Afferent renal inputs to paraventricular nucleus vasopressin and oxytocin neurosecretory neurons

CNS and CNS diseases in relation to their immune system

The central nervous system is the most important nervous system in vertebrates, which is responsible for transmitting information to the peripheral nervous system and controlling the body's activities. It mainly consists of the brain and spinal cord, which contains rich of neurons, the precision of the neural structures susceptible to damage from the outside world and from the internal factors of inflammation infection, leading to a series of central nervous system diseases, such as traumatic brain injury, nerve inflammation, etc., these diseases may cause irreversible damage on the central nervous or lead to subsequent chronic lesions. After disease or injury, the immune system of the central nervous system will play a role, releasing cytokines to recruit immune cells to enter, and the immune cells will differentiate according to the location and degree of the lesion, and become specific immune cells with different functions, recognize and phagocytose inflammatory factors, and repair the damaged neural structure. However, if the response of these immune cells is not suppressed, the overexpression of some genes can cause further damage to the central nervous system. There is a need to understand the molecular mechanisms by which these immune cells work, and this information may lead to immunotherapies that target certain diseases and avoid over-activation of immune cells. In this review, we summarized several immune cells that mainly play a role in the central nervous system and their roles, and also explained the response process of the immune system in the process of some common neurological diseases, which may provide new insights into the central nervous system.

The Interaction of Central Nervous System and Acute Kidney Injury: Pathophysiology and Clinical Perspectives

Acute kidney injury (AKI) is a common disorder in critically ill hospitalized patients. Its main pathological feature is the activation of the sympathetic nervous system and the renin-angiotensin system (RAS). This disease shows a high fatality rate. The reason is that only renal replacement therapy and supportive care can reduce the impact of the disease, but those measures cannot significantly improve the mortality. This review focused on a generalization of the interaction between acute kidney injury and the central nervous system (CNS). It was found that the CNS further contributes to kidney injury by regulating sympathetic outflow and oxidative stress in response to activation of the RAS and increased pro-inflammatory factors. Experimental studies suggested that inhibiting sympathetic activity and RAS activation in the CNS and blocking oxidative stress could effectively reduce the damage caused by AKI. Therefore, it is of significant interest to specify the mechanism on how the CNS affects AKI, as we could use such mechanism as a target for clinical interventions to further reduce the mortality and improve the complications of AKI.

Systematic Review Registration: [www.ClinicalTrials.gov], identifier [registration number].

Impact of anesthesia and sex on sympathetic efferent and hemodynamic responses to renal chemo- and mechanosensitive stimuli

Activation of renal sensory nerves by chemo- and mechanosensitive stimuli produces changes in efferent sympathetic nerve activity (SNA) and arterial blood pressure (ABP). Anesthesia and sex influence autonomic function and cardiovascular hemodynamics, but it is unclear to what extent anesthesia and sex impact SNA and ABP responses to renal sensory stimuli. We measured renal, splanchnic, and lumbar SNA and ABP in male and female Sprague-Dawley rats during contralateral renal infusion of capsaicin and bradykinin or during elevation in renal pelvic pressure. Responses were evaluated with a decerebrate preparation or Inactin, urethane, or isoflurane anesthesia. Intrarenal arterial infusion of capsaicin (0.1-30.0 μM) increased renal SNA, splanchnic SNA, or ABP but decreased lumbar SNA in the Inactin group. Intrarenal arterial infusion of bradykinin (0.1-30.0 μM) increased renal SNA, splanchnic SNA, and ABP but decreased lumbar SNA in the Inactin group. Elevated renal pelvic pressure (0-20 mmHg, 30 s) significantly increased renal SNA and splanchnic SNA but not lumbar SNA in the Inactin group. In marked contrast, SNA and ABP responses to every renal stimulus were severely blunted in the urethane and decerebrate groups and absent in the isoflurane group. In the Inactin group, the magnitude of SNA responses to chemo- and mechanosensory stimuli were not different between male and female rats. Thus, chemo- and mechanosensitive stimuli produce differential changes in renal, splanchnic, and lumbar SNA. Experimentally, future investigations should consider Inactin anesthesia to examine sympathetic and hemodynamic responses to renal sensory stimuli.NEW & NOTEWORTHY The findings highlight the impact of anesthesia, and to a lesser extent sex, on sympathetic efferent and hemodynamic responses to chemosensory and mechanosensory renal stimuli. Sympathetic nerve activity (SNA) and arterial blood pressure (ABP) responses were present in Inactin-anesthetized rats but largely absent in decerebrate, isoflurane, or urethane preparations. Renal chemosensory stimuli differentially changed SNA: renal and splanchnic SNA increased, but lumbar SNA decreased. Future investigations should consider Inactin anesthesia to study SNA and hemodynamic responses to renal sensory nerve activation.

Specific Afferent Renal Denervation Prevents Reduction in Neuronal Nitric Oxide Synthase Within the Paraventricular Nucleus in Rats With Chronic Heart Failure

Renal denervation (RDN) has been shown to restore endogenous neuronal nitric oxide synthase (nNOS) in the paraventricular nucleus (PVN) and reduce sympathetic drive during chronic heart failure (CHF). The purpose of the present study was to assess the contribution of afferent renal nerves to the nNOS-mediated sympathetic outflow within the PVN in rats with CHF. CHF was induced in rats by ligation of the left coronary artery. Four weeks after surgery, selective afferent RDN (A-RDN) was performed by bilateral perivascular application of capsaicin on the renal arteries. Seven days after intervention, nNOS protein expression, nNOS immunostaining signaling, and diaphorase-positive stained cells were significantly decreased in the PVN of CHF rats, changes that were reversed by A-RDN. A-RDN reduced basal lumbar sympathetic nerve activity in rats with CHF (8.5%±0.5% versus 17.0%±1.2% of max). Microinjection of nNOS inhibitor L-NMMA (L-N^G-monomethyl arginine citrate) into the PVN produced a blunted increase in lumbar sympathetic nerve activity in rats with CHF. This response was significantly improved after A-RDN (Δ lumbar sympathetic nerve activity: 25.7%±2.4% versus 11.2%±0.9%). Resting afferent renal nerves activity was substantially increased in CHF compared with sham rats (56.3%±2.4% versus 33.0%±4.7%). These results suggest that intact afferent renal nerves contribute to the reduction of nNOS in the PVN. A-RDN restores nNOS and thus attenuates the sympathoexcitation. Also, resting afferent renal nerves activity is elevated in CHF rats, which may highlight a crucial neural mechanism arising from the kidney in the maintenance of enhanced sympathetic drive in CHF.

Neuroanatomical circuitry between kidney and rostral elements of brain: a virally mediated transsynaptic tracing study in mice

The identity of higher-order neurons and circuits playing an associative role to control renal function is not well understood. We identified specific neural populations of rostral elements of brain regions that project multisynaptically to the kidneys in 3-6 days after injecting a retrograde tracer pseudorabies virus (PRV)-614 into kidney of 13 adult male C57BL/6J strain mice. PRV-614 infected neurons were detected in a number of mesencephalic (e.g. central amygdala nucleus), telencephalic regions and motor cortex. These divisions included the preoptic area (POA), dorsomedial hypothalamus (DMH), lateral hypothalamus, arcuate nucleus (Arc), suprachiasmatic nucleus (SCN), periventricular hypothalamus (PeH), and rostral and caudal subdivision of the paraventricular nucleus of the hypothalamus (PVN). PRV-614/Tyrosine hydroxylase (TH) double-labeled cells were found within DMH, Arc, SCN, PeH, PVN, the anterodorsal and medial POA. A subset of neurons in PVN that participated in regulating sympathetic outflow to kidney was catecholaminergic or serotonergic. PRV-614 infected neurons within the PVN also contained arginine vasopressin or oxytocin. These data demonstrate the rostral elements of brain innervate the kidney by the neuroanatomical circuitry.

Integration of renal sensory afferents at the level of the paraventricular nucleus dictating sympathetic outflow

The sympathetic nervous system has been identified as a major contributor to the pathophysiology of chronic heart failure (CHF) and other diseases such as hypertension and diabetes, both in experimental animal models and patients. The kidneys have a dense afferent sensory innervation positioning it to be the origin of multimodal input to the central nervous system. Afferent renal nerve (ARN) signals are centrally integrated, and their activation results in a general increase in sympathetic tone, which is directed toward the kidneys as well as other peripheral organs innervated by the sympathetic nerves. In the central nervous system, stimulation of ARN increases the neuronal discharge frequency and neuronal activity in the paraventricular nucleus (PVN) of the hypothalamus. The activity of the neurons in the PVN is attenuated during iontophoretic application of glutamate receptor blocker, AP5. An enhanced afferent renal input to the PVN may be critically involved in dictating sympathoexcitation in CHF. Furthermore, renal denervation abrogates the enhanced neuronal activity within the PVN in rats with CHF, thereby possibly contributing to the reduction in sympathetic tone. Renal denervation also restores the decreased endogenous levels of neuronal nitric oxide synthase (nNOS) in the PVN of rats with CHF. Overall, these data demonstrate that sensory information originating in the kidney excites pre-autonomic sympathetic neurons within the PVN and this "renal-PVN afferent pathway" may contribute to elevated sympathetic nerve activity in hyper-sympathetic disease conditions such as CHF and hypertension.

Renal Denervation Improves Exaggerated Sympathoexcitation in Rats With Heart Failure: A Role for Neuronal Nitric Oxide Synthase in the Paraventricular Nucleus

Renal denervation (RDN) has been postulated to reduce sympathetic drive during heart failure (HF), but the central mechanisms are not completely understood. The purpose of the present study was to assess the contribution of neuronal nitric oxide synthase (nNOS) within the paraventricular nucleus (PVN) in modulating sympathetic outflow in rats with HF that underwent RDN. HF was induced in rats by ligation of the left coronary artery. Four weeks after surgery, bilateral RDN was performed. Rats with HF had an increase in FosB-positive cells in the PVN with a concomitant increase in urinary excretion of norepinephrine, and both of these parameters were ameliorated after RDN. nNOS-positive cells immunostaining, diaphorase staining, and nNOS protein expression were significantly decreased in the PVN of HF rats, findings that were ameliorated by RDN. Microinjection of nNOS inhibitor N(G)-monomethyl l-arginine into the PVN resulted in a blunted increase in lumbar sympathetic nerve activity (11±2% versus 24±2%) in HF than in sham group. This response was normalized after RDN. Stimulation of afferent renal nerves produced a greater activation of PVN neurons in rats with HF. Afferent renal nerve stimulation elicited a greater increase in lumbar sympathetic nerve activity in rats with HF than in sham rats (45±5% versus 22±2%). These results suggest that intact renal nerves contribute to the reduction of nNOS in the PVN, resulting in the activation of the neurons in the PVN of rats with HF. RDN restores nNOS and thus attenuates the sympathoexcitation commonly observed in HF.

Activation of afferent renal nerves modulates RVLM-projecting PVN neurons

Renal denervation for the treatment of hypertension has proven to be successful; however, the underlying mechanism/s are not entirely clear. To determine if preautonomic neurons in the paraventricular nucleus (PVN) respond to afferent renal nerve (ARN) stimulation, extracellular single-unit recording was used to investigate the contribution of the rostral ventrolateral medulla (RVLM)-projecting PVN (PVN-RVLM) neurons to the response elicited during stimulation of ARN. In 109 spontaneously active neurons recorded in the PVN of anesthetized rats, 25 units were antidromically activated from the RVLM. Among these PVN-RVLM neurons, 84% (21/25) were activated by ARN stimulation. The baseline discharge rate was significantly higher in these neurons than those PVN-RVLM neurons not activated by ARN stimulation (16%, 4/25). The responsiveness of these neurons to baroreflex activation induced by phenylephrine and activation of cardiac sympathetic afferent reflex (CSAR) was also examined. Almost all of the PVN neurons that responded to ARN stimulation were sensitive to baroreflex (95%) and CSAR (100%). The discharge characteristics for nonevoked neurons (not activated by RVLM antidromic stimulation) showed that 23% of these PVN neurons responded to ARN stimulation. All the PVN neurons that responded to ARN stimulation were activated by N-methyl-D-aspartate, and these responses were attenuated by the glutamate receptor blocker AP5. These experiments demonstrated that sensory information originating in the kidney is integrated at the level of preautonomic neurons within the PVN, providing a novel mechanistic insight for use of renal denervation in the modulation of sympathetic outflow in disease states such as hypertension and heart failure.

The crosstalk between the kidney and the central nervous system: the role of renal nerves in blood pressure regulation

NEW FINDINGS

What is the topic of this review? This review describes the role of renal nerves as the key carrier of signals from the kidneys to the CNS and vice versa; the brain and kidneys communicate through this carrier to maintain homeostasis in the body. What advances does it highlight? Whether renal or autonomic dysfunction is the predominant contributor to systemic hypertension is still debated. In this review, we focus on the role of the renal nerves in a model of renovascular hypertension. The sympathetic nervous system influences the renal regulation of arterial pressure and body fluid composition. Anatomical and physiological evidence has shown that sympathetic nerves mediate changes in urinary sodium and water excretion by regulating the renal tubular water and sodium reabsorption throughout the nephron, changes in the renal blood flow and the glomerular filtration rate by regulating the constriction of renal vasculature, and changes in the activity of the renin-angiotensin system by regulating the renin release from juxtaglomerular cells. Additionally, renal sensory afferent fibres project to the autonomic central nuclei that regulate blood pressure. Hence, renal nerves play a key role in the crosstalk between the kidneys and the CNS to maintain homeostasis in the body. Therefore, the increased sympathetic nerve activity to the kidney and the renal afferent nerve activity to the CNS may contribute to the outcome of diseases, such as hypertension.

Do delivery routes of intranasally administered oxytocin account for observed effects on social cognition and behavior? A two-level model

Accumulating evidence demonstrates the important role of oxytocin (OT) in the modulation of social cognition and behavior. This has led many to suggest that the intranasal administration of OT may benefit psychiatric disorders characterized by social dysfunction, such as autism spectrum disorders and schizophrenia. Here, we review nasal anatomy and OT pathways to central and peripheral destinations, along with the impact of OT delivery to these destinations on social behavior and cognition. The primary goal of this review is to describe how these identified pathways may contribute to mechanisms of OT action on social cognition and behavior (that is, modulation of social information processing, anxiolytic effects, increases in approach-behaviors). We propose a two-level model involving three pathways to account for responses observed in both social cognition and behavior after intranasal OT administration and suggest avenues for future research to advance this research field.

A novel method of selective ablation of afferent renal nerves by periaxonal application of capsaicin

Renal denervation has been shown to lower arterial pressure in some hypertensive patients, yet it remains unclear whether this is due to ablation of afferent or efferent renal nerves. To investigate the role of afferent renal nerves in arterial pressure regulation, previous studies have used methods that disrupt both renal and nonrenal afferent signaling. The present study was conducted to develop and validate a technique for selective ablation of afferent renal nerves that does not disrupt other afferent pathways. To do this, we adapted a technique for sensory denervation of the adrenal gland by topical application of capsaicin and tested the hypothesis that exposure of the renal nerves to capsaicin (renal-CAP) causes ablation of afferent but not efferent renal nerves. Renal-CAP had no effect on renal content of the efferent nerve markers tyrosine hydroxylase and norepinephrine; however, the afferent nerve marker, calcitonin gene-related peptide was largely depleted from the kidney 10 days after intervention, but returned to roughly half of control levels by 7 wk postintervention. Moreover, renal-CAP abolished the cardiovascular responses to acute pharmacological stimulation of afferent renal nerves. Renal-CAP rats showed normal weight gain, as well as cardiovascular and fluid balance regulation during dietary sodium loading. To some extent, renal-CAP did blunt the bradycardic response and increase the dipsogenic response to increased salt intake. Lastly, renal-CAP significantly attenuated the development of deoxycorticosterone acetate-salt hypertension. These results demonstrate that renal-CAP effectively causes selective ablation of afferent renal nerves in rats.

Sex differences and central protective effect of 17beta-estradiol in the development of aldosterone/NaCl-induced hypertension

The present study tested the hypotheses that male and female rats respond differently to subcutaneous infusions of aldosterone (Aldo; 1.8 microg.kg(-1).h(-1), 1% NaCl to drink; 28 days) and that central estrogen plays a protective role against the development of hypertension. In rats with blood pressure (BP) and heart rate (HR) measured by Data Sciences International telemetry, chronic Aldo/NaCl treatment induced a greater increase in BP in males (Delta25.4 +/- 2.4 mmHg) than in females (Delta7.1 +/- 2.2 mmHg). Gonadectomy augmented Aldo/NaCl-induced hypertension in females (Delta18.2 +/- 2.0 mmHg) but had no effect in males (Delta23.1 +/- 2.9 mmHg). Immunohistochemistry for Fra-like activity was higher in the paraventricular nucleus of intact males, castrated males, and ovariectomized (OVX) females compared with intact females after 28 days of Aldo/NaCl treatment. In intact males, central 17beta-estradiol (E(2)) inhibited the Aldo/NaCl increase in BP (Delta10.5 +/- 0.8) compared with that in central vehicle plus systemic Aldo/NaCl (Delta26.1 +/- 2.5 mmHg) rats. Combined administration of E(2) and estrogen receptor antagonist ICI182780 (ICI) blocked the protective effect of E(2) (Delta23.2 +/- 2.4 mmHg). In intact females central, but not peripheral, infusions of ICI augmented the Aldo/NaCl (Delta20.4 +/- 1.8 mmHg) BP increase. Finally, ganglionic blockade after Aldo infusions resulted in a smaller reduction in BP in intact females (-23.9 +/- 2.5 mmHg) and in central estrogen-treated males (-30.2 +/- 1.0 mmHg) compared with other groups (intact males, -39.3 +/- 3.4; castrated males, -41.8 +/- 1.9; intact males with central E(2) + ICI, -42.3 +/- 2.1; OVX females, -40.3 +/- 3.3; and intact females with central ICI, -39.1 +/- 1.3 mmHg). Chronic Aldo infusion produced increases in NaCl intake and decreases in HR that were both similar in all groups. Taken together, the results indicate that central estrogen plays a protective role in the development of Aldo/NaCl-induced hypertension and that this may result from reduced sympathetic outflow.

Cardiac effects of oxytocin: is there a role for this peptide in cardiovascular homeostasis?

Oxytocin is well known for its role in reproduction. However, evidence has emerged suggesting a role in cardiovascular and hydroelectrolytic homeostasis. Although its renal effects have been characterized, the cardiac ones have not been much studied. Therefore, we aimed to investigate the cardiac effects of oxytocin both in vivo and in vitro. In unanesthetized rats (n=6) intravenous oxytocin (1 mug) decreased dP/dt(max) by 15% (P<0.05) and heart rate by 20% (P<0.001), at the first minute after injection. dP/dt(max) was still lower in OT-treated rats than in controls (n=8) after 15 min (P<0.05), while heart rate returned to control values after 5 min. In isolated hearts, oxytocin was able to promote negative inotropic and chronotropic effects. Perfusion with 10(-5), 10(-6) and 10(-7)M oxytocin resulted in approximately 60% (P<0.01), 25% (P<0.01) and 10% (P<0.05) reduction of left ventricle developed pressure, without effect in lower concentrations (10(-10) to 10(-8) M). Also, dP/dt(max) was reduced by 45 and 20% (10(-5) e 10(-6) M; P<0.01), while diastolic pressure raised and heart rate fell only with 10(-5)M oxytocin (P<0.05). Intravenous oxytocin (1 mug; n=6) increased arterial pressure by 22% at the first minute (+23+/-3 mm Hg; P<0.001), returning to control value thereafter. Thus, oxytocin is able to promote directly negative inotropic and chronotropic effects, but its in vivo effect also involves a reflex mechanism, originated from its pressor effect.

Acute increases in arterial blood pressure do not reduce plasma vasopressin levels stimulated by angiotensin II or hyperosmolality in rats

The present study sought to determine whether an acute increase in arterial blood pressure (ABP) reduces plasma vasopressin (VP) levels stimulated by ANG II or hyperosmolality. During an intravenous infusion of ANG II (100 ng·kg−1·min−1), attenuation of the ANG II-evoked increase in ABP with diazoxide or minoxidil did not further enhance plasma VP levels in rats. When VP secretion was stimulated by an infusion of hypertonic saline, coinfusion of the α-adrenergic agonist phenylephrine (PE) significantly increased ABP but did not reduce plasma VP levels. In fact, plasma VP levels were enhanced. The enhancement of plasma VP levels cannot be explained by a direct stimulatory action of PE, as plasma VP levels of isosmotic rats did not change during a similar infusion of PE. An infusion of endothelin-1 in hyperosmotic rats significantly raised ABP but did not reduce plasma VP levels; rather, VP levels increased as observed with PE. In α-chloralose-anesthetized rats infused with hypertonic saline, inflation of an aortic cuff to increase ABP and stimulate arterial baroreceptors did not reduce plasma VP levels. In each experiment, plasma oxytocin levels paralleled plasma VP levels. Collectively, the present findings suggest that an acute increase in ABP does not inhibit VP secretion.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

The oxytocin receptor system: structure, function, and regulation

The neurohypophysial peptide oxytocin (OT) and OT-like hormones facilitate reproduction in all vertebrates at several levels. The major site of OT gene expression is the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. In response to a variety of stimuli such as suckling, parturition, or certain kinds of stress, the processed OT peptide is released from the posterior pituitary into the systemic circulation. Such stimuli also lead to an intranuclear release of OT. Moreover, oxytocinergic neurons display widespread projections throughout the central nervous system. However, OT is also synthesized in peripheral tissues, e.g., uterus, placenta, amnion, corpus luteum, testis, and heart. The OT receptor is a typical class I G protein-coupled receptor that is primarily coupled via G(q) proteins to phospholipase C-beta. The high-affinity receptor state requires both Mg(2+) and cholesterol, which probably function as allosteric modulators. The agonist-binding region of the receptor has been characterized by mutagenesis and molecular modeling and is different from the antagonist binding site. The function and physiological regulation of the OT system is strongly steroid dependent. However, this is, unexpectedly, only partially reflected by the promoter sequences in the OT receptor gene. The classical actions of OT are stimulation of uterine smooth muscle contraction during labor and milk ejection during lactation. While the essential role of OT for the milk let-down reflex has been confirmed in OT-deficient mice, OT's role in parturition is obviously more complex. Before the onset of labor, uterine sensitivity to OT markedly increases concomitant with a strong upregulation of OT receptors in the myometrium and, to a lesser extent, in the decidua where OT stimulates the release of PGF(2 alpha). Experiments with transgenic mice suggest that OT acts as a luteotrophic hormone opposing the luteolytic action of PGF(2 alpha). Thus, to initiate labor, it might be essential to generate sufficient PGF(2 alpha) to overcome the luteotrophic action of OT in late gestation. OT also plays an important role in many other reproduction-related functions, such as control of the estrous cycle length, follicle luteinization in the ovary, and ovarian steroidogenesis. In the male, OT is a potent stimulator of spontaneous erections in rats and is involved in ejaculation. OT receptors have also been identified in other tissues, including the kidney, heart, thymus, pancreas, and adipocytes. For example, in the rat, OT is a cardiovascular hormone acting in concert with atrial natriuretic peptide to induce natriuresis and kaliuresis. The central actions of OT range from the modulation of the neuroendocrine reflexes to the establishment of complex social and bonding behaviors related to the reproduction and care of the offspring. OT exerts potent antistress effects that may facilitate pair bonds. Overall, the regulation by gonadal and adrenal steroids is one of the most remarkable features of the OT system and is, unfortunately, the least understood. One has to conclude that the physiological regulation of the OT system will remain puzzling as long as the molecular mechanisms of genomic and nongenomic actions of steroids have not been clarified.

Effects of right atrial distension on the activity of magnocellular neurons in the supraoptic nucleus

A small balloon placed at the junction of the superior vena cava and right atrium was used to stimulate cardiac volume receptors in pentobarbital sodium-anesthetized male rats. Extracellular recordings were obtained from antidromically identified vasopressinergic and oxytocinergic neurosecretory cells of the supraoptic nucleus. Cells were considered sensitive to the stimulus if balloon inflation resulted in a 30% change in firing frequency. Balloon inflation that did not stretch the caval-atrial junction had no significant effect on vasopressin neurons (n = 51, P > 0.05). Stretch of the caval-atrial junction decreased the firing activity in 64 of 83 putative vasopressin neurons (P < 0.01 compared with control). Stretch of the caval-atrial junction influenced the firing activity of only 3 of 26 antidromically activated oxytocinergic neurons, an effect not statistically different from control (P > 0. 05). When bilateral vagotomy was performed while recording from vasopressin neurons (n = 5), sensitivity to stretch of the caval-atrial junction was eliminated. Cardiac receptors located at the junction of the superior vena cava and right atrium may be important in regulating the activity of vasopressinergic but not oxytocinergic neurons of the supraoptic nucleus.

Neural control of renal function

The renal nerves are the communication link between the central nervous system and the kidney. In response to multiple peripheral and central inputs, efferent renal sympathetic nerve activity is altered so as to convey information to the major structural and functional components of the kidney, the vessels, glomeruli, and tubules, each of which is innervated. At the level of each of these individual components, information transfer occurs via interaction of the neurotransmitter released at the sympathetic nerve terminal-neuroeffector junction with specific postjunctional receptors coupled to defined intracellular signaling and effector systems. In response to normal physiological stimuli, changes in efferent renal sympathetic nerve activity contribute importantly to homeostatic regulation of renal blood flow, glomerular filtration rate, renal tubular epithelial cell solute and water transport, and hormonal release. Afferent input from sensory receptors located in the kidney participates in this reflex control system via renorenal reflexes that enable total renal function to be self-regulated and balanced between the two kidneys. In pathophysiological conditions, abnormal regulation of efferent renal sympathetic nerve activity contributes significantly to the associated abnormalities of renal function which, in turn, are of importance in the pathogenesis of the disease.