Centrally administered orexin/hypocretin activates HPA axis in rats

The effects of i.c.v. administration of orexin/hypocretin on plasma ACTH, corticosterone and c-fos mRNA in the paraventricular nucleus (PVN) of the rat were examined. Plasma ACTH levels were markedly increased at 30 min after i.c.v. administration of orexin-A. Plasma corticosterone levels were significantly increased in a dose-related manner 30 min after i.c.v. administration of orexin-A and orexin-B. In situ hybridization histochemistry revealed that the induction of the c-fos mRNA in the parvocellular division of the PVN was increased in a dose-related manner 30 min after i.c.v. administration of orexin-A and orexin-B. These results suggest that central orexin/hypocretin activates hypothalamo-pituitary-adrenal (HPA) axis and may be involved in stress-induced activation of the HPA axis.

Postnatal development of orexin/hypocretin in rats

We examined developmental changes of orexins/hypocretins and their receptors (OX1R and OX2R) in the rat hypothalamus from postnatal day 0 to 10 weeks, using in situ hybridization histochemistry for the prepro-orexin, OX1R and OX2R mRNAs and immunohistochemistry for orexin-A and orexin-B. The prepro-orexin mRNA was weakly detected in the lateral hypothalamic area (LHA) from days 0 to 15. Orexin-A- and -B-like immunopositive cells and fibers were not detected from days 0 to 10, but they were observed after day 15. The prepro-orexin mRNA in the LHA markedly increased between days 15 and 20. The OX1R mRNA was detected in the ventromedial hypothalamic area (VMH) at day 0. The OX2R mRNA was not detected in the paraventricular nucleus (PVN) at days 0 and 1, but weakly observed on day 5. The OX1R mRNA in the VMH and OX2R mRNA in the PVN gradually increased throughout the postnatal period. Next, we examined the effects of milk deprivation and intraperitoneal (i.p.) administration of leptin on the hypothalamic prepro-orexin mRNA in pups. Although 24-h milk deprivation did not affect the level of the prepro-orexin mRNA at days 5 and 10, i.p. administration of leptin from days 0 to 3 caused a significant increase in the prepro-orexin mRNA on days 5 and 10. These results suggest that the development of orexins may be associated with developmental changes such as increase of leptin, weaning, feeding and sleep/wakefulness states.

Induction of pituitary adenylate cyclase-activating polypeptide mRNA in the medial parvocellular part of the paraventricular nucleus of rats following kainic-acid-induced seizure

We examined the effects of kainic acid (KA)-induced seizure on the expression of the pituitary adenylate cyclase-activating polypeptide (PACAP) gene in the paraventricular nucleus (PVN) of rats using in situ hybridization histochemistry. Subcutaneous administration of KA (12 mg/kg) in adult male Sprague-Dawley rats caused a progressive development of seizure behavior. An induction of the PACAP gene expression in the medial parvocellular part of the PVN (mpPVN) was observed 3, 6, 12, 24 and 48 h after subcutaneous administration of KA. From a nearly undetectable level, PACAP gene expression increased in the mpPVN and reached maximum 12 h after subcutaneous administration of KA. PACAP gene expression returned to near basal level 48 h after stimulation with KA. Using a specific monoclonal PACAP antibody, PACAP immunoreactivity (-IR) gradually increased during the following 24 h after KA administration. In controls, PACAP-IR was located exclusively in nerve fibers of the mpPVN, whereas KA administration induced PACAP-IR in cell bodies of the mpPVN, and a dense accumulation of PACAP-IR nerve fibers in the external zone of the median eminence was observed. Induction of the PACAP gene expression following KA-induced seizure was significantly reduced by pretreatment with diazepam or MK-801 (nonselective N-methly-D-aspartate receptor antagonist). These results suggest that PACAP in the hypothalamo-adenohypophysial system may have a hypophysiotropic role during KA-induced seizure.

Effects of food restriction on the hypothalamic prepro-orexin gene expression in genetically obese mice

Orexins, which are identical to hypocretins, are novel hypothalamic orexigenic peptides. We examined the effects of food restriction on the expression of the prepro-orexin gene in control (C57Bl/6J) and genetically obese mice (ob/ob and db/db), using in situ hybridization histochemistry. Dry food was given 3 g/day to each obese mouse for 2 weeks. Food restriction caused a significant increase of the prepro-orexin gene expression in obese mice in comparison with ad libitum fed animals. Although the levels of the expression of the prepro-orexin gene in obese mice were significantly lower than those in C57Bl/6J mice during feeding ad libitum, food restriction caused an increase in the expression of the prepro-orexin gene in the hypothalamus of obese mice. The expression of the neuropeptide Y (NPY) gene was increased significantly in the arcuate nucleus of obese mice compared to that of control mice during feeding ad libitum. Food restriction for 2 weeks also caused a significant increase of the expression in the NPY gene in all groups. These results indicate that the hypothalamic prepro-orexin gene could be upregulated by food restriction without leptin signal in genetically obese mice.

Distribution of orexin/hypocretin in the rat median eminence and pituitary

We determined the distribution of orexin-A and orexin-B (also known as hypocretin-1 and hypocretin-2) and their receptors in the rat median eminence and pituitary using sensitive radioimmunoassays coupled with high-performance liquid chromatography, immunohistochemistry, and in situ hybridization. Orexin-A and -B were present in the median eminence, adenohypophysis, and neurohypophysis. Orexin fibers were abundant in the median eminence, and a few fibers projected to the neurohypophysis. Both the orexin(1)- and orexin(2)-receptor mRNAs were expressed robustly in the pituitary intermediate lobe, whereas in the anterior lobe, the orexin(1) receptor was more markedly expressed than the orexin(2) receptor. These two receptor mRNAs were also found in the posterior lobe. These findings may implicate orexin's involvement in additional as yet undefined physiological functions in the hypothalamo-hypophyseal tract.

Pre- and postsynaptic modulation of the electrical activity of rat supraoptic neurones

The release of vasopressin and oxytocin is regulated by the electrical activity of magnocellular neurosecretory cells in the supraoptic and paraventricular nuclei, which is under the control of a great variety of neurotransmitters and neuromodulators. The major neural signals to the supraoptic nucleus are from excitatory glutamate inputs and inhibitory GABA inputs. In recent studies, the voltage-clamp mode of the whole-cell patch-clamp technique has been applied to slice preparations from rat hypothalamus to monitor synaptic inputs to supraoptic neurones. Spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) are abolished by CNQX and picrotoxin, respectively, but are insensitive to tetrodotoxin, indicating that they represent quantal release of glutamate and GABA, respectively, from nerve terminals of presynaptic neurones. GABA and glutamate show remarkable suppressive effects on both EPSCs and IPSCs via presynaptic GABA(B) and mGlu receptors, respectively. Noradrenaline, which excites supraoptic neurones via postsynaptic alpha1-receptors, also suppresses IPSCs and potentiates EPSCs. On the other hand, prostaglandin E2, which excites supraoptic neurones via postsynaptic prostaglandin E2 (EP) receptors of the EP4 subclass, also suppresses IPSCs via EP3 receptors but has little effect on EPSCs. Thus pre- and postsynaptic mechanisms may act cooperatively to excite supraoptic neurones. Nitric oxide, which inhibits supraoptic neurones, potentiates IPSCs without affecting EPSCs. This provides another example for the preferential modulation of IPSCs of supraoptic neurones. On the other hand, PACAP, which causes a long-lasting increase in the firing frequency via the postsynaptic receptors, has no effect on EPSCs and IPSCs, suggesting that some ligands act only at postsynaptic receptors. Thus multiple patterns for pre- and postsynaptic modulation are present in the supraoptic nucleus, and the electrical activity of supraoptic neurones is regulated via complex mechanisms at both pre- and postsynaptic sites.

Preferential potentiation by nitric oxide of spontaneous inhibitory postsynaptic currents in rat supraoptic neurones

Magnocellular neurones in the supraoptic nucleus and paraventricular nucleus express mRNA for nitric oxide synthase (NOS) and the expression becomes more prominent when the release of vasopressin or oxytocin is stimulated. It has also been reported that NO donors inhibit the electrical activity of supraoptic nucleus neurones, but the mechanism involved in the inhibition remains unclear. In the present study, to know whether modulation of synaptic inputs into supraoptic neurones is involved in the inhibitory effect of NO, we measured spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) from rat supraoptic nucleus neurones in slice preparations identified under a microscope using the whole-cell mode of the slice-patch-clamp technique. The NO donor, S-nitroso-N-acetylpenicillamine (SNAP), reversibly increased the frequency of spontaneous IPSCs mediated by GABAA receptors, without affecting the amplitude, indicating that NO potentiated IPSCs via a presynaptic mechanism. The NO scavenger, haemoglobin, suppressed the potentiation of IPSCs by SNAP. On the other hand, SNAP did not cause significant effects on EPSCs mediated by non-NMDA glutamate receptors. The membrane permeable analogue of cGMP, 8-bromo cGMP, caused a significant reduction in the frequency and amplitude of both IPSCs and EPSCs. The results suggest that NO preferentially potentiates the inhibitory synaptic inputs into supraoptic nucleus neurones by acting on GABA terminals in the supraoptic nucleus, possibly via a cGMP-independent mechanism. The potentiation may, at least in part, account for the inhibitory action of NO on the neural activity of supraoptic neurones.

A physiological role for adrenomedullin in rats; a potent hypotensive peptide in the hypothalamo-neurohypophysial system

Adrenomedullin, a potent hypotensive peptide, was originally isolated from human phaeochromocytoma. Adrenomedullin immunoreactivity and gene expression are found not only in peripheral organs but also in the central nervous system. Adrenomedullin labelled cells were localised in the hypothalamus, including in the paraventricular and supraoptic nuclei, in rats. Abundant adrenomedullin-immunoreactive fibres and varicosities were found in the hypothalamo-neurohypophysial tract and the internal zone of the median eminence in colchicine-treated and hypophysectomized rats, whereas in control rats few adrenomedullin-labelled fibres were observed. We examined the effects of intracerebroventricular administration of adrenomedullin on neurosecretory cells in the paraventricular and supraoptic nuclei of rats, using immunohistochemistry for Fos protein and in situ hybridisation histochemistry for c-fos mRNA. Intracerebroventricular administration of adrenomedullin caused a marked induction of Fos-like immunoreactivity in the paraventricular nucleus and the dorsal part of the supraoptic nucleus. In the paraventricular and supraoptic nuclei, nuclear Fos-like immunoreactivity was predominantly in oxytocin-immunoreactive cells rather than vasopressin-immunoreactive cells. The induction of c-fos mRNA in the paraventricular and supraoptic nuclei was increased in a dose-related manner 30 min after intracerebroventricular administration of adrenomedullin. This induction was reduced by pre-treatment with the adrenomedullin receptor antagonist, human adrenomedullin-(22-52)-NH2. Intracerebroventricular administration of adrenomedullin also caused a marked increase in the plasma concentration of oxytocin. Extracellular recordings from magnocellular neurosecretory cells in the paraventricular nucleus revealed that putative oxytocin-secreting cells were activated by intracerebroventricular administration of adrenomedullin. These results suggest that central adrenomedullin preferentially stimulates the secretion of oxytocin by activating hypothalamic oxytocin-secreting cells and may have an important role in salt appetite and body fluid homeostasis in rats.

Detection of mononuclear cells as the source of the increased tissue factor mRNA in the liver from lipopolysaccharide-treated rats

Tissue factor (TF) triggers the coagulation cascade reaction in vivo. Overexpression of TF mRNA is one leading cause of disseminated intravascular coagulation and thrombosis-related organ failure. In response to lipopolysaccharide (LPS) stimulation, various cell types can produce TF mRNA in vitro. However, there is currently no agreement on what types of cells in the liver overexpress TF mRNA after LPS treatment. For the first report, we found the increased TF mRNA with reverse transcription-polymerase chain reaction (RT-PCR), and confirmed a fourfold increase (p<0.001 vs. control, t-test) of the TF mRNA level with RT-competitive PCR in the liver of LPS-treated (2.0 mg/kg i.v. injection) rats. There was no significant difference in the glyceraldehyde-3-phosphate dehydrogenase mRNA level between LPS-treated rats and control rats. To clarify the localization and cellular source of LPS-induced TF mRNA, we performed in situ hybridization analysis with [35S]-labeled oligonucleotides probes, which we originally designed. We detected intense signals of TF mRNA in mononuclear cells but not in endothelial cells around the hepatic vein of LPS-treated rats. In this study, we showed that the TF mRNA level induced by LPS treatment, which may indicate mononuclear cells associated, significantly increased in the liver of rats. These results will provide circumstantial support for the therapeutic strategy that mononuclear cell should be one of the target cells to be treated in the early phase of disseminated intravascular coagulation in the liver, and that the need to suppress its overexpression of TF mRNA is essential for preventing hypercoagulable condition.

Increase of urocortin-like immunoreactivity in the supraoptic nucleus of Dahl rats given a high salt diet

Urocortin-like immunoreactivity (Ucn-LI) in the supraoptic nucleus (SON) of Dahl rats was examined. Dahl salt-sensitive (S) rats fed with a high salt diet developed hypertension. Numbers of Ucn-LI neurons in the SON in Dahl S on a high salt diet were markedly increased, compared with those in Dahl salt-resistant (R) rats on the same. Sporadic Ucn-LI neurons were found in the SON of both Dahl S and R on a normal diet. Numbers of Ucn-LI neurons in the SON of spontaneously hypertensive rat (SHR) and stroke-prone SHR, genetic models of hypertension, and control rats (Sprague-Dawley and Wistar-Kyoto) were similar. These results suggest that Ucn in the SON is associated with salt loading-induced hypertension rather than spontaneous hypertension.

Activation of gastric afferents increases noradrenaline release in the paraventricular nucleus and plasma oxytocin level

Effects of electrical stimulation of the gastric vagal nerves on plasma levels of oxytocin (OXT) and arginine vasopressin (AVP) were examined in rats anesthetized with urethane. Electrical stimulation of the gastric vagal nerves increased the plasma levels of OXT, but not AVP. The concentrations of extracellular noradrenaline (NA) in the paraventricular nucleus (PVN) were measured by in vivo microdialysis in rats anesthetized with urethane. Electrical stimulation of the gastric vagal nerves evoked an increase followed by a slight decrease in the concentrations of NA. The responses of spontaneous firing magnocellular neurosecretory neurons in the PVN to both electrical stimulation of the gastric vagal nerves and intravenous (i.v.) administration of CCK-8 were examined. Most of the putative OXT-secreting cells recorded were excited by both electrical stimulation of gastric vagal nerves and i.v. administration of CCK-8. These results suggest that gastric vagal afferents activate the central noradrenergic system from the brainstem to the PVN and secretion of OXT.

Effects of leptin on fasting-induced inhibition of neuronal nitric oxide synthase mRNA in the paraventricular and supraoptic nuclei of rats

Fasting induced a reduction in neuronal nitric oxide synthase (nNOS) mRNA in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of rats. The effect of intracerebroventricular (i.c.v.) administration of leptin on the nNOS mRNA level in the PVN and SON of fasting rats was studied by in situ hybridization histochemistry. Leptin (10 microg/kg b.wt) or vehicle was administered i.c.v. at 1700 h on two successive days fasting for 2 days. Fasting for 2 days with i.c.v. administration of vehicle induced a significant reduction of nNOS mRNA in the PVN and SON. Central administration of leptin prevented the fasting-induced reduction of nNOS mRNA in the PVN and SON. Administration of leptin also prevented the fasting-induced reductions of thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH) mRNAs in the parvocellular division of the PVN. These results suggest that leptin is associated with fasting-induced reduction of nNOS mRNA in the PVN and SON as well as TRH and CRH mRNAs in the PVN.

Prostaglandin E2 inhibits spontaneous inhibitory postsynaptic currents in rat supraoptic neurones via presynaptic EP receptors

Prostaglandin E2 (PGE2) has been implicated in the excitatory regulation of magnocellular neurones in the supraoptic nucleus (SON). We have recently reported that PGE2 excited SON neurones by directly activating postsynaptic PGE2 receptors (EP receptors) of a subclass other than EP1-3, but did not affect excitatory postsynaptic currents (EPSCs). In the present study, we examined presynaptic effects of PGE2 on rat SON neurones by measuring spontaneous inhibitory postsynaptic currents (IPSCs) by a slice patch-clamp technique. PGE2 inhibited spontaneous IPSCs in a dose-dependent and reversible manner. PGE2 selectively suppressed the frequency of IPSCs without affecting the amplitude of IPSCs in the presence of tetrodotoxin, a blocker of Na+ channels, indicating that the effects were presynaptic. The inhibitory effects of PGE2 on the frequency of IPSCs were mimicked by the EP1/EP3 agonists, 17PT-PGE2 and sulprostone, and the EP2/EP3 agonist, misoprostol, whereas the EP2 agonist, butaprost, or the FP agonist, fluprostenol, had little effect. The effects of PGE2 on IPSCs were unaffected by the selective EP1 antagonist, SC-51322. They were unaffected also by antagonists of GABAB and alpha2 adrenergic receptors, which are present at presynaptic terminals of GABA neurones in the SON and cause suppression of spontaneous IPSCs. The inhibitor of PG synthesis, indomethacin, had little effect on spontaneous IPSCs and on the inhibitory effects of PGE2 as well as of the GABAB agonist, baclofen, and noradrenaline. These results suggest that PGE2 inhibits release of GABA from the GABAergic terminals innervating SON neurones by activating presynaptic EP receptors, presumably of the EP3 subclass, and that such a presynaptic mechanism may play a role in the excitatory regulation of SON neurones by PGE2.

Prostaglandin E2 induces Ca2+ release from ryanodine/caffeine-sensitive stores in bovine adrenal medullary cells via EP1-like receptors

Prostaglandin E2 (PGE2) causes Ca2+ release from intracellular Ca2+ stores and stimulates phosphoinositide metabolism in bovine adrenal medullary cells. These results have been interpreted as PGE2 induces Ca2+ release from inositol trisphosphate (IP3)-sensitive stores. However, we have recently shown that pituitary adenylate cyclase-activating polypeptide (PACAP), bradykinin, and angiotensin II release Ca2+ from caffeine/ryanodine-sensitive stores, although they cause a concomitant increase of intracellular IP3. In light of these results, the mechanism of PGE2-induced Ca2+ release was investigated in the present study. PGE2 dose-dependently caused a transient but consistent Ca2+ release from internal Ca2+ stores. The PGE2-induced Ca2+ release was unaffected by cinnarizine, a blocker of IP3-induced Ca2+ release. By contrast, it was potently inhibited by prior application of caffeine and ryanodine. Although IP3 production in response to PGE2 was abolished by the phospholipase C inhibitor U-73122, Ca2+ release in response to PGE2 was unaffected by U-73122. The PGE2-induced Ca2+ release was unaffected by Rp-adenosine 3',5'-cyclic monophosphothioate, an inhibitor of protein kinase A, and forskolin, a cyclic AMP (cAMP)-elevating agent, did not cause Ca2+ release. The EP1 agonist 17-phenyl-trinorPGE2 and the EP1/EP3 agonist sulprostone mimicked the Ca(2+)-releasing effects of PGE2, whereas the EP2 agonist butaprost or the EP2/EP3 agonist misoprostol caused little or no Ca2+ release. The EP1 antagonist SC-51322 significantly suppressed the Ca2+ release response induced by PGE2, whereas the EP4 antagonist AH-23828B had little effect. These results suggest that PGE2, acting on EP1-like receptors, induces Ca2+ release from ryanodine/caffeine-sensitive stores through a mechanism independent of IP3 and cAMP and that PGE2 may share the same mechanism with PACAP and the other peptide ligands in causing Ca2+ release in bovine adrenal medullary cells.

Increase of vasopressin mRNA in the hypothalamus of inbred polydipsic mice

The genetically inbred polydipsic mice, STR/N strain, are characterized by extreme polydipsia and polyuria without arginine vasopressin (AVP) deficiency. The expression of AVP gene in the hypothalamus of polydipsic and non-polydipsic mice was examined by Northern blot analysis and in situ hybridization histochemistry. Northern blot analysis revealed that the total amount of AVP mRNA in the hypothalamus of the STR/N mice was approximately three-fold of that in the control, ICR mice. In situ hybridization histochemistry showed that the signals of AVP mRNA in the paraventricular (PVN) and supraoptic nuclei (SON) of the STR/N were stronger than those in the ICR. Although AVP gene transcripts were detected in the anteroventral parts of the PVN (avPVN) in the STR/N, there was a few AVP transcripts in the same area (avPVN) in the ICR. There were no differences in plasma osmolality and hematocrit between STR/N and ICR mice. These results suggest that upregulation of AVP mRNA in the hypothalamus of STR/N may be involved in the central mechanism responsible for the polydipsia in genetically polydipsic mice.

The mechanism of inhibitory actions of propofol on rat supraoptic neurons

BACKGROUND

In the perioperative period, plasma osmotic pressure, systemic blood pressure, and blood volume often change dramatically. Arginine vasopressin is a key factor in the regulation of these parameters. This study was performed to evaluate the direct and the mechanism of the actions of propofol on arginine vasopressin release from magnocellular neurosecretory neurons in the rat supraoptic nucleus.

METHODS

Somatodendritic arginine vasopressin release from supraoptic nucleus slice preparations was measured by radioimmunoassay. Ionic currents were measured using the whole-cell mode of the patch-clamp technique in supraoptic nucleus slice preparations or in single dissociated supraoptic nucleus neurons of the rat.

RESULTS

Propofol at concentrations greater than 10(-5) M inhibited the arginine vasopressin release stimulated by potassium chloride (50 mM). This inhibition by propofol was not reversed by picrotoxin, a gamma-aminobutyric acid(A)(GABA(A)) receptor antagonist, whereas arginine vasopressin release induced by glutamate (10(-3) M) was also inhibited by propofol at a clinically relevant concentration (10(-6) M). The latter effect was reversed by picrotoxin. Propofol evoked Cl- currents at concentrations ranging 10(-6) to 10(-4) M. Propofol (10(-6) M) enhanced the GABA (10(-6) M)-induced current synergistically. Moreover, propofol (10(-6) M) prolonged the time constant of spontaneous GABA-mediated inhibitory postsynaptic currents. Furthermore, propofol (10(-5) M and 10(-4) M) reversibly inhibited voltage-gated Ca2+ currents, whereas it did not affect currents induced by glutamate (10(-3) M).

CONCLUSIONS

Propofol inhibits somatodendritic arginine vasopressin release from the supraoptic nucleus, and the enhancement of GABAergic inhibitory synaptic inputs and the inhibition of voltage-gated Ca2+ entry are involved in the inhibition of arginine vasopressin release.

A TSH/dibutyryl cAMP activated Cl-/I- channel in FRTL-5 cells

An iodide (I) and chloride (Cl) channel has been identified in the continuously cultured FRTL-5 thyroid cell line using a cell attached patch clamp technique. The channel is activated by TSH and dibutyryladenosine cyclic monophosphate (Bt2-cAMP) but not by phorbol 12-myristate 13-acetate (TPA). Gluconate can not replace chloride or iodide and the channel is impermeable to Na+,K+ and tetraethylammonium ions. The current-voltage relationship demonstrates that the single channel current is a linear function of the clamp voltage. Single channel currents reversed at a pipette potential close to 0 mV. The mean single channel conductance was 60 pS for Cl- and 50 pS for I-. From the I-V relationship there was a strong outward rectification with Cl-, and a complete block with I-, in the single channel current above +40 mV. The feature of the channel is manifested in the single channel records by four distinct, equally spaced conductance levels. We suggest the channel is important for the transport of I and Cl ions across the apical membrane into the colloid space and is important for hormone synthesis and follicle formation.

Enterochromaffin-like cells, a cellular source of uroguanylin in rat stomach

Uroguanylin is an endogenous peptide ligand for guanylyl cyclase-C, an apical membrane receptor predominantly located in the gastrointestinal epithelium. It regulates intestinal and renal fluid and electrolyte transport through the second messenger, cyclic GMP. Uroguanylin messenger RNA and the peptide are present in rat stomach, but the cellular source has not been identified. We separated gastric mucosal cells by size into seven fractions (F1-F7) and enriched endocrine cells into F1-F3 using counterflow elutriation. Uroguanylin messenger RNA and peptide were found in F1-F3 by Northern blot analysis and an RIA specific for rat uroguanylin. Uroguanylin-producing cells were identified as endocrine cells by immunocytochemical methods using antisera for uroguanylin, prouroguanylin, and chromogranin A, as well as by in situ hybridization cytochemistry. Double-staining showed that uroguanylin and histamine are colocalized in enterochromaffin-like (ECL) cells that release histamine, leading to the stimulation of gastric acid secretion from parietal cells. Uroguanylin is synthesized in ECL cells. These findings should contribute to elucidating the physiological functions of ECL cells and the cyclic GMP-mediated gastric ion transport mechanism.

Centrally administered adrenomedullin increases plasma oxytocin level with induction of c-fos messenger ribonucleic acid in the paraventricular and supraoptic nuclei of the rat

The effects of intracerebroventricular (i.c.v.) administration of adrenomedullin (AM) on plasma oxytocin (OXT), c-Fos protein (Fos), and c-fos messenger RNA (mRNA) in the paraventricular (PVN) and supraoptic nuclei (SON) of the rat were investigated using RIA for OXT, immunohistochemistry for Fos, and in situ hybridization histochemistry for c-Fos mRNA. Central administration of AM caused a significant increase in the plasma OXT level. Intracerebroventricular administration of AM caused a marked induction of Fos-like immunoreactivity (LI) in the PVN and in the dorsal parts of the SON. In the PVN and SON, OXT-LI cells predominantly exhibited nuclear Fos-LI in comparison with arginine vasopressin-LI cells. In situ hybridization histochemistry revealed that the induction of c-fos mRNA in the PVN and SON was increased in a dose-related manner 30 min after i.c.v. administration of AM. This induction was reduced by pretreatment with the AM receptor antagonist, human AM-(22-52)-NH2. These results suggest that central AM is responsible for activating the neurosecretory cells in the PVN and SON via selective AM receptors, and that AM stimulates the secretion of OXT by activating hypothalamic OXT-producing cells.

Effects of centrally administered pituitary adenylate cyclase-activating polypeptide on c-fos gene expression and heteronuclear RNA for vasopressin in rat paraventricular and supraoptic nuclei

The effects of intracerebroventricular (i.c.v.) administration of pituitary adenylate cyclase-activating polypeptide (PACAP) on the expression of c-fos gene as well as heteronuclear (hn) RNA for arginine vasopressin (AVP) in paraventricular (PVN) and supraoptic nuclei (SON) of rats were investigated by immunohistochemistry for c-fos protein (Fos) and in situ hybridization histochemistry for c-fos mRNA and AVP hnRNA. The i.c.v. administration of PACAP (200 pmol/rat) caused a marked induction of Fos-like immunoreactivity (LI) in PVN and SON. The nuclear Fos-LI existed in AVP-LI containing cells in the PVN and SON. The expression of the c-fos gene in the PVN and SON was increased in a dose-related manner 30 min after i.c. v. administration of PACAP. PACAP-induced expression of the c-fos gene was significantly reduced by pretreatment with a PACAP receptor antagonist, PACAP-(6-38)-NH2. In addition, Fos-LI and the expression of the c-fos gene were also observed in the periventricular region of the third ventricle after i.c.v. administration of PACAP. The induction of c-fos gene expression in the PVN and SON reached a maximum 30 min after PACAP administration. The expression of c-fos gene in the PVN and SON induced by i.c.v. administration of vasoactive intestinal peptide (200 pmol/rat) was weaker than that induced by PACAP. The hnRNA for AVP in the PVN and SON was significantly increased 30 min after i.c.v. administration of PACAP (200 pmol/rat). Our results suggest that PACAP activates PVN and SON neurons via PACAP receptors and, in parallel, transcription of the AVP gene in the PVN and SON.

Down regulation of the prepro-orexin gene expression in genetically obese mice

The gene expression of prepro-orexin, the precursor of orexin-A and orexin-B which are hypothalamic pepetides that are associated with feeding behavior, were examined in control (C57B1/6J) and obese (ob/ob and db/db) mice using in situ hybridization histochemistry. Orexins are identical with hypocretins that have been identified by directional tag PCR subtractive hybridization method. In situ hybridization histochemistry revealed that the expression of the prepro-orexin gene was significantly decreased in ob/ob and db/db mice compared with control mice. The gene expression of neuropeptide Y (NPY), a potent feeding stimulant, is known to be increased in ob/ob and db/db mice. The expression of the NPY gene in the arcuate nucleus was increased remarkably in ob/ob and db/db mice compared to that of control mice. An immunohistochemical study showed that orexin-A and orexin-B immunoreactive neurons exhibited in the lateral and posterior hypothalamic areas and the perifornical nucleus were distributed similarly in control, ob/ob and db/db mice. These results suggest that the regulatory mechanism of orexins/hypocretins may be different from that of NPY in genetically obese mice.

Development of primary hypothyroidism with the appearance of blocking-type antibody to thyrotropin receptor in Graves' disease in late pregnancy

Spontaneous remission of Graves' disease with a decrease of thyroid stimulating antibody (TSAb) activity is commonly observed in pregnancy. In this article, however, a Graves' patient who developed primary hypothyroidism with an appearance of thyroid stimulation-blocking antibody (TSBAb) activity in late pregnancy is reported. A 25-year-old woman presented with clinical and biochemical hyperthyroidism with an elevation of 99mTcO4- thyroid uptake (4.7%; normal range, 0.7%-3.0%) and mildly elevated activity of thyrotropin-binding inhibitory immunoglobulin (TBII; 30.4%). She was euthyroid with normal TBII (8.0%) and TSAb (126%) before pregnancy, when the patient was taking a 5-mg daily dose of methimazole (MMI). MMI was stopped by the patient when she became pregnant. Subsequently, the patient progressed into primary hypothyroidism with a marked elevation of TBII activity (78.4%) in the third trimester of the pregnancy (at that time, TSAb activity was not detected). TSBAb measured 2 weeks later was detected at the activity of 85.0%. Replacement therapy was initiated with levothyroxine (LT4) (0.05-0.1 mg/day), which was discontinued on the 55th day postpartum because of the onset of mild thyrotoxicosis followed by short-term euthyroid state despite high TSBAb activity. Subsequently, because the patient developed primary hypothyroidism 5 months after delivery, replacement therapy with LT4 (0.1-0.125 mg/day) was readministered. Thus, it is suggested that the development of hypothyroidism with the appearance of TSBAb in Graves' patients can occur even in late pregnancy.

Orexins, orexigenic hypothalamic peptides, interact with autonomic, neuroendocrine and neuroregulatory systems

We determined the immunohistochemical distributions of orexin-A and orexin-B, hypothalamic peptides that function in the regulation of feeding behavior and energy homeostasis. Orexin-A and -B neurons were restricted to the lateral and posterior hypothalamus, whereas both orexin-A and -B nerve fibers projected widely into the olfactory bulb, cerebral cortex, thalamus, hypothalamus, and brainstem. Dense populations of orexin-containing fibers were present in the paraventricular thalamic nucleus, central gray, raphe nuclei, and locus coeruleus. Moderate numbers of these fibers were found in the olfactory bulb, insular, infralimbic and prelimbic cortex, amygdala, ventral, and dorsolateral parts of the suprachiasmatic nucleus, paraventricular nucleus except the lateral magnocellular division, arcuate nucleus, supramammillary nucleus, nucleus of the solitary tract, and dorsal motor nucleus of the vagus. Small numbers of orexin fibers were present in the perirhinal, motor and sensory cortex, hippocampus, and supraoptic nucleus, and a very small number in the lateral magnocellular division of the paraventricular nucleus. Intracerebroventricular injections of orexins induced c-fos expression in the paraventricular thalamic nucleus, locus coeruleus, arcuate nucleus, central gray, raphe nuclei, nucleus of the solitary tract, dorsal motor nucleus of the vagus, suprachiasmatic nucleus, supraoptic nucleus, and paraventricular nucleus except the lateral magnocellular division. The unique neuronal distribution of orexins and their functional activation of neural circuits suggest specific complex roles of the peptides in autonomic and neuroendocrine control.

Evidence that multiple P2X purinoceptors are functionally expressed in rat supraoptic neurones

1. The expression, distribution and function of P2X purinoceptors in the supraoptic nucleus (SON) were investigated by reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and Ca2+-imaging and whole-cell patch-clamp techniques, respectively. 2. RT-PCR analysis of all seven known P2X receptor mRNAs in circular punches of the SON revealed that mRNAs for P2X2, P2X3, P2X4, P2X6 and P2X7 receptors were expressed in the SON, and mRNAs for P2X3, P2X4 and P2X7 were predominant. 3. In situ hybridization histochemistry for P2X3 and P2X4 receptor mRNAs showed that both mRNAs were expressed throughout the SON and in the paraventricular nucleus (PVN). 4. ATP caused an increase in [Ca2+]i in a dose-dependent manner with an ED50 of 1.7 x 10-5 M. The effects of ATP were mimicked by ATPgammaS and 2-methylthio ATP (2MeSATP), but not by AMP, adenosine, UTP or UDP. alphabeta-Methylene ATP (alphabetaMeATP) and ADP caused a small increase in [Ca2+]i in a subset of SON neurones. 5. The P2X7 agonist 2'- & 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) at 10-4 M increased [Ca2+]i, but the potency of BzATP was lower than that of ATP. In contrast, BzATP caused a more prominent [Ca2+]i increase than ATP in non-neuronal cells in the SON. 6. The effects of ATP were abolished by extracellular Ca2+ removal or by the P2 antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), and inhibited by extracellular Na+ replacement or another P2 antagonist, suramin, but were unaffected by the P2X7 antagonist oxidized ATP, and the inhibitor of Ca2+-ATPase in intracellular Ca2+ stores cyclopiazonic acid. 7. Two patterns of desensitization were observed in the [Ca2+]i response to repeated applications of ATP: some neurones showed little or moderate desensitization, while others showed strong desensitization. 8. Whole-cell patch-clamp analysis showed that ATP induced cationic currents with marked inward rectification. The ATP-induced currents exhibited two patterns of desensitization similar to those observed in the [Ca2+]i response. 9. The results suggest that multiple P2X receptors, including P2X3, are functionally expressed in SON neurones, and that activation of these receptors induces cationic currents and Ca2+ entry. Such ionic and Ca2+-signalling mechanisms triggered by ATP may play an important role in the regulation of SON neurosecretory cells.

Adrenomedullin-like immunoreactivity in the rat hypothalamo-neurohypophysial tract

Adrenomedullin-like immunoreactivity in the hypothalamo-neurohypophysial tract in colchicine-treated and hypophysectomized rats was examined by immunohistochemistry. Adrenomedullin-like immunoreactive (AM-LI) neurons were localized in the hypothalamic areas, including the paraventricular nuclei and the supraoptic nuclei. Abundant AM-LI fibers and varicosities were found in the hypothalamoneurohypophysial tract and the internal zone of the median eminence in the colchicine-treated and hypophysectomized rats, whereas in control rats few AM-LI fibers were observed. These results suggest that the axons of the AM-LI neurons in the hypothalamus may terminate in the neurohypophysis.