Lesion of the perinuclear zone attenuates cardiac sensitivity of vasopressinergic supraoptic neurons

Discrete stretch of the caval-atrial junction decreases the activity of vasopressin-secreting neurons in the supraoptic nucleus (SON). The perinuclear zone (PNZ) of the SON is necessary for inhibition of vasopressin neurons following an increase in blood pressure. To determine whether the PNZ is necessary for cardiopulmonary regulation of vasopressin neurons, male rats received three unilateral injections of the excitotoxin ibotenic acid (n = 9) or phosphate-buffered saline vehicle (n = 10) into the PNZ. Extracellular activity of antidromically identified phasic vasopressin neurons in the ipsilateral SON was recorded. Of the 26 neurons recorded from vehicle-injected rats 26 were inhibited by an increase in blood pressure and 22 of those neurons were sensitive to caval-atrial distension. Of the neurons recorded from PNZ-lesion rats, only 12 of 29 were inhibited by an increase in blood pressure (P < 0.05), and only 11 neurons were sensitive to caval-atrial stretch (P < 0.05). Functional lesion of the PNZ significantly attenuates both arterial and cardiopulmonary baroreceptor-mediated inhibition of supraoptic vasopressin neurons, suggesting that the PNZ is a necessary component of both pathways.     

Influence of right atrial stretch on plasma renin activity in the conscious rat

Rats were prepared with inflatable balloons at the superior vena cava - right atrium junction. After recovery 1 week later, when blood was taken from conscious, normovolaemic animals plasma renin activity was found not to be influenced by right atrial stretch. Plasma renin activity was then measured in rats in which an extracellular fluid deficit had been produced by peritoneal dialysis against a hyperoncotic, isotonic solution. Although basal plasma renin activity was elevated (6.8 +/- 0.9 from 1.5 +/- 0.2 ng X mL X h, n = 19), no depression was observed in the experimental group after 15 or 90 min of balloon inflation. In rats pretreated with isoprenaline (10 micrograms/kg body wt.) plasma renin activity was also increased over basal levels, but again balloon inflation caused no reduction in plasma renin activity. It would appear that right atrial stretch has little, if any, influence on renin release in the conscious rat.     

Water deprivation increases Fos expression in hypothalamic corticotropin-releasing factor neurons induced by right atrial distension in awake rats

Atrial mechanoreceptors, sensitive to stretch, contribute in regulating heart rate and intravascular volume. The information from those receptors reaches the nucleus tractus solitarius and then the paraventricular nucleus (PVN), known to have a crucial role in the regulation of cardiovascular function. Neurons in the PVN synthesize CRF, AVP, and oxytocin (OT). Stimulation of atrial mechanoreceptors was performed in awake rats implanted with a balloon at the junction of the superior vena cava and right atrium. Plasma ACTH, AVP, and OT concentrations and Fos, CRF, AVP, and OT immunolabeling in the PVN were determined after balloon inflation in hydrated and water-deprived rats. The distension of the balloon increased the plasma ACTH concentrations, which were higher in water-deprived than in hydrated rats (P < 0.05). In addition, the distension in the water-deprived group decreased plasma AVP concentrations (P < 0.05), compared with the respective control group. The distension increased the number of Fos- and double-labeled Fos/CRF neurons in the parvocellular PVN, which was higher in the water-deprived than in the hydrated group (P < 0.01). There was no difference in the Fos expression in magnocellular PVN neurons after distension in hydrated and water-deprived groups, compared with respective controls. In conclusion, parvocellular CRF neurons showed an increase of Fos expression induced by stimulation of right atrial mechanoreceptors, suggesting that CRF participates in the cardiovascular reflex adjustments elicited by volume loading. Activation of CRF neurons in the PVN by cardiovascular reflex is affected by osmotic stimulation.     

P2X receptors are differentially expressed on vasopressin- and oxytocin-containing neurons in the supraoptic and paraventricular nuclei of rat hypothalamus

In the present study, the distribution of P2X receptor protein and colocalization of P2X receptors with vasopressin and oxytocin in the supraoptic and paraventricular nuclei of rat hypothalamus was studied using double-labeling fluorescence immunohistochemistry. The results showed that vasopressin-containing neurons expressed P2X₂, P2X₄, P2X₅ and P2X₆ receptor and oxytocin-containing neurons expressed P2X₂, P2X₄ and P2X₅ receptors in the supraoptic nucleus. In the paraventricular nucleus, vasopressin-containing neurons expressed P2X₄, P2X₅ and P2X₆ receptors, while oxytocin-containing neurons expressed P2X₄ receptors. This study provides the first evidence that P2X receptor subunits are differentially expressed on vasopressin- and oxytocin-containing neurons in the supraoptic and paraventricular nuclei, and hence, provides a substantial neuroanatomical basis for possible functional interactions between the purinergic and vasopressinergic systems, and the purinergic and oxytocinergic systems in the rat hypothalamus. Wei Guo and Jihu Sun contributed equally to this work.     

Immunocytochemical demonstration of separate vasopressin-neurophysin and oxytocin-neurophysin neurons in the human hypothalamus

Summary With the use of immunocytochemistry, it was shown that both the supraoptic and paraventricular hypothalamic nuclei in humans contain at least two different neurophysins. These two human neurophysins are immunologically related to bovine neurophysin I and neurophysin II, respectively. One human neurophysin is associated with vasopressin, the other with oxytocin. Human vasopressin-neurophysin and oxytocin-neurophysin are located separately in two different types of neurons, which correspond respectively to the vasopressinergic and oxytocinergic neurons of both the supraoptic and paraventricular nuclei. The neurophysin of the human vasopressinergic suprachiasmatic neurons appears to be closely related to or identical with neurophysin of the vasopressinergic neurons of the human magnocellular hypothalamic nuclei.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

Intrinsic membrane properties of magnocellular neurosecretory neurons recorded in vitro

Over the past 15 years, extracellular recordings from the rat supraoptic and paraventricular nuclei have revealed two populations of endocrine neurons that can be antidromically activated from neurosecretory axons in the neurohypophysis. Both the oxytocinergic and vasopressinergic populations of magnocellular neuroendocrine cells (MNCs) fire bursts of action potentials that facilitate hormone release from neurohypophyseal terminals. Moreover, both populations are osmosensitive, increasing their firing rate as osmolarity is elevated. Recently, slice and explant preparations of hypothalamus have enabled intracellular recording of these cells in normal and modified saline solutions. Spiking, bursting, and osmosensitivity can occur independently of synaptic input, enabling MNCs, for example, to transform an unpatterned depolarizing influence into the repetitive bursting pattern associated with vasopressin release. Current-clamp studies have started to characterize the repertoire of conductances across the MNC membrane that are responsible for action potential discharge, afterpotentials, bursting, and osmosensitivity. This provides a basis not only for further voltage-clamp studies, but for understanding transmitter effects that act by modulating intrinsic MNC currents.     

Co-localization of putative vasopressin receptors and vasopressinergic neurons in rat hypothalamus

Summary Vasopressin and oxytocin are synthesized by neurons in the paraventricular and supraoptic nuclei of hypothalamus. Dense concentrations of vasopressin binding sites have also been localized in these nuclei. Using a vasopressin anti-idiotypic antiserum, a dual immunocytochemical labeling procedure has been employed to elucidate the distribution of putative vasopressin receptors in anatomical relation to vasopressin and oxytocin immunoreactive cells in rat brain. Putative vasopressin receptors are observed in relation to magnocellular neurons in hypothalamus that are vasopressin immunoreactive. They do not appear to be associated with parvocellular vasopressinergic cells or oxytocin immunoreactive neurons. The presence of these presumed autoreceptors would support evidence that vasopressin may autoregulate the activity of magnocellular vasopressinergic neurons in hypothalamus.     

Co-localization of putative vasopressin receptors and vasopressinergic neurons in rat hypothalamus

Vasopressin and oxytocin are synthesized by neurons in the paraventricular and supraoptic nuclei of hypothalamus. Dense concentrations of vasopressin binding sites have also been localized in these nuclei. Using a vasopressin anti-idiotypic antiserum, a dual immunocytochemical labeling procedure has been employed to elucidate the distribution of putative vasopressin receptors in anatomical relation to vasopressin and oxytocin immunoreactive cells in rat brain. Putative vasopressin receptors are observed in relation to magnocellular neurons in hypothalamus that are vasopressin immunoreactive. They do not appear to be associated with parvocellular vasopressinergic cells or oxytocin immunoreactive neurons. The presence of these presumed autoreceptors would support evidence that vasopressin may autoregulate the activity of magnocellular vasopressinergic neurons in hypothalamus.     

Immunocytochemical localization of the vasopressinergic and the oxytocinergic neurons in the human hypothalamus

Summary The human hypothalamic-neurohypophysial hormone-producing nuclei were investigated with the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique at the light microscopic level. The size, shape and location of the supraoptic, paraventricular, accesssory supraoptic and suprachiasmatic nuclei were determined. It was demonstrated in the human hypothalamus, as well as in the hypothalamus of other mammals, that vasopressin and oxytocin are synthesized in separate neurons. In each of the nuclei of the magnocellular neurosecretory system, the distribution, ratios and structural features of the vasopressinergic and oxytocinergic neurons were determined. It was shown that the human suprachiasmatic nuclei contain numerous neurophysin-vasopressin-producing neurons.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

Responses in discharge of vasopressinergic neurons in the hypothalamic paraventricular nucleus elicited by water application to the pharyngolaryngeal regions in the rat

Magnocellular neurosecretory cells were antidromically identifiedin the hypothalamic paraventricular nucleus of urethane-anesthetized,ovariectomized female rats following electrical stimulationof the neurohypophysis The vasopressinergic cells with a phasicpattern of spontaneous discharge and the oxytocinergic cellswith a tonic pattern of discharge were distinguished and usedto examine the response associated with water or NaCl (154 mM)application to the pharyngolaryngeal regions. The water applicationproduced a reduction in the discharge of vasopressinergic cellsin the non-dehydrated condition, while there was no appreciablechange in the discharge of oxytocinergic cells after water application.The discharges in the vasopressinergic and oxytocinergic neuronswere unchanged after NaCl application. Because neural dischargein the vasopressinergic cell has been shown to be linked tovasopressin secretion, these findings suggest that pharyngolaryngealwater signals may actively modulate the fluid balance throughvasopressin.     

Role of Catecholamines in Regulation of the Functional State of Vasopressinergic Cells of the Rat Hypothalamus

In in vivo and in vitro experiments there have been shown different mechanisms of regulation of hypothalamic vasopressinergic neurons, including regulation due to changes of activity level of brain catecholaminergic and NPY-ergic neurons innervating hypothalamic vasopressinergic cells. We demonstrated in in vitro experiments that dopamine and noradrenaline had no effects on vasopressin expression, but inhibited its release from cell perikarya in supraoptic and paraventricular nuclei of hypothalamus. Besides, activity of vasopressinergic neurons might probably be regulated via activation of synthesis of these neurotransmitters in vasopressinergic cells themselves in the supraoptic and paraventricular nuclei. To activate synthesis of various neurotransmitters, in our case, catecholamines and NPY, in vasopressinergic neurons, different stimuli adequate to trigger or activate synthesis of these substances are required. Synthesis of catecholamines in vasopressinergic cells of supraoptic and paraventricular nuclei was revealed after immobilization stress and adrenalectomy. NPY is synthesized in neurons of hypothalamic neurosecretory centers in norm, and its synthesis increases at disturbances of NPY-ergic innervation of vasopressinergic cells.     

Antisense oligodeoxynucleotide effects on the hypothalamic-neurohypophysial system and the hypothalamic-pituitary-adrenal axis

The possibility of sequence-dependent, transient, and local inhibition of neuropeptide or neuropeptide receptor expression within the brain makes antisense targeting an attractive approach for those interested in the involvement of brain neuropeptide systems in behavioral and neuroendocrine regulation. Here, I describe our attempts to manipulate the synthetic activity of peptidergic systems of the hypothalamic-neurohypophysial system, i.e. , oxytocin and vasopressin, and the hypothalamic-pituitary-adrenal (HPA) axis by antisense oligodeoxynucleotides. Detailed experimental protocols including different approaches for intracerebral antisense application in anesthetized or conscious rats are provided. As a consequence of local oxytocin or vasopressin antisense treatment within the hypothalamic supraoptic nucleus, various aspects of the neuronal activity are already altered after a few hours. Thus, we monitored electrophysiological parameters of oxytocinergic and vasopressinergic neurons, stimulus-induced expression of the Fos protein in oxytocin neurons, and stimulated release of oxytocin or vasopressin into blood as well as within the hypothalamus by dendrites and cell bodies as measured by simultaneous microdialysis in blood and brain, shortly after a single acute antisense infusion. We also employed chronic antisense infusion via osmotic minipumps or by repeated local infusion into the targeted brain region; for example, septal vasopressin receptor downregulation impairs the ability of male rats to discriminate between juvenile rats. Further, reduction of the amount of available CRH, vasopressin, and oxytocin within the hypothalamic paraventricular nuclei alters the neuroendocrine stress response of the HPA axis.     

Vasopressinergic neurons in rats during ontogenesis: reaction to salt-loading and its modulation by noradrenergic afferents

Salt-loading in adult mammals stimulates vasopressin secretion by vasopressinergic neurons of the supraoptic nucleus that is under control by a number of hormones and neurotransmitters including noradrenalin. This study was aimed to determine at what period of ontogenesis the vasopressinergic neurons begin to respond to salt-loading and when the noradrenergic control of this process is switched on. Rats on the 21st embryonic day (E), the 3rd postnatal day (P) and P13 were salt-loaded, sometimes under simultaneous treatment with prasozin, an inhibitor of al -adrenoreceptors. Thereafter, the hypothalamic nuclei of the animals were processed for immunocytochemistry and in situ hybridization. Salt-loading provoked increased synthesis of vasopressin mRNA and, most probably, vasopressin itself in rats in all studied age groups. Under salt-loading, the intraneuronal content of vasopressin increased significantly at E21 and P3, whereas it did not change at P13. No change in the intracellular contents of vasopressin mRNA and vasopressin was observed in foetuses following salt-loading and treatment with prasozin though the same treatment provoked an increase of both parameters at P3. These data show that noradrenalin provides an inhibitory control of vasopressin expression at least since P3. Thus, vasopressinergic neurons begin to respond to salt-loading at the since P3. Thus, life by the increased expression of vasopressin that is postnatally under the inhibitory control by noradrenalin.     

Anatomic Twist to a Straightforward Ablation

Atrioventricular (AV) junction ablation for treatment of refractory atrial fibrillation is a well defined, standardized procedure and the simplest of commonly performed radiofrequency ablations in the field of cardiac electrophysiology. We report successful AV junction ablation using an inferior approach in a case of inferior vena cava interruption. Inability during the procedure to initially pass the ablation catheter into the right ventricle, combined with low amplitude electrograms, led to suspicion of an anatomic abnormality. This was determined to be a heterotaxy syndrome with inferior vena cava interruption and azygos continuation, draining in turn into the superior vena cava. Advancing Schwartz right 0 (SRO) sheath through the venous abnormality into the right atrium allowed adequate catheter stability to successfully induce complete AV block with radiofrequency energy.     

Joint time-frequency analysis of visible laser reflections in a sheep heart

Limited methods exist to confirm the position of cardiovascular devices in the superior vena cava or right atrium of the heart. The aim of this study was to design, test and validate the feasibility of whether an optical fiber-based instrument could accurately distinguish when a cardiovascular catheter was located in the superior vena cava vs in the right atrium. An optical fiber was placed in a cardiovascular catheter which was inserted into a living sheep and guided to the vicinity of the heart where diode laser-based reflection intensity data were simultaneously gathered from two visible wavelengths of light reflected from the venous and atrial tissue surfaces near the cavoatrial junction. The time series data were postoperatively analyzed using methods of joint time-frequency analysis and validated against catheter positions determined with fluoroscopy and ECG. The system was successful in distinguishing the location of the superior vena cava from the right atrium.     

Development of oxytocin- and vasopressin-network in the supraoptic and paraventricular nuclei of fetal sheep

The hypothalamic supraoptic and paraventricular nuclei consist of oxytocin and arginine vasopressin synthesizing neurons that send projections to the neurohypophysis. A growing body of evidence in adult animals and young animals at near term confirmed the structure and function in the vasopressinergic and oxytocinergic network. However, whether those distinctive neural networks are formed before near term is largely unknown. This study determined the special patterns in location and distribution of oxytocin- and vasopressin-neurons in the paraventricular and supraoptic nuclei from preterm to term in the ovine fetuses. The results showed that oxytocin- and vasopressin-neurons were present in both nuclei at the three gestational time periods (preterm, near term, and term). In the paraventricular nuclei, vasopressin-cells concentrated mainly in the core of the middle magnocellular paraventricular nuclei, and oxytocin-cells were scattered surrounding the core. In the supraoptic nuclei, vasopressin-cells mostly located in the ventral part, and oxytocin-cells in the dorsal part. The data demonstrated that the special distributed patterns of vasopressin- and oxytocin-neuron network have formed in those two nuclei at least from preterm. Intracerebroventricular injection of angiotensin II significantly increased fetal plasma oxytocin and vasopressin levels at preterm, which was associated with an increase of oxytocin- and vasopressin-neuron activity marked with c-fos expression. The data provided new evidence for the structural and functional development of the oxytocin- and vasopressin-network before birth.     

Immunocytochemistry of magnocellular neurons of supraoptic and paraventricular nuclei of normal and Brattleboro rats with vasopressin anti-idiotype antibody

Summary A vasopressin anti-idiotype antibody was generated by immunization with purified IgG of a primary vasopressin antiserum. The anti-idiotype antibody immunostained neurons in the supraoptic and paraventricular nuclei of the hypothalamus of normal and Brattleboro rats. The distribution of immunostained perikarya in these hypothalamic nuclei together with the staining of fibers in median eminence and neural lobe was similar to that observed in normal rats with anti-vasopressin and suggests strongly that vasopressinergic neurons are being stained. Absorption studies with vasopressin and a vasopressin-binding receptor protein further indicate that a receptor associated with vasopressinergic neurons is recognized by the anti-idiotype antibody.Supported by NIH grants ES03239, NS18626 and NSF grant BNS-8310914. D.T.P. is the receipient of RCDA award NS00869     

Oxytocin and vasopressin involved in restraint water-immersion stress mediated by oxytocin receptor and vasopressin 1b receptor in rat brain

Aims

Vasopressin (AVP) and oxytocin (OT) are considered to be related to gastric functions and the regulation of stress response. The present study was to study the role of vasopressinergic and oxytocinergic neurons during the restraint water-immersion stress.

Methods

Ten male Wistar rats were divided into two groups, control and RWIS for 1h. The brain sections were treated with a dual immunohistochemistry of Fos and oxytocin (OT) or vasopressin (AVP) or OT receptor or AVP 1b receptor (V_1bR).

Results

(1) Fos-immunoreactive (Fos-IR) neurons dramatically increased in the hypothalamic paraventricular nucleus (PVN), the supraoptic nucleus (SON), the neucleus of solitary tract (NTS) and motor nucleus of the vagus (DMV) in the RWIS rats; (2) OT-immunoreactive (OT-IR) neurons were mainly observed in the medial magnocellular part of the PVN and the dorsal portion of the SON, while AVP-immunoreactive (AVP-IR) neurons mainly distributed in the magnocellular part of the PVN and the ventral portion of the SON. In the RWIS rats, Fos-IR neurons were indentified in 31% of OT-IR neurons and 40% of AVP-IR neurons in the PVN, while in the SON it represented 28%, 53% respectively; (3) V_1bR-IR and OTR-IR neurons occupied all portions of the NTS and DMV. In the RWIS rats, more than 10% of OTR-IR and V_1bR-IR neurons were activated in the DMV, while lower ratio in the NTS.

Conclusion

RWIS activates both oxytocinergic and vasopressinergic neurons in the PVN and SON, which may project to the NTS or DMV mediating the activity of the neurons by OTR and V_1bR.