Super-normal length song preferences of female zebra finches (Taeniopygia guttata) and a theory of the evolution of bird song

Two way choice tests show a preference of female zebra finches for male songs four standard deviations longer than normal song. Further tests show the ontogeny of this preference to parallel song learning in general as well as a preference for songs with entirely heterogeneous notes compared to songs with four note repeats. These findings are discussed in relation to a theory of the evolution of bird song from bird calls due to female preferences for longer, more complex vocalizations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Horizontal transmission of the father's song in the zebra finch (Taeniopygia guttata)

As is the case for human speech, birdsong is transmitted across generations by imitative learning. Although transfer of song patterns from adults to juveniles typically occurs via vertical or oblique transmission, there is also evidence of horizontal transmission between juveniles of the same generation. Here, we show that a young male zebra finch (Taeniopygia guttata) that has been exposed to its father during the sensitive period for song learning can lead a brother, that has never heard the paternal song, to imitate some sounds of the father. Moreover, song similarity between the two brothers was higher than the similarity measured between the paternal song and the song of the brother that had a week-long exposure to the father. We speculate that the phenomenon of within-generation song learning among juveniles may be more widespread than previously thought and that when a juvenile evaluates potential models for imitative learning, a sibling may be as salient as an adult.     

Adrenocortical responses in zebra finches (Taeniopygia guttata): individual variation, repeatability, and relationship to phenotypic quality

Although individual variation is a key requirement for natural selection, little is known about the magnitude and patterns of individual variation in endocrine systems or the functional significance of that variation. Here we describe (1) the extent and repeatability of inter-individual variation in adrenocortical responses and (2) its relationship to sex-specific phenotypic quality, such as song duration and frequency and timing of egg laying. We measured adrenocortical responses to a standardized stressor in zebra finches (Taeniopygia guttata) at two life history stages: approximately day 16 (nestlings) and 3 months of age (sexually mature adults). Subsequently, we assessed phenotypic (reproductive) quality of all individuals as adults. Marked inter-individual variation in the adrenocortical response was seen in both sexes and ages, e.g., stress-induced corticosterone ranged from 2.2 to 62.5 ng/mL in nestlings and 5.0-64.0 ng/mL in adults. We found sex differences in (a) inter-individual variation in the adrenocortical response, (b) repeatability, and (c) relationships between corticosterone levels and phenotypic quality. In males, variation in nestling corticosterone was weakly but positively correlated with brood size and negatively correlated with nestling mass (though this relationship was dependent on one individual). There was no significant correlation of adrenocortical responses between two stages in males and adult phenotypic quality was significantly correlated only with adult corticosterone levels. In contrast, in females there was no relationship between nestling corticosterone and brood size or mass but adrenocortical response was repeatable between two stages (r2=0.413). Phenotypic quality of adult females was correlated with nestling baseline and adrenocortical response.     

Contralateral projections of the optic tectum in the zebra finch (Taenopygia guttata castanotis)

Summary Efferent projections of the optic tectum of zebra finches were investigated by injection of the radioactive anterograde tracer ³H-proline. In addition to a variety of ipsilateral projections, some contralateral connections were found. Quantitative evaluation of the recrossing tecto-rotundal and nucleus subpraetectalis/nucleus interstitio-praetecto-subpraetectalis projection revealed that these connections are much stronger than previously believed. In contrast, the tecto-tectal projection is very weak, as has been shown previously. Further support for this comes from results obtained using injections of retrograde tracers. The role of the different projections in conveying information from the ipsilateral eye to the ectostriatum, the telencephalic end-station of the tectofugal pathway, is discussed.     

Spatial and behavioural measures of social discrimination by captive male zebra finches: Implications of sexual and species differences for recognition research

All bird species reproduce sexually and individuals need to correctly identify conspecifics for successful breeding. Captive zebra finches are a model system for studying the factors involved in species recognition and mate choice. However, male zebra finches’ behavioural responses in a spatial preference paradigm to a range of estrildid finch species, other than domesticated Bengalese finches, remain unknown. We investigated spatial and display responses of male zebra finch subjects to stimulus females between conspecific and four phylogeographically relevant finch species, in addition to female Bengalese finches. Surprisingly, male subjects did not show consistent spatial association with conspecific over heterospecific females. Overall, as predicted by sexual selection theory, the spatial proximity responses of males were less discriminatory compared to female zebra finches’ responses tested previously using the same paradigm. However, male subjects showed consistently more behavioural displays towards female conspecifics than heterospecifics which were positively related to the behavioural display rates of the respective female stimuli. Some male behavioural responses, other than song, also showed significant differences between the different stimulus species and consistently differed across individual test subjects, with the most individual subject variation seen in choice trials between female conspecific and Bengalese finch stimuli. The results are important for the design and interpretation of future behavioural and neurobiological experiments on species recognition systems using the zebra finch as a model species.     

Crystal structure of the vitamin D nuclear receptor ligand binding domain in complex with a locked side chain analog of calcitriol

The crystal structures of vitamin D nuclear receptor (VDR) have revealed that all compounds are anchored by the same residues to the ligand binding pocket (LBP). Based on this observation, a synthetic analog with a locked side chain (21-nor-calcitriol-20(22),23-diyne) has been synthesized in order to gain in entropy energy with a predefined active side chain conformation. The crystal structure of VDR LBD bound to this locked side chain analogue while confirming the docking provides a structural basis for the activity of this compound.     

The vitamin D receptor is necessary for 1alpha,25-dihydroxyvitamin D(3) to suppress experimental autoimmune encephalomyelitis in mice

The active metabolite of vitamin D, 1alpha,25-dihydroxyvitamin D(3), suppresses autoimmune disease in several animal models including experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. The molecular mechanism of this immunosuppression is at present unknown. While 1alpha,25-dihydroxyvitamin D(3) is believed to function through a single vitamin D receptor, there are reports of other vitamin D receptors as well as a "nongenomic" mode of action. We have prepared the EAE model possessing the vitamin D receptor null mutation and determined if 1alpha,25-dihydroxyvitamin D(3) can suppress this disease in the absence of a functional vitamin D receptor. Vitamin D receptor null mice develop EAE although the incidence rate is one-half that of wild-type controls. The administration of 1alpha,25-dihydroxyvitamin D(3) had no significant effect on the incidence of EAE in the vitamin D receptor null mice, while it completely blocked EAE in the wild-type mice. We conclude that 1alpha,25-dihydroxyvitamin D(3) functions to suppress EAE through the well-known VDR and not through an undiscovered receptor or through a "nongenomic" mechanism.     

Distribution of neuropeptide Y-like immunoreactivity in the brain and hypophysis of the cloudy dogfish,Scyliorhinus torazame

Summary Using a specific antiserum raised against synthetic neuropeptide Y, we examined the localization of immunoreactivity in the brain and hypophysis of the cloudy dogfish, Scyliorhinus torazame, by the peroxidase-antiperoxidase method. Immunoreactive perikarya were demonstrated in the ganglion of the nervus terminalis, the dorsocaudal portions of the pallium dorsale, the basal telencephalon, and the nucleus lateralis tuberis and the nucleus lobi lateralis in the hypothalamus. Labeled perikarya were also found in the tegmentum mesencephali, the corpus cerebelli, and the medulla oblongata. Some of the immunoreactive neurons in the hypothalamus were of the CSF-contacting type. The bulk of the labeled fibers in the nervus terminalis ran toward the basal telencephalon, showing radial projections and ramifications. Large numbers of these fibers coursed into the nucleus septi caudoventralis and the nucleus interstitialis commissurae anterioris, where they became varicose and occasionally formed fine networks or invested immunonegative perikarya. In the diencephalon, immunoreactive fibers were observed throughout the hypothalamus, e.g., in the pars neurointermedia of the hypophysis, the subependymal layer of the lobus inferior hypothalami, and in the neuropil of the posterior (mammillary) recess organ. Labeled fibers were scattered throughout the rest of the brain stem and were also seen in the granular layer of the cerebellum. These results suggest that, in the dogfish brain, neuropeptide Y or a related substance is involved in a variety of physiological processes in the brain, including the neuroendocrine control of the hypophysis.     

Enriched uranium affects the expression of vitamin D receptor and retinoid X receptor in rat kidney

An increasing awareness of the radiological impact of the nuclear power industry and other nuclear technologies is observed nowadays on general population. This led to renew interest to assess the health impact of the use of enriched uranium (EU). The aim of this work was to investigate in vivo the effects of a chronic exposure to EU on vitamin D(3) metabolism, a hormone essential in mineral and bone homeostasis. Rats were exposed to EU in their drinking water for 9 months at a concentration of 40 mg l(-1) (1mg/rat day). The contamination did not change vitamin D plasma level. Vitamin D receptor (vdr) and retinoid X receptor alpha (rxralpha), encoding nuclear receptors involved in the biological activities of vitamin D, showed a lower expression in kidney, while their protein levels were paradoxically increased. Gene expression of vitamin D target genes, epithelial Ca(2+) channel 1 (ecac1) and Calbindin-D28k (cabp-d28k), involved in renal calcium transport were decreased. Among the vitamin D target organs examined, these molecular modifications occurred exclusively in the kidney, which confirms that this organ is highly sensitive to uranium exposure. In conclusion, this study showed that a chronic exposure to EU affects both mRNA and protein expressions of renal nuclear receptors involved in vitamin D metabolism, without any modification of the circulating vitamin D.     

The response of the hypothalamo-gonadal system to environmental factors in the zebra finch,Poephila guttata castanotis

Summary Studies of the hypothalamo-gonadal response of the zebra finch (Poephila guttata castanotis) to environmental factors were conducted by the use of adult birds captured in arid regions of South Australia. In these birds breeding activity is not photoperiodically induced but follows rainfall. The hypothalamo-hypophysial system participating in this response involves centres of the rostral and mediobasal (tuberal) hypothalamus. Parvocellular neurones in both hypothalamic portions are arranged in clusters. In the rostral hypothalamus magnocellular neurosecretory perikarya are spatially closely associated with the clusters which contain different types of parvocellular peptidergic neurones. Extended, complex neuropile formations, rich in synapses, encompass the neuronal clusters and provide important loci of neural-neuroendocrine interaction.Experiments were undertaken to correlate indicators of breeding activity, such as increased size and mass of testes, spermatogenesis, and plasma levels of androgens and luteinizing hormone, with a greater availability of drinking water, increased air humidity, and green vegetation, all of which follow rainfall. Birds maintained in male/female pairs in controlled-environment rooms at 27° C on 14L10D received a diet of seeds (containing 10% water). Thirty-two birds were given drinking water at a basal level of 1 ml/week and one of eight different treatments, consisting of different combinations of drinking water, relative air humidity, and green grass, for two weeks (4 males/treatment). The size of the left testis was estimated at laparotomy and blood samples were taken from a wing vein before and after treatment. The observations suggest that, in moisture-deprived (1 ml water/week) adult zebra finches, an increase in testicular size is associated with a free supply of water; synergistic effects of supplying both water and green grass, or water and high humidity, were also observed. However, in six other groups (8–16 males/treatment), receiving a higher basal level of water (access for 3 min/day), an increase in testicular mass was associated with high humidity, while smaller non-significant increases followed the provision of free water or green grass. Spermatogenic activity was not significantly correlated with testicular size or mass. Leydig cells were sparse in all groups. Plasma androgen levels and luteinizing hormone levels were not obviously correlated with the treatments and were lower than values in zebra finches breeding in outdoor aviaries.According to K.C. Parkes; see Note on Taxonomy, p. XVII, Avian Biology, Vol. IV (D.S. Farner, J.R. King, eds.), Academic Press, New York/London, 1974. Taeniopygia guttata castanotis is widely used for this subspecies in non-taxonomic literature.     

Localization and identification of nuclear radioactivity in the pituitary gland and genital tract after administering 3H-testosterone, 3H-dihydrotestosterone,or 3H-estradiol to male rhesus monkeys

Summary Target cells for testosterone, dihydrotestosterone, and estradiol in the pituitary gland and genital tract of the male primate were localized by thaw-mount autoradiography, and high performance liquid chromatography was used to identify the metabolites of these steroids in cell nuclei. Castrated rhesus monkeys were injected with ³H-testosterone, ³H-dihydrotestosterone, or ³H-estradiol and killed 60 min later. In the anterior pituitary gland, fewer cells were labeled and less radioactivity was taken up by cell nuclei following the administration of either ³H-testosterone (4% of pars distalis cells and 5 dpm/g DNA) or ³H-dihydrotestosterone (5% of cells and 13 dpm/g DNA) than following the administration of ³H-estradiol (43% of cells and 214 dpm/g DNA). Most of the radioactivity in nuclei was in the form of the unmetabolized parent compound (78–94%). In prostate, seminal vesicles, and penis, ³H-dihydrotestosterone was the predominant form of nuclear radioactivity following both ³H-testosterone (67–90%) and ³H-dihydrostestosterone (94–97%) administration, and both androgens labeled epithelial and smooth muscle cells. In contrast, ³H-estradiol was taken up in unchanged form, by cell nuclei of the genital tract and it labeled connective tissue fibroblasts, but not epithelial cells. Thus, the distributions of target cells for androgens and estrogens were clearly different in all these tissues, and the uptake of testosterone resembled that of its androgenic rather than that of its estrogenic metabolite.     

Distribution of aromatase-immunoreactive cells in the forebrain of zebra finches (Taeniopygia guttata): Implications for the neural action of steroids and nuclear definition in the avian hypothalamus

Cells immunoreactive for the enzyme aromatase were localized in the forebrain of male zebra finches with the use of an immunocytochemistry procedure. Two polyclonal antibodies, one directed against human placental aromatase and the other directed against quail recombinant aromatase, revealed a heterogeneous distribution of the enzyme in the telencephalon, diencephalon, and mesencephalon. Staining was enhanced in some birds by the administration of the nonsteroidal aromatase inhibitor, R76713 (racemic Vorozole) prior to the perfusion of the birds as previously described in Japanese quail. Large numbers of cells immunoreactive for aromatase were found in nuclei in the preoptic region and in the tuberal hypothalamus. A nucleus was identified in the preoptic region based on the high density of aromatase immunoreactive cells within its boundaries that appears to be homologous to the preoptic medial nucleus (POM) described previously in Japanese quail. In several birds alternate sections were stained for immunoreactive vasotocin, a marker of the paraventricular nucleus (PVN). This information facilitated the clear separation of the POM in zebra finches from nuclei that are adjacent to the POM in the preoptic area-hypothalamus, such as the PVN and the ventromedial nucleus of the hypothalamus. Positively staining cells were also detected widely throughout the telencephalon. Cells were discerned in the medial parts of the ventral hyperstriatum and neostriatum near the lateral ventricle and in dorsal and medial parts of the hippocampus. They were most abundant in the caudal neostriatum where they clustered in the dorsomedial neostriatum, and as a band of cells coursing along the dorsal edge of the lamina archistriatalis dorsalis. They were also present in high numbers in the ventrolateral aspect of the neostriatum and in the nucleus taeniae. None of the telencephalic vocal control nuclei had appreciable numbers of cells immunoreactive for aromatase within their boundaries, with the possible exception of a group of cells that may correspond to the medial part of the magnocellular nucleus of the neostriatum. The distribution of immunoreactive aromatase cells in the zebra finch brain is in excellent agreement with the distribution of cells expressing the mRNA for aromatase recently described in the finch telencephalon. This widespread telencephalic distribution of cells immunoreactive for aromatase has not been described in non-songbird species such as the Japanese quail, the ring dove, and the domestic fowl. © 1996 John Wiley & Sons, Inc.     

Increased nuclear expression and transactivation of vitamin D receptor by the cardiotonic steroid bufalin in human myeloid leukemia cells

The active form of vitamin D₃, 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], is a potent ligand for the nuclear receptor vitamin D receptor (VDR) and induces myeloid leukemia cell differentiation. The cardiotonic steroid bufalin enhances vitamin D-induced differentiation of leukemia cells and VDR transactivation activity. In this study, we examined the combined effects of 1,25(OH)₂D₃ and bufalin on differentiation and VDR target gene expression in human leukemia cells. Bufalin in combination with 1,25(OH)₂D₃ enhanced the expression of VDR target genes, such as CYP24A1 and cathelicidin antimicrobial peptide, and effectively induced differentiation phenotypes. An inhibitor of the Erk mitogen-activated protein (MAP) kinase pathway partially inhibited bufalin induction of VDR target gene expression. 1,25(OH)₂D₃ treatment induced transient nuclear expression of VDR in HL60 cells. Interestingly, bufalin enhanced 1,25(OH)₂D₃-induced nuclear VDR expression. The MAP kinase pathway inhibitor increased nuclear VDR expression induced by 1,25(OH)₂D₃ and did not change that by 1,25(OH)₂D₃ plus bufalin. A proteasome inhibitor also enhanced 1,25(OH)₂D₃-induced CYP24A1 expression and nuclear VDR expression. Bufalin-induced nuclear VDR expression was associated with histone acetylation and VDR recruitment to the CYP24A1 promoter in HL60 cells. Thus, the Na⁺,K⁺-ATPase inhibitor bufalin modulates VDR function through several mechanisms, including Erk MAP kinase activation and increased nuclear VDR expression.     

The distribution of GABA-like-immunoreactive neurons in the brain of the newt,Triturus cristatus carnifex,and the green frog,Rana esculenta

Summary The distribution of -aminobutyric acid (GABA) immunoreactivity was studied in the brain of two amphibian species (Triturus cristatus carnifex, Urodela; Rana esculenta, Anura) by employing a specific GABA antiserum. A noteworthy immunoreactive neuronal system was found in the telencephalic dorsal and medial pallium (primordium pallii dorsalis and primordium hippocampi) and in the olfactory bulbs. In the diencephalic habenular nuclei there was a rich GABAergic innervation, and immunoreactive neurons were observed in the dorsal thalamus. In the hypothalamus the GABA immunoreactivity was found in the preoptic area, the paraventricular organ and in the hypothalamo-hypophysial complex. In the preoptic area of the frog some GABA-immunoreactive CSF-contacting cells were shown. In the optic tectum immunolabeled neurons were present in all the cellular layers. A rich GABAergic innervation characterized both the fibrous layers of the tectum and the neuropil of the tegmentum and interpeduncular nucleus. In the cerebellum, in addition to the Purkinje cells showing a variable immunopositivity, some immunoreactive cell bodies appeared in the central grey. Abundant immunolabeled nerve fibers in the acoustico-lateral area and some immunopositive neurons in the region of the raphe nucleus were observed. In conclusion, the GABAergic central systems, well-developed in the amphibian species studied, were generally characterized by close similarities to the pattern described in mammals.Dedicated to Professor Valdo Mazzi (Dipartimento di Biologia Animale, Università di Torino), in honor of his 70th birthday     

Immunohistochemical localization of neuropeptide Y-like substance in the brain and hypophysis of the brown hagfish,Paramyxine atami

The distribution of neuropeptide Y-like immunoreactivity in the brain and hypophysis of the brown hagfish, Paramyxine atami, was examined by use of the peroxidase-antiperoxidase method. Immunoreactive cells were found in two areas of the brain, the nucleus hypothalamicus of the diencephalon and the ventrolateral area of the caudal tegmentum, at the level of the nucleus motorius V–VII. The labeled cells of the nucleus hypothalamicus were loosely grouped and recognized as bipolar neurons. Immunolabeled fibers were widely distributed in the brain, showing the highest density in the diencephalon. They were sparse, or absent, in the olfactory bulb, habenula, primordium hippocampi, neurohypophysis, corpus interpedunculare, and dorsolateral area of the medulla oblongata. The fibers appeared to project exclusively from the ventral hypothalamus to various other portions of the brain: the anterolateral areas of the telencephalon via the basal hypothalamus, the pars dorsalis thalami, the dorsocaudal region of the mesencephalon, and the ventromedial portions of the tegmentum and anterior medulla oblongata. These findings suggest that, in the brown hagfish, NPY-like substance is involved in neuroregulation of various cerebral areas, but it may be of little significance in the control of pituitary function.     

Ultrastructure of Merkel corpuscles in the tongue of the finch,Lonchura striata

Summary Merkel corpuscles in the lingual mucosa of the finch, Lonchura striata, were examined by means of the argyrophilic reaction and electron microscopy. These corpuscles are composed of 12 to 20 flattened Merkel cells and enclosed nerve terminals. The present study demonstrated for the first time argyrophilia in avian subepithelial Merkel cells with the use of Grimelius silver stain. Electron-microscopically, the Merkel cell was characterized by the presence of numerous densecore granules, approximately 80 to 140 nm in diameter, as well as specialized contacts with nerve terminals. The granules showed a tendency to accumulate in the cytoplasm in close association with both nerve terminals and basal lamina. This study also provided unequivocal evidence for exocytotic discharge of Merkel-cell granules at the plasma membrane facing not only the nerve terminals but also the basal lamina. The exocytotic figures toward the nerve terminals can be regarded as synaptic discharge of Merkel-cell granules, but the possibility also exists that the Merkel-cell granules may exert a trophic effect on the nerve terminals. The exocytotic release of Merkel-cell granules toward the basal lamina with no relation to nerve terminals may suggest an endocrine (paracrine) function for the Merkel cell. The avian subepithelial Merkel cells qualify as paraneurons, but their exact nature and function remain enigmatic as is the case of intraepithelial Merkel cells in other vertebrates.