Vasopressin and neuronal nitric oxide synthase in hypothalamic paraventricular nucleus (PVN) of pregnant rats.

Abstract

Decreased baseline GABAergic sympathoinhibition within the PVN of pregnant (P) rats is associated with decreased neuronal nitric oxide synthase (nNOS) activity (NADPH Diaphorase), and presumably decreased GABA release. nNOS is colocalized with vasopressin (VP) in both parvo‐ and magno‐cellular PVN neurons. Our goal was to determine if pregnancy changed the number of spinally projecting PVN neurons (presympathetic) containing nNOS or VP. The retrograde tracer fluorogold (FG) was injected unilaterally into the spinal cord of female nonpregnant (NP, n=3) and P (n=3) rats. After 7 days, ipsilateral FG and immunohistochemical staining for VP and nNOS in PVN sections (30 ìm) was counted at 3 levels: rostral (lev‐1) and intermediate (lev‐2) PVN contained the posterior magnocellular cell group, while lev‐3 (caudal) contained the majority of spinally projecting (FG) neurons. In both groups, distribution of VP cells was: lev2 > lev 1 > lev 3. Approximately 7% of all VP cells were spinally projecting, with the majority at level 3 in both groups (~ 19%). Of spinally projecting cells the % also containing nNOS tended to be less in P (16 ±2.9 %) compared to NP rats (24 ±2.4 %). Although preliminary, these data are consistent with decreased nNOS in presympathetic neurons in the PVN of P rats which could contribute to the previously reported decrease in GABAergic sympathoinhibition in the PVN in pregnancy. (HL36245; HL55306)