In vivo inhibition of vitellogenesis in the Dermapteran Labidura riparia by 20-hydroxyecdysone

In previous studies we have described the existence of cyclical changes in ecdysteroid levels during the female reproductive life of the earwig Labidura riparia. High levels of ecdysteroids are observed at the end of each vitellogenic period just before follicle degeneration, in coincidence with the beginning of each non-vitellogenic period. In the present work, using in vivo [(35)S]methionine incorporation, electrophoresis and electron microscopy, we study the effects on fat body and ovaries of 20-hydroxyecdysone (20E) injections into young vitellogenic females. This resulted in a reduction of proteosynthetic organelles (scarce Golgi complexes and fragmented RER cisternae), inhibition of vitellogenin synthesis in adipocytes, vitellogenesis arrest and premature follicular atresy. All these effects are suppressed when juvenile hormone treatment is associated with 20E injections. 20E does not inhibit vitellogenesis when applied to pars lateralis deprived females, which display continuous vitellogenesis. Thus, 20E does not act directly on ovaries nor on corpus allatum: the presence of the pars lateralis cells is required for 20E to inhibit vitellogenesis. These findings are explained in terms of the existence of a 20E feed back loop. This hormone acts via lateral neurosecretory cells of the brain which probably have an allatostatic effect.     

Ecdysone during ovarian development in Locusta migratoria

Considerable amounts of ecdysteroids are produced during each ovarian cycle in adult females of Locusta when vitellogenesis is almost completed. The hormonal molecules are synthesized at the end of the maturation of the terminal oöcytes during each cycle, at the time when vitellogenesis is almost completed. No synthesis takes place in the absence of ovarian development (allatectomy, ovariectomy), whereas extirpation of the prothoracic glands at the beginning of adult life does not affect ecdysteroid production. More than 95% of the total ecdysteroid content of female adults can be recovered from the ovaries. In vitro studies show that the ovaries produce ecdysteroids and convert labelled cholesterol into ecdysone. Microsurgical experiments indicate that this synthesis takes place in the follicle cells surrounding the oöcyte. The newly synthesized ecdysteroids do not enter massively into the blood, but pass into the oöplasm where they are progressively converted to polar compounds; as a result, at the end of each ovarian cycle, egg-laying corresponds to the disappearance of ecdysteroids from the female insects, the hormonal molecules can easily be recovered from the eggs. A gas chromatographic analysis coupled to mass spectrometry shows that the principal ecdysteroid synthesized by the adult females of Locusta is by far ecdysone. Ecdysterone, the paramount ecdysteroid of the larvae of Locusta, is not present in noticeable amounts in the female adult of this species.     

The hypothalamo-hypophysial system in acipenseridae

Summary The percentage of peptidergic (A₁ and A₂) and adrenergic (B) neurosecretory terminals was studied in the neurohypophysis of sexually mature female sturgeons. Neurosecretory terminals of the A₂ type prevail in the neurohypophysis, whereas A₁ and B terminals are rare. The activity of these types of terminals was established (1) during upstream migration, (2) shortly after spawning, and (3) three to six weeks after spawning. Terminals of B type are the most active elements during all the periods studied. These elements become strongly activated in sturgeons during upstream migration, i.e., earlier than the peptidergic neurosecretory terminals. Peptidergic terminals, especially elements of type A₂, become synchronously and strongly activated in fish shortly after spawning. In the late postspawning period neurosecretory terminals of all three types become synchronously inactive, persisting in a quiescent state in comparison to the two previous periods. The appearance of neurosecretory material discharged into the intercellular clefts by exocytosis correlates on the whole with the activity level of the A₁ and A₂ terminals in each individual studied. A functional correlation exists between the activity of the peptidergic and adrenergic neurosecretory terminals in the neurohypophysis. The data obtained are discussed with reference to a concept regarding spawning in some fish species as a physiological stress (Polenov et al., 1976). A possible dual control (peptide and monoamine neurohormones) over the function of visceral organs and glandular cells of the intermediate lobe of the hypophysis is also suggested (Polenov, 1970, 1975, 1978; Polenov and Belenky, 1973).Dedicated to the memory of Professor Wolfgang Bargmann, a great scientist and a generous friend     

Effects of electrocoagulation of cerebral neurosecretory cells and implantation of corpora allata on oöcyte development in Locusta migratoria

The implantation of active corpora allata into intact Locusta females during growth accelerates pre-vitellogenic oöcyte growth and vitellogenesis. Localised stimulation of yolk deposition follows the implantation of active corpora allata between the ovarioles demonstrating a gonadotrophic rôle for the corpus allatum hormone. Electrocoagulation of the median neurosecretory cells of the brain prevents vitellogenesis whilst pre-vitellogenic oöcyte growth occurs normally. Implantation of active corpora allata into females with ablated cerebral neurosecretory cells promotes vitellogenesis in a proportion of test animals although mature oöcytes are never produced.It is suggested that the rôle of the median neurosecretory cells during egg development in Locusta is primarily concerned with the activation and maintenance of activity of the corpora allata. The corpus allatum hormone acts both metabolically and gonadotrophically.     

Ultrastructure of retrocerebral complex of the earwig, Euborellia annulipes, and rôle of aorta as a neurohaemal organ

The ultrastructure of the retrocerebral endocrine-aortal complex of the earwig, Euborellia annulipes has been studied. The space between the inner and outer stromal layers of the aorta is occupied by numerous axon terminals and pre-terminals containing large electron dense granules (NS-I) of approximately 100 to 220 nm and a few axon terminals having small granules (NS-II) of approximately 40 to 90 nm; the former appear to belong to medial neurosecretory A-cells, and the latter to the B-cells of the brain. The corpora cardiaca consist of intrinsic cells with mitochondria and multivesicular bodies. Granules of type NS-II and NS-III are observed in the axon terminals and pre-terminals in the corpora cardiaca. The NS-II are identical to those found in the aorta and are probably the secretions of the lateral B-cells. Granules of type NS-III are 40 to 120 nm and electron dense, and are intrinsic in origin. Similar granules occur in the intrinsic cells of the corpora cardiaca. E M studies have confirmed the rôle of the aorta as a neurohaemal organ for the medial neurosecretory cells, and the corpora cardiaca for the lateral neurosecretory cells of the brain. The corpora cardiaca also act as a reservoir for the intrinsic secretion. The corpus allatum is a solid body consisting of parenchymal cells with prominent nuclei, mitochondria, and endoplasmic reticulum. In between its cells are occasional glial cells and also neurosecretory as well as non-neurosecretory axons. The gland is devoid of A-cell NSM.     

The role of adipokinetic hormone in the control of vitellogenesis in locusts

Vitellogenesis in locusts is synchronized with the cyclic maturation of oocytes. Vitellogenesis by excised fat body of gravid females is differentially inhibited 80–90% when locust adipokinetic hormone I (AKH-I) is added to the incubation media. Hemolymph methanolic extracts completely inhibit fat body protein synthesis in vitro when the donor females are at the end of the ovarian cycle (6 mm stage), but not when taken from earlier stages. Hemolymph methanolic extracts from vitellogenic females at the 6 mm stage are separated by HPLC into three distinct inhibitors of protein synthesis, one of which is AKH-I. AKH-RIA of hemolymph during the first ovarian cycle reveals no AKH-I during active vitellogenesis, but a marked increase to about 5 ng per female at the end of egg maturation. A development of responsiveness to AKH-I is evident in female fat body as vitellogenesis proceeds. AKH-I is involved in the negative control of vitellogenesis.     

Age-dependent neurosecretion release induced by dopamine in the corpora cardiaca of Blattella germanica (L.) (Dictyoptera : Blattellidae)

In addition to glial cells, intrinsic glandular cells and ordinary axons, the corpora cardiaca of Blattella germanica (L.) (Dictyoptera : Blattellidae) contain 4 types of neurosecretory fibers originating from the brain (types 1, 2, 3, and 4), which can be recognized on the basis of the size, form, and electron density of their neurosecretory granules. A comparative ultrastructural study of the corpora cardiaca from normal females and from dopamine-treated (1 μg) females has been carried out at different stages within the first ovarian cycle (freshly emerged: day 0; 2-day-old: pre-vitellogenesis; 4-day-old: beginning of vitellogenesis; 6-day-old: full vitellogenesis; 8-day-old: post-vitellogenesis, period of ootheca transport). Quantitative data on the exocytotic configurations observed in each type of fiber (1–4) have led to the following conclusions: (a) the exocytotic configurations in control specimens are too infrequent to prompt any inference about the dynamics of neurosecretion release in the different types of fibers; (b) dopamine treatment induces a stimulation of the exocytotis phenomenon, whose extent depends on the specimen age and on the type of fiber. Therefore, on days 2 and 6, dopamine: preferentially stimulates neurosecretion release in the fibers of types 3 and 4 respectively.     

Effect of extirpation of median neurosecretory cells on reproduction in the female red cotton bug, Dysdercus cingulatus

Extirpation of the cerebral neurosecretory cells of the pars intercerebralis of the red cotton bug, Dysdercus cingulatus, does not prevent maturation of the first batch of eggs in the female. However, vitellogenesis is visibly inhibited by the operation. There is considerable individual variation in the degree of inhibition of vitellogenesis in experimental animals. But in these experimental animals ovaries are shorter, their oöcytes smaller, the number of oöcytes undergoing vitellogenesis fewer: also the follicle cells and their nuclei are smaller. On the contrary, the protein concentration in the blood of experimental animals is higher but is subject to considerable variation and it appears to have no significance. It is concluded that the median neurosecretory cells stimulate vitellogenesis in this animal to a considerable extent.     

Distribution of tachykinin-related neuropeptide in the developing central nervous system of the moth Spodoptera litura

Neuropeptides with similarities to vertebrate tachykinins, designated tachykinin-related peptides (TRPs), have been identified in several insect species. In this investigation we have utilized an antiserum raised to one of the locust TRPs, locustatachykinin-I (LomTK-I), to determine the distribution pattern of LomTK-like immunoreactive (LTKLI) neurons in the developing nervous system of the moth Spodoptera litura. A number of LTKLI neurons could be followed from the larval to the adult nervous system: a set of median neurosecretory cells (MNCs) in the brain, a pair of brain descending neurons and a few sets on neurons in the ventral nerve cord. The distribution of LTKLI neurons in the adult brain is very similar to that seen in other insect species with prominent arborizations in the central body, antennal lobes, mushroom body calyces, optic lobe neuropils and other distinct neuropil areas in the protocerebrum and tritocerebrum. A new finding is the presence of LTKLI neurosecretory cells with axon terminals in the anterior aorta and corpora cardiaca, suggesting for the first time a neurohormonal role of tachykinin-related peptide(s) in insects. During postembryonic development the number of LTKLI neurons in the ventral nerve cord decreases somewhat, whereas the number increases in the brain. Thus the functional roles of TRPs may change to some extent during development.     

Neurosecretory system of the earwig Labedura riparia, and the rôle of the aorta as a neurohaemal organ

The neurosecretory system of Labedura riparia has been described from sections and whole mounts using a variety of techniques. The pars intercerebralis contains two clusters of medial neurosecretory cells (MNC), each cluster consisting of 8 to 10 A-cells and occasional B-cells. The lateral sides of the brain have a few B-cells. The axons of the median neurosecretory cells terminate in the cephalic aorta (AO), whereas the axons of the lateral neurosecretory cells (LNC) terminate in the corpora cardiaca (CC). It appears that the neurosecretory material (NSM) elaborated in the MNC is stored in the cephalic aorta and that elaborated in the LNC is stored in the corpora cardiaca, which are two oval or elongate bodies composed of large chromophobe and small chromophil cells. Posteriorly there is the oval or elongate corpus allatum (CA) attached to the CC by thick nerves. The CA consists of one cell type only. Both CC and CA contain no A-cell neurosecretory material. It has been suggested that the neurosecretory system of L. riparia is composed of two complexes. One is formed by the medial neurosecretory cells for which the aorta functions as a neurohaemal organ, and the other is formed by lateral neurosecretory cells-lateral neurosecretory pathways-nervi corporis cardiaci-II in which the corpora cardiaca function as a neurohaemal organ.     

Activité des corpora allata et contrôle photopériodique de la maturation ovarienne chez Locusta migratoria

Locusta migratoria migratoria females of the ‘Kazalinsk’ strain show a sustained inhibition of ovarian maturation when submitted to long-day photoperiodic conditions ($\text{17}\text{hr}\text{24}\text{hr}$). A full ovarian cycle can be initiated at any time throughout adult life by implantation of corpora allata (CA) taken from egg-laying females. Therefore, in inhibited females, the gonadotropic activity of the CA fail to allow normal vitellogenesis. However, if such females receive CA taken from females conditioned in the same way, a full ovarian cycle still occurs. If CA taken from 5-week-old, either mature or immature, females are implanted into 5-day-old females reared without males under long-day lighting, a single ovarian cycle results, no matter what the state of the donor females. The possibility is discussed that in L. migratoria females neurosecretory material may be involved in the functional development of adult CA, whereas the gonadotropic hormone is released from the CA under nervous control, as far as a photoperiod-sensitive strain is concerned.     

Oviposition in Triatoma protracta: Role of mating and relationship to egg growth

Yolk deposition begins in the terminal oocytes of virgins of Triatoma protracta a few days after adult eclosion, and while a few eggs may be matured before vitellogenesis ceases, none are laid. Mating at day four stimulates egg maturation and oviposition in fed and unfed females, egg-laying beginning as early as nine days after eclosion. If mating is delayed until day 16, by which time vitellogenesis normally has ceased, stored eggs are laid within two to four days and yolk deposition is resumed. Removal of the brain prevents oviposition, as does the severance of the ventral nerve cord. Thus, an intact central nervous system is required for egg-laying. Also, since neither operation inhibits egg maturation or ovulation, it appears that the latter reproductive responses to mating are independent of oviposition.     

Localization and physiological effects of RFamides in the corpora allata of the cockroach Diploptera punctata in relation to allatostatins

The distribution of FMRFamide immunoreactivity in the brain-retrocerebral complex of adult female Diploptera punctata was examined. Immunoreactivity was observed in the brain and corpus allatum as well as in the corpus cardiacum. Immunoreactivity co-localized with allatostatin immunoreactivity within several lateral neurosecretory cells of the brain and in their endings within the corpus allatum. By in vitro radiochemical assay of juvenile hormone release, the effect of two native D. punctata RFamides, an FLRFamide (Leucomyosuppressin) and an FIRFamide were examined. The latter, for which the sequence (SKPANFIRFamide) is reported here, stimulated juvenile hormone release but acted only on corpora allata from females at the end of vitellogenesis (day 6). The interaction of these two RFamides and three D. punctata allatostatins, Dippu-AST 2, 5, and 7 were similarly examined. Only Dippu-AST 2 stimulated release of RFamides from the corpora allata and only on day 6 whereas both RFamides were able to attenuate the inhibitory activity of Dippu-AST 2.     

Exo-endocytosis in isolated peptidergic nerve terminals occurs in the sub-second range

Exo- and endocytotic processes induced by depolarization of isolated neurosecretory nerve terminals show a close temporal correlation, which suggests a short time of integration of the neurosecretory granule membrane with the plasma membrane. In order to determine minimal time requirements for exocytosis-coupled endocytosis to occur, we have analyzed by electron microscopy uptake of horserdish peroxidase (HRP) as a fluid phase marker at the onset of depolarization. We have applied rapid mixing and sampling (quenched flow) to assess events in subsecond time peroids after stimulation. A significant number of labelled endocytotic vacuoles was observed during the first second of depolarization. This number then further increased by a factor of about 2 (within 5 s) and 4 (within 50s). Thus, as for exocytosis, the rate of endocytosis decreased considerably during prolonged stimulation. These data indicate i) that a substantial proportion of secretory granules undergoes exocytosis very shortly after stimulation, and ii) that, following exocytosis, the minimal time required for consecutive membrane retrieval is in the sub-second range.     

二点委夜蛾卵巢发育分级及在预测预报中的应用

对室内饲养的二点委夜蛾Athelis lepigone(Moschler)雌成虫分时段进行解剖,观察其卵巢的结构及发育进程。结果显示二点委夜蛾具有1对卵巢,各由4个卵巢小管组成。发育进程可分为5个阶段:透明期、卵黄沉积期、成熟待产期、产卵盛期和产卵末期。河北省石家庄地区2011年7月下旬至8月上旬田间卵巢发育的监测结果显示,Ⅰ级卵巢在整个发生期所占比例较高,Ⅳ级卵巢所占比例较低,推测其下一代幼虫的发生量将较低,并与田间调查结果吻合,因此卵巢解剖分级法可以用于二点委夜蛾的预测预报工作。     

A neurosecretory hormone-releasing factor from ovaries of mosquitoes fed blood

In mosquitoes, a hormone (egg development neurosecretory hormone or EDNH), produced by the medial neurosecretory cells and stored in the corpus cardiacum soon after eclosion, is released after a blood meal, and vitellogenesis begins a few hours later. When either the ovaries or the neurosecretory cells and corpus cardiacum are removed before the blood meal, vitellogenin is not synthesized. Therefore, we tested the hypothesis that the release of EDNH from the corpus cardiacum is dependent on the secretion of a releasing factor from the ovaries.Using a bioassay for EDNH in the corpus cardiacum, we found that the gland of an ovariectomized female remained active after blood feeding, and therefore, has not released EDNH. When an ovary was implanted before the blood meal, the corpus cardiacum was inactive, and therefore, had released EDNH. We concluded that the ovaries secrete an EDNH-releasing factor, and that this factor and EDNH must both be in circulation before vitellogenesis can begin. Although releasing factor alone did not stimulate vitellogenesis, it was the rate limiting process that controlled the onset of vitellogenesis.Using a bioassay for the EDNH-releasing factor from the ovaries and using rocket-immuno-electrophoresis, we showed that a Culex ovary, but not an Anopheles ovary, could replaces Aedes ovaries as a source of the releasing factor.In Ae. aegypti, EDNH-releasing factor was required again after oviposition in order to reinitiate the vitellogenic process in females that took a second blood meal. Thus, the releasing factor is part of the mechanism regulating cyclic egg maturation in mosquitoes.     

Juvenile hormone-like substances can induce vitellogenesis in the tick Ornithodoros moubata (Acarina: Argasidae)

Topical application of different juvenile hormone analogs (JHA) or of a mixture of stereoisomers of insect juvenile hormone (JH) 1 and 3 to fed virgin female Ornithodoros moubata immediately after feeding induced vitellogenesis and egg-laying in up to 70% of treated females. In controls only 13.7% oviposited. The eggs were sterile, with abnormal shape, but their number versus the weight of engorged females was normal or sometimes greater than in mated females. However, preoviposition period was longer than in mated females.

It was more difficult to induce egg-laying by similar topical applications 100 days after feeding of virgin females. A maximum of 58% of ovipositing females was obtained with a very high dosage of JH mixture (500 fig). Injection of this mixture into the females was more potent; 15 to 50 fig induced oviposition in about 60% of the females. The preoviposition period was also longer than in control females.

Our results suggest the presence of a JH-like substance which is involved in the hormonal control of vitellogenesis. However, since natural isomers of JH were much less efficient than isomeric mixtures or JHA, we suppose that the natural tick hormone does not correspond to JH, but rather to a JH-like substance.     

Endocrine control of vitellogenesis in the harlequin bug, Dindymus versicolor

An active corpus allatum is essential for the maturation of eggs in the harlequin bug, Dindymus versicolor. The corpus allatum of virgin females remains virtually inactive and the oöcytes are resorbed once they have grown to the stage at which they become competent to incorporate yolk. Mating provides a stimulus which is essential for the initiation and maintenance of corpus allatum activity and, therefore, vitellogenesis. Corpus allatum activity (and vitellogenesis) can be induced in virgin females either by cutting the allatic nerves or by excision of a certain part of the protocerebrum. It is concluded that the corpus allatum of virgin females is inhibited nervously by the brain and that copulation provides a nervous stimulus which lifts this cerebral inhibition thereby permitting allatum activity.The median neurosecretory cells are not essential for vitellogenesis in Dindymus; however, it is suggested that they are necessary for maximum allatum activity. Evidence is provided to show that the growth and maintenance of the previtellogenic oöcytes are also under the control of the corpus allatum. A mechanism is described whereby the number of vitellogenic oöcytes in the ovarioles is maintained constant.     

Cytophysiological study of neurosecretory and pheromonal influences on sexual development in Ophryotrocha puerilis (Polychaeta,Dorvilleidae)

Summary

Prominent secretory nerve endings are found at the posterior margin of the supraesophageal ganglion in the protandric polychaete, Ophryotrocha puerilis. Solitary juveniles developing as primary males, and then as females, accumulate neurosecretory material in the nerve endings which thereby swell and become filled with granules. Females maintained in mass culture have similar terminals, whereas in secondary males (males which had been females before), these axon terminals are very small and contain no material. When such males are isolated, they accumulate neurosecretory material within the nerve endings and become females. When formerly isolated females are put together, their stores of neurosecretory material are rapidly discharged. Subsequently they lay egg masses and switch to the male state. These effects are mediated by a pheromone released during social contact of formerly isolated females. The complexity of the relationship between neurosecretory activity and sexual state is indicated by the situation in animals maintained in pairs, when both male and female partners have swollen nerve endings packed with secretory material.