The tubulin content and biochemical components were determined in the cerebrum, cerebellum and hypothalamus from intact and T3-treated male and female rats during early life. T3-treatment between 0 and 9 days of age increased soluble protein, RNA DNA and tubulin content (mg per g tissue) in the 10-day-old male cerebellum but not in the cerebrum and hypothalamus except for soluble protein and tubulin (mg per g tissue), respectively. Intracellular tubulin content (mg per mg DNA) was increased by the T3-treatment in the 10-day-old male hypothalamus but not the other regions. When T3 was administered between 10 and 19 days, there was little effect of the treatment; increased tubulin (mg per g tissue) in the cerebrum and decreased RNA (mg per g tissue) and a ratio of tubulin to protein in the cerebellum from 20-day-old males. Less response to T3-treatment was observed in female cerebrum and hypothalamus but not in the cerebellum, compared with the male. These results suggest that the effect of T3-treatment on brain is modified by several factors such as tissue specificity, age-dependency and sexual differences. Modification by these factors might depend, at least in part, on changes in the number of T3-receptors due to the hormone treatment.

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The effects of Rb and Cs on the electrogenic Na-pump of the rabbit sinoatrial node cell were studied, using conventional microelectrode techniques. Hyperpolarizations induced by K or its substitutes were recorded from the preparations which were perfused previously with an extracellular K-free solution. The K-induced hyperpolarizations after K-depletion depended linearly on K-concentration in the range of 1.35

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