Affective Behavior Shows Sex Differences in Mid-adulthood Rats Following Postnatal Immune Stimulation.

Mid-adulthood represents the critical window period usually associated with the development of age-related diseases. Despite several attempts to delineate the pathological mechanisms underlying postnatal immune challenge and altered brain functions, the role of sex-dependent changes in affective behaviors of middle-aged animals requires more attention. In this study, we sought to investigate behavioral and molecular response patterns at mid-adulthood linked to early-life immune activation. Using affective behavioral test batteries, we showed that lipopolysaccharide (LPS)-induced postnatal immune challenge caused anxiety-like behaviors in both male and female Wistar rats at mid-adulthood, whereas only female rats exhibited depression-like behaviors. Our data further demonstrated a significant increase in microglial complexity and increased levels of tumor necrosis factor (TNFα), nitric oxide (NOx), and lipid peroxidation in the prefrontal cortex of female rats compared to their male counterparts and phosphate-buffered saline (PBS) littermate controls. With these results, we established significant interaction between sex differences and LPS-induced alterations in behavior and associated oxidative and immunohistochemical changes. These findings may provide an insight to better understand the neuroimmunological mechanisms of sex-dependent brain pathological manifestations occurring at mid-adulthood.

The sex differences of the behavior response to early Life immune stimulation: Microglia and astrocytes involvement.

It is well known that inflammatory challenge during the prenatal period results in permanent changes in glial cells and behavior in adulthood. However, it is unknown whether inflammatory challenge during the infantile period may have permanent sexually-dimorphic effects on microglia and astrocytes in vivo, which in turn may be associated with sex differences in adult behavior. In this study, we have evaluated whether postnatal injection of lipopolysaccharide (LPS; 250µg/kg, i.p. on postnatal day 14) induces depressive and less anxiety-like behaviors, glial cell activation, pro-inflammatory cytokine (TNF-alpha) secretion and sexually dimorphic responses in adulthood. Postnatal day 14 (P14) male and female Wistar rats received an intraperitoneal (ip) injection of LPS or PBS. Three months later, animals were tested in the Open Field (OF), the Elevated Plus Maze (EPM) and the Forced Swimming Test (FST) to assess the level of anxiety and depression-like behavior. Hippocampal proinflammatory cytokine TNF-alpha concentration and the number of astrocytes and microglia were estimated in the dentate gyrus, CA1, and CA3 in two regions of the hippocampus (ventral and dorsal). Our results showed that the administration of LPS resulted in less anxiety and depression-like behavior in males but not in females. However, the LPS-administration increased the number of microglia in the dorsal and ventral hippocampus areas in females more than male, while no significant differences in TNFα level had been detected between the LPS-rats treated and their controls. Interestingly, LPS resulted in an increase in the number of astrocytes in both areas of the hippocampus in a female. While in a male, our results showed a decrease in astrocytes number in the dorsal hippocampus, but no significant differences observed in ventral hippocampus. These findings indicate that an immune challenge in infantile rats induces a ventral and dorsal hippocampus damage in female more than in male, without affecting significantly the affective behavior changes in the female. The results also showed that small changes in the male hippocampus can affect the behavior and induce a depression-like behavior.

Thymelaea lythroides extract attenuates microglial activation and depressive-like behavior in LPS-induced inflammation in adult male rats.

Thymelaea lythroides extract is widely used as a traditional folk medicine in Morocco, especially for the treatment of diabetes, rheumatism and Inflammatory disease. The aim of the study is to evaluate the possible effect of methanolic extract of Thymelaea lythroides in repressing the inflammatory responses and long-lasting depression-like behavior associated with neuroinflammation in adult rats after neonatal LPS exposure. Male rat pups were treated systemically with either LPS (250??g/kg) or vehicle (phosphate buffer saline) on postnatal day 14. Six hours later, the LPS groups were assigned to intraperitoneal (ip) injection of Minocycline (50?mg/kg) or Thymelaea lythroides (200?mg/kg). Thereafter, in adulthood (postnatal days 90-97), the spontaneous locomotor activity and depression-like behavior were assessed successively in open field and forced swim tests. The levels of proinflammatory cytokines, oxidative damage, and activation of microglia were determined in the hippocampus (HP) of male rats on (PND90-97). Our results showed that open field hypoactivity and increased immobility period in LPS-induced adult rats were normalized on treatment with Thymelaea lythroides and minocycline. Both treatments attenuate the overactivated microglial cells in the CA1 and CA3 of hippocampus (HP) and significantly reduced the oxidative-nitrosative stress markers and cytokine (TNF ?) production in the HP. Thymelaea lythroides seems to have similar neuroprotective effects to Minocycline, and such protection may be due to: reduction of oxidative stress, upregulation of inflammatory mediators production, antidepressant behavior which all are associated with neuroinflammation.

Postnatal melatonin treatment protects against affective disorders induced by early-life immune stimulation by reducing the microglia cell activation and oxidative stress.

BACKGROUND: Systemic inflammation induced by neonatal infection may result as long-term hyper-activation of microglial cells followed by an overproduction of pro-inflammatory cytokines, such as tumor necrosis factor-alpha, nitric oxide and lipid peroxidation. Those inflammation mediators can trigger behavioral disruption and/or cognitive disorders. OBJECTIVE: The present work aims to evaluate the effect of melatonin (a cytokine release modulator and antioxidant agent) in the reduction of the prefrontal microglia activation and depressive-like behaviors induced by lipopolysaccharide (LPS) injection in adult rats. RESULTS: The effect of melatonin (5 mg/kg) was compared to minocycline (50 mg/kg), a well-known anti-inflammatory drug with potent inhibitory effect on microglial activation. Our results showed that LPS injection induced a significant increase in prefrontal cortex tumor necrosis factor-alpha and nitric oxide levels. Furthermore, lipid peroxidation and microglial activation were highly increased in the prefrontal cortex compared to control. The melatonin treatment induced a significant decrease on nitric oxide and lipid peroxidation levels in the prefrontal cortex and significant decrease on tumor necrosis factor-alpha and microglia activation. Melatonin can also induce a significant reduction in the anxiety and depression-like effect induced by PND9 LPS administration. CONCLUSION: Our results demonstrated that melatonin possesses potent protective effect against the depression and anxiety induced by LPS. The underlying effect of melatonin is probably due to the reduction of nitric oxide toxic effect and lipid peroxidation in addition to its anti-inflammatory effect.

Preventive effects of flaxseed and sesame oil on bone loss in ovariectomized rats.

A study was designed to examine the effects of dietary flaxseed oil (FO) and sesame oil (SO) which are rich successively in n-3 and (n-9 and n-6) on biochemical parameters and histological status of bone. Sixty-four 90-day-old female wistar rats were randomly assigned to 6 groups: sham-operated rat (sham)+ control diets, ovariectomized rat (OVX) + control diets, OVX + 7% FO, OVX + 7% SO, OVX + 10% FO, OVX + 10% SO. After 4 weeks of treatments, rats were euthanized; blood and tissues were collected for analyses. Markers of bone formation which is alkaline phosphatase activity and markers of bone resorption which is tartrate resistant acid phosphatase activity were measured. Present results showed that OVX increased significantly ALP and TRAP activity and the examination of bone tissue showed disruptive and lytic bone trabeculae. Animals fed 10% FO and 10% SO of fat reduced these parameters and improved bone microarchitecture. Whereas, there was no improvement in biochemical and histological states in OVX rats that received 7% of PUFAs successively provided from FO and SO diets. In conclusion, our results are encouraging because they suggest that PUFAs intake may help to prevent osteoporosis associated with estrogens deficiency. However, further studies are needed to determine the mechanism by which a diet rich in n-3 or lignans modulate bone tissue.

Effects of photoperiod regimen on emotional behaviour in two tests for anxiolytic activity in Wistar rat.

Seasonal changes are often gone with mood and behaviour changes which are probably linked to change in day length or photoperiod. The experiments developed in this work are based on the hypothesis that changes in photoperiod affect emotionality in rats. To check this hypothesis, female rats were exposed to four different photoperiods (LP: 16L/8D; MP: 12L/12D; SP: 8L/16D; SP-F: 8L/16D with a light pulse in midpoint of the dark phase). Eight or 14 weeks later, rats were subjected to two behavioural tests to quantify anxiety level. Independently of duration, rats exposed to SP exhibited higher levels of anxious-like behaviour than rats raised in LP and SP-F, in an open field test (OFT) and in elevated plus maze (EPM). Significant differences in EPM are obtained only after 14 weeks of treatment. Moreover rats treated more long time showed greater suprarenal gland mass. Compared to all other groups, females exposed to SP had greater suprarenal gland. Our results indicate that changes in day length are associated with different levels of anxious-like behaviours consistent with the conjecture that short days may have an anxiogenic effect in female rats.

[Cortex-wall connections in the apical cell of Sphacelaria]. / Connexions cortex-paroi chez la cellule apicale de Sphacelaria.

The apical cell of Sphacelaria (Fucophyceae) exhibits a permanent polarized organization throughout asymmetric divisions. The apex organization was studied by immunolocalization of tubulin, vitronectin, alpha-actinin and beta 1 integrin. Microfilaments were stained directly by fluorescein phalloidin. The apex was highly organized around a patch of microfilaments densely packed at the tip, where vitronectin-like and alpha-actinin-like proteins colocalized. In the same area, an actin-dependent targeted secretion of sulfated polysaccharides was shown. The permanent localization of these components throughout cell elongation suggests that a cortical site involving transmembrane connections between the cytoskeleton and the extracellular matrix is required for cell polarity. A model of the organization of the tip is proposed.

Presynaptic and postsynaptic effects of neuropeptide Y in the rat pineal gland.

Neuropeptide Y is colocalized with noradrenaline in sympathetic fibers innervating the rat pineal gland. In this article we present a study of the effects and mechanisms of action of neuropeptide Y on the pineal noradrenergic transmission, the main input leading to the rhythmic secretion of melatonin. At the presynaptic level, neuropeptide Y inhibits by 45%, with an EC50 of 50 nM, the potassium-evoked noradrenaline release from pineal nerve endings. This neuropeptide Y inhibition occurs via the activation of pertussis toxin-sensitive G protein-coupled neuropeptide Y-Y2 receptors and is independent from, but additive to, the alpha 2-adrenergic inhibition of noradrenaline release. At the postsynaptic level, neuropeptide Y decreases by a maximum of 35%, with an EC50 of 5 nM, the beta-adrenergic induction of cyclic AMP elevation via the activation of neuropeptide Y-Y1 receptors. This moderate neuropeptide Y-induced inhibition of cyclic AMP accumulation, however, has no effect on the melatonin secretion induced by a beta-adrenergic stimulation. On the contrary, in the presence of 1 mM ascorbic acid, neuropeptide Y potentiates (up to threefold) the melatonin secretion. In conclusion, this study has demonstrated that neuropeptide Y modulates the noradrenergic transmission in the rat pineal gland at both presynaptic and postsynaptic levels, using different receptor subtypes and transduction pathways.

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates melatonin synthesis from rat pineal gland.

The effect of pituitary adenylate cyclase polypeptide (PACAP) on rat pineal was examined. PACAP stimulated melatonin release from cultured dissociated pinealocytes with a 10(4) higher potency than isoproterenol (EC50 were 30 pM and 250 nM, respectively). The 10(-9) M PACAP stimulation was not inhibited by 5 x 10(-6) M VIP antagonist whereas that of 10(-9) M VIP was reduced by 54%. Kinetic analysis of melatonin release indicated that PACAP acts postsynaptically via receptor activation.

Delta-sleep-inducing peptide stimulates melatonin, 5-methoxytryptophol and serotonin secretion from perifused rat pineal glands.

The pineal gland is known to synthesize numerous indolamines. Since delta-sleep-inducing peptide (DSIP, a tryptophan nonapeptide) is found in the pineal gland, its effect on the secretion of indolamines was investigated. DSIP stimulated melatonin (MEL), 5-methoxytryptophol (5-ML) and serotonin (5-HT) synthesis and release, whereas it did not affect pineal cyclic AMP levels. The stimulatory effect of DSIP on MEL secretion was dose dependent between 5 x 10(-6) and 10(-4) M, whereas the minimal effective concentration of DSIP on 5-ML secretion was higher than 10(-5) M. The effect of DSIP (10(-4) M) was compared to the effect of isoproterenol (ISO, 10(-6) M) on MEL and 5-HT release. ISO stimulated MEL secretion and concomitantly decreased 5-HT release. With regard to kinetic characteristics, the effect of DSIP (10(-4) M) on MEL release was faster and of shorter duration than the effect of ISO (10(-6) M; 2 and 4 h, respectively). At 10(-4) M, DSIP potentiated the ISO-induced increase of MEL secretion. The DSIP-stimulated release of MEL was not significantly altered when the pineal glands were treated with 10(-5) M propranolol (a beta-adrenergic antagonist), 10(-5) M prazosin (an alpha 1-adrenergic antagonist) or 10(-5) M naloxone (an opioidergic antagonist). This study demonstrates that the DSIP-induced secretion of indolamines from rat pineal glands may not be elicited through the well-known noradrenergic or opioid systems.

Implication of tryptophan in the stimulatory effect of delta-sleep-inducing peptide on indole secretion from perifused rat pineal glands.

We have recently demonstrated that delta-sleep-inducing peptide (DSIP) stimulates indolamine secretion from rat pineal glands. In the present study, we show that tryptophan (TRP), as well as DSIP, stimulate melatonin (MEL) and 5-methoxy-tryptophol (5-ML) secretion in a dose-dependent manner between 5 x 10(-6) and 10(-4) M. The kinetic characteristics of the MEL and 5-ML secretion and the response induced by the two substances were similar. The increase in MEL secretion in response to 10(-4) M DSIP was completely inhibited by pretreatment of the pineals with 10(-5) M phenanthroline (amino-peptidase inhibitor), suggesting that stimulatory effect of DSIP was due to TRP liberated by peptide degradation. This mechanism occurring in the pineal was confirmed using 10(-4) M para-chlorophenylalamine (TRP hydroxylase inhibitor), which reduced the pineal response to 10(-4) and 10(-5) M DSIP by 50 and 100%, respectively.

Vasopressin and oxytocin modulation of melatonin secretion from rat pineal glands.

The rat pineal gland is known to release melatonin in response to noradrenergic stimulation. Since vasopressin (VP)- and oxytocin (OT)-containing fibers innervate the pineal gland, the effects of VP and OT on melatonin release from perifused rat pineal glands were investigated. VP (10(-7) M) and OT (10(-6) M) decreased the basal melatonin secretion. No dose-dependent effect was observed. At high concentrations (10(-5)) these peptides potentiated the isoproterenol-induced increase of melatonin secretion. Below 10(-5) M no potentiation was observed. Fragments of VP ([pGlu4,Cys6]VP(4-9] and OT (pGlu4,Cys6]OT(4-9] did not display any effect on the isoproterenol-induced melatonin secretion.

Vasoactive intestinal peptide stimulates melatonin release from perifused pineal glands of rats.

The rat pineal gland is known to release melatonin in response to noradrenergic stimulation. The effect of vasoactive intestinal peptide (VIP), one of the neuropeptides present in the pineal, was examined on perifused rat pineal glands. VIP stimulated melatonin release with a dose-dependent effect above 10(-7) M. In regard of kinetic characteristics, the pattern of melatonin release after VIP stimulation was similar to that after isoproterenol stimulation. 10(-6) M VIP-stimulated melatonin release was not altered when the pineal glands were treated with 10(-5) M propranolol (a beta-adrenergic antagonist) or 10(-5) M prazosin (an alpha 1-adrenergic antagonist). Thus VIP has a noradrenergic-independent effect on melatonin secretion. Conversely, this VIP effect is greatly inhibited by the specific action of a VIPergic antagonist. This suggests that VIP acts on melatonin synthesis through its own binding sites. This study demonstrates that melatonin secretion from rat pineal glands may be elicited through a VIPergic system which is independent of the well-known noradrenergic system.

Kinetic study of melatonin release from rat pineal glands using a perifusion technique.

In previous studies, noradrenaline was found to elicit a rise of melatonin secretion through activation of typical beta-adrenergic receptors. In the present study, a perifusion system was developed to characterize the kinetics of melatonin release from rat pineal glands. Isolated pineal glands from adult male rats were continuously perifused for 15 h in a Krebs-Ringer solution, and the concentration of melatonin in the effluent perifusate was monitored using a specific radioimmunoassay. The rate of release of melatonin declined during the first 3-4 h of perifusion and then remained fairly stable for at least 11 h. The spontaneous release of melatonin was around 20 pg per min and per gland. When pineal glands were stimulated with isoproterenol, melatonin release output linearly increased for at least 2 h after the stimulation. The increase in melatonin release depended on the isoproterenol concentration and on the duration of the stimulation. The analysis of the pattern of melatonin secretion by a single rat pineal gland showed that the secretion was irregular but did not present a clear feature of pulsatile or oscillatory release over a 11 h-long study. The perifusion system was found useful in order to follow the characteristics of melatonin release from pineal glands and should allow investigations of neuronal or hormonal control of pineal gland activities.