Raphe magnus nucleus is involved in ventilatory but not hypothermic response to CO2

There is evidence that serotonin [5-hydroxytryptamine (5-HT)] is involved in the physiological responses to hypercapnia. Serotonergic neurons represent the major cell type (comprising 15-20% of the neurons) in raphe magnus nucleus (RMg), which is a medullary raphe nucleus. In the present study, we tested the hypothesis 1) that RMg plays a role in the ventilatory and thermal responses to hypercapnia, and 2) that RMg serotonergic neurons are involved in these responses. To this end, we microinjected 1) ibotenic acid to promote nonspecific lesioning of neurons in the RMg, or 2) anti-SERT-SAP (an immunotoxin that utilizes a monoclonal antibody to the third extracellular domain of the serotonin reuptake transporter) to specifically kill the serotonergic neurons in the RMg. Hypercapnia caused hyperventilation and hypothermia in all groups. RMg nonspecific lesions elicited a significant reduction of the ventilatory response to hypercapnia due to lower tidal volume (Vt) and respiratory frequency. Rats submitted to specific killing of RMg serotonergic neurons showed no consistent difference in ventilation during air breathing but had a decreased ventilatory response to CO(2) due to lower Vt. The hypercapnia-induced hypothermia was not affected by specific or nonspecific lesions of RMg serotonergic neurons. These data suggest that RMg serotonergic neurons do not participate in the tonic maintenance of ventilation during air breathing but contribute to the ventilatory response to CO(2). Ultimately, this nucleus may not be involved in the thermal responses to CO(2).

Neuroexcitatory actions of Tamiflu and its carboxylate metabolite

Oseltamivir (Tamiflu) is now being stockpiled by several governments as a first line treatment for an anticipated outbreak of avian influenza caused by H5N1. However, abnormal behaviors and death associated with the use of Tamiflu have developed into a major issue in Japan where Tamiflu is often prescribed for seasonal influenza. Thus, it is critical to determine neuropsychiatric effects of oseltamivir and to establish methods for safe administration. Using juvenile rats and rat hippocampal slices, we investigated whether oseltamivir has adverse effects on the central nervous system. Systemic injection of oseltamivir (50mg/kg i.p.) produced no change in behavior within 2h. However, prior injection of oseltamivir significantly altered the duration of loss of lightning reflex following ethanol injection (3.3g/kg, i.p.). Ethanol injection in the presence of oseltamivir also resulted in enhanced hypothermia. In the CA1 region of hippocampal slices, oseltamivir (100 microM) induced paired-pulse facilitation in population spikes without changes in excitatory postsynaptic potentials. Similarly, 3 microM oseltamivir carboxylate, the active metabolite of oseltamivir, facilitated neuronal firing, though the facilitation did not involve GABAergic disinhibition. Moreover, oseltamivir carboxylate produced further facilitation following administration of 60mM ethanol. These findings indicate that oseltamivir has effects on the central nervous system, especially when combined with other agents.

Immunohistochemical investigation of ubiquitin and myoglobin in the kidney in medicolegal autopsy cases

We examined the immunohistochemical distributions of ubiquitin (Ub) and myoglobin (Mb) in human kidney tissues to assist the pathological assessment of death due to trauma. Medicolegal autopsy cases at our institute (n=138: 0-96 years of age, 105 males and 33 females) were examined. Causes of death were blunt injury (n=31), sharp injury (n=15), poisoning (n=11), drowning (n=10), fire fatalities (n=25), hypothermia (n=7), asphyxiation (n=14), hyperthermia (n=3), and natural diseases (n=22) for controls. Immunostaining of Ub and Mb was performed on the formalin-fixed paraffin-embedded kidney tissue sections. Quantitative analyses by estimating the proportion of Ub- and Mb-positive cells (%positivity) of renal tubule epithelial cells showed that the positivities for Ub and Mb were higher in subjects who died due to fire, blunt injury, sharp injury and fatal hypothermia than in other groups. The Ub-positivity correlated with the severity of airway thermal injury in fire deaths, survival time in blunt injury, and serum markers for renal failure in deaths due to sharp injury. Concomitant increases in the tubular Mb- and Ub-positivities were characteristic to deaths from injury and hypothermia. These findings suggest that Ub may serve as a sensitive indicator of the fatal influence of traumas.

Hypothermia versus torpor in response to cold stress in the native Australian mouse Pseudomys hermannsburgensis and the introduced house mouse Mus musculus

This study compared torpor as a response to food deprivation and low ambient temperature for the introduced house mouse (Mus musculus) and the Australian endemic sandy inland mouse (Pseudomys hermannsburgensis). The house mouse (mass 13.0+/-0.48 g) had a normothermic body temperature of 34.0+/-0.20 degrees C at ambient temperatures from 5 degrees C to 30 degrees C and a basal metabolic rate at 30 degrees C of 2.29+/-0.07 mL O2 g(-1) h(-1). It used torpor with spontaneous arousal at low ambient temperatures; body temperature during torpor was 20.5+/-3.30 degrees C at 15 degrees C. The sandy inland mouse (mass 11.7+/-0.16 g) had a normothermic T(b) of 33.0+/-0.38 degrees C between T(a) of 5 degrees C to 30 degrees C, and a BMR of 1.45+/-0.26 mL O2 g(-1) h(-1) at 30 degrees C. They became hypothermic at low T(a) (T(b) about 17.3 degrees C at T(a)=15 degrees C), but did not spontaneously arouse. They did, however, survive and become normothermic if returned to room temperature (23 degrees C). We conclude that this is hypothermia, not torpor. Consequently, house mice (Subfamily Murinae) appear to use torpor as an energy conservation strategy whereas sandy inland mice (Subfamily Conilurinae) do not, but can survive hypothermia. This may reflect a general phylogenetic pattern of metabolic reduction in rodents. On the other hand, this may be related to differences in the social structure of house mice (solitary) and sandy inland mice (communal).

Noninvasive and three-dimensional imaging of CMRO(2) in rats at 9.4 T: reproducibility test and normothermia/hypothermia comparison study

Ability to image cerebral metabolic rate of oxygen (CMRO(2)) is essential for studying the fundamental role of oxidative metabolism in brain function and disease. We have demonstrated recently that three-dimensional (3D) CMRO(2) images can be obtained in the rat brain during a 2-min (17)O(2) inhalation using the (17)O MR spectroscopic imaging (MRSI) approach at high field. The feasibility for establishing a completely noninvasive approach for imaging CMRO(2) has also been demonstrated. In this study, we further explored the feasibility of (17)O MRSI approach for performing repeated CMRO(2) measurements within a short period of time and evaluated the reproducibility of the repeated measurements. Subsequently, we applied the (17)O MRSI approach to measure CMRO(2) and cerebral blood flow (CBF) values at two brain temperatures in the alpha-chloralose anesthetized rat brain at 9.4 T. Finally, we tested the validity of simplified model for noninvasively determining CMRO(2) in normothermic and hypothermic rat brain. The results show (i) an excellent reproducibility among repeated measurements of 3D CMRO(2) images under the same physiologic condition; (ii) a 44% decrease of CMRO(2) across the rat brain at mild hypothermic (32 degrees C) condition as compared with normothermic (37 degrees C) condition; and (iii) a close correlation between CMRO(2) and CBF within a relatively wide physiologic range. This study demonstrates the capability of (17)O MRSI approach for noninvasively imaging CMRO(2) and its changes caused by physiologic perturbation. This approach, thus, should provide a promising neuroimaging modality for studying oxidative metabolism and bioenergetics associated with brain functions and diseases.

Is there a self-preserving hypothermic mechanism in shock?

Hypoxia-induced hypothermia (HIH) is regarded as an adaptive response to hypoxia in a variety of creatures, but no details of the mechanism have yet been elucidated in the clinical setting. This study was designed to analyze alteration of core body temperature with hemorrhagic shock and to clarify HIH in the clinical setting. Patients were categorized in the hemorrhage shock (S, n = 15) or cardiopulmonary arrest (C, n = 88) group. The tympanic membrane temperature (TMT) was measured, and the length of the interval of call-to-arrival (CTA) at a hospital was set as the time-course parameter. There was a significant negative linear relationship between CTA interval and TMT (S group: TMT = -0.055 degrees C, CTA = +36.1 min, r = -0.833, P < 0.001; C group: TMT = -0.046 degrees C, CTA = +36.3 min, r = -0.548, P < 0.001). Analysis of variance revealed no significant difference in the slope of the regression lines of both groups. However, when the CTA interval was used as a covariate, there was a significant difference in the TMT (P = 0.014), which means that the regression line of the S group was significantly lower than that of the C group with time. Furthermore, in the S group, all patients were hypothermic (<35 degrees C) when their CTA interval was more than 20 min; on the other hand, in the C group, only 64 (75%) of 85 were hypothermic. Patients in S group were more likely to become hypothermic (P < 0.05). In humans with cellular hypoxia, HIH takes place, as seen in other animals. This result emphasizes the necessity for studies of analysis of the mechanisms of temperature control and determination of optimal body temperature during acute critical care.

Hypoxia tolerance in reptiles, amphibians, and fishes: life with variable oxygen availability

The ability of fishes, amphibians, and reptiles to survive extremes of oxygen availability derives from a core triad of adaptations: profound metabolic suppression, tolerance of ionic and pH disturbances, and mechanisms for avoiding free-radical injury during reoxygenation. For long-term anoxic survival, enhanced storage of glycogen in critical tissues is also necessary. The diversity of body morphologies and habitats and the utilization of dormancy have resulted in a broad array of adaptations to hypoxia in lower vertebrates. For example, the most anoxia-tolerant vertebrates, painted turtles and crucian carp, meet the challenge of variable oxygen in fundamentally different ways: Turtles undergo near-suspended animation, whereas carp remain active and responsive in the absence of oxygen. Although the mechanisms of survival in both of these cases include large stores of glycogen and drastically decreased metabolism, other mechanisms, such as regulation of ion channels in excitable membranes, are apparently divergent. Common themes in the regulatory adjustments to hypoxia involve control of metabolism and ion channel conductance by protein phosphorylation. Tolerance of decreased energy charge and accumulating anaerobic end products as well as enhanced antioxidant defenses and regenerative capacities are also key to hypoxia survival in lower vertebrates.

Anesthesia leads to tau hyperphosphorylation through inhibition of phosphatase activity by hypothermia

Postoperative cognitive dysfunction, confusion, and delirium are common after general anesthesia in the elderly, with symptoms persisting for months or years in some patients. Even middle-aged patients are likely to have postoperative cognitive dysfunction for months after surgery, and Alzheimer's disease (AD) patients appear to be particularly at risk of deterioration after anesthesia. Several investigators have thus examined whether general anesthesia is associated with AD, with some studies suggesting that exposure to anesthetics may increase the risk of AD. However, little is known on the biochemical consequences of anesthesia on pathogenic pathways in vivo. Here, we investigated the effect of anesthesia on tau phosphorylation and amyloid precursor protein (APP) metabolism in mouse brain. We found that, regardless of the anesthetic used, anesthesia induced rapid and massive hyperphosphorylation of tau, rapid and prolonged hypothermia, inhibition of Ser/Thr PP2A (protein phosphatase 2A), but no changes in APP metabolism or Abeta (beta-amyloid peptide) accumulation. Reestablishing normothermia during anesthesia completely rescued tau phosphorylation to normal levels. Our results indicate that changes in tau phosphorylation were not a result of anesthesia per se, but a consequence of anesthesia-induced hypothermia, which led to inhibition of phosphatase activity and subsequent hyperphosphorylation of tau. These findings call for careful monitoring of core temperature during anesthesia in laboratory animals to avoid artifactual elevation of protein phosphorylation. Furthermore, a thorough examination of the effect of anesthesia-induced hypothermia on the risk and progression of AD is warranted.

Monocytes from familial cold autoinflammatory syndrome patients are activated by mild hypothermia

BACKGROUND

Familial cold autoinflammatory syndrome (FCAS) is characterized by rash, fever, and arthralgia in response to cold exposure. CIAS1, the gene that codes for cryopyrin, is mutated in FCAS. Treatment with anakinra (IL-1 receptor antagonist) prevents symptoms, indicating a crucial role for IL-1 in this disease.

OBJECTIVE

To study cytokine responses to cold exposure in monocytes from subjects with FCAS.

METHODS

Adherence-enriched monocytes were incubated at 32 degrees C or 37 degrees C. Transcription and release of IL-1beta, IL-6, and TNF-alpha were monitored by quantitative PCR and ELISA.

RESULTS

The FCAS monocytes but not control cells responded to 4 h incubation at 32 degrees C with significant secretion of IL-1beta. At 16 h, IL-1beta, IL-6, and TNF-alpha were all significantly elevated in FCAS monocytes at 32 degrees C. Increased cytokine transcription was observed in all monocytes at 4 hours, but at 16 hours it was only seen in FCAS monocytes incubated at 32 degrees C. Incubation at 32 degrees C for as little as 1 hour sufficed to induce measurable IL-1beta release. Caspase-1 inhibitors prevented the cold-induced IL-1beta release, whereas a purinergic antagonist did not. Anakinra had no effect on the early IL-1beta release but significantly reduced the late-phase transcription and release of all cytokines.

CONCLUSION

FCAS monocytes respond to mild hypothermia with IL-1beta release, which in turn induces autocrine transcription and secretion of IL-6 and TNF-alpha as well as stimulation of further IL-1beta production.

CLINICAL IMPLICATIONS

These results confirm the central role of IL-1beta in FCAS and support the use of IL-1 targeted therapy in these patients.

Oxidative stress time course in the rat diaphragm after freezing–thawing cycles

Hyperthermia was shown to induce oxidative stress by uncoupling mitochondrial respiratory chain and to reduce superoxide dismutase (SOD) activity in muscles. Reactive carbonyl groups, malondialdehyde (MDA)-protein adducts, 3-nitrotyrosine immunoreactivity, Mn-SOD, and catalase were detected using immunoblotting in rat diaphragm specimens and homogenates thawed at room temperature (after previous storage at -80 degrees C) for 5, 15, 30, and 60 min, and 3, 6, and 24h to be subsequently and immediately stored at -80 degrees C. Mn-SOD activity was also measured in all muscles. Both total protein carbonylation (reactive carbonyl groups and MDA-protein adducts) and nitration were significantly increased over time, reaching their peaks in the diaphragms of the 60- and 15-min groups, respectively. Mn-SOD expression and activity were significantly reduced over time, while catalase expression showed no significant variation. Protein oxidation was significantly increased in the rat diaphragms exposed to freezing-thawing cycles of different time lengths, while Mn-SOD was substantially reduced in all muscles.

Hypothermia reduces ischemia- and stimulation-induced myocardial interstitial norepinephrine and acetylcholine releases

Although hypothermia is one of the most powerful modulators that can reduce ischemic injury, the effects of hypothermia on the function of the cardiac autonomic nerves in vivo are not well understood. We examined the effects of hypothermia on the myocardial interstitial norepinephrine (NE) and ACh releases in response to acute myocardial ischemia and to efferent sympathetic or vagal nerve stimulation in anesthetized cats. We induced acute myocardial ischemia by coronary artery occlusion. Compared with normothermia ( n = 8), hypothermia at 33°C ( n = 6) suppressed the ischemia-induced NE release [63 nM (SD 39) vs. 18 nM (SD 25), P < 0.01] and ACh release [11.6 nM (SD 7.6) vs. 2.4 nM (SD 1.3), P < 0.01] in the ischemic region. Under hypothermia, the coronary occlusion increased the ACh level from 0.67 nM (SD 0.44) to 6.0 nM (SD 6.0) ( P < 0.05) and decreased the NE level from 0.63 nM (SD 0.19) to 0.40 nM (SD 0.25) ( P < 0.05) in the nonischemic region. Hypothermia attenuated the nerve stimulation-induced NE release from 1.05 nM (SD 0.85) to 0.73 nM (SD 0.73) ( P < 0.05, n = 6) and ACh release from 10.2 nM (SD 5.1) to 7.1 nM (SD 3.4) ( P < 0.05, n = 5). In conclusion, hypothermia attenuated the ischemia-induced NE and ACh releases in the ischemic region. Moreover, hypothermia also attenuated the nerve stimulation-induced NE and ACh releases. The Bezold-Jarisch reflex evoked by the left anterior descending coronary artery occlusion, however, did not appear to be affected under hypothermia.

Systemic hypothermia increases PAI-1 expression and accelerates microvascular thrombus formation in endotoxemic mice

Introduction

Hypothermia during sepsis significantly impairs patient outcome in clinical practice. Severe sepsis is closely linked to activation of the coagulation system, resulting in microthrombosis and subsequent organ failure. Herein, we studied whether systemic hypothermia accelerates microvascular thrombus formation during lipopolysacharide (LPS)-induced endotoxemia in vivo, and characterized the low temperature-induced endothelial and platelet dysfunctions.

Methods

Ferric-chloride induced microvascular thrombus formation was analyzed in cremaster muscles of hypothermic endotoxemic mice. Flow cytometry, ELISA and immunohistochemistry were used to evaluate the effect of hypothermia on endothelial and platelet function.

Results

Control animals at 37°C revealed complete occlusion of arterioles and venules after 759 ± 115 s and 744 ± 112 s, respectively. Endotoxemia significantly (p < 0.05) accelerated arteriolar and venular occlusion in 37°C animals (255 ± 35 s and 238 ± 58 s, respectively). This was associated with an increase of circulating endothelial activation markers, agonist-induced platelet reactivity, and endothelial P-selectin and plasminogen activator inhibitor (PAI)-1 expression. Systemic hypothermia of 34°C revealed a slight but not significant reduction of arteriolar (224 ± 35 s) and venular (183 ± 35 s) occlusion times. Cooling of the endotoxemic animals to 31°C core body temperature, however, resulted in a further acceleration of microvascular thrombus formation, in particular in arterioles (127 ± 29 s, p < 0.05 versus 37°C endotoxemic animals). Of interest, hypothermia did not affect endothelial receptor expression and platelet reactivity, but increased endothelial PAI-1 expression and, in particular, soluble PAI-1 antigen (sPAI-Ag) plasma levels.

Conclusion

LPS-induced endotoxemia accelerates microvascular thrombus formation in vivo, most probably by generalized endothelial activation and increased platelet reactivity. Systemic hypothermia further enhances microthrombosis in endotoxemia. This effect is associated with increased endothelial PAI-1 expression and sPAI-Ag in the systemic circulation rather than further endothelial activation or modulation of platelet reactivity.

Differences in postmortem urea nitrogen, creatinine and uric acid levels between blood and pericardial fluid in acute death

Previous studies showed significant differences in postmortem urea nitrogen (UN), creatinine (Cr) and uric acid (UA) levels in heart blood depending on the causes of death, including acute death. In addition, the levels in pericardial fluid approximated the clinical serum reference ranges, and their elevations may be assessed based on clinical criteria. The present study investigated difference between blood and pericardial levels of these markers. Medicolegal autopsy cases (n=556, within 48h postmortem) of the following causes of death were examined: injury (n=136), asphyxiation (n=50), drowning (n=39), fire fatalities (n=99), hyperthermia (n=11), hypothermia (n=8), poisoning (n=26), delayed traumatic death (n=44) and natural diseases (n=143). When serum UN, Cr and UA levels were compared with the pericardial levels, there was an equivalency for delayed traumatic death and chronic renal failure, although each level was markedly elevated. Parallel increases in serum and pericardial UA and/or Cr levels were also observed for hypothermia and gastrointestinal bleeding. However, in drowning cases, the left cardiac and pericardial UN levels were lower than the right cardiac and peripheral levels, suggesting the influence of water aspiration. Significant elevations in serum and pericardial Cr and UA levels with a higher serum/pericardial UA ratio for fatal methamphetamine intoxication suggest progressive skeletal muscle damage due to advanced hypoxia/acidosis. Similar findings were often observed for other acute and subacute deaths. These findings suggest that a comparison between blood and pericardial nitrogenous compounds would be useful for investigating the cause and process of death.

The 5-HT1A Receptor Full Agonist, 8-OH-DPAT Inhibits ACTH-Induced 5-HT2A Receptor Hyperfunction in Rats: Involvement of 5-HT1A Receptors in the DOI-Induced Wet-Dog Shakes in ACTH-Treated Rats

We examined the influence of 8-hydroxy-2-di-n-propylamino tetralin (8-OH-DPAT), a serotonin 1A (5-HT1A) receptor full agonist, on the wet-dog shake response induced by the (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), a 5-HT2A receptor agonist, in adrenocorticotropic hormone (ACTH)-treated rats. Chronic ACTH (100 microg/rat, s.c.) treatment for 14 d increased the wet-dog shake response induced DOI. The 8-OH-DPAT inhibited the wet-dog shake response induced by DOI in rats with ACTH for 14 d. On the other hand, the 8-OH-DPAT-induced hypothermia and flat body posture were inhibited when ACTH was administered for 14 d. These findings suggest that chronic treatment with ACTH decreased the sensitivity of the 5-HT1A receptor system; however, the inhibitory effects from the 5-HT1A receptors to the 5-HT2A receptor system is not inhibited in ACTH-treated rats.

[Lipid peroxidation during extreme hyperthermia of rats]

The influence of extremal cryoeffects on the state of prooxidant and antioxidant systems in the blood serum and heart tissues was studied in young and old rats. It is shown that kinematic parameters of chemiluminescence after cold effects are less expressed in the blood serum of old animals than in young ones. The level of TBA-active products in the blood of young rats was lower than in old ones. After the 6th and 9th cold effect the content of TBA-active products in old animal appoaches such indices in young animals. Three weeks after the cold effects the content of TBA-active products in the myocardium of old rats corresponded to control indices, while in the young ones they were considerably lower. The fermentative link state was investigated in the antioxidant protection system. After the extremal cryoeffects glutathione reductase and glutathione peroxidase activity in old animals approaches its indices in intact rats, while catalase activity increases. Three weeks after cryoeffects one can observe a stable increase of fermentative activity of heart tissues both in old and young animals compared with the control that can evidence for the increase of the organism cold resistance.

Advances in molecular biology of hibernation in mammals

Mammalian hibernation is characterized by profound reductions in metabolism, oxygen consumption and heart rate. As a result, the animal enters a state of suspended animation where core body temperatures can plummet as low as -2.9 degrees C. Not only can hibernating mammals survive these physiological extremes, but they also return to a normothermic state of activity without reperfusion injury or other ill effects. This review examines recent findings on the genes, proteins and small molecules that control the induction and maintenance of hibernation in mammals. The molecular events involved with remodeling metabolism, inducing hypothermia and maintaining organ function are discussed and considered with respect to analogous processes in non-hibernating mammals such as mice and humans. The advent of sequenced genomes from three distantly related hibernators, a bat, hedgehog and ground squirrel, provides additional opportunities for molecular biologists to explore the mechanistic aspects of this biological adaptation in greater detail.

Correcting arterial blood gases for temperature: (when) is it clinically significant?

Interpreting arterial blood gases (ABGs) is a common practice in intensive care units. The use of the temperature correction facility, however, is not standardized, and the effects of temperature correction on the ABG result may affect the overall management of the patient. The aim of this study was to discuss the significance of temperature correction. Current practice in the UK and Australia is discussed along with a review of physiological principles of oxygenation and acid-base balance. The alpha-stat and pH-stat methods of blood gas analysis are presented, with arguments for and against using the temperature correction facility for blood gas analysis. The study concludes with recommendations for practice.

The neonatal energy triangle. Part2: Thermoregulatory and respiratory adaption

In the second part of this two part article the neonatal energy triangle elements of hypoxia and hypothermia are explored and the physiology of the first few hours of neonatal life drawn together into an integrated whole. This framework can assist in understanding the three most common difficulties encountered by the preterm baby and directing integrated and holistic care.

In vivo evidence that N-oleoylglycine acts independently of its conversion to oleamide

Oleamide (cis-9-octadecenamide) is a member of an emerging class of lipid-signaling molecules, the primary fatty acid amides. A growing body of evidence indicates that oleamide mediates fundamental neurochemical processes including sleep, thermoregulation, and nociception. Nevertheless, the mechanism for oleamide biosynthesis remains unknown. The leading hypothesis holds that oleamide is synthesized from oleoylglycine via the actions of the peptide amidating enzyme, peptidylglycine alpha-amidating monooxygenase (PAM). The present study investigated this hypothesis using pharmacologic treatments, physiologic assessments, and measurements of serum oleamide levels using a newly developed enzyme-linked immunosorbant assay (ELISA). Oleamide and oleoylglycine both induced profound hypothermia and decreased locomotion, over equivalent dose ranges and time courses, whereas, closely related compounds, stearamide and oleic acid, were essentially without effect. While the biologic actions of oleamide and oleoylglycine were equivalent, the two compounds differed dramatically with respect to their effects on serum levels of oleamide. Oleamide administration (80mg/kg) elevated blood-borne oleamide by eight-fold, whereas, the same dose of oleoylglycine had no effect on circulating oleamide levels. In addition, pretreatment with the established PAM inhibitor, disulfiram, produced modest reductions in the hypothermic responses to both oleoylglycine and oleamide, suggesting that the effects of disulfiram were not mediated through inhibition of PAM and a resulting decrease in the formation of oleamide from oleoylglycine. Collectively, these findings raise the possibilities that: (1) oleoylglycine possesses biologic activity that is independent of its conversion to oleamide and (2) the increased availability of oleoylglycine as a potential substrate does not drive the biosynthesis of oleamide.

Hypothermia-enhanced splenic cytokine gene expression is independent of the sympathetic nervous system

Splenic nerve denervation abrogates enhanced splenic cytokine gene expression responses to acute heating, demonstrating that hyperthermia-induced activation of splenic sympathetic nerve discharge (SND) increases splenic cytokine gene expression. Hypothermia alters SND responses; however, the role of the sympathetic nervous system in mediating splenic cytokine gene expression responses to hypothermia is not known. The purpose of the present study was to determine the effect of hypothermia on the relationship between the sympathetic nervous system and splenic cytokine gene expression in anesthetized F344 rats. Gene expression analysis was performed using a microarray containing 112 genes, representing inflammatory cytokines, chemokines, cytokine/chemokine receptors and housekeeping genes. A subset of differentially expressed genes was verified by real-time RT-PCR analysis. Splenic SND was decreased significantly during cooling (core temperature decreased from 38 to 30 degrees C) in splenic-intact rats but remained unchanged in sham-cooled splenic-intact rats (core temperature maintained at 38 degrees C). Hypothermia upregulated the transcripts of several genes, including, chemokine ligands CCL2, CXCL2, CXCL10, and CCL20, and interleukins IL-1alpha, IL-1beta, and IL-6. Gene expression responses to hypothermia were similar for the majority of cytokine genes in splenic-intact and splenic-denervated rats. These results suggest that hypothermia-enhanced splenic cytokine gene expression is independent of splenic SND.

Aging alters regulation of visceral sympathetic nerve responses to acute hypothermia

Hypothermia produced by acute cooling prominently alters sympathetic nerve outflow. Skin sympathoexcitatory responses to skin cooling are attenuated in aged compared with young subjects, suggesting that advancing age influences sympathetic nerve responsiveness to hypothermia. However, regulation of skin sympathetic nerve discharge (SND) is only one component of the complex sympathetic nerve response profile to hypothermia. Whether aging alters the responsiveness of sympathetic nerves innervating other targets during acute cooling is not known. In the present study, using multifiber recordings of splenic, renal, and adrenal sympathetic nerve activity, we tested the hypothesis that hypothermia-induced changes in visceral SND would be attenuated in middle-aged and aged compared with young Fischer 344 (F344) rats. Colonic temperature (Tc) was progressively reduced from 38°C to 31°C in young (3 to 6 mo), middle-aged (12 mo), and aged (24 mo) baroreceptor-innervated and sinoaortic-denervated (SAD), urethane-chloralose anesthetized, F344 rats. The following observations were made. 1) Progressive hypothermia significantly ( P < 0.05) reduced splenic, renal, and adrenal SND in young baroreceptor-innervated F344 rats. 2) Reductions in splenic, renal, and adrenal SND to progressive hypothermia were less consistently observed and, when observed, were generally attenuated in baroreceptor-innervated middle-aged and aged compared with young F344 rats. 3) Differences in splenic, renal, and adrenal SND responses to reduced Tc were observed in SAD young, middle-aged, and aged F344 rats, suggesting that age-associated attenuations in SND responses to acute cooling are not the result of age-dependent modifications in arterial baroreflex regulation of SND. These findings demonstrate that advancing chronological age alters the regulation of visceral SND responses to progressive hypothermia, modifications that may contribute to the inability of aged individuals to adequately respond to acute bouts of hypothermia.

In vivo inhibition of neuropeptide FF agonism by BIBP3226, an NPY Y1 receptor antagonist

BIBP3226 {(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)-methyl]-argininamide} was recently shown to display relatively high affinities for neuropeptide FF (NPFF) receptors and exhibit antagonist activities towards NPFF receptors in vitro. The present study was undertaken to investigate the antagonistic effects of BIBP3226 on several in vivo pharmacologic profiles induced by exogenous NPFF and NPVF. (1) BIBP3226 (5 nmol) injected into the third ventricle completely antagonized the hypothermic effects of NPFF (30 nmol) and NPVF (30 nmol) after cerebral administration in mice; (2) BIBP3226 (5 nmol, i.c.v.) prevented the anti-morphine actions of NPFF (10 nmol, i.c.v.) in the mouse tail-flick assay; (3) in urethane-anaesthetized rats, both NPFF (200 nmol/kg, i.v.) and NPVF (200 nmol/kg, i.v.) increased the mean arterial blood pressure, which were significantly reduced by pretreatment with BIBP3226 (500 nmol/kg, i.v.). Collectively, these data suggest that BIBP3226, a mixed antagonist of NPY Y1 and NPFF receptors, shows in vivo antagonistic effects on NPFF receptors. In addition, it seems to be clear that the in vivo pharmacological profiles of NPFF are mediated directly by NPFF receptors.

Hypothermic responses to 8-OH-DPAT in the Ts65Dn mouse model of Down syndrome

Recently, we have demonstrated that potassium channels containing G-protein-activated potassium channel 2 (GIRK2) subunits play a significant role in hypothermia induced by several neurotransmitter receptor agonists, including the serotonin (5-HT)1A/5-HT7 receptor agonist 8-OH-DPAT [R-(+)-8-hydroxy-2-(di-n-propylamino) tetralin]. The GIRK2 gene is located in human chromosome 21 (its mouse ortholog, Girk2, is in mouse chromosome 16). Down syndrome is produced by the trisomy of chromosome 21. Here, we used quantitative radiotelemetry to investigatehypothermic responses to 8-OH-DPAT in the Down syndrome mouse model Ts65Dn (which carries an extra chromosomal 16 segment containing Girk2). Our results indicate that, in relation to euploid controls, Ts65Dn mice display significantly increased hypothermic responses to 8-OH-DPAT. This finding may be relevant to the understanding of previously reported differences in serotoninergic neurotransmission in persons with Down syndrome.

The neonatal energy triangle. Part 1: Metabolic adaptation

The first part of this two part series on the neonatal energy triangle gives a general overview of the transition period during the first six to ten hours of life. Although all elements of the triangle, hypothermia, hypoglycaemia and hypoxia, are interlinked this first part of the series describes the normal metabolic adaptation at birth and the difficulties involved in recognising and treating hypoglycaemia. In the second part of the series the two other elements of the triangle, hypoxia and hypothermia, will be addressed.