Donald S. Farner

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.

Bioenergetic Basis of Light-induced Fat Deposition in the White-crowned Sparrow.

Summary In Zonotrichia leucophrys gambelii there is a striking deposition of fat in subcutaneous and visceral depots following prenuptial molt and preceding beginning of vernal migration. During the last 2 weeks of April, in natural populations, mean lipid indices increase from about 5% to more than 20%. A similar premigratory fat deposition occurs in captive birds under natural conditions of photoperiod and temperature. Similarly in these captive birds this fat deposition is followed by development of migratory behavior (Zugunruhe). Measurements of metabolizable energy intake in these birds show that fat deposition is accompanied by a marked increase in energy intake to levels of 30 to 50% above the preceding minima. This temporary hyperphagia represents an altered physiologic state rather than simply the effect of more daylight for feeding since, during hyperphagia, the amount of daylight increases only 9%. The temporary hyperphagia is the principal factor responsible for positive energy balance required for premigratory fat deposition. The role of daily photoperiod in development of temporary hyperphagia was demonstrated experimentally by subjecting birds in mid-winter to 20 hours of light per day. These developed a hyperphagia and an accompanying fat deposition very similar to those observed in spring under natural conditions.

A POSSIBLE ENDOCRINE BASIS FOR PREMIGRATORY FATTENING IN THE WHITE-CROWNED SPARROW, ZONOTRICHIA LEUCOPHRYS GAMBELII (NUTTALL).

Abstract The white-crowned sparrow, Zonotrichia leucophrys gambelii , has been shown to become hyperphagic, deposit fat, and gain weight prior to the vernal migration. Similar effects have been induced during the winter by artificially increasing the duration of the daily photoperiod. It appears that the mechanism involved in these photoperiodically induced changes in metabolism may include the hypothalamus, and possibly also the anterior pituitary. In the investigation reported herein, it was possible to induce similar changes with exogenous hormones. Prolactin promoted a rapid fat deposition that was reflected in conspicuous daily increments in body weight. Gonadotropin, alone, was ineffective but was synergistic with prolactin in promoting an increase in lipid reserves. These effects were obtained in winter with photosensitive birds as well as in summer with photorefractory birds.

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.

Pituitary gonadotropins in the Japanese quail (Coturnix coturnix japonica) during photoperiodically induced gonadal growth

The gonadotropin content of the anterior pituitary in Japanese quail (Coturnix coturnix japonica) was studied in relation to photoperiodically induced gonadal development. The content was low in birds held on short daily photoperiods and in which there was no gonadal development. Long daily photoperiods caused complete gonadal development and a steady increase in gonadotropin content during the first 21 days with a slight decline thereafter. The anterior pituitary gland increased in weight under a long daily photoperiod. The results are discussed with respect to the balance between hormone synthesis and hormone release.

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”.

The effects of the daily photoperiod on gonadal growth, neurohypophysial hormone content, and neurosecretion in the hypothalamo-hypophysial system of the Japanese quail (Coturnix coturnix japonica) ☆

Abstract The photoperiodic control of gonadal development was examined in the Japanese quail (Coturnix coturnix japonica). Long (20 hours) daily photoperiods caused a quantitatively uniform growth of testes and ovaries to full reproductive condition, whereas no development occurred in birds held on 6-hour daily photoperiods. Arginine vasotocin and oxytocin were identified by pharmacological and chromatographic methods in both the pars nervosa and the median eminence. The concentrations of these peptides showed no significant correlations with the rate of gonadal development. Similarly, no significant changes were detected in the hypothalamic neurosecretory system under different photoperiodic regimes, although there appeared to be a trent towards a greater accumulation of stainable material in the reticular layer of the median eminence of birds held on short daily photoperiods. Dehydration resulted in a correlated depletion of neurosecretory material and neurohypophysial hormones from the median eminence and pars nervosa with a greater loss of arginine vasotocin than oxytocin from the pars nervosa.

A possible endocrine basis for migratory behaviour in the White-crowned Sparrow, Zonotrichia leucophrys gambelii☆

Abstract By using hormone preparations, a simulated migratory behaviour has been induced in caged Z. l. gambelii , a nocturnal migrant. Daily injections of prolactin increase nocturnal restlessness in photosensitive birds under outdoor conditions prior to spring migration and also initiate nocturnal locomotor activity in photo-refractory birds held indoors on a long daily photoperiod. These effects are augmented by adrenocortical hormones which, however, are ineffective when administered alone. In addition, metapirone, an inhibitor of adrenocortical synthesis, suppresses nocturnal activity. Simultaneous injections of corticosterone eliminate the metapirone-induced suppression of nocturnal activity. In prolactin-treated birds, there is a reduction of locomotor activity during the last two hours of light that is strikingly similar to the late afternoon reduction in activity as natural Zugunruhe developes. The dual role of prolactin in promoting fattening and nocturnal locomotor activity, and the augmentation of nocturnal activity by adrenocortical hormones have been discussed in regard to their possible involvement in the physiologic events of migration. Assays of pituitary prolactin at several times during the annual cycle appear to be compatible with a hypothesis involving prolactin in the development and maintenance of migratory behaviour.

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.