Raphe System Research Articles

Light and Scanning Observations on a Denticula species reported from South Africa and endemism of the diatom genus Tetralunata (Rhopalodiales, Bacillariophyceae)

Denticula costata Hustedt was originally described from fossil material from Sumatra and later assigned to the genus Tetralunata. Although Tetralunata was thought to be endemic to Indonesia, D. costata has been reported from wetwalls from South Africa. This disparity in locality prompted us to investigate the D. costata in South Africa further. D. costata (now T. costata) specimens and the species reported from South Africa were different in size, shape, and structure of the raphe system. These differences, as well as comparisons to other Denticula species, allowed us to determine that the South African specimens have not been described previously. Valve ultrastructure, including the canal raphe, areolae with volate occlusions, and presence/structure of the septa suggest this new species belongs to the genus Tetralunata. This is the first report of Tetralunata from outside of Indonesia. Herein, we describe Tetraluanata schoemanii sp. nov. and its systematic placement close to, but separate from, Epithemia. This first report of Tetralunata from outside of Indonesia, increases our understanding of the genus range and displays a unique biogeographical pattern that warrants further investigation in the future.

Gomphonema rajaguruii sp. nov., a new diatom (Bacillariophyceae) species from the Western Ghats, India

A new freshwater diatom species, Gomphonema rajaguruii sp. nov., is described from a wet wall at Mahabaleshwar, Western Ghats, Maharashtra, India. The new species is described based on light and scanning electron microscopy. Features that distinguish this new species from morphologically-similar species such as G. kallarense and G. lujanense include valve shape, which is broad at the centre and narrower near the poles, a distinctly lateral, undulate raphe system and costa-like striae, which are comprised of two rows of slit-like areolae. Although G. rajaguruii also resembles some taxa from the genus Gomphoneis, such as G. eriense and its close allies, it differs from them by lacking an axial plate. The description of G. rajaguruii sp. nov. increases the knowledge on the diatom diversity in the region.

Xenobennettella coralliensis a new monoraphid diatom genus characterized by the alveolate sternum valve with cavum, observed from coral reef habitats.

During a survey of benthic diatoms from the coral reefs of the Indian Ocean (Scattered Islands) and Pacific Ocean (Tuamotu Archipelago), an interesting monoraphid diatom was observed and examined by light microscopy and various electron microscopy methods including Focus Ion Beam milling. Our thorough analysis revealed the similarity of this diatom to Bennettella R.W.Holmes, which we reference in the name: Xenobennettella Witkowski & Riaux-Gobin gen. nov., with Xenobennettella coralliensis Witkowski & Riaux-Gobin sp. nov. as the generitype. The type habitat for this new species is the sublittoral coral reef of Juan de Nova in the Mozambique Channel. The sternum valve of the new genus is characterized by an alveolate ultrastructure with the rim of the alveola opening along the valve margin, resembling the sternum valve of Bennettella. Internally, Xenobennettella differs from the latter by possessing a cavum (horseshoe-shaped chamber) on one side of the valve, in a central axial position. The raphe valve of Xenobennettella has small, marginal, apically elongate chambers, which are internally delineated by transapical ribs that are very similar to Bennettella. However, the raphe in the new genus is different from the latter, resembling some Cocconeis and Planothidium with internal raphe endings bent in the opposite direction, while resembling some Planothidium taxa externally by ending on the apical part of the mantle. This contrasts to Bennettella, which has a unique raphe system, with external raphe endings below the apices, a prominent axial structure and a transapically expanded central area. Likewise, the external surface of Bennettella is different from that of the new genus with a complex mantle structure and biseriate striae. In Xenobennettella, the valve mantle of the raphe valve is simple and perforated by areola. The transapical striae occur in the valve margin and the axial area is ornamented along its course with a single row of densely packed areola on both sides. The characteristics of the raphe valve and alveolate sternum valve place the new genus among the Achnanthidiaceae.

Descriptions of three new diatom species in the genus Eunotia (Eunotiaceae, Bacillariophyta) from the Eocene Arctic

Eunotia is the largest and most diverse genus within the family Eunotiaceae, a primarily freshwater group of diatoms often found in dilute, acidic and humic-stained environments. Species in this genus are characterized by being asymmetric along their apical axis, symmetric about the transapical axis, and with a simple and reduced raphe system situated largely on the mantle and restricted to the apical ends of the valve. In addition, Eunotia taxa have one or more rimoportula per valve, usually close to the apex. Because of their reduced raphe system, coupled with the presence of rimoportulae, Eunotia and its relatives are often viewed as the oldest lineage of raphe-bearing diatoms. To date, the oldest remains of Eunotia species have been reported from the early to middle Eocene, including from the Giraffe Pipe locality, an ancient Eocene fossil site located in northern Canada near the Arctic Circle. Rocks from this site contain a large and diverse assemblage of Eunotia taxa. The purpose of this study is to begin to characterize this assemblage with descriptions of three new species, Eunotia giraffensis sp. nov., E. petasum sp. nov. and E. pseudonaegelii sp. nov. The new species, representing the longest specimens found at the Giraffe Pipe locality, each possess characteristics common to Eunotia making them easily assigned to this genus. Because the Eunotia lineage was well established by the early part of the Eocene, it is likely to be significantly older.

Vladinikolaevia, gen. nov. - a new enigmatic freshwater diatom genus (Cymbellaceae; Bacillariophyceae) from Mongolia

We studied a new freshwater cymbelloid diatom taxon collected from Mongolia with light and scanning electron microscopy. The monotypic genus Vladinikolaevia gen. nov., based on V. mongolica sp. nov, is described. The new genus is characterized by a combination of morphological features found in two well-known genera such as Cymbella and Encyonema. The raphe system is morphologically-similar to Encyonema but the presence of apical pore fields is similar to the genus Cymbella as presently circumscribed. There are other very interesting peculiarities found in V. mongolica sp. nov. that show it to be a distinct taxon. We discuss the morphology of this new genus in the context of valve morphogenesis and presence of primary and secondary valves. The description of this new genus from Mongolia supports our contention that Asia is home to many endemics, interesting and not yet described cymbelloid taxa.

Navicula fuxianturriformis sp. nov. (Bacillariophyceae), a new species from southwest China

Navicula fuxianturriformis sp. nov., collected from Lake Fuxian, Yunnan Province, China, is described as a new species based on light and scanning electron microscope observations. N. fuxianturriformis sp. nov. has lineolate areolae closed by hymenes internally and a peculiar structure of the raphe system where the raphe is elevated internally on a thin longitudinal rib that is laterally expanded at the central area; features that assign it to the genus Navicula. The key diagnostic features of this new species include: 1) lanceolate valves with the cuneate to apiculate apices, 2) mostly long, slit-like, partly round-rectangular areolae on the valve exterior and round to rectangular areolae internally, 3) external distal raphe fissures that are hooked opposite one another, and 4) the oval-elliptical central area, with two to five pairs of irregularly shortened striae. This combination of features distinguishes N. fuxianturriformis from congers such as N. turriformis, N. turris, N. reinhardtii, N. hoevsgoelreinhardtii, N. mongolreinhardtii, N. apiculatoreinhardtii or N. apiculatoreinhardtii f. biseriata. A discussion of the morphological features of this taxon and morphologically-similar species is presented. These findings increase our understanding about the morphology and distribution of the genus Navicula in China.

Serotonergic Neurons in the Chick Brainstem Express Various Serotonin Receptor Subfamily Genes.

Serotonin (5-hydroxytryptamine, 5-HT) is a phylogenetically conserved modulatory neurotransmitter. In mammals, 5-HT plays an important role in the regulation of many mental states and the processing of emotions in the central nervous system. Serotonergic neurons in the central nervous system, including the dorsal raphe (DR) and median raphe (MR) nuclei, are spatially clustered in the brainstem and provide ascending innervation to the entire forebrain and midbrain. Both between and within the DR and MR, these serotonergic neurons have different cellular characteristics, developmental origin, connectivity, physiology, and related behavioral functions. Recently, an understanding of the heterogeneity of the DR and MR serotonergic neurons has been developed at the molecular level. In birds, emotion-related behavior is suggested to be modulated by the 5-HT system. However, correspondence between the raphe nuclei of birds and mammals, as well as the cellular heterogeneity in the serotonergic neurons of birds are poorly understood. To further understand the heterogeneity of serotonergic neurons in birds, we performed a molecular dissection of the chick brainstem using in situ hybridization. In this study, we prepared RNA probes for chick orthologs of the following serotonin receptor genes: 5-HTR1A, 5-HTR1B, 5-HTR1D, 5-HTR1E, 5-HTR1F, 5-HTR2A, 5-HTR2B, 5-HTR2C, 5-HTR3A, 5-HTR4, 5-HTR5A, and 5-HTR7. We showed that the expression pattern of 5-HT receptors in the serotonin neurons of chick DR and MR may vary, suggesting heterogeneity among and within the serotonin neurons of the DR and MR in the chick brainstem. Our findings regarding the molecular properties of serotonergic neurons in the bird raphe system will facilitate a good understanding of the correspondence between bird and mammalian raphes.

A simple method for making transverse cleavages of diatom frustules for scanning electron microscopy and its application

The surface structures of diatom valves have been primarily studied using scanning electron microscopy (SEM), while the frustule shape and internal cellular structures have been elucidated in cross-sections by transmission electron microscopy (TEM). However, ultrathin sections can show neither the part of the whole frustule that is cut nor reflect the relationship between the sectioned portion and the surrounding structure. Therefore, we developed a simple method for obtaining a clean cleavage surface of the frustule. In this method, a drop of diatom suspension was frozen on a custom-made bundle of metal joints pre-soaked in liquid nitrogen, followed by sample preparation for SEM. The three-dimensional (3D) structure of the entire frustule and cross-sectional features, such as the thickness of the valve and bands, the angle of projection, and the internal structures of the areolae, raphe systems, and isolated pores, were visible within each half of the cleaved frustule. Applying this method shortly after cell division revealed differences in the silica deposition profiles between parental and newly forming valves at the corresponding sites. The utility of the information obtained from the cleaved frustule is discussed.

Diploid genomic architecture of Nitzschia inconspicua, an elite biomass production diatom

A near-complete diploid nuclear genome and accompanying circular mitochondrial and chloroplast genomes have been assembled from the elite commercial diatom species Nitzschia inconspicua. The 50 Mbp haploid size of the nuclear genome is nearly double that of model diatom Phaeodactylum tricornutum, but 30% smaller than closer relative Fragilariopsis cylindrus. Diploid assembly, which was facilitated by low levels of allelic heterozygosity (2.7%), included 14 candidate chromosome pairs composed of long, syntenic contigs, covering 93% of the total assembly. Telomeric ends were capped with an unusual 12-mer, G-rich, degenerate repeat sequence. Predicted proteins were highly enriched in strain-specific marker domains associated with cell-surface adhesion, biofilm formation, and raphe system gliding motility. Expanded species-specific families of carbonic anhydrases suggest potential enhancement of carbon concentration efficiency, and duplicated glycolysis and fatty acid synthesis pathways across cytosolic and organellar compartments may enhance peak metabolic output, contributing to competitive success over other organisms in mixed cultures. The N. inconspicua genome delivers a robust new reference for future functional and transcriptomic studies to illuminate the physiology of benthic pennate diatoms and harness their unique adaptations to support commercial algae biomass and bioproduct production.

Bacillariophyta of the Yavorivsky National Park, Broadleaf Forest Zone of Ukraine, including Сaloneis albus-columba, sp. nov.

Diatoms (Bacillariophyta) are one of the major biological components in all kinds of aquatic ecosystems both in freshwater and marine ones. The nature reserve fund of Ukraine includes 52 national parks, in the vast majority of which Bacillariophyta have not been studied. This investigation presents first data on the diatoms in Yavorivsky National Park located in Lviv region. The material consists of the epiphytic samples of microalgae that were collected from different substrates in aquatic ecosystems of the Yavorivsky National Park in 2014. In the hydrotopes of the park 180 diatom species from 56 genera were found, among them Achnanthidium catenatum (Bily & Marvan) Lange-Bertalot, Cymbopleura apiculata Krammer, Fallacia sublucidula (Hustedt) D. G. Mann in Round, Crawford & Mann, Gomphonema lagenula Kützing, G. supersedens Reichardt, G. pseudopusillum Reichardt, Paraplaconeis minor (Grunow) Lange-Bertalot, Placoneis constans (Hustedt) E. J. Cox, Psammothidium bioretii (Germain) Bukhtiyarova & Round, P. vernadskyi Bukhtiyarova et Stanislavskaya, Sellaphora gracillima Zidarova, Kopalová & Van de Vijver, S. insolita (Manguin) Hamilton et Antoniades, Stauroneis fluminopsis Van de Vijver et Lange-Bertalot were recorded for the first time in Ukraine. Besides that, Amphora hemicycla Stoermer & J. J. Yang and Sellaphora bacilloides (Hustedt) Levkov, Krstic & Nakov also were new findings in the country from the Broadleaf Forest Zone of Ukraine. Many species rare in the world flora and in Ukraine were found. A new diatom species Сaloneis albus-columba Bukhtiyarova, sp. nov., was described from the pond in stationary recreation area Kozulka. This new species possesses strongly three-undulate valves with three rhombic segments, which in morphology is most similar to Caloneis lamella Zakrzewski, however it differs from it by having rhombic distal valve segments instead of oval ones as well as noticeably smaller width of the central valve segment. The morphology of other similar species is discussed. For proper description of the new species new definitions for the raphe system morphology were grounded on functional morphology of the diatom frustule. New combinations Iconella alaskaensis (Foged) Bukhtiyarova, comb. et stat. nov., Iconella baltica (Schumann) Bukhtiyarova, comb. nov., Iconella brebissonii (Krammer & Lange-Bertalot) Bukhtiyarova, comb. nov., Iconella brightwellii (W. Smith) Bukhtiyarova, comb. nov., Iconella constricta (Grunow) Bukhtiyarova, comb. et stat. nov., Iconella didyma (Kützing) Bukhtiyarova, comb. nov. and Iconella elegans (Ehrenberg) Bukhtiyarova, comb. nov. were formally proposed. The lectotype for Eunotia glacialis F. Meister was designated here. Illustrations with light and scanning electron microscopy are presented. A primary inventory of Bacillariophyta and their subsequent study on protected territories in Ukraine is still an important task in the context of preservation of biodiversity of the country.

Cocconeis vaiamanuensis sp. nov. (Bacillariophyceae) from Raivavae (South Pacific) and allied taxa: ultrastructural specificities and remarks about the polyphyletic genus Cocconeis Ehrenberg

A small marine monoraphid diatom with a linear-elliptic shape and simple terminal raphe endings was present on Raivavae (South Pacific). Particularly due to its different stria structure on both valves, this taxon is here classified as Cocconeis. The new species was present on the rocky intertidal shore of the coral-reef lagoon, as an epiphyte on a turf. Cocconeis vaiamanuensis sp. nov. can be compared to some other monoraphids with a simple raphe system and a rod-like shape. The new taxon has small marginal processes on the sternum valve (SV) mantle, as previously reported for Cocconeis peltoides. Such processes were also previously observed in Platessa and Psammothidium. A cladistic analysis based on ultrastructure shows an affiliation between several close-by taxa. Cocconeis of the C. peltoides section are close to Psammothidium, whereas other Cocconeis without processes are closer to Platessa and Achnanthidium. A clone of Cocconeis cf. sigillata (SZCZCH1200) allowed for a molecular phylogeny to be reconstructed. The molecular signature of Cocconeis cf. sigillata is close to that of Lemnicola hungarica. Cocconeis is a genus with different and complex morphologies that may be split into independent clades (genera). The SV processes may be a vestigial character reminiscent of an ancestral state.

<strong><em>Cymbella xiaojinensis sp. nov.</em>, a new cymbelloid diatom species (Bacillariophyceae) from high altitude lakes, China</strong>

This paper describes a new species of Cymbella from an alpine lake in the Hengduan Mountains, southwestern China. The detailed morphological description of the new species, named Cymbella xiaojinensis sp. nov. is presented, based on light and scanning electron microscopy. The main features of C. xiaojinensis are characterized by strongly dorsiventral, triangular valves with a strongly reverse-lateral raphe system positioned near the proximal ends and an asymmetrical, larger central area, occupying approximately 1/2 of the width with the valve. Most morphological characteristics of the new species are similar to C. shudunensis, C. terrafuegiana, C. pamirensis, and C. gravida, but differ in details of size, valve shape, striae density, central area, and number of stigmata.

Torgania coronata gen. et sp. nov.: a new needle-shaped genus, with comments on the raphe system as a diagnostic character in Eunotiales (Ochrophyta, Bacillariophyceae)

ABSTRACT The diatom Torgania coronata gen. et sp. nov. from the Brazilian Amazon is described based on light and scanning electron microscopy. Members of this genus have the raphe system entirely located on the valve surface, needle-shaped, isopolar valves with one rimoportula at each apex, and isovalvar frustules. Under the light microscope, members of Torgania can be confused with some species of Fragilaria, such as F. tenera, due to the aciculiform valve outline and inconspicuous striae. We consider that the presence of the raphe on the valve surface prevents Torgania from being placed in the Eunotiaceae. We also consider that Torgania’s placement within Peroniaceae is inadequate due to its isovalvar frustules and isopolar valves. Therefore, we did not include Torgania in this family either. Fragilaria braunii was recently transferred to the genus Peronia due to the discovery of a vestigial raphe system, along with the presence of rimoportulae, and characteristics of the girdle elements. However, in our opinion, this species better fits in the newly proposed Torgania than in Peronia and we therefore propose the new combination, Torgania braunii comb. nov. The characteristics found in the newly proposed genus indicate that the traditional dichotomy between Eunotiaceae/Peroniaceae is no longer appropriate. We argue that the eunotioid clade should be defined mainly by the raphe system non-integrated with the sternum, and that terms such as ‘simple’ or ‘short’ in reference to the raphe should be avoided. In addition, we provide a morphological key for the identification of Eunotiales genera.

<p><strong><em>Scoliolyra</em> <em>elliptica</em> gen. et sp. nov. (Bacillariophyceae), a new marine genus from sandy beach in Southern China</strong></p>

Observation of sand samples collected from an estuarine sandy beach in Southern China revealed the presence of a new biraphid diatom. It is characterized by the presence of a twisted raphe system, apically elongate areolae, and striae interrupted by longitudinal H-shaped lateral areas in a form of valve face depressions, as well as girdle composed of open, plain copulae. The structure of valve outline, the raphe sternum and striae bears some resemblance to some established genera including e.g., Lyrella, Fallacia, Scolioneis, Scoliopleura and Scoliotropis, however, these characters are uniquely combined in this novel taxon. The new species, Scoliolyra elliptica, belongs to a new biraphid genus, Scoliolyra, and it is tentatively placed within the family Scolioneidaceae.

<p><strong>Taxonomy, valve ultrastructure, nomenclature and a comparison of two species of Bacillariales from freshwaters of Puerto Rico</strong></p>

We have investigated two canal-raphe bearing taxa from two freshwater long-term ecological monitoring sites in the NEON program from Puerto Rico. The identity of these two taxa have been misunderstood, and they have been mistaken for one another, due to being similar in size, shape and having interrupted striae across the valve face. Denticula occidentalis Østrup was described from the U.S. Virgin Islands, and like its congeners has fibulae that extend across the valve face as thickened ribs. The species also has valvocopulae that are typical for the genus, with arched sections that clasp onto the knob-like fibulae. Denticula occidentalis has a discontinuous raphe system, and external proximal raphe ends are hooked towards the valve center and elongated. Grunowia portoricensis, sp. nov. has fibulae restricted to the raphe side of the valve, though unlike most members of the genus the fibulae are knob-like. The raphe is continuous across the central area. Though described here as new to science, the species has been illustrated previously from Venezuela. Distinctions between Nitzschia, Denticula and Grunowia are discussed.

A new freshwater Psammodictyon species in the Taihu Basin, Jiangsu Province, China

We describe a new species of diatom, Psammodictyon taihuensis sp. nov., collected from the Taihu Basin, Jiangsu Province, China. There are several features of this diatom that suggest it should be included in the genus Psammodictyon, notably the possession of panduriform valves characterized by a longitudinal fold near the apical axis, coarsely areolate striae, and a keeled raphe system present on the valve margin. This species is distinct from others in the genus by its small size, being only 16.5-25.0 μm long and 10.0-12.5 μm wide in the central region, and with the widest valve being 10.5-13.5 μm in width. There are 8-11 distinct fibulae per 10 μm and the striae are composed of 18-22 coarse areolae per 10 μm. This is the first report of a freshwater member of the genus Psammodictyon in China, which expands the known geographical and ecological distributions of the genus and enhances our understanding of freshwater diatom diversity in China.

The genus Eunotia Ehrenb. (Bacillariophyta) in the Cheremsky Nature Reserve, Ukrainian Polissya, and refined terminology relevant to the raphe system morphology.

Numerous species of Eunotia Ehrenb., widely distributed in the world flora, prefer acidic, dystrophic or oligotrophic freshwater habitats with low conductivity and usually occur in epiphytic or epilithic hydrotopes. In Ukraine, only 32 species and eight varieties of Eunotia were known until this study. For the first time, 9 more species have been recorded mainly from the Cheremsky Nature Reserve, located in Ukrainian Polissya. New findings include 2 species widely distributed in the world flora on most continents and 7 rare species known from several locations, among them E.genuflexa, E.jarensis and E.ruzickae, which are probably European endemics as they have not been reported from other continents. For the present time in the Cheremsky Nature Reserve, the 20 species recorded here, the highest species richness of Eunotia in Ukraine, bring the total number of Eunotia in Ukraine to 41 species, which comprises only 7% of Eunotia species in the world flora. This is indirect evidence of insufficient investigation of the wetlands in Ukraine where Eunotia usually is represented with high species richness. Several definitions are suggested to describe morphological features that are peculiar to the diatom frustule particular to the Eunotia species. The genus Eunotia possesses a mirror-symmetric, mantle-offset, brevisslit raphe system, which may or may not have terminal raphe fissures. Morphological analysis provided in this study revealed the absence of terminal raphe fissures for many species of Eunotia. Instead, the distal ends of the raphe slits finish on the outer valve surface by funnel holes, sometimes pore-like ones, connected with the helictoglossae. However, in the literature those distal ends of the raphe slits were described erroneously as terminal raphe fissures. For the first time different types of raphe system are grounded. Two species Eunotiaimplicata Nörpel-Schempp et al. in Alles et al. and Eunotiaincisa W. Smith ex Gregory were lectotypified.

Concomitant in Vivo Voltammetric and Electrophysiological Analysis Indicate that Nociceptin/Orphanin FQ Affects Dopamine and then Serotonin Activities in Brain Substancia Nigra.

Nociceptin/orphanin-FQ (NOCI) together with its receptor NOP are widely expressed in cortical and subcortical motor areas and it is known that NOCI acts as an anxiolytic attenuating the behavioral inhibition of animals acutely exposed to stressful/anxiogenic conditions. Influence of NOCI upon the dopaminergic system has been observed in the ventral tegmental area and in the nucleus accumbens as well as an inhibitory action of NOCI is described upon serotoninergic mechanisms at cells and terminal levels. In particular, it is known that serotoninergic fibers from the raphe system project to the substancia nigra (SN) and that this modulation is behaviourally relevant. In the present work, the effect of exogenous NOCI injected into the SN upon DA and 5-HT levels have been analyzed by means of differential pulse voltammetry and nafion-carbon fiber microelectrodes. Electrophysiological monitoring of multicell activity was concomitantly performed with the same microsensor. It appeared that both levels of these biogenic amines were specularly altered, with possibly a driving influence of the DA activity upon the serotoninergic function(s).

Three new diatom species of the genus Diploneis (Bacillariophyta) from Lake Baikal

We present three new species, Diploneis implicatus, Diploneis lacustris and Diploneis pumicosus, from the littoral zone of Lake Baikal. Descriptions of these species are based on light and scanning electron microscopical features that distinguish them from other taxa. Diploneis implicatus exhibits external openings of each stria areola flanked by short siliceous thickenings of the vimenes and virgae forming a regular pattern on the external valve that is unique for the genus. Similar structures have previously been reported only in the distantly related and ecologically different Craticula citroides. Diploneis lacustris possesses a conopeum, uncommon in Diploneis and known only in Diploneis aokiensis from Japan. In our species, the conopeum is variable in structure and only developed in the apical quarter of the valve. The third species, Diploneis pumicosus, has a distinctive raphe system morphology similar to that in the single valve of Diploneis conopeospongiosa from Lake Baikal. All three species inhabit silty bottom habitats at depth of 20 m or more, and have so far been found in the southern basin of Lake Baikal. The diversity of Diploneis species in Lake Baikal is a rich resource for further understanding the genus.

Acute perturbation of Pet1-neuron activity in neonatal mice impairs cardiorespiratory homeostatic recovery

Cardiorespiratory recovery from apneas requires dynamic responses of brainstem circuitry. One implicated component is the raphe system of Pet1-expressing (largely serotonergic) neurons, however their precise requirement neonatally for homeostasis is unclear, yet central toward understanding newborn cardiorespiratory control and dysfunction. Here we show that acute in vivo perturbation of Pet1-neuron activity, via triggering cell-autonomously the synthetic inhibitory receptor hM4Di, resulted in altered baseline cardiorespiratory properties and diminished apnea survival. Respiratory more than heart rate recovery was impaired, uncoupling their normal linear relationship. Disordered gasp recovery from the initial apnea distinguished mice that would go on to die during subsequent apneas. Further, the risk likelihood of apnea-related mortality associated with suppression of Pet1 neurons was higher for animals with baseline elevated ventilatory equivalents for oxygen. These findings establish that Pet1 neurons play an active role in neonatal cardiorespiratory homeostasis and provide mechanistic plausibility for the serotonergic abnormalities associated with SIDS.