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At least 127 records · Page 7Linked to original sources
PubMed1978

Neurosecretion. XVII. Experimentally induced release of neurosecretory material by exocytosis in the insect Leucophaea maderae.

In the corpora cardiaca of the insect Leucophaea the administration of serotonin elicits ultrastructural features indicative of the extrusion of neurosecretory material by exocytosis. The response to the stimulus and the process of extrusion seem to occur at considerable speed. Nearly all of the 30 test animals, fixed at various intervals starting as early as 3 min after the injection of the drug, show granules captured at the moment of leaving the axon as well as fully exteriorized secretory material. The fact that many of these granules are much smaller than the typical neurosecretory type speaks for intracellular fragmentation of the latter prior to the discharge of this cellular product. After 25 min or more the extruded electron dense structures show signs of breakdown. 3the apparent speed of these phenomena accounts for the dearth of omega-type configurations observed in unstimulated specimens of this species. The possible relationship between the membrane phenomena involved in exocytosis and the transient protrusions of bounding membranes of neurosecretory granules described in earlier papers remains to be clarified.

Animals↗
PubMed1977

"Gomori-positive" neurosecretion in the rat after deafferentation of the medial basal hypothalamus.

A portion of the "Gomori-positive" peptidergic neurosecretory (NS) cells in the paraventricular and especially in the supraoptic and postoptic nuclei degenerate three weeks after deafferentation of the medial basal hypothalamus. Most of the remaining NS cells show signs of high activity. Regenerating NS fibres form "muffs" around the blood vessels laterally from the lesion; some of them enter the "isolated" area or persist there if a thin layer of the brain tissue is left somewhere untouched under the basal end of the cut. The regenerating NS fibres are also found outside the nervous tissue: within the scar tissue, in the proliferating connective tissue of the brain sheet below the basal end of the cut and in the mantel plexus area. The NS fibres make close contact with blood vessels invading or penetrating the vascular wall. It is suggested that peptide neurohormones discharged from the "Gomori-positive" NS terminals enter the general blood circulation as well as the portal blood at the site of these newly formed axovasal contacts. It is supposed that under these conditions monoaminergic terminals do not discharge monoamines because no stimulation of monoamine-producing NS cells occurs with deafferentation.

Animals↗
PubMed1975

Correlations between brain catecholamines, neurosecretion, and serum corticoid levels in osmotically stressed mallard ducks (Anas platyrhynchos).

The effects of depleting brain catecholamines with a combined treatment of reserpine and alpha-methyl-p-tyrosine on serum corticosterone levels and release of immunoreactive neurophysin from the median eminence, in osmotically stressed and unstressed mallard ducks, were studied. Corticoid levels in salt loaded birds were more than three times that of unstressed birds. The combined treatment of reserpine and alpha-methyl-p-tyrosine significantly decreased the concentration of brain monoamines in all experimental groups and raised serum corticoid levels in non-stressed birds to the same level found in the osmotically stressed animals. Immunoreactive neurophysin in the zona externa of the median eminence was depleted in all birds subjected to either osmotic stress and/or reserpine treatment but not in unstressed control birds. These preliminary data indicate that catecholamines may exert an inhibitory influence on both ACTH release from the anterior pituitary and neurophysin from the median eminence and that these two events may in some way be interrelated in the duck.

Animals↗
PubMed1977

Neurosecretion. XVI. Protrusions of bounding membranes of neurosecretory granules.

Protrusions of bounding membranes of neurosecretory granules, comparable to those demonstrated by Castel (1977) in the mammalian neurohypophysis, were observed under various experimental conditions in the corpora cardiaca of the insects Leucophaea maderae and Periplaneta americana. Electrical stimulation in vitro of the nervus corporis cardiaci I, which elicited a marked rise in the amount of neurohormone discharged, as determined by bioassay, also yielded a significantly larger number of membrane protrusions than were observed in unstimulated controls. However, no comparable response was obtained in glands subjected to stimulation of hormone release by exposure to serotonin or high potassium concentrations. On the other hand, membrane protrusions were numerous under certain conditions not expected to stimulate neurohormone release, i.e., in tissue exposed to a zinc iodide mixture without prior fixation. The present results support the conclusion drawn by Castel that these configurations appear to be related to the process by which neurosecretory material is discharged. Too transient to be much in evidence under physiological condition, they become more prominent not only after appropriate acceleration of the rate of release, but also when such membrane arrangements are "frozen" by procedures that interfere with the regular milieu.

Animals↗
PubMed1977

An ultrastruct study of the innervation of the musculature of the pond snail Lymnaea stagnalis (L.) with reference to peripheral neurosecretion.

The ultrastructure of nerve endings in the musculature of Lymnaea stagnalis was studied. Seventeen different types of axon ending were distinguished according to the size and morphology of the granules or vesicles they contain. Nine types of axon endings form neuromuscular synapses. Some of these types also form axo-somatic synapses on peripheral neurones. One axon may innervate several muscle cells. Furthermore more than one type of axon may innervate one muscle cell. One type of axon ending forms axo-axonic synapses on the presynaptic part of neuromuscular junctions. In the connective tissue near muscle cells seven types of free axon endings were found. These seem to be peripheral neurosecretory endings. Some of these are probably derived from known types of neurosecretory cells in the central nervous system, whereas others appear to originate from peripheral neuronal perikarya. Body wall muscles appear to be innervated by neuromusculatur synapses, whereas in the visceral musculature both neuromuscular junctions and free axon endings are found.

Animals↗
PubMed1975

Neurosecretion in the sinus gland of the fiddler crab, Uca pugnax.

The ultrastructure of the sinus gland of the fiddler crab, Uca pugnax, was investigated and found to be similar to that in other crustaceans. Five types of neurosecretory axon terminals were tentatively identified on the basis of the size, shape, and electron density of granules within the axons. Release of neuro-secretory material appears to be by exocytosis.

Animals↗