Gastrin-releasing peptide mediated regulation of 5-HT neuronal activity in the hypothalamic paraventricular nucleus under basal and restraint stress conditions

The purpose of this study was to examine the gastrin-releasing peptide (GRP) mediated regulation of 5-HT neuronal activity in the paraventricular nucleus of the hypothalamus under basal and restraint stress conditions. Intracerebroventricular (icv) administration of GRP (1, 10, 100 ng/rat) increased 5-HIAA concentrations in the paraventricular nucleus (PVN) of the hypothalamus, but was without effect in the accumbens, suprachiasmatic and arcuate nuclei. Administration of (Leu(13)-psi-CH(2)NH-Leu(14)) Bombesin (10, 100 and 1000 ng/rat; icv), a GRP antagonist, had no effect by itself on PVN serotonergic activity; however, a dose of 1 microg/rat of this compound, completely blocked the increase of 5-HIAA concentrations induced by GRP (10 ng). Restraint stress increased serotonergic activity -as shown by an elevation of 5-HIAA in the PVN- as well as plasma ACTH and corticosterone. This stress-induced activation of both the serotonergic neurons and the hypothalamus-pituitary-adrenal axis was blocked by CRF and GRP antagonists. Interestingly, when the activation of hypothalamic 5-HT neurons was induced by GRP administration, alpha-helical (9-41) CRF was ineffective.These data suggest that GRP, by acting on GRP receptors but not via CRF receptors, increases 5-HT neuronal activity in the PVN. In turn, it appears that endogenous GRP and CRF receptor ligands are both simultaneously involved in the regulation of the increase in 5-HT neuronal activity, ACTH and corticosterone secretion, under stress conditions.     

下丘脑室旁核的心血管调节功能研究进展

下丘脑室旁核 (PVN)是自主性和内分泌性反应的重要整合中枢 ,且在维持心血管活动的动态平衡中起着关键作用。本文简要归纳了PVN的形态结构、纤维联系 ,并详细叙述其对心血管活动的调节及与心血管疾病的关系。     

Feeding inhibition by urocortin in the rat hypothalamic paraventricular nucleus

Ventricular administration of urocortin (UCN) inhibits feeding, but specific site(s) of UCN action are unknown. In the current studies we examined the effect of UCN in the hypothalamic paraventricular nucleus (PVN) on feeding. We tested UCN administered into the PVN in several paradigms: deprivation-induced, nocturnal, and neuropeptide Y (NPY)-induced feeding. We compared the effect of equimolar doses of UCN and corticotrophin releasing hormone (CRH) on NPY-induced and nocturnal feeding, determined whether UCN in the PVN produced a conditioned taste aversion (CTA) and induced changes in c-Fos immunoreactivity (c-Fos-ir) after UCN and NPY administration in the PVN. UCN in the PVN significantly decreased NPY and nocturnal and deprivation-induced feeding at doses of 1, 10, and 100 pmol, respectively. UCN anorectic effects lasted longer than those attributed to CRH. Ten and thirty picomoles UCN did not induce a CTA, whereas 100 pmol UCN produced a CTA. UCN (100 pmol) in the PVN neither increased c-Fos-ir in any brain region assayed nor altered c-Fos-ir patterns resulting from PVN NPY administration. These data suggest the hypothalamic PVN as a site of UCN action.     

Effect of chronic psychogenic stress exposure on enkephalin neuronal activity and expression in the rat hypothalamic paraventricular nucleus

This study tested the hypothesis that the activation pattern of enkephalinergic (ENKergic) neurons within the paraventricular nucleus of the hypothalamus (PVH) in response to psychogenic stress is identical whether in response to repeated exposure to the same stress (homotypic; immobilization) or to a novel stress (heterotypic; air jet puff). Rats were assigned to either acute or chronic immobilization stress paradigms (90 min/day for 1 or 10 days, respectively). The chronic group was then subjected to an additional 90-min session of either heterotypic or homotypic stress. A single 90-min stress session (immobilization or air jet) increased PVH-ENK heteronuclear (hn) RNA expression. In chronically stressed rats, exposure to an additional stress session (whether homotypic or heterotypic) continued to stimulate ENK hnRNA expression. Acute immobilization caused a marked increase in the numbers of Fos-immunoreactive and Fos-ENK double-labeled cells in the dorsal and ventral medial parvicellular, and lateral parvicellular subdivisions of the PVH. Chronic immobilization caused an attenuated Fos response ( approximately 66%) to subsequent immobilization. In contrast, chronic immobilization did not impair ENKergic neuron activation within the PVH following homotypic or heterotypic stress. These results indicate that within the PVH, chronic psychogenic stress markedly attenuates the Fos response, whereas ENKergic neurons resist habituation, principally within the ventral neuroendocrine portion of the nucleus. This suggests an increase in ENK effect during chronic stress exposure. Homotypic (immobilization) and heterotypic (air jet) psychogenic stressors produce similar responses, including Fos, ENK-Fos, and ENK hnRNA, within each subdivision of the PVH, suggesting similar processing for painless neurogenic stimuli.     

Competitive peptide antagonists of ANF-induced cyclic guanosine monophosphate production

Atrial natriuretic factor (isoleucine ANF 101-126), cleaved ANF (isoleucine ANF 101-105/106-126) and des (Gln 18, Ser 19, Gly 20, Leu 21, Gly 22) ANF 4-23-NH2 (C-ANF 4-23) stimulated cyclic guanosine monophosphate production (cGMP) by rat aortic vascular smooth muscle cells (VSMC) in culture. Cleaved ANF and ANF C4-23 also antagonised or diminished the response to ANF 101-126. Agonist and antagonist actions of both peptides were dose-related. In contrast, prepro ANF (104-123), an ANF precursor fragment, exhibited no agonist or antagonist effect on cGMP production.     

Role of AgRP on Ghrelin-induced feeding in the hypothalamic paraventricular nucleus

MT II, agonist for MC3/4-Rs, inhibited Ghrelin's orexigenic effect in the paraventricular nucleus of the hypothalamus (PVN). To further investigate the role of the melanocortin system as mediator of ghrelin's orexigenic actions, we explored the involvement of AgRP in Ghrelin's orexigenic effect by testing the effect on food intake after their co-administration in the PVN, during the light and dark phases of feeding in rats. During both the phases of feeding, co-administration of Ghrelin with either AgRP 50 or AgRP 100 pmol into the PVN did not produce a synergistic effect on the food intake, suggesting that ghrelin induction of feeding occurs by recruiting Agrp as one of the obligatory mediators of its orexigenic effect.     

Lesions of the hypothalamic paraventricular nucleus and norepinephrine turnover in rats

The effects of bilateral lesions of the hypothalamic paraventricular nuclei (PVN), of rats with a mean weight of 260 g body, on eating habits and body weight, as well as on sympathetic nervous system (SNS) activity in interscapular brown adipose tissue (IBAT) were investigated. In 59 of 131 Sprague-Dawley female rats, PVN lesions resulted in hyperphagia and obesity. Although lesions were considered successful when more than 50% of the PVN was destroyed histologically, such lesions were observed in 35.9% (47/131) of all lesioned rats and all of these 47 rats were obese. Therefore, in this study, these 47 rats which were confirmed histologically, were designated as "PVN-lesioned rats". Plasma insulin levels in these 47 PVN-lesioned ats were more than double those of the controls. However, no significant differences were observed between plasma glucose levels in PVN-lesioned and control groups. Norepinephrine turnover, a reliable indicator of SNS activity, in IBAT, heart and pancreas was similar in PVN-lesioned and sham-operated control animals, even under contrasting conditions of feeding (ad libitum and fasting) and temperature (22 degrees C and 4 degrees C). It is concluded that PVN lesions produce hyperphagia, obesity and hyperinsulinemia in rats with an average body weight of 260g without affecting the SNS activity in IBAT, heart or pancreas.     

下丘脑室旁核内雌激素受体的表达与意义

下丘脑室旁核 (paraventricularnucleus ,PVN)包括大细胞部、小细胞部和背侧帽部等几个部分 ,其中大细胞部主要合成催产素和加压素 ,小细胞部主要合成促肾上腺皮质激素释放激素、甘丙肽等多种神经肽。研究发现PVN的神经内分泌活动受到雌激素的调节 ,进而影响动物的分娩、摄食、脂肪代谢、体重增加等生理功能。雌激素有α和 β两种受体 (即ER α和ER β)。在不同种属动物的PNV内两种雌激素受体的表达水平不同 ,如大鼠PVN主要表达ER β ,而小鼠PVN内除了表达ER β以外也能表达少量ER α ,提示两种ER在不同动物的PVN内功能可能不同 ,它们单独或协同介导雌激素在PVN内参与多种肽能神经元有关的生理功能。     

Brain-derived neurotrophic factor in the hypothalamic paraventricular nucleus reduces energy intake

Recent studies show that brain-derived neurotrophic factor (BDNF) decreases feeding and body weight after peripheral and ventricular administration. BDNF mRNA and protein, and its receptor tyrosine kinase B (TrkB) are widely distributed in the hypothalamus and other brain regions. However, there are few reports on specific brain sites of actions for BDNF. We evaluated the effect of BDNF in the hypothalamic paraventricular nucleus (PVN) on feeding. BDNF injected unilaterally or bilaterally into the PVN of food-deprived and nondeprived rats significantly decreased feeding and body weight gain within the 0- to 24-h and 24- to 48-h postinjection intervals. Effective doses producing inhibition of feeding behavior did not establish a conditioned taste aversion. PVN BDNF significantly decreased PVN neuropeptide Y (NPY)-induced feeding at 1, 2, and 4 h following injection. BDNF administration in the PVN abolished food-restriction-induced NPY gene expression in the hypothalamic arcuate nucleus. In conclusion, BDNF in the PVN significantly decreases food intake and body weight gain, suggesting that the PVN is an important site of action for BDNF in its effects on energy metabolism. Furthermore, BDNF appears to interact with NPY in its anorectic actions, although a direct effect on NPY remains to be established.     

The neurosteroid allopregnanolone modulates oxytocin expression in the hypothalamic paraventricular nucleus

Virgin, ovariectomized rats exposed to 2 wk of sequential estradiol (E(2)) and progesterone (P) followed by P withdrawal have increased hypothalamic oxytocin (OT) mRNA and peptide levels relative to sham-treated animals. This increase is prevented if P is sustained. In the central nervous system, P is metabolized to the neurosteroid allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), which exerts effects by acting as a positive allosteric modulator of GABA(A) receptor/Cl(-)-channel complexes. In the present study, ovariectomized rats that received sequential E(2) and P for 2 wk followed by P withdrawal were administered allopregnanolone at the time of P withdrawal. Hypothalamic and plasma allopregnanolone concentrations, serum E(2) and P concentrations, and hypothalamic OT mRNA levels were measured at death. Steroid-induced increases in OT mRNA were attenuated in animals treated with allopregnanolone at the time of P withdrawal. The results suggest that allopregnanolone plays an important modulatory role in steroid-mediated increases in hypothalamic OT.     

Agouti-related protein in the hypothalamic paraventricular nucleus: effect on feeding

Agouti-related protein (Agrp) is an endogenous melanocortin-4 receptor antagonist implicated in the regulation of food intake. Effects of Agrp on feeding under varying conditions were investigated. Agrp (10 to 100 pmol) was injected into the hypothalamic paraventricular nucleus of satiated (a.m. and p.m. injections) and food-deprived rats, or was co-administered with 117 pmol Neuropeptide Y (NPY). Agrp significantly stimulated light-phase feeding by 24 h post-injection. However, Agrp stimulated dark-phase and deprivation-induced feeding by 4 and 2 h, respectively. Animals receiving NPY and Agrp consumed more than animals receiving either peptide alone, the effect remaining by 24 h.     

Rhodopsin-detergent micelles aggregate upon activation of cyclic guanosine monophosphate phosphodiesterase

In the presence of G protein and phosphodiesterase, GTP induces aggregation of phospholipid-free rhodopsin-detergent micelles or rhodopsin reconstituted in phospholipid vesicles. The net electrical charge of the vesicle is not critical to the aggregation process since this phenomenon is not altered by reconstitution with phospholipids with different charge. The aggregation process is observed by monitoring changes in the light-scattering properties of the detergent micelles or vesicle suspension and by phase-contrast microscopy. The lowest light intensity which triggers the aggregation process and concomitant light-scattering changes in a rhodopsin-detergent micellar suspension bleaches 6% rhodopsin. Under these conditions, the signal saturates at 30% rhodopsin bleaching. The aggregation process appears likely to depend on the protein-protein interaction, and the presence of a disk membrane is not necessary for this process.     

Neuropeptide-stimulated cyclic guanosine monophosphate immunoreactivity in the neurosecretory terminals of a neurohemal organ

The neuropeptide eclosion hormone acts on the nervous system of the tobacco hornworm, Manduca sexta, to increase cyclic guanosine monophosphate (cGMP) levels. In this study I describe the localization of some of the sites where these increases occur. Prior to pupal ecdysis, eclosion hormone stimulates an increase in cGMP in a network of fibers in the transverse nerve of each abdominal ganglion. Double-label experiments with propidium iodide suggest that the cGMP immunoreactivity is primarily localized in neurosecretory nerve endings. The time course of the increase in cGMP immunoreactivity and its requirement for lipid metabolism is similar to that of the cGMP increase measured by radioimmunoassay. The cGMP response in the transverse nerve is stage-specific, occurring prior to pupal ecdysis and not prior to larval or adult ecdysis. © 1996 John Wiley & Sons, Inc.     

Induction of thymidylate synthetase activity in Tetrahymena by cyclic guanosine monophosphate.

The induction of TMP synthetase activity in Tetrahymena pyriformis depended upon growth conditions. Enzymatic activity was low in cells grown in complex medium, and was high in cells grown in, or shifted to, defined medium. TMP synthetase activity rose 5 hours after the shift from complex to defined medium using uracil as the pyrimidine source. The time of induction was decreased to $\text{3}\text{1}\text{2}$ hours using dUMP as the pyrimidine source. cGMP or its dibutyryl derivative, but not cAMP, caused the induction of TMP synthetase activity in cells grown in complex medium. Caffeine, but not theophylline, mimicked the cGMP response. cAMP decreased both the cGMP and caffeine mediated increases in TMP synthetase activity. This is the first demonstration of an effect of cGMP on induction of an enzyme of pyrimidine metabolism in any cellular system.     

Purinergic and glutamatergic interactions in the hypothalamic paraventricular nucleus modulate sympathetic outflow

P2X receptors are expressed on ventrolateral medulla projecting paraventricular nucleus (PVN) neurons. Here, we investigate the role of adenosine 5′-triphosphate (ATP) in modulating sympathetic nerve activity (SNA) at the level of the PVN. We used an in situ arterially perfused rat preparation to determine the effect of P2 receptor activation and the putative interaction between purinergic and glutamatergic neurotransmitter systems within the PVN on lumbar SNA (LSNA). Unilateral microinjection of ATP into the PVN induced a dose-related increase in the LSNA (1 nmol: 38 ± 6 %, 2.5 nmol: 72 ± 7 %, 5 nmol: 96 ± 13 %). This increase was significantly attenuated by blockade of P2 receptors (pyridoxalphosphate-6-azophenyl-20,40-disulphonic acid, PPADS) and glutamate receptors (kynurenic acid, KYN) or a combination of both. The increase in LSNA elicited by L-glutamate microinjection into the PVN was not affected by a previous injection of PPADS. Selective blockade of non-N-methyl-D-aspartate receptors (6-cyano-7-nitroquinoxaline-2,3-dione disodium salt, CNQX), but not N-methyl-D-aspartate receptors (NMDA) receptors (DL-2-amino-5-phosphonopentanoic acid, AP5), attenuated the ATP-induced sympathoexcitatory effects at the PVN level. Taken together, our data show that purinergic neurotransmission within the PVN is involved in the control of SNA via P2 receptor activation. Moreover, we show an interaction between P2 receptors and non-NMDA glutamate receptors in the PVN suggesting that these functional interactions might be important in the regulation of sympathetic outflow.     

Optogenetic manipulation of cyclic guanosine monophosphate to probe phosphodiesterase activities in megakaryocytes

Cyclic guanosine monophosphate (cGMP) signalling plays a fundamental role in many cell types, including platelets. cGMP has been implicated in platelet formation, but mechanistic detail about its spatio-temporal regulation in megakaryocytes (MKs) is lacking. Optogenetics is a technique which allows spatio-temporal manipulation of molecular events in living cells or organisms. We took advantage of this method and expressed a photo-activated guanylyl cyclase, Blastocladiella emersonii Cyclase opsin (BeCyclop), after viral-mediated gene transfer in bone marrow (BM)-derived MKs to precisely light-modulate cGMP levels. BeCyclop-MKs showed a significantly increased cGMP concentration after illumination, which was strongly dependent on phosphodiesterase (PDE) 5 activity. This finding was corroborated by real-time imaging of cGMP signals which revealed that pharmacological PDE5 inhibition also potentiated nitric oxide-triggered cGMP generation in BM MKs. In summary, we established for the first-time optogenetics in primary MKs and show that PDE5 is the predominant PDE regulating cGMP levels in MKs. These findings also demonstrate that optogenetics allows for the precise manipulation of MK biology.     

The renin-angiotensin-aldosterone system excites hypothalamic paraventricular nucleus neurons in heart failure

The paraventricular nucleus (PVN) of the hypothalamus has critical homeostatic functions, including the regulation of fluid balance and sympathetic drive. It has been suggested that altered activity of this nucleus contributes to the progression of congestive heart failure (HF). We hypothesized that forebrain influences of the renin-angiotensin-aldosterone system augment the activity of PVN neurons in HF. The rate of PVN neurons (n = 68) from rats with ischemia-induced HF was higher than that of PVN neurons (n = 42) from sham-operated controls (8.7 +/- 0.8 vs. 2.7 +/- 0.3 spikes/s, P < 0.001, HF vs. SHAM). Forebrain-directed intracarotid artery injections of the angiotensin type 1 receptor antagonist losartan, the angiotensin-converting enzyme inhibitor captopril, and the mineralocorticoid receptor antagonist spironolactone all significantly (P < 0.05) reduced PVN neuronal activity in HF rats. These findings demonstrate that the renin-angiotensin-aldosterone system drives PVN neuronal activity in HF, likely resulting in increased sympathetic drive and volume accumulation. This mechanism of neurohumoral excitation in HF is accessible to manipulation by blood-borne therapeutic agents.