Differential effects of bupropion on acquisition and performance of an active avoidance task in male mice

Bupropion is an antidepressant drug that is known to aid smoking cessation, although little experimental evidence exists about its actions on active avoidance learning tasks. Our aim was to evaluate the effects of this drug on two-way active avoidance conditioning. In this study, NMRI mice received bupropion (10, 20 and 40mg/kg) or saline before a daily training session (learning phase, days 1-4) in the active avoidance task. Performance was evaluated on the fifth day (retention phase): in each bupropion-treated group half of the mice continued with the same dose of bupropion, and the other half received saline. Among the vehicle-treated mice, different sub-groups were challenged with different doses of bupropion. Results indicated that mice treated with 10 and 20mg/kg bupropion exhibited more number of avoidances during acquisition. The response latency confirmed this learning improvement, since this parameter decreased after bupropion administration. No differences between groups were observed in the retention phase. In conclusion, our data show that bupropion influences the learning process during active avoidance conditioning, suggesting that this drug can improve the control of emotional responses.

Scriptaid and 5-aza-2'deoxycytidine enhanced expression of pluripotent genes and in vitro developmental competence in interspecies black-footed cat cloned embryos

Somatic cell nuclear transfer offers the possibility of preserving endangered species including the black-footed cat, which is threatened with extinction. The effectiveness and efficiency of somatic cell nuclear transfer (SCNT) depends on a variety of factors, but 'inappropriate epigenetic reprogramming of the transplanted nucleus is the primary cause of the developmental failure of cloned embryos. Abnormal epigenetic events such as DNA methylation and histone modifications during SCNT perturb the expression of imprinted and pluripotent-related genes that, consequently, may result in foetal and neonatal abnormalities. We have demonstrated that pregnancies can be established after transfer of black-footed cat cloned embryos into domestic cat recipients, but none of the implanted embryos developed to term and the foetal failure has been associated to aberrant reprogramming in cloned embryos. There is growing evidence that modifying the epigenetic pattern of the chromatin template of both donor cells and reconstructed embryos with a combination of inhibitors of histone deacetylases and DNA methyltransferases results in enhanced gene reactivation and improved in vitro and in vivo developmental competence. Epigenetic modifications of the chromatin template of black-footed cat donor cells and reconstructed embryos with epigenetic-modifying compounds enhanced in vitro development, and regulated the expression of pluripotent genes, but these epigenetic modifications did not improve in vivo developmental competence.

Differential sensitivity to the effects of nicotine and bupropion in adolescent and adult male OF1 mice during social interaction tests

Few studies have compared the action of both nicotine (NIC) and bupropion (BUP), an antidepressant used to treat NIC dependence, on social and aggressive behavior at different ages. This study aims to determine whether these drugs produce differential effects in adolescent (postnatal day: 36-37) and adult (postnatal day: 65-66) mice that have been housed individually for 2 weeks in order to induce aggressive behavior. Mice received BUP (40, 20, or 10 mg/kg), NIC (1, 0.5, and 0.25 mg/kg as base), or vehicle earlier to a social interaction test. BUP (40 mg/kg) decreased social investigation and increased nonsocial exploration in both adolescent and adult mice. The same effects were also observed in adult mice administered with a lower dose of the same drug (20 mg/kg). In adolescents, NIC (1 mg/kg) decreased social investigation, but this effect did not reach statistical significance in adults. In conclusion, a differential sensitivity to the effects of NIC or BUP emerged in some of the behavioral categories when the two age groups were compared.

High temporal resolution measurements of ozone precursors in a rural background station. A two-year study

We present a very complete database of individual non-methane hydrocarbon (NMHC) measurements with high temporal resolution (hourly) in a rural background atmosphere. We show their use to characterize the biogenic NMHC as well as to identify the transport and impact of anthropogenic NMHC on rural areas. In January 2003 an automatic GC-FID analyzer of volatile organic compounds between 2 and 10 carbon atoms (C2-C10 VOCs) was placed in the centre of the Valderejo Natural Park in northern Iberia (42.87 degrees N, 3.22 degrees W), far away from important cities. The system operated continuously until December 2004. Data coverage was higher than 70% for a total of 59 VOC of both anthropogenic and biogenic origin, with detection limits in the range of pptv. Our results allow for the description of the behaviour of these compounds, in order to identify external impacts arriving to the sampling site which has been recognized to be highly representative of a rural background atmosphere. Biogenic VOC concentrations have been compared also with the calculated emissions, using Guenther's algorithm, and the discrepancies interpreted in terms of the different reactivity of such compounds.

Isolation, culture and characterisation of somatic cells derived from semen and milk of endangered sheep and eland antelope

Semen and milk are potential sources of somatic cells for genome banks. In the present study, we cultured and characterised cells from: (1) cooled sheep milk; (2) fresh, cooled and frozen–thawed semen from Gulf Coast native (GCN) sheep (Ovis aries); and (3) fresh eland (Taurotragus oryx) semen. Cells attached to the culture surface from fresh (29%), cooled (43%) and slow-frozen (1°C/min; 14%) ram semen, whereas no attachment occurred in the fast-frozen (10°C/min) group. Proliferation occurred in fresh (50%) and cooled (100%) groups, but no cells proliferated after passage 1 (P1). Eland semen yielded cell lines (100%) that were cryopreserved at P1. In samples from GCN and cross-bred milk, cell attachment (83% and 95%, respectively) and proliferation (60% and 37%, respectively) were observed. Immunocytochemical detection of cytokeratin indicated an epithelial origin of semen-derived cells, whereas milk yielded either fibroblasts, epithelial or a mixture of cell types. Deoxyribonucleic acid microsatellite analysis using cattle-derived markers confirmed that eland cells were from the semen donor. Eland epithelial cells were transferred into eland oocytes and 12 (71%), six (35%) and two (12%) embryos cleaved and developed to morulae or blastocyst stages, respectively. In conclusion, we have developed a technique for obtaining somatic cells from semen. We have also demonstrated that semen-derived cells can serve as karyoplast donors for nuclear transfer.

Nuclear transfer in cats and its application

Nuclear transfer (NT) technology is typically used for generating identical individuals, but it is also a powerful resource for understanding the cellular and molecular aspects of nuclear reprogramming. Most recently, the procedure has been used in humans for producing patient-specific embryonic stem cells. The successful application of NT in cats was demonstrated by the birth of domestic and non-domestic cloned kittens at a similar level of efficiency to that reported for other mammalian species. In cats, it has been demonstrated that either in vivo or in vitro matured oocytes can be used as donor cytoplasts. The length of in vitro oocyte maturation affects in vitro development of reconstructed embryos, and oocytes matured in vitro for shorter periods of time are the preferred source of donor cytoplasts. For NT, cat somatic cells can be synchronized into the G0/G1 phase of the cell cycle by using different methods of cell synchronization without affecting the frequency of in vitro development of cloned embryos. Also, embryo development to the blastocyst stage in vitro is not influenced by cell type, but the effect of cell type on the percentage of normal offspring produced requires evaluation. Inter-species NT has potential application for preserving endangered felids, as live offspring of male and female African wildcats (AWC, Felis silvestris lybica) have been born and pregnancies have been produced after transferring black-footed cat (Felis nigripes) cloned embryos into domestic cat (Felis silvestris catus) recipients. Also, successful in vitro embryo development to the blastocyst stage has been achieved after inter-generic NT of somatic cells of non-domestic felids into domestic cat oocytes, but no viable progeny have been obtained. Thus, while cat cytoplasm induces early nuclear remodeling of cell nuclei from a different genus, the high incidence of early embryo developmental arrest may be caused by abnormal nuclear reprogramming. Fetal resorption and abortions were frequently observed at various stages of pregnancy after transfer of AWC cloned embryos into domestic cat recipients. Abnormalities, such as abdominal organ exteriorization and respiratory failure and septicemia were the main causes of death in neonatal cloned kittens. Nonetheless, several live domestic and AWC cloned kittens have been born that are seemingly normal and healthy. It is important to continue evaluating these animals throughout their lives and to examine their capability for natural reproduction.

In vitro production and transfer of cat embryos in the 21st century

Appreciable progress has been made in the development of assisted reproductive technology (ART) for creating in vitro embryos in cats. Moreover, the extent of advancement in the last decade has been similar, albeit of more modest magnitude, to that seen in some other domestic and laboratory species, particularly when the disparities in financial, and, hence, scientific, resources are considered. The recent progress in domestic felid ART has made it possible to envisage their potential role in supporting the conservation of endangered felid species, which, in reality, is a multifarious process requiring wide-ranging, yet coordinated approaches. The prospect of incorporating ART into that intricate domain, with limited exceptions, remains a long-term, but highly motivating objective. Meanwhile, the straightforward accessibility and abundant supply of domestic cat gametes from local veterinary clinics provides a valuable and practical source of material for further research on the basic aspects of in vitro oocyte maturation, fertilization and early embryo development. Furthermore, extrapolating the domestic biotechniques to non-domestic felids has produced encouraging results in some species.

Effects of acute bupropion administration on locomotor activity in adolescent and adult mice

Responses to some psychoactive substances seem to differ between adolescents and adults. Bupropion, an antidepressant which is also used for smoking cessation, induces a dose-dependent increase in locomotor activity in adult mice, although its behavioral actions in adolescents have not been evaluated. In the present study the effects of acute bupropion administration (5, 10, 15 and 20 mg/kg) on locomotor activity were examined in early adolescent (postnatal day (pnd): 29-31 days), late adolescent (pnd: 47-49 days) and adult (pnd > 70 days) male NMRI mice, using an infrared photocell system. Locomotion was recorded for a total period of 90 min. Results indicated that there were significant differences in motor activity counts between the three ages evaluated, with late adolescents being more active than early adolescents. Bupropion (at doses 20, 15 and 10 mg/kg) induced a significant increase in locomotion, but there was no significant interaction between age and treatment. This suggests that the locomotor-stimulating effects of bupropion can be observed at different ages (early adolescence, late adolescence and adulthood), although the detailed analysis of the temporal course of locomotion changes induced by different bupropion doses reflected some differences between ages. The lowest dose (5 mg/kg) failed to induce hyperactivity in either adolescent or adult mice.

Births of kittens produced by intracytoplasmic sperm injection of domestic cat oocytes matured in vitro

In Experiment 1, cleavage frequency and in vitro development of domestic cat embryos produced after in vitro maturation of oocytes obtained from ovaries after ovariohysterectomy (in vitro) with that of oocytes retrieved from follicle-stimulating hormone-treated donors at 24 h after administration of luteinizing hormone (in vivo) and fertilization by intracytoplasmic sperm injection (ICSI) or IVF were compared. In each group presumptive zygotes were assessed for cleavage on IVC Days 1 and 4 and for development to blastocysts on IVC Day 7. In vitro matured oocytes had lower frequencies of meiotic maturation (59.2% v. 66.5%), cleavage at Day 1 (41.4% v. 64.9%) and development to the morula stage at Day 4 (65.8% v. 87.9%) than did in vivo matured oocytes, after ICSI and IVF. Development to the blastocyst stage was lower in in vitro matured oocytes (19.0%) than in vivo matured oocytes (29.5%) after ICSI. In Experiment 2, we evaluated the capacity of sperm injected oocytes without a visible polar body to undergo cleavage and in vitro development. More in vivo matured than in vitro matured oocytes underwent cleavage at Day 1 (46.6% v. 12.6%) and developed to the morula stage by Day 4 (66.7% v. 46.1%), but no blastocysts were obtained at Day 7 in either group. In Experiment 3, we evaluated the in vivo viability of domestic cat embryos derived from ICSI of in vitro matured oocytes. Morula stage embryos were transferred to 18 domestic cat recipients either on Day 4 or 5 after oocyte recovery. A total of 3 domestic cat recipients were pregnant after transfer to recipients on Day 5. Two pregnant cats delivered two normal and healthy live male kittens on Day 68 of gestation and the remaining cat delivered a male kitten on Day 62 that died during the last two days of gestation. These results demonstrate that: (1) inadequate cytoplasmic maturation of in vitro matured domestic cat oocytes is the main cause of deficient oocyte activation; (2) the injection of oocytes without a visible polar body is a useful technique to evaluate oocyte cytoplasmic maturation; and (3) blastocysts obtained after ICSI of in vitro matured oocytes are viable and not a result of parthenogenesis.

Evaluation of two slide agglutination tests and a novel immunochromatographic assay for rapid diagnosis of infectious mononucleosis

The results of three tests used for the rapid diagnosis of infectious mononucleosis (IM) were compared with those of Epstein-Barr virus-specific serology. The sensitivities ranged from 15 to 33% in children under 13 years of age and from 59 to 81% in patients over 13 years. The specificities ranged from 86 to 100% in both age groups. These tests have a poor sensitivity for the diagnosis of IM, particularly in children.

[Comparative study of the Brucellacapt test versus the Coombs test for Brucella]

BACKGROUND

To compare the results obtained by Brucella Coombs' test with those obtained by Brucellacapt.

MATERIAL AND METHODS

145 serum samples from 112 patients with brucellosis or with brucellar infection suspected on clinical grounds and a history of occupational exposure were analyzed. All serum samples were tested for Rose Bengal, agglutinations whenever Rose Bengal was positive, Brucella Coombs' test and Brucellacapt.

RESULTS

There was a direct correlation between both methods (p < 0.01). Negative serum samples and most serum samples with titers between 1/40 and 1/2,560 as tested by Brucella Coombs' test showed similar results into a range of one to two dilutions by Brucellacapt. However, serum samples with titres between 1/5,120 and 1/40,960 by Brucella Combs' test yielded also higher titres by Brucellacapt and for this reason we were unable to define a titre.

CONCLUSIONS

Brucellacapt is a rapid assay to exclude infection and yield results comparable to Brucella Coombs' test in range 1/40 to 1/2,560. Significantly higher and more rapid titres were obtained in acute brucellosis by Brucellacapt as compared with those obtained by Brucella Coombs' test. Titre's evolutions by Brucellacapt is similar to Brucella Coombs' test. Unfortunately it was difficult the titres definition of Brucellacapt at high titres.

Effect of extra-virgin olive oil and fish-oil supplementation on plasma lipids and susceptibility of low-density lipoprotein to oxidative alteration in free-living spanish male patients with peripheral vascular disease

The aim of this study was to analyse the in vivo effect of a diet rich in extra-virgin olive oil and a fish-oil supplement on plasma and lipoprotein fatty-acid composition and on LDL susceptibility to oxidative modification in free-living Spanish male patients with peripheral vascular disease. A total of 12 patients were included in the experimental group which received extra virgin olive oil and a fish oil supplement (group OF). On the other hand, 13 patients which had refined olive oil as the main visible fat were considered as Control group. Plasma triglycerides decreased significantly after three months of dietary intervention. The LDL and plasma fatty-acid pattern in the group OF was characterized by a significant increase in n-3 polyunsaturated fatty acids, mainly 20:5 n-3 and 22:6 n-3. The slopes of LDL oxidative susceptibility were similar between baseline and endpoint values in both groups. However, the uptake of oxidized LDL by macrophages was significantly reduced in OF patients in comparison with the Control group. In conclusion, the daily intake of about 40 g/d of extra-virgin olive oil in combination with a daily supplement of 16 g of fish oil for 3 months in patients with peripheral vascular disease leads to a plasma-lipid profile less atherogenic than in patients having refined olive oil as the main visible food fat. The simultaneous consumption of alpha-tocopherol and natural antioxidants provided by extra-virgin olive oil seems to have a protective effect on the LDL susceptibility to oxidative modifications in spite of a higher proportion of n-3 polyunsaturated fatty acids.

Induction of a protective antibody response to foot and mouth disease virus in mice following oral or parenteral immunization with alfalfa transgenic plants expressing the viral structural protein VP1

The utilization of transgenic plants expressing recombinant antigens to be used in the formulation of experimental immunogens has been recently communicated. We report here the development of transgenic plants of alfalfa expressing the structural protein VP1 of foot and mouth disease virus (FMDV). The presence of the transgenes in the plants was confirmed by PCR and their specific transcription was demonstrated by RT-PCR. Mice parenterally immunized using leaf extracts or receiving in their diet freshly harvested leaves from the transgenic plants developed a virus-specific immune response. Animals immunized by either method elicited a specific antibody response to a synthetic peptide representing amino acid residues 135-160 of VP1, to the structural protein VP1, and to intact FMDV particles. Additionally, the immunized mice were protected against experimental challenge with the virus. We believe this is the first report demonstrating the induction of a protective systemic antibody response in animals fed transgenic plants expressing a viral antigen. These results support the feasibility of producing edible vaccines in transgenic forage plants, such as alfalfa, commonly used in the diet of domestic animals even for those antigens for which a systemic immune response is required.

Sheep oocyte activation after intracytoplasmic sperm injection (ICSI)

The effect of calcium concentration on fertilization and activation was examined in oocytes injected in vitro with sperm. Oocytes were subjected to sperm injection, to sham injection or remained uninjected, and were then cultured for 19 h in bicarbonate-buffered synthetic oviduct fluid (BSOF) without calcium, or containing either calcium chloride or calcium ionophore. There was no difference in fertilization rates after ICSI when oocytes were cultured in vitro in media containing calcium chloride or calcium ionophore but the rate was lower in calcium-free media. There was also no difference in the fertilization rate after ICSI when oocytes were cultured in vivo compared with that observed in vitro in media containing calcium chloride or calcium ionophore. In calcium chloride-treated oocytes, activation was induced by mechanical injection, and in calcium ionophore-treated oocytes, by the ionophore. In uninjected oocytes, calcium itself did not cause oocyte activation. It is concluded that it is possible to induce activation by the injection process, but that manipulation alone is inadequate to cause proper oocyte activation unless calcium is also present. No difference in oocyte activation between ICSI and sham injection was found, indicating that the sperm may play no role in the early events of oocyte activation.

Time course of pronuclear formation and fertilisation after insemination in vitro and intracytoplasmic sperm injection of in vitro matured sheep oocytes

The time course of sperm decondensation, oocyte activation, pronuclear formation and the possible causes of abnormalities after intracytoplasmic sperm injection (ICSI) and in vitro fertilisation (IVF) were examined. Frozen-thawed and pooled fresh semen from three different rams were washed and capacitated for ICSI or IVF. In vitro matured oocytes were cultured after sperm injection for 0.5, 0.75, 1, 2, 3, 4, 5, 6, 8, 18, 21 and 23 h, and oocytes were cultured after in vitro insemination for the same times other than 18 and 23 h. All oocytes were cultured in bicarbonate-buffered synthetic oviduct fluid medium (BSOF) supplemented with 2% oestrous sheep serum. A total of 746 metaphase II oocytes were injected with a single spermatozoon and 986 oocytes were inseminated for IVF. The earliest oocyte activation after ICSI was observed at 0.5 h, when 14.8% of oocytes were in anaphase II; this was earlier than after IVF, when only 6.4% of the oocytes exhibited anaphase II 1 h after insemination. Decondensing spermatozoa were first observed 1 h after ICSI and 3 h after insemination for IVF. The earliest female and male pronuclei after ICSI were observed at 2 and 3 h respectively, while the female and male pronuclei after IVF were observed at 4 h after insemination. The overall fertilisation rate was lower after ICSI (28.6%) than IVF (70.4%) but the percentage of abnormal fertilisation was not different between ICSI (8.7%) and IVF (15.2%). It was concluded that the fertilisation events were more advanced for ICSI than IVF, using injection and insemination time as reference points. The formation of male and female pronuclei were asynchronous after ICSI, in contrast to IVF when they appeared simultaneously at 4 h. Abnormalities found in fertilisation after ICSI may therefore be induced by the injection technique.

Effect of culture, incubation and acrosome reaction of fresh and frozen-thawed ram spermatozoa for in vitro fertilization and intracytoplasmic sperm injection

This study evaluated different sperm treatments for fertilization of sheep oocytes by intracytoplasmic sperm injection (ICSI) and in vitro fertilization (IVF). In Experiment 1, fresh and frozen semen was separated by Percoll centrifugation and incubated at 30 degrees C or 39 degrees C in HSOF or BSOF medium for 1 h before use for IVF or ICSI. For IVF, oocytes were inseminated and incubated with sperm for 30 min, 4 h and 19 h. Sperm were assessed for acrosome integrity after Percoll centrifugation and 1 h incubation, and those used for IVF were assessed after each period of exposure to the oocytes. Fertilization rates after ICSI were higher for fresh than for frozen-thawed sperm and were highest 19 h after IVF with fresh or frozen-thawed sperm in the presence of HSOF at 30 degrees C. In Experiment 2, fresh semen was separated by Percoll centrifugation and incubated for 5 h in HSOF, and the acrosome reaction was induced with lysophosphatidylcholine. Acrosome integrity was then assessed. Fertilization rates after ICSI were similar for acrosome-reacted and control spermatozoa. These results suggest that induction of the acrosome reaction in spermatozoa before ICSI is unnecessary, whereas a capacitating treatment of spermatozoa is required before IVF.

Cleavage, development and competence of sheep embryos fertilized by intracytoplasmic sperm injection and in vitro fertilization

More abnormal fertilization has been found in sheep oocytes after intracytoplasmic sperm injection (ICSI) than after in vitro fertilization (IVF). Although the birth of a normal lamb has been reported, the efficiency of blastocyst production is low. We therefore evaluated the cleavage, development and viability of sheep embryos obtained from ICSI, IVF and sham injection. In vitro matured oocytes either injected or inseminated with spermatozoa were assessed for cleavage 1 and 4 d after injection or insemination, and for development to blastocyst after 7 d of culture. A total of 699 oocytes was injected (ICSI); 198 (30.6%) were activated and 55 (8.5%) developed to the blastocyst stage. Of the 17 recipient ewes with 1, 2, 3 or 4 embryos, 15 (88.2%) were pregnant on Day 18; of these 17 recipients, 7 (41.1%) and 6 (35.2%) ewes remained pregnant on Days 45 and 110, respectively. Two normal lambs were born, one ewe died on Day 110 with 2 normal male fetuses, another ewe aborted on Day 90 and 4 pregnancies were maintained. A total of 517 oocytes was inseminated (IVF); 296 (62%) were activated and 90 (18.8%) reached the blastocyst stage. A total of 19 ewes received 1, 2, 3 or 4 embryos; of these, 13 (68.4%) were pregnant on Day 18, 8 (42.1%) ewes remained pregnant on each of Days 45 and 110. Three ewes delivered 5 lambs. Five pregnancies were maintained. A total of 156 oocytes was sham injected, 38 (24.3%) were activated and no blatocysts were obtained after culture. The results of this study showed that blastocysts obtained after ICSI are potentially viable and are not a result of parthenogenesis.

Serum angiotensin converting enzyme and C4 protein of complement as a combined diagnostic index in alcoholic liver disease

Diagnosis of liver cirrhosis relies on hepatic biopsy. So far, attempts have failed to achieve a serologic test that differentiates cirrhosis from other hepatic conditions. The aim of this work was to assess the diagnostic value of the ratio of serum angiotensin converting enzyme activity (SACE) and the levels of protein C4 of serum complement (SACE/C4) in differentiating cirrhotic from noncirrhotic alcoholic liver diseases. In this study, 68 active alcoholic patients (17 with fatty liver or minimal changes, 11 with acute alcoholic hepatitis and 40 with cirrhosis) were included. Twenty healthy subjects were studied as a control group. Liver biopsy was performed in all patients. SACE levels were significantly higher in the group with cirrhosis when compared with the group of patients without cirrhosis and the control. On the other hand, serum C4 level decreased as liver damage progressed. SACE values above 25 IU/l had a sensitivity of 92.5 percent (95 percent confidence interval, 87.5 to 97.5) and a specificity of 79 percent (95% percent confidence interval, 70.5 to 87.5), in detecting those patients with liver cirrhosis. The sensitivity further increased to 95 percent (95 percent confidence interval, 90.5 to 99.5) and the specificity to 100 percent when the SACE/C4 ratio was used and a cutoff point of 145 was chosen. To conclude, in alcoholics SACE is specifically elevated in patients with cirrhosis, and the SACE/C4 ratio is a excellent biochemical index for the diagnosis of cirrhosis in alcoholic patients.

New cardiotonic agents related to amrinone: synthesis of 1,2-dihydro-5-arylpyridin-2-ones

For development of new cardiotonic agents a series of 5-aryl-3,4-dihydropyridin-2(1H)-ones, related to amrinone have been prepared from methylquinolines, 2-arylacetic acid or 3-arylethanones by direct aminomethylenation and subsequent condensation-cyclization with malonamide and cyanacetamide in classic basic media or phase-transfer catalysis, in good to excellent yields. Preliminary pharmacological assays have shown that these compounds, especially 5h and 5i, have a remarkable cardiotonic effect and present a selective inhibition of PDE-III/PDE-I isolated from cat heart.

Effect of the combination of clavulanic acid and cephalothin on an experimental infection with Yersinia enterocolitica in iron-overloaded mice

Iron-overloaded mice were infected with a virulent strain of Yersinia enterocolitica by the oral route to study the effect of antimicrobial treatments. The effects of therapy were assessed by enumeration of viable yersiniae in Peyer's patches and in ileal contents. Combinations of cephalothin and clavulanic acid showed therapeutic effects, which were interpreted as in-vivo synergism, since each component alone was ineffective. Ceftazidime, which is relatively beta-lactamase resistant, showed in-vivo activity similar to that of the combination of cephalothin and clavulanic acid. These results suggest that clavulanic acid is able to protect cephalothin against Y. enterocolitica beta-lactamases in vivo, as has been shown previously in vitro.