In situ hybridization analysis of vasopressin mRNA expression in the mouse hypothalamus: diurnal variation in the suprachiasmatic nucleus.

The distribution, and diurnal variation of AVP mRNA-expressing neurons in the hypothalamus of the mouse has been investigated using in situ hybridization histochemistry. In general, cells hybridizing with an AVP mRNA-specific oligonucleotide probe in the mouse hypothalamus exhibit a similar distribution to the well-characterized distribution of AVP nuclei in the rat, but species-specific patterns of expression have been observed, a finding that confirms the results of earlier immunocytochemical studies. For example, prominent groups of AVP mRNA expressing cells are found in the region between the paraventricular (PVN) and suprachiasmatic (SCN) nuclei, forming the distinct mouse accessory nucleus, and a periventricular group that merges with the PVN neurons. Sampling of brains during both phases of the daily cycle (either 10.00 h (light) or 22.00 h (dark)) revealed a marked and significant variation in AVP mRNA abundance in the SCN whereas a similar variation was not consistently observed in the magnocellular neurons of the supraoptic nucleus (SON). This study has confirmed the distribution of AVP-synthesizing neurons in the mouse hypothalamus, and provided an anatomical substrate for molecular genetic studies in this species that are designed to investigate the basis of neuronal rhythmicity.