Febrile response to infection in the American alligator (Alligator mississippiensis)

Temperature probes were inserted into the stomachs of juvenile American alligators (Alligator mississippiensis) maintained outdoors at ambient fluctuating temperatures. Internal body temperatures (T_b) were measured every 15 min for two days, and then the alligators were injected with bacterial lipopolysaccharide (LPS), pyrogen-free saline, or left untreated. Alligators injected intraperitoneally with LPS exhibited maximum T_bs 2.6 ± 1.1 °C and 3.5 ± 1.2 °C higher than untreated control animals on days one and two after treatment, respectively. T_bs for these animals fell to within control ranges by day three postinjection. Similarly, mean preferred body temperatures (MPBTs) were significantly higher for LPS-injected alligators on days one (4.2 ± 1.8 °C) and two (3.5 ± 1.6 °C) after treatment. Intraperitoneal injection of heat-killed Aeromonas hydrophila, a gram-negative bacterium known to infect crocodilians, resulted in a fever while injection of Staphylococcus aureus (gram positive) did not elicit a febrile response. Injection of LPS in alligators maintained indoors in a constant temperature environment resulted in no increase in internal T_b. These results indicate that alligators did not exhibit a febrile response in the absence of a thermal gradient, and suggest that febrile responses observed are probably behavioral in nature.     

Periodic arousal from hibernation is necessary for initiation of immune responses in ground squirrels

Golden-mantled ground squirrels (Spermophilus lateralis) undergo seasonal hibernation during which core body temperature (T(b)) values are maintained 1-2 degrees C above ambient temperature. Hibernation is not continuous. Squirrels arouse at approximately 7-day intervals, during which T(b) increases to 37 degrees C for approximately 16 h; thereafter, they return to hibernation and sustain low T(b)s until the next arousal. Over the course of the hibernation season, arousals consume 60-80% of a squirrel's winter energy budget, but their functional significance is unknown and disputed. Host-defense mechanisms appear to be downregulated during the hibernation season and preclude normal immune responses. These experiments assessed immune function during hibernation and subsequent periodic arousals. The acute-phase response to bacterial lipopolysaccharide (LPS) was arrested during hibernation and fully restored on arousal to normothermia. LPS injection (ip) resulted in a 1-1.5 degrees C fever in normothermic animals that was sustained for > 8 h. LPS was without effect in hibernating squirrels, neither inducing fever nor provoking arousal, but a fever did develop several days later, when squirrels next aroused from hibernation; the duration of this arousal was increased sixfold above baseline values. Intracerebroventricular infusions of prostaglandin E(2) provoked arousal from hibernation and induced fever, suggesting that neural signaling pathways that mediate febrile responses are functional during hibernation. Periodic arousals may activate a dormant immune system, which can then combat pathogens that may have been introduced immediately before or during hibernation.     

Central CO-heme oxygenase pathway raises body temperature by a prostaglandin-independent way.

Recently, the carbon monoxide (CO)-heme oxygenase pathway has been shown to play an important role in fever generation by acting on the central nervous system, but the mechanisms involved have not been assessed. Thus the present study was designed to determine whether prostagandins participate in the rise in body temperature (T(b)) observed after induction of the CO-heme oxygenase pathway in the central nervous system. Intracerebroventricular (ICV) injection of heme-lysinate (152 nmol/4 microl), which is known to induce the CO-heme oxygenase pathway, caused an increase in T(b) [thermal index (TI) = 5.3 +/- 0.5 degrees C. h], which was attenuated by ICV administration of the heme oxygenase inhibitor ZnDPBG (200 nmol/4 microl; TI = 2.5 +/- 1.7 degrees C. h; P < 0.05). No change in T(b) was observed after intraperitoneal injection of the cyclooxygenase inhibitor indomethacin (5 mg/kg), whereas indomethacin at the same dose attenuated the fever induced by ICV administration of lipopolysaccharide (LPS) (10 ng/2 microl) (vehicle/LPS: TI = 4.5 +/- 0.5 degrees C. h; indomethacin/LPS: TI = 1.7 +/- 1.0 degrees C. h; P < 0.05). Interestingly, indomethacin did not affect the rise in T(b) induced by heme-lysinate (152 nmol/4 microl) ICV injection (vehicle/heme: TI = 4.5 +/- 1.4 degrees C. h; indomethacin/heme: TI = 4.2 +/- 1.0 degrees C. h). Finally, PGE(2) (200 ng/2 microl) injected ICV evoked a rise in T(b) that lasted 1.5 h. The heme oxygenase inhibitor ZnDPBG (200 nmol/4 microl) failed to alter PGE(2)-induced fever. Taken together, these results indicate that the central CO-heme oxygenase pathway increases T(b) independently of prostaglandins.     

The spleen modulates the febrile response of guinea pigs to LPS

The febrile responses of splenectomized (Splex) or sham-operated (Sham) guinea pigs challenged intravenously or intraperitoneally with lipopolysaccharide (LPS) 7 and 30 days after surgery were evaluated. FITC-LPS uptake by Kupffer cells (KC) was additionally assessed 15, 30, and 60 min after injection. LPS at 0.05 microg/kg iv did not evoke fever in Sham animals but caused a 1.2 degrees C core temperature (T(c)) rise in the Splex animals. LPS at 2 microg/kg iv induced a 1.8 degrees C greater T(c) rise of the Splex animals than of their controls. LPS at 2 and 8 microg/kg ip 7 days postsurgery induced 1.4 and 1.8 degrees C higher fevers, respectively, in the Splex than Sham animals. LPS at 2 and 8 microg/kg ip 30 days postsurgery also increased the febrile responses of the asplenic animals by 1.6 and 1.8 degrees C, respectively. FITC-LPS at 7 days was detected in the controls within KC 15 min after its administration; the label density was reduced at 30 min and almost 0 at 60 min. In the Splex group, in contrast, the labeling was significantly denser and remained unchanged through all three time points; this effect was still present 30 days after surgery. Similar results were obtained at 60 min after FITC-LPS intraperitoneal injection. Gadolinium chloride pretreatment (-3 days) of the Splex group significantly reduced both their febrile responses to LPS (8 microg/kg ip) and their KC uptake of FITC-LPS 7 days postsurgery. Thus splenectomy increases the magnitude of the febrile response of guinea pigs and the uptake of systemically administered LPS.     

Acetaminophen: antipyretic or hypothermic in mice? In either case, PGHS-1b (COX-3) is irrelevant

Acetaminophen (AC) reduces the core temperatures (T(c)) of febrile and non-febrile mice alike. Evidence has been adduced that the selectively AC-sensitive PGHS isoform, PGHS-1b (COX-3), mediates these effects. PGHS-1b, however, has no catalytic potency in mice. To resolve this contradiction, AC was injected intravenously (i.v.) into conscious PGHS-1 gene-sufficient (wild-type (WT)) and -deficient (PGHS-1(-/-)) mice 60 min before or after pyrogen-free saline (PFS) or E. coli LPS (10 microg/kg) i.v. T(c) was monitored continuously; brain and plasma PGE(2) levels were determined hourly. AC at <160 mg/kg did not affect T(c) when given before PFS or LPS; at 160 mg/kg, it caused a approximately 2.5 degrees C T(c) fall in 60 min. LPS given after AC (all doses) induced a approximately 1 degrees C fever, not different from that in AC-untreated mice. But this rise was insufficient to overcome the hypothermia of the 160 mg/kg-treated mice; their T(c) culminated 1 degrees C below baseline. LPS given before AC similarly elevated T(c) approximately 1 degrees C. This rise was reduced to baseline in 30 min by 80 mg AC/kg; T(c) rebounded to its febrile level over the next 30 min. At 160 mg/kg, AC reduced T(c) to 4 degrees C below baseline in 60 min, where it remained until the end of the experiment. WT and PGHS-1(-/-) mice responded similarly to all the treatments. The basal brain and plasma PGE(2) levels of PFS mice and the elevated plasma levels of LPS mice were unchanged by AC at 160 mg/kg; but the latter's brain levels were reduced at 1h, then recovered. Thus, AC could exert an anti-PGHS-2 effect when this enzyme is upregulated in the brain of febrile mice. The hypothermia it induces in non-febrile mice, therefore, is due to another mechanism. PGHS-1b is not involved in either case.     

Fever and behavioral thermoregulation in young and old rats

At standard laboratory ambient temperatures (T(a)) of 20-24 degrees C, peripheral injections of lipopolysaccharide (LPS) reliably produce fever in young rats. In contrast, old rats may show a blunted fever, no fever, or even hypothermia after LPS. In the present study we hypothesized that old rats might use behavioral thermoregulation to help them develop a fever. Young and old rats were implanted with temperature transmitters. At least 1 wk postoperatively they were placed in a thermally graded alleyway (T(a) 10-40 degrees C). On the third and sixth day they were taken out of the gradient, placed at an T(a) of 23 degrees C, injected intraperitoneally with LPS or saline, and left at 23 degrees C for 3 h. At the end of that time, all young rats had become febrile, whereas the old rats had not. When the rats were replaced in the thermal gradient, the young animals continued to develop a fever that was similar to fever in young rats left at 23 degrees C. The old animals chose significantly warmer positions in the thermal gradient than did the young animals and only then became febrile. Although there was a tendency for the young rats to prefer higher T(a) after LPS than after saline, these differences were not significant. However, the differences in the old rats were significant. These results suggest that the LPS had increased the thermal set point in the old rats, but they could develop febrile responses only at the warm T(a) they selected.     

Suppression of endotoxin-induced fever in near-term pregnant rats is mediated by brain nitric oxide

Over the last three decades, experiments in several mammalian species have shown that the febrile response to bacterial endotoxin is attenuated late in pregnancy. More recent evidence has established that the expression of nitric oxide synthase (NOS) enzymes is increased in the brain late in pregnancy. The current study investigated the possible role of brain nitric oxide in mediating the phenomenon of fever suppression. Core body temperature (Tb) of near-term pregnant rats (day 19 and 20) was measured following inhibition of brain NOS and intraperitoneal injection of LPS (50 microg/kg); they were compared with both day 15 pregnant and virgin animals. Intracerebroventricular injection with an inhibitor of NOS, NG-monomethyl-L-arginine citrate (L-NMMA; 280 microg), in near-term pregnant rats restored the febrile response to LPS. As expected, near-term dams that received intracerebroventricular vehicle + IP LPS did not increase Tb, in contrast to the 1.0 +/- 0.2 degrees C rise in Tb in dams treated with ICV L-NMMA + IP LPS (P < 0.01). In virgin females and day 15 pregnant controls receiving this treatment, the increases in Tb were 1.5 +/- 0.3 degrees C and 1.6 +/- 0.4 degrees C, respectively. Thus, blockade of brain NOS restored the febrile response to LPS in near-term dams; at 5 h postinjection, Tb was 60-70% of that observed in virgins and day 15 pregnant animals. Intracerebroventricular L-NMMA alone did not induce a significant change in Tb in any group. These results suggest that the mechanism underlying the suppression of the febrile response in near-term pregnancy is mediated by nitric oxide signaling in the brain.     

Endogenous opioids: role in prostaglandin-dependent and -independent fever

This study evaluated the participation of mu-opioid-receptor activation in body temperature (T(b)) during normal and febrile conditions (including activation of heat conservation mechanisms) and in different pathways of LPS-induced fever. The intracerebroventricular treatment of male Wistar rats with the selective opioid mu-receptor-antagonist cyclic d-Phe-Cys-Try-d-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP; 0.1-1.0 microg) reduced fever induced by LPS (5.0 microg/kg) but did not change T(b) at ambient temperatures of either 20 degrees C or 28 degrees C. The subcutaneous, intracerebroventricular, and intrahypothalamic injection of morphine (1.0-10.0 mg/kg, 3.0-30.0 microg, and 1-100 ng, respectively) produced a dose-dependent increase in T(b). Intracerebroventricular morphine also produced a peripheral vasoconstriction. Both effects were abolished by CTAP. CTAP (1.0 microg icv) reduced the fever induced by intracerebroventricular administration of TNF-alpha (250 ng), IL-6 (300 ng), CRF (2.5 microg), endothelin-1 (1.0 pmol), and macrophage inflammatory protein (500 pg) and the first phase of the fever induced by PGF(2alpha) (500.0 ng) but not the fever induced by IL-1beta (3.12 ng) or PGE(2) (125.0 ng) or the second phase of the fever induced by PGF(2alpha). Morphine-induced fever was not modified by the cyclooxygenase (COX) inhibitor indomethacin (2.0 mg/kg). In addition, morphine injection did not induce the expression of COX-2 in the hypothalamus, and CTAP did not modify PGE(2) levels in cerebrospinal fluid or COX-2 expression in the hypothalamus after LPS injection. In conclusion, our results suggest that LPS and endogenous pyrogens (except IL-1beta and prostaglandins) recruit the opioid system to cause a mu-receptor-mediated fever.     

Increased neural damage to global hemispheric hypoxic ischemia (GHHI) in febrile but not nonfebrile lipopolysaccharide Escherichia coli injected rats

Experiments were conducted to compare the impact of febrile versus nonfebrile lipopolysaccharide (LPS) induced bacterial infection at the time of global hemispheric hypoxic ischemia (GHHI) on the neural damage evoked by the GHHI insult. In the first study acute intraperitoneal (i.p.) sterile saline (SS) or LPS Escherichia coli (60 microg/kg) was given to groups of male, conscious Long Evans rats, and core (colonic, Tc) temperatures were monitored over 6 h postinjection. Peak febrile response occurred approximately 5 h after the LPS E. coli was injected. Upon sacrifice 7 days later, no hemispheric or regional brain damage occurred in the saline or LPS-injected groups of this first study. In the second study, GHHI was applied (ligation of right common carotid artery + 35 min of 12% O2) in groups of anesthetized, male Long Evans rats previously given an acute i.p. injection of sterile saline or 60 microg/kg LPS E. coli 5 h earlier. Temperatures (Tc) were monitored before, during, and 1.5 and 24 h following GHHI. The LPS-injected group was subdivided into a febrile (Tc > 38 degrees C before and (or) after GHHI) and nonfebrile (Tc < 38 degrees C before and after GHHI) subgroups. A significant correlation was found between the peak temperature rise from preinjection control values following drug administration of either saline or LPS E. coli and the resultant hemispheric damage caused by GHHI. Moreover, upon sacrifice 7 days later ipsilateral hemispheric and regional (i.e., hippocampal, thalamic) damage to GHHI of the febrile LPS E. coli group was significantly increased from respective hemispheric, hippocampal, and thalamic damage of the saline and nonfebrile, LPS groups given the same ischemic insult. Results suggest that the heightened Tc of a LPS infection at the time of global ischemia exacerbated the neural damage of GHHI, a finding similar to that reported with heightened core temperatures induced by external heating.     

Intracerebroventricular injection of neuronal and inducible nitric oxide synthase inhibitors attenuates fever due to LPS in rats.

Nitric oxide (NO) has been shown to be an important mediator of febrile response to lipopolisaccharide (LPS). To clarify the role of different isoforms of NO synthase (NOS) in febrile response to immune challenge, effects of selective iNOS and nNOS inhibitors on fever to LPS were examined in freely moving biotelemetered rats. Vinyl-L-NIO (N(5) - (1-Imino-3-butenyl) - ornithine (vL-NIO), a neuronal nitric oxide synthase (nNOS) inhibitor, and aminoguanidine hydrochloride, an inducible nitric oxide synthase (iNOS) inhibitor, were injected intracerebroventricularly at a dose of 10 microg/rat just before intraperitoneal injection of LPS at a dose of 50 microg/kg. Both inhibitors injected at a selected doses had no effect on normal day-time body temperature (T(b)) and normal night-time T(b). vinyl-L-NIO and aminoguanidine injected intracerebroventricularly at a dose of 10 microg/animal suppressed the LPS-induced fever in rats. The fever index calculated for rats pretreated with v-LNIO or with aminoguanidine and injected with LPS was reduced by 43% and 72%, respectively, compared to that calculated for water-pretreated and LPS-injected rats. Whereas vL-NIO partly attenuated both phases of febrile rise in T(b), administration of aminoguanidine into the brain completely prevented fever induced by LPS. These data indicate that activation of iNOS inside the brain is not only responsible for triggering but also for maintaining of LPS-induced fever in rats. It is, therefore, reasonable to hypothesize that, activation of iNOS inside the brain is more important in fever development than activation of nNOS.     

Rewarming rates and thermogenesis in hibernating echidnas.

We measured body temperatures (T(b)) in 14 free-ranging echidnas (Tachyglossus aculeatus) using implanted data-loggers. An average of 1020+/-744 days of T(b) data was recorded from each animal. The average maximum T(b) was 35.3+/-0.7 degrees C (n=14), and the lowest T(b) was 4.7 degrees C. Detailed analysis of rewarming events from four echidnas showed rewarming time to be dependent on initial T(b) (rewarming time in hours=15.6-0.41T(initial), n=31) with an average rewarming rate of 1.9+/-0.4 degrees C h(-1). Based on an hourly sampling rate, the peak rewarming rate was found to be 7.2+/-0.8 degrees C h(-1) (n=12), which was measured at a mean T(b) of 26.2+/-2.4 degrees C. This rate of heating was calculated to be equivalent to a peak oxygen consumption rate of 1.4+/-0.2 ml O2 g h(-1), approximately 9 times the basal metabolic rate. We found that a plot of rate of change of T(b) against T(b) for the entire data set from an individual echidna provided a useful summary and analytical tool.     

Rewarming rates and thermogenesis in hibernating echidnas

We measured body temperatures (T(b)) in 14 free-ranging echidnas (Tachyglossus aculeatus) using implanted data-loggers. An average of 1020+/-744 days of T(b) data was recorded from each animal. The average maximum T(b) was 35.3+/-0.7 degrees C (n=14), and the lowest T(b) was 4.7 degrees C. Detailed analysis of rewarming events from four echidnas showed rewarming time to be dependent on initial T(b) (rewarming time in hours=15.6-0.41T(initial), n=31) with an average rewarming rate of 1.9+/-0.4 degrees C h(-1). Based on an hourly sampling rate, the peak rewarming rate was found to be 7.2+/-0.8 degrees C h(-1) (n=12), which was measured at a mean T(b) of 26.2+/-2.4 degrees C. This rate of heating was calculated to be equivalent to a peak oxygen consumption rate of 1.4+/-0.2 ml O2 g h(-1), approximately 9 times the basal metabolic rate. We found that a plot of rate of change of T(b) against T(b) for the entire data set from an individual echidna provided a useful summary and analytical tool.     

Thermoregulatory and metabolic changes during fever in young and old rats

We injected old and young rats with lipopolysaccharide (LPS; 50 microg/kg ip) at two ambient temperatures (Ta; 21 and 31 degrees C). Young rats mounted equivalent fevers at both Tas [peak body temperatures (Tb) of 38.3 and 38.7 degrees C, respectively]. The Tb of old rats was not different from baseline (37.3 degrees C) after LPS at Ta 21 degrees C, whereas, at 31 degrees C, their Tb rose to a mean peak of 38.4 degrees C. We also measured the associated thermoregulatory responses by use of calorimetry. At 21 degrees C, young rats developed a fever by increasing both O2 consumption and heat conservation. Old rats did not become febrile, and O2 consumption fell by 15%. Heat loss was the same in old and young rats. At 31 degrees C, young and old rats developed similar fevers with similar increases in heat production and conservation. Our results suggest that the lack of LPS fever in old rats at 21 degrees C is due mainly to the lowered metabolic rate.     

Relationship between body heat content and finger temperature during cold exposure.

The purpose of the present experiment was to examine the relationship between rate of body heat storage (S), change in body heat content (DeltaH(b)), extremity temperatures, and finger dexterity. S, DeltaH(b), finger skin temperature (T(fing)), toe skin temperature, finger dexterity, and rectal temperature were measured during active torso heating while the subjects sat in a chair and were exposed to -25 degrees C air. S and DeltaH(b) were measured using partitional calorimetry, rather than thermometry, which was used in the majority of previous studies. Eight men were exposed to four conditions in which the clothing covering the body or the level of torso heating was modified. After 3 h, T(fing) was 34.9 +/- 0.4, 31.2 +/- 1.2, 18.3 +/- 3.1, and 12.1 +/- 0.5 degrees C for the four conditions, whereas finger dexterity decreased by 0, 0, 26, and 39%, respectively. In contrast to some past studies, extremity comfort can be maintained, despite S that is slightly negative. This study also found a direct linear relationship between DeltaH(b) and T(fing) and toe skin temperature at a negative DeltaH(b). In addition, DeltaH(b) was a better indicator of the relative changes in extremity temperatures and finger dexterity over time than S.     

High hemoglobin affinity to oxygen and its relationships with lipid peroxidation during fever

The effects of high hemoglobin-oxygen affinity (HOA) on rectal temperature and lipid free radical oxidation were investigated in red blood cells, heart, liver and kidneys of male rats during fever. Fever was induced by intraperitoneal injection of Salmonella typhi lipopolysaccharide (LPS; 5.0 mg kg(-1)). HOA was increased by addition of 0.5% sodium cyanate to drinking water for eight weeks. HOA modification (actual half-saturation oxygen pressure, P50act, decreased to 23.3+/-0.7 vs. 31.6+/-0.7 Torr in control; p < 0.001) weakened a febrile response: rise of temperature after 4 hours was 0.79+/-0.2 degrees C vs. 1.38+/-0.1 degrees C in rats with normal HOA (p < 0.05). In red cells and tissues of rats with normal HOA, concentrations of conjugated dienes and Schiff bases increased during fever, and alpha-tocopherol level and catalase activity decreased. Rats with increased HOA had an inverse pattern of such changes. Changes in rectal temperature and markers of free radical oxidation correlated with a shift of oxyhemoglobin dissociation curve leftwards. The present results indicate that the intentional increment of HOA may substantially diminish lipid peroxidation activity, increase the body antioxidant content during fever and decrease the febrile response on LPS.     

Comparative demography of the sand fly Phlebotomus papatasi (Diptera: Psychodidae) at constant temperatures.

We measured reproductive and population parameters of adult sand flies, Phlebotomus papatasi (Scopoli, 1786) (Diptera: Psychodidae), in environmental chambers maintained at temperatures of 15, 18, 20, 25, 28, and 32 degrees C. Based on cohorts of adults at each temperature regime, horizontal life tables were constructed using established laboratory colonies initiated from specimens collected in Sanliurfa Province, southeastern Anatolia, Turkey. The fecundity and longevity of the insects were both highly variable, depending on the temperature. At 15 degrees C, all of the cohort females died before laying eggs, so the construction of a life table for this temperature regime was not possible. Within a range of 18 to 32 degrees C, the longevity of adult P. papatasi increased as the temperature decreased; at 15 degrees C, the mean survival times of females and males were 19.04 +/- 6.94 days (9-35) and 17.84 +/- 7.11 days (9-33), respectively. While the highest number of eggs was found in the cohort at 28 degrees C (44.08 +/- 7.79), this was only 3.60 +/- 1.55 in the cohort at 32 degrees C and 2.8 +/- 0.9 in the cohort at 18 degrees C. This result showed that extreme temperatures negatively affect the fecundity of this species. The cohort reared at 28 degrees C exhibited the highest intrinsic rates of population increase (r(m)) for P. papatasi. The r(m) ranged from 0.098 at 28 degrees C to 0.007 at 18 degrees C. The cohort placed at 28 degrees C was found to be significantly different (P < 0.01) from the other cohorts producing the fewest progeny in terms of net reproductive rate, R(0), (15.87). The values for mean generation time (T) were estimated to vary from 36 days to 271 days depending on temperature. Principal Component Analysis (PCA) confirmed results from the previous studies that the cohort at 28 degrees C orientated and clustered as a distinct group along the first two PCs.     

Effect of water temperature on the immune response and infectivity pattern of white spot syndrome virus (WSSV) in freshwater crayfish

The susceptibility of two species of freshwater crayfish, Pacifastacus leniusculus and Astacus astacus, to white spot syndrome virus (WSSV) by intramuscular injection was compared and the results show that both species are susceptible to WSSV. The effect of water temperature on the development of white spot disease in crayfish was also studied. Crayfish were exposed to different temperatures after WSSV injection or oral exposure and the mortalities were recorded over a period of 45 days. No mortality was observed when crayfish were held at 4+/-2 degrees C or 12+/-2 degrees C and reached 100% when these crayfish transferred to 22+/-2 degrees C. The mortalities of nearly moribund crayfish at 22+/-2 degrees C with WSSV could be delayed after transfer to temperature below 16 degrees C. These results clearly show that low temperature affects the WSSV pathogenicity in crayfish. Moreover, haemocyte counts, phenoloxidase activity, mRNA levels of prophenoloxidase (proPO) and the lipopolysaccharide and beta-1,3-glucan binding protein (LGBP) in crayfish exposed to various water temperatures were studied. Total haemocyte and granular cell counts of crayfish held at different temperatures were not significantly (P>0.05) different, except for the total haemocyte number at 18 degrees C was significantly (P<0.05) higher than in crayfish at 4 degrees C. The percentage of granular cells in crayfish held at 4 degrees C was the highest compared to crayfish maintained at other temperatures. The phenoloxidase activities in haemocyte lysate supernatant (HLS) of crayfish at all temperature groups remained similar. The amount of proPO-mRNAs in haemocytes was much higher than the amount of LGBP-m RNAs in all the experimental groups. However, there was no change in the level of pro PO-mRNA at the tested temperatures. Interestingly, the level of LGBP-mRNA of crayfish kept at 22 degrees C was much lower than in those held at lower temperatures. Proliferation of the haematopoietic tissues was higher at high temperatures which may support replication of WSSV, and explain the high mortality of crayfish with WSSV infection at high temperature. Based on these studies it is concluded that crayfish might act as a carrier of WSSV at low water temperature and could develop white spot disease if the water temperature is increased.     

AMP does not induce torpor

Torpor, a state characterized by a well-orchestrated reduction of metabolic rate and body temperature (T(b)), is employed for energetic savings by organisms throughout the animal kingdom. The nucleotide AMP has recently been purported to be a primary regulator of torpor in mice, as circulating AMP is elevated in the fasted state, and administration of AMP causes severe hypothermia. However, we have found that the characteristics and parameters of the hypothermia induced by AMP were dissimilar to those of fasting-induced torpor bouts in mice. Although administration of AMP induced hypothermia (minimum T(b) = 25.2 +/- 0.6 degrees C) similar to the depth of fasting-induced torpor (24.9 +/- 1.5 degrees C), ADP and ATP were equally effective in lowering T(b) (minimum T(b): 24.8 +/- 0.9 degrees C and 24.0 +/- 0.5 degrees C, respectively). The maximum rate of T(b) fall into hypothermia was significantly faster with injection of adenine nucleotides (AMP: -0.24 +/- 0.03; ADP: -0.24 +/- 0.02; ATP: -0.25 +/- 0.03 degrees C/min) than during fasting-induced torpor (-0.13 +/- 0.02 degrees C/min). Heart rate decreased from 755 +/- 15 to 268 +/- 17 beats per minute (bpm) within 1 min of AMP administration, unlike that observed during torpor (from 646 +/- 21 to 294 +/- 19 bpm over 35 min). Finally, the hypothermic effect of AMP was blunted with preadministration of an adenosine receptor blocker, suggesting that AMP action on T(b) is mediated via the adenosine receptor. These data suggest that injection of adenine nucleotides into mice induces a reversible hypothermic state that is unrelated to fasting-induced torpor.     

Growth performance and concentrations of thyroid hormones and growth hormone in plasma of broilers at high temperatures

Responses of broiler chickens to a high ambient temperature (35 degrees C) were measured in two experiments. In one experiment temperatures were increased abruptly from 21 degrees C to a daily range of 21-35 degrees C whereas, in the other, temperatures were increased more gradually over 6 days. The high temperatures were maintained for 5 h/day. In both experiments, birds exposed to the high temperatures ate less food and gained less liveweight than birds maintained at 21 degrees C. Efficiency of food conversion to liveweight gain and body composition were not affected by high temperature but there was a tendency for thyroid weight to decrease. Overall, the plasma concentration of triiodothyronine (T3) decreased and the plasma concentration of thyroxine (T4) increased, resulting in a decreased T3/T4 molar ratio, during exposure to high temperature. The concentration of plasma growth hormone, but not plasma reverse T3, was increased by high temperature. The initial responses to increased temperature were variable, with birds exposed more gradually adjusting relatively well until the maximum temperature was increased to 35 degrees C. All heated birds readjusted quickly to the daily reduction in temperature to 21 degrees C.     

Restraint increases afebrile body temperature but attenuates fever in Pekin ducks (Anas platyrhynchos)

In mammals, procedures such as handling, restraint, or exposure to open spaces induces an increase in body temperature (T(b)). The increase in temperature shares some characteristics with pyrogen-induced fever and so is often called "stress fever." Birds also respond to acute handling with a stress fever, which may confound thermoregulatory studies that involve animal restraint. We have measured the T(b) responses of Pekin ducks on days when they were restrained and compared them to days when the birds remained unrestrained. Restraint induced a 0.5 degrees C increase in T(b) that was sustained for the entire 8 h of restraint. To determine whether the restraint-induced increase in T(b) is mediated by prostaglandins (PGs) we compared the T(b) responses during restraint after intraperitoneal injection with saline to the responses during restraint after injection with diclofenac sodium (15 mg/kg). There was no difference in response, suggesting that restraint affects T(b) by a PG-independent mechanism. We also compared the T(b) response to intramuscular injection of lipopolysaccharide (LPS; 100 microg/kg), a bacterial pyrogen, when the ducks were restrained or unrestrained. Despite T(b) being higher at the time of LPS injection when the ducks were restrained, the maximum temperature reached after LPS injection was higher, and the period that T(b) remained elevated was longer when the ducks were unrestrained. We conclude that restraint should be considered as a potential confounder in thermoregulatory studies in birds and presumably other species too.