Pregnancy and lactation are metabolically challenging states, where the mother must supply all the energy requirements for the developing fetus and growing pups respectively. The aim of the current study was to characterize many aspects of energy homeostasis before and during pregnancy in the mouse, and to examine the role of voluntary activity on changes in energy expenditure during pregnancy. In a secondary aim, we evaluate measures of energy homeostasis during pregnancy in mice that successfully reared their litter or in mice that went on to abandon their litter, to determine if an impairment in pregnancy-induced adaptation of energy homeostasis might underlie the abandonment of pups soon after birth. During pregnancy, food intake was increased, characterized by increased meal size and duration but not number of meals per day. The duration of time spent inactive, predicted to indicate sleep behaviour, was increased both early and late in pregnancy compared to pre-pregnancy levels. Increased x + y beam breaks, as a measure of activity increased during pregnancy and this reflected an increase in ambulatory behaviour in mid pregnancy and an increase in non-ambulatory movement in late pregnancy. Energy expenditure, as measured by indirect calorimetry, increased across pregnancy, likely due to the growth and development of fetal tissue. There was also a dramatic reduction in voluntary wheel running as soon as the mice became pregnant. Compared with successful pregnancies and lactations, pregnancies where pups were abandoned soon after birth were associated with reduced body weight gain and an increase in running wheel activity at the end of pregnancy, but no difference in food intake or energy expenditure. Overall, during pregnancy there are multiple adaptations to change energy homeostasis, resulting in partitioning of provisions of energy to the developing fetus and storing energy for future metabolic demands.

In the stargazer mouse model of absence epilepsy, altered corticothalamic excitation of reticular thalamic nucleus (RTN) neurons has been suggested to contribute to abnormal synchronicity in the corticothalamic-thalamocortical circuit, leading to spike-wave discharges, the hallmark of absence seizures. AMPA receptor expression and function are decreased in stargazer RTN, due to a mutation of AMPAR auxiliary subunit stargazin. It is unresolved and debated, however, if decreased excitation of RTN is compatible with epileptogenesis. We tested the hypothesis that relative NMDAR expression may be increased in RTN and/or thalamic synapses in stargazers using Western blot on dissected thalamic nuclei and biochemically isolated synapses, as well as immunogold cytochemistry in RTN. Expression of main NMDAR subunits was variable in stargazer RTN and relay thalamus; however, mean expression values were not statistically significantly different compared to controls. Furthermore, no systematic changes in synaptic NMDAR levels could be detected in stargazer thalamus. In contrast, AMPAR subunits were markedly decreased in both nucleus-specific and synaptic preparations. Thus, defective AMPAR trafficking in stargazer thalamus does not appear to lead to a ubiquitous compensatory increase in total and synaptic NMDAR expression, suggesting that elevated NMDAR function is not mediated by changes in protein expression in stargazer mice.

Among its many functions, prolactin has been implicated in energy homeostasis, particularly during pregnancy and lactation. The arcuate nucleus is a key site in the regulation of energy balance. The present study aimed to examine whether arcuate nucleus neuronal populations involved in energy homeostasis are prolactin responsive and whether they can mediate the effects of prolactin on energy homeostasis. To determine whether Agrp neurones or Rip‐Cre neurones are prolactin responsive, transgenic mice expressing the reporter td‐tomato in Agrp neurones (td‐tomato/Agrp‐Cre) or Rip‐Cre neurones (td‐tomato/Rip‐Cre) were treated with prolactin and perfused 45 minutes later. Brains were processed for double‐labelled immunohistochemistry for pSTAT5, a marker of prolactin‐induced intracellular signalling, and td‐tomato. In addition, Agrp‐Cre mice and Rip‐Cre mice were crossed with mice in which the prolactin receptor gene (Prlr) was flanked with LoxP sites (Prlrlox/lox mice). The Prlrlox/lox construct was designed such that Cre‐mediated recombination resulted in deletion of the Prlr and expression of green fluorescent protein (GFP) in its place. In td‐tomato/Rip‐Cre mice, prolactin‐induced pSTAT5 was co‐localised with td‐tomato, indicating that there is a subpopulation of Rip‐Cre neurones in the arcuate nucleus that respond to prolactin. Furthermore, mice with a specific deletion of Prlr in Rip‐Cre neurones had lower body weights, increased oxygen consumption, increased running wheel activity and numerous cells in the arcuate nucleus had positive GFP staining indicating deletion of Prlr from Rip‐Cre neurones. By contrast, no co‐localisation of td‐tomato and pSTAT5 was observed in td‐tomato/Agrp‐Cre mice after prolactin treatment. Moreover, Prlrlox/lox/Agrp‐Cre mice had no positive GFP staining in the arcuate nucleus and did not differ in body weight compared to littermate controls. Overall, these results indicate that Rip‐Cre neurones in the arcuate nucleus are responsive to prolactin and may play a role in the orexigenic effects of prolactin, whereas prolactin does not directly affect Agrp neurones.

Prolactin is a pleiotropic peptide hormone produced by the lactotrophs in the anterior pituitary. Its rate of secretion is primarily regulated by a negative-feedback mechanism where prolactin stimulates the activity of the tuberoinfundibular dopaminergic (TIDA) neurones, increasing their release of dopamine, which accesses the pituitary via the median eminence to suppress further prolactin secretion. In addition to its well established role in lactation, circulating prolactin is secreted in response to stress, although the mechanism by which this is achieved or its cellular targets remains unknown. In the present study, we show that 15minutes of restraint stress causes an approximately seven-fold increase in circulating prolactin concentration in male mice. Monitoring prolactin receptor activation, using immunohistochemistry to determine the level and distribution of tyrosine phosphorylated signal transducer and activator of transcription 5 (pSTAT5), we show that this stress-induced increase in prolactin interacts with both central and peripheral targets. Restraint stress for 15minutes significantly increased pSTAT5 staining in the arcuate nucleus, median eminence and the zona fasciculata of the adrenal cortex. In each case, this response was prevented by pretreating the animals with bromocriptine to block prolactin secretion from the pituitary. Interestingly, in contrast to many cells in the arcuate nucleus, stress reduced pSTAT5 staining of the TIDA neurones (identified by dual-labelling for tyrosine hydroxylase). This suggests that there is reduced prolactin signalling in these cells and thus potentially a decline in their inhibitory influence on prolactin secretion. These results provide evidence that prolactin secreted in response to acute stress is sufficient to activate prolactin receptors in selected target tissues known to be involved in the physiological adaptation to stress.

In common forms of obesity, leptin fails to convey its regulatory effect. This so called “leptin resistance” is not well understood, and solving this puzzle is a key to understanding how obesity develops. In the present study, we investigated the temporal and regional onset of leptin resistance in response to a diet enriched with long‐chain saturated fatty acids (high‐fat diet; HFD) in mice. Mice were exposed to either a low‐fat diet (LFD) or a HFD for 4 hours, 24 hours, 10 days and 28 days. Mice in each group received an i.p. injection of either phosphate‐buffered saline or leptin and the number of phosphorylated signal transducer and activator of transcription‐3 (pSTAT3) immunoreactive (‐IR) cells in the arcuate nucleus (ARC), ventromedial nucleus of the hypothalamus (VMH) and dorsomedial nucleus of the hypothalamus (DMH) was analysed 30 or 120 minutes after treatment. In the ARC, as soon as 24 hours of HFD, the molecular leptin response was reduced by 40% (P≤.01). Compared to at 24 hours, after 10 days, the number of leptin‐induced pSTAT3‐IR cells was elevated after 120 minutes, suggesting a sustained response and a partial return of leptin sensitivity. After 28 days, leptin failed to induce the number of pSTAT3‐IR over control levels, suggesting a markedly reduced sensitivity to leptin. In the VMH after 24 hours, we observed a 50% reduction in leptin‐induced pSTAT‐3‐IR cells, followed by a further decline after 10 days. However, after 28 days, there was a significant increase in pSTAT‐3‐IR cells (P≤.05), indicating partial recovery of leptin sensitivity. By contrast to these two regions, in the DMH, no loss of leptin sensitivity was observed at any time‐point. These findings demonstrate that a loss of sensitivity to leptin occurs rapidly after exposure to HFD in the ARC and VMH but not the DMH. However, there appears to be a biphasic pattern of leptin responsiveness, with a partial return of leptin sensitivity occurring after 10 days in the arcuate nucleus, and after 28 days in the VMH. By 28 days, the response to leptin in the arcuate nucleus was completely lost. These findings suggest that the molecular responses to leptin are altered after high‐fat feeding in a time‐ and region‐specific manner.

Maternal stress is associated with negative health consequences for both the mother and her offspring. To prevent these adverse outcomes, activity of the hypothalamic‐pituitary‐adrenal (HPA) axis is attenuated during pregnancy and lactation. Although the mechanisms generating this adaptive change have not been defined fully, the anterior pituitary hormone prolactin may play a significant role. The present study investigated the role of prolactin in regulating the basal activity of the HPA axis during pregnancy and lactation in the mouse, focussing upon the corticotrophin‐releasing hormone (CRH) neurones. Using in situ hybridisation, a decrease in Crh mRNA‐expressing cell number in pregnant (55.6±9.0 cells per section) and lactating (97.4±4.9) mice compared to virgin controls was characterised (186.8±18.7, P <.01 Tukey‐Kramer test; n=6‐7 per group). Removal of the pups (24 hours) and thus the associated suckling‐induced prolactin secretion, restored CRH neurone number (180.1±19.7). To specifically test the role of prolactin in suppressing Crh mRNA expression in lactation, prolactin levels were selectively manipulated in lactating mice. Lactating mice were treated with ovine prolactin (1500 μg day ‐1 , osmotic minipump, s.c.; n=7) or vehicle (n=6) for 24 hours following pup removal. This was sufficient to suppress Crh mRNA expression from 108.0±13.5 to 53.7±16.7 cells per section ( P <.05 Student's t‐test). Additional cohorts of lactating mice were treated with bromocriptine (300 μg over 24 hours, s.c.; n=7) or vehicle (n=5) to suppress endogenous prolactin secretion; however, no change in Crh mRNA expression was detected. Thus, although prolactin was sufficient to suppress Crh mRNA expression in the paraventricular nucleus, it does not appear to be required for the ongoing regulation of the CRH neurones in lactation.

Estrogen deficiency results in disruption of maxillary alveolar bone microarchitecture. Most of the actions of estrogen in long bones occur via estrogen receptor α (ERα). However, the function of ERα in the maxillary bone has not been defined. We aimed to investigate the role and underlying mechanisms of ERα in the physiological and mechanically induced alveolar bone remodeling in female and male mice. Wild-type (WT) and ERα(-/-) (ERKOα) mice were subjected to mechanically stimulated bone remodeling by inducing orthodontic tooth movement (OTM). The maxillary bone was analyzed using histomorphometric analysis, micro-computed tomography, quantitative polymerase chain reaction, and energy-dispersive spectroscopy. Bone marrow cells (BMCs) from WT and ERKOα mice were tested for their capacity to differentiate into osteoblasts and osteoclasts. Both male and female ERKOα mice exhibited marked reduction of alveolar bone mass and increased OTM. This response was associated with an increased number of osteoclasts and reduced number of apoptotic cells and osteoblasts in the periodontium and alveolar bone. Consistently, ERKOα mice exhibited lower levels of calcium in bone and increased expression of IL-33 (interleukin-33), TNF-α (tumor necrosis factor α), and IL-1β (interleukin-1β) and decreased expression of dentin matrix acidic phosphoprotein and alkaline phosphatase in periodontal tissues. Moreover, the differentiation of osteoclasts and osteoblasts in vitro was significantly higher in BMCs obtained from ERKOα. ERα is required to maintain the microarchitecture of maxillary alveolar bone. This process is linked to bone cell differentiation and apoptosis, as well as local production of inflammatory molecules such as IL-33, TNF-α, and IL-1β.

The provision of yolk precursor proteins to the oviparous egg is crucial for normal embryo development. In Echinodermata, a transferrin-like yolk component termed major yolk protein (MYP) is a major precursor protein in Echinoidea and Holothuroidea. In contrast, in Asteroidea a single vitellogenin (Vtg) was recently identified, but its role as primary yolk protein remains unclear. To resolve the apparent MYP-Vtg dichotomy in sea stars and to understand the dynamics of candidate yolk protein gene expression during the reproductive cycle, we investigated the molecular structures of sea star Vtg and MYP and quantified their transcript levels during oogenesis. By combining protein sequencing of the predominant proteins in ovulated eggs of Patiriella regularis with ovarian transcriptome sequencing and molecular cloning, we characterized two cDNAs encoding two bona fide Vtgs (PrVtg1 and PrVtg2) and a partial cDNA encoding MYP (PrMYP). PrMYP mRNA was found in low abundance in growing oocytes, possibly as maternal transcripts for translation after ovulation. In contrast, PrVtg transcripts, whose levels varied during the reproductive cycle, were not found in developing oocytes – rather, they were detected in ovarian follicle cells and pyloric caeca, indicating an extra-oocytic origin. Vtg accumulating in oocytes was stored in the form of cleaved products, which constituted the most abundant yolk polypeptides in ovulated sea star eggs; their levels decreased during early embryonic and larval development. Together, these traits are the hallmarks of a classical yolk protein – and hence, we contend that Vtg, and not MYP, is the main yolk protein in asteroids.

Despite increased leptin concentrations during pregnancy, fat mass and food intake are increased. The satiety response to central leptin is suppressed, indicating a state of leptin insensitivity in the hypothalamus. Although the regulation of food intake is a major function of leptin, this hormone also influences a wide range of functions within the body. These actions include the regulation of glucose homeostasis, which undergoes major adaptation in the maternal body to generate optimal conditions for foetal development and growth. The present study aimed to investigate the effects of central leptin treatment on glucose homeostasis in pregnant rats to determine whether pregnancy‐induced leptin insensitivity is functionally specific, and to further investigate changes in glucose homeostasis during pregnancy. After an overnight fast, nonpregnant and day 14 pregnant rats received an i.c.v. injection of leptin (100 ng or 4 μg) or vehicle then underwent a glucose tolerance test (GTT). Further groups of nonpregnant and day 14 pregnant rats were killed 30 min after leptin (doses ranging from 40 ng–4 μg) or vehicle i.c.v. injections for western blot analysis of phospho‐signal transducer and activator of transcription 3 (STAT3) and phospho‐Akt in various hypothalamic nuclei. Central leptin injection prior to a GTT lead to lowered basal insulin concentrations and impaired glucose tolerance in nonpregnant female rats, whereas the same doses of leptin had no significant effect on glucose tolerance in day 14 pregnant rats, indicating that, similar to the satiety actions of leptin, the effects of leptin on glucose homeostasis are suppressed during pregnancy. Furthermore, in the arcuate nucleus and ventromedial and dorsomedial nuclei of the hypothalamus, comprising three leptin‐sensitive areas, there was no evidence that leptin induced Akt phosphorylation despite significant increases in phospho‐STAT3, suggesting that leptin does not act through phospho‐Akt in these areas in female rats.

La prolactine (PRL) exerce un rétrocontrôle négatif sur sa propre sécrétion et la prolifération des cellules lactotropes par l’activation du tonus inhibiteur dopaminergique de l’hypothalamus. Des modèles murins et des données in vitro suggèrent que la PRL agirait aussi directement sur la cellule lactotrope via son récepteur (PRLR). Notre objectif est de démontrer cet effet autocrine de la PRL. Nous avons généré au laboratoire un modèle de souris invalidé pour le Prlr spécifiquement dans la cellule lactotrope, la souris pit-Prlr KO (PrlCre/+; Prlrflox/flox). Elle a été obtenue par le croisement de souris Prlrflox/flox avec des souris PrlCre/+ exprimant la recombinase Cre sous le contrôle du promoteur hypophysaire de la PRL. Le phénotype des souris femelles pit-Prlr KO est évalué par le suivi des cycles œstriens, le dosage de la prolactine sérique et la réalisation d’IRM hypophysaires à la recherche d’une hyperplasie ou d’un adénome lactotrope. Dès 6 mois, 25 % des souris pit-Prlr KO présentent une hyperprolactinémie versus 0 % des contrôles (Prlrflox/flox et PrlCre/+; Prlrflox/+). L’hyperprolactinémie est associée à une irrégularité des cycles œstriens chez ces souris. À cet âge, les IRM hypophysaires ne mettent pas encore en évidence d’hyperplasie hypophysaire. Le suivi longitudinal et prospectif à 8, 10 et 12 mois, permettra d’affiner leur phénotype. Cette étude préliminaire confirme l’existence d’un rétrocontrôle négatif de la prolactine sur la cellule lactotrope indépendamment du tonus dopaminergique. Ainsi, un défaut de cette voie de signalisation autocrine pourrait être une cause de survenue de prolactinome chez l’homme.

During pregnancy, a state of positive energy balance develops to support the growing fetus and to deposit fat in preparation for the subsequent metabolic demands of lactation. As part of this maternal adaptation, the satiety response to the anorectic peptide -melanocyte stimulating hormone (-MSH) is suppressed. To investigate whether pregnancy is associated with changes in the response of hypothalamic -MSH target neurons, non-pregnant and pregnant rats were treated with -MSH or vehicle and c-fos expression in hypothalamic nuclei was then examined. Furthermore, the firing rate of supraoptic nucleus (SON) oxytocin neurons, a known -MSH responsive neuronal population, was examined in non-pregnant and pregnant rats following -MSH treatment. Intracerebroventricular injection of -MSH significantly increased the number of c-fos-positive cells in the paraventricular, arcuate and ventromedial hypothalamic nuclei in non-pregnant rats, but no significant increase was observed in any of these regions in pregnant rats. In the SON, -MSH did induce expression of c-fos during pregnancy, but this was significantly reduced compared to that observed in the non-pregnant group. Furthermore, during pregnancy, SON oxytocin neurons did not demonstrate the characteristic -MSH-induced inhibition of firing rate that was observed in non-pregnant animals. Melanocortin receptor mRNA levels during pregnancy were similar to non-pregnant animals, suggesting that receptor down-regulation is unlikely to be a mechanism underlying the attenuated responses to -MSH during pregnancy. Given the known functions of -MSH in the hypothalamus, the attenuated responses will facilitate adaptive changes in appetite regulation and oxytocin secretion during pregnancy.

Prolactin is a hormone that is involved in multiple physiological functions in vertebrates. Prolactin receptor mRNA has been identified in the subfornical organ (SFO) through microarray analysis (Hindmarch et al 2008). The current study was therefore carried out in order to determine the effects of prolactin on the excitability of SFO neurons. We used the whole‐cell patch clamp technique to determine the influence of prolactin on the membrane potential of dissociated SFO neurons. We found that 55% (11 of 20) of neurons responded when treated with prolactin (1 uM and 100nM). Of the cells that responded, 54% (n=6) depolarized with a mean depolarization of 7.7 ± 3.3 mV and 46% (n=5) hyperpolarized with a mean hyperpolarization of ‐8.0 ± 3.6 mV. This study suggests the SFO as a potential central nervous system site at which prolactin may act to influence central autonomic integration.Grant Funding Source: Canadian Institutes for Health Research

Hyperprolactinaemia is a major cause of infertility in both males and females, although the mechanism by which prolactin inhibits the reproductive axis is not clear. The aim of the present study was to test the hypothesis that elevated prolactin causes suppression of kisspeptin expression in the hypothalamus, resulting in reduced release of gonadotrophin‐releasing hormone (GnRH) and consequent infertility. In oestrogen‐treated ovariectomised mice, chronic prolactin‐treatment prevented the rise in luteinising hormone (LH) seen in vehicle‐treated mice. Kiss1 mRNA was significantly suppressed in both the rostral periventricular region of the third ventricle (RP3V) and arcuate nucleus after prolactin treatment. Exogenous prolactin treatment induced phosphorylated signal transducer and activator of transcription 5 (pSTAT5) in kisspeptin neurones, and suppression of endogenous prolactin using bromocriptine reduced levels of pSTAT5 in kisspeptin neurones, suggesting that prolactin acts directly on kisspeptin neurones. By contrast, fewer than 1% of GnRH neurones expressed pSTAT5 in either dioestrous or lactating mice. As reported previously, there was significant suppression of kisspeptin mRNA and protein in the RP3V on day 7 of lactation, although not in the arcuate nucleus. Bromocriptine treatment significantly increased Kiss1 mRNA expression in the RP3V, although not to dioestrous levels. Unilateral thelectomy, aiming to eliminate sensory inputs from nipples on one side of the body, failed to alter the reduction in the number of kisspeptin neurones observed in the RP3V. These data demonstrate that chronic prolactin administration suppressed serum LH, and reduced Kiss1 mRNA levels in both the RP3V and arcuate nucleus, consistent with the hypothesis that prolactin‐induced suppression of kisspeptin secretion might mediate the inhibitory effects of prolactin on GnRH secretion. During lactation, however, the suppression of Kiss1 mRNA in the RP3V was only partially reversed by the administration of bromocriptine to block elevated levels of prolactin, suggesting that, although elevated prolactin contributes to lactational anovulation, additional non‐neural factors must also contribute to the lactation‐induced suppression of kisspeptin neurones.

The preoptic area is a well-established centre for the control of maternal behaviour. An intact medial preoptic area (mPOA) is required for maternal responsiveness because lesion of the area abolishes maternal behaviours. Although hormonal changes in the peripartum period contribute to the initiation of maternal responsiveness, inputs from pups are required for its maintenance. Neurones are activated in different parts of the mPOA in response to pup exposure. In the present review, we summarise the potential inputs to the mPOA of rodent dams from the litter that can activate mPOA neurones. The roles of potential indirect effects through increased prolactin levels, as well as neuronal inputs to the preoptic area, are described. Recent results on the pathway mediating the effects of suckling to the mPOA suggest that neurones containing the neuropeptide tuberoinfundibular peptide of 39 residues in the posterior thalamus are candidates for conveying the suckling information to the mPOA. Although the molecular mechanism through which these inputs alter mPOA neurones to support the maintenance of maternal responding is not yet known, altered gene expression is a likely candidate. Here, we summarise gene expression changes in the mPOA that have been linked to maternal behaviour and explore the idea that chromatin remodelling during mother-infant interactions mediates the long-term alterations in gene expression that sustain maternal responding.

Journal of NeuroendocrinologyVolume 25, Issue 12 p. 1239-1240 Editorial Why Should We Choose to Publish in the Journal of Neuroendocrinology? Dave Grattan, Dave Grattan [email protected] Centre for Neuroendocrinology, University of Otago, Dunedin, New ZealandSearch for more papers by this author Dave Grattan, Dave Grattan [email protected] Centre for Neuroendocrinology, University of Otago, Dunedin, New ZealandSearch for more papers by this author First published: 07 November 2013 https://doi.org/10.1111/jne.12119Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume25, Issue12December 2013Pages 1239-1240 RelatedInformation