Neurosecretion: XV. An electron microscopic study of the corpora cardiaca ofPeriplaneta americana after experimentally induced hormone release

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.

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.

Axoglial synaptoid contacts in the neural lobe of the human fetus

Axoglial synaptoid contacts as well as junctional specializations were examined in the neural lobe of five human fetuses ranging from 7.5 to 19 weeks of ovulation age. Because synapselike contacts (SLC), which have both presynaptic and postsynaptic densities, were observed only in the younger fetus (7.5 weeks), they may be transient structures. Axoglial SLC were also found in older fetuses, but their structural characteristics were different from those found in a 7.5-week fetus in that the cytoplasmic membrane density was found only on the presynaptic side and its extent was decreased. In the youngest fetus observed here (7.5 weeks), puncta adherentia were observed. In the fetuses older than 11 weeks, gap junctions, long adherentia-type junctions with thick filamentous structures, and mixed junctions with both types of contact were found between pituicytes.