Quantitative Magnetic Resonance Imaging of Human Brain Development: Ages 4-18

Brain magnetic resonance images (MRI) of 104 healthy childrenand adolescents, aged 4–18, showed significant effectsof age and gender on brain morphometry. Males had larger cerebral(9%) and cerebellar (8%) volumes (P < 0.0001 and P = 0.008.respectively), which remained significant even after correctionfor height and weight After adjusting for cerebral size, theputamen and globus pallidus remained larger in males, whilerelative caudate size was larger in females. Neither cerebralnor cerebellar volume changed significantly across this agerange. Lateral ventricular volume increased significantly inmales (trend for females), with males showing an increase inslope after age 11. In males only, caudate and putamen decreasedwith age (P = 0.007 and 0.05, respectively). The left lateralventricles and putamen were significantly greater than the rightP = 0.01 and 0.0001, respectively). In contrast, the cerebralhemispheres and caudate showed a highly consistent right greater-than-leftasymmetry (P < 0.0001 for both). All volumes demonstrateda high degree of variability. These findings highlight gender-specificmaturational changes of the developing brain and the need forlarge gender-matched samples in pediatric neuropsychiatric studies.     

Evolution of immune surveillance and tumor immunity: studies in Xenopus

Summary: We have developed a novel experimental model of cancer immunity in the frog, Xenopus , which may provide a useful alternative to murine tumor models and a way to assess whether the control of tumor development is a fundamental function of the immune system of vertebrates. In Xenoptis , tumor immunity can be studied in two developmentally distinct immune systems. The larval immune system reflects characteristics of an ancestral system that appears to function without classical MHC class I antigen presentation and an efficient effector mechanism. The adult system appears more highly evolved in that it is remarkably similar to that of mammals and is able to generate a potent antitumor response. This amphibian model also provides a unique system with which to investigate a postulated role of heat shock proteins as components of an ancestral system of antigen presentation and/or immune surveillance that predates the antigen presentation pathway that exclusively involves MHC molecules.     

Frequency of T-Cell Progenitors in Nude Mice

The hypothesis that prothymocytes are distinct from and regulated independently of multilineage hemopoietic progenitors was tested by enumeration of these two cell populations in normal versus congenitally athymic (nude) mice. The absence of a thymus and of peripheral T cells in nude mice had no effect on the frequency of either multilineage progenitors (day 12 CFU-S) or prothymocytes (CFU-T), suggesting that there is no feedback regulation of CFU-T frequency. Thymus seeding from the bone marrow is therefore likely to be regulated by the availability of niches for prothymocyte maturation, rather than by feedback control of prothymocyte production.     

Vasodepressor reactions after orthotopic cardiac transplantation: Relationship to reinnervation status

Ventricular vagal nerve endings are thought to trigger vasodepressor syncope. Reports of vasodepressor reactions associated with donor bradycardia after cardiac transplantation have led to speculation that vagal reinnervation occurs. We assessed reinnervation status in seven patients 23–36 months (median 24 months) post-transplantation. Heart rate responses to vagal manoeuvres (respiration, Valsalva) and sympathetic stimuli (exercise and injection of tyramine into the coronary artery supplying the sinus node) were measured. All patients underwent 60 min of 60° head-up tilt with foot plate support. During tilt four of the seven had vasodepressor reactions with a fall in mean arterial pressure of 20–90 mmHg. During vasodepression two patients had falls in donor heart rate of 13 and 40% relative to peak heart rate during tilt. These two patients had evidence of functional sympathetic reinnervation. By contrast the two patients without donor bradycardia during vasodepression had only limited or no evidence of sympathetic reinnervation. No patient had consistent evidence of parasympathetic reinnervation as judged by the heart rate response to vagal manoeuvres. Headup tilt can thus produce vasodepressor reactions with donor bradycardia after cardiac transplantation in the absence of consistent evidence of vagal reinnervation. Left ventricular nerve endings may not be the only mediators of tilt-induced vasodepressor reactions in man. Donor bradycardia during vasodepression may reflect sympathetic withdrawal and not vagal reinnervation.     

A nuclear mutant of Chlamydomonas that exhibits increased sensitivity to UV irradiation,reduced recombination of nuclear genes,and altered transmission of chloroplast genes

Summary Meiotic progeny of Chlamydomonas reinhardtii normally receive chloroplast genomes only from the mt ⁺ parent. However, exceptional zygotes, which transmit the chloroplast genomes of both parents or, more rarely, only those of the mt ^- parent, arise at a low frequency. Mutations at the mt ⁺-linked mat-3 locus were found previously to elevate the transmission of chloroplast genomes from the mt-parent, resulting in a much higher than normal frequency of exceptional zygotes. In this paper we demonstrate that an ultraviolet-sensitive nuclear mutation mapping at the uvsE1 locus, which is unlinked to mating type, also promotes chloroplast genome transmission from the mt ^- parent. This mutant, which was previously shown to reduce recombination of nuclear genes in meiosis, acts synergistically which the mat3-3 mutation to produce an extremely high frequency of exceptional zygotes. Through the use of restriction fragment length polymorphisms existing in the chloroplast genomes of C. reinhardtii and the interfertile strain C. smithii, we show that chloroplast DNA fragments from the mt ^- parent normally begin to disappear shortly after zygote formation. However, this process appears to be blocked totally in the absence of wild-type uvsE1 and mat-3 gene products. Our findings are consistent with the hypothesis that both gene products contribute to the mechanism responsible for uniparental inheritance of the chloroplast genome from the mt ⁺ parent.