Esteban M. Rodríguez

Vascularization of the hypophysial region of the normal and adenohypophysectomized toad

SummaryThe study of standarized sections of the hypophysial regions, and in vivo observations showed the presence of communicating vessels between the capillary network of the median eminence and the large capillaries of the neurointermediate junction. Moreover, direct branches from the hypophysial artery are described which give off branches, at the level of the neural stalk, to the median eminence and to the large capillaries of the neurointermediate junction.A second portal system similar to the one described by Cruz has been observed. Its primary plexus originates in several encephalic regions, and its secondary plexus is distributed through the neural lobe and thence to the pars intermedia. The course of flow in this system is a descending one. The arterial contribution to this system appears to arise from branches from the basilar and retroinfundibular arteries. — There are small venous-type vessels between the large capillaries of the neurointermediate junction and the posterodorsal region of the pars distalis. — After adenohypophysectomy, the blood which normally goes towards the pars distalis, flows towards the pars intermedia, following the path of the communicating vessels between the median eminence and the pars intermedia.

NEUROSECRETORY SYSTEM OF THE TOAD BUFO ARENARUM HENSEL AND ITS CHANGES DURING INANITION.

Abstract Studies have been carried out on the neurosecretory system of the toad Bufo arenarum Hensel in normal conditions and in different states of inanition. Extreme inanition produces an increase in neurosecretory material (NSM) which can be due to a decreased demand of the hypofunctioning adenohypophysis, or to a blockage of liberation of NSM. Furthermore, this accumulation of NSM in the hypothalamus could indicate that inanition does not stop its production. In normal conditions and especially in cases of extreme inanition the axons that form the hypothalamus-hypophysial tract show three different images of the NSM. This suggests the possibility that we are dealing with different secretory materials. At the same time the parallel increase of the NSM in the neuronal processes which go toward the third ventricle and of the Gomori-positive granules of the choroid plexus leads us to believe that other extrahypophysial pathways exist for the elimination of the NSM. A description is given, both in the controls and in the experimentals, of a group of neurosecretory axons which leave from the tract and run ventrally toward the optic chiasma.

Differences between median eminence and neural lobe in amphibians

SummaryThe neurohypophysis of the toad Bufo arenarum Hensel can be subdivided into two well defined zones: the median eminence and the neural lobe. In its turn, the median eminence consists of two zones: a neural subependymal one, containing the axons of the hypothalamic-neurohypophysial tract; and a glandular one, made up of the capillaries of the primary plexus of the portal hypophysial system and of neurosecretory axons.Different staining techniques and certain experimental procedures (inanition, dehydration and adenohypophysectomy) showed that there are differences between the neurosecretory material of the neural lobe, which is a place of hormone liberation into the systematic circulation, and the neurosecretory material of the median eminence, which is the site of release of adenohypophysis-stimulating substances into the portal vessels.

The different origins of the neurosecretory hypothalamo-hypophysial tracts of the toad Bufo arenarum hensel.

Abstract In one group of toads, the external region of the median eminence containing the nerve fibres ending on the portal capillaries was severed by electrocoagulation whereas most or all the fibres going to the neural lobe were left intact. In a second group of animals, the whole median eminence was electrocoagulated, and therefore, all the fibres entering the median eminence and the neural lobe were interrupted. Four and 7 days after the operation, the animals with a partial destruction of the median eminence showed an increase in neurosecretory material in the axons leading from the dorsal group of neurons of the preoptic nucleus (DPO). After 14 days, these neurons became hypertrophied, vacuolated and very deeply stained by the aldehyde fuchsin. After a complete destruction of the median eminence, the changes after 4, 7 and 14 days appeared not only in the DPO but also in the ventral group of neurons of the preoptic nucleus (VPO). It is concluded that in the toad, the preoptic nucleus gives origin to two different aldehyde-fuchsin positive tracts; the VPO → neural lobe tract, and the DPO → median eminence tract.

Light and electron microscopy of granules in the toad choroid plexus

SummaryTwo types of granules can be distinguished in the toad choroid plexus under the light microscope: pigment granules, mainly localized in the cells that line the free ends of the choroidal villi, and Gomori-positive granules, present in most epithelial cells.The ultrastructural analysis of the choroid plexus reveals three types of granules: multivesicular bodies (MVB), multigranulous bodies (MGB) and dense bodies (DB), and intermediate stages between the last two bodies. The pigment granules seen under the light microscope probably correspond to the DB of the electron micrographs, and the Gomori-positive granules to the MGB. The probable role of these bodies is discussed and so is the significance of the glycogen present in the choroidal cells, their processes and endothelium.

The effects of adenohypophysectomy on the hypothalamic-hypophysial neurosecretory system and the adrenal gland of the toad Bufo arenarum Hensel

SummaryThe effects of adenohypophysectomy were studied on the hypothalamichypophysial neurosecretory system and the adrenal glands of Bufo arenarum Hensel. An increase in vascularization of the pars intermedia was found and the neurosecretory material (NSM) in the glandular region of the median eminence disappeared. Its reappearance later was accompanied by hypertrophy of the pars intermedia; differentiated chromophil cells appeared in the pars intermedia around the vessels and, at the same time, the adrenal reverted to normal. These findings are interpreted as hypertrophy and differentiation of the pars intermedia with replacement, at least partly, of the functions of the pars distalis. The probable mechanism of differentiation and the functions of chromophil cells of the pars intermedia are discussed.

Comparative aspects of nervous control of pars intermedia

Abstract The comparative study of pars intermedia control clearly indicates that both nerve and blood supplies are essential pathways for the control of MSH release. Most of the blood vessels penetrating the pars intermedia of tetrapods derive from a dense vascular plexus interposed between the neural and intermediate lobes. In many species this plexus intermedius represents the only vascular supply to the pars intermedia. In turn, this plexus is supplied by capillaries draining the neural lobe, and in some species, also by capillaries coming from the median eminence. Therefore, the blood irrigating the pars intermedia comes from two important neurohemal areas. Based on histochemical and ultrastructural characteristics more than one type of nerve fiber has been described in the pars intermedia of most species studied. The application of the zinc iodide-osmium tetroxide impregnation method (ZIO) to the pars intermedia showed that all types of nerve fibers have ZIO-positive material. Several histochemical, pharmacological and experimental studies strongly suggest that certain variations of the ZIO method and the histochemical fluorescence methods for biogenic amines stain the same group of substances. It is, therefore, postulated that all pars intermedia nerve fibers contain a biogenic amine. Consequently, the distinction between “ordinary” and catecholamine-containing fibers in the pars intermedia should be reconsidered. Instead, the different types of fibers of the pars intermedia may be recognized by considering their histochemical, ultrastructural and electrophysiological characteristics, or their different origins. In lower vertebrates the pars intermedia is poorly vascularized and richly innervated. On the contrary, the innervation of the pars intermedia of higher vertebrates is poor or completely absent and blood vessels are more numerous. However, the pars intermedia of most species studied appears to be under hypothalamic inhibitory control, regardless of the pattern of innervation. All the evidence available points to the possibility that the purely nervous mechanism inhibiting MSH release in lower vertebrates has shifted to a neurovascular mechanism in higher vertebrates.

Ultrastructure of the rat pineal gland grafted under the kidney capsule.

SummaryPineal glands were grafted under the kidney capsule of mature male rats for periods of 20, 40, 60 and 100 days. Each grafted gland was then excised and divided into two halves. One half was processed for conventional electron microscopy and the other was fixed in aldehydes and then incubated in a zinc iodide-osmium tetroxide mixture at pH 4.4 (A-ZIO-4.4). During the forty days following the operation pinealocytes showed the typical ultrastructural features associated with cells with a high protein and/or peptide secretory activity. On the other hand, during this period, the number of granular vesicles decreased progressively. From day 40 on, the grafted pinealocytes lacked granular vesicles. During the second half of the experimental period the ultrastructure of the pinealocytes indicated that their secretory activity was considerably decreased. During the acute phase of the experimental period numerous structures regarded as the tip of growing axons as well as typical nerve fibres appeared around blood vessels and within the parenchyma of the grafted gland. In the transplanted tissue obtained 60 and 100 days after the operation the growth cones were scarce, whereas typical nerve endings became numerous. These endings contained small clear vesicles which reacted positively when the tissue was treated with A-ZIO-4.4. The secretory activity of the grafted pineal gland and the nature of the nerve fibres which innervate the graft are discussed.The authors wish to thank Mrs. E.M. Rodríguez de Calderón for her valuable help

The reticular substance of the medulla oblongata of the albino rat

SummaryThe region of the reticular giganto-cellular nucleus, perfused with formalin and postfixed in osmium tetroxide, was studied with histochemical and electron microscopic techniques. The perikarya of the neurons have two zones. The peripheral cytoplasm contains Nissl bodies, mitochondria, and free RNP particles. The juxtanuclear cytoplasm contains the Golgi complex, mitochondria, RNP particles and dense bodies. The nucleus is indented and has a prominent nucleolus and a paranucleolar body. Dense bodies are found along the axon and dendrites as well. Three different types of synapses are described and two types of synaptic vesicles (spherical and ellipsoidal) are shown.The capillary endothelium shows microvilli and marginal flaps. The endothelial cytoplasm contains vacuoles, micropinocytotic vesicles, and a few dense bodies. Processes of pericapillary cells, surrounded by a basement membrane, also contain dense bodies. The dense bodies found in the neurons and endothelial cells show acid phosphatase activity. On the basis of their morphology and their enzymatic activity these bodies are identified as lysosomes.

Ultrastructure of the male rat hypophysis chronically grafted under the kidney capsule

SummaryMale rats were divided in two experimental groups. In group I two partes distales of the hypophysis were grafted under the kidney capsule and in group II two complete hypophyses were transplanted. Animals were killed 5 to 22 months after the operation. The grafted tissue was excised and processed for light and electron microscopy.The transplanted pars distalis tissue showed a well developed vascularisation in contrast to the pars intermedia which appeared poorly vascularised. Six different cell types were observed in grafted pars distalis. They correspond to the different types of cells found in the rat pars distalis “in situ”. The predominant cell type in the graft displayed all the morphological characteristics of stimulated prolactotrophs. Pars intermedia cells appeared hypertrophied resembling the MSH cells under stimulation. Two types of syncytial formations were frequently seen. One of them appeared to originate from prolactotrophs and the other from MSH cells. Bodian impregnated fibres and structures resembling either growth cones of axons or typical nerve endings were observed in the pars intermedia of long-term grafted hypophyses. Pituicytes remained as isolated clusters of cells. Canaliculi lined by two or more pituicytes were observed. Saccular formations resembling the hypophyseal cleft appeared in all grafts studied. The present findings suggest that in the male rat the chronically grafted pituitary gland is capable of synthesising most or all the hormones which are known to be produced by the gland “in situ”. Furthermore, prolactin and MSH seem to be the predominant secretion of the transplanted pituitary.