FACTORS INVOLVED IN CONTROL OF ACTIVITY OF TUBERO-INFUNDIBULAR DOPAMINE NEURONS DURING PREGNANCY AND LACTATION

The tubero-infundibular DA neurons were studied in pregnancy, pseudopregnancy, and lactation by means of a histochemical fluorescence method for the demonstration of DA and NA. The turnover in the DA nerve terminals in the median eminence was studied by the use of a tyrosine-hydroxylase inhibitor, α-methyl-tyrosine methyl ester. The results suggest that there is a marked and selective activation of the tubero-infundibular DA neurons in pregnancy, pseudopregnancy, and lactation. The activation of the neuron system, which may be sensitized by estrogen, is probably triggered by the neural stimuli at mating. The maintenance of this high degree of activation in pregnancy and lactation is probably dependent, to a certain degree, on neural stimuli. The ovarian hormones do not seem to play any important role in the persistence of the high activation of the tubero-infundibular DA neurons in these endocrinological states. The results strongly indicate that the tubero-infundibular DA neurons participate in the regulation of gonadotrophin secretion. The marked activation of this system in pregnancy, pseudopregnaney, and lactation is probably related to the blockade of FSH-LH release, the increased prolactin secretion, and to blocking of ovulation. The hypothesis is forward that the DA released acts locally in the median eminence to block the synthesis and/or release of the releasing and/or inhibitory factors involved in the regulation of gonadotrophin secretion, possibly mainly the LMRF. © 1969 S. Karger AG, Basel.