Neuro-pharmacological studies on firefly light organs during metamorphosis

Luminescences in response to electrical stimulation and pharmacological treatment were characterized during progressive degeneration of the larval light organ and differentiation of the adult light organ during metamorphosis. It was found that: (1) neural control of the larval light organ persists during pupation, (2) the differentiating adult light organ, while frequently luminescing, is not directly or neurally excitable until eclosion (3), a gradual loss of postsynaptic receptor chemical responsiveness occurs in parallel with declining neural excitability of the larval light organ, (4) postsynaptic chemical sensitivity of the adult light organ appears prior to establishment of neural control, (5) both larval and adult light organs spontaneously luminesce in the absence of neural control, and (6) synapses between nerve terminals and photocytes of the larval light organ are present throughout pupation.     

Biochemical and morphological changes accompanying light organ development in the firefly, Photuris pennsylvanica

The larval light organs of the firefly, Photuris pennsylvanica, regress and are replaced by the adult lantern during metamorphosis. Larval and adult light organs are present and capable of periodic light emission during the latter stages of pupation and the early adult. The whole pupa emits a continuous, low level, glow throughout pupation.During pupation levels of luciferase and luciferin, the enzyme and substrate required in the light reaction, were found to remain constant in the posterior half of the pupa and to show an initial increase followed by a decrease in the anterior half. Levels of luciferase and luciferin in anterior halves were not affected by ablation of the larval light organs. The ratio of luciferase to luciferin concentrations changed from less than 1, in larval and pupal stages, to greater than 1, in the adult. Changes in the concentration and the localization of luciferase and luciferin were correlated with observed light organ development.     

Developmental and Microbiological Analysis of the Inception of Bioluminescent Symbiosis in the Marine Fish Nuchequula nuchalis (Perciformes: Leiognathidae)

Many marine fish harbor luminous bacteria as bioluminescent symbionts. Despite the diversity, abundance, and ecological importance of these fish and their apparent dependence on luminous bacteria for survival and reproduction, little is known about developmental and microbiological events surrounding the inception of their symbioses. To gain insight on these issues, we examined wild-caught larvae of the leiognathid fish Nuchequula nuchalis, a species that harbors Photobacterium leiognathi as its symbiont, for the presence, developmental state, and microbiological status of the fish's internal, supraesophageal light organ. Nascent light organs were evident in the smallest specimens obtained, flexion larvae of 6.0 to 6.5 mm in notochord length (NL), a developmental stage at which the stomach had not yet differentiated and the nascent gasbladder had not established an interface with the light organ. Light organs of certain of the specimens in this size range apparently lacked bacteria, whereas light organs of other specimens of 6.5 mm in NL and of all larger specimens harbored large populations of bacteria, representatives of which were identified as P. leiognathi. Bacteria identified as Vibrio harveyi were also present in the light organ of one larval specimen. Light organ populations were composed typically of two or three genetically distinct strain types of P. leiognathi, similar to the situation in adult fish, and the same strain type was only rarely found in light organs of different larval, juvenile, or adult specimens. Light organs of larvae carried a smaller proportion of strains merodiploid for the lux-rib operon, 79 of 249 strains, than those of adults (75 of 91 strains). These results indicate that light organs of N. nuchalis flexion and postflexion larvae of 6.0 to 6.7 mm in NL are at an early stage of development and that inception of the symbiosis apparently occurs in flexion larvae of 6.0 to 6.5 mm in NL. Ontogeny of the light organ therefore apparently precedes acquisition of the symbiotic bacteria. Furthermore, bacterial populations in larval light organs near inception of the symbiosis are genetically diverse, like those of adult fish.     

Metamorphosis of the olfactory organ of the sea lamprey (Petromyzon marinus L.): Morphological changes and morphometric analysis

In larval sea lampreys (Petromyzon marinus), a small, relatively inconspicuous olfactory organ sac contains small, densely packed olfactory receptor neurons and sustentacular cells. During metamorphosis, the larval organ transforms into a prominent lamellar structure with large distinct olfactory epithelial cells that is characteristic of the adult lamprey. In the present study, scanning electron microscopy and light microscopy are used to examine changes during the seven stages (1–7) of metamorphosis. The magnitude of growth over the course of metamorphosis is evident from the doubling of the relative weight of the nasal sac. During early metamorphosis (stages 1 and 2), the larval olfactory organ enlarges, and by stage 3 specific adult structures begin to form, namely a nasal valve between the nasal tube and the organ, lamellar folds, and diverticuli of the accessory olfactory organ. Subsequent development involves widening of the cells lining the lamellar folds to the form characteristic of postmetamorphic lampreys. Although the cells in the troughs initially retain numerical density values that are significantly higher than those on the lamellar surfaces, by stage 7 values decline both in troughs and along lamellar surfaces to those observed in adults. These results show that although expansion of the olfactory organ is ongoing throughout metamorphosis, remodeling occurs early (by stage 3). This timing provides space for extensive olfactory receptor neuron neurogenesis and differentiation and correlates with the transformation of some organs that were previously examined. This is the first report in any species of olfactory receptor neuron zonation based on morphometric characteristics. J. Morphol. 231:41–52, 1997. © 1997 Wiley-Liss, Inc.     

条背萤成虫与幼虫发光器的超微结构观察

对水生萤火虫——条背萤Luciola substriata(Gorham)成虫和幼虫发光器的超微结构进行研究。结果表明,成虫发光器由明显的2层组成:反射层和发光层。反射层由排列紧密的“尿酸囊泡”构成,具有发达的气管结构,对光起反射作用;发光层由大量发光细胞构成,内含典型的发光颗粒、线粒体、内质网及大量糖原,该层通过发光细胞胞质内的生化反应而发光。2层均由非细胞层膜包被,间距25~30μm。发光器腹节由外向内依次为表皮、发光层、反射层和内部细胞层。幼虫发光器球形,由背射层和发光层构成,由非细胞层膜包被。背射层由单层柱状细胞构成,内含大量“尿酸囊泡”。发光层细胞膜相互绞缠,含有2种类型的发光颗粒:“致密”型和“凋亡”型,含有大量的线粒体和无定形颗粒,发光细胞之间分布着大量的气管、微气管及神经末梢,可观察到神经突触。与条背萤相比,陆生种成虫反射层和发光层均无非细胞层膜包被,2层间无明显间距,发光颗粒形状不规则,气管通常形成2分支;陆栖种幼虫发光层形状差异较大,背射层由单层或2~4层细胞构成;相似点在于,成虫发光器都由均由反射层和发光层构成,发光细胞内都含发光颗粒、线粒体及大量糖原,都具有发达的气管结构,发光颗粒相似。幼虫发光器都由背射层和发光层构成,都具有发达的气管和直接的神经支配,发光颗粒相似,都由非细胞层膜包被。     

Circadian pacemaker neurons transmit and modulate visual information to control a rapid behavioral response

Circadian pacemaker neurons contain a molecular clock that oscillates with a period of approximately 24 hr, controlling circadian rhythms of behavior. Pacemaker neurons respond to visual system inputs for clock resetting, but, unlike other neurons, have not been reported to transmit rapid signals to their targets. Here we show that pacemaker neurons are required to mediate a rapid behavior. The Drosophila larval visual system, Bolwig's organ (BO), projects to larval pacemaker neurons to entrain their clock. BO also mediates larval photophobic behavior. We found that ablation or electrical silencing of larval pacemaker neurons abolished light avoidance. Thus, circadian pacemaker neurons receive input from BO not only to reset the clock but also to transmit rapid photophobic signals. Furthermore, as clock gene mutations also affect photophobicity, the pacemaker neurons modulate the sensitivity of larvae to light, generating a circadian rhythm in visual sensitivity.     

Is the Schwabe Organ a Retained Larval Eye? Anatomical and Behavioural Studies of a Novel Sense Organ in Adult Leptochiton asellus (Mollusca,Polyplacophora) Indicate Links to Larval Photoreceptors

The discovery of a sensory organ, the Schwabe organ, was recently reported as a unifying feature of chitons in the order Lepidopleurida. It is a patch of pigmented tissue located on the roof of the pallial cavity, beneath the velum on either side of the mouth. The epithelium is densely innervated and contains two types of potential sensory cells. As the function of the Schwabe organ remains unknown, we have taken a cross-disciplinary approach, using anatomical, histological and behavioural techniques to understand it. In general, the pigmentation that characterises this sensory structure gradually fades after death; however, one particular concentrated pigment dot persists. This dot is positionally homologous to the larval eye in chiton trochophores, found in the same neuroanatomical location, and furthermore the metamorphic migration of the larval eye is ventral in species known to possess Schwabe organs. Here we report the presence of a discrete subsurface epithelial structure in the region of the Schwabe organ in Leptochiton asellus that histologically resembles the chiton larval eye. Behavioural experiments demonstrate that Leptochiton asellus with intact Schwabe organs actively avoid an upwelling light source, while Leptochiton asellus with surgically ablated Schwabe organs and a control species lacking the organ (members of the other extant order, Chitonida) do not (Kruskal-Wallis, H = 24.82, df = 3, p < 0.0001). We propose that the Schwabe organ represents the adult expression of the chiton larval eye, being retained and elaborated in adult lepidopleurans.     

Postembryonic development of the olfactory and vomeronasal organs in the frog Rana chensinensis

We studied by light microscopy the histological development of the olfactory and vomeronasal organ in tadpoles of the Chinese forest frog, Rana chensinensis, from postembryonic periods to the end of metamorphosis. Unlike Bufo americanus, the olfactory epithelium in larval R. chensinensis is not divided into dorsal and ventral branches in the rostral and mid-nasal regions. The olfactory epithelium in the dorsal portion of the buccal cavity in larval R. chensinensis may correspond to the ventral olfactory epithelium of Bufo, which has been argued to provide a chemosensory function in the tadpoles analogous to the role of taste buds in adults. Bowman's glands were present in the olfactory epithelium of R. chensinensis only after the appearance of the forelimbs during metamorphosis. The appearance of Bowman's glands in the olfactory epithelium at this time suggests that the nose first begins to detect odorants in the air, and this is thus also a metamorphic event. The vomeronasal epithelium appeared a little earlier than the vomeronasal gland in R. chensinensis, unlike in toads (bufonids). This study supports Eisthen's hypothesis that the most recent common ancestor to the tetrapods was aquatic and once had a vomeronasal organ, and that this has been lost in various evolutionary lineages.     

Development of the nasal chemosensory organs in two terrestrial anurans: the directly developing frog, Eleutherodactylus coqui (Anura: Leptodactylidae), and the metamorphosing toad, Bufo americanus (Anura: Bufonidae)

Nearly all vertebrates possess an olfactory organ but the vomeronasal organ is a synapomorphy for tetrapods. Nevertheless, it has been lost in several groups of tetrapods, including aquatic and marine animals. The present study examines the development of the olfactory and vomeronasal organs in two terrestrial anurans that exhibit different developmental modes. This study compares the development of the olfactory and vomeronasal organs in metamorphic anurans that exhibit an aquatic larva (Bufo americanus) and directly developing anurans that have eliminated the tadpole (Eleutherodactylus coqui). The olfactory epithelium in larval B. americanus is divided into dorsal and ventral branches in the rostral and mid-nasal regions. The larval olfactory pattern in E. coqui has been eliminated. Ontogeny of the olfactory system in E. coqui embryos starts to vary substantially from the larval pattern around the time of operculum development, the temporal period when the larval stage is hypothesized to have been eliminated. The nasal anatomy of the two frogs does not appear morphologically similar until the late stages of embryogenesis in E. coqui and the terminal portion of metamorphosis in B. americanus. Both species and their respective developing offspring, aquatic tadpoles and terrestrial egg/embryos, possess a vomeronasal organ. The vomeronasal organ develops at mid-embryogenesis in E. coqui and during the middle of the larval period in B. americanus, which is relatively late for neobatrachians. Development of the vomeronasal organ in both frogs is linked to the developmental pattern of the olfactory system. This study supports the hypothesis that the most recent common ancestor of tetrapods possessed a vomeronasal organ and was aquatic, and that the vomeronasal organ was retained in the Amphibia, but lost in some other groups of tetrapods, including aquatic and marine animals.     

Ultrastructure of the Anterior End in Three Ontogenetic Stages of Nectonema munidae (Nematomorpha)

Abstract The structure of the anterior end of three ontogenetically successive stages of Nectonema munidae (Nematomorpha) is investigated by light and transmission electron microscopy. During development, an adult cuticle is formed under a larval cuticle, which is subsequently moulted. Only one moult can be documented for Nectonema. The brain has a main subpharyngeal portion and a weak suprapharyngeal commissure. It is circumpharyngeal only in early developmental stages, the dorsal commissure is reduced in the adult stage. Four giant cells and a cerebral cavity are adult features. Although the morphology of the giant cells is elucidated, their function remains unclear, but a sensory function is probable. A septum marks the posterior border of the anterior end and divides a cerebral cavity from a body cavity. A precursor of the septum is present in the first stage observed, but it lies next to the epidermis and does not separate a cerebral cavity. Cuticular structures in the pre-pharyngeal region of the early stages are interpreted as remnants of the larval boring organ. They are moulted together with the larval cuticle. The morphology of the pharynx and the anterior part of the intestine is shown.     

Development of the olfactory and vomeronasal organs in Discoglossus pictus (Discoglossidae,Anura)

Using histological techniques and computer‐aided three‐dimensional reconstructions of histological serial sections, we studied the development of the olfactory and vomeronasal organs in the discoglossid frog Discoglossus pictus. The olfactory epithelium in larval D. pictus represents one continuous unit of tissue not divided into two separate portions. However, a small pouch of olfactory epithelium (the “ventromedial diverticulum”) is embedded into the roof of the buccal cavity, anteromedial to the internal naris. The lateral appendix is present in D. pictus through the entire larval period and disappears during the onset of metamorphosis. The disappearance of the lateral appendix at this time suggests that it is a typical larval organ related to aquatic life. The vomeronasal organ develops during hindlimb development, which is comparatively late for anurans. The development of the vomeronasal organ in D. pictus follows the same general developmental pattern recognized for neobatrachians. As with most anurans, the vomeronasal glands appear later than the vomeronasal organ. After metamorphosis, the olfactory organ of adult D. pictus is composed of a series of three interconnected chambers: the cavum principale, cavum medium, and cavum inferius. We suggest that the ventromedial diverticulum at the anterior border of the internal naris of larval D. pictus might be homologous with the ventral olfactory epithelium of bufonids and with the similar diverticulum of Alytes. J. Morphol. 2013. © 2012 Wiley Periodicals, Inc.     

The morphology and ultrastructure of the peripheral olfactory organ in newly metamorphosed coral-dwelling gobies, Paragobiodon xanthosomus Bleeker (Gobiidae, Teleostei)

We examined the peripheral olfactory organ in newly metamorphosed coral-dwelling gobies, Paragobiodon xanthosomus (SL=5.8mm+/-0.8mm, N=15), by the aid of electron microscopy (scanning and transmission) and light microscopy. Two bilateral olfactory placodes were present in each fish. They were oval-shaped and located medio-ventrally, one in each of the olfactory chambers. Each placode had a continuous cover of cilia. The placode epithelium contained three different types of olfactory receptor neurons: ciliated, microvillous and crypt cells. The latter type was rare. Following a pelagic larval phase, P. xanthosomus settle to the reef and form an obligate association with one species of coral, Seriatopora hystrix. Their well-developed olfactory organs likely enable larvae of P. xanthosomus to detect chemical cues that assist in navigating towards and selecting appropriate coral habitat at settlement. Our findings support past studies showing that the peripheral olfactory organ develops early in coral reef fishes.     

The larval ant-organs of Thisbe irenea (Lepidoptera: Riodinidae) and their effects upon attending ants

Observations and experiments are presented on the use oflarval ant-organs by the riodinid butterfly Thisbe irenea with emphasis on their function in myrmecophily. The results indicate that each ant organ plays a distinct role in larval-ant association and that all influence the behaviour of attending ants. Interpretations of the roles that lycaenid larval organs play in ant associations are evaluated and discussed in light of myrmecophilous riodinids. Finally, an 'enticement and binding' process, involving the concerted use of the larval organs, is proposed as the behavioural mechanism that T. irenea and other riodinid larvae use to secure the attentions of individual ants for extended periods of time.     

Organization of the Nervous System and Sensory Organs in the Larva of the Marine Bryozoan Bowerbankia gracilis (Ctenostomata: Vesiculariidae): Functional Significance of the Apical Disc and Pyriform Organ

The organization of the nervous system and the histology and ultrastructure of the apical disc and the pyriform organ have been investigated by serial sections with light and electron microscopy for the larva of the vesiculariid ctenostome bryozoan Bowerbankia gracilis Leidy 1855. The nervous system consists of four major internal components: (1) a median-anterior nerve nodule; (2) an equatorial, subcoronal nerve ring; (3) paired aboral nerve cords; (4) paired antero-lateral nerve tracts. The nervous system is associated with the ciliated larval surface at the apical disc, the pyriform organ, the corona and the intercoronal cells. The paired aboral nerve cords extend from the apical disc to the nerve nodule, which gives rise to the paired antero-lateral nerve tracts to the pyriform organ and to paired lateral tracts that form the equatorial nerve ring. Ultrastructural evidence is provided for the designation of primary sensory cells in the neural plate of the apical disc and in the juxtapapillary regions of the pyriform organ. Efferent synapses are described between the equatorial nerve ring and the overlying coronal cells, which constitute the primary locomotory organ of the larva. The repertoire of potential functions of the apical disc and pyriform organ are discussed. It is concluded that the apical disc and pyriform organ constitute larval sensory organs involved in orientation and substrate selection, respectively. Their association with the major effector organs of the larva (the corona and the musculature) via the nervous system supports this interpretation.     

In vitro studies of hematopoiesis in the silkworm: cell proliferation in and hemocyte discharge from the hematopoietic organ

The lepidopteran hematopoietic process is poorly understood. We therefore examined the fundamental properties of hematopoiesis in the silkworm Bombyx mori using hematopoietic organ culture. In a medium containing larval plasma taken from the fourth day of the final larval stadium, over 50,000 hemocytes per hematopoietic organ were discharged within 48 h, with the number of cells comprising the hematopoietic organ simultaneously increasing from approximately 20,000 to 40,000. However, in the absence of plasma, cell numbers comprising the hematopoietic organ were unchanged and the number of discharged cells was much less. Hematopoietic organs cultured with plasma showed strong mitotic indices in a BrdU incorporation assay, but did not when cultured without plasma, indicating that plasma contains hematopoietic factor(s). The hematopoietic stimulation ability of larval plasma was observed from the last day of the penultimate larval stadium to the prepupal stage. The response of the hematopoietic organs to larval plasma was highest at the beginning of the final larval stadium and decreased with aging. Most cells discharged from the hematopoietic organ were plasmatocytes and prohemocytes, irrespective of location and developmental stage. Using this in vitro culture method, we tested the effects of 20-hydroxyecdysone (20E) and juvenile hormone-I (JH-I) on B. mori hematopoiesis. 20E showed a weak, but significant, hematopoietic activity, whereas JH-I did not, suggesting that a part of larval hematopoiesis is endocrinally regulated.     

The specification of sensory neuron identity in Drosophila

Different types of sense organs are present on the larva of Drosophila. Several genes that specify the type of sense organ that will form at a particular position have been recently identified. Here we review the functional and molecular analyses of these genes, and summarize the evidence which supports a role in the choice of which type of organ will be formed. Most or all of these genes are required for the appropriate specification of adult as well as larval sense organs, suggesting that the larval and adult systems share many gene requirements. Interestingly, the specifying genes identified so far in the peripheral nervous system are also expressed in subsets of cells in the central nervous system, where they might have similar roles.     

Photoreception in pineal organs of larval and adult lampreys,Lampetra japonica

A comparative study of the larval and adult pineal organs, which are sensitive to incident light, was carried out in the river lamprey Lampetra japonica, using intracellular recording from the pineal photoreceptors. The tissue overlying the larval pineal organ is transparent, whereas that over the adult pineal is translucent. The optical density of this oval pineal window in the adult lamprey was 1.2. In order to elucidate the early development of the larval pineal, the ratio r of the diameter (micron) of the pineal to the body-length (cm) was measured. The value of r was 62.5 in a small larva of 2.8 cm, 29.7 in a larger one of 14.3 cm, and 9.3 in an adult of 54 cm body-length. The intracellular response to light of the larval pineal was a hyperpolarization, showing fundamentally the same pattern as that of the adult pineal. It was possible to record a typical response even from the pineal of the smallest larva, 2.8 cm in body length, used in this study. The intensity-amplitude relationship was analysed after Naka-Rushton's hyperbolic equation. The value of sigma of isolated larval pineals was 0.88 log unit higher than that of adults. The value of n was larger in larvae, suggesting a sensitive reaction to changing photic stimulus. The spectral sensitivity was compared. The peak was at 505 nm in the larva, but 525 nm in the adult. A change of visual pigment in the pineal during metamorphosis is suggested.     

Olfactory metamorphosis in the coastal tailed frog Ascaphus truei (Amphibia,Anura, Leiopelmatidae)

The structure of the olfactory organ in larvae and adults of the basal anuran Ascaphus truei was examined using light micrography, electron micrography, and resin casts of the nasal cavity. The larval olfactory organ consists of nonsensory anterior and posterior nasal tubes connected to a large, main olfactory cavity containing olfactory epithelium; the vomeronasal organ is a ventrolateral diverticulum of this cavity. A small patch of olfactory epithelium (the “epithelial band”) also is present in the preoral buccal cavity, anterolateral to the choana. The main olfactory epithelium and epithelial band have both microvillar and ciliated receptor cells, and both microvillar and ciliated supporting cells. The epithelial band also contains secretory ciliated supporting cells. The vomeronasal epithelium contains only microvillar receptor cells. After metamorphosis, the adult olfactory organ is divided into the three typical anuran olfactory chambers: the principal, middle, and inferior cavities. The anterior part of the principal cavity contains a “larval type” epithelium that has both microvillar and ciliated receptor cells and both microvillar and ciliated supporting cells, whereas the posterior part is lined with an “adult‐type” epithelium that has only ciliated receptor cells and microvillar supporting cells. The middle cavity is nonsensory. The vomeronasal epithelium of the inferior cavity resembles that of larvae but is distinguished by a novel type of microvillar cell. The presence of two distinct types of olfactory epithelium in the principal cavity of adult A. truei is unique among previously described anuran olfactory organs. A comparative review suggests that the anterior olfactory epithelium is homologous with the “recessus olfactorius” of other anurans and with the accessory nasal cavity of pipids and functions to detect water‐borne odorants. J. Morphol. 2011. © 2011 Wiley Periodicals, Inc.