Hypothalamic paraventricular nucleus stimulation enhances c-Fos expression in spinal and supraspinal structures related to pain modulation.

The hypothalamic paraventricular nuclei (PVN) inhibits spinal nociception. Furthermore, projections from the PVN to other structures related to pain modulation exist, but a functional interaction has not yet been fully demonstrated. As an initial approach, we show here that PVN electric stimulation with the same parameters used to induce analgesia in rats enhances c-Fos expression not only in the dorsal horn of the spinal cord but also in the nucleus raphe magnus, locus coeruleus and the periaqueductal gray area. These results suggest that a functional interaction between these structures could occur, possibly to assure a mechanism of endogenous analgesia.