The ultrastructure of certain components of the corpora cardiaca in orthopteroid insects

A local insulin reservoir in Drosophila alpha cell homologs ensures developmental progression under nutrient shortage

Insulin/insulin-like growth factor (IGF) signaling (IIS) controls many aspects of development and physiology. In Drosophila, a conserved family of insulin-like peptides called Dilps is produced by brain neurosecretory cells, and it regulates organismal growth and developmental timing. To accomplish these systemic functions, the Dilps are secreted into the general circulation, and they signal to peripheral tissues in an endocrine fashion. Here, we describe the local uptake and storage of Dilps in the corpora cardiaca (CC), an endocrine organ composed of alpha cell homologs known to produce the glucagon-like adipokinetic hormone (AKH). We show that Dilp uptake by the CC relies on the expression of an IGF-binding protein called ImpL2. Following their uptake, immunogold staining demonstrates that Dilps are co-packaged with AKH in dense-core vesicles for secretion. In response to nutrient shortage, this specific Dilp reservoir is released and activates IIS in a paracrine manner in the prothoracic gland. This stimulates the production of the steroid hormone ecdysone and initiates entry into pupal development. We therefore uncover a sparing mechanism whereby insulin stores in CC serve to locally activate IIS and the production of ecdysone in the PG, accelerating developmental progression in adverse food conditions.

Cardioaccelerator release in Periplaneta americana (L)

Focal electrical stimulation of the brain of Periplaneta americana evokes the release of a factor with high cardioaccelerator activity. Results of extirpation of components of the retrocerebral complex from an isolated head preparation imply that the corpus cardiacum is the critical component of this system. The cardioaccelerator is a heat-stable proteinaceous compound.

HYDROLYZING ENZYME ACTIVITY IN THE BRAIN AND THE RETROCEREBRAL SYSTEM OF THE AMERICAN COCKROACH (PERIPLANETA AMERICANA (L)) WITH SPECIAL REFERENCE TO THE NEUROSECRETORY MATERIALS

Some hydrolyzing enzymes have been investigated by histochemical and biochemical methods. Almost all neurons in the brain contain acid phosphatases. About half of the total activity is associated with subcellular particles. Most of the acid-phosphatase activity in the corpora cardiaca (CC) is associated with the neurosecretory materials (NSM). Elementary neurosecretory granules (ENG) have been isolated from the CC by fractionation and subfractionation procedures and subjected to in vitro enzyme activity studies. Electron micrographs of the subfraction having the highest acid-phosphatase activity are discussed in relation to three types or "stages" of ENG. About 80% of the total esterase activity in the brain and the retrocerebral system has been found to be in a "soluble" form. The remaining 20%, the "insoluble" forms, may be associated with subcellular organelles. The methods of Gomori and Burstone for acid-phosphatase localizations are compared, and differing results discussed. The possible roles or functions of acid phosphatases and esterases in the neurosecretory system are discussed.

Insect Neurosecretory Material Separated by Differential Centrifugation

The factor which accelerates the beating of the insect heart was found to be concentrated in a "large granule" fraction of the corpora cardiaca of the cockroach, Periplaneta americana (L.).