Polymorphism in the serotonin transporter gene and moderators of prolactin response to meta-chlorophenylpiperazine in African-American cocaine ...
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Psychiatry Research 144 (2006) 99 – 108
www.elsevier.com/locate/psychres
Polymorphism in the serotonin transporter gene and moderators
of prolactin response to meta-chlorophenylpiperazine
in African-American cocaine abusers and controls☆
Paolo Mannelli a , Ashwin A. Patkar a,⁎, Kathleen Peindl a , Haresh Tharwani a ,
Raman Gopalakrishnan b , Kevin P. Hill c , Wade H. Berrettini d
a
Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC, USA
b
Department of Psychiatry, Thomas Jefferson University, Philadelphia, PA, USA
c
Department of Psychiatry, Yale University, New Haven, CT, USA
d
Center for Neurobiology and Behavior, Department of Psychiatry, University of Pennsylvania, Philadelphia, PA, USA
Received 16 October 2005; received in revised form 6 January 2006; accepted 15 January 2006
Abstract
Serotonin (5-HT) function is altered in several psychiatric disorders, including cocaine dependence (CD), and its role in
impulsive-aggressive behaviors has been widely studied. However, the relationship between psychopathological and behavioral
dimensions and mechanisms of 5-HT alterations remains unclear. We investigated the relationship of a polymorphism in the 5′
promoter region of the serotonin transporter gene (5-HTTLPR) with prolactin (PRL) response to meta-chlorophenylpiperazine (m-
CPP) in a sample of 68 African-American individuals, 35 CD subjects and 33 controls. We also examined whether measures of
impulsivity, hostility and sensation seeking influenced the relationship between the 5-HTTLPR polymorphism and PRL response to
m-CPP in this sample. Individuals with the SS genotype showed significantly heightened PRL response to the challenge compared
with the LL and LS genotypes. No influence of gender or substance abuse condition was observed. Hostility was associated with
blunted PRL response in the total sample. Cocaine abuse was the most significant moderator of ΔPRL (peak PRL − baseline PRL),
and the interaction of genetic, behavioral and psychopathological measures helped predict most of the observed ΔPRL (62.5%).
Although these results need replication, variation in the 5-HTTLPR gene appears to influence measures of 5-HT function and
interact with disease state and personality dimensions to account for 5-HT disturbances in African-American populations.
© 2006 Elsevier Ireland Ltd. All rights reserved.
Keywords: Serotonin; m-CPP; 5-HTTLPR; Substance abuse; Aggression; Behavior
☆
Work carried out at: Department of Psychiatry and Behavioral
1. Introduction
Sciences, Duke University, Durham NC; Department of Psychiatry
and Human Behavior, Thomas Jefferson University, Philadelphia PA; Altered serotonin (5-HT) function has been sug-
Center for Neurobiology and Behavior, Department of Psychiatry, gested in a range of psychiatric illnesses and behavioral
University of Pennsylvania, Philadelphia, PA. phenotypes, including alcohol and cocaine dependence
⁎ Corresponding author. Duke University Medical Center, 4323 Ben
Franklin Boulevard, Suite 700, Durham, NC 27704, USA. Tel.: +1 919
(Johnson, 2004; Muller et al., 2003), with or without
471 3826; fax: +1 919 620 0346. heightened impulsivity and hostility (Badaway, 2003;
E-mail address: Ashwin.Patkar@duke.edu (A.A. Patkar). Patkar et al., 2003; Cunningham and Breslin, 2004).
0165-1781/$ - see front matter © 2006 Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/j.psychres.2006.01.012100 P. Mannelli et al. / Psychiatry Research 144 (2006) 99–108
There is strong evidence linking impulsive and ag- results were obtained following fenfluramine challenge
gressive behaviors with alterations in central 5-HT, not in recovering alcoholics and non-patient male volunteers
only in clinical populations (Stein et al., 1996), but also (Reist et al., 2001), and in healthy subjects of low socio-
in healthy volunteers (Manuck et al., 1998, 2002). economic status (Manuck et al., 2004). Low PRL
Although these findings are well documented, the response to citalopram was also associated with the
mechanisms of altered 5-HT function are not known. short/short genotype and specific cerebral metabolic
For example, it is unclear whether 5-HT disturbances responses in another non-patient group (Smith et al.,
predate or are a consequence of substance dependence. 2004), while no association was found with depression
One approach to clarify these mechanisms is to examine following dexfenfluramine (Strickland et al., 2003).
the relationship between genetic variants and functional Among 5-HT challenge agents, m-chlorophenylpiper-
expression in a neurotransmitter system. azine (m-CPP) shows greater specificity for postsynaptic
Genetic studies of the 5-HT system have identified 5-HT receptors and has considerably lower affinity for
several variations that may have a link with central the human 5-HT transporter (b 4.0) and for dopamine
neurotransmitter function and psychopathology. receptors (Hoyer et al., 1994), at the 0.5-mg/kg dose
Among them, the 44-bp insertion/deletion polymor- commonly used in oral challenge paradigms (Gijsman et
phism in the serotonin transporter gene (5-HTTLPR) al., 2004). The effects of m-CPP on PRL, ACTH/cortisol,
has been widely studied. The promoter polymorphism temperature and cocaine discriminative stimulus effects
is biallelic, and the short allele is associated with have been attributed to partial agonist activity at the 5-
altered activity, reduced transcriptional efficiency HT2C receptor (Murphy et al., 1991; Aulakh et al., 1992;
(Heils et al., 1996), and lower mRNA production Calogero et al., 1993; Frankel and Cunningham, 2004).
with decreased 5-HT uptake in cultured cells (Lesch et m-CPP has been widely used to explore central 5-HT
al., 1996). Similar properties of 5-HTTLPR were receptor function in healthy as well as psychiatrically ill
replicated in some but not all investigations of direct subjects (Kahn and Wetzler, 1991; Murphy et al., 1991;
biological indices of 5-HT function, such as platelet 5- Yatham and Steiner, 1993). m-CPP can elicit anxiety,
HT uptake (Greenberg et al., 1999; Patkar et al., 2004a, dysphoria and euphoria in normal subjects (Broocks et
b), transporter availability (Little et al., 1998; van Dyck al., 1998, 2001) and intoxication-like effects in alcohol
et al., 2004) and CSF 5-hydroxyindolacetic acid (5- and cocaine abusers (Buydens-Branchey et al., 1993;
HIAA) levels (Jönsson et al., 1998; Williams et al., Krystal et al., 1994). Cocaine abusers have shown either
2001). Recent studies show that 5-HTTLPR genotypes no difference in PRL response (Handelsman et al., 1998),
may in part influence serotonin activity by affecting or a blunted PRL response compared with controls
postsynaptic 5-HT receptor availability (David et al., following m-CPP stimulation (Buydens-Branchey et al.,
2005). This polymorphism has been related to aggres- 1997, 2000; Patkar et al., 2006), similar to alcoholics
sion and violence (Arango et al., 2003a,b; Retz et al., (Handelsman et al., 1996). Thus, m-CPP-induced PRL
2004), early and severe alcohol dependence (Hallikainen release seems to be a valid tool to probe the physiological
et al., 1999; Feinn et al., 2005) and outcome in cocaine link between 5-HTTLPR genotypes, psychopathological
and alcohol abuse treatment (Mannelli et al., 2005). On dimensions and behavioral traits.
the other hand, investigations have found no association The objectives of the present study were twofold:
of 5-HTTLPR with impulsivity, aggression and cocaine First we investigated whether allelic variations in 5-
abuse (Patkar et al., 2002a,b), heroin dependence (Kotler HTTLPR genotypes are associated with the PRL
et al., 1999; Li et al., 2002), or the addictive effects of responses to the m-CPP challenge in recently abstinent
smoking (Gallinat et al., 2005). Besides possible cocaine-dependent individuals and healthy volunteers.
methodological limitations or influences of concomitant Second, we examined the relative contribution of
morbidity, the less consistent association of 5-HTTLPR genotype, behavioral measures and cocaine abuse to
with a risk of substance abuse may be explained by other the m-CPP challenge response.
sources of sample heterogeneity, such as gender and
ethnicity (Williams et al., 2003). 2. Methods
Several lines of evidence suggest that neuroendocrine
responses to different pharmacologic challenges that 2.1. Subjects
result in stimulated 5-HT transmission may be associated
with 5-HTTLPR genotypes. For example, a reduced This study was conducted with approval from the
prolactin (PRL) response to clomipramine was found in Institutional Review Board of Thomas Jefferson Uni-
women with the short allele (Whale et al., 2000). Similar versity, Philadelphia, PA, in accordance with theP. Mannelli et al. / Psychiatry Research 144 (2006) 99–108 101
Helsinki Declaration of 1975. Thirty-five subjects were (form V) is a widely used 40-item self-report question-
recruited from individuals attending a publicly funded, naire to measure four dimensions of sensation-seeking
outpatient cocaine treatment program. Following a behavior: disinhibition, thrill- and adventure-seeking,
complete description of the study, written informed experience-seeking, and boredom susceptibility. All the
consent was obtained from all subjects. The Structured above questionnaires provide a total score as well as
Clinical Interview (SCID) for DSM-IV Axis I Disorders partial scores on single subscales. The BDI is a 21-item
(First et al., 1997) was then administered to volunteers. self-report questionnaire to assess depressive symptoms.
Among those with an Axis I diagnosis of cocaine
dependence, subjects who used or abused other sub- 2.3. Genotyping
stances were included only if their primary drug was
cocaine. Individuals with a diagnosis of schizophrenia, Genomic DNA was isolated from 20 ml of EDTA-
major depression, bipolar disorder, schizoaffective treated venous blood obtained by each individual using
disorder, a serious medical illness, or pregnancy, and standard techniques (Miller and Costa, 1988). Genotyp-
those who were referred from the criminal justice ing for a 44 base pair insertion/deletion polymorphism
system or receiving psychotropic medications in the in the 5′ promotor region was performed as described by
previous 4 weeks were excluded. Urine drug screens Heils et al. (1996). Briefly, the 5-HTTLPR region was
and breath-alcohol levels were obtained for all subjects. amplified using polymerase chain reaction with oligo-
Nearly 92% of the patients in the treatment program nucleotide primers (5′-GGCGTTGCCGCTCTG
were African American and the study sample was AATTGC and 5′-GAGGGACTGAGCTGGACAA
restricted to African-American subjects to represent the CCCAC) to generate a 484 base pair (S) or a 528 base
clinical population. pair (L) fragment, according to the definition of Lesch et
Thirty-three African-American controls were re- al. (1996). DNA was denaturated at 95°C for 5 min and
cruited from those responding to local advertisements. subjected to 35 cycles of 45-s denaturation at the same
Consent and screening procedures were similar to those temperature, 1-min annealing at 66 °C and 1-min ex-
followed for cocaine subjects. Control subjects were tension at 72 °C. The amplified fragments were sep-
excluded if they had a history of substance abuse or arated on 2% agarose gels, and bands were visualized by
dependence, a major psychiatric disorder (schizophre- ethidium bromide staining and ultraviolet illumination.
nia, major depression or bipolar disorder), a positive Genotypes were evaluated by investigators who were
urine drug screen or had taken psychotropic medications blind to the status of the subject, and any discrepancies
in the previous 4 weeks. were resolved by test replication.
2.2. Behavioral assessments 2.4. m-CPP challenge test
Subjects and controls were assessed using a battery 2.4.1. Procedure
of psychological tests. The instruments were selected Subjects had their medical health documented by
based on evidence of a significant biological basis for history, physical examination and laboratory tests. To
disinhibition and aggression (Lesch and Merchdorf, minimize any effects of recent substance use on PRL
2000) and previous studies linking scores on these levels, cocaine-using subjects and controls underwent
scales to indices of 5-HT function (Buydens-Branchey the m-CPP challenge procedure after at least 2 weeks of
et al., 1997; Coccaro et al., 1996). These included the abstinence from illicit drugs and alcohol. The 2-week
Buss–Durkee Hostility Inventory (BDHI) (Buss and abstinence period was documented by monitoring urines
Durkee, 1957), the Barratt Impulsiveness Scale (BIS) and breath alcohol thrice a week including on the test
(Barratt, 1965), the Sensation Seeking Scale-form V day. Women were studied in the initial follicular phase
(SSS) (Zuckerman, 1993), and the Beck Depression of the menstrual cycle, defined clinically as the 10-day
Inventory (BDI) (Beck and Steer, 1987). period following the end of the menstrual phase.
The BDHI is a 75-item questionnaire used to measure Subjects were instructed to have a low monoamine
aggression. It is composed of eight subscales, rating diet for 3 days before the procedure. On the test day,
direct, indirect verbal aggression and irritability, resent- subjects came in the morning after an overnight fast
ment and suspiciousness, guilt and negativism. The BIS (except water), were placed in a semi-recumbent
is a 26-item self-report questionnaire with a four-factor position, and had their vital signs assessed. A peripheral
impulsivity score: speed of cognitive response; impul- indwelling catheter was inserted for blood collection.
siveness; adventure-seeking; and risk-taking. The SSS Subjects were not allowed to eat, drink or smoke during102 P. Mannelli et al. / Psychiatry Research 144 (2006) 99–108
the procedure. Two baseline blood samples were drawn the relationship of these measures with PRL responses.
at 30-min intervals and 0.5-mg/kg of oral encapsulated All calculations were performed using SPSS11.0
m-CPP (Sigma-Aldrich, St Louis, MO) was adminis- software. Bonferroni corrections were applied to
tered. Six serial blood samples were obtained for PRL multiple comparisons. All data are reported as mean ±
levels at 30-min intervals along with measurement of S.D. unless otherwise specified.
vital signs. The time schedule for blood draw included
the period of increase in neuroendocrine parameters in 3. Results
previous studies (Kalus et al., 1992). The 30, 60, 120
150 and 180 min samples were also examined for m- 3.1. Subject characteristics
CPP levels.
A total of 68 subjects (44 [65%] male) participated in
2.4.2. PRL determination the m-CPP procedure. Cocaine subjects (22 [63%] male)
Blood samples were centrifuged within 2 h of and controls (22 [66%] male) did not differ significantly
collection; the sera were separated and frozen at in gender (χ2 = 0.08, df = 1, P = 0.92) or age (sub-
− 70°C. Samples were identified by code numbers for jects = 34.33 ± 4.7, controls = 33.06 ± 4.15, df = 67,
blinding purposes. PRL was assayed using the Active P = 0.33). However, cocaine users were significantly
PRL DSL-4500 Immunoradiometric Assay Kit (Diag- more likely to be unemployed (82%) compared with
nostic Systems Laboratories, Texas). This assay em- controls (34%) (χ2 = 34.6, df = 1, P b 0.001). Similarly,
ploys a standardized two-site immunoradiometric assay significant differences were observed in marital status
technique (Miles et al., 1974) to provide quantitative between patients (71% single) and controls (44% single)
estimates of PRL in the serum. The assay sensitivity was (χ2 = 5.22, df = 1, P b 0.01). Nearly 85% of drug abusers
0.1 ng/ml, and specificity tests carried out by the man- fulfilled all seven DSM-IV criteria of cocaine depen-
ufacturer indicate that other hormones were unlikely to dence and were abstinent for 15.6 ± 3.7 days before the
cross-react with the PRL antibody. The interassay and m-CPP procedure. Cocaine users scored higher on
intraassay coefficients of variation were 11% and 4.0%, baseline PRL levels (F = 3.91, df = 1,66, P = 0.052) and
respectively. rates of depression (F = 20.63, df = 1,66, P = 0.000),
hostility (F = 11.61, df = 1,67, P = 0.001), impulsivity
2.5. Statistics (F = 6.56, df = 1,66, P = 0.022) and sensation seeking
(F = 4.36, df = 1,66, P = 0.040) than did controls.
The association of genetic variants with behavioral
and biological baseline measures in the total sample and 3.1.1. HTTPLR genotype
in the two subgroups was studied using two-tailed t-tests Genotype and allele frequencies for the 5-HT
and chi-square tests as appropriate. The same tests were transporter polymorphism in our sample are shown in
used in the comparison of cocaine users and controls on Table 1. The genotype distributions conformed to
baseline measures. Chi-square tests were also used to Hardy–Weinberger equilibrium in the whole sample
compare the genotype's frequency in the total sample and in the subgroups of cocaine users and healthy
and in the subgroups of cocaine patients and controls
with the predicted Hardy–Weinberg equilibrium (Lesch
et al., 1996). To evaluate the association of m-CPP test Table 1
5-HTTLPR genotype distribution and allele frequency in the sample
response and genotype, cocaine use and total scores of
behavioral scales, PRL response curves were analyzed Total sample Cocaine users Controls
for each variable in the whole sample and in the sub- (n = 68)1 (n =35)2 (n = 33)3
groups employing analysis of covariance (ANCOVA) % (%Male) % (%Male) % (%Male)
with repeated measures, to assess the main effects of LL 43 (65) 43 (60) 43 (71)
group and time and their interaction. Baseline PRL, age LS 35 (67) 37 (69) 33 (64)
and gender were used as covariates. SS 22 (60) 20 (57) 24 (63)
L (n = 82) 60 (67) 61 (63) 59 (69)
The maximum change in PRL after m-CPP (ΔPRL)
S (n = 54) 40 (65) 39 (63) 41 (63)
was calculated by subtracting baseline PRL values from
Hardy–Weinberger χ22 = 0.041 1, ns χ22 = 0.033 2, ns χ22=0.053 3, ns
peak PRL values following m-CPP (120 min). Univar-
distribution
iate ANOVA was performed with ΔPRL as the M/F distribution χ22 = 0.081 1, ns χ22 = 0.390 2, ns χ22 = 0.764 3, ns
independent variable and cocaine use, genotype, Chi-square test was used for comparisons. All analyses had 2 degrees
hostility and their interaction as predictors, to examine of freedom. ns = no a significant association between groups.P. Mannelli et al. / Psychiatry Research 144 (2006) 99–108 103
controls. No differences in genotype distributions were of the S allele were found for the response to m-CPP (L
found between men and women or between patients and vs S: F = 0.20, P = 0.656; LS + SS vs LL: F = 0.15,
controls (χ2 = 0.209). P = 0.892).
We then evaluated the relationship of the genetic The SS genotype was associated with a trend toward
variants with behavioral and baseline PRL measures higher PRL levels following the challenge, both in
obtained before the challenge test in the entire sample. cocaine users (F = 2.71, df = 2,31, P = 0.089,
No significant correlations of the 5-HT transporter power = 0.396) and in the control groups (F = 1.81,
promoter polymorphism were detected either comparing df = 2,29, P = 0.081, power = 0.361). ΔPRL values (Peak
genotypes and alleles, or assuming a dominant effect of PRL − Baseline PRL) were also significantly higher in
S, with demographic and baseline measures (data not SS (ANOVA F(2,68) = 4.402, P=0.016) (Fig. 2).
shown).
3.2.2. Cocaine users and controls
3.2. Relationship of prolactin response to m-CPP with Repeated measures ANOVA of the response curves
genetic and behavioral measures showed a significant time effect on PRL levels in both
cocaine patients (F = 34.7, df = 2.4, P b 0.001) and
3.2.1. HTTPLR genotype controls (F = 17.37, df = 2.4, P b 0.001). Repeated mea-
Repeated measures ANCOVA showed a different sures ANCOVA demonstrated significant blunting in the
PRL response across genotypes in the whole sample. We response of cocaine subjects compared with non-users
observed a significant main effect of time in the (F = 21.931,65, P = 0.001, Fig. 3), when adjusted for
response (F = 7.33, df = 2,64, P = 0.0001), and an baseline prolactin and age.
interaction between genotype and time (F = 4.40, To control for possible gender differences in PRL
df = 2,64, P = 0.016), when baseline and PRL and gender response (New et al., 2004), we performed specific
were controlled. Post hoc analyses using tests for analyses and found that ΔPRL values were not
pairwise comparisons of differences in the means significantly different between men (n = 22) (5.23
showed that SS had heightened PRL response compared ± 3.08) and women (n = 13) (6.85 ± 2.64) among cocaine
with LS (P = 0.004) and LL (P = 0.032), with no patients (F = 2.48, df = 1,34, P = 0.12) or controls (men
significant differences between LS and LL (P = 0.259) (n = 22) = 8.97 ± 2.88, women (n = 11) = 9.28 ± 3.34,
(Fig. 1). Neither allele differences nor a dominant effect F = 0.08, df = 1,32, P = 0.99). Consistent with the overall
20
18
16
mean prolactin (ng/ml)
14
12
10
LL n=29
LS n=24
8
SS n=15
6
0 30 60 90 120 150 180
minutes
Fig. 1. Mean PRL plasma levels (±S.E.) following m-CPP stimulation in LL (dashed line), LS (continuous line with triangles) and SS (continuous line
with squares). The SS genotype showed an enhanced PRL response (ANCOVA with repeated measures, F(2,64) = 4.40, P = 0.016).104 P. Mannelli et al. / Psychiatry Research 144 (2006) 99–108
10
9
8
Mean change in Prolactin (ng/ml)
7
6
5
4
3
2
1
0
LL n=29 LS n=24 SS n=15
Genotype
Fig. 2. Difference in PRL plasma levels from baseline (mean ΔPRL, ±S.E.), following m-CPP among 5-HTTLPR genotypes. SS showed increased
ΔPRL (ANOVA: F(2,68) = 4.402, P = 0.016).
group differences, ΔPRL values were significantly 3.2.3. Behavioral measures
lower in cocaine-dependent men compared with We found no significant correlation between PRL
healthy men (F = 20.2, df = 1,43, P b 0.001) and among release after m-CPP and measures of depression,
cocaine-dependent women compared with healthy impulsivity and sensation seeking in our sample, using
women (F = 4.12, df = 1,23, P b 0.05). univariate ANOVA (F = 8.39, P = 0.674; F = 0.59,
18
16
mean prolactin (ng/ml)
14
12
10
8 control n=33
cocaine n=35
6
0 30 60 90 120 150 180
minutes
Fig. 3. Mean PRL plasma levels (±S.E.) following m-CPP stimulation in cocaine-dependent subjects (continuous line) and controls (dashed line).
Cocaine users showed significant blunting in PRL response (ANCOVA with repeated measures, F(1,65) = 21.93, P = 0.001).P. Mannelli et al. / Psychiatry Research 144 (2006) 99–108 105
Table 2 4. Discussion
Maximum change in PRL (ΔPRL) from genetic, group and behavioral
variables
In the present study individuals with the SS genotype
ΔPRL (Outcome variable) F Predicted of the 5-HTTLPR polymorphism differed from LL and
variance (%)
LS genotypes in their PRL response to m-CPP
Model 1. Group assignment 22.81(1,69) 23.1 challenge. Cocaine abusers in our sample showed a
Model 2. 5-HTTPLR polymorphism 4.402(2,68) 29.5
blunted PRL response compared with controls, in
Model 3. Total scores on Buss–Durkee
Hostility Inventory 2.312(23,68) 39.5 accordance with previous investigations (Buydens-
Model 4. Three-way interaction 3.2272(51,17) 62.5 Branchey et al., 1997, 2000; Patkar et al., 2006).
1
P = 0.000. Other studies in community volunteers (Whale et al.,
P ≤ 0.03.
2 2000; Manuck et al., 2004; Smith et al., 2004), and in
One-way analysis of variance (ANOVA) was used for model analyses. alcoholics and non-drinking controls (Reist et al., 2001)
have described a blunting in PRL response following
serotonin-mediated stimulation among SS individuals
and we found a relative increase in PRL in the same
P = 0.923; and F = 1.30, P = 0.236, respectively). On the genotype. A consistent trend in the expected direction
other hand, hostility scores were significantly associated was observed both in cocaine subjects and controls,
with PRL levels in the total sample (F = 2.19, df = 1,66, although it failed to reach significance due to sample
P = 0.023), but not in the cocaine users (F = 0.71, size limitations in the subgroups. Our results may only
df = 23,10, P = 0.791) or controls (F = 0.92, df = 14,14, seem in contrast with the above-mentioned findings. In
P = 0.931). fact, the pharmacological probes used in earlier studies,
such as fenfluramine, act both at presynaptic and
3.3. Moderators of prolactin response to m-CPP postsynaptic levels (Broocks et al., 1997), while m-
CPP is a more selective serotonin postsynaptic agonist
We built an ANOVA model to explore the relative (Bourson et al., 1996). A reduced transcriptional
contribution of variables that significantly affected the efficiency of the 5-HT transporter promoter hypothe-
PRL response to the m-CPP challenge toward predict- sized for the SS genotype (Heils et al., 1996) would be
ing ΔPRL values in our sample. The cocaine/control expected to reduce transporter expression (Lesch et al.,
condition explained 23.1% of the variance, while 1996). This, in turn, might lead to increased postsyn-
genotype accounted for 9% and hostility for 17%. We aptic activity, to compensate for the presynaptic deficit.
first entered in the model subject group condition as Such an explanation would be consistent with a
the strongest correlate, followed by genotype and heightened PRL response observed in our study and is
subsequently added the scores on the hostility scale supported by recent results indicating the existence of an
(Table 2). association between SS genotype and indices of
The combination of the first two variables signifi- postsynaptic activity (David et al., 2005). Another
cantly explained 29.5% of the variance in PRL and explanation could be associated to ethnicity. Differences
hostility added about 10%. However, including the in patterns of linkage disequilibrium between poly-
interactions of group condition with genotype (F = 1.20, morphisms of the serotonin transporter gene have been
P = 0.307), and hostility scores (F = 1.20, P = 0.324), or previously identified, leading to contrasting results in
those of genotype with hostility scores (F = 0.50, African and European populations (Gelernter et al.,
P = 0.930), failed to improve prediction of ΔPRL and 1999). More specifically, African American homozy-
these variables were eliminated from the model. gotes for the S allele have shown elevated serotonergic
Similarly, entering the condition of unemployment or function compared with LL and LS groups or Caucasian
its interaction with genotype to assess the influence of subjects (Williams et al., 2003), and our findings of
socio-economic status did not account for additional increased transcriptional activity in the SS genotype
variance (F = 0.91, P = 0.572; F = 1.37, P = 0.203, re- would be consistent with these results.
spectively). At this point the total PRL variance Other characteristics specific of the sample, such as
explained by the model was still inferior to the sum of the co-presence of abstinent cocaine users and non-
the single contributions. Finally, adding a three-way dependent subjects of both sexes, did not influence the
group, genotype and hostility interaction resulted in a genetic association with PRL response to the challenge.
more efficient model and accounted for 62.5% of PRL Likewise, we found no association between socio-
changes from baseline. economic status and 5-HTTLPR functionality, as it was106 P. Mannelli et al. / Psychiatry Research 144 (2006) 99–108
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behavioral and neuroendocrine responses to meta-chlorophenylpi-
differences in genotype distribution or allele frequency perazine and to ipsapirone in untrained healthy subjects.
between the two groups, similar to previous investiga- Psychopharmacology 155, 234–241.
tions (Patkar et al., 2000, 2002a,b). In addition, both Buss, A., Durkee, A., 1957. An inventory for assessing different kinds
groups uniformed with the Hardy–Weinberger equilib- of hostility. Journal of Consulting Psychology 21, 343–348.
rium and showed similar allele frequencies to those Buydens-Branchey, L., Branchey, M., Gribomont, B., Handelsman, L.,
Holloway, K., Silverman, J., 1993. Morbidity risk for alcoholism
reported across populations of different ethnicity in and drug abuse in relatives of cocaine addicts. American Journal of
substance abusers (Sander et al., 1998; Edenberg et al., Drug and Alcohol Abuse 19, 347–357.
1998a,b; Heinz et al., 2000), or healthy controls from Buydens-Branchey, L., Branchey, M., Fergeson, P., Hudson, J.,
either Western Europe or the United States (Lesch et al., McKernin, C., 1997. The meta-chlorophenylpiperazine challenge
test in cocaine addicts: hormonal and psychological responses.
1996; Heinz et al., 2000; Hoehe et al., 1998).
Biological Psychiatry 41, 1071–1086.
In conclusion, our findings suggest that variations in Buydens-Branchey, L., Branchey, M., Hudson, J., Fergeson, P., 2000.
the 5-HTTLPR gene appear to influence measures of 5- Low HDL cholesterol, aggression, and altered central serotonergic
HT function in African American populations. More- activity. Psychiatry Research 93, 93–102.
over, genetic variants seem to interact with disease state Calogero, A., Bagdy, G., Moncada, M., D'Agata, R., 1993. Effect of
and personality dimensions to account for 5-HT selective serotonin agonists on basal, corticotrophin-releasing
hormone- and vasopressin-induced ACTH release in vitro from rat
disturbances. While these results need replication they pituitary cells. Journal of Endocrinology 136, 381–387.
indicate that, although important, genetic influence is Coccaro, E., Berman, M., Kavoussi, R., Hauger, R., 1996. Relation-
not the only factor contributing to functional 5-HT ship of prolactin response to d-fenfluramine to behavioral and
alterations in cocaine dependence. questionnaire assessments of aggression in personality disordered
men. Biological Psychiatry 40, 157–164 (Aug).
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