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Behavioral Responses to Catecholamine Depletion in Unmedicated, Remitted Subjects with Bulimia Nervosa and Healthy Subjects

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Behavioral Responses to Catecholamine Depletion in Unmedicated, Remitted Subjects with Bulimia Nervosa and Healthy Subjects
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  A RCHIVAL  R EPORT Behavioral Responses to Catecholamine Depletion inUnmedicated, Remitted Subjects with BulimiaNervosa and Healthy Subjects Simona Grob, Jair Stern, Lara Gamper, Hanspeter Moergeli, Gabriella Milos, Ulrich Schnyder,and Gregor Hasler Background:  Bulimia nervosa (BN) has been associated with dysregulation of the central catecholaminergic system. An instructive wayto investigate the relationship between catecholaminergic function and psychiatric disorder has involved behavioral responses toexperimental catecholamine depletion (CD). The purpose of this study was to examine a possible catecholaminergic dysfunction in thepathogenesis of bulimia nervosa. Methods:  CD was achieved by oral administration of alpha-methyl-para-tyrosine (AMPT) in 18 remitted female subjects with BN (rBN)and 31 healthy female control subjects. The study design consisted of a randomized, double blind, placebo-controlled crossover, single-site experimental trial. The main outcome measures were bulimic symptoms assessed by the Eating Disorder Examination — Questionnaire. Measures were assessed before and 26, 30, 54, 78, 102 hours after the  fi rst AMPT or placebo administration. Results:  In the experimental environment (controlled environment with a low level of food cues) rBN subjects had a greater increase ineating disorder symptoms during CD compared with healthy control subjects (condition    diagnosis interaction,  p    .05). In theexperimental environment, rBN subjects experienced fewer bulimic symptoms than in the natural environment (uncontrolledenvironment concerning food cues) 36 hours after the  fi rst AMPT intake (environment    diagnosis interaction,  p    .05). Serumprolactin levels increased signi fi cantly, and to a comparable degree across groups, after AMPT administration. Conclusions:  This study suggests that rBN is associated with vulnerability for developing eating disorder symptoms in response toreduced catecholamine neurotransmission after CD. The  fi ndings support the notion of catecholaminergic dysfunction as a possible traitabnormality in BN. Key Words:  Behavioral effects, bulimia nervosa, catecholaminedepletion, dopamine, norepinephrine, pathophysiology B ulimia nervosa (BN) is a psychiatric disorder characterizedby recurrent episodes of binge eating and inappropriatecompensatory behavior to prevent weight gain. The path-ophysiology of BN is poorly understood; however, there isgrowing evidence that neurobiological vulnerabilities contrib-ute to the pathogenesis of BN. Bulimia nervosa has beenassociated with dysregulation of central catecholaminergicsystem especially with decreased norepinephrine neurotrans-mission (1,2). Dopamine (DA) has been implicated in the valuation of the rewarding properties of food (3) and inaddiction (4), which are likely related to the pathogenesisof BN.One instructive technique for assessing the relationshipbetween catecholaminergic function and psychiatric disordershas involved the behavioral responses to catecholamine deple-tion (CD) achieved by oral administration of alpha-methyl-paratyrosine (AMPT) (5 – 7). AMPT is a competitive inhibitor of the rate-limiting enzyme in catecholamine synthesis, tyrosinehydroxylase (8), and temporarily decreases catecholamine trans-mission by depleting central dopamine and norepinephrinestores, evidenced by reduced concentrations of catecholaminesand their metabolites in plasma, urine, and cerebrospinal  fl uid(9,10) and decreased occupancy of striatal DA receptors by DA (11).Most studies using CD have been conducted in affectivedisorders (7,12 – 14). In BN, several studies using tryptophandepletion (TD) have demonstrated a relationship betweendiminished serotonin activity and lowered mood, irritability,body image concerns, and loss of control of eating (15 – 18).Thus far, no study has used CD to evaluate the roles playedby norepinephrine and dopamine in the pathophysiologyof BN.Monoamine depletion may not induce psychiatric symptomsin untreated acutely ill patients (15,19), possibly because of a ceiling effect. The marked depressive responses following CD insubjects in the remitted phase of major depressive disorder whoeither were medicated with norepinephrine reuptake inhibitingantidepressant drugs (12 – 14) or were drug free (5,7) raised the possibility that manifesting speci fi c symptoms following catechol-amine depletion may constitute a neurobiological trait marker fordepression (6).The purpose of this study was to identify a potential traitlikehypersensitivity to catecholamine depletion in BN by measuringthe CD-induced behavioral responses in remitted subjects withBN (rBN). We hypothesized that CD would induce more eatingdisorder symptoms in rBN subjects than in healthy controlsubjects. Given that the risk of BN is associated with the risk of mood and anxiety disorders (20), we also predicted that CDwould induce mood and anxiety symptoms in remitted subjectswith BN. From the Department of Psychiatry and Psychotherapy (SG, LG, HM, GM,US), University Hospital; Collegium Helveticum (JS), Swiss FederalInstitute of Technology Zurich and University of Zurich, Zurich; andPsychiatric University Hospital (GH), University of Bern, Bern,Switzerland.Address correspondence to Simona Grob, M.Sc., Department of Psychiatryand Psychotherapy, University Hospital, Culmannstrasse 8, 8091 Zurich,Switzerland; E-mail: simona.grob@bluewin.ch.Received Apr 19, 2011; revised Sep 5, 2013; accepted Sep 6, 2013. 0006-3223/$36.00 BIOL PSYCHIATRY 2013; ] : ]]]  –  ]]] http://dx.doi.org/10.1016/j.biopsych.2013.09.013  &  2013 Society of Biological Psychiatry   Methods and Materials Female subjects aged 19 to 39 years who had previously metDSM-IV criteria for BN and had been in remission from BN for atleast 6 months (index subjects;  n  ¼  18; length of illness, mean  ¼ 53.7 months; time in remission, mean  ¼  29.2 months) or had nohistory of any psychiatric disorder and no major psychiatriccondition in  fi rst-degree relatives (control subjects;  n  ¼  31) took part in this study. The screening visit included a diagnosticinterview with a psychiatrist, the Structured Clinical Interviewfor DSM-IV  (21), and a physical examination. Both study groupswere recruited by advertisements in local newspapers andannouncements at the University of Zurich and the Swiss FederalInstitute of Technology Zurich. Exclusion criteria for participationwere current Axis I psychiatric disorders, a lifetime diagnosis of psychosis, major medical or neurological illness, psychoactivemedication exposure within the previous 6 months, lifetimehistory of substance dependence, pregnancy, suicidal ideation,and a history of suicide attempts. Remitted subjects with a historyof BN (rBN) had been in remission for at least 6 months; moreprecisely they had no recurrent episodes of binge eating and norecurrent inappropriate compensatory behavior to preventweight gain during the last 6 months (mean time in remissionfrom BN  ¼  29.2 months [SD  ¼  23.6], range: 6 – 84 months) at thetime of study participation.All subjects gave written, informed consent before participa-tion. The study protocol was approved by the ethics committee of the Canton Zurich. The sample of this study overlaps with thesample of previous published data (22,23). We used a random- ized, double-blind, placebo-controlled, crossover design in whicheach subject underwent two identical sessions separated by atleast 7 days in which they received either AMPT or placebo. Eachsession included 2 days at the Department of Psychiatry andPsychotherapy of the University Hospital of Zurich. On a segre-gated  fl oor, a one-bed room with separate lavatory was availablefor all participants. Thus, participants had no contact with otherhospitalized subjects. None of the rBN subjects had beenhospitalized at the Department of Psychiatry and Psychotherapybefore. During hospitalization, participants received regularnonvegetarian meals with standardized amounts of calories(Day 1 at 7  PM  650 kcal; day 2 at 7:30  AM  650 kcal, and at 12  PM 700 kcal).For the subsequent 3 days after each trial, subjects werecontacted daily by telephone for follow-up interviews. To avoidany risk of adverse reaction, a body weight – adjusted AMPT doseof 40 mg/kg body weight orally, to a maximum of 4 g, over 22hours (on Day 1 at 9  AM , 12  PM , and 7  PM ; on Day 2 at 7  AM ) wasadministered. During sham depletion, subjects received inactiveplacebo on Day 1 at 9  AM  and 12  PM  and 25 mg diphenhydramineorally on Day 1 at 7  PM  and on Day 2 at 7  AM  because AMPT frequently induces mild sedation. To prevent the formation of crystalluria during AMPT administration, subjects were instructedto drink at least 2 L of water daily. Possible adverse reactions wereassessed regularly (26, 30, 54, 78, 102 hours after the  fi rst AMPT orplacebo administration) during hospitalization by a medicalexamination including blood pressure measurement and forsubsequent 3 days after each trial within the daily telephonefollow-up interview.In each session, blood samples were drawn 26 hours after the fi rst AMPT dose to measure serum prolactin levels.Behavioral ratings were conducted immediately before the fi rst AMPT or placebo intake (prechallenge) and 26, 30, 54, 78, 102hours after the  fi rst AMPT or placebo administration.Bulimic symptoms were assessed using the German Version of the Eating Disorder Examination — Questionnaire (EDE-Q) (24).EDE-Q is a 28-items self-report scale srcinated from the EDEinterview (25,26) designed to measure behavioral and cognitive features of eating disorders. Respondents indicate the value of particular feelings and attitudes toward eating behavior and bodyconcerns over a de fi nite time frame. Six of the 28 items assess thefrequencies of eating disorder-related behavior in terms of number of binge-eating episodes and compensatory behavior.These items do not contribute to scale score. An EDE-Q globalscore and four separate EDE-Q subscales scores for the subscales:1,  “ control of eating/drive for thinness ” ; 2,  “ urge to eat/fear of binge eating ” ; 3,  “ weight concerns ” ; 4,  “ feeling fat/body dissat-isfaction ”  can be derived from the instrument. For the purpose of this study, the EDE-Q was adapted to a shorter time frame frompast 28 days used in the srcinal version (24) to past 12 hours tomeasure bulimic symptoms in response to AMPT or placebo. Wetested this adapted scale in a pilot study. On the basis of ourclinical assessments, we came to the conclusion that it providesvalid data. Additional behavioral ratings included theMontgomery-Åsberg Depression Rating Scale (MADRS), YoungMania Rating Scale (YMRS), Beck Anxiety Inventory (BAI), Snaith-Hamilton Pleasure Scale (SHAPS), and Stanford SleepinessScale (SSS).Full factorial linear mixed models with restricted maximumlikelihood estimation were applied to determine the effects of condition (cond), diagnosis (dx), and time on each behavioralmeasure. SPSS subcommand for  fi xed effects: /FIXED  ¼  cond dxtime cond*dx cond*time dx*time cond*dx *time  |  SSTYPE (3).Mixed models effects were computed based on change scores foreach behavioral measure. For each condition (AMPT or Placebo),and each participant change scores were calculated by subtract-ing the baseline (time point 0 hours) from the score of each timepoint (26, 30, 54, 78, and 102 hours). For all models, a randomeffect for the subjects was included.Because of the crossover study design, period was handled as2*2 (and 5, respectively) repeated measures. SPSS subcommand:/REPEATED  ¼  sequence*time ♠ SUBJECT(id) COVTYPE(covst), wheresequence captures the real sequence of AMPT or Placebo admin-istration (randomly assigned to each patient). For each behavioralmeasure an appropriate covariance structure (covst) for theresiduals was chosen considering the lowest Akaike ’ s InformationCriterion. A  fi rst-order ante-dependence covariance structure (AD1)was best for the EDE-Q, a  fi rst-order factor analytic structure (FA1)for MADRS, a heterogenous  fi rst-order autoregressive structure(ARH1) for YMRS and BAI, a  fi rst-order autoregressive structure(AR1) for SHAPS, and an AD1 for SSS.Estimated marginal means regarding the interaction betweendiagnosis and condition allowed analysis of the diagnostic groupsseparately.The analyses of the behavioral ratings EDE-Q, MADRS, BAI,SHAPS, and SSS refer to the time in the controlled environment(time points 26 and 30 hours) since the main hypothesis appliedto this condition and time frame. An exception represented theYMRS for which a different time frame was considered (timepoints 26, 30, 54, 78, and 102 hours), given that hypomanicsymptoms were not observed before 48 hours after the  fi rst AMPT administration in our previous study (27).To determine whether the environment had an effect onbulimic symptoms, the experiment time frame of 102 hours wasdivided into two parts: controlled environment versus uncon-trolled environment. The controlled environment refers to thetime of the stay at the Department of Psychiatry and 2  BIOL PSYCHIATRY 2013; ] : ]]]  –  ]]]  S. Grob  et al  . www.sobp.org/journal  Psychotherapy (time points 26 and 30 hours). By contrast, theuncontrolled environment refers to the time after the stay at theDepartment of Psychiatry and Psychotherapy (time points 54, 78,and 102 hours).To assess details regarding the type of BN symptoms, we ranexploratory analyses on the EDE-Q subscales.To verify whether past episodes of depression ( n  ¼  4), historyof anorexia nervosa ( n ¼ 6), and the intake of psychotropic drugs( n  ¼  6) had an impact on the obtained results within the rBNgroup, the effect of these variables was also analyzed using linearmixed models.To evaluate the relationship between CD-induced bulimicsymptoms (EDE-Q) and other clinical scales (MADRS, YMRS, BAI,SHAPS, and SSS) in the controlled environment, mixed modelsincluding clinical scales as covariates were applied.The inclusion of a period effect and its interactions did notlead to important changes in the results; as result, we did notinclude a period effect in the analyses reported in this article. Theresults of analyses on raw scores instead of change scores alsodid not change the main  fi ndings of this study. As a result, wereport only the analyses on change scores, assuming they aremore conclusive than the raw score analyses.Analyses were performed using SPSS 18.0 statistical software(SPSS, Chicago, Illinois). The statistical signi fi cance level was set atalpha  ¼  .05. Results Demographic and clinical characteristics of the subject sampleare summarized in Table 1. Figure 1 shows the behavioral responses in rBN and control subjects after AMPT/placeboadministration. In the controlled environment (time points 26and 30 hours), there was a signi fi cant condition    diagnosisinteraction for bulimic symptoms assessed by the EDE-Q (EDE-Qglobal score,  F  1,41.9 ¼ 4.19,  p ¼ .047). rBN subjects reported morebulimic symptoms in the conditions in which they received AMPT compared with the placebo condition ( F  1,41.4  ¼  4.78,  p  ¼  .03),whereas AMPT did not induce bulimic symptoms in controls( F  1,42.6 ¼ .27,  p ¼ .61). Moreover, there was a signi fi cant condition  time interaction for bulimic symptoms assessed by the EDE-Q(EDE-Q global score,  F  1,81.7  ¼  6.81,  p  ¼  .01).The triple interaction of diagnosis    condition    time (EDE-Qglobal score,  F  1,81.7  ¼  4.71,  p  ¼  .03) was signi fi cant as well. Theeffects of diagnosis (EDE-Q global score,  F  1,51.7  ¼  2.52,  p  ¼  .12),condition (EDE-Q global score,  F  1,41.9  ¼  2.01,  p  ¼  .16) and time(EDE-Q global score,  F  1,83.9  ¼  1.44,  p  ¼  .23) did not reachsigni fi cance. There was no signi fi cant diagnosis  time interaction(EDE-Q global score,  F  1,83.4  ¼  2.77,  p  ¼  .10). The type of environment (controlled vs. uncontrolled) had a signi fi cantin fl uence on the experience of bulimic symptoms (environment   diagnosis interaction,  F  1,70.3  ¼  4.77,  p  ¼  .03). In the controlledenvironment, rBN subjects experienced signi fi cantly fewer bulimicsymptoms than in the uncontrolled environment ( F  1,71.4  ¼  17.84,  p    .001), whereas this effect was much smaller in controlsubjects ( F  1,68.0  ¼  4.24,  p  ¼  .04).In the controlled environment, none of the subjects experi-enced any binge and/or purge episodes in response to AMPT versus placebo, whereas in the uncontrolled environment (54hours after the  fi rst AMPT intake), one rBN subject in the AMPT condition showed a binge-eating episode without subsequentcompensatory behavior.Exploratory analyses regarding EDE-Q subscales showed atriple interaction of diagnosis    condition    time for subscale 2, “ urge to eat/fear of binge eating ”  ( F  1,91.3  ¼  6.15,  p  ¼  .01), andsubscale 4,  “ feeling fat/body dissatisfaction ”  ( F  1,70.3 ¼ 6.69,  p ¼ .01).Moreover, there was a signi fi cant condition  time interaction onsubscale 3,  “ weight concerns ”  ( F  1,77.5  ¼  4.56,  p  ¼  .04), whereasthere were no signi fi cant interactions on EDE-Q subscale 1 “ control of eating/drive for thinness. ”  In none of the four EDE-Qsubscales was a signi fi cant condition    diagnosis interactionevident (subscale 1,  “ control of eating/drive for thinness, ”  F  1,46.5 ¼ 2.35,  p  ¼  .13; subscale 2,  “ urge to eat/fear of binge eating, ” F  1,41.9  ¼  1.76,  p ¼  .19; subscale 3  “ weight concerns, ”  F  1,40.4  ¼  .72,  p ¼ .40, and subscale 4,  “ feeling fat/body dissatisfaction, ”  F  1,46.0 ¼ 1.98,  p  ¼  .16).The type of environment (controlled vs. uncontrolled) had asigni fi cant in fl uence on the experience of bulimic symptoms alsoregarding EDE-Q subscale 1,  “ control of eating/drive for thinness ” (environment    diagnosis interaction,  F  1,218.7  ¼  4.02,  p  ¼  .04),and subscale 4,  “ feeling fat/body dissatisfaction ”  ( F  1,210.8  ¼  4.19,  p  ¼  .04).In subsequent analyses, the effects of past episodes of depression, anorexia nervosa, and intake of psychotropic drugson EDE-Q scores were analyzed within the rBN group. Nosigni fi cant effects were evident.Baseline mean (SD) EDE-Q global scores were for rBN subjects:drug ¼ 4.05 (5.66), placebo ¼ 3.62 (3.12), and for controls: drug ¼ 1.79 (2.14), placebo ¼ 1.99 (2.40). A signi fi cant effect of diagnosiswas evident in EDE-Q baseline scores ( F  1,47.0  ¼  5.05,  p  ¼  .029),while there was no diagnosis  condition interaction (rBN,  F  1,47.0 ¼ .495,  p  ¼  .485).Regarding depressive symptoms assessed by the MADRS, inthe controlled environment, the effects of AMPT on MADRSscores did not differ between diagnostic groups (condition   diagnosis interaction  F  1,42.2 ¼ 1.02,  p ¼ .32). A signi fi cant effect of diagnosis ( F  1,47.1  ¼  6.63,  p  ¼  .01) and an effect of drug with ahigher mean value in the AMPT condition compared with theplacebo condition ( F  1,42.1  ¼  4.92,  p  ¼  .03) were evident. Toinvestigate the depressive response to AMPT in rBN individualswith a history of major depressive disorder (MDD), we speci fi callycompared rBN-MDD subjects with rBN-only subjects. In the Table 1.  Demographic and Clinical Characteristics of Unmedicated Sub- jects with rBN and Healthy Controls *  rBN Subjects ControlsCharacteristic ( n  ¼  18) ( n  ¼  31)Sex F FAge, Mean (SD), y 25.6 (4.7) 25.8 (3.8)Age at Onset, Mean (SD), y 14.4 (4.2) NABody Mass Index, Mean (SD), kg/m 󰂲   21.2 (1.7) 22.4 (2.2)Range, kg/m 󰂲   18.3 – 24.7 18.6 – 26.6Time in Remission from BN, Mean (SD), mo 29.2 (23.6) NARange, mo 6 – 84 NAMajor Depression Preceding or During BN,  n  4 NAPrevious AN,  n  6 NATime in Remission from AN, Mean (SD), mo 98 NARange, mo 36 – 132 NAPrevious Psychoactive Medication, y n  6 0Time Medication Free, Mean (SD), mo 10 (3.5) NARange, mo 6 – 12 NAAN, anorexia nervosa; BN, bulimia nervosa; NA, not applicable; rBN,bulimia nervosa in remission. n Subjects with rBN and control subjects did not differ signi fi cantly inage and body mass index. y Selective serotonin reuptake inhibitor or tricyclic antidepressant. S. Grob  et al  .  BIOL PSYCHIATRY 2013; ] : ]]]  –  ]]]  3 www.sobp.org/journal  controlled environment, there was a difference in the MADRSresponse to AMPT between these two groups (condition   diagnosis interaction,  F  1,17.1  ¼  12.5,  p  ¼  .003). Compared withplacebo medication rBN-MDD subjects reported a signi fi cant Figure 1.  Behavioral responses to catecholamine depletion and placebo in unmedicated subjects with bulimia nervosa in remission (rBN group,  n ¼ 18)and healthy control subjects ( n  ¼  31). *Signi fi cant diagnosis effect (rBN vs. controls,  p  .05).  † Signi fi cant condition effect for rBN.  ‡ Signi fi cant conditioneffect for controls. Behavioral ratings are shown as changes scores that were calculated by subtracting baseline scores from raw scores of each time pointto increase visibility of depletion effects. AMPT, alpha-methyl-para-tyrosine; BAI, Beck Anxiety Inventory; MADRS, Montgomery-Åsberg Depression RatingScale; SHAPS, Snaith-Hamilton Pleasure Scale; SSS, Stanford Sleepiness Scale; YMRS, Young Mania Rating Scale. 4  BIOL PSYCHIATRY 2013; ] : ]]]  –  ]]]  S. Grob  et al  . www.sobp.org/journal  increase in depressive symptoms under AMPT ( F  1,16.4  ¼  12.1,  p  ¼  .003), whereas this was not the case for rBN-only subjects( F  1,15.1 ¼ .85,  p ¼ .37). Baseline mean (SD) MADRS scores were forrBN subjects: drug  ¼  2.83 (3.48), placebo  ¼  2.61 (2.77); and forcontrols: drug  ¼  .52 (.99), placebo  ¼  1.16 (2.83). A signi fi canteffect of diagnosis was evident in MADRS baseline scores ( F  1,47.0 ¼ 9.39,  p  ¼  .004), whereas there was no diagnosis    conditioninteraction (rBN,  F  1,47.0  ¼  .996,  p  ¼  .323).Hypomanic symptoms as assessed by the YMRS (across alltime points), were signi fi cantly higher in rBN subjects relative tocontrol subjects ( F  1,61.0  ¼  7.07,  p  ¼  .01). A signi fi cant effect of drug was evident across groups ( F  1,94.8  ¼  8.82,  p  ¼  .004).However, there was no signi fi cant condition    diagnosis inter-action ( F  1, 94.8  ¼  1.96,  p  ¼  .16).Regarding anxiety symptoms assessed by the BAI, in thecontrolled environment no effect of diagnosis ( F  1,51.1  ¼  .17,  p  ¼ .68), no effect of drug ( F  1,89.1  ¼  .15,  p  ¼  .70) and no signi fi cantcondition    diagnosis interaction ( F  1,89.1  ¼  .39,  p  ¼  .53) wasevident.Concerning the ability to experience pleasure as assessed bythe SHAPS, in the controlled environment, there was no effect of diagnosis ( F  1,39.2  ¼  .23,  p  ¼  .64), no effect of drug ( F  1,111.2  ¼  .62,  p  ¼  .43) and no signi fi cant condition    diagnosis interaction( F  1,111.2  ¼  1.70,  p  ¼  .19).In the controlled environment, rBN subjects had highersleepiness scores assessed by the SSS than control subjects( F  1,46.7  ¼  11.74,  p  ¼  .001). Across groups, AMPT induced moresleepiness than the active placebo with a total of 100 mgdiphenhydramine ( F  1,47.3  ¼  9.49,  p  ¼  .003). However, no signi fi -cant condition    diagnosis interaction was evident ( F  1,47.3  ¼  .48,  p  ¼  .49).In the controlled environment, the covariates MADRS ( F  1,117.4  ¼ .21,  p  ¼  .65), YMRS (across all time points;  F  1,106.5  ¼  1.68,  p  ¼  .19),BAI ( F  1,116.2  ¼  .93,  p  ¼  .34), SHAPS ( F  1,77.2  ¼  .45,  p  ¼  .50), and SSS( F  1,97.9  ¼  .79,  p  ¼  .37) had no signi fi cant effect on bulimicsymptoms as assessed by the EDE-Q global score.Serum prolactin levels were signi fi cantly higher in the AMPT condition versus the placebo condition (mean [SD], 42.0 [2.5] vs.29.5 [2.6]  μ g/L;  F  1,36.5  ¼  20.93,  p  .001). There was no diagnosiseffect ( F  1,39.3  ¼  .09,  p  ¼  .76) and no diagnosis    conditioninteraction ( F  1,36.5  ¼  .16,  p  ¼  .69) regarding serum prolactinconcentration. Discussion To our knowledge, this is the  fi rst study that examined thebehavioral effects of CD in BN. The results indicate that CDinduced a transient reappearance of mild eating disorder symp-toms in remitted subjects with a history of BN. Moreover, theinduction of mild BN symptoms through exposure to theuncontrolled environment is consistent with persistent vulner-ability to BN in fully remitted subjects (28). Contrary to ourhypothesis, we did not  fi nd any signi fi cant condition  diagnosisinteractions regarding depressive, manic, anxiety, anhedonia, andsleepiness symptoms in rBN. As in our previous CD study in fullyremitted subjects with MDD (7), rBN subjects with a MDD historyshowed a signi fi cant return of depressive symptoms after CD.These results suggest that depression comorbid with BN hasneurochemistry no different from major depression alone.Several types of indirect evidence suggest that dysfunction of the central noradrenergic system contributes to the risk of BN. Astudy with BN subjects abstinent from bingeing and vomiting (29)showed reduced basal plasma and cerebrospinal  fl uids, suggest-ing that noradrenergic disturbance might be a traitlike character-istic of BN. The effectiveness of noradrenergic antidepressants inBN (30) underlines the clinical relevance of these  fi ndings. AlteredDA activity in BN has been identi fi ed, although the evidence isless consistent. Low DA metabolite concentrations in cerebrospi-nal  fl uid have been reported in BN subjects with frequent bingeepisodes (31,32). In addition, highly palatable foods induce potent release of DA into the nucleus accumbens (33), similar to drugs of abuse, and DA is a key neurotransmitter in novelty seeking andthe development of addiction (4), which suggests that abnor-mal DA activity may contribute to binge-eating episodes andother impulsive behaviours associated with BN. A study usingpositron emission tomography with [ 11 C]raclopride detecteddecreased striatal DA neurotransmission in patients with BNrelative to controls, a similar pattern to that described inaddiction disorders (34). This  fi nding may relate to reward-processing dysfunctions that have been found in remitted BN.Moreover, in rBN, compared with control subjects, a functionalmagnetic resonance imaging study using a glucose tasteparadigm found reduced anterior cingulate cortex activity, anarea that is involved in error monitoring but also in theanticipation of reward (35). These results suggest that DA-related reward-processing dysfunctions are traitlike character-istics associated with BN.Several strengths of the current study deserve mention.Whereas in previous studies using AMPT doses greater than 4g, subjects experienced adverse reactions such as dystonicreactions (36), restlessness (37), crystals in urine, and decreased blood pressure (38), none of our participants reported anysigni fi cant adverse reactions, probably because of the use of alow, body-weight-adjusted AMPT dose. The sample size wasrelatively large for a complex pharmacologic challenge study.The use of an active placebo (diphenhydramine) to mimic theside effects of the experimental drug (AMPT) contributed to aneffective blinding of the study drug and reduced the potentiallyconfounding effect of sleepiness, one of the main adverse effectsof AMPT, on psychiatric ratings. As expected, CD-induced sleepi-ness did not correlate with CD-induced bulimic symptoms. Thefact that CD induced the same amount of prolactin in rBNsubjects and healthy controls suggests that there was no differ-ence of the CD effect on catecholamine synthesis betweengroups (39).Some limitations of this study should be considered. Thepsychiatric symptoms induced by CD were minor, which calls theclinical relevance of the  fi ndings into question. However, usingthe same low, body-weight-adjusted AMPT dose, a previous studyin fully remitted subjects with MDD also induced only milddepressive symptoms, which helped to elucidate a neurocircuitrythat plausibly relates to the catecholamine-related pathogenesisof depression (7). A previous TD study also induced only minorbulimic symptoms in rBN (17), suggesting that this is a generallimitation of modern monoamine depletion studies using safeand ethically justi fi able dosages. Our cross-sectional design couldnot establish whether the bulimic response to CD in rBN re fl ectedan endophenotypic vulnerability to eating disorders or a con-sequence of illness. The lack of more objective outcome measure-ments represents a shortcoming of this study. The inclusion of afood challenge would have provided more reliable data. Theinclusion of lab values such as potassium would have contributedto a more objective de fi nition of recovery. We did not reliablyassess the phase of the menstrual cycle, and subjects were testedin both the follicular and luteal phases, which may represent a S. Grob  et al  .  BIOL PSYCHIATRY 2013; ] : ]]]  –  ]]]  5 www.sobp.org/journal
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