Portal Capillaries Research Articles

Immunohistochemical localization of gonadotropin‐releasing hormone (GnRH) in the fetal and early postnatal mouse brain

The objectives were to (a) determine the age in development when GnRH is first detectable in the brain and (b) observe the distribution of GnRH throughout the fetal and early postnatal period. GnRH was localized immunohistochemically in fetal (15, 16, 17 and 19 days of gestation) and early postnatal (1- and 7-day-old) mice with the peroxidase-antiperoxidase (PAP) method of Sternberger. In the organum vasculosum of the lamina terminalis (OVLT) and in the median eminence of the fetus, GnRH was first detected at 17 days of gestation. In the OVLT, GnRH was found ventral to the preoptic recess of the third ventricle near the ventral surface of the brain. In addition, GnRH was located adjacent to the superficial portal capillaries near the surface of the median eminence. At 19 days of gestation, the distribution of GnRH was similar to that observed at 17 days and there was a marked increase in amount. In the newborn mouse, GnRH was undetectable in the OVLT and its content in the median eminence was decreased as compared to that observed in the fetus. By the seventh postnatal day, a considerable accumulation of GnRH had occurred in the OVLT and median eminence. In the OVLT, it was associated with capillaries ventral to the preoptic recess, and its distribution in the median eminence was similar to that in the adult mouse. In both the OVLT and median eminence of the fetal and early postnatal mouse GnRH appeared to be stored in axons and axon endings, but was not detectable in nerve cell bodies or ependymal cells. These observations suggest that the potential for neuroendocrine control of gonadotropin secretion exists in the fetal mouse early as 17 days of gestation.

Ultrastructural studies on the localization of neurohypophysial hormones and their carrier proteins.

Neurophysin, vasopressin and oxytocin were localized in different portions of the supraopticohypophysial tract (SHT) using the unlabeled antibody enzyme technique at the ultrastructural level. In vasopressin-positive supraoptic perikarya, vasopressin and neurophysin were present in all neurosecretory granules. Within the zona interna of the median eminence, vasopressin and neurophysin were present in two populations of axons, one with granules of 1300-1500 A and one with granules of 900-1300 A. Following exposure of thin sections of median eminence to antiserum to neurophysin, reaction products were present in granules and in the extragranular cytoplasm in the axons with larger granules; in all other cases reaction product was confined to the granules. Vasopressin-positive fibers were also presented in large numbers of the zona externa of the median eminence and many terminated on the pituitary primary portal plexus. A few oxytocin fibers were present on the portal capillaries in the infundibular stalk. In the posterior pituitary all axon profiles were neurophysin positive. Neurophysin was present as both a granular and cytoplasmic pool. Vasopressin-containing axons account for 90% of the neuronal elements in the posterior pituitary and oxytocin for the remaining 10%. Findings on the subcellular distribution of these peptides are related to current theories on transport and release of neurohormones.

The hypothalamo-hypophysial system in acipenseridae. VI. The proximal neurosecretory contact region.

The proximal neurosecretory contact region (PCR) of Acipenseridae, a homologue of the tetrapod median eminence, has been studied by light, fluorescence and electron microscopy. It occupies the rostral and chiefly the ventral surfaces of the hypothalamic tuber cinereum. PAF-positive fibres occur in the zone of the preoptico-hypophysial tract but their terminal enlargements are concentrated mainly in the external zone. They make contact with the primary portal capillaries situated in the pia mater. Monoaminergic fibres and terminals with an intense green fluorescence are localized in the same regions. The fibres of some bipolar monoaminergic neurons of the PCR make contact both with the third ventricle and the primary portal capillaries. Three types of granule-containing neurosecretory fibres and terminals have been recognized in the PCR. Fibres of types A1 (d = 120-300 nm) and A2 (D = 100-170 nm) are peptidergic PAR-positive, although some fibres, including some of type A1, belong possibly to PAF-negative type. Monoaminergic type B fibres have granules 80-100 nm in diameter. Neurosecretory terminals and vascular "endfeet" of tanycytes make contact with the 70 nm thick outer basement membrane of the primary portal capillaries. Several laminae of thin horizontally oriented tanycyte processes form a boundary between the external zone and the preoptico-hypophysial tract. Few neuroglial cells with pale cytoplasm, numerous lysosomes and lipofuscin granules are seen in this region. It is hypothesized that, as in other vertebrates both peptide hypophysiotropic neurohormones and monoamines are discarged from the PCR into the portal circulation and affect the activity of the glandular cells of the pars distalis.

Response of tanycytes of rat median eminence to intraventricular administration of colchicine and vinblastine.

The effects of colchicine and vinblastine on tanycytes of the rat median eminence have been studied using the electron microscope. Colchicine and vinblastine were administered by intraventricular cannulation into the third ventricle and demonstrated distinct morphological effects on tanycyte microtubules. Highest drug doses administered were 50.0 mug in 5.0 mul of saline initially, followed by an additional 50.0 mug of these agents infused in a volume of 13.0 mul saline over an hour. Colchicine treatment resulted in the formation of large crystalloids within tanycytes, coincident with the disappearance of microtubules, all along the ventricular surface. Nonetheless the tanycytes appeared able to maintain a continuous, tight lining, as in controls, although some crystalloids were observed beneath the ventricular surface, either within tanycyte processes or within neuronal processes. Vinblastine treatment also resulted in the formation of identical crystalloids but at highest doses thoroughly destroyed the tanycyte lining of the median eminence and exposed cellular elements below the surface to the drug. Portal capillaries approaching the ventricular surface were generally free of any signs of drug response to either colchicine or vinblastine.

Influence of castration on incorporation of exogenous peroxidase into "synaptic" vesicles of the median eminence. II. The perivascular part of the palisade zone in male rats.

In the median eminence of male rats, nerve profiles in the immediate vicinity of portal capillaries have been divided into 4 categories on the basis of their vesicular content: profiles a with agranular "synaptic" vesicles of about 50 nm, b with similar agranular vesicles and also with granular vesicles of mainly 60-140 nm, c with granular vesicles alone and d without vesicles. Twenty-four hours after castration, the percentage of profiles of category a was significantly increased when compared with sham-operated animals, whereas the percentage of profiles of category b was significantly decreased. After intravenous injection of exogenous peroxidase, especially the nerve profiles located in direct contact with the outer basement membrane of the portal capillaries contained peroxidase positive "synaptic" vesicles. Injection off peroxidase after castration resulted in a significant increase in the percentage of nerve profiles containing both peroxidase positive and peroxidase negative "synaptic" vesicles (category a). It is suggested that, in certain nerve terminals, castration may lead to release off the content of granular vesicles, which may contain gonadotropin releasing factor. This release then may cause that nerve terminals with agranular vesicles and granular vesicles (category b) change in their vesicular content and are therefore classified as terminals with only agranular vesicles (category a). An increased turnover rate in the ultrastructurally affected terminals may be reflected in increased uptake of exogenous peroxidase. The observations imply that certain neurones projecting to portal capillaries in the median eminence are, directly or indirectly, sensitive to changes in the level of gonadal steroids.

Immunofluorescence study of the preoptico-infundibular LRF neurosecretory pathway in the normal, gastrated or testosterone-treated male guinea pig.

Luteinizing hormone-releasing factor (LRF) has been localized in a preopticoinfundibular pathway in normal, castrated and testosterone-treated male guinea pigs, by an immunofluorescence technique. Some animals of each group were injected into the lateral ventricle with10% to 50% methanol, with or without melatonin, prior to study. Controls for the specificity of the antisera to LRF were carried out by immunohemolysis, radioimmunoassays, or blocking experiments on tissue sections, using synthetic LRF, vasopressin, oxytocin, TRF, or a lipid-free brain extract. Immunoreactive cell bodies were counted in 100 serial 10 µ sagittal sections, between two symmetric paramedian planes 1 mm apart. A maximum of 5 to 15 positive cells⁄100 sections were found in all the animals, except the castrates treated with methanol in which as many as 20 times more reactivecells were found; melatonin did not produce a further increase in number, but it did produce an increase in the intensity of the immunoreactivity of the perikarya and their processes. The perikarya of cells containing LRF were localized in 3 groups: the main group was found in the pre- and suprachiasmatic region; smaller groups were located in front of the anterior commissure and the parolfactory region. Beaded axonal pathways containing LRF traveled from the perikarya of the two first groups through the hypothalamus, in a caudal direction to end in the infundibulum around portal capillaries. Along their course these axons appeared to branch and at times to make synaptic contacts with cell bodies. In addition to the“preoptico-infundibular pathway”, some extrahypophyseal LRF pathways have been observed, some of which suggested a role for LRF in the control of sexual behavior. (Endocrinology95: 1416, 1974)

Ultrastructure of Hypothalamic Neurons and of the Median Eminence

Ultrastructure of Hypothalamic Neurons and of the Median Eminence

Vasopressin and neurophysin: high concentrations in monkey hypophyseal portal blood.

Vasopressin and its binding protein, neurophysin, were measured by radioimmunoassay in the hypophyseal portal blood of monkeys after cannulation of individual long portal veins. Mean vasopressin concentrations (13,800 picograms per milliliter) in portal blood were more than 300 times as high as those in the systemic circulation (42 picograms per milliliter). Neurophysin concentration was approximately 25 times as high in portal as in systemic blood. By immunoperoxidase techniques, high concentrations of neurophysin were demonstrated around portal capillaries of the median eminence. These studies indicate direct secretion of vasopressin and neurophysin into the portal circulation; the quantities secreted during stress may be sufficient to exert significant effects on secretion of anterior pituitary hormone.

Electron microscopic studies of the development of new neurohaemal contacts in the median eminence of the rat after hypophysectomy

In the normal rat the axons of the parvicellular neurosecretory system form terminals which are characterised by dense core vesicles of 80–160 nm diameter and which lie against the fenestrated portal capillaries in the upper neurohypophysis (median eminence). The magnocellular neurosecretory axons traverse the interanal zone of the median eminence and form terminals against the fenestrated capillaries of the distal neurohypophysis (neural lobe). In the neural lobe it is assumed that the more electron dense vesicles (of around 200 nm diameter) characterise the vasopressin containing terminals of neurones in the supraoptic nucleus and that the less numerous terminals with the more electron lucent vesicles (also of around 200 nm diameter) belong to the axons of the paraventricular neurones and contain oxytocin. For the first few days after hypophysectomy, the proximal stumps of the cut neurosecretory axons in the internal zone of the median eminence are distended with neurosecretory material while axonal sprouts which are rich in neurotubules and completely ensheathed in satellite cell cytoplasm gradually penetrate the external zone. Subsequently there is a massive hypertrophy of fenestrated capillaries and the newly formed axonal sprouts progressively lose their satellite cell cover and thus acquire neurohaemal contacts with the outer basement membrane of the perivascular space. The development of these contacts is associated with the appearance of increasing numbers of synaptic vesicles and prejunctional dense projections. This reconstitution of the morphological features of the normal neurohaemal contacts is associated with recovery of antidiuretic function. In the hypertrophic median eminence the neurosecretory axon terminals with the electron lucent type of vesicles far outnumber those with the electron dense vesicles. It is suggested that the greater degree of cell loss from the supraoptic as opposed to the paraventricular nuclei puts the paraventricular axons at an advantage in competing for space on the basement membrane around the perivascular space of the newly formed capillaries. It is suggested that an important factor in promoting the regeneration of the neurosecretory axons is the remarkable hypertrophy of the fenestrated capillaries against which they come to terminate.

Post-coital depletion of dense-core vesicles from the external layer of the rabbit median eminence.

The effects of mating on the depletion of osmiophilic material from dense-core vesicles (DCV) within the external layer of the rabbit median eminence (ME) were investigated. Two different populations of DCV were demonstrated within the ME external layer of the non-mated control animals. A plot of the diameters of these vesicles showed two peaks, one at 90–100 nm, and the other at 120–130 nm. These two populations of DCV were found in separate axons and axon terminals in contact with, or near the perivascular spaces of, portal capillaries. Within these axons and terminals an occasional membrane profile or “vesicle ghost” was also observed.

Further Observations on the Structure and Function of Median Eminence, With Reference to the Organization of RF-producing Elements in the Endocrine Hypothalamus

Publisher Summary This chapter offers additional morphological and functional data suggesting that ependyma of the median eminence are capable of recovering thyrotrophin-releasing factor (TRF) from cerebrospinal fluid (CSF) and delivering it to the portal vessels. This capability is necessarily a fundamental requisite to a hypothesis in which the CSF is a part of the route of delivery of releasing factors from brain to the anterior pituitary. A major unresolved problem is the identity and location of those specialized parvicellular neurones in the central nervous system (CNS) responsible for secretion of the releasing factors. On the assumption that the parvicellular, releasing factor (RF)-producing neurosecretory system projects directly to the median eminence, much work is done to identify morphological correlates of their neuroendocrine activity in terminals and axonal inclusions of the palisade layer. Infusion of TRF into the lateral ventricle of the rat results in plasma thyrotrophin (TSH) responses whose time course is similar to that following intravenous infusion of TRF. It is suggested that the ependyma of median eminence are capable of transporting TRF from cerebrospinal fluid to the pituitary portal capillaries; thyroxine, and possibly catecholamines, influence the rate of this transport.

Fine structure of sinusoids and portal capillaries in the liver of the adult sheep and the newborn lamb.

AbstractIn adult sheep, the hepatic sinusoids have an endothelial lining with numerous gaps and fenestrae and are surrounded by a complete basal lamina. In newborn lambs, the sinusoids have a relatively thick endothelium with fewer gaps, and the space of Disse contains a partially formed endothelial basal lamina. In both adult sheep and lambs, perisinusoidal cells appear to form a network around the sinusoid. In portal areas, the endothelium of the smaller capillaries is fenestrated, but the larger capillaries have unfenestrated walls and are enmeshed in processes of pericytes. Projections of endothelial cells partially or completely occlude the lumen of some portal capillaries, and of a large majority of sinusoids scattered throughout the lobule.

Ultrastructural study of neurovascular contacts in the median eminence of the rat.

In the median eminence of the rat axons of the supraoptic-paraventricular-hypophyseal tract with elementary neurosecretory granules (150–200 mμ) traverse the internal zone. Terminals containing dense core vesicles 60–120 mμ in diameter end on the portal capillaries of the median eminence. A unique organisation of the primary portal capillaries is shown. Endothelial cells have many fenestrae. The pericapillary space has numerous extensions all of which represent a special zone around the endothelial tube. The fine structural organisation and function of the neurovascular contacts in the median eminence are discussed.

Monoamine oxidase in the neurohypophysis of the newt (Cynops pyrrhogaster pyrrhogaster), the toad (Bufo bufo japonicus) and the tortoise (Clemmys japonica).

Distribution of monoamine oxidase (MAO) was histochemically determined in the neurohypophysis of the newt (Cynops pyrrhogaster pyrrhogaster), the toad (Bufo bufo japonicus), and the tortoise (Clemmys japonica) by means of a tryptamine-tetrazolium (TNBT) method. The median eminence in all of these species gave a similar MAO reaction. The ependymal cells showed a very slight or no MAO activity. MAO-positive fibers, which extended rostro-caudally to the pars nervosa, were observed in the fiber layer of the median eminence. In the external layer of the median eminence, a large number of strongly MAO-positive fibers were identified around blood capillaries of the primary portal plexus. In the tortoise, these fibers were more conspicuous in the posterior region of the median eminence than in its anterior region. The presence of MAO-positive fibers around the portal blood capillaries suggests that a monoaminergic mechanism is functional in the regulation of the secretion of releasing factors at the level of the median eminence. MAO-positive fibers in the pars nervosa were, like in the median eminence, thickly distributed around the blood capillaries. In the pars intermedia, there were a considerable number of MAO-positive fibers among the intermedia cells and sometimes in close contact with them. These fibers appeared to innervate the pars intermedia via the pars nervosa.

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

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.

The influence of specific chemical factors in the solvent on the absorption of macromolecular substances from the small intestine of the new-born calf.

1. The absorption, without change, of [(131)I] and [(125)I]solutes of high molecular weight after duodenal infusion has been measured in anaesthetized calves less than 20 hr old by analysis of lymph collected from the thoracic or intestinal duct.2. Factors present in boiled bovine colostrum whey known to be necessary for the rapid absorption of [(131)I]bovine serum gamma-globulin have now been shown to accelerate the passage of [(131)I]polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000 (K.60) into the lymph in a comparable manner.3. [(131)I]PVP K.30 (mean mol. wt. 40,000) and [(131)I]human serum albumin could be absorbed to some degree in the absence of solvent factors necessary for the absorption of solutes of higher mol. wt. and a large proportion of the solute thus absorbed passed directly into the portal capillaries.4. Lactate and pyruvate and salts of certain lower volatile fatty acids resemble factors in colostrum whey in their facilitation of the absorption of both gamma-globulin and PVP K.60: these active compounds were not however found in colostrum in significant quantities.5. Potassium isobutyrate was the most effective of the compounds tested and at concentrations of 56.7 m-mole/l. generally accelerated absorption to a greater degree than did colostrum whey itself.6. Absorption of both gamma-globulin and PVP K.60 from colostrum whey was characterized by a profuse flow of lymph containing relatively low concentrations of labelled solute. In contrast, when these solutes were fed in solutions containing simple compounds such as potassium isobutyrate they appeared in very high concentrations in the lymph, the flow of which remained relatively scant.7. When [(125)I]PVP was administered in water, little was absorbed. If, however, such an infusion was followed 3 hr later by a duodenal infusion of colostrum, [(125)I]PVP passed into the lymph almost immediately. This response was too rapid for the colostrum to have reached the absorbing cells in the terminal ileum.8. Intravenous infusions of L+lactate have been found to facilitate the absorption of [(125)I]PVP K.60 introduced into the duodenum in water. This indicates that some of the solvent factors which accelerate absorption may reach the terminal ileum via the blood vascular system after they themselves have been absorbed from the upper small intestine.

Hypothalamic neurosecretion in the refractory and post-refractory periods and its relationship to the rate of photoperiodically induced testicular growth in Zonotrichia leucophrys gambelii.

1. In late summer and autum many temperate-zone birds pass through a refractory period during which testicular growth cannot be induced experimentally with long daily photoperiods. This phenomenon is caused naturally by the long days of spring and early summer. It involves a decrease in release of gonadotropins by the adenohypophysis. Since previous investigations indicate that the release of gonadotropin is mediated by the hypothalamic neurosecretory system, a study of neurosecretory activity during refractoriness is basic for the understanding of this phenomenon. 2. Preliminary morphological studies on refractory birds revealed lateral divisions of neurosecretory cells lying between the supraoptic and paraventricular nuclei regions previously described (Okscheet al. 1959). Neurosecretory axons from these divisions join the tracts which pass to the median eminence. 3. Birds maintained in outdoor aviaries and killed from May through September showed a pronounced increase of neurosecretory material in the median eminence in late June, when testes regressed. This was accompanied by increases in neurosecretory material in the tracts and lateral division of neurosecretory cells described above, with reduction in sizes of cells and cell nuclei. The amount of neurosecretory material in the supraoptic nucleus was variable, but showed some increase, and the cells, again, decreased strikingly in size. 4. A series of birds was killed in the field from September through December. In the first part of this period there were considerable quantities of neurosecretory material in the median eminence. A pronounced reduction occurred in mid-October shortly before the earliest date at which positive testicular responses to long daily photoperiods have been obtained experimentally. The pathways from the lateral divisions of neurosecretory cells contained material initially (September) and at the end of the period (December) but were empty in late October and early November. The lateral divisions of neurosecretory cells contained minimal quantities of neurosecretory material at this time; the cells and nuclei appeared larger. Cells of the nucleus supraopticus contained variable amounts of neurosecretory material, but cells and nuclei reached a maximum in size, and presumably in activity, in late October and early November. 5. In studies of photoperiodic testicular response, birds were tested with 15-hour and 20-hour photoperiods at intervals from September through May. A positive response to long daily photoperiods first appeared in late October and early November. In adult birds the rate of response to 15-hour photoperiods was initially low, but increased significantly over November–December. The response of first-year birds (i.e. birds hatched during the previous summer) to 15-hour photoperiods proved difficult to interpret. On 20-hour photoperiods, however, the testicular growth rate was initially low, and increased significantly over November, December and January to an apparent maximum for this day length. 6. It is suggested that during refractoriness a factor required for the synthesis and/or release of gonadotropins cannot be transferred from the axons of the median eminence via the portal capillaries to the adenohypophysis in sufficient quantities to cause a testicular response. The inhibition at the level of the median eminence expresses itself histologically as an accumulation of neurosecretory material in the hypothalamus and a reduction in the amount of cytoplasm and the size of cell nuclei in neurosecretory regions. This inhibition sinks below an effective level for complete refractoriness in middle and late October, while days are still long enough to cause some activity of the neurosecretory system. This minor resumption of activity in autumn is probably associated with the autumnal gonadal recrudescence observed in some species. The reduced rates of testicular response obtained experimentally in November–December are attributed to persistent low-level activity of the inhibitory process. The reduced activity of the neurosecretory system after late autumn in wild birds is apparently attributable to the essentially nonstimulating effect of the shorter day lengths of this season.

肝炎時の脾腫竝に肝循環に関する研究

The author pursued the changes of portal pressures and closed venous capillary pressures in normal dogs and in the normal dogs with experimental liver disturbances induced by allyl formate and carbontetrachloride and at the same time studied the picture of intrahepatic portal and intrahepatic venous capillaries by X-rays, and obtained the following results.1. The portal pressures in normal dogs show the maximum of 120 mm H2O and the minimum of 70 mm H2O with average of 93 mm H2O, and the pressures of closed hepatic venous capillaries show the maximum of 136 mm H2O and the minimum of 95 mm H2O, with the average of 118 mm H2O. In the roentgenograms intrahepatic venous and portal capillaries can be traced to their fine ends as they flow in slow curves.2. In the observations conducted at the interval of every 30 minutes for 5-6 hours after subcutaneous injection of 0.04 cc/kg allyl formate both portal pressure and closed hepatic venous pressure shew a marked rise, reaching their maximum one and half to two and half hours after the injection, thereafter showing a decreasing tendency. In the roentgengrams of intrahepatic veins and portal the shadow of blood vessels is poor and especially the direction of peripheral capillaries is indistinct.3. In the observations conducted for 5-6 hours after the subcutaneous injection of 2.0 cc/kg carbon tetrachloride, both portal pressure and pressure of closed hepatic venous capillaries, rising graudally, reach the maximum three or three and half hours after the injection, thereafter showing a falling tendency. The roentgenograms of intrahepatic veins and portal veins show irregular or nodular blood flow and the decrease in the number of venous branches.4. After subcutaneous injections of 0.01 cc/kg allyl formate or 0.3 cc/kg carbon tetrachloride per day successively for five days and measuring the portal pressures and pressure of closed hepatic veins on the sixth day, both show higher values than in the case given one single acute injection of a large dose. Roentgenograms of intrahepatic veins and portal veins reveal the nodular uneven direction of vessels markedly and irregularly.5. Braching of intrahepatic venous capillaries and portal veins both present almost the same findings in their roentgenegrams.