Pioglitazone abolishes cognition impairments as well as BDNF and neurotensin disturbances in a rat model of autism.

We have shown that exposure of rats to lipopolysaccharide (LPS) during gestation induces autistic-like behaviors in juvenile offspring and pioglitazone post treatment corrects social and communication deficits. The first objective of the present study was to evaluate the cognition of the rats, because this is also a behavioral sphere committed in autism. Second, biomarkers related to pioglitazone pathways and autism were studied to try to understand their mechanisms. We used our rat model of autism and pioglitazone was administered daily to these young offspring. T-maze spontaneous alternations tests, plasma levels of brain-derived neurotrophic factor (BDNF), beta-endorphin, neurotensin, oxytocin, and substance P were all studied. Exposure of rats to LPS during gestation induced cognitive deficits in the young offspring, elevated BDNF levels and decreased neurotensin levels. Daily postnatal pioglitazone treatment abolished cognition impairments as well as BDNF and neurotensin disturbances. Together with our previous studies, we suggest pioglitazone as a candidate for the treatment of autism, because it improved the responses of the three most typical autistic-like behaviors. BDNF and neurotensin also appeared to be related to the autistic-like behaviors and should be considered for therapeutic purposes.

Zinc Alleviates Lipopolysaccharide Interference with Both Body Temperature and Sickness Behavior in Virgin Female Rats.

OBJECTIVES: Previous studies from our group showed that lipopolysaccharide (LPS) exposure induces several signs of sickness behavior, including a decrease in food consumption, body weight gain, adipsia, and a biphasic effect in tympanic temperature with a first phase of hypothermia, followed by an increased tympanic temperature. LPS can activate a chain of nonspecific host responses, including the immune response, and decreased zinc levels. In addition, there are differences in the immune response between males and females, particularly fever, with sex hormones interfering with body temperature. This study aims to characterize the effects of zinc treatment on tympanic temperature, body weight gain, food and water consumption, and general activity in open field of virgin female rats exposed to a dose of LPS that was previously reported to induce sickness behavior. METHODS: Virgin female Wistar rats were treated with either saline (S) or LPS. One hour later, the S group received another injection of saline (S + S group), half of the LPS group received saline (LPS + S group) and the other half received zinc (LPS + Zn group). Tympanic temperature, body weight, and water and food consumption were measured for 96 h. Measurements and observations started 2 h after LPS administration. RESULTS: Treatment with zinc attenuated LPS-increased temperature, decreased the body weight gain and food consumption, and water consumption was increased. CONCLUSION: Zinc treatment is beneficial as it reduces the increased tympanic temperature induced by LPS, but it does not influence other sickness behavior caused by exposure to LPS.

The weaning period promotes alterations in the orexin neuronal population of rats in a suckling-dependent manner.

The orexin-immunoreactive neurons are part of an important arousal-promoting hypothalamic population. Several groups have investigated these neurons during the lactation period, when numerous physiological alterations occur in the dam's body to cope with the newly acquired metabolic needs of the litter. Although those studies have probed this population during the early and intermediate stages of lactation, few works have examined its response to weaning, including the cessation of the tactile suckling stimulus as the litter stops nursing. Using double immunohistochemistry for orexin and FOS combined with three-dimensional reconstruction techniques, we investigated orexin-synthesizing neurons and their activation at different times during weaning, in addition to the role played by the suckling stimulus. We report here that weaning promoted a decline in the anterior population of orexin-immunoreactive neurons and decreased the number of double orexin-FOS neurons labeled in the central dorsomedial hypothalamus, in addition to reducing the overall number of FOS-immunoreactive cells in the whole tuberal hypothalamus. Disruption of the suckling stimulus from the pups impaired the decrease in the number of anteriorly located orexin-immunoreactive neurons, attenuated the activation of orexin-synthesizing cells in the dorsomedial hypothalamus and reduced the number of FOS-immunoreactive neurons across the tuberal hypothalamus. When taken together, our data suggest that the weaning period is necessary to restore neurochemical pathways altered during the lactation period and that the suckling stimulus plays a significant role in this process.

Short-Term Hyperprolactinemia Reduces the Expression of Purinergic P2X7 Receptors during Allergic Inflammatory Response of the Lungs.

PURPOSE: We have previously shown that domperidone-induced short-term hyperprolactinemia reduces the lung's allergic inflammatory response in an ovalbumin antigenic challenge model. Since purinergic receptor P2X7R activity leads to proinflammatory cytokine release and is possibly related to the pathogenesis of allergic respiratory conditions, the present study was designed to investigate a possible involvement of purinergic and prolactin receptors in this phenomenon. METHODS: To induce hyperprolactinemia, domperidone was injected intraperitoneally in rats at a dose of 5.1 mg × kg-1 per day for 5 days. P2X7 expression was evaluated by lung immunohistochemistry while prolactin receptor expression in bronchoalveolar lavage leukocytes was analyzed through flow cytometry. RESULTS: Previous reports demonstrated that rats subjected to short-term hyperprolactinemia exhibited a decrease in leukocyte counts in bronchoalveolar lavage, especially granulocytes. Here, it is revealed that hyperprolactinemia promotes an increased expression of prolactin receptors in granulocytes. Also, increased expression of purinergic P2X7R observed in allergic animals was significantly reduced by hyperprolactinemia. CONCLUSIONS: Both purinergic and prolactin receptor expression changes occur during the anti-asthmatic effect of hyperprolactinemia.

Pioglitazone abolishes autistic-like behaviors via the IL-6 pathway.

Autism is characterized by social deficits, communication abnormalities, and repetitive behaviors. The risk factors appear to include genetic and environmental conditions, such as prenatal infections and maternal dietary factors. Previous investigations by our group have demonstrated that prenatal exposure to lipopolysaccharide (LPS), which mimics infections by gram-negative bacteria, induces autistic-like behaviors. No effective treatment yet exists for autism. Therefore, we used our rat model to test a possible treatment for autism. We selected pioglitazone to block or ease the impairments induced by LPS because although this drug was designed as an anti-diabetic drug (it has an insulin effect), it also exerts anti-inflammatory effects. Juvenile offspring were treated daily with pioglitazone, and the main behaviors related to autism, namely, socialization (play behavior) and communication (50-kHz ultrasonic vocalizations), were studied. Biomarkers linked to autism and/or pioglitazone were also studied to attempt to understand the mechanisms involved, namely, IL-6, TNF-alpha, MCP-1, insulin, and leptin. Prenatal LPS exposure induced social deficits and communicational abnormalities in juvenile rat offspring as well as elevated plasma IL-6 levels. Daily postnatal pioglitazone treatment blocked the impairments found in terms of the time spent on social interaction, the number of vocalizations (i.e., autistic-like behaviors) and the elevated plasma IL-6 levels. Thus, pioglitazone appears to be a relevant candidate for the treatment of autism. The present findings may contribute to a better understanding and treatment of autism and associated diseases.

Buried Food-seeking Test for the Assessment of Olfactory Detection in Mice.

The sense of smell allows animals to discriminate a large number of volatile environmental chemicals. Such chemical signaling modulates the behavior of several species that depend on odorant compounds to locate food, recognize territory, predators, and toxic compounds. Olfaction also plays a role in mate choice, mother-infant recognition, and social interaction among members of a group. A key assay to assess the ability to smell odorants is the buried food-seeking test, which checks whether the food-deprived mice can find the food pellet hidden beneath the bedding in the animal's cage. The main parameter observed in this test is the latency to uncover a small piece of chow, cookie, or other pleasant food, hidden beneath a layer of cage bedding, within a limited amount of time. It is understood that food-restricted mice which fail to use odor cues to locate food within a given time period are likely to have deficits in olfactory abilities. Investigators who used the buried food test, or versions of the buried food test, demonstrated that it is possible to evaluate olfactory deficits in different models of murine studies (Alberts and Galef, 1971; Belluscio et al., 1998 ; Luo et al., 2002 ; Li et al., 2013 ). We have recently used this assay to demonstrate that olfactory-specific Ric-8B knock-out mice (a guanine nucleotide exchange factor that interacts with olfactory-specific G-protein) show an impaired sense of smell ( Machado et al., 2017 ). Here we describe the protocol of the buried food-seeking test, as adopted in our assays.

Conditional Deletion of Ric-8b in Olfactory Sensory Neurons Leads to Olfactory Impairment.

The olfactory system can discriminate a vast number of odorants. This ability derives from the existence of a large family of odorant receptors expressed in the cilia of the olfactory sensory neurons. Odorant receptors signal through the olfactory-specific G-protein subunit, Gαolf. Ric-8b, a guanine nucleotide exchange factor, interacts with Gαolf and can amplify odorant receptor signal transduction in vitro To explore the function of Ric-8b in vivo, we generated a tissue specific knock-out mouse by crossing OMP-Cre transgenic mice to Ric-8b floxed mice. We found that olfactory-specific Ric-8b knock-out mice of mixed sex do not express the Gαolf protein in the olfactory epithelium. We also found that in these mice, the mature olfactory sensory neuron layer is reduced, and that olfactory sensory neurons show increased rate of cell death compared with wild-type mice. Finally, behavioral tests showed that the olfactory-specific Ric-8b knock-out mice show an impaired sense of smell, even though their motivation and mobility behaviors remain normal.SIGNIFICANCE STATEMENT Ric-8b is a guanine nucleotide exchange factor (GEF) expressed in the olfactory epithelium and in the striatum. Ric-8b interacts with the olfactory Gαolf subunit, and can amplify odorant signaling through odorant receptors in vitro However, the functional significance of this GEF in the olfactory neurons in vivo remains unknown. We report that deletion of Ric-8b in olfactory sensory neurons prevents stable expression of Gαolf. In addition, we demonstrate that olfactory neurons lacking Ric-8b (and consequently Gαolf) are more susceptible to cell death. Ric-8b conditional knock-out mice display impaired olfactory guided behavior. Our results reveal that Ric-8b is essential for olfactory function, and suggest that it may also be essential for Gαolf-dependent functions in the brain.

Attenuated allergic inflammatory response in the lungs during lactation.

AIMS: To evaluate the influence of lactation on lung immune function during allergic inflammation. MAIN METHODS: Female rats, 60-90days old, were divided into three groups: no lung allergy virgins (N group), ovalbumin (OVA)-immunized and sensitized virgins (V group), and OVA-immunized and sensitized lactating females (L group). On gestation day (GD) 10, all animals in L group received a subcutaneous injection of 0.1mg·kg(-1) OVA plus aluminum hydroxide. On GD17, the L group received a subcutaneous booster injection of 10µg OVA plus 10mg aluminum hydroxide. After 7days, an inhalatory challenge with 1% OVA was given in 15min sessions for 3 consecutive days. Animals from the V group received the same treatment, meaning both tests and time intervals between OVA treatment and inhalatory challenge were the same as in the L group. Twenty-four hours after the last inhalation session, the animals were euthanized, and the following tests were performed: total and differential bronchoalveolar lavage (BAL) and femoral marrow lavage (FML) leukocyte counts, quantification of tumor necrosis factor α (TNF-α) and interferon γ (IFN-γ) levels in BAL fluid, and quantification of plasma corticosterone and catecholamine levels. KEY FINDINGS: The L group presented lower BAL total leukocyte counts and decreases in the number of eosinophils and macrophages compared with the V group. They also expressed higher BAL IFN-γ and lower plasma corticosterone levels. Plasma norepinephrine levels were higher in the L group than in the N and V groups. SIGNIFICANCE: Lactating female rats presented less intense allergic lung inflammation. Our findings suggest that lactation may protect females from asthmatic crises.

Short-term hyperprolactinemia decreases allergic inflammatory response of the lungs.

AIMS: Prolactin is a major immunomodulator. The present study evaluated the effects of short-term hyperprolactinemia induced by domperidone before ovalbumin antigenic challenge on the lung's allergic inflammatory response. MAIN METHODS: To induce hyperprolactinemia, domperidone was injected in rats at a dose of 5.1mg·kg(-1) per day, i.p., for 5days from 10th to 14th day after OVA immunization. Total and differential leukocyte counts from bronchoalveolar lavage (BAL), femoral marrow lavage (FML), and blood were analyzed. The percentages of mucus and collagen production were evaluated. Levels of corticosterone and prolactin in serum, interleukin-4 (IL-4), IL-6, IL-10, tumor necrosis factor α (TNF-α) in lung explants supernatants were measured and interferon gamma (IFN-γ) in bronchiolar lavage cells suspensions (BAL) was measured. KEY FINDINGS: The rats that were subjected to short-term hyperprolactinemia exhibited a decrease in leukocyte counts in bronchoalveolar lavage, cellularity decrease in femoral marrow lavage fluid, a lower percentage of mucus, and an increase in lung IL-4, IL-6, IL-10, TNF-α and IFN-γ expression. SIGNIFICANCE: Hyperprolactinemia induced before antigenic challenge decreased allergic lung inflammation. These data suggest that prolactin may play a role in the pathophysiology of asthma. The present study demonstrates a prospective beneficial side effect of domperidone for asthmatic patients.

Lipopolysaccharide Exposure Induces Maternal Hypozincemia, and Prenatal Zinc Treatment Prevents Autistic-Like Behaviors and Disturbances in the Striatal Dopaminergic and mTOR Systems of Offspring.

Autism is characterized by social deficits, repetitive behaviors, and cognitive inflexibility. The risk factors appear to include genetic and environmental conditions, such as prenatal infections and maternal dietary factors. Previous investigations by our group have demonstrated that prenatal exposure to lipopolysaccharide (LPS), which mimics infection by gram-negative bacteria, induces autistic-like behaviors. To understand the causes of autistic-like behaviors, we evaluated maternal serum metal concentrations, which are involved in intrauterine development and infection/inflammation. We identified reduced maternal levels of zinc, magnesium, selenium and manganese after LPS exposure. Because LPS induced maternal hypozincemia, we treated dams with zinc in an attempt to prevent or ease the impairments in the offspring. We evaluated the social and cognitive autistic-like behaviors and brain tissues of the offspring to identify the central mechanism that triggers the development of autism. Prenatal LPS exposure impaired play behaviors and T-maze spontaneous alternations, i.e., it induced autistic-like behaviors. Prenatal LPS also decreased tyrosine hydroxylase levels and increased the levels of mammalian target of rapamycin (mTOR) in the striatum. Thus, striatal dopaminergic impairments may be related to autism. Moreover, excessive signaling through the mTOR pathway has been considered a biomarker of autism, corroborating our rat model of autism. Prenatal zinc treatment prevented these autistic-like behaviors and striatal dopaminergic and mTOR disturbances in the offspring induced by LPS exposure. The present findings revealed a possible relation between maternal hypozincemia during gestation and the onset of autism. Furthermore, prenatal zinc administration appears to have a beneficial effect on the prevention of autism.

Prenatal zinc prevents communication impairments and BDNF disturbance in a rat model of autism induced by prenatal lipopolysaccharide exposure.

Aims: Previous investigations by our group have shown that prenatal exposure to lipopolysaccharide (LPS),which mimics infections by Gram-negative bacteria, induced autistic-like behavior. No effective treatment yet exists for autism. Therefore, we used our rat model to test a possible treatment for autism.We selected zinc as the prenatal treatment to prevent or ease the impairments induced by LPS because LPS induces hypozincaemia.Materials and methods:We evaluated the effects of LPS and zinc on female reproductive performance. Communication,which is impaired in autism,was tested in pups by ultrasonic vocalizations. Plasma levels of brain-derived neurotrophic factor (BDNF) were determined because it has been considered an autism important biomarker.Key findings: Prenatal LPS exposure reduced offspring number and treatment with zinc prevented this reduction.Moreover, pups that were prenatally exposed to LPS spent longer periods without calling their mothers, and posttreatment with zinc prevented this impairment induced by LPS to the same levels as controls. Prenatal LPS also increased BDNF levels in adult offspring, and posttreatment with zinc reduced the elevation of BDNF to the same levels as controls.Significance: BDNF hyperactivity was also found in several studies of autistic patients. Together with our previous studies, our model of prenatal LPS induced autistic-like behavioral, brain, and immune disturbances. This suggests that it is a valid rat model of autism. Prenatal zinc prevented reproductive, communication, and BDNF impairments.The present study revealed a potential beneficial effect of prenatal zinc administration for the prevention of autism with regard to the BDNF pathway.

Lipopolysaccharide-induced sickness behavior in lactating rats decreases ultrasonic vocalizations and exacerbates immune system activity in male offspring.

OBJECTIVE: The present study analyzed the effects of lipopolysaccharide (LPS) on maternal behavior during lactation and possible correlations with changes in emotional and immune responses in offspring. METHODS: Lactating rats received 100 µg/kg LPS, and the control group received saline solution on lactation day (LD) 3. Maternal general activity and maternal behavior were observed on LD5 (i.e. the day that the peak of fever occurred). In male pups, hematological parameters and ultrasonic vocalizations (USVs) were assessed on LD5. At weaning, an additional dose of LPS (50 µg/kg, i.p.) was administered in male pups, and open-field behavior, oxidative burst and phagocytosis were evaluated. RESULTS: A reduction in the time in which dams retrieved the pups was observed, whereas no effects on maternal aggressive behavior were found. On LD5, a reduction of the frequency of USVs was observed in pups, but no signs of inflammation were found. At weaning, an increase in immune system activity was observed, but no differences in open-field behavior were found. CONCLUSION: These results indicate that inflammation in lactating mothers disrupted mother/pup interactions and may have produced short- and long-term effects on pup behavior as well as biological pathways that modulate inflammatory responses to bacterial endotoxin challenge in pups.

The mother as hunter: significant reduction in foraging costs through enhancements of predation in maternal rats.

In previous laboratory investigations, we have identified enhanced cognition and reduced stress in parous rats, which are likely adaptations in mothers needing to efficiently exploit resources to maintain, protect and provision their immature offspring. Here, in a series of seven behavioral tests on rats, we examined a natural interface between cognition and resource gathering: predation. Experiment 1 compared predatory behavior (toward crickets) in age-matched nulliparous mothers (NULLs) and postpartum lactating mothers (LACTs), revealing a highly significant enhancement of predation in LACT females (mean = -65s in LACTs, vs. -270s in NULLs). Experiment 2 examined the possibility that LACTs, given their increased metabolic rate, were hungrier, and thus more motivated to hunt; doubling the length of time of food deprivation in NULLs did not decrease their predatory latencies. Experiments 3-5, which examined sensory regulation of the effect, indicated that olfaction (anosmia), audition (blockade with white noise), and somatosensation (trimming the vibrissae) appear to play little role in the behavioral enhancement observed in the LACTs; Experiment 6 examined the possibility that visual augmentations may facilitate the improvements in predation; testing LACTs in a 0-lux environment eliminated the behavioral advantage (increasing their latencies from -65s to -212s), which suggests that temporary augmentation to the visual system may be important, and with hormone-neural alterations therein a likely candidate for further study. In contrast, testing NULLS in the 0-lux environment had the opposite effect, reducing their latency to catch the cricket (from -270s to -200s). Finally, Experiment 7 examined the development of predatory behavior in Early-pregnant (PREG), Mid-PREG, and Late-PREG females. Here, we observed a significant enhancement of predation in Mid-PREG and Late-PREG females--at a time when maternity-associated bodily changes would be expected to diminish predation ability--relative to NULLs. Therefore, as with the increasing reports of enhancements to the maternal brain, it is apparent that meaningful behavioral adaptations occur that likewise promote the survival of the mother and her infants at a crucial stage of their lives.

Maternal treatment with picrotoxin in late pregnancy improved female sexual behavior but did not alter male sexual behavior of offspring.

Previous studies from our laboratory investigated the effects of picrotoxin (PT), a γ-aminobutyric acid receptor antagonist administered during several perinatal periods, on the sexual behavior of male and female rats. We observed that the time of perinatal exposure to PT is critical to determine either facilitation or impairment of sexual behavior. The present study evaluated the effects of prenatal administration of a single dose of PT on gestation day 18 of dams (the first critical period of male brain sexual differentiation) on sexual behavior of male and female offspring. Thus, female Wistar rats were mated with males and, on gestation day 18, received 0.6 mg/kg of PT or 0.9% saline solution subcutaneously. On postnatal day 1, the offspring were weighed and several measures of sexual development were assessed. The sexual behaviors and the general activity in the open field of adult male and ovariectomized, hormone-treated female rats were observed. On comparison with the control group, maternal PT treatment: (i) did not alter the maternal weight, pup weight, anogenital distance, or male and female general activity; (ii) increased female sexual behavior, that is, decreased the latencies to first mount, first lordosis, and tenth lordosis, and the percentage of females presenting lordosis; and (iii) did not alter male sexual behavior. It is suggested that prenatal PT exposure interfered with epigenetic mechanisms related to the development of sex differences in the brain, leading to the observed sexually dimorphic effects on sexual behavior.

Prior reproductive experience alters prolactin-induced macrophage responses in pregnant rats.

Reproductive experience (i.e., pregnancy and lactation) induces physiological changes in mammals. A previous reproductive experience was recently shown to modulate the activity of dopaminergic hypothalamic systems while decreasing serum prolactin levels and oxidative burst activity in peritoneal macrophages. Dopamine receptor antagonists increase serum prolactin levels, and both prolactin and dopamine receptors may be involved in the modulation of macrophage activity, providing a means of communication between the nervous and immune systems. The present study evaluated the in vitro effects of prolactin and a dopamine D2 receptor antagonist on the peritoneal activity of macrophages from primigravid and multigravid female rats during the third trimester of pregnancy. Oxidative bursts and phagocytosis in peritoneal macrophages were evaluated by flow cytometry. Primigravid and multigravid Wistar rats, during the third trimester of pregnancy (i.e., days 17-21), were used. Peritoneal fluid samples from these rats were first incubated with prolactin (10 and 100 nM) for different periods of time. The same procedure was repeated to evaluate the effects of domperidone (10 and 100 nM) on macrophage activity. Our results showed that macrophages from multigravid rats responded more effectively to in vitro incubation with prolactin, especially with regard to the intensity and percentage of phagocytosis. Additionally, these effects were more pronounced after incubation periods of 30 min or 4 h. These data suggest that macrophages during a second pregnancy become more sensitive to the phagocytotic effects of prolactin.

Maternal exposure to picrotoxin modifies the response of the GABAA receptor during sexual behavior of adult male rat offspring.

This study investigated whether perinatal exposure to picrotoxin, a GABAA antagonist, modifies the effect of muscimol, a GABAA agonist, on the sexual behavior of adult male rats. Two hours after birth and then once daily during the next 9 days of lactation, dams received picrotoxin (0.75 mg/kg subcutaneously) or saline (1 ml/kg subcutaneously). The adult male offspring from the picrotoxin and saline groups received saline (1 ml/kg intraperitoneally) or muscimol (1 mg/kg intraperitoneally), and 15 min later, their sexual behavior was assessed. Muscimol treatment in the saline-exposed group increased the mount and intromission latencies. However, these effects were absent in the picrotoxin-exposed groups. The latencies to first ejaculation, postejaculatory mount, and intromission were decreased in both picrotoxin-exposed groups relative to the saline-exposed groups. The picrotoxin+muscimol-treated rats required more intromissions to ejaculate and the picrotoxin-exposed groups made more ejaculations than the saline-exposed groups. Thus, muscimol treatment did not increase the mount and intromission latencies following picrotoxin exposure, but increased the ejaculation frequency, which did not differ between the picrotoxin+muscimol and the picrotoxin+saline groups. These data indicate that perinatal picrotoxin treatment interfered with GABAA receptor development.

Dual effects of hyperprolactinemia on carrageenan-induced inflammatory paw edema in rats.

OBJECTIVES: The effects of short-term 5-day and long-term 30-day hyperprolactinemia induced by domperidone (1.7 mg/kg/day, s.c.) or ectopic pituitary graft on the acute inflammatory response induced by carrageenan were evaluated in male rats. Both models of hyperprolactinemia effectively increased serum prolactin (PRL) levels. METHODS: The volume in milliliters of inflammatory edema was measured by plethysmography 1, 2, 3, 4, 6, 8 and 24 h after carrageenan injection. The areas under the inflammatory time-response curves were compared. Additionally, the effects of hyperprolactinemia on body weight and serum corticosterone levels were evaluated. RESULTS: In both domperidone-treated and pituitary graft-implanted animals, short-term 5-day hyperprolactinemia increased the inflammatory response, while long-term 30-day hyperprolactinemia had anti-inflammatory effects. Body weight was not affected by either short- or long-term hyperprolactinemia. CONCLUSION: These results show that PRL has biphasic effects on the carrageenan-induced inflammatory response.

Prolactin differentially modulates the macrophage activity of lactating rats: possible role of reproductive experience.

Reproductive experience (i.e., pregnancy and lactation) induces physiological changes in mammals. We recently showed that a previous reproductive experience can modulate the activity of dopaminergic hypothalamic systems while decreasing serum prolactin (PRL) levels and oxidative burst activity in peritoneal macrophages. Dopamine receptor antagonists increase serum PRL levels, and both PRL and dopamine receptors might be involved in the modulation of macrophage activity, providing a means of communication between the nervous and immune systems. The present study evaluated the in vitro effects of PRL and the dopamine receptor D2 antagonist domperidone (DOMP) on the peritoneal activity of macrophages from primiparous and multiparous female rats during lactation. Oxidative bursts and phagocytosis in peritoneal macrophages were evaluated by flow cytometry. Primiparous and multiparous Wistar rats, during the period of lactation (i.e., days 5-7 after parturition) were used. Samples of peritoneal fluid from these rats were first incubated with PRL (10 and 100 nM) for different periods of time. The same procedure was repeated to evaluate the effects of DOMP (10 and 100 nM). Our results showed that macrophages from multiparous rats respond more effectively to in vitro incubation with PRL, especially with regard to oxidative bursts and the percentage of phagocytosis. Additionally, these effects were more pronounced after 30 min of incubation. These data suggest that reproductive experience is associated with a reduction in serum PRL levels, and cells in experienced female animals, including their macrophages, become more sensitive to the effects of PRL.

Plasticity of opioid receptors in the female periaqueductal gray: multiparity-induced increase in the activity of genes encoding for mu and kappa receptors and a post-translational decrease in delta receptor expression.

The periaqueductal gray (PAG) has been reported as a potential site for opioid regulation of behavioral selection. Opioid-mediated behavioral and physiological responses differ between nulliparous and multiparous females. This study addresses the effects of multiple reproductive experiences on µ-, κ- and δ-opioid receptor (Oprm1, Oprk1, and Oprd1 respectively) gene activity and µ, κ and δ protein expression (MOR, KOR and DOR respectively) in the PAG of the female rats. This was done by evaluating the opioid gene expression using real-time (RT-PCR) and quantification of each protein receptor by Western blot analysis. The RT-PCR results show that multiple reproductive experiences increase Oprm1 and Oprk1 gene expression. Western blot analysis revealed increased MOR and KOR while DOR protein was decreased in multiparous animals. Taken together, these data suggest that multiple reproductive experiences influence both gene activity and opioid receptor expression in the PAG. Post-translational mechanisms seem particularly relevant for DOR expression. Thus, opioid transmission in the PAG might be modulated by different mechanisms of multiparity-induced plasticity according to the opioid receptor type.

Prior parity positively regulates learning and memory in young and middle-aged rats.

Reproductive experience in female rats modifies acquired behaviors, induces long-lasting functional neuroadaptations and can also modify spatial learning and memory. The present study supports and expands this knowledge base by employing the Morris water maze, which measures spatial memory. Age-matched young adult (YNG) nulliparous (NULL; nonmated) and primiparous (PRIM; one pregnancy and lactation) female rats were tested 15 d after the litter's weaning. In addition, corresponding middle-aged (AGD) PRIM (mated in young adulthood so that pregnancy, parturition, and lactation occurred at the same age as in YNG PRIM) and NULL female rats were tested at 18 mo of age. Behavioral evaluation included: 1) acquisition of reference memory (platform location was fixed for 14 to 19 d of testing); 2) retrieval of this information associated with extinction of the acquired response (probe test involving removal of the platform 24 h after the last training session); and 3) performance in a working memory version of the task (platform presented in a novel location every day for 13 d, and maintained in a fixed location within each day). YNG PRIM outperformed NULL rats and showed different behavioral strategies. These results may be related to changes in locomotor, mnemonic, and cognitive processes. In addition, YNG PRIM exhibited less anxiety-like behavior. Compared with YNG rats, AGD rats showed less behavioral flexibility but stronger memory consolidation. These data, which were obtained by using a well-documented spatial task, demonstrate long lasting modifications of behavioral strategies in both YNG and AGD rats associated with a single reproductive experience.