Melanin-concentrating hormone regulation by estradiol and progesterone in the incerto-hypothalamic area.

Melanin-concentrating hormone (MCH) is a peptide related to the reproductive function by interacting with the hypothalamus-pituitary-gonadal axis. In addition to the MCH central production, it is also found in the blood with a putative role as a neurohormone. Thereby, our focus is on steroid hormones' role in regulating centrally produced MCH in the incerto-hypothalamic area (IHy) and the peripheral MCH in the serum. For this, we investigated the effect of estradiol and/or progesterone injection on the number of MCH immunoreactive (MCH-ir) neurons at the IHy and serum levels. For further study of the role of progesterone, we analyzed the effect of blockade of progesterone receptors by its antagonist on MCH-ir neurons at the IHy and serum. To identify whether such regulation over MCH is established before sexual maturation, we assessed the effect of peripubertal removal of steroid hormones on MCH-ir neurons at the IHy and serum levels at adult age. Our results show that injecting estradiol in ovariectomized female rats reduces the number of MCH-ir neurons in the IHy, in addition to its serum levels. Blockade of progesterone receptors in intact females increases the number of MCH-ir neurons in the IHy and its serum concentration. The regulation of these hormones over the MCH peptidergic system is established before sexual maturation, once the peripubertal removal of the ovaries changes the serum levels of MCH and the number of MCH-ir neurons in the IHy of adult females. Such results support the inhibitory role of steroid hormones over the MCH system.

The effect of estrogen and progesterone on melanin-concentrating hormone producing-neurons in brain areas related to reproductive behavior in lactating dams.

The hypothalamus plays a role in reproductive cycle control, and it is a site of action of steroid hormones. Throughout the production of melanin-concentrating hormone (MCH), the hypothalamus shows adaptive changes during lactation. Therefore, in this work, we aimed to test the effects of estrogen and progesterone manipulation on MCH-immunoreactive (ir) neurons in hypothalamic brain areas related to reproductive behavior and on the MCH serum concentration. Our results show that the removal of steroid hormones by ovariectomy increases the number of MCH-ir neurons in the medial preoptic area (MPOA) and incerto-hypothalamic area (IHy) but not in the anterior part of the paraventricular nucleus of the hypothalamus (PVHa). The MCH in the serum levels also increases. In accordance, the injection of estradiol alone or estradiol and progesterone decreased the number of MCH-ir neurons in the MPOA and IHy, as well as its serum levels. The MPOA and IHy are the brain areas targeted by the steroid hormone inhibitory effect of the MCH system during lactation. This effect is also reflected in the MCH serum levels.