Prolactin activates mitogen-activated protein kinase signaling and corticotropin releasing hormone transcription in rat hypothalamic neurons

Dose Optimization of Anxiolytic Compounds Group in Valeriana jatamansi Jones and Mechanism Exploration by Integrating Network Pharmacology and Metabolomics Analysis

Anxiety disorder impacts the quality of life of the patients. The 95% ethanol extract of rhizomes and roots of Valeriana jatamansi Jones (Zhi zhu xiang, ZZX) has previously been shown to be effective for the treatment of anxiety disorder. In this study, the dose ratio of each component of the anxiolytic compounds group (ACG) in a 95% ethanol extract of ZZX was optimized by a uniform design experiment and mathematical modeling. The anxiolytic effect of ACG was verified by behavioral experiments and biochemical index measurement. Network pharmacology was used to determine potential action targets, as well as predict biological processes and signaling pathways, which were then verified by molecular docking analysis. Metabolomics was then used to screen and analyze metabolites in the rat hippocampus before and after the administration of ZZX-ACG. Finally, the results of metabolomics and network pharmacology were integrated to clarify the anti-anxiety mechanism of the ACG. The optimal dose ratio of ACG in 95% ethanol extract of ZZX was obtained, and our results suggest that ACG may regulate ALB, AKT1, PTGS2, CYP3A4, ESR1, CASP3, CYP2B6, EGFR, SRC, MMP9, IGF1, and MAPK8, as well as the prolactin signaling pathway, estrogen signaling pathway, and arachidonic acid metabolism pathway, thus affecting the brain neurotransmitters and HPA axis hormone levels to play an anxiolytic role, directly or indirectly.

The brain as a source and a target of prolactin in mammals

Prolactin is a polypeptide hormone associated with an extensive variety of biological functions. Among the roles of prolactin in vertebrates, some were preserved throughout evolution. This is the case of its function in the brain, where prolactin receptors, are expressed in different structures of the central nervous system. In the brain, prolactin actions are principally associated with reproduction and parental behavior, and involves the modulation of adult neurogenesis, neuroprotection, and neuroplasticity, especially during pregnancy, thereby preparing the brain to parenthood. Prolactin is mainly produced by specialized cells in the anterior pituitary gland. However, during vertebrate evolution many other extrapituitary tissues do also produce prolactin, like the immune system, endothelial cells, reproductive structures and in several regions of the brain. This review summarizes the relevance of prolactin for brain function, the sources of prolactin in the central nervous system, as well as its local production and secretion. A highlight on the impact of prolactin in human neurological diseases is also provided.

Prolactin and Its Altered Action in Alzheimer's Disease and Parkinson's Disease

BACKGROUND

Prolactin (PRL) is one of the most diverse pituitary hormones and is known to modulate normal neuronal function and neurodegenerative conditions. Many studies have described the influence that PRL has on the central nervous system and addressed its contribution to neurodegeneration, but little is known about the mechanisms responsible for the effects of PRL on neurodegenerative disorders, especially on Alzheimer's disease (AD) and Parkinson's disease (PD).

SUMMARY

We review and summarize the existing literature and current understanding of the roles of PRL on various PRL aspects of AD and PD.

KEY MESSAGES

In general, PRL is viewed as a promising molecule for the treatment of AD and PD. Modulation of PRL functions and targeting of immune mechanisms are needed to devise preventive or therapeutic strategies.

Decoding signaling pathways involved in prolactin-induced neuroprotection: A review

It has been well recognized that prolactin (PRL), a pleiotropic hormone, has many functions in the brain, such as maternal behavior, neurogenesis, and neuronal plasticity, among others. Recently, it has been reported to have a significant role in neuroprotection against excitotoxicity. Glutamate excitotoxicity is a common alteration in many neurological and neurodegenerative diseases, leading to neuronal death. In this sense, several efforts have been made to decrease the progression of these pathologies. Despite various reports of PRL's neuroprotective effect against excitotoxicity, the signaling pathways that underlie this mechanism remain unclear. This review aims to describe the most recent and relevant studies on the molecular signaling pathways, particularly, PI3K/AKT, NF-κB, and JAK2/STAT5, which are currently under investigation and might be implicated in the molecular mechanisms that explain the PRL effects against excitotoxicity and neuroprotection. Remarkable neuroprotective effects of PRL might be useful in the treatment of some neurological diseases.

The maternal hormone in the male brain: Sexually dimorphic distribution of prolactin signalling in the mouse brain

Research of the central actions of prolactin is highly focused on females, but this hormone has also documented roles in male physiology and behaviour. Here, we provide the first description of the pattern of prolactin-derived signalling in the male mouse brain, employing the immunostaining of phosphorylated signal transducer and activator of transcription 5 (pSTAT5) after exogenous prolactin administration. Next, we explore possible sexually dimorphic differences by comparing pSTAT5 immunoreactivity in prolactin-supplemented males and females. We also assess the role of testosterone in the regulation of central prolactin signalling in males by comparing intact with castrated prolactin-supplemented males. Prolactin-supplemented males displayed a widespread pattern of pSTAT5 immunoreactivity, restricted to brain centres showing expression of the prolactin receptor. Immunoreactivity for pSTAT5 was present in several nuclei of the preoptic, anterior and tuberal hypothalamus, as well as in the septofimbrial nucleus or posterodorsal medial amygdala of the telencephalon. Conversely, non-supplemented control males were virtually devoid of pSTAT5-immunoreactivity, suggesting that central prolactin actions in males are limited to situations concurrent with substantial hypophyseal prolactin release (e.g. stress or mating). Furthermore, comparison of prolactin-supplemented males and females revealed a significant, female-biased sexual dimorphism, supporting the view that prolactin has a preeminent role in female physiology and behaviour. Finally, in males, castration significantly reduced pSTAT5 immunoreactivity in some structures, including the paraventricular and ventromedial hypothalamic nuclei and the septofimbrial region, thus indicating a region-specific regulatory role of testosterone over central prolactin signalling.

Integrative neuro-humoral regulation of oxytocin neuron activity in pregnancy and lactation

Oxytocin is required for normal birth and lactation. Oxytocin is synthesised by hypothalamic supraoptic and paraventricular nuclei neurons and is released into the circulation from the posterior pituitary gland. Under basal conditions, circulating oxytocin levels are relatively constant but during birth and lactation, pulsatile oxytocin release triggers rhythmic contraction of the uterus during birth and milk ejection during suckling. Oxytocin levels are principally determined by the pattern of action potential firing that is, in turn, determined by the interplay between the intrinsic properties of the oxytocin neurons, regulation of their excitability by surrounding glia as well as by synaptic drive from their afferent inputs. During birth and suckling, oxytocin neurons fire high-frequency bursts of action potentials that are coordinated across the population of neurons and these bursts underpin the pulsatile secretion of oxytocin required for normal birth and lactation. Neuroglial regulation of oxytocin neurons changes during pregnancy to favour burst firing. However, these changes still require afferent input activity to drive activity. While it has long been known that noradrenergic inputs to oxytocin neurons are activated during birth and lactation, the involvement of other afferent inputs is less clear. Here, we provide a brief overview of the current understanding of the mechanisms that regulate oxytocin neuron activity during pregnancy and lactation, and focus on recent evidence from our laboratory identifying an input that increases kisspeptin production to excite oxytocin neurons in late pregnancy. This article is protected by copyright. All rights reserved.

Adaptive Modifications of Maternal Hypothalamic-Pituitary-Adrenal Axis Activity during Lactation and Salsolinol as a New Player in this Phenomenon

Both basal and stress-induced secretory activities of the hypothalamic-pituitary-adrenal (HPA) axis are distinctly modified in lactating females. On the one hand, it aims to meet the physiological demands of the mother, and on the other hand, the appropriate and stable plasma cortisol level is one of the essential factors for the proper offspring development. Specific adaptations of HPA axis activity to lactation have been extensively studied in several animal species and humans, providing interesting data on the HPA axis plasticity mechanism. However, most of the data related to this phenomenon are derived from studies in rats. The purpose of this review is to highlight these adaptations, with a particular emphasis on stress reaction and differences that occur between species. Existing data on breastfeeding women are also included in several aspects. Finally, data from the experiments in sheep are presented, indicating a new regulatory factor of the HPA axis-salsolinol-which typical role was revealed in lactation. It is suggested that this dopamine derivative is involved in both maintaining basal and suppressing stress-induced HPA axis activities in lactating dams.

Effects of Pup Separation on Stress Response in Postpartum Female Rats

There is a complex collection of neuroendocrine function during the postpartum period. Prolactin (PRL) released by suckling stimulus and its PRL receptors (PRL-R) in the central nervous system (CNS) are involved in hyporesponsiveness of the hypothalamic-pituitary-adrenal (HPA) axis in lactating mammals including rodents and humans. It is not clear how long it takes to reestablish the attenuated HPA axis activity of lactating rats to a pre-pregnancy state after pup separation. We first tested the hypothesis that HPA axis activity in response to an acute stress in postpartum rats would return to a pre-pregnancy state after pup separation. Restraint stress for 30 min was performed at the end of pup separation as an acute stressor. Plasma levels of corticosterone (CORT) were measured following restraint stress or no-stress (control) in virgin rats and postpartum rats housed with their pups or with pup removal for different periods of time of one hour, 24 h, or eight days. We then tested the hypothesis that circulating PRL level and CNS PRL-R gene expression were involved in mediating the acute stress response in postpartum rats. Plasma levels of PRL and PRL-R mRNA levels in the choroid plexus of the CNS were determined in both no-stress and stress, virgin rats, and postpartum rats housed with their pups or with pup removal for various periods, and their correlation with plasma CORT levels was assessed. The results demonstrated that PRL levels declined to virgin state in all postpartum rats separated from their pups, including the dams with one-hour pup separation. Stress-induced HPA activity dampened in lactating rats housed with pups, and returned to the pre-pregnancy state after 24 h of pup separation when both circulating PRL level and CNS PRL-R expression were restored to a pre-pregnancy state. Additionally, basal plasma CORT and CNS PRL-R expression were significantly correlated in rats with various pup status. This study suggested that stress-induced HPA activation occurred when PRL-R expression was similar to the level of virgin females, indicating that PRL-R upregulation contributes to an attenuated HPA response to acute stress. Understanding neuroendocrine responses to stress during the postpartum period is critical to understand postpartum-related neuropsychiatric illnesses and to maintain mental health in postpartum women.

Prolactin regulation of oxytocin neurone activity in pregnancy and lactation

KEY POINTS

During lactation, prolactin promotes milk synthesis and oxytocin stimulates milk ejection. In virgin rats, prolactin inhibits the activity of oxytocin-secreting neurones. We found that prolactin inhibition of oxytocin neurone activity is lost in lactation, and that some oxytocin neurones were excited by prolactin in lactating rats. The change in prolactin regulation of oxytocin neurone activity was not associated with a change in activation of intracellular signalling pathways known to couple to prolactin receptors. The change in prolactin regulation of oxytocin neurone activity in lactation might allow coordinated activation of both populations of neurones when required for successful lactation.

ABSTRACT

Secretion of prolactin for milk synthesis and oxytocin for milk secretion is required for successful lactation. In virgin rats, prolactin inhibits oxytocin neurones but this effect would be counterproductive during lactation when secretion of both hormones is required for synthesis and delivery of milk to the newborn. Hence, we determined the effects of intracerebroventricular (i.c.v.) prolactin on oxytocin neurones in urethane-anaesthetised virgin, pregnant and lactating rats. Prolactin (2 μg) consistently inhibited oxytocin neurones in virgin and pregnant rats (by 1.9 ± 0.4 and 1.8 ± 0.5 spikes s^-1 , respectively), but not in lactating rats; indeed, prolactin excited six of 27 oxytocin neurones by >1 spike s^-1 in lactating rats but excited none in virgin or pregnant rats (χ²₂  = 7.2, P = 0.03). Vasopressin neurones were unaffected by prolactin (2 μg) in virgin rats but were inhibited by 1.1 ± 0.2 spikes s^-1 in lactating rats. Immunohistochemistry showed that i.c.v. prolactin increased oxytocin expression in virgin and lactating rats and increased signal transducer and activator of transcription 5 phosphorylation to a similar extent in oxytocin neurones of virgin and lactating rats. Western blotting showed that i.c.v. prolactin did not affect phosphorylation of extracellular regulated kinase 1 or 2, or of Akt in the supraoptic or paraventricular nuclei of virgin or lactating rats. Hence, prolactin inhibition of oxytocin neurones is lost in lactation, which might allow concurrent elevation of prolactin secretion from the pituitary gland and activation of oxytocin neurones for synthesis and delivery of milk to the newborn.

Gene networks activated by specific patterns of action potentials in dorsal root ganglia neurons

Gene regulatory networks underlie the long-term changes in cell specification, growth of synaptic connections, and adaptation that occur throughout neonatal and postnatal life. Here we show that the transcriptional response in neurons is exquisitely sensitive to the temporal nature of action potential firing patterns. Neurons were electrically stimulated with the same number of action potentials, but with different inter-burst intervals. We found that these subtle alterations in the timing of action potential firing differentially regulates hundreds of genes, across many functional categories, through the activation or repression of distinct transcriptional networks. Our results demonstrate that the transcriptional response in neurons to environmental stimuli, coded in the pattern of action potential firing, can be very sensitive to the temporal nature of action potential delivery rather than the intensity of stimulation or the total number of action potentials delivered. These data identify temporal kinetics of action potential firing as critical components regulating intracellular signalling pathways and gene expression in neurons to extracellular cues during early development and throughout life.

Effects of High-Fat Diet on Stress Response in Male and Female Wildtype and Prolactin Knockout Mice

Prolactin (PRL) is well characterized for its roles in initiation and maintenance of lactation, and it also suppresses stress-induced responses. Feeding a high-fat diet (HFD) disrupts activity of the hypothalamic-pituitary-adrenal (HPA) axis. Whether PRL regulates HPA axis activation under HFD feeding is not clear. Male and female wildtype (WT) and PRL knockout (KO) mice were fed either a standard low-fat diet (LFD) or HFD for 12 weeks. Circulating corticosterone (CORT) levels were measured before, during, and after mice were subjected to an acute restraint stress or remained in their home cages as no stress controls. HFD feeding increased leptin levels, but the increase was lower in KO than in WT mice. All stressed female groups and only LFD-fed stressed males had elevated CORT levels compared to their no stress same-sex counterparts regardless of genotype. These results indicated that HFD consumption blunted the HPA axis response to acute stress in males but not females. Additionally, basal hypothalamic CRH content was lower in HFD than LFD males, but was similar among female groups. Furthermore, although basal CORT levels were similar among KO and WT groups, CORT levels were higher in KO mice than their WT counterparts during stress, suggesting that loss of PRL led to greater HPA axis activation. Basal PRL receptor mRNA levels in the choroid plexus were higher in HFD than LFD same-sex counterparts, suggesting activation of central PRL’s action by HFD feeding in both males and females. Current results confirmed PRL’s roles in suppression of the stress-induced HPA axis activation. Although HFD feeding activated central PRL’s action in both sexes, only the male HPA axis was dampened by HFD feeding.

Mood, Food, and Fertility: Adaptations of the Maternal Brain

Successfully rearing young places multiple demands on the mammalian female. These are met by a wide array of alterations in maternal physiology and behavior that are coordinated with the needs of the developing young, and include adaptations in neuroendocrine systems not directly involved in maternal behavior or lactation. In this article, attenuations in the behavioral and neuroendocrine responses to stressors, the alterations in metabolic pathways facilitating both increased food intake and conservation of energy, and the changes in fertility that occur postpartum are described. The mechanisms underlying these processes as well as the factors that contribute to them and the relative contributions of these stimuli at different times postpartum are also reviewed. The induction and maintenance of the adaptations observed in the postpartum maternal brain are dependent on mother-young interaction and, in most cases, on suckling stimulation and its consequences for the hormonal profile of the mother. The peptide hormone prolactin acting on receptors within the brain makes a major contribution to changes in metabolic pathways, suppression of fertility and the attenuation of the neuroendocrine response to stress during lactation. Oxytocin is also released, both into the circulation and in some hypothalamic nuclei, in response to suckling stimulation and this hormone has been implicated in the decrease in anxiety behavior seen in the early postpartum period. The relative importance of these hormones changes across lactation and it is becoming increasingly clear that many of the adaptations to motherhood reviewed here reflect the outcome of multiple influences. © 2016 American Physiological Society. Compr Physiol 6:1493-1518, 2016.

Reproductive Regulation of Gene Expression in the Hypothalamic Supraoptic and Paraventricular Nuclei

Oxytocin secretion is required for successful reproduction. Oxytocin is synthesised by magnocellular neurones of the hypothalamic supraoptic and paraventricular nuclei and the physiological demand for oxytocin synthesis and secretion is increased for birth and lactation. Therefore, we used a polymerase chain reaction (PCR) array screen to determine whether genes that might be important for synthesis and/or secretion of oxytocin are up- or down-regulated in the supraoptic and paraventricular nuclei of late-pregnant and lactating rats, compared to virgin rats. We then validated the genes that were most highly regulated using real time-quantitative PCR. Among the most highly regulated genes were those that encode for suppressors of cytokine signalling, which are intracellular inhibitors of prolactin signalling. Prolactin receptor activation changes gene expression via phosphorylation of signal transducer and activator of transcription 5 (STAT5). Using double-label immunohistochemistry, we found that phosphorylated STAT5 was expressed in almost all oxytocin neurones of late-pregnant and lactating rats but was almost absent from oxytocin neurones of virgin rats. We conclude that increased prolactin activation of oxytocin neurones might contribute to the changes in gene expression by oxytocin neurones required for normal birth and lactation.

A Genetic Animal Model of Alcoholism for Screening Medications to Treat Addiction

The purpose of this review is to present up-to-date pharmacological, genetic, and behavioral findings from the alcohol-preferring P rat and summarize similar past work. Behaviorally, the focus will be on how the P rat meets criteria put forth for a valid animal model of alcoholism with a highlight on its use as an animal model of polysubstance abuse, including alcohol, nicotine, and psychostimulants. Pharmacologically and genetically, the focus will be on the neurotransmitter and neuropeptide systems that have received the most attention: cholinergic, dopaminergic, GABAergic, glutamatergic, serotonergic, noradrenergic, corticotrophin releasing hormone, opioid, and neuropeptide Y. Herein, we sought to place the P rat's behavioral and neurochemical phenotypes, and to some extent its genotype, in the context of the clinical literature. After reviewing the findings thus far, this chapter discusses future directions for expanding the use of this genetic animal model of alcoholism to identify molecular targets for treating drug addiction in general.

Actions of Prolactin in the Brain: From Physiological Adaptations to Stress and Neurogenesis to Psychopathology

Prolactin (PRL) is one of the most versatile hormones known. It is considered an adaptive hormone due to the key roles it plays in the modulation of the stress response and during pregnancy and lactation. Within the brain, PRL acts as a neuropeptide to promote physiological responses related to reproduction, stress adaptation, neurogenesis, and neuroprotection. The action of PRL on the nervous system contributes to the wide array of changes that occur in the female brain during pregnancy and result in the attenuation of the hypothalamic-pituitary-adrenal axis. Together, all these changes promote behavioral and physiological adaptations of the new mother to enable reproductive success. Brain adaptations driven by PRL are also important for the regulation of maternal emotionality and well-being. PRL also affects the male brain during the stress response, but its effects have been less studied. PRL regulates neurogenesis both in the subventricular zone and in the hippocampus. Therefore, alterations in the PRL system due to stress or exposure to substances that reduce neurogenesis or other conditions, could contribute to maladaptive responses and pathological behavioral outcomes. Here, we review the PRL system and the role it plays in the modulation of stress response and emotion regulation. We discuss the effects of PRL on neurogenesis and neuroprotection, the putative neuronal mechanisms underlying these effects, and their contribution to the onset of psychopathological states such as depression.

Reproductive Stage and Modulation of Stress-Induced Tau Phosphorylation in Female Rats

Chronic stress is implicated as a risk factor for Alzheimer's disease (AD) and other neurodegenerative disorders. Although the specific mechanisms linking stress exposure and AD vulnerability have yet to be fully determined, our laboratory and others have shown that acute and repeated restraint stress in rodents leads to an increase in hippocampal tau phosphorylation (tau-P) and tau insolubility, a critical component of tau pathology in AD. Although tau phosphorylation induced by acute psychological stress is dependent on intact signaling through the type 1 corticotropin-releasing factor receptor, how sex steroids or other modulators contribute to this effect is unknown. A naturally occurring attenuation of the stress response is observed in female rats at the end of pregnancy and throughout lactation. To test the hypothesis that decreased sensitivity to stress during lactation modulates stress-induced tau-P, cohorts of virgin, lactating and weaned female rats were subjected to 30 min of restraint stress or no stress (control) and were killed 20 min or 24 h after the episode. Exposure to restraint stress induced a significant decrease in tau-P in the hippocampus of lactating rats killed 20 min after stress compared to lactating controls and virgins subjected to stress treatment. Lactating rats killed 24 hr after restraint stress exposure showed significant elevation in tau-P compared to lactating cohorts killed 20 min after stress. Levels of tau-P in these latter cohorts did not differ signficantly from control animals. Furthermore, glycogen synthase kinase (GSK)3-α levels were significantly decreased in stressed lactating animals at both timepoints. This suggests a steep, yet transient stress-induced dephosphorylation of tau, influenced by GSK3, in the hippocampus of lactating rats.

Mitogen-Activated Protein Kinase 8 (MAP3K8) Mediates the Signaling Pathway of Estradiol Stimulating Progesterone Production Through G Protein-Coupled Receptor 30 (GPR30) in Mouse Corpus Luteum

The corpus luteum (CL) is a transient endocrine gland developed from the ovulated follicles, and the most important function is to synthesize and secrete progesterone (P(4)), a key hormone to maintain normal pregnancy and estrous cycle in most mammals. It is known that estrogen has a vital role in stimulating P(4) synthesis in CL, but it still remains unclear about the mechanism of estradiol (E(2)) regulating P(4) production in CL. Our results here first show that all of the CL cells express MAPK 8 (MAP3K8), and the MAP3K8 level is much higher at the midstage than at the early and late stages during CL development. The further functional studies show that the forced inhibition of endogenous MAP3K8 by using MAP3K8 small interfering RNA and MAP3K8 signaling inhibitor (MAP3K8i) in the luteal cells significantly block the P(4) synthesis and neutralize the enhancing effect of E(2) on P(4) production in the CL. In addition, our results here demonstrate that the stimulating effect of E(2) on P(4) synthesis relies on the estrogen no-classical protein-coupled receptor 30, and MAP3K8 is involved in mediating the protein-coupled receptor 30signaling of E(2) affecting P(4) synthesis via stimulating ERK phosphorylation. These novel findings are critical for our understanding the ovary physiology and pathological mechanism.

Early life stress and hippocampal neurogenesis in the neonate: sexual dimorphism, long term consequences and possible mediators

Adverse early life experience decreases adult hippocampal neurogenesis and results in increased vulnerability to neuropsychiatric disorders. Despite that the effects of postnatal stress on neurogenesis have been widely studied in adult individuals, few efforts have been done to evaluate its immediate effects on the developing hippocampus. Moreover, it is not clear whether postnatal stress causes a differential impact in hippocampus development in male and female neonates that could be related to emotional deficits in adulthood. It has been proposed that the long term effects of early stress exposure rise from a persistent HPA axis activation during sensitive time windows; nevertheless the exact mechanisms and mediators remain unknown. Here, we summarize the immediate and late effects of early life stress on hippocampal neurogenesis in male and female rat pups, compare its later consequences in emotionality, and highlight some relevant mediator peptides that could be potentially involved in programming.

Light-induced rapid Ca²⁺ response and MAPK phosphorylation in the cells heterologously expressing human OPN5

Molecular imaging is a powerful tool for investigating intracellular signalling, but it is difficult to acquire conventional fluorescence imaging from photoreceptive cells. Here we demonstrated that human opsin5 (OPN5) photoreceptor mediates light-induced Ca(2+) response in human embryonic kidney (HEK293) and mouse neuroblastoma (Neuro2a) cell lines using a luminescence imaging system with a fluorescent indicator and a newly synthesized bioluminescent indicator. Weak light fluorescence and bioluminescence imaging revealed rapid and transient light-stimulated Ca(2+) release from thapsigargin-sensitive Ca(2+) stores, whereas long-lasting Ca(2+) elevation was observed using a conventional fluorescence imaging system. Bioluminescence imaging also demonstrated that OPN5 activation in HEK293 cells induced a decrease in pertussis toxin-sensitive cAMP, confirming previous reports. In addition, ultraviolet radiation induced the phosphorylation of mitogen-activated protein kinases when OPN5 was stimulated in Neuro2a cells. These findings suggest that the combination of these imaging approaches may provide a new means to investigate the physiological characteristics of photoreceptors.

Increased STAT5 signaling in the ring dove brain in response to prolactin administration and spontaneous elevations in prolactin during the breeding cycle

Prolactin acts on target cells in the central nervous system (CNS) to stimulate behavioral changes associated with parental care in birds, but the signaling mechanisms that mediate these actions have not been characterized. In mammals, the Janus Kinase 2-Signal Transducer and Activator of Transcription 5 (JAK2-STAT5) signaling pathway mediates many of the actions of prolactin. To assess the importance of this pathway in prolactin-sensitive target cells in the avian brain, we measured changes in activated (phosphorylated) STAT5 (pSTAT5) in the forebrain of female ring doves sampled as plasma prolactin levels change during the breeding cycle and in prolactin-treated, non-breeding females. The anatomical distribution of cells exhibiting pSTAT5 immunoreactivity in dove brain closely paralleled the distribution of prolactin receptors in this species. The density of pSTAT5 immunoreactive (pSTAT5-ir) cells was highest in the preoptic area, the suprachiasmatic, paraventricular, and ventromedial hypothalamic nuclei, the lateral and tuberal hypothalamic regions, the lateral bed nucleus of the stria terminalis, and the lateral septum. Mean pSTAT5-ir cell densities in these eight brain areas were several fold higher in breeding females during late incubation/early post-hatching when plasma prolactin levels have been observed to peak than in non-breeding females or breeding females sampled at earlier stages when prolactin titers have been reported to be lower. Similar differences were observed between prolactin-treated and vehicle-treated females in all three of the forebrain regions that were compared. We conclude that JAK2-STAT5 signaling is strongly activated in response to prolactin stimulation in the ring dove brain and could potentially mediate some of the centrally-mediated behavioral effects of this hormone.

Mitogen-activated protein kinase phosphatase 1 negatively regulates MAPK signaling in mouse hypothalamus

Mitogen-activated protein kinase phosphatase 1 (MKP-1) is shown to negatively regulate MAPK signaling in various peripheral tissues as well as the central nervous system such as cortex, striatum and hippocampus. In this study, we examined whether MKP-1 regulates MAPK signaling in the mouse hypothalamus. Intraperitoneal injection of TNFα significantly increased MKP-1 mRNA expression in paraventricular and arcuate nuclei in the hypothalamus. TNFα treatment induced increases in MKP-1 expression at both mRNA and protein levels, accompanied by the inactivation of MAPK signaling in mouse hypothalamic explants. Inhibition of MKP-1 by its inhibitor or siRNA increased MAPK activity in the explants. Our data indicate that MKP-1 negatively regulates MAPK signaling in the mouse hypothalamus.

Extracellular signal-regulated kinase phosphorylation in forebrain neurones contributes to osmoregulatory mechanisms

Vasopressin secretion from the magnocellular neurosecretory cells (MNCs) is crucial for body fluid homeostasis. Osmotic regulation of MNC activity involves the concerted modulation of intrinsic mechanosensitive ion channels, taurine release from local astrocytes as well as excitatory inputs derived from osmosensitive forebrain regions. Extracellular signal-regulated protein kinases (ERK) are mitogen-activated protein kinases that transduce extracellular stimuli into intracellular post-translational and transcriptional responses, leading to changes in intrinsic neuronal properties and synaptic function. Here, we investigated whether ERK activation (i.e. phosphorylation) plays a role in the functioning of forebrain osmoregulatory networks. We found that within 10 min after intraperitoneal injections of hypertonic saline (3 m, 6 m) in rats, many phosphoERK-immunopositive neurones were observed in osmosensitive forebrain regions, including the MNC containing supraoptic nuclei. The intensity of ERK labelling was dose-dependent. Reciprocally, slow intragastric infusions of water that lower osmolality reduced basal ERK phosphorylation. In the supraoptic nucleus, ERK phosphorylation predominated in vasopressin neurones vs. oxytocin neurones and was absent from astrocytes. Western blot experiments confirmed that phosphoERK expression in the supraoptic nucleus was dose dependent. Intracerebroventricular administration of the ERK phosphorylation inhibitor U 0126 before a hyperosmotic challenge reduced the number of both phosphoERK-immunopositive neurones and Fos expressing neurones in osmosensitive forebrain regions. Blockade of ERK phosphorylation also reduced hypertonically induced depolarization and an increase in firing of the supraoptic MNCs recorded in vitro. It finally reduced hypertonically induced vasopressin release in the bloodstream. Altogether, these findings identify ERK phosphorylation as a new element contributing to the osmoregulatory mechanisms of vasopressin release.

Stress susceptibility-specific phenotype associated with different hippocampal transcriptomic responses to chronic tricyclic antidepressant treatment in mice

Background

The effects of chronic treatment with tricyclic antidepressant (desipramine, DMI) on the hippocampal transcriptome in mice displaying high and low swim stress-induced analgesia (HA and LA lines) were studied. These mice displayed different depression-like behavioral responses to DMI: stress-sensitive HA animals responded to DMI, while LA animals did not.

Results

To investigate the effects of DMI treatment on gene expression profiling, whole-genome Illumina Expression BeadChip arrays and qPCR were used. Total RNA isolated from hippocampi was used. Expression profiling was then performed and data were analyzed bioinformatically to assess the influence of stress susceptibility-specific phenotypes on hippocampal transcriptomic responses to chronic DMI. DMI treatment affected the expression of 71 genes in HA mice and 41 genes in LA mice. We observed the upregulation of Igf2 and the genes involved in neurogenesis (HA: Sema3f, Ntng1, Gbx2, Efna5, and Rora; LA: Otx2, Rarb, and Drd1a) in both mouse lines. In HA mice, we observed the upregulation of genes involved in neurotransmitter transport, the termination of GABA and glycine activity (Slc6a11, Slc6a9), glutamate uptake (Slc17a6), and the downregulation of neuropeptide Y (Npy) and corticotropin releasing hormone-binding protein (Crhbp). In LA mice, we also observed the upregulation of other genes involved in neuroprotection (Ttr, Igfbp2, Prlr) and the downregulation of genes involved in calcium signaling and ion binding (Adcy1, Cckbr, Myl4, Slu7, Scrp1, Zfp330).

Conclusions

Several antidepressant treatment responses are similar in individuals with different sensitivities to stress, including the upregulation of Igf2 and the genes involved in neurogenesis. However, the findings also reveal that many responses to antidepressant treatments, involving the action of individual genes engaged in neurogenesis, neurotransmitter transport and neuroprotection, depend on constitutive hippocampal transcriptomic profiles and might be genotype dependent. The results suggest that, when and if this becomes feasible, antidepressant treatment should take into consideration individual sensitivity to stress.

Stress-related biomarkers of dream recall and implicit memory under anaesthesia

The aim of this study was to investigate whether auditory presentation of a story during general anaesthesia might influence stress hormone changes and thus affecting dream recall and/or implicit memory. One hundred and ten patients were randomly assigned either to hear a recording of a story through headphones or to have routine care with no auditory recording while undergoing laparoscopic cholecystectomy. Anaesthesia was standardised. Blood samples for cortisol and prolactin assays were collected 20 min before anaesthesia and 5 min after pneumoperitoneum. Dream recall and explicit/implicit memory were investigated upon awakening from anaesthesia and approximately 24 h after the end of the operation. Auditory presentation was associated with lower intra-operative serum prolactin concentration compared with control (p = 0.0006). Twenty-seven patients with recall of dreaming showed higher intra-operative prolactin (p = 0.004) and lower cortisol (p = 0.03) concentrations compared with those without dream recall. The knowledge of this interaction might be useful in the quest to ensure postoperative amnesia.

Sex differences in the effects of chronic stress and food restriction on body weight gain and brain expression of CRF and relaxin-3 in rats

This study investigated sex-specific effects of repeated stress and food restriction on food intake, body weight, corticosterone plasma levels and expression of corticotropin-releasing factor (CRF) in the hypothalamus and relaxin-3 in the nucleus incertus (NI). The CRF and relaxin-3 expression is affected by stress, and these neuropeptides produce opposite effects on feeding (anorexigenic and orexigenic, respectively), but sex-specific regulation of CRF and relaxin-3 by chronic stress is not fully understood. Male and female rats were fed ad libitum chow (AC) or ad libitum chow and intermittent palatable liquid Ensure without food restriction (ACE), or combined with repeated food restriction (60% chow, 2 days per week; RCE). Half of the rats were submitted to 1-h restraint stress once a week. In total, seven weekly cycles were applied. The body weight of the RCE stressed male rats significantly decreased, whereas the body weight of the RCE stressed female rats significantly increased compared with the respective control groups. The stressed female RCE rats considerably overate chow during recovery from stress and food restriction. The RCE female rats showed elevated plasma corticosterone levels and low expression of CRF mRNA in the paraventricular hypothalamic nucleus but not in the medial preoptic area. The NI expression of relaxin-3 mRNA was significantly higher in the stressed RCE female rats compared with other groups. An increase in the expression of orexigenic relaxin-3 and misbalanced hypothalamic-pituitary-adrenal axis activity may contribute to the overeating and increased body weight seen in chronically stressed and repeatedly food-restricted female rats.

Identifying links in the chain: the dynamic coupling of catecholamines, peptide synthesis, and peptide release in hypothalamic neuroendocrine neurons

Compared to neurons that communicate using synapses, some neuroendocrine neurons release relatively large quantities of peptide into the vasculature to control neuroendocrine function. Maintaining adequate amounts of peptide for release through controlled biosynthesis is therefore critical for their function. But how neuroendocrine-or in fact, any neuropeptide-neurons link appropriate levels of peptide biosynthesis with the action potentials that drive peptide release is unknown. Here, we review possible mechanisms in paraventricular hypothalamic CRH neuroendocrine neurons to coordinate these processes in response to catecholaminergic inputs. We show that CRH synthesis and release mechanisms are not invariably linked as CRH neurons are activated. Instead, coupling mechanisms exist in the premotor network that provides their synaptic inputs and in their intracellular signal transduction mechanisms, where transmitter-regulated phosphorylation of p44/42 mitogen-activated protein kinases (ERK1/2) may play a prominent role. These versatile and dynamic coupling mechanisms provide a way to link peptide biosynthesis and release.

Differential sensitivity of specific neuronal populations of the rat hypothalamus to prolactin action

Prolactin stimulates dopamine release from neuroendocrine dopaminergic (NEDA) neurons in the hypothalamic arcuate nucleus (ARC) to maintain low levels of serum prolactin. Elevated prolactin levels during pregnancy and lactation may mediate actions in other hypothalamic regions such as the paraventricular nucleus (PVN) and rostral preoptic area (rPOA). We predicted that NEDA neurons would be more sensitive prolactin targets than neurons in other regions because they are required to regulate basal prolactin secretion. Moreover, differences in the accessibility of the ARC to prolactin in blood may influence the responsiveness of this population. Therefore, we compared prolactin-induced signaling in different hypothalamic neuronal populations following either systemic or intracerebroventricular (icv) prolactin administration. Phosphorylation of the signal transduction factor, STAT5 (pSTAT5), was used to identify prolactin-responsive neurons. In response to systemic prolactin, pSTAT5-labeled cells were widely observed in the ARC but absent from the rPOA and PVN. Many of these responsive cells in the ARC were identified as NEDA neurons. The lowest icv prolactin dose (10 ng) induced pSTAT5 in the ARC, but with higher doses (>500 ng) pSTAT5 was detected in numerous regions, including the rPOA and PVN. NEDA neurons were maximally labeled with nuclear pSTAT5 in response to 500 ng prolactin and appeared to be more sensitive than dopaminergic neurons in the rPOA. Subpopulations of oxytocin neurons in the hypothalamus were also found to be differentially sensitive to prolactin. These data suggest that differences in the accessibility of the arcuate nucleus to prolactin, together with intrinsic differences in the NEDA neurons, may facilitate homeostatic feedback regulation of prolactin release.

Effects of chronic stress on prefrontal cortex transcriptome in mice displaying different genetic backgrounds

There is increasing evidence that depression derives from the impact of environmental pressure on genetically susceptible individuals. We analyzed the effects of chronic mild stress (CMS) on prefrontal cortex transcriptome of two strains of mice bred for high (HA)and low (LA) swim stress-induced analgesia that differ in basal transcriptomic profiles and depression-like behaviors. We found that CMS affected 96 and 92 genes in HA and LA mice, respectively. Among genes with the same expression pattern in both strains after CMS, we observed robust upregulation of Ttr gene coding transthyretin involved in amyloidosis, seizures, stroke-like episodes, or dementia. Strain-specific HA transcriptome affected by CMS was associated with deregulation of genes involved in insulin secretion (Acvr1c, Nnat, and Pfkm), neuropeptide hormone activity (Nts and Trh), and dopamine receptor mediated signaling pathway (Clic6, Drd1a, and Ppp1r1b). LA transcriptome affected by CMS was associated with genes involved in behavioral response to stimulus (Fcer1g, Rasd2, S100a8, S100a9, Crhr1, Grm5, and Prkcc), immune effector processes (Fcer1g, Mpo, and Igh-VJ558), diacylglycerol binding (Rasgrp1, Dgke, Dgkg, and Prkcc), and long-term depression (Crhr1, Grm5, and Prkcc) and/or coding elements of dendrites (Crmp1, Cntnap4, and Prkcc) and myelin proteins (Gpm6a, Mal, and Mog). The results indicate significant contribution of genetic background to differences in stress response gene expression in the mouse prefrontal cortex.

MAP kinases couple hindbrain-derived catecholamine signals to hypothalamic adrenocortical control mechanisms during glycemia-related challenges

Physiological responses to hypoglycemia, hyperinsulinemia, and hyperglycemia include a critical adrenocortical component that is initiated by hypothalamic control of the anterior pituitary and adrenal cortex. These adrenocortical responses ensure appropriate long-term glucocorticoid-mediated modifications to metabolism. Despite the importance of these mechanisms to disease processes, how hypothalamic afferent pathways engage the intracellular mechanisms that initiate adrenocortical responses to glycemia-related challenges are unknown. This study explores these mechanisms using network- and cellular-level interventions in in vivo and ex vivo rat preparations. Results show that a hindbrain-originating catecholamine afferent system selectively engages a MAP kinase pathway in rat paraventricular hypothalamic CRH (corticotropin-releasing hormone) neuroendocrine neurons shortly after vascular insulin and 2-deoxyglucose challenges. In turn, this MAP kinase pathway can control both neuroendocrine neuronal firing rate and the state of CREB phosphorylation in a reduced ex vivo paraventricular hypothalamic preparation, making this signaling pathway an ideal candidate for coordinating CRH synthesis and release. These results establish the first clear structural and functional relationships linking neurons in known nutrient-sensing regions with intracellular mechanisms in hypothalamic CRH neuroendocrine neurons that initiate the adrenocortical response to various glycemia-related challenges.

Transcriptional control of adrenal steroidogenesis: novel connection between Janus kinase (JAK) 2 protein and protein kinase A (PKA) through stabilization of cAMP response element-binding protein (CREB) transcription factor

In the adrenal gland, adrenocorticotropin (ACTH) acting through the cAMP protein kinase (PKA) transduction pathway is the main regulator of genes involved in glucocorticoid synthesis. The prolactin (PRL) receptor is expressed in the adrenal cortex of most mammals, but experimental proof that PRL ensures direct control on glucocorticoid synthesis in rodents remains elusive. To unravel the physiological importance of PRL in adrenocortical functions, we measured steroidogenic capacity of Prlr-deficient mice (Prlr(-/-)) and explored the influence of JAK/STAT signaling, the major PRL transduction pathway, on the steroidogenic activity of adrenocortical cell cultures. We demonstrate that lack of Prlr does not affect basal (nor stress-induced) corticosterone levels in mice. PRL triggers JAK2/STAT5-dependent transcription in adrenal cells, but this does not influence corticosterone release. In contrast, pharmacological or siRNA-mediated inhibition of JAK2 reveals its essential role in both basal and ACTH/cAMP-induced steroidogenesis. We demonstrate that nuclear JAK2 regulates the amount of active transcription factor CREB (cAMP response element-binding protein) through tyrosine phosphorylation and prevention of proteasomal degradation, which in turn leads to transcriptional activation of the rate-limiting steroidogenic Star gene. Hence, we describe a novel link between PKA and JAK2 by which nuclear JAK2 signaling controls adrenal steroidogenesis by increasing the stability of CREB.

Region-, neuron-, and signaling pathway-specific increases in prolactin responsiveness in reproductively experienced female rats

Pregnancy and lactation cause long-lasting enhancements in maternal behavior and other physiological functions, along with increased hypothalamic prolactin receptor expression. To directly test whether reproductive experience increases prolactin responsiveness in the arcuate, paraventricular, and supraoptic nuclei and the medial preoptic area, female rats experienced a full pregnancy and lactation or remained as age-matched virgin controls. At 5 wk after weaning, rats received 2.5, 100, or 4000 ng ovine prolactin or vehicle intracerebroventricularly. The brains underwent immunohistochemistry for the phosphorylated forms of signal transducer and activator of transcription 5 (pSTAT5) or ERK1/2 (pERK1/2). There was a marked increase in pSTAT5 and pERK1/2 in response to prolactin in the regions examined in both virgin and primiparous rats. Primiparous rats exhibited approximately double the number of prolactin-induced pSTAT5-immunoreactive cells as virgins, this effect being most apparent at the higher prolactin doses in the medial preoptic area and paraventricular and supraoptic nuclei and at the lowest prolactin dose in the arcuate nucleus. Dual-label immunohistochemistry showed that arcuate kisspeptin (but not oxytocin or dopamine) neurons displayed increased sensitivity to prolactin in reproductively experienced animals; these neurons may contribute to the reduction in prolactin concentration observed after reproductive experience. There was no effect of reproductive experience on prolactin-induced pERK1/2, indicating a selective effect on the STAT5 pathway. These data show that STAT5 responsiveness to prolactin is enhanced by reproductive experience in multiple hypothalamic regions. The findings may have significant implications for understanding postpartum disorders affecting maternal care and other prolactin-associated pathologies.

Differential action of two prolactin isoforms on ischemia and re-perfusion-induced arrhythmias in rats in vivo

BACKGROUND

The different influences of one of the PRL isoforms (PRL I) on the cardiovascular system have been described in the past.

AIM

Our goal was to establish an appropriate iv dose of 2 PRL isoforms (PRL I and PRL II) in intact rats. After establishing this dose, PRL I (0.01 mg/kg) or PRL II (0.001 mg/kg) was administered in bolus 10 min before left anterior descending coronary artery occlusion (7 min) followed by re-perfusion (15 min). We then aimed to study and compare the effects of these isoforms on ischemia- and re-perfusion-induced arrhythmias in the ischemia and re-perfusion-induced arrhythmias model in rats.

MATERIALS AND METHODS

Mortality index, ventricular fibrillation and tachycardia (VF, VT) incidence and duration, systolic, diastolic, and mean arterial blood pressure, heart rate and myocardial index of oxygen consumption [pressure rate product (PRP)] were measured and calculated.

RESULTS

Both PRL isoforms reduced animal mortality (from 50 to 18.75 and 25%, respectively). PRL II significantly reduced VF incidence (to 25%) as well as VT duration (18.21 ± 3.09) and these effects were markedly different from PRL I and from the control group (p<0.05). Both PRL reduced PRP in the recovery phase (p<0.05).

CONCLUSIONS

We proved that supraphysiological doses of PRL isoforms administered in bolus could protect against sudden cardiac death as well as severe arrhythmias episodes during re-perfusion. Because of PRL's positive influence on the cardiovascular system and as an endogenous, well-tolerated substance, it might be of potential clinical use.

Identification of SPRED2 (sprouty-related protein with EVH1 domain 2) as a negative regulator of the hypothalamic-pituitary-adrenal axis

Sprouty-related proteins with EVH1 (enabled/vasodilator-stimulated phosphoprotein homology 1) domain (SPREDs) are inhibitors of MAPK signaling. To elucidate SPRED2 in vivo function, we characterized body homeostasis in SPRED2(-/-) mice. They showed a doubled daily water uptake, induced by elevated serum osmolality, originating from increased blood salt load. Accordingly, serum aldosterone was doubled, accompanied by augmented adrenal aldosterone synthase (AS) expression. Surprisingly, serum vasopressin (AVP) was unaltered, and, as evidenced by halved angiotensin II (Ang II) levels, the renin angiotensin system (RAS) was down-regulated. Adrenocorticotropic hormone (ACTH) was significantly elevated in SPRED2(-/-) mice, together with its secretagogue corticotropin-releasing hormone (CRH) and its downstream target corticosterone. ERK phosphorylation in brains was augmented, and hypothalamic CRH mRNA levels were elevated, both contributing to the increased CRH release. Our data were supported by CRH promoter reporter assays in hypothalamic mHypoE-44 cells, revealing a SPRED-dependent inhibition of Ets (ERK/E-twenty-six)-dependent transcription. Furthermore, SPRED suppressed CRH production in these cells. In conclusion, our study suggests that SPRED2 deficiency leads to an increased MAPK signaling, which results in an augmented CRH promoter activity. The subsequent CRH overproduction causes an up-regulation of downstream hypothalamic-pituitary-adrenal (HPA) hormone secretion. This constitutes a possible trigger for the observed compulsive grooming in SPRED2(-/-) mice and may, together with hyperplasia of aldosterone-producing cells, contribute to the hyperaldosteronism and homeostatic imbalances.

Bridging the gap between GPCR activation and behaviour: oxytocin and prolactin signalling in the hypothalamus

Neuropeptides of the brain are important neuromodulators, controlling behaviour and physiology. They signal through G protein-coupled receptors (GPCR) that couple to complex intracellular signalling pathways. These signalling networks integrate information from multiple sources, resulting in appropriate physiological and behavioural responses to environmental and internal cues. This paper will focus on the neuropeptides oxytocin and prolactin with respect to (1) the regulation of neuroendocrine stress responses and anxiety, and (2) the receptor-mediated molecular mechanisms underlying these actions of the neuropeptides. Besides its significant reproductive functions when released into the bloodstream, brain oxytocin reduces the activity of the hypothalamo-pituitary-adrenal (HPA) axis as well as anxiety-related behaviour in male and female rats. Oxytocin mediates its anxiolytic effect, at least in part, via binding to its GPCR in the hypothalamic paraventricular nucleus, followed by transactivation of the epidermal growth factor receptor, and subsequent activation of a MEK-extracellular signal-regulated kinase (ERK) MAP kinase pathway. Prolactin, by binding to its GPCR receptors, of which there are short and long forms, also activates ERK, and this is necessary for the control of the expression of corticotrophin-releasing hormone-an important regulator of the HPA axis. Liganded oxytocin and prolactin may also recruit other signalling pathways, but how these pathways contribute to the observed behavioural and physiological effects remains to be established. GPCR-mediated oxytocin and prolactin neuronal signalling are illustrative of the complexity of GPCR-activated regulation of appropriate neuroendocrine and behavioural responses to environmental and physiological demands.

Prolactin induces Egr-1 gene expression in cultured hypothalamic cells and in the rat hypothalamus

Prolactin (PRL), the major lactogenic hormone, acts also as neuromodulator and regulator of neuronal and glial plasticity in the brain. There is an increase in synthesis and release of PRL within the hypothalamus during peripartum and in response to stress. To identify mechanisms by which PRL induces neuroplasticity, we studied the ability of PRL to induce the transcription factor Egr-1 in the hypothalamic cell line, 4B, in vitro, and in specific neuronal cell types of the hypothalamus in vivo. PRL induced Egr-1 mRNA expression in 4B cells, an effect which was prevented by the MEK inhibitor, U0126. In vivo, intracerebroventricular PRL (1 microg) increased Egr-1 mRNA levels in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON) of female rats. The increase in mRNA paralleled elevated Egr-1 protein expression in the PVN and SON. Double staining immunohistochemistry revealed Egr-1 localization in oxytocin neurons of the PVN and SON, but not in vasopressin neurons in these regions. In the dorsomedial PVN, a population of non-oxytocin or vasopressin cells localized in a region corresponding to corticotropin-releasing hormone neurons also showed marked Egr-1 immunoreactivity. The data suggest that PRL modulates plasticity in oxytocinergic neurons, through MAP kinase-dependent induction of Egr-1.