Abstract
1. By means of a microfluorimetric technique, the intensity of the catecholamine fluorescence was measured in nerve cells of the arcuate and periventricular hypothalamic nuclei of ovariectomized rats pre-treated with oestrogen and progesterone. In such animals the fluorescence intensity is in the range of the lowest intensities that were observed during the oestrous cycle.2. Unilateral intermittent electrical stimulation of the arcuate nucleus or of the medial preoptic area induced an acute increase of the fluorescence intensity in the cell bodies of the tuberal catecholamine-containing nerve cell group. The change was already manifest 5 min after the onset of stimulation and within 10 min the mean fluorescence intensity reached levels that are among the highest so far observed in this cell group. Prolonged stimulation of the medial preoptic area led to a biphasic response, as shown by a decrease in intensity between 30 and 60 min of stimulation.3. The increase in fluorescence intensity caused by stimulation of the arcuate nucleus was completely prevented by pre-treatment with the tyrosine hydroxylase inhibitor alpha-methyl-tyrosine. Thus, the effect appears to be due to an enhancement of amine synthesis.4. The intensity values found after synthesis inhibition were used for a preliminary estimation of the catecholamine turnover time in the nerve cell bodies of the arcuate nucleus.5. In conclusion, electrical stimulation appears to induce a characteristic type of concentration change in the nerve cell body, at least under certain experimental conditions. It is compared with similar responses to physiological changes such as the reaction to acute cold exposure.