Andreas Oksche

The hypothalamo-hypophysial neurosecretory system of the white-crowned sparrow, Zonotrichia leucophrys gambelii

Summary1.The North American fringillid finch, Zonotrichia leucophrys gambelii, has a well developed hypothalamic neurosecretory system.2.Compared with the nucleus supraopticus, the nucleus paraventricularis is poorly developed and poor in neurosecretory material.3.The median eminence can contain so much neurosecretory material that it may be regarded as a depot of such material second only to the neurohypophysis.4.The nucleus supraopticus contains already in the nestling a considerable quantity of neurosecretory material; however, the neurosecretory content of the neurohypophysis is quite low. In the median eminence of the nestling there are only scattered neurosecretory granules.5.In early summer the neurosecretory hypothalamic nuclei and the median eminence contain only very small amounts of neurosecretory material. However in autumn, when the birds are refractory to photoperiodic stimulation, there are very extensive accumulations of neurosecretory material. The ganglionic cells, in which the numerous neurosecretory granules are stored, appear to be relatively inactive in late spring.6.Birds which had been held since late-autumn or winter on short daily photoperiods of 8 hours, also in spring and early summer, had large amounts of neurosecretory material in the cells of the hypothalamic nuclei and in the median eminence.7.During June–August, with birds held since previous autumn on 8-hour days, the increase of the daily photoperiod from 8 hours to 20 hours caused, in 20 days, a marked increase in testicular weight and body weight. Simultaneously there was a decrease in the amount of neurosecretory material in the cells of the hypothalamic nuclei and especially in the median eminence whereas the quantity of neurosecretory material in the neurohypophysis appeared to be unaffected. The reduced quantity of neurosecretory material in the median eminence was particularly noticeable during the second half of the daily photoperiod. During the dark period in the 20-hour birds, as well as in the 8-hour birds and birds on natural photoperiod, there was a reaccumulation of neurosecretory material.8.From December to February the response to increases in daily photoperiod are not as pronounced as in spring; the 8-hour and 20-hour birds have no observable differences in the neurosecretory picture.9.Osmotic stress by addition of NaCl to the drinking water causes in the nucleus supraopticus and the nucleus paraventricularis a marked increase in nuclear volume and an increase in the formation of neurosecretory material. Simultaneously there is a depletion of the store of neurosecretory material in the neurohypophysis.10.The increase in body weight, which follows the increase in daily photoperiod, is the result primarily of an extensive deposition of subcutaneous and visceral fat. This is the result of a hyperphagia and an alteration in intermediary metabolism in which glycogen storage in the liver is extensively reduced.11.In early summer (June) the median eminence of the castrates of both sexes had substantially more neurosecretory material than those of the control birds. However, in autumn there were no apparent differences between castrates and normal birds, because of the increased neurosecretory material in the latter.12.The causes and significance of these observations in respect to hypothalamic control of the endocrine system are discussed.

The hypothalamo-hypophysial neuro secretory system of the zebra finch, Taeniopygia castanotis

General RésuméThe investigations described herein were made primarily to obtain information for an adequate description of the hypothalamic neurosecretory system of the Zebra Finch, Taeniopygia castanotis, but further, to obtain some indication of the morphologic variations associated with functional changes. Comparisons have been made with a similar previous study of the White-crowned Sparrow, Zonotrichia leucophrys gambelii.1.The neurosecretory system of the Zebra Finch differs from that of Zonotrichia leucophrys gambelii as follows: a) The median division of the supraoptic nucleus is relatively poorly developed and lacks the very large cells that are so characteristic of Z. l. gambelii. The most rostral part of the preoptic recess of the Zebra Finch is neither as thin-walled nor as strongly extended rostrally as in Z. l. gambelii. b) In the perikarya of the neurosecretory ganglionic cells of the Zebra Finch the neurosecretory material is predominantly in the form of droplets and globules in contrast to the predominance of fine granules in Z. l. gambelii. c) The median eminence has a somewhat different structure than that of Z. l. gambelii. In silver preparations the looping fibers, characteristic of the posterior division of the median eminence and especially of the infundibular stem in Z. l. gambelii, are less prominent; the fine neural structure is somewhat reticular, consisting of fine endings whose relationships to the supraoptico-hypophysial tract and tubero-hypophysial tract must be investigated more closely. The neuroglia of the median eminence of the Zebra Finch show cytologic indications of activity. Selectively stainable ependymal and glial loops are lacking. d) The neurosecretory tract, which passes in a rostro-caudal direction through the zona interna, is especially conspicuous. Its repletion with neurosecretory material is in contrast to the neurosecretory content of the zona externa. This suggests that the zona externa, with its palisade layer, has a functional role that is independent of that of the fibers leading to the neurohypophysis. e) The neurohypophysis of the Zebra Finch is much more variable than that of Z. l. gambelii; there are sac-like, diverticular, and compact types.2.Among wild Zebra Finches there are extensive differences in amount of neurosecretory material. The density of neurosecretory material in the palisade layer of the median eminence appears to have an inverse relationship to gonadal development.3.The neurosecretory system is well differentiated in nestlings. The neurosecretory ganglionic cells contain extensive amounts of neurosecretory material. There is also some neurosecretory material in the median eminence whereas the neurohypophysis contains the smallest amounts.4.The neurosecretory system of Zebra Finches in captivity with water ad libitum is relatively rich in neurosecretory material. In the neurosecretory cells the droplet form is most prevalent. When Zebra Finches are subjected to restricted water intake by permitting 1. a single two-minute drink per day (approximately 5 ml intake per week) or 2. a single two-minute drink per week (0.5–1.0 ml intake per week) the neurosecretory system becomes more active with enlargement of the neurosecretory cells, their nuclei, and their nucleoli. In the first group the occurrence of neurosecretory droplets increases significantly. Large neurosecretory globules become common. In the second group fine granular neurosecretory material and paranuclear cap-like accumulations of granules appear. Herring bodies develop frequently in the infundibular stem and neural lobe. Water restriction does not appear to affect the amount of neurosecretory material in the palisade layer of the median eminence. When Zebra Finches are given solution of NaCl up to 0.5 M in concentration as the sole source of drinking fluid, there is a moderate activation of the system characterized by the appearance of fine granular neurosecretory material. Birds that are able to tolerate 0.7 or 0.8 M NaCl have extremely enlarged neurosecretory cells with conspicuous fine granular neurosecretory material although homogeneous globules of neurosecretory material continue to be present. Herring bodies appear. The neurohypophyses are not completely depleted.5.Many Zebra Finches maintain normal body weight with 0.6 M NaCl as the only drinking fluid. With 0.5 M the daily volume intake is of the order of 1 to 2.5 times body weight. Some individuals survive in apparently good health with 0.7–0.8 M although fluid intake is drastically reduced and body weight decreases somewhat. NaCl intake as high as 70 mg per gram body weight per day may occur in birds drinking hypertonic NaCl solutions. The ability of the Zebra Finch to tolerate high concentrations of NaCl in drinking water exceeds that of other passerine species studied thus far. Similarly the ability to survive in cages in a dry, hot environment with a water intake of ca. 1 ml per week is remarkable for a small bird.6.Increasing the duration of the daily photoperiod from 9 to 18 hours neither depletes the neurosecretory content of the median eminence nor causes gonadal development. This is consistent with field studies that indicate that the reproductive activities of this species are not timed photoperiodically.

Vascularization of the hypothalamo-hypophysial-complex in the white-crowned sparrow,Zonotrichia leucophrys gambelii

Summary1.The main arterial supply to the hypothalamo-hypophysial neurosecretory system of theZonotrichia leucophrys gambelii is provided by the anterior rami of the right and left internal carotid arteries.2.The supraoptic and paraventricular nuclei are supplied by the preoptic arteries which are the branches of the right and left anterior cerebral arteries. Distinctive capillary plexus occur in the vicinity of the supraoptic and paraventricular nuclei.3.The median eminence and neural lobe are supplied by the infundibular artery which is a constant branch of the anterior ramus.4.There aredistinct anterior and posterior capillary plexus corresponding to the anterior and posterior divisions of the median eminence.5.Distinct anterior and posterior groups of portal vessels drain the anterior and posterior primary capillary plexus, respectively. Only minor capillary-caliber anastomoses occur between the two groups.6.The anterior group of portal vessels is mainly distributed into the sinusoids of the cephalic lobe of the pars distalis, whereas the posterior group of the portal vessels supplied mainly the sinusoids of the caudal lobe of the pars distalis.7.The blood from the pars distalis is drained into the cavernous-sinus system and via the carotid veins into the jugular venous system.8.The venous blood from the neural lobe is also drained directly into the cavernous sinuses. There is no evidence that the venous blood from the neural lobe enters the sinusoids of the pars distalis.9.The venous drainage from the supraoptic and paraventricular nuclei is into the preoptic radicles of the middle cerebral vein and thence via the transverse sinus and the occipital vein into the jugular system.10.The differentiation of the primary eminential capillary plexus into the anterior and posterior divisions correlates well with the arrangement of the neural components in the anterior and posterior divisions of the median eminence. The peculiar arrangement and distribution of the portal vessels into the cephalic and caudal lobes of the pars distalis may be related to a cytological and functional differentiation of these lobes.

Neurosecretion in birds.

Abstract Morphologically the hypothalamic neurosecretory system of birds includes (1) two rather diffuse neurosecretory nuclei, the paraventricular nucleus and supraoptic nucleus which, according to the species concerned, consist of several more or less distinct divisions; (2) two hypothalamo-hypophysial neurosecretory tracts, the paraventriculo-hypophysial tract and the supraoptico-hypophysial tract , which are not separately identifiable in many species; (3) the neurosecretion-rich infundibular branches of the hypothalamo-hypophysial neurosecretory tract in the median eminece ; and (4) the neurohypophysis and the neurosecretory fibers leading thereto. Specific functions cannot be assigned as yet to the individual neurosecretory nuclei or to their divisions. For the distal parts of the system, functions may be divided into those of the neurohypophysial and eminential components . The former is identified primarily with the regulation of water balance and apparently also with the ecbolic function in ovulation. The hormone involved is probably arginine vasotocin which is probably produced by hypothalamic neurosecretory cells and transported in association with the stainable neurosecretory material via the hypothalamo-hypophysial neurosecretory tract to the posterior lobe. Although oxytocin occurs in the posterior pituitary its function is unknown. The eminential component , whose radial neurosecretory fibers emanate from the eminential plexus and extend outwardly into juxtaposition with the primary capillaries of the hypophysial portal system, is primarily involved in control of the function of the adenohypophysis. This component is best known from the studies on species in which the gonadotropic function of the adenohypophysis is photoperiodically controlled. To us, the best hypothesis of the general functional mechanism of the eminential component is that the “releasing factor” or “releasing factors” are formed in hypothalamic neurosecretory cells where they become associated with neurosecretory material, which is usually stainable with aldehyde-fuchsin or chromalum hematoxylin, and which passes via neurosecretory fibers into the radial fibers of the zona externa of the median eminence. It seems evident that the control of the adenohypophysis is exerted primarily through the transfer of such “releasing factors” from these fibers into the primary capillaries of the portal system. It is possible that this transfer involves a functional relationship between the neurosecretory fibers and fibers from the nonneurosecretory tubero-hypophysial tract. The very fragmentary data available suggest that the gonadotropic function of the adenohypophysis is almost completely dependent on such “releasing factors” although the gland does have basic adrenocorticotropic and thyrotropic functions that are independent of the median eminence. However, higher levels of thyrotropic and adrenocorticotropic activity by the adenohypophysis apparently require the appropriate “releasing factors”.

Compartments and perivascular arrangement of the meninges covering the cerebral cortex of the rat

SummaryThe intercellular clefts of the brain and the leptomeninges, and the perivascular spaces were studied with reference to the results obtained in a previous study (Krisch et al. 1983). The spatial relationships of these compartments were analyzed at the electron-microscopic level. Horse-radish peroxidase (HRP) was injected into the brain or into the contralateral ventricle.The pattern of distribution of HRP depends on the boundary situation in the individual compartments. The inner and outer pial layers accompany the vessels intruding into the brain. In the Virchow-Robin space the pial funnel obliterates within a short distance. The inner arachnoid layer is continuous with the outer arachnoid layer when it covers the vessels traversing the meningeal space. The perivascular compartment is not in communication with the arachnoid space; moreover, the pial funnel within the Virchow-Robin space is sealed off against the arachnoid space.Thus, blood vessels traversing the meningeal spaces and subsequently penetrating the brain surface are exposed to the common intercellular compartment represented by the intercellular clefts of the brain and the leptomeninges; this compartment does not communicate with the other compartments. The cerebrospinal fluid located in this intercellular compartment is preferentially drained into the upper cervical lymph nodes.

THE HYPOTHALAMIC NEUROSECRETORY SYSTEM OF COTURNIX COTURNIX JAPONICA.

Summary1.The neurosecretory cells of Coturnix coturnix japonica occur in two areas, the supraoptic nucleus and the paraventricular nucleus. These nuclear areas consist of a series of extended groups of cells (divisions) that are interconnected through irregular chains of neurosecretory cells. The paraventricular nucleus is large and well-developed.2.Morphologically the neurosecretory cells vary extensively even in normal or control birds. There may by indistinct, small cells with very little neurosecretory material or relatively large cells filled with homogeneous neurosecretory material. In the latter the initial sections of axons are frequently conspicuous because of the presence of neurosecretory granules. The large paraventricular nucleus is striking because of its very intense neurosecretory activity. The initial part of the neurosecretory tract is clearly evident because of stainable neurosecretory substance.3.In addition to the accumulation of neurosecretory material in the neural lobe there is a second storage site in the zona externa of the median eminence.4.When NaCl solution is used for drinking fluid the neurosecretory cells are activated. With NaCl concentrations of 0.1–0.15 M only a mild enlargement of these cells occurs and the amount neurosecretory material in the neural lobe is only gradually decreased. However, with 0.2–0.25 M there are significant changes. The neurosecretory cells attain a very marked enlargement with the neurosecretory material being in the form of fine granules. Simultaneously there is a marked depletion of neurosecretory material in the posterior lobe.5.When the neurosecretory material of the posterior lobe is depleted because of the drinking of NaCl solutions of 0.2–0.25 M, the neurosecretory material in the zona externa of the median eminence appears to be unaffected. In contrast to the complete depletion of neurosecretory material in the neurosecretory pathway leading to the neural lobe, the fiber bundles leading to the zona externa contain a significant amount of neurosecretory material.6.It is not possible, on the basis of this investigation, to indicate the relative participation of axons from the supraoptic nucleus and paraventricular nucleus with respect to the median eminence and neural lobe.7.The functional significance of individual divisions of neurosecretory nuclei is still unknown. The higher concentrations of NaCl used in our experiments stimulated all parts of the neurosecretory nuclei. What significance can be attached to certain regional differences in activity in untreated quail or in experiments with low concentrations of NaCl, is still not clear.

A comparison of the effect of long daily photoperiods on the pattern of energy storage in migratory and non-migratory finches

Abstract Caged white-crowned sparrows, Zonotrichia leucophyrs gambelli , when subjected to long daily photoperiods in mid-winter, deposit large amounts of subcutaneous and visceral fat and develop migratory behavior comparable to natural vernal migratory behavior. The altered metabolic state involved in this deposition of fat is characterized by a reduction in glycogen content of the pectoral muscles and liver and a suppression of the diurnal glycogen cycle in these organs. There is also a marked increase in the fat content of these tissues so that the total mobilizable energy in them is considerably greater than in the short-day winter birds. The thigh muscles show a similar reduction in glycogen content but only a very slight increase in fat content. This change in the pattern of energy storage may be regarded as one feature of the scheme which produces the metabolic alterations necessary for sustained migratory flight. The wintering population of the Oregon Junco, Junco oreganus montanus , in southeastern Washington responds, although less extensively, to long daily photoperiods. This may be correlated with its more restricted migratory movements. The non-migratory English sparrow, Passer domesticus , when subjected to long daily photoperiods, shows no such alteration in the pattern of energy storage in pectoral muscle and liver; rather there is a tendency toward a lower level of energy storage. Although Zonotrichia leucophrys gambelii in mid-winter have much less glycogen in pectoral muscle and liver than the indoor caged birds, the pattern of energy storage may be consistent with that of the latter in experimentally induced migratory state if the restricted flight activity of the latter, the precapture activity of the former, and possible differences in temporal pattern of food intake are taken into consideration. The relatively small amount of glycogen available, and the extensive storage of fat, suggest that there must be very extensive use of fat or fatty acids directly by the pectoral muscles during flight.

The effect of dehydration on acid-phosphatase activity, catheptic-proteinase activity, and neurosecretion in the hypothalamo-hypophysial system of the white-crowned Sparrow, Zonotrichia leucophrys gambelii

General SummaryThe investigations described herein were made primarily to ascertain the effects of dehydration on acid-phosphatase and catheptic-proteinase activities in the hypothalamo-hypophysial neurosecretory system of Zonotrichia leucophrys gambelii, thereby providing a basis for comparison with the previously demonstrated changes in the activities of these enzymes in photoperiodically induced gonadotropic activity. Thus they provide a further test of the hypothesis that the accumulations of neurosecretory material in the pars nervosa and the palisade layer of the median eminence are under essentially independent controls. They also provide further information concerning the usefulness of data on the activities of these enzymes as indicators of the functional state of the hypothalamo-hypophysial neurosecretory system. 1.Dehydration by deprivation of drinking water for 8–32 hours was found to have the following effects:a)Region of supraoptic nucleus. Initial increase in acid-phosphatase activity with return to normal by 24 hours after the beginning of the period without water; increase in proteinase activity that becomes significant between 8 and 32 hours of deprivation from water; increase in nuclear diameter in neurosecretory cells and reduced amounts of coarse, dense aldehyde-fuchsin positive material with an increase in fine granules. Similar, although less extensive changes in nuclear size and neurosecretory material were observed also in the paraventricular nucleus.b)Regions of the median eminence. No clearly significant change in acid phosphatase activity; marked increase in proteinase activity; no change in density of neurosecretory material in the posterior division; an initial increase followed by a subsequent, marked decrease in neurosecretory material in the zona externa of the anterior median eminence (regions I and II).c)Pars nervosa. Marked increase in acid-phosphatase and proteinase activities and in weight of gland; decrease in neurosecretory material.d)Adenohypophysis (pars distalis). No significant change in acid-phosphatase activity; increase in proteinase activity.e)Adrenal gland. Increase in volume of cortical tissue; decrease in sudanophilic material.2.The results of these experiments, when compared with the results of experiments with photoperiodic stimulation of the hypothalamo-hypophysial neurosecretory system, support the hypothesis of independent functions of the eminential and neurohypophysial components.3.It appears that dehydration may exert two separate effects on the hypothalamo-hypophysial system of this species: a) The well-known reduction of the density of neurosecretory material in the neurosecretory cells and in the pars nervosa (also in the hypothalamo-hypophysial neurosecretory tract) now associated with the release of antidiuretic hormone (probably arginine vasotocin in birds). b) Possibly also an effect operating through the median eminence and adenohypophysis (pars distalis) that causes an increase in activity in the cortical cells of the adrenal gland and a reduction in the amount of sudanophilic material therein. It is suggested that the latter may be associated with the salt-excreting and/or reabsorbing functions of the kidney.

Fluorescence microscopy of neurons containing primary catecholamines in the ventral hypothalamus of the white-crowned sparrow, Zonotrichia leucophrys gambelii

SummaryThe ventral hypothalamus of White-crowned Sparrows, Zonotrichia leucophrys gambelii, was examined for primary catecholamines with the fluorescence technique of Falck-Hillarp and Owman. Photorefractory and photosensitive birds, photoperiodically stimulated and non-stimulated, were used.Four groups of catecholaminergic fibers were demonstrated: (1) afferent fibers of extra-hypothalamic origin to the infundibular nucleus where there are extensive synaptic contacts with non-fluorescent perikarya; (2) fibers apparently extending ventrally from an area with fluorescent perikarya in the vicinity of the paraventricular organ to the infundibular nucleus via the stratum cellulare internum and lateral pathways; (3) afferent fibers to the subependymal layer of the median eminence; and (4) afferent fibers to the zona externa of the median eminence. Fluorescent fibers that pass transversely through the median eminence may be derived from any of the last three categories. It appears that the fibers of the zona externa (4) are not derived to any appreciable extent from those of the subependymal layer (3). Because fluorescent perikarya could not be demonstrated in the infundibular nucleus no conclusion can be reached with respect to this nucleus as an origin for fibers (3) and (4).Diurnal cycles in the number of fluorescent terminals observable and in the intensity of the fluorescence in the palisade layer in photosensitive birds subjected to different photoperiodic regimes, in castrates, and in photorefractory birds are described tentatively on the basis of subjective assessments. Some possible implications of the differences are discussed.

The meningeal compartments of the median eminence and the cortex

SummaryThe intervascular segments of the leptomeninges of the rat were studied by the use of horseradish peroxidase (HRP) in short-term experiments. HRP was injected (i) intravenously, (ii) into the lateral ventricle, (iii) into the cortex, and (iv) into the meninges. The composition of the meninges covering the median eminence (ME) was analyzed in comparison to the results obtained with the parietal cortex.The meninges covering the cortex show the following pattern of layers and compartments: The intercellular compartment comprises the intercellular clefts of the neuropil, the subpial space, and the intercellular clefts of the leptomeninges. The pial space establishes a second compartment. The third compartment is the arachnoid space. The intercellular clefts of the dura form the fourth compartment.At the border of the ME, the neurothelium and the outer arachnoid layer are rolled up to form a tissue frame around a hollow pit that is covered by a diaphragm consisting of meningeal cells; the latter separate the hemal milieu of the ME from that of the dura. The hemal and the cerebrospinal fluid (CSF) milieus may communicate to a limited extent only within the subpial space adjacent to the ME. The CSF-containing compartments of the pial and arachnoid spaces terminate at the brain-facing insertion of the tissue frame.According to the present results, an anatomical basis for a short-loop feedback from and to the neurohemal region of the ME via the CSF does not exist.