The role of the glandular lobes of the corpora cardiaca during flight in Locusta

ABSTRACT. Flight performance in Locusta is reduced following severance of the major afferent nerves to the corpora cardiaca or removal of the glandular lobes of the corpora cardiaca. These operations prevent the release of adipokinetic hormone and the consequent mobilization of stored lipid. However, locusts deprived of about 90% of their glandular lobe tissue, while flying poorly, did mobilize lipid. It is suggested that the remaining glandular parenchyma cells are capable of secreting enough hormone to stimulate lipid mobilization, but that the concentration may be inadequate to encourage lipid utilization. After removal of all the glandular lobe parenchyma, the blood carbohydrate concentration was temporarily depressed. Nevertheless flight performance was equally poor, both when haemolymph carbohydrate levels were low and when they had returned to normal. After the injection of trehalose into operated control locusts and locusts deprived of their glandular lobes, flight was still markedly poorer in the operated insects, even though the injection of trehalose prevented adipokinetic hormone release in the intact locust. It seems that the poor flight performance of locusts deprived of their glandular lobes cannot be fully explained by the simple absence of adipokinetic hormone.     

The hormonal content of the locust corpus cardiacum

Summary The amounts of adipokinetic and diuretic hormone in the separate storage and glandular lobes of the locust corpora cardiaca during the imaginal moult and up to the onset of sexual maturation have been measured. The levels of the hormones are high prior to the imaginal moult, fall at emergence and increase during the somatic growth period. The effects of surgical interference with the neuroendocrine system upon the hormonal content of the corpora cardiaca have been investigated. Cautery of the brain neurosecretory cells or allatectomy in mature locusts has no effect on the content of adipokinetic hormone. Diuretic hormone is absent from the storage lobes of locusts deprived of their cerebral neurosecretory cells but normal levels are present in the corpora cardiaca of allatectomised animals. Severance of the nervus corporis cardiacum I and II reduces the level of diuretic hormone in the storage lobes of the corpora cardiaca but is without effect on the levels of adipokinetic hormone in the glandular lobes. This work is supported by grants from the Science Research Council and the Royal Society.     

Neuroendocrine control of blood lipids in the locust, Locusta migratoria

In order to determine the best conditions, the influence of various parameters on the haemolymph lipid concentration were studied. These parameters are the age, the sex and the feeding of the animals, the time and the number of the haemolymph sample-taking and the temperature of the locust culture. A large in vivo increase in haemolymph lipid concentration was obtained in locusts which received extracts of the whole CC and of their glandular or neurohemal lobes. Reversely, a decrease in this concentration was obtained in locusts operated 7 days before (cardiacectomy or glandular lobe removal). Moreover the pars intercerebralis extracts increased the level of haemolymph lipids. We conclude that adipokinetic factors are present, both in the glandular lobes of the CC and in their neurohemal lobes. It is likely that the latter partly originate from the pars intercerebralis. Results of allatectomy and injections of corpora allata extracts led to the conclusion that corpora allata contain an adipokinetic factor, the juvenile hormone. and factors that inhibit the haemolymph lipid concentration. Finally, from different injections of neurotransmitters and drugs it is argued that it is mainly octopamine which is involved in the mechanism governing the increase of the level of haemolymph lipids.     

Mobilization of lipid and carbohydrate reserves in the migratory grasshopper Melanoplus sanguinipes

Abstract. The North American migratory grasshopper Melanoplus sanguinipes Fabricius (Orthoptera: Acrididae) exhibits heritable variation in predisposition to make long-duration flights, and performance of long-duration flight enhances reproductive output. As a first step in understanding the physiological basis of these phenomena, we examined the mobilization of lipid and carbohydrate reserves during flight and in response to injection of extracts of the corpora cardiaca. Extract of conspecific corpora cardiaca elevates the concentration of haemolymph lipid. Both synthetic locust adipokinetic hormone I (AKH I) and synthetic Locusta migratoria AKH II raise the concentration of lipid in the haemolymph. However, although AKH I is more active than AKH II in locusts, dose-response curves for the two peptides are similar in M.sanguinipes. Neither extract of conspecific corpora cardiaca nor locust AKH I affects haemolymph carbohydrate in this species. Haemolymph carbohydrate and total glycogen reserves are Diminished by tethered flight; in contrast, haemolymph lipid is elevated by flight. Grasshoppers identified as presumptive migrants or non-migrants do not differ significantly in body composition. Total lipid reserves did not decrease measurably after extended flight, even though total reserves of carbohydrate do not appear to be sufficient to maintain the durations of flight performed.     

Adipokinetic hormone and flight metabolism in the locust

In adult male Schistocerca 20 min of tethered flight causes a halving of the haemolymph carbohydrate concentration. Injection of a proteinaceous emulsion of diglyceride 30 min before flight reduces both flight speed and carbohydrate utilisation. This effect can be overcome by the injection of trehalose immediately before the flight. If, in addition to the diglyceride, a dilute extract of the glandular lobes of the corpora cardiaca is injected immediately before flight, either with or without additional trehalose, carbohydrate utilisation is drastically reduced whereas flight speed is unaffected. It is argued that diglyceride competes with trehalose as a substrate for the flight muscles and that adipokinetic hormone from the glandular lobes of the corpora cardiaca stimulates the oxidation of diglyceride in these muscles during flight. This brings about a more complete (non-competitive) inhibition of trehalose utilisation by the flight muscles.     

An active principle from the corpora cardiaca,corpora allata and suboesophageal ganglion of the locust,inducing egg diapause in Bombyx mori

The activity of the substance(s) which are contained in the cephalic endocrine organs of the locust which induce egg diapause in Bombyx mori was examined by implantation and injection of saline extracts of these organs. Extracts from the median and lateral neurosecretory parts of the locust brain were not effective in inducing egg diapause. Extracts of the corpora cardiaca, corpora allata, and suboesophageal ganglion of the locust induced diapause eggs in Bombyx pharate adults from which the suboesophageal ganglion had been removed. The first two extracts could induce egg diapause even in isolated abdomens of pharate adults of Bombyx. In the locust corpora cardiaca, the activity was present only in the glandular lobe and not in the nervous region. This activity decreased when the nervi corporis cardiaci I and II and of nervi corporis allati I were cut. Allatectomy also brought about a decrease in the activity in the glandular lobe which could not be restored by the injection of juvenile hormone. The activity in the corpora allata was enhanced slightly by the disconnection though not significantly.From these results, it is assumed that the corpora cardiaca, corpora allata and suboesophageal ganglion of the locust contain and active principle(s) capable of inducing egg diapause in Bombyx mori. The nervous connections between the brain, corpora cardiaca, and corpora allata are essential for the accumulation of the active substance(s) in the glandular lobes of the corpora cardiaca.     

A comparative study on the isolation of adipokinetic and hypertrehalosaemic factors from insect corpora cardiaca

ABSTRACT. Extracts of corpora cardiaca from two cockroaches, Nauphoeta cinerea Olivier and Leucophaea maderae F., from a cricket, Gryllus bimaculatus De Geer, from the Colorado potato beetle, Leptinotarsa decemlineata Say, and from the sphinx moth, Sphinx ligustri L. were assayed for adipokinetic and hypertrehalosaemic activity, in acceptor locusts ( Locusta migratoria L.) and cockroaches ( Periplaneta americana L.) respectively. Both bioassays give positive results with all corpus cardiacum material tested except that from the sphinx moth; in this insect haemolymph lipid concentrations (but not those of the total carbohydrate) are, however, increased after injection of an extract of corpora cardiaca from the same species. A similar result is obtained when specimens of G. bimaculatus are injected with an extract of corpora cardiaca from G. bimaculatus. Biological activities of corpus cardiacum extracts from all species investigated can be resolved on reversed-phase high-performance liquid chromatography. Gland extracts from the two cockroach species each show a single absorbance peak which has hypertrehalosaemic activity, but with a (common) retention time distinct from all previously described arthropod neuropeptides. The corpora cardiaca of G. bimaculatus contain also a novel adipokinetic factor with a retention time distinct from previously characterized arthropod hormones, as well as from the new cockroach factor described in this study. The two hypertrehalosaemic factors from the corpora cardiaca of the potato beetle coelute with the hypertrehalosaemic hormones I and II of the American cockroach. The active (adipokinetic) compound from glands of S. ligustri appears to coelute with locust adipokinetic hormone I.     

The effect of Metarhizium anisopliae var acridum on haemolymph energy reserves and flight capability in the desert locust, Schistocerca gregaria

Adult desert locusts, Schistocerca gregaria , 3 days after inoculation with the entomopathogenic fungus Metarhizium anisopliae var acridum , had significantly less carbohydrate and lipid in the haemolymph than controls. This was not due to reduced food intake as 3 days of complete starvation had no effect on haemolymph titres of energy reserves in controls. Furthermore injection of an extract of the corpora cardiaca (the source of adipokinetic hormone, AKH) caused a large significant increase in haemolymph lipid in mycosed locusts, indicating the availability of significant quantities of lipid in the fat body, the target for AKH. Haemolymph carbohydrate declined significantly during tethered flight of control locusts but not in mycosed individuals. An injected supplement of trehalose significantly boosted flight performance of mycosed insects but not controls. The results are discussed in the light of the hypothesis that the poor flight capability of mycosed locusts is due in part to a fungus-induced reduction in mobile energy reserves.     

Adipokinetic Hormone and Flight Fuel Related Characteristics of Density-Dependent Locust Phase Polymorphism: A Review

Recent findings on differences between the gregarious and solitary phases of locusts are reviewed in relation to flight fuel utilization, adipokinetic responses, and adipokinetic hormones. Laboratory results obtained with Locusta migratoria migratorioides show that the amount of lipid reserves, resting levels of haemolymph lipids, and hyperlipaemic responses to flight and to injection of corpus cardiacum extract or of synthetic adipokinetic hormones, are higher in crowded than in isolated locusts. No major phase-dependent differences seem to exist in flight-related carbohydrate metabolism. The adipokinetic hormone content of the corpora cardiaca is higher in younger isolated locusts than in crowded ones. Adipokinetic hormone precursor-related peptide content of the corpora cardiaca is also higher in isolated than in crowded locusts. Crowded locusts have higher lipid reserves and higher hyperlipaemic responses to flight than isolated locusts also in Schistocerca gregaria and, following injection of synthetic adipokinetic hormone, the formation of low density lipophorin is higher in crowded than in isolated locusts of this species. The laboratory results obtained with isolated and crowded locusts are extrapolated to understand the ecophysiology of the migrations of solitary and gregarious field populations of L.m. migratorioides according to available information on the differences in the migration of the two phases. It is inferred that in this species solitary locusts have a rather coarse adipokinetic strategy focused on a single prereproductive long-distance migratory flight, whereas gregarious locusts possess a fine adipokinetic balance for reiterative, sometimes unpredictably long-distance, migrations in the prereproductive, as well as reproductive, periods. The differences between the adipokinetic strategies of solitary and gregarious S. gregaria seem to be less dramatic, nevertheless, they indicate a better adaptation of the gregarious phase to prolonged flights.     

Fuels for flight in Locusta

In Locusta migratoria, carbohydrate is the predominant energy source for the first 20 to 30 min of flight. During this time carbohydrate is utilized at the rate of 120 μg/min, but thereafter it is used at only 8 to 9 per cent of the initial rate. Initially carbohydrate is not mobilized to any extent from body stores. Lipid, however, is mobilized (from stores in the fat body) in response to adipokinetic hormone released from the glandular lobes of the corpora cardiaca. The mobilized lipid is diglyceride, and 16 : 18 and 18 : 18 diglycerides predominate. The rate of diglyceride mobilization is rapid, both during flight and in response to extracts of corpora cardiaca. The release of adipokinetic hormone during flight has also been estimated and is found to be more rapid than previously suggested. It is calculated that the rate of lipid utilization increases during flight from virtually zero during the first few minutes to 35 μg/min (15 to 30 min) and finally reaches about 85 μg/min during the second 30 min of flight.     

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.     

Hormonal regulation of proline synthesis and glucose release in the fat body of the Colorado potato beetle, Leptinotarsa decemlineata

In the adult males of the Colorado potato beetle, Leptinotarsa decemlineata, corpora cardiaca extract injected in vivo gives rise to an increase in glucose and a decrease in alanine concentration of the haemolymph. The regulation of proline synthesis and glucose release in the fat body of the Colorado potato beetle was investigated further in vitro. Proline regulates its own synthesis by a feedback inhibition. Moreover, a factor present in extracts from the corpora cardiaca stimulates synthesis in the fat body in vitro. This effect was demonstrated with corpora cardiaca extracts from beetles, locusts and cokroaches. Also, synthetic adipokinetic hormone stimulates proline synthesis in the fat body of the Colorado beetle. In addition, a release of glucose from the fat body of the beetle could be evoked by the addition of locust and beetle corpora cardiaca extracts or synthetic adipokinetic hormone. The physiological significance of both effects is discussed.     

Comparative immunocytochemical study of release sites of insulin,glucagon and AKH-like products in Locusta migratoria,Periplaneta americana,and Carausius morosus

Summary Insulin, glucagon and adipokinetic hormone antisera were applied to the corpora cardiaca, perisympathetic organs, neurohemal areas and peripheral neurosecretory cells of three insect species, the locust Locusta migratoria, the cockroach Periplaneta americana, and the stick insect Carausius morosus. The neurohemal part of the corpora cardiaca was shown to be immunoreactive to both insulin and glucagon antisera while the glandular cells reacted to adipokinetic hormone antisera. The perisympathetic organs seem to be devoid of these three substances, but certain peripheral neurohemal areas contained AKH and glucagon immunoreactive products. The latter were found to originate in the peripheral neurosecretory cells.     

Number and size of intracisternal granules in the adipokinetic hormone-secreting cells of locusts: a phase-dependent characteristic

Abstract.The intracisternal (= ergastoplasmic) granules in the adipokinetic hormone-secreting cells of the glandular lobes of the corpora cardiaca in Locusta migratoria migratorioides represent accumulations of adipokinetic prohormones within cisternae of the rough endoplasmic reticulum. Solitary locusts have more and larger intracisternal granules than gregarious locusts. This coincides with the general locomotor activity and thus the energy metabolism in solitary locusts being quite different from that of gregarious locusts, which apparently has consequences for the amounts of adipokinetic hormones synthesized and/or released and, consequently, for the storage of these hormones in the intracisternal granules. These granules apparently function as supplementary stores of secretory material.     

In vivo studies on the release of hormones from the corpora cardiaca of locusts

Summary Sectioning of the afferent nerves (NCCl and NCCll) to the locust corpus cardiacum prevents thein vivo release of adipokinetic hormone from the glandular lobes. This failure to release the hormone during flight and the consequent lack of lipid mobilisation brings about an impairment of flight performance which can be corrected by injections of corpus cardiacum extracts. Sectioning of the NCCl and NCCll reduces markedly the activity of the corpora allata. However, the poor flight performance of allatectomised locusts is not related to an inability to mobilise lipid since injections of corpus cardiacum extract which will mobilise fat body lipid in these locusts have no effect on flight performance. The results of individual sectioning of the NCCl and NCCll suggest that a double innervation of the glandular lobes functionsin vivo to control adipokinetic hormone release but that the NCCl alone may control the release of the diuretic hormone.     

A possible role of Schisto FLRFamide in inhibition of adipokinetic hormone release from locust corpora cardiaca

The distribution and actions of FMRFamide-related peptides (FaRPs) in the corpora cardiaca of the locust Locusta migratoria were studied. Antisera to FMRFamide and SchistoFLRFamide (PDVDHVFLRFamide) label neuronal processes that impinge on glandular cells in the glandular lobe of the corpora cardiaca known to produce adipokinetic hormones. Electron microscopic immunocytochemistry revealed that these FaRP-containing processes form synaptoid contacts with the glandular cells. Approximately 12% of the axon profiles present in the glandular part of the corpus cardiacum contained SchistoFLRFamide-immunoreactive material. Retrograde tracing of the axons in the nervus corporis cardiaci II with Lucifer yellow revealed 25–30 labelled neuronal cell bodies in each lateral part of the protocerebrum. About five of these in each hemisphere reacted with the SchistoFLRFamide-antiserum. Double-labelling immunocytochemistry showed that the FaRP-containing processes in the glandular lobe of the corpora cardiaca are distinct from neuronal processes, reacting with an antiserum to the neuropeptide locustatachykinin. The effect of the decapeptide SchistoFLRFamide and the tetrapeptide FMRFamide on the release of adipokinetic hormone I (AKH I) from the cells in the glandular part of the corpus cardiacum was studied in vitro. Neither the deca- nor the tetrapeptide had any effect on the spontaneous release of AKH I. Release of AKH I induced by the phosphodiesterase inhibitor IBMX, however, was reduced significantly by both peptides. These results point to an involvement of FaRPs as inhibitory modulators in the regulation of the release of adipokinetic hormone from the glandular cells.     

Locust corpora cardiaca contain an inactive adipokinetic hormone

A neuropeptide from the migratory locust, Locusta migratoria, has been identified as a novel member of the family of adipokinetic hormones (AKHs). The peptide is probably synthesised in the brain because it is the first AKH found in the storage lobe, whilst the three 'classic' Locusta AKHs are present in the glandular lobe of the corpora cardiaca. In locusts, the peptide has no biological activity usually associated with AKHs. There is only 36-56% sequence identity with the three Lom-AKHs, but 78% identity with the Drosophila melanogaster AKH, Drm-HrTH. The new peptide is active in the American cockroach, Periplaneta americana, and was provisionally named 'L. migratoria hypertrehalosaemic hormone', Lom-HrTH; its biological role in locusts remains to be established. The high degree of identity with Drm-HrTH suggests that Lom-HrTH is an ancient molecule.     

Adipokinetic and hyperglycaemic factor(s) in the corpora cardiaca/corpora allata complex of the stick insect, Carausius morosus.

ABSTRACT. The neurosecretory corpora cardiaca/corpora allata complex of Carausius morosus , a wingless insect of the superorder Orthopteroidea, contains adipokinetic and hyperglycaemic factor(s) capable of elevating lipids in locusts, and carbohydrates in cockroaches. Neither activity can be demonstrated in the stick insect itself, however. In addition, in locusts the Carausius gland extract is able to elevate levels of cyclic AMP in the fat body.     

Isolation and structure of a novel charged member of the red-pigment-concentrating hormone-adipokinetic hormone family of peptides isolated from the corpora cardiaca of the blowfly Phormia terraenovae (Diptera).

A hypertrehalosaemic neuropeptide from the corpora cardiaca of the blowfly Phormia terraenovae has been isolated by reversed-phase h.p.l.c., and its primary structure was determined by pulsed-liquid phase sequencing employing Edman chemistry after enzymically deblocking the N-terminal pyroglutamate residue. The C-terminus was also blocked, as indicated by the lack of digestion when the peptide was incubated with carboxypeptidase A. The octapeptide has the sequence pGlu-Leu-Thr-Phe-Ser-Pro-Asp-Trp-NH2 and is clearly defined as a novel member of the RPCH/AKH (red-pigment-concentrating hormone/adipokinetic hormone) family of peptides. It is the first charged member of this family to be found. The synthetic peptide causes an increase in the haemolymph carbohydrate concentration in a dose-dependent fashion in blowflies and therefore is named 'Phormia terraenovae hypertrehalosaemic hormone' (Pht-HrTH). In addition, receptors in the fat-body of the American cockroach (Periplaneta americana) recognize the peptide, resulting in carbohydrate elevation in the blood. However, fat-body receptors of the migratory locust (Locusta migratoria) do not recognize this charged molecule, and thus no lipid mobilization is observed in this species.     

Release of identified adipokinetic hormones during flight and following neural stimulation in Locusta migratoria

Fractionation of methanol extracts of perfusate and haemolymph on thin-layer chromatography was used to separate hormones associated with haemolymph lipid regulation in Locusta. Electrical stimulation of the nervi corporis cardiaci II (NCC II) of isolated corpora cardiaca resulted in the release of three hormones into the perfusate; hypolipaemic hormone and two adipokinetic hormones. The two adipokinetic hormones co-migrated with synthetic adipokinetic hormone (adipokinetic hormone I) and with the R_F value similar to Carlsen's peptide (adipokinetic hormone II).These two adipokinetic hormones were also present in small amounts in the haemolymph of unflown Locusta, and shown to be released during a 30-min flight. The adipokinetic hormone II fraction from the NCC II-stimulated perfusate and haemolymph also possessed hyperglycaemic activity when assayed in ligated locusts.It is concluded that NCC II controls the release of adipokinetic hormones during flight and that two adipokinetic hormones are released during flight. One of these hormones adipokinetic hormone II also acts as a hyperglycaemic hormone illustrating that a hyperglycaemic hormone is released, during flight.