Bo Ekengren

Localization of Monoamines in the Forebrain of Two Salmonid Species, with Special Reference to the Hypothalamo-Hypophysial System

SummaryIn the salmon and trout aminergic cell bodies were found in the nucleus recessus lateraralis (NRL) and the nucleus recessus posterioris (NRP), both of which are situated near the third ventricle. Three cell types could be distinguished. Type 1 produces a green and type 2 a yellow fluorescence. The former type probably contains dopamine and the latter 5-hydroxytryptamine. Both types possess intraventricular protrusions in contact with the cerebrospinal fluid. The third cell type produces a less intense blue-green fluorescence; relatively few cells of this type have thick processes in contact with the ventricle. In addition, large fluorescent cells were found in the salmon, dorsal from the caudal part of the NRL. The various parts of the NRL and NRP are interconnected by thick bundles of nerve fibers; tracts leaving the nuclei could be traced for short distances only. The cells of the nucleus praeopticus (NPO), those of the medial part and to a much lesser extent also of the lateral part of the nucleus lateralis tuberis (NLT) have an aminergic innervation which probably originates from the NRL and/or NRP. All parts of the neurohypophysis contain many monoaminergic fibers, with aminergic material concentrated at the neuro-adenohypophysial interface. Fibers were not observed to penetrate the basal lamina. In the salmon and trout the fibers have a similar distribution, but differ in the intensity of fluorescence, being high in the salmon and low in the trout. Only in the trout have fluorescent cells been found in the adenohypophysis and very occasionally in the neurohypophysis. A number of these cells are basophilic and show a PAS-positive reaction.

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.

Aminergic nuclei in the hypothalamus of the roach Leuciscus rutilus.

SummaryIn the hypothalamus of the roach (Leuciscus rutilus) green and yellow fluorescent cells were found in the nucleus recessus lateralis (NRL) and the nucleus recessus posterioris (NRP) and green fluorescent cells in the nucleus recessus preopticus (NRPO). The green fluorescence indicates the presence of noradrenaline or dopamine and the yellow one the presence of 5-hydroxytryptamine. The cells of the NRL and NRP contained electron dense granules averaging 70 nm in diameter. The NRL is divided into two parts. These and the NRP are connected by large fluorescent tracts. The NRL and NRP send axons towards the nucleus lateralis tuberis (NLT) and the NRPO sends axons towards the nucleus preopticus (NPO). It could not be established whether the aminergic nuclei described are the origin of the fluorescent fibers in the hypophysis of the roach.

Nucleus praeopticus and nucleus lateralis tuberis of Salmo salar and Salmo gairdneri: structure and relationship to the hypophysis.

SummaryThe nucleus praeopticus (NPO) is located on both sides of the preoptic recess and is composed of a pars parvocellularis and a pars magnocellularis. Only in the rainbow trout does the pars magnocellularis consist of separately located medium-sized cells and very large cells. Cytologically, three cell types can be distinguished: 1) unipolar cells ending in the cerebrospinal fluid (CSF), 2) bipolar cells also ending in the CSF and forming an axon, and 3) multipolar cells which generally do not have a direct connection with the ventricle.Axons originate from the cell bodies forming the paired preopticohypophysial tract that runs along the border of the diencephalon and the optic tract. A considerable number of NPO fibers leading to the hypophysis makes close contact with the cell bodies of the pars lateralis of the nucleus lateralis tuberis, indicating a functional relationship. Most NPO fibers terminate in the caudal part of the neurohypophysis, around blood capillaries and at the basal lamina of the pars intermedia. Far fewer fibers appear to terminate near the boundary of the neurohypophysis and the rostral and proximal pars distalis.The nucleus lateralis tuberis (NLT) is located in the caudal hypothalamus, beginning at the rostral end of the horizontal commissure and extending caudally beyond the hypophysial stalk. It consists of the partes rostralis, medialis, lateralis and ventrolateralis. In both species the p. rostralis contains small subependymal neurons and some larger ones. Only in the p. medialis of the Atlantic salmon are large cells present. In both species the most prominent part is the p. lateralis, which consists solely of large cells. Cells situated between the p. medialis and the p. lateralis are grouped in the p. ventrolateralis. It was impossible to trace the axons originating in the NLT, since the cyto- and axoplasm could not be stained specifically.The structure of the NPO and NLT in the two salmonid species is compared with that of other teleosts.

The nucleus preopticus and the nucleus lateralis tuberis in the roach, Leuciscus rutilus

SummaryThe hypothalamus of the teleost fish Leuciscus rutilus was investigated with the Falck-Hillarp technique. The nucleus preopticus (NPO) and the nucleus lateralis tuberis (NLT) contain no fluorescent, i.e. catecholaminergic cells. Green fluorescent fibers probably originating from the paraventricular organ and/or the preoptic recess organ, are intermingled with the cells.The electron microscopical study was based on the three fixatives glutaraldehyde-osmium tetroxide, osmium tetroxide and potassium permanganate. In the NPO two cell types are recognized, characterized mainly by dense core vesicles (dcv) with measured diameter of 130 nm and 170 nm across respectively. The endoplasmic reticulum in the former cell type generally has large dark inclusions measuring from 175 to 375 nm across, which are also found in the neurite. In the NLT, four different cell types are identified, some of which are subject to considerable variations. The rostral and the medial parts of the nucleus include a large cell type (I) with dcv of diameter 170 nm. The medial part also has a small cell type (II) with dcv of 80 nm. The lateral part is characterized by two cell types (III, IV). Cell type III occurs in three forms with dcv of about 140 nm. The fourth cell type (IV) is rare and contains irregularly formed granules, the most circular ones measuring about 130 nm and the most elongated ones 110 nm×210 nm. The ventrolateral part contains the same cell types (except for type II) as those found in the lateral and medial parts.The morphological differentiation of the NLT as well as its different cell types strongly indicates its functional diversity.After permanganate fixation the secretory granules of the different cell types in the NPO and the NLT appear as “empty” vesicles. This method also reveals that the cell types of the two nuclei have dcv of about 90 nm. The possible monoaminergic content and the role of these dcv are discussed.

The aminergic innervation of the pituitary gland in the roach Leuciscus rutilus

SummaryFluorescent (aminergic) fibers were demonstrated by the Falck-Hillarp technique in all parts of the neurohypophysis (NH) in the roach (Leuciscus rutilus). The fibers are very thin and few in number in the rostral (RNH) and proximal neurohypophysis (PNH) but slightly more numerous in the NH adjacent to the pars intermedia (PI). The fibers occur in normal fish as well as in specimens pre-treated with α-methyl-noradrenaline. It is proposed that all parts of the adenohypophysis have a very sparse aminergic innervation. There is no correlation between the number of type “B” fibers and fluorescent fibers in the roach NH. The technical difficulties in obtaining good and reliable results in teleost material are discussed.