HEMOPOIETIC SPLEEN COLONY STUDIES : IV. PHYTOHEMAGGLUTININ AND HEMOPOIETIC REGENERATION

The effects of phytohemagglutinin (PHA) were studied in irradiated mice to see if a definite myeloproliferative effect could be demonstrated in vivo. The data obtained suggested the following conclusions. PHA treatment of the bone marrow donor only, causes a consistent but slight reduction in transplantable spleen colony-forming unit (CFU) content of the bone marrow 24 hr after the last PHA injection, but no change was found in the proportion of the various colony types. PHA treatment of the irradiated recipient of normal bone marrow causes no change in the number of spleen colonies. However, 8-day colonies are only about half normal size, are much more likely to be of mixed cell types, contain many large undifferentiated blastoid cells, but fewer transplantable CFU. The spleen sinusoids are packed with hemopoietic cells. Spleen colonies developing in hosts receiving daily injections of PHA show, in addition to the usual spectrum of cell types, a high proportion of unusual blastoid cells resembling the PHA transformed peripheral lymphocytes seen in vitro. The function of these cells is not known, but they may represent augmented proliferation and/or transformation of stem cells. PHA administered after irradiation significantly increased the number of endogenous spleen colonies, and, at certain doses of irradiation, improved postirradiation survival. PHA administered before irradiation had no effect on the number of endogenous spleen colonies formed, or on postirradiation survival. On the basis of these and other data, possible modes of action of PHA are discussed

HEMOPOIETIC COLONY STUDIES : V. EFFECT OF HEMOPOIETIC ORGAN STROMA ON DIFFERENTIATION OF PLURIPOTENT STEM CELLS

In heavily irradiated mice, bone marrow regeneration of either endogenous or exogenous origin was shown to occur in discrete foci comparable to the more intensively studied spleen colonies. The number of endogenous bone marrow colonies was inversely related to dose of whole body X-irradiation. Endogenous marrow colonies were found after higher doses of irradiation than were endogenous spleen colonies. Most of them were granulocytic in nature. Exogenous bone marrow colonies in lethally irradiated mice injected with bone marrow cells were proportional in number to the dose of cells injected, appeared at a time comparable to spleen colonies like which, at 7 or 8 days, they were of single differentiated cell line, either granuloid or erythroid or megakaryocytic, with a small percentage of "mixed" colonies. Whereas erythroid colonies outnumber granuloid colonies in spleen, either in situ or subcutaneously transplanted (E:G colony ratio of about 3.5), granuloid colonies outnumber erythroid in bone marrow (E:G colony ratio of about 0.7). The characteristic E:G colony ratios of spleen and marrow appear more likely to be the result of a hemopoietic organ stromal influence on pluripotent colony forming units (CFU's) than of selective lodgment of committed (unipotent) granuloid and erythroid CFU's in bone marrow and spleen, respectively, as indicated by the following. Bone marrow stem cells (CFU) which had reseeded the marrow cavity of irradiated primary recipients 18–24 hr earlier, were reharvested and retransplanted intravenously into irradiated secondary hosts. The E:G colony ratio of the colonies formed in the spleen of the secondary hosts was typical of primary spleen colonies (2.8), that of the colonies formed in the marrow cavity was typical of bone marrow colonies (0.6). Pieces of marrow stroma containing reseeded CPU's from the contralateral femur of these same primary recipients were implanted by trocar directly into the spleens of other irradiated secondary recipients. Those CPU's that developed in the intrasplenic-implanted marrow stroma yielded an. E:G colony ratio of 0.1. Those that migrated into the contiguous and remote portions of the spleen gave E:G colony ratios of 2.9 and 2.4, respectively. Irradiated marrow stroma and normal spleen CPU's (a 1 mm cube of spleen) were loaded into the same trocar and implanted directly into the spleens of irradiated mice. The spleen CFU's that migrated into the implanted marrow stroma yielded five granuloid and two mixed colonies. The larger number that developed in the host spleen yielded an E:G colony ratio of 2.9 or higher. Of those 19 mixed colonies that bridged the junction of spleen and implanted marrow stroma in each of the above two experiments, in every case, the erythroid portion of the colony was in the splenic stroma, the granuloid portion was in the marrow stroma

HEMOPOIEITC SPLEEN COLONY STUDIES : II. ERYTHROPOIESIS

The polycythemic repression of erythropoiesis and the restoration of erythropoiesis by specific stimulation were studied in the spleen colony system in irradiated mice. 1. A 5 day period of erythropoietin stimulation (exogenous erythropoietin) or repression (polycythemia) of the bone marrow donor only, does not significantly alter the number or type of colonies formed by the transplanted marrow cells. 2. Erythropoietin stimulation did not alter the number or type of endogenous colonies formed in mice receiving 580 R. Erythropoietin repression (polycythemia) markedly reduced the growth but not the number of erythroid colonies, while not affecting the other types of colonies formed endogenously. 3. Erythropoietin stimulation of the irradiated recipient during colony growth did not alter the number or type of spleen colonies formed by transplanted marrow. Erythropoietin repression by polycythemia during colony growth completely suppressed the appearance of morphologically erythroid colonies without significantly altering the incidence of the other colony types. This effect of polycythemia was completely prevented by exogenous erythropoietin. Irradiated mice are therefore presumed to be secreting sufficient erythropoietin for maximal erythroid colony development. 4. The erythroid colonies suppressed by polycythemia were recognizable as microscopic foci of undifferentiated cells. Exposure of these foci to erythropoietin stimulation at different periods in their development was manifested by different degrees of growth and differentiation, from which it is apparent that erythropoietin stimulates not only morphological differentiation but also rapid mitosis. Retransplantation of either erythroid or of neutrophilic primary spleen colonies gave rise to both erythroid and neutrophilic secondary spleen colonies. The percentage of erythroid secondary colonies was slightly but significantly higher among the progeny of transplanted erythroid primary colonies than among the progeny of transplanted neutrophilic primary colonies. On the basis of these and other results, a working hypothesis is proposed for factors controlling the growth and differentiation of spleen colonies from transplanted bone marrow. It is postulated that most but perhaps not all spleen colony-forming units are pluripotent hemopoietic stem cells. It is further postulated that hemopoietic-inductive microenvironments (HIM) of different kinds exist in both the spleen and the bone marrow, and that these determine the differentiation of pluripotent stem cells into each of the lines of hemopoietic differentiation. Erythropoietin therefore may "induce" erythroid differentiation of only those stem cells under the influence of an erythroid HIM. Alternatively erythropoietin may act only as a growth and function stimulant of those stem cells that have been "induced" by an erythroid HIM into a state of erythropoietin responsiveness. In the latter case morphological differentiation presumably results from the functional activity stimulated by ESF

Umidade do solo estimada por TDR em vertissolo e luvissolo na região da Campanha do RS.

CONGREGA URCAMP 2012

Learning activation functions from data using cubic spline interpolation

Neural networks require a careful design in order to perform properly on a given task. In particular, selecting a good activation function (possibly in a data-dependent fashion) is a crucial step, which remains an open problem in the research community. Despite a large amount of investigations, most current implementations simply select one fixed function from a small set of candidates, which is not adapted during training, and is shared among all neurons throughout the different layers. However, neither two of these assumptions can be supposed optimal in practice. In this paper, we present a principled way to have data-dependent adaptation of the activation functions, which is performed independently for each neuron. This is achieved by leveraging over past and present advances on cubic spline interpolation, allowing for local adaptation of the functions around their regions of use. The resulting algorithm is relatively cheap to implement, and overfitting is counterbalanced by the inclusion of a novel damping criterion, which penalizes unwanted oscillations from a predefined shape. Experimental results validate the proposal over two well-known benchmarks.Comment: Submitted to the 27th Italian Workshop on Neural Networks (WIRN 2017

Comparação de métodos de estimativa de evapotranspiração de referência para a região da Campanha.

SIEPE

The experimental development of the mammary gland with special reference to the interaction of the pituitary and ovarian hormones

Publication authorized May 13, 1948.Digitized 2007 AES.Includes bibliographical references (pages 41-48)

Perfilhamento de Eragrostis plana Ness sob estresse hídrico.

CONGREGA