Neuropeptide Y signaling in the dorsal raphe nucleus inhibits male sexual behavior in mice

Effects of prenatal exposure to fluoxetine on circadian rhythmicity in the locomotor activity and neuropeptide Y and 5-HT expression in male and female adult Wistar rats

Serotonin (5-HT) reuptake inhibitors, such as fluoxetine, are the most prescribed antidepressant for maternal depression. In this sense, it exposes mothers and the brains of infants to increased modulatory and trophic effects of serotonergic neurotransmission. 5-HT promotes essential brain changes throughout its development, which include neuron migration, differentiation, and organization of neural circuitries related to emotional, cognitive, and circadian behavior. Early exposure to the SSRIs induces long-term effects on behavioral and neural serotonergic signalization. We have aimed to evaluate the circadian rhythm of locomotor activity and the neurochemical content, neuropeptide Y (NPY) and 5-HT in three brain areas: intergeniculate leaflet (IGL), suprachiasmatic nuclei (SCN) and raphe nuclei (RN), at two zeitgebers (ZT6 and ZT18), in male and female rat's offspring early exposed (developmental period GD13-GD21) to fluoxetine (20mg/kg). First, we have conducted daily records of the locomotor activity rhythm using activity sensors coupled to individual cages over four weeks. We have lastly evaluated the immunoreactivity of NPY in both SCN and IGL, and as well the 5-HT expression in the dorsal and medial RN. In summary, our results showed that (1) prenatal fluoxetine affects phase entrainment of the rest/activity rhythm at ZT6 and ZT18, more in male than female specimens, and (2) modulates the NPY and 5-HT expression. Here, we show male rats are more susceptible to phase entrainment and the NPY and 5-HT misexpression compared to female ones. The sex differences induced by early exposure to fluoxetine in both the circadian rhythm of locomotor activity and the neurochemical expression into SCN, IGL, and midbrain raphe are an important highlight in the present work. Thus, our results may help to improve the knowledge on neurobiological mechanisms of circadian rhythms and are relevant to understanding the "broken brains" and behavioral abnormalities of offspring early exposed to antidepressants.

Structure-Based Design of High-Affinity Fluorescent Probes for the Neuropeptide Y Y1 Receptor

The recent crystallization of the neuropeptide Y Y₁ receptor (Y₁R) in complex with the argininamide-type Y₁R selective antagonist UR-MK299 (2) opened up a new approach toward structure-based design of nonpeptidic Y₁R ligands. We designed novel fluorescent probes showing excellent Y₁R selectivity and, in contrast to previously described fluorescent Y₁R ligands, considerably higher (∼100-fold) binding affinity. This was achieved through the attachment of different fluorescent dyes to the diphenylacetyl moiety in 2 via an amine-functionalized linker. The fluorescent ligands exhibited picomolar Y₁R binding affinities (pK_i values of 9.36-9.95) and proved to be Y₁R antagonists, as validated in a Fura-2 calcium assay. The versatile applicability of the probes as tool compounds was demonstrated by flow cytometry- and fluorescence anisotropy-based Y₁R binding studies (saturation and competition binding and association and dissociation kinetics) as well as by widefield and total internal reflection fluorescence (TIRF) microscopy of live tumor cells, revealing that fluorescence was mainly localized at the plasma membrane.

Neuropeptide Y interaction with dopaminergic and serotonergic pathways: interlinked neurocircuits modulating hedonic eating behaviours

Independent from homeostatic needs, the consumption of foods originating from hyperpalatable diets is defined as hedonic eating. Hedonic eating can be observed in many forms of eating phenotypes, such as compulsive eating and stress-eating, heightening the risk of obesity development. For instance, stress can trigger the consumption of palatable foods as a type of coping strategy, which can become compulsive, particularly when developed as a habit. Although eating for pleasure is observed in multiple maladaptive eating behaviours, the current understanding of the neurobiology underlying hedonic eating remains deficient. Intriguingly, the combined orexigenic, anxiolytic and reward-seeking properties of Neuropeptide Y (NPY) ignited great interest and has positioned NPY as one of the core neuromodulators operating hedonic eating behaviours. While extensive literature exists exploring the homeostatic orexigenic and anxiolytic properties of NPY, the rewarding effects of NPY continue to be investigated. As deduced from a series of behavioural and molecular-based studies, NPY appears to motivate the consumption and enhancement of food-rewards. As a possible mechanism, NPY may modulate reward-associated monoaminergic pathways, such as the dopaminergic and serotoninergic neural networks, to modulate hedonic eating behaviours. Furthermore, potential direct and indirect NPYergic neurocircuitries connecting classical homeostatic and hedonic neuropathways may also exist involving the anti-reward centre the lateral habenula. Therefore, this review investigates the participation of NPY in orchestrating hedonic eating behaviours through the modulation of monoaminergic pathways.

Hunger-driven adaptive prioritization of behavior

In order to survive, an animal must adapt its behavioral priorities to accommodate changing internal and external conditions. Hunger, a universally recognized interoceptive signal, promotes food intake though increasingly well-understood neural circuits. Less understood, is how hunger is integrated into the neural computations that guide nonfeeding behaviors. Within the brain, agouti-related peptide neurons in the arcuate nucleus of the hypothalamus have been found to powerfully stimulate feeding in addition to mediating other hunger-driven behavioral phenotypes. In this review, we compile the behavioral plasticity downstream of hunger and present identified or potential molecular and neural circuit mechanisms. We catalogue hunger's ability to increase exploration, decrease anxiety, and alter social behavior, among other phenotypes. Finally, we suggest paths forward for understanding hunger-driven behavioral adaptation and discuss the benefits of understanding state-dependent modulation of neural circuits controlling behavior.

Brain profiling of endogenous Neuropeptide Y (NPY) in distinct reproductive phases of adult male Microhyla ornata

Neuropeptide Y(NPY) is known to play a pivotal role in various physiological functions including appetite and reproduction. While studies in mammals, fishes and reptiles suggest a temporal and evolutionary conserved role of NPY, the information in amphibian is scanty. We have investigated the reproductive phase related variations of NPY in the brain of Microhyla ornata (M. ornata), using immunohistochemistry and reverse transcription quantitative PCR (RT-qPCR). The highest expression of NPY peptide was observed in the preoptic area (Poa), nucleus infundibularis ventralis (NIV) and nucleus reticularis isthmi (NRIS) of M. ornata in breeding season compared to pre-breeding as well as post-breeding season. In parallel, highest mRNA levels of NPY were also observed in the breeding season in the middle region of brain that includes hypothalamus of M. ornata. Variation in the levels of NPY peptide and mRNA levels in the brain of M. ornata point towards seasonal control of appetite and reproduction.

Integrating Hunger with Rival Motivations

Motivated behaviors have fascinated neuroscientists and ethologists for decades due to their necessity for organism survival. Motivations guide behavioral choice through an intricate synthesis of internal state detection, external stimulus exposure, and learned associations. One critical motivation, hunger, provides an accessible example for understanding purposeful behavior. Neuroscientists commonly focus research efforts on neural circuits underlying individual motivations, sacrificing ethological relevance for tight experimental control. This restrictive focus deprives the field of a more nuanced understanding of the unified nervous system in weighing multiple motivations simultaneously and choosing, moment-to-moment, optimal behaviors for survival. Here, we explore the reciprocal interplay between hunger, encoded via hypothalamic neurons marked by the expression of Agouti-related peptide, and alternative need-based motivational systems.

Are neuropeptides relevant for the mechanism of action of SSRIs?

Selective serotonin reuptake inhibitors (SSRIs) are drugs of first choice in the therapy of moderate to severe depression and anxiety disorders. Their primary mechanism of action is via influence of the serotonergic (5-HT) system, but a growing amount of data provides evidence for other non-monoaminergic players in SSRI effects. It is assumed that neuropeptides, which play a role as neuromodulators in the CNS, are involved in their mechanism of action. In this review we focus on six neuropeptides: corticotropin-releasing factor - CRF, galanin - GAL, oxytocin - OT, vasopressin - AVP, neuropeptide Y - NPY, and orexins - OXs. First, information about their roles in depression and anxiety disorders are presented. Then, findings describing their interactions with the 5-HT system are summarized. These data provide background for analysis of the results of published preclinical and clinical studies related to SSRI effects on the neuropeptide systems. We also report findings showing how modulation of neuropeptide transmission influences behavioral and neurochemical effects of SSRIs. Finally, future research necessary for enriching our knowledge of SSRI mechanisms of action is proposed. Recognition of new molecular targets for antidepressants will have a significant effect on the development of novel therapeutic strategies for mood-related disorders.

Need-based prioritization of behavior

When presented with a choice, organisms need to assimilate internal information with external stimuli and past experiences to rapidly and flexibly optimize decisions on a moment-to-moment basis. We hypothesized that increasing hunger intensity would curb expression of social behaviors such as mating or territorial aggression; we further hypothesized social interactions, reciprocally, would influence food consumption. We assessed competition between these motivations from both perspectives of mice within a resident-intruder paradigm. We found that as hunger state escalated, resident animal social interactions with either a female or male intruder decreased. Furthermore, intense hunger states, especially those evoked via AgRP photoactivation, fundamentally altered sequences of behavioral choice; effects dependent on food availibility. Additionally, female, but not male, intrusion attenuated resident mouse feeding. Lastly, we noted environmental context-dependent gating of food intake in intruding mice, suggesting a dynamic influence of context cues on the expression of feeding behaviors.

The role of neuropeptides and neurotransmitters on kisspeptin/kiss1r-signaling in female reproduction

Reproductive function is regulated by the hypothalamic-pituitary-gonads (HPG) axis. Hypothalamic neurons synthesizing kisspeptin play a fundamental role in the central regulation of the timing of puberty onset and reproduction in mammals. Kisspeptin is a regulator of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH). In female rodent, the kisspeptin (encoded by kiss1 gene), neurokinin B (Tac3) and dynorphin neurons form the basis for the "KNDy neurons" in the arcuate nucleus and play a fundamental role in the regulation of GnRH/LH release. Furthermore, various factors including neurotransmitters and neuropeptides may cooperate with kisspeptin signaling to modulate GnRH function. Many neuropeptides including proopiomelanocortin, neuropeptide Y, agouti-related protein, and other neuropeptides, as well as neurotransmitters, dopamine, norepinephrine and γ-aminobutyric acid are suggested to control feeding and HPG axis, the underlying mechanisms are not well known. Nonetheless, to date, information about the neurochemical factors of kisspeptin neurons remains incomplete in rodent. This review is intended to provide an overview of KNDy neurons; major neuropeptides and neurotransmitters interfere in kisspeptin signaling to modulate GnRH function for regulation of puberty onset and reproduction, with a focus on the female rodent.

Hypercaloric diet prevents sexual impairment induced by maternal food restriction

Prenatal undernutrition impairs copulatory behavior and increases the tendency to become obese/overweight, which also reduces sexual behavior. Re-feeding rats prenatally undernourished with a normocaloric diet can restore their physiological conditions and copulatory behavior. Thus, the present study investigated whether a hypercaloric diet that is administered in rats during the juvenile period prevents sexual impairments that are caused by maternal food restriction and the tendency to become overweight/obese. Female rats were prenatally fed a 40% restricted diet from gestational day 2 to 18. The pups received a hypercaloric diet from postnatal day (PND) 23 to PND65 (food restricted hypercaloric [FRH] group) or laboratory chow (food restricted control [FRC] group). Pups from non-food-restricted dams received laboratory chow during the entire experiment (non-food-restricted [NFR] group). During the juvenile period and adulthood, body weight gain was evaluated weekly. The day of balanopreputial separation, sexual behavior, sexual organ weight, hypodermal adiposity, striatal dopamine and serotonin, serum testosterone, and tumor necrosis factor α (TNF-α) were evaluated. The FRH group exhibited an increase in body weight on PND58 and PND65. The FRC group exhibited an increase in the latency to the first mount and intromission and an increase in serum TNF-α levels but a reduction of dopaminergic activity. The hypercaloric diet reversed all of these effects but increased adiposity. We concluded that the hypercaloric diet administered during the juvenile period attenuated reproductive impairments that were induced by maternal food restriction through increases in the energy expenditure but not the tendency to become overweight/obese.

A novel neuropeptide Y neuronal pathway linking energy state and reproductive behavior

Animals consume energy for reproduction, as well as survival. Excess or insufficient energy investment into reproduction, respectively, threatens the survival of parents or leads to the failure of reproduction. Management of energy consumption in reproduction is important, not only for the success of the process, but also for the survival of the parents. Reproductive behaviors, such as mating and parental behavior, are indispensable for achieving each event of reproduction including gametogamy, parturition, and lactation. Therefore, reproductive behavior is one of the important factors in managing energy consumption for reproduction. Orexigenic and anorexigenic molecules in the hypothalamus have been implicated in the regulation of reproductive functions. An orexigenic neuropeptide, neuropeptide Y (NPY), has been also implicated in the regulation of both reproduction and energy state of animals. In this review, we will first summarize the neuronal mechanism for regulating reproductive functions by orexigenic and anorexigenic molecules in the hypothalamus. Second, we will focus on the NPY neuronal pathways regulating reproductive behavior in the intra- and extra-hypothalamic brain areas. We will highlight the NPY neuronal pathway from the arcuate nucleus to the dorsal raphe nucleus as a novel extra-hypothalamic pathway for energy state-dependent regulation of reproductive behavior. Finally, we will propose a biological significance of the extra-hypothalamic NPY neuronal pathway, which plays an important role in the associative control of feeding and reproductive behaviors.