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J. MOLL, E. MARTENS and H. G. JANSEN

SUMMARY

Lesions aimed at the area of the paraventricular hypothalamic nuclei were made by means of stereotaxic electrocoagulation in intact and gonadectomized mice, which were subsequently treated with methylthiouracil. Lesions could be placed with an acceptable degree of precision and with moderate postoperative mortality. Correctly placed lesions made in intact females and castrated males caused a marked inhibition of goitre development, indicating a depressed secretion of thyrotrophin. However, in intact males and spayed females inhibition of goitre formation could not be demonstrated convincingly.

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V Geenen, JF Poulin, ML Dion, H Martens, E Castermans, Hansenne I, M Moutschen, RP Sekaly and R Cheynier

Although the thymus constitutes a target organ for most protein and steroid hormones, it has been quite difficult to determine the precise control exerted in vivo by the endocrine system upon thymic function. The biological role of the thymus is to ensure the generation of a diversified population of peripheral T cells able to respond to non-self-antigens but nevertheless tolerant to self-antigens. For a long time, thymic function could not be monitored, as a consequence of the absence of adequate technology to differentiate recent thymic emigrants from naive T cells. The generation of T cell receptor (TCR) diversity occurs in the thymus through recombination of gene segments encoding the variable parts of the TCR alpha and beta chains. During these processes, by-products of the rearrangements are generated in the form of TCR excision circles (TRECs). As these molecules are lost upon further cell division, their quantification is actually considered as a very valuable tool to estimate thymic function. The most appropriate TREC is deltaRec-Psi(J)alpha TREC or signal joint TREC resulting from deltaRec-Psi(J)alpha rearrangement (TCRD deletion) that occurs late during thymopoiesis, before V(alpha)-J(alpha) rearrangement. Here we describe how TREC quantification is a powerful and reliable method to evaluate the impact of hormones and endocrine disorders upon thymic function.