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A Alvarez-Buylla

Publications and source records attributed to A Alvarez-Buylla.

At least 19 recordsLinked to original sources
PubMed1992

High vocal center growth and its relation to neurogenesis, neuronal replacement and song acquisition in juvenile canaries.

It is generally thought that most circuits of the adult central nervous system (CNS) are sculpted, in part at least, by selective elimination of some of the neurons present in an initial overabundant set. In this scenario, the birth of neurons precedes the period when brain functions, such as learning, first occur. In contrast to this form of brain assembly, we describe here the delayed development of the high vocal center (HVC) and one of its efferent pathways in canaries. The retrograde tracer Fluoro-Gold (FG) was injected into one of HVC's two efferent targets, the nucleus robustus archistriatalis (RA), to define the boundaries of HVC. The HVC grows markedly between 1 and 4 months, invading neighboring territories of the caudal telencephalon. During this same period, 0.43%-0.64% of the HVC neurons present at 1 year of age are labeled per day of [3H]-thymidine injection. [3H]-Thymidine labeling is a marker of cell birth, and during the first 4 months HVC neuron number increases, probably accounting for part of the HVC growth observed. Thereafter, the number of HVC neurons remains constant, but neuronal birth persists. We infer from this that neuronal replacement starts as early as 4 months after hatching and perhaps before then. About half of the neurons born after posthatching day 10 grow an axon to RA to form the main efferent pathway exiting from HVC. HVC growth, neurogenesis, axogenesis, and the observed replacement of neurons happen during the period of juvenile vocal learning. However, the recruitment of neurons that are still present at 1 year shows no particular inflections corresponding to the various stages in song learning, and continues at essentially the same rate after the more stereotyped adult song has been acquired. We suggest that a combination of neurogenesis and neuronal replacement provides unique advantages for learning.

Animals↗
PubMed1992

Neurogenesis and plasticity in the CNS of adult birds.

Neurogenesis, typically a developmental phenomenon, continues into adult life in song birds. Cells born in the walls of the lateral ventricle migrate and differentiate throughout the adult telencephalon. I will argue here that birds take advantage of these new neurons as a form of plasticity. Most of the neurons connecting the different song control nuclei are born early in development. One important exception is the central efferent motor pathway for learned vocalization. This pathway is formed by projection neurons born during juvenile and adult life. Recruitment of new projection neurons at different times of the year and in different species correlates with vocal learning. Adult neurogenesis as a form of plasticity may serve learning and it may also teach us how to repair the damaged brain.

Animals↗
PubMed1991

Production and survival of projection neurons in a forebrain vocal center of adult male canaries.

Neurons are produced in the adult canary telencephalon. Many of these cells are incorporated into the high vocal center (nucleus HVC), which participates in the control of learned song. In the present work, 3H-thymidine and fluorogold were employed to follow the differentiation and survival of HVC neurons born in adulthood. We found that many HVC neurons born in September grow long axons to the robust nucleus of the archistriatum (nucleus RA) and thus become part of the efferent pathway for song control. Many of these new neurons have already established their connections with RA by 30 d after their birth. By 240 d, 75-80% of the September-born HVC neurons project to RA. Most of these new projection neurons survive at least 8 months. The longevity of HVC neurons born in September suggests that these cells remain part of the vocal control circuit long enough to participate in the yearly renewal of the song repertoire.

Animals↗
PubMed1990

On variables that affect estimates of the true sizes and densities of radioactively labeled cell nuclei.

Tritiated thymidine has been widely used as a nuclear marker of cell birth. The true diameters and packing densities (nuclei/microns 3) of such radioactively labeled nuclei cannot be measured directly from tissue sections. Here we show that existing stereological corrections cannot be applied to data from radioactively labeled nuclei. We empirically measured the number of silver grains exposed by nuclei containing tritiated thymidine. The nuclei were separated from the photographic emulsion by known thicknesses of fixed, embedded avian telencephalon. The results of this experiment were used to develop an equation that estimates the number of silver grains exposed by a cell nucleus of any given diameter, containing a given amount of radioactive label, and located at any given distance from the photographic emulsion. The equation also allows one to calculate the probability that a label-containing nucleus will be correctly classified as labeled. Simulations of the equation revealed that not all label-containing nuclei are correctly classified by using commonly employed identification procedures and that larger nuclei are less likely to be correctly classified than smaller nuclei, given the same amount of label. The equation can be used to modify one class of existing stereological equations so as to be applicable to measurements of radioactively labeled nuclei. Finally, we discuss the assumptions and limitations of this modification.

Animals↗
PubMed1990

Birth of projection neurons in adult avian brain may be related to perceptual or motor learning.

Projection neurons that form part of the motor pathway for song control continue to be produced and to replace older projection neurons in adult canaries and zebra finches. This is shown by combining [3H]thymidine, a cell birth marker, and fluorogold, a retrogradely transported tracer of neuronal connectivity. Species and seasonal comparisons suggest that this process is related to the acquisition of perceptual or motor memories. The ability of an adult brain to produce and replace projection neurons should influence our thinking on brain repair.

Animals↗
PubMed1990

Mechanism of neurogenesis in adult avian brain.

Adult neurogenesis in birds offers unique opportunities to study basic questions addressing the birth, migration and differentiation of neurons. Neurons in adult canaries originate from discrete proliferative regions on the walls of the lateral ventricles. They migrate away from their site of birth, initially at high rates, along the processes of radical cells. The rates of dispersal diminish as the young neurons invade regions devoid of radial fibers, probably under the guidance of other cues. The discrete sites of birth in the ventricular zone generate neurons that end up differentiating throughout the telencephalon. New neurons may become interneurons or projection neurons; the latter connect two song control nuclei between neostriatum and archistriatum. Radial cells, that in mammals disappear as neurogenesis comes to an end, persist in the adult avian brain. The presence of radial cells may be key to adult neurogenesis. Not only do they serve as guides for initial dispersal, they also divide and may be the progenitors of new neurons.

Animals↗
PubMed1990

Song learning in birds: the relation between perception and production.

The vocal control system of oscine songbirds has some perplexing properties--e.g. laterality, adult neurogenesis, neuronal replacement--that are not predicted by common views of how vocal learning takes place. Similarly, we do not understand the relation between the direct pathway for the control of learned song and the recursive pathway necessary for song learning. Some of the paradoxes of the vocal system of birds may disappear once the relation between the perception and production of learned vocalizations is better understood. To some extent, perception and production may be two closely related states of a same system.

Animals↗
PubMed1990

Cresyl violet: a red fluorescent Nissl stain.

Cresyl violet is widely used by neurobiologists to visualize Nissl substance in bright-field microscopy. Here we describe a method for using this dye as a red fluorescent Nissl stain. Unlike the bright-field staining technique, fluorescent cresyl is compatible with other fluorescent dyes and tracers, such as fluorescein, Fluoro-Gold and Fast Blue. The procedure requires only minor modifications of routine bright-field cresyl staining, the most significant being dilution of the stain. Thus, fluorescent red cresyl violet is simple to implement and may be of general use in fluorescence microscopy.

Animals↗
PubMed1990

Proliferation "hot spots" in adult avian ventricular zone reveal radial cell division.

Neurogenesis in the adult avian brain is restricted to the telencephalon. New neurons originate in the ventricular zone (VZ) from cells that have not been identified. We mapped the position of [3H]thymidine-labeled cells in the walls of the ventricles of the adult canary brain. Labeled VZ cells were restricted to the telencephalon (lateral ventricles) and concentrated in "hot spots". The coincidence of these hot spots with regions rich in radial cells suggested that radial cells may be the cells undergoing mitosis. We used smears prepared from fragments of the VZ containing the hot spots to show directly that radial cells accumulate [3H]thymidine. In addition, grain counts at different survival times demonstrated that these cells divide. Hot spots of VZ cell division also coincided with sites of neuronal origin. We suggest that radial cell division may give rise to new neurons.

Animals↗
PubMed1989

Expression of the yes proto-oncogene in cerebellar Purkinje cells.

To identify the kinds of cells in the brain that express the yes proto-oncogene, we examined chicken brains by using immunofluorescent staining and in situ hybridization. Both approaches showed that the highest level of the yes gene product was in cerebellar Purkinje cells. In addition, we analyzed Purkinje cell degeneration (pcd) mutant mice. The level of yes mRNA in cerebella of pcd mutants was four times lower than that found in cerebella of normal littermates. Our studies point to Purkinje cells as an attractive model for functional studies of the yes protein.

Animals↗
PubMed1989

In situ hybridization using PEG-embedded tissue and riboprobes: increased cellular detail coupled with high sensitivity.

We describe a procedure for preparing tissue sections by embedding in polyethylene glycol for subsequent in situ hybridization analysis using single-stranded RNA probes. Improved tissue morphology is obtained as compared to frozen sections, and the embedding procedure is milder and faster than paraffin embedding. Sections as thin as 2 microns are readily cut from PEG-embedded brain tissue. A simplified hybridization protocol (Clayton et al.: Neuron 1:249, 1988) supports the detection of even low-abundance brain mRNAs (less than or equal to 10(-4) fractional mRNA mass). By employing high stringency washes in place of ribonuclease treatment after hybridization, cell RNA is retained for cresyl violet staining, and high signal:noise ratios are achieved. Solutions to problems with section mounting and adherence to glass slides are presented. The combination of improved morphology, high signal levels, and relative simplicity should make this procedure useful in a variety of applications.

Animals↗
PubMed1988

Migration of young neurons in adult avian brain.

Neurons are born in the ventricular walls of the vertebrate central nervous system. From there, the young neurons migrate to their final destinations, where differentiation occurs. Neuronal migration has been described during the ontogeny of the avian and mammalian brain. Whereas in mammals most neurogenesis occurs during early development, in the adult avian forebrain wide-spread neurogenesis continues to occur. How do neurons born in adulthood reach their final destination? We report here that small elongated cells, born in the ventricular zone adjacent to the lateral ventricle, differentiate into mature neurons 20-40 days later, after migrating over distances of up to 5 mm. Migration rates are highest (28 micron h-1) when young neurons migrate through regions which are rich in radial glia. The adult vertebrate brain offers unique opportunities for studying factors that regulate neuronal migration, pathfinding and differentiation.

Animals↗
PubMed1988

Simple microcomputer system for mapping tissue sections with the light microscope.

We describe a method for two-dimensional mapping of tissue sections that makes use of a drawing tube, microscope stage encoders and a microcomputer. The drawing tube views the graphics monitor and superimposes the image of the screen cursor and on-screen menus on the specimen image. Thus, the position of every landmark in each microscopic field can be mapped without stage movement while directly viewing the specimen through the microscope. A mouse is used for data entry and program control. Fields mapped in this way are then assembled into a complete map, which can include line drawings as well as up to 20 landmark types. The coordinate values of all landmarks mapped are stored and remain accessible for editing and analysis. High resolution plots are produced. Specialized functions include grain counting, area and perimeter calculations as well as a perimeter limiter that predefines the area to be mapped. The system uses general purpose hardware that is widely available. Many hitherto time-consuming tasks, such as detailed mapping of cell positions, regions of immunocytochemical staining, degenerating fibers, neuronal connections or any other anatomical feature, can be done in a fraction of the time and effort previously involved. These labor savings can be realized while maintaining the highest resolution and enabling statistical analysis since the data are already in digital form.

Animals↗
PubMed1988

Birth of projection neurons in the higher vocal center of the canary forebrain before, during, and after song learning.

The higher vocal center (HVc) of the canary brain projects to two forebrain nuclei: robustus archistriatalis (RA) and area X of lobus parolfactorius. The time of birth of HVc neurons projecting to these two regions was determined by combining [3H]thymidine autoradiography and retrograde fluorogold uptake. Birds were sacrificed at 13 months of age, 4 days after fluorogold injections into area X or RA. A single injection of [3H]thymidine in ovo (embryonic day 9) labeled 76% of area X-projecting cells and 0.8% of cells projecting to RA. The great majority of RA-projecting cells were produced during posthatching development (posthatching day 10-240; P10-P240), with a peak at P60 and a hiatus at P120. HVc reaches full adult size by P240, yet at that age the production of new RA-projecting cells continued at a rate comparable to that recorded during posthatching development. Late production of neurons interconnecting two distant regions of the brain may regulate source to target cell population size. Male canaries start to sing at P40. During subsequent months, they imitate external models and their song becomes more structured and stereotyped. At sexual maturity (P240), song is stable. Three interpretations are offered: (i) neurogenesis of RA-projecting cells is related to learning, and learning continues even after achievement of pattern stability; (ii) neurogenesis of RA-projecting cells is not related to learning; (iii) the production of RA-projecting cells serves different purposes during development and after sexual maturity.

Aging↗
PubMed1988

Differential developmental expression of cellular yes and cellular src proteins in cerebellum.

To identify the specific areas of the brain that express c-yes and c-src proteins, we examined chicken brains dissected from two-week-old birds using an immune complex kinase assay and an immune blot analysis. Highest levels of both proto-oncogene proteins were found in the cerebellum, whereas other parts of the brain, including telencephalon, diencephalon, mesencephalon and spinal cord, showed three- to six-times lower levels. Relatively low levels of the two proteins were detected in pineal body and pituitary. When the cerebellum was further dissected into three layers, molecular, granular and fibrous, both the c-yes and c-src proteins were found to be concentrated in the molecular layer and, to a lesser degree, also in the granular layer. In cerebellum and in chicken embryo fibroblasts the c-yes protein was predominantly associated with the membrane fraction, and in chicken embryo fibroblasts c-yes was labeled with radioactive myristic acid. Adult cerebellum showed a two- to three-fold increase in the c-yes protein level over that detected in embryonal cerebellum. Conversely, c-src expression in the embryonic cerebellum was relatively high and it was diminished in the adult cerebellum. Differential developmental expression of c-yes and c-src proteins in cerebellum suggests that these proteins fulfill different functions or different aspects of the same function.

Age Factors↗
PubMed1988

Mapping of radial glia and of a new cell type in adult canary brain.

Frontal and coronal sections of adult male and female canary brain were stained with a monoclonal antibody to vimentin using an immunoperoxidase technique; some sections were counterstained with cresyl violet. The position of radial glia cells was mapped using a computer-linked microscope. The telencephalon was found to have a rich set of radial glia. The long processes of these radial glia showed a mediolateral orientation, and were much more abundant in some parts of the telencephalon (e.g., hyperstriatum, caudal neostriatum, and lobus parolfactorius) than in others (e.g., anterior neostriatum, archistriatum, and septum), which had few or no radial glia fibers. A small, elongated cell type not previously described in adult avian brain was frequently seen to be associated with the long processes of the radial glia, oriented in the same direction and often in close apposition. The position of these cells was also systematically mapped, and they were found to be virtually absent outside of the telencephalon. The relation between radial glia fibers and the small, elongated cells was most commonly seen close to the lateral ventricle of the forebrain, where the radial glia cells have their cell bodies. The above observations suggest that there may be a functional relation between radial glia and the small, elongated cells. We hypothesize that the latter cells are young migrating neurons. This hypothesis is tested in a separate publication (A. Alvarez-Buylla and F. Nottebohm, unpublished observations).

Animals↗
PubMed1987

Monoclonal antibody reveals radial glia in adult avian brain.

An antibody prepared against adult canary brain, 40E-C, stains ventricular zone cells that send long, unbranched processes into the forebrain parenchyma. We identify these cells as radial glia. The same antibody also stains a subset of brain astroglia and reacts with nonbrain material such as mesenchyme, Sertoli cells, and the Z-line of muscle. A weaker reaction is given by erythrocytes and some endothelial cells. 40E-C also reacts with the radial glia of the developing rat brain but fails to show any such glia in adult rodent brain. Western blot analysis shows that this antibody recognizes vimentin, a molecule shared by all 40E-C-positive cell types. We believe that the presence of radial glia in the adult avian forebrain and their apparent absence in mammals is related to neurogenesis in adulthood, which occurs in birds and much less or not at all in mammals. In addition, the presence of radial glia in adult birds may also relate to other, still-hypothetical, differences in the physiology of adult avian and mammalian brains.

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