Response of interleukin-1beta in the magnocellular system to salt-loading

Oxytocin and microglia in the development of social behaviour

Oxytocin is a well-established regulator of social behaviour. Microglia, the resident immune cells of the central nervous system, regulate brain development and maintenance in health and disease. Oxytocin and microglia interact: microglia appear to regulate the oxytocin system and are, in turn, regulated by oxytocin, which appears to have anti-inflammatory effects. Both microglia and oxytocin are regulated in sex-specific ways. Oxytocin and microglia may work together to promote experience-dependent circuit refinement through multiple developmental-sensitive periods contributing to individual differences in social behaviour. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

The predictive value of plasma osmolality for in-hospital mortality in patients with acute pulmonary embolism

INTRODUCTION AND OBJECTIVES

Prior studies demonstrated that plasma osmolality may have a predictive value for in-hospital mortality in patients with heart failure and acute coronary syndrome. In addition, plasma glucose and blood urea nitrogen (BUN) levels, the components of plasma osmolality, have been shown to be an important contributor for in-hospital mortality in acute pulmonary embolism (APE) patients. Hence, the objective of the current study is to evaluate the effect of plasma osmolality upon admission with in-hospital mortality in patients with APE.

METHODS

A total of 245 consecutive intermediate or high risk APE patients were enrolled into the study. The study population was divided into three tertile groups (T1, T2 and T3) based on the increased plasma osmolality. The in-hospital mortality was the primary end-point.

RESULTS

After adjusting for all risk factors, in-hospital mortality was significantly higher in the T3 group compared to T1 and T2 groups (OR: 3.6, 95% CI: 1.3 to 18.8, P < .001). In addition, the incidence of asystolia, hypotension and cardiogenic shock were significantly higher in the T3 group. An area under the receiver operating characteristic curve value of plasma osmolality for the in-hospital mortality was 0.76 with sensitivity 67.2% and specificity 74.1% 95% CI: (0.66-0.87, P < .001).

CONCLUSION

This is the first study to demonstrate that elevated levels of plasma osmolality may have a predictive value for in-hospital mortality in APE patients. Our findings are novel and deserve further studies whether the treatment of higher plasma osmolality may reduce the risk of in-hospital mortality in APE patients.

Cytokine analysis by immunoaffinity capillary electrophoresis

Immunoaffinity capillary electrophoresis (ICE) is a powerful tool used to detect and quantify target proteins of interest in complex biological fluids. The target analyte is captured and bound to antibodies immobilized onto the wall of a capillary, labeled in situ with a fluorescent dye, eluted and detected online using laser-induced fluorescence following electrophoretic separation. Here, we illustrate how to construct an immunoaffinity capillary and utilize it to run ICE in order to capture and quantify target cytokines and chemokines from a clinical sample.

Peripheral osmotic stimulation inhibits the brain's innate immune response to microdialysis of acidic perfusion fluid adjacent to supraoptic nucleus

During the brain's innate immune response microglia, astroglia and ependymal cells resolve/repair damaged tissue and control infection. Released interleukin-1beta (IL-1beta) reaching cerebroventricles stimulates circumventricular organs (CVOs; subfornical organ, SFO; organum vasculosum lamina terminalis, OVLT), the median preoptic nucleus (MePO), and magnocellular and parvocellular neurons in the supraoptic (SON) and paraventricular (PVN) nuclei. Hypertonic saline (HS) also activates these osmosensory CVOs and neuroendocrine systems, but, in contrast to IL-1beta, inhibits the peripheral immune response. To examine whether the brain's innate immune response is attenuated by osmotic stimulation, sterile acidic perfusion fluid was microdialyzed (2 microl/min) in the SON area of conscious rats for 6 h with sterile HS (1.5 M NaCl) injected subcutaneously (15 ml/kg) at 5 h. Immunohistochemistry identified cytokine sources (IL-1beta(+); OX-42(+) microglia) and targets (IL-1R(+); inducible cyclooxygenase, COX-2(+); c-Fos(+)) near the probe, in CVOs, MePO, ependymal cells, periventricular hypothalamus, SON, and PVN. Inserting the probe stimulated magnocellular neurons (c-Fos(+); SON; PVN) via the MePO (c-Fos(+)), a response enhanced by HS. Microdialysis activated microglia (OX-42(+); amoeboid/hypertrophied; IL-1beta(+)) in the adjacent SON and bilaterally in perivascular areas of the PVN, periventricular hypothalamus and ependyma, coincident with c-Fos expression in ependymal cells and COX-2 in the vasculature. These microglial responses were attenuated by HS, coincident with activating parvocellular and magnocellular neuroendocrine systems and elevating circulating IL-1beta, oxytocin, and vasopressin. Acidosis-induced cellular injury from microdialysis activated the brain's innate immune response by a mechanism inhibited by peripheral osmotic stimulation.

Chronic stress plasticity in the hypothalamic paraventricular nucleus

Proper integration and execution of the physiological stress response is essential for maintaining homoeostasis. Stress responses are controlled in large part by the paraventricular nucleus (PVN) of the hypothalamus, which contains three functionally distinct neural populations that modulate multiple stress effectors: (1) hypophysiotrophic PVN neurons that directly control the activity of the hypothalamic-pituitary-adrenocortical (HPA) axis; (2) magnocellular neurons and their secreted neurohypophysial peptides; and (3) brainstem and spinal cord projecting neurons that regulate autonomic function. Evidence for activation of PVN neurons during acute stress exposure demonstrates extensive involvement of all three effector systems. In addition, all PVN regions appear to participate in chronic stress responses. Within the hypophysiotrophic neurons, chronic stress leads to enhanced expression of secreted products, reduced expression of glucocorticoid receptor and GABA receptor subunits and enhanced glutamate receptor expression. In addition, there is evidence for chronic stress-induced morphological plasticity in these neurons, with chronic drive causing changes in cell size and altered GABAergic and glutamatergic innervation. The response of the magnocellular system varies with different chronic exposure paradigms, with changes in neurohypophysial peptide gene expression, peptide secretion and morphology seen primarily after intense stress exposure. The preautonomic cell groups are less well studied, but are likely to be associated with chronic stress-induced changes in cardiovascular function. Overall, the PVN is uniquely situated to coordinate responses of multiple stress effector systems in the face of prolonged stimulation, and likely plays a role in both adaptation and pathology associated with chronic stress.

Interleukin-1beta release in the supraoptic nucleus area during osmotic stimulation requires neural function

Interleukin (IL)-1beta is present throughout the magnocellular neuroendocrine system and co-depletes with oxytocin and vasopressin from the neural lobe during salt-loading. To examine whether IL-1beta is released from the dendrites/soma of magnocellular neurones during osmotic stimulation, microdialysis adjacent to the supraoptic nucleus (SON) in conscious rats was combined with immunocapillary electrophoresis and laser-induced fluorescence detection to quantify cytokine in 5-min dialysates collected before (0-180 min; basal), and after (180-240 min), hypertonic saline injected s.c. (1.5 m NaCl). Osmotic release of IL-1beta was compared after inhibiting local voltage-gated channels for Na+ (tetrodotoxin) and Ca2+ (cadmium and nickel) or by reducing intracellular Ca2+ stores (thapsigargin). Immunohistochemistry combined with microdialysis was used to localise cytokine sources (IL-1beta+) and microglia (OX-42+). Under conditions of microdialysis, the basal release of IL-1beta+ in the SON area was measurable and stable (pg/ml; mean +/- SEM) from 0-60 min (2.2 +/- 0.06), 60-120 min (2.32 +/- 0.05) and 120-180 min (2.33 +/- 0.06), likely originating locally from activated microglia (OX42+; IL-1beta+; ameboid, hypertrophied) and magnocellular neurones expressing IL-1beta. In response to osmotic stimulation, IL-1beta increased progressively in dialysates of the SON area by a mechanism dependent on intracellular Ca2+ stores sensitive to thapsigargin and, similar to dendritic secretion of oxytocin and vasopressin, required local voltage-gated Na+ and Ca2+ channels for activation by osmoregulatory pathways from the forebrain. During osmotic stimulation, neurally dependent release of IL-1beta in the SON area likely upregulates osmosensitive cation currents on magnocellular neurones (observed in vitro by others), to facilitate dendritic release of neurohypophysial hormones.

CNTF receptor alpha is expressed by magnocellular neurons and expression is upregulated in the rat supraoptic nucleus during axonal sprouting

Ciliary neurotrophic factor (CNTF) is expressed by glial cells at multiple levels of the magnocellular neurosecretory system (MNS). CNTF is present in astrocytes in the hypothalamic supraoptic nucleus (SON) as well as in perivascular cells in the neurohypophysis, and a several fold increase in CNTF immunoreactivity occurs in the SON following either axotomy of magnocellular neurons or during axonal sprouting by intact magnocellular neurons. CNTF also promotes survival and stimulates process outgrowth from magnocellular neurons in vitro. While these findings suggest that CNTF may act as a growth factor in support of neuronal plasticity in the MNS, little is known regarding possible expression of receptors for CNTF in the MNS. We have therefore used immunocytochemistry and in situ hybridization to examine the expression of CNTF receptor alpha (CNTFRalpha) in the rat MNS. Robust immunoreactivity for CNTFRalpha was observed associated with oxytocinergic and vasopressinergic neurons distributed throughout the SON. Astrocytes located within the ventral glial lamina (VGL) of the SON were also immunoreactive for CNTFRalpha. Robust hybridization of an anti-sense [(35)S]-cRNA probe to CNTFRalpha mRNA was observed throughout the SON, while binding of a control sense probe was much lower. Grains were found clustered predominantly over neuronal somata, indicative of expression by magnocellular neurons within the SON. We next examined changes in expression of CNTFRalpha mRNA by magnocellular neurons 7 days following unilateral transection of the hypothalamo-neurohypophysial tract. The level of CNTFRalpha mRNA was increased 32% (compared to age-matched intact controls; p<0.05) in magnocellular neurons in the SON contralateral to the lesion, which are undergoing extensive collateral axonal sprouting, but was unchanged in axotomized magnocellular neurons in the SON ipsilateral to the lesion. These findings suggest that CNTF produced by MNS glia and acting via CNTFRalpha may exert neurotrophic effects on magnocellular neurons.

Differential kinetics of oxytocin and vasopressin heteronuclear RNA expression in the rat supraoptic nucleus in response to chronic salt loading in vivo

Previous studies have shown that the secretion of oxytocin and vasopressin from the posterior pituitary always accompanies systemic hyperosmotic stimuli in rats, and that oxytocin and vasopressin mRNAs consistently increase in response to prolonged hyperosmotic stimuli. Hence, it has been widely interpreted that oxytocin and vasopressin secretion and gene expression are closely coupled. In the present study, we used both vasopressin and oxytocin intron- specific probes to measure vasopressin and oxytocin heteronuclear RNA (hnRNA) levels, respectively, by in situ hybridisation in the rat supraoptic nucleus (SON) in conjunction with radioimmunoassays of vasopressin and oxytocin peptide levels in plasma and in the posterior pituitary in normally hydrated rats and after 1-5 days of salt loading. Increased oxytocin secretion in response to hyperosmotic stimuli exceeded vasopressin secretion at every time point studied. Vasopressin hnRNA in the SON increased to near maximal levels within minutes after the hyperosmotic stimulus, and was maintained throughout all 5 days of salt loading. By contrast, oxytocin hnRNA did not significantly change from control levels until approximately 2 days after hyperosmotic stimulation, and was not maximal until 3 days. In summary, increases in oxytocin gene transcription in response to osmotic stimuli are dramatically delayed compared to increases in vasopressin gene transcription under the same conditions. These data indicate that oxytocin gene transcription is not as closely correlated with pituitary peptide secretion as is vasopressin gene transcription, and suggests that there is a fundamental difference in excitation-secretion-transcription coupling mechanisms that regulate these two closely related genes in the rat magnocellular neurones in the SON.