Factors affecting angiotensin II-induced hypothermia in rats

Systemic administration of angiotensin II (AII) to the rat has previously been shown to induce a dose-dependent, hypothermic response manifested by a fall in colonic temperature (CT), a decrease in heat production and an increase in tail skin temperature (TST). The factors mediating AII-induced hypothermia and their site of action were the subjects of the present investigation. To this end, intracerebroventricular administration of 1 microgram of AII induced a 0.4 degrees C reduction in CT and a 2.4 degrees C increase in TST. In contrast, SC administration of 200 micrograms angiotensin III/kg induced a slight increase in CT but had no affect on TST. Pretreatment with the AII-receptor antagonist, saralasin, at either 1 or 10 micrograms/kg, SC did not affect either the fall in CT or the increase in TST induced by administration of 200 micrograms AII/kg, SC. However, the administration of 100 micrograms saralasin/kg, SC attenuated both the fall in CT and the increase in TST induced by either 100 or 200 micrograms AII/kg. Since both the presynaptic alpha adrenoceptor agonist, clonidine, and the opioid antagonist, naloxone, modulate the pressor and dipsogenic responses to AII, their effects on AII-induced hypothermia were tested. Both clonidine (25 micrograms/kg, SC) and naloxone (1 mg/kg, IP) enhanced the fall in CT. Clonidine lengthened the duration of the increase in TST while naloxone had no effect. Pretreatment with the presynaptic adrenoceptor antagonist, yohimbine (300 micrograms/kg, SC), did not alter the hypothermic response to administration of AII. To determine whether vasodilation of the tail of the rat was mediated by AII-induced prostaglandin release, indomethacin (4 and 6 mg/kg) was administered.(ABSTRACT TRUNCATED AT 250 WORDS)     

冬眠哺乳动物心血管机能特点

冬眠动物心血管系统适应于冬眠和激醒过程的特殊生理条件形成了其显著的机能稳定性。我们在总结已有研究的基础提出了冬眠动物心血管系统具有耐低体温,抗主律失常,耐缺氧三大机能特点。这些特点不仅是冬眠动物五非冬眠动物的区别,也是冬眠动物在冬眠季机能强化的方面。     

Hypothermia elicited by the intracerebral microinjection of neurotensin

Changes in rectal temperature were measured after the intracerebral microinjection of neurotensin (2.5 μg/0.5 μl) at 135 sites in the rat. At 63 of the 135 microinjection sites, the tridecapeptide produced a rapid onset of hypothermia ranging in magnitude from 0.8 to 2.3°C below the baseline rectal temperature. The drop in rectal temperature persisted for 2–4 hours following the microinjection. The greatest concentrations of neurotensin-sensitive sites were found in the medial preoptic region of the hypothalamus and in the periaqueductal gray area, both of which contain relatively large amounts of endogenous neurotensin. Other active sites were found in the ventral thalamus, the dorsomedial hypothalamus, and in the diagonal band of Broca. At no injection site did neurotensin evoke an increase in rectal temperature. These data support the proposition that neurotensin may act endogenously to mediate heat-loss mechanisms in the rat. The data provide further evidence indicating a potent neuromodulatory role for neurotensin.     

The influence of hypothermia on the restoration of neural activity of brain slices from hibernating ground squirrels

1. 1. Neural activity was recorded in hippocampal slices from deep hibernating Yakut ground squirrels and in hippocampal and septal slices from non-hibernating animals.

2. 2. Slices were placed immediately after preparation in hypothermic conditions (3–4°C). Their activity was tested under standard conditions at 31°C in the incubation chamber. Some of the prepared slices were tested after maintenance in hypothermia for 2 or 24 h.

3. 3. In the hippocampal slices of hibernating ground squirrels, neural activity was present, irrespective of the period in hypothermia.

4. 4. Slices from guinea-pigs and hamsters did not possess neural activity after either 2 or 24 h of hypothermic treatment.

     

Cryopreservation of rat hippocampal slices by vitrification

Although much interest has attended the cryopreservation of immature neurons for subsequent therapeutic intracerebral transplantation, there are no reports on the cryopreservation of organized adult cerebral tissue slices of potential interest for pharmaceutical drug development. We report here the first experiments on cryopreservation of mature rat transverse hippocampal slices. Freezing at 1.2 degrees C/min to -20 degrees C or below using 10 or 30% v/v glycerol or 20% v/v dimethyl sulfoxide yielded extremely poor results. Hippocampal slices were also rapidly inactivated by simple exposure to a temperature of 0 degree C in artificial cerebrospinal fluid (aCSF). This effect was mitigated somewhat by 0.8 mM vitamin C, the use of a more "intracellular" version of aCSF having reduced sodium and calcium levels and higher potassium levels, and the presence of a 25% w/v mixture of dimethyl sulfoxide, formamide, and ethylene glycol ("V(EG) solutes"; Cryobiology 48, pp. 22-35, 2004). It was not mitigated by glycerol, aspirin, indomethacin, or mannitol addition to aCSF. When RPS-2 (Cryobiology 21, pp. 260-273, 1984) was used as a carrier solution for up to 50% w/v V(EG) solutes, 0 degree C was more protective than 10 degrees C. Raising V(EG) concentration to 53% w/v allowed slice vitrification without injury from vitrification and rewarming per se, but was much more damaging than exposure to 50% w/v V(EG). This problem was overcome by using the analogous 61% w/v VM3 vitrification solution (Cryobiology 48, pp. 157-178, 2004) containing polyvinylpyrrolidone and two extracellular "ice blockers." With VM3, it was possible to attain a tissue K(+)/Na(+) ratio after vitrification ranging from 91 to 108% of that obtained with untreated control slices. Microscopic examination showed severe damage in frozen-thawed slices, but generally good to excellent ultrastructural and histological preservation after vitrification. Our results provide the first demonstration that both the viability and the structure of mature organized, complex neural networks can be well preserved by vitrification. These results may assist neuropsychiatric drug evaluation and development and the transplantation of integrated brain regions to correct brain disease or injury.     

Pathology of Tnf-deficient mice infected with Plasmodium chabaudi adami 408XZ

Tumor necrosis factor alpha (Tnf) plays a pleiotropic role in murine malaria. Some investigations have correlated Tnf with hypothermia, hyperlactatemia, hypoglycemia, and a suppression of the erythropoietic response, although others have not. In this study, we have evaluated parasitemia, survival rate and several pathological features in C57BL/6JTnf^−/− and C57BL/6JTnf^+/+ mice after infection with Plasmodium chabaudi adami 408XZ. Compared to the C57BL/6JTnf^+/+ mice, C57BL/6JTnf^−/− mice showed increased parasitemia and decreased survival rate, whereas blood glucose, blood lactate and body weight were not significantly different. However, C57BL/6JTnf^−/− mice suffered significantly more from severe anemia and hypothermia than C57BL/6JTnf^+/+ mice. These results suggest that Tnf is an important mediator of parasite control, but not of anemia development. We hypothesize that the high mortality observed in the Tnf knock-out mice is due to increased anemia and pathology as a direct result of increased levels of parasitemia.     

Role of STIM1 in Regulation of Store-Operated Ca<Superscript>2+</Superscript> Influx in Pheochromocytoma Cells

Changes in the local environment such as pH (acidosis/alkalosis), temperature (hypothermia/hyperthermia), and agonist (glutamate) can adversely affect neuronal function, and are important factors in clinical situations such as anesthesia and intensive care. Regulation of intracellular Ca²⁺ ([Ca²⁺]_i) is key to neuronal function. Stromal interaction molecule (STIM1) has been recently recognized to trigger store-operated Ca²⁺ entry (SOCE), an important component of [Ca²⁺]_i regulation. Using differentiated, fura-2 loaded rat pheochromocytoma (PC12) cells transfected with small interference RNA for STIM1 (or vehicle), we examined the role of STIM1 in SOCE sensitivity to temperature, pH, and glutamate. SOCE was triggered following endoplasmic reticulum depletion. Cells were washed and exposed to altered pH (6.0–8.0), altered temperature (34–40°C), or to glutamate. In non-transfected cells, SOCE was inhibited by acidosis or hypothermia, but increased with alkalosis and hyperthermia. Increasing glutamate concentrations progressively stimulated SOCE. STIM1 siRNA decreased SOCE at normal temperature and pH, and substantially decreased sensitivity to acidosis and hypothermia, eliminating the concentration-dependence to glutamate. Sensitivity of SOCE to these environmental parameters was less altered by decreased extracellular Ca²⁺ alone (with STIM1 intact). We conclude that STIM1 mediates exquisite susceptibility of SOCE to pH, temperature, and glutamate: factors that can adversely affect neuronal function under pathological conditions.     

Loss of heart phospholipid arachidonic acid without phospholipid peroxidation in anaesthetized rats rewarmed after prolonged deep hypothermia

Hypothermia–rewarming of the heart results in contractile dysfunction under in vitro as well as in vivo conditions. Increase in reactive oxygen species (ROS), lipid peroxidation and calcium overload are proposed mechanisms. In the first protocol of this study, the effect of putative phospholipase and calcium channel modulator mepacrine during deep hypothermia (4 h 14 °C) plus rewarming was tested in an isolated perfused rat heart model previously reported not to involve increase in lipid peroxides. Contractile function was measured under isovolumetric conditions using an intra-ventricular balloon connected to a transducer and recording system. Mepacrine completely reversed hypothermia–rewarming induced contractile failure in this model (LV dP/dt_max: 3236 ± 517 vs. 1058 ± 185 mm Hg/s in untreated hearts). In the second part of the study, lipid peroxidation of the heart was examined in vivo in anesthetized rats subjected to 4 h of deep hypothermia followed by rewarming. In this model recovery of heart function judged by cardiac output is decreased whereas blood pressure and heart rate recover fully. Peroxy conjugated diene isomers of unsaturated fatty acids were measured in heart phospholipids. The composition of the non-esterified fatty acids and the phospholipid fatty acid pool was examined in order to reveal signs of membrane remodeling. The results demonstrated no significant changes in phospholipid peroxidation after rewarming (91.07 ± 5.23 vs. 88.63 ± 7.73 nmol/g dry wt. in control). There was significant relative reduction in the content of arachidonic acid in the phospholipid fraction (29.55 ± 1.65 vs. 24.76 ± 1.48%). There was marked decrease in non-esterified fatty acids in myocardial tissue (1992 ± 291 vs. 1069 ± 189 nmol/g dry wt.), but a significant relative increase in arachidonic acid (20:4) in this fraction (3.46 ± 0.42 vs. 4.99 ± 0.30%). In conclusion, rewarming from deep hypothermia is not associated with increased phospholipid peroxidation. There is, however, a significant remodeling of the phospholipid fraction of myocardial lipids in vivo probably as a result of receptor or calcium stimulated phospholipase activity. Calcium or calcium stimulated phospholipase activity could contribute to posthypothermic contractile dysfunction.     

Seasonality in daily body mass variation in a hoarding boreal passerine

We studied the body mass variation from autumn to winter, in a free-living population of willow tits (Parus montanus), a food-hoarding passerine living year-round in boreal forests. Our aim was to find out whether this population exhibits winter fattening as part of the annual body mass cycle. True winter fattening is considered to be a strategic response to winter conditions. The strategy includes an increase in both the morning mass and the daily mass increase, as winter approaches. A multivariate approach was used to find which predictors (year, date, age, sex, body size, temperature and snow depth) explained the mass variation in birds measured twice per day. Morning mass variation was explained by sex, age, wing length and snow depth. Independently, date explained morning mass variation only in adult males. None of the predictors explained the variation observed in daily mass increase in any age or sex class. Therefore, we failed to detect winter fattening in our study population of willow tits. Response to increasing night length is not due to higher absolute intake, but to higher energy acquisition rate and decreased night-time energy consumption. The results suggest that willow tits at high latitudes manage increasing energy demands on a short-term basis and respond flexibly to changing conditions by adjusting foraging efficiency and especially night-time energy expenditure.