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RESUMEN En 2005 se inició un programa de mejoramiento de arveja para aumentar la producción en cantidad y calidad en la Facultad de Ciencias Agrarias (FCA), Universidad Nacional de Rosario (UNR). Los primeros pasos fueron reunir una colección activa de germoplasma de todo el mundo y analizar la variabilidad genética a través de rasgos morfo-agronómicos y moleculares. En 2014, el Instituto Nacional de Tecnología Agropecuaria (INTA) y la FCAUNR unieron esfuerzos para promover el desarrollo local de genotipos de arveja adaptados a la región. Este programa, utilizando metodologías convencionales, ha obtenido hasta el momento una nueva variedad comercial (Primogénita FCA-INTA) de color de cotiledón verde, semi-áfila, con alta adaptación a las condiciones agroecológicas locales y alto potencial de rendimiento. El mejoramiento genético, sin embargo, es un proceso lento. El desarrollo de nuevas variedades requiere una década o más utilizando metodologías tradicionales, por lo que se propusieron diferentes alternativas para la reducción de este período. Los haploides duplicados y el cultivo in vitro han sido algunas de las metodologías desarrolladas, sin embargo, en legumbres no se han podido implementar de manera eficiente en los programas de mejoramiento. En este contexto, Speed Breeding surge como una tecnología que permite incrementar la eficiencia de los programas, reduciendo los costos y el trabajo requerido.

ABSTRACT A pea breeding program to increase production in quantity and quality was started in 2005 in the College of Agrarian Sciences (FCA), National University of Rosario (UNR). The first steps were to gather an active collection of germplasm from around the world and to analyze genetic variability through morpho-agronomic and molecular traits in order to set objectives. In 2014, the National Institute of Agropecuarian Technology (INTA) and the FCAUNR, joined forces to unite inter-institutional efforts for promoting the local development of pea genotypes adapted to the region. This program, using conventional methodologies, has so far obtained a new commercial line (Primogénita FCA-INTA) of green cotyledons, semileafless, with high adaptation to local agro ecological conditions and high yield potential. Breeding, nevertheless, is a slow process. Developing new pea varieties usually takes a decade or more when using traditional methodologies; thus, different alternatives were proposed for the reduction of this period. Doubled haploids and in vitro culture have been some of the methodologies developed; in pulses, however, they have not been efficiently implemented in breeding programs. In this context, Speed Breeding emerges as a technology that allows increasing the efficiency of the programs, while reducing costs and the required labor.

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RESUMEN El mejoramiento convencional puede ser complementado mediante diferentes estrategias que incrementen la eficiencia de las metodologías y la tasa actual de aumento de los rendimientos a fin de satisfacer la demanda. El uso de marcadores moleculares con el objetivo de desarrollar mapas de ligamiento de la especie, el uso de Blup (Best Linear Unbiased Prediction) para una selección eficiente de progenitores a hibridar, el uso del cultivo in vitro para incrementar artificialmente el número de plantas F1 o el uso de fenotipificación digital para una eficiente caracterización digital que puede realizarse durante la regeneración periódica y rutinaria de accesiones en colecciones de germoplasma.

ABSTRACT Conventional breeding can be complemented by different strategies that increase the efficiency of the methodologies and the current rate of increase in yields in order to meet demand. The use of molecular markers with the aim of developing linkage maps of the species, the use of Blup (Best Linear Unbiased Prediction) for an efficient selection of progenitors to hybridize, the use of in vitro culture to artificially increase the number of F1 plants or the use of digital phenotyping for efficient digital characterization that can be performed during the periodic and routine regeneration of accessions in germplasm collections.

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RESUMEN La lenteja (Lens culinaris Medik.) es una especie diploide autógama (2n=2x=14) perteneciente a la familia Fabaceae. Es uno de los cultivos más antiguos que se conocen, con 8.000 a 9.000 años de historia, y se encuentra entre los primeros domesticados en Medio Oriente. Las semillas tienen un alto valor nutricional. Este cultivo es un interesante sustituto del trigo en las rotaciones de cereales, pero su importancia es baja debido a la falta de buenas variedades con adaptación local. Uno de los principales problemas que enfrentan los mejoradores en nuestro país es la estrecha base genética del germoplasma cultivado y su bajo potencial de rendimiento. En 2004 se inició un programa de mejoramiento de lentejas para desarrollar nuevas variedades con adaptación a las condiciones predominantes en las áreas de cultivo de Argentina. El germoplasma se obtuvo del ICARDA (Centro Internacional de Investigación Agrícola en las Zonas Áridas) y de productores locales. Se utilizan métodos convencionales de mejoramiento basados en la hibridación y selección. Se han obtenido dos nuevas variedades, una del tipo macrosperma (Boyerito FCA) y la otra del tipo microsperma (Tacuarita FCA) mediante la aplicación de selección masal en poblaciones F2 provenientes de la hibridación de materiales seleccionados. Este programa complementa los métodos de mejora tradicional con técnicas biotecnológicas como la transgénesis, el uso de marcadores moleculares, el cultivo de embriones in vitro combinado con el método SSD para acortar el ciclo generacional, y el fenotipado digital.

ABSTRACT Lentil (Lens culinaris Medik.) is a self-pollinating diploid (2n=2x=14) species belonging to the Fabaceae family. It is one of the oldest crops known, with 8,000 to 9,000 years of history and it is among the earliest domesticates from the Near East Fertile Crescent. The seeds have high nutritional value. This crop is an interesting substitute to wheat in cereal rotations but its importance is low due to a lack of suitable varieties with local adaptation. Some of the major problems that Argentinian lentil breeders face are the narrow genetic base of the current cultivated germplasm and its low yield potential. A lentil breeding program was initiated in 2004 to develop new varieties with adaptation to prevalent conditions in growing areas of Argentina. Germplasm was obtained from ICARDA (International Center for Agricultural Research in the Dry Areas) and local producers. Conventional breeding methods using hybridization and selection are being carried out to develop improved varieties, broad the genetic base, and isolate superior recombinant inbred lines. Two new varieties have been obtained, one of the macrosperm type (Boyerito FCA) and the other of the microsperm type (Tacuarita FCA) through the application of mass selection in F2 populations from the cross of selected materials. This program complements traditional breeding methods with biotechnological techniques such as transgenesis, use of molecular markers, in vitro embryo culture combined with the SSD method to shorten the breeding time, and digital phenotyping.

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The purpose of this systematic review was to evaluate the evidence that the injection of carbohydrate-based solutions into embryonated eggs improves broiler performance. A literature search was conducted in April 2017 using the keywords broiler, carbohydrate, in ovo, nutrition and poultry. Only papers that involved in ovo carbohydrate injections in poultry were used in this study. After specific selection criteria, 17 papers were selected. The quality scoring system of the selected studies was based on the injection methodology, use of control groups, type of solution injected, period of injection, egg and hens characteristics, number of variables analysed and the statistical design. Among papers, there was no standardised procedure in to inoculate the solutions. Nevertheless, in general, in ovo feeding of carbohydrates decreases the hatch rate, improves the hatch weight, but it does not seem to influence the post-hatch performance of broilers. The inoculation of 75 mg of glucose in the albumen seems to bring better results. Further studies are needed to improve the technical methodology of in ovo injections for commercial use.

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Abstract The buriti, Mauritia flexuosa, is the most common palm in Brazil, where it has considerable ecological and economic importance. However, few data are available on the phenology of the species, mainly in coastal restinga ecosystems. The present study monitored the reproductive phenology of M. flexuosa in the restinga of Barreirinhas, in the Brazilian Northeast, and investigated the relationship between phenophases and climatic variables. The presence/absence of flowers and fruits was recorded monthly in 25 individuals of each sex between August, 2009, and October, 2012. There was no difference in the phenology of male and female specimens, with flowering and fruiting occurring exclusively in the dry season. We believe that the specific abiotic characteristics of the study environment, such as the intense sunlight and availability of water in the soil, contribute to the reproductive success of M. flexuosa in the dry season, with consequent germination and establishment of seedlings occurring during the subsequent rainy season.

Resumo Popularmente conhecido como buriti, Mauritia flexuosa é a palmeira mais abundante no Brasil, com grande importância ecológica e econômica, porém ainda são poucos os estudos sobre a sua fenologia, não existindo nenhum em ambiente de Restinga. O presente trabalho teve como objetivo estudar a fenologia reprodutiva de M. flexuosa na Restinga de Barreirinhas, no Nordeste do Brasil, verificando como as fenofases se correlacionam com os fatores climáticos. Foram acompanhados mensalmente 25 indivíduos de cada sexo, de agosto/2009 a outubro/2012, verificando a presença/ausência de floração e frutificação. Não houve diferença no padrão fenológico entre indivíduos femininos e masculinos de M. flexuosa, com floração e queda dos frutos exclusivamente na estação seca. Acreditamos que as características abióticas específicas do ambiente estudado, como a forte incidência solar e a disponibilidade de água no solo, contribuíram para o sucesso reprodutivo de M. flexuosa na estação seca, com consequente germinação e estabelecimento de plântulas no período chuvoso.

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The buriti, Mauritia flexuosa, is the most common palm in Brazil, where it has considerable ecological and economic importance. However, few data are available on the phenology of the species, mainly in coastal restinga ecosystems. The present study monitored the reproductive phenology of M. flexuosa in the restinga of Barreirinhas, in the Brazilian Northeast, and investigated the relationship between phenophases and climatic variables. The presence/absence of flowers and fruits was recorded monthly in 25 individuals of each sex between August, 2009, and October, 2012. There was no difference in the phenology of male and female specimens, with flowering and fruiting occurring exclusively in the dry season. We believe that the specific abiotic characteristics of the study environment, such as the intense sunlight and availability of water in the soil, contribute to the reproductive success of M. flexuosa in the dry season, with consequent germination and establishment of seedlings occurring during the subsequent rainy season.(AU)

Popularmente conhecido como buriti, Mauritia flexuosa é a palmeira mais abundante no Brasil, com grande importância ecológica e econômica, porém ainda são poucos os estudos sobre a sua fenologia, não existindo nenhum em ambiente de Restinga. O presente trabalho teve como objetivo estudar a fenologia reprodutiva de M. flexuosa na Restinga de Barreirinhas, no Nordeste do Brasil, verificando como as fenofases se correlacionam com os fatores climáticos. Foram acompanhados mensalmente 25 indivíduos de cada sexo, de agosto/2009 a outubro/2012, verificando a presença/ausência de floração e frutificação. Não houve diferença no padrão fenológico entre indivíduos femininos e masculinos de M. flexuosa, com floração e queda dos frutos exclusivamente na estação seca. Acreditamos que as características abióticas específicas do ambiente estudado, como a forte incidência solar e a disponibilidade de água no solo, contribuíram para o sucesso reprodutivo de M. flexuosa na estação seca, com consequente germinação e estabelecimento de plântulas no período chuvoso.(AU)

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The buriti, Mauritia flexuosa, is the most common palm in Brazil, where it has considerable ecological and economic importance. However, few data are available on the phenology of the species, mainly in coastal restinga ecosystems. The present study monitored the reproductive phenology of M. flexuosa in the restinga of Barreirinhas, in the Brazilian Northeast, and investigated the relationship between phenophases and climatic variables. The presence/absence of flowers and fruits was recorded monthly in 25 individuals of each sex between August, 2009, and October, 2012. There was no difference in the phenology of male and female specimens, with flowering and fruiting occurring exclusively in the dry season. We believe that the specific abiotic characteristics of the study environment, such as the intense sunlight and availability of water in the soil, contribute to the reproductive success of M. flexuosa in the dry season, with consequent germination and establishment of seedlings occurring during the subsequent rainy season.

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Um experimento foi realizado com 276 frangos do tipo caipira da linhagem Gauchão, para avaliar a suplementação de cana de açúcar triturada (CAT) na dieta sobre o desempenho, valor energético das rações e rendimento de carcaça. As aves foram distribuídas em um delineamento inteiramente casualizado com três tratamentos e quatro repetições de 23 aves cada. Os tratamentos foram constituídos da inclusão ou não de CAT de forma on top em uma ração balanceada (RB), (100% RB; 85% RB + 15% CAT e 70% RB + 30% CAT). As rações experimentais foram fornecidas dos 29 aos 85 dias de idade e ao final do período experimental procedeu-se a avaliação do consumo de ração, conversão alimentar e rendimento de carcaça dos frangos. Aos 52 dias de idade foi realizado ensaio de metabolismo, para determinação da energia metabolizável aparente (EMA), energia metabolizável aparente corrigida pelo nitrogênio retido (EMAn) e coeficientes de metabolizabilidade aparente da matéria seca (CMMS), proteína bruta (CMPB), fibra em detergente neutro (CMFDN) e do extrato etéreo (CMEE). A suplementação de CAT na dieta proporcionou aumento no consumo de ração e piora no ganho de peso de acordo com o aumento no nível de inclusão. Os CMMS, CMFDN e CMEE foram superiores para os frangos que receberam o tratamento com 85% RB + 15% CAT, quando comparadas aos frangos alimentados com o tratamento controle (100% RB), com exceção do CMPB que não foi influenciado pela suplementação de CAT. O rendimento de carcaça, cortes e peso de órgãos não diferiram com a inclusão da CAT, porém o peso do pâncreas e da moela foram maiores nos frangos que receberam a dieta com 70% RB + 30% CAT em relação aos que receberam apenas RB. A inclusão da cana de açúcar triturada on top na dieta de frangos tipo caipira, como alimento alternativo, justifica-se até o nível de 15%, pois não afeta o conversão alimentar das aves e melhora o aproveitamento dos nutrientes da ração...(AU)

An experiment was conducted using 276 free-range broiler chickens of the Gauchão lineage to evaluate the effect of dietary supplementation with ground sugarcane (GSC) on performance, energy value of the diets, and carcass yield. The animals were assigned to three treatments and four repetitions of 23 animals each in a completely randomized design. The treatments consisted of the on-top inclusion or not of GSC in a balanced diet (BD) (100% BD; 85% BD + 15% GSC, and 70% BD + 30% GSC). The experimental diets were offered from 29 to 85 days of age and feed intake, feed conversion and carcass yield of the chickens were evaluated at the end of the experimental period. A metabolism assay was conducted at 52 days of age to determine apparent metabolizable energy, apparent metabolizable energy corrected for retained nitrogen, and apparent metabolizability coefficients of dry matter (MCDM), crude protein (MCCP), neutral detergent fiber (MCNDF) and ether extract (MCEE). Dietary supplementation with GSC increased feed intake and worsened weight gain with increasing level of inclusion. MCDM, MCNDF and MCEE were higher for chickens receiving 85% BD + 15% GSC when compared to animals fed the control diet (100% BD), except for MCCP which was not influence by supplementation with GSC. Carcass yield, cut yield or organ weight did not differ between diets with and without GSC inclusion, while the weights of pancreas and gizzard were higher in chickens receiving 70% BD + 30% GSC compared to those receiving only BD. The on-top inclusion of GSC in the diet of free-range broiler chickens as a feed alternative is justified up to a level of 15% since it does not affect feed conversion of the animals and improves the utilization of dietary nutrients...(AU)

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Um experimento foi realizado com 276 frangos do tipo caipira da linhagem Gauchão, para avaliar a suplementação de cana de açúcar triturada (CAT) na dieta sobre o desempenho, valor energético das rações e rendimento de carcaça. As aves foram distribuídas em um delineamento inteiramente casualizado com três tratamentos e quatro repetições de 23 aves cada. Os tratamentos foram constituídos da inclusão ou não de CAT de forma on top em uma ração balanceada (RB), (100% RB; 85% RB + 15% CAT e 70% RB + 30% CAT). As rações experimentais foram fornecidas dos 29 aos 85 dias de idade e ao final do período experimental procedeu-se a avaliação do consumo de ração, conversão alimentar e rendimento de carcaça dos frangos. Aos 52 dias de idade foi realizado ensaio de metabolismo, para determinação da energia metabolizável aparente (EMA), energia metabolizável aparente corrigida pelo nitrogênio retido (EMAn) e coeficientes de metabolizabilidade aparente da matéria seca (CMMS), proteína bruta (CMPB), fibra em detergente neutro (CMFDN) e do extrato etéreo (CMEE). A suplementação de CAT na dieta proporcionou aumento no consumo de ração e piora no ganho de peso de acordo com o aumento no nível de inclusão. Os CMMS, CMFDN e CMEE foram superiores para os frangos que receberam o tratamento com 85% RB + 15% CAT, quando comparadas aos frangos alimentados com o tratamento controle (100% RB), com exceção do CMPB que não foi influenciado pela suplementação de CAT. O rendimento de carcaça, cortes e peso de órgãos não diferiram com a inclusão da CAT, porém o peso do pâncreas e da moela foram maiores nos frangos que receberam a dieta com 70% RB + 30% CAT em relação aos que receberam apenas RB. A inclusão da cana de açúcar triturada on top na dieta de frangos tipo caipira, como alimento alternativo, justifica-se até o nível de 15%, pois não afeta o conversão alimentar das aves e melhora o aproveitamento dos nutrientes da ração...

An experiment was conducted using 276 free-range broiler chickens of the Gauchão lineage to evaluate the effect of dietary supplementation with ground sugarcane (GSC) on performance, energy value of the diets, and carcass yield. The animals were assigned to three treatments and four repetitions of 23 animals each in a completely randomized design. The treatments consisted of the on-top inclusion or not of GSC in a balanced diet (BD) (100% BD; 85% BD + 15% GSC, and 70% BD + 30% GSC). The experimental diets were offered from 29 to 85 days of age and feed intake, feed conversion and carcass yield of the chickens were evaluated at the end of the experimental period. A metabolism assay was conducted at 52 days of age to determine apparent metabolizable energy, apparent metabolizable energy corrected for retained nitrogen, and apparent metabolizability coefficients of dry matter (MCDM), crude protein (MCCP), neutral detergent fiber (MCNDF) and ether extract (MCEE). Dietary supplementation with GSC increased feed intake and worsened weight gain with increasing level of inclusion. MCDM, MCNDF and MCEE were higher for chickens receiving 85% BD + 15% GSC when compared to animals fed the control diet (100% BD), except for MCCP which was not influence by supplementation with GSC. Carcass yield, cut yield or organ weight did not differ between diets with and without GSC inclusion, while the weights of pancreas and gizzard were higher in chickens receiving 70% BD + 30% GSC compared to those receiving only BD. The on-top inclusion of GSC in the diet of free-range broiler chickens as a feed alternative is justified up to a level of 15% since it does not affect feed conversion of the animals and improves the utilization of dietary nutrients...

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Dexosarcophaga tupinamba n. sp. is described based on male specimens from the Brazilian states of Pará and Maranhão; Dexosarcophaga bermudezi Silva & Mello-Patiu is newly recorded from Pará and South America; and Dexosarcophaga avispaensis Mello is newly recorded from Pará (new to Brazil). The Brazilian species Dexosarcophaga limitata (Lopes) and Dexosarcophaga pusilla (Lopes) are both recorded from Pará, which are new records from the Brazilian Amazon, Dexosarcophaga aurifacies (Lopes) is newly recorded from the state of Alagoas and Dexosarcophaga carvalhoi (Lopes) is newly recorded from the states of Mato Grosso, Maranhão, and Pará. A key to the identification of males of the subgenus Bezzisca is provided.

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The superfamily Oestroidea, comprising ∼15,000 species, is a large and ecologically diverse clade within the order Diptera. Among its six commonly recognized families, Calliphoridae seems to be crucial for understanding evolutionary relationships in the group, as it is recognized as a controversial paraphyletic grouping. To further investigate this matter, the ITS2, 28S, COI and 16S regions were used to infer phylogenetic relationships in Oestroidea with maximum-parsimony (MP), maximum-likelihood (ML) and Bayesian inference (BI) methods. For the BI analyses, a deep evaluation of different data partitioning strategies was conducted, including consideration of structural conformation (ITS2 and 16S) and codon position (COI) information. Results suggest the existence of two main clades in Oestroidea: (Tachinidae+Mesembrinellinae) and (Rhiniinae, (Sarcophagidae+Calliphoridae sensu stricto)). Oestridae was recovered as sister group of the remaining Oestroidea in the MP trees while it was placed closer to the (Rhiniinae+Sarcophagidae+Calliphoridae sensu stricto) group in the ML and BI trees. A paraphyletic Calliphoridae was recovered, confirming the exclusion of Rhiniinae, a clade recently promoted to family status and therefore already excluded. Mesembrinellinae could also be considered a distinct group apart from Calliphoridae, although further studies are required. Consideration of structural and codon position information led to a significant increase in the log-likelihoods of the analyses, which were accompanied by small changes in the inferred topologies, branch lengths and posterior probability support values. However, as model complexity increases, so does uncertainty across the estimated parameters, including tree topologies, and phylogenies inferred under very parameter-rich models may be less reliable even when possessing higher log-likelihoods.

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In breeding programs, a large number of F2 individuals are required to perform the selection process properly, but often few such plants are available. In order to obtain more F2 seeds, it is necessary to multiply the F1 plants. We developed a rapid, efficient and reproducible protocol for in vitro shoot regeneration and rooting of seeds using 6-benzylaminopurine. To optimize shoot regeneration, basic medium contained Murashige and Skoog (MS) salts with or without B5 Gamborg vitamins and different concentrations of 6-benzylaminopurine (25, 50 and 75 µM) using five genotypes. We found that modified MS (B5 vitamins + 25 µM 6-benzylaminopurine) is suitable for in vitro shoot regeneration of pea. Thirty-eight hybrid combinations were transferred onto selected medium to produce shoots that were used for root induction on MS medium supplemented with α-naphthalene-acetic acid. Elongated shoots were developed from all hybrid genotypes. This procedure can be used in pea breeding programs and will allow working with a large number of plants even when the F1 plants produce few seeds.

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We characterized 13 accessions of dry peas of different origins from various growing regions in Argentina, based on three replications of 20 plants cultivated in 2009 and 2010 in a greenhouse, with the objective of selecting those with favorable characteristics for use in breeding programs. Significant differences were found for length and width of stipule and pod, length of the internodes and leaflets, plant height, total number of nodes, number of nodes at the first pod, number of days to flowering and to harvest, number of pods and seeds per pod, 100-seed weight and grain diameter, demonstrating a high degree of genetic variability. Phenotypic correlation analysis demonstrated that large pods produced more seeds per pod, but the seed weight decreased. Plants with smaller number of nodes in the first pod were more productive. Estimates of genotypic correlation coefficients indicated a strong inherent association among the different traits. Clustering methods grouped the accessions into five clusters. Cluster 5 included two accessions and showed the highest values for length and width of stipules (4.9 and 4.5 cm, respectively), length of leaflets (7.43 cm) and days to flowering (122.6), while cluster 3, with one accession, and cluster 4, with two accessions, showed the highest values for number of seeds per pod (3.78 and 4.39), number of pods per plant (5.33 and 5.70), length of pods (5.54 and 5.72 cm), and width of pods (1.21 and 1.20 cm, respectively). We conclude that accessions in clusters 3 and 4 would be useful for crosses with other cultivars in pea breeding programs.

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The adult hippocampus continuously generates new cohorts of immature neurons with increased excitability and plasticity. The window for the expression of those unique properties in each cohort is determined by the time required to acquire a mature neuronal phenotype. Here, we show that local network activity regulates the rate of maturation of adult-born neurons along the septotemporal axis of the hippocampus. Confocal microscopy and patch-clamp recordings were combined to assess marker expression, morphological development, and functional properties in retrovirally labeled neurons over time. The septal dentate gyrus displayed higher levels of basal network activity and faster rates of newborn neuron maturation than the temporal region. Voluntary exercise enhanced network activity only in the temporal region and, in turn, accelerated neuronal development. Finally, neurons developing within a highly active environment exhibited a delayed maturation when their intrinsic electrical activity was reduced by the cell-autonomous overexpression of Kir2.1, an inward-rectifying potassium channel. Our findings reveal a novel type of activity-dependent plasticity acting on the timing of neuronal maturation and functional integration of newly generated neurons along the longitudinal axis of the adult hippocampus.

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This study was carried out in the Base Operacional Geólogo Pedro de Moura (BOGPM) in the Urucu River Basin, Coari, state of Amazonas, Brazil, during April, June, and October 2007, in 16 areas, 4 in primary forests (environment MT) and 12 in gaps (environments C1, C2, and C3) at different stages of vegetation recovery, with different plant cover height. We collected 3,547 specimens of flesh flies. The 3,525 individuals identified to species level included 10 genera, 6 subgenera, and 23 species. Sarcodexia lambens (Wiedemann) (47.1%) and Peckia (Peckia) chrysostoma (Wiedemann) (19.1%) were the most abundant species. The abundance patterns and estimated richness differed between the environments, and were separated in two groups, one of the gaps (C1, C2, and C3) and another of forests (MT). Both abundance and estimated richness were higher in the gaps (C1, C2, and C3) than in the forest (MT).

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Neurons born in the adult dentate gyrus develop, mature, and connect over a long interval that can last from six to eight weeks. It has been proposed that, during this period, developing neurons play a relevant role in hippocampal signal processing owing to their distinctive electrical properties. However, it has remained unknown whether immature neurons can be recruited into a network before synaptic and functional maturity have been achieved. To address this question, we used retroviral expression of green fluorescent protein to identify developing granule cells of the adult mouse hippocampus and investigate the balance of afferent excitation, intrinsic excitability, and firing behavior by patch clamp recordings in acute slices. We found that glutamatergic inputs onto young neurons are significantly weaker than those of mature cells, yet stimulation of cortical excitatory axons elicits a similar spiking probability in neurons at either developmental stage. Young neurons are highly efficient in transducing ionic currents into membrane depolarization due to their high input resistance, which decreases substantially in mature neurons as the inward rectifier potassium (Kir) conductance increases. Pharmacological blockade of Kir channels in mature neurons mimics the high excitability characteristic of young neurons. Conversely, Kir overexpression induces mature-like firing properties in young neurons. Therefore, the differences in excitatory drive of young and mature neurons are compensated by changes in membrane excitability that render an equalized firing activity. These observations demonstrate that the adult hippocampus continuously generates a population of highly excitable young neurons capable of information processing.

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