Neuroendocrine control of photoperiodically induced fat deposition in white-crowned sparrows

Regulatory mechanisms for the development of the migratory phenotype: roles for photoperiod and the gonad

This article is part of a Special Issue "Energy Balance". Male white-crowned sparrows, Zonotrichia leucophrys gambelii, were studied to investigate roles of natural day length and the testes in regulating development and expression of the vernal migration phenotype. Previous work suggested that a pulse of androgen during winter months followed by the vernal increase in photoperiod promotes fueling (fat deposition) to support long distance flight; however, other traits required for successful migration remain untested. To investigate these points, birds were captured on their wintering grounds and castrated prior to winter solstice following Mattocks (1976). A subset of the castrates received 8mm Silastic implants of testosterone (T-castrates) and others blank implants (Blank-castrates) for 16 days in February. Shams were surgical controls. Migratory traits measured were as follows: 24h locomotor activity, prenuptial molt, body mass, fat score, flight muscle profile, cloacal protuberance (CPL) and plasma androgens measured over 28 weeks divided into 3 experimental periods (pre-implant, implant, and post-implant). Under short day lengths, castration increased diurnal locomotor activity over Shams. Testosterone implants temporarily enhanced CPL, plasma androgens and flight muscle enlargement, but failed to induce migratory restlessness. Whereas all groups exhibited seasonal increases in mass, fat score and muscle profile, only Shams showed timely onset and completion of prenuptial molt and migratory restlessness. Thus, for castrated males exposed to naturally increasing day lengths, the organizational effects of a transient testosterone surge were not sufficient to actuate a timely spring molt and migratory behavior. A fully functional testis that can organize central processes is required for the entire expression of the spring migratory phenotype.

Contributions of endocrinology to the migration life history of birds

Migration is a key life cycle stage in nearly 2000 species of birds and is a greatly appreciated phenomenon in both cultural and academic arenas. Despite a long research tradition concerning many aspects of migration, investigations of hormonal contributions to migratory physiology and behavior are more limited and represent a comparatively young research field. We review advances in our understanding of the hormonal mechanisms of migration with particular emphasis on the sub-stages of the migration life history: development, departure, flight and arrival. These sub-stages vary widely in their behavioral, ecological and physiological contexts and, as such, should be given appropriate individual consideration.

Role of the basomedial hypothalamus in regulation of adiposity, food intake, and reproductive traits in the domestic fowl

Bilateral basomedial hypothalamic (BMH) electrolytic lesions in White Leghorn cockerels produced six main physiological categories characterized by typical sets of symptoms: 1) functional castration (FC); hyperphagia, obesity, occasional diabetes insipidus, involuted adenohypophysis, dwarfism, atrophied comb and testes, reduced hematocrit, reduced plasma testosterone and thyroid activity, involuted thymus and adrenal cortex and elevated liver fat and plasma triglycerides and free fatty acids. The FC birds demonstrated defective immune response for the first 12 to 16 wk post-surgery. 2) functional castration with large comb (FCLC); hyperphagia, obesity, transient diabetes insipidus, slight diminution of adenohypophy-seal weight with marked reduction in basophilic cell population, fully atrophied testes but only slight reduction in comb size and hematocrit, plasma testosterone levels between those found in the first category and the control. 3) obese with normal testes (ONT); hyperphagia, obesity, high level of plasma lipids, normal histological organization of the adenohypophysis, normal testes, semen production and comb size. The next three categories exhibited physiological syndromes identical to the former three categories except for food intake, which operationally could be defined as normal. A marked difference among the BMH-lesioned birds was found in sexual behavior when the FC birds completely lost their libido. None of the replacement therapy regimens caused complete rehabilitation from adiposity or restoration of reproductive traits. Lipoprotein lipase activity increased at an early stage postlesioning and preceeded the development of hyperphagia. Placement of BMH lesions in newly hatched chicks resulted in marked dwarfism and obesity without hyperphagia. The BMH-lesioned heavy breed White Rock cockerels exhibited a lesser degree of adiposity than the light White Leghorn birds. Removal of the olfactory bulbs and destruction of the septal area resulted in increased thyroid activity, with secondary hyperphagia without obesity. In a short-term study, administration of sodium pentobarbital to the BMH area resulted in increased feeding. Conversely, glucose administration to the same area suppressed feeding in satiated but not in food-deprived chickens.

Effects of ovariectomy on long-day-induced premigratory fat deposition, plasma levels of luteinizing hormone and prolactin, and molt in white-crowned sparrows, Zonotrichia leucophrys gambelii

Long days initiate the hyperphagia, fat deposition, and nocturnal restlessness, characteristic of the vernal migratory state in white-crowned sparrows. Ovariectomy, when performed in November, but not when performed in January, prevented induction by long days (20L:4D) of vernal fat deposition, whereas autumnal fat deposition was not affected. This is consistent with results obtained previously with males. Very high plasma levels of luteinizing hormone (LH) after photostimulation of ovariectomized females did not interfere with fat deposition. During fat deposition, levels of prolactin were not different from short-day levels and similar in ovariectomized and control females. However, ovariectomy performed in November suppressed the maximum levels of prolactin produced by long-day stimulation and inhibited or disturbed postnuptial molt. These effects were absent when ovariectomy was performed in January. Long-day-induced prolactin levels were higher when birds were photostimulated during a later phase of the annual cycle. It is suggested that castration does not interfere with long-day-induced vernal fat deposition via reduced secretion of prolactin in the absence of ovarian hormones or via supernormal secretion of LH, but that vernal fat deposition, prolactin secretion, and postnuptial molt require the presence of ovarian hormones prior to photostimulation. Autumnal migratory fat deposition, which is part of the cluster of events associated with photorefractoriness, has no requirement for gonadal hormones.

The fine structure of the hypothalamic secretory neurons of the white-crowned sparrow, Zonotrichia leucophrys gambelii (Passeriformes: Fringillidae). I. Parvocellular tuberal nuclei

The fine structure of the parvocellular tuberal nuclei and that of the ependyma bordering the third ventricle in the basal hypothalamus of the White-crowned Sparrow, Zonotrichia leucophrys gambelii, have been investigated. Photoperiodically stimulated birds have been compared with birds held on short days. The perikarya of the neurons of the basal infundibular (tuberal) nucleus, and in part, of the more dorsal layers, contain dense-cored granules (1000-1500 A). The granules in the anterior part of the nucleus are somewhat larger than those of the posterior part. The synapses and the synaptic relationships of these cells are described. The single-layered ependyma of the third ventricle in the basal hypothalamus may be divided into the dorsal typical ependyma, the ventrolateral "glandular" ependyma, and the ventral "glandular" ependyma. Cells of the ventral ependyma lack apical cilia but bear a few microvillous processes. They have well-developed Golgi apparatus, conspicuous polysomes, and frequently dense, irregularly-shaped granules. Basal cytoplasmic processes extend ventrally to the outer surface of the median eminence. Photoperiodic stimulation appears to increase the numbers of apical protrusions of the cells in the ventral glandular ependyma and to cause an increase in size of the nerve cells of the basal infundibular nucleus.