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L H Rademakers

Publications and source records attributed to L H Rademakers.

60 records · Page 4Linked to original sources
PubMed1977

Identification of a secretomotor centre in the brain of Locusta migratoria, controlling the secretory activity of the adipokinetic hormone producing cells of the corpus cardiacum.

After retrograde filling of axons terminating in the glandular lobe of the corpus cardiacum (CC) of Locusta migratoria with cobalt chloride, a paired group of about 15 cobalt containing cells was demonstrated in the lateral area of the protocerebrum. The axons of these cells run via the NCC II into the glandular lobe of the CC. These small neurons have the characteristics of secretory cells; they contain secretory granules of about 1000 A in diameter. The axon terminals in the glandular lobe, making synaptic contacts with the glandular cells, contain secretory granules of the same size. It is therefore concluded that the cell groups in the protocerebrum control the activity of the glandular cells which produce an adipokinetic hormone. Arborizations of fibers of the lateral secretomotor cells are present in the dorsal neuropile of the protocerebrum, ventral of the mushroom bodies and along the tracts of the NCC I within the brain. It is proposed that these arborizations are sites of synaptic input. It is discussed that the axons of these cells might receive additional synaptic input in the storage lobe of the CC. The localization of cell bodies, the axons of which enter the storage part of the CC is described. The course of the axon tracts of the various cell groups in the protocerebrum and their connections with the NCC I and NCC II are demonstrated.

Animals↗
PubMed1977

Effects of isolation and transplantation of the corpus cardiacum on hormone release from its glandular cells after flight in Locusta migratoria. A quantitative electron microscopical study.

The glandular lobe of the corpus cardiacum (CC) of Locusta migratoria contains secretory cells and axon terminals. It is generally accepted that the glandular cells produce an adipokinetic hormone which stimulates the release of diglycerides from the fat body. The axon terminals are supposed to be involved in the regulation of the secretory activity of these cells. CC were transplanted into locust hosts. The secretory activity of the glandular cells and axons was studied in the transplants as well as the intact host CC. Quantitative electron microscopical examination of the glandular cells of the CC in animals both at rest and after flight shows that only in the host CC the secretory activity of the glandular cells is stimulated by flight, as indicated by an increase in the activity of the Golgi zones and in the number of exocytotic pits. In the axon terminals release of secretory products, indicated by synaptic vesicles and membrane indentations, is reduced as a result of the transplantation. It is concluded that the glandular cells need excitatory input from outside the CC for stimulation of their secretory activity. Furthermore, it is proposed that the transplanted glandular cells decrease the level of activity of the intact host cells by way of a negative feedback mechanism.

Animals↗
PubMed1977

Changes in the secretory activity of the glandular lobe of the corpus cardiacum of Locusta migratoria induced by flight. A quantitative electron microscopic study.

The glandular lobe of the corpus cardiacum of Locusta migratoria is characterized by the presence of one type of secretory cells containing secretory granules with a diameter of 2000-3000 A, and of axons with small granules (diameter 950 A). The axons form synaptic contacts with the cells. The secretory products of the glandular cell are released by exocytosis in the gland proper. In the axon terminals, release is indicated by the presence of synaptic vesicles and omega-shaped indentations. In order to study possible changes in the secretory activity of the gland during flight, three groups of locusts were studied with quantitative electron microscopical methods, i.e., resting insects, having flown for 5 min (short flight, SF), and insects after prolonged flight (PF, 60 min). After flight, greater secretory activity of the glandular cells is indicated by a marked increase in the number of exocytotic pits in SF and PF insects, by an enlarged nuclear volume as well as an increased amount of secretory products in the Golgi cisterns of PF animals. Flight also causes greater release activity in the axon terminals. From these results it is concluded that an intrinsic hormone, apparently the adipokinetic hormone, is released from the glandular lobe and regulates the substrate supply from the fat body during flight. It is suggested that the secretory activity of the glandular cells is controlled by the axon terminals on these cells.

Animals↗
PubMedDate not supplied

Ultrastructural evidence for the presence of ferritin-iron in the biliary system of patients with iron overload.

Ferritin-like particles were observed in bile canaliculi of patients with iron overload. These particles have been further investigated by: a staining method enhancing the size and contrast of ferritin protein, and electron probe microanalysis detecting the presence of the elements iron and phosphorus. Morphological observation of coated vesicles in the cytoplasm adjacent to the bile canaliculi and coated pits in the canalicular membrane suggests a transport mechanism via membrane-bound organelles. Support is given to the theory that part of the iron, stored in the liver, leaves the hepatocyte by excretion of ferritin into the bile.

Anemia, Sideroblastic↗
PubMedDate not supplied

Iron content and acid phosphatase activity in hepatic parenchymal lysosomes of patients with hemochromatosis before and after phlebotomy treatment.

Lysosomal structures in liver parenchymal cells of 3 patients with iron overload and of 3 subjects without iron-storage disorders were investigated. A combination of enzyme cytochemistry--with cerium as a captive ion to demonstrate lysosomal acid phosphatase activity--and electron probe X-ray microanalysis (EPMA) was used. We were able (1) to define and quantify lysosomal structures as lysosomes, siderosomes, or residual bodies, (2) to quantify the amount of iron and cerium simultaneously in these structures, and (3) to evaluate a possible relation between iron storage and enzyme activity. With histopathologically increased iron storage, the number of siderosomes had increased at the cost of lysosomes, with a corresponding increase in acid phosphatase activity in both organelles. In histopahtologically severe iron overload, however, acid phosphatase activity was low or not detectable and most of the iron was stored in residual bodies. After phlebotomy treatment, the number of siderosomes had decreased in favor of the lysosomes, approaching values obtained in control subjects, and acid phosphatase activity was present in all iron-containing structures. In this way a relationship between iron storage and enzyme activity was established. The iron content of the individual lysosomal structures per unit area had increased with histopathologically increased iron storage and had decreased after phlebotomy treatment. From this observation, it is concluded that the iron status of the patient is not only reflected by the amount of iron-containing hepatocytes but, as well, by the iron content lysosomal unit area.

Acid Phosphatase↗