Absence of selective brain cooling in pyrogen-induced fever in rabbits

In 9 rabbits the effect of intravenous administration of E. coli pyrogen 0.5 microgram/kg on the reaction of selective brain cooling was studied at ambient temperatures of 20, 30 and 40 degrees C. In the freely moving animals the temperatures of the brain, carotid artery and nuchal muscles were measured with an accuracy down to 0.05 degree C and the temperatures of the ear pinna and nasal mucosa were measured accurate to 0.5 degree C. The respiratory rate was measured as well. It was found that the spontaneous febrile reaction without the component of passive hyperthermia failed to cause selective brain cooling, even if its temperature reached higher values than in case of brain temperature rise caused only by high ambient temperature. On the other hand, when the high ambient temperature caused thermal panting, pyrogen administration at an ambient temperature of 30 degrees C could reduce panting, while at an ambient temperature of 40 degrees C intense panting initiated prior to the appearance of the febrile reaction and was associated with the fever and outlasted it.     

Thermogenic responses to body cooling during fever induced by Staphylococcus aureus cell walls in rabbits

Hypothalamic temperature (T _hypo) and metabolic heat production (M) were measured in seven conscious rabbits injected intravenously with either saline or with Staphylococcus aureus, (8 · 10⁷ cell walls · kg⁻¹) while being subjected to a 3-h period of ramp-like total body cooling using a chronically implanted intravascular heat exchanger. In pyrogen-injected animals cooling started (1) at the time of injection or (2) 70 min after injection. In (1) the fall in T _hypo induced by heat extraction was similar (1.0 °C) in afebrile and febrile animals. In (2) there was a transient increase in T _hypo of about 0.5 °C at a time corresponding to the start of fever resulting in a significantly smaller fall in T _hypo at the end of the 3-h cooling period (0.5 °C vs 0.9 °C, P < 0.05, n = 5). At this time in both (1) and (2) M was lower than theoretically expected from the increase in shivering threshold during fever. However, most of this effect can be explained when available data showing a decrease in thermosensitivity during S. aureus-induced fever are taken into account. After cessation of cooling in both groups of febrile animals T _hypo rose to about 1 °C higher than the precooling level, which is comparable to the fever level in a separate series of experiments with S. aureus injection without cooling (1.2 °C). Accepted: 23 September 1997     

Amphotericin B fever in rabbits

The slow intravenous infusion of amphotericin B (amB) induced a moderate, partially dose-dependent fever in male adult rabbits, whereas the iv bolus injection of the drug was less pyrogenic and only at higher doses. Higher, more sustained fevers occured with doses of 2.5 and 5.0 mg of amB. The threshold pyrogenic dose of amB in the rabbits tested approached 0.16 mg per Kg (ΔT greater than 0.4°C). Endotoxin-tolerant rabbits had a lower increase in rectal temperature when challenged with amB. No fever occured in mice treated with amB.     

The effect of NO-synthase inhibition on the blood oxygen transport function during fever in rabbits

I.v. administration of NG-nitro-L-arginine attenuated a fever response in rabbit. Preliminary administration of L-arginine for prevention of the NO-synthase inhibition suppressed the blood oxygen transport function and augmented the fever response.     

Analysis of shivering in nonperiheral cooling during pyrogen fever

The shivering reaction to nonperipheral cooling was monitored in goats. No difference in reaction between normothermic and fevered animals was found. It is concluded that fever is not caused by a change of gain in thermosensors.     

Limbico-reticular relations during formation of various motivation responses in rabbits subjected to ethanol administration

Chronic experiments on rabbits with electrodes implanted into different limbic-midbrain structures were made to study the effects of a single intravenous injection of ethanol (0.5 g/kg) on the background EEG during formation of food motivation and avoidance behavior from the criterion of the power of the main EEG rhythms. Intravenous injection of ethanol resulted in an increase in the power of beta-, alpha- and theta-rhythms in the frontal cortex, and in that of alpha- and theta-rhythms in the occipital area of the neocortex. New patterns of the powers of the main EEG rhythms recorded in animals exposed to ethanol during electric stimulation of the lateral and ventromedial hypothalamus, evoking food motivation and avoidance behavior, as well as during electrical stimulation of the dorsal hippocamp and mesencephalic reticular formation that correlate with changes in the functions of the study limbic-mesencephalic structures attest to profound ethanol-induced abnormalities of the central mechanisms of food motivation and avoidance behavior.     

Transiently enhanced LPS-induced fever following hyperthermic stress in rabbits

Hyperthermia has been shown to induce an enhanced febrile response to the bacterial-derived endotoxin lipopolysaccharide (LPS). The aim of the present study was to test the hypothesis that the enhanced LPS-induced fever seen in heat stressed (HS) animals is caused by leakage of intestinal bacterial LPS into the circulation. Male rabbits were rendered transiently hyperthermic (a maximum rectal temperature of 43°C) and divided into three groups. They were then allowed to recover in a room at 24°C for 1, 2 or 3 days post-HS. One day after injection with LPS, the post-HS rabbits exhibited significantly higher fevers than the controls, though this was not seen in rabbits at either 2 or 3 days post-HS. The plasma levels of endogenous LPS were significantly increased during the HS as compared to those seen in normothermic rabbits prior to HS. LPS fevers were not induced in these animals. One day post-HS, rabbits that had been pretreated with oral antibiotics exhibited significantly attenuated LPS levels. When challenged with human recombinant interleukin-1 instead of LPS, the 1-day post-HS rabbits did not respond with enhanced fevers. The plasma levels of TNF increased similarly during LPS-induced fevers in both the control and 1-day post-HS rabbits, while the plasma levels of corticosterone and the osmolality of the 1-day post-HS rabbits showed no significant differences to those seen prior to the HS. These results suggest that the enhanced fever in the 1-day post-HS rabbits is LPS specific, and may be caused by increased leakage of intestinal endotoxin into blood circulation.     

地塞米松对家兔乙二醇双(2-氨基乙醚)四乙酸性发热的解热作用

本文用脑室灌注和Fura-2 测定细胞内游离钙技术观察了地塞米松 (dexamethasone, DEX) 对家兔乙二醇双(2-氨基乙醚)四乙酸性发热效应和下丘脑细胞内游离钙浓度([Ca2+]I)的影响, 借此深入探讨地塞米松解热作用的中枢机制.结果发现: 脑室灌注乙二醇双(2-氨基乙醚)四乙酸(0.6 nmol)引起家兔结肠温度明显升高, 静脉注射地塞米松(5 mg/kg)显著抑制家兔乙二醇双(2-氨基乙醚)四乙酸性发热, 地塞米松(60～120 μmol/L)并不影响下丘脑细胞内[Ca2+]I, 而事先脑室灌注抑制基因转录的放线菌素D(3 nmol)则完全取消了地塞米松对乙二醇双(2-氨基乙醚)四乙酸性发热的解热作用.这些结果提示: 地塞米松显著抑制家兔乙二醇双(2-氨基乙醚)四乙酸性发热, 其机制与地塞米松激活脑内某些基因的表达有关, 而与下丘脑神经细胞跨膜钙离子流无关.