Gunnar Fridberg

The praeoptico-hypophysial system, Nucleus tuberis lateralis and the subcommissural organ of Gasterosteus aculeatus after changes in osmotic stimuli

SummaryThe histology and cytology of the praeoptico-hypophysial system, nucleus tuberis lateralis and subcommissural organ in Gasterosteus aculeatus were analyzed after the fishes had been put in waters of different salinity (see Tables 1–4).These three structures are all identical in fishes which are accustomed to fresh water and to 32‰ salt-water. A transference to hypertonic water causes changes in the neurosecretory system which suggest the existence of an antidiuretic principle in the neurosecretory substance. No such relationship is found when the fishes are put into hypotonic water. Further, no connection is found between either the secretion production in nucleus tuberis lateralis or in the subcommissural organ and variations in osmotic value.

Gonadotropic cells in the Atlantic salmon, Salmo salar

SummaryThe gonadotropin-producing cells (GTH-cells) in the Atlantic salmon were studied light and electron microscopically before, during and after spawning, and after injections of luteinizing hormone-releasing hormone (LH-RH). The double immunofluorescent technique was applied using rabbit anti-carp GTH as the first antibody. Numerous immunofluorescent cells were observed throughout the pars distalis, but very few in the pars intermedia. These cells are basophilic and PAS-positive, and ultrastructurally classified as globular gonadotropes. Only one gonadotropic cell type could be identified; its size, morphology and fine structure vary considerably. In the same specimen the GTH-cells can be predominantly globular or vesicular in appearance, depending on the reproductive phase of the fish. At spawning and after LH-RH injection, many GTH-cells reach a vacuolar stage; the content of the vacuoles is not immunofluorescent. Another cell type, which resembles GTH-cells in semithin sections, did not show gonadotropic properties; its nature and functional significance are unknown. In addition, the present study revealed an increase in the synthetic and exocytotic activity of prolactin cells after LH-RH injections. It is suggested that LH-RH mediates this effect via LH and eventually via estradiol.

The presence of somatomedin in the Baltic salmon, Salmo salar, with special reference to smoltification

Abstract Serum obtained from Baltic salmon cross-reacted in the human placental radioreceptor assay for somatomedin. The salmon serum displaced radiolabelled somatomedin A (SMA) parallel to the human reference serum. The salmon serum was equipotent to human SMA in the radioreceptor assay but did not cross-react in a radioimmuno-assay for SMA. It is therefore proposed that Baltic salmon produce a somatomedin analogous to human somatomedin. The serum levels of this salmon somatomedin were higher during smoltification than prior to and after the period of smoltification.

The fine structure of the caudal neurosecretory system in Raia batis

SummaryThe fine structure of the caudal neurosecretory system in Raia batis was studied. Far-reaching similarities with ultrastructural details of other vertebrate neurosecretory systems were noted. The secretion is present in all parts of the system in the form of elementary neurosecretory granules which seem to be formed in the Golgi complex of the cell body. The morphology of the terminal region is discussed in relation to the possible mode of secretion release and in connection with the routes of secretion to the vascular lumen.The Dahlgren cell is not considered to be a secretory neuron, but a specialized glandular cell type, which has, to some extent, the same properties as nerve cells.

The caudal neurosecretory system in some elasmobranchs

A caudal neurosecretory system is found to be present in the elasmobranch species investigated. The secretion is transported along the neurosecretory processes to the peripheral area of the spinal cord, where the processes connect up with meningeal vessels. In comparison with the neurosecretory cells in the teleost spinal cord, the Dahlgren cells have a more extensive distribution, and the terminals of their secretion-carrying processes are not concentrated into a urophysis, but extend through an area corresponding to the distribution of the cells. The most primitive organization of the caudal neurosecretory system is met with in Squalus acanthias, Raia batis and Raia radiata, in which the terminals are situated within the nervous tissue immediately under the meninx. This is characteristic also of the early stages of development of the primitive urophysis in the pike. A more advanced form of organization occurs in Torpedo ocellata, where the neurosecretory processes enter the meninx of the ventromedian part of the spinal cord. The secretion, which is a protein, with possibly a low lipid content, is subject to morphological variations identical with those described in teleosts. The presence of the secretion in the form of submicroscopic granules is assumed, and these granules may coalesce to form larger granules and droplets visible in the light microscope. It is suggested that the Dahlgren cell is a specialized type of glandular cell of great phylogenetic age, developed independently out of primitive glandular cells which may have been present is the neural epithelium of ancestral vertebrates.

Ultrastructural studies on the ontogenesis of the caudal neurosecretory system in the roach, Leuciscus rutilus.

SummaryThe ontogenesis of the urophysial system (caudal neurosecretory system) in the roach (Leuciscus rutilus) was ultrastructurally analyzed. In newly hatched spawns the urophysial components are differentiated in the form of neurosecretory perikarya, axons and terminals and display the characteristics of a functional system although the neurohemal area is not developed. It is assumed that the system is active simultaneously with the preopticohypophysial system during ontogenesis. On the contrary, organogenesis of the urophysis is late, and only at the 14 mm stage do the neurosecretory axons first penetrate the meninx to participate in the formation of the organ.Assumed aminergic cell types associated with the urophysial system are differentiated at the time of hatching, thus indicating a functional relationship. A secretory ependyma releasing its granules into the central canal is described.