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.

Pharmacology of insecticide-induced release of hyperlipaemic hormone in the locust, Locusta migratoria

1. The mechanism of insecticide-induced release of hyperlipaemic hormone from the glandular lobe of the isolated corpora cardiaca (CC) of locusts has been studied using pharmacological agents. 2. Treatment of isolated CC with various insecticides induces the release of hyperlipaemic hormone as judged by bioassay. 3. Reserpinisation of CC (25 micrograms/locust) or treatment of isolated CC with the alpha-adrenergic-receptor blocker phentolamine had no effect on the action of DDT or bioresmethrin, but partially blocked the action of dieldrin and chlorfenvinphos. 4. Treatment of isolated CC with the postsynaptic cholinergic blocker hexamethonium bromide abolished the effect of dieldrin and chlorfenvinphos, but did not block the action of DDT or bioresmethrin. 5. The effects of all the insecticides tested in this study were completely blocked by treatment of the CC with 10(-6) M tetrodotoxin. 6. The results indicate that DDT and bioresmethrin may act directly on the glandular cells via a sodium-dependent mechanism. The results with dieldrin and chlorfenvinphos suggest the presence of two distinct cholinergic pathways, one of which acts via the pre-synaptic aminergic terminals which control the glandular cells, whereas the other acts elsewhere in the CC. Sodium channels are also involved in the ultimate expression of these two insecticides.

Is octopamine a transmitter mediating hormone release in insects?

The release of hyperlipemic hormone from the glandular cells of the corpus cardiacum (CC) of Locusta migratoria is under the synaptic control of axons in nervus corpus cardiacum II (NCC II). The effects of aminergic agonists and antagonists on the release of the hyperlipemic hormone induced by electrical stimulation of NCC II have been examined. CC isolated from reserpine-injected locusts did not release hormone when subjected to electrical stimulation of NCC II but continued to release hormone in response to high-potassium saline. The electrically stimulated release of hormone from isolated CC was abolished by the alpha-adrenergic blocking agent, phenoxybenzamine, but potentiated by the beta-adrenergic blocking agent, propranolol. Phenoxybenzamine did not interfere with release induced by high-potassium saline. It is suggested that the postsynaptic receptors on the glandular cells are similar to the alpha-adrenergic receptors of vertebrates. Octopamine was found to be present in the glandular lobe of the CC at concentrations of 0.62 pmole per gland pair. Reserpine depleted the content to 0.3 pmole per pair. Bathing the CC in 10(-7) M octopamine resulted in the release of hyperlipemic hormone, and this release was blocked by phenoxybenzamine. It is concluded that the neurotransmitter involved in the synapse between axons of NCC II and the cells releasing hyperlipemic hormone is aminergic, possibly octopaminergic. Octopamine may well be a transmitter mediating hormone release in insects.

Isolation of material displaying insulin-like immunological biological activity from the brain of the blowfly Calliphora vomitoria

An insulin-like material from the brain of the blowfly Calliphora vomitoria was partially purified by acid alcohol extraction, gel filtration and ion-exchange cellulose chromatography. In addition, the RF value on polyacrylamide-gel electrophoresis was determined. The material was characterized by its ability to cross-react with bovine insulin antibody and by displaying diminished immunoreactivity on dilution. It displaced specifically bound 125I-labelled insulin from rat liver plasma membrane insulin receptors and displayed insulin-like biological activity on the isolated rat fat-cell. Within 30 min of injection into Calliphora, made hypertrehalocaemic and hyperglucaemic as a result of median neurosecretory cell removal, it caused the concentrations of both sugars to return to normal. The hypothesis is put forward that the median neurosecretory cells are the source of the material.

Demonstration of an ecdysteroid receptor in a cultured cell line of Drosophila melanogaster

Incubation of the high-speed supernatant from the Kc cell line of Drosophila melanogaster with [3H]ponasterone A results in significant binding of the ligand as determined by gel filtration and dextran-coated charcoal binding assays. In vivo exposure of the Kc line to [3H]ponasterone A for 30 min results in a marked binding of the ligand by a KCl-soluble nuclear extract. With both the cytosol and nuclear preparations the binding has specificity and a low dissociation constant (3 X 10(-9) M). In addition the labeling of the nuclear preparation exhibits a saturation at approximately 7 X 10(-10) M which probably reflects the molar concentration of cytoplasmic receptors.

Possible involvement of monoamines in the release of adipokinetic hormone in the locust Schistocerca gregaria

1. The adipokinetic hormone release, which can be induced by anticholinesterases, is reduced by depleting the content of monoamines in the nervous system. 2. The participation of monoamines in the pathway of release of adipokinetic hormone is studied in vivo and in vitro. 3. A possible mechanism for anticholinesterase-induced release of this hormone involving cholinergic and aminergic transmission is postulated.