Etude ultrastructurale des corpora cardiaca et de quelques formations annexes chez Locusta migratoria L

Multifactorial control of the release of hormones from the locust retrocerebral complex

The retrocerebral complex of locusts consists of the corpus cardiacum, the corpora allata, and the nerves that connect these glands with the central nervous system. Both corpus cardiacum and corpora allata are neuroendocrine organs and consist of a glandular part, which synthesizes adipokinetic hormones and juvenile hormone, respectively, and of a neurohemal part. The glandular adipokinetic cells in the corpus cardiacum appear to be subjected to a multitude of regulatory stimulating, inhibiting, and modulating substances. Neural influence comes from secretomotor cells in the lateral part of the protocerebrum. Up to now, only peptidergic factors have been established to be present in the neural fibres that make synaptic contact with the adipokinetic cells. Humoral factors that act on the adipokinetic cells via the hemolymph are of peptidergic and aminergic nature. In addition, high concentrations of trehalose inhibit the release of adipokinetic hormones. Although there is evidence that neurosecretory cells in the protocerebrum are involved in the control of JH biosynthesis, the nature of the factors involved remains to be resolved.

The ultrastructure of the prothoracic gland/corpus allatum/corpus cardiacum ring complex of the Australian sheep blowfly larva Lucilia cuprina (Wied.) (Insecta: Diptera)

The ultrastructure of the constituent endocrine glands within the ring complex of Lucilia cuprina larvae has not been previously described. This study investigated the ring complex of mid-third instar larvae. Three distinct endocrine cell types were identified: (1) prothoracic gland (PTG) cells which constituted the major cell type; (2) corpus allatum (CA) cells, localized in the anterior central region, and (3) corpus cardiacum (CC) cells, located posteriorly, ventral to the aorta. PTG cells were identifiable by their large ovoid nuclei (9-14 microns dia, length 12-18 microns) and numerous cytoplasmic lipid vacuoles. The plasma membrane of peripheral PTG cells were invaginated to form intercellular channels. The CA cells are characterized by ovoid nuclei (6-7.5 microns dia, 6.5-9 microns length) and electron dense staining cytoplasm. Compared to PTG cells the CA cells had smaller nuclei and lower nucleus:cytoplasm cell ratio. Extensive networks of highly irregular, electron-lucent intracellular spaces, dispersed throughout the cytoplasm were also characteristic of CA cells at this developmental stage. These spaces often contained membrane bound lipid vacuoles occurring singly or as aggregates. The CC contained both intrinsic and extrinsic neural components. The intrinsic cells were characterized by circular nuclei (6.5-8.5 microns dia), prominent nucleolus and numerous cytoplasmic electron-dense neurosecretory granules (100-240 nm dia). The extrinsic axons and terminals within the CC contained electron-dense neurosecretory granules (80-150 nm), neurotubules and mitochondria.

Neuronal maps of the frontal ganglion of the cockroach, Periplaneta americana, prepared by heavy metal iontophoresis

Neurons in whole mount preparations of the frontal ganglion (FG) of the cockroach, Periplaneta americana, were mapped with the aid of cobalt chloride staining and silver intensification techniques. Eighty-six neurons were counted in the FG after staining with reduced methylene blue. The cell size ranged between 20 to 35 microns in diameter. Of the somata located in the FG, 44 were found to contribute their fibers to the nervus recurrens, 26 to the right frontal commissure, 28 to the left frontal commissure, and 6 to the nervus connectivus. In addition, a few neurons presumably from the tritocerebral region also contribute their fibers in the formation of nervus connectivus. The present study has helped delineate the neuronal connections of the FG with the brain and neuroendocrine system (corpora cardiaca and corpora allata). This information will be useful in facilitating the positioning of microelectrodes in our future electrophysiological experiments.

Immunocytochemical demonstration of neuron-specific enolase in neuronal cell bodies of an insect

This study demonstrates the presence of neuron-specific enolase immunoreactivity in neuronal cell bodies in brain and retrocerebral complex of the insect Locusta migratoria. Immunoreactivity was found in all neurons but not in the neuroendocrine glandular cells of the corpus cardiacum. Cells in tissues and organs outside the nervous system do not display any immunoreactivity.

Ultrastructural demonstration of exocytosis of neural, neuroendocrine and endocrine secretions with an in vitro tannic acid (TARI-) method

The release of neural, neuroendocrine, and endocrine secretory products by exocytosis was ultrastructurally studied by means of tissue incubation in Ringer containing tannic acid (Tannic Acid Ringer Incubation-method; TARI -method), followed by conventional fixation. Tannic acid strongly enhances the electron density of extracellular (secretory) substances. During TARI -treatment of tissues exocytosis proceeds, but the exteriorized contents of the secretory granules are immediately fixed by tannic acid and do not diffuse away into the extracellular space. In this way detection of exocytosis is markedly facilitated since the number of exocytosis phenomena visible at the ultrastructural level considerably increases with progressing incubation time. Studies of the central nervous system of the mollusc Lymnaea stagnalis show that the occurrence of exocytosis during TARI -treatment is calcium-dependent. With the TARI -method exocytosis has been clearly demonstrated in a variety of structures (endocrine cells, neurohaemal axon terminals, synapses) of L. stagnalis, the insect Locusta migratoria, and the rat, including cell types where exocytotic release had not been shown before.

Ultrastructural comparison of the perisympathetic organs in three Coleoptera: Chrysocarabus auronitens F., Oryctes rhinoceros L. and Tenebrio molitor L

Ultrastructural comparison of different types of perisympathetic organs (POs) in three species of Coleoptera (Chrysocarabus auronitens, Oryctes rhinoceros, and Tenebrio molitor) showed that the structure of these organs was not related to their morphological types but to their topography. Two kinds of PO structure may be distinguished: compact median and diffuse lateral. They were similar in that both were surrounded by thin neural lamellae and exhibited numerous glial cells originating in the perineurium (type I perineurial cells) as well as abundant neurosecretory endings. They were different in as much as in median POs, the neurosecretory endings were generally surrounded by perineurial processes but in transverse POs, these endings were sheathless. Only one type of neurosecretory axon was distinguished in the median organs but three or four in the transverse. The nature of the processes by which neurosecretory granules are released may depend on the type of neurosecretory axon. For instance, exocytosis always occurred for dense spherical granules, and granule fragmentation was visualized for granules of smaller size.