Circadian Rhythms in Bacterial Sepsis Pathology: What We Know and What We Should Know

Sepsis is a syndrome caused by a deregulated host response to infection, representing the primary cause of death from infection. In animal models, the mortality rate is strongly dependent on the time of sepsis induction, suggesting a main role of the circadian system. In patients undergoing sepsis, deregulated circadian rhythms have also been reported. Here we review data related to the timing of sepsis induction to further understand the different outcomes observed both in patients and in animal models. The magnitude of immune activation as well as the hypothermic response correlated with the time of the worst prognosis. The different outcomes seem to be dependent on the expression of the clock gene Bmal1 in the liver and in myeloid immune cells. The understanding of the role of the circadian system in sepsis pathology could be an important tool to improve patient therapies.

Neuroadaptive Changes in 5-HT1A Autoreceptor Sensitivity Following High-Dose MDMA Treatment

<p>Rationale: There is evidence that the serotonin (5-HT) deficits and related cognitive and mood impairments caused by +/-3,4- methylenedioxymethamphetamine (MDMA) may be mediated by neuroadaptations of the 5-HT1A autoreceptor. Objectives: The increase in sensitivity of the 5-HT1A autoreceptor caused by highdose, repeated MDMA treatment was assessed neurochemically, by measuring 5- HTP accumulation, and physiologically, via changes in body temperature. Methods: Experiment 1 confirmed the effects of 8-hydroxy-2-(di-npropylamino) tetralin (8-OH-DPAT) (0, 0.025, 0.05, 0.1 mg/kg s.c.) on 5- hydroxytryptophan (5-HTP) accumulation following 3-hydroxybenzylhydrazine dihydrochloride (NSD-1015) administration as a valid measure of 5-HT synthesis and hence 5-HT1A autoreceptor sensitivity in rats. Experiment 2 performed these procedures in additional animals, with half receiving MDMA (4x 10 mg/kg i.p. at 2 hour intervals) two weeks before testing. Body temperature changes due to the 8-OH-DPAT hypothermic response were tested using a rectal probe. Experiment 2b repeated the procedures in additional groups with lower doses of 8-OH-DPAT (0.0125 and 0.00625 mg/kg s.c.). Results: No significant changes in 5-HTP accumulation levels or changes in the hypothermic response to 8-OH-DPAT were found between MDMA pretreated rats and controls in Experiments 2 and 2b. Moreover, there was no substantial evidence of expected 5-HT deficits due to high-dose MDMA treatment. Conclusion: The results do not indicate an increase in sensitivity of the 5-HT1A autoreceptor, and hence the original hypothesis is not supported. However, there were a number of methodological issues, as indicated by the lack of MDMAinduced 5-HT deficits, which prevent a firm conclusion from being drawn. Future research is outlined to overcome these issues.</p>

Neuroadaptive Changes in 5-HT1A Autoreceptor Sensitivity Following High-Dose MDMA Treatment

<p>Rationale: There is evidence that the serotonin (5-HT) deficits and related cognitive and mood impairments caused by +/-3,4- methylenedioxymethamphetamine (MDMA) may be mediated by neuroadaptations of the 5-HT1A autoreceptor. Objectives: The increase in sensitivity of the 5-HT1A autoreceptor caused by highdose, repeated MDMA treatment was assessed neurochemically, by measuring 5- HTP accumulation, and physiologically, via changes in body temperature. Methods: Experiment 1 confirmed the effects of 8-hydroxy-2-(di-npropylamino) tetralin (8-OH-DPAT) (0, 0.025, 0.05, 0.1 mg/kg s.c.) on 5- hydroxytryptophan (5-HTP) accumulation following 3-hydroxybenzylhydrazine dihydrochloride (NSD-1015) administration as a valid measure of 5-HT synthesis and hence 5-HT1A autoreceptor sensitivity in rats. Experiment 2 performed these procedures in additional animals, with half receiving MDMA (4x 10 mg/kg i.p. at 2 hour intervals) two weeks before testing. Body temperature changes due to the 8-OH-DPAT hypothermic response were tested using a rectal probe. Experiment 2b repeated the procedures in additional groups with lower doses of 8-OH-DPAT (0.0125 and 0.00625 mg/kg s.c.). Results: No significant changes in 5-HTP accumulation levels or changes in the hypothermic response to 8-OH-DPAT were found between MDMA pretreated rats and controls in Experiments 2 and 2b. Moreover, there was no substantial evidence of expected 5-HT deficits due to high-dose MDMA treatment. Conclusion: The results do not indicate an increase in sensitivity of the 5-HT1A autoreceptor, and hence the original hypothesis is not supported. However, there were a number of methodological issues, as indicated by the lack of MDMAinduced 5-HT deficits, which prevent a firm conclusion from being drawn. Future research is outlined to overcome these issues.</p>

The Hypothermic Effect of Hydrogen Sulfide Is Mediated by the Transient Receptor Potential Ankyrin-1 Channel in Mice

Hydrogen sulfide (H2S) has been shown in previous studies to cause hypothermia and hypometabolism in mice, and its thermoregulatory effects were subsequently investigated. However, the molecular target through which H2S triggers its effects on deep body temperature has remained unknown. We investigated the thermoregulatory response to fast-(Na2S) and slow-releasing (GYY4137) H2S donors in C57BL/6 mice, and then tested whether their effects depend on the transient receptor potential ankyrin-1 (TRPA1) channel in Trpa1 knockout (Trpa1−/−) and wild-type (Trpa1+/+) mice. Intracerebroventricular administration of Na2S (0.5–1 mg/kg) caused hypothermia in C57BL/6 mice, which was mediated by cutaneous vasodilation and decreased thermogenesis. In contrast, intraperitoneal administration of Na2S (5 mg/kg) did not cause any thermoregulatory effect. Central administration of GYY4137 (3 mg/kg) also caused hypothermia and hypometabolism. The hypothermic response to both H2S donors was significantly (p < 0.001) attenuated in Trpa1−/− mice compared to their Trpa1+/+ littermates. Trpa1 mRNA transcripts could be detected with RNAscope in hypothalamic and other brain neurons within the autonomic thermoeffector pathways. In conclusion, slow- and fast-releasing H2S donors induce hypothermia through hypometabolism and cutaneous vasodilation in mice that is mediated by TRPA1 channels located in the brain, presumably in hypothalamic neurons within the autonomic thermoeffector pathways.

Physiological basis underlying antidepressant-induced activation of TrkB receptors

We show that both pharmacological and non-pharmacological treatments of depression activate TrkB receptors - a well-established target of antidepressants - by inducing a physiological response coupled to sedation. Several rapid-acting antidepressants trigger TrkB signaling by evoking a state associated with electroencephalographic slow-wave activity, behavioral immobility, reduced cerebral glucose utilization, and lowered body temperature. Remarkably, antidepressant-induced TrkB signaling was not compromised in animals exhibiting reduced activity-dependent release of BDNF but was diminished by maintaining animals in warm ambient temperature. Most importantly, prevention of the hypothermic response attenuated the behavioral effects produced by rapid-acting antidepressant nitrous oxide. Our results suggest that the phenomenon underlying TrkB transactivation - changes in energy expenditure and thermoregulation - is essential, but not sufficient, for antidepressant responses. Indeed, regardless of differential clinical and pharmacodynamic properties, all drugs that disrupt energy metabolism and induce hypothermia activated TrkB. This study challenges pharmacology-centric hypotheses regarding antidepressant effects and highlight the role of complex changes in bioenergetics and thermoregulation.

Enhancement of Transgene Expression by Mild Hypothermia Is Promoter Dependent in HEK293 Cells

Mild hypothermia has been widely used to enhance transgene expression and improve the cellular productivity of mammalian cells. This study investigated mild hypothermia-responsive exogenous promoters in human embryonic kidney 293 (HEK293) cells using site-specific integration of various promoter sequences, including CMV, EF1α, SV40, and TK promoters, into the well-known genomic safe harbor site, AAVS1. EGFP expression driven by the CMV promoter increased up to 1.5-fold at 32 °C versus 37 °C under stable expression, while others showed no hypothermic response. Integration of short CMV variants revealed that the CMV-enhancer region is responsible for the positive hypothermic response. CMV-enhancer-specific transcription factors (TFs) were then predicted through in silico analysis and RNA-sequencing analysis, resulting in the selection of one TF, NKX3-1. At 37 °C, overexpression of NKX3-1 in recombinant HEK293 cells expressing EGFP through the CMV promoter (CMV-EGFP) increased EGFP expression up to 1.6-fold, compared with that in CMV-EGFP, the expression level of which was comparable to that of CMV-EGFP at 32 °C. Taken together, this work demonstrates promoter-dependent hypothermia responses in HEK293 cells and emphasizes interactions between endogenous TFs and promoter sequences.

Explication of CB1 receptor contributions to the hypothermic effects of Δ9-tetrahydrocannabinol (THC) when delivered by vapor inhalation or parenteral injection in rats

The use of Δ9-tetrahydrocannabinol (THC) by inhalation using e-cigarette technology grows increasingly popular for medical and recreational purposes. This has led to development of e-cigarette based techniques to study the delivery of THC by inhalation in laboratory rodents. Inhaled THC reliably produces hypothermic and antinociceptive effects in rats, similar to effects of parenteral injection of THC. This study was conducted to determine the extent to which the hypothermic response depends on interactions with the CB1 receptor, using pharmacological antagonist (SR141716, AM-251) approaches. Groups of rats were implanted with radiotelemetry devices capable of reporting activity and body temperature, which were assessed after THC inhalation or injection. SR141716 (4 mg/kg, i.p.) blocked or attenuated antinociceptive effects of acute THC inhalation in male and female rats. SR141716 was unable to block the initial hypothermia caused by THC inhalation, but temperature was restored to normal more quickly. Alterations in antagonist pre-treatment time, dose and the use of a rat strain with less sensitivity to THC-induced hypothermia did not change this pattern. Pre-treatment with SR141716 (4 mg/kg, i.p.) blocked hypothermia induced by i.v. THC and reversed hypothermia when administered 45 or 90 minutes after THC (i.p.). SR141716 and AM-251 (4 mg/kg, i.p.) sped recovery from, but did not block, hypothermia caused by vapor THC in female rats made tolerant by prior repeated THC vapor inhalation. The CB2 antagonist AM-630, had no effect. These results suggest that hypothermia consequent to THC inhalation is induced by other mechanisms in addition to CB1 receptor activation.