The V1a and V1b, but not V2, vasopressin receptor genes are expressed in the supraoptic nucleus of the rat hypothalamus, and the transcripts are essentially colocalized in the vasopressinergic magnocellular neurons

We have identified and visualized the vasopressin (VP) receptors expressed by hypothalamic magnocellular neurons in supraoptic and paraventricular nuclei. To do this, we used RT-PCR on total RNA extracts from supraoptic nuclei or on single freshly dissociated supraoptic neurons, and in situ hybridization on frontal sections of hypothalamus of Wistar rats. The RT-PCR on supraoptic RNA extracts revealed that mainly V-1a, but also V-1b, subtypes of VP receptors are expressed from birth to adulthood. No V-2 receptor messenger RNA (mRNA) was detected. Furthermore, the single-cell RT-nested PCR indicated that the V-1a receptor mRNA is present in vasopressinergic magnocellular neurons. In light of these results, in situ hybridization was performed to visualize the V-1a and V-1b receptor mRNAs in supraoptic and paraventricular nuclei. Simultaneously, we coupled this approach to: 1) in situ hybridization detection of oxytocin or VP mRNAs; or 2) immunocytochemistry to detect the neuropeptides. This provided a way of identifying the neurons expressing perceptible amounts of V-1a or V-1b receptor mRNAs as vasopressinergic neurons. Here, we suggest that the autocontrol exerted specifically by VP on vasopressinergic neurons is mediated through, at least, V-1a and V-1b subtype receptors.