5,7-Dihydroxytryptamine and gonadal steroid manipulation alter spine density in ventromedial hypothalamic neurons

Golgi impregnation was used to examine changes in dendritic spine density in the ventromedial hypothalmic nucleus (VMN) of intact and gonadectomized (GDX) rats treated with 5,7-dihydroxytryptamine (5,7-DHT) and/or estrogen. In intact rats of both sexes 5,7-DHT injection resulted in a large increase in dendritic spine density in the VMN. The combination of 5,7-DHT and estrogen treatment in GDX females resulted in a further increase in dendritic spine density. In male rats gonadectomy increased dendritic spine density on VMN neurons, and estrogen treatment partially reversed this effect. When GDX males were treated with 5,7-DHT and estrogen, there was no effect on dendritic spine density. These results complement a previous study in which it was demonstrated that dendritic spine density in the VMN was greatest during proestrus and after estrogen administration to ovariectomized females. The relevance of these findings to gonadal-steroid-mediated lordosis is discussed.