Système endocrine et physiologie de la diapause imaginale chez le criquet égyptien, Anacridium aegyptium

The Egyptian locust, Anacridium aegyptium, has four protocerebral neurosecretory centres: the A to B neurosecretory cells of the pars intercerebralis (the A cells are rich in fuchsinophil material and the B cells are devoid of fuchsinophil neurosecretion), the voluminous C neurosecretory cells poor in neurosecretion, and the median sub-ocellar neurosecretory cells.From September to the beginning of January, imaginal diapause is characterized by an accumulation of the median neurosecretion in the pars intercerebralis-corpora cardiaca system, by small corpora allata, and, in the female, by a stop in oöcyte development although the male's sexual activity is still not altered. Allatectomy suppresses neither the male's sexual behaviour nor its fecundity. From January, the increase of the photoperiod causes a release of the median neurosecretion in both sexes, an increase of the volume of the corpora allata, and breaks ovarian diapause.In autumn, the implantation of the male's or female's corpora allata of Anacridium does not stimulate ovarian growth of diapausing females. On the contrary, the implantation of corpora allata or of pars intercerebralis or of corpora cardiaca of Locusta migratoria migratorioides (locust without diapause) causes ovarian development of the diapausing females of Anacridium. Thus, in the two sexes of the Egyptian locust, the corpora allata are inactive during the female ovarian diapause. The imaginal diapause of Anacridium affects both sexes (stocking of median neurosecretion, arrest of the corpora allata). If diapause does not seem to affect the male's development, it is because its sexual activity is free from the pars intercerebralis and corpora allata.The corpora allata of Anacridium show a sexual dimorphism in the active adult: they are smaller in the male and have more mitosis in the female. An explanation of this dimorphism is advanced.     

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.     

Rupture de la diapause ovarienne d'Anacridium aegyptium par stimulation électrique des cellules neurosécrétrices médianes de la pars intercerebralis

Oögenesis and the physiological activity of the corpora allata were studied in adult females of the Egyptian locust (Anacridium aegyptium), in ovarian diapause, after electrical stimulation in vivo of the pars intercerebralis. This stimulation provokes (1) a decrease in the quantity of fuchsinophilic material present in the median neurosecretory cell bodies and in the internal cardiac tract, (2) an increase in the physiological activity of the corpora allata (measured by its chromatropic effect on larvae of Locusta), and (3) rupture of the ovarian diapause (advance of maturation of the oöcytes and oviposition by 5 months, and initiation of the ovarian cycle).In the control animals, the same electrical stimulations of various regions of the central nervous system (tritocerebrum, first ganglion of the abdominal cord) have no effect on these phenomena.In allatectomized females, electrical stimulations of the pars intercerebralis are followed by a slight growth of oöcytes, without a deposit of yellow vitellus. The diapause is not broken. Section of the allatocardiac nerves or rupture of the allatocardiac and allato-suboesophageal nervous connexions do not change the physiological state of the corpora allata. In the case of females in which the corpora allata have been disconnected, electrical stimulations of the pars intercerebralis succeed in activating the corpora allata and breaking the ovarian diapause. The aggregate of these results confirms that in locusts the control of the brain over the physiological activity of the corpora allata is above all neuroendocrine.     

L'action exercée par l'appareil endocrine sur les phases tardives de l'ovogenèse chez Locusta migratoria

Most studies dealing with the endocrine control of oogenesis are focused on vitellogenesis, but the later events of oogenesis: vitelline membrane formation and choriogenesis have received less atention. In Locusta migratoria, the corpora allata evidently control vitellogenesis, but seem to have no bearing upon the formation of the vitelline membrane or the chorion. If the insects are deprived of their CA at the time when the oocyte length is around 3.5 to 4 mm, (normal length at egg laying: 6.5 mm) vitelline membrane formation and the chorion production are unaffected. In the same species, the electrocoagulation of the pars intercerebralis or excision of corpora cardiaca disturb oogenesis; vitelline membrane material is synthesized and secreted, but the primary granules fail to join each other and to transform into vitelline membrane and the production of chorionic material is disturbed.The rER of the follicle cell seems quite active but the substance elaborated accumulates in the Golgi saccules, and therefore the cytoplasm contains only very few secretory granules. The implantation of supernumerary pars intercerebralis and corpora cardiaca into immature females induces precocious deposition of the vitelline membrane which is complete in 5.0 mm oocytes (instead of 5.6 to 6.0 mm) and chorion formation is completed in 5.5 mm oocytes (instead of 6.0 to 6.3 mm). Ecdysone is secreted in the ovaries at the end of oogenesis. We tested the result of injecting ecdysone to immature females. It results in hastening oocyte growth during 24 hr, but this accelerated growth is followed by degeneration.     

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.     

Moulting and ecdysone release in response to electrical stimulation of protocerebral neurosecretory cells in Locusta migratoria

Locusta migratoria larvae were submitted to electrical stimulation of the protocerebral neurosecretory cells (median neurosecretory cells of the pars intercerebralis and lateral neurosecretory cells), during the last larval instar. The effects of the treatment were observed both on the duration of the stage and on the variations in haemolymph ecdysone levels. In untreated larvae, there was an initial ecdysone peak at the beginning of day 5, which was followed by 4 larger peaks between days 6 and 8. Stimulation of the median neurosecretory cells at the beginning of the instar resulted in the formation of one very large hormonal peak at the end of day 3: a day and a half earlier than in the control groups. Moulting was likewise accelerated. Stimulation also increased the size of the peaks, as compared with the controls. Stimulation of the lateral neurosecretory cells had a weaker ecdysiotropic effect; neither the number nor the size of the peaks were changed, though, like ecdysis, they occurred earlier. Stimulation of the deutocerebrum had no effect on either ecdysone titres or moulting. Electrical stimulation of the median neurosecretory cells at the end of day 5, that is after the occurrence of the first ecdysone peak, shortened the larval stage while having no significant effect on ecdysone levels in the haemolymph. The neuroendocrine control of ecdysis in Locusta is discussed.     

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.     

Restricted occurrence of Locusta migratoria ovary maturing parsin in the brain-corpora cardiaca complex of various insect species

Ovary maturing parsin (OMP) is a gonadotrophic molecule previously isolated from the neurosecretory lobes of the corpora cardiaca of Locusta migratoria (acridian Orthoptera). A polyclonal antiserum directed against the two biologically active domains of the L. migratoria (Lom) OMP was used to investigate the occurrence of Lom OMP-like substances in brain-corpora cardiaca complexes of other insect species. Using immunohistochemistry, specimens of 40 different insect species belonging to 13 insect orders were tested. The Lom OMP-like substance was strictly limited to specimens of insect species belonging to the Acridae. It occurred in non-basophilic cells of the pars intercerebralis that project to the corpora cardiaca, as in Locusta. Although the antiserum only detected Lom OMP-like material in the Acridae, it is possible that related molecules exist in other insects. The antiserum may be very specific for domains of the Lom OMP molecule that have not been highly conserved during evolution or possibly these domains are not accessible to the antiserum in other insects.     

Intervention des cellules neurosecretrices medianes dans la castration parasitaire d'Anacridium aegyptium (Orthoptère)

The median neurosecretory cells (M-NSC) of Anacridium aegyptium were studied by light and electron microscopy during the ovarian diapause (autumn and winter) and the ovarian activity (spring) in normal females and in females infected by a tachinid fly Metacemyia calloti. In spring, the M-NSC contain comparatively much stainable material in normal females than in parasitized ones. This difference results from the ovarian maturity of normal females and the ovarian immaturity of parasitized females.The activity of the M-NSC was assessed in spring using the evolution of the radioactivity of the pars intercerebralis (PI) and corpora cardiaca (CC) after injection of ³⁵S-cysteine. The activity of the M-NSC is impaired in the parasitized females without ovarian development.The ovarian diapause was broken by massive implantations of corpora allata (CA) or electrical stimulations of the PI. Implantations of CA induce in parasitized females the same state of ovarian development than during natural activity in spring. Electrical stimulations of the PI. which increase the activity of the M-NSC. enhance the ovarian development of the parasitized females. A hypoactivity of the M-NSC is involved in the ‘castration’ of the Egyptian grasshopper.     

Early immunohistochemical detection of somatostatin-like and methionine-enkephablin-like neuropeptides in the brain of the migratory locust embryo

The two groups of neurosecretory cells producing neuropeptides related to somatostatin (SRIF) and methionine-enkephalin (met-enkephalin), previously high-lighted in the brain of adult migratory locusts, were detected by immunofluorescent techniques during the embryonic development of these insects. The earliest detection of these neurosecretory products occurred firstly in the terminal arborizations, then in the fibres, and finally in the perikarya. SRIF-like material is present in the corpora cardiaca already four days before hatching, i.e. at two-thirds of embryonic life, whereas immunoreactivity can be detected only after hatching in the perikarya located in the pars intercerebralis. The synthesis of met-enkephalin-like neuropeptide starts in the four cells of this system at least two days before hatching as shown by the immunofluorescence in the terminal arborizations along the tractus I to the corpora cardiaca. SRIF-like and met-enkephalin-like neurosecretory products are synthesized and carried to their release areas whilst the formation of brain structures and of the corpora cardiaca has not yet been completed.     

ACTIVATION OF THE CORPORA ALLATA IN RELATION TO OVARIAN MATURATION IN THE SEASONAL FORMS OF THE BUTTERFLY, POLYGONIA C-AUREUM L.

In Polygonia c-aureum , there are two seasonal forms, viz. , the summer form and the autumn form. Previous experiments (E ndo , 1970) showed that the corpora allata of the summer form accelerate the maturation of ovarian follicles soon after imaginal ecdysis. On the other hand, the corpora allata of the autumn form do not stimulate ovarian maturation during a period of 2 to 3 weeks after the emergence.
In the summer form (S) as well as in the autumn form (A), the corpora allata remained in an inactive state for about 15 days after emergence when they had been isolated microsurgically from the brain and the corpora cardiaca during the larval period. Further, when separation of the brain into the right and left hemispheres or ablation of the medial neurosecretory group cells of the pars intercerebralis had been carried out on S-pupae of 28 hr after pupation or of earlier ages, they developed into autumn form in respect to wing pattern and their corpora allata did not stimulate ovarian maturation until 2 to 3 weeks after emergence. On the other hand, when the above operations had been performed 34 hr after the pupation or of later ages, they developed into summer form in respect to wing pattern and ovarian maturation was evident soon after the emergence. In these cases, stimulation of the corpora allata is closely connected with the development of seasonal-forms of wing pattern.
From these experiments, it is clear that the medial neurosecretory group cells of the pars intercerebralis in S-insects stimulate the corpora allata about 30 hr after pupation by way of the nervi corporis cardiaci and the activated corpora allata promote ovarian maturation throughout adult life. In A-insects, on the other hand, the medial neurosecretory group cells of the brain are inactive and fail to activate the corpora allata which in turn have no influence on ovarian maturation.     

Controle neuroendocrine du fonctionnement du corpus allatum chez Rhodnius prolixus

Cauterization of the dorsal portion of the protocerebrum effected immediately after cessation of feeding in adult females blocks vitellogenesis. The growth of the oöcytes can be re-established by the implantation of corpora allata or by the application of juvenile hormone analogue, and it is suggested that the protocerebrum has a corpus allatum stimulating influence. The corpus allatum deprived of all its cerebral nervous connexions by cutting the aorta just behind the corpora cardiaca induces abundant vitellogenesis. Females with denervated corpora allata or pars intercerebralis cauterized 24 hr after a meal show a phase of vitellogenesis more active than that in normal female adults. This suggests the existence of a cerebral inhibitory centre: its activity through a nervous or endocrine path is discussed.     

Fonction chromatrope de la pars intercerebralis chez l'acridien Oedipoda coerulescens

The median neurosecretory cells of the protocerebrum of fifth instar larvae and 1- or 2-day-old adults of Oedipoda coerulescens produced more fuchsinophilic material when reared on dark backgrounds than on pale ones. In the latter case, the neurosecretory cell bodies were almost completely devoid of neurosecretion. The same differences were found in the anterior lobes of the corpora cardiaca. Individuals implanted with pars intercerebralis from donors reared on a dark background showed dark pigmentation no matter what their own background colour (and conversely). Black or red pigmentation appeared on absorbent grounds whereas a pale one was produced on reflecting grounds with high levels of incident light predominantly between 576 and 588 mμ. The significance of these results is discussed. A possible scheme for the interaction of environmental factors and pigmentation is suggested.     

The influence of some chemosterilants and caffeine on the neuroendocrine system of adult male Ephestia kühniella

Injection of caffeine into adult male Ephestia kühniella induced a reduction in the amount of neurosecretory material in the resorcin fuchsin stainable (A-) cells of the pars intercerebralis. Both hemel (hexamethyl melamine) and tepa (tris (1-aziridinyl) phosphine oxide) treatments resulted in an increase in stainable neurosecretory products in the cytoplasm of the A-cells. The increase after hemel treatment was largely a result of increased synthesis of neurosecretory material as indicated by increased nuclear volume and nuclear-cytoplasmic ratio. No changes were induced by hemel in the corpora cardiaca and allata of the adult male E.kühniella. This disruption in neuroendocrine function is believed to be involved in the observed mating aberrations (permanent copulation and sterile matings) by adult males after hemel treatment.     

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.     

Evidence for a crustacean hyperglycemic hormone-like molecule in the nervous system of the stick insect,Carausius morosus

Summary Histological sections of the brain, suboesophageal ganglion, and the corpora cardiaca/corpora allata complex were examined for the presence of crustacean hyperglycemic hormone-like immunoreactive material. With the use of an antiserum directed against the hyperglycemic hormone of Carcinus maenas, immunofluorescence was found in the median portion of the pars intercerebralis, and the corpora cardiaca. Extracts of corpora cardiaca were examined by radioimmunoassay for competitive binding to the antiserum; one pair of corpora cardiaca contains at least 7 pg crustacean hyperglycemic hormone-like material.     

Changes in follicle cell morphology,ovarian protein synthesis and ovarian DNA synthesis during oöcyte maturation in Leucophaea maderae: Role of juvenile hormone

Changes in follicle cell morphology were correlated with changes in rates of protein synthesis and DNA synthesis by the ovary during ovarian maturation in Leucophaea maderae. During the vitellogenic period of oöcyte development, which lasts approx, 15 days, morphological changes in the follicle cells are accompanied by moderate rates of ovarian protein synthesis and rapid rates of ovarian DNA synthesis. At approx. 15 days after mating, the shape of the follicle cells changes from cuboidal to squamous, ovarian DNA synthesis is arrested, and ovarian protein synthesis increases slightly. During the final period of oöcyte development, which lasts approx, two days, the interfollicular channels between the follicle cells have disappeared and the squamous follicle cells, which contain an extensive rough endoplasmic reticulum, deposit a chorion around the mature oöcyte. These morphological changes are accompanied by a radical increase in ovarian protein synthesis, while ovarian DNA synthesis remains arrested. Immediately before ovulation, ovarian protein synthesis starts to decline, reaching a minimal level 24 hr post-ovulation.Ovarian maturation is dependent on the presence of juvenile hormone (JH) only during the vitellogenic stage of oöcyte development. Decapitation of insects at any point during the first 10 days after mating arrests the synthesis of DNA and retards the synthesis of protein by the ovary, resulting in degeneration of the oöcyte. Subsequent injection of JH restores both events to normal levels within 72 hr. Decapitation on or after the tenth day following mating does not alter normal oöcyte development, chorion deposition, ovulation or egg case formation.Primary induction of protein synthesis in ovaries from virgin females can be achieved by either an in vivo or in vitro exposure of the tissue to JH, thus confirming a site of action for JH to be ovarian tissue. Electrophoretic analysis of the soluble proteins from JH-exposed ovaries in vivo reveals that JH stimulates general protein synthesis, rather than the synthesis of a specific major protein such as vitellogenin.     

Effects of precocene I and II on flight behaviour in Oncopeltus fasciatus, the migratory milkweed bug

Treatment of newly emerged adult Oncopeltus fasciatus with the corpus allatum inhibitors. 7-methoxy-2,2-dimethyl chromene or 6,7-dimethoxy-2,2-dimethyl chromene (preocene I and II) results in an inhibition of long-term flight (presumed migratory) behaviour in both males and females and inhibition of oögenesis in females. Treatment of reproductive females with precocene briefly stimulates flight behaviour (which ceases in such females as oviposition begins) and then subsequently inhibits it. Oviposition also ceases in such females and oöcyte resorption occurs. Topical application or injections of JH III to precocenetreated animals results in immediate restoration of the tendency to make long tethered flights while corpora cardiaca extract injections, corpora cardiaca implantation, sham implantation, sham injections and sham topical applications were ineffective in restoring prolonged flight behaviour to precocene-treated animals.Restoration of flight by JH III injection was observed within 1 hr after treatment with the hormone. These results indicate that JH is necessary for prolonged flight and presumably migratory behaviour in this species and its stimulatory effect on flight behaviour is immediate. Possible mechanisms of action of the hormone on flight behaviour are discussed.     

The effects of corpora cardiaca on tethered flight in the Locust

Summary Removal of the cerebral neurosecretory cells tas no effect on the tethered flight pattern of adult maleLocusta. However, the flight pattern is markedly influenced by removal of the glandular lobes of the corpora cardiaca or by injection of 0.01 pair of corpora cardiaca. Changes in flight speed, brought about by such injections, may reflect differences in substrate utilisation in response to hormonal factor(s) from the corpora cardiaca. It is suggested that one effect of corpus cardiacum factor(s) may be the suppression of carbohydrate utilisation by the flight muscles.     

Immunocytochemical localization of Bombyx-PTTH-like molecules in neurosecretory cells of the brain of the migratory locust,Locusta migratoria

Summary Using a monoclonal antibody directed against a synthetic pentadecapeptide corresponding to the N-terminus of the prothoracicotropic hormone (PTTH) of Bombyx mori, we report the presence of immunoreactive molecules in a large number of median neurosecretory cells of the pars intercerebralis of the migratory locust, Locusta migratoria. These cells correspond to the A₁ cell type which we show to contain also neuroparsins, a family of predominant neurohormones of the migratory locust. In contrast, PTTH-like molecules are absent from A₂ cells of the pars intercerebralis which contain Locusta insulin-related peptide (LIRP). Developmental studies show the presence of PTTH-related substances in neurosecretory cells of Locusta migratoria from late embryogenesis to adult development, including ageing vitellogenic female adults.