Antidepressants Attenuate Increased Susceptibility to Colitis in a Murine Model of Depression
2006; Elsevier BV; Volume: 130; Issue: 6 Linguagem: Inglês
10.1053/j.gastro.2006.02.007
ISSN1528-0012
AutoresAshwin Varghese, Elena F. Verdú, Přemysl Berčík, Waliul I. Khan, Patricia Blennerhassett, Henry Szechtman, Stephen M. Collins,
Tópico(s)Maternal Mental Health During Pregnancy and Postpartum
ResumoBackground & Aims: Psychiatric factors may determine gastrointestinal health outcomes. Here, we used a model of depression based on neonatal maternal separation (MS) to identify alterations in gut physiology and to assess its association with increased sensitivity to experimental colitis in adulthood. We also examined whether antidepressant therapy attenuates the increased susceptibility to colitis. Methods: C57BL/6 mouse pups were separated from mothers for 3 hours per day at 1–21 days of age. Maternally unseparated (US) litters served as controls. At 8 weeks of age mice were examined for changes in behavior, intestinal permeability, and sensitivity to colitis. Separate sets of MS and US mice were given either saline or the antidepressant desipramine 15 mg/kg once daily at 23–36 days of age. Testing of mice occurred at 8 weeks of age. Results: Adult MS mice showed evidence of depressive-like behavior and enhanced intestinal permeability but showed no evidence of spontaneous inflammation. A more severe colitis was seen in MS compared with US mice. Antidepressant therapy improved parameters of depressive-like behavior and reduced the vulnerability to dextran sulphate sodium colitis in MS mice but had no effect on colitis in US mice. Conclusions: MS may lead to depression and increased responsiveness to stress, to impaired intestinal barrier function, and to enhanced vulnerability to colitis in adulthood. This vulnerability is reversed by antidepressant therapy. Depression increases vulnerability to intestinal inflammation. We speculate that pre-existing depression may facilitate the expression of inflammatory bowel diseases. Background & Aims: Psychiatric factors may determine gastrointestinal health outcomes. Here, we used a model of depression based on neonatal maternal separation (MS) to identify alterations in gut physiology and to assess its association with increased sensitivity to experimental colitis in adulthood. We also examined whether antidepressant therapy attenuates the increased susceptibility to colitis. Methods: C57BL/6 mouse pups were separated from mothers for 3 hours per day at 1–21 days of age. Maternally unseparated (US) litters served as controls. At 8 weeks of age mice were examined for changes in behavior, intestinal permeability, and sensitivity to colitis. Separate sets of MS and US mice were given either saline or the antidepressant desipramine 15 mg/kg once daily at 23–36 days of age. Testing of mice occurred at 8 weeks of age. Results: Adult MS mice showed evidence of depressive-like behavior and enhanced intestinal permeability but showed no evidence of spontaneous inflammation. A more severe colitis was seen in MS compared with US mice. Antidepressant therapy improved parameters of depressive-like behavior and reduced the vulnerability to dextran sulphate sodium colitis in MS mice but had no effect on colitis in US mice. Conclusions: MS may lead to depression and increased responsiveness to stress, to impaired intestinal barrier function, and to enhanced vulnerability to colitis in adulthood. This vulnerability is reversed by antidepressant therapy. Depression increases vulnerability to intestinal inflammation. We speculate that pre-existing depression may facilitate the expression of inflammatory bowel diseases. Although ulcerative colitis initially was considered to represent a psychosomatic disease,1Daniels G.E. Nonspecific ulcerative colitis as a psychosomatic disease.Med Clin North Am. 1944; 28: 593-598Google Scholar the role of behavioral factors in inflammatory bowel disease (IBD) is controversial.2North C.S. Clouse R.E. Spitznagel E.L. Alpers D.H. The relation of ulcerative colitis to psychiatric factors a review of findings and methods.Am J Psychiatry. 1990; 147: 974-981PubMed Google Scholar With increased understanding of the role of the immune system in the pathogenesis of IBD,3Collins S.M. Stress and the gastrointestinal tract IV. Modulation of intestinal inflammation by stress: basic mechanisms and clinical relevance.Am J Physiol. 2001; 280: G315-G318Google Scholar less attention has been paid to the impact of behavioral factors on the natural history of these diseases. Some studies have shown that there is a higher than expected incidence of depression in both ulcerative colitis (UC)4Kurina L.M. Goldacre M.J. Yeates D. Gill L.E. Depression and anxiety in people with inflammatory bowel disease.J Epidemiol Community Health. 2001; 55: 716-720Crossref PubMed Scopus (275) Google Scholar and Crohn’s disease (CD),5Helzer J.E. Chammas S. Norland C.C. Stillings W.A. Alpers D.H. A study of the association between Crohn’s disease and psychiatric illness.Gastroenterology. 1984; 86: 324-330PubMed Scopus (134) Google Scholar and in other studies depression correlated well with disease activity, suggesting that it might be secondary to the disability imposed by IBD.6Mardini H.E. Kip K.E. Wilson J.W. Crohn’s disease a two-year prospective study of the association between psychological distress and disease activity.Dig Dis Sci. 2004; 49: 492-497Crossref PubMed Scopus (170) Google Scholar However, in another study depression was unrelated to disease activity,7Addolorato G. Capristo E. Stefanini G.F. Gasbarrini G. Inflammatory bowel disease a study of the association between anxiety and depression, physical morbidity, and nutritional status.Scand J Gastroenterol. 1997; 32: 1013-1021Crossref PubMed Scopus (201) Google Scholar and in other studies it actually predated the onset of CD8Tarter R.E. Switala J. Carra J. Edwards K.L. Van Thiel D.H. Inflammatory bowel disease psychiatric status of patients before and after disease onset.Int J Psychiatry Med. 1987; 17: 173-181Crossref PubMed Google Scholar and UC.4Kurina L.M. Goldacre M.J. Yeates D. Gill L.E. Depression and anxiety in people with inflammatory bowel disease.J Epidemiol Community Health. 2001; 55: 716-720Crossref PubMed Scopus (275) Google Scholar It is therefore unclear whether depression is merely an unrelated epiphenomenon that occurs as a result of the disease and the disability it imposes, or whether the presence of depression plays a role in facilitating the expression of IBD.Although major depressive disorder has long been associated with central neural changes such as cognitive impairment9Richardson J.S. Keegan D.L. Bowen R.C. Blackshaw S.L. Cebrian-Perez S. Dayal N. Saleh S. Shrikhande S. 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A prospective population-based study.Diabetes Care. 1996; 19: 1097-1102Crossref PubMed Scopus (493) Google Scholar peptic ulcer disease,13Levenstein S. Kaplan G.A. Smith M.W. Psychological predictors of peptic ulcer incidence in the Alameda County Study.J Clin Gastroenterol. 1997; 24: 140-146Crossref PubMed Scopus (67) Google Scholar immune dysfunction,14Glaser R. Robles T.F. Sheridan J. Malarkey W.B. Kiecolt-Glaser J.K. Mild depressive symptoms are associated with amplified and prolonged inflammatory responses after influenza virus vaccination in older adults.Arch Gen Psychiatry. 2003; 60: 1009-1014Crossref PubMed Scopus (192) Google Scholar and cardiovascular disease.15Wulsin L.R. Singal B.M. Do depressive symptoms increase the risk for the onset of coronary disease? A systematic quantitative review.Psychosom Med. 2003; 65: 201-210Crossref PubMed Scopus (577) Google Scholar, 16Ford D.E. Erlinger T.P. Depression and C-reactive protein in US adults data from the Third National Health and Nutrition Examination Survey.Arch Intern Med. 2004; 164: 1010-1014Crossref PubMed Scopus (438) Google Scholar The increased risk for ischemic heart disease in depressed patients has been linked with increases in the acute phase reactant C-reactive protein.16Ford D.E. Erlinger T.P. Depression and C-reactive protein in US adults data from the Third National Health and Nutrition Examination Survey.Arch Intern Med. 2004; 164: 1010-1014Crossref PubMed Scopus (438) Google Scholar, 17Suarez E.C. C-reactive protein is associated with psychological risk factors of cardiovascular disease in apparently healthy adults.Psychosom Med. 2004; 66: 684-691Crossref PubMed Scopus (129) Google Scholar, 18Wong N.D. Pio J. Valencia R. Thakal G. Distribution of C-reactive protein and its relation to risk factors and coronary heart disease risk estimation in the National Health and Nutrition Examination Survey (NHANES) III.Prev Cardiol. 2001; 4: 109-114Crossref PubMed Scopus (103) Google Scholar Indeed, depression and anger per se may result in increased C-reactive protein levels,17Suarez E.C. C-reactive protein is associated with psychological risk factors of cardiovascular disease in apparently healthy adults.Psychosom Med. 2004; 66: 684-691Crossref PubMed Scopus (129) Google Scholar thus creating a potential link between behavior and risk for inflammatory-based disorders.Childhood exposure to emotional trauma, such as maternal loss, is recognized as a risk factor for the development of psychiatric disorders, including depression in adulthood.19Kendler K.S. Neale M.C. Kessler R.C. Heath A.C. Eaves L.J. Childhood parental loss and adult psychopathology in women. A twin study perspective.Arch Gen Psychiatry. 1992; 49: 109-116Crossref PubMed Scopus (313) Google Scholar During the postnatal period, the infant depends on the mother not only for nursing and protection but also for normal brain development.20Huot R.L. Thrivikraman K.V. Meaney M.J. Plotsky P.M. Development of adult ethanol preference and anxiety as a consequence of neonatal maternal separation in Long Evans rats and reversal with antidepressant treatment.Psychopharmacology. 2001; 158: 366-373Crossref PubMed Scopus (431) Google Scholar Rodent models have shown that neonatal maternal separation (MS) leads to depressive-like behavior that may be treated with antidepressants in adult life.21MacQueen G.M. Ramakrishnan K. Ratnasingan R. Chen B. Young L.T. Desipramine treatment reduces the long-term behavioural and neurochemical sequelae of early-life maternal separation.Int J Neuropsychopharmacol. 2003; 6: 391-396Crossref PubMed Scopus (85) Google Scholar We exploited this model to test the hypothesis that exposure to neonatal psychologic stress that induces depressive-like symptoms leads to altered intestinal physiology and an enhanced vulnerability to intestinal inflammation in adulthood. To investigate a causal link between the behavioral changes and intestinal events, we also examined whether antidepressant therapy of MS mice attenuated the susceptibility to inflammatory stimuli later in life.Materials and MethodsAnimalsSpecific pathogen-free, pregnant C57BL/6 female mice (whose conception date was known) were obtained from Taconic Farms (Germantown, NY) on gestational days 15–16. Dams were housed individually in cages containing bedding material on a 12-hour light-dark cycle (lights on at 8:00 am) and provided with food and water ad libitum. All procedures were approved by the Animal Rights Ethics Board at McMaster University.Maternal SeparationThe MS protocol used in the present study was a slight modification of one previously published.21MacQueen G.M. Ramakrishnan K. Ratnasingan R. Chen B. Young L.T. Desipramine treatment reduces the long-term behavioural and neurochemical sequelae of early-life maternal separation.Int J Neuropsychopharmacol. 2003; 6: 391-396Crossref PubMed Scopus (85) Google Scholar Dams and their litters were assigned at random to the control (unseparated) group or the MS group. MS pups were removed from their home cages and dams at postnatal day (PND) 1 to PND 21 for 180 minutes daily by placing them as a litter in a new isolation cage. The isolation cages were lined with chip bedding and kept at 37°C ± 5°C by using a heating pad placed under the cages. Dams of the MS group also were removed from the home cages and transferred to separate holding cages during the MS procedure. The technician’s gloved hands were rubbed in the bedding of each litter before handling of pups to prevent rejection by dams on reunion. Unseparated (US) litters were left undisturbed, except for routine cage care by the technician. At weaning (PND 23), male offspring were identified and served as subjects in the study. Subjects were weighed at PND 60.Antidepressant Treatment After MSTreatment of animals with the antidepressant desipramine (DMI) after MS was according to a slight modification of a previously published regimen.21MacQueen G.M. Ramakrishnan K. Ratnasingan R. Chen B. Young L.T. Desipramine treatment reduces the long-term behavioural and neurochemical sequelae of early-life maternal separation.Int J Neuropsychopharmacol. 2003; 6: 391-396Crossref PubMed Scopus (85) Google Scholar DMI treatment began on PND 23. Half of the animals in both the MS and US groups were given intraperitoneal injections of 15 mg/kg DMI once daily between 10:00 am and 12:00 pm, whereas control animals from both the MS and US groups received equivalent volumes of saline intraperitoneally. DMI or saline treatment continued until PND 36. After completion of the DMI treatment, animals were left undisturbed except for routine cage cleaning until behavior (tail suspension) testing or colitis induction was begun on PND 60.Antidepressant Treatment in Adult US MiceTo examine any direct effect of desipramine on colitis, DMI was administered once daily by intraperitoneal injections (15 mg/kg) for 1 week before and during induction of colitis by dextran sulphate sodium (DSS) in drinking water.Tail Suspension TestThe tail suspension test, conducted as previously described, is a test of depressive-like behavior in rodents.22Holmes A. Yang R.J. Murphy D.L. Crawley J.N. Evaluation of antidepressant-related behavioral responses in mice lacking the serotonin transporter.Neuropsychopharmacology. 2002; 27: 914-923Crossref PubMed Scopus (239) Google Scholar Mice were fastened securely by the distal end of the tail to a flat metallic surface and suspended in a visually isolated area (40 × 40 × 40 cm white Plexiglas box). The presence or absence of immobility, defined as the absence of limb movement, was sampled every 5 seconds over a 6-minute test session by a highly trained observer who was blinded to neonatal manipulation.Assessment of Behavioral Responses to StressAdult mice at PND 60 were tested for evidence of increased behavioral responsiveness to stress, consistent with depressive-like symptoms as suggested by previous studies.21MacQueen G.M. Ramakrishnan K. Ratnasingan R. Chen B. Young L.T. Desipramine treatment reduces the long-term behavioural and neurochemical sequelae of early-life maternal separation.Int J Neuropsychopharmacol. 2003; 6: 391-396Crossref PubMed Scopus (85) Google Scholar The open field test and the novel object tests are used to assess behavioral reactivity to stress by exposing rodents to novel environments and novel objects, respectively, and combinations of both tests also may be used.23van Gaalen M.M. Steckler T. Behavioural analysis of four mouse strains in an anxiety test battery.Behav Brain Res. 2000; 115: 95-106Crossref PubMed Scopus (212) Google Scholar The behavior tests used in the present study were slightly modified from those published previously.24Sakic B. Szechtman H. Talangbayan H. Denburg S.D. Carbotte R.M. Denburg J.A. Disturbed emotionality in autoimmune MRL-lpr mice.Physiol Behav. 1994; 56: 609-617Crossref PubMed Scopus (120) Google Scholar Two weeks before the start of the experiment (at PND 46), mice were separated from littermates and were housed individually. Mice were handled briefly by the experimenter every day for 5 days before the start of the experiment. Testing was conducted between 6 pm and 12 am in a dimly lit room.Each mouse was placed gently in the center of an open field (a Plexiglas cube [450 × 450 × 450 cm] custom built at McMaster University) and allowed to explore the novel environment for 10 minutes. At 10 minutes, a novel object (a white Styrofoam cup) was introduced into the center of the field and mice were allowed to respond to the novel object for a further 10 minutes. All sessions were filmed using a Sony video camera (Toronto, Canada). At the end of each session the open field was cleaned with paper towels that were moistened with an ammonium glass cleaner (Windex, SC Johnson & Son, Inc., Brantford, Ontario, Canada) to remove urinary trails. During each session, mice from both the MS and US groups were tested simultaneously by placing 2 open fields adjacent to each other under the camera’s optical field. Locomotor activity of mice throughout the 20-minute trial was measured from the video records using the EthoVision 2.3 tracking software system (Noldus Information Technology, Leesburg, VA). The distance traveled per movement bout (the mean length of a locomotor bout) was chosen as the index of stress reactivity to the novel environment because it combines both the amount and rate of activity. The time-course of the amount and duration of locomotion across the session was taken as a reflection of the rate of habituation to the stressful novel environment.Assessment of Feeding PatternsFeeding patterns were assessed over 24 hours in MS and US adult mice on PND 60. Two weeks before the start of the experiment, mice were separated from littermates and were housed individually. The experimental feeding apparatus consisted of food pellets fastened onto feeding trays (diameter, 3 cm) positioned 5 cm above the bottom of the cage. Mice were allowed to habituate to the experimental feeding trays for 1 week before the start of experiments. During the experiment, day/night cycles were adjusted with lights turning on at 7:30 am and turning off at 7:30 pm. At the start of the experiment, feeding trays were connected to computer-monitored force transducers placed above the cage. Weights of the feeding trays with food pellets were recorded continuously throughout the experiment by custom-written computer software, Acquire 5.1 and GraphView 5.1. The beginning of each feeding bout was marked by an abrupt increase in weight (as the mouse leaned on the feeding tray to gain access to the food pellets), and the end of the bout was characterized by an abrupt return to near baseline weight (as the mouse released the feeding tray). The difference in weight between before and after a feeding bout corresponded to the amount of food consumed during that bout. A feeding bout was defined as an episode of food consumption lasting more than 20 seconds; 2 bouts were considered independent from each other if the interval of inactivity was longer than 5 minutes, as defined previously.25Smith J.C. Microstructure of the rat’s intake of food, sucrose and saccharin in 24-hour tests.Neurosci Biobehav Rev. 2000; 24: 199-212Crossref PubMed Scopus (62) Google ScholarIntestinal Permeability MeasurementAdult mice underwent intestinal permeability testing on PND 60. Isolation and preparation of intestinal loops were according to a protocol by Bercik et al26Bercik P. Armstrong D. Fraser R. Dutoit P. Emde C. Primi M.P. Blum A.L. Kucera P. Origins of motility patterns in isolated arterially perfused rat intestine.Gastroenterology. 1994; 106: 649-657PubMed Google Scholar that was adapted to mice for the assessment of intestinal permeability using recovery of radioactivity in venous outflow after intraluminal perfusion of jejunal loops with 51-chromium–ethylenediaminetetraacetic acid (51Cr-EDTA). The luminal perfusate containing 51Cr-EDTA was a slight modification of the solution used previously27Behrens R.H. Szaz K.F. Northrop C. Elia M. Neale G. Radionuclide tests for the assessment of intestinal permeability.Eur J Clin Invest. 1987; 17: 100-105Crossref PubMed Scopus (26) Google Scholar in clinical studies of intestinal permeability.Briefly, mice were anesthetized with intraperitoneal ketamine/xylazine. After a midline incision was made, a 2.5- to 3.5-cm segment or loop of the jejunum was selected and the terminal branch of the superior mesenteric artery was cannulated with a polyethylene catheter. Tissue oxygenation was maintained by perfusion of the arterial branch with Hemolink, a hemoglobin-based oxygen carrier, in lactated Ringer’s solution (Hemosol Inc., Mississauga, ON) equilibrated with O2 (100%) using a peristaltic pump (Ismatec SA, Zurich, Switzerland). Nutrition for the loop was provided by the addition of 0.1% (wt/vol) glucose and 0.6 mmol/L glutamine to the arterial perfusate. Normal mouse serum 10% (wt/vol) also was added to the arterial perfusate to prevent methylation of hemoglobin and to provide additional nutrition. Both oral and aboral ends of the jejunal segment were cannulated using polyethylene cannulas and fastened with double ligatures. The jejunal loop was dissected from its mesentery and transferred to an organ chamber containing phosphate-buffered saline (PBS) at 37°C and perfused intraluminally in an aboral direction with PBS at 5 mL/h using a syringe infusion pump (Harvard, Boston, MA).After isolation of the intestinal loop, all preparations were allowed to equilibrate for 10 minutes before venous outflow collection. Venous outflow was collected continuously for the remainder of the experiment in 3-minute fractions. After equilibration, perfusion of PBS was stopped and the lumen was perfused with the 51Cr-EDTA solution for 15 minutes at 5 mL/h. The 51Cr-EDTA solution, adjusted to 300 mOsm, contained 51Cr-EDTA (0.6 μCi/mL) (Perkin Elmer, Boston, MA), mannitol (3 mg/mL) (Sigma-Aldrich Corporation, Oakville, Ontario, Canada), and NaCl (0.4% wt/vol) (Sigma-Aldrich Corporation) in distilled H2O. At 15 minutes, intraluminal perfusion of the 51Cr-EDTA solution was stopped and the lumen was perfused with PBS at 5 mL/h for a wash period of 30 minutes. After the end of each experiment, the length of the jejunal loop was measured and 2 full-thickness tissue samples were excised from proximal and distal regions of the loop, fixed in formalin, stained with H&E, and examined for tissue damage by light microscopy.The γ radiation from 51Cr-EDTA in the venous outflow fractions was measured by counting a 150-μL aliquot of each fraction in a well-type γ-counter (1282 Compugamma, LKB WALLAC; Fisher Scientific, Toronto, ON) for 1 minute. Counts were compared with a 51Cr-EDTA standard curve prepared previously from the luminal perfusate. The recovery of radioactivity in each venous outflow fraction was calculated as a proportion of that found in an identical volume of the luminal perfusate, corrected for length of the jejunal loop. The total recovery of radioactivity was determined as the sum of the radioactivity recovery of individual fractions.Assessment of Spontaneous InflammationMS and US mice were killed on PND 60 for assessment of basal-state immunity. Whole blood was collected by cardiac puncture in mice while under anesthesia before death for a serum amyloid P-component (SAP) level measurement. Samples of the distal colon were prepared for histology by fixation in 10% formalin followed by H&E staining. Additional samples of the distal colon were snap-frozen in liquid nitrogen for assessment of myeloperoxidase (MPO) activity and inflammatory cytokine levels.Histologic Assessment of Colonic TissueMicroscopic scoring was based on a scheme that accounted for the loss of mucosal architecture and infiltration by inflammatory cells.28Verdu E.F. Bercik P. Cukrowska B. Farre-Castany M.A. Bouzourene H. Saraga E. Blum A.L. Corthesy-Theulaz I. Tlaskalova-Hogenova H. Michetti P. Oral administration of antigens from intestinal flora anaerobic bacteria reduces the severity of experimental acute colitis in BALB/c mice.Clin Exp Immunol. 2000; 120: 46-50Crossref PubMed Scopus (46) Google Scholar Microscopic scoring was conducted by 2 experimenters in a blinded fashion.MPO AssayAcute inflammation was assessed by MPO activity in intestinal tissue. The assay was performed on frozen samples as described previously.29Barbara G. Vallance B.A. Collins S.M. Persistent intestinal neuromuscular dysfunction after acute nematode infection in mice.Gastroenterology. 1997; 113: 1224-1232Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar MPO activity is reported in units per mg of wet tissue, where 1 unit of MPO is defined as the quantity of enzyme able to convert 1 μmol of hydrogen peroxide to water in 1 minute at room temperature.Tissue Cytokine AssayLevels of interleukin (IL)-1β were assessed in intestinal tissue. Total protein was extracted from frozen tissue according to a protocol previously described.30Gabaglia C.R. Pedersen B. Hitt M. Burdin N. Sercarz E.E. Graham F.L. Gauldie J. Braciak T.A. A single intramuscular injection with an adenovirus-expressing IL-12 protects BALB/c mice against Leishmania major infection, while treatment with an IL-4-expressing vector increases disease susceptibility in B10.D2 mice.J Immunol. 1999; 162: 753-760PubMed Google Scholar Total protein levels were measured using a commercially available variant of the Lowry assay (Bio-Rad Laboratories, Hercules, CA). IL-1β levels in the protein extracts were measured using an enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, MN). IL-1β levels are reported as pg of IL-1β per mg of total protein.SAP Enzyme-Linked Immunosorbent AssaySAP is considered the prototype acute-phase reactant in mice.31Taktak Y.S. Stenning B. Solid phase enzyme immunoassays for the quantification of serum amyloid P (SAP) and complement component 3 (C3) proteins in acute-phase mouse sera.Horm Metab Res. 1992; 24: 371-374Crossref PubMed Scopus (25) Google Scholar Serum was extracted from whole-blood samples by centrifugation. SAP levels were measured using a sandwich enzyme-linked immunosorbent assay technique according to Taktak and Stenning.31Taktak Y.S. Stenning B. Solid phase enzyme immunoassays for the quantification of serum amyloid P (SAP) and complement component 3 (C3) proteins in acute-phase mouse sera.Horm Metab Res. 1992; 24: 371-374Crossref PubMed Scopus (25) Google Scholar SAP levels are reported as μg of SAP per mL of serum.DSS-Induced ColitisAcute colitis was induced in adult mice by 6% DSS in drinking water for 5 days (PNDs 60–65). At the end of DSS feeding, blood was obtained for SAP levels. Clinical disease scores graded the presence of rectal prolapse, rectal bleeding, and weight loss as described previously.28Verdu E.F. Bercik P. Cukrowska B. Farre-Castany M.A. Bouzourene H. Saraga E. Blum A.L. Corthesy-Theulaz I. Tlaskalova-Hogenova H. Michetti P. Oral administration of antigens from intestinal flora anaerobic bacteria reduces the severity of experimental acute colitis in BALB/c mice.Clin Exp Immunol. 2000; 120: 46-50Crossref PubMed Scopus (46) Google Scholar Samples of the distal colon were obtained for histology, assessment of MPO activity, and IL-1β levels.Dinitrobenzenesulfonic Acid–Induced ColitisColitis was induced by intracolonic administration of 6 mg dinitrobenzenesulfonic acid (DNB) in a 50% ethanol solution as previously described.32Qiu B.S. Vallance B.A. Blennerhassett P.A. Collins S.M. The role of CD4+ lymphocytes in the susceptibility of mice to stress-induced reactivation of experimental colitis.Nat Med. 1999; 5: 1178-1182Crossref PubMed Scopus (24) Google Scholar The mortality level at day 3 post-DNB administration was used as a measure of vulnerability to colitis. Mice surviving beyond day 3 post-DNB administration were not assessed for colitis severity owing to inadequate numbers for statistical testing.Statistical AnalysisData are means ± SEM. Measures of locomotion were analyzed using a 2-way analysis of variance with repeated measures24Sakic B. Szechtman H. Talangbayan H. Denburg S.D. Carbotte R.M. Denburg J.A. Disturbed emotionality in autoimmune MRL-lpr mice.Physiol Behav. 1994; 56: 609-617Crossref PubMed Scopus (120) Google Scholar where 1 factor was between-subjects (neonatal manipulation with 2 levels: MS vs US), and the other factor was a repeated-measures factor also with 2 levels (time interval, 0–10 min vs 10–20 min). The tail suspension test was analyzed using a 1-way analysis of variance with a Bonferroni posttest. Statistical testing for the remaining experiments was performed using a t test. In all cases a P value of less than .05 was considered significant.ResultsTail Suspension Test Before and After Antidepressant TreatmentDMI treatment attenuated depressive-like behavior in adult MS animals. As shown in Figure 1, maternally separated animals spent more time immobile (63.75 ± 9.44 s) as compared with US animals (32.75 ± 5.33 s; P < .05). Treatment with desipramine significantly attenuated immobility in maternally separated animals (32.88 ± 4.92 s; P < .05). Significant differences in immobility were not seen between unseparated animals and maternally separated animals treated with DMI.Behavioral Responses to StressAs shown in Figure 2, MS mice traveled less distance per movement bout during the 20-minute exposure to the open field as compared with US mice (neonatal manipulation effect, F(1,34) = 5.08; P = .031). After the introduction of a novel object after 10 minutes of exposure to the open field, the mean length of locomotor bouts was shorter compared wit
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