Age and sex influence the response in lipid metabolism of dehydrated Wistar rats.

Aging is associated a decrease in thirst sensation, which makes old people more susceptible to dehydration. Dehydration produces energy metabolism alterations. Our objective was to determinate the effect of water deprivation (WD) in the lipid metabolism of old male and female rats. Here we show that in the state of WD, aging and sex alters retroperitoneal white adipose tissue (R-WAT) weight of rats, WD old female rats had more lipolysis products than old male rats, a sexual dimorphism in the hormonal response related with metabolism of the adipose tissue of old rats during WD, the expression of P-para mRNA in R-WAT did not present any alteration in animals submitted to WD, the expression of Aqp7 mRNA in R-WAT is altered by WD, age, and sex. Also, WD stimulated an increase in the plasma concentration of oxytocin and the expression of mRNA of the oxytocin receptors in R-WAT.

AMPA and angiotensin type 1 receptors are necessary for hemorrhage-induced vasopressin secretion.

Hypovolemia induced by hemorrhage is a common clinical complication, which stimulates vasopressin (AVP) secretion by the neurohypophysis in order to retain body water and maintain blood pressure. To evaluate the role of brain L-glutamate and angiotensin II on AVP secretion induced by hypovolemia we induced hemorrhage (∼25% of blood volume) after intracerebroventricular (icv) administration of AP5, NBQX, or losartan, which are NMDA, AMPA, and AT1 receptor antagonists, respectively. Hemorrhage significantly increased plasma AVP levels in all groups. The icv injection of AP5 did not change AVP secretion in response to hemorrhage. Conversely, icv administration of both NBQX and losartan significantly decreased plasma AVP levels after hemorrhage. Therefore, the blockade of AMPA and AT1 receptors impaired AVP secretion in response to hemorrhage, suggesting that L-glutamate and angiotensin II acted in these receptors to increase AVP secretion in response to hemorrhage-induced hypovolemia.

AMPA and angiotensin type 1 receptors are necessary for hemorrhage-induced vasopressin secretion

Hypovolemia induced by hemorrhage is a common clinical complication, which stimulates vasopressin (AVP) secretion by the neurohypophysis in order to retain body water and maintain blood pressure. To evaluate the role of brain L-glutamate and angiotensin II on AVP secretion induced by hypovolemia we induced hemorrhage (∼25% of blood volume) after intracerebroventricular (icv) administration of AP5, NBQX, or losartan, which are NMDA, AMPA, and AT1 receptor antagonists, respectively. Hemorrhage significantly increased plasma AVP levels in all groups. The icv injection of AP5 did not change AVP secretion in response to hemorrhage. Conversely, icv administration of both NBQX and losartan significantly decreased plasma AVP levels after hemorrhage. Therefore, the blockade of AMPA and AT1 receptors impaired AVP secretion in response to hemorrhage, suggesting that L-glutamate and angiotensin II acted in these receptors to increase AVP secretion in response to hemorrhage-induced hypovolemia.

Effects of Hyperosmolality on Hypothalamic Astrocytic Area, mRNA Expression and Glutamate Balance In Vitro.

During prolonged dehydration, body fluid homeostasis is challenged by extracellular fluid (ECF) hyperosmolality, which induce important functional changes in the hypothalamus, in parallel with other effector responses, such as the activation of the local renin-angiotensin system (RAS). Therefore, in the present study we investigated the role of sodium-driven ECF hyperosmolality on glial fibrillary acid protein (GFAP) immunoreactivity and protein expression, membrane capacitance, mRNA expression of RAS components and glutamate balance in cultured hypothalamic astrocytes. Our data show that hypothalamic astrocytes respond to increased hyperosmolality with a similar decrease in GFAP expression and membrane capacitance, indicative of reduced cellular area. Hyperosmolality also downregulates the transcript levels of angiotensinogen and both angiotensin-converting enzymes, whereas upregulates type 1a angiotensin II receptor mRNA. Incubation with hypertonic solution also decreases the immunoreactivity to the membrane glutamate/aspartate transporter (GLAST) as well as tritiated-aspartate uptake by astrocytes. This latter effect is completely restored to basal levels when astrocytes previously exposed to hypertonicity are incubated under isotonic conditions. Together with a direct effect on two important local signaling systems (glutamate and RAS), these synaptic rearrangements driven by astrocytes may accomplish for a coordinated increase in the excitatory drive onto the hypothalamic neurosecretory system, ultimately culminating with increased AVP release in response to hyperosmolality.

Brain osmo-sodium sensitive channels and the onset of sodium appetite.

The aim of the present study was to determine whether the TRPV1 channel is involved in the onset of sodium appetite. For this purpose, we used TRPV1-knockout mice to investigate sodium depletion-induced drinking at different times (2/24 h) after furosemide administration combined with a low sodium diet (FURO-LSD). In sodium depleted wild type and TRPV1 KO (SD-WT/SD-TPRV1-KO) mice, we also evaluated the participation of other sodium sensors, such as TPRV4, NaX and angiotensin AT1-receptors (by RT-PCR), as well as investigating the pattern of neural activation shown by Fos immunoreactivity, in different nuclei involved in hydromineral regulation. TPRV1 SD-KO mice revealed an increased sodium preference, ingesting a higher hypertonic cocktail in comparison with SD-WT mice. Our results also showed in SD-WT animals that SFO-Trpv4 expression increased 2 h after FURO-LSD, compared to other groups, thus supporting a role of SFO-Trpv4 channels during the hyponatremic state. However, the SD-TPRV1-KO animals did not show this early increase, and maybe as a consequence drank more hypertonic cocktail. Regarding the SFO-NaX channel expression, in both genotypes our findings revealed a reduction 24 h after FURO-LSD. In addition, there was an increase in the OVLT-NaX expression of SD-WT 24 h after FURO-LSD, suggesting the participation of OVLT-NaX channels in the appearance of sodium appetite, possibly as an anticipatory response in order to limit sodium intake and to induce thirst. Our work demonstrates changes in the expression of different osmo­sodium-sensitive channels at specific nuclei, related to the body sodium status in order to stimulate an adequate drinking.

Interaction of central angiotensin II and aldosterone on sodium intake and blood pressure.

Recent studies demonstrated an important natriorexigenic mechanism activated by aldosterone acting in the hindbrain. Studies have also shown that aldosterone effects are intensified by angiotensin II (ANG II) and vice-versa. Thus, the aim of the present work was to test if angiotensinergic mechanisms in the forebrain are involved on sodium appetite to aldosterone infused into the 4th V and also if aldosterone into the 4th V might facilitate ingestive and cardiovascular responses to central ANG II. Male Holtzman rats with stainless steel cannulas implanted into the 4th ventricle (4th V) and lateral ventricle (LV) had access to 1.8% NaCl during 2 h/day. Chronic infusion of aldosterone (100 ng/h) into the 4th V for 7 days strongly increased 1.8% NaCl intake (16.1 ±â€¯2.2 ml/2h/day). Losartan (AT1 receptor antagonist, 50 µg/1 µl) acutely injected into the LV reduced 1.8% NaCl intake induced by aldosterone infusion into the 4th V (8.8 ±â€¯2.3 ml/2h/day). The pressor response to ANG II (50 ng/1 µl) into the LV increased in rats treated with aldosterone into the 4th V (45 ±â€¯5 mmHg, vs. vehicle infusion: 26 ±â€¯4 mmHg). Similarly, fluid intake (water + 1.8% NaCl) also increased when rats receiving aldosterone infusion were treated with ANG II acutely into the LV. These results suggest that forebrain angiotensinergic mechanisms are important for sodium intake produced by aldosterone acting in the hindbrain. In addition, aldosterone in the hindbrain produces sensitization of the central pressor mechanisms activated by ANG II acting in the forebrain.

Renal developmental disturbances and their long-term consequences in female pups from vitamin D-deficient mothers: involved mechanisms.

The mechanisms involved in kidney disturbances during development, induced by vitamin D3 deficiency in female rats, that persist into adulthood were evaluated in this study. Female offspring from mothers fed normal (control group, n=8) or vitamin D-deficient (Vit.D-, n=10) diets were used. Three-month-old rats had their systolic blood pressure (SBP) measured and their blood and urine sampled to quantify vitamin D3 (Vit.D3), creatinine, Na+, Ca+2 and angiotensin II (ANGII) levels. The kidneys were then removed for nitric oxide (NO) quantification and immunohistochemical studies. Vit.D- pups showed higher SBP and plasma ANGII levels in adulthood (P<0.05) as well as decreased urine osmolality associated with increases in urinary volume (P<0.05). Decreased expression of JG12 (renal cortex and glomeruli) and synaptopodin (glomeruli) as well as reduced renal NO was also observed (P<0.05). These findings showed that renal disturbances in development in pups from Vit.D- mothers observed in adulthood may be related to the development of angiogenesis, NO and ANGII alterations.

17ß-Estradiol attenuates p38MAPK activity but not PKCα induced by angiotensin II in the brain.

17ß-Estradiol (E2) has been shown to modulate the renin-angiotensin system in hydromineral and blood pressure homeostasis mainly by attenuating angiotensin II (ANGII) actions. However, the cellular mechanisms of the interaction between E2 and angiotensin II (ANGII) and its physiological role are largely unknown. The present experiments were performed to better understand the interaction between ANGII and E2 in body fluid control in female ovariectomized (OVX) rats. The present results are the first to demonstrate that PKC/p38 MAPK signaling is involved in ANGII-induced water and sodium intake and oxytocin (OT) secretion in OVX rats. In addition, previous data from our group revealed that the ANGII-induced vasopressin (AVP) secretion requires ERK1/2 signaling. Therefore, taken together, the present observations support a novel concept that distinct intracellular ANGII signaling gives rise to distinct neurohypophyseal hormone release. Furthermore, the results show that E2 attenuates p38 MAPK phosphorylation in response to ANGII but not PKC activity in the hypothalamus and the lamina terminalis, suggesting that E2 modulates ANGII effects through the attenuation of the MAPK pathway. In conclusion, this work contributes to the further understanding of the interaction between E2 and ANGII signaling in hydromineral homeostasis, as well as it contributes to further elucidate the physiological relevance of PKC/p38 MAPK signaling on the fluid intake and neurohypophyseal release induced by ANGII.

A single episode of high intensity sound inhibits long-term potentiation in the hippocampus of rats.

Exposure to loud sounds has become increasingly common. The most common consequences of loud sound exposure are deafness and tinnitus, but emotional and cognitive problems are also associated with loud sound exposure. Loud sounds can activate the hipothalamic-pituitary-adrenal axis resulting in the secretion of corticosterone, which affects hippocampal synaptic plasticity. Previously we have shown that long-term exposure to short episodes of high intensity sound inhibited hippocampal long-term potentiation (LTP) without affecting spatial learning and memory. Here we aimed to study the impact of short term loud sound exposure on hippocampal synaptic plasticity and function. We found that a single minute of 110 dB sound inhibits hippocampal Schaffer-CA1 LTP for 24 hours. This effect did not occur with an 80-dB sound exposure, was not correlated with corticosterone secretion and was also observed in the perforant-dentate gyrus synapse. We found that despite the deficit in the LTP these animals presented normal spatial learning and memory and fear conditioning. We conclude that a single episode of high-intensity sound impairs hippocampal LTP, without impairing memory and learning. Our results show that the hippocampus is very responsive to loud sounds which can have a potential, but not yet identified, impact on its function.

Sodium appetite elicited by low-sodium diet is dependent on p44/42 mitogen-activated protein kinase (extracellular signal-regulated kinase 1/2) activation in the brain.

Sodium appetite is regulated by several signalling molecules, among which angiotensin II (Ang II) serves as a key driver of robust salt intake by binding to Ang II type 1 receptors (AT1R) in several regions in the brain. The activation of these receptors recruits the mitogen-activated protein kinase (MAPK) pathway, which has previously been linked to Ang II-induced increases in sodium appetite. Thus, we addressed the involvement of MAPK signalling in the induction of sodium appetite after 4 days of low-sodium diet consumption. An increase in extracellular signal-regulated kinase (ERK) phosphorylation in the laminae terminalis and mediobasal hypothalamus was observed after low-sodium diet consumption. This response was reduced by i.c.v. microinjection of an AT1R antagonist into the laminae terminalis but not the hypothalamus. This result indicates that low-sodium diet consumption activates the MAPK pathway via Ang II/AT1R signalling on the laminae terminalis. On the other hand, activation of the MAPK pathway in the mediobasal hypothalamus after low-sodium diet consumption appears to involve another extracellular mediator. We also evaluated whether a low-sodium diet could increase the sensitivity for Ang II in the brain and activate the MAPK pathway. However, i.c.v. injection of Ang II increased ERK phosphorylation on the laminae terminalis and mediobasal hypothalamus; this increase achieved a response magnitude similar to those observed in both the normal and low-sodium diet groups. These data indicate that low-sodium diet consumption for 4 days is insufficient to change the ERK phosphorylation response to Ang II in the brain. To investigate whether the MAPK pathway is involved in sodium appetite after low-sodium diet consumption, we performed i.c.v. microinjections of a MAPK pathway inhibitor (PD98059). PD98059 inhibited both saline and water intake after low-sodium diet consumption. Thus, the MAPK pathway is involved in promoting the sodium appetite after low-sodium diet consumption.

Differential Role of Neurohypophysial Hormones in Hypotension and Nitric Oxide Production During Endotoxaemia.

Besides their well-established endocrine roles, vasopressin and oxytocin are also important regulators of immune function, participating in a complex neuroendocrine-immune network. In the present study, we investigated whether and how vasopressin and oxytocin could modulate lipopolysaccharide (LPS)-induced nitric oxide (NO) production in a well-established model of experimental endotoxaemia. Male Wistar rats were previously treated i.v. with vasopressin V1 or oxytocin receptor antagonists and then received either an i.v. LPS injection to induce endotoxaemia or a saline imjection as a control. The animals were divided into two groups: in the first group, blood was collected at 2, 4 and 6 h after LPS injection; in the second group, mean arterial blood pressure (MABP) and heart rate (HR) were recorded over 6 h. Plasma vasopressin and oxytocin values were higher in LPS- compared to saline-injected animals at 2 and 4 h but returned to basal levels at 6 h. NO levels exhibited an opposite pattern, showing a progressive increase over the entire period. The previous administration of a vasopressin V1 receptor antagonist significantly reduced NO plasma concentrations at 2 and 4 h but not at 6 h. By contrast, oxytocin receptor agonist pre-treatment had no effect on the NO plasma concentration. In relation to MABP, previous treatment with vasopressin V1 receptor antagonist reversed the LPS-induced hypotension at 4 h, although this was not the case for oxytocin antagonist-treated animals. None of the antagonists affected HR. Our findings indicate that vasopressin (but not oxytocin) has effects on NO production during endotoxaemia in rats, although they do not lend support to the proposed anti-inflammatory actions of vasopressin during endotoxaemia.

Estradiol and angiotensin II crosstalk in hydromineral balance: Role of the ERK1/2 and JNK signaling pathways.

The angiotensin II (ANGII) receptor AT1 plays an important role in the control of hydromineral balance, mediating the dipsogenic and natriorexigenic effects and neuroendocrine responses of ANGII. While estradiol (E2) is known to modulate several actions of ANGII in the brain, the molecular and cellular mechanisms of the interaction between E2 and ANGII and its physiological role in the control of body fluids remain unclear. We investigated the influence of E2 (40 µg/kg) pretreatment and extracellular-signal-regulated kinase (ERK1/2) and c-Jun N-terminal kinase (JNK) cell signaling on the dipsogenic and natriorexigenic effects, as well as the neuroendocrine responses to angiotensinergic central stimulation in ovariectomized rats (OVX). We showed that the inhibitory effect of E2 on ANGII-induced water and sodium intake requires the ERK1/2 and JNK signaling pathways. On the other hand, E2 pretreatment prevents the ANGII-induced phosphorylation of ERK and JNK in the lamina terminalis. E2 therapy decreased oxytocin (OT) and vasopressin (AVP) secretion and decreased ERK1/2 phosphorylation in the supraoptic and paraventricular nuclei (SON and PVN, respectively). We found that the AVP secretion induced by ANGII required ERK1/2 signaling, but OT secretion did not involve ERK1/2 signaling. Taken together, these results demonstrate that E2 modulates ANGII-induced water and sodium intake and AVP secretion by affecting the ERK1/2 and JNK pathways in the lamina terminalis and ERK1/2 signaling in the hypothalamic nuclei (PVN and SON) in OVX rats.

The type-1 cannabinoid receptor modulates the hydroelectrolytic balance independently of the energy homeostasis during salt load.

Hydroelectrolytic imbalances, such as saline load (SL), trigger behavioral and neuroendocrine responses, such as thirst, hypophagia, vasopressin (AVP) and oxytocin (OT) release and hypothalamus­pituitary­adrenal (HPA) axis activation. To investigate the participation of the type-1 cannabinoid receptor (CB1R) in these homeostatic mechanisms,male adult Wistar rats were subjected to SL (0.3MNaCl) for four days. SL induced not only increases in the water intake and plasma levels of AVP, OT and corticosterone, as previously described, but also increases in CB1R expression in the lamina terminalis, which integrates sensory afferents, aswell as in the hypothalamus, the main integrative and effector area controlling hydroelectrolytic homeostasis. A more detailed analysis revealed that CB1R-positive terminals are in close apposition with not only axons but also dendrites and secretory granules of magnocellular neurons, particularly vasopressinergic cells. In satiated and euhydrated animals, the intracerebroventricular administration of the CB1R selective agonist ACEA (0.1 µg/5 µL) promoted hyperphagia, but this treatment did not reverse the hyperosmolality-induced hypophagia in the SL group. Furthermore, ACEA pretreatment potentiated water intake in the SL animals during rehydration as well as enhanced the corticosterone release and prevented the increase in AVP and OT secretion induced by SL. The same parameters were not changed by ACEA in the animals whose daily food intake was matched to that of the SL group (Pair-Fed). These data indicate that CB1Rs modulate the hydroelectrolytic balance independently of the food intake during sustained hyperosmolality and hypovolemia.

Methylmercury inhibits prolactin release in a cell line of pituitary origin

Heavy metals, such as methylmercury, are key environmental pollutants that easily reach human beings by bioaccumulation through the food chain. Several reports have demonstrated that endocrine organs, and especially the pituitary gland, are potential targets for mercury accumulation; however, the effects on the regulation of hormonal release are unclear. It has been suggested that serum prolactin could represent a biomarker of heavy metal exposure. The aim of this study was to evaluate the effect of methylmercury on prolactin release and the role of the nitrergic system using prolactin secretory cells (the mammosomatotroph cell line, GH3B6). Exposure to methylmercury (0-100 μM) was cytotoxic in a time- and concentration-dependent manner, with an LC50 higher than described for cells of neuronal origin, suggesting GH3B6 cells have a relative resistance. Methylmercury (at exposures as low as 1 μM for 2 h) also decreased prolactin release. Interestingly, inhibition of nitric oxide synthase by N-nitro-L-arginine completely prevented the decrease in prolactin release without acute neurotoxic effects of methylmercury. These data indicate that the decrease in prolactin production occurs via activation of the nitrergic system and is an early effect of methylmercury in cells of pituitary origin.

Methylmercury inhibits prolactin release in a cell line of pituitary origin.

Heavy metals, such as methylmercury, are key environmental pollutants that easily reach human beings by bioaccumulation through the food chain. Several reports have demonstrated that endocrine organs, and especially the pituitary gland, are potential targets for mercury accumulation; however, the effects on the regulation of hormonal release are unclear. It has been suggested that serum prolactin could represent a biomarker of heavy metal exposure. The aim of this study was to evaluate the effect of methylmercury on prolactin release and the role of the nitrergic system using prolactin secretory cells (the mammosomatotroph cell line, GH3B6). Exposure to methylmercury (0-100 µM) was cytotoxic in a time- and concentration-dependent manner, with an LC50 higher than described for cells of neuronal origin, suggesting GH3B6 cells have a relative resistance. Methylmercury (at exposures as low as 1 µM for 2 h) also decreased prolactin release. Interestingly, inhibition of nitric oxide synthase by N-nitro-L-arginine completely prevented the decrease in prolactin release without acute neurotoxic effects of methylmercury. These data indicate that the decrease in prolactin production occurs via activation of the nitrergic system and is an early effect of methylmercury in cells of pituitary origin.

Temporal dissociation between sodium depletion and sodium appetite appearance: Involvement of inhibitory and stimulatory signals.

Our aim was to analyze the participation of inhibitory and stimulatory signals in the temporal dissociation between sodium depletion (SD) induced by peritoneal dialysis (PD) and the appearance of sodium appetite (SA), particularly 2h after PD, when the rats are hypovolemic/natremic but SA is not evident. We investigated the effects of bilateral injections of the serotonin (5-HT) receptor antagonist, methysergide, into the lateral parabrachial nucleus (LPBN) on hypertonic NaCl and water intake 2h vs. 24h after PD. We also studied plasma renin activity (PRA) and aldosterone (ALDO) concentration 2h vs. 24h after PD. Additionally, we combined the analysis of brain Fos immunoreactivity (Fos-ir) with the detection of double immunoreactivity in 5HT and oxytocinergic (OT) cells 2h after PD. Bilateral LPBN injections of methysergide (4µg/200nl at each site) increased NaCl intake when tested 2h after PD compared to controls. We found a significant increase in PRA and ALDO concentration after PD but no differences between 2 and 24h after PD. We also found for the first time a significant increase 2h after PD in the number of Fos-ir neurons in the brainstem nuclei that have been shown to be involved in the inhibition of SA. In summary, the results show that 5HT-mechanisms in the LPBN modulate sodium intake during the delay of SA when the renin angiotensin aldosterone system (RAAS) is increased. In addition, the activation of brainstem areas previously associated with the satiety phase of SA is in part responsible for the temporal dissociation between SD and behavioral arousal.

Effects of hydrogen sulfide (H2S) on water intake and vasopressin and oxytocin secretion induced by fluid deprivation.

During dehydration, responses of endocrine and autonomic control systems are triggered by central and peripheral osmoreceptors and peripheral baroreceptors to stimulate thirst and sodium appetite. Specifically, it is already clear that endocrine system acts by secreting vasopressin (AVP), oxytocin (OT) and angiotensin II (ANG II), and that gaseous molecules, such as nitric oxide (NO) and carbon monoxide (CO), play an important role in modulating the neurohypophyseal secretion as well as ANG II production and thirst. More recently, another gas-hydrogen sulfide (H2S)-has been studied as a neuronal modulator, which is involved in hypothalamic control of blood pressure, heart frequency and temperature. In this study, we aimed to investigate whether H2S and its interaction with NO system could participate in the modulatory responses of thirst and hormonal secretion induced by fluid deprivation. For this purpose, Wistar male rats were deprived of water for 12 and 24h, and the activity of sulfide-generating enzymes was measured. Surprisingly, 24-h water deprivation increased the activity of sulfide-generating enzymes in the medial basal hypothalamus (MBH). Furthermore, the icv injection of sodium sulfide (Na2S, 260nmol), a H2S donor, reduced water intake, increased AVP, OT and CORT plasma concentrations and decreased MBH nitrate/nitrite (NOX) content of 24-h water-deprived animals compared to controls. We thus suggest that H2S system has an important role in the modulation of hormonal and behavioral responses induced by 24-h fluid deprivation.

Carbon monoxide and nitric oxide interactions in magnocellular neurosecretory neurones during water deprivation.

Nitric oxide (NO) and carbon monoxide (CO) are diffusible gas messengers in the brain. Previously, we have shown their independent involvement in central fluid/electrolyte homeostasis control. In the present study, we investigated a possible functional interaction between NO/CO in the regulation of vasopressin (VP) and oxytocin (OT) magnocellular neurosecretory cells (MNCs) activity in euhydrated (EU) and dehydrated [48-h water-deprived (48WD)] rats. Using brain slices from EU and 48WD rats, we measured, by immunohistochemistry, the expression of neuronal NO synthase (nNOS, which synthesises NO) and haeme-oxygenase (HO-1, which synthesises CO) in the hypothalamic supraoptic nucleus (SON). In addition, we used patch-clamp electrophysiology to investigate whether regulation of SON MNC firing activity by endogenous CO was dependent on NO bioavailability and GABAergic inhibitory synaptic function. We found a proportion of OT and VP SON MNCs in EU rats to co-express both of HO-1 and nNOS (33.2 ± 2.9% and 15.3 ± 1.4%, respectively), which was increased in 48WD rats (55.5 ± 0.9% and 21.0 ± 1.7%, respectively, P < 0.05 for both). Inhibition of endogenous HO activity [chromium mesoporphyrin IX chloride (CrMP) 20 µm] induced MNC membrane hyperpolarisation and decreased firing activity, and these effects were blunted by previous blockade of endogenous NOS activity (l-NAME, 2 mm) or blockade of inhibitory GABA function [Picrotoxin (Sigma-Aldrich, St Louis, MO, USA), 50 µm]. No significant changes in SON NO bioavailability (4,5 diaminofluorescein diacetate fluorescence) were observed after CrMP treatment. Taken together, our results support a state-dependent functional inter-relationship between NO and CO in MNCs, in which CO acts as an excitatory gas molecule, whose effects are largely dependent on interactions with the inhibitory SON signals NO and GABA.

Oestradiol modulates the effects of leptin on energy homeostasis by corticotrophin-releasing factor type 2 receptor.

In addition to its action in the control of the hypothalamic-pituitary-adrenal axis, corticotrophin-releasing factor (CRF) has been described as an anorexigenic neuropeptide, modulating food intake and energy expenditure. CRF synthesis is influenced by leptin, which would act to increase CRF neurone activation in the paraventricular nucleus (PVN). Gonadal hormones also participate in the regulation of energy homeostasis. The reduction of food intake and body weight gain in ovariectomised (OVX) rats treated with oestradiol is associated with an increase in CRF mRNA expression in the PVN. The present study aimed to investigate the role of CRF as a mediator of leptin responsiveness in the presence of oestradiol. Wistar female rats were bilaterally OVX and divided into three groups: OVX, OVX+E (i.e. treated with oestradiol) and OVX+PF (i.e. OVX pairfed with OVX+E). The rats received daily s.c. injections of either oestradiol cypionate or vehicle for 8 days. To evaluate the role of CRF on the effects of leptin, we performed an i.c.v. leptin injection (10 µg/5 µl) with or without previous i.c.v. treatment with an CRF-R2 antagonist. We observed that oestradiol replacement in OVX rats reduced body weight gain and food intake. The effects of exogenous leptin administration with respect to decreasing food intake and body weight, and increasing uncoupling protein-1 expression in the brown adipose tissue and neuronal activation in the arcuate nucleus, were reversed by previous administration of a CRF-R2 antagonist only in oestradiol-treated OVX rats. These effects appear to be mediated by CRF-2 receptor because the antagonist of this receptor reversed the action of oestradiol on the effects of leptin.

The endocannabinoid system and the neuroendocrine control of hydromineral balance.

Endocannabinoids (ECBs) are ubiquitous lipophilic agents, and this characteristic is consistent with the wide range of homeostatic functions attributed to the ECB system. There is an increasing number of studies showing that the ECB system affects neurotransmission within the hypothalamic neurohypophyseal system. We provide an overview of the primary roles of ECBs in the modulation of neuroendocrine function and, specifically, in the control of hydromineral homeostasis. Accordingly, the general aspects of ECB-mediated signalling, as well as the specific contributions of the central component of the ECB system to the integration of behavioural and endocrine responses that control body fluid homeostasis, are discussed.