Role for kisspeptin/neurokinin B/dynorphin (KNDy) neurons in cutaneous vasodilatation and the estrogen modulation of body temperature

Estrogen withdrawal in menopausal women leads to hot flushes, a syndrome characterized by the episodic activation of heat dissipation effectors. Despite the extraordinary number of individuals affected, the etiology of flushes remains an enigma. Because menopause is accompanied by marked alterations in hypothalamic kisspeptin/neurokinin B/dynorphin (KNDy) neurons, we hypothesized that these neurons could contribute to the generation of flushes. To determine if KNDy neurons participate in the regulation of body temperature, we evaluated the thermoregulatory effects of ablating KNDy neurons by injecting a selective toxin for neurokinin-3 expressing neurons [NK₃-saporin (SAP)] into the rat arcuate nucleus. Remarkably, KNDy neuron ablation consistently reduced tail-skin temperature (T_SKIN), indicating that KNDy neurons facilitate cutaneous vasodilatation, an important heat dissipation effector. Moreover, KNDy ablation blocked the reduction of T_SKIN by 17β-estradiol (E₂), which occurred in the environmental chamber during the light phase, but did not affect the E₂ suppression of T_SKIN during the dark phase. At the high ambient temperature of 33 °C, the average core temperature (T_CORE) of ovariectomized (OVX) control rats was significantly elevated, and this value was reduced by E ₂ replacement. In contrast, the average T_CORE of OVX, KNDy-ablated rats was lower than OVX control rats at 33 °C, and not altered by E₂ replacement. These data provide unique evidence that KNDy neurons promote cutaneous vasodilatation and participate in the E₂ modulation of body temperature. Because cutaneous vasodilatation is a cardinal sign of a hot flush, these results support the hypothesis that KNDy neurons could play a role in the generation of flushes.