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Introduction: The medial preoptic area (mPOA) participates in thermoregulatory control and blood pressure modulation as shown by studies with electrical stimulation of this area or cobalt chloride injection, a non-selective synapse inhibitor. This study aimed to investigate whether angiotensin II (Ang II) and GABA could act or not in the mPOA to mediate the cardiovascular and micturition control pathways. Methods: Female Wistar rats were submitted to stereotaxic surgery for implantation of a guide cannula into the mPOA 7 days prior to the experiments. Afterwards, the animals were isoflurane- anesthetized and submitted to the catheterization of the femoral artery and vein and urinary bladder cannulation for mean arterial pressure (MAP), heart rate (HR), and intravesical pressure (IP) recordings, respectively. After the baseline MAP, HR, and IP recordings for 15 min, Ang II (0.1 nM, 1 µL), losartan (AT-1 receptor antagonist, 100 nM, 1 µL), GABA (50 mM, 1 µL) or saline (1 µL) were injected into the mPOA, and the variables were measured for additional 30 min. In a different group of rats, the AT-1 receptor, angiotensin II converting enzyme (ACE), and GABAa receptor gene expression was evaluated in mPOA samples by qPCR. The data are as mean ± SEM and submitted to One-way ANOVA (Tukey posttest) or paired Student t-test (P <0.05). Results: The injection of Ang II into the mPOA evoked a significant hypotension (-37±10 mmHg, n = 6, p = 0.024) and bradycardia (-47 ± 20 bpm, p = 0.030) compared to saline (+1 ± 1 mmHg and +6 ± 2 bpm, n = 6). A significant increase in IP was observed after Ang II injection into the mPOA (+72.25 ± 17.91%, p = 0.015 vs. -1.80 ± 2.98%, n = 6, saline). No significant changes were observed in MAP, HR and IP after the losartan injection in the mPOA compared to saline injection. Injection of GABA into the mPOA evoked a significant fall in MAP and HR (-68 ± 2 mmHg, n = 6, p < 0.0001 and -115 ± 14 bpm, n = 6, p = 0.0002 vs. -1 ± 1 mmHg and +4 ± 2 bpm, n = 6, saline), but no significant changes were observed in IP. The AT-1 receptor, ACE and GABAa receptor mRNA expression was observed in all mPOA samples. Discussion: Therefore, in female rats, Ang II mediated transmission in the mPOA is involved in the cardiovascular regulation and in the control of central micturition pathways. A phasic control dependent on AT-1 receptors in the mPOA seems to be involved in the regulation of those cardiovascular and intravesical 3 parameters. In contrast, GABAergic transmission in the mPOA participates in the pathways of cardiovascular control in anesthetized female rats, nevertheless, this neurotransmission is not involved in the micturition control.

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The postpartum period is a demanding time during which mothers experience numerous physiological adaptations that enable them to care for their offspring while maintaining their wellbeing. Hypocretins, also known as orexins, are neuropeptides synthesized by hypothalamic neurons that play a fundamental role in several functions, including the promotion of wakefulness and motivated behaviors, such as maternal care. In this regard, several findings suggest that the activity of the hypocretinergic system increases in the early postpartum period and begins to decline as weaning approaches. In particular, hypocretins within the medial preoptic area, a crucial region during this period, modulate both maternal behavior and sleep. Although further studies are necessary to obtain a comprehensive understanding of the role of hypocretins in lactating females, current research suggests that this system participates in promoting active components of maternal behavior and regulating wakefulness and sleep adjustments during the postpartum period, potentially leading to increased wakefulness during this stage. These adaptive adjustments enable the mother to cope with the continuously changing demands of the pups.

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Hypoxic-ischemic encephalopathy is a severe clinical condition, among others, affecting the brain after offspring exposure to neonatal anoxia, which causes persistent sensorimotor and cognitive deficits. During peripartum, maternal behaviors are crucial for the healthy development of the offspring. In rats, the vocalization of newborns, around 40 kHz, corresponds to separation calls that encourage their mothers to retrieve them. Alterations in this pattern affect the maternal behavior addressed to the offspring. This study aimed to evaluate the maternal behavior of primiparous rats whose offspring were exposed to neonatal anoxia in P2 (postpartum day) during the lactation period, to assess mother-pup interactions through the pups' vocalization from P3 to P18. It also intends to quantify eventual neuronal alterations in the mothers' medial preoptic area after the last weaning (P21) through FOS protein expression. Anoxia offspring were found to reduce maternal behaviors toward them, increased frequency of separation calls in the male anoxia group, and reduced vocalization rate in the female anoxia group compared to their respective controls. Body weight gain reduction of males' and females' anoxia was observed. We concluded that anoxia exerts deleterious effects on the vocalization patterns of the pups, with sex differences that alter maternal behavior toward them. Impaired USV makes an additional negative impact on the already noxious effects of neonatal anoxia. Understanding those phenomena applies/contributes to guiding procedures and strategies to mitigate the deleterious outcomes and orient research concerning the complexity of neonatal anoxia events and the influence of maternal care quality concerning the pups, which should also be considered sex differences.

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The medial preoptic area (mPOA) undergoes through neuroanatomical changes across the postpartum period, during which its neurons play a critical role in the regulation of maternal behavior. In addition, this area is also crucial for sleep-wake regulation. We have previously shown that hypocretins (HCRT) within the mPOA facilitate active maternal behaviors in postpartum rats, while the blockade of endogenous HCRT in this area promotes nursing and sleep. To explore the mechanisms behind these HCRT actions, we aimed to evaluate the effects of juxta-cellular HCRT-1 administration on mPOA neurons in urethane-anesthetized postpartum and virgin female rats. We recorded mPOA single units and the electroencephalogram (EEG) and applied HCRT-1 juxta-cellular by pressure pulses. Our main results show that the electrophysiological characteristics of the mPOA neurons and their relationship with the EEG of postpartum rats did not differ from virgin rats. Additionally, neurons that respond to HCRT-1 had a slower firing rate than those that did not. In addition, administration of HCRT increased the activity in one group of neurons while decreasing it in another, both in postpartum and virgin rats. This study suggests that the mechanisms by which HCRT modulate functions controlled by the mPOA involve different cell populations.

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This study aimed to evaluate the physical exercise-induced neuronal activation in brain nuclei controlling thermoregulatory responses in hypertensive and normotensive rats. Sixteen-week-old male normotensive Wistar rats (NWRs) and spontaneously hypertensive rats (SHRs) were implanted with an abdominal temperature sensor. After recovery, the animals were subjected to a constant-speed treadmill running (at 60% of the maximum aerobic speed) for 30 min at 25 °C. Core (Tcore) and tail-skin (Tskin) temperatures were measured every minute during exercise. Ninety minutes after the exercise, the rats were euthanized, and their brains were collected to determine the c-Fos protein expression in the following areas that modulate thermoregulatory responses: medial preoptic area (mPOA), paraventricular hypothalamic nucleus (PVN), and supraoptic nucleus (SON). During treadmill running, the SHR group exhibited a greater increase in Tcore and an augmented threshold for cutaneous heat loss relative to the NWR group. In addition, the SHRs showed reduced neuronal activation in the mPOA (< 49.7%) and PVN (< 44.2%), but not in the SON. The lower exercise-induced activation in the mPOA and PVN in hypertensive rats was strongly related to the delayed onset of cutaneous heat loss. We conclude that the enhanced exercise-induced hyperthermia in hypertensive rats can be partially explained by a delayed cutaneous heat loss, which is, in turn, associated with reduced activation of brain areas modulating thermoregulatory responses.

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Leptin mediates the interaction between reproductive function and energy balance. However, leptin receptors are not expressed in neurons that produce gonadotropin-releasing hormone (GnRH), likely indicating an indirect action through interneurons. Among likely neurons that modulate the secretion of GnRH are NO (nitric oxide) neurons. We assessed whether estradiol and feeding conditions modulate a possible interaction between leptin and NO in brain areas related to the control of reproductive function. Estradiol-treated and untreated ovariectomized rats were normally fed or fasted for 48 h. Then, saline (control) or leptin (3 µg/1 µl) intracerebroventricular microinjections were administered, and after thirty minutes, the brains collected subsequent to the decapitation or transcardially perfusion. Leptin and estradiol increased NO synthase (nNOS) gene expression (RT-PCR) and content (Western blotting) in the medial preoptic area (MPOA) and medial basal hypothalamus (MBH) only in fasted rats. Leptin increased: 1-phosphorylated-signal transducer and activator of transcription-3(pSTAT3) (immunohistochemistry) in the MPOA and various hypothalamic nuclei [arcuate (ARC); ventromedial (VMH); dorsal/ventral dorsomedial (dDMH/vDMH); premammilar ventral (PMV)], effects potentiated by estradiol/fasting interaction; 2- nNOS/pSTAT3 coexpression in the MPOA only in estradiol-treated, fasted rats; 3- nNOS-immunoreactive cell expression in the VMH, DMH and PMV (areas related to reproductive function control) of estradiol -treated rats. Thus, when leptin is reduced during fasting, leptin replacement effectively increased the expression of nitric oxide, which activated the HPG axis only in the presence of estradiol. Estradiol modulates the nitrergic system, leptin sensitivity and consequently leptin's effects on the nitrergic system in hypothalamus and in particular vDMH and PMV.

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Although the melanin-concentrating hormone (MCH) and its coding mRNA are predominantly found in the tuberal hypothalamus, there is detectable synthesis of MCH in the preoptic hypothalamus exclusively in lactating dams, suggesting a participation of MCH in the alterations that take place after parturition. Also implicated in the dam physiology is oxytocin, a neurohormone released from the posterior pituitary that is necessary for milk ejection. Because the projection fields from oxytocin-immunoreactive (-IR) neurones and the mediobasal preoptic hypothalamus overlap and MCH-IR neurones are found in proximity to oxytocin neurones, we investigated the spatial relationship between MCH and oxytocin fibres. Accordingly, we employed multiple immunohistochemistry labelling for MCH and oxytocin for light and electron microscopy techniques, in addition to i.v. tracer injection combined with in situ hybridisation to identify MCH neurones that project to neurosecretory areas. As described for other strains, lactating Long-Evans dams also display immunoreactivity for MCH in the preoptic hypothalamus on days 12 and 19 of lactation. The appearance of these neurones is contemporaneous with an increase in MCH-IR fibres in both the internal layer of the median eminence and the posterior pituitary. In both regions, MCH- and oxytocin-IR fibres were found in great proximity, although there was no evidence for synaptic interaction between these two populations at the ultrastructural level. The tracer injection revealed that only mediobasal preoptic MCH neurones project to the posterior pituitary, suggesting a neuroendocrine-modulatory role for this population. When taken together, the results obtained in the present study indicate that neuroplasticity events at the mediobasal preoptic hypothalamus that occur during late lactation may be part of a neuroendocrinology control loop involving both MCH and oxytocin.

Assuntos

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The medial preoptic area (mPOA) participates in the temperature and cardiovascular control. The mPOA receives inputs from limbic structures and sends projections to hypothalamus and brainstem. Moreover, stress elicits pronounced neuronal activation in mPOA, suggesting its involvement in central neural pathway mediating stress responses. In the present study, we report the effect of acute mPOA neurotransmission inhibition using cobalt chloride (CoCl2-nonselective synapse blocker) on the mean arterial pressure (MAP), heart rate (HR), body and tail temperature (Tbody and Ttail, respectively), as well as on the HR component of baroreflex. We also verified the participation of mPOA in the autonomic changes evoked by acute restraint stress (RS). Our results demonstrated that microinjection of CoCl2 into mPOA caused tachycardia, hyperthermia and a Ttail decrease, without altering MAP. The inhibition of mPOA with CoCl2 increased the sympathetic component of cardiac baroreflex when assessed 10min after its administration. In addition, pretreatment of mPOA with CoCl2 increased RS-evoked tachycardic and hyperthermic responses evoked by RS when compared with aCSF-treated animals, without affecting the RS-evoked pressor response and the fall in Ttail. In summary, our results suggest that mPOA exerts a tonic inhibitory influence on the sympathetic cardiac tone under both rest and stress conditions, modulating negatively the sympathetic component of baroreflex. Results also confirm the mPOA involvement in the control of body temperature because its inhibition was followed by a sustained increase in body temperature and vasoconstriction in the tail artery territory.

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AIMS: Melanin-concentrating hormone (MCH) is implicated in the control of food intake, body weight regulation and energy homeostasis. Lactation is an important physiological model to study the hypothalamic integration of peripheral sensory signals, such as suckling stimuli and those related to energy balance. MCH can be detected in the medial preoptic area (MPOA), especially around the 19th day of lactation, when this hormone is described as displaying a peak synthesis followed by a decrease after weaning. The physiological significance of this phenomenon is unclear. Therefore, we aimed to investigate hypothalamic changes associated to sensory stimulation by the litter, in special its influence over MCH synthesis. MAIN METHODS: Female Wistar rats (n=56) were euthanized everyday from lactation days 15-21, with or without suckling stimulus (WS and NS groups, respectively). MCH and Fos immunoreactivity were evaluated in the MPOA and lateral and incerto-hypothalamic areas (LHA and IHy). KEY FINDINGS: Suckling stimulus induced Fos synthesis in all regions studied. An increase on the number of suckling-induced Fos-ir neurons could be detected in the LHA after the 18th day. Conversely, the amount of MCH decreased in the MPOA from days 15-21, independent of suckling stimulation. No colocalization between MCH and Fos could be detected in any region analyzed. SIGNIFICANCE: Suckling stimulus is capable of stimulating hypothalamic regions not linked to maternal behavior, possibly to mediate energy balance aspects of lactation. Although dams are hyperphagic before weaning, this behavioral change does not appear to be mediated by MCH.

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The control of gonadotropin-releasing hormone (GnRH) secretion depends on the action of ovarian steroids and several substances, including nitric oxide (NO). NO in the medial preoptic area (MPOA) stimulates the proestrus surge of luteinizing hormone (LH). We studied the effect of estrogen (Tamoxifen-TMX) and progesterone (RU-486) antagonists on mRNA and protein expression of NO synthase (NOS), the enzyme that produces NO, as well as its activity within MPOA. Female rats received s.c. injections of TMX (3mg/animal) on first and second days of the estrous cycle (9 am), RU-486 (2mg/animal) on first, second, (8 am and 5 pm) and third days of the estrous cycle (8 am) or oil (controls) and were killed on the third day (5 pm). Real time-PCR and western blotting were performed to study NOS mRNA and protein expressions. The NOS activity was indirectly assessed by measuring the conversion from [(14)C]-L-arginine into [(14)C]-L-citrulline. TMX significantly decreased neuronal NOS (nNOS) mRNA expression (90%), and the activity of NOS, but did not alter nNOS protein expression. Also, TMX significantly decreased LH, FSH, estrogen and progesterone plasma levels. RU-486 nor affected NOS mRNA and protein expressions neither the NOS activity in the MPOA, but reduced FSH levels. The nitrergic system in the MPOA can be stimulated by estrogen whereas TMX decreased NOS activity and mRNA expression. In conclusion, the involvement of the nitrergic system in the MPOA to induce the surge of LH on proestrus depends on the estrogen action to stimulate the mRNA-nNOS expression and the activity of nNOS but it does not seem to depend on progesterone action.

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Rodents exhibit leptin resistance and high levels of prolactin/placental lactogens during pregnancy. A crosstalk between prolactin and leptin signaling has been proposed as a possible mechanism to explain the changes in energy balance during gestation. However, it remains unclear if specific neuronal populations co-express leptin and prolactin receptors. Therefore, our present study was undertaken to identify in the mouse brain prolactin-responsive cells that possibly express the leptin receptor (LepR). In addition, we assessed the leptin response in different brain nuclei of pregnant and nulliparous mice. We used a LepR-reporter mouse to visualize LepR-expressing cells with the tdTomato fluorescent protein. Prolactin-responsive cells were visualized with the immunohistochemical detection of the phosphorylated form of the signal transducer and activator of transcription-5 (pSTAT5-ir). Notably, many neurons that co-expressed tdTomato and pSTAT5-ir were observed in the medial preoptic area (MPA, 27-48% of tdTomato cells), the retrochiasmatic area (34-51%) and the nucleus of the solitary tract (NTS, 16-24%) of prolactin-treated nulliparous mice, pregnant mice and prolactin-treated leptin-deficient (ob/ob) mice. The arcuate nucleus of the hypothalamus (8-22%), the medial tuberal nucleus (11-15%) and the ventral premammillary nucleus (4-10%) showed smaller percentages of double-labeled cells among the groups. Other brain nuclei did not show significant percentages of neurons that co-expressed tdTomato and pSTAT5-ir. Late pregnant mice exhibited a reduced leptin response in the MPA and NTS when compared with nulliparous mice; however, a normal leptin response was observed in other brain nuclei. In conclusion, our findings shed light on how the brain integrates the information conveyed by leptin and prolactin. Our results corroborate the hypothesis that high levels of prolactin or placental lactogens during pregnancy may directly interfere with LepR signaling, possibly predisposing to leptin resistance.

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Ghrelin is a stomach-derived peptide hormone that acts in the brain to regulate many important physiological functions. Ghrelin receptor, named the growth hormone secretagogue receptor (GHSR), is present in many brain areas with or without obvious direct access to ghrelin circulating in the bloodstream. Ghrelin is also present in the cerebrospinal fluid (CSF) but the brain targets of CSF ghrelin are unclear. Here, we studied which brain areas are accessible to ghrelin present in the CSF. For this purpose, we centrally injected mice with fluorescein-labeled ghrelin (F-ghrelin) peptide tracer and then systematically mapped the distribution of F-ghrelin signal through the brain. Our results indicated that centrally injected F-ghrelin labels neurons in most of the brain areas where GHSR is present. Also, we detected F-ghrelin uptake in the ependymal cells of both wild-type and GHSR-null mice. We conclude that CSF ghrelin is able to reach most of brain areas expressing GHSR. Also, we propose that the accessibility of CSF ghrelin to the brain parenchyma occurs through the ependymal cells in a GHSR-independent manner.

Assuntos