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At least 757 records · Page 42Linked to original sources
PubMed1994

An alternative Fc gamma-receptor ligand: potential role in T-cell development.

Fetal pre-T cells express low-affinity receptors for IgG (Fc gamma R) at a developmental stage prior to the rearrangement and expression of immunoglobulin genes. The present studies investigated the possible functional significance of Fc gamma R on fetal pre-T cells. Between 13 and 17 days of fetal development a subpopulation of T-cell receptor-, Thy-1+ thymocytes express for gamma R. The same cells contain mRNA for several forms of Fc gamma R (Fc gamma RII beta 1, beta 2, and Fc gamma RIII). Concurrently, a Pgp-1-, Thy-1-, surface-immunoglobulin- fetal thymic cell binds recombinant soluble Fc gamma R. In principle this cell can interact with the pre-T cells through this counter-receptor. To test this possibility anti-Fc gamma RII/III antibody (2.4G2) was injected into pregnant mice and then into their offspring for 6 wk postpartum. The injected antibody induced a slight increase in the proportion of CD4 or CD8 single-positive, alpha/beta T cells in the thymus. However, in fetal thymic cultures in the presence of 2.4G2 or the recombinant soluble Fc gamma R there was an accelerated differentiation of thymocytes to single-positive, CD3-bright, heat-stable antigen-dull, alpha/beta T cells. These experiments show that Fc gamma Rs are present on pre-T cells during early fetal thymic development, and that a non-IgG ligand of the Fc gamma R is expressed concurrently on Thy- fetal thymocytes. Furthermore, the presumed interaction of Fc gamma R and the alternative ligand(s) influences T-cell development. IgG binding could be an adapted function of Fc gamma Rs, and, as shown for many members of the Ig super family, these receptors may have originally served as cell-cell recognition/interaction molecules required for hematopoietic development.

Animals↗
PubMed1995

Mandibular growth rates in human fetal development.

A morphometric analysis of changing proportions in the developing mandible was undertaken in 18 human embryos and fetuses of both sexes (developmental age from 8 to 14 weeks, crown-rump length, CRL, from 34 to 110 mm), previously cleared and stained with a specific method for bone (alizarin red S). Reference points were located on the mandible, i.e. condylar process (Pcl), coronoid process (Pco), gnathion (GN), gonion (GO), superior symphyseal point (SSP), for measuring linear dimensions, i.e. Pcl-GN, Pcl-Pco, Pco-GN, GO-GN, SSP-GN. The gonial (Pcl-GO-GN) and the (Pcl-GN-Pcl) angles were also measured. All linear dimensions were correlated with the CRL by bivariate allometry (1n y = 1n a+b 1n x): they all grew with positive allometry, except GO-GN with isometry. The mandibular ramus grew relatively faster than the body, both in length and height, and the greatest growth rate was found for ramus height. The relation between mandibular shape and the craniofacial structures was investigated using scale drawings obtained from photographs of fetal skulls in lateral view. In the youngest fetuses the mandible was prognathic, then became retrognathic. During the period investigated the zygomatic process and squama of the temporal bone were in a lower and more inclined position in relation to the transverse plane passing through the zygomatic arch than in the newborn and adult. This study identifies parameters fitting changing trends in height, length and shape of the human mandible during the prenatal period (8-14 weeks); moreover, it emphasizes that the mandibular growth patterns differ significantly from those of successive development periods.

Adult↗
PubMed1994

Cerebrovascular autoregulation during fetal development in sheep.

There are scant data regarding the development of cerebrovascular autoregulation in fetuses. We tested the hypothesis that a decrease in cerebrovascular resistance (CVR) at reduced cerebral perfusion pressure (CPP) is absent in midgestation and near-term fetal sheep. Catheters were chronically implanted for microsphere determination of cerebral blood flow (CBF) in 9 fetuses at 92 days and in 10 fetuses at 132 days gestation (full term = 145 days). CPP was reduced by ventricular infusion of artificial cerebrospinal fluid. In 92-day fetuses, CPP was reduced stepwise from 35 to 25 and 18 mmHg and CBF decreased from 52 +/- 5 to 43 +/- 4 and 27 +/- 5 (SE) ml.min-1 x 100 g-1, respectively. Half of the immature fetuses showed some reduction in CVR at moderate reduction in CPP; however, there was no significant change in CVR in the group as a whole (from 0.72 +/- 0.06 to 0.61 +/- 0.04 and 0.89 +/- 0.20 mmHg.ml-1.min.100 g). In 132-day fetuses, CPP was reduced from 45 to 33 and 28 mmHg and CBF was unchanged (from 105 +/- 7 to 97 +/- 11 and 89 +/- 8 ml.min-1 x 100 g-1). CVR decreased from 0.45 +/- 0.05 to 0.41 +/- 0.08 and 0.33 +/- 0.03 mmHg.ml-1.min.100 g. There were no significant changes in arterial blood gases at reduced CPP in either age group. We conclude that cerebrovascular autoregulation at reduced CPP is not well developed at 92 days (0.63 gestation) in fetal sheep but that autoregulatory capacity is evident near term. We speculate that poor autoregulation may place the premature fetal brain at risk for injury.

Animals↗
PubMed1993

Establishment of vagal sensorimotor circuits during fetal development in rats.

The differentiation of vagal motor neurons and their emerging central relationship with vagal sensory afferents was examined in fetal rats. To identify peripherally projecting sensory and motor neurons, 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (DiI) was inserted into the proximal gut or cervical vagus nerve in fixed preparations. At embryonic day (E) 12, labeled vagal sensory neurons are present in the nodose ganglia and a few sensory axons project into the dorsolateral medulla. Central sensory processes become increasingly prevalent between E13 and E14 but remain restricted to the solitary tract. Vagal motor neurons are first labeled at E13, clustered within a region corresponding to the nucleus ambiguus (NA). Additional motor neurons appear to be migrating toward the NA from the germinal zone of the fourth ventricle. Motor neurons in the dorsal motor nucleus of the vagus (DMV) first project to the gut at E14 and have processes that remain in physical contact with the ventricular zone through E16. Sensory axons emerge from the solitary tract at E15 and project medially through the region of the nucleus of the solitary tract (NST) to end in the ventricular zone. A possible substrate for direct vagovagal, sensorimotor interaction appears at E16, when vagal sensory fibers arborize within the DMV and DMV dendrites extend into the NST. By E18, the vagal nuclei appear remarkably mature. These data suggest specific and discrete targeting of vagal sensory afferents and motor neuron dendrites in fetal rats and define an orderly sequence of developmental events that precedes the establishment of vagal sensorimotor circuits.

Animals↗
PubMed1999

Expression and location of IGF binding proteins-2, -4, and -5 in developing fetal tissues.

Insulin-like growth factors are associated with myogenesis in vivo, and their actions are mediated by IGF binding proteins (IGFBP). Sites of IGFBP production and their location during early development are not clear. The objective of this research was to examine the developmental expression and location of IGFBP-2, -4, and -5 mRNA and peptides in developing porcine skeletal muscle and liver. Pregnant pigs were euthanatized at various times postconception (pc). Developmental expression of IGFBP was evaluated using total RNA extracted from skeletal muscle and liver of 30-, 44-, 59-, 68-, 75-, 89-, and 109-d pc fetuses and from adult and neonatal pigs. Localization of IGFBP-2, -4, and -5 mRNA and peptides was examined by in situ hybridization and immunocytochemistry of muscle samples from contralateral pelvic limbs of each pig. Overall muscle IGFBP gene expression decreased (P < .05) with increasing age. Moreover, expression of liver IGFBP-2 and -5, but not of IGFBP-4, was greater (P < .05) during prenatal than during postnatal periods. The majority of immunoreactive IGFBP was located in developing muscle cells, with little localized to connective tissue, except at later stages of development. These data show that IGFBP-2, -4, and -5 expression is time- and tissue-dependent in fetal liver and muscle.

Animals↗