Reducing Mouse Anxiety during Handling: Effect of Experience with Handling Tunnels

Handling stress is a well-recognised source of variation in animal studies that can also compromise the welfare of research animals. To reduce background variation and maximise welfare, methods that minimise handling stress should be developed and used wherever possible. Recent evidence has shown that handling mice by a familiar tunnel that is present in their home cage can minimise anxiety compared with standard tail handling. As yet, it is unclear whether a tunnel is required in each home cage to improve response to handling. We investigated the influence of prior experience with home tunnels among two common strains of laboratory mice: ICR(CD-1) and C57BL/6. We compared willingness to approach the handler and anxiety in an elevated plus maze test among mice picked up by the tail, by a home cage tunnel or by an external tunnel shared between cages. Willingness to interact with the handler was much greater for mice handled by a tunnel, even when this was unfamiliar, compared to mice picked up by the tail. Once habituated to handling, C57BL/6 mice were most interactive towards a familiar home tunnel, whereas the ICR strain showed strong interaction with all tunnel handling regardless of any experience of a home cage tunnel. Mice handled by a home cage or external tunnel showed less anxiety in an elevated plus maze than those picked up by the tail. This study shows that using a tunnel for routine handling reduces anxiety among mice compared to tail handling regardless of prior familiarity with tunnels. However, as home cage tunnels can further improve response to handling in some mice, we recommend that mice are handled with a tunnel provided in their home cage where possible as a simple practical method to minimise handling stress.     

Estrogen Alters MPTP-Induced Neurotoxicity in Female Mice: Effects on Striatal Dopamine Concentrations and Release

Abstract: The effects of estrogen on MPTP-induced neurotoxicity of the nigrostriatal dopaminergic system were examined in C57Bl and CD-1 mice. Ovariectomized mice with and without estrogen were treated with MPTP or its vehicle. The effects of these treatments on striatal dopamine concentrations and l -DOPA-stimulated dopamine and l -3,4-dihydroxyphenylacetic acid (DOPAC) release in vitro were determined. Dopamine concentrations of C57Bl mice receiving estrogen before MPTP were significantly greater than those of non-estrogen-treated MPTP mice as well as estrogen-treated mice receiving the MPTP vehicle. Dopamine concentrations of the CD-1 mice did not differ with these treatments. l -DOPA-evoked dopamine release values of estrogen-treated C57Bl mice were significantly increased compared with non-estrogen-treated mice. No such differences were observed in the MPTP-treated C57Bl mice. DOPAC release rates were similar to that of dopamine in these C57Bl mice. In the CD-1 mice estrogen also produced a significant increase in l -DOPA-evoked dopamine release; however, this response was unaltered by MPTP treatment. A significant increase in l -DOPA-evoked DOPAC output was obtained only for estrogen-treated CD-1 mice. Both strains show very similar responses to the estrogen treatment, but differential responses of dopamine release to l -DOPA between the C57Bl and CD-1 mice were obtained with regard to the interactive effects of estrogen and MPTP. Our results suggest that in addition to its role as modulator, estrogen may also function as a neuroprotectant against MPTP neurotoxicity of the nigrostriatal dopaminergic system in the C57Bl mouse.     

Differential thiol status in blood of different mouse strains exposed to cigarette smoke

C57Bl/6J, DBA/2 and ICR mouse strains are known to possess different susceptibilities to developing emphysema after exposure to cigarette smoke with DBA/2 and C57Bl/6J strains being significantly more susceptible to pulmonary damage than the ICR strain. This study was aimed at analysing the occurrence of systemic oxidative stress in the blood of these different mouse strains after exposure to cigarette smoke. This study did not observe a significant decrease in glutathione in erythrocytes or in plasma cysteine, cysteinylglycine, homocysteine and glutathione in C57Bl/6J or DBA/2 mice, whereas a significant increase in the corresponding oxidized forms was observed in plasma. However, the ICR strain showed a significant increase in glutathione in erythrocytes and a significant decrease in most of the oxidized forms of cysteine, cysteinylglycine, homocysteine and glutathione in plasma after the same exposition. These experiments demonstrate that exposure to cigarette smoking induces systemic oxidative stress only in some mouse strains which are susceptible to developing emphysema.     

The characteristics of the manifestation of hereditarily induced anxiety in male C57Bl/6J and CBA/Lac mice

Behavior of male mice of C57Bl/6J and CBA/Lac strains was tested in the elevated plus-maze and open field in order to estimate state anxiety in novel conditions. The cube and partition tests were used to reveal trait anxiety in the familiar conditions of the home cage. It is concluded that genetically defined state anxiety is more pronounced in CBA/Lac mice and trait anxiety in C57Bl/6J strain.     

Long-term effects of husbandry procedures on stress-related parameters in male mice of two strains

In socially unstable groups of male laboratory mice, individuals may experience a chronic stress situation. Previous experiments have shown that the transfer of specific olfactory cues during cage cleaning, and the provision of nesting material decrease aggression and stress in group-housed male mice. In this study, the combined effect of these husbandry procedures were tested for their long-term effect on stress in groups of moderately aggressive (BALB/c) and severely aggressive (CD-1) male mice. The physiological and behavioural stress-related parameters used were body weight, food and water intake, spleen and thymus weight, adrenal tyrosine hydroxylase activity, urine corticosterone levels and behaviour in a cage emergence test. Long-term provision of nesting material and its transfer during cage cleaning was found to influence several stress-related physiological parameters. Mice housed in cages enriched with nesting material had lower urine corticosterone levels and heavier thymuses, and they consumed less food and water than standard-housed mice. Furthermore, marked differences were found between strains. CD-1 mice were less anxious in the cage emergence test, weighed more, ate and drank more, and had heavier thymuses but lighter spleens and lower corticosterone levels than BALB/c mice. We conclude that the long-term provision of nesting material, including the transfer of nesting material during cage cleaning, reduces stress and thereby enhances the welfare of laboratory mice.     

Co-Housing Rodents with Different Coat Colours as a Simple,Non-Invasive Means of Individual Identification: Validating Mixed-Strain Housing for C57BL/6 and DBA/2 Mice

Standard practice typically requires the marking of laboratory mice so that they can be individually identified. However, many of the common methods compromise the welfare of the individuals being marked (as well as requiring time, effort, and/or resources on the part of researchers and technicians). Mixing strains of different colour within a cage would allow them to be readily visually identifiable, negating the need for more invasive marking techniques. Here we assess the impact that mixed strain housing has on the phenotypes of female C57BL/6 (black) and DBA/2 (brown) mice, and on the variability in the data obtained from them. Mice were housed in either mixed strain or single strain pairs for 19 weeks, and their phenotypes then assessed using 23 different behavioural, morphological, haematological and physiological measures widely used in research and/or important for assessing mouse welfare. No negative effects of mixed strain housing could be found on the phenotypes of either strain, including variables relevant to welfare. Differences and similarities between the two strains were almost all as expected from previously published studies, and none were affected by whether mice were housed in mixed- or single-strain pairs. Only one significant main effect of housing type was detected: mixed strain pairs had smaller red blood cell distribution widths, a measure suggesting better health (findings that now need replicating in case they were Type 1 errors resulting from our multiplicity of tests). Furthermore, mixed strain housing did not increase the variation in data obtained from the mice: the standard errors for all variables were essentially identical between the two housing conditions. Mixed strain housing also made animals very easy to distinguish while in the home cage. Female DBA/2 and C57BL/6 mice can thus be housed in mixed strain pairs for identification purposes, with no apparent negative effects on their welfare or the data they generate. This suggests that there is much value in exploring other combinations of strains.     

B cell response during infection with the MAT a and MAT alpha mating types of Cryptococcus neoformans

In the present study, we compared the B cell response of BALB/c and C57Bl/6 mice during Cryptococcus neoformans infection. This response was investigated using virulent serotype D forms of mating types alpha and a (MAT alpha and MAT a). C57Bl/6 mice showed massive (mainly cerebral) infection by both types, while BALB/c were resistant to infection. Some resistance of C57Bl/6 mice was induced by previous immunization with the capsular polysaccharide from MAT alpha. Passive immunization of C57Bl/6 mice with purified antibody (Ab) obtained from capsular polysaccharide-immunized mice also increased resistance to infection. Both mouse strains showed comparable low IgM response to the capsular polysaccharide from MAT alpha, and only C57Bl/6 mice produced IgM to the polysaccharide of MAT a. Comparable levels of different immunoglobulin (Ig) isotypes against capsular components of MAT alpha and MAT a were detected, and the response of C57Bl/6 mice was higher when compared to that of BALB/c mice. FACS analysis indicated an increase in the percentage of a high-granulosity (side-scatter) splenic subpopulation and in the percentage of splenic Gr-1+ cells in infected C57Bl/6 mice. In addition, the percentage of follicular splenic B cells was decreased after C. neoformans infection of C57Bl/6 mice. This response was more pronounced when we investigated infection induced by the MAT a mating type. Taken together, our results indicate that capsular polysaccharide derived from MAT alpha and MAT a types of C. neoformans have a stimulatory effect upon B cells but that there is no correlation between resistance of BALB/c mice and Ab production. However, the increase in resistance of C57Bl/6 mice parallels the production of Abs and a major change in splenic cell populations.     

不同品系小鼠对代谢性高尿酸血症造模的影响

目的：分别以昆明种小鼠及ICR、C57BL/6J小鼠为研究对象,比较在复制高尿酸血症模型时可能的小鼠品系差异,并通过降尿酸药物别嘌呤醇与非布索坦验证选择降尿酸药物筛选时选用不同品系动物造模的影响。方法：采用不同剂量次黄嘌呤腹腔注射联用尿酸酶抑制剂氧嗪酸钾皮下注射给药,测定不同造模时段各品系小鼠血清尿酸值。结果：ICR、C57BL/6J小鼠对高尿酸血症造模耐受显著高于昆明种小鼠,在腹腔注射次黄嘌呤500mg/kg,皮下注射氧嗪酸钾300mg/kg时,才可获得稳定的可用于药物筛选的高尿酸血症模型。结论：选择高尿酸血症在体模型时,昆明种小鼠灵敏度高于ICR小鼠以及近交系的C57BL/6J小鼠。     

Dysregulation of the inflammatory response to the parasite, Toxoplasma gondii, in P2X7 receptor-deficient mice

The P2X(7) receptor (P2X(7)R) is a two transmembrane receptor that is highly expressed on the surface of immune cells. Loss of function polymorphisms in this receptor have been linked to increased susceptibility to intracellular pathogens. P2X(7)R gene knockout (P2X(7)R(-/-); on a C57Bl/6J background), C57Bl/6J and BALB/c mice were infected with the avirulent ME49 strain of the intracellular parasite, Toxoplasma gondii, and susceptibility determined by monitoring weight loss. P2X(7)R(-/-) mice lost significantly more weight than C57Bl/6J mice from day 8p.i. C57Bl/6J, in turn, lost significantly more weight than BALB/c mice. Thus, by day 10p.i., P2X(7)R(-/-) mice had lost 5.7 ± 0.7% of their weight versus 2.4 ± 0.6% for C57Bl/6J mice, whereas BALB/c mice had gained 1.9 ± 0.5%; by day 12p.i., P2X(7)R(-/-) mice had lost 15.1±0.6%, C57Bl/6J had lost 10.1±0.8% and BALB/c had lost 4.8 ± 0.8% of their weight. Neither parasite burden nor liver pathology was greater in the P2X(7)R(-/-) mice than in C57Bl/6J mice but BALB/c mice had significantly smaller numbers of parasites and less pathology in their livers than these strains. Absence of the P2X(7) receptor did not affect IFN-γ, IL-12, IL-1β, monocyte chemoattractant protein-1 (MCP-1) or TNF production. However, both P2X(7)R(-/-) and C57Bl/6J mice produced more IL-1β and TNF than BALB/c mice. There was one important point of differentiation between the P2X(7)R(-/-) and C57Bl/6J mice, namely the significantly enhanced and prolonged production of nitric oxide, accompanied by delayed production of IL-10 in the P2X(7)R-deficient mice.     

Response,use and habituation to a mouse house in C57BL/6J and BALB/c mice

Animal welfare depends on the possibility to express species-specific behaviours and can be strongly compromised in socially and environmentally deprived conditions. Nesting materials and refuges are very important resources to express these behaviours and should be considered as housing supplementation items. We evaluated the effects of one item of housing supplementation in standard settings in laboratory mice. C57BL/6JOlaHsd (B6) and BALB/cOlaHsd (BALB) young male and female mice, upon arrival, were housed in groups of four in standard laboratory cages and after 10 days of acclimatization, a red transparent plastic triangular-shaped Mouse House™ was introduced into half of the home cages. Animals with or without a mouse house were observed in various contexts for more than one month. Body weight gain and food intake, home cage behaviours, emotionality and response to standard cage changing procedures were evaluated. The presence of a mouse house in the home cage did not interfere with main developmental and behavioural parameters or emotionality of BALB and B6 male and female mice compared with controls. Both strains habituated to the mouse house in about a week, but made use of it differently, with BALB mice using the house more than the B6 strain. Our results suggest that mice habituated to the mouse house rather quickly without disrupting their home cage activities. Scientists can thus be encouraged to use mouse houses, also in view of the implementation of the EU Directive (2010/63/EU).     

Behavioural studies in different strains of mice and the problem of heterosis

Significant differences between strains were found for open field activity and emotionality, exploratory activity, initial reaction to shock, conditioned avoidance learning, and weight for three inbred strains (Balb/c, C57Bl and C3H), such that the heaviest strain (Balb/c) was the least active and most emotional in the open field, gave the lowest score for exploratory activity and longest reaction to shock times, and was the poorest at conditioned avoidance learning.The hybrids from crosses with C57Bl tended more towards complete dominance and overdominance than did the Balb/c × C3H hybrid, probably because the Balb/c and C3H strains have some common ancestry.Heterosis was most marked for traits involving exploration or learning. Variability of the hybrids for these traits was often lower than the parents, i.e. they showed behavioural homeostasis. For other traits variability of the hybrids tended towards the parent whose genotype was dominant for the trait.Of the non-genetic factors studied, age and litter size were found to have the greatest effect on the behavioural traits. Parity was found only to affect weight. Sex differences were found for weight and emotionality.     

Heligmosomoides polygyrus: decreased apoptosis in fast responder FVB mice during infection

Primary infection with Heligmosomoides polygyrus in some strains of mice is chronic although fast responder mouse strains eliminate the parasite in a short period of time. The reason for the differences is unknown. In this study apoptosis, proliferation, IL-2 and IL-6 production of mesenteric lymph node (MLN) and spleen cells in vitro from fast (FVB) and slow (C57Bl/6) responder mice were compared during H. polygyrus infection. FVB cells showed decreased apoptosis, more proliferation and more cytokine production than cells from C57Bl/6 mice during infection. At the beginning of infection in C57Bl/6 mice the apoptosis of CD4(+) but not CD8(+) cells significantly increased in MLN and spleen cell cultures. Apoptosis, when the first immune signal is given by infective larvae, might play an important role in the modulation of the response in slow responder mice.     

Modulatory Effects of Testosterone on 1-Methyl-4-Phenyl- 1, 2, 3, 6-Tetrahydropyridine-Induced Neurotoxicity

Abstract: In this experiment, we examined the modulatory effects of testosterone on the parkinsonism-inducing drug 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) in two strains of mice. Orchidectomized male CD-1 and C57/BI mice were implanted with either empty Silastic capsules or capsules containing testosterone and subsequently treated with MPTP. A small area of the corpus striatum was removed for determination of dopamine (DA) content, whereas the remainder was superfused and used to measure L-DOPA (5 μ M )-evoked DA release. In animals treated with MPTP, L-DOPA-evoked DA release was reduced significantly in CD-1 mice, but not in C57/BI mice, treated with testosterone. No differences in L-DOPA-stimulated DA release between MPTP- versus vehicle-treated mice was observed in either the CD-1 or C57/BI mice receiving empty Silastic capsules. Corpus striatum DA contents were more severely depleted in the MPTP-sensitive C57/BI versus the CD-1 mouse strain irrespective of hormone treatment. These results confirm previous results demonstrating differences in these two mouse strains in response to the neurotoxic effects of MPTP upon corpus striatum DA content. More interestingly, they show an important differential modulatory effect of testosterone upon L-DOPA-evoked DA release as a function of MPTP treatment and indicate that testosterone significantly alters the neurotoxic effects of MPTP in the CD-1 mouse.     

Pregnancy-induced changes in renin gene expression in mice.

A puzzling feature of the renin-angiotensin system during pregnancy is the appearance in the maternal circulation of a large increase in the concentration of prorenin and renin. The physiologic role of these changes is not understood. We determined that high levels of renin protein occur in the circulation of pregnant mice, thereby establishing the mouse as a valuable model for understanding gestation-induced changes in the renin-angiotensin system. We used the murine model to show that high levels of renin gene expression occur at the mother-fetus interface, first in maternal decidua and subsequently in placentas. These results were obtained using ICR mice that have 2 related renin genes, Ren1 and Ren2. We also examined renin gene expression in C57Bl/6 mice that have only the Ren1 gene. In these mice, very little renin gene expression was observed in placentas but instead was upregulated in kidneys during pregnancy. In both ICR and C57Bl/6 mice, there is an increase in renin protein in the maternal circulation during pregnancy. However, these mice differ with regard to gestation-induced sites of increased renin gene expression. These studies suggest that mice are a convenient and valuable model for studying renin gene expression during pregnancy.     

V gamma 1+ T cells suppress and V gamma 4+ T cells promote susceptibility to coxsackievirus B3-induced myocarditis in mice

Coxsackievirus B3 infections of C57BL/6 mice, which express the MHC class II IA but not IE Ag, results in virus replication in the heart but minimal myocarditis. In contrast, Bl.Tg.Ealpha mice, which are C57BL/6 mice transgenically induced to express IE Ag, develop significant myocarditis upon Coxsackievirus B3 infection. Despite this difference in inflammatory damage, cardiac virus titers are similar between C57BL/6 and Bl.Tg.Ealpha mice. Removing gammadelta T cells from either strain by genetic manipulation (gammadelta knockout(ko)) changes the disease phenotype. C57BL/6 gammadelta ko mice show increased myocarditis. In contrast, Bl.Tg.Ealpha gammadelta ko mice show decreased cardiac inflammation. Flow cytometry revealed a difference in the gammadelta cell subsets in the two strains, with Vgamma1 dominating in C57BL/6 mice, and Vgamma4 predominating Bl.Tg.Ealpha mice. This suggests that these two Vgamma-defined subsets might have different functions. To test this possibility, we used mAb injection to deplete each subset. Mice depleted of Vgamma1 cells showed enhanced myocarditis, whereas those depleted of Vgamma4 cells suppressed myocarditis. Adoptively transfusing enriched Vgamma4(+) cells to the C57BL/6 and Bl.Tg. Ealpha gammadelta ko strains confirmed that the Vgamma4 subset promoted myocarditis. Th subset analysis suggests that Vgamma1(+) cells biased the CD4(+) T cells to a dominant Th2 cell response, whereas Vgamma4(+) cells biased CD4(+) T cells toward a dominant Th1 cell response.     

The effects of genetic variation in N-acetyltransferases on 4-aminobiphenyl genotoxicity in mouse liver

Inbred, congenic and transgenic strains of mice were characterized for acetylation of p-aminobenzoic (PABA) and the carcinogen 4-aminobiphenyl (4ABP). C57Bl/6 mice have the NAT2*8 allele, A/J mice have NAT2*9 and congenic B6.A mice have NAT2*9 on the C57Bl/6 background. The first transgenic strain with human NAT1, the functional equivalent of murine NAT2, was also tested. The murine NAT2*9 allele correlated with a slow phenotype measured with the murine NAT2 selective substrate PABA. The two strains having this allele also had a lower capacity to acetylate 4ABP. A line with five copies of the human NAT1 transgene was bred for at least five generations with either C57Bl/6 or A/J mice. There was no significant change in PABA NAT activity on the C57Bl/6 background but a 2.5-fold increase was seen in hNAT1:A/J compared with A/J. The effect of variation in NATs on 4ABP genotoxicity was assessed in these strains. Twenty-four hours after exposure to a single oral dose of 120 mg 4ABP/kg, hepatic 4ABP-DNA adducts were detected by immunofluoresence in all strains. Nuclear fluorescence intensities (mean+/-S.D.) were 41.1+/-3.6 for C57Bl/6, 37.9+/-1.11 for A/J and 36.3+/-2.44 for B6.A. There was no correlation between murine NAT2 alleles and 4ABP-DNA adduct levels. Similar results were seen with the transgenic strains. The data indicate that the range of variation present in these strains of mice was insufficient to alter susceptibility to 4ABP genotoxicity. The impact of these relatively modest differences in the acetylation of the activation of 4ABP may be masked by other competing biotransformation reactions since 4ABP is a substrate for both NAT1 and NAT2. Mouse models with variation in both isoforms are needed to adequately assess the role of variation in NATs in susceptibility to 4ABP genotoxicity.     

Susceptibility of several strains of mice to Echinostoma hortense infection

Susceptibilities of 5 different mice strains, including C3H/HeN, BALB/c, C57BL6, FvB and ICR, to Echinostoma hortense infection, was evaluated. The worm expulsion rate, worm size and egg production were observed from 1 to 8 weeks after infection with 30 metacercariae. C3H/HeN and ICR mice showed the highest worm maturation rates. The worm recovery rate and the number of eggs per gram (EPG) of feces was also higher in C3H/HeN and ICR mice than in BALB/c, C57BL6, and FvB mice. It is suggested that E. hortense is highly infectious to ICR and C3H/HeN mice, but not to the other strains of mice. Based on the results obtained, we believe that the susceptibility of different mouse strains to E. hortense infection is dependent on the genetic and immunologic background of mice.     

Antibodies to catecholamines and serotonin during alcoholic intoxication in animals with different predispositions to the development of experimental alcoholism

Experiments on C57Bl/6, CBA and DBA/2 mice characterized by different preferences for ethanol have shown that during chronic administration of alcohol to animals with natural ethanol motivation (strain C57Bl/6) the level of antibodies to catecholamines and serotonin was increased on the 3rd month of ethanol intoxication, with the voluntary alcohol consumption in mice decreased by this time. On the contrary in mice rejecting alcohol (strains DBA/2, CBA) no antibodies to catecholamines and serotonin have been found.     

Strain differences of ether susceptibility in mice

The susceptibility to ether in the following six strains of mice was tested: C57BL/6, DBA/2, BALB/c, C3H/He, ICR and ddY. Mice of 4 weeks old were exposed to a flow of air containing various concentrations of ether for 90 min and the mortalities were assessed. The C57BL/6 strain was the most resistant and the C3H/He strain was the most sensitive to the lethal effect of ether. The susceptibilities of the closed colony mice, ICR and ddY, were intermediate between those of C57BL/6 and C3H/He mice. The DBA/2 and BALB/c strains were more sensitive than these closed colony mice and made up a sensitive group with the C3H/He strain. The LD50 values for ether in male mice of C57BL/6 and C3H/He were 6.0 and 3.1% atm, and in female mice of these strains were 6.6 and 3.2% atm, respectively. The ED50 value of ether which was accompanied by loss of righting reflex after exposure for 10 min was also higher in male C57BL/6 mice than in male C3H/He mice.     

Hemodynamics of anesthetized ventilated mouse models: aspects of anesthetics,fluid support,and strain

This study evaluates the effects of anesthesia and fluid support on hemodynamic parameters of the mechanically ventilated mouse of four different strains. All experiments were performed at a similar surgical level of anesthesia, as indicated by the probing of the pedal withdrawal reflex. Three anesthetic regimens [fentanyl-fluanisone-midazolam (FFM), ketamine-medetomidine-atropine (KMA), and isoflurane (ISO)], four commonly used mouse strains (Swiss, CD-1, BalbC, and C57Bl6), and three different fluid support strategies (no fluid, 0.2 ml x h(-1) x 10 g(-1) of 6% polystarch solution, and 0.5 ml x h(-1) x 10 g(-1) saline) were studied. Mean arterial pressure (MAP) or heart rate (HR) was similar among the four strains of mice except a trend toward lower HR for the BalbC mice. In terms of MAP, KMA is the preferred anesthetic for the Swiss and CD-1 mice, whereas KMA or ISO are recommended for BalbC or C57Bl6 mice. In terms of HR, ISO is the preferred anesthetic for the Swiss, CD-1, and C57Bl6 strains. No differences in HR for the three anesthetics were observed for the BalbC strain. Compared with administration of no fluid, both saline and polystarch administration similarly increased MAP by 7 +/- 2, 10 +/- 2, and 11 +/- 2 mmHg at t = 1, 2, and 3 h, respectively, whereas fluid administration was without effect on HR. Saline supplementation resulted in an increased dry-to-wet ratio of the heart and both fluid regimens decreased total hemoglobin in the blood from 12.6 +/- 0.5 to 10.4 +/- 0.5 g/100 ml. Saline administration was associated with blood acidosis (pH 7.20 +/- 0.03) compared with the Haes (pH 7.29 +/- 0.02) or no-fluid group (pH 7.34 +/- 0.03), whereas PCO(2) was approximately 30 mmHg for all groups. We conclude that at similar surgical levels of anesthesia, the preferable type of anesthesia (ISO or KMA, but never FFM) depends on the strain used and whether MAP or HR is the focus of study. Additional fluid support is beneficial in terms of raising arterial blood pressure, although this is at the cost of changes in organ water content and increased anemia.