Peanut agglutinin and chondroitin-6-sulfate are molecular markers for tissues that act as barriers to axon advance in the avian embryo

Axon outgrowth between the spinal cord and the hindlimb of the chick embryo is constrained by three tissues that border axon pathways. Growth cones turn to avoid the posterior sclerotome, perinotochordal mesenchyme, and pelvic girdle precursor during normal development and after experimental manipulation. We wanted to know if these functionally similar barriers to axon advance also share a common molecular composition. Since the posterior sclerotome differentially binds peanut agglutinin (PNA) and since PNA binding is also typical of prechondrogenic differentiation, we examined the pattern of expression of PNA binding sites and cartilage proteoglycan epitopes in relation to axon outgrowth. We found that all three barrier tissues preferentially express both PNA binding sites and chondroitin-6-sulfate (C-6-S) immunoreactivity at the time when growth cones avoid these tissues. Moreover, both epitopes are expressed in the roof plate of the spinal cord and in the early limb bud, two additional putative barriers to axon advance. In contrast, neither epitope is detected in peripheral axon pathways. In the somites, this dichotomous pattern of expression clearly preceded the invasion of the anterior sclerotome by either motor growth cones or neural crest cells. However, in the limb, barrier markers disappeared from presumptive axon pathways in concert with the invasion of axons. Since this coordinate pattern suggested that the absence of barrier markers in these axon pathways requires an interaction with growth cones, we analyzed the pattern of barrier marker expression following unilateral neural tube deletions. We found that PNA-negative axon pathways developed normally even in the virtual absence of axon outgrowth. We conclude that the absence of staining with carbohydrate-specific barrier markers is an independent characteristic of the cells that comprise axon pathways. These results identify two molecular markers that characterize known functional barriers to axon advance and suggest that barrier tissues may impose patterns on peripheral nerve outgrowth by virtue of their distinct molecular composition.     

The ultrastructure and cytochemistry of microbodies inPorphyridium

Summary This work establishes the presence of a microbody-like organelle in a unicellular red alga,Porphyridium purpureum (Bory) Drew et Ross. There are several of these per cell. They are spherical or slightly ovoid in shape and 0.2–0.4 microns in diameter. A strongly positive reaction to the diaminobenzidine cytochemical test was noted in this organelle. Inhibition of the DAB reaction with standard reagents gave unusual results. These results suggest that catalase may be absent, the staining in the microbodies being due to peroxidase. Staining was noted in the chloroplast lamellae in neutral conditions in the presence of light. No staining was noted in the mitochondria. To our knowledge this is the first report of a microbody-like structure in a member of theRhodophyceae.     

The morphology and physiology of CAP organs in Jasus novaehollandiae (crustacea,decapoda, reptantia,macrura)

The location and external anatomy of the CAP organs of Jasus novaehollandiae were examined and found to be similar to those in Homarus gammarus (Laverack, 1978a). Histological examination of the organs showed threads or filaments arising from the internal surface of the spines to run through canals in the cuticle and join with dendrites of CAP sensory cells in the region of the hypodermis. The CAP neuron cell bodies lie in the nearby chordotonal organ strand. It is demonstrated that flexion of the limb causes the articulating membrane to deflect the spines of the sensillae distally. A variety of experimental techniques used to investigate the physiology of the organs reveals why previously reported attempts to record from the receptors failed. Direct stimulation of the sensillae with an analogue of the membrane and summation of many traces revealed phase constant responses at points corresponding to the covering and uncovering of the sensillae.     

Uncertainty in prior elicitations: a nonparametric approach

A key task in the elicitation of expert knowledge is to constructa distribution from the finite, and usually small, number ofstatements that have been elicited from the expert. These statementstypically specify some quantiles or moments of the distribution.Such statements are not enough to identify the expert's probabilitydistribution uniquely, and the usual approach is to fit somemember of a convenient parametric family. There are two cleardeficiencies in this solution. First, the expert's beliefs areforced to fit the parametric family. Secondly, no account isthen taken of the many other possible distributions that mighthave fitted the elicited statements equally well. We presenta nonparametric approach which tackles both of these deficiencies.We also consider the issue of the imprecision in the elicitedprobability judgements.     

A comparison of different sources of information about pregnancy and childbirth

Different methods of obtaining information in medical and social research present problems of interpretation for the researcher. However, there are few systematic studies on the extent of the lack of concordance yielded by different methods. This paper uses data from a randomized controlled trial of social support in pregnancy to examine this issue in relation to three methods of data collection--medical records, home interviews and a postal questionnaire--on the following topics: obstetric history; smoking, alcohol use, number of antenatal hospital visits, bleeding and depression in pregnancy; length of labour; baby's sex, birthweight and neonatal health problems; and ethnicity. Considerable discrepancies are found comparing the different data sources. These suggest that mothers may be more reliable sources of information than medical records, and that the anonymity of a postal questionnaire may provide higher estimates than home interviews on some sensitive topics, such as smoking in pregnancy.