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PubMedDate not supplied

The electroretinogram of the rhodopsin knockout mouse.

The electroretinogram (ERG) of the rhodopsin knockout (rho-/-) mouse of Humphries et al. (1997) (Humphries et al., 1997) was studied for evidence of light-evoked rod activity and to describe the cone function. The rho-/- retina develops normal numbers of rod and cone nuclei, but the rods have no outer segments, and no rhodopsin is found by immunohistochemistry. The dark-adapted ERG threshold was elevated 4.7 log units above wild-type (WT) control mice, indicating that any residual rod responses were reduced >50,000-fold, consistent with a complete functional knockout. The dark-adapted rho-/- ERG had a cone waveform, and the spectral sensitivity peaked near 510 nm for both dark-adapted and light-adapted conditions, without evidence of a Purkinje shift. The light-adapted ERG b-wave amplitude of young rho-/- mice was the same as WT. The amplitude remained steady up to postnatal day P47, but thereafter it declined to only 1-2% by P80 when no cone outer segments remained. Cone b-wave threshold of dark-adapted rho-/- mice was -1.07 +/- 0.39 log cd-s/m2 (n = 17), which is 1.27 log units more sensitive than light-adapted thresholds against a rod-suppressing Ganzfeld background of 1.61 log scotopic cd/m2. This indicates that dark-adapted WT responses to still dimmer stimuli are exclusively rod driven with minimal cone intrusion. Above this cone threshold intensity, the dark-adapted b-wave of WT will be a summation of rod and cone responses. Threshold versus intensity (TVI) studies gave no evidence of a rod influence on the mouse cone b-wave.

Animals↗

PubMed2005

Bile acid transport in sister of P-glycoprotein (ABCB11) knockout mice.

In vertebrates, bile flow is essential for movement of water and solutes across liver canalicular membranes. In recent years, the molecular motor of canalicular bile acid secretion has been identified as a member of the ATP binding cassette transporter (ABC) superfamily, known as sister of P-glycoprotein (Spgp) or bile salt export pump (Bsep, ABCB11). In humans, mutations in the BSEP gene are associated with a very low level of bile acid secretion and severe cholestasis. However, as reported previously, because the spgp(-)(/)(-) knockout mice do not express severe cholestasis and have substantial bile acid secretion, we investigated the "alternative transport system" that allows these mice to be physiologically relatively normal. We examined the expression levels of several ABC transporters in spgp(-)(/)(-) mice and found that the level of multidrug resistance Mdr1 (P-glycoprotein) was strikingly increased while those of Mdr2, Mrp2, and Mrp3 were increased to only a moderate extent. We hypothesize that an elevated level of Mdr1 in the spgp(-)(/)(-) knockout mice functions as an alternative pathway to transport bile acids and protects hepatocytes from bile acid-induced cholestasis. In support of this hypothesis, we showed that plasma membrane vesicles isolated from a drug resistant cell line expressing high levels of P-glycoprotein were capable of transporting bile acids, albeit with a 5-fold lower affinity compared to Spgp. This finding is the first direct evidence that P-glycoprotein (Mdr1) is capable of transporting bile acids.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2002

Murine monoclonal anti-tNF antibody administration has a beneficial effect on inflammatory bowel disease that develops in IL-10 knockout mice.

Although the etiology of inflammatory bowel disease (IBD) is unknown, there is increasing evidence for the pivotal role played by tumor necrosis factor-alpha (TNF-alpha). Recent work has shown an increased concentration of TNF-alpha in both the bowel wall and in the stools of patients with IBD, and in children with that disease there are increased serum levels. Coincidental studies have shown that IL-10 knockout mice have increased levels of TNF-alpha and are known to develop a syndrome of stunted growth, anemia, bloody diarrhea, and colon tumors that mimics IBD. By injecting monoclonal antibodies intraperitoneally into IL-10 knockout mice, we were able to demonstrate significant histologic improvement of inflammation that correlates well with a resolution of diarrhea and rectal bleeding. This finding is consistent with a role for anti-TNF-alpha in the pathogenesis of IBD and suggests that this model may be of use for examining the effects of anti-TNF-alpha antibody administration.

Animals↗

PubMed1999

Characterization of plasmid DNA binding and uptake by peritoneal macrophages from class A scavenger receptor knockout mice.

PURPOSE: Plasmid DNA (pDNA) has become an important class of macromolecular agent suitable for non-viral gene therapy as well as DNA vaccination. Our recent study has suggested that pDNA is taken up by mouse peritoneal macrophages via a specific mechanism mediated by a receptor similar to the scavenger receptor (SR). This study was designed to further characterize the pDNA uptake by macrophages in order to elucidate the mechanism. METHODS: The binding and uptake of pDNA labeled with 32P or a fluorescent marker were studied in vitro using cultured Chinese hamster ovary (CHO) cells expressing the class A scavenger receptor (SRA) and peritoneal macrophages from SRA-knockout mice. RESULTS: pDNA binding and uptake by CHO(SRA) cells were minimal and almost identical to that by wild-type CHO cells. Macrophages from the knockout mice showed pronounced pDNA binding and uptake as did the control macrophages. In both types of macrophage, pDNA binding was significantly inhibited by cold pDNA, polyinosinic acid and dextran sulfate but not by polycytidylic acid or Ac-LDL. These results provide direct evidence that SRA is not responsible for the significant binding and subsequent uptake of pDNA by mouse peritoneal macrophages. Further binding experiments revealed that, in addition to polyinosinic acid and dextran sulfate, heparin was a potent inhibitor among a variety of polyanionic compounds such as polynucleotides, anionic polysaccharides and modified proteins including Ox-LDL. CONCLUSIONS: The present study suggest that pDNA binding and uptake by mouse peritoneal macrophages are mediated by a specific mechanism to some defined polyanions not by scavenger receptors. The finding would be an important basis for further studies to elucidate the mechanism(s) of pDNA uptake by macrophages.

Animals↗

PubMed2003

Disposition kinetics of alpha-tocopherol in apolipoprotein B knockout mice.

PURPOSE: We examined the effects of apolipoprotein B (apoB) on the disposition kinetics of alpha-tocopherol by using apoB knockout mice. METHODS: The concentrations of alpha-tocopherol in plasma and tissues were measured by gas chromatography-mass spectrometry. RESULTS: In apob (-/-) mice, the endogenous levels of alpha-tocopherol in plasma and tissues (except liver) were significantly lower, and the liver concentration was significantly higher than those in wild-type mice. After single i.v. administration of alpha-tocopherol (25 mg/kg), the area under the plasma concentration-time curve (AUC) and the distribution volume at steady state were significantly decreased, whereas the total clearance of alpha-tocopherol was significantly increased in apob (-/-) vs. wild-type mice. Alpha-Tocopherol was highly distributed to the liver, compared with other tissues. After an oral administration of alpha-tocopherol (100 mg/kg), the intestinal absorption of alpha-tocopherol was very low in apoB knockout mice, as the value of AUC0-32h for apob (-/-) mice (17.7 +/- 8.3 (microg h/mL) was significantly less than that for apob (+/+) wild-type mice (96.5 +/- 15.8 microg h/mL, mean +/- SD of five experiments, p < 0.01). The biliary excretion of alpha-tocopherol was significantly greater in apob (+/-) mice than in apob (+/+) mice. CONCLUSIONS: These results show that apoB plays a role in hepatic secretion and intestinal absorption of alpha-tocopherol.

Administration, Oral↗

PubMed2000

Enrichment induces structural changes and recovery from nonspatial memory deficits in CA1 NMDAR1-knockout mice.

We produced CA1-specific NMDA receptor 1 subunit-knockout (CA1-KO) mice to determine the NMDA receptor dependence of nonspatial memory formation and of experience-induced structural plasticity in the CA1 region. CA1-KO mice were profoundly impaired in object recognition, olfactory discrimination and contextual fear memories. Surprisingly, these deficits could be rescued by enriching experience. Using stereological electron microscopy, we found that enrichment induced an increase of the synapse density in the CA1 region in knockouts as well as control littermates. Therefore, our data indicate that CA1 NMDA receptor activity is critical in hippocampus-dependent nonspatial memory, but is not essential for experience-induced synaptic structural changes.

Animals↗

PubMed2001

Differential modulation of endothelin ligand-induced contraction in isolated tracheae from endothelin B (ET(B)) receptor knockout mice.

The role of endothelin B (ET(B)) receptors in mediating ET ligand-induced contractions in mouse trachea was examined in ET(B) receptor knockout animals. Autoradiographic binding studies, using [(125)I]-ET-1, confirmed the presence of ET(A) receptors in tracheal and bronchial airway smooth muscle from wild-type (+/+) and homozygous recessive (-/-) ET(B) receptor knockout mice. In contrast, ET(B) receptors were not detected in airway tissues from (-/-) mice. In tracheae from (+/+) mice, the rank order of potencies of the ET ligands was sarafotoxin (Stx) S6c>ET-1>ET-3; Stx S6c had a lower efficacy than ET-1 or ET-3. In tissues from (-/-) mice there was no response to Stx S6c (up to 0.1 microM), whereas the maximum responses and potencies of ET-1 and ET-3 were similar to those in (+/+) tracheae. ET-3 concentration-response curve was biphasic in (+/+) tissues (via ET(A) and ET(B) receptor activation), and monophasic in (-/-) preparations (via stimulation of only ET(A) receptors). In (+/+) preparations SB 234551 (1 nM), an ET(A) receptor-selective antagonist, inhibited the secondary phase, but not the first phase, of the ET-3 concentration-response curve, whereas A192621 (100 nM), an ET(B) receptor-selective antagonist, had the opposite effect. In (-/-) tissues SB 234551 (1 nM), but not A192621 (100 nM), produced a rightward shift in ET-3 concentration-response curves. The results confirm the significant influence of both ET(A) and ET(B) receptors in mediating ET-1-induced contractions in mouse trachea. Furthermore, the data do not support the hypothesis of atypical ET(B) receptors. In this preparation ET-3 is not an ET(B) receptor-selective ligand, producing contractions via activation of both ET(A) and ET(B) receptors.

Animals↗

PubMed2001

Interactive contribution of NK(1) and kinin receptors to the acute inflammatory oedema observed in response to noxious heat stimulation: studies in NK(1) receptor knockout mice.

1. Scald injury in Sv129+C57BL/6 mice induced a temperature and time dependent oedema formation as calculated by the extravascular accumulation of [(125)I]-albumin. Oedema formation was suppressed in NK(1) knockout mice compared to wildtypes at 10 (P<0.01) and 30 min (P<0.001). However, at 60 min a similar degree of extravasation was observed in the two groups. 2. Kinin B(1) (des-Arg(10) Hoe 140; 1 micromol kg(-1)) and B(2) (Hoe 140; 100 nmol kg(-1)) antagonists caused an inhibition of oedema in wildtype mice at 10 and 30 min (P<0.001), but not at 60 min or at 30 min in NK(1) receptor knockout mice. 3. The inhibition of thermic oedema by des-Arg(10) Hoe 140 was reversed by des-Arg(9) bradykinin (0.1 micromol kg(-1); P<0.01) and also observed with a second B(1) receptor antagonist (des-Arg(9) Leu(8) bradykinin; 3 micromol kg(-1); P<0.01). Furthermore des-Arg(10) Hoe 140 had no effect on capsaicin (200 microg ear(-1)) ear oedema, but this was significantly reduced with Hoe 140 (P<0.05). 4. Scalding induced a large neutrophil accumulation at 4 h, as assessed by myeloperoxidase assay (P<0.001). This was not suppressed by NK(1) receptor deletion or kinin antagonists. 5. These results confirm an essential role for the NK(1) receptor in mediating the early, but not the delayed phase of oedema formation or neutrophil accumulation in response to scalding. The results also demonstrate a pivotal link between the kinins and sensory nerves in the microvascular response to burn injury, and for the first time show a rapid involvement of the B(1) receptor in murine skin.

Administration, Topical↗

PubMed2005

Insights into the functional roles of alpha(1)-adrenoceptor subtypes in mouse carotid arteries using knockout mice.

1. alpha(1)-Adrenoceptor (AR) subtypes in mouse carotid arteries were characterised using a combination of agonist/antagonist pharmacology and knockout (KO) mice. 2. Phenylephrine (PE) was most potent in the alpha(1B)-KO (pEC(50)=6.9+/-0.2) followed by control (pEC(50)=6.3+/-0.06) and alpha(1D)-KO (pEC(50)=5.5+/-0.07). Both N-[5-(4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl] methanesulphonamide hydrobromide (A-61603) and 5-hydroxytryptamine (5-HT) were more potent in the alpha(1D)-KO (pEC(50)=7.4+/-0.27 and 7.4+/-0.05, respectively) than the control (pEC(50)=6.9+/-0.09 and 6.9+/-0.08, respectively) and equipotent with the control in the alpha(1B)-KO (pEC(50)=6.7+/-0.07 and 6.8+/-0.04). Maximum responses to PE and A-61603 were reduced in the alpha(1D)-KO compared to control; there was no difference in maximum responses to 5-HT. 3. In control arteries, prazosin and 5-methylurapidil acted competitively with pA(2) of 9.6 and 7.5, respectively. BMY7378 produced antagonism only at the highest concentration used (100 nM; pK(B) 8.3). 4. Prazosin, 5-methylurapidil and BMY7378 acted competitively in alpha(1B)-KO carotid arteries with pA(2) of 10.3, 7.6 and 9.6, respectively. 5. In the alpha(1D)-KO, against PE, 5-methylurapidil produced a pA(2) of 8.1. pK(B) values were calculated for prazosin (10.6) and BMY7378 (7.0). Against A-61603, 5-methylurapidil had a pA(2) of 8.5, prazosin 8.6, while BMY7378 had no effect. 6. In conclusion, the alpha(1B)-KO mediates contraction solely through alpha(1D)-ARs and the alpha(1D)-KO through alpha(1A)-ARs. Extrapolating back to the control from the knockout data suggests that all three subtypes could be involved in the responses, but we propose that the alpha(1D)-AR causes the contractile response and that the role of the alpha(1B)-AR is mainly regulatory.

Adrenergic alpha-1 Receptor Agonists↗

PubMed2005

Caveolin-1 gene knockout impairs nitrergic function in mouse small intestine.

Caveolin-1 is a plasma membrane-associated protein that is responsible for caveolae formation. It plays an important role in the regulation of the function of different signaling molecules, among which are the different isoforms of nitric oxide synthase (NOS). Nitric oxide (NO) is known to be an important inhibitory mediator in the mouse gut. Caveolin-1 knockout mice (Cav1(-/-)) were used to examine the effect of caveolin-1 absence on the NO function in the mouse small intestine (ileum and jejunum) compared to their genetic controls and BALB/c controls. Immunohistochemical staining showed loss of caveolin-1 and NOS in the jejunal smooth muscles and myenteric plexus interstitial cells of Cajal (ICC) of Cav1(-/-) mice; however, nNOS immunoreactive nerves were still present in myenteric ganglia. Under nonadrenergic noncholinergic (NANC) conditions, small intestinal tissues from Cav1(-/-) mice relaxed to electrical field stimulation (EFS), as did tissues from control mice. Relaxation of tissues from control mice was markedly reduced by N-omega-nitro-L-arginine (10(-4) M), but relaxation of Cav1(-/-) animals was affected much less. Also, Cav1(-/-) mice tissues showed reduced relaxation responses to sodium nitroprusside (100 microM) compared to controls; yet there were no significant differences in the relaxation responses to 8-bromoguanosine-3': 5'-cyclic monophosphate (100 microM). Apamin (10(-6) M) significantly reduced relaxations to EFS in NANC conditions in Cav1(-/-) mice, but not in controls. The data from this study suggest that caveolin-1 gene knockout causes alterations in the smooth muscles and the ICC, leading to an impaired NO function in the mouse small intestine that could possibly be compensated by apamin-sensitive inhibitory mediators.

Animals↗

PubMed2004

CB1 cannabinoid receptor knockout in mice leads to leanness, resistance to diet-induced obesity and enhanced leptin sensitivity.

OBJECTIVE: There is growing evidence for an implication of the CB1 receptor subtype of the endocannabinoid system in the regulation of eating and fat deposition. To further define the physiological role of these receptors in the control of energy balance, we characterized the phenotype of CB1 receptor knockout (CB1(-/-)) mice maintained on an obesity-prone regimen or on a standard chow. DESIGN: CB1(-/-) male mice were compared to wild-type animals (CB1(+/+) male mice) in two feeding paradigms: (1) with a standard laboratory regimen (3.5 kcal/g, 14.5% of energy as fat) and (2) on a free-choice paradigm consisting of offering both the standard laboratory chow and a high-fat diet (HFD) (4.9 kcal/g, 49% of energy as fat). RESULTS: When maintained on the standard diet, CB1(-/-) mice are lean. At the age of 20 weeks, their body weight and adiposity are, respectively, 24 and 60% lower than that of CB1(+/+) mice. They are slightly hypophagic, but when expressed as percent of body weight, their relative energy intake is similar to that of the wild-type animals. Furthermore, inactivation of CB1 receptors reduces plasma insulin and leptin levels, and enhances the response to intracerebroventricular leptin injection. The free-choice paradigm shows that the preference for a high-fat highly palatable chow is slightly delayed in onset but maintained in CB1(-/-) mice. However, loading CB1(-/-) mice with this obesity-prone diet does not result in development of obesity. Knockout mice do not display hyperphagia or reduction of their relative energy intake in contrast to CB1(+/+) mice, and their feeding efficiency remains low. These data suggest an improved energetic metabolism with the high-fat regimen. Furthermore, the insulin resistance normally occurring in HFD-fed mice is not present in CB1(-/-) mice. CONCLUSION: These results provide evidence that the stimulation of CB1 receptors is a key component in the development of diet-induced obesity, and that these receptors and their endogenous ligands are implicated not only in feeding control but also in peripheral metabolic regulations. The lack of effect of SR141716, a selective CB1 receptor antagonist, in CB1(-/-) mice further supports this hypothesis, as this compound was previously shown to display potent anti-obesity properties in diet-induced obese C57BL/6 mice.

Animals↗

PubMed2003

Reduced behavioral effects of cocaine in heterozygous brain-derived neurotrophic factor (BDNF) knockout mice.

Brain-derived neurotrophic factor (BDNF) affects the development of brain neurotransmitter systems, including dopamine and serotonin systems that are important for cocaine's rewarding and locomotor stimulatory properties. Human genomic markers within or near the BDNF locus have been linked to or associated with substance abuse. Post-mortem human brain specimens reveal individual differences in the levels of BDNF mRNA and in mRNA splicing patterns. To assess the effects of lifelong alterations in the levels of BDNF expression on a measure of psychostimulant reward, we have compared locomotor stimulant and rewarding effects of cocaine in heterozygous BDNF knockout mice with effects in their wild-type littermates. Heterozygous BDNF knockout mice displayed less locomotion during habituation and less locomotion after cocaine injections. Cocaine-conditioned place preferences were reduced in the BDNF heterozygotes. These mice displayed no significant difference from saline control values at a dose of 10 mg/kg s.c. cocaine, although they exhibited cocaine-induced preference at a 20 mg/kg dose. These data confirm important roles for BDNF in psychostimulant actions, presumably via neurotrophic effects on dopamine and serotonin systems. Furthermore, these data support suggestions that differences in human BDNF expression may underlie associations between markers near the human BDNF gene locus and drug addiction.

Animals↗

PubMed2005

CB1 receptor knockout mice display reduced ethanol-induced conditioned place preference and increased striatal dopamine D2 receptors.

Cannabinoids and ethanol activate the same reward pathways, and recent advances in the understanding of the neurobiological basis of alcoholism suggest that the CB1 receptor system may play a key role in the reinforcing effects of ethanol and in modulating ethanol intake. In the present study, male CB1 receptors knockout mice generated on a CD1 background displayed decreased ethanol-induced conditioned place preference (CPP) compared to wild-type (CB1(+/+)) mice. Ethanol (0.5, 1.0, 1.5, and 2.0 g/kg) induced significant CPP in CB1(+/+) mice at all doses tested, whereas it induced significant CPP only at the highest dose of ethanol (2.0 g/kg) in CB1(-/-) mice. However, there was no genotypic difference in cocaine (20 mg/kg)-induced CPP. There was also no genotypic difference, neither in cocaine (10-50 mg/kg) nor in D-amphetamine (1.2-5 mg/kg)-induced locomotor effects. In addition, mutant and wild-type mice did not differ in sensitivity to the anxiolytic effects of ethanol (1.5 g/kg) when tested using the elevated plus maze. Interestingly, this decrease in ethanol efficacy to induce CPP in CB1(-/-) mice was correlated with an increase in D2/D3 receptors, as determined by [3H]raclopride binding, whereas there was no difference in D1-like receptors, as determined by [3H]SCH23390 binding, measured in the striatum from drug-naive mice. This increase in D2/D3 binding sites observed in CB1 knockout mice was associated with an altered locomotor response to the D2/D3 agonist quinpirole (low doses 0.02-0.1 mg/kg) but not to an alteration of quinpirole (0.1-1.0 mg/kg)-induced CPP compared to wild-type mice. Altogether, the present results indicate that lifelong deletion of CB1 receptors reduced ethanol-induced CPP and that these reduced rewarding effects of ethanol are correlated to an overexpression of striatal dopamine D2 receptors.

Alcohol Drinking↗

PubMed2005

Dissociation of analgesic and hormonal responses to forced swim stress using opioid receptor knockout mice.

Exposure to stress triggers hormonal and behavioral responses. It has been shown that the endogenous opioid system plays a role in some physiological reactions to stress. The opioid system was described to mediate analgesia induced by mild stressors and to modulate the activation of the hypothalamic-pituitary-adrenal axis. Our study assessed the contribution of opioid receptors in stress-induced analgesia and adrenocorticotropic hormone (ACTH) and corticosterone release by a genetic approach. We performed a parallel analysis of mice deficient in mu, delta, or kappa opioid receptors, as well as of triple opioid receptor knockout mice, following exposure to a mild stress (3-min swim at 32 degrees C). In wild-type mice, stress elicited an increase in jumping latency on the hot plate, which was influenced by gender and genetic background. This analgesic response was reversed both by naloxone and by the triple mutation, and decreased in mu and delta opioid receptor knockout females. In wild-type females, stress also delayed front- and hindpaw behaviors in the hot plate test and increased tail-flick latency in the tail immersion test. Opioid receptor deletion however did not affect these stress responses. In addition, stress produced an increase in ACTH and corticosterone plasma levels. This endocrine response remained unchanged in all mutant strains. Therefore our data indicate that, under our stress conditions, the endogenous opioid system is recruited to produce some analgesia whereas it does not influence hypothalamic-pituitary-adrenal axis activity. This implies that brain circuits mediating analgesic and hormonal responses to stress can be dissociated.

Adrenocorticotropic Hormone↗

PubMed2001

Mouse anxiety: the power of knockout.

The role of the neurokinine 1 receptors (NK1R) and its endogenous ligand, the neuropeptide substance P (SP) in the pathophysiology and treatment response of anxiety and depression has been controversial. In a new study, however, mice with a targeted inactivation of the NK1R show a phenotype that is associated with anxiety-related behaviors and stress responses. Since this behavioral phenotype was associated with an increase in serotonergic function, NK1R knockout mice represent a systematic model for advanced investigations of SP/NK1R and serotonin system interaction in anxiety responses. The availability of an increasing number of knockout mouse anxiety models as well as integration of emerging tools and technologies for genetic analysis will provide the groundwork for the genetic dissection of anxiety and related disorders.

Animals↗

PubMed2001

Comparative impacts of glutathione peroxidase-1 gene knockout on oxidative stress induced by reactive oxygen and nitrogen species in mouse hepatocytes.

Selenium-dependent glutathione peroxidase-1 (GPX1) protects against reactive-oxygen-species (ROS)-induced oxidative stress in vivo, but its role in coping with reactive nitrogen species (RNS) is unclear. Our objective was to compare the protection of GPX1 against cytotoxicity of superoxide generator diquat (DQ), NO donor S-nitroso-N-acetyl-penicillamine (SNAP) and peroxynitrite generator 3-morpholinosydnonimine (SIN-1). Primary hepatocytes were isolated from GPX1-knockout (KO) and wild-type (WT) mice and cultured in complete Williams's medium E with various levels of these agents alone or in combination for up to 12 h. While the KO cells were more susceptible to cell death, DNA fragmentation and protein carbonyl formation induced by 0.25-1 mM DQ, these cells were as tolerant as the WT cells to cytotoxicity of 0.1-1 mM SNAP or 0.5-2 mM SIN-1. Treating cells with SNAP (0.1 or 0.25 mM) in addition to DQ produced synergistic cytotoxicity that minimized differences in apoptotic cell death and oxidative injuries between the KO and WT cells. Less protein nitrotyrosine was induced by 0.05-0.5 mM DQ+0.25 mM SNAP in the KO than in the WT cells. Total GPX activity in the WT cells was reduced by 65 and 25% by 0.5 mM DQ+0.1 mM SNAP and 0.5 mM DQ, respectively. Decreases in Cu,Zn-superoxide dismutase (SOD) activity and increases in Mn-SOD activity in response to DQ or DQ+SNAP were greater in the KO cells than in the WT cells. In conclusion, GPX1 was more effective in protecting hepatocytes against oxidative injuries mediated by ROS alone than by ROS and RNS together. Knockout of GPX1 did not enhance cell susceptibility to RNS-associated cytotoxicity. Instead, it attenuated protein nitration induced by DQ+SNAP.

Animals↗

PubMed2001

Prolactin receptor signal transduction pathways and actions determined in prolactin receptor knockout mice.

Prolactin-receptor-deficient mice are a good model in which to study the various actions of prolactin. Female homozygous knockout mice are completely infertile and show a lack of mammary development, while hemizogotes are unable to lactate following their first pregnancy. Male and female homozygotes have markedly elevated serum prolactin levels, and in some instances pituitary hyperplasia is present. Maternal behaviour is severely affected in both hemizygous and homozygous animals. Bone formation is reduced in young animals and in adults (males and females). Finally, older males and females show a slight reduction in body weight, which seems to be due to reduced abdominal fat deposition in the knockout animals.

Animals↗

PubMed2002

Knockout models are useful tools to dissect the pathophysiology and genetics of insulin resistance.

OBJECTIVE: The development of type 2 diabetes is linked to insulin resistance coupled with a failure of pancreatic beta-cells to compensate by adequate insulin secretion. DESIGN: Here, we review studies obtained from genetically engineered mice that provide novel insights into the pathophysiology of insulin resistance. RESULTS: Knockout models with monogenic impairment in insulin action have highlighted the potential role for insulin signalling molecules in insulin resistance at a tissue-specific level. Polygenic models have strengthened the idea that minor defects in insulin secretion and insulin action, when combined, can lead to diabetes, emphasizing the importance of interactions of different genetic loci in the production of diabetes. Knockout models with tissue-specific alterations in glucose or lipid metabolism have dissected the individual contributions of insulin-responsive organs to glucose homeostasis. They have demonstrated the central role of fat as an endocrine tissue in the maintenance of insulin sensitivity and the development of insulin resistance. Finally, these models have shown the potential role of impaired insulin action in pancreatic beta-cells and brain in the development of insulin deficiency and obesity.

Adipose Tissue↗