Neurogenesis in an adult avian song nucleus is reduced by decreasing caspase-mediated apoptosis

Neuron death and replacement are fundamental components of brain plasticity. Much remains unknown, however, about the mechanistic interaction between neuron death and neurogenesis in adult vertebrates. In seasonally breeding adult male white-crowned sparrows, the song system nucleus HVC loses ∼26% of its neurons via caspase-dependent apoptosis within 4 d after a transition to nonbreeding physiological conditions. To determine whether neuronal death is necessary for the recruitment of new neurons, we infused caspase inhibitors into HVC in vivo and suppressed neurodegeneration for at least 20 d after the transition to nonbreeding conditions. The blockade of HVC neuron death reduced the number and density of new neurons recruited to the ipsilateral HVC by 48 and 29%, respectively, compared with contralateral HVC. Our results are the first to show that reducing neuronal death in the adult brain decreases the recruitment of new neurons

Seasonal changes in patterns of gene expression in avian song control brain regions.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Photoperiod and hormonal cues drive dramatic seasonal changes in structure and function of the avian song control system. Little is known, however, about the patterns of gene expression associated with seasonal changes. Here we address this issue by altering the hormonal and photoperiodic conditions in seasonally-breeding Gambel's white-crowned sparrows and extracting RNA from the telencephalic song control nuclei HVC and RA across multiple time points that capture different stages of growth and regression. We chose HVC and RA because while both nuclei change in volume across seasons, the cellular mechanisms underlying these changes differ. We thus hypothesized that different genes would be expressed between HVC and RA. We tested this by using the extracted RNA to perform a cDNA microarray hybridization developed by the SoNG initiative. We then validated these results using qRT-PCR. We found that 363 genes varied by more than 1.5 fold (>log(2) 0.585) in expression in HVC and/or RA. Supporting our hypothesis, only 59 of these 363 genes were found to vary in both nuclei, while 132 gene expression changes were HVC specific and 172 were RA specific. We then assigned many of these genes to functional categories relevant to the different mechanisms underlying seasonal change in HVC and RA, including neurogenesis, apoptosis, cell growth, dendrite arborization and axonal growth, angiogenesis, endocrinology, growth factors, and electrophysiology. This revealed categorical differences in the kinds of genes regulated in HVC and RA. These results show that different molecular programs underlie seasonal changes in HVC and RA, and that gene expression is time specific across different reproductive conditions. Our results provide insights into the complex molecular pathways that underlie adult neural plasticity

Emerging from the bottleneck: benefits of the comparative approach to modern neuroscience

Neuroscience has historically exploited a wide diversity of animal taxa. Recently, however, research has focused increasingly on a few model species. This trend has accelerated with the genetic revolution, as genomic sequences and genetic tools became available for a few species, which formed a bottleneck. This coalescence on a small set of model species comes with several costs that are often not considered, especially in the current drive to use mice explicitly as models for human diseases. Comparative studies of strategically chosen non-model species can complement model species research and yield more rigorous studies. As genetic sequences and tools become available for many more species, we are poised to emerge from the bottleneck and once again exploit the rich biological diversity offered by comparative studies. Biological diversity as a resource for neuroscience Model species such as the fruit fly (Drosophila melanogaster), the nematode 'worm' (Caenorhabditis. elegans), zebrafish (Danio rerio), the rat (Rattus rattus), and, most predominantly, the mouse (Mus musculus) have played an important role in biology. A given species may offer particular advantages for the study of a biological process, such as rapid embryonic development, accessible nervous systems, or ease of maintenance in the laboratory. The advantages of model species have become more pronounced with the advent of the genomic revolution. Until recently, sequencing genomes was expensive and laborious, limiting the number of species for which genomic sequences were available. As the database of information for a given model species grows over time, there is an increasing incentive to use that species to investigate topics outside the narrow field of inquiry for which the species was initially chosen. 'Repurposing' of model species, however, can raise concerns -as seen in the ongoing debate about the value of inbred mouse (M. musculus) strains as models for understanding human mental disorders Potential limitations of the model species approach Over the past 20 years or so, neuroscience and much of biology in general has coalesced from the traditional embrace of diverse species down to a small number of model species. There are various practical reasons for this process of concentration. Model species tend to be readily available, easily maintained in captivity, and are feasible to breed in large numbers. As a species becomes a wellestablished model for a research community, there is an exponential growth in the amount of available information that serves as a platform for future research. With the advent of the genomic revolution, and the ensuing development of powerful molecular tools such as combinatorial systems for gene expression and optogenetics, the incentive to concentrate on a small number of species has become even more pronounced. Conservation of orthologous genes across diverse taxa shows that we can understand much about basic genomic structure and function by studying model species. The current enthusiasm for a model species approach, however, brings with it several limitations that are too rarely acknowledged. The standard model species represent a vanishingly small percentage of the total biological diversity. As Manger et al

Review TRENDS in Ecology and Evolution Vol.20 No.3 March 2005 Functional aspects of song learning in songbirds

The oscine passerines, or ‘songbirds’, are one of the few animal taxa in which individuals learn their vocal signals. Recent comparative studies reveal a remarkable diversity of song-learning strategies in the songbirds. Here, we discuss recent studies that shed light on the possible functional basis of different song-learning programs. We argue that further insights into the evolution and ecology of song learning will require that comparative data and functional hypotheses be analyzed in a phylogenetic context, and we review recent studies that we feel might be the first steps in this process. Songs are complex species-specific signals given by animals of many taxa in mating and intrasexual contexts, most commonly by males to attract females and to repel rival males [1]. In most animal taxa, these species-specifi

Immediate and long-term effects of testosterone on song plasticity and learning in juvenile song sparrows

Steroid sex hormones play critical roles in the development of brain regions used for vocal learning. It has been suggested that puberty-induced increases in circulating testosterone (T) levels crystallize a bird's repertoire and inhibit future song learning. Previous studies show that early administration of T crystallizes song repertoires but have not addressed whether new songs can be learned after this premature crystallization. We brought 8 juvenile song sparrows (Melospiza melodia) into the laboratory in the late summer and implanted half of them with subcutaneous T pellets for a two week period in October. Birds treated with T tripled their singing rates and crystallized normal songs in 2 weeks. After T removal, subjects were tutored by 4 new adults. Birds previously treated with T tended toward learning fewer new songs post T, consistent with the hypothesis that T helps to close the song learning phase. However, one T-treated bird proceeded to learn several new songs in the spring, despite singing perfectly crystallized songs in the fall. His small crystallized fall repertoire and initial lag behind other subjects in song development suggest that this individual may have had limited early song learning experience. We conclude that an exposure to testosterone sufficient for crystallization of a normal song repertoire does not necessarily prevent future song learning and suggest that early social experiences might override the effects of hormones in closing song learning. (c) 2012 Elsevier B.V. All rights reserved.</p