In Purkinje cell dendrites of the young rat, thyroid hormone controls the resistance of microtubules to fixation at low temperature

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Abstract
Microtubules were studied in parallel fibres and Purkinje cell dendrites of 14-day-old normal and propylthiouracil-treated rats after fixation of the cerebellum at room and low temperature (4°C). In both control and propylthiouracil-treated animals, nearly all the microtubules of parallel fibres disappeared after fixation at low temperature. In Purkinje cell dendrites of control animals, 60% of the microtubules persisted at low temperature. Propylthiouracil treatment led to a 78% decrease in the density of these cold-stable microtubules. In contrast, the density of cold-labile microtubules remained normal. Administration of low doses of thyroxine to the propylthiouracil-treated rats produced a rapid increase in the density of cold-labile microtubules, but long-term treatment with the hormone was necessary to obtain normal density of cold-stable microtubules. Thyroid hormone thus seems to regulate some properties of microtubules involved in their resistance to fixation at low temperature. These properties could be of importance in growth and branching of dendrites.