Intracellular stimulation of an identified neuron evokes cardioacceleratory peptide release

The central nervous system of the tobacco hawkmoth, Manduca sexta, is known to contain two cardioacceleratory peptides (CAP's), both of which function in vivo as cardioregulatory neurohormones. Intracellular electrical stimulation of a single abdominal ganglion neuron evokes the release of CAP-like bioactivity. This stimulation-evoked bioactivity is destroyed by prior treatment with protease. The possibility that intracellular stimulation of a CAP-containing neuron synaptically activated additional spiking neurons is eliminated.

Identification of neurones containing cardioacceleratory peptides (CAPs) in the ventral nerve cord of the tobacco hawkmoth, Manduca sexta

The abdominal ganglion neurosecretory cells responsible for the synthesis and release of two insect neurohormones, cardioacceleratory peptides 1 and 2 (CAP1 and CAP2), from the perivisceral organs (PVOs) have been identified in the tobacco hawkmoth, Manduca sexta. Previous work established the existence of two groups of abdominal ganglion cell bodies with axons projecting to the PVO: four laterally-situated pairs and five pairs lying on the midline (Taghert & Truman, 1982b). Micro-dissection and bioassay of various parts of an abdominal ganglion revealed that CAP activity was greatest in the medial portion of the ganglion, the portion containing the 10 midline neurones. Six of the 10 midline neurosecretory cells, the new midline bilateral (MB) cells, appeared to differentiate post-embryonically, commencing differentiation late in the last larval instar and reaching maturity midway through adult development. The development of the new MB cells was mirrored by the accumulation of CAP activity in the abdominal nerve cord. Not present in measurable amounts in larvae, CAP activity was first detectable a few days after pupation and reached maximal levels midway through adult development. CAP-like bioactivity was collected from the PVO in response to antidromic stimulation of the nerve containing the new MB axons. No CAP-like bioactivity was detected in those preparations in which the new MB axons were severed or in which other nerves were stimulated. Intracellular stimulation of a new MB neurone evoked the release from the PVO of measurable levels of CAP bioactivity. It was shown that this stimulation-evoked, cardioacceleratory activity was sensitive to protease treatment, and was released only from the cell that was stimulated. On the basis of these experiments, it was concluded that the CAPs are synthesized and secreted from the new MB cells.

Oxygen supply and limiting oxygen pressures in an insect larva

Larvae of the moth, Carpocapsa saltitans, demonstrate a diurnal activity pattern of rhythmic twitching which, under conditions of controlled light and temperature, is characterized by a predictable frequency and regularity. The twitching activity is shown to be sensitive to the partial pressure of environmental oxygen, and it ceases altogether at a particular PO2 called 'critical'. Use is made of the 'critical' PO2 in normobaric and hypobaric conditions to deduce the roles of diffusion and convection in the larval oxygen transport mechanisms; and also as a value for the total decrement of PO2 from ambient air to mitochondria, in order to evaluate predicted values based on calculations of resistance to oxygen flow. For this latter study 'porosity' of the larva and the seed pod in which it is normally housed was inferred from measured rates of water vapor loss, and oxygen uptake rates of the larvae were measured by the manometric technique of Warburg. Applying these data to a model system the conclusion was reached that almost the total resistance to oxygen flow is at the spiracle.

Purification and characterization of a biliverdin-associated protein from the hemolymph of Manduca sexta

A biliverdin binding protein, insecticyanin, has been isolated from the hemolymph of the fourth instar tobacco hornworm Manduca sexta. The protein has been purified to apparent homogeneity by conventional chromatography with a cumulative yield of 40-50%. The protein (Mw 71 600) is composed of three subunits (Mr 23 000). Each subunit binds one biliverdin molecule. Proton magnetic resonance spectroscopy and absorption spectroscopy demonstrate that the bilin is the biliverdin IX gamma isomer.

Chloride transport across the integumentary epithelium of Manduca sexta (Lepidoptera: Sphingidae)

Moulting fluid of Manduca sexta contains high concentrations of potassium and bicarbonate (100 mM) and low concentrations of chloride (5 mM). This fluid begins to disappear from the exuvial space approximately 9-10 h before the actual shedding of the integument. During this time, the integument can be isolated in an Ussing cell and electrical properties measured in vitro. In a normal 32 mM KHCO3 saline, potential difference (PD) is around 10 mV, exuvial side positive, and short-circuit current (SCC) is 15-20 microA cm-2. Substitution of chloride slightly reduces both PD and SCC, although resistance does not change significantly. Measurement of chloride transport in the absence of K+ indicates that 100% of the SCC can be accounted for by the net chloride flux (approximately 2 microA cm-2). The Km and Jmax for transepithelial chloride transport are 14 mM and 0.1 microEq cm-2 h-1. Bilateral potassium addition stimulates chloride transport, doubling net chloride flux as potassium concentration increases from 2 to 5 mM. Chloride net flux is not inhibited by the presence of furosemide (1 mM), nor in HCO3- -free saline by thiocyanate (1 or 10 mM) or acetazolamide (0.1 mM), but is inhibited by 100% N2. The pattern of chloride transport in M. sexta is similar to that previously reported for the rectum of locusts. As chloride is normally at low concentrations in the moulting fluid, it is suggested that this transport system acts to maintain low intracellular concentrations which may be necessary for enzymatic functions in the epidermal cells and has little importance in fluid transport.

Cuticular cavities: storage chambers for cyanoglucoside-containing defensive secretions in larvae of a Zygaenid moth

As a defensive reaction against predators the larvae of Zygaena trifolii Esper. 1783, release highly viscous fluid droplets out of cuticular cavities. The fluid appears on the cuticular surface upon contraction of the irritated segments, with no specialized muscles being involved. Two morphologically different types of cavities have been found: the larger ones are located beneath pigment spots, the smaller ones occupy the remaining surface except in the ventral region. Both types have complicated cuticular opening structures. The defensive fluid contains the cyanoglucosides linamarin and lotaustralin, the amino acid beta-cyano-L-alanine, proteins and water. Although a considerable amount of fluid (3-6 microliter per sixth-instar larva) is stored in the cuticle, fine structural examinations of the epidermis do not show any specific cells or cell areas with morphological adaptations for secretion. Further, there do not exist any major cytological differences between the cells below the cavities and in the ventral region, where those cavities are absent.

Soluble peptidoglycan fragments stimulate antibacterial protein synthesis by fat body from larvae of Manduca sexta

Both hemocytes and fat body from larvae of Manduca sexta, which have been injected with inducers of antibacterial protein synthesis, contain immunoreactive lysozyme. However, fat body is a richer source and has been demonstrated to synthesize and release lysozyme and cecropin-like peptides (bactericidins) in vitro. Fat body secretion of lysozyme and bactericidins is stimulated by addition of soluble peptidoglycan fragments to culture medium. The rate of lysozyme secretion by fat body varies as a function of peptidoglycan inducer concentration. These data are consistent with the hypothesis that, in vivo, bacteria must be phagocytized and partially degraded (processed) by hemocytes to generate a signal (peptidoglycan) that subsequently induces antibacterial protein synthesis by fat body.

The antibacterial effect of attacins from the silk moth Hyalophora cecropia is directed against the outer membrane of Escherichia coli

The attacins are antibacterial proteins which accumulate in the hemolymph of the giant silk moth, Hyalophora cecropia, in response to a bacterial infection. Here we show that the permeability barrier function of the outer membrane is affected shortly after addition of attacin to growing cultures of Escherichia coli. Specifically, the penetration through the outer membrane of beta-lactam antibiotics, chicken egg white lysozyme and the detergent Triton X-100 was found to be facilitated. The sensitivity of E. coli to cecropin B, another antibacterial protein present in the hemolymph of H. cecropia, was also found to be increased after treatment with attacin. The results suggest that the target of the attacins in E. coli is the outer membrane. Other effects of the attacins which have been observed are likely to be indirect consequences of the alteration in the properties of the outer membrane. These effects include changes in the cell shape, irregular patterns of cell division and lysis. The minimal concentration at which the attacins affected the growth of E. coli was 1 and 0.5 microM for the neutral (pI 7) and basic (pI 9) attacins, respectively, which corresponds to less than 2% of the concentration of the attacins in the hemolymph of infected pupae.

Characterization of monovalent ion transport systems in an insect cell line (Manduca sexta embryonic cell line CHE)

The monovalent ion transport systems of an immortalized insect cell line (CHE) have been investigated. These cells are unusual in that unlike most vertebrate cells, their normal extracellular environment consists of high potassium and low sodium concentrations. CHE cells maintained high intracellular [K+] through both a furosemide-inhibitable and a vanadate-inhibitable transport system. Intracellular exchangeable [Na+] was slightly lower than the extracellular [Na+] and was maintained at this level through a vanadate-sensitive transport system. Na+ uptake was also inhibited by furosemide: however, the stoichiometry of furosemide-sensitive Na+ uptake when compared with furosemide-sensitive K+ uptake indicated that these cations are not cotransported. 4,4'-Diisothiocyano-2,2'-disulfonic acid stilbene (DIDS) inhibited Na+, K+, and Cl- uptake. Vanadate and furosemide decreased cytoplasmimic pH, while cytoplasmic pH increased in the presence of DIDS. A model is presented explaining how Na+, K+, Cl-, H+ and HCO3-fluxes are regulated in these cells.

Isolation of 2-fluorocitrate produced by in vivo dealkylation of 29-fluorostigmasterol in an insect

A novel pro-insecticide, 29-fluorostigmasterol, is proposed to cause mortality due to release of fluoroacetate during side chain dealkylation. The 29-3H-labeled substrate was fed to third instar tobacco hornworms (Manduca sexta) and erythro-2-fluoro-[2-3H] citrate was isolated in 0.012% yield by ion-exchange, silica gel, and reverse-phase chromatography of the tricarboxylic acid, trimethyl ester, and trimethyl ester benzoate, respectively. The less toxic 29-fluoro-[29-3H]sitosterol did not provide sufficient labeled fluorocitrate to allow isolation, while a more toxic 16-3H-labeled 16-fluorofatty acid gave nearly 1% conversion to labeled fluorocitrate. This is the first direct chemical evidence for the fate of the two carbons removed during phytosterol dealkylation in an insect. It is also the first use of labeled fluoroacetate precursors to identify labeled 2-fluorocitrate as an in vivo metabolite of these precursors.

Stereochemical course of pheromone biosynthesis in the arctiid moth, Creatonotos transiens

The biosynthetic conversion of a pyrrolizidine alkaloid (heliotrine, IV) to a male moth pheromone (hydroxydanaidal, III) is found to proceed with inversion of configuration at the remaining asymmetric center (C-7).

Regulation of melanization of tobacco hornworm larval cuticle in vitro

When tobacco hornworm larvae (Manduca sexta) are allatectomized 5-6 hr before head capsule slippage in the molt to the fifth (final) larval instar, the new cuticle melanizes 3 hr before ecdysis. After explantation between 7 and 3 hr before the onset of melanization, the new cuticle was found to melanize in vitro in Grace's medium only if beta-alanine was removed. When explanted at the onset of melanization, the presence of beta-alanine had no effect on melanization. The addition of either dopa or dopamine was found to be necessary for complete melanization of pieces explanted before the onset of melanization with 0.3 mM of either dopa or dopamine being optimal. Both of these compounds were incorporated into the cuticular melanin. In this optimal medium, melanization occurred over about a 9-hr period after a 5- to 6-hr lag period presumably required for adjustment to the medium. Fifty ng/ml 20-hydroxyecdysone was found to inhibit melanization of pieces explanted 7 hr but not 3 hr before melanization. The hormone neither inhibited uptake of dopa into the epidermis nor prevented melanization in the cuticle once the prophenoloxidase in the premelanin granules was activated. Therefore, 20-hydroxyecdysone may inhibit the activation of the phenoloxidase in the pre-melanin granules, or may inhibit the incorporation of dopa into the granules.

Detection of pheromone biosynthetic and degradative enzymes in vitro

Highly sensitive, luminescent assays have been developed to measure enzyme activities involved in the metabolism of a major class of insect pheromones which includes fatty aldehydes, alcohols, and their acetate esters. These assays have been applied to measure the in vitro biosynthesis and degradation of the sex pheromone (trans:cis-11-tetradecenal, 96:4) of the eastern spruce budworm, Choristoneura fumiferana. Three activities were detected on analyses of extracts of the female moths: (a) an esterase that hydrolyzes both the cis and trans isomers of 11-tetradecenyl acetate, (b) an oxidase that converts fatty alcohols to aldehydes in the presence of O2, and (c) an NAD-dependent aldehyde dehydrogenase. The coupled luminescent response of bacterial luciferase to long chain aldehydes was used to measure rates of reaction as low as 0.1 pmol/min since only low amounts of material can be analyzed. Specific activities of these enzymes were higher in the pheromone producing gland than in other parts of the moth, implicating these enzymes, and the oxidase in particular, in the pathway of pheromone biosynthesis. The pathway was supported in vivo by demonstrating that topical application of 3H-labeled tetradecanyl acetate onto the insect gland resulted in the formation of [3H]tetradecanol and [3H]tetradecanoic acid, thus providing evidence that all three enzymes were functional in the living insects.

Induction by carrot allelochemicals of insecticide-metabolising enzymes in the southern armyworm (Spodoptera eridania)

Carrot foliage monoterpenes induce cytochrome P-450 up to 2.9-fold, NADPH cytochrome c (P-450) reductase up to 1.6-fold, NADPH-oxidation up to 3.8-fold, aldrin epoxidation up to 1.5-fold in southern armyworm larval midgut tissues when incorporated in their diet at 0.2% for 3 days. Stigmasterol and ergosterol did not substantially induce microsomal oxidase activities and significantly inhibited GSH S-aryltransferase activity and sulfotransferase activity. Coumarin did not substantially affect microsomal oxidase and sulfotransferase activity but is the most potent inducer of GSH S-aryltransferase activity, increasing this activity 7-fold. None of the chemicals is acutely toxic to the sixth instar larvae or affect the larval weight gain except coumarin which significantly depressed the maximal body weight attained.

The in vitro generation of an antibacterial activity from the fat body and hemolymph of non-immunized larvae of Galleria mellonella

A state of immunity in Galleria mellonella against the pathogen Pseudomonas aeruginosa is known to be induced by the injection of lipopolysaccharide (LPS), isolated from the homologous organism. An in vitro mixture of the LPS and whole or cell-free hemolymph from non-immunized larvae is not antibacterial. In vitro mixtures of fat body and cell-free hemolymph from non-immunized larvae, incubated at 25 degrees C for 20 hours generated a proteinaceous antibacterial activity. The generation of this activity was enhanced by the presence in the incubation mixture of LPS and/or hemocytes from non-immunized larvae. It is suggested that LPS causes the release of a hemocyte factor(s) which acts in conjunction with or directly on the fat body resulting in an enhanced production of antibacterial factors.

Purification and properties of microvitellogenin of Manduca sexta role of juvenile hormone in appearance and uptake

Microvitellogenin, a female specific protein found in hemolymph and eggs of adult female Manduca sexta (tobacco hornworm moth) has been purified to homogeneity. It is a 31,000 dalton protein lacking covalently bound carbohydrate. It appears in the hemolymph near the time of adult eclosion. The appearance of microvitellogenin in adult hemolymph is not dependent upon the presence of juvenile hormone. Uptake of both vitellogenin and microvitellogenin are greatly reduced in the absence of juvenile hormone.

Farnesol and farnesal dehydrogenase(s) in corpora allata of the tobacco hornworm moth, Manduca sexta

The metabolism of [3H]farnesol was studied in cell-free preparations of corpora allata from the tobacco hornworm, Manduca sexta, to assess the role of this presumed biosynthetic precursor of juvenile hormone (JH) III. A reversed-phase ion-pair liquid chromatographic (RP-IPC) procedure was devised to separate farnesol from several potential intermediates in its presumed metabolism to JH III: farnesal, farnesoic acid, 10,11-epoxyfarnesoic acid, and methyl farnesoate. Following incubation of (2E,6E)-[1,5,9-3H]farnesol with homogenates of corpora allata from fifth instar larvae or adult female M. sexta, and analysis by RP-IPC, the major radiolabeled products corresponded to farnesoic acid, farnesal, and a polar product(s) presumably derived from the tritium on C-1 of farnesol. Inclusion of NAD+ in the incubations conducted with crude homogenates resulted in enhanced [3H]farnesol metabolism, decreased accumulation of [3H]farnesal, and increased levels of [3H]farnesoic acid. Substitution of NADP+ for NAD+ was ineffective, suggesting that farnesol and/or farnesal dehydrogenase were NAD+-dependent enzymes. Pellet fractions obtained by differential centrifugation of crude homogenates exhibited both farnesol and farnesal dehydrogenase activity but only the latter was clearly stimulated by addition of NAD+. The alcohol/aldehyde dehydrogenase(s) showed some substrate specificity for the 2E isomer; nerol and (2Z,6E)-farnesol were barely metabolized under conditions in which either geraniol or (2E,6E)-farnesol were rapidly oxidized. The identity of the [3H]farnesal zone obtained from RP-IPC was further established by normal-phase liquid chromatography and by gas-liquid chromatography-mass spectrometry.(ABSTRACT TRUNCATED AT 250 WORDS)

Locust adipokinetic hormone stimulates lipid mobilization in Manduca sexta

Adipokinetic hormone, a decapeptide isolated from the locust, stimulates mobilization of diacylglycerols from the locust fat body and loading of the lipid transport protein, lipophorin. Injection of the synthetic locust adipokinetic hormone into a sphinx moth, Manduca sexta, causes lipid loading of lipophorin. The lipophorin decreases in density from 1.11 to 1.06 g/ml, and a soluble protein from the hemolymph (apolipophorin III) associates with the lipophorin particle. Administration of intermediate doses of hormone indicates that lipophorin is converted directly to the low density form; no appreciable amounts of intermediate density particles are formed.

Histamine in the insect nervous system: distribution, synthesis and metabolism

The distribution of histamine in the nervous systems of the locust, the cockroach, and the sphinx moth was mapped and the capacity of locust nervous tissue to synthesise and metabolise histamine was assessed. In all three species the highest levels of histamine were present in the retina and in the lamina neuropil of the optic lobe. Lower levels of histamine were detectable throughout the nervous system. In the locust the retina was shown to synthesise considerable quantities of histamine. The optic lobe and metathoracic ganglion synthesised smaller, though significant, amounts of histamine. Metabolic inactivation of histamine in locust nervous tissue was shown to occur primarily via oxidation to imidazole-4-acetic acid and via N-acetylation to N-acetyl histamine. Whereas the retina and the optic lobe formed the two metabolic products in approximately equal proportions, the metathoracic ganglion produced almost three times as much N-acetyl histamine as imidazole-4-acetic acid.

Immunohistochemical investigations of neuropeptides in the brain, corpora cardiaca, and corpora allata of an adult lepidopteran insect, Manduca sexta (L)

In the brain of adult specimens of the tobacco hornworm moth, Manduca sexta (L), cells immunoreactive for several kinds of neuropeptides were localized by means of the PAP procedure, by use of antisera raised against mammalian hormones or hormonal peptides. In contrast, no such neurosecretory cells were found in the corpora cardiaca and corpora allata (CC/CA); in the CC/CA, however, immunoreactive nerve fibres were observed, reaching these organs from the brain. The neurosecretory cells found in the brain were immunoreactive with at least one of the following mammalian antisera, namely those raised against the insulin B-chain, somatostatin, glucagon C-terminal, glucagon N-terminal, pancreatic polypeptide (PP), secretin, vasoactive intestinal polypeptide (VIP), glucose-dependent insulinotropic peptide (GIP), gastrin C-terminus, enkephalin, alpha- and beta-endorphin, Substance P, and calcitonin. No cells were immunoreactive with antisera specific for detecting neurons containing the insulin A-chain, nerve growth factor, epidermal growth factor, insulin connecting peptide (C-peptide), polypeptide YY (PYY), gastrin mid-portion (sequence 6-13), cholecystokinin (CCK) mid-portion (sequences 9-20 and 9-25), neurotensin C-terminus, bombesin, motilin, ACTH, or serotonin. All the neuropeptide-immunoreactive cells observed emitted nerve fibers passing through the brain to the CC and in some cases also to the CA. In CC these immunoreactive nerve fibers tended to accumulate near the aorta. It was speculated that neuropeptides are released into the circulating haemolymph and act as neurohormones.

The rate of substrate cycling between glucose and glucose 6-phosphate in muscle and fat-body of the hawk moth (Acherontia atropos) at rest and during flight

1. The rate of substrate cycling between glucose and glucose 6-phosphate was measured in tissues of the hawk moth (Acherontia atropos). 2. The insect was injected with [2-3H,2-14C]glucose, and after periods of time at rest or flying the animal was freeze-clamped. Separation of glucose and hexose monophosphate from the tissues was performed by paper chromatography and t.l.c., and the 3H and 14C radioactivities in these compounds were measured. 3. On the basis of the 3H/14C ratios in these compounds and the measured rate of glycolysis, the rate of cycling was calculated. The rates of cycling were 0.03, 0.10, 0.06 and 3.9 mumol/min per g for fat-body at rest and during flight and for flight muscle at rest and during flight respectively. 4. The marked increase in the cycling rate between glucose and glucose 6-phosphate upon flight contrasts with the finding of Clark, Bloxham, Holland & Lardy [(1973) Biochem. J. 134, 589-597] in the bumble-bee, in which this condition inhibited cycling. It is suggested that the increased rate of cycling increases the sensitivity of glucose phosphorylation to changes in the concentrations of effectors of hexokinase should it be necessary to increase the rate of glycolysis in muscle, for example, to increase power output of the flight muscle for increased speed of flight.

Side chain modified sterols as probes into insect molting hormone metabolism. II: synthesis of monofluorocholesterols

The hydroxylations of the cholesterol side chain at C-20, 22, and 25 are key terminal events in ecdysone biogenesis. We have prepared the C-20, C-22, C-24, and C-25 monofluorinated cholesterols as potential inhibitors of these hydroxylation events, and preliminary bioassay results in Manduca sexta are reported. The synthesis of [26(14)C]-20-fluorocholesterol is also described. Although the 20-, 22-, and 25-monofluorocholesterols do not appear to affect larval growth and development, the 24-fluoro isomer shows a moderate retardation of growth and a modest increase in mortality.