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

Effects of salt intake on sympathetic neural and pressor responses to cold pressor test in premenopausal women with a history of normal pregnancy

Excessive salt intake is considered a risk factor for the development of hypertension. Additionally, aberrant neurocirculatory responses to a cold stimulus are associated with an increased risk of hypertension. This study aimed to determine whether salt loading versus salt reduction would impact hemodynamic and sympathetic neural responses during the cold pressor test (CPT) in premenopausal women with a history of normal pregnancy. Nine healthy premenopausal women [42 ± 3 (SD) yr] were given a standardized isocaloric high-salt (HS; 250 mEq sodium/day) or low-salt (LS; 50 mEq sodium/day) diet for 1-wk each (∼2 mo apart with the order randomized), while water intake was ad libitum. Laboratory testing was performed following each HS and LS period in the mid-luteal phase of the menstrual cycle. Subjects were in the supine position and beat-by-beat blood pressure (BP), heart rate (HR), and muscle sympathetic nerve activity (MSNA) were continuously measured during 1-min baseline followed by 2-min CPT, and 3-min recovery. BP and HR increased during the CPT (both P < 0.001); the responses were similar between HS and LS. MSNA increased during the CPT, but the increment (Δ) was greater during HS than LS (29 ± 6 vs. 15 ± 4 bursts/min; P < 0.001). The transduction of MSNA for vasoconstriction during the CPT was lower in HS (P < 0.05). Thus, salt loading augments sympathetic neural reactivity to the cold stimulus with similar pressor responses compared with salt reduction, which may be attributed to the blunted neurovascular transduction-a compensatory mechanism for hemodynamic homeostasis in premenopausal women with a history of normal pregnancy.

Nitric Oxide and the Neuroendocrine Control of the Osmotic Stress Response in Teleosts

The involvement of nitric oxide (NO) in the modulation of teleost osmoresponsive circuits is suggested by the facts that NO synthase enzymes are expressed in the neurosecretory systems and may be regulated by osmotic stimuli. The present paper is an overview on the research suggesting a role for NO in the central modulation of hormone release in the hypothalamo-neurohypophysial and the caudal neurosecretory systems of teleosts during the osmotic stress response. Active NOS enzymes are constitutively expressed by the magnocellular and parvocellular hypophysiotropic neurons and the caudal neurosecretory neurons of teleosts. Moreover, their expression may be regulated in response to the osmotic challenge. Available data suggests that the regulatory role of NO appeared early during vertebrate phylogeny and the neuroendocrine modulation by NO is conservative. Nonetheless, NO seems to have opposite effects in fish compared to mammals. Indeed, NO exerts excitatory effects on the electrical activity of the caudal neurosecretory neurons, influencing the amount of peptides released from the urophysis, while it inhibits hormone release from the magnocellular neurons in mammals.

Neuronal nitric oxide synthase and affective disorders

Affective disorders including major depressive disorder (MDD), bipolar disorder (BPD), and general anxiety affect more than 10% of population in the world. Notably, neuronal nitric oxide synthase (nNOS), a downstream signal molecule of N-methyl-D-aspartate receptors (NMDARs) activation, is abundant in many regions of the brain such as the prefrontal cortex (PFC), hippocampus, amygdala, dorsal raphe nucleus (DRN), locus coeruleus (LC), and hypothalamus, which are closely associated with the pathophysiology of affective disorders. Decreased levels of the neurotransmitters including 5-hydroxytryptamine or serotonin (5-HT), noradrenalin (NA), and dopamine (DA) as well as hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are common pathological changes of MDD, BPD, and anxiety. Increasing data suggests that nNOS in the hippocampus play a crucial role in the etiology of MDD whereas nNOS-related dysregulation of the nitrergic system in the LC is closely associated with the pathogenesis of BPD. Moreover, hippocampal nNOS is implicated in the role of serotonin receptor 1 A (5-HTR1 A) in modulating anxiety behaviors. Augment of nNOS and its carboxy-terminal PDZ ligand (CAPON) complex mediate stress-induced anxiety and disrupting the nNOS-CAPON interaction by small molecular drug generates anxiolytic effect. To date, however, the function of nNOS in affective disorders is not well reviewed. Here, we summarize works about nNOS and its signal mechanisms implicated in the pathophysiology of affective disorders. On the basis of this review, it is suggested that future research should more fully focus on the role of nNOS in the pathomechanism and treatment of affective disorders.

Effects of a subconvulsive dose of kainic acid on the gene expressions of the arginine vasopressin, oxytocin and neuronal nitric oxide synthase in the rat hypothalamus

Arginine vasopressin (AVP) synthesis in the hypothalamo-neurohypophysial system (HNS) is up-regulated by kainic acid (KA)-induced seizure in rats. However, it remains unknown whether a subconvulsive dose of KA affects the HNS. Here we examined the effects of subcutaneous (s.c.) administration of a low dose of KA (4 mg/kg) on the gene expressions of the AVP, oxytocin (OXT) and neuronal nitric oxide synthase (nNOS) in the supraoptic (SON) and paraventricular nuclei (PVN) of the rat hypothalamus, using in situ hybridization histochemistry. The expression of the AVP gene in the SON and PVN was judged to be up-regulated in KA-treated rats in comparison with saline-treated rats as controls. Next, the expression of the OXT gene was significantly increased in the SON at 6-24h and in the PVN at 6 and 12h after s.c. administration of KA. Finally, the expression of the nNOS gene was significantly increased in the SON and PVN at 3 and 6h after s.c. administration of KA. These results suggest that up-regulation of the gene expressions of the AVP, OXT and nNOS in the rat hypothalamus may be differentially affected by peripheral administration of a subconvulsive dose of KA.

[Visualization of the response in the central nervous system after nociceptive stimulation using transgenic animals]

Physiological response to acute and chronic nociceptive stimulation are important for living organisms. In our laboratory, we generated transgenic rats expressing the arginine vasopressin (AVP) and enhanced green fluorescent protein (eGFP) fusion gene, and the c-fos and monomeric red fluorescent protein 1 (mRFP1) fusion gene in the central nervous system. We made it possible to visualize the pain response in the living cells. Using these transgenic rats, the aim of our studies is the elucidation of the physiological role of AVP after nociceptive stimulation and the pathophysiology of work-related pain. We describe the previous findings of nociceptive response, using these transgenic animals.

Prolactin promotes oxytocin and vasopressin release by activating neuronal nitric oxide synthase in the supraoptic and paraventricular nuclei

Prolactin (PRL) stimulates the secretion of oxytocin (OXT) and arginine AVP as part of the maternal adaptations facilitating parturition and lactation. Both neurohormones are under the regulation of nitric oxide. Here, we investigate whether the activation of neuronal nitric oxide synthase (nNOS) in the hypothalamo-neurohypophyseal system mediates the effect of PRL on OXT and AVP release and whether these effects operate in males. Plasma levels of OXT and AVP were measured in male rats after the intracerebroventricular injection of PRL or after inducing hyperprolactinemia by placing two anterior pituitary glands under the kidney capsule. NOS activity was evaluated in the paraventricular (PVN) and supraoptic (SON) hypothalamic nuclei by NADPH-diaphorase histochemistry and in hypothalamic extracts by the phosphorylation/inactivation of nNOS at Ser847. Elevated central and systemic PRL correlated with increased NOS activity in the PVN and SON and with higher OXT and AVP circulating levels. Notably, treatment with 7-nitroindazole, a selective inhibitor of nNOS, prevented PRL-induced stimulation of the release of both neurohormones. Also, phosphorylation of nNOS was reduced in hyperprolactinemic rats, and treatment with bromocriptine, an inhibitor of anterior pituitary PRL secretion, suppressed this effect. These findings suggest that PRL enhances nNOS activity in the PVN and SON, thereby contributing to the regulation of OXT and AVP release. This mechanism likely contributes to the regulation of processes beyond those of female reproduction.

Exaggerated response of a vasopressin-enhanced green fluorescent protein transgene to nociceptive stimulation in the rat

Nociceptive stimulation elicits neuroendocrine responses such as arginine vasopressin (AVP) release as well as activation of the hypothalamo-pituitary-adrenal axis. We have generated novel transgenic rats expressing an AVP-enhanced green fluorescent protein (eGFP) fusion gene, and we examined the effects of nociceptive stimulation on transgene expression in the hypothalamus after subcutaneous injection of saline or formalin into the bilateral hindpaws in these rats. We have assessed (1) AVP levels in plasma and the changes of eGFP mRNA and AVP heteronuclear RNA (hnRNA) in the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) using in situ hybridization histochemistry, (2) gene expression changes in distinct magnocellular and parvocellular divisions of the PVN, (3) eGFP fluorescence in the SON, the PVN, the median eminence (ME), and the posterior pituitary gland (PP). Plasma AVP levels were significantly increased 15 min after formalin injection. In the same time period, the AVP hnRNA levels in the PVN were increased, especially in the parvocellular division of the PVN in formalin-injected rats. In the same region, eGFP mRNA levels after formalin injection were also significantly increased to a much greater extent than those of AVP hnRNA. The eGFP fluorescence in the SON, the PVN, the ME, and the PP was markedly increased in formalin-injected rats and especially increased in the parvocellular divisions of the PVN. Together, our results demonstrate robust and rapid changes in the expression of the AVP-eGFP transgene in the rat hypothalamus after acute nociceptive stimulation.

The single-prolonged stress paradigm alters both the morphology and stress response of magnocellular vasopressin neurons

Vasopressin (AVP) plays an important role in anxiety-related and social behaviors. Single-prolonged stress (SPS) has been established as an animal acute severe stress model and has been shown to induce a lower adrenocorticotropic hormone (ACTH) response upon cortisol challenge. Here, we show results from immunoassays for AVP, ACTH, and corticosterone (CORT), and in situ hybridizations for AVP mRNA performed 7 days after SPS exposure. Immunofluorescence for AVP was also performed during the 7-day period following SPS exposure and after an additional forced swimming stress paradigm. We observed that the plasma concentrations of AVP, ACTH, and CORT were not altered by SPS; ACTH content in the pituitary and AVP mRNA expression in the supraoptic nucleus (SON) were significantly reduced by SPS. During the 7-day period following SPS, the intensity of immunoreactivity, the size of the soma, and the immunoreactive optical density of the dendrites of AVP neurons in the SON all increased. An apparent reduction in the intensity of AVP immunoreactivity was observed in the SON at 4 h after additional stress. Additional forced swimming led to a rapid increase in the dendritic AVP content only in the controls and not in the SPS-treated rats. These findings suggest that AVP is a potential biomarker for past exposure to severe stress and that alterations in AVP may affect the development of pathogenesis in stress-related disorders.

An intron-based real-time PCR method for measuring vasopressin gene transcription

The hypothalamus contains distinct neuronal populations that express distinguishing neuropeptides. The supraoptic nucleus contains magnocellular neurons that predominantly express either vasopressin or oxytocin. Transcriptional activators of vasopressin and other neuropeptides have been the subject of much research. Here we present a method of measuring neuropeptide transcription by tailoring one-step quantitative real-time PCR (qRT-PCR) for the analysis of processed and pre-mRNA (heteronuclear RNA). Using moderate and strong hyperosmotic stimuli to induce transcription, we report an increase in vasopressin transcription (pre-mRNA) of 141% and 406% over control levels in response to a 2% injection of 900 mOsm saline or a 1% body weight i.p. injection of 2 M NaCl, respectively. These results agree with a host of studies employing the more labor-intensive method of in situ hybridization histochemistry by which investigators also measured intron-containing heteronuclear RNAs. Furthermore, these results confirm that qRT-PCR with intron-specific primers can be used to rapidly analyze transcription, and suggest an important further benefit of a real-time PCR analysis, such as the ability of measuring transcription of multiple neuropeptides along with other genes from a single sample.

Up-regulation of galanin and corticotropin-releasing hormone mRNAs in the key hypothalamic and amygdaloid nuclei in a mouse model of visceral pain

Cyclophosphamide (CP)-induced cystitis is often used as an animal model of visceral pain. Various neuropeptides in the hypothalamic and amygdaloid nuclei are implicated in pain-induced responses. However, little information is available regarding the regulation of the neuropeptides in response to visceral pain. In the present study, we examined the effects of CP-induced cystitis on the levels of mRNAs encoding galanin, corticotropin-releasing hormone (CRH), substance P, and enkephalins in the hypothalamic and limbic nuclei using in situ hybridization histochemistry in mouse. Galanin mRNA levels in CP-treated group increased significantly in the arcuate nucleus and the paraventricular nucleus (PVN) but not in the medial preoptic area after the intraperitoneal administration of CP (200 mg/kg body weight) in comparison to those in saline-treated group. CRH mRNA levels in CP-treated group also increased significantly in the central amygdala as well as the PVN after the CP administration. In contrast, CP-induced cystitis failed to upregulate the preprotachykinin-A and preproenkephalin genes which encode substance P and enkephalins, respectively in the hypothalamic and limbic nuclei at any of the time points examined. These results suggest that visceral nociception may upregulate both galanin and CRH gene expression in the hypothalamic and limbic nuclei.

Regulation of neuronal nitric oxide synthase mRNA expression in the rat magnocellular neurosecretory system

We examined the activation of nNOS mRNA expression within the supraoptic and paraventricular nuclei (SON and PVN) of the hypothalamus. In salt-loaded rats nNOS mRNA expression was significantly increased in both nuclei. In rats given i.p. injections of 1.5 M NaCl (4 ml/kg), a small but significant increase in nNOS mRNA expression in the SON and PVN was found 6 h after injection; no change was detected 2 or 4 h after injection. In rats in which hyponatraemia had been induced experimentally, nNOS mRNA was downregulated in the SON, and expression levels were not increased within 4 h after intense acute osmotic stimuli. Finally, neurons of the SON were antidromically-activated by neural stalk stimulation for 2 h. No increase of nNOS mRNA expression in the SON was observed 2 h after stimulation. Thus, increased electrical activity is not directly coupled to rapidly increased expression of nNOS mRNA, and hence acute increases in nNOS mRNA expression are unlikely to play a role in short-term adaptation of the magnocellular system to osmotic stimulation.

Upregulation of corticotropin-releasing hormone gene expression in the paraventricular nucleus of cyclophosphamide-induced cystitis in male rats

We examined the effects of cyclophosphamide (CP)-induced cystitis on the expression of corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus (PVN) and the serum levels of adrenocorticotropic hormone (ACTH) using in situ hybridization histochemistry and radioimmunoassay. In addition, the expression of AVP heteronuclear (hn) RNA and neuronal nitric oxide synthase (nNOS) mRNA was also examined in the PVN of a CP-induced cystitis model. We found that the levels of CRH mRNA were significantly increased in the PVN at 2 h after intraperitoneal administration of CP compared to those in saline-treated rats. The CRH mRNA levels in the PVN peaked at 12 h after CP administration and the levels were still significantly higher than those in saline-treated group at 24 h after CP administration. The serum ACTH levels in CP-treated group were also significantly higher compared to those in saline-treated group at any of the time points examined. Unlike previous findings showing upregulation of nNOS mRNA and AVP hnRNA under somatic nociceptive states, the levels of nNOS mRNA and AVP hnRNA were unchanged in the PVN following CP-induced cystitis, visceral nociceptive stimulation. These results suggest that visceral nociceptive stimulation as well as somatic nociceptive stimulation may activate the hypothalamo-pituitary axis but the hypothalamic neuroendocrine responses produced by visceral nociceptive stimulation may be different from those produced by somatic nociceptive stimulation.

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.

Induction of galanin-like peptide gene expression in the rat posterior pituitary gland during endotoxin shock and adjuvant arthritis

Galanin-like peptide (GALP) was recently isolated from the porcine hypothalamus. The GALP mRNA is restricted in the hypothalamic arcuate nucleus and pituicytes in the posterior pituitary grand (PP) of the rat. The physiological function of the GALP is not clear in both areas. We focused on the regulation of the GALP gene expression to determine the role of GALP in the PP. We examined the effects of potent stressors to modulate a pituitary function, nociceptive stimuli and acute and chronic inflammatory stresses on the expression of the GALP gene in the PP using in situ hybridization histochemistry. Subcutaneous (s.c.) injection of 5% formalin in the bilateral hind paws caused a moderate increase of GALP gene expression in the PP. Intraperitoneal (i.p.) injection of lipopolysaccharide (LPS) also caused a marked increase of GALP gene expression in the PP. Effects of i.p. injection of LPS on the expression of the GALP gene in the PP were attenuated by pretreatment with i.p. injection of indomethacin. The levels of GALP mRNA in the PP were markedly increased by two peaks at 24 h and 15 days after s.c. injection of heat-inactivated M. butyricum that induced adjuvant arthritis. These results suggested that inflammatory stresses may be a potent stimulant to induce the expression of the GALP gene in the PP.

Gene expression in the supraoptic nucleus

The magnocellular neurosecretory cells (MNCs) in the supraoptic nucleus (SON) express multiple kinds of genes, including not only the classical hormones arginine vasopressin (AVP) and oxytocin (OXT), but also other physiologically active substances including neuropeptides, their receptors, and nitric oxide (NO) synthase, the rate-limiting enzyme in the synthesis of NO under physiological condition. For example, osmotic stimuli such as dehydration and chronic salt loading cause a wide range of changes of the expression levels of the genes and marked induction of the expression of the genes in the SON. The expression of the NO synthase gene in the SON under physiological conditions is reviewed.