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The Rol
e of BDNF, Leptin and Catecholamines in Reward
Learning in Bulimia Nervosa
Journal:
The International Journal of Neuropsychopharmacology
Manuscript ID:
IntJNP-14-0321.R2
Manuscript Type:
Regular Research Article
Date Submitted by the Author:
28-Oct-2014
Complete List of Authors:
Homan, Philipp; University Hospital of Psychiatry, University of Bern,
Department of Molecular Psychiatry
Grob, Simona; University Hospital Zurich, Department of Psychiatry and
Psychotherapy
Milos, Gabriella; University Hospital Zurich, Department of Psychiatry and
Psychotherapy
Schnyder, Ulrich; University Hospital Zurich, Department of Psychiatry and
Psychotherapy
Eckert, Anne; Psychiatric University Clinics Basel, Neurobiology Laboratory
For Brain Aging and Mental Health
Lang, Undine; Psychiatric University Clinics Basel,
Hasler, Gregor; University Hospital of Psychiatry, University of Bern,
Department of Molecular Psychiatry
Research Focus: Choose one
or more (maximum 5) that
best describe the research
focus of your paper:
Challenge studies < Translational, Psychoneuroendocrinology <
Translational
Keywords: Enter up to 5
(minimum 3) keywords that
best reflect the research
reported in your paper.:
BDNF, catecholamines, reward, bulimia nervosa, leptin
The International Journal of Neuropsychopharmacology International Journal of Neuropsychopharmacology Advance Access published December 7, 2014
To be submitted as a Regular Research Article to the Int J Neuropsychopharmacol
The Role of BDNF, Leptin and Catecholamines in
Reward Learning in Bulimia Nervosa
Philipp Homan1*, MD, PhD, Simona Grob2, MSc, Gabriella Milos2, MD, Ulrich Schnyder2, MD, Anne
Eckert3, PhD, Undine Lang4, MD, PhD, Gregor Hasler1, MD
1 Department of Molecular Psychiatry, University Hospital of Psychiatry, University of Bern, Switzerland
2 Department of Psychiatry and Psychotherapy, University Hospital, Zurich, Switzerland
3 Neurobiology Laboratory For Brain Aging and Mental Health, Psychiatric University Clinics Basel,
Switzerland
4 Psychiatric University Clinics Basel, Switzerland
*Corresponding author: Philipp Homan
Department of Molecular Psychiatry,
University Hospital of Psychiatry, University of Bern
Bolligenstrasse 111, 3000 Bern, Switzerland.
Tel.: +41 31 930-9111; Fax: +41 31 932 8283
homan@puk.unibe.ch
Short title: BDNF, Catecholamines and Reward in Bulimia
Abstract word count: 252
Body word count: 4358
References: 54
Tables: 1
Figures: 1
© The Author 2014. Published by Oxford University Press on behalf of CINP.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/
by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided
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Page 1 of 25 The International Journal of Neuropsychopharmacology
1
Abstract
Background: A relationship between bulimia nervosa (BN) and reward-related behavior is supported by
several lines of evidence. The dopaminergic dysfunctions in the processing of reward-related stimuli have
been shown to be modulated by the neurotrophin brain derived neurotrophic factor (BDNF) and the
hormone leptin.
Methods: Using a randomized, double-blind, placebo-controlled, crossover design, a reward learning task
was applied to study the behavior of 20 female subjects with remitted BN (rBN) and 27 female healthy
controls under placebo and catecholamine depletion with alpha-methyl-para-tyrosine (AMPT). The
plasma levels of BDNF and leptin were measured twice during the placebo and the AMPT condition,
immediately before and 1 h after a standardized breakfast.
Results: AMPT-induced differences in plasma BDNF levels were positively correlated with the AMPT-
induced differences in reward learning in the whole sample (p = 0.05). Across conditions, plasma BDNF
levels were higher in rBN subjects compared to controls (diagnosis effect; p = 0.001). Plasma BDNF and
leptin levels were higher in the morning before compared to after a standardized breakfast across groups
and conditions (time effect; p < 0.0001). The plasma leptin levels were higher under catecholamine
depletion compared to placebo in the whole sample (treatment effect; p = 0.0004).
Conclusions: This study reports on preliminary findings that suggest a catecholamine-dependent
association of plasma BDNF and reward learning in subjects with rBN and controls. A role of leptin in
reward learning is not supported by this study. However, leptin levels were sensitive to a depletion of
catecholamine stores in both rBN and controls.
Key words: BDNF; leptin; reward; catecholamines; bulimia nervosa; alpha-methyl-para-tyrosine
Page 2 of 25The International Journal of Neuropsychopharmacology
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Introduction
Bulimia nervosa (BN) is a complex eating disorder and its etiology is still largely unknown. A biological
basis is widely accepted, and therefore an extensive effort has been taken to study neurotransmitters,
neuropeptides, and neuromodulators implicated in the regulation of eating behavior. Eating behavior is
influenced not only by metabolic but also non-metabolic factors (Monteleone and Maj, 2013) including
cognition, emotion, and reward. Specifically, food intake can be triggered by reward-related processes
even in the absence of a homeostatic requirement. Appetite-regulating substances such as BDNF and
leptin have been shown to additionally mediate the rewarding aspects of food (Monteleone and Maj, 2013)
by promoting the food intake of highly rewarding food rich in sugar or fat. In line with this, BN can be
conceptualized as a disease where binge eating is aimed at reducing the patient's negative emotions by
increasing food-derived feelings of pleasure. Negative emotions might be associated with a dysfunctional
processing of rewards. Consequently, several lines of evidence support a relationship between BN and
alterations in reward-related behavior (Harrison et al., 2010; Wagner et al., 2010; Grob et al., 2012). We
have previously shown a dopamine-related deficit in reward learning in subjects with remitted BN (rBN)
(Grob et al., 2012). Critically, the dopaminergic dysfunctions in the processing of reward-related stimuli
have been shown to be modulated by the brain derived neurotrophic factor (BDNF) and leptin. BDNF, a
neurotrophin involved in neuronal outgrowth and differentiation, synaptic connectivity and neuronal
repair, plays a role in dopaminergic neurons within the mesolimbic reward pathway including the ventral
tegmental area (VTA) and their projections to the nucleus accumbens (NAc) and medial prefrontal cortex
(mPFC) (Rios, 2013). The mesolimbic reward pathway is involved in what has been termed hedonic
feeding, that is the intake of highly rewarding food even in the absence of a metabolic requirement
(Bassareo and Di Chiara, 1999; Rada et al., 2005). Within this circuitry, BDNF is expressed in the VTA
and in the mPFC and is anterogradely transported to the NAc where little or no BDNF is expressed (Rios,
2013). Specifically, BDNF levels in dopaminergic cells within the VTA/NAc pathway seem to be related
Page 3 of 25 The International Journal of Neuropsychopharmacology
3
to the neuroadaptive changes following reward responses in animal models (Blochl and Sirrenberg, 1996;
Horger et al., 1999; Cordeira et al., 2010). In humans, there is initial evidence suggesting that the
decreased BDNF activity in carriers of a valine-methionine polymorphism at codon 66 results in a
decreased dopamine tone in the NAc (Pecina et al., 2014).
Leptin, on the other hand, an adipocyte-derived hormone involved in the regulation of energy balance
(Blundell et al., 2001), has also been reported to modulate reward-related behavior. Within the mesolimbic
pathway, leptin receptors have been detected on the VTA dopaminergic neurons (Scott et al., 2009),
suggesting that leptin decreases the firing of mesolimbic dopaminergic neurons as well as the dopamine
release and concentrations in the NAc (Krugel et al., 2003). This might ultimately lead to a negative
modulation of reward-related behaviors in animals (Carroll et al., 1984; Fulton et al., 2000; Cowley et al.,
2001; Shalev et al., 2001; Figlewicz et al., 2006; Davis et al., 2011) and in humans (Farooqi et al., 2007).
The current study aimed at elucidating the roles of BDNF, leptin and dopamine in reward-related behavior
of rBN subjects. To this end, we used a reward learning task to study the participants behavior as a
function of reward (Pizzagalli et al., 2005) during a pharmacological challenge with placebo and alpha-
methyl-para-tyrosine (AMPT) (Berman et al., 1999) that has been shown to deplete central dopamine and
norepinephrine stores (Stine et al., 1997; Verhoeff et al., 2003). In addition, we measured the plasma
levels of BDNF and leptin twice during the placebo and the AMPT condition, immediately before and 1 h
after a standardized breakfast.
Since we were not aware of any studies that have measured the relationship of BDNF and leptin in
reward-related behavior of rBN subjects, the corresponding analyses were performed in an exploratory
fashion. Previous studies did, however, measure the plasma and serum levels of BDNF and leptin in
subjects with BN but the results were inconsistent for BDNF (Nakazato et al., 2003; Monteleone et al.,
2005; Mercader et al., 2007; Saito et al., 2009; Yamada et al., 2012) while plasma leptin levels were found
to be decreased (Jimerson et al., 2000; Monteleone et al., 2000b; Monteleone et al., 2000a; Monteleone et
Page 4 of 25The International Journal of Neuropsychopharmacology
4
al., 2002b; Monteleone et al., 2002a). Consequently, and because of the fact that our study differed from
previous studies by measuring non-medicated BN subjects that were in remission, the BDNF and leptin
plasma analyses were also performed in an exploratory fashion.
Methods
Participants
We used the data from the study sample described in (Grob et al., 2012) that also overlaps with other
previously published results (Grob et al., 2013; Homan et al., 2013). We recruited females aged 19 to 39
years who had previously met DSM-IV criteria for BN and had been in remission from BN for at least six
months (n = 20) or who had no history of any psychiatric disorder and no major psychiatric condition in
first-degree relatives (control subjects; n = 30). Subjects with rBN had no recurrent episodes of binge
eating and no recurrent inappropriate compensatory behavior to prevent weight gain during the last 6
months. The screening visit included a diagnostic Structured Clinical Interview for DSM-IV with a
psychiatrist and a physical examination. In order to obtain comparable samples, participants for both study
groups were recruited by advertisements in local newspapers and announcements at the University of
Zurich and the Swiss Federal Institute of Technology Zurich (ETH). Exclusion criteria included current
Axis I psychiatric disorders, a lifetime diagnosis of psychosis, major medical or neurological illness,
psychoactive medication exposure within six months, pregnancy, lifetime history of substance
dependence, and suicidal ideation or a history of suicide attempts. All subjects gave written, informed
consent before participation. The study protocol was approved by the ethics committee of the Canton
Zurich (Kantonale Ethikkommission Zürich).
Experimental Design
This was a randomized, double-blind, placebo-controlled, crossover study during which all subjects
underwent two identical sessions separated by at least seven days wherein they received either AMPT or
Page 5 of 25 The International Journal of Neuropsychopharmacology
5
placebo. Each session included a two-day stay at the Department of Psychiatry and Psychotherapy of the
University Hospital of Zurich. One-bed rooms with a separate lavatory were available on a separated floor
for all participants, and they had no contact with other hospitalized subjects. None of the rBN subjects had
been previously hospitalized at this Department of Psychiatry and Psychotherapy. Participants received
regular standardized meals during the hospital sessions. Each subject was contacted daily by telephone for
three subsequent days after each trial for follow-up interviews. In order to avoid any risk of adverse
reaction, body weight-adjusted oral doses of AMPT of 40 mg/kg, to a maximum of 4 g over 22 h (at 0900
h, 1200 h, and 1900 h on day one and 0700 h on day two), were administered. During sham depletion,
subjects received inactive placebo on day one at 0900 h and 1200 h and 25 mg oral diphenhydramine on
day one at 1900 h and on day two at 0700 h to imitate the mild sedation effect that is often induced by
AMPT. To prevent formation of crystalluria during AMPT administration, the subjects were instructed to
drink at least 2 L of water daily. Possible adverse reactions were assessed regularly (26, 30, 54, 78, and
102 h after the first AMPT/placebo administration) during hospitalization by medical examination
including blood pressure measurement, and for three subsequent days after each trial session as part of the
daily telephone follow-up interview.
Blood Samples
During each session, blood samples were drawn before and at 26 h after the first AMPT dose (because the
depletion effect is evident from 24 hours after the first AMPT dose) in order to measure plasma BDNF
and leptin levels. The first sample was drawn immediately before, the second one within 1 h after eating a
regular standardized breakfast. Blood samples were drawn before the reward learning task.
Plasma BDNF levels were measured using a BDNF Emax Immunoassay Kit (Promega, Switzerland;
specificity: cross-reactivity to related neurotrophins < 3%; sensitivity: detects a minimum of about 15
pg/ml). Plasma leptin concentrations were measured using a commercial Radioimmunoassay (Millipore,
Page 6 of 25The International Journal of Neuropsychopharmacology
6
Millipore Corporation, Billerica, MA, USA; specificity: 100%; sensitivity: detects a minimum of 1.0
ng/ml).
Behavioral Assessment
Depressive symptoms were assessed with the Montgomery-Åsberg Depression Rating Scale (MADRS)
and the Hamilton Scale of Depression (HAMD). In addition, participants completed various self-report
ratings, including the German version of the Eating Disorder Examination-Questionnaire (EDE-Q)
(Hilbert, 2006). Symptoms were assessed immediately before the first AMPT/placebo dose (pre-
challenge) and at 26, 30, 54, 78, and 102 h after the first dose.
Reward Learning Task
Thirty hours after the first AMPT/placebo administration subjects participated in a 25-min probabilistic
reward task presented on a PC using E-prime software that has been described previously (Grob et al.,
2012). Briefly, participants were instructed that the goal of that task was to win as much money as
possible. The task included 300 trials, divided into 3 blocks of 100 trials. An asymmetric reinforcement
ratio was used to induce a response bias, i.e., subjects received a reward three times more frequently for
correct identification of a rich stimulus than for correct identification of a lean stimulus. Each participant
was exposed to the same reward ratio. Reward learning was defined as the difference in response bias
between Block 1 and Block 3 (Pizzagalli et al., 2005; Bogdan and Pizzagalli, 2006; Pizzagalli et al.,
2008).
Statistical Analysis
Full factorial linear mixed models with restricted maximum likelihood estimation were applied to
determine the effects of treatment, diagnosis, and treatment-by-diagnosis on each hormone. An additional
factor time was included as fixed effect to account for the two measurements in each condition. In all
Page 7 of 25 The International Journal of Neuropsychopharmacology
7
models, a various components or compound symmetry covariance structure, chosen considering the
lowest Akaike’s Information Criterion (AIC), was appropriate for the repeated measures. Subject number
and treatment sequence were included as random effects in all models. To evaluate the relationship
between alterations induced by catecholamine depletion in hormone levels and reward learning, additional
Spearman rank correlation coefficients were calculated. Therefore, the differences in plasma BDNF and
leptin levels between the second and first measurement were calculated for each subject and each
condition. The difference obtained from the AMPT condition was then subtracted from the difference
obtained from the placebo condition, reflecting the AMPT-induced change in plasma levels. In the same
manner, the differences between the reward learning scores obtained for each subject in the AMPT session
versus the placebo session were calculated to reflect the magnitude of AMPT-induced effect on reward
learning. We also assessed the effect that feeding might have had on the relationship between plasma
BDNF and leptin levels and reward learning by calculating the difference of plasma BDNF and leptin
levels between 10 h and 7 h in the placebo condition in each subject and by correlating these differences
with the results of the reward learning task in the placebo condition with a Spearman rank correlation. To
account for the possible influence of past episodes of anorexia nervosa, all analyses were repeated
excluding patients with a history of anorexia nervosa. The significance threshold for these contrasts was
set at alpha = 0.05, two-tailed. SAS 9.3 (SAS Institute, Cary, North Carolina, USA, http://www.sas.com)
was used for all analyses. Means are reported with their associated standard deviations.
Results
Three control subject had to be excluded from the study because of inadequate or missing (e.g.,
insufficient quantity or hemolysis) blood samples in all measurements, leaving 20 rBN subjects and 27
healthy controls for the measurements of plasma BDNF and leptin level. Four rBN subjects and 2 controls
had to be excluded from the correlational analysis of reward learning, BDNF, and leptin because of
missing trials in the reward learning task, leaving 16 rBN subjects and 25 healthy controls for the
Page 8 of 25The International Journal of Neuropsychopharmacology
8
correlational analysis. The clinical and demographic characteristics of study participants, including
baseline parameters, are detailed in Table 1. The rBN subjects had significantly more depressive
symptoms at baseline versus the healthy controls as measured with the HAMD (t [1, 45] = 2.51, p = 0.02)
and they had histories of significantly lower minimal body mass indexes (BMI) (t [1, 45] = -2.1, p = 0.04).
The rBN subjects retained a significantly greater number of bulimic symptoms at study entry compared to
the healthy controls (t [1, 45] = 2.53, p = 0.01). Plasma leptin levels at the first measurement at 7 h during
the placebo condition were positively correlated with BMI in subjects with rBN (r = 0.88, p < 0.0001)
while this correlation approached significance in controls (r = 0.34, p = 0.08). This correlation was also
significant for the whole study sample (r = 0.63, p < 0.0001). Effects of AMPT on reward learning as well
as depressive and bulimic symptoms have been reported previously (Grob et al., 2012; Grob et al., 2013).
Briefly, rBN subjects showed significantly lower reward learning (diagnosis-effect; F [1, 76] = 10.66, p =
0.002) across conditions. In addition, there was a significant treatment-by-diagnosis interaction (F [1, 76]
= 4.94, p = 0.03) that was attributable to significantly lower reward learning in rBN subjects compared to
controls under AMPT (t [1, 76] = 3.88, p = 0.001).
BDNF Concentrations in Plasma and Correlation with Reward Learning
At the first measurement at 7 h during the placebo condition, subjects with rBN had higher levels of
BDNF compared to healthy controls at a trend level (t [1, 45] = 1.82, p = 0.08). Mean plasma levels of
BDNF under catecholamine depletion and placebo are shown in Figure 1A. The plasma BDNF levels
were significantly higher in rBN subjects compared to healthy controls across conditions (diagnosis effect;
F [1, 181] = 10.71, p = 0.001, Figure 1B). In addition, plasma BDNF levels were significantly higher
across groups and conditions at the first measurement at 7 h after fasting compared to the second
measurement at 10 h after a standardized breakfast (time effect; F [1, 181] = 43.37, p < 0.0001). There
was no effect of treatment (p = 0.99) and no treatment-by-diagnosis interaction (p = 0.35). After repeating
Page 9 of 25 The International Journal of Neuropsychopharmacology
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the analysis excluding patients with a history of anorexia nervosa the diagnosis effect decreased (F [1,
161] = 3.77, p = 0.05).
The Spearman rank correlation between the AMPT-induced differences in plasma BDNF levels and the
AMPT-induced differences in reward learning approached significance (rho = 0.3, p = 0.05; Figure 1B).
The correlation between meal-induced changes in plasma BDNF levels and reward learning under placebo
was not significant (p > 0.1). After repeating the analysis excluding patients with a history of anorexia
nervosa this correlation was slightly stronger (rho = 0.33, p < 0.05). Repeating the analysis for each of the
diagnostic groups separately did not reveal any significant results (all p’s > 0.05).
Leptin Concentrations in Plasma and Correlation with Reward Learning
At the first measurement at 7 h during the placebo condition, no difference in plasma leptin levels between
rBN subjects and controls was evident (p = 0.79). Mean plasma levels before and after catecholamine
depletion are shown in Figure 1C. Under catecholamine depletion, the plasma leptin levels were
significantly higher across groups (treatment effect; F [1, 181] = 12.78, p = 0.0004, Figure 1C). Plasma
leptin levels were significantly higher across groups and conditions at the first measurement at 7 h after
fasting compared to the second measurement at 10 h after a standardized breakfast (time effect; F [1, 181]
= 47.5, p < 0.0001; Figure 1C). No diagnosis effect (p = 0.92) and no treatment-by-diagnosis interaction
(p = 0.63) were evident. An additional analysis excluding patients with a history of anorexia nervosa did
not change the results.
The Spearman rank correlation between the AMPT-induced differences in plasma leptin levels and the
AMPT-induced differences in reward learning was not significant (p = 0.37). The correlation between
meal-induced changes in plasma leptin levels and reward learning under placebo was not significant (p >
0.1). An additional analysis excluding patients with a history of anorexia nervosa did not change the
results. Repeating the analysis for each of the diagnostic groups separately did not reveal any significant
results (all p’s > 0.05).
Page 10 of 25The International Journal of Neuropsychopharmacology
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Discussion
The current study was the first to investigate the relationship of BDNF, leptin, and dopamine in reward-
related behavior of remitted BN subjects and controls. We used a pharmacological challenge paradigm
with AMPT to deplete central dopamine and norepinephrine stores. We found that the AMPT-induced
differences in plasma BDNF levels were positively correlated at a trend level with the AMPT-induced
differences in reward learning in the whole sample. At the first measurement under placebo, plasma
BDNF levels were higher at a trend level in rBN subjects compared to controls. Across conditions, plasma
BDNF levels were significantly higher in rBN subjects compared to controls. Plasma BDNF and leptin
levels were significantly higher in the morning before breakfast compared to after a standardized breakfast
across groups and conditions. The plasma leptin levels were higher under catecholamine depletion
compared to placebo in the whole sample.
The current study investigated plasma BDNF and leptin levels in unmedicated subjects with rBN and
assessed their association to reward-related behavior during an experimentally induced depletion of
central dopamine and norepinephrine stores. We found a positive association at a trend level between the
AMPT-induced differences in plasma BDNF levels and reward learning in the whole study population that
is compatible with a function of BDNF in reward-related behaviors. It has been demonstrated that BDNF
and its tyrosine kinase receptor are expressed in dopaminergic neurons of the ventral tegmental area and
that BDNF is anterogradely transported to the NAc (Numan and Seroogy, 1999), which suggests a role for
BDNF in modulating reward. Specifically, BDNF levels in dopaminergic cells within the VTA/NAc
pathway might be related to the neuroadaptive changes following reward responses in animal models. In
line with this, BDNF stimulates the release of dopamine in mesencephalic neurons of rodents (Blochl and
Sirrenberg, 1996), and BDNF infusions into the NAc of rats have shown that this dopamine release is
associated with a facilitation of reward-related stimuli (Horger et al., 1999). In addition, recent work has
shown that mutant mice depleted of central BDNF exhibited a marked decrease in the evoked release of
Page 11 of 25 The International Journal of Neuropsychopharmacology
11
dopamine in the NAc and dorsal striatum (Cordeira et al., 2010). Notably, the VTA-specific deletion of
the BDNF gene resulted in increased ingestion of a palatable high fat diet but not of a standard diet. These
results suggest a positive modulation of hedonic eating by BDNF through increasing mesolimbic
dopaminergic activity. In humans, initial evidence suggests a BDNF-effect of dopamine-mediated
responses to reward in the VTA/NAc pathway (Pecina et al., 2014). The positive association at a trend
level of AMPT-induced changes in plasma BDNF levels and the corresponding changes in reward
learning under a condition of experimentally depleted dopamine as found in our study supports the view
of a tight connection between BDNF, dopamine and reward also in humans.
With respect to the plasma BDNF levels, we found higher concentrations at the first measurement under
placebo in rBN subjects compared to controls. Across all conditions, these levels were higher in rBN
subjects compared to controls, and higher in both groups under catecholamine depletion compared to
placebo. Previous studies have found reduced BDNF concentrations in BN compared to controls
(Nakazato et al., 2003; Monteleone et al., 2005; Yamada et al., 2012) but this reduction was not always
significant (Saito et al., 2009) or even found in controls compared to BN (Mercader et al., 2007). Our
study differed in an important aspect from the aforementioned studies in that we measured subjects with
BN in remission that were off medication. This allowed for an investigation without potential medication
confounds and during a period of experimentally induced eating disorder symptoms (Grob et al., 2013).
During this relapse-like period we did not observe a decrease of plasma BDNF concentrations; instead, the
levels were higher in rBN compared to controls across conditions. Increased BDNF concentrations with
respect to BN have previously been interpreted as high BDNF levels in the central nervous system that
would alter eating behavior (Mercader et al., 2007). In line with this, BDNF-infusions into the rodents
brains have been reported to induce weight loss while increasing feeding and food retrieval (Lapchak and
Hefti, 1992; Pelleymounter et al., 1995; Martin-Iverson and Altar, 1996). In addition, it has been found
that mice with a heterozygous BDNF knockout display hyperphagia and obesity (Lyons et al., 1999;
Page 12 of 25The International Journal of Neuropsychopharmacology
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Kernie et al., 2000; Rios et al., 2001). However, it has been suggested that the site and dose of BDNF
infusion has to be considered since only intra-VTA but not NAc infusions produced weight loss in mice
(Horger et al., 1999). Further, a recent study in anorexia nervosa, an eating disorder closely related to BN,
has reported on different levels of BDNF depending on the stage of disease. Specifically, BDNF
concentrations were significantly higher in recovered compared to underweight patients and increased
with short-term weight gain (Zwipp et al., 2014). This might indicate that the higher plasma BDNF levels
in rBN compared to controls found in our study might be a relevant factor in achieving remission.
Our study is the first to report on a decrease between preprandial and postprandial plasma BDNF levels in
rBN subjects and healthy controls. The interpretation of this finding is not straightforward since BDNF
has been suggested to induce appetite suppression and weight loss through a central mechanism in
previous animal studies (Lapchak and Hefti, 1992; Pelleymounter et al., 1995; Martin-Iverson and Altar,
1996). In humans, genetic BDNF polymorphisms are linked to severe obesity (Yeo et al., 2004; Friedel et
al., 2005; Gray et al., 2006; Beckers et al., 2008; Burns et al., 2010). Consequently, this finding challenges
the current view that BDNF modulates appetite suppression (Unger et al., 2007). A possible explanation
for this differential result in our study is that previous work has focused on the role of BDNF in obesity
and corresponding overeating behavior whereas the subjects assessed in the current study had BN in
remission with a normal eating behavior.
The current study also investigated the association of reward learning and plasma leptin levels. Although
leptin has been reported to modulate reward-related behavior by decreasing the firing of mesolimbic
dopaminergic neurons as well as dopamine release and concentrations in the NAc (Krugel et al., 2003), we
did not find an association of reward learning and plasma leptin levels in the current study. We found that
plasma leptin levels were comparable at the first measurement under placebo in both rBN and controls,
and that the increasing effect of the pharmacological manipulation with AMPT was evident in both
groups. These results are in contrast to previous studies which have found reduced plasma and serum
Page 13 of 25 The International Journal of Neuropsychopharmacology
13
leptin levels in normal weight BN subjects (Jimerson et al., 2000; Monteleone et al., 2000b; Monteleone et
al., 2000a; Monteleone et al., 2002b; Monteleone et al., 2002a). One of these studies has also measured
BN subjects in remission with a mean remission time comparable to our study and has confirmed the
reduction of leptin levels in this sample (Jimerson et al., 2000). Monteleone and Maj have recently
reviewed the role of leptin in BN (Monteleone and Maj, 2013). Based on their own findings (Monteleone
et al., 2000b; Monteleone et al., 2002a), these authors have suggested that the role of leptin as a peripheral
signal of available energy stores seems to be preserved in subjects with BN whereas its signal function of
acute changes in the energy balance is lost (Monteleone and Maj, 2013). In line with this suggestion is our
finding of a positive correlation of plasma leptin levels and BMI in subjects with rBN which is also
consistent with previous reports (reviewed in Monteleone and Maj (2013)). However, with respect to our
conflicting findings of comparable plasma leptin levels in rBN and controls under placebo and higher
levels under catecholamine depletion, it has to be considered that our study differed in an important aspect
from the aforementioned studies since we measured subjects with BN in remission during a
pharmacological challenge with AMPT (Grob et al., 2013). The findings itself might indicate that the
plasma leptin levels are restored in remitted subjects with BN and are a relevant factor in achieving
remission.
The current study had some limitations that merit comment. Because of the relatively small sample size
the findings should be considered preliminary and should be replicated in larger samples in future studies.
It should also be noted that the patients included in this study were in remission, so the findings may not
necessarily apply to unremitted patients. The catecholamine-dependent association of plasma BDNF and
reward learning was modest and only approached significance (p = 0.05). However, this effect was
significant after excluding rBN subjects with a history of anorexia nervosa, suggesting that anorexia
nervosa might be a confounder in this relationship. In addition, the fact that we measured peripheral and
not central BDNF and leptin levels as well as the fact that AMPT might have had peripheral effects should
Page 14 of 25The International Journal of Neuropsychopharmacology
14
be considered. It is thus possible that a peripheral modulation of BDNF and leptin levels caused by AMPT
might have contributed to the present findings. Furthermore, it is important to note that the correlational
analysis could not establish a causal relationship between AMPT-induced changes in plasma BDNF levels
and reward learning. Finally, the specificity of our results was limited by the fact that AMPT reduces not
only the synthesis of dopamine but also norepinephrine. Consequently, an influence of reduced
norepinephrine on reward learning and BDNF and leptin levels cannot be entirely ruled out.
In conclusion, the current study reports on preliminary findings that suggest a catecholamine-dependent
association of plasma BDNF and reward learning in subjects with rBN and controls. A role of leptin in
reward learning is not supported by this study. However, leptin levels were sensitive to a depletion of
catecholamine stores in both rBN and controls.
Acknowledgements
This research was supported by the Swiss National Science Foundation Nr. 32003B-117763.
We are grateful to M. Seiler for valuable help in organizing the biochemical analyses.
Statement of Interest
None.
Page 15 of 25 The International Journal of Neuropsychopharmacology
15
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Table and Figure Legends
Table 1
Demographic and clinical characteristics of unmedicated subjects with remitted bulimia nervosa (rBN)
and healthy controls. BMI = Body Mass Index. ; BMI min = minimal Body Mass Index during disease;
BMI max = maximal Body Mass Index during disease; HAMD = Hamilton Scale of Depression; MADRS
= Montgomery-Åsberg Depression Rating Scale; EDE-Q = Eating Disorder Examination-Questionnaire;
n.a. = not applicable; * indicates a significant difference at p < 0.05.
Figure 1
(A) Boxplots of plasma BDNF concentrations before and after catecholamine depletion in subjects with
remitted bulimia nervosa (n = 20) and healthy controls (n = 27). The first sample was drawn immediately
before, the second one within 1 h after eating a regular standardized breakfast. HC pre = healthy controls
before treatment; HC post = healthy controls after treatment; BN pre = remitted bulimia nervosa patients
before treatment; BN post = remitted bulimia nervosa patients after treatment. (B) AMPT-induced
differences in plasma BDNF levels plotted against the AMPT-induced differences in reward learning in
subjects with remitted bulimia nervosa and healthy controls. Reward learning was defined as the
difference in response bias between Block 1 and Block 3 of a probabilistic reward task. The Spearman
rank correlation between the AMPT-induced differences in plasma BDNF levels and the AMPT-induced
differences in reward learning approached significance (rho = 0.3, p = 0.05). (C) Boxplots of plasma
leptin concentrations before and after catecholamine depletion in subjects with remitted bulimia nervosa
(n = 20) and healthy controls (n = 27). The first sample was drawn immediately before, the second one
within 1 h after eating a regular standardized breakfast. HC 07 am = healthy controls before eating a
standardized breakfast; HC 10 am = healthy controls after eating a standardized breakfast; rB 07 am =
remitted bulimia nervosa patients before eating a standardized breakfast; rB 10 am = remitted bulimia
nervosa patients after eating a standardized breakfast.
Page 23 of 25 The International Journal of Neuropsychopharmacology
Table 1
Characteristic rBN (n=20) Controls (n=27) p-value
Sex, No. f/m 20/0 27/0 n.a.
Age, mean (SD), y 29.1 (4.7) 28.5 (3.8) 0.65
BMI, mean (SD), kg/m
2
21.7 (3.1) 22.2 (2.3) 0.47
BMI min, mean (SD), kg/m2 17.2 (2.2) 19.3 (4.2) 0.04*
BMI max, mean (SD), kg/m2 24.0 (3.5) 22.7 (5.4) 0.35
Age at onset, mean (SD), y 15.5 (4.7) n. a. n.a.
Educational level (SD), y 16.5 (3.1) 17.3 (3.0) 0.4
Time in remission, mo
Mean (SD)
Range
31.9 (28.1)
6 – 84
n. a.
n. a.
n.a.
n.a.
History of anorexia nervosa 7 n.a. n.a.
First degree relative(s) with a history of bulimia nervosa,
No. 2 0 0.2
First degree relative(s) with a history of anorexia
nervosa, No. 2 0 0.2
Remote (> 1 y ago) history of alcohol abuse, No. 2 0 0.2
History of drug abuse, No. 2 1 0.6
Plasma BDNF concentration at first measurement under
placebo, mean (SD), pg/ml 3058.0 (1506.6) 2383.2 (1281.4) 0.08
Plasmal leptin concentration at first measurement under
placebo, mean (SD), ng/ml 12.7 (9.4) 13.1 (7.9) 0.81
MADRS score at first measurement, mean (SD) 2.0 (2.6) 1.0 (2.8) 0.19
HAMD score at first measurement, mean (SD) 1.0 (1.4) 0.3 (0.6) 0.02*
EDE-Q score at first measurement, mean (SD) 6.3 (9.3) 1.7 (2.0) 0.01*
Page 24 of 25The International Journal of Neuropsychopharmacology
(A) Boxplots of plasma BDNF concentrations before and after catecholamine depletion in subjects with
remitted bulimia nervosa (n = 20) and healthy controls (n = 27). The first sample was drawn immediately
before, the second one within 1 h after eating a regular standardized breakfast. HC pre = healthy controls
before treatment; HC post = healthy controls after treatment; BN pre = remitted bulimia nervosa patients
before treatment; BN post = remitted bulimia nervosa patients after treatment. (B) AMPT-induced
differences in plasma BDNF levels plotted against the AMPT-induced differences in reward learning in
subjects with remitted bulimia nervosa and healthy controls. Reward learning was defined as the difference
in response bias between Block 1 and Block 3 of a probabilistic reward task. The Spearman rank correlation
between the AMPT-induced differences in plasma BDNF levels and the AMPT-induced differences in reward
learning approached significance (rho = 0.3, p = 0.05). (C) Boxplots of plasma leptin concentrations before
and after catecholamine depletion in subjects with remitted bulimia nervosa (n = 20) and healthy controls (n
= 27). The first sample was drawn immediately before, the second one within 1 h after eating a regular
standardized breakfast. HC 07 am = healthy controls before eating a standardized breakfast; HC 10 am =
healthy controls after eating a standardized breakfast; rB 07 am = remitted bulimia nervosa patients before
eating a standardized breakfast; rB 10 am = remitted bulimia nervosa patients after eating a standardized
breakfast.
306x248mm (300 x 300 DPI)
Page 25 of 25 The International Journal of Neuropsychopharmacology
