Patrick Meurling

The arrangement of neurosecretory and catecholamine fibres in relation to the pituitary intermedia cells of the skate, Raja radiata

SummaryThe innervation pattern of the intermediate lobe of the skate (Raja radiata) was studied with histological and fluorescence histochemical methods. Neurosecretory fibres, stained with i.a. pseudo-iso-cyanine, were found running in bundles in the central parts of the cell cords. They terminated partly around the perinuclear parts of the intermedia cells, partly around the apices of the cells close to the vascular walls.A catecholamine innervation of the intermedia was also established. Catecholaminecontaining fibres with the appearance of nerve terminals were found around the intermedia cell apices close to the vessels. In some specimens, catecholamine fibres also seemed to terminate at the perinuclear parts of the cells.Thus it is possible, judging solely from structural relations, that both the cell body (the synthesis pole) and the cell apex (the release pole) receive a dual innervation. Recent experimental evidence indicates that the release of MSH from the pars intermedia is controlled by catecholamine fibres, but as yet there is only structural evidence for a special control of hormone synthesis.

The relations between neural and intermediate lobes in the pituitary of Squalus acanthias

Summary1.The neural and intermediate lobes of Squalus are separated by a connective tissue membrane, which is absent in only few places.2.The neural lobe consists of three layers: ependymal, fibre and external layer. The ependymal layer contains two cell types, ependymal cells and secretory cells (Sterzi). The fibre layer is mainly formed by neurosecretory nerves, which end within the lobe. The external layer consists of a stroma of branched ependymel fibres, and neurosecretory material.3.Along the membrane between the two lobes is a capillary network, the neural lobe plexus.4.The intermediate lobe consists of irregular cell columns and large blood sinuses. The cell columns have a zone of strongly staining cytoplasm nearest the vessels.5.Inside the cell columns is a system of intra-columnar connective tissue and intra-columnar arteries, the latter ending in the neural lobe plexus.6.Nerves from the neural lobe sometimes enter the intermediate lobe, either directly through the membrane, or at places where the membrane is absent. The nerves may run between the intermedia cells or in the intra-columnar connective tissue.7.The intermediate lobe of Squalus is penetrated by nerves only to a slight degree, in contrast to other Elasmobranch species (Scyllium, Mustelus, Pristiurus, Raja, Dasyatis, Torpedo).8.A comparison is made between different types of Elasmobranch neurointermediate lobes, and with the neurohypophysis of other Vertebrates. It is found that Squalus has a neural lobe of fairly primitive structure, while its intermediate lobe reaches a high degree of specialization.

Nerves of the neuro-intermediate lobe of Etmopterus spinax (elasmobranchi)

Summary1.The neural and intermediate lobes of Etmopterus are separated by a connective tissue membrane, which is absent only in restricted areas.2.The histology of the neural and intermediate lobes shows similarities with Squalus acanthias.3.Neurosecretory nerves enter the intermediate lobe either singly or in bundles. They form terminal swellings from which neurosecretory material or hormones probably disappear.4.“Non-neurosecretory” nerves also enter the intermediate lobe, reaching the intermedia cells of the whole lobe. The nerves are interpreted as a secreto-motor innervation of the lobe.5.The stainability of nerves in the neuro-intermediate lobe is discussed. It is made probable that the distal parts of the neurosecretory neurons do not become stained with silver, and that the silver-stained nerves present are of a different kind.

The paraventricular and posterior recess organs of elasmobranchs: A system of cerebrospinal fluid-contacting neurons containing immunoreactive serotonin and somatostatin

SummaryThe paraventricular organ (PVO) and the posterior recess organ (PRO) of two elasmobranch species, the spiny dogfish,Squalus acanthias, and the skate,Raja radiata, were investigated by use of scanning and transmission electron microscopy and immunocytochemistry employing a series of primary antisera. The PVO and PRO contained four types of cerebrospinal fluid (CSF)-contacting neurons. One type was free of secretory granules and projected a dendrite-like process into the ventricle. The other three types were distinguished according to the size of their secretory granules. The ventricular extensions of these cells were filled with secretory granules. By means of immunocytochemistry three types of CSF-contacting neurons were observed in the PVO and PRO. Type I contained only serotonin; type 2 displayed only somatostatin; type 3 was endowed with both serotonin and somatostatin. Type I dominated in the PRO, whereas type 3 was the most frequent in the PVO. The latter cells appear to be the site of origin of a loose tract formed by serotonin- and somatostatinimmunoreactive fibers projecting from the PVO into the neuropil of the PRO. Compact bundles formed exclusively by serotonin fibers were also shown to extend between the PVO and PRO. The basal processes of the CSF-contacting neurons of the PRO penetrated into the underlying neuropil. This neuropil is rich in synapses and can be regarded as an integrative area to which the basal processes of the local CSF-contacting neurons, serotonin and somatostatin fibers from the PVO, and fibers containing immunoreactive thyrotropin-releasing hormone of unknown origin, support a conspicuous input. The present findings indicate that the PVO and PRO of elasmobranchs are functionally integrated structures.

Catecholamine fluorescence in the pituitary of the eel, Anguilla anguilla, with special reference to its variation during background adaptation.

SummaryIn the neuro-intermediate lobe (NIL) of the eel, Anguilla anguilla, a specific formaldehyde-induced fluorescence, indicating a catecholamine (CA) innervation, has been demonstrated in the neural lobe processes. Microspectrofluorimetric analyses and pharmacological treatments indicate noradrenaline or dopamine or both to be responsible for the fluorescence.The fluorescence in the NIL has displayed a definite tendency toward variation during the adaptation to a white and to a black background. The highest amounts of fluorescence were generally found in animals adapted to a black background, especially when adapted for a rather long period, and in animals recently transferred to a white background. The lowest amounts of fluorescence were generally found in animals adapted to a white background.This and the result of injections of CA-depleting drugs suggest that the monoaminergic nerves are active when the animal is on a white background, inhibiting the MSH release directly or indirectly or both, or in co-operation with other factors.Specific green fluorescent structures were also found in other parts of the neural lobe supplying the pars distalis.In some pharmacologically untreated specimens and in animals treated with CA-depleting drugs, the intermedia cells fluoresced. Microspectrofluorimetric analyses indicated that this fluorophore was not a CA.We wish to express our sincere thanks to Miss Ingrid Carlsen for excellent technical assistance, Mr. Lajos Erdös for the photography and the technical staff of the Department of Histology in Lund. We are also indepted to Dr. Anders Björklund for valuable discussion and advice.

Effect of social rank on the growth of the preputial glands in male bank voles, Clethrionomys glareolus.

Abstract The relation of preputial gland weight to dominance in male bank voles, Clethrionomys glareolus , was studied. Adult males, reared initially in isolation, were used. After excising one preputial gland, the subjects were allocated to groups of five. After 2–3 weeks, when a social hierarchy had been established, dominant males were recognized by introducing an alien male into the group. These dominant males had significantly larger remaining preputial glands than subordinates or isolated males. The remaining glands in dominants were also significantly larger than the excised ones. No differences in the initial weights of the excised glands between males which were later classified as dominant or subordinate could be seen. The conclusions are, that the social dominance causes growth of the preputial glands in male bank voles, but that the preputial gland size when a group is formed is not critical in determining social position.

Pars Intermedia Control with and without Innervation - Studies in Elasmobranchs and a Lizard *

In recent years the structure and function of the pituitary pars intermedia of vertebrates have attracted a great deal of interest (see reviews by Etkin, 1967; Dodd et al., 1971; Rodriguez and Gimenez, 1972; Bagnara and Hadley, 1973). Apart from mammals, in which the function of the intermedia is still enigmatic, the Amphibia have, for a number of reasons, been the most thoroughly investigated. This report will deal chiefly with work from our laboratory on the control of the pars intermedia in Elasmobranchs and in the lizard Anolis carolinensis.

Control of pars intermedia activity in late embryos of the spiny dogfish, Squalus acanthias

SummaryNearly full-term yolk sac embryos of Squalus acanthias exhibit background adaptation with melanophore responses that are dependent on the pituitary pars intermedia. Whereas the intermedia cells of other Elasmobranchs are doubly innervated by adrenergic and peptidergic fibres, probably only a small adrenergic innervation is present in Squalus. Still, the activity of the gland is regulated in a manner similar to that of other species, as evidenced by experiments with neuro-intermediate lobectomy, hormone substitution, and hypothalamic lesions. An adrenergic release-inhibiting mechanism seems to have a central role, but the possibility of peptidergic involvement is not ruled out.