Passage of progesterone into the brain changes with photoperiod in the ewe

Photoperiod alters the choroid plexus response to LPS-induced acute inflammation in EWES

This study determined the influence of photoperiod on the expression of toll-like receptor 2 and 4 (TLR2 and TLR4), interleukin 1□ (IL1B), IL-1 receptor type I (IL1R1) and II (IL1R2), interleukin 6 (IL6), the IL-6 receptor (IL6R) and signal transducer (IL6ST), tumor necrosis factor α (TNF), and TNF□ receptor type I (TNFRSF1A) and II (TNFRSF1B) in the choroid plexus (ChP) of ewes with lipopolysaccharide (LPS)-induced acute inflammation. Under short-days (SD, n = 12, anestrous) and long-days (LD, n = 12, synchronized follicular phase), ewes were treated with saline or LPS. Compared to LD conditions, the ewes under SD were characterized by a greater (P<0.05) area under the curve (AUC) of cortisol in the LPS-treated group and by a lower (P<0.05) AUC of prolactin in the saline-treated group. Under both photoperiods, LPS increased (P<0.05) the expression of all examined genes except for TNFRSF1B (only under SD), TNF and TNFRSF1A (no stimulation), and IL6R (decreased (P<0.05) under SD). The LPS-induced increases in TLR2, TLR4, IL1B and its receptors, IL6 and TNFRSF1B were higher (P<0.05) under SD than LD. TLR4 was positively correlated with IL1B and IL6 in both saline- (r2 = 0.64, P<0.01 and r2 = 0.52, P<0.01) and LPS-treated (r2 = 0.81, P<0.0001 and r2 = 0.51, P<0.001) ewes. IL1B (r2 = 0.56, P<0.01 and r2 = 0.77, P<0.0001) and IL6 (r2 = 0.77, P<0.005 and r2 = 0.35, P<0.05) were positively correlated with TLR2 in saline- and LPS-treated ewes, respectively. This indicates that in ewes, the ChP response to acute systemic inflammation is dependent upon the photoperiod with stronger effects being observed under SD. Our results also suggest that gonadal hormones altering TLR4 signaling events are involved in the photoperiodic modulation of the ChP response to LPS. Further experiments are required to explain the mechanism involved in this phenomenon.

Photoperiod Affects Leptin Action on the Choroid Plexus in Ewes Challenged with Lipopolysaccharide-Study on the mRNA Level

The ovine choroid plexus (ChP) expresses the long isoform of the leptin receptor, which makes this structure a potential target for leptin action. In sheep, leptin concentration in plasma is higher during long days (LD) than short days (SD). This study evaluates the influence a of photoperiod on leptin impact on the gene expression of Toll-like receptor 4 (TLR4), proinflammatory cytokines (IL1B, IL6), their receptors (IL1R1, IL1R2, ILRN, IL6R, IL6ST) and inflammasome components necessary for pro-IL-1β activation (NLRP3, PYCARD, CASP1), chemokine (CCL2), leptin receptor isoforms (LEPRa, LEPRb) and a suppressor of cytokine signalling (SOCS3) in the ChP of ewes treated or not with lipopolysaccharide (LPS). Studies were conducted on adult female sheep divided into four groups (n = 6 in each): control, leptin (20 μg/kg), LPS (400 ng/kg), and LPS and leptin injected under SD and LD photoperiods. The leptin alone did not affect the gene expression but in co-treatment with LPS increased (p < 0.05) IL1B but only during SD, and SOCS3, IL1R2, IL1RN, IL6ST and CCL2 only during LD, and decreased (p < 0.05) the IL1R1 expression only during SD photoperiod. This indicates that the immunomodulatory action of leptin on the ChP is manifested only under the LPS challenge and is photoperiodically dependent.

Steroid profiles in quail brain and serum: Sex and regional differences and effects of castration with steroid replacement

Both systemic and local production contribute to the concentration of steroids measured in the brain. This idea was originally based on rodent studies and was later extended to other species, including humans and birds. In quail, a widely used model in behavioural neuroendocrinology, it was demonstrated that all enzymes needed to produce sex steroids from cholesterol are expressed and active in the brain, although the actual concentrations of steroids produced were never investigated. We carried out a steroid profiling in multiple brain regions and serum of sexually mature male and female quail by gas chromatography coupled with mass spectrometry. The concentrations of some steroids (eg, corticosterone, progesterone and testosterone) were in equilibrium between the brain and periphery, whereas other steroids (eg, pregnenolone (PREG), 5α/β-dihydroprogesterone and oestrogens) were more concentrated in the brain. In the brain regions investigated, PREG sulphate, progesterone and oestrogen concentrations were higher in the hypothalamus-preoptic area. Progesterone and its metabolites were more concentrated in the female than the male brain, whereas testosterone, its metabolites and dehydroepiandrosterone were more concentrated in males, suggesting that sex steroids present in quail brain mainly depend on their specific steroidogenic pathways in the ovaries and testes. However, the results of castration experiments suggested that sex steroids could also be produced in the brain independently of the peripheral source. Treatment with testosterone or oestradiol restored the concentrations of most androgens or oestrogens, respectively, although penetration of oestradiol in the brain appeared to be more limited. These studies illustrate the complex interaction between local brain synthesis and the supply from the periphery for the steroids present in the brain that are either directly active or represent the substrate of centrally located enzymes.

Plasma and cerebrospinal fluid interleukin-1β during lipopolysaccharide-induced systemic inflammation in ewes implanted or not with slow-release melatonin

Background

Interleukin-1β (IL-1β) is important mediator of inflammatory-induced suppression of reproductive axis at the hypothalamic level. At the beginning of inflammation, the main source of cytokines in the cerebrospinal fluid (CSF) is peripheral circulation, while over time, cytokines produced in the brain are more important. Melatonin has been shown to decrease pro-inflammatory cytokines concentration in the brain. In ewes, melatonin is used to advance the onset of a breading season. Little is known about CSF concentration of IL-1β in ewes and its correlation with plasma during inflammation as well as melatonin action on the concentration of IL-1β in blood plasma and the CSF, and brain barriers permeability in early stage of lipopolysaccharide (LPS)-induced inflammation.

Methods

Systemic inflammation was induced through LPS administration in melatonin- and sham-implanted ewes. Blood and CSF samples were collected before and after LPS administration and IL-1β and albumin concentration were measured. To assess the functions of brain barriers albumin quotient (QAlb) was used. Expression of IL-1β (Il1B) and its receptor type I (Il1r1) and type II (Il1r2) and matrix metalloproteinase (Mmp) 3 and 9 was evaluated in the choroid plexus (CP).

Results

Before LPS administration, IL-1β was on the level of 62.0 ± 29.7 pg/mL and 66.4 ± 32.1 pg/mL in plasma and 26.2 ± 5.4 pg/mL and 21.3 ± 8.7 pg/mL in the CSF in sham- and melatonin-implanted group, respectively. Following LPS it increased to 159.3 ± 53.1 pg/mL and 197.8 ± 42.8 pg/mL in plasma and 129.8 ± 54.2 pg/mL and 139.6 ± 51.5 pg/mL in the CSF. No correlations was found between plasma and CSF IL-1β concentration after LPS in both groups. The QAlb calculated before LPS and 6 h after was similar in all groups. Melatonin did not affected mRNA expression of Il1B, Il1r1 and Il1r2 in the CP. The mRNA expression of Mmp3 and Mmp9 was not detected.

Conclusions

The lack of correlation between plasma and CSF IL-1β concentration indicates that at the beginning of inflammation the local synthesis of IL-1β in the CP is an important source of IL-1β in the CSF. Melatonin from slow-release implants does not affect IL-1β concentration in plasma and CSF in early stage of systemic inflammation.

Analytical challenges for measuring steroid responses to stress, neurodegeneration and injury in the central nervous system

Levels of steroids in the adult central nervous system (CNS) show marked changes in response to stress, degenerative disorders and injury. However, their analysis in complex matrices such as fatty brain and spinal cord tissues, and even in plasma, requires accurate and precise analytical methods. Radioimmunoassays (RIA) and enzyme-linked immunosorbent assays, even with prepurification steps, do not provide sufficient specificity, and they are at the origin of many inconsistent results in the literature. The analysis of steroids by mass spectrometric methods has become the gold standard for accurate and sensitive steroid analysis. However, these technologies involve multiple purification steps prone to errors, and they only provide accurate reference values when combined with careful sample workup. In addition, the interpretation of changes in CNS steroid levels is not an easy task because of their multiple sources: the endocrine glands and the local synthesis by neural cells. In the CNS, decreased steroid levels may reflect alterations of their biosynthesis, as observed in the case of chronic stress, post-traumatic stress disorders or depressive episodes. In such cases, return to normalization by administering exogenous hormones or by stimulating their endogenous production may have beneficial effects. On the other hand, increases in CNS steroids in response to acute stress, degenerative processes or injury may be part of endogenous protective or rescue programs, contributing to the resistance of neural cells to stress and insults. The aim of this review is to encourage a more critical reading of the literature reporting steroid measures, and to draw attention to the absolute need for well-validated methods. We discuss reported findings concerning changing steroid levels in the nervous system by insisting on methodological issues. An important message is that even recent mass spectrometric methods have their limits, and they only become reliable tools if combined with careful sample preparation.

Interface between metabolic balance and reproduction in ruminants: focus on the hypothalamus and pituitary

This article is part of a Special Issue "Energy Balance". The interface between metabolic regulators and the reproductive system is reviewed with special reference to the sheep. Even though sheep are ruminants with particular metabolic characteristics, there is a broad consensus across species in the way that the reproductive system is influenced by metabolic state. An update on the neuroendocrinology of reproduction indicates the need to account for the way that kisspeptin provides major drive to gonadotropin releasing hormone (GnRH) neurons and also mediates the feedback effects of gonadal steroids. The way that kisspeptin function is influenced by appetite regulating peptides (ARP) is considered. Another newly recognised factor is gonadotropin inhibitory hormone (GnIH), which has a dual function in that it suppresses reproductive function whilst also acting as an orexigen. Our understanding of the regulation of food intake and energy expenditure has expanded exponentially in the last 3 decades and historical perspective is provided. The function of the regulatory factors and the hypothalamic cellular systems involved is reviewed with special reference to the sheep. Less is known of these systems in the cow, especially the dairy cow, in which a major fertility issue has emerged in parallel with selection for increased milk production. Other endocrine systems--the hypothalamo-pituitary-adrenal axis, the growth hormone (GH) axis and the thyroid hormones--are influenced by metabolic state and are relevant to the interface between metabolic function and reproduction. Special consideration is given to issues such as season and lactation, where the relationship between metabolic hormones and reproductive function is altered.

Pattern of expression of vascular endothelial growth factor and its receptors in the ovine choroid plexus during long and short photoperiods

Vascular endothelial growth factor (VEGF-A) plays an important role in maintaining cerebrospinal fluid (CSF) homeostasis and the function of the choroid plexuses (CPs). The objective of the study was to determine the expression of vascular endothelial growth factor (VEGF-A), tyrosine kinase receptors Flt-1 and KDR and KDR co-receptor neuropilin 1 (NRP-1) in ovine CPs during different photoperiods. CPs were collected from the lateral brain ventricles from ovariectomized, estradiol-treated ewes during long day (LD; 16L:8D, n = 5) and short day (SD; 8L:16D, n = 5) photoperiods. We analyzed mRNA expression levels of two VEGF-A isoforms, VEGF-A₁₂₀ and VEGF-A₁₆₄ and our results indicate that VEGF-A₁₆₄ was the predominant isoform. Expression levels of VEGF-A and Flt-1 were similar during the SD and LD photoperiods. There were significant increases in KDR mRNA and protein expression (p < 0.05) and NRP-1 mRNA expression (p < 0.05) during SD. These data show that expression of KDR and its co-receptor NRP-1 are up-regulated by short photoperiod and that this effect is not dependent on ovarian steroids. Our results suggest that the VEGF-A-system may be involved in photoperiodic plasticity of CP capillaries and may therefore be responsible for photoperiodic changes in the CSF turnover rate in ewes.

Photoperiod modulates access of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) to the brain and its effect on gonadotropin and thyroid hormones in adult ewes

The effects of photoperiod on the cerebrospinal fluid (CSF) concentration of six ortho-substituted polychlorinated biphenyls (PCBs: PCB28, PCB52, PCB101, PCB138, PCB153, and PCB180), the effects of an orally administered low dose of PCB153 (0.3mg/kg, three times a week for three weeks) on PCBs and thyroid hormones (THs) concentrations in the CSF and plasma, and the release of luteinizing hormone (LH) were determined in ovariectomized, estradiol-implanted ewes (2.5 years old) maintained indoors under artificial long day (LD, 16L: 8D) and short day (SD, 8L: 16D) conditions. Concentrations of two PCBs (PCB28 and PCB153) in the plasma and four PCBs in the CSF (PCB101, PCB138, PCB153, and PCB180) were significantly higher during LD than SD. Following PCB153 treatment, its concentration in the plasma was higher in SD (1.2 ± 0.3 ng/ml) than LD (0.2 ± 0.05 ng/ml), but similar in the CSF (10.2 ± 3.7 pg/ml vs. 13 ± 0.7 pg/ml) under both photoperiods. During SD, the concentration of PCB153 in the CSF was higher in treated animals than controls, while no differences were noted under LD. These findings indicate that in ewes, exposure of the brain to more highly chlorinated, ortho-substituted PCBs may be modulated by photoperiod. PCB153 treatment had no effect on plasma THs, but reduced total triiodothyronine concentration during LD and free thyroxine during SD in the CSF. Under both photoperiods, PCB153 reduced basal plasma LH and reinforced the inhibition of pulsatile LH release during LD. As PCB153 reduced LH and THs (which are involved in the seasonal control of reproduction in ewes), it may have a braking effect on seasonal transitions between active and inactive phases of reproduction.

Tight junction proteins vary in the choroid plexus of ewes according to photoperiod

Sheep from temperate latitudes exhibit seasonal variations in many physiological functions such as reproduction, food intake, body weight, and pelage growth. Majority of seasonal changes are controlled by the annual photoperiodic cycle and melatonin secretion. For reproduction, the resulting key event is a modulation of the negative feedback of steroids on gonadotropin secretion. However, this seasonal effect could also depend on variable uptake of steroids by the brain. Seasonal regulation of food intake also involves numerous peripheral hormones, among which the protein hormone leptin informs the brain on the metabolic status of the animal. It has been shown previously that access of progesterone, estradiol and leptin to the cerebrospinal fluid (CSF) increases under long days. This physiological modulation of the passage of hormones to the brain could depend on regulation of the permeability of the blood-CSF barrier. This study therefore compared the tight junction proteins in the choroid plexus of ewes exposed to short days or long days. Levels of occludin, zonula occludens proteins (ZO) ZO-1 and ZO-2, afadin and cadherin were significantly higher during short days, but no statistical difference was observed for junctional adhesion molecule 1 (JAM-1), ZO-3 or claudins 1 and 5. These results are consistent with an increase in the blood-CSF barrier permeability during long days through a regulation of tight junctions and show that the permeability could depend upon physiological conditions such as photoperiodic status.

Turnover rate of cerebrospinal fluid in female sheep: changes related to different light-dark cycles

BACKGROUND

Sheep are seasonal breeders. The key factor governing seasonal changes in the reproductive activity of the ewe is increased negative feedback of estradiol at the level of the hypothalamus under long-day conditions. It has previously been demonstrated that when gonadotropin secretions are inhibited during long days, there is a higher concentration of estradiol in the cerebrospinal fluid (CSF) than during short days. This suggests an involvement of the CSF and choroid plexus in the neuroendocrine regulatory loop, but the mechanisms underlying this phenomenon remain unknown. One possible explanation of this difference in hormonal content is an effect of concentration or dilution caused by variations in CSF secretion rate. The aim of this study was thus to investigate changes in the CSF turnover rate related to light-dark cycles.

METHODS

The turnover rate of the CSF was estimated by measuring the time taken for the recovery of intraventricular pressure (IVP) after removal of a moderate volume (0.5 to 2 ml) of CSF (slope in mmHg/min). The turnover rate was estimated three times in the same group of sheep: during a natural period of decreasing day-length corresponding to the initial period when gonadotropin activity is stimulated (SG1), during a long-day inhibitory period (IG), and finally during a short-day stimulatory period (SG2).

RESULTS

The time taken and the speed of recovery of initial IVP differed between groups: 8 min 30 sec, 0.63 +/- 0.07 mmHg/min(SG1), 11 min 1 sec, 0.38 +/- 0.06 mmHg/min (IG) and 9 min 0 sec, 0.72 +/- 0.15 mmHg/min (SG2). Time changes of IVP differed between groups (ANOVA, p < 0.005, SG1 different from IG, p < 0.05). The turnover rate in SG2: 183.16 +/- 23.82 mul/min was not significantly different from SG1: 169. 23 +/- 51.58 mul/min (Mann-Whitney test, p = 0.41), but was significantly different from IG: 71.33 +/- 16.59 mul/min (p = 0.016).

CONCLUSION

This study shows that the turnover rate of CSF in ewes changes according to the light-dark cycle; it is increased during short day periods and reduced in long day periods. This phenomenon could account for differences in hormonal concentrations in the CSF in this seasonal species.

5-hydroxyoxindole, an indole metabolite, is present at high concentrations in brain

5-Hydroxyoxindole has been identified as a urinary metabolite of indole, which is produced from tryptophane via the tryptophanase activity of gut bacteria. We have demonstrated recently that 5-hydroxyoxindole is an endogenous compound in blood and tissues of mammals, including humans. To date, 5-hydroxyoxindole's role is unknown. The aim of this study was to compare 5-hydroxyoxindole levels in plasma and cerebrospinal fluid (CSF) during day-night and seasonal changes, as a common approach to pilot physiological characterization of any compound. Simultaneous blood and CSF sampling was performed in the ewe, because its size allows collection in quantities suitable for 5-hydroxyoxindole assay (HPLC-ED) in awake animals, without obvious physiological or behavioral disturbance. 5-Hydroxyoxindole concentration was quite stable in plasma (2-6 nM range), whereas, in CSF, it displayed marked day-night and photoperiodic variations (4-116 nM range). 5-Hydroxyoxindole levels in CSF were twofold higher at night than during the day and at least one order of magnitude higher during the long compared with the short photoperiod. These day/night and photoperiodic variations persisted after pinealectomy, indicating that 5-hydroxyoxindole rhythms in CSF are independent of melatonin formation. In conclusion, high levels of 5-hydroxyoxindole in the CSF during long photoperiod and its daily modulation suggest physiological involvement of 5-hydroxyoxindole in rhythmic adjustments in the brain, independently of the pineal gland.

Concentrations of estradiol in ewe cerebrospinal fluid are modulated by photoperiod through pineal-dependent mechanisms

In the ewe, seasonal anestrus results from an increased responsiveness of the hypothalamus to the negative feedback of estradiol (E2) on the gonadotropic axis under long-day conditions. However, this seasonal effect could also depend upon variable uptake of steroids by the brain. The aim of the present experiment was to compare the concentration of E2 in the blood plasma and in the cerebrospinal fluid (CSF) from the third ventricle in groups of ovariectomized, estradiol treated ewes maintained under short day (SD) or long day (LD) conditions and to study the involvement of the pineal gland in this photoperiodic regulation. Pinealectomized and sham-operated ewes were equipped with an intracerebral cannula to sample the CSF. The plasma E2 concentrations showed no difference between LD and SD in sham-operated and pinealectomized animals. In contrast, in the CSF, E2 concentration was higher in the LD than the SD group, and pinealectomy suppressed this effect of photoperiod. Concomitantly, the stimulatory effect of SD on luteinizing hormone levels observed in sham-operated ewes was abolished by pinealectomy. The results demonstrate that LD increases the E2 concentration in the CSF by a mechanism involving the pineal gland.

Seasonal Regulation of Reproductive Activity in Sheep

Sheep in temperate latitudes are seasonal breeders. In female sheep, ovarian activity decreases during the anestrous period due to modification of secretion of luteinizing hormone (LH). The seasonal changes in the hormonal LH pattern mainly reflect an increase in the brain responsiveness to the negative feedback exerted by estradiol during long days (LD) on the frequency of pulsatile LH secretion, under neurohormonal GnRH control. The resulting seasonal inhibition of LH secretion mainly involves the activation of dopaminergic systems by E2, which in turn inhibits the GnRH cells from the preoptico-hypothalamic structures. The increased responsiveness of the brain during LD could lead to increased expression of central E2 receptors. In addition, our study shows that steroid access to the brain could be modulated by photoperiodism, thus increasing the availability of steroids to the nervous structures during LD.