Regulation and Possible Functions of Kisspeptin in the Medial Amygdala

Kisspeptin fiber and receptor distribution analysis suggests its potential role in central sensorial processing and behavioral state control

Background

Kisspeptin (KP) signaling in the brain is defined by the anatomical distribution of KP-producing neurons, their fibers, receptors, and connectivity. Technological advances have prompted a re-evaluation of these chemoanatomical aspects, originally studied in the early years after the discovery of KP and its receptor Kiss1r. We have previously characterized(1) seven KP neuronal populations in the mouse brain at the mRNA level, including two novel populations, and examined their short-term response to gonadectomy.

Methods

In this study, we mapped KP fiber distribution in rats and mice using immunohistochemistry under intact and short- and long-term post-gonadectomy conditions. Kiss1r mRNA expression was examined via RNAscope, in relation to vesicular GABA transporter ( Slc32a1 ) in whole mouse brain and to KP and vesicular glutamate transporter 2 ( Kiss1 and Slc17a6 ) in hypothalamic RP3V and arcuate regions.

Results

We identified KP fibers in 118 brain regions, primarily in extra-hypothalamic areas associated with sensorial processing and behavioral state control. KP-immunoreactive fiber density and distribution were largely unchanged by gonadectomy. Kiss1r was expressed prominently in sensorial and state control regions such as septal nuclei, the suprachiasmatic nucleus, locus coeruleus, hippocampal layers, thalamic nuclei, and cerebellar structures. Co-expression of Kiss1r and Kiss1 was observed in hypothalamic neurons, suggesting both autocrine and paracrine KP signaling mechanisms.

Conclusion

These findings enhance our understanding of KP signaling beyond reproductive functions, particularly in sensorial and behavioral state regulation. This study opens new avenues for investigating KP's role in controlling complex physiological processes, including those not related to reproduction.

A GnRH neuronal population in the olfactory bulb translates socially relevant odors into reproductive behavior in male mice

Hypothalamic gonadotropin-releasing hormone (GnRH) neurons regulate fertility and integrate hormonal status with environmental cues to ensure reproductive success. Here we show that GnRH neurons in the olfactory bulb (GnRHOB) of adult mice can mediate social recognition. Specifically, we show that GnRHOB neurons extend neurites into the vomeronasal organ and olfactory epithelium and project to the median eminence. GnRHOB neurons in males express vomeronasal and olfactory receptors, are activated by female odors and mediate gonadotropin release in response to female urine. Male preference for female odors required the presence and activation of GnRHOB neurons, was impaired after genetic inhibition or ablation of these cells and relied on GnRH signaling in the posterodorsal medial amygdala. GnRH receptor expression in amygdala kisspeptin neurons appear to be required for GnRHOB neurons' actions on male mounting behavior. Taken together, these results establish GnRHOB neurons as regulating fertility, sex recognition and mating in male mice.

A comprehensive chemotyping and gonadal regulation of seven kisspeptinergic neuronal populations in the mouse brain

Herein, we present a systematic analysis, using dual and multiplex RNAscope methods, of seven kisspeptinergic neuronal populations, based on their chemotyping and distribution throughout the mouse brain. The co-expression of mRNAs coding for neuropeptides, for excitatory and inhibitory transmitter vesicular transporters, and for sex steroid receptors are described in four hypothalamic and three extra-hypothalamic nuclei. These include a newly characterized kisspeptin-expressing ventral premammillary nucleus cell group co-expressing vesicular glutamate transporter 2, pituitary adenylate cyclase-activating polypeptide and neurotensin mRNAs. Kisspeptin mRNA ( Kiss1) was observed within both somatic and dendritic compartments at a single-cell level in two hypothalamic sites, a prominent and previously undescribed feature of kisspeptin neurons in these two cell groups. Patterns of altered Kiss1 expression following gonadectomy among these seven KP populations suggest that androgen receptor signaling may also play a previously unremarked role in gonadal feedback regulation of kisspeptinergic neuronal function. Data from this study provide a chemoanatomical basis for hypothesis generation regarding the functional diversity of kisspeptinergic signaling in hypothalamic and extrahypothalamic brain.

Kisspeptin neuron electrophysiology: Intrinsic properties, hormonal modulation, and regulation of homeostatic circuits

The obligatory role of kisspeptin (KISS1) and its receptor (KISS1R) in regulating the hypothalamic-pituitary-gonadal axis, puberty and fertility was uncovered in 2003. In the few years that followed, an impressive body of work undertaken in many species established that neurons producing kisspeptin orchestrate gonadotropin-releasing hormone (GnRH) neuron activity and subsequent GnRH and gonadotropin hormone secretory patterns, through kisspeptin-KISS1R signaling, and mediate many aspects of gonadal steroid hormone feedback regulation of GnRH neurons. Here, we review knowledge accrued over the past decade, mainly in genetically modified mouse models, of the electrophysiological properties of kisspeptin neurons and their regulation by hormonal feedback. We also discuss recent progress in our understanding of the role of these cells within neuronal circuits that control GnRH neuron activity and GnRH secretion, energy balance and, potentially, other homeostatic and reproductive functions.

Metabolic actions of kisspeptin signaling: Effects on body weight, energy expenditure, and feeding

Kisspeptin (encoded by the Kiss1 gene) and its receptor, KISS1R (encoded by the Kiss1r gene), have well-established roles in stimulating reproduction via central actions on reproductive neural circuits, but recent evidence suggests that kisspeptin signaling also influences metabolism and energy balance. Indeed, both Kiss1 and Kiss1r are expressed in many metabolically-relevant peripheral tissues, including both white and brown adipose tissue, the liver, and the pancreas, suggesting possible actions on these tissues or involvement in their physiology. In addition, there may be central actions of kisspeptin signaling, or factors co-released from kisspeptin neurons, that modulate metabolic, feeding, or thermoregulatory processes. Accumulating data from animal models suggests that kisspeptin signaling regulates a wide variety of metabolic parameters, including body weight and energy expenditure, adiposity and adipose tissue function, food intake, glucose metabolism, respiratory rates, locomotor activity, and thermoregulation. Herein, the current evidence for the involvement of kisspeptin signaling in each of these physiological parameters is reviewed, gaps in knowledge identified, and future avenues of important research highlighted. Collectively, the discussed findings highlight emerging non-reproductive actions of kisspeptin signaling in metabolism and energy balance, in addition to previously documented roles in reproductive control, but also emphasize the need for more research to resolve current controversies and uncover underlying molecular and physiological mechanisms.

Conserved functions of hypothalamic kisspeptin in vertebrates

Hypothalamic kisspeptin encoded by KISS1/Kiss1 gene emerged as a regulator of the reproductive axis in mammals following the discovery of the kisspeptin receptor (Kissr) and its role in reproduction. Kisspeptin-Kissr systems have been investigated in various vertebrates, and a conserved sequence of kisspeptin-Kissr has been identified in most vertebrate species except in the avian linage. In addition, multiple paralogs of kisspeptin sequences have been identified in the non-mammalian vertebrates. The allegedly conserved role of kisspeptin-Kissr in reproduction became debatable when kiss/kissr genes-deficient zebrafish and medaka showed no apparent effect on the onset of puberty, sexual development, maturation and reproductive capacity. Therefore, it is questionable whether the role of kisspeptin in reproduction is conserved among vertebrate species. Here we discuss from a comparative and evolutional aspect the diverse functions of kisspeptin and its receptor in vertebrates. Primarily this review focuses on the role of hypothalamic kisspeptin in reproductive and non-reproductive functions that are conserved in vertebrate species.

Hypothalamic Kisspeptin Neurons and the Control of Homeostasis

Hypothalamic kisspeptin (Kiss1) neurons provide indispensable excitatory transmission to gonadotropin-releasing hormone (GnRH) neurons for the coordinated release of gonadotropins, estrous cyclicity, and ovulation. But maintaining reproductive functions is metabolically demanding so there must be a coordination with multiple homeostatic functions, and it is apparent that Kiss1 neurons play that role. There are 2 distinct populations of hypothalamic Kiss1 neurons, namely arcuate nucleus (Kiss1ARH) neurons and anteroventral periventricular and periventricular nucleus (Kiss1AVPV/PeN) neurons in rodents, both of which excite GnRH neurons via kisspeptin release but are differentially regulated by ovarian steroids. Estradiol (E2) increases the expression of kisspeptin in Kiss1AVPV/PeN neurons but decreases its expression in Kiss1ARH neurons. Also, Kiss1ARH neurons coexpress glutamate and Kiss1AVPV/PeN neurons coexpress gamma aminobutyric acid (GABA), both of which are upregulated by E2 in females. Also, Kiss1ARH neurons express critical metabolic hormone receptors, and these neurons are excited by insulin and leptin during the fed state. Moreover, Kiss1ARH neurons project to and excite the anorexigenic proopiomelanocortin neurons but inhibit the orexigenic neuropeptide Y/Agouti-related peptide neurons, highlighting their role in regulating feeding behavior. Kiss1ARH and Kiss1AVPV/PeN neurons also project to the preautonomic paraventricular nucleus (satiety) neurons and the dorsomedial nucleus (energy expenditure) neurons to differentially regulate their function via glutamate and GABA release, respectively. Therefore, this review will address not only how Kiss1 neurons govern GnRH release, but how they control other homeostatic functions through their peptidergic, glutamatergic and GABAergic synaptic connections, providing further evidence that Kiss1 neurons are the key neurons coordinating energy states with reproduction.

The relation between obesity, kisspeptin, leptin, and male fertility

Over the past decades, obesity and infertility in men increased in parallel, and the association between both phenomena have been examined by several researchers. despite the fact that there is no agreement, obesity appears to affect the reproductive potential of men through various mechanisms, such as changes in the hypothalamic-pituitary-testicular (HPT) axis, spermatogenesis, sperm quality and/or alteration of sexual health. Leptin is a hormone produced by the adipose tissue, and its production elevates with increasing body fat. Many studies have supported the relationship between raised leptin production and reproductive function regulation. In fact, Leptin acts on the HPT axis in men at all levels. However, most obese men are insensitive to increased production of endogenous leptin and functional leptin resistance development. Recently, it has been recommended that Kisspeptin neurons mediate the leptin's effects on the reproductive system. Kisspeptin binding to its receptor on gonadotropin-releasing hormone (GnRH) neurons, activates the mammal's reproductive axis and stimulates GnRH release. Increasing infertility associated with obesity is probably mediated by the Kisspeptin-GnRH pathway. In this review, the link between obesity, kisspeptin, leptin, and male fertility will be discussed.

Expression of type one cannabinoid receptor in different subpopulation of kisspeptin neurons and kisspeptin afferents to GnRH neurons in female mice

The endocannabinoids have been shown to target the afferents of hypothalamic neurons via cannabinoid 1 receptor (CB1) and thereby to influence their excitability at various physiological and/or pathological processes. Kisspeptin (KP) neurons form afferents of multiple neuroendocrine cells and influence their activity via signaling through a variation of co-expressed classical neurotransmitters and neuropeptides. The differential potency of endocannabinoids to influence the release of classical transmitters or neuropeptides, and the ovarian cycle-dependent functioning of the endocannabinoid signaling in the gonadotropin-releasing hormone (GnRH) neurons initiated us to study whether (a) the different subpopulations of KP neurons express CB1 mRNAs, (b) the expression is influenced by estrogen, and (c) CB1-immunoreactivity is present in the KP afferents to GnRH neurons. The aim of the study was to investigate the site- and cell-specific expression of CB1 in female mice using multiple labeling in situ hybridization and immunofluorescent histochemical techniques. The results support that CB1 mRNAs are expressed by both the GABAergic and glutamatergic subpopulations of KP neurons, the receptor protein is detectable in two-thirds of the KP afferents to GnRH neurons, and the expression of CB1 mRNA shows an estrogen-dependency. The applied estrogen-treatment, known to induce proestrus, reduced the level of CB1 transcripts in the rostral periventricular area of the third ventricle and arcuate nucleus, and differently influenced its co-localization with vesicular GABA transporter or vesicular glutamate transporter-2 in KP neurons. This indicates a gonadal cycle-dependent role of endocannabinoid signaling in the neuronal circuits involving KP neurons.

Mating-induced increase in Kiss1 mRNA expression in the anteroventral periventricular nucleus prior to an increase in LH and testosterone release in male rats

Kisspeptin has an indispensable role in gonadotropin-releasing hormone/gonadotropin secretion in mammals. In rodents, kisspeptin neurons are located in distinct brain regions, namely the anteroventral periventricular nucleus-periventricular nucleus continuum (AVPV/PeN), arcuate nucleus (ARC), and medial amygdala (MeA). Among them, the physiological role of AVPV/PeN kisspeptin neurons in males has not been clarified yet. The present study aims to investigate the acute effects of the olfactory and/or mating stimulus with a female rat on hypothalamic and MeA Kiss1 mRNA expression, plasma luteinizing hormone (LH) and testosterone levels in male rats. Intact male rats were exposed to the following stimuli: exposure to clean bedding; exposure to female-soiled bedding as a female-olfactory stimulus; exposure to female-soiled bedding and mating stimulus with a female rat. The mating stimulus significantly increased the number of the AVPV/PeN Kiss1 mRNA-expressing cells in males within 5 minutes after the exposure, and significantly increased LH and testosterone levels, followed by an increase in male sexual behavior. Whereas, the males exposed to female-soiled bedding showed a moderate increase in LH levels and no significant change in testosterone levels and the number of the AVPV/PeN Kiss1 mRNA-expressing cells. Importantly, none of the stimuli affected the number of Kiss1 mRNA-expressing cells in the ARC and MeA. These results suggest that the mating-induced increase in AVPV/PeN Kiss1 mRNA expression may be, at least partly, involved in stimulating LH and testosterone release, and might consequently ensure male mating behavior. This study would be the first report suggesting that the AVPV/PeN kisspeptin neurons in males may play a physiological role in ensuring male reproductive performance.

Kisspeptin Neurons in the Infundibular Nucleus of Ovariectomized Cats and Dogs Exhibit Unique Anatomical and Neurochemical Characteristics

Neurons co-synthesizing kisspeptin (KP), neurokinin B (NKB), and dynorphin (“KNDy neurons”) in the hypothalamic arcuate/infundibular nucleus (INF) form a crucial component of the gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) “pulse generator.” The goal of our study was to characterize KP neuron distribution, neuropeptide phenotype and connectivity to GnRH cells in ovariectomized (OVX) dogs and cats with immunohistochemistry on formalin-fixed hypothalamic tissue sections. In both species, KP and NKB neurons occurred in the INF and the two cell populations overlapped substantially. Dynorphin was detected in large subsets of canine KP (56%) and NKB (37%) cells and feline KP (64%) and NKB (57%) cells; triple-labeled (“KNDy”) somata formed ∼25% of all immunolabeled neurons. Substance P (SP) was present in 20% of KP and 29% of NKB neurons in OVX cats but not dogs, although 26% of KP and 24% of NKB neurons in a gonadally intact male dog also contained SP signal. Only in cats, cocaine- and amphetamine regulated transcript was also colocalized with KP (23%) and NKB (7%). In contrast with reports from mice, KP neurons did not express galanin in either carnivore. KP neurons innervated virtually all GnRH neurons in both species. Results of this anatomical study on OVX animals reveal species-specific features of canine and feline mediobasal hypothalamic KP neurons. Anatomical and neurochemical similarities to and differences from the homologous KP cells of more extensively studied rodent, domestic and primate species will enhance our understanding of obligate and facultative players in the molecular mechanisms underlying pulsatile GnRH/LH secretion.

Women with drug-resistant epilepsy: Surgery or pregnancy first?

OBJECTIVE

We compared women with drug-resistant focal epilepsy who had undergone surgery (WWE-S) with those who were managed medically (WWE-M) for maternal and fetal outcomes of their pregnancies.

METHODS

We classified all WWE-S who were enrolled in a prospective registry of epilepsy and pregnancy (1998-2015) as those who underwent the surgery before pregnancy (WWE-SF) or after pregnancy (WWE-PF). The comparator group (WWE-M) was twice that number of age-matched women with focal epilepsy in this registry. Their clinical profile, anti-epileptic drug (AED) use, and pregnancy outcomes were extracted from the records of the registry.

RESULTS

The number of completed pregnancies with known outcome was 74 for WWE-S (67 WWE-SF and 7 WWE-PF) and 134 for WWE-M. Seizures increased during pregnancy for fewer WWE-SF than for WWE-M (14.9% vs 39.6%, P = .001). Compared to WWE-M, fewer WWE-SF had dose escalation during pregnancy (28.4% vs 14.9%, P = .025). Preterm deliveries were more frequent in WWE-SF than WWE-M (24.6% vs 12.2%, P = .029). The differences between the WWE-SF and WWE-M regarding the rates of fetal loss (10.4% vs 6.7%, P = .255), major congenital malformations (8.5% vs. 11.1%, P = .395), and development quotient at 1 year of age <85 (42.5% vs 42.3%, P = .569) were not statistically significant. Compared to WWE-PF, fewer WWE-SF had AED dose escalation (14.9% vs 85.7%, P = .001) or increase in seizures (14.9% vs 100%, P = .001) during pregnancy. WWE-SF had fewer infants with development quotient <85 (41.0% vs 100%, P = .005).

SIGNIFICANCE

WWE-SF can expect better control of seizures and decreased AED burden during pregnancy than WWE with focal epilepsies managed with medicines only. WWE who undergo surgery for epilepsy before their pregnancies can expect fewer seizures and lower AED burden during pregnancy.

Multiple failures in the lutenising hormone surge generating system in GABAB1KO female mice

Female mice lacking GABAB receptors, GABAB1KO, show disrupted oestrous cycles, reduced pregnancies and increased hypothalamic Gnrh1 mRNA expression, whereas anteroventral periventricular/periventricular preoptic nucleus (AVPV/PeN) Kiss1 mRNA was not affected. In the present study, we characterise the important components of the gonadotrophic preovulatory surge, aiming to unravel the origin of this reproductive impairment. In GABAB1KO and wild-type (WT) females, we determined: (i) hypothalamic oestrogen receptor (ER)α and β and aromatase mRNA and protein expression; (ii) ovulation index and oestrus serum follicle-stimulating hormone (FSH) and pituitary Gnrh1r expression; (iii) in ovariectomised-oestradiol valerate-treated mice, we evaluated ex vivo hypothalamic gonadotrophin-releasing hormone (GnRH) pulsatility in the presence/absence of kisspeptin (Kiss-10, constant or pulsatile) and oestradiol (constant); and (iv) in ovariectomised-oestradiol silastic capsule-treated mice (proestrous-like environment), we evaluated morning and evening kisspeptin neurone activation (c-Fos+) and serum luteinising homrone (LH). In the medial basal hypothalamus of oestrus GABAB1KOs, aromatase and ERα mRNA and protein were increased, whereas ERβ was decreased. In GABAB1KOs, the ovulation index was decreased together with decreased first oestrus serum FSH and increased pituitary Gnrh1r mRNA. Under constant Kiss-10 stimulation, hypothalamic GnRH pulse frequency did not vary, although GnRH mass/pulse was increased in GABAB1KOs. In WTs, pulsatile Kiss-10 together with constant oestradiol significantly increased GnRH pulsatility, whereas, in GABAB1KOs, oestradiol alone increased GnRH pulsatility and this was reversed by pulsatile Kiss-10 addition. In GABAB1KOs AVPV/PeN kisspeptin neurones were similarly activated (c-Fos+) in the morning and evening, whereas WTs showed the expected, marked evening stimulation. LH correlated with activated kisspeptin cells in WT mice, whereas GABAB1KO mice showed high, similar LH levels both in the morning and evening. Taken together, all of these alterations point to impairment in the trigger of the preovulatory GnRH surge that entails the reproductive alterations described.

Identification of feline Kiss1 and distribution of immunoreactive kisspeptin in the hypothalamus of the domestic cat

In recent years, the Kiss1 gene has been reported in a number of vertebrate species, and a substantial dataset has been acquired to demonstrate the critical role of kisspeptins in the reproductive system; yet limited information is available for carnivores. In the present study, we identified and characterized feline Kiss1 by isolating and cloning its full-length cDNA in the domestic cat hypothalamus and caracal testis, using the method of rapid amplification of cDNA ends. Additionally, we isolated and cloned the 3′ end of Kiss1 cDNA, containing kisspeptin-10 (Kp10), from the ovaries of a clouded leopard and Siberian tiger. Nucleotide sequencing revealed that domestic cat Kiss1 cDNA is of 711 base pairs and caracal Kiss1 cDNA is of 792 base pairs, both having an open reading frame of 450 base pairs, encoding a precursor protein Kiss1 of 149 amino acids. The core sequence of the feline kisspeptin Kp10 was found to be identical in all species analyzed here and is highly conserved in other vertebrate species. Using an anti-Kp10 antibody, we found the immunoreactive kisspeptin to be localized in the periventricular and infundibular nuclei of the cat hypothalamus. The results show that kisspeptin is highly conserved among different feline families, and its immunoreactive distribution in the hypothalamus may indicate its physiological function in the domestic cat.

Kisspeptin Neurons in the Arcuate Nucleus of the Hypothalamus Orchestrate Circadian Rhythms and Metabolism

Successful reproduction in female mammals is precisely timed and must be able to withstand the metabolic demand of pregnancy and lactation. We show that kisspeptin-expressing neurons in the arcuate hypothalamus (Kiss1^ARH) of female mice control the daily timing of food intake, along with the circadian regulation of locomotor activity, sleep, and core body temperature. Toxin-induced silencing of Kiss1^ARH neurons shifts wakefulness and food consumption to the light phase and induces weight gain. Toxin-silenced mice are less physically active and have attenuated temperature rhythms. Because the rhythm of the master clock in the suprachiasmatic nucleus (SCN) appears to be intact, we hypothesize that Kiss1^ARH neurons signal to neurons downstream of the master clock to modulate the output of the SCN. We conclude that, in addition to their well-established role in regulating fertility, Kiss1^ARH neurons are a critical component of the hypothalamic circadian oscillator network that times overt rhythms of physiology and behavior.

Conspecific odor exposure predominantly activates non-kisspeptin cells in the medial nucleus of the amygdala

A small neuronal subpopulation in the medial nucleus of the amygdala (MeA), expressing the Kiss1 gene, is now considered an important mediator that integrates socio-sexual behavior and odor information in order to modulate the Hypothalamic-Pituitary-Gonadal (HPG) axis. Previous studies demonstrated that exogenous kisspeptin administration or selective activation of Kiss1-expressing neurons in the MeA modulates the onset of puberty, LH secretion and sexual behavior. These functions are supported by the known MeA neuronal connections. In the MeA, as well as in the hypothalamus, Kiss1 mRNA expression mostly depends on sex steroids levels. However, the percentage of Kiss1-expressing cells that co-express estrogen receptor α (ERα) in the MeA is currently unknown. Additionally, whether MeA kisspeptin neurons show Fos expression due to pheromone exposure is still undisclosed. In the present study, we used adult male and female mice that express a reporter protein under the Kiss1 promoters to determine the percentage of Kiss1-expressing neurons that co-express the ERα in the MeA and, whether those cells are activated by olfactory cues. We found a high percentage of Kiss1-expressing neurons in the MeA co-expressing the ERα. The proportion of co-expression was similar between male and female mice in diestrus. Interestingly, a low percentage of Kiss1-expressing neurons in the MeA co-express Fos after conspecific odor exposure, despite a significant increase of Fos positive cells in the MeA. Additionally, odor exposition leads to a sexually dimorphic change in Kiss1 expression in the posterior subdivision of the MeA. Our findings suggest that olfactory signals predominantly activate non-kisspeptin cells in the MeA to modulate responses to pheromones and therefore the HPG axis.

Effect of long-term treatment with classical neuroleptics on NPQ/spexin, kisspeptin and POMC mRNA expression in the male rat amygdala

Neuroleptics modulate the expression level of some regulatory neuropeptides in the brain. However, if these therapeutics influence the peptidergic circuits in the amygdala remains unclear. This study specifies the impact profile of the classical antipsychotic drugs on mRNA expression of the spexin/NPQ, kisspeptin-1 and POMC in the rat amygdala. Animals were treated with haloperidol and chlorpromazine for 28 days prior to transcript quantification via qPCR. Haloperidol and chlorpromazine induced a change in the expression of all neuropeptides analyzed. Both drugs led to the decrease of Kiss-1 expression, whereas in POMC and spexin/NPQ their up-regulation in the amygdala was detected. These modulating effects on may represent alternative, so far unknown mechanisms, of classical antipsychotic drugs triggering pharmacological responses.

Biological Significance of Kisspeptin-Kiss 1 Receptor Signaling in the Habenula of Teleost Species

Kisspeptin is a neuropeptide, encoded by kisspeptin 1 (KISS1)/Kiss1 gene, which primarily acts as the regulator of reproductive functions via its receptor, kisspeptin receptor (KissR) in vertebrates. In the brain, Kiss1 gene is mainly expressed in the hypothalamic region, but KissR gene is widely distributed throughout the brain, suggesting that kisspeptin-KissR system may be involved in not only reproductive, but also non-reproductive functions. In non-mammalian vertebrates, there are two or more kisspeptin and KissR types. The zebrafish (Danio rerio) possess two kisspeptin (Kiss1 and Kiss2) and their respective receptors [Kiss1 receptor (KissR1) and KissR2]. In the brain of zebrafish, while Kiss2 is expressed in the preoptic-hypothalamic area, Kiss1 is predominantly expressed in the habenula, an evolutionarily conserved epithalamic structure. Similarly, KissR1 is expressed only in the habenula, while KissR2 is widely distributed in the brain, suggesting that the two kisspeptin systems play specific roles in the brain. The habenular Kiss1 is involved in the modulation of the raphe nuclei and serotonin-related behaviors such as fear response in the zebrafish. This review summarizes the roles of multiple kisspeptin-KissR systems in reproductive and non-reproductive functions and neuronal mechanism, and debates the biological and evolutional significance of habenular kisspeptin-KissR systems in teleost species.