Heterosynaptic LTP in early development.

The formation of precise synaptic connections in the developing central nervous system involves activity-dependent control of synaptic strength. Correlated activity between the afferent input and postsynaptic neuron strengthens connections through long-term potentiation (LTP), while uncorrelated synaptic inputs are selectively diminished. In this issue of Neuron, Tao et al. report that LTP in young animals has less synaptic specificity than in older animals, indicating that the properties of LTP change during development.     

Polarity in early mammalian development.

Although overall polarity is discernable morphologically in both the growing and mature oocyte in mammals, it is typically relatively inconspicuous in the zygote. Furthermore, the conceptus exhibits an essentially radial organization during cleavage which was long held to persist until the primitive streak forms at the onset of gastrulation. This view has been challenged by various recent studies which clearly show that asymmetries are evident both morphologically and at the molecular level from very early in development. Collectively, these new findings argue that specification of the anterior-posterior axis of the fetus depends on information that is localized extra-embryonically in cells which begin to differentiate before the conceptus implants in the uterus.     

Inductive interactions in early embryonic development.

This is an update of a previous review (Current Opinion in Cell Biology 2:969-974) in which we discussed recent work attempting to understand the sequence of inductive interactions responsible for establishing the body plan of the early embryo. As before, we concentrate on inductive interactions in amphibian embryos, where significant progress has been made in the past two years. In this update, however, we also consider recent embryological data obtained with amniote embryos such as the chick, together with complementary data provided by genetic analyses of mouse and Drosophila development.     

Extra-articular features in early rheumatoid disease.

One hundred and two patients who presented with rheumatoid disease within the first year of onset were studied prospectively every four months for a mean 4.5 years to assess the incidence of extra-articular features. The features that seemed to be common in the early stages included hand-muscle wasting, carpal tunnel syndrome, lymphadenopathy, non-specific ankle swelling, and rheumatoid nodules, and to a lesser extent hepatomegaly, being underweight, conjunctivitis, skin transparency, and a palpable thyroid gland. Those features which seldom occurred early included scleromalacia, temporal artery inolvement, salivary gland enlargement, distal-motor neuropathy, splenomegaly, digital vasculitis, and pulmonary and cardiac complications. Being underweight indicated a significantly more severe outcome.     

Computations in the early visual cortex.

This paper reviews some of the recent neurophysiological studies that explore the variety of visual computations in the early visual cortex in relation to geometric inference, i.e. the inference of contours, surfaces and shapes. It attempts to draw connections between ideas from computational vision and findings from awake primate electrophysiology. In the classical feed-forward, modular view of visual processing, the early visual areas (LGN, V1 and V2) are modules that serve to extract local features, while higher extrastriate areas are responsible for shape inference and invariant object recognition. However, recent findings in primate early visual systems reveal that the computations in the early visual cortex are rather complex and dynamic, as well as interactive and plastic, subject to influence from global context, higher order perceptual inference, task requirement and behavioral experience. The evidence argues that the early visual cortex does not merely participate in the first stage of visual processing, but is involved in many levels of visual computation.     

The femur in early human evolution.

Uni- and multivariate analyses of 5 fossil and 215 extant hominoid femora show that two morphological patterns of hominid femora existed about two million years ago. Femora classified as Homo sp. indet. (KNMER 1472 and 1481) are more like Homo sapiens although not identical.Those classified as Australopithecus robustus (SK 82 and 97) and A. boisei (KNM-ER 1503) are similar to one another but uniquely different from any living hominoid. The strong mophological constrasts imply biomechanical and possible locomotor differences, although these are as yet unknown.     

Cellular interactions in early C. elegans embryos

In normal development both the anterior and posterior blastomeres in a 2-cell C. elegans embryo produce some descendants that become muscles. We show that cellular interactions appear to be necessary in order for the anterior blastomere to produce these muscles. The anterior blastomere does not produce any muscle descendants after either the posterior blastomere or one of the daughters of the posterior blastomere is removed from the egg. Moreover, we demonstrate that a daughter of the anterior blastomere that normally does not produce muscles appears capable of generating muscles when interchanged with its sister, a cell that normally does produce muscles. Embryos develop normally after these blastomeres are interchanged, suggesting that cellular interactions play a major role in determining the fates of some cells in early embryogenesis.     

Systematic variation in early hominid corpus dimensions.

Regression analysis is used to show that the same breadth/height relation characterizes all of the early Plio-Pleistocene hominids, regardless of the number of taxa represented.