Differential distributions of neuropeptides in hypothalamic paraventricular nucleus neurons projecting to the rostral ventrolateral medulla in the rat.

The hypothalamic paraventricular nucleus (PVN) exerts a major regulatory role in the endocrine and the autonomic system. It has anatomically and functionally distinct cell populations, one of which projects to the rostral ventrolateral medulla (PVN-RVLM) and are involved in the sympathetic regulation of the cardiovascular system. To investigate the expression and the distributional patterns of peptides in the PVN-RVLM neurons of rats, we used single cell RT-PCR analysis in combination with retrograde tracing. Approximately 80% of PVN-RVLM neurons expressed oxytocin (OT) and 60% expressed dynorphin (Dyn). There were differential distributions of peptides between the subdivisions of PVN-RVLM neurons. The posterior parvocellular subdivision predominantly expressed OT; the dorsal cap subdivision contained much less vasopressin (VP) compared to other subdivisions. In addition, PVN-RVLM neurons preponderantly co-expressed multiple peptides. These results suggest that peptides may contribute to elaborate responses of PVN to various stimuli.