Estrogen withdrawal increases gonadotropin secretion and body weight, but the critical cell populations mediating these effects are not well understood. Recent studies have focused on a subpopulation of hypothalamic arcuate neurons that coexpress estrogen receptor α, neurokinin 3 receptor (NK(3)R), kisspeptin, neurokinin B, and dynorphin for the regulation of reproduction. To investigate the function of kisspeptin/neurokinin B/dynorphin (KNDy) neurons, a novel method was developed to ablate these cells using a selective NK(3)R agonist conjugated to the ribosome-inactivating toxin, saporin (NK(3)-SAP). Stereotaxic injections of NK(3)-SAP in the arcuate nucleus ablated KNDy neurons, as demonstrated by the near-complete loss of NK(3)R, NKB, and kisspeptin-immunoreactive (ir) neurons and depletion of the majority of arcuate dynorphin-ir neurons. Selectivity was demonstrated by the preservation of proopiomelanocortin, neuropeptide Y, and GnRH-ir elements in the arcuate nucleus and median eminence. In control rats, ovariectomy (OVX) markedly increased serum LH, FSH, and body weight, and these parameters were subsequently decreased by treatment with 17β-estradiol. KNDy neuron ablation prevented the rise in serum LH after OVX and attenuated the rise in serum FSH. KNDy neuron ablation did not completely block the suppressive effects of E(2) on gonadotropin secretion, a finding consistent with redundant pathways for estrogen negative feedback. However, regardless of estrogen status, KNDy-ablated rats had lower levels of serum gonadotropins compared with controls. Surprisingly, KNDy neuron ablation prevented the dramatic effects of OVX and 17β-estradiol (E(2)) replacement on body weight and abdominal girth. These data provide evidence that arcuate KNDy neurons are essential for tonic gonadotropin secretion, the rise in LH after removal of E(2), and the E(2) modulation of body weight.

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 [NK 3 -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 (E 2 ), which occurred in the environmental chamber during the light phase, but did not affect the E 2 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 E 2 replacement. These data provide unique evidence that KNDy neurons promote cutaneous vasodilatation and participate in the E 2 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.reproduction | gonadotropin-releasing hormone | thermoregulation E strogen withdrawal leads to hot flushes in the majority of menopausal women (1). Hot flushes are also experienced by men and women treated with tamoxifen for breast cancer, men undergoing androgen-ablation therapy for prostate cancer, young oophorectomized women, and hypogonadal men (2, 3). A hot flush is characterized by episodic activation of heat dissipation effectors, including cutaneous vasodilatation, sweating, and behavioral thermoregulation. After a flush is initiated, the activation of heat dissipation mechanisms is so effective that core temperature frequently drops (4). Despite the vast numbers of individuals affected, the etiology of flushes remains an enigma.Hot flushes are closely timed with luteinizing hormone (LH) pulses, providing a clue that the generation of flushes is linked to the hypothalamic neural circuitry controlling pulsatile gonadotropin-releasing hormone (GnRH) secretion (5, 6). Current evidence suggests that pulsatile GnRH secretion is modulated by a subpopulation of neurons in the arcuate (infundibular) nucleus that express estrogen receptor α (ERα), neurokinin 3 receptor (NK 3 R), kisspeptin, neurokinin B (NKB), and dynorphin (7-11). In the hypothalamus of postmenopausal women, ...

In the rat, tail skin vasomotion is a primary heat loss mechanism that can be monitored by changes in tail skin temperature (T(SKIN)). Previous studies showed that ovariectomy and estrogen replacement modify T(SKIN) in the rat. Based on these findings, the ovariectomized (OVX) rat has been used as a model to study the mechanisms and treatment of menopausal hot flushes. It is not known, however, if T(SKIN) changes across the estrous cycle in intact rats. Here, we describe an improved method for monitoring T(SKIN) in freely moving rats using a SubCue Mini datalogger mounted on the ventral surface of the tail. This method is noninvasive, cost-effective, and does not require restraints or tethering. We observed a distinct pattern of T(SKIN) across the estrous cycle characterized by low T(SKIN) on proestrous night. To determine whether this pattern was secondary to secretion of ovarian steroids, we monitored the thermoregulatory effects of 17β-estradiol (E(2)) and E(2) plus progesterone, administered via SILASTIC capsules to OVX rats. E(2) treatment of OVX rats significantly reduced T(SKIN) in the dark phase from 2 to 21 d after hormone treatment. The T(SKIN) of E(2)-treated OVX animals was not significantly different from OVX rats receiving E(2) plus progesterone. These data provide evidence that the reduction in T(SKIN) on proestrous night was secondary to elevated levels of ovarian estrogens. This study provides the first description of T(SKIN) changes with the estrous cycle and supports the role of estrogens in normal thermoregulation in the rat.

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