whether preBötC SST neurons represent a functionally specialised population is unknown. We tested the effects on respiratory and vocal behaviors of eliminating SST neuron glutamate release by Cre-Lox-mediated genetic ablation of the vesicular glutamate transporter 2 (VGlut2). We found the targeted loss of VGlut2 in SST neurons had no effect on viability in vivo, or on respiratory period or responses to neurokinin 1 or µ-opioid receptor agonists in vitro. We then compared medullary SST peptide expression in mice with that of two species that share extreme respiratory environments but produce either high or low frequency vocalisations. In the Mexican free-tailed bat, SST peptide-expressing neurons extended beyond the preBötC to the caudal pole of the VII motor nucleus. In the naked mole-rat, however, SST-positive neurons were absent from the ventrolateral medulla. We then analysed isolation vocalisations from SST-Cre;VGlut2(F/F) mice and found a significant prolongation of the pauses between syllables during vocalisation but no change in vocalisation number. These data suggest that glutamate release from preBötC SST neurons is not essential for breathing but play a species- and behavior-dependent role in modulating respiratory networks. They further suggest that the neural network generating respiration is capable of extensive plasticity given sufficient time.

Atoh1-dependent rhombic lip neurons are required for temporal delay between independent respiratory oscillators in embryonic mice.

All motor behaviors require precise temporal coordination of different muscle groups. Breathing, for example, involves the sequential activation of numerous muscles hypothesized to be driven by a primary respiratory oscillator, the preBötzinger Complex, and at least one other as-yet unidentified rhythmogenic population. We tested the roles of Atoh1-, Phox2b-, and Dbx1-derived neurons (three groups that have known roles in respiration) in the generation and coordination of respiratory output. We found that Dbx1-derived neurons are necessary for all respiratory behaviors, whereas independent but coupled respiratory rhythms persist from at least three different motor pools after eliminating or silencing Phox2b- or Atoh1-expressing hindbrain neurons. Without Atoh1 neurons, however, the motor pools become temporally disorganized and coupling between independent respiratory oscillators decreases. We propose Atoh1 neurons tune the sequential activation of independent oscillators essential for the fine control of different muscles during breathing.DOI: http://dx.doi.org/10.7554/eLife.02265.001.

Interpnictogen cations: exploring new vistas in coordination chemistry.

Pnictine derivatives can behave as both 2e(-) donors (Lewis bases) and 2e(-) acceptors (Lewis acids). As prototypical ligands in the coordination chemistry of transition metals, amines and phosphines also form complexes with p-block Lewis acids, including a variety of pnictogen-centered acceptors. The inherent Lewis acidity of pnictogen centers can be enhanced by the introduction of a cationic charge, and this feature has been exploited in recent years in the development of compounds resulting from coordinate Pn-Pn and Pn-Pn' interactions. These compounds offer the unusual opportunity for homoatomic coordinate bonding and the development of complexes that possess a lone pair of electrons at the acceptor center. This Review presents new directions in the systematic extension of coordination chemistry from the transition series into the p-block.