Localization and dynamics of oxytocin mRNA as revealed by in situ hybridization histochemistry.

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Mechanisms of the gene expression of oxytocin neuron system were investigated by using in situ hybridization histochemistry. The first attempt was done to make specific probes for oxytocin mRNA because of the similar sequence of nucleotides to vasopressin mRNA, and this reflected the evaluation of specific hybridization signals to analyze. After designing the specific nucleotide sequence for oxytocin mRNA, 25-30mer oligonucleotides were synthesized. A particular attention was paid to make probes having least homology to mRNAs of vasopressin and other bioactive substances. The probes were labeled by radioactive mononucleotides such as ^3H・dCTP, ^<35>S・dATP. Second attempt was done to investigate the effects of estrogen and/or progesterone to oxytocin gene expression. Estrogen treatment did not induce changes of oxytociin mRNA both in neurons of the paraventricular and supraoptic nuclei. However, estrogen and progesterone treatment caused a significant increase of oxytocin mRNA in neurons, particularly in the ventromedial subnucleus of the paraventricular nucleus. Neurons in the supraoptic nucleus did not show any changes of oxytocin mRNA by estrogen and progesterone treatment. Third experiment was carried out to investigate whether a substained increase in oxytocin secretion, with or without enhanced electrical activity of the cell bodies of oxytocin neurons, leads to a rapid increase in oxytocin mRNA content in these neurons. To stimulate oxytocin release, naloxone was given to female rats after intracerebroventricular morphine infusion. Naloxone increased oxytocin content in plasma 40 fold for at least 40 min in morphine-infused rats. Naloxone had no significant effect on the oxytocin mRNA content in labeled cells in the supraoptic nucleus, and no effect on the proportion of labeled cells.We concluded that there exist differences in mechanisms of gene expression of oxytocin neurons at the nuclear, cell body and terminal levels.