Periods Of Normothermia Research Articles

Specific features of the record of hibernation on the incisor surface in Allocricetulus hamsters

To evaluate how the course of irregular winter hibernation is recorded in the incisor teeth of Allocricetulus hamsters, an analysis was performed of the incisor surface in seven A. curtatus and two A. eversmanni hamsters and stained section of the incisors in one A. curtatus hamster. The animals were kept in cages at natural temperature and photoperiod. Five hamsters were implanted with a temperature data logger, and another five received tetracycline injections (5–20 days before death). In addition, the incisor surface was examined in eight A. curtatus and eight A. eversmanni hamsters trapped in the field. In hibernating hamsters, the duration of alternating periods of hypothermia (torpor bouts) and normothermia (arousals) and their ratio varied irregularly and randomly within and between individuals. Increments on the incisor surface were of two types: wide and poorly defined or narrow and distinct. The increments in hamsters trapped in the field were slightly more distinct than in experimental captive animals, and those in two hamsters that failed to hibernate were similarly wide and indistinct. In hibernating hamsters, wide increments proved to correspond to long periods of normothermia, while narrow increments were formed when torpor bouts alternated with short arousals. More distinct narrow increments formed when torpor bouts followed by short (no more than 1.5-days) arousals occurred in a series rather than singly. Although the number of narrow increments was approximately similar to that of short arousals, in was impossible to localize the record of each particular hypo/normothermia episode on the incisor surface. Dentin layers in stained preparations had no definite pattern and corresponded to these episodes no better than the increments on the incisor surface. In general, the narrow and distinct increments in a given Allocricetulus hamster is evidence that the animal did hibernate, and the number of such increments indicates the approximate minimum number of torpor bouts followed by arousals. The record of winter hibernation on the incisors of Allocricetulus hamsters has a pattern similar to that in Mesocricetus brandti (Batavia et al., 2013) but significantly differs from the pattern described in M. raddei (Klevezal et al., 2012).

Antagonism of soluble guanylyl cyclase attenuates cutaneous vasodilation during whole body heat stress and local warming in humans

We hypothesized that nitric oxide activation of soluble guanylyl cyclase (sGC) participates in cutaneous vasodilation during whole body heat stress and local skin warming. We examined the effects of the sGC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), on reflex skin blood flow responses to whole body heat stress and on nonreflex responses to increased local skin temperature. Blood flow was monitored by laser-Doppler flowmetry, and blood pressure by Finapres to calculate cutaneous vascular conductance (CVC). Intradermal microdialysis was used to treat one site with 1 mM ODQ in 2% DMSO and Ringer, a second site with 2% DMSO in Ringer, and a third site received Ringer. In protocol 1, after a period of normothermia, whole body heat stress was induced. In protocol 2, local heating units warmed local skin temperature from 34 to 41°C to cause local vasodilation. In protocol 1, in normothermia, CVC did not differ among sites [ODQ, 15 ± 3% maximum CVC (CVC(max)); DMSO, 14 ± 3% CVC(max); Ringer, 17 ± 6% CVC(max); P > 0.05]. During heat stress, ODQ attenuated CVC increases (ODQ, 54 ± 4% CVC(max); DMSO, 64 ± 4% CVC(max); Ringer, 63 ± 4% CVC(max); P < 0.05, ODQ vs. DMSO or Ringer). In protocol 2, at 34°C local temperature, CVC did not differ among sites (ODQ, 17 ± 2% CVC(max); DMSO, 18 ± 4% CVC(max); Ringer, 18 ± 3% CVC(max); P > 0.05). ODQ attenuated CVC increases at 41°C local temperature (ODQ, 54 ± 5% CVC(max); DMSO, 86 ± 4% CVC(max); Ringer, 90 ± 2% CVC(max); P < 0.05 ODQ vs. DMSO or Ringer). sGC participates in neurogenic active vasodilation during heat stress and in the local response to direct skin warming.

Roles of nitric oxide synthase isoforms in cutaneous vasodilation induced by local warming of the skin and whole body heat stress in humans

Nitric oxide (NO) participates in the cutaneous vasodilation caused by increased local skin temperature (Tloc) and whole body heat stress in humans. In forearm skin, endothelial NO synthase (eNOS) participates in vasodilation due to elevated Tloc and neuronal NO synthase (nNOS) participates in vasodilation due to heat stress. To explore the relative roles and interactions of these isoforms, we examined the effects of a relatively specific eNOS inhibitor, N(omega)-amino-l-arginine (LNAA), and a specific nNOS inhibitor, N(omega)-propyl-l-arginine (NPLA), both separately and in combination, on skin blood flow (SkBF) responses to increased Tloc and heat stress in two protocols. In each protocol, SkBF was monitored by laser-Doppler flowmetry (LDF) and mean arterial pressure (MAP) by Finapres. Cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP). Intradermal microdialysis was used to treat one site with 5 mM LNAA, another with 5 mM NPLA, a third with combined 5 mM LNAA and 5 mM NPLA (Mix), and a fourth site with Ringer only. In protocol 1, Tloc was controlled with combined LDF/local heating units. Tloc was increased from 34 degrees C to 41.5 degrees C to cause local vasodilation. In protocol 2, after a period of normothermia, whole body heat stress was induced (water-perfused suits). At the end of each protocol, all sites were perfused with 58 mM nitroprusside to effect maximal vasodilation for data normalization. In protocol 1, at Tloc = 34 degrees C, CVC did not differ between sites (P > 0.05). LNAA and Mix attenuated CVC increases at Tloc = 41.5 degrees C to similar extents (P < 0.05, LNAA or Mix vs. untreated or NPLA). In protocol 2, in normothermia, CVC did not differ between sites (P > 0.05). During heat stress, NPLA and Mix attenuated CVC increases to similar extents, but no significant attenuation occurred with LNAA (P < 0.05, NPLA or Mix vs. untreated or LNAA). In forearm skin, eNOS mediates the vasodilator response to increased Tloc and nNOS mediates the vasodilator response to heat stress. The two isoforms do not appear to interact during either response.

Normothermic treatment in acute clinical encephalitis: a case report

IntroductionEncephalitis is a common infection of the brain, associated with a high risk of mortality and morbidity despite intensive supportive therapy. This report describes a patient with acute clinical meningoencephalitis who responded dramatically when her body temperature was decreased to normothermia (36 to 37°C) in combination with barbiturate therapy.Case presentationA 15-year-old, previously healthy girl presented with a 2-day history of headache and meningeal stiffness and pyrexia. Cranial magnetic resonance imaging showed high-intensity signals in the splenium of the corpus callosum on T2-weighted and diffusion-weighted images. On day 4 of admission, the level of consciousness decreased and ataxic respiration and apnea appeared. After that, fever (body temperature >40°C) developed with remarkable tachycardia. The body temperature was decreased with the use of a forced-air-cooling blanket and head cooling. The core temperature, measured in the bladder, was maintained at between 36 and 37°C for 5 days. During the period of normothermia, thiopental sodium was given continuously for 3 days. After normothermia, the level of consciousness increased without the development of fever, and ventilatory support was withdrawn.ConclusionOur experience suggests that normothermic treatment in combination with barbiturate therapy may be an effective option for the management of brain swelling associated with acute meningoencephalitis, particularly when accompanied by a persistent high fever.

Roles of eNOS and nNOS in cutaneous vasodilation induced by local warming of the skin and by whole body heat stress in humans

We hypothesized that endothelial nitric oxide synthase(eNOS) generation of NO mediates skin vasodilation due to increased local skin temperature(Tloc) and neuronal nitric oxide synthase(nNOS) mediates skin vasodilation due to whole body heat stress(HS). We examined the effects of an eNOS inhibitor, NG‐amino‐L‐arginine(LNAA) and a nNOS inhibitor, N‐omega‐propyl‐L‐arginine(NPLA) on skin blood flow(SkBF) responses to increased Tloc and HS in 2 protocols. In each protocol, 4 microdialysis probes were inserted into skin. SkBF was monitored(LDF). In each protocol, one site was treated with LNAA, another with NPLA, the third with combined LNAA and NPLA(MIX), and the fourth site was untreated. In Protocol 1, LDF/local heating probe holders were used to initially hold Tloc at 34°C and then at 41.5°C. In protocol 2, after a period of normothermia, whole body HS was induced. Results: Protocol‐1: At Tloc=34°C, SkBF did not differ between sites(p&gt;0.05). LNAA and MIX caused similar attenuation of SkBF increases at Tloc=41.5C, but NPLA caused none(p&lt; 0.05 LNAA or MIX vs untreated or NPLA). Protocol‐2: In normothermia, SkBF did not differ between sites(p&gt;0.05). In HS, NPLA and MIX caused similar attenuations of SkBF increases, but LNAA caused none(p&lt; 0.05 NPLA or MIX vs untreated or LNAA). We conclude that eNOS mediates increases in SkBF due to increased Tloc and nNOS mediates increases in SkBF in response to HS.(NIH Grant HL065599)

Cochlear temperature correlates with both temporalis muscle and rectal temperatures. Application for testing the otoprotective effect of hypothermia

Conclusions. During systemic hypothermia, the internal temperature of the rat cochlea correlates best with the temporalis muscle and rectal temperatures. These positive correlations will be used in future studies to assess the efficacy of mild and moderate hypothermia to protect hearing against the progressive loss caused by electrode insertion in a clinically relevant model of cochlear implantation trauma. Objective. To monitor the internal temperature of the cochlea during induced systemic hypothermia using a reference tissue instead of an internal cochlear temperature probe. Material and methods. The temperatures of the cochlea, brain, temporalis muscle and rectum were determined during periods of normothermia (37°C), mild (33°C) and moderate (30°C) hypothermia and slow rewarming in anesthetized adult Fisher rats. These values were compared using statistical analysis to establish the best correlations between the temperature of the cochlea and the temperature at the three other temperature measurement sites. Results. The strongest correlations with the internal temperature of the cochlea during the induction of mild-to-moderate hypothermia were obtained for the temperatures of the ipsilateral temporalis muscle and rectum.

The effects of early post-traumatic hyperthermia in female and ovariectomized rats.

Episodes of post-traumatic hyperthermia commonly occur in the head-injured patient population. Although post-traumatic hyperthermia has been shown to worsen outcome in experimental studies using male rats, the consequences of secondary hyperthermia following traumatic brain injury (TBI) have not been investigated in female animals. Thus, the purpose of this study was to examine the effects of post-traumatic hyperthermia after fluid-percussion (F-P) brain injury in intact and ovariectomized female rats. Thirty-eight female Sprague-Dawley rats were used in these experiments. Intact female rats underwent TBI followed 30 min later by a 4-h period of normothermia (37 degrees C) or brain hyperthermia (40 degrees C). Female rats that had been ovariectomized 10 days prior to TBI were also traumatized and followed by a period of normothermia or hyperthermia. At 72 h after TBI, rats were perfusion-fixed for quantitative histopathological and immunocytochemical evaluation. Following normothermic TBI, intact female rats demonstrated significantly smaller contusion volumes, decreased frequency of axonal beta-amyloid precursor protein (beta-APP) profiles, and greater numbers of NeuN-positive cortical neurons compared to traumatized ovariectomized females. Although post-traumatic hyperthermia increased contusion volume, cortical neuronal cell death and axonal damage in both intact and ovariectomized female groups, the effects of the induced hyperthermic period were more pronounced in ovariectomized animals. These findings demonstrate for the first time that post-traumatic hyperthermia worsens histopathological outcome in female rats, and that neural hormones, including estrogen and progesterone, may protect against secondary hyperthermic insults.

Body temperature and above‐ground patterns during hibernation in European hamsters (Cricetus cricetus L.)

AbstractThe purpose of this study was to determine whether hibernating European hamsters Cricetus cricetus, L., 1758 stay in their burrows all winter or if they occasionally spent time above ground. If ‘time (spent) above ground’ (TAG) occurred regularly throughout hibernation, the second objective of this work was to categorize and quantify the patterns of TAG during winter. For this purpose, 11 European hamsters were individually housed in wire mesh cages that were buried in the ground of an outdoor enclosure. Each cage was filled with soil up to ground level allowing the animals to construct their own burrows within the cages. Antennae in the bottom and top of the cage were calibrated to receive signals only when the hamsters were in their burrows or above the ground, respectively. This method enabled continuous recordings of the animal's TAG and provided ecologically meaningful results as the animals were housed in a way that closely resembled their natural habitat. About half of the hamsters stayed continuously below ground. Of these hamsters, almost all showed a dense pattern of episodes of reduced body temperature separated by only brief periods of normothermia. In contrast, the other half of the animals moved either episodically or even regularly above ground. For all of these hamsters, TAG was significantly reduced as compared to normothermic values. One hamster did not show any hibernation but did have a significantly reduced normothermic body temperature and did not leave its burrow for periods of up to 3 weeks.

THERMONEUTRALITY: AN EVOLUTIONARY ADVANTAGE AGAINST AGEING?

The immune system has been suggested as a possible cause of the ageing process. Many experimental studies have shown that immunological mechanisms and host defences against bacterial disease function better at slightly elevated (fever) temperatures than at the normal body temperature. The hypothesis proposed is that the mechanism of fever during infection and the intervening long periods of normothermia when the immune system is functioning below its optimum may have evolved as a way of controlling the immune system's contribution to degenerative processes, including ageing.