Opioid regulation of pituitary gonadotropins and prolactin in women using oral contraceptives

The human hypothalamic kisspeptin system: Functional neuroanatomy and clinical perspectives

In mammals, kisspeptin neurons are the key components of the hypothalamic neuronal networks that regulate the onset of puberty, account for the pulsatile secretion of gonadotropin-releasing hormone (GnRH) and mediate negative and positive estrogen feedback signals to GnRH neurons. Being directly connected anatomically and functionally to the hypophysiotropic GnRH system, the major kisspeptin cell groups of the preoptic area/rostral hypothalamus and the arcuate (or infundibular) nucleus, respectively, are ideally positioned to serve as key nodes which integrate various types of environmental, endocrine, and metabolic signals that can influence fertility. This chapter provides an overview of the current state of knowledge on the anatomy, functions, and plasticity of brain kisspeptin systems based on the wide literature available from different laboratory and domestic species. Then, the species-specific features of human hypothalamic kisspeptin neurons are described, covering their topography, morphology, unique neuropeptide content, plasticity, and connectivity to hypophysiotropic GnRH neurons. Some newly emerging roles of central kisspeptin signaling in behavior and finally, clinical perspectives, are discussed.

Neuroanatomy of the human hypothalamic kisspeptin system

Hypothalamic kisspeptin (KP) neurons are key players in the neuronal network that regulates the onset of puberty and the pulsatile secretion of gonadotropin-releasing hormone (GnRH). In various mammalian species, the majority of KP-synthesizing neurons are concentrated in two distinct cell populations in the preoptic region and the arcuate nucleus (ARC). While studies of female rodents have provided evidence that preoptic KP neurons play a critical sex-specific role in positive estrogen feedback, KP neurons of the ARC have been implicated in negative sex steroid feedback and they have also been hypothesized to contribute to the pulse generator network which regulates episodic GnRH secretion in both females and males. Except for relatively few morphological studies available in monkeys and humans, our neuroanatomical knowledge of the hypothalamic KP systems is predominantly based on observations of laboratory species which are phylogenetically distant from the human. This review article discusses the currently available literature on the topographic distribution, network connectivity, neurochemistry, sexual dimorphism, and aging-dependent morphological plasticity of the human hypothalamic KP neuronal system.

Hormonal contraceptive use diminishes salivary cortisol response to psychosocial stress and naltrexone in healthy women

The use of hormonal contraception (HC) may affect salivary cortisol levels at rest and in response to a pharmacological or stress challenge. Therefore, the current study used a secondary data analysis to investigate the effect of HC on salivary cortisol levels in response to the mu-opioid receptor antagonist naltrexone and a psychosocial stressor, and also across the diurnal curve. Two hundred and nine women (n=72 using hormonal contraception; HC+) completed a two-session stress response study that consisted of a stress day, in which they were exposed to public speaking and mental arithmetic, and a rest day, in which unstimulated cortisol levels were measured to assess the diurnal rhythm. A subset of seventy women (n=24 HC+) also completed a second study in which they were administered oral naltrexone (50mg) or placebo in a randomized, placebo-controlled, double blind fashion. Women who were HC+ had a significantly reduced salivary cortisol response to both the psychosocial stressor (p<0.001) and naltrexone (p<0.05) compared to HC- women. Additionally, HC+ women had a significantly altered morning diurnal cortisol rhythm (p<0.01), with a delayed peak and higher overall levels. The results of the current study confirm that HC attenuates salivary cortisol response to a psychosocial stressor and mu-opioid receptor antagonism, and also alters the morning diurnal cortisol curve.

Low degree of overlap between kisspeptin, neurokinin B, and dynorphin immunoreactivities in the infundibular nucleus of young male human subjects challenges the KNDy neuron concept

Previous immunohistochemical and in situ hybridization studies of sheep, goats, and rodents indicated that kisspeptin (KP), neurokinin B (NKB), and dynorphin A (DYN) are extensively colocalized in the hypothalamic arcuate nucleus, thus providing a basis for the KP/NKB/DYN (KNDy) neuron concept; in both sexes, KNDy neuropeptides have been implicated in the generation of GnRH neurosecretory pulses and in the negative feedback effects of sexual steroids to the reproductive axis. To test the validity and limitations of the KNDy neuron concept in the human, we carried out the comparative immunohistochemical analysis of the three neuropeptides in the infundibular nucleus (Inf; also known as arcuate nucleus) and stalk of young male human individuals (<37 yr). Results of quantitative immunohistochemical experiments established that the regional densities of NKB immunoreactive (IR) perikarya and fibers, and the incidence of afferent contacts they formed onto GnRH neurons, were about 5 times as high as those of the KP-IR elements. Dual-immunofluorescent studies confirmed that considerable subsets of the NKB-IR and KP-IR cell bodies and fibers are separate, and only about 33% of NKB-IR perikarya and 75% of KP-IR perikarya were dual labeled. Furthermore, very few DYN-IR cell bodies could be visualized in the Inf. DYN-IR fibers were also rare and, with few exceptions, distinct from the KP-IR fibers. The abundance and colocalization patterns of the three immunoreactivities showed similar trends in the infundibular stalk around portal blood vessels. Together these results indicate that most NKB neurons in the Inf do not synthesize detectable amounts of KP and DYN in young male human individuals. These data call for a critical use of the KNDy neuron terminology when referring to the putative pulse generator system of the mediobasal hypothalamus. We conclude that the functional importance of these three neuropeptides in reproductive regulation considerably varies among species, between sexes, and at different ages.

Short-term effects of alcohol consumption on the hormonal milieu and mood states in nulliparous women

The present study was designed to determine the short-term effects of alcohol consumption on hormonal responses and mood states in nulliparous women who have regular menstrual cycles. To this aim, we conducted a within-subjects design study in which eight women consumed a 0.4-g/kg dose of alcohol in orange juice during one test session (alcohol condition) and an equal volume of orange juice (control condition) during the other. Changes in plasma prolactin, oxytocin and cortisol levels, blood alcohol concentrations (BACs), and mood states were compared. BAC peaked at approximately 36.7+5.4 min after the consumption of the alcoholic beverage and decreased thereafter. Alcohol consumption significantly increased the area under the concentration-time curve (AUC) of prolactin (P<.01) and decreased the oxytocin AUC (P=.04) when compared to the control condition. Cortisol AUCs were not different across the two experimental conditions. Similar to that previously observed in lactating women, changes in prolactin and oxytocin paralleled changes in feelings of drunkenness. The magnitude and persistence of the alcohol-induced hormonal changes in nulliparous women were significantly less pronounced than those observed in lactating women, further highlighting the dynamics of the system under study during lactation.

The effect of estrogen-progestin treatment on opioid control of gonadotropin and prolactin secretion in postmenopausal women

Naloxone (10 mg) was given intravenously to seven postmenopausal women not receiving hormone treatment and to six postmenopausal women receiving Premarin-Provera treatment during the Premarin phase and also during the Premarin-Provera phase of therapy. Baseline estrone and estradiol levels (mean +/- SEM) were significantly lower in the group not receiving hormones (46.0 +/- 5.2 pg/ml and 28.4 +/- 3.1 pg/ml, respectively) than in the group in the Premarin phase of therapy (154 +/- 14 pg/ml and 79 +/- 13 pg/ml) and the group in the Premarin-Provera phase (135.1 +/- 8.3 pg/ml and 57.5 +/- 3.0 pg/ml) (p less than 0.005). Follicle-stimulating hormone, luteinizing hormone, and prolactin levels were 118.7 +/- 5.3 mIU/ml, 118.7 +/- 9.5 mIU/ml, and 9.2 +/- 0.7 ng/ml, respectively, with no significant change after naloxone administration in untreated women. With hormone therapy the basal follicle-stimulating hormone and luteinizing hormone levels decreased significantly while basal plasma estrone and estradiol increased significantly. In both the group in the Premarin phase of therapy and the group in the Premarin-Provera phase, luteinizing hormone levels increased significantly at 30 (135% +/- 10%, 144% +/- 8%), 45 (150% +/- 12%, 133% +/- 11%), 60 (149% +/- 15%, 128% +/- 11%), and 90 (139% +/- 15%, 132% +/- 13%) minutes after naloxone administration (p less than 0.01 to p less than 0.001). Follicle-stimulating hormone levels did not change significantly whereas prolactin levels showed a trend toward a decrease. These findings indicate that opioid inhibition of gonadotropins is reduced in postmenopausal women but increased with Premarin-Provera treatment. The effect of sex steroid on the opioid system in the postmenopausal women differs from that in the premenopausal women.