Exaggerated response of arginine vasopressin-enhanced green fluorescent protein fusion gene to salt loading without disturbance of body fluid homeostasis in rats

We examined the effects of chronic salt loading on the hypothalamic expressions of the enhanced green fluorescent protein (eGFP), arginine vasopressin (AVP) and oxytocin (OXT) genes in AVP-eGFP transgenic rats that expressed eGFP in the hypothalamic AVP-containing neurones. In these rats, salt loading for 5 days caused a marked increase of the eGFP fluorescence in the magnocellular divisions of the paraventricular nucleus (PVN), the supraoptic nucleus (SON) and the internal layer of the median eminence. Expression of the eGFP gene was increased seven- to eight-fold in the PVN and SON of salt-loaded rats in comparison with euhydrated rats. By contrast, none of these changes were observed in the suprachiasmatic nucleus. The expression of the AVP and OXT genes was increased 1.5- to two-fold in the PVN and SON of salt-loaded nontransgenic (control) and transgenic rats. There were no differences in the expression levels of the AVP and OXT genes in the PVN and SON between nontransgenic (control) and transgenic animals under normal conditions and after salt loading. In the posterior pituitary gland, the intensity of the eGFP fluorescence did not change after salt loading for 5 days, but increased after 10 days of salt loading. Upon salt loading, significant increases in the plasma AVP concentrations, plasma osmolality and plasma Na+ were observed. Furthermore, there were no significant differences in changes of water intake, food intake, urine volume, urine osmolality, urine Na+ concentrations, and the body weights in both models under normal or salt-loaded conditions. Our results show that the response of the AVP-eGFP fusion gene to chronic salt loading is exaggerated, and humoral responses such as AVP and OXT and the body fluid homeostasis are maintained in AVP-eGFP transgenic rats. The AVP-eGFP transgenic rat gives us a new opportunity to study the dynamics of the AVP system in vivo.

Prolactin-releasing peptide is a potent mediator of stress responses in the brain through the hypothalamic paraventricular nucleus

The effects of i.c.v. administration of prolactin-releasing peptide on neurons in the paraventricular nucleus of rats and plasma corticosterone levels were examined by measuring changes in Fos-like immunoreactivity, c-fos mRNA using in situ hybridization histochemistry, and plasma corticosterone using a specific radioimmunoassay. Approximately 80% of corticotropin-releasing hormone immunoreactive cells exhibited Fos-like immunoreactivity in the parvocellular division of the paraventricular nucleus 90 min after i.c.v. administration of prolactin-releasing peptide. The greatest induction of the c-fos mRNA expression in the paraventricular nucleus was observed 30 min after administration of prolactin-releasing peptide, and occurred in a dose-related manner. Plasma corticosterone levels were also significantly increased 30 min after administration of prolactin-releasing peptide. Next, the effects of restraint stress, nociceptive stimulus and acute inflammatory stress on the expression of the prolactin-releasing peptide mRNA in the dorsomedial hypothalamic nucleus, nucleus of the solitary tract and ventrolateral medulla were examined using in situ hybridization histochemistry for prolactin-releasing peptide mRNA. Restraint stress and acute inflammatory stress upregulated the prolactin-releasing peptide mRNA expression in the nucleus of the solitary tract and ventrolateral medulla. Nociceptive stimulus upregulated the prolactin-releasing peptide mRNA expression in the ventrolateral medulla. Finally, we observed that pretreatment (i.c.v. administration) with an anti-prolactin-releasing peptide antibody significantly attenuated nociceptive stimulus-induced c-fos mRNA expression in the paraventricular nucleus. These results suggest that prolactin-releasing peptide is a potent and important mediator of the stress response in the brain through the hypothalamic paraventricular nucleus.

Cannabinoids modulate synaptic activity in the rat supraoptic nucleus

In the present study, we investigated the effects of the cannabinoid receptor agonist CP55,940 on excitatory and inhibitory synaptic transmission in the rat supraoptic nucleus. Whole-cell patch clamp recordings were performed on supraoptic neurones in in vitro brain slice preparations. CP55,940 significantly reduced the frequency of spontaneous excitatory and inhibitory postsynaptic currents in a concentration-dependent manner. These changes were potently reversed by the CB1 receptor antagonist AM251. The results indicate that cannabinoids modulate the activity of magnocellular neurosecretory neurones by presynaptic inhibition of both excitatory and inhibitory synaptic transmission.

Expression of immediate early genes and vasopressin heteronuclear RNA in the paraventricular and supraoptic nuclei of rats after acute osmotic stimulus

Monitoring the expression of immediate early genes (IEGs) is useful for following stress-induced cellular responses in the neuroendocrine system. We have examined the transcriptional activities of four IEGs (c-fos, junB, NGFI-A and NGFI-B) and of the arginine vasopressin (AVP) gene in the hypothalamic paraventicular (PVN) and supraoptic nuclei (SON) of rats after acute osmotic stimuli, using in situ hybridization histochemistry. After intraperitoneal (i.p.) administration of hypertonic saline (2% body weight, 900 mOsm/kg), the expression levels of all IEG mRNAs were increased significantly both in the PVN and SON at as early as 10 min, peaked at 30 min and remained elevated until 60 min. The expression of AVP heteronuclear (hn)RNA also peaked at 30 min, and remained elevated until 180 min. Thirty min after i.p. administration of hypertonic saline (600 mOsm/kg), the expression levels of all IEG mRNAs in the PVN and SON were significantly increased in comparison with those after i.p. administration of isotonic saline (290 mOsm/kg). Regression analysis revealed that expression levels of the IEG mRNAs and AVP hnRNA were positively correlated with the plasma concentration of sodium, and the rates of increase of the expression levels of all IEG mRNAs were similar. The expression levels of all IEG mRNAs examined are useful markers for following the changes of the AVP gene transcription in the PVN and SON after acute osmotic stimuli in rats.

Stomach regulates energy balance via acylated ghrelin and desacyl ghrelin

BACKGROUND/AIMS

The gastric peptide ghrelin, an endogenous ligand for growth-hormone secretagogue receptor, has two major molecular forms: acylated ghrelin and desacyl ghrelin. Acylated ghrelin induces a positive energy balance, while desacyl ghrelin has been reported to be devoid of any endocrine activities. The authors examined the effects of desacyl ghrelin on energy balance.

METHODS

The authors measured food intake, gastric emptying, c-Fos expression in the hypothalamus, and gene expression of hypothalamic neuropeptides in mice after administration of desacyl ghrelin. To explore the effects of long term overexpression of desacyl ghrelin, transgenic mice that overexpressed desacyl ghrelin were created.

RESULTS

Administration of desacyl ghrelin decreased food intake and gastric emptying rate through an action on the paraventricular nucleus and the arcuate nucleus in the hypothalamus. Gene expression of anorexigenic cocaine and amphetamine regulated transcript and urocortin in the hypothalamus was increased by desacyl ghrelin. Desacyl ghrelin overexpressing mice exhibited a decrease in body weight, food intake, and fat pad mass weight accompanied by moderately decreased linear growth. Gastric emptying was also decreased in desacyl ghrelin overexpressing mice.

CONCLUSIONS

These findings indicate that in contrast to acylated ghrelin, desacyl ghrelin induces a negative energy balance by decreasing food intake and delaying gastric emptying. The effect is mediated via the hypothalamus. Although derived from the same precursor, the inverse effects of these two peptides suggest that the stomach might be involved as an endocrine organ in the regulation of the energy balance.

Potentiation by angiotensin II of spontaneous excitatory postsynaptic currents in rat supraoptic magnocellular neurones

The physiological actions of angiotensin II in the supraoptic (SON) and paraventricular nuclei have been widely demonstrated, including the modulation of firing rate and release of arginine vasopressin and oxytocin. Here, we investigated whether angiotensin II modulates synaptic inputs into the SON. To do this, we measured spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) from rat SON neurones in thin slice preparations using the whole-cell patch-clamp technique. Angiotensin II reversibly increased the frequency of spontaneous EPSCs in a dose-related manner without affecting the amplitude, indicating that angiotensin II potentiated EPSCs via a presynaptic mechanism. Angiotensin II-induced potentiation of EPSCs was unaffected in the presence of tetrodotoxin. On the other hand, angiotensin II did not cause significant effects on IPSCs. The potentiation of EPSCs by angiotensin II was potently suppressed by previous exposure to the angiotensin type 1 (AT1) receptor antagonist, losartan. Our results suggest that angiotensin II potentiates the excitatory synaptic inputs into SON neurones, via the AT1 receptors.

Novel G-protein coupled receptor ligands and neurohypophysial hormones

Recently, novel peptides have been identified as unknown ligands of orphan G-protein coupled receptors. In the paraventicular (PVN) and supraoptic nuclei (SON), the expression of the G-protein genes are abundant. In this review, we focus on the physiological role of neuromedin U and galanin-like peptide, which were recently identified as ligands of G-protein coupled receptors, in the regulation of neurohypophysial hormones. Intracerebroventricular (i.c.v) administration of neuromedin U induced the expression of c-fos mRNA in both the magnocellular and parvocellular division of the PVN and throughout the SON. Administration of i.c.v. neuromedin U caused a significant increase in plasma concentrations of vasopressin and oxytocin as well as adrenocorticotropic hormone. The expression of galanin-like peptide mRNA was observed in the pituicytes of rat posterior pituitary gland. The expression of galanin-like peptide mRNA in the posterior pituitary gland was markedly increased after dehydration, salt loading and intraperitoneal administration of lipopolysaccaride, challenges that stimulate the secretion of vasopressin and oxytocin, and which activate the hypothalamic-pituitary adrenal axis. These results suggest that neuromedin U and galanin-like peptide may have an important role in the regulation of both the hypothalamic-neurohypophysial system and the hypothalamic-adrenohypophysial system.

Expression of the arginine vasopressin gene in response to salt loading in oxytocin gene knockout mice

Accumulating evidence suggests that both oxytocin and arginine vasopressin (AVP) are vital components in the regulation of body fluid balance. However, the physiological role of oxytocin and possible cooperative interactions between oxytocin and AVP in sodium balance remain obscure, even though recent studies using oxytocin knockout (OTKO) mice suggested that oxytocin may contribute to the regulation of salt appetite. In the present study, we examined the effects of salt loading (drinking 2% NaCl for 5 days) on the expression of the AVP gene in the paraventricular (PVN) and supraoptic nuclei (SON) of wild-type, OTKO and heterozygous littermates using in situ hybridization histochemistry. In addition, the effects of salt loading on the expression of the oxytocin gene were also examined in wild-type and heterozygous mice. Under the non salt-loaded condition, the levels of AVP mRNA in the PVN and SON of OTKO mice were significantly decreased compared to those in wild-type mice. Nevertheless, the up-regulation of the expression of the AVP gene in response to salt loading was preserved in OTKO mice. The degree of the up-regulation in OTKO mice tended to be greater compared to those in wild-type mice, suggesting compensatory up-regulation of the expression of the AVP gene in OTKO mice after salt loading. The basal levels of oxytocin mRNA in the PVN and SON of heterozygous mice were significantly lower than those in wild-type mice. Salt loading caused an increase of oxytocin mRNA levels in the PVN and SON of both wild-type and heterozygous mice. The ratios of increase of oxytocin mRNA levels were very similar between wild-type and heterozygous mice, suggesting that the single remaining oxytocin gene in heterozygous mice responds normally to an osmotic cue. Finally, salt loading tended to increase the serum concentration of sodium regardless of genotype, and there were no genotype differences in both the control and salt-loaded groups. These results suggest ways in which oxytocin may play a cooperative role together with AVP in the regulation of sodium balance.

Enhanced up-regulation of corticotropin-releasing hormone gene expression in response to restraint stress in the hypothalamic paraventricular nucleus of oxytocin gene-deficient male mice

The neuropeptide oxytocin is released not only into the blood, but also within the brain in response to various stressors. Accumulating evidence suggests that central oxytocin may play a major role in the regulation of neuroendocrine responses to stress. In the present study, using the oxytocin knockout mouse model, we tested whether oxytocin might act to attenuate stress-induced up-regulation of corticotropin-releasing hormone (CRH) mRNA expression in the brain. The expression of CRH mRNA in the paraventricular nucleus (PVN) after 4 h of restraint stress was examined in oxytocin gene-deficient (OTKO), wild-type and heterozygous male mice using in situ hybridization histochemistry. We found that basal levels of CRH mRNA were not different among the three genotypes. Although restraint stress resulted in a significant increase of CRH mRNA expression in the PVN regardless of genotype, the degree of stress induced-up-regulation was significantly higher in OTKO mice than in wild-type mice. The effects of restraint stress on the expression of the arginine vasopressin (AVP) and the oxytocin genes were also examined. Unlike CRH mRNA, basal expression (in nonstressed control groups) of AVP mRNA in OTKO mice, as well as oxytocin mRNA in heterozygous mice, was significantly lower in the PVN and the supraoptic nucleus than in wild-type mice. After restraint stress, the expression of AVP mRNA was significantly increased in the PVN of OTKO mice compared to the nonstressed control group, whereas the expression of both AVP and oxytocin mRNA were unchanged in the PVN and the supraoptic nucleus of wild-type and heterozygous mice. Finally, in a separate set of mice, restraint stress-induced Fos expression was also examined in several brain regions involved in stress response, including the lateral septum, the bed nucleus of the stria terminalis (BNST), the medial preoptic area, the PVN, the medial and central amygdala using immunohistochemistry. After 90 min of restraint stress, the number of Fos-expressing cells significantly increased in all brain regions examined regardless of genotype. However, the number of stress-induced Fos-expressing cells in the BNST and the medial amygdala of OTKO mice was significantly lower than in wild-type mice. Collectively, the findings in the present study suggest that oxytocin may regulate stress-induced CRH gene expression in the PVN. Furthermore, neuronal activity in the BNST and the medial amygdala may be involved in this neuroendocrine regulatory system.

Intermittent footshock facilitates dendritic vasopressin release but suppresses vasopressin synthesis within the rat supraoptic nucleus

Emotional stress inhibits vasopressin release from the pituitary but may facilitate its release from the dendrites in the hypothalamus. We examined effects of intermittently applied footshock upon the amount of vasopressin heteronuclear RNA in the hypothalamus. The footshock decreased plasma vasopressin concentration but increased its extracellular concentration within the supraoptic nucleus. The contents of the vasopressin heteronuclear RNA in the supraoptic nucleus were significantly decreased after the shock. These data suggest that intermittent footshock decreases not only vasopressin release from the axon terminals in the pituitary, but also vasopressin synthesis in the cell bodies in the hypothalamus while the stimulus facilitates vasopressin release from the dendrites in the hypothalamus. The data also suggest differential control of dendritic vasopressin release and synthesis in the hypothalamus.

Chronic adrenomedullin treatment improves blood-brain barrier function but has no effects on expression of tight junction proteins

We previously found that the production of adrenomedullin (AM) is one magnitude higher in cerebral endothelial cells (CECs) than in the peripheral endothelium and the AM concentration in the cerebral circulation is significantly higher than in other tested parts of the circulation. We also showed that CECs express AM receptors, and AM as an autocrine hormone is important to regulate the intracellular cAMP level in CECs. Further we reported that acute AM treatment has cAMP-like effects on specific BBB functions: AM decreased endothelial fluid phase endocytosis, activated the P-glycoprotein, increased transendothelial electrical resistance (TEER) and reduced endothelial permeability for sodium fluorescein, which suggests a tightening of intercellular junctions. In the present study, we found chronic AM exposure also increased TEER. In contrast, we could not detect significant effect of AM on the expression of tight junction proteins (claudin-1, occludin and zonula occludens-1). While not affecting expression of tight junction proteins, chronic AM treatment may influence the localization of these proteins which has been reported to correlate with functional changes of the BBB without a change in protein expression.

Mechanisms of cytosolic Ca2+ suppression by prostaglandin E2 receptors in rat melanotrophs

We have previously reported that voltage-dependent Ca2+ (VDC) channels of rat melanotrophs are inhibited by prostaglandin E2 (PGE2). In this study, mechanisms involved in the inhibitory actions of PGE2 receptors of rat melanotrophs were analysed using reverse transcriptase-polymerase chain reaction (RT-PCR), Ca2+-imaging and whole-cell, patch-clamp techniques with recently developed EP agonists, each of which is selective for the known four subclasses of EP receptors (EP1-4). PGE2 reversibly suppressed the cytosolic Ca2+ concentration ([Ca2+]i). The maximum reduction in [Ca2+]i by PGE2 was comparable to that by dopamine or to that by extracellular Ca2+ removal. RT-PCR analysis of all four EP receptors revealed that EP3 and EP4 receptor mRNAs were expressed in the intermediate lobe. The effects of PGE2 to suppress [Ca2+]i were mimicked by the selective EP3 agonist, ONO-AE-248, whereas three other EP agonists, ONO-DI-004 (EP1), ONO-AE1-259 (EP2) and ONO-AE1-329 (EP4), had little or no effect on [Ca2+]i. All four G-protein activated inward rectifying K+ (GIRK) channel mRNAs were identified in intermediate lobe tissues by RT-PCR. Dopamine concentration-dependently activated GIRK currents, whereas PGE2 did not activate GIRK currents, even at the concentration causing maximal inhibition of VDC channels. These results suggest that PGE2 acts on EP3 receptors to suppress Ca2+ entry of rat melanotrophs by selectively inhibiting VDC channels of these cells. We have compared the possible cellular and molecular mechanisms of inhibition by dopamine and PGE2.

Cerebral endothelial cells are a major source of adrenomedullin

Adrenomedullin is a peptide hormone with multifunctional biological properties. Its most characteristic effects are the regulation of circulation and the control of fluid and electrolyte homeostasis through peripheral and central nervous system actions. Although adrenomedullin is a vasodilator of cerebral vasculature, and it may be implicated in the pathomechanism of cerebrovascular diseases, the source of adrenomedullin in the cerebral circulation has not been investigated thus far. We measured the secretion of adrenomedullin by radioimmunoassay and detected adrenomedullin mRNA expression by Northern blot analysis in primary cultures of rat cerebral endothelial cells (RCECs), pericytes and astrocytes. We also investigated the expression of specific adrenomedullin receptor components by reverse transcriptase-polymerase chain reaction and intracellular cAMP concentrations in RCECs and pericytes. RCECs had approximately one magnitude higher adrenomedullin production (135 +/- 13 fmol/10(5) cells per 12 h; mean +/- SD, n = 10) compared to that previously reported for other cell types. RCECs secreted adrenomedullin mostly at their luminal cell membrane. Adrenomedullin production was not increased by thrombin, lipopolysaccharide or cytokines, which are known inducers of adrenomedullin release in peripheral endothelial cells, although it was stimulated by astrocyte-derived factors. Pericytes had moderate, while astrocytes had very low basal adrenomedullin secretion. In vivo experiments showed that adrenomedullin plasma concentration in the jugular vein of rats was approximately 50% higher than that in the carotid artery or in the vena cava. Both RCECs and pericytes, which are potential targets of adrenomedullin in cerebral microcirculation, expressed adrenomedullin receptor components, and exhibited a dose-dependent increase in intracellular cAMP concentrations after exogenous adrenomedullin administration. Antisense oligonucleotide treatment significantly reduced adrenomedullin production by RCECs and tended to decrease intraendothelial cAMP concentrations. These findings may suggest an important autocrine and paracrine role for adrenomedullin in the regulation of cerebral circulation and blood-brain barrier functions. Cerebral endothelial cells are a potential source of adrenomedullin in the central nervous system, where adrenomedullin can also be involved in the regulation of neuroendocrine functions.

Involvement of postsynaptic EP4 and presynaptic EP3 receptors in actions of prostaglandin E2 in rat supraoptic neurones

We have reported that supraoptic nucleus (SON) neurones are excited by prostaglandin E2 (PGE2) presumably via dual postsynaptic PG receptors, FP receptors and unidentified EP receptors, and that presynaptic EP receptors may also be involved in the excitation. In the present study, to clarify the receptor mechanism of the PGE2-mediated actions on SON neurones, we studied the pre- and postsynaptic effects of four newly developed EP agonists that are selective for each of the four EP receptors, EP1-4, on rat SON neurones using extracellular recording and whole-cell patch-clamp techniques. The EP4 agonist ONO-AE1-329 mimicked the excitatory effects of PGE2, whereas the EP1 agonist ONO-DI-004, the EP2 agonist ONO-AE1-257 and the EP3 agonist ONO-AE-248 had little or no effect. The effects of ONO-AE1-329 were unaffected by the EP1/FP/TP antagonist, ONO-NT-012, which potently suppressed the excitation caused by the FP agonist fluprostenol and PGE2. ONO-AE1-329 caused marked excitation when responses to fluprostenol were desensitized by repeated applications of fluprostenol. Patch-clamp analysis in SON neurones showed that ONO-AE1-329 induced inward currents at a holding potential of -70 mV and the reversal potential of the currents was -35.1 +/- 2.3 mV. On the other hand, the frequency of spontaneous inhibitory postsynaptic currents recorded from SON slice preparations was suppressed by ONO-AE-248, but unaffected by the other three EP agonists. These results suggest that SON neurones possess postsynaptic EP4 receptors and that gamma-aminobutyric acid neurones innervating SON neurones possess presynaptic EP3 receptors in their terminals. Activation of the two EP receptors may be involved in the excitatory regulation of SON neurones by PGE2.

Adrenomedullin regulates blood-brain barrier functions in vitro

Adrenomedullin (AM) is an important vasodilator in cerebral circulation, and cerebral endothelial cells are a major source of AM. This in vitro study aimed to determine the AM-induced changes in blood-brain barrier (BBB) functions. AM administration increased, whereas AM antisense oligonucleotide treatment decreased transendothelial electrical resistance. AM incubation decreased BBB permeability for sodium fluorescein (mol. wt 376 Da) but not for Evan's blue albumin (mol. wt 67 kDa), and it also attenuated fluid-phase endocytosis. AM treatment resulted in functional activation of P-glycoprotein efflux pump in vitro. Our results indicate that AM as an autocrine mediator plays an important role in the regulation of BBB properties of the cerebral endothelial cells.

Production of cAMP by adrenomedullin in human oligodendroglial cell line KG1C: comparison with calcitonin gene-related peptide and amylin

The actions and the presence of adrenomedullin (AM) were investigated in cultured human oligodendroglial cell line KG1C. AM and AM mRNA were detected in KG1C cells by immunohistochemistry and RT-PCR. mRNAs for calcitonin receptor-like receptor (CRLR) and receptor-activity-modifying proteins (RAMPs) 1, 2 and 3 but not for calcitonin receptors were detected in the cells, while mRNAs for CRLR, calcitonin receptors and all RAMPs were detected in the human cerebellum. Application of AM resulted in time- and concentration-dependent increases in the cAMP level of KG1C cells. Calcitonin gene-related peptide (CGRP) and amylin, peptides structurally related to AM, also increased cAMP. The potencies for the cAMP production of the three peptides were CGRP > or =AM >> amylin with EC(50) of 8, 18, 90 nM, respectively. The responses induced by AM were strongly inhibited by the CGRP(1) receptor antagonist human CGRP(8-37), and inhibited also by the AM receptor antagonist human AM(22-52). In contrast, the responses induced by CGRP or amylin were inhibited only by CGRP(8-37) and not by AM(22-52). The responses induced by all three peptides were unaffected by the amylin receptor antagonist human amylin(8-37). The CGRP(2) receptor agonist human [Cys(Acm)(2,7)]CGRP significantly increased the cAMP level but the increase was smaller than that caused by CGRP. This increase in cAMP was unaffected by CGRP(8-37), AM(22-52) or by amylin(8-37). These results suggest that in KG1C cells, AM increases cAMP through AM and CGRP(1) receptors, whereas CGRP does so through CGRP(1) and CGRP(2) receptors, and amylin exerts its effects through CGRP(1) receptors. Collectively, these findings imply that AM released from oligodendroglial cells may play a role in the regulation of oligodendrocytes via autocrine/paracrine through AM receptors and CGRP(1) receptors.

Characterization of nuclear factors that bind to the human thymidylate synthase gene in HL-60 cells differentiated by all-trans retinoic acid treatment

HL-60 cells differentiate into granulocyte-like cells by all-trans retinoic acid (ATRA) treatment, and the cellular proliferation is markedly reduced during the differentiation. To elucidate the molecular mechanisms of the growth arrest during the cellular differentiation, we examined the regulated expression of the thymidylate synthase (TS) gene. Northern blot analysis revealed that the expression of the TS gene was almost suppressed in the differentiated HL-60 cells. The change in the levels of nuclear factors, NF-TS2 and NF-TS3, that bind to the 5'-terminal regulatory region of the human TS gene was examined during the differentiation of the HL-60 cells. The amount of NF-TS2 did not change significantly during the differentiation, whereas that of NF-TS3 clearly increased as the cells differentiated. We previously reported that NF-TS2 and NF-TS3 bind to the sequence around the initiation codon ATG of the human TS gene. Further analyses revealed that the DNA sequences of NF-TS2 and NF-TS3 are very similar, and the first and second positions of the ATG triplet codon are important for the formation of rigid DNA-protein complexes. The present findings concerning the binding site and changes during the differentiation induced by ATRA treatment are very similar to those previously reported on the differentiation induced by 1,25-dihydroxyvitamin D3 treatment. These findings suggest that NF-TS3 is involved in regulating the expression of the human TS gene during the differentiation of HL-60 cells, regardless of the terminal cell type: macrophage-like cells or granulocyte-like cells.

Adrenomedullin in the cerebral circulation

The central nervous system requires an effective autoregulation of cerebral circulation in order to meet the critical and unusual demands of the brain. In addition, cerebral microvessels has a unique feature, the formation of the blood-brain barrier, which contributes to the stability of the brain parenchymal microenvironment. Many factors are known to be involved in the regulation of cerebral circulation and blood-brain barrier functions. In the last few years a new potential candidate, adrenomedullin, a hypotensive peptide was added to this list. Adrenomedullin has a potent vasodilator effect on the cerebral vasculature, and it may be implicated in the pathologic mechanism of cerebrovascular diseases. In this review, we describe current knowledge about the origin and possible role of adrenomedullin in the regulation of cerebral circulation and blood-brain barrier functions.

Action sites of adrenomedullin in the rat brain: functional mapping by Fos expression

The effects of intracerebroventricular (icv) administration of adrenomedullin (AM) and proadrenomedullin NH2-terminal 20 peptide (PAMP) on the expression of Fos in the central nervous system (CNS) were examined in conscious rats, using immunohistochemistry. Fos-like immunoreactivity (LI) was detected in various brain areas of the rats, including the supraoptic nucleus, the paraventricular nucleus, the locus coeruleus, the area postrema and the nucleus of the tractus solitarius 90 min after icv administration of AM. Few cells with Fos-LI were found in the CNS 90 min after icv administration of saline. Fos-LI was also detected in the various hypothalamic areas after icv administration of PAMP. These results suggest that centrally administered AM and PAMP may cause physiological responses through the activation of a neural network in the hypothalamus and the brainstem.

[Involvement of orexins/hypocretins in multiple physiological functions]

Orexins (orexin-A and orexin-B)/hipocretins (hypocretin-1 and hypocretin-2) are novel neuropetides discovered in 1998. Orexin-producing neurons are exclusively distributed in the lateral hypothalamic area (LHA), the posterior hypothalamic area and the perifornical nucleus in rats. The LHA is known to be a feeding center in the hypothalamus. Central administration of orexins stimulated feeding in rats and mice. Therefore, orexins are recognized as potent orexigenic peptides. In a positional cloning study, genetically narcoleptic dogs had a deletion of the orexin receptor 2 gene, resulting in a truncated, nonfunctional receptor. Orexin knockout mice were found to exhibit narcoleptic behavior. In human narcoleptic patients, hypocretin-1 in cerebrospinal fluid was undetectable in almost all patients with narcolepsy. Although the physiological role of feeding seems to be independent of sleep, it is very interesting that orexins may be common bioactive substances that are involved in regulating feeding and sleep. The discovery of orexins may contribute to clarify the pathogenesis of disorders in feeding and sleep and to develop drugs for those disorders.

Enhanced activity of the purine nucleotide cycle of the exercising muscle in patients with hyperthyroidism

Myopathy frequently develops in patients with hyperthyroidism, but its precise mechanism is not clearly understood. In this study we focused on the purine nucleotide cycle, which contributes to ATP balance in skeletal muscles. To investigate purine metabolism in muscles, we measured metabolites related to the purine nucleotide cycle using the semiischemic forearm test. We examined the following four groups: patients with untreated thyrotoxic Graves' disease (untreated group), patients with Graves' disease treated with methimazole (treated group), patients in remission (remission group), and healthy volunteers (control group). To trace the glycolytic process, we measured glycolytic metabolites (lactate and pyruvate) as well as purine metabolites (ammonia and hypoxanthine). In the untreated group, the levels of lactate, pyruvate, and ammonia released were remarkably higher than those in the control group. Hypoxanthine release also increased in the untreated group, but the difference among the patient groups was not statistically significant. The accelerated purine catabolism did not improve after 3 months of treatment with methimazole, but it was completely normalized in the remission group. This indicated that long-term maintenance of thyroid function was necessary for purine catabolism to recover. We presume that an unbalanced ATP supply or conversion of muscle fiber type may account for the acceleration of the purine nucleotide cycle under thyrotoxicosis. Such acceleration of the purine nucleotide cycle is thought to be in part a protective mechanism against a rapid collapse of the ATP energy balance in exercising muscles of patients with hyperthyroidism.

Nociceptive stimulation increases NO synthase mRNA and vasopressin heteronuclearRNA in the rat paraventricular nucleus

Nociceptive stimulation causes neuroendocrine responses such as arginine vasopressin (AVP) release and activation of the hypothalamo-pituitary-adrenal (HPA) axis. We examined the effects of nociceptive stimulation on the expression levels of neuronal nitric oxide synthase (nNOS) mRNA, heteronuclear (hn)RNA for AVP and AVP mRNA in the rat paraventricular nucleus (PVN) and supraoptic nucleus (SON), using in situ hybridization histochemistry. For nociceptive stimulation, formalin (5%) or saline was injected subcutaneously (s.c.) into the bilateral hind paws of rats. The expression of the nNOS gene in the PVN was significantly increased 2 and 6 h after s.c. injection of formalin in comparison with that in untreated and saline injected rats. The expression of the nNOS gene in the SON did not change in the untreated, saline- and formalin-injected rats. The AVP hnRNA in the PVN and SON was also significantly increased 15, 30 min and 2 h after s.c. injection of formalin, though AVP mRNA did not change at any time points that we studied. Plasma concentration of AVP was significantly increased 15 min after s.c. injection of formalin. These results suggest that NO in the PVN may be involved in nociceptive stimulation-induced neuroendocrine responses.

Increased levels of hypothalamic neuronal nitric oxide synthase and vasopressin in salt-loaded Dahl rat

The plasma concentration of arginine vasopression (AVP) and the expression level of the neuronal nitric oxide synthase (nNOS) gene in the paraventricular nucleus (PVN) and the Supraoptic nucleus (SON) of Sprague-Dawley (SD). Dahl salt-sensitive (S) and Dahl salt-resistant (R) rats on a high salt diet were examined by radioimmunoassay for AVP and in situ hybridization histochemistry for nNOS. The high salt diet containing 8.0% NaCl was given for 4 weeks. The concentrations of AVP in hypertensive Dahl S rats were significantly increased in comparison with those in SD rats and Dahl R rats on a high salt diet. The levels of nNOS mRNA and NADPH-diaphorase activity in the PVN and SON of hypertensive Dahl S rats were greater than those in Dahl R rats on a high salt diet. The antihypertensive drugs, either nicardipine or captopril were administered to the Dahl S rats for 2 weeks beginning 2 weeks after the start of the high salt diet The nNOS mRNA in the PVN and SON of Dahl S rats given a high salt diet was not upregulated by treatment with nicardipine, while the nNOS mRNA in salt loaded Dahl S rats was greater upregulated by treatment with captopril to that greater than without the antihypertensive drug. Our results suggest that the increased NO production in the PVN and SON of hypertensive Dahl S rats may be ineffective in decreasing blood pressure or inhibiting AVP secretion.

Activation of hypothalamic neuronal nitric oxide synthase in lithium-induced diabetes insipidus rats

The expression of the neuronal nitric oxide synthase (nNOS) gene in the paraventricular (PVN) and supraoptic nuclei (SON) in rats with lithium (Li)-induced polyuria was examined by using in situ hybridization histochemistry. The state of the thyroid axis in these rats was also examined by in situ hybridization histochemistry for thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH) mRNAs and radioimmunoassay for circulating thyroid hormones. Adult male Wistar rats consuming a diet that contained LiCl (60 mmol/kg) for 4 weeks developed remarkable polyuria. The urine in the Li-treated rats was hypotonic and had a large volume and low ionic concentration. The nNOS mRNA in the PVN and SON was significantly increased in the Li-treated rats in comparison with that in control. The increased levels of the nNOS mRNA in the PVN and SON were confirmed by NADPH-diaphorase histochemical staining. There were no differences of TRH mRNA in the PVN, TSH mRNA in the anterior pituitary and plasma concentrations of free T3 and free T4 between Li-treated rats and control rats. These results suggest that Li-induced diabetes insipidus may activate nNOS in the PVN and SON without change of the thyroid axis.

Upregulation of synapsin IIa and IIb mRNAs in the paraventricular and supraoptic nuclei in chronic salt loaded and lactating rats

The effects of chronic salt loading (2% saline to drink for 5 and 10 days), gestation, lactation and adrenalectomy on the expression of synapsin IIa and IIb genes were examined in the rat paraventricular (PVN) and supraoptic nuclei (SON), using in situ hybridization histochemistry. In each control, synapsin IIa and IIb genes were moderately expressed in the magnocellular division of the PVN and SON, while few transcripts of synapsin IIa and IIb were observed in the parvocellular division of the PVN. Chronic salt loading, gestation on day 21 and lactation on day 10 caused significant increases in synapsin IIa and IIb transcripts in the magnocellular division of the PVN and SON, compared to each control. Although corticotropin-releasing hormone transcripts in the parvocellular division of the PVN were significantly increased in the adrenalectomized rats, no changes in the transcripts of synapsin IIa and IIb were observed throughout the PVN. These results suggest that physiological stimuli such as osmotic challenge and lactation potently increase synapsin IIa and IIb mRNAs in the magnocellular neurons of the PVN and SON.