RESUMEN
Seasonal differences in hippocampal morphology have been reported in food-storing birds. Non food-storing species have not been investigated however. It is therefore unclear whether seasonal changes in the hippocampus are specifically related to food-storing or reflect a more general seasonal mechanism that occurs in both food-storing and non food-storing birds alike. We determined the volumes of the hippocampal formation and remaining telencephalon in the non-storing male song sparrow (Melospiza melodies morphna) in two experiments comparing birds collected in the spring and fall of 1992-94 (Experiment 1) and 1997 (Experiment 2). Although pronounced seasonal changes in song control nuclei such as the HVC and RA were previously reported for the same brains used in Experiment 1, we found that hippocampal volume did not change with season in either Experiment 1 or 2 for these song sparrow brains. These results suggest that seasonal changes in the hippocampus do not occur in this non food-storing species and may be specific to food-storing birds.
Asunto(s)
Conducta Alimentaria/fisiología , Hipocampo/fisiología , Memoria/fisiología , Plasticidad Neuronal/fisiología , Estaciones del Año , Pájaros Cantores/fisiología , Percepción Espacial/fisiología , Animales , Conducta Animal/fisiología , Hipocampo/citología , Masculino , Tamaño de los Órganos/fisiología , Factores Sexuales , Pájaros Cantores/anatomía & histologíaRESUMEN
In seasonally breeding adult songbirds, the brain regions that control song undergo dramatic seasonal morphological changes. During late winter and early spring, increasing day length triggers an increase in circulating testosterone that ultimately causes several song nuclei to grow in volume. The timing of this growth relative to the seasonal development of the reproductive system is not known. This question was investigated in two populations of wild song sparrows (Melospiza melodia morphna). Both populations live at the same latitude (46 degrees N), but breed at different altitudes. One population resides on the Pacific coast in Washington, and the other resides in the foothills of the Cascade Mountains. Both populations experienced the same photoperiodic conditions, but the timing of seasonal reproductive development differed between populations. Coastal birds initiated gonadal recrudescence approximately 2 weeks earlier than montane birds. Despite this temporal difference in reproductive development, there were no differences between these groups in the seasonal growth of two song control nuclei, HVc and RA. During late February, both groups had low circulatory levels of testosterone (mean for coastal birds was 1.01 +/- 0.37 ng/ml; mean for montane birds was 1.41 +/- 0.26 ng/ml) and fully recrudesced song nuclei (for example, mean HVc volume in coastal birds was 1.77 +/- 0.08 mm(3); mean HVc volume in montane birds was 1.76 +/- 0.09). Also at this time, both populations were in the earliest stages of seasonal reproductive development as judged by the degree of gonadal recrudescence (mean gonad volume was less than 10% of typical breeding size in both populations). It is concluded that seasonal song system growth is completed before seasonal reproductive development in response to submaximal levels of circulating testosterone.
Asunto(s)
Neostriado/fisiología , Reproducción , Estaciones del Año , Pájaros Cantores/fisiología , Animales , Masculino , Fotoperiodo , Testículo/anatomía & histología , Testículo/fisiología , Testosterona/sangre , Tráquea/fisiología , Vocalización AnimalRESUMEN
For many years, it was assumed that neurons and glia in the central nervous system were produced from two distinct precursor pools that diverged early during embryonic development. This theory was partially based on the idea that neurogenesis and gliogenesis occurred during different periods of development, and that neurogenesis ceased perinatally. However, there is now abundant evidence that neural stem cells persist in the adult brain and support ongoing neurogenesis in restricted regions of the central nervous system. Surprisingly, these stem cells have the characteristics of fully differentiated glia. Neuroepithelial stem cells in the embryonic neural tube do not show glial characteristics, raising questions about the putative lineage from embryonic to adult stem cells. In the developing brain, radial glia have long been known to produce cortical astrocytes, but recent data indicate that radial glia might also divide asymmetrically to produce cortical neurons. Here we review these new developments and propose that the stem cells in the central nervous system are contained within the neuroepithelial --> radial glia --> astrocyte lineage.
Asunto(s)
Linaje de la Célula , Neuroglía/citología , Neuronas/citología , Células Madre/citología , Envejecimiento , Animales , Astrocitos/citología , Embrión de Mamíferos/citología , Embrión no Mamífero , Células Epiteliales/citología , Modelos BiológicosRESUMEN
Many studies have demonstrated that male aggression is regulated by testosterone. The conversion of testosterone to estradiol by brain aromatase is also known to regulate male aggression in the breeding season. Male song sparrows (Melospiza melodia morphna) are territorial not only in the breeding season, but also in the nonbreeding season, when plasma testosterone and estradiol levels are basal. Castration has no effect on nonbreeding aggression. In contrast, chronic (10 day) aromatase inhibitor (fadrozole) treatment decreases nonbreeding aggression, indicating a role for estrogens. Here, we show that acute (1 day) fadrozole treatment decreases nonbreeding territoriality, suggesting relatively rapid estrogen effects. In spring, fadrozole decreases brain aromatase activity, but acute and chronic fadrozole treatments do not significantly decrease aggression, although trends for some behaviors approach significance. In gonadally intact birds, fadrozole may be less effective at reducing aggression in the spring. This might occur because fadrozole causes a large increase in plasma testosterone in intact breeding males. Alternatively, estradiol may be more important for territoriality in winter than spring. We hypothesize that sex steroids regulate male aggression in spring and winter, but the endocrine mechanisms vary seasonally.
Asunto(s)
Agresión/efectos de los fármacos , Inhibidores de la Aromatasa , Inhibidores Enzimáticos/farmacología , Antagonistas de Estrógenos/farmacología , Fadrozol/farmacología , Conducta Sexual Animal/efectos de los fármacos , Pájaros Cantores/fisiología , Animales , Peso Corporal/efectos de los fármacos , Encéfalo/efectos de los fármacos , Encéfalo/enzimología , Estradiol/sangre , Masculino , Territorialidad , Testosterona/sangreRESUMEN
Extensive research has focused on territorial aggression during the breeding season and the roles of circulating testosterone (T) and its conversion to 17beta-oestradiol (E2) in the brain. However, many species also defend territories in the non-breeding season, when circulating T-levels are low. The endocrine control of non-breeding territoriality is poorly understood. The male song sparrow of Washington State is highly territorial year-round, but plasma T is basal in the non-breeding season (autumn and winter). Castration has no effect on aggression in autumn, suggesting that autumnal territoriality is independent of gonadal hormones. However, non-gonadal sex steroids may regulate winter territoriality (e.g. oestrogen synthesis by brain aromatase). In this field experiment, we treated wild non-breeding male song sparrows with a specific aromatase inhibitor (fadrozole, FAD) using micro-osmotic pumps. FAD greatly reduced several aggressive behaviours. The effects of FAD were reversed by E2 replacement. Treatment did not affect body condition or plasma corticosterone, suggesting that all subjects were healthy These data indicate that E2 regulates male aggression in the non-breeding season and challenge the common belief that aggression in the non-breeding season is independent of sex steroids. More generally, these results raise fundamental questions about how sexual and/or aggressive behaviours are maintained in a variety of model vertebrate species despite low circulating levels of sex steroids or despite castration. Such non-classical endocrine mechanisms may be common among vertebrates and play an important role in the regulation of behaviour.
Asunto(s)
Agresión/fisiología , Estradiol/farmacología , Antagonistas de Estrógenos/farmacología , Estrógenos/fisiología , Fadrozol/farmacología , Conducta Sexual Animal/fisiología , Agresión/efectos de los fármacos , Animales , Masculino , Reproducción , Estaciones del Año , Conducta Sexual Animal/efectos de los fármacos , Pájaros Cantores , Territorialidad , Testosterona/sangre , WashingtónRESUMEN
Seasonal plasticity of structure and function is a fundamental feature of nervous systems in a wide variety of animals that occupy seasonal environments. Excellent examples of seasonal brain changes are found in the avian song control system, which has become a leading model of morphological and functional plasticity in the adult CNS. The volumes of entire brain regions that control song increase dramatically in anticipation of the breeding season. These volumetric changes are induced primarily by vernal increases in circulating sex steroids and are accompanied by increases in neuronal size, number and spacing. In several species, these structural changes in the song control circuitry are associated with seasonal changes in song production and learning. Songbirds provide important insights into the mechanisms and behavioral consequences of plasticity in the adult brain.
Asunto(s)
Encéfalo/fisiología , Plasticidad Neuronal/fisiología , Estaciones del Año , Pájaros Cantores/fisiología , Factores de Edad , AnimalesRESUMEN
In adult songbirds, seasonal changes in photoperiod and circulating testosterone (T) stimulate structural changes within the neural song control circuitry. The mechanisms that control this natural plasticity are poorly understood. To determine how quickly and in what sequence the song nuclei respond to changing daylength and circulating T, we captured 18 adult male white-crowned sparrows and kept them on short days for 12 weeks. We killed five of these birds and exposed the rest to long days (LD) and elevated T. We killed these birds either 7 or 20 d after LD + T exposure. We measured song nuclei volumes and cellular attributes, the mass of the vocal production organ (the syrinx), and song behavior. The neostriatal song control nucleus HVC (also known as "high vocal center"), added 50,000 neurons and increased in size within 7 d of exposure to LD + T. Efferent targets of HVC, the robust nucleus of the archistriatum (RA), and area X of the parolfactory lobe grew more slowly and were not significantly larger until day 20 of the study. The tracheosyringeal portion of the hypoglossal nucleus (nXIIts), which receives projections from RA and normally grows in response to seasonal cues, did not grow over the time course of this study. Syringeal mass increased within 7 d of LD + T treatment. The anatomical changes in the brain were accompanied by behavioral changes in song production. On day 7 when the song circuitry was incompletely developed, male sparrows sang less stereotyped songs than males at day 20 with more completely developed song circuits. These results suggest that the song circuitry responds rapidly and sequentially to breeding-typical conditions (long days and elevated T), and that song stereotypy increases as nuclei within this circuitry grow.
Asunto(s)
Encéfalo/fisiología , Fotoperiodo , Reproducción/fisiología , Estaciones del Año , Pájaros Cantores/fisiología , Vocalización Animal/fisiología , Animales , Laringe/fisiología , Masculino , Receptores Androgénicos/fisiología , Receptores de Estrógenos/fisiología , Testículo/crecimiento & desarrollo , Testículo/fisiología , Testosterona/sangreRESUMEN
Large numbers of new neurons are born continuously in the adult subventricular zone (SVZ). The molecular niche of SVZ stem cells is poorly understood. Here, we show that the bone morphogenetic protein (BMP) antagonist Noggin is expressed by ependymal cells adjacent to the SVZ. SVZ cells were found to express BMPs as well as their cognate receptors. BMPs potently inhibited neurogenesis both in vitro and in vivo. BMP signaling cell-autonomously blocked the production of neurons by SVZ precursors by directing glial differentiation. Purified mouse Noggin protein promoted neurogenesis in vitro and inhibited glial cell differentiation. Ectopic Noggin promoted neuronal differentiation of SVZ cells grafted to the striatum. We thus propose that ependymal Noggin production creates a neurogenic environment in the adjacent SVZ by blocking endogenous BMP signaling.
Asunto(s)
Proteínas Morfogenéticas Óseas/antagonistas & inhibidores , Neuronas/metabolismo , Proteínas/metabolismo , Receptores de Factores de Crecimiento , Transducción de Señal/fisiología , Animales , Receptores de Proteínas Morfogenéticas Óseas , Proteínas Morfogenéticas Óseas/biosíntesis , Proteínas Morfogenéticas Óseas/farmacología , Trasplante de Tejido Encefálico , Proteínas Portadoras , Diferenciación Celular/efectos de los fármacos , División Celular/efectos de los fármacos , Línea Celular , Supervivencia Celular/efectos de los fármacos , Cuerpo Estriado/citología , Cuerpo Estriado/metabolismo , Epéndimo/citología , Epéndimo/metabolismo , Trasplante de Tejido Fetal , Expresión Génica , Humanos , Ratones , Ratones Mutantes , Ratones Transgénicos , Microinyecciones , Neuronas/citología , Neuronas/trasplante , Proteínas/farmacología , Receptores de Superficie Celular/biosíntesis , Transducción de Señal/efectos de los fármacosRESUMEN
Adult songbirds can incorporate new neurons into HVc, a telencephalic song control nucleus. Neuronal incorporation into HVc is greater in the fall than in the spring in adult canaries (open-ended song learners) and is temporally related to seasonal song modification. We used the western song sparrow, a species that does not modify its adult song, to test the hypothesis that neuronal incorporation into adult HVc is not seasonally variable in age-limited song learners. Wild song sparrows were captured during the fall and the spring, implanted with osmotic pumps containing [3H]thymidine, released onto their territories, and recaptured after 30 days. The density, proportion, and number of new HVc neurons were all significantly greater in the fall than in the spring. There was also a seasonal change in the incorporation of new neurons into the adjacent neostriatum that was less pronounced than the change in HVc. This is the first study of neuronal recruitment into the song control system of freely ranging wild songbirds. These results indicate that seasonal changes in HVc neuronal incorporation are not restricted to open-ended song learners. The functional significance of neuronal recruitment into HVc therefore remains elusive.
Asunto(s)
Aprendizaje/fisiología , Plasticidad Neuronal/fisiología , Estaciones del Año , Pájaros Cantores/fisiología , Telencéfalo/crecimiento & desarrollo , Telencéfalo/fisiología , Vocalización Animal/fisiología , Factores de Edad , Animales , Conducta Animal/fisiología , Recuento de Células , Inmunohistoquímica , Masculino , Neostriado/metabolismo , Neuronas/metabolismo , Proyectos de Investigación , Testosterona/sangre , Timidina/farmacocinéticaRESUMEN
In seasonally breeding birds, the vernal growth of the song system is thought to result primarily from increased daylength and the associated increase in circulating testosterone. Other environmental factors such as social cues between mates influence the timing of reproduction, but less is known about how social cues might affect the song system and song behavior. We used white-crowned sparrows (Zonotrichia leucophrys gambelii) to test the hypothesis that the presence of a female in breeding condition influences song nuclei and song behavior of adult males. There were four treatment groups: (1) eight males housed individually in the same room on long days and paired with estradiol-implanted females; (2) eight males housed similarly on long days but without females; (3) four males isolated on long days; and (4) four males isolated on short days. The volumes of two song nuclei, HVc and RA, were significantly larger in males housed with females than in any other treatment group. Males isolated on short days had smaller HVc, RA, and area X volumes than all other groups. The volumes of Rt (a thalamic nucleus not involved in song) and the telencephalon did not differ among groups. Plasma androgen levels did not differ among the three long-day, social treatment groups at the times sampled, but were lower in the short-day isolates. Males paired with females sang at a higher maximum rate than males housed together, who sang at a higher rate than long-day isolates. These results suggest that seasonal plasticity in the adult song system is influenced by social cues.
Asunto(s)
Señales (Psicología) , Plasticidad Neuronal/fisiología , Fotoperiodo , Conducta Social , Pájaros Cantores/fisiología , Vocalización Animal/fisiología , Animales , Femenino , Masculino , Estaciones del Año , Maduración Sexual , Telencéfalo/fisiología , Núcleos Talámicos/fisiologíaRESUMEN
Differences in neuron density and number are associated with seasonal plasticity and sexual dimorphism in the avian song control system. In previous studies, neuron density and number in this system have been quantified primarily through nonstereological approaches in thick tissue sections by using the nucleolus as the unit of count. The reported differences between seasons and sexes may be inaccurate due to biases introduced by neuron splitting during sectioning. We used the unbiased optical disector technique on tissue from three previous studies (two investigations of seasonal plasticity and one investigation of sexual dimorphism in avian song nuclei) to assess seasonal and sex differences in neuron density and number. In two song nuclei, HVc and the robust nucleus of the archistriatum (RA), the optical disector yielded intergroup differences in neuron density and number that coincided well with the three previous reports. We also estimated neuron number and density with a random, systematic, nonstereological counting protocol that used the neuronal nucleolus as the unit of count. We compared this method directly to the optical disector. In all cases, the two neuron-counting methods produced similar estimates of neuron number and density; the differences between treatment groups were equally discernible regardless of the counting method used. This study confirms previously reported seasonal and sex differences in the HVc and the RA by use of stereology and indicates that a random, systematic, nonstereological neuron-counting protocol is accurate and is well suited to the study of these phenomena in the avian song control system.