Neuronal activation in the CNS during different forms of acute renal failure in rats

Beyond the brain: General intensive care considerations in pediatric neurocritical care

Managing children with critical neurological conditions requires a comprehensive understanding of several principles of critical care. Providing a holistic approach that addresses not only the acute interactions between the brain and different organ systems, but also critical illness-associated complications and recovery is essential for improving outcomes in these patients. The brain reacts to an insult with autonomic responses designed to optimize cardiac output and perfusion, which can paradoxically be detrimental. Managing neuro-cardiac interactions therefore requires balancing adequate cerebral perfusion and minimizing complications. The need for intubation and airway protection in patients with acute encephalopathy should be individualized following careful risk/benefit deliberations. Ventilatory strategies can have profound impact on cerebral perfusion. Therefore, understanding neuro-pulmonary interactions is vital to optimize ventilation and oxygenation to support a healing brain. Gastrointestinal dysfunction is common and often complicates the care of patients with critical neurological conditions. Kidney function, along with fluid status and electrolyte derangements, should also be carefully managed in the acutely injured brain. While in the pediatric intensive care unit, prevention of critical illness-associated complications such as healthcare-associated infections and deep vein thrombosis is vital in improving outcomes. As the brain emerges from the acute injury, rehabilitation and management of delirium and paroxysmal sympathetic hyperactivity is paramount for optimal recovery. All these considerations provide a foundation for the care of pediatric patients with critical neurological conditions in the intensive care unit.

Acute kidney injury in neurocritical care

Approximately 20% of patients with acute brain injury (ABI) also experience acute kidney injury (AKI), which worsens their outcomes. The metabolic and inflammatory changes associated with AKI likely contribute to prolonged brain injury and edema. As a result, recognizing its presence is important for effectively managing ABI and its sequelae. This review discusses the occurrence and effects of AKI in critically ill adults with neurological conditions, outlines potential mechanisms connecting AKI and ABI progression, and highlights AKI management principles. Tailored approaches include optimizing blood pressure, managing intracranial pressure, adjusting medication dosages, and assessing the type of administered fluids. Preventive measures include avoiding nephrotoxic drugs, improving hemodynamic and fluid balance, and addressing coexisting AKI syndromes. ABI patients undergoing renal replacement therapy (RRT) are more susceptible to neurological complications. RRT can negatively impact cerebral blood flow, intracranial pressure, and brain tissue oxygenation, with effects tied to specific RRT methods. Continuous RRT is favored for better hemodynamic stability and lower risk of dialysis disequilibrium syndrome. Potential RRT modifications for ABI patients include adjusted dialysate and blood flow rates, osmotherapy, and alternate anticoagulation methods. Future research should explore whether these strategies enhance outcomes and if using novel AKI biomarkers can mitigate AKI-related complications in ABI patients.

Association between acute kidney injury and brain injury on term-equivalent age brain magnetic resonance imaging in very preterm infants

BACKGROUND

This study aimed to investigate the relationship between acute kidney injury (AKI) in the first 2 weeks of life and brain injury on term-equivalent age magnetic resonance imaging in very preterm infants.

METHODS

We included 116 infants with a birth weight of < 1500 g who were born at the King Saud Medical City at ≤ 32 gestational weeks. They were admitted to the neonatal intensive care unit and underwent term-equivalent age and pre-discharge brain magnetic resonance imaging. A negative binomial with generalized linear models and a robust variance estimator (Huber-White) was applied for univariate relative risk analysis. The Kidokoro score was then used to determine the effect of AKI on brain morphology and growth at term-equivalent age.

RESULTS

Sixty-eight (64.2%) infants had developed an AKI in the first 2 weeks of life. AKI was significantly associated with cerebellum signal abnormalities, cerebellar volume reduction, and a high total cerebellum score (P = 0.04, P < 0.001, P < 0.001, respectively).

CONCLUSIONS

AKI in the first 2 weeks of life is associated with brain insult, especially in the cerebellum. More well-designed studies are required to investigate the association and impact of AKI on the central nervous system. A higher resolution version of the Graphical abstract is available as Supplementary information.

Acute Kidney Injury at the Neurocritical Care Unit

Neurocritical care has advanced substantially in recent decades, allowing doctors to treat patients with more complicated conditions who require a multidisciplinary approach to achieve better clinical outcomes. In neurocritical patients, nonneurological complications such as acute kidney injury (AKI) are independent predictors of worse clinical outcomes. Different research groups have reported an AKI incidence of 11.6% and an incidence of stage 3 AKI, according to the Kidney Disease: Improving Global Outcomes, that requires dialysis of 3% to 12% in neurocritical patients. These patients tend to be younger, have less comorbidity, and have a different risk profile, given the diagnostic and therapeutic procedures they undergo. Trauma-induced AKI, sepsis, sympathetic overstimulation, tubular epitheliopathy, hyperchloremia, use of nephrotoxic drugs, and renal hypoperfusion are some of the causes of AKI in neurocritical patients. AKI is the result of a sum of events, although the mechanisms underlying many of them remain uncertain; however, two important causes that merit mention are direct alteration of the physiological brain-kidney connection and exposure to injury as a result of the specific medical management and well-established therapies that neurocritical patients are subjected to. This review will focus on AKI in neurocritical care patients. Specifically, it will discuss its epidemiology, causes, associated mechanisms, and relationship to the brain-kidney axis. Additionally, the use and risks of extracorporeal therapies in this group of patients will be reviewed.

Effects of renal ischemia injury on brain in diabetic and non-diabetic rats: Role of angiotensin II type 2 receptor and angiotensin-converting enzyme 2

Clinically, patients with diabetes mellitus (DM) are more susceptible to ischemic renal injury (IRI) than non-diabetic (ND) patients. Besides, IRI predisposes distant organ dysfunctions including, neurological dysfunction, in which the major contributor remains renin-angiotensin system (RAS). Interestingly, the role of depressor arm of RAS on IRI-associated neurological sequalae remains unclear. Hence, this study aimed to delineate the role of angiotensin II type 2 receptor (AT2R) and angiotensin-converting enzyme 2 (ACE2) under the same. ND and Streptozotocin-induced DM rats with bilateral IRI were treated with AT2R agonist-Compound 21 (C21) (0.3 mg/kg/day, i.p.) or ACE2 activator-Diminazene Aceturate (Dize), (5 mg/kg/day, p.o.) either alone or as combination therapy. Effect of IRI on neurological functions were assessed by behavioural, biochemical, and histopathological analysis. Immunohistochemistry, ELISA and qRT-PCR experiments were conducted for evaluation of the molecular mechanisms. We found that in ND and DM rats, IRI causes increased hippocampal MDA and nitrite levels, augmented inflammatory cytokines (granulocyte-colony stimulating factor, glial fibrillary acidic protein), altered protein levels of Ang II, Ang-(1-7) and mRNA expressions of At1r, At2r and Masr. Treatment with C21 and Dize effectively normalised above-mentioned pathological alterations. Moreover, the protective effect of C21 and Dize combination therapy was better than respective monotherapies, and more likely, exerted via augmentation of protein and mRNA levels of depressor arm components. Thus, AT2R agonist and ACE2 activator therapy prevents the development of IRI-associated neurological dysfunction by attenuating oxidative stress and inflammation, upregulating depressor arm of RAS in brain under ND and DM conditions.

The Impact of Acute Kidney Injury in the Perioperative Period on the Incidence of Postoperative Delirium in Patients Undergoing Coronary Artery Bypass Grafting-Observational Cohort Study

Recent data indicate that acute kidney damage leads to inflammation in the brain and other distant organs. The purpose of this study was to investigate the effect of acute kidney injury (AKI) according to the Kidney Disease Improving Global Outcome (KDIGO) criteria on the occurrence of postoperative delirium in patients undergoing coronary artery bypass grafting (CABG). We performed a retrospective cohort analysis that included all consecutive patients undergoing elective CABG. The CAM-ICU (Confusion Assessment Method for Intensive Care Unit) was used for delirium assessment. Patients were divided into four groups, depending on the occurrence of AKI in the perioperative period according to KDIGO criteria. Overall, 902 patients were included in the final analysis, the mean age was 65.95 ± 8.01 years, and 76.83% were males (693/957). The majority of patients presented with normal kidney function-baseline creatinine level of 0.91 ± 0.21 (mg/dL). The incidence of AKI in the perioperative setting was 22.17% (200/902). Postoperative delirium was diagnosed in 115/902 patients (12.75%). Compared with no AKI, the odds of developing POD were increased for KDIGO stage 1 (OR 2.401 (95% confidence interval 1.484–3.884), p < 0.001); KDIGO stage 2 (OR 3.387 (95% confidence interval 1.459–7.866), p = 0.005); and highest for KDIGO stage 3 (OR equal to 9.729 (95% confidence interval 2.675–35.382), p = 0.001). Acute kidney injury, based on AKI staging, should be regarded as an independent risk factor for postoperative delirium after cardiac surgery.

The role of pericytes in brain disorders: from the periphery to the brain

It is becoming increasingly apparent that disorders of the brain microvasculature contribute to many neurological disorders. In recent years it has become clear that a major player in these events is the capillary pericyte which, in the brain, is now known to control the blood-brain barrier, regulate blood flow, influence immune cell entry and be crucial for angiogenesis. In this review we consider the under-explored possibility that peripheral diseases which affect the microvasculature, such as hypertension, kidney disease and diabetes, produce central nervous system (CNS) dysfunction by mechanisms affecting capillary pericytes within the CNS. We highlight how cellular messengers produced peripherally can act via signalling pathways within CNS pericytes to reshape blood vessels, restrict blood flow or compromise blood-brain barrier function, thus causing neuronal dysfunction. Increased understanding of how renin-angiotensin, Rho-kinase and PDGFRβ signalling affect CNS pericytes may suggest novel therapeutic approaches to reducing the CNS effects of peripheral disorders.

Oxidative stress in the brain caused by acute kidney injury

Uremic encephalopathy is a severe complication of renal failure. The underlying pathogenesis is unknown although several mechanisms have been suggested. Renal failure causes oxidative stress leading to cardiovascular complications. It has been suggested as the potential mediator of uremic encephalopathy as well, but it is largely unknown whether brain tissue itself undergoes oxidative damage in uremia. The aim of our experiment was to analyze oxidative stress markers in different brain regions in an animal model of acute kidney injury (AKI). AKI was induced by ischemia-reperfusion injury in male Wistar rats. Urine was collected in metabolic cages after 24 h. Samples of plasma and several brain regions were collected after 48 h. Markers of lipid peroxidation, protein oxidation and total antioxidant capacity were assessed. Renal failure was confirmed by high plasma creatinine, urea and urinary albumin to creatinine ratio. Our data confirmed increased systemic oxidative stress in the AKI group with plasma concentrations of markers of oxidative damage being twice as high compared to the sham-operated control group. No effect was seen in the urine. In the hippocampus, lipid and protein oxidation was higher, while antioxidant capacity was lower in the rats with AKI. Lipid oxidation markers in the frontal cortex were higher by 33%. No differences to controls were found in the cerebellum and hypothalamus. In conclusion, our results indicate that AKI leads to oxidative stress in the brain, especially in the hippocampus and in the frontal cortex. This kidney-brain crosstalk mediated by increased oxidative stress might explain some of the symptoms of uremic encephalopathy. The causes and consequences of oxidative damage observed in the brain during AKI remain to be elucidated.

Mechanisms of Organ Dysfunction in Sepsis

Sepsis-associated organ dysfunction involves multiple responses to inflammation, including endothelial and microvascular dysfunction, immune and autonomic dysregulation, and cellular metabolic reprogramming. The effect of targeting these mechanistic pathways on short- and long-term outcomes depends highly on the timing of therapeutic intervention. Furthermore, there is a need to understand the adaptive or maladaptive character of these mechanisms, to discover phase-specific biomarkers to guide therapy, and to conceptualize these mechanisms in terms of resistance and tolerance.

Reno-Cerebral Reflex Activates the Renin-Angiotensin System, Promoting Oxidative Stress and Renal Damage After Ischemia-Reperfusion Injury

AIMS

A kidney-brain interaction has been described in acute kidney injury, but the mechanisms are uncertain. Since we recently described a reno-cerebral reflex, we tested the hypothesis that renal ischemia-reperfusion injury (IRI) activates a sympathetic reflex that interlinks the renal and cerebral renin-angiotensin axis to promote oxidative stress and progression of the injury.

RESULTS

Bilateral ischemia-reperfusion activated the intrarenal and cerebral, but not the circulating, renin-angiotensin system (RAS), increased sympathetic activity in the kidney and the cerebral sympathetic regulatory regions, and induced brain inflammation and kidney injury. Selective renal afferent denervation with capsaicin or renal denervation significantly attenuated IRI-induced activation of central RAS and brain inflammation. Central blockade of RAS or oxidative stress by intracerebroventricular (ICV) losartan or tempol reduced the renal ischemic injury score by 65% or 58%, respectively, and selective renal afferent denervation or reduction of sympathetic tone by ICV clonidine decreased the score by 42% or 52%, respectively (all p < 0.05). Ischemia-reperfusion-induced renal damage and dysfunction persisted after controlling blood pressure with hydralazine.

INNOVATION

This study uncovered a novel reflex pathway between ischemic kidney and the brain that sustains renal oxidative stress and local RAS activation to promote ongoing renal damage.

CONCLUSIONS

These data suggest that the renal and cerebral renin-angiotensin axes are interlinked by a reno-cerebral sympathetic reflex that is activated by ischemia-reperfusion, which contributes to ischemia-reperfusion-induced brain inflammation and worsening of the acute renal injury. Antioxid. Redox Signal. 27, 415-432.

Uraemia: an unrecognized driver of central neurohumoral dysfunction in chronic kidney disease?

Chronic kidney disease (CKD) carries a large cardiovascular burden in part due to hypertension and neurohumoral dysfunction - manifesting as sympathetic overactivity, baroreflex dysfunction and chronically elevated circulating vasopressin. Alterations within the central nervous system (CNS) are necessary for the expression of neurohumoral dysfunction in CKD; however, the underlying mechanisms are poorly defined. Uraemic toxins are a diverse group of compounds that accumulate as a direct result of renal disease and drive dysfunction in multiple organs, including the brain. Intensive haemodialysis improves both sympathetic overactivity and cardiac baroreflex sensitivity in renal failure patients, indicating that uraemic toxins participate in the maintenance of autonomic dysfunction in CKD. In rodents exposed to uraemia, immediate early gene expression analysis suggests upregulated activity of not only pre-sympathetic but also vasopressin-secretory nuclei. We outline several potential mechanisms by which uraemia might drive neurohumoral dysfunction in CKD. These include superoxide-dependent effects on neural activity, depletion of nitric oxide and induction of low-grade systemic inflammation. Recent evidence has highlighted superoxide production as an intermediate for the depolarizing effect of some uraemic toxins on neuronal cells. We provide preliminary data indicating augmented superoxide production within the hypothalamic paraventricular nucleus in the Lewis polycystic kidney rat, which might be important for mediating the neurohumoral dysfunction exhibited in this CKD model. We speculate that the uraemic state might serve to sensitize the central actions of other sympathoexcitatory factors, including renal afferent nerve inputs to the CNS and angiotensin II, by way of recruiting convergent superoxide-dependent and pro-inflammatory pathways.

Kidney-Organ Interaction

The practice of critical care nephrology demands an intimate understanding of the interactions and “crosstalk” that occurs between the kidney and multiple organ systems, in particular the heart, lung, gut, and brain. Accumulating evidence suggests that acute injury and dysfunction to the kidney can incite and propagate cardiac, pulmonary, gastrointestinal, and neurologic injury and dysfunction through a host of mechanisms.

Brain-kidney crosstalk

Encephalopathy and altered higher mental functions are common clinical complications of acute kidney injury. Although sepsis is a major triggering factor, acute kidney injury predisposes to confusion by causing generalised inflammation, leading to increased permeability of the blood–brain barrier, exacerbated by hyperosmolarity and metabolic acidosis due to the retention of products of nitrogen metabolism potentially resulting in increased brain water content. Downregulation of cell membrane transporters predisposes to alterations in neurotransmitter secretion and uptake, coupled with drug accumulation increasing the risk of encephalopathy. On the other hand, acute brain injury can induce a variety of changes in renal function ranging from altered function and electrolyte imbalances to inflammatory changes in brain death kidney donors.

Neuronal activation in the central nervous system of rats in the initial stage of chronic kidney disease-modulatory effects of losartan and moxonidine

The effect of mild chronic renal failure (CRF) induced by 4/6-nephrectomy (4/6NX) on central neuronal activations was investigated by c-Fos immunohistochemistry staining and compared to sham-operated rats. In the 4/6 NX rats also the effect of the angiotensin receptor blocker, losartan, and the central sympatholyticum moxonidine was studied for two months. In serial brain sections Fos-immunoreactive neurons were localized and classified semiquantitatively. In 37 brain areas/nuclei several neurons with different functional properties were strongly affected in 4/6NX. It elicited a moderate to high Fos-activity in areas responsible for the monoaminergic innervation of the cerebral cortex, the limbic system, the thalamus and hypothalamus (e.g. noradrenergic neurons of the locus coeruleus, serotonergic neurons in dorsal raphe, histaminergic neurons in the tuberomamillary nucleus). Other monoaminergic cell groups (A5 noradrenaline, C1 adrenaline, medullary raphe serotonin neurons) and neurons in the hypothalamic paraventricular nucleus (innervating the sympathetic preganglionic neurons and affecting the peripheral sympathetic outflow) did not show Fos-activity. Stress- and pain-sensitive cortical/subcortical areas, neurons in the limbic system, the hypothalamus and the circumventricular organs were also affected by 4/6NX. Administration of losartan and more strongly moxonidine modulated most effects and particularly inhibited Fos-activity in locus coeruleus neurons. In conclusion, 4/6NX elicits high activity in central sympathetic, stress- and pain-related brain areas as well as in the limbic system, which can be ameliorated by losartan and particularly by moxonidine. These changes indicate a high sensitivity of CNS in initial stages of CKD which could be causative in clinical disturbances.

Ghrelin regulates the hypothalamic-pituitary-adrenal axis and restricts anxiety after acute stress

BACKGROUND

Ghrelin plays important roles in glucose metabolism, appetite, and body weight regulation, and recent evidence suggests ghrelin prevents excessive anxiety under conditions of chronic stress.

METHODS

We used ghrelin knockout (ghr-/-) mice to examine the role of endogenous ghrelin in anxious behavior and hypothalamic-pituitary-adrenal axis (HPA) responses to acute stress.

RESULTS

Ghr-/- mice are more anxious after acute restraint stress, compared with wild-type (WT) mice, with three independent behavioral tests. Acute restraint stress exacerbated neuronal activation in the hypothalamic paraventricular nucleus and medial nucleus of the amygdala in ghr-/- mice compared with WT, and exogenous ghrelin reversed this effect. Acute stress increased neuronal activation in the centrally projecting Edinger-Westphal nucleus in WT but not ghr-/- mice. Ghr-/- mice exhibited a lower corticosterone response after stress, suggesting dysfunctional glucocorticoid negative feedback in the absence of ghrelin. We found no differences in dexamethasone-induced Fos expression between ghr-/- and WT mice, suggesting central feedback was not impaired. Adrenocorticotropic hormone replacement elevated plasma corticosterone in ghr-/-, compared with WT mice, indicating increased adrenal sensitivity. The adrenocorticotropic hormone response to acute stress was significantly reduced in ghr-/- mice, compared with control subjects. Pro-opiomelanocortin anterior pituitary cells express significant growth hormone secretagogue receptor.

CONCLUSIONS

Ghrelin reduces anxiety after acute stress by stimulating the HPA axis at the level of the anterior pituitary. A novel neuronal growth hormone secretagogue receptor circuit involving urocortin 1 neurons in the centrally projecting Edinger-Westphal nucleus promotes an appropriate stress response. Thus, ghrelin regulates acute stress and offers potential therapeutic efficacy in human mood and stress disorders.

Peptidergic Edinger-Westphal neurons and the energy-dependent stress response

The continuously changing environment demands for adequate stress responses to maintain the internal dynamic equilibrium of body and mind. A successful stress response requires energy, in an amount matching the severity of the stressor and the type of response ('fight, flight or freeze'). The stress response is generated by the central nervous system, which needs to be informed about both the threatening stressor and the availability of energy. In this review, evidence is considered for a role of the midbrain Edinger-Westphal centrally projecting neuron population (EWcp; synonym: non-preganglionic Edinger-Westphal nucleus) in the energy-dependent stress adaptation response. It deals with studies on the neurochemical organization of the EWcp with particular reference to the neuropeptides urocortin-1 and cocaine- and amphetamine-regulated transcript peptide, on the EWcp responses to different types of stressor (e.g., acute and chronic) and a changed energy state (e.g., fasting and leptin change), and on the sex-specificity of these responses. Finally, a model is presented for the way the EWcp might contribute to the coordination of the energy-dependent stress adaptation response.

Urocortins: CRF's siblings and their potential role in anxiety, depression and alcohol drinking behavior

It is widely accepted that stress, anxiety, depression and alcohol abuse-related disorders are in large part controlled by corticotropin-releasing factor (CRF) receptors. However, evidence is accumulating that some of the actions on these receptors are mediated not by CRF, but by a family of related Urocortin (Ucn) peptides Ucn1, Ucn2 and Ucn3. The initial narrow focus on CRF as the potential main player acting on CRF receptors appears outdated. Instead it is suggested that CRF and the individual Ucns act in a complementary and brain region-specific fashion to regulate anxiety-related behaviors and alcohol consumption. This review, based on a symposium held in 2011 at the research meeting on "Alcoholism and Stress" in Volterra, Italy, highlights recent evidence for regulation of these behaviors by Ucns. In studies on stress and anxiety, the roles of Ucns, and in particular Ucn1, appear more visible in experiments analyzing adaptation to stressors rather than testing basal anxiety states. Based on these studies, we propose that the contribution of Ucn1 to regulating mood follows a U-like pattern with both high and low activity of Ucn1 contributing to high anxiety states. In studies on alcohol use disorders, the CRF system appears to regulate not only dependence-induced drinking, but also binge drinking and even basal consumption of alcohol. While dependence-induced and binge drinking rely on the actions of CRF on CRFR1 receptors, alcohol consumption in models of these behaviors is inhibited by actions of Ucns on CRFR2. In contrast, alcohol preference is positively influenced by actions of Ucn1, which is capable of acting on both CRFR1 and CRFR2. Because of complex distribution of Ucns in the nervous system, advances in this field will critically depend on development of new tools allowing site-specific analyses of the roles of Ucns and CRF.

The Edinger-Westphal nucleus: a historical, structural, and functional perspective on a dichotomous terminology

The eponymous term nucleus of Edinger-Westphal (EW) has come to be used to describe two juxtaposed and somewhat intermingled cell groups of the midbrain that differ dramatically in their connectivity and neurochemistry. On one hand, the classically defined EW is the part of the oculomotor complex that is the source of the parasympathetic preganglionic motoneuron input to the ciliary ganglion (CG), through which it controls pupil constriction and lens accommodation. On the other hand, EW is applied to a population of centrally projecting neurons involved in sympathetic, consumptive, and stress-related functions. This terminology problem arose because the name EW has historically been applied to the most prominent cell collection above or between the somatic oculomotor nuclei (III), an assumption based on the known location of the preganglionic motoneurons in monkeys. However, in many mammals, the nucleus designated as EW is not made up of cholinergic, preganglionic motoneurons supplying the CG and instead contains neurons using peptides, such as urocortin 1, with diverse central projections. As a result, the literature has become increasingly confusing. To resolve this problem, we suggest that the term EW be supplemented with terminology based on connectivity. Specifically, we recommend that 1) the cholinergic, preganglionic neurons supplying the CG be termed the Edinger-Westphal preganglionic (EWpg) population and 2) the centrally projecting, peptidergic neurons be termed the Edinger-Westphal centrally projecting (EWcp) population. The history of this nomenclature problem and the rationale for our solutions are discussed in this review.

Does midbrain urocortin 1 matter? A 15-year journey from stress (mal)adaptation to energy metabolism

This review summarizes some of the milestones of the research on the biological functions(s) of midbrain urocortin 1 (Ucn1) since its discovery 15 years ago. Detailed characterization of Ucn1 in the midbrain revealed its overall significance in food intake and regulation of homeostatic equilibrium and mood under stress. In addition, we have recently found a conspicuous alteration in midbrain Ucn1 levels in brains of depressed suicide victims. Furthermore, from the results from the genetically modified animals, a picture is emerging where corticotrophin-releasing factor promotes the initial reactions to stress, whereas Ucn1 seems to be crucial for management of the later adaptive phase. In the case of imbalance in action of these principle stress mediators, vulnerability to stress-related brain diseases is enhanced.

Sympathetic nervous system overactivity and its role in the development of cardiovascular disease

This review examines how the sympathetic nervous system plays a major role in the regulation of cardiovascular function over multiple time scales. This is achieved through differential regulation of sympathetic outflow to a variety of organs. This differential control is a product of the topographical organization of the central nervous system and a myriad of afferent inputs. Together this organization produces sympathetic responses tailored to match stimuli. The long-term control of sympathetic nerve activity (SNA) is an area of considerable interest and involves a variety of mediators acting in a quite distinct fashion. These mediators include arterial baroreflexes, angiotensin II, blood volume and osmolarity, and a host of humoral factors. A key feature of many cardiovascular diseases is increased SNA. However, rather than there being a generalized increase in SNA, it is organ specific, in particular to the heart and kidneys. These increases in regional SNA are associated with increased mortality. Understanding the regulation of organ-specific SNA is likely to offer new targets for drug therapy. There is a need for the research community to develop better animal models and technologies that reflect the disease progression seen in humans. A particular focus is required on models in which SNA is chronically elevated.