Synergistic promotion of transient transgene expression in CHO cells by PDI/XBP-1s co-transfection and mild hypothermia

Transient gene expression system is an important tool for rapid production of recombinant proteins in Chinese hamster ovary (CHO) cells. However, their low productivity is the main hurdle to overcome. An effective approach through which to obtain high protein yield involves targeting transcriptional, post-transcriptional events (PTEs), and culture conditions. Here, we investigated the effects of protein disulfide isomerase (PDI) and spliced X-box binding protein 1 (XBP-1s) co-overexpression combined with mild hypothermia on the transient yields of recombinant proteins in CHO cells. The results showed that the gene of interest (GOI) and the PDI/XBP-1s helper vector at a co-transfection ratio of 10:1 could obviously increase transient expression level of recombinant protein in CHO cells. However, PDI/XBP-1s overexpression had no significance effect on the mRNA levels of the recombinant protein, suggesting that it targeted PTEs. Moreover, the increased production was due to the enhancing of cell specific productivity, not related to cell growth, viability, and cell cycle. In addition, combined PDI/XBP-1s co-overexpression and mild hypothermia could further improve Adalimumab expression, compared to the control/37 °C and PDI/XBP-1s/37 °C, the Adalimumab volume yield of PDI/XBP-1s/33 °C increased by 203% and 142%, respectively. Mild hypothermia resulted in 3.52- and 2.33-fold increase in the relative mRNA levels of PDI and XBP-1s, respectively. In conclusion, the combination of PDI/XBP-1s overexpression and culture temperature optimization can achieve higher transient expression of recombinant protein, which provides a synergetic strategy to improve transient production of recombinant protein in CHO cells.

Cold-shock proteins accumulate in centrosomes and their expression and primary cilium morphology are regulated by hypothermia and shear stress

Primary cilia act as cellular sensors for multiple extracellular stimuli and regulate many intracellular signaling pathways in response. Here we investigate whether the cold-shock proteins (CSPs), CIRP and RBM3, are present in the primary cilia and the physiological consequences of such a relationship. R28, an immortalized retinal precursor cell line, was stained with antibodies against CIRP, RBM3, and ciliary markers. Both CSPs were found in intimate contact with the basal body of the cilium during all stages of the cell cycle, including migrating with the centrosome during mitosis. In addition, the morphological and physiological manifestations of exposing the cells to hypothermia and shear stress were investigated. Exposure to moderately cold (32°C) temperatures, the hypothermia mimetic small molecule zr17-2, or to shear stress resulted in a significant reduction in the number and length of primary cilia. In addition, shear stress induced expression of CIRP and RBM3 in a complex pattern depending on the specific protein, flow intensity, and type of flow (laminar versus oscillatory). Flow-mediated CSP overexpression was detected by qRT-PCR and confirmed by Western blot, at least for CIRP. Furthermore, analysis of public RNA Seq databases on flow experiments confirmed an increase of CIRP and RBM3 expression following exposure to shear stress in renal cell lines. In conclusion, we found that CSPs are integral components of the centrosome and that they participate in cold and shear stress sensing.

Study on the protective effect of RNA-binding motif protein 3 in mild hypothermia oxygen-glucose deprivation/reoxygenation cell model

Mild hypothermia is proven neuroprotective in clinical practice. While hypothermia leads to the decrease of global protein synthesis rate, it upregulates a small subset of protein including RNA-binding motif protein 3 (RBM3). In this study, we treated mouse neuroblastoma cells (N2a) with mild hypothermia before oxygen-glucose deprivation/reoxygenation (OGD/R) and discovered the decrease of apoptosis rate, down-regulation of apoptosis-associated protein and enhancement of cell viability. Overexpression of RBM3 via plasmid exerted similar effect while silencing RBM3 by siRNAs partially reversed the protective effect exerted by mild hypothermia pretreatment. The protein level of Reticulon 3(RTN3), a downstream gene of RBM3, also increased after mild hypothermia pretreatment. Silencing RTN3 weakened the protective effect of mild hypothermia pretreatment or RBM3 overexpression. Also, the protein level of autophagy gene LC3B increased after OGD/R or RBM3 overexpression while silencing RTN3 decreased this trend. Furthermore, immunofluorescence observed enhanced fluorescence signal of LC3B and RTN3 as well as a large number of overlaps after RBM3 overexpressing. In conclusion, RBM3 plays a cellular protective role by regulating apoptosis and viability via its downstream gene RTN3 in the hypothermia OGD/R cell model and autophagy may participate in it.

Regulation of Dihydropyrimidinase-like 3 Gene Expression by MicroRNAs in PC12 Cells with Induced Ischaemia and Hypothermia

Although hypothermic treatment has been reported to have some beneficial effects on ischaemia at the clinical level, the mechanism of ischaemia suppression by hypothermia remains unclear due to a lack of mechanism understanding and insufficient data. The aim of this study was to isolate and characterize microRNAs specifically expressed in ischaemia-hypothermia for the dihydropyrimidinase-like 3 (Dpysl3) gene. PC12 cells were induced with CoCl2 for chemical ischaemia and incubated at 32 ℃ for hypothermia. In ischaemia-hypothermia, four types of microRNAs (miR-106b-5p, miR-194-5p, miR-326-5p, and miR-497-5p) were highly related to the Dpysl3 gene based on exosomal microRNA analysis. Dpysl3 gene expression was up-regulated by miR-497-5p but down-regulated by miR-106b-5p, miR-194-5p and miR-326-5p. Our results suggest that these four microRNAs are involved in the regulation of Dpysl3 gene expression. These findings provide valuable clues that exosomal microRNAs could be used as therapeutic targets for effective treatment of ischaemia.

rno-miR-203a-3p and Mex3B contribute to cell survival of iliopsoas muscle via the Socs3-Casp3 axis under severe hypothermia in rats

Forensic diagnosis of fatal hypothermia is considered difficult because no specific findings, such as molecular markers, have been identified. Therefore, determining the molecular mechanism in hypothermia and identifying novel molecular markers to assist in diagnosing fatal hypothermia are important. This study aimed to investigate microRNA (miRNA) and mRNA expression in iliopsoas muscle, which plays a role in homeostasis in mammals, to resolve the molecular mechanism in hypothermia. We generated rat models of mild, moderate, and severe hypothermia, then performed body temperature-dependent miRNA and mRNA expression analysis of the iliopsoas muscle using microarray and next-generation sequencing. Analysis showed that rno-miR-203a-3p expression was lower with decreasing body temperature, while Socs3 expression was significantly increased only by severe hypothermia. Luciferase reporter assays suggested that Socs3 expression is regulated by rno-miR-203a-3p. Socs3 and Mex3B small interfering RNA-mediated knockdown showed that suppressing Mex3B could induce the activation of Socs3, followed by a change in caspase 3/7 activity and adenosine triphosphate levels in iliopsoas muscle cells. These findings indicate that rno-miR-203a-3p and Mex3B are deactivated by a decrease in body temperature, whereby it contributes to suppressing apoptosis by accelerating Socs3. Accordingly, the rno-miR-203a-3p-Socs3-Casp3 or Mex3B-Socs3-Casp3 axis may be the part of the biological defense response to maintain homeostasis under extreme hypothermia.

Estrogen-sensitive medial preoptic area neurons coordinate torpor in mice

Homeotherms maintain a stable internal body temperature despite changing environments. During energy deficiency, some species can cease to defend their body temperature and enter a hypothermic and hypometabolic state known as torpor. Recent advances have revealed the medial preoptic area (MPA) as a key site for the regulation of torpor in mice. The MPA is estrogen-sensitive and estrogens also have potent effects on both temperature and metabolism. Here, we demonstrate that estrogen-sensitive neurons in the MPA can coordinate hypothermia and hypometabolism in mice. Selectively activating estrogen-sensitive MPA neurons was sufficient to drive a coordinated depression of metabolic rate and body temperature similar to torpor, as measured by body temperature, physical activity, indirect calorimetry, heart rate, and brain activity. Inducing torpor with a prolonged fast revealed larger and more variable calcium transients from estrogen-sensitive MPA neurons during bouts of hypothermia. Finally, whereas selective ablation of estrogen-sensitive MPA neurons demonstrated that these neurons are required for the full expression of fasting-induced torpor in both female and male mice, their effects on thermoregulation and torpor bout initiation exhibit differences across sex. Together, these findings suggest a role for estrogen-sensitive MPA neurons in directing the thermoregulatory and metabolic responses to energy deficiency.

Differential genetic risk for methamphetamine intake confers differential sensitivity to the temperature-altering effects of other addictive drugs

Mice selectively bred for high methamphetamine (MA) drinking (MAHDR), compared with mice bred for low MA drinking (MALDR), exhibit greater sensitivity to MA reward and insensitivity to aversive and hypothermic effects of MA. Previous work identified the trace amine-associated receptor 1 gene (Taar1) as a quantitative trait gene for MA intake that also impacts thermal response to MA. All MAHDR mice are homozygous for the mutant Taar1 m1J allele, whereas all MALDR mice possess at least one copy of the reference Taar1 + allele. To determine if their differential sensitivity to MA-induced hypothermia extends to drugs of similar and different classes, we examined sensitivity to the hypothermic effect of the stimulant cocaine, the amphetamine-like substance 3,4-methylenedioxymethamphetamine (MDMA), and the opioid morphine in these lines. The lines did not differ in thermal response to cocaine, only MALDR mice exhibited a hypothermic response to MDMA, and MAHDR mice were more sensitive to the hypothermic effect of morphine than MALDR mice. We speculated that the μ-opioid receptor gene (Oprm1) impacts morphine response, and genotyped the mice tested for morphine-induced hypothermia. We report genetic linkage between Taar1 and Oprm1; MAHDR mice more often inherit the Oprm1 D2 allele and MALDR mice more often inherit the Oprm1 B6 allele. Data from a family of recombinant inbred mouse strains support the influence of Oprm1 genotype, but not Taar1 genotype, on thermal response to morphine. These results nominate Oprm1 as a genetic risk factor for morphine-induced hypothermia, and provide additional evidence for a connection between drug preference and drug thermal response.

Statistical differences resulting from selection of stable reference genes after hypoxia and hypothermia in the neonatal rat brain

Real-time reverse transcription PCR (qPCR) normalized to an internal reference gene (RG), is a frequently used method for quantifying gene expression changes in neuroscience. Although RG expression is assumed to be constant independent of physiological or experimental conditions, several studies have shown that commonly used RGs are not expressed stably. The use of unstable RGs has a profound effect on the conclusions drawn from studies on gene expression, and almost universally results in spurious estimation of target gene expression. Approaches aimed at selecting and validating RGs often make use of different statistical methods, which may lead to conflicting results. Based on published RG validation studies involving hypoxia the present study evaluates the expression of 5 candidate RGs (Actb, Pgk1, Sdha, Gapdh, Rnu6b) as a function of hypoxia exposure and hypothermic treatment in the neonatal rat cerebral cortex–in order to identify RGs that are stably expressed under these experimental conditions–using several statistical approaches that have been proposed to validate RGs. In doing so, we first analyzed RG ranking stability proposed by several widely used statistical methods and related tools, i.e. the Coefficient of Variation (CV) analysis, GeNorm, NormFinder, BestKeeper, and the ΔCt method. Using the Geometric mean rank, Pgk1 was identified as the most stable gene. Subsequently, we compared RG expression patterns between the various experimental groups. We found that these statistical methods, next to producing different rankings per se, all ranked RGs displaying significant differences in expression levels between groups as the most stable RG. As a consequence, when assessing the impact of RG selection on target gene expression quantification, substantial differences in target gene expression profiles were observed. Altogether, by assessing mRNA expression profiles within the neonatal rat brain cortex in hypoxia and hypothermia as a showcase, this study underlines the importance of further validating RGs for each individual experimental paradigm, considering the limitations of the statistical methods used for this aim.

Taar1 gene variants have a causal role in methamphetamine intake and response and interact with Oprm1

We identified a locus on mouse chromosome 10 that accounts for 60% of the genetic variance in methamphetamine intake in mice selectively bred for high versus low methamphetamine consumption. We nominated the trace amine-associated receptor 1 gene, Taar1, as the strongest candidate and identified regulation of the mu-opioid receptor 1 gene, Oprm1, as another contributor. This study exploited CRISPR-Cas9 to test the causal role of Taar1 in methamphetamine intake and a genetically-associated thermal response to methamphetamine. The methamphetamine-related traits were rescued, converting them to levels found in methamphetamine-avoiding animals. We used a family of recombinant inbred mouse strains for interval mapping and to examine independent and epistatic effects of Taar1 and Oprm1. Both methamphetamine intake and the thermal response mapped to Taar1 and the independent effect of Taar1 was dependent on genotype at Oprm1. Our findings encourage investigation of the contribution of Taar1 and Oprm1 variants to human methamphetamine addiction.

Physiology and effects of nucleosides in mice lacking all four adenosine receptors

Adenosine is a constituent of many molecules of life; increased free extracellular adenosine indicates cell damage or metabolic stress. The importance of adenosine signaling in basal physiology, as opposed to adaptive responses to danger/damage situations, is unclear. We generated mice lacking all four adenosine receptors (ARs), Adora1^−/−;Adora2a^−/−;Adora2b^−/−;Adora3^−/− (quad knockout [QKO]), to enable investigation of the AR dependence of physiologic processes, focusing on body temperature. The QKO mice demonstrate that ARs are not required for growth, metabolism, breeding, and body temperature regulation (diurnal variation, response to stress, and torpor). However, the mice showed decreased survival starting at about 15 weeks of age. While adenosine agonists cause profound hypothermia via each AR, adenosine did not cause hypothermia (or bradycardia or hypotension) in QKO mice, indicating that AR-independent signals do not contribute to adenosine-induced hypothermia. The hypothermia elicited by adenosine kinase inhibition (with A134974), inosine, or uridine also required ARs, as each was abolished in the QKO mice. The proposed mechanism for uridine-induced hypothermia is inhibition of adenosine transport by uridine, increasing local extracellular adenosine levels. In contrast, adenosine 5′-monophosphate (AMP)–induced hypothermia was attenuated in QKO mice, demonstrating roles for both AR-dependent and AR-independent mechanisms in this process. The physiology of the QKO mice appears to be the sum of the individual knockout mice, without clear evidence for synergy, indicating that the actions of the four ARs are generally complementary. The phenotype of the QKO mice suggests that, while extracellular adenosine is a signal of stress, damage, and/or danger, it is less important for baseline regulation of body temperature.

A study of mice lacking all four adenosine receptors shows that while they mediate effects of uridine, inosine and adenosine, these receptors are dispensable for growth, metabolism, breeding, and body temperature regulation. This suggests that extracellular adenosine is a damage or danger signal, rather than a major regulator of baseline physiology.

Elevated extracellular adenosine generally indicates metabolic stress or cell damage and regulates many aspects of physiology. We studied “QKO” mice lacking all four adenosine receptors. Young QKO mice do not appear obviously ill, but do show decreased survival later in life. QKO mice demonstrate that adenosine receptors are not required for growth, metabolism, breeding, and body temperature regulation. QKO mice are missing the pharmacologic effects of adenosine on body temperature, heart rate, and blood pressure. Therefore, all of these effects are mediated by the four adenosine receptors. We also determined that the hypothermic effects of a pharmacologic adenosine kinase inhibitor (A134974), uridine, or inosine each requires adenosine receptors. The uridine-induced hypothermia is likely due to its inhibition of adenosine uptake into cells. QKO mouse physiology appears to be the sum of the individual knockout mice, without evidence for synergy, indicating that the actions of the four adenosine receptors are generally complementary.

Cold Shock Proteins Are Expressed in the Retina Following Exposure to Low Temperatures

Hypothermia has been proposed as a therapeutic intervention for some retinal conditions, including ischemic insults. Cold exposure elevates expression of cold-shock proteins (CSP), including RNA-binding motif protein 3 (RBM3) and cold inducible RNA-binding protein (CIRP), but their presence in mammalian retina is so far unknown. Here we show the effects of hypothermia on the expression of these CSPs in retina-derived cell lines and in the retina of newborn and adult rats. Two cell lines of retinal origin, R28 and mRPE, were exposed to 32°C for different time periods and CSP expression was measured by qRT-PCR and Western blotting. Neonatal and adult Sprague-Dawley rats were exposed to a cold environment (8°C) and expression of CSPs in their retinas was studied by Western blotting, multiple inmunofluorescence, and confocal microscopy. RBM3 expression was upregulated by cold in both R28 and mRPE cells in a time-dependent fashion. On the other hand, CIRP was upregulated in R28 cells but not in mRPE. In vivo, expression of CSPs was negligible in the retina of newborn and adult rats kept at room temperature (24°C). Exposure to a cold environment elicited a strong expression of both proteins, especially in retinal pigment epithelium cells, photoreceptors, bipolar, amacrine and horizontal cells, Müller cells, and ganglion cells. In conclusion, CSP expression rapidly rises in the mammalian retina following exposure to hypothermia in a cell type-specific pattern. This observation may be at the basis of the molecular mechanism by which hypothermia exerts its therapeutic effects in the retina.

Liver PPARα is crucial for whole-body fatty acid homeostasis and is protective against NAFLD

OBJECTIVE

Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor expressed in tissues with high oxidative activity that plays a central role in metabolism. In this work, we investigated the effect of hepatocyte PPARα on non-alcoholic fatty liver disease (NAFLD).

DESIGN

We constructed a novel hepatocyte-specific PPARα knockout (Pparα(hep-/-)) mouse model. Using this novel model, we performed transcriptomic analysis following fenofibrate treatment. Next, we investigated which physiological challenges impact on PPARα. Moreover, we measured the contribution of hepatocytic PPARα activity to whole-body metabolism and fibroblast growth factor 21 production during fasting. Finally, we determined the influence of hepatocyte-specific PPARα deficiency in different models of steatosis and during ageing.

RESULTS

Hepatocyte PPARα deletion impaired fatty acid catabolism, resulting in hepatic lipid accumulation during fasting and in two preclinical models of steatosis. Fasting mice showed acute PPARα-dependent hepatocyte activity during early night, with correspondingly increased circulating free fatty acids, which could be further stimulated by adipocyte lipolysis. Fasting led to mild hypoglycaemia and hypothermia in Pparα(hep-/-) mice when compared with Pparα(-/-) mice implying a role of PPARα activity in non-hepatic tissues. In agreement with this observation, Pparα(-/-) mice became overweight during ageing while Pparα(hep-/-) remained lean. However, like Pparα(-/-) mice, Pparα(hep-/-) fed a standard diet developed hepatic steatosis in ageing.

CONCLUSIONS

Altogether, these findings underscore the potential of hepatocyte PPARα as a drug target for NAFLD.

Changes in cardiac thrombomodulin and heat shock transcription factor 1 expression and peripheral thrombomodulin and catecholamines during hypothermia in rats

Effects of hypothermia and rewarming on thrombomodulin, catecholamines and heat shock transcription factor 1 (HSF1) were studied in rats. The aims of this study were to clarify whether cold stress, under anesthesia, is sufficient to change levels of thrombomodulin in healthy endothelium and in the circulation and whether adrenaline, noradrenaline and HSF1 could act as regulators in the process. Rats were divided into control, mild hypothermia (2 and 4.5 hours at + 21 °C; MH1, MH2), severe hypothermia (2 and 4.5 h at + 10 °C; SH1, SH2) and two rewarming groups (2 h at + 10 °C followed by 2 h at + 21 °C or 3 h at + 28 °C; SHW1, SHW2) (n = 15/group, except n = 6 in MH1). Fentanyl-fluanisone-midazolam was used as anesthetic. Low levels of thrombomodulin in plasma and myocardial arterioles/venules measured by ELISA and immunohistochemistry were associated with significant increase of thrombomodulin transcript level in SH1 rats analyzed by quantitative PCR. Plasma adrenaline correlated negatively with the relative amount of myocardial thrombomodulin transcripts and positively with plasma thrombomodulin in SH. Transcript levels of thrombomodulin and HSF1 correlated strongly (r = 0.83; p < 0.001) in SH. Plasma/urine ratio of thrombomodulin and plasma adrenaline (r = 0.87; p = 0.005) or noradrenaline (r = 0.78; p = 0.023) were strongly correlated in SHW1 rats. Hence, cellular and soluble levels of thrombomodulin are modified by cold stress in healthy rats, possibly via catecholamines and HSF1.

Hypothermia inhibits expression of CD11b (MAC-1) and CD162 (PSGL-1) on monocytes during extracorporeal circulation

AIM

The aim of the present study was to investigate the effect of different hypothermic temperatures on the expression of cellular adhesion molecules on leukocytes.

MATERIALS AND METHODS

Circulation of blood from six volunteers was performed in an extracorporeal circulation model at 36°C, 28°C and 18°C for 30 minutes. Expression of CD11b, CD54 and CD162 on monocytes was measured using flow cytometry.

RESULTS

Expression of CD11b significantly decreased at 18°C and at 28°C compared to 36°C. A significant reduction of CD162 expression was found at 18°C compared to 28°C and 36°C and at 28°C compared to 36°C. No association was found between temperature and expression of CD54.

CONCLUSION

Expression of CD11b and CD162 on monocytes has a temperature-dependent regulation, with decreased expression during hypothermia, which may result in an inhibition of leukocyte-endothelial and leukocyte-platelet interaction. This beneficial effect may influence the extracorporeal circulation-related inflammatory response and tissue damage.

The impact of biosampling procedures on molecular data interpretation

The separation between biological and technical variation without extensive use of technical replicates is often challenging, particularly in the context of different forms of protein and peptide modifications. Biosampling procedures in the research laboratory are easier to conduct within a shorter time frame and under controlled conditions as compared with clinical sampling, with the latter often having issues of reproducibility. But is the research laboratory biosampling really less variable? Biosampling introduces within minutes rapid tissue-specific changes in the cellular microenvironment, thus inducing a range of different pathways associated with cell survival. Biosampling involves hypoxia and, depending on the circumstances, hypothermia, circumstances for which there are evolutionarily conserved defense strategies in the range of species and also are relevant for the range of biomedical conditions. It remains unclear to what extent such adaptive processes are reflected in different biosampling procedures or how important they are for the definition of sample quality. Lately, an increasing number of comparative studies on different biosampling approaches, post-mortem effects and pre-sampling biological state, have investigated such immediate early biosampling effects. Commonalities between biosampling effects and a range of ischemia/reperfusion- and hypometabolism/anoxia-associated biological phenomena indicate that even small variations in post-sampling time intervals are likely to introduce a set of nonrandom and tissue-specific effects of experimental importance (both in vivo and in vitro). This review integrates the information provided by these comparative studies and discusses how an adaptive biological perspective in biosampling procedures may be relevant for sample quality issues.

Ethanol sensitivity in high drinking in the dark selectively bred mice

BACKGROUND

Mouse lines are being selectively bred in replicate for high blood ethanol concentrations (BECs) achieved after a short period of ethanol (EtOH) drinking early in the circadian dark phase. High Drinking in the Dark-1 (HDID-1) mice were in selected generation S18, and the replicate HDID-2 line in generation S11.

METHODS

To determine other traits genetically correlated with high DID, we compared naïve animals from both lines with the unselected, segregating progenitor stock, HS/Npt. Differences between HDID-1 and HS would imply commonality of genetic influences on DID and these traits.

RESULTS

HDID-1 mice showed less basal activity, greater EtOH stimulated activity, and greater sensitivity to EtOH-induced foot slips than HS. They showed lesser sensitivity to acute EtOH hypothermia and longer duration loss of righting reflex than HS. HDID-1 and control HS lines did not differ in sensitivity on 2 measures of intoxication, the balance beam and the accelerating rotarod. None of the acute response results could be explained by differences in EtOH metabolism. HDID-2 differed from HS on some, but not all, of the above responses.

CONCLUSIONS

These results show that some EtOH responses share common genetic control with reaching high BECs after DID, a finding consistent with other data regarding genetic contributions to EtOH responses.

A microarray analysis of the effects of moderate hypothermia and rewarming on gene expression by human hepatocytes (HepG2)

The gene expression changes produced by moderate hypothermia are not fully known, but appear to differ in important ways from those produced by heat shock. We examined the gene expression changes produced by moderate hypothermia and tested the hypothesis that rewarming after hypothermia approximates a heat-shock response. Six sets of human HepG2 hepatocytes were subjected to moderate hypothermia (31 degrees C for 16 h), a conventional in vitro heat shock (43 degrees C for 30 min) or control conditions (37 degrees C), then harvested immediately or allowed to recover for 3 h at 37 degrees C. Expression analysis was performed with Affymetrix U133A gene chips, using analysis of variance-based techniques. Moderate hypothermia led to distinct time-dependent expression changes, as did heat shock. Hypothermia initially caused statistically significant, greater than or equal to twofold changes in expression (relative to controls) of 409 sequences (143 increased and 266 decreased), whereas heat shock affected 71 (35 increased and 36 decreased). After 3 h of recovery, 192 sequences (83 increased, 109 decreased) were affected by hypothermia and 231 (146 increased, 85 decreased) by heat shock. Expression of many heat shock proteins was decreased by hypothermia but significantly increased after rewarming. A comparison of sequences affected by thermal stress without regard to the magnitude of change revealed that the overlap between heat and cold stress was greater after 3 h of recovery than immediately following thermal stress. Thus, while some overlap occurs (particularly after rewarming), moderate hypothermia produces extensive, time-dependent gene expression changes in HepG2 cells that differ in important ways from those induced by heat shock.

Homozygous carnitine palmitoyltransferase 1b (muscle isoform) deficiency is lethal in the mouse

Carnitine palmitoyltransferase-1 (CPT-1) catalyzes the rate-limiting step of mitochondrial beta-oxidation of long chain fatty acids (LCFA), the most abundant fatty acids in mammalian membranes and in energy metabolism. Human deficiency of the muscle isoform CPT-1b is poorly understood. In the current study, embryos with a homozygous knockout of Cpt-1b were lost before embryonic day 9.5-11.5. Also, while there were normal percentages of CPT-1b+/- pups born from both male and female CPT-1b+/- mice crossed with wild-type mates, the number of CPT-1b+/- pups from CPT-1b+/- breeding pairs was under-represented (63% of the expected number). Northern blot analysis demonstrated approximately 50% Cpt-1b mRNA expression in brown adipose tissue (BAT), heart and skeletal muscles in the CPT-1b+/- male mice. Consistent with tissue-specific expression of Cpt-1b mRNA in muscle but not liver, CPT-1+/- mice had approximately 60% CPT-1 activity in skeletal muscle and no change in total liver CPT-1 activity. CPT-1b+/- mice had normal fasting blood glucose concentration. Consistent with expression of CPT-1b in BAT and muscle, approximately 7% CPT-1b+/- mice (n=30) developed fatal hypothermia following a 3h cold challenge, while none of the CPT-1b+/+ mice (n=30) did. With a prolonged cold challenge (6h), significantly more CPT-1b+/- mice developed fatal hypothermia (52% CPT-1b+/- mice vs. 21% CPT-1b+/+ mice), with increased frequency in females of both genotypes (67% female vs. 38% male CPT-1b+/- mice, and 33% female vs. 8% male CPT-1b+/+ mice). Therefore, lethality of homozygous CPT-1b deficiency in the mice is consistent with paucity of human cases.

Induction of Micronuclei by Phenol in the Mouse Bone Marrow: I. Association with Chemically Induced Hypothermia

Doses of xenobiotics at or near LD50 may result in substantial hypothermia in mice. Hypothermia has previously been associated with an increase in micronuclei (MN) formation. The present series of investigations examined the potential for phenol to induce hypothermia in mice and its correlation to previously reported MN induction. In order to examine the potential etiology of phenol-induced MN, evaluation of kinetochore status of MN was also carried out. Phenol-induced hypothermia was assessed in CD1 mice following a single ip dose of phenol ranging from 0-500 mg/kg. Phenol at 300 mg/kg or above caused significant and prolonged hypothermia in male and female mice (up to 7 degrees C decrease). In the micronucleus test, single ip doses of phenol to CD1 mice at 0, 30, 100, or 300 mg/kg produced a significant and prolonged hypothermia and a significant increase in MN only at 300 mg/kg; no marked effect on either body temperature or MN was observed at lower doses. A statistically significant increase in kinetochore-positive MN was observed at the 300-mg/kg dose; however, the response was considerably less than that observed for a known spindle poison. Hence, the induction of MN by phenol occurred only at a dose that produced substantial and prolonged physiologic hypothermia, but interruption of the cell spindle apparatus appeared to play only a minor role in MN formation. These data are suggestive of a threshold mechanism for the induction of MN by phenol treatment in mice.

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.

Hypothermia modulates circadian clock gene expression in lizard peripheral tissues

The molecular mechanisms whereby the circadian clock responds to temperature changes are poorly understood. The ruin lizard Podarcis sicula has historically proven to be a valuable vertebrate model for exploring the influence of temperature on circadian physiology. It is an ectotherm that naturally experiences an impressive range of temperatures during the course of the year. However, no tools have been available to dissect the molecular basis of the clock in this organism. Here, we report the cloning of three lizard clock gene homologs (Period2, Cryptochrome1, and Clock) that have a close phylogenetic relationship with avian clock genes. These genes are expressed in many tissues and show a rhythmic expression profile at 29 degrees C in light-dark and constant darkness lighting conditions, with phases comparable to their mammalian and avian counterparts. Interestingly, we show that at low temperatures (6 degrees C), cycling clock gene expression is attenuated in peripheral clocks with a characteristic increase in basal expression levels. We speculate that this represents a conserved vertebrate clock gene response to low temperatures. Furthermore, these results bring new insight into the issue of whether circadian clock function is compatible with hypothermia.

Effect of moderate hypothermia on gene expression by THP-1 cells: a DNA microarray study

The mechanisms by which moderate hypothermia (32°C for 12–72 h) affect human cellular function are unclear. We tested the hypothesis that it produces broad changes in mRNA expression in vitro. Acute monocytic leukemia (THP-1) cells were incubated under control conditions (37°C) or moderate hypothermia (32°C) for 24 h. RNA was extracted, and the hypothermic response was confirmed by examining the expression of the cold-induced RNA-binding protein (CIRBP) gene by RT-PCR. Gene expression analysis was performed on seven sets of paired samples with Affymetrix U133A chips using established statistical methods. Sequences were considered affected by cold if they showed statistically significant changes in expression and also met published post hoc filter criteria (changes in geometric mean expression of ≥2-fold and expression calls of “present” or “marginal” in at least half of the experiments). Changes in the expression of selected sequences were further confirmed by PCR. Sixty-seven sequences met the criteria for increased expression (including cold-inducible genes CIRBP and RNA binding motif 3), and 100 sequences showed decreased expression as a result of hypothermia. Functional categories affected by hypothermia included genes involved in immune responses; cell growth, proliferation, and differentiation; and metabolism and biosynthesis. Several heat shock proteins (HSPs) showed decreases in expression. Moderate hypothermia produces substantial changes in gene expression, in categories potentially of systemic importance. Cold exposure without rewarming decreased the expression of several HSPs. These in vitro findings suggest that prolonged hypothermia in vivo might be capable of producing physiologically relevant changes in gene expression by circulating leukocytes.

Effects of genetic and procedural variation on measurement of alcohol sensitivity in mouse inbred strains

Mice from eight inbred strains were studied for their acute sensitivity to ethanol as indexed by the degree of hypothermia (HT), indexed as the reduction from pre-injection baseline of their body temperature. Two weeks later, mice were tested for their loss of righting reflex (LRR) after a higher dose of ethanol. The LRR was tested using the "classical" method of watching for recovery in animals placed on their backs in a V-shaped trough and recording duration of LRR. In a separate test, naive animals of the same strains were tested for HT repeatedly to assess the development of rapid (RTOL) and chronic tolerance (CTOL). We have recently developed a new method for testing LRR that leads to a substantial increase in the sensitivity of the test. Strains also have been found to differ in the new LRR test, as well as in the development of acute functional tolerance (AFT) to this response. In addition, our laboratory has periodically published strain difference data on the older versions of the HT and LRR responses. The earlier tests used some of the exact substrains tested currently, while for some strains, different substrains (usually, Nih versus Jax) were tested. We examined correlations of strain means to see whether patterns of strain differences were stable across time and across different test variants assessing the same behavioral construct. HT strain sensitivity scores were generally highly correlated across a 10-23 years period and test variants. The CTOL to HT was well-correlated across studies, and was also genetically similar to RTOL. The AFT, however, was related to neither RTOL nor CTOL, although this may be because different phenotypic end points were compared. The LRR data, which included a variant of the classical test, were not as stable. Measures of LRR onset were reasonably well correlated, as were those taken at recovery (e.g., duration). However, the two types of measures of LRR sensitivity to ethanol appear to be tapping traits that differ genetically. Also, the pattern of genetic correlation between HT and LRR initially reported in 1983 was not seen in current and contemporaneous studies. In certain instances, substrain seems to matter little, while in others, substrains differed a great deal. These data are generally encouraging about the stability of genetic differences.

Differential sensitivity to the motor and hypothermic effects of the GABA B receptor agonist baclofen in various mouse strains

RATIONALE

Comparison of different mouse strains can provide valuable information about the genetic control of behavioural and molecular phenotypes. Recent evidence has demonstrated the importance of GABA B receptors in anxiety and depression. Investigation of the phamacogenetics of GABA B receptor activation may aid in the understanding of mechanisms underlying the role of GABA B in affect.

OBJECTIVES

The aim of current study was to determine the relative sensitivity of different mouse strains to GABA B receptor agonism in two models of GABA B receptor function, namely hypothermia and motor incoordination.

METHODS

Mice each from 11 strains (BALB/cByJIco, DBA/2JIco, OF1, FVB/NIco, CD1, C3H/HeOuJIco, 129/SvPasIco, NMRI, C57BL/6JIco, A/JOlaHsd and Swiss) were trained to walk on a rotarod for 300 s. On the following day, mice received 0, 3, 6 or 12 mg/kg of L: -baclofen PO. Rectal temperature and rotarod performance were measured at 0, 1, 2 and 4 h after drug application.

RESULTS

L: -Baclofen produced a significant dose-dependent hypothermia and ataxia in most, but not all, mouse strains examined. The magnitude and duration of response was influenced by strain, with mice of the 129/SvPasIco strain showing largest hypothermic response to 12 mg/kg l-baclofen and C3H/HeOuJIco the lowest, whereas the BALB/cByJIco strain demonstrated greatest ataxic response on the rotarod, and NMRI the least. Interestingly, some strains (notably C3H/HeOuJIco) had marked differential hypothermic and ataxic responses, with minimal body temperature responses to L: -baclofen but significant ataxia on the rotarod observed.

CONCLUSION

There is differential genetic control on specific GABA B receptor populations that mediate hypothermia and ataxia. Further, these studies demonstrate that background strain is an important determinant of GABA B receptor mediated responses, and that hypothermic and ataxic responses may be influenced by independent genetic loci.

Cloning and expression of hypoxia-inducible factor 1α from the hibernating ground squirrel, Spermophilus tridecemlineatus

Mammalian hibernation is associated with apnoic breathing patterns and a hypoxia-hypothermia connection has been suggested as part of the mechanism by which body temperature is reduced as animals enter torpor. Hence, we hypothesized that changes in the expression of the hypoxia inducible factor (HIF-1) may potentially be involved in regulating hibernation-responsive gene targets. The expression of the alpha subunit of HIF-1 was quantified at both gene and protein levels in four organs of the thirteen-lined ground squirrel, Spermophilus tridecemlineatus. Reverse transcription-PCR showed no change in hif-1alpha transcript levels in the liver, lung, skeletal muscle or brown adipose tissue of euthermic versus hibernating animals but HIF-1alpha protein levels were elevated by 60-70% in the two organs responsive for thermogenesis (brown adipose and skeletal muscle). Furthermore, assessment of DNA binding by HIF-1 in nuclear extracts from brown adipose revealed 6-fold higher levels in hibernator tissue than in euthermic controls suggesting increased expression of HIF-1 responsive genes during hibernation. The complete nucleotide sequence of hif-1alpha from ground squirrels, the first hif-1alpha sequence amplified from a hibernating mammal, was obtained using PCR amplification and 3' and 5' RACE. Amino acid sequence analysis revealed 90-95% identity with the HIF-1alpha protein from other mammals. Several unique amino acid sequence substitutions were identified that may affect protein conformation and could possibly function to counteract low temperature effects on HIF-1alpha conformation at near 0 degrees C body temperatures during torpor.

Lower core body temperature and attenuated nicotine-induced hypothermic response in mice lacking the beta4 neuronal nicotinic acetylcholine receptor subunit

Diverse physiological and pathological effects of nicotine, including the alteration of body temperature, are presumably mediated by neuronal nicotinic acetylcholine receptors (nAChR). Previous studies have suggested the involvement of distinct nAChR subunits in nicotine-induced thermoregulation. We studied genetically manipulated knockout mice lacking the alpha7, alpha5 or beta4 subunit genes, in order to assess the effects of subunit deficiency on temperature regulation. Using a telemetry system, core body temperature was monitored continuously prior to and following nicotine administration in mutant mice and in wild-type littermates. Mice lacking in the beta4 nAChR subunit gene had significantly lower baseline core body temperature than all other mouse strains studied. beta4 null mice also demonstrated a reduced nicotine-induced hypothermic response and impaired desensitization following repeat nicotine exposure. These findings suggest the involvement of the beta4 nAChR subunit in both core body temperature homeostasis and nicotine-elicited thermo-alterations in mice.

Differential regulation of glomerular and interstitial endothelial nitric oxide synthase expression in the kidney of hibernating ground squirrel

Hibernating animals transiently reduce renal function during their hypothermic periods (torpor), while completely restoring it during their periodical rewarming to euthermia (arousal). Moreover, structural integrity of the kidney is preserved throughout the hibernation. Nitric oxide (NO) generated by endothelial nitric oxide synthase (eNOS) is a crucial vasodilatory mediator and a protective factor in the kidney. We investigated renal NOS expression in hibernating European ground squirrels after 1 day and 7 days of torpor (torpor short, TS, and torpor long, TL, respectively), at 1.5 and at 10 h of rewarming (arousal short, AS, and arousal long, AL, respectively), and in continuously euthermic animals after hibernation (EU). For that purpose, we performed NOS activity assay, immunohistochemistry and real-time PCR analysis. Immunohistochemistry revealed a decreased glomerular eNOS expression in hibernating animals (TS, TL, AS, and AL) compared to non-hibernating animals (EU, p < 0.05), whereas no difference was found in the expression of interstitial eNOS. Expression of iNOS and nNOS did not differ between all groups. The reduced glomerular eNOS was associated with a significantly lower eNOS mRNA levels and NOS activity of whole kidney during torpor and arousal (TS, TL, AS, and AL) compared to EU. In all methods used, torpid and aroused squirrels did not differ. These results demonstrate differential regulation of eNOS in glomeruli and interstitium of hibernating animals, which is unaffected during arousal. The differential regulation of eNOS may serve to reduce ultrafiltration without jeopardizing tubular structures during hibernation.

Lack of stearoyl-CoA desaturase 1 upregulates basal thermogenesis but causes hypothermia in a cold environment

Stearoyl-CoA desaturase (SCD) is a microsomal enzyme involved in the biosynthesis of oleate and palmitoleate. Mice with a targeted disruption of the SCD1 isoform (SCD1-/-) exhibit reduced adiposity and increased energy expenditure. To address whether the energy expenditure is attributable to increased thermogenesis, we investigated the effect of SCD1 deficiency on basal and cold-induced thermogenesis. SCD1-/- mice have increased expression of uncoupling proteins in brown adipose tissue (BAT) relative to controls. The beta3-adrenergic receptor (beta3-AR) expression was increased and the phosphorylation of cAMP response element binding protein and the protein level of peroxisome proliferator-activated receptor-gamma coactivator-1alpha were increased in the SCD1-/- mice. Both lipolysis and fatty acid oxidation were increased in the SCD1-/- mice. When exposed to 4 degrees C, SCD1-/- mice showed hypothermia, hypoglycemia, and depleted liver glycogen. High levels of dietary oleate partially compensated for the hypothermia and rescued plasma glucose and liver glycogen. These results suggest that SCD1 deficiency stimulates basal thermogenesis through the upregulation of the beta3-AR-mediated pathway and a subsequent increase in lipolysis and fatty acid oxidation in BAT. The hypothermia and hypoglycemia in cold-exposed SCD1-/- mice and the compensatory recovery by oleate indicate an important role of SCD1 gene expression in thermoregulation.

Acetaminophen-induced hypothermia in mice is mediated by a prostaglandin endoperoxide synthase 1 gene-derived protein

Acetaminophen is a widely used antipyretic analgesic, reducing fever caused by bacterial and viral infections and by clinical trauma such as cancer or stroke. In rare cases in humans, e.g., in febrile children or HIV or stroke patients, acetaminophen causes hypothermia while therapeutic blood levels of the drug are maintained. In C57/BL6 mice, acetaminophen caused hypothermia that was dose related and maximum (>2 degrees C below normal) with a dose of 300 mg/kg. The reduction and recovery of body temperature was paralleled by a fall of >90% and a subsequent rise of prostaglandin (PG)E(2) concentrations in the brain. In cyclooxygenase (COX)-2(-/-) mice, acetaminophen (300 mg/kg) produced hypothermia accompanied by a reduction in brain PGE(2) levels, whereas in COX-1(-/-) mice, the hypothermia to this dose of acetaminophen was attenuated. The brains of COX-1(-/-) mice had approximately 70% lower levels of PGE(2) than those of WT animals, and these levels were not reduced further by acetaminophen. The putative selective COX-3 inhibitors antipyrine and aminopyrine also reduced basal body temperature and brain PGE(2) levels in normal mice. We propose that acetaminophen is a selective inhibitor of a COX-1 variant and this enzyme is involved in the continual synthesis of PGE(2) that maintains a normal body temperature. Thus, acetaminophen reduces basal body temperature below normal in mice most likely by inhibiting COX-3.

Nicotinic acetylcholine receptor α5 subunits modulate oxotremorine-induced salivation and tremor

Neuronal nicotinic acetylcholine receptors (nAChRs) are composed of 12 subunits (alpha2-alpha10 and beta2-beta4). alpha5 Subunits, expressed throughout the central nervous system (CNS) and the autonomic nervous system (ANS), possess unique pharmacological properties. The effects of oxotremorine (OXO) on autonomic functions and tremor were examined in mice lacking alpha5 nAChR subunits (alpha5-/-) and compared with those in wild-type (WT) control mice. The alpha5-/- mice showed significantly increased salivation and tremor responses to OXO. The hypothermia, bradycardia and defecation induced by OXO were of similar magnitudes in the two mouse strains. The enhanced OXO effects in alpha5-/- mice indicate inhibitory effects of alpha5 subunits in autonomic ganglia, and support the participation of these subunits in cholinergic transmission in autonomic ganglia.

Are lethal audiogenic seizures a missing link to the sudden infant death syndrome?

The pathogenesis of human seizure disorders has largely been derived from rodent models. A number of rodent and chick strains exhibit a genetic predisposition for lethal audiogenic seizures (AGSs) in the first year of life. Consideration is warranted that this disorder may be linked to the sudden infant death syndrome (SIDS). Factors that carry a strong association with SIDS such as hyperthermia and the prone sleeping position would conceivably play a significant role in a human AGS syndrome. Importantly, there is data to support the likelihood that motor seizure activity may be absent in infants with an AGS syndrome. Rodent AGSs may hold important clues to unraveling the mystery of SIDS.

γ-Aminobutyric Acid Type A Receptor β2 Subunit Mediates the Hypothermic Effect of Etomidate in Mice

Background

The authors have previously described that the gamma-aminobutyric acid type A (GABAA) receptor beta 2N265S mutation results in a knock-in mouse with reduced sensitivity to etomidate. After recovery from etomidate anesthesia, these mice have improved motor performance and less slow wave sleep. Because most clinically used anesthetics produce hypothermia, the effect of this mutation on core body temperature was investigated.

Methods

The effect of etomidate and propofol on core body temperature were measured using radiotelemetry in freely moving GABAA receptor beta 2N265S mutant mice and wild-type controls.

Results

beta 2N265S mutant mice have a reduced hypothermic response to anesthetic doses of etomidate compared with wild-type controls and after a transient loss of righting reflex regain normothermia more rapidly compared with wild-type controls. Subanesthetic doses of etomidate produce hypothermia, which was not observed in the mutant mice. Vehicle administration resulted in a stress-induced hyperthermic response in both genotypes. Propofol produced a hypothermic response that was similar in both genotypes.

Conclusions

The GABAA receptor beta 2 subunit mediates a significant proportion of the hypothermic effects of etomidate. As the beta 2 subunit mediates postrecovery ataxia and sedation, anesthetic agents that do not have in vivo potency at beta 2 subunit-containing receptors offer the potential for surgical anesthesia with improved recovery characteristics.

Oxygen-regulated expression of the RNA-binding proteins RBM3 and CIRP by a HIF-1-independent mechanism

The transcriptional regulation of several dozen genes in response to low oxygen tension is mediated by hypoxia-inducible factor 1 (HIF-1), a heterodimeric protein composed of two subunits, HIF-1alpha and HIF-1beta. In the HIF-1alpha-deficient human leukemic cell line, Z-33, exposed to mild (8% O(2)) or severe (1% O(2)) hypoxia, we found significant upregulation of two related heterogenous nuclear ribonucleoproteins, RNA-binding motif protein 3 (RBM3) and cold inducible RNA-binding protein (CIRP), which are highly conserved cold stress proteins with RNA-binding properties. Hypoxia also induced upregulation of RBM3 and CIRP in the murine HIF-1beta-deficient cell line, Hepa-1 c4. In various HIF-1 competent cells, RBM3 and CIRP were induced by moderate hypothermia (32 degrees C) but hypothermia was ineffective in increasing HIF-1alpha or vascular endothelial growth factor (VEGF), a known HIF-1 target. In contrast, iron chelators induced VEGF but not RBM3 or CIRP. The RBM3 and CIRP mRNA increase after hypoxia was inhibited by actinomycin-D, and in vitro nuclear run-on assays demonstrated specific increases in RBM3 and CIRP mRNA after hypoxia, which suggests that regulation takes place at the level of gene transcription. Hypoxia-induced RBM3 or CIRP transcription was inhibited by the respiratory chain inhibitors NaN(3) and cyanide in a dose-dependent fashion. However, cells depleted of mitochondria were still able to upregulate RBM3 and CIRP in response to hypoxia. Thus, RBM3 and CIRP are adaptatively expressed in response to hypoxia by a mechanism that involves neither HIF-1 nor mitochondria.

The cyclic AMP/protein kinase A signal transduction pathway modulates tolerance to sedative and hypothermic effects of ethanol

BACKGROUND

An expanding body of literature indicates the important role of the cAMP/PKA signaling pathway in establishing initial sensitivity to alcohol as well as being involved in certain forms of tolerance to ethanol. The use of mice with heterozygous inactivation of the Gnas gene encoding Gsalpha allowed us to explore the relationship between tolerance to ethanol and cAMP/PKA signaling.

METHODS

Mice with the targeted disruption of one Gsalpha allele were compared with wild-type littermates in their initial sensitivity to ethanol-induced sedation and hypothermia and then monitored for the development of tolerance during two subsequent bouts of intoxication. Components of the cAMP/PKA signaling pathway were analyzed in ethanol-naïve mice and again following the development of tolerance to ethanol to better understand the contribution of this signaling pathway to the acquisition of tolerance.

RESULTS

During the initial exposure to ethanol, mice with the targeted disruption of one Gsalpha allele (Gnas) were more sensitive to the sedative effects of ethanol compared with wild-type littermates. Wild-type mice developed within-session tolerance to ethanol-induced hypothermia whereas Gnas mice did not. Following the subsequent ethanol treatments, wild-type mice developed between-session tolerance to the sedative effects of ethanol to a greater degree than mice with heterozygous inactivation of the Gnas gene. The development of tolerance to the sedative effects of ethanol was accompanied by increased expression of phospho-CREB in the cerebellum, hippocampus, and frontal cortex. No changes in phospho-CREB expression were detected in these brain regions in mice with heterozygous inactivation of the Gnas gene.

CONCLUSION

The results show that cAMP/PKA signal transduction modulates sensitivity to sedative and hypothermic effects of ethanol. This signal transduction system also influences the acquisition of within-session and between-session tolerance. The mechanism through which cAMP/PKA signaling modulates the development of tolerance remains to be elucidated but may involve changes in phospho-CREB expression.

Interaction between S-propranolol and ethanol in mice selectively bred for ethanol sensitivity: the inbred short- and long-sleep mice

BACKGROUND

We have studied the effect of a beta-adrenergic blocking agent, S-propranolol, on the response of mice to anesthetic doses of ethanol. We used the selectively bred short and long sleep (ISS and ILS) mice. These mice were selected for their differential sensitivity to anesthetic doses of ethanol and then inbred. The study was prompted by the finding that the effect of ethanol on the firing rate of cerebellar Purkinje cells is modulated by beta-adrenergic input. In addition, this firing rate depression by ethanol is highly correlated with the anesthetic potency of ethanol. We were attempting to find a behavioral correlate of this effect of beta-adrenergic agents in the ISS and ILS mice.

METHODS

We studied the effect of S-propranolol plus ethanol on the sleep time and blood ethanol at awakening in the inbred ILS and ISS mice. We administered anesthetic doses of ethanol with and without S-propranolol. We conducted studies of the rate of disappearance of ethanol in the presence of S-propranolol and carried out sleep time and metabolic studies with mice in an incubator held at 32 to 33 degrees C.

RESULTS

We found that S-propranolol caused a prolonged anesthetic time brought about by ethanol but only in ISS mice. There was no significant difference in the blood ethanol levels at awakening with or without S-propranolol, indicating that S-propranolol had no effect on the brain sensitivity. Subsequently, we showed that this was due to a profound hypothermia caused by a combination of S-propranolol and ethanol. This was greater in the ISS mice because a larger dose of ethanol was required for the anesthetic effect of ethanol. The effect on ethanol disappearance rate, temperature drop, and anesthesia time all were largely reversed by placing the animals in an incubator at 32 to 33 degrees C.

CONCLUSIONS

Profound hypothermia lowers the ethanol disappearance rate when both S-propranolol and ethanol are given. The effect of S-propranolol is likely due to the blockade of beta-adrenergic receptors that prevents thermogenic responses to the hypothermia brought about by ethanol. The results indicated that there might be a genetic effect controlling the hypothermic response to the combination of S-propranolol and ethanol. Further experiments to investigate this are reported in a subsequent article. We could find no evidence of a central nervous system effect of S-propranolol on the hypnotic actions of ethanol in these strains of mice.

Genetic analyses of ethanol-induced hyperglycemia

BACKGROUND

Genetic sensitivity to ethanol-induced hyperglycemia was hypothesized to be related to sensitivity to ethanol-induced hypothermia and conditioned taste aversion. These hypotheses were explored by characterizing blood glucose changes after ethanol exposure in BXD recombinant inbred mice.

METHODS

Adult male and female BXD recombinant inbred mice were acutely exposed to 4 g/kg of ethanol or saline with the order of exposure counterbalanced, and separated by a 1-week interval. Tail blood samples and rectal temperatures were determined immediately before ethanol/saline exposure and 2 hr after exposure.

RESULTS

Substantial strain differences in ethanol-induced hyperglycemia and hypothermia were noted. In addition, sex also determined sensitivity to ethanol-induced hyperglycemia and interacted with strain. Correlational analyses using strain means indicated that ethanol-induced hyperglycemia was genetically independent from ethanol-induced hypothermia or conditioned taste aversion. Quantitative trait locus (QTL) analyses indicated provisional QTL for ethanol-induced hyperglycemia on chromosomes 1, 3, 4, 6, 7, 9, 12, 14, and 18, which, in part, were sex specific.

CONCLUSIONS

These findings indicate important sex differences in the glycemic response to ethanol. In addition, multiple genes likely control this response, independent from genes that are important for the thermic or aversive effects of ethanol.

Episodic spontaneous hypothermia: a periodic childhood syndrome

Episodic spontaneous hypothermia is an infrequent disorder, with unknown pathogenic mechanisms. A systemic cause or underlying brain lesion has not been found for the disease. We report four new patients, 3-9 years old, with episodic hypothermia lower than 35 degrees C, marked facial pallor, and absent shivering. The episodes could last a few hours or four days, and recurred once a week or every 2-3 months. Two patients also demonstrated bradycardia, mild hypertension, and somnolence during the events; in one of them, profuse sweating was also a feature, and all four presented with either headache, a periodic childhood syndrome, or both (recurrent abdominal pain, cyclic vomiting, or vertigo). Three patients reported a family history of migraine. Neurologic examination, endocrine function, and imaging studies were normal. Migraine prophylactic therapy was of moderate efficacy. Spontaneous resolution was observed in one patient. The clinical characteristics of the syndrome allow for its inclusion as a childhood periodic syndrome related to migraine.

Possible pleiotropic effects of genes specifying sedative/hypnotic sensitivity to ethanol on other alcohol-related traits

BACKGROUND

Initial sensitivity to ethanol is a predictor of alcohol abuse that has been studied extensively in both human and animal populations. Selection for initial sensitivity to the sedative/hypnotic effects of ethanol resulted in the long-sleep and short-sleep lines of mice. Some of the genes selected in these lines could also specify differential responses in other ethanol-related phenotypes and, perhaps, for other drugs of abuse. We assessed congenic mice carrying a single quantitative trait locus (QTL) from the inbred long-sleep (ILS) or inbred short-sleep (ISS) strain on the reciprocal background for a number of ethanol- and pentobarbital-related phenotypes.

METHODS

Each congenic strain was tested for ethanol elimination rates at 4.1 g/kg, ethanol-induced ataxia at 2.0 g/kg, ethanol-induced hypothermia at 4.1 g/kg, and pentobarbital-induced loss of righting reflex (LORR) at 60 mg/kg. Additionally, the ILS.ISS congenics were tested for low-dose ethanol-induced activation (LDA) at five doses ranging from 0.6 to 1.2 g/kg ethanol, and the ISS.ILS congenics were tested for LDA at 1.8 g/kg of ethanol.

RESULTS

There was little difference in the ethanol elimination rate between congenics and background strains, although a modest sex effect was found, with the females eliminating ethanol more rapidly than the males. We were unable to replicate previous differences found in LDA for the congenic on the ISS background, because none of the congenics differed from controls for LDA. congenics showed a differential effect of pentobarbital-induced LORR in the expected directions. The congenics on the ISS background showed more ethanol-induced ataxia than the ISS controls. Additionally, the hypothermic response seems affected by and and maybe others.

CONCLUSIONS

At least two regions carrying a QTL specifying sensitivity to high doses of ethanol cospecify altered sensitivity in other measures of alcohol action. Specifically, these QTLs clearly affect ethanol-induced hypothermia and pentobarbital-induced LORR and possibly ethanol-induced ataxia.

Strain differences in urocortin expression in the Edinger-Westphal nucleus and its relation to alcohol-induced hypothermia

The Edinger-Westphal nucleus is the primary source of urocortin in rodent brain. Mapping of inducible transcription factors has shown that the Edinger-Westphal nucleus is preferentially sensitive to ethanol self-administration. In the present study we have immunohistochemically compared expression of urocortin and c-Fos in naive and ethanol-treated C57BL/6J and DBA/2J mouse inbred strains. We found that C57BL/6J mice possess significantly higher numbers of urocortin-expressing cells in the Edinger-Westphal compared to DBA/2J mice. Subsequent histological analysis confirmed a lower number of large neurons in the DBA/2J Edinger-Westphal nucleus. Surprisingly, despite the differences in structure, no strain differences were observed in the number of c-Fos-containing cells after acute (0.6-4.8 g/kg, i.p.) and repeated (2.4 g/kg, 14 days, one injection/day) administration of ethanol. Double-label immunohistochemistry showed that ethanol-induced c-Fos expression is present in different sets of Edinger-Westphal cells between the strains. Specifically, expression of c-Fos in C57BL/6J mice is preferentially induced in urocortin cells, while c-Fos in DBA/2J mice occurs in a mixed population of cells. Behavioral analysis of the B6D2 F2 intercross, a heterogeneous mouse strain, showed that the number of urocortin cells is positively correlated with basal temperatures and ethanol-induced hypothermia. Involvement of the Edinger-Westphal in alcohol-induced hypothermia is further confirmed by analysis of urocortin cells in the HOT/COLD selected lines. These results provide evidence that C57BL/6J and DBA/2J mice have structural differences in the Edinger-Westphal that can result in activation of different populations of neurons upon alcohol intoxication contributing to differential thermoregulation between these inbred strains.

Behavioral characteristics of rat lines selected for differential hypothermic responses to cholinergic or serotonergic agonists

The present review will describe the formation of two pharmacologically selected lines of rats, their behavioral phenotypes, their responses to select drugs, their possible neurochemical correlates, and their use to detect the therapeutic potential of antidepressant drugs. The Flinders Line rats were established at Flinders University in Australia by selectively breeding for differential responses to an anticholinesterase agent from outbred Sprague-Dawley (SD) rats; the Flinders Sensitive Line (FSL) rats were more sensitive to the hypothermic and behavioral suppressing effects of this agent than the Flinders Resistant Line (FRL) rats. The 8-OH-DPAT line rats were established at the University of North Carolina at Chapel Hill by selectively breeding for differential hypothermic responses to the 5-HT1A receptor agonist, 8-OH-DPAT; the high DPAT sensitive (HDS) line rats were more sensitive to the hypothermic effects of 8-OH-DPAT than the low DPAT sensitive (LDS) line rats. Studies of these two pairs of lines have indicated that the FSL and HDS rats are both more susceptible to stress-induced behavioral disturbances. Their usefulness in detecting potential antidepressant drugs and the relationship between mood disorders and drug abuse will be discussed.

Genetic determinants of sensitivity to pentobarbital in inbred mice

RATIONALE

We postulated that genetic determinants of different responses to pentobarbital (PB) in mice would differ from response to response.

OBJECTIVES

Mice from 14 standard inbred strains were tested for sensitivity to several effects of acute PB.

METHODS

Strains were tested for sensitivity to PB-induced low-dose stimulation and high-dose depression of locomotor activity, reduced rearing, hypothermia, and ataxia assessed on a rotarod, using four doses of PB or saline.

RESULTS

Strains differed in sensitivity to PB for all responses. Correlations among strain means indicated that strain sensitivity to a particular effect of PB generalized rather well across doses. Sensitivities to some of the different behavioral responses were also significantly correlated. For example, strains less sensitive to PB-induced enhanced locomotor activity were also significantly more sensitive to the drug's hypothermic effects. Some responses were genetically independent. Brain PB concentrations were also determined, and appeared to be unrelated to inbred strain drug sensitivities.

CONCLUSIONS

Overall, these results suggest that there are multiple genetic determinants of behavioral sensitivity to PB effects. That is, genetically influenced sensitivity to PB is not monolithic, but is somewhat specific to the particular response variable studied, a result that also characterizes genetic control of responses to other drugs.

The lethal form of Cushing's in 7B2 null mice is caused by multiple metabolic and hormonal abnormalities

The neuroendocrine-specific protein 7B2, which serves as a molecular escort for proPC2 in the secretory pathway, promotes the production of enzymatically active PC2 and may have non-PC2 related endocrine roles. Mice null for 7B2 exhibit a lethal phenotype with a complex Cushing's-like pathology, which develops from intermediate lobe ACTH hypersecretion as a consequences of interruption of PC2-mediated peptide processing as well as undefined consequences of the loss of 7B2. In this study we investigated the endocrine and metabolic alterations of 7B2 null mice from pathological and biochemical points of view. Our results show that 7B2 nulls exhibit a multisystem disorder that includes severe pathoanatomical and histopathologic alterations of vital organs, including the heart and spleen but most notably the liver, in which massive steatosis and necrosis are observed. Metabolic derangements in glucose metabolism result in glycogen and fat deposition in liver under conditions of chronic hypoglycemia. Liver failure is also likely to contribute to abnormalities in blood coagulation and blood chemistry, such as lactic acidosis. A hypoglycemic crisis coupled with respiratory distress and intensive internal thrombosis most likely results in rapid deterioration and death of the 7B2 null.

Sensitivity and tolerance to ethanol-induced incoordination and hypothermia in HAFT and LAFT mice

Acute functional tolerance (AFT) manifests as rapid adaptation during a single ethanol exposure, leading to a decrease in the behavioral response to ethanol. In order to investigate the genetic and environmental components of the development of AFT, mice were selectively bred in replicate from HS/Ibg mice. High (HAFT) and low (LAFT) acute functional tolerance selected lines were bred to differ in the rate of development and magnitude of AFT to ethanol's intoxicating effects using a static dowel-balancing task. In the present set of experiments, HAFT and LAFT mice were tested for development of AFT on a fixed-speed rotarod using a protocol similar to that for which they were selected. HAFT mice developed greater AFT to ethanol than did LAFT mice. In a separate experiment, other mice from these lines were tested for initial sensitivity and the development of chronic tolerance to ethanol-induced hypothermia, and ethanol-induced incoordination in the grid test. Previous research has detected possible common genetic control of these phenotypes. No differences between lines were found in initial sensitivity to ethanol or in the development or magnitude of chronic tolerance in either test. These experiments show that genetic factors influencing the development of acute tolerance to ethanol-induced intoxication are at least partially distinct from those influencing initial sensitivity and the development of chronic tolerance to ethanol-induced hypothermia and incoordination. Furthermore, these experiments show that AFT measured by the stationary dowel generalizes to AFT measured by the fixed-speed rotarod.

Mitochondrial respiratory chain deficiency revealed by hypothermia

We observed a 17-month-old girl with profound and initially isolated episodes of hypothermia. Thereafter, she developed growth delay, repetitive corneal and bone lesions. Persistent hyperlactataemia in plasma and in CSF prompted us to investigate respiratory chain enzymes. A deficit in respiratory chain complexes III and IV was demonstrated in isolated skeletal muscle mitochondria, circulating lymphocytes and fibroblasts by spectrophotometric and polarographic studies. Moreover, UCP3 mRNA expression in muscle was decreased.

Impaired adipogenesis and lipolysis in the mouse upon selective ablation of the retinoid X receptor mediated by a tamoxifen-inducible chimeric Cre recombinase (Cre-ERT2) in adipocytes

Retinoid X receptor alpha (RXRalpha) is involved in multiple signaling pathways, as a heterodimeric partner of several nuclear receptors. To investigate its function in energy homeostasis, we have selectively ablated the RXRalpha gene in adipocytes of 4-week-old transgenic mice by using the tamoxifen-inducible Cre-ERT2 recombination system. Mice lacking RXRalpha in adipocytes were resistant to dietary and chemically induced obesity and impaired in fasting-induced lipolysis. Our results also indicate that RXRalpha is involved in adipocyte differentiation. Thus, our data demonstrate the feasibility of adipocyte-selective temporally controlled gene engineering and reveal a central role of RXRalpha in adipogenesis, probably as a heterodimeric partner for peroxisome proliferator-activated receptor gamma.

Selective breeding of 5-HT(1A) receptor-mediated responses: application to emotion and receptor action

Rat lines that were selectively bred for high (high DPAT-sensitive, HDS) or low (low DPAT-sensitive, LDS) hypothermic responses to the specific 5-HT(1A) receptor agonist, 8-hydroxy-di-n-propylaminotetralin (8-OH-DPAT), differ in receptor binding and certain behaviors related to anxiety and depression. After reviewing this literature, the present communication summarizes new experiments designed to clarify and extend the nature of the pharmacological and biochemical differences between the lines. A challenge with the 5-HT(2) receptor agonist, DOI, produced similar degrees of head shakes and skin crawls in the HDS and LDS rats, suggesting similar sensitivity of 5-HT(2A) and 5-HT(2C) receptors. In contrast, DOI-induced flat body posture (FBP), which has been linked to 5-HT(1A) receptor stimulation, was observed more readily in the HDS rats. The HDS and LDS rats exhibited similar degrees of increase in 8-OH-DPAT-stimulated [35S]GTPgammaS binding in several brain regions. This result suggests that the dramatic differences in hypothermia in HDS and LDS rats cannot be related to 5-HT(1A) receptor-mediated action on G proteins. Overall, these findings indicate that the selective breeding for 5-HT(1A)-mediated hypothermia has been fairly selective, and that differences in emotionally relevant behaviors between these two rat lines can strongly be associated with an unidentified component of the 5-HT(1A) receptor signaling pathway.

Altered behavior and alcohol tolerance in transgenic mice lacking MAO A: a comparison with effects of MAO A inhibitor clorgyline

The influence of deficiency of monoamine oxidase A (MAO A) gene and the lack of enzyme MAO A on the behavior of transgenic mouse strain (Tg8) was studied. It was shown that MAO-A-lacking mice differed from mice of the wild-type strain C3H/HeJ (C3H) by an attenuated acoustic startle response, prepulse inhibition (PPI) was unchanged. In Tg 8 mice, the exploratory nose-poking in the holeboard test as well as exploratory line crossing in the "light-dark" test were decreased. No effect of MAO A deficiency on locomotor activity was found. No alcohol preference or difference between Tg8 and C3H in ethanol consumption in the free-choice test has been found, although an increase in alcohol tolerance has been demonstrated. Ethanol-induced (0.3 g/100 g ip) sleep latency was longer, duration of sleep was shorter and ethanol hypothermia was reduced in MAO-A-lacking mice. Comparison of effects of MAO A knockout with those of irreversible MAO A inhibitor clorgyline (5 and 10 mg/kg ip) on C3H mice showed a similar reducing effect on ethanol-induced sleep, but potentiated ethanol-induced hypothermia. Clorgyline administration provoked a tendency to decrease of exploratory activity in the nose-poking test and decreased the frequency of exploratory rearings in the light-dark test. Clorgyline (5 and 10 mg/kg) did not affect the acoustic startle response, but a dose of 5 mg/kg diminished PPI. Therefore, Tg8 mice exhibited a decreased startle response and exploratory activity and an increased tolerance to ethanol. A similar increase in tolerance to ethanol-induced sleep and a tendency to decrease exploratory behavior were displayed by clorgyline. Other effects on behavior were different, suggesting the influence of long-lasting action of MAO A knockout and the involvement of a compensatory mechanism in Tg8 mice.

Sensitivity and tolerance to ethanol in mouse lines selected for ethanol-induced hypothermia

Within-family selective breeding techniques have been used to create two lines of mice to be insensitive (HOT) and two lines to be sensitive (COLD) to the hypothermic effects of an acute 3.0-g/kg ethanol (EtOH) injection. Previous studies have found HOT mice to be relatively resistant to the development of tolerance to this effect, whereas COLD mice readily develop tolerance. The breeding program is currently in selected Generation 52, and the HOT and COLD mice differ by about 10 degrees C (average of both replicates) in their selected hypothermic response. Starting with selection Generation 20, separate lines of mice were inbred from the HOT-2 and COLD-2 selected lines, while selection continued for the original two replicate lines of HOT and COLD mice. To assess whether different dose treatments would produce differential tolerance development in the HOT and COLD selected lines, we administered different dose regimens across 5 days to HOT and COLD mice. The COLD mice developed tolerance while the HOT mice did not, regardless of total EtOH administered. In a separate study, we administered EtOH (3.0 g/kg) to mice for 3 days to assess a shorter tolerance paradigm. We also present here responses to the selection dose of 3.0-g/kg EtOH in the inbred HOT (IHOT-2) and COLD (ICOLD-2) mice tested after 41 generations of brother-sister mating. In addition, we report recent attempts to find doses of EtOH that would produce an equivalent initial hypothermic response in each of the six lines (HOT-1, COLD-1, HOT-2, COLD-2, ICOLD-2, and IHOT-2). When doses were selected to produce similar initial hypothermic sensitivity, tolerance was tested by giving three daily doses and examining the attenuation of the hypothermic response on the third day. All three COLD lines developed significant tolerance, while the HOT lines did not. The HOT and COLD mice provide a genetic model to study mechanisms mediating acute EtOH-induced hypothermia as well as tolerance development.

Acute neuroactive steroid withdrawal in withdrawal seizure-prone and withdrawal seizure-resistant mice

Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one) is an endogenously derived metabolite of progesterone, and a potent positive modulator of gamma-aminobutyric acid(A) (GABA(A)) receptors. A withdrawal syndrome, characterized by central nervous system (CNS) hyperexcitability, has been demonstrated following abrupt discontinuation of high progesterone levels in rats, which was due in part to altered levels of allopregnanolone. The purpose of the present study was to determine if a single administration of pregnanolone or allopregnanolone could produce an acute withdrawal response in mice selected for susceptibility (Withdrawal Seizure-Prone, WSP) or resistance (Withdrawal Seizure-Resistant, WSR) to ethanol withdrawal convulsions. WSP mice administered 75 mg/kg pregnanolone showed a significant increase in handling-induced convulsion (HIC) scores over a 25-h testing period. In contrast, HIC scores in WSR mice were negligible after acute administration of 25, 50, 75, or 100 mg/kg pregnanolone. WSP mice also showed a similar increase in HIC after withdrawal from 75 mg/kg allopregnanolone. This effect was evident at both the 10-h and 25-h overall withdrawal severity assessment. These results demonstrate that neuroactive steroids can elicit an acute withdrawal response similar to that of other positive modulators of GABA(A) receptors in WSP mice, supporting the notion that a common set of genes underlie acute and chronic withdrawal severity from multiple agents with depressant effects on the central nervous system.